Putative Anticancer Compounds from Plant-Derived Endophytic Fungi: A Review.

Endophytic fungi are microorganisms that exist almost ubiquitously inside the various tissues of living plants where they act as an important reservoir of diverse bioactive compounds. Recently, endophytic fungi have drawn tremendous attention from researchers; their isolation, culture, purification, and characterization have revealed the presence of around 200 important and diverse compounds including anticancer agents, antibiotics, antifungals, antivirals, immunosuppressants, and antimycotics. Many of these anticancer compounds, such as paclitaxel, camptothecin, vinblastine, vincristine, podophyllotoxin, and their derivatives, are currently being used clinically for the treatment of various cancers (e.g., ovarian, breast, prostate, lung cancers, and leukemias). By increasing the yield of specific compounds with genetic engineering and other biotechnologies, endophytic fungi could be a promising, prolific source of anticancer drugs. In the future, compounds derived from endophytic fungi could increase treatment availability and cost effectiveness. This comprehensive review includes the putative anticancer compounds from plant-derived endophytic fungi discovered from 1990 to 2020 with their source endophytic fungi and host plants as well as their antitumor activity against various cell lines.

1. Introduction

In 1866, de Bary introduced the term “endophyte” [1]. An endophyte may be a fungal or bacterial microorganism that colonizes various interior parts of plants causing no apparent pathogenic effects on its host plants. The endophytes, most commonly endophytic fungi, are believed to help plants adapt to abiotic factors (high temperature and salinity, drought, metal toxicity, and harmful effects of light) as well as biotic factors (herbivores, insects, nematodes, and pathogens). This is mainly achieved by the secondary bioactive metabolites produced by the endophytic fungi. In their symbiotic relation, the endophytes are fed and protected by the host plant, and in return, these microorganisms produce bioactive secondary metabolites, enhancing the growth of the host plant and protecting the plant from pathogens and herbivores [2]. Therefore, endophytic fungal metabolites can also be exploited as drugs for the treatment of various types of human diseases, including cancer [3].

This group of microorganisms has drawn tremendous attention from researchers since the isolation, culture, purification, and characterization of this fascinating group of microorganisms revealed the presence of hundreds of important and diverse chemical classes of compounds. The interest of scientists in endophytes is also growing as they are a good reservoir of bioactive metabolites [4,5]. Until now, many cytotoxic agents including paclitaxel (also known as Taxol) [6] have been isolated from endophytes. Secondary metabolites with cytotoxic properties have the potential to be explored as anticancer drugs.

Recent studies revealed that naphthoquinone derivatives fusarubins including anhydrofusarubin and fusarubin (FUS) produced by endophytic fungi Cladosporium species [7] and Fusarium species [8] showed promising cytotoxicity against cancer cells. Although FUS was reported earlier to have antibacterial activity, its cytotoxic activity was reported recently. Very recently, for the first time, we have revealed the molecular mechanism of cytotoxic action of fusarubin isolated from a Cladosporium species inhabiting the leaves of Rauwolfia serpentina. We have reported that fusarubin and anhydrofusarubin inhibit proliferation and increase apoptosis in leukemia and other hematological tumor cells lines in different manners through the p21/p53-mediated pathway [9]. Our findings urge us to write this review on endophytic fungal metabolites as a fascinating group of bioactives or putative anticancer compounds. Many of these putative anticancer compounds have very promising cytotoxicity against a broad spectrum of cancer cell lines; some compounds are already used as treatments for different cancer types such as breast, bladder, colorectal, esophageal, lung, ovarian, prostate, melanoma, testicular, leukemia, and lymphoma.

2. Anticancer Activity of Endophytic Fungi

Endophytic fungi have been a known source of anticancer agents since the discovery of the valuable drug Taxol (also known as paclitaxel, a diterpenoid) isolated for the first time from an endophytic fungus Taxomyces andreanae obtained from the Pacific Yew bark (Taxus brevifolia) [6]. Since then, other anticancer drugs have been isolated from endophytic fungi, and among these 9-methoxycamptothecin and 10-hydroxycamptothecin from Fusarium solani [10], camptothecin from Entrophospora infrequens [11]; the anticancer lead compounds podophyllotoxin from Phialocephala fortinii [12] and deoxypodophyllotoxin from Aspergillus fumigatus [13] fueled further research on endophytic fungi to discover many other important known and novel anticancer compounds. According to this review, until now, more than 100 different fungal species have been identified to produce more than two hundred putative anticancer compounds (Figure 1 and Figure 2) reported to possess antiproliferative and/or cytotoxic properties against more than 60 different cell lines (Table 1, Table 2 and Table 3). Figure 1 indicates that endophytic fungal-derived anticancer agents gained attention from scientists over the past three decades. Meanwhile, Figure 2 represents the abundance of different chemical classes and diversity of fungal metabolites. The anticancer compounds isolated from endophytic fungi are effective against diverse cell lines that could be helpful in combating any particular type of cancer (Table 1).

Figure 1

Discovery of anticancer agents from endophytic fungi over time.

Figure 2

Relative abundance of anticancer agents from endophytic fungi.

Table 1

Different cell lines against which endophytic fungal derived metabolites showed cytotoxicity.

Cell Lines		Cell Lines
A2780S	Ovarian tumor cell line	Int-407	Human intestine cancer
A2058	Human melanoma	Jurkat	T cell leukemia
A549	Lung carcinoma epithelial	KB	Human nasopharyngeal epidermoid tumor
A431	Skin carcinoma	K562	Human leukemia cells
ACHN	Renal cells	L5178Y	Mouse lymphoma cells
AsPC-1	Human pancreatic cancer cells	MIA Pa Ca-2	Pancreatic carcinoma
B16F10	Skin carcinoma	MiaPaka-2	Pancreatic cancer
BC	Human breast cancer cell line	MDA-MB-231	Breast cancer cell line
BC-1	Breast cancer	MDA-MB-435	Human breast cancer cell line
BEL-7402	Human hepatocellular carcinoma/human hepatoma cell line	MFC	Gastric cancer cells in mice
BEL-7404	Human hepatocellular carcinoma/human hepatoma cell line	MCF-7	Breast cancer cell line
BGC-823	Gastric carcinoma	MOLT-4	Lymphoblastic leukemia
BT-220	Breast cancer cell line	MRC-5	Fibroblast-like fetal lung cells
BT474	Human breast cancer	MV4-11	Human FLT3-ITD mutant AML cell line
CHO	Chinese hamster ovary	NCI-H187	Human small-cell lung cancer
DU145	Human prostate carcinoma	NCI-H460	Non-small-cell lung cancer
EAC	Ehrlich ascites carcinoma	NEC	Colorectal neuroendocrine cell carcinoma
H116	Human colon adenocarcinoma	OVCAR-5	Human ovarian cancer
HeLa	Cervical cancer	PANC-1	Human pancreatic carcinoma
HEp-2	Human liver cancer	P388	Murine leukemia cells
HepG2	Human hepatocellular liver carcinoma	PC-3	Prostate cancer
Hep3B	Human hepatoma cell line	PC-3 M	Metastatic prostate cancer
HM02	Human gastric carcinoma	RAW264.7	Mouse macrophage cell
HL-60	Human promyelocytic leukemia cell line	SF-268	CNS glioma
HL251	Human lung cancer	SW480	Human colon cancer cells
HL-7702	Normal hepatocyte	SW-620	Colon tumor cell line
HLK 210	Human leukemia	SW1116	Human colon cancer cell line
HCT-8	Human colorectal adenocarcinoma	SW1990	Human pancreatic cancer cells
HCT-116	Colon tumor cell line	T24	Bladder carcinoma
H22	Hepatic cancer cells in mice	T47D	Breast cancer
H1975	Non-small-cell lung cancer cells/human lung adenocarcinoma	THP-1	Human monocytic cell line
H522-T1	Non-small cell lung cancer	WI-38	Normal human fibroblast cells
HT-29	Human colon cancer line	U2OS	Human osteosarcoma cells

Table 2

Anticancer compounds from plant-derived endophytic fungi.

Compounds	Chemical Class	Fungal Endophytes	Host Medicinal Plant	Activity Against Cell Lines	IC50 Values	Ref.
Leucinostatin A	Peptide	Acremonium spp.	Taxus baccata twig	BT-20	2 nM (LD50)	[14]
Allantopyrone A	α-Pyrone	Allantophomopsis l. KS-97		A549 cells, HL-60	˃32, 0.32 µM	[15]
Alternariol, Altenusin, Alternariol 5-O-sulfate, Alternariol 5-O-methyl ether, Desmethylaltenusin	Polyketide	Alternaria spp	Polygonum senegalense leaves	L5178Y	˂1 × 10−6, 1 × 10−5, 1 × 10−5, 1 × 10−5, 1 × 10−5 g/mL	[16]
Lapachol	Naphtho-quinone	Alternaria spp.	Tabebuia argentea leaf	DU145, HepG2, Hep3B & MCF-7(β-Lapachone)	3.5, 3.5, 3.5 & 5 µM	[17,18,19,20,21,22]
Resveratrodehydes A & B	Stilbenoid (Resveratrol dervatives)	Alternaria spp. R6	Myoporum bontioides root	MDA-MB-435,HCT-116	˂10 µM	[23]
Alterporriol K, Alterporriol L	Quinones	Alternaria spp. ZJ9-6B	Aegiceras corniculatum	MDA-MB-435,MCF-7	26.97, 29.11 & 13.11, 20.04 µM	[24]
Alternariol-10-methyl ether	Polyketide	Alternaria a.	Capsicum annum	HL-60, A549, PC-3, HeLa, A431,MiaPaka-2 and T47D	85, ˃100, ˃100, ˃100, 95, ˃100 and ˃100 µM	[25]
Camptothecine (CPT),9-methoxy CPT, 10-hydroxy CPT	Alkaloids	Alternaria a.	Miquelia dentata fruit and seed regions	HCT-116,SW-480,MCF-7	6.59, 7.2, 10.24 µg/mL (crude fungal ethyl acetate extract)	[26]
Chrysin (5,7-dihydroxy flavone)	Flavone	Alternaria a. (KT380662)	Passiflora incarnata leaves	MCF-7	34.066 µg/mL	[27]
Alternariol 9-methyl ether	Dibenzopyranone	Alternaria a.	Camellia sinensis branches	U2OS	28.3 µM	[28]
Lapachol	Naphtho-quinone	Alternaria a.	Tabebuia argentea bark, leaf and stem	DU145, HepG2, Hep3B & MCF-7(β-Lapachone)	3.5, 3.5, 3.5 & 5 µM	[17,18,19,20,21,22]
(6aR,6bS,7S)-3, 6a, 7,10-tetrahydroxy- 4,9-dioxo-4, 6a, 6b, 7, 8,9-hexahydroperylene	Perylenes	Alternaria t.	Erythrophleum fordii bark	HCT-8	1.78 µM	[29]
1. Flavasperone,2. Rubrofusarin B3. Fonsecinone D	Naphthopyrones	Aspergillus sp.	Limonia acidissima seeds	1. Hep 3B and U87 MG2. SW11163. SMMC-7721 and A549	1. Between 19.92 and 47.98 µM2. 4.5 µg/mL3. ˃10 µg/mL	[30]
Brefeldin A	Lactone	Aspergillus c.	Torreya grandis bark	HL-60, KB, Hela, MCF-7 and Spc-A-1	1.0–10.0 ng/mL	[31]
9-Deacetoxy fumigaclavine C	Alkaloids	Aspergillus f.	Cynodon dactylonstem	K562	3.11 µM	[32]
1. Fumitremorgin D,2. 4,8,10,14-tetramethyl-6-acetoxy-14-[16-acetoxy-19-(20,21- dimethyl)-18-ene]-phenanthrene-1-ene-3,7-dione3. 12,13-dihydroxy-fumitremorgin C4. Verruculogen	Alkaloids	Aspergillus f.	Diphylleia sinensis mainly roots, rhizomes	HepG2	1. 47.5 µM2. 139.9 µM3. 4.5 µM4. 9.8 µM	[33]
2,14-Dihydrox-7-drimen-12,11-olide	Sesquiterpenes	Aspergillus g.	Ipomoea batatas plant	Hep-G2, MCF-7	61, 41.7 µg/mL	[34]
Nigerapyrones B, D & EAsnipyrones A	Pyrones	Aspergillus n. MA-132	Avicennia marina plant	HepG2, MCF-7, A549, SW1990, MDA-MB-231	86, 105, 43, 38, 48 µM	[35]
Rubrofusarin B	Naphtho-γ-pyrones	Aspergillus n.	Cynodon dactylon	SW1116	4.5 µg/mL	[36]
Lapachol	Naphtho-quinone	Aspergillus n.	Tabebuia argentea leaves	DU145, HepG2, Hep3B & MCF-7(β-Lapachone)	3.5, 3.5, 3.5 & 5 µM	[17,18,19,20,21,22]
1. Sequoiatones A & B2. Sequoiamonascin A & B	Polyketide	Aspergillus p.	Sequoia sempervirens inner bark	1. BC2. MCF7, NCI-H460, SF-268	1. 4 to 10 µM2. 19 × 10−4, 4 × 10−4, 15 × 10−4 M	[37,38]
Butyrolactone I and Butyrolactone V	Butenolide	Aspergillus t.—F7	Hyptis suaveolens	MDA-MB-231 and MCF-7	34.4, 17.4 & 22.1, 31.9 µM	[39]
Terrein		Aspergillus t. JAS-2	Achyranthus aspera	A-549	121.9 µg/mL	[40]
1. Violaceoid A,2. Violaceoid C, Violaceoid D,3. Violaceoid F	Hydroquinones	Aspergillus v.	Wild Moss (Bryophyta unidentified species)	1. HeLa, MCF-7, Jurkat, MOLT-4, HCT116, RAW264.72. Jurkat, MOLT-43. HCT116, RAW264.7	1. 24.6, 14.8, 3.1, 3.0, 5.8, 5.6 µM (LD50)2. 8.2, 5.9 & 8.3, 6.2 µM (LD50)3. 6.4, 6.5 µM (LD50)	[41]
Taxol	Terpene	Bartalinia r.	Aegle marmelosleaves	BT 220, H116,Int 407, HL 251 and HLK 210	-	[42]
Depsidone 1	Depsidone	Pleosporales (BCC 8616)	unidentified plant leaf of the Hala-Bala forest origin	KB, BC	6.5, 4.1 µg/mL	[43]
1. Diepoxin δ,Palmarumycin C82. Diepoxins κ & ζ	Spirobis-naphthalenes	Berkleasmium spp.	Dioscorea zingiberensis	1. HCT-8, Bel-7402, BGC-823, A 549, A27802. Bel-7402 and A 549	1. 1.7, 3.3, 3.3, 3.2, 5.8 & 4.2, 2.5, 2.6, 1.6, 1.3µM2. 6.4, 8.7 & 5.1, 8.8 µM	[44]
Verticillin D	Peptide	Bionectria o.	Sonneratia caseolaris Inner leaf tissues	L5178Y	<0.1 µg/mL (EC50)	[45]
Ophiobolin A	Sesterterpenoid	Bipolaris s.	Unidentified	MDA-MB-231	0.4–4.3 µM	[46]
1. Stemphyperylenol2. Altenuene	1. Polyketide2. Mycotoxin	Botryosphaeria d. KJ-1	Melia azedarach stem bark	HCT116	3.13 µM	[47]
Botryorhodine A and B	Depsidone	Botryosphaeria r.	Bidens pilosa stem	HeLa, K-562	96.97, 36.41 & 0.84, 0.003 µM (CC50)	[48]
Cercosporene F	Guanacastane Diterpenes	Cercospora spp.	Fallopia japonica leaves	HeLa, A549, MCF-7, HCT116 and T24	19.3, 29.7, 46.1, 21.3 & 8.16 µM	[49]
Ceriponol F, Ceriponol G, Ceriponol K	Sesquiterpenes	Ceriporia l.	Huperzia serrata	HeLa, HepG2, SGC7901	173.2, 32.3, 77.5; 185.1, ˃500.0, ˃500.0 & 47.8, 35.8, 60.2 µM	[50]
Cochliodinol, Isocochliodinol	Quinones	Chaetomium spp.	Salvia officinalis Stem	L5178Y	7.0, 71.5 µg/mL (EC50)	[51]
Chaetocochin C	Diketopiperazine	Chaetomium spp.	Cymbidium goeringii root	SW-480	0.63 µM	[52]
Chaetocochin G	Indole diketo-piperazines	Chaetomium spp. 88194	Cymbidium goeringii	MCF-7	8.3 mg/mL	[53]
Chaetominine	Alkaloids	Chaetomium spp. IFB-E015	Adenophoraaxilliflora leaves	K562, SW1116	21.0, 28.0 nM	[54]
Radicicol	Lactone	Chaetomium c.	Ephedra fasciculate stem	MCF-7	0.03 µM	[55]
Chaetoglobosin X	Alkaloids	Chaetomium g. L18	Curcuma wenyujin	H22, MFC	3.125, 6.25 µg/mL	[56]
Chaetoglobosin C, E, F & U,Penochalasin A	Alkaloids	Chaetomium g. IFB-E019	Imperata cylindrica stem	KB cell line	34.0, 40.0, 48.0 & 16.0, 48.0 µM	[57]
Globosumone A & B	Ester	Chaetomium g.	Ephedra fasciculata	NCI-H460, MCF-7, SF-268, MIA Pa Ca-2, WI-38	6.50, 21.30, 8.80, 10.60, 13.00 & 24.80, 21.90, 29.10, 30.20, 14.20 µM	[58]
Chaetoglobosins A, Fex, Fa & 20-dihydrochaetoglobosin	Alkaloids (cytochalasan mycotoxins)	Chaetomium g.	Ginkgo biloba leaves	HCT116	3.15, 4.43, 5.85, 8.44 µM	[59]
Anhydrofusarubin andmethyl ether of Fusarubin	Naphtho-quinones	Cladosporium spp.	Rauwolfia serpentina leaves	K-562	3.97 & 3.58 µg/mL	[7]
Taxol	Diterpene	Cladosporium c.	Taxus media inner bark	MCF-7, BT220, H116, INT-407, HL251, HLK210	0.005 to 5 µM	[60,61]
Taxol	Diterpene	Cladosporium o.	Aegle marmelos, Coccinia indica and Moringa oleifera	HCT 15, T47D	3.5, 2.5 µM	[62,63]
Taxol	Diterpene	Colletotrichum c.	Capsicum annuum fruit	MCF-7, HL 251, HLK 210, BEL7402	0.005 to 5 µM	[64,65]
Tyrosol C	#	Colletotrichum g.	Pandanus amaryllifoliusleaves	A549, HT29, HCT116	-	[66]
Deacetylcytochalasin C and Zygosporin D	Cytochalasins	Cordyceps t.	unidentified	95-D	3.67 & 4.04 µM	[67]
1. Cytospolide P,2. Cytospolide Q	Lactones	Cytospora spp.	Ilex canariensis	1. A-549, QGY, U9732. A-549	1. 2.05, 15.82, 28.26 µg/mL2. 10.55 µg/mL	[68]
Xylarolide	#	Diaporthe t. GG3F6.	Glycyrrhiza glabra rhizomes	T47D	7 µM	[69]
Taxol	Diterpenes	Didymostilbe spp.	Taxus chinensis var. mairei old inner bark	MCF-7, HL 251, HLK 210, BEL7402	0.005 to 5 µM	[64,65]
Camptothecin	Alkaloids	Entrophospora i.	Nothapodytes foetida inner bark	A-549, HEP-2, OVCAR-5	-	[11]
1. Eutypellin A,2. ent-4(15)-eudesmen-11-ol-1-one	1. γ-Lactone2. Sesquiterpene	Eutypella sp. BCC 13199	Etlingera littoralis	NCI-H187, MCF7, KB, Vero cells	1. 12, 84, 38, 88 µM2. 11, 20, 32, 32 µM	[70]
Camptothecine (CPT),9-methoxy CPT, 10-hydroxy CPT	Alkaloids	Fomitopsis spp.	Miquelia dentata fruit and seed regions	HCT-116,SW-480,MCF-7	5.63, 23.5, 10.32 µg/mL (crude fungal ethyl acetate extract)	[26]
Beauvericin	Depsipeptide	Fusarium o.	Cinnamomum kanehirae bark	PC-3, PANC-1, A549	49.5, 47.2, 10.4 µM	[71]
Taxol	Diterpenes	Fusarium o.	Rhizomphora annamalayana leaves	BT220, HL251,HLK 210	0.005 to 5 µM	[72,73]
Vincristine	Alkaloids	Fusarium o.	Catharanthus roseus inner bark	HeLa, MCF7, A549, U251, A431 & HEK293	4.2, 4.5, 5.5, 5.5, 5.8 µg/mL	[74,75]
Beauvericin	Depsipeptide	Fusarium o.	Cinnamomum kanehirae bark	PC-3, PANC-1, A549	49.5, 47.2, 10.4 µM	[71]
Beauvercin	Depsipeptide	Fusarium o.	Ephedra fasciculata root	NCI-H460, MIA Pa Ca-2, MCF-7, SF-268, PC-3 M, MDA-MB-231, MRC-5, Hep-G2	1.41, 1.66, 1.81, 2.29, 3.0, 5.0, 4.7–5.0, 8.8–22.2 µM	[76,77]
Beauvercin	Depsipeptide	Fusarium o. EPH2RAA	Cylindropuntia echinocarpusstem	NCI-H460, MIA Pa Ca-2, MCF-7, SF-268, PC-3 M, MDA-MB-231	1.41, 1.66, 1.81, 2.29, 3.0, 5.0 µM	[77]
Bikaverin	Polyketide	Fusarium o.CECIS	Cylindropuntia echinocarpusstem	NCI-H460, MIA Pa Ca-2, MCF-7, SF-268, EAC, leukemia L 5178, sarcoma 37	1.41, 1.66, 1.81, 2.29, 0.5, 1.4, 4.2 µg/mL (ED50)	[77,78]
Camptothecin (CPT) and 9-methoxy CPT	Alkaloids	Fusarium s.(MTCC 9667 and MTCC 9668)	Apodytes dimidiata	HCT-116,SW-480,MCF-7	7, 8.5, 8 &7, 8.5, 8 µg/mL	[10,26]
Podophyllotoxin	Lignans	Fusarium s.	Podophyllum hexandrum roots	#	-	[79]
Camptothecine (CPT),9-methoxy CPT, 10-hydroxy CPT	Alkaloids	Fusarium s.	Camptotheca acuminata inner bark	OVCAR-5, HCT-116SW-480, MCF-7	7, 8.5, 8 &7, 8.5, 8 µg/mL	[26,80]
Gliocladicillins A & B	Epipolythiodi-oxopiperazines	Gliocladium spp. XZC04-CC-302	Cordyceps sinensis bark.	HeLa, HepG2,MCF-7	0.50, 0.50,0.20 µg/mL (GI50)	[81]
Guignarenone A	Tricyclo-alternarene	Guignardia b. PSU-G11	Garcinia hombroniana leaves	KB, Vero	0.38, 2.24 µM	[82]
Guignardones Q & S	Meroterpenoids	Guignardia m. A348	Smilax glabraleaves	MCF-7	83.7 & 92.1 µM	[83]
Cajanol (5-hydroxy-3-(4- hydroxy-2-methoxyphenyl)-7-methoxychroman-4-one)	Flavonoids	Hypocrea l.	Cajanus cajan roots, stems and leaves	1. A549 2. PC-3, HT-29,HepG2	1. 20.5 µg/mL after 72 h treatment, 24.6 µg/mL after 48 h; and 32.8 µg/mL after 24 h2. 29.8, 21.4, 33.6 µg/mL (Fungal crude extract)	[84]
Daldinone C & D	Benzo[j]fluoranthene	Hypoxylon t. IFB-18	Artemisia annua surface-sterilized fresh stems	SW1116	49.5 & 41.0 µM	[85]
1. * Brefeldin A, trichothecolone,7α-hydroxy-scirpene2. 8-deoxy-trichothecin,7α-hydroxytrichodermol	* Lactone, Sesquiterpenes (trichothecenes)	KLAR 5 (Hypocreales)	Knema laurinahealthy twig	1. KB, BC-1, NCI-H1872. BC-1, NCI-H187	1. 0.18, 0.04, 0.1; 12.90, 10.06, 11.31 & ˃75.10, 2.37, 1.73 µM2. ˃62.81, 0.88, 1.48 & 8.47, 21.53, 27.76 µM	[86]
Taxol	Diterpenes	Lasiodiplodia t.	Morinda citrifolia leaves	1. MCF-72. BT220, H116, INT-407, HL251, HLK210	1. 300 µg/mL2. 0.005–5.00 µM	[60,87]
Lasiodiplodin	Macrolide	Lasiodiplodia t. (MUB-65)	Myracrodruon urundeuvabranches	HCT-116	11.2 µg/mL	[88]
Vincristine	Alkaloids	Mycelia s. 97CY (3)	Catharanthus roseus leaves	HeLa, MCF7, U251, A549, A431 & HEK293	4.2, 4.5, 5.5, 5.5, 5.8 µg/mL	[74,89]
Spiromamakone A	Spirobis naphthalene	Mycelia s.	Knightia excelsa surface-sterilized leaves	P388	0.33 µM	[90]
Cercosporin	Quinones	Mycosphaerella spp.	Psychotria horizontalis	MCF7	4.68µM	[91]
Arundinone B	Coumarins	Microsphaeropsis a.	Ulmus macrocarpa stems	T24, A549	35.4, 81.6 µM	[92]
Mycoleptodiscin B	Alkaloids	Mycoleptodiscus spp. F0194	Desmotes incomparabilis healthy mature leaves	H460, A2058,H522-T1, PC-3,IMR-90	0.66, 0.78, 0.63, 0.60, 0.41 µM	[93]
Myrotheciumone A	Lactone	Myrothecium r.	Ajuga decumbens	HepG2, SMMC-7721, A549, MCF-7 cells, QSG-7701, HL-7702	5.36, 6.56, 5.88, 7.56, 16.30, 20.69 µM	[94]
Dihydromyrothecine C	Trichothecene Macrolide	Myrothecium r. IFB-E012	Artemisia annua	KB	44.48 µM	[95]
Camptothecin	Alkaloids	Neurospora c.	Nothapodytes foetida seed	A-549, HEP-2, OVCAR-5	-	[11,96]
(2R*,4R*)-3,4-dihydro- 4-methoxy-2-methyl-2H-1-benzopyran-5-ol	Pyrans	Nodulisporium spp.	Aquilaria sinensis stem	SF-268	-	[97]
Brefeldin A	Lactone	Paecilomyces spp.	1. Torreya grandis2. Taxus maireibark	HL-60, KB, Hela, MCF-7 and Spc-A-1	10.0, 9.0, 1.8, 2.0 & 1.0 ng/mL	[31]
(22E,24R)-8,14-epoxyergosta-4,22-diene-3,6- dione	Steroids	Papulaspora i.	Smallanthus sonchifolius roots & leaves	MDA-MB435, HCT-8, SF295, HL-60	3.3, 14.7, 5.0, 1.6 µM	[98]
1. 19-(α-d-glucopyranosyloxy) isopimara-7,15-dien-3β-ol,2. 19-(2-acetamido-2- deoxy-α-d glucopyranosyloxy) isopimara- 7,15-dien-3β-ol,3. 19-(α-d-glucopyranosyloxy) isopimara-7,15-dien-3-one	Diterpenes	Paraconiothyrium spp. MY-42	Fagus stem	HL60	1. 11.2 µM,2. 6.7 µM,3. 9.8 µM	[99]
Brasilamides E	Bisabolane Sesquiterpenoids	Paraconiothyrium b. (M3-3341)	Acer truncatum branches	MCF-7 and MGC	8.4 & 14.7 µM	[100]
5-Methyl-8-(3-methylbut-2-enyl) furanocoumarin	Coumarins	Penicillium spp. ZH16	Avicennia sp. leaves	KB, KBV200	5, 10 µg/mL	[101]
1. Penicillenol A1,2. Penicillenol B1	Polyketides (tetramic acids derivatives)	Penicillium spp. GQ-7	Aegiceras corniculatuminner bark	1. A-549, BEL-7402, P388, HL-602. HL-60	1. 23.8, 13.03, 8.85, 0.76 µM2. 3.20 µM	[102]
1. Leptosphaerone C2. Penicillenone	Polyketides	Penicillium spp. JP-1	Aegiceras corniculatuminner bark	1. A5492. P388	1. 1.45 µM2. 1.38 µM	[103]
Penifupyrone	Funicone	Penicillium spp. HSZ-43	Tripterygium wilfordii leaves	KB	4.7 µM	[104]
Lapachol	Naphtho-quinone	Penicillium spp.	Tabebuia argentia leaves	DU145, HepG2, Hep3B & MCF-7(β-Lapachone)	-	[17,18,19,20,21,22]
Arisugacin B, Arisugacin F	Meroterpenoids	Penicillium spp. SXH-65	Tamarix chinensis leaves	Hela, HL-60 and K562	59.9, 24.2, 36.2 & 44.4, 45.9, 46.6 µM	[105]
1. TMC-264,2. PR-toxin	1. Heptaketide2. Mycotoxin	Penicillium ch.HLit-ROR2	Hertiera littoralis root	1,2 >> HuCCA-1, HepG2, A549,MOLT-3, HeLa T47D, MDAMB231, MRC-5,2. >> HL-60	1,2. 5.62, 3.27, 8.01, 1.36, 4.49, 1.08, 2.81, 12.64 & 0.81, 3.41, 3.59, 0.09, 1.22, 1.00, 2.19, 3.66 µM2. 0.06 µM	[106]
Citriquinochroman	Alkaloids	Penicillium ci.	Ceratonia siliqua stem	L5178Y	6.1 µM	[107]
1. (+)-(3S,6S,7 R,8S)- periconone A,2. (−)-(1R, 4R, 6S, 7S)-2-caren-4,8-olide	Triterpenes	Periconia spp.	Annona muricata leaves	HCT-8, Bel-7402, BGC-823, A549, A2780, MCF-7	˃10−5 M	[108]
Periconicin B	Diterpene	Periconia a.	Xylopia aromaticaleaves	HeLa and CHO	8.0 µM	[109]
Pestalotiopsone F	Chromone	Pestalotiopsis spp.	Rhizophora mucronate leaves	L5178Y	8.93 µg/mL (EC50)	[110]
Pestalactam A, Pestalactam B	Alkaloids	Pestalotiopsis spp.	Melaleuca quinquenervia stem	MCF-7, NFF	64.4, 20.2 & 58.5, 12.8 µM	[111]
1. (4S,6S)-6-[(1S,2R)-1, 2-dihydroxybutyl]-4-hydroxy-4-methoxytetrahydro-2H-pyran-2-one,2. (6S,2E)-6-hydroxy-3-methoxy-5-oxodec-2-enoic acid, 3. LL-P880γ 4. LL-P880α5. Ergosta-5,7,22-trien-3b-ol	Monoterpenoids(1,2)	Pestalotiopsis spp. DO14	Dendrobium officinale	1–4 >> HL-601, 2, 4 and 5 >> LOVO	1–4. 15.24, 30.09, 64.87, 30.75 µM1,2,4,5. 50.97, 41.91, 68.88 & 65.20 µM	[112]
Siccayne [2-(3-Methyl-3-buten-1-ynyl) Hydroquinone]	Alkyne	Pestalotiopsis f.	Camellia sinensis branches	HeLa, HT29	48.2, 33.9 µM	[113]
1. Pestalofone F, G & H,Pestalodiol C,2. Pestaloficiol I, J, K & L	1. Epoxycyclo-hexanediol2. Isoprenylated chromone	Pestalotiopsis f.	Camellia sinensis branches	HeLa, MCF-7	1. 14.4, 36.4, 36.4, 16.7 & 11.9, 33.6, 33.6, 57.5 µM2. ˃136.1, 21.2, 99.3, 8.7 & 136.1, ˃153.8, ˃132.5, 17.4 µM	[114,115]
Pestalrone B	Benzophenones	Pestalotiopsis k.	Camellia sasanqua stems	HeLa, HepG2, U-251	12.6, 31.7, 5.4 µg/mL	[116]
Taxol	Diterpene	Pestalotiopsis m. EF01	Plectranthus amboinicus healthy leaves	Hep G2, MCF-7, BT220, HL251	0.5 µM	[117,118]
Torreyanic acid	Quinones	Pestalotiopsis m.	Torreya taxifolia	NEC, A549	3.5, 45 µg/mL	[119]
Taxol	Diterpene	Pestalotiopsis m.	Taxus wallichiana	BT220, H116, INT-407, HL251, HLK210,MCF-7	0.005–0.5 µM	[60,120]
Taxol	Diterpenes	Pestalotiopsis p. VM1	Tabebuia pentaphylla	MCF-7 breast cancer cell line	350 µg/mL	[121]
Photinides A–F,Photipyrone B	γ-Lactones	Pestalotiopsis p.	Roystonea regia	MDA-MB-231	10 µg/mL (IC25)	[122,123]
Taxol	Diterpenes	Pestalotiopsis t.	Terminalia arjuna leaves	BT220, H116, INT-407, HL251, HLK210,MCF-7	-	[60,121]
Taxol	Diterpenes	Pestalotiopsis v., Pestalotiopsis n.	Taxus cuspidate leaves and inner bark	BT220, HL251, HLK 210	-	[73]
Podophyllotoxin	Lignan	Phialocephala f.	Podophyllum peltatum	Topoisomerase I	-	[12]
Phialomustin A–D	Azaphilone	Phialophora m.	Crocus sativus	T47D	10, 1, 7, 9.2 µM	[124]
1. 4-hydroxymellein2. 4,8-dihydroxy-6-methoxy-3-methyl-3,4-dihydro-1H-isochromen-1-one	1. Polyketide2. Benzopyran	Phoma spp.	Cinnamomum mollissimum	P388	1. 94.6 (%)2. 48.8 (%)	[125]
Taxol	Diterpenes	Phoma b.	Ginkgo biloba leaves	MCF-7, A549, T98G	-	[117]
Camptothecine (CPT)9-methoxy CPT (9-MeO-CPT),10-hydroxy CPT (10-OH-CPT)	Alkaloids	Phomposis spp.	Miquelia dentata fruit and seed regions	HCT-116,SW-480,MCF-7	-	[26]
1. 2-(7′-hydroxyoxooctyl)-3-hydroxy-5-methoxybenzene-acetic acid ethyl ester2. 3-O-(6-O-a-L-arabinopyranosyl)- β-d-glucopyranosyl-1,4-dimethoxyxanthone	1. Polyketide2. Xanthone O-glycoside	Phomopsis spp.ZSU-H76	Excoecaria agallocha stem	HEp-2 and HepG2	32–64 µg/mL (MIC)	[126,127]
1. Phomopsidone A2. Diaporthelactone,7-hydroxy-4,6-dimethyl-3H-isobenzofuran-1-one and7-methoxy-4,6-dimethyl-3H-isobenzofuran-1-one	1. Depsidone2. Isobenzo-furanones	Phomopsis spp. A123	Kandelia candelfoliage	1. MDA-MB-4352. Raji cell line	1. 63 µM2. 27, 47 & 18 µM	[128]
Phomoxanthone A and B	Xanthone	Phomopsis spp. BCC 1323	Tectona grandis	KB, BC-1, Vero	0.99, 0.51, 1.4 & 4.1, 0.70, 1.8 µg/mL	[129]
1. Oblongolide Y2. Oblongolide Z	Polyketide(hexaketide γ-lactone)	Phomopsis spp.BCC 9789	Musa acuminata leaf	1. BC2. KB, BC, NCI-H187, Vero cells	1. 48 µM2. 37, 26, 32, 60 µM	[130]
18-metoxycytochalasin J, Cytochalasins H and J	Cytochalasins	Phomopsis spp.	Garcinia kola nut	HeLa	8.18, 35.69 & 3.66 µg/mL (LC50)	[131]
Dicerandrol A, B & C	Ergochromes	Phomopsis l.	Dicerandra frutescens stem	A549, HCT-116	7, 1.8, 1.8 & 7, 1.8, 7 µg/mL (IC100)	[132]
Tauranin	Sesquiterpene Quinone	Phyllosticta s.	Platycladus orientalisleaf tissue	NCI-H460, PC-3 M, MCF-7, SF-268, MIA Pa Ca-2	4.3, 3.5, 1.5, 1.8, 2.8 µM	[133]
Ergoflavin	Ergochrome	PM0651480	Mimusops elengi	TNF-a, IL-6, ACHN, H460, Panc1, HCT116, and Calu1	1.9, 1.2, 1.2, 4, 2.4, 8, & 1.5 µM	[134]
Spiropreussione A	Spirobis naphthalene	Preussia spp.	Aquilaria sinensis	A2780, BEL-7404	2.4, 3.0 µM	[135]
Cytochalasin 1, 2, 3 and E	Alkaloids	Rhinocladiella spp.	Tripterygium wilfordii dead tree limbs	A2780S, HCT-116,SW-620	3.91, 15.6, 3.91; 15.6, 62.5, 15.6; 3.91, -, 15.6 & ˂0.0153, 0.977, 0.244 µg/mL (IC100)	[136]
1. Rhytidones B2. Rhytidones C, MK3018,Palmarumycin CR1	Spirobisnaphthalenes	Rhytidhysteron spp.	Azima sarmentosa leaves	1. CaSKi2. MCF-7 and CaSki	1. 22.812. 17.30, 20.10, 14.47 & 24.44, 25.59, 21.95 µM	[137]
TMC-264	Heptaketide	Rhizopycnis v. Nitaf22	Nicotiana tabacum	HCT-116, HepG2, BGC-823, NCIH1650, and A2780	4.2, 5.9, 7.8, 3.2, 3.6 µM	[138]
Rhytidenone H & F	Spirobisnaphthalenes	Rhytidhysteron r. AS21B	Azima sarmentosa	Ramos and H1975	0.018, 0.252 & 0.048, 1.17 µM	[139]
1. Secalonic acid A, Penicillixanthone A2. Hypothemycin	1. Tetrahydro-xanthone2. RAL	Setophoma t.	Unidentified (leaf litter collected in a mangrove habitat)	MDA-MB-435 and SW-620	1. 0.16, 0.41 & 0.18, 0.21 µM2. 0.58, 2.14 µM	[140]
Sphaeropsidin A, Sphaeropsidin D	Diterpenes	Smardaea spp. AZ0432	Ceratodon purpureus living photosynthetic tissue	MDA-MB-231	1.4, 3.7 µM	[141]
Taxol	Diterpenes	Stemphylium s. SBU-16	Taxus baccata inner bark	MCF-7, A549, T98G	-	[117,142]
1. Altersolanol A,2. Alterporriol G and H	Quinones	Stemphylium g.	Mentha pulegium stem	1. K562, A549,2. L5178Y	1. ˃1, ˃2 µM2. 2.7 µg/mL (EC50)	[143,144]
1. 3-Dehydroxymethylbisde-thio-3,10a-bis(methylthio)-gliotoxin2. Bisdethiobis(methylthio)-Gliotoxin3. Didehydrobisdethiobis(methylthio)gliotoxin	Alkaloids	Talaromyces spp. LGT-2	Tripterygium wilfordi	B16	86, 82 & 78% at 500 µg/mL	[145]
Talaperoxide B, Talaperoxide D	Peroxides	Talaromyces f.	Sonneratia apetala healthy leaves	MCF-7, MDA-MB-435, HepG2, HeLa, PC-3	1.33, 2.78, 1.29, 1.73, 0.89 & 1.92, 0.91, 0.90, 1.31, 0.70 µg/mL	[146]
Vincristine and Vinblastine	Alkaloids	Talaromyces r. CrP20	Catharanthus roseus leaf tissues	HeLa, MCF7, U251, A549, A431	4.2, 4.5, 5.5, 5.5, 5.8 µg/mL	[74]
Taxol	Terpenes	Taxomyces a.	Taxus brevifoliainner bark	BT220, H116, INT-407, HL251, MCF-7HLK210	-	[6,60]
Hypericin, Emodin	Polyketides	Thielavia s.	Hypericum perforatum stem	THP-1	-	[147]
Podophyllotoxin	Lignan	Trametes h.	Podophyllum hexandrum	Topoisomerase I	-	[148]
Aspochalasin D, Aspochalasin J	Cytochalasan	Trichoderma g.	Panax notoginseng	HeLa	5.72, 27.4 µM	[149]
Trichothecinol-A	Mycotoxins	Trichothecium spp.	Phyllanthus amarus	MDA-MBA-231, B16F10	500 µM (LC25), 500 µM (LC50)	[150]
Merulin AMerulin C	Sesquiterpenes	XG8D(a basidiomycete, not better identified)	Xylocarpus granatum plant	BT474, SW620	4.98, ˃10 & 4.84, ˃10 µg/mL	[151]
Eremophilanolide 1,2 & 3	Sesquiterpenes	Xylaria spp. BCC 21097	Licuala spinosa	KB, MCF-7, NCI-H187, Vero cells	3.8–21 µM	[152]
1. 2-Chloro-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione2. Xylariaquinone A	Benzoquinone	Xylaria spp.	Sandoricum koetjape	Vero cells	1.35, ˃184 µM	[153]
1. Cytochalasin D2. Cytochalasin C and Q	Cytochalasins	Xylaria spp. NC1214	Hypnum sp.	1,2 >> NCI-H460, PC-3M, SF-268, MDA-MB-231;1. >> MCF-7,	D: 1.03, 0.22, 0.43, 1.01 µM; C: 1.65, 1.06, 0.96, 1.72 µM; Q: 1.53, 1.51, 1.31, 1.32; 1.44 µM	[154]
Cytochalasin E	Alkaloids	Xylaria spp. XC-16	Toona sinensis	brine shrimp	2.79 µM (LC50)	[155]
1. Cytochalasin D2. Ergosterol peroxide	1. Cytochalasins2. Steroid	Xylaria cf. c. PK108	Unidentified	1. NCI-H187, KB, Vero cell2. NCI-H187, Vero cell	1. 5.95, 3.25, 0.36 µg/mL2. 5.81, 47.95 µg/mL	[156]
Xylariacin AXylariacin BXylariacin C	Triterpenes	Xylarialean spp. A45	Annona squamosalphloem	HepG2	48, 9.7, 46.7% at 20 µg/mL	[157]
Secalonic acid D	Ergochrome	ZSU44 (not better identified)	(unidentified) mangrove plant	HL-60, K562	0.38, 0.43 µM	[158]

* Compounds with IC50 values less than 10 μM are reported.

Table 3

Recently (2018–2020) reported potential cytotoxic metabolites isolated from medicinal-plant-associated endophytic fungi.

Sl	Isolated Metabolites *	Fungus Name	Host Medicinal Plant	Reported Activity	References
1	Penicolinate A	Bionectria spp.	Raphia taedigera	Displayed potent cytotoxicity against cells with an IC50 value of 4.1 μM.	[159]
2	Fusarithioamide B	Fusarium c.	Anvillea arcinia (Burm.f.) DC.	Showed selective and potent effect towards BT-549, MCF-7, SKOV-3, and HCT-116 cell lines with IC50s 0.09, 0.21, 1.23, and 0.59 μM, respectively	[160]
3	3-(4-nitrophenyl)-5-phenyl isoxazole	Aspergillus n. spp.		Exhibited potent cytotoxic effect on HepG2 and SMCC-7721 cells with the IC50 values were 0.347 and 0.380 mM, respectively	[161]
4	Spiciferone F	Phoma b.	Kalidium foliatum (Pall.) Moq	Exhibited strong biological effect against MCF7 with a half-maximal inhibitory concentration value at 7.73 ± 0.11 μM	[162]
5	Xylariphthalide A	Diaporthe spp.	Tylophora ouata	Displayed cytotoxic activity against human tumor cell lines BGC-823 cells with IC50 values of 1.5 μmol·L−¹	[163]
6	Cis -4-hydroxy-6-deoxytalone	Diaporthe spp.	Tylophora ouata	Displayed cytotoxic activity against human tumor cell lines BGC-823 cells with IC50 8.6 μmol·L−¹	[163]
7	Xylarolide A	Diaporthe spp.	Datura inoxia	Showed promisingly inhibited growth of MIAPaCa-2 and PC-3 cells with an IC50 values of 20 14 µM	[164]
8	Jammosporin A	Rosellinia sanctae-cruciana	Albizia lebbeck	Exhibited promising cytotoxic potential against the human leukemia cancer cell line (MOLT-4)	[165]
9	Pyrrocidine A (Pyridone alkaloid)	Cylindrocarpon spp.	Sapium ellipticum	Showed potent cytotoxicity against the human ovarian cancer cell line A2780 with an IC50 value of 1.7 μM	[166]
10	Bostrycoidin	Fusarium s.	Cassia alata Linn.plant	Significant cytotoxicity against vero cell line	[8]
11	Anhydrofusarubin
12	1-Monolinolein	Streptomyces c. YBQ59	Cinnamomum cassiaplant	Exhibited cytotoxicity against human lung adenocarcinoma EGFR-TKI-resistant A549 cells with IC50 values of 3.6 µM	[167]
13	Bafilomycin D			Showed activity against EGFR-TKI-resistant A549 cells with IC50 values 6.7 µM
14	3′-Hydroxydaidzein			Showed activity against EGFR-TKI-resistant A549 cells with IC50 values 7.8 µM
15	Colletotricone A	Colletotrichum g. A12	Aquilaria sinensis	Inhibited growth of MCF-7, NCI-H460, HepG-2, and SF-268 tumor cells with IC50 values ranging from 15.7 to 46.8 μM	[168]
16	Mollicellin G	Chaetomium spp. Eef-10	Eucalyptus exserta	Cytotoxic against two human cancer cell lines HepG2 and Hela withIC50 values of 19.64 and 13.97 µg/mL, respectively	[169]
17	Demethylincisterol A3	Pestalotiopsis spp.	Rhizophora mucronata	Showed potent activity against the Hela, A549 and HepG, with IC50 values ranging from 0.17 to 14.16 nM	[170]
18	Shearilicine (1), Paspalinine-13-ene (2), 7-Hydroxypaxilline-13-ene (3), Shearinine O (6), Shearinine P (7), emindole SB (10), paspaline (18), 7-hydroxy-13-dehydroxypaxilline (19) *	Penicillium spp. (strain ZO-R1-1)	Zingiber officinale	1 showed the most pronounced cytotoxicity against L5178Y (IC50 is 3.6 μM) whereas 2, 3, 6, 7 & 19 exhibited cytotoxicity with IC50 values ranging between 5.3 and 8.1 μM. 1, 6, 10 and 18 displayed pronounced cytotoxicity with IC50 values ranging between 5.3 and 8.7 μM against A2780	[171]
19	Flavipin	Chaetomium g.	Couroupita guianensis Aubl. leaves	Exhibited cytotoxicity toward A549, HT-29, and MCF-7 cancer cells with an IC50 concentration of 9.89 µg/mL, 18 µg/mL, and 54 µg/mL, respectively	[172]
20	Bellidisin D	Phoma b.	Tricyrtis maculate leaves	Exhibited significant cytotoxicity against HL-60, A549, SMMC-7721, MCF-7, and SW480 cells with IC50 value ranged from 3.40 to 15.25 μM	[173]
21	Epicorazine A	Epicoccum n.	Salix sp.	Displayed strong to moderate cytotoxic activities against L5178Y, Ramos, and Jurkat J16 cell lines with IC50s ranging from 1.3 to 28 mM	[174]
22	Cytochalasin E	Aspergillus spp.	Pinellia ternata tubers	Exhibited significant cytotoxicity with an IC50 value of 7.8 μM	[175]
23	Asperchalasin A-F (seco-cytochalasins), Asperlactone G-H (asperlactones)			All the compounds showed cytotoxicity against A-549 with IC50 values ranging from 23.3 to 70.2 μM
24	Demethylchaetocochin C, dethiotetra(methylthio)chetomin, chaetoperazine A, 4-formyl-N-(30-hydroxypyridin-20-yl) benzamide	Chaetomium g. 7951	Panax notoginseng root	Showed cytotoxicity against MCF-7, MDA-MB-231, H460, and HCT-8 cell lines with IC50 values ranging from 4.5 to 65 μM	[176]
25	Chetoseminudin F (1), chaetocochin C (6), ergosterol (8), chetomin A (9), chetomin (12)	Chaetomium spp. SYP-F7950	Panax notoginsengStem	1 displayed more potent cytotoxic activity against MDA-MB-231 cells than paclitaxel with IC50 of 26.49 μM. 6, 8, 9 and 12 exhibited strong cytotoxicity with IC50 values ranging between 2.75 and 8.68 μM against A549 and MDA-MB-231	[177]
26	Ascomylactam A to C (1–3)	Didymella spp. CYSK-4	Pluchea indica healthy branch	1 and 3 exhibited moderate cytotoxic activities against MDA-MB-231, MDA-MB-435, NCI-H460, PC-3 & HCT116 cell lines with IC50 values ranging between 4.2 and 7.8 μM. 2 showed cytotoxicity towards the MDA-MB-231 and HCT116 cells with IC50s of 6.6 and 4.5 μM, respectively	[178]
27	Pleosporalin F	Pleosporales spp. F46	Mahonia fortunei	Exhibited moderate cytotoxicity towards MDA-MB-231 cell line with an IC50 value of 22.4 ± 1.1 μM.	[179]
28	19,20-epoxycytochalasins C (1) and D (2), and 18-deoxy-19,20-epoxy-cytochalasin C (3)	Nemania spp. UM10M	Torreya taxifolia leaf	1 and 3 displayed moderate toxicity against SK-MEL and BT-549 cell lines. 2 showed moderate toxicity against BT-549 and LLC-PK11 cell lines	[180]
29	Gartryprostatins A to C (1–3)	Aspergillus spp. GZWMJZ-258	Garcinia multiflora fruit	1–3 showed selective cytotoxicity against the cell line, MV4–11, with IC50 values of 7.2, 10.0, and 0.22 μM, respectively	[181]
30	19,20-epoxycytochalasin C	Xylaria cf. c.	Solanum tuberosum stem tissues	Displayed significant specific cytotoxic activity against HL-60 cells with an IC50 of 1.11 μM.	[182]
31	Sporulosaldein F	Paraphaeosphaeria spp. F03	Paepalanthus planifolius leaves	Displayed weak cytotoxic activities against MCF-7 and LM3 cells, with IC50 values of 34.4 and 39.2 µM, respectively.	[183]
32	Trichodermic acid	Penicillium o.	Taxus media roots	Displayed moderate cytotoxicity towards A549, LN229, MGC, LOVO, and MDA231 with IC50 values of 51.45, 23.43, 39.16, 46.97, and 42.85 μg/mL, respectively.	[184]
33	Stemphyperylenol (5), (17R)-4-hydroxy-17-methylincisterol (10)	Alternaria a.	Psidium littorale Raddi leaves	5 showed cytotoxicity against MCF-7 and HepG-4 cell lines (IC50 values of 4.2 ± 0.6 and 7.9 ± 0.9 μM, respectively); 10 exhibited cytotoxicity against HepG-4 cell line with an IC50 value of 9.73 ± 1.2 μM.	[185]
34	Aspergisocoumrins A & B	Aspergillus spp. HN15-5D	Acanthus ilicifolius fresh leaves	Exhibited cytotoxicity against MDA-MB-435 cells (IC50 values of 5.08 ± 0.88 and 4.98 ± 0.74 μM, respectively)	[186]
35	Phomoxanthone A (1) and Penialidin A (2)	Coniochaeta spp. F-8	Ageratina adenophora	1 showed a stronger cytotoxicity than 2	[187]
36	Macrophin	Phoma m.	Glycyrrhiza glabra Linn	Exhibited prominent cytotoxic activity against all the cancer-cell lines (MDA-MB-231, T47D, MCF-7, and MIAPaCa-2 with IC50 values of 14.8, 8.12, 13.0, and 0.9 μM, respectively).	[188]
37	Myrothecines D–G (1–4), 16-hydroxymytoxin B (5), and 14′-dehydrovertisporin (6)	Myrothecium r., IFB-E008, IFB-E009, and IFB-E012 strains	Trachelospermum jasminoides	Showed cytotoxicity against K562 and SW1116 cells (IC50 values ranging between 56 nM and 16 μM).	[189]
38	Giluterrin	Aspergillus t. P63	Axonopus leptostachyus roots	Exhibited cytotoxicity against 786-0 and PC-3 cell lines (IC50 of 22.93 μM and 48.55 μM, respectively).	[190]
39	2′-aminodechloromaldoxin (1) and 2′-aminodechlorogeodoxin (2)	Pestalotiopsis f.	Cinnamomum camphora branches	1 & 2 displayed moderate cytotoxicity against NCI-H460, SF-268, MCF-7 and PC-3cell lines (IC50 values of 18.63, 20.23, 23.53, 20.48 μM and 16.47, 17.57, 20.79, 19.43 μM, respectively).	[191]
40	Stachybochartins A, B, C, D and G.	Stachybotrys c. PT2–12	Pinellia ternata	Showed cytotoxicity against MDA-MB-231 and U-2OS cells (IC50 values ranging between 4.5 to 21.7 μM).	[192]
41	(S)-3,6-dihydroxy-8-methoxy-3-methylisochroman-4-one (1a), 6-methoxy-3-methylisochromane-3,8-diol (2).	Aspergillus f.	Cordyceps sinensis fruiting body	1a & 2 exhibited moderate growth inhibition against MV4–11 (IC50 values of 38.39 μM and 30.00 μM, respectively).	[193]
42	Flavoglaucin	Aspergillus spp.AV-2	Avicennia marina healthy leaves	Exhibited most potent cytotoxicity against Caco-2 cells (IC50 of 2.87 μM)	[194]
43	Peniquinone A (1) & peniquinone B (2)	Penicillium spp. L129	Limonium s.	1 showed cytotoxicity against the cell lines, MCF-7, U87, and PC3 (IC50 ranging between 9.01 and 14.59 µM); 2 exhibited relatively weak cytotoxicity against the same cells (IC50 ranging between 13.45 and 25.32 µM)	[195]
44	Pestalolide B (1), pestalotether F (4)	Pestalotiopsis spp.	Melaleuca alternifolia leaves	1 displayed remarkable inhibitory effect against the cell lines, HL60, U87MG, MDA-MB-231, and HEP-3B cells (IC50 ranging from 1.42 to 5.90 μM); 4 exhibited significant inhibitory potency against HL60 (IC50 5.05 μM)	[196]
45	Emeridone B (2), Emeridone D (4), Emeridone F (6)	Emericella spp. TJ29	Hypericum perforatum root	2, 4, and 6 showed cytotoxicity against cell lines, SMMC-7721 & SW-480 (IC50 values ranging between 8.19 and 18.80 μM). Compound 4 also exhibited cytotoxicity against A-549 (IC50 of 11.33 μM)	[197]
46	Lithocarin B & C, Tenellone H	Diaporthe l. A740	Morinda officinalis twigs	Displayed weak inhibitory activities against SF-268, MCF-7, HepG-2, and A549 cell lines with IC50 values ranging between 30 and 100 μM	[198]
47	Cytosporaquinone A–D, leucomelone.	Cytospora spp. CCTU A309	Juglans (Walnut tree)	All Showed significant cytotoxicity against the cell lines, L929 and KB-3-1 (IC50 values ranging from 2.4 to 26 μg/mL)	[199]
48	Ilanpyrone (1), methyl Asterrate (4)	Annulohypoxylon i.	Cinnamomum sp.	1 showed moderate cytotoxicity against MCF-7 cells (IC50 is 4.79 µM). 4 displayed cytotoxicity towards MCF-7, NCI-H460, and SF-268 cells (IC50 values ranging between 5.46 to 8.56 μM)	[200]
49	Rhinomilisin A (1), Rhinomilisin G (7) and Gliocladic acid (15)	Rhinocladiella s.	Acrostichum aureum	1, 7 & 15 exhibited cytotoxic activities against L5178Y (IC50 values of 5.0, 8.7, and 24.4 μM, respectively).	[201]
50	Koninginol B (2), 1R,3S,6S,7R,10S-7-isopropyl-4,10-dimethylbicyclo[4.4.0]dec-4-en-3,10-diol (15), 1R,3R,6S,7R,10S-7-isopropyl-4,10-dimethylbicyclo[4.4.0]dec-4-en-3,10-diol (16)	Trichoderma k. A729	Morinda officinalis branches	2, 15, and 16 showed antiproliferative activities against A549 (IC50 values of 46.6, 31.3, and 22.2 μM, respectively)	[202]
51	Cytochalasin D1 (1) and C1 (2)	Xylaria cf. cu.	Solanum tuberosum stem tissues	1 and 2 showed moderate cytotoxicity against HL-60 (IC50 value of 12.7 and 22.3 μM, respectively)	[203]
52	Bipolahydroquinone C (3), cochlioquinone I (4), cochlioquinones K-M (6–8)	Bipolaris spp. L1–2	Lycium barbarum fresh leaves	3, 4, and 6–8 exhibited cytotoxic activities against NCIH226 and/or MDA-MB-231 (IC50 values ranging between 5.5 to 9.5 μM)	[204]
53	Botryosulfuranol A	Botryosphaeria m. strain E224	Bixa orellana fresh leaves	Exhibited cytotoxicity against HT-29, HepG2, Caco-2, HeLa, IEC6, and vero cells (IC50 values ranging between 8 to 23.5 μM)	[205]
54	Chloroisosulochrin	Pestalotiopsis t. (N635)	Camellia sinensis (Theaceae)	Exhibited moderate cytotoxicity towards the HeLa cell line with an IC50 value of 35.2 μM	[206]
55	Pestalotether D			Exerted cytotoxicity against HeLa and MCF-7 cell lines with IC50 values of 60.8 and 22.6 M, respectively
56	Cytosporins W *	Pseudopestalotiopsis t.	Rhizophora racemosamangrove plants	Exhibited potent cytotoxicity towards mouse lymphoma cell line L5178Y with an IC50 value of 3.0 μM	[207]
57	Terezine E and 14-hydroxyterezine D	Mucor spp.	Centaurea stoebe	Showed potent activity against K-562 and HUVEC cell lines	[208]
58	Citrinin (CIT) and dicitrinin-A	Penicillium ci.	Dichotomaria marginata	Showed toxicity in A. saline, with LC50 (24 h) 1.71 μg/mL and 2.29 μg/mL, and LC50 (48 h) of 0.54 μg/mL and 0.54 μg/mL, respectively	[209]
59	Allantopyrone E	Aspergillus v.	Avicennia marina mangrove	Showed cytotoxic effect on HeLa cells with IC50 = 50.97 μM	[210]
60	Integracin A and B	Cytospora spp.	Ceriops tagal (Chinese mangrove)	Both compounds showed promising cytotoxicity towards HepG2 Cells with IC50 values of 5.98 ± 0.12 µM and 9.97 ± 0.06 µM, respectively	[211]
61	(±)-Asperteretone F (3a/3b)	Aspergillus t.	Hypericum perforatum	Potent cytotoxic activities against human pancreatic cancer cells, including AsPC-1, SW1990 and PANC-1 cells, with IC50 values ranging from 1.2 to 15.6 μM	[212]
62	Sterigmatocystin	Paecilamyces spp. TE-540	Nicotiana tabacum L.	showed moderate to strong cytotoxicity towards A549, BT-549, HepG2, and MCF-7 cells with IC50 values ranging from 5.6 to 14.2 µM	[213]
63	Methyl 3-chloroasterric acid	Pleosporales spp. SK7.	Kandelia candel leaves	Exhibited cytotoxicity against MDA-MB-435 cell with an IC50 of 25.96 ± 0.32 μM	[214]
64	Rhizoperemophilane N	Rhizopycnis v.	Nicotiana tabacum	Exhibited selective cytotoxicity against NCI-H1650 and BGC823 tumor cells	[215]
65	Pramanicin A	Aplosporella j.	Orychophragmus violaceus (L.) O. E. Schul	exhibited strong cytotoxic activities against human lymphoma (Ramos) and leukemia (Jurkat J16) cells with IC50 values of 4.7 and 4.4 μM, respectively	[216]
66	Myrothecines H and I	Paramyrothecium r.	Morinda officinalis	Both the compounds exhibited promising cytotoxicity against SF-268, NCI-H460, and HepG-2 tumor cell lines with the IC50 ranging from 0.0002–16.2 μM and induced apoptosis of HepG-2 cells	[217]
67	Colletotrichalactone A and colletotrichalactone Ca	Colletotrichum spp. JS-0361	Morus alba	Exhibited moderate-to-potent cytotoxic activities against MCF7 cells with IC50s of 35.06 and 25.20 µM, respectively	[218]
68	Emodin, (an anthraquinone)	Diaporthe l.	Artocarpus heterophyllus	exhibited cytotoxicity against murine leukemia P-388 cells with an IC50 value of 0.41 μg/mL	[219]
69	Demethyli cisterol A3	Aspergillus t. YP-2.	Taxus yunnanensis bark	Showed cytotoxicity against the A549 and HepG2 cell with IC50 values of 5.34 and 12.03 μM, respectively	[220]
70	Demethylincisterol A5			Showed cytotoxicity against the A549 and HepG2 cell with IC50 values of 11.05 and 19.15 μM, respectively

* Compounds with IC50 values less than 10 μM are reported in bold.

The genera of endophytic fungi containing two or more putative anticancer-agent-producing species are Acremonium, Alternaria, Aspergillus, Ceriporia, Chaetomium, Colletotrichum, Cytospora, Emericella, Eurotium, Eutypella, Fusarium, Guignardia, Hypocrea, Penicillium, Pestalotiopsis, Phomposis, Periconia, Stemphylium, Talaromyces, Thielavia, and Xylaria [4,221]. These endophytic fungi offer an alternative source of bioactive compounds. We may be able to increase their yield of specific anticancer compounds by employing biotechnology and genetic engineering [221].

2.1. Anti-Cancer Agents in Clinical Use Shared by Plants and Endophytic Fungi

Plants are prolific sources of anticancer agents. In the area of cancer, of the 175 approved small molecules over the years from the 1940s to 2014, 75% (131) are other than synthetic and 49% (85) are either natural products or their derivatives [222]. Very recently, it was reported that among the approved 321 anticancer molecules from all sources during the period of 1946 to 2019, 35 (10.9%) were unaltered natural products and 65 (20.2%) were natural product derivatives compared to 53 (16.5%) completely synthetic drug molecules. Some of these agents obtained from plants are also found in their corresponding endophytic fungi. The following are some examples of plant/endophytic fungi-derived cancer effective agents [1,6] (Figure 3a,b).

Figure 3

Anticancer compounds of different chemical classes from endophytic fungi-alkaloidal compounds and their derivatives: (a) (1–8), benzo[j]fluoranthene (9), Chromone (10), coumarin (11), depsidones (12, 13), depsideptide (14), ergochromes (15, 16), ester (17), lactones (18–22), lignans (23–24), peptide (25), polykedites (26); (b) polyketides (27–32), quinones (33–39), spirobisnaphthalenes (40–42), terpenes (43–54), xanthones (55), naphthoquinones (56, 57).

Paclitaxel (Taxol®) is used in combination with other anti-cancer drugs in ovarian, breast, non-small cell lung cancer (NSCLC), and Kaposi sarcoma. An active paclitaxel analogue, docetaxel is used in breast and non-small cell lung cancer (NSCLC) treatment [223]. Even though camptothecin exerted severe bladder toxicity in its clinical trial in the 1970s and therefore, was dropped, its two water-soluble derivatives, topotecan and irinotecan, have been shown to be more effective anti-cancer agents and are being utilized for these purposes [223]. Topotecan (Hycamtin®) was the first CPT derivative that was orally available and has been approved for cervical (when used in combination with cisplatin), ovarian, and non-small cell lung cancer treatment. Irinotecan (Camptosar®) has been approved for colorectal cancer treatment. These agents show cytotoxicity on account of their ability to inhibit a fundamental enzyme, topoisomerase-I, involved in the winding and unwinding process of DNA during replication or protein synthesis [1,223]. The vinca alkaloids, vinblastine and vincristine, and their semi-synthetic analogs, vinorelbine and vindesine, are primarily used in combination with other chemotherapeutic drugs in the treatment of advanced testicular cancer, breast cancer, Kaposi’s sarcoma, lung cancer, leukemias, and lymphomas [223]. Etoposide and teniposide are clinically effective semi-synthetic derivatives of a podophyllotoxin isomer, epipodophyllotoxin, which are used in bronchial cancers, lymphomas, and testicular cancer treatments [223].

2.2. Putative Anticancer Compounds from Endophytic Fungi

2.2.1. Alkaloids and Nitrogen-Containing Heterocycles

Camptothecin (CPT) (1), a pentacyclic quinoline alkaloid, was, at first, isolated from the Camptotheca (happy tree) woods showing antileukemic and anti-cancer effects in animals [1]. It exerts its cytotoxicity by inhibition and dissociation of the DNA-topoisomerase-I complex during DNA replication [224,225]. However, recently, CPT has been isolated from some endophytic fungi, Entrophospora i., residing in these plants. Since Entrophospora i. also lives inside the inner bark of Nothapodytes foetida [11], in 2008, CPT was isolated from a Nothapodytes foetida seed endophyte, Neurospora c., and both authentic and fungal CPT exhibited comparable cytotoxic effects in human cancer cell lines HEP-2 (liver cancer), A549 (lung cancer), and OVCAR-5 (ovarian cancer) [96]. In 2009, CPT along with its two derivatives, 9-methoxycamptothecin and 10-hydroxycamptothecin, were isolated from a Camptotheca acuminata inner bark endophyte, Fusarium s. (Figure 3a). These derivatives are more water soluble and more potent inhibitors of the topoisomerase-I enzyme [80] (Table 2).

Cytochalasins (2a–2d) are fungal metabolites that inhibit cell division by means of inhibiting actin filament polymerization [226]. Four cytochalasins (cytochalasin 1, 2, 3, and E) have been isolated from an endophytic fungus, Rhinocladiella spp. from the Tripterygium wilfordii dead tree limbs and were tested against HCT-116 (colon tumor cell line), A2780S (ovarian tumor cell line), and SW-620 (colon tumor cell line) showing cytotoxic activities [136].

The vinca alkaloid (3a, 3b), vincristine (leurocristine), was isolated from Catharanthus roseus [227]. This alkaloid has also been isolated from some fungal endophytes of Catharanthus roseus such as Fusarium o. (inner bark), Mycelia s. 97CY(3) (Leaves), and Talaromyces r. CrP20 (Leaves) [74,75,89]. Vincristine irreversibly binds to the spindle proteins and microtubules during the S-phase of cell cycle hampering mitotic spindle formation and therefore arresting tumor cell division in the metaphase [1].

Chaetominine (4) was isolated from an endophyte, Chaetomium sp. IFB-E015 from the healthy leaves of Adenophora axilliflora, and it was cytotoxic against K562 (human leukemia cells) and SW1116 (human colon cancer cells) [54].

Cytochalasan-based alkaloids (5a–5c, 6), namely chaetoglobosin C, E, F, U, and penochalasin A (6), were obtained from the endophyte Chaetomium g. IFB-E019 residing inside the Imperata cylindrica healthy stem. Chaetoglobosin U was cytotoxically active against the KB cell line (human nasopharyngeal epidermoid tumor) with an IC50 value of 16.0 µM, whereas chaetoglobosin C (IC50 34.0 µM), E (IC50 40.0 µM), F (IC50 52.0 µM), and penochalasin A (IC50 48.0 µM) were moderately active against the KB cell line [57]. Endophytic fungus Chaetomium g. L18 from the plant Curcuma wenyujin produces chaetoglobosin X that exerted cytotoxic activity against H22 (hepatic cancer cells in mice) and MFC (gastric cancer cells in mice) cell lines [56] (Table 2).

2.2.2. Benzo[j]fluoranthenes

Daldinone C (9a) and D (9b) were discovered from an Artemisia Artemisia annua endophyte, Hypoxylon t. IFB-18, where both agents exerted strong cytotoxic action against the human colorectal cancer SW1116 cell line at IC50 values of 49.5 and 41.0 μM, respectively [85] (Table 2, Figure 3a).

2.2.3. Chromones

A novel chromone, Pestalotiopsone F (10), was isolated from an endophytic fungus Pestalotiopsis spp. associated with a mangrove plant Rhizophora mucronata. Pestalotiopsone F showed moderate cytotoxicity to L5178Y (murine cancer cell line) at an EC50 value of 8.93 μg/mL [110]. Pestaloficiol I, J, K, and L are new isoprenylated chromone derivatives discovered from a Camellia sinensis endophyte, Pestalotiopsis f., that displayed cytotoxicity against HeLa (Cervical cancer) and MCF-7 (Breast cancer) cell lines [115] (Table 2).

2.2.4. Coumarins

Arundinone B (11) was isolated from an endophyte Microsphaeropsis a. associated with Ulmus macrocarpa. The compound showed cytotoxicity to T24 (Bladder carcinoma) and A549 (Lung carcinoma epithelial) cell lines [92] (Table 2).

2.2.5. Depsidones

Botryorhodines A (12a) and B (12b), two depsidones, were isolated from the endophytic fungus Botryosphaeria r. associated with Bidens pilosa. These compounds exhibited weak antitumor activity against the HeLa cell line at a concentration of 96.97 and 36.41 μM, respectivel [48]. Depsidone 1 was discovered from a fungus of the Pleosporales order (BCC 8616) isolated from an unidentified plant leaf of the Hala-Bala forest origin. Depsidone 1 displayed weak cytotoxicity to KB and BC cell lines with IC50 values 6.5 and 4.1μg/mL, respectively [43] (Table 2).

2.2.6. Depsipeptides

Beauvericin (14), a depsipeptide, was isolated from two fungi, Fusarium o. EPH2RAA and Fusarium o., associated with the plants Cylindropuntia echinocarpus and Ephedra fasciculate, respectively. Beauvericin displayed cytotoxicity to NCI-H460 (human non-small cell lung cancer), MIA Pa Ca-2 (human pancreatic carcinoma), MCF-7 (human breast cancer), and SF-268 (human CNS cancer) cell lines with IC50 values of 1.41, 1.66, 1.81, and 2.29 μM, respectively, showing selective cytotoxicity toward MIA PaCa-2 and NCI-H460 (Table 2). Beauvericin also inhibited the metastasis of MDA-MB-231 (Breast cancer) and PC-3M (metastatic prostate cancer) cells at concentrations ranging between 3.0–4.0 and 2.0–2.5 µM, respectively [77]. According to other studies, beauvericin displayed cytotoxicity against A549 (Lung carcinoma epithelial), PC-3 (Prostate cancer), and PANC-1 (human pancreatic carcinoma) cell lines with IC50 values of 10.4 ± 1.6, 49.5 ± 3.8, and 47.2 ± 2.9 μM, respectively [71]. Additionally, in 2006, Ivanova et al. demonstrated the cytotoxicity of beauvericin against Hep-G2 (hepatocellular carcinoma) and MRC-5 (fibroblast-like fetal lung cell line) cells as well [76].

2.2.7. Ergochromes

Phomopsis l., an endophytic fungus of Dicerandra frutescens, produced three compounds dicerandrols A, B, and C (15a–15c), structurally related to the ergochromes and secalonic acids as they also have the same tricyclic C15 system with a similar arrangement of substituents. These compounds displayed modest antitumor activities toward A549 (lung adenocarcinoma epithelial cell line) and HCT-116 (colon tumor cell line) cell lines [132] (Table 2).

Secalonic acid D (16), isolated from mangrove plant endophytic fungus no. ZSU44, displayed potent cytotoxicity against HL60 (the human promyelocytic leukemia cell line) and K562 (human leukemia cells) cells with IC50 values of 0.38 and 0.43 μM, respectively. It caused apoptosis in those cell lines and cell cycle arrest in the G(1) phase as well [158].

2.2.8. Esters

Globosumones A (17a) and B (17b), isolated from the endophyte Chaetomium g. associated with Ephedra fasciculate, were shown to have cytotoxicity to MCF-7 (breast cancer), MIA PaCa-2 (pancreatic carcinoma), NCI-H460 (non-small cell lung cancer), SF-268 (CNS glioma), and WI-38 (normal human fibroblast cells) cell lines [58].

2.2.9. Lactones

The lactone compound Brefeldin A (18) was obtained from two endophytic fungi, Aspergillus c. and Paecilomyces spp., isolated from the plants Taxus mairei and Torreya grandis. Brefeldin A exhibited antitumor activities to Hela, HL-60, KB, MCF-7, and Spc-A-1 with IC50 values of 1.8, 10.0, 9.0, 2.0, and 1.0 ng/mL [31]. Brefeldin A was also obtained from the endophyte Acremonium spp. isolated from the healthy Knema laurina twig. It showed cytotoxicity to BC-1 (breast cancer), KB (epidermoid cancer of the mouth), and NCIH187 (human small-cell lung cancer), with IC50 values of 0.04, 0.18, and 0.11 μM, respectively [86] (Table 2).

Radicicol (19) was obtained from Chaetomium c. associated with Ephedra fasciculate and it is a HSP90 (heat shock protein) inhibitor, which is frequently expressed highly in cancer cells. It also showed cytotoxicity to the MCF-7 (breast cancer) cell line at an IC50 value 0.03 μM [55].

Photinides A–F (20a–20f) were obtained from the endophyte Pestalotiopsis p. associated with Roystonea regia, and all of these γ-lactones at 10 μg/mL exerted cytotoxicity against the MDA-MB-231 (breast cancer) cell line with inhibitory rates of 24.4, 24.2, 23.1, 24.4, and 24.6%, respectively [123] (Table 2).

Eutypellin A (21), isolated from the endophyte Eutypella spp. BCC 13199 associated with Etlingera littoralis, showed cytotoxicity to KB, MCF-7NCI-H187 (human small-cell lung cancer cells), and nonmalignant Vero cells with IC50 values of 38, 84, 12, and 88 μM, respectively [70].

2.2.10. Lignans

Podophyllotoxin (22), a precursor to the topoisomerase-I-inhibiting anticancer drugs teniposide (23), etoposide (24), and etoposide phosphate, were isolated from the endophyte Phialocephala f. associated with Podophyllum peltatum [12]. This was also obtained from the endophyte Trametes h. associated with Podophyllum hexandrum and from the endophyte Fusarium s. associated with Podophyllum hexandrum [1,79,148] (Table 2).

2.2.11. Peptides

Leucinostatin A was isolated from the endophyte Acremonium spp. associated with Taxus baccata and was shown to be effective against BT-20 (breast cancer) cell line with an LD50 value of 2 nM [14]. It inhibits the growth of prostate cancer cells through the suppression of IGF-I (Insulin-Like Growth Factor-I) expression in PrSC (prostate stromal cells) [228] (Table 2).

2.2.12. Polyketides

Two novel oblongolides, Y (26a) and Z (26b) (Figure 3a), are produced by the endophyte Phomopsis spp. BCC 9789 housed in Musa acuminate (a wild banana). Oblongolide Y exhibited cytotoxicity against BC (human breast cancer) cell line (IC50 48 μM) and Oblongolide Z showed cytotoxicity against BC (human breast cancer), KB (human oral epidermoid cancer), NCI-H187 (small-cell lung cancer), and nonmalignant (Vero) cell lines with IC50 values of 26 μM, 37 μM, 32 μM, and 60 μM, respectively [130] (Table 2).

Five tricyclic lactone polyketides, alternariol (27a), alternariol 5-O-sulfate (27b), alternariol 5-O-methyl ether (27c), altenusin (28a), and desmethylaltenusin (28b) (Figure 3b), were isolated from the endophyte Alternaria spp. housed in the leaves of Polygonum senegalense. All these compounds manifested significant cytotoxicity against L5178Y (mouse lymphoma cells) with EC50 values of 1.7, 4.5, 7.8, 6.8, and 6.2 μg/mL, respectively [16]. According to another study conducted by Devari et al. in 2014, alternariol 5-O-methyl ether showed antiproliferative activity against HL-60 (human promyelocytic leukemia), A549 (lung cancer), PC-3 (prostate cancer), HeLa (cervical cancer), A431 (skin carcinoma), MiaPaka-2 (pancreatic cancer), and T47D (breast cancer) cell lines. Among all these cell lines, HL-60 (human promyelocytic leukemia) cells were most sensitive (IC50 85 μM) to alternariol 5-O-methyl ether [25].

Two novel polyketides, leptosphaerone C (29) and penicillenone (30), are produced by an endophytic fungus Penicillium spp. JP-1, isolated from Aegiceras corniculatum. Leptosphaerone C showed cytotoxicity to A549 (lung carcinoma epithelial) with an IC50 value of 1.45 μM, and penicillenone exhibited activity against P388 (leukemia cells) with an IC50 value of 1.38 μM [103].

Bikaverin (31) was isolated from an endophytic fungus Fusarium o. strain CECIS associated with Cylindropuntia echinocarpa [77]. It exerted cytotoxic activities against cancer cell lines, MIA PaCa-2 (pancreatic carcinoma), NCI-H460 (non-small cell lung cancer), MCF-7 (human breast cancer), and SF-268 (human CNS cancer) with IC50 values of 0.26, 0.43, 0.42, and 0.38 μM, respectively, showing selective cytotoxicity toward MIA PaCa-2 and NCI-H460. Bikaverin was also proven to be cytotoxic against EAC (Erlich ascites carcinoma), leukemia L5178, and sarcoma 37 cell lines affecting precursor utilization of nucleic acid and protein synthesis [78].

Sequoiatone A (32a) and B (32b), two novel polyketides (Figure 3b), were isolated from a Sequoia sempervirens bark endophyte, Aspergillus p. These polyketide compounds were tested against 60 diverse human tumor cell lines, and among them, breast cancer cell lines showed the greatest sensitivity [37] (Table 2).

2.2.13. Quinones

Torreyanic acid (33) (Figure 3b), a dimeric quinine, was isolated from an endophyte of Torreya taxifolia, Pestalotiopsis m. It causes cytotoxicity by apoptosis against A549 (lung carcinoma epithelial) and NEC (human colorectal neuroendocrine cell carcinoma) cell lines with IC50 values of 3.5 μg/mL and 45 μg/mL, respectively [119] (Table 2).

Four endophytes, Alternaria spp., Alternaria a., Aspergillus n., and Penicillium spp., associated with Tabebuia argentea, produced the antitumor and anti-metastatic agent lapachol (34) [17,20,21,22]. It acts by interfering with the bioactivities of the topoisomerase enzymes, which are crucial for DNA replication [22]. β-Lapachone showed activity on DU145 (human prostate carcinoma) and MCF-7 (breast cancer cell line) cell lines [20,22]. Additionally, its antitumor and anti-metastatic activities were evident in HepG2 (human hepatocellular liver carcinoma) and Hep3B (human hepatoma cell line) cell lines [19]. Notably, Aspergillus n. can be used to produce lapachol in a large scale within a short time [18].

Two bianthraquinone derivatives, Alterporriol K (35a) and L (35b), are produced by the endophytic fungus Alternaria spp. ZJ9-6B associated with the mangrove Aegiceras corniculatum. Alterporriol K and L exerted moderate cytotoxicity against MDA-MB-435 and MCF-7 (breast cancer cell line) cell lines with IC50 values between 13.1 and 29.1 μM [24].

Cercosporin (36) was isolated from the endophytic fungus Mycosphaerella spp., associated with Psychotria horizontalis, and exhibited cytotoxicity against MCF-7 [91].

Another endophytic fungus, isolated from the Salvia officinalis stem, was Chaetomium spp., which produced the cytotoxically active agents, cochliodinol (37) and isocochliodinol (38) (Figure 3b). These compounds were tested against the L5178Y (mouse lymphoma cells) cell line where cochliodinol showed higher cytotoxicity (EC50 7.0 µg/mL) than isocochliodinol (EC50 71.5 µg/mL) [51] (Table 2).

Azaanthraquinones, 7-desmethylscorpinone (39), and 7-desmethyl-6-methylbostrycoidin (40) (Figure 3b) isolated form Fusarium s. showed cytotoxic activity against four human tumor cell lines, MDA MB 231, MIA PaCa2, HeLa, and NCI H1975 [229].

2.2.14. Spirobisnaphthalenes

Mycelia s., an endophytic fungus isolated from the leaves of Knightia excelsa, was shown to produce Spiromamakone A (41) (Figure 3b) that exhibited cytotoxicity to P388 (murine leukemia cell line) at an IC50 value 0.33 μM [90] (Table 2).

A novel spirobisnaphthalene, spiropreussione A (42), was isolated from the endophyte Preussia spp. associated with Aquilaria sinensis. It displayed cytotoxicity to A2780 (human ovarian carcinoma) and BEL-7404 (human liver carcinoma) cell lines with IC50 values of 2.4 and 3.0 μM, respectively [135].

Diepoxin δ (43), palmarumycin C8 (44), and diepoxins κ and ζ were isolated from the endophytic fungus Berkleasmium spp. associated with Dioscorea zingiberensis. Diepoxin δ and palmarumycin C8 displayed pronounced cytotoxicity to A-549, A-2780, Bel-7402, BGC-823, and HCT-8 cell lines with IC50 values between 1.28 and 5.83 μM, while diepoxins κ and ζ selectively inhibited A-549 and Bel-7402 cells’ growth showing moderate to weak cytotoxicity [44] (Table 2).

2.2.15. Terpenes (Diterpenes, Sesquiterpenes, Triterpenes)

Several terpenes of plant and fungal origin have been established as potential anticancer drugs (Figure 3b, structures 45–54). Among these, paclitaxel (Taxol) (45) was isolated from Taxus brevifolia (Pacific yew tree) [230,231]. However, due to less availability of the pacific yew tree and insignificant yield of this metabolite, scientist have set up other approaches, including tissue culture, chemical synthesis, and semi-synthesis [230,232]. However, this diterpenoid was also reported to be produced by an endophytic fungus, Taxomyces a., isolated from the Taxus brevifolia [6]. Following this report, a number of paclitaxel producing other endophytes were reported. Some of them are Bartalinia r. from the leaves of Aegle marmelos [42] and Pestalotiopsis n. and Pestalotiopsis v. from the plant Taxus cuspidate [73]. This metabolite has been found to induce apoptosis when screened against INT-407, BT220, H116, HL251, and HLK210 cell lines [42] (Table 2).

A fusicoccane diterpene, periconicin B (46), was isolated from a Xylopia aromatica endophyte, Periconia a. It exerted potent cytotoxicity against HeLa (cervical cancer) and CHO (Chinese hamster ovary) cell lines [109].

Four sesquiterpens, trichothecolone (47), 7α-hydroxy-scirpene (48), 8-deoxy-trichothecin (49), and 7α-hydroxytrichodermol (50), were isolated from an endophyte, KLAR 5, housed in the healthy twig of Knema laurina. Compounds 47 and 48 were moderately active against BC-1 (human breast cancer cells), KB (Human nasopharyngeal epidermoid tumor), and NCI-H187 (human small-cell lung cancer cells), whereas compounds 49 and 50 showed selective cytotoxic activity against BC-1 and NCI-H187 [86].

Ent-4(15)-eudesmen-11-ol-1-one (51), an eudesmane sesquiterpene, isolated from an Etlingera littoralis endophyte, Eutypella spp. BCC 13199, showed weak cytotoxicity against KB, MCF7, NCI-H187, and Vero cells with IC50 values of 32, 20, 11, and 32 μM, respectively [70].

Two sesquiterpenes, Merulin A (52a) and Merulin C (52b), are produced by a Xylocarpus granatum endophytic fungi, XG8D, where both of them showed significant cytotoxic activity against SW620 (colon cancer) and BT474 (breast cancer) cell lines with IC50 values of 4.84 and 4.11 μg/mL for SW620 and 4.98 and 1.57 μg/mL for BT474, respectively [151].

Three novel eremophilane-type sesquiterpenes (Figure 3b), eremophilanolides 1, 2, and 3 (53a–53c), were isolated from the endophytic fungi Xylaria spp. BCC 21097 of the Licuala spinose plant and were moderately cytotoxic against KB, MCF-7, and NCI-H187 cell lines [152].

Tauranin (54) is produced by a Platycladus orientalis endophyte, Phyllosticta s., exhibiting cytotoxicity against MCF-7 (breast cancer), MIA Pa Ca-2 (pancreatic carcinoma), NCI-H460 (non-small cell lung cancer), PC-3 M (metastatic prostate cancer), and SF-268 (CNS cancer- glioma) cell lines with IC50 values of 1.5, 2.8, 4.3, 3.5, and 1.8 μM, respectively [133] (Table 2).

2.2.16. Xanthones

Phomoxanthone A (55a) and B (55b) (Figure 3b), isolated from the endophyte Phomopsis spp. BCC 1323 associated with Tectona grandis, exerted significant cytotoxicity against KB, BC-1, and nonmalignant Vero cells with IC50 values of 0.99, 0.51, and 1.4 μg/mL, respectively, for phomoxanthone A and 4.1, 0.70, and 1.8 μg/mL, respectively, for phomoxanthone B [129] (Table 2).

2.3. Recently Reported Metabolites with Potential Cytotoxicity and the Case of Fusarubin

More than one hundred metabolites have been isolated and evaluated for putative anticancer activities in the years 2018 to 2020. Cytotoxic activities of these endophytic metabolites have been summarized in Table 3. Among the reported metabolites, penicolinate A isolated form Bionectria spp. [159] and pyrrocidine A isolated from Cylindrocarpon spp. [166] exhibited potent cytotoxicity against against the human ovarian cancer cell line A2780. Fusarithioamide B, a new type benzamide, isolated form Fusarium c., showed potent activity against several cell lines [160]. 3-(4-nitrophenyl)-5-phenyl isoxazole was reported to have a potent effect against HepG2 and SMCC-7721 cells [161], while spiciferone F was reported to have a strong effect against MCF7 [162]. Liu et al. isolated two metabolies, namely xylariphthalide A and cis-4-hydroxy-6-deoxytalone, and Sharma V. et al. isolated Xylarolide A from Diaporthe spp. [163,164]. All these metabolites showed activity towards cancer cells. Three naphthaquinones, anhydrofusarubin, fusarubin, and 3-deoxyfusarubin, and one aza-anthraquinone, bostrycoidin, have potentiality as bioactive compounds against cytotoxicity on vero cells. These metabolites were isolated from a Fusarium s. strain isolated from Casia alata. [8]. Monolinolein, bafilomycin d, and 3′-hydroxydaidzein displayed a strong effect against A549 cells. These metabolites were isolated from actinomycete strain YBQ59 residing in Cinnamomum cassia [167]. Colletotrichum g. A12 produced colletotricone A, which showed moderate activity against MCF-7, NCI-H460, HepG-2m and SF-268 tumor cell lines [168]. Mollicellin G, a depsidone, was reported as a moderately active cytotoxic metabolite towards HepG2 and Hela cells [169]. A metabolite of Pestalotiopsis spp., named demethylincisterol A3, showed potential cytotoxicity against human cancer cell lines Hela, A549, and HepG [170].

A new type of cytochalasin, named jammosporin A, isolated from endophytic fungi Rosellinia s.-c., exhibited cytotoxic potential towards MOLT-4 cells [165]. Prenylated diphenyl ethers, namely diorcinol N and analogues isolated from Arthrinium a. TE-3, showed moderate cytotoxicity against the human monocytic cell line (THP-1 cell line), with IC50 values of 40.2, 28.3, and 25.9 μM, respectively [233].

An indole diterpenoid, shearilicine, isolated form Penicillium spp. (strain ZO-R1-1) of Zingiber officinale, showed potent cytotoxicity towards L5178Y cells and A2780 cells [171]. Flavipin from Chaetomium g. displayed activity against A549, HT-29, and MCF-7 cells [172]. Emodin, an anthraquinone from Diaporthe l., significantly inhibited the growth of murine leukemia P-388 cells [219].

Recently reported metabolites, namely chloroisosulochrin from Pestalotiopsis t. (N635) [206], cytosporin W from Pseudopestalotiopsis t. [207], terezine E and 14-hydroxyterezine D from Mucor spp. [208], citrinin (CIT) and dicitrinin-A from Penicillium c. [209], allantopyrone E from Aspergillus v. [210], integracin A and B from Cytospora spp. [211], (±)-asperteretone F (3a/3b), and compound 6 (name not established in the paper) Aspergillus t. [212], sterigmatocystin, a xanthone, from Paecilamyces spp. TE-540 [213], mutolide [234] and pramanicin A from Aplosporella j. [216], myrothecines H and I from Paramyrothecium r. A697 [217], and colletotrichalactone A and colletotrichalactone Ca from Colletotrichum spp. JS-0361, exhibited promising activity against different cancer cells [218]. A summary of the putative cytotoxic effects of recently reported endophytic fungal metabolites are summarized in Table 3.

Fusarubin and anhydrofusarubin have been isolated from the endophytic fungi Cladosporium residing inside Rauwolfia leaves. These compounds inhibited the cell growth of different leukemia cell lines (OCI-AML3, HL-60, U937, and Jurkat) by arresting the cell cycle and augmenting apoptosis. Whereas fusarubin exerted an antiproliferative effect on OCI-AML3 cells by up-regulating p21 in a p53-dependent manner, apoptosis was induced only in a small sub-population of leukemic cells by inducing the production of the Fas ligand (Figure 4) [9].

Figure 4

Fusarubin (FUS) and FUS analogues with proposed mechanism of action. (A) Structures of FUS derivatives and (B) Proposed mechanism of action of FUS on OCI-AML3 cells.

3. Conclusions

Several hundred endophytic fugal metabolites have been isolated to have cytotoxic and antimicrobial effects. Many metabolites are currently available as drugs on the market. Given that plants host endophytes as part of a symbiotic relationship, some plant metabolites might have an endophytic fungal origin. In fact, increasing evidence indicates that some of these plant metabolites are also produced by fungi. Many of the isolated metabolites of endophytic fungi inhabitant medicinal plants have been proved to have cytotoxic effects in vitro. Several of these compounds have been investigated at the molecular level to elucidate the mechanism, since these metabolites are produced in very small quantities by endophytes of plant origin. Due to very insignificant yields and isolation difficulties, these secondary metabolites may not be available to carry out in vivo studies in animal models. Some laboratories applied synthetic approaches to produce natural product derivatives, and one group also tried to synthesize some of these compounds. Optimizing derivatization and synthetic approaches is critical to attain higher yields for animal studies. These approaches will be key for investigating and developing these putative anticancer compounds into treatments.