Zanthoxylum usambarense (Engl.) Kokwaro (Rutaceae) extracts inhibit the growth of the breast cancer cell lines MDA-MB-231 and MCF-7, but not the brain tumour cell line U251 in vitro.

Zanthoxylum usambarense (Engl.) Kokwaro has traditionally been used for the treatment of malaria, upper respiratory tract infections, cough, rheumatism, tooth decay and sore gums in Kenya and other African countries. Dried ground parts of Z. usambarense were extracted by maceration using methanol (MeOH) at room temperature, extract was dried and reconstituted in 70% aq. MeOH and partitioned against n-hexane and chloroform (CHCl3 ) to obtain MeOH, n-hexane and CHCl3 extracts. All extracts were assessed for cytotoxicity against two breast cancer cell lines, MDA-MB-231 and MCF-7, and the brain tumour cell line U251 by the MTT assay. The free-radical scavenging activity of the extracts was also determined by the 2,2-diphenyl-1-picryhydrazyl (DPPH) assay. In the DPPH assay, the MeOH extract was found to be the most active free-radical scavenger with a RC50 value of 41.1 × 10(-3)  mg/mL. It also displayed significant cytotoxicity against the MCF-7 cell line (IC50 42.9 µg/mL) and appeared to have induced cell death through apoptosis. None of the test extracts showed any activity against the U251 cell line at test concentrations. The present findings demonstrated that Z. usambarense could be a potential source for new cytotoxic compounds for possible anticancer drug development.