Pyranocarbazole derivatives as potent anti-cancer agents triggering tubulin polymerization stabilization induced activation of caspase-dependent apoptosis and downregulation of Akt/mTOR in breast cancer cells.

A series of new pyranocarbazole derivatives were synthesized via semi-synthetic modification of koenimbine (1a) and koenidine (1b) isolated from the leaves of Murraya koenigii. Among all, compound 3bg displayed significant anti-cancer activity against MDA-MB-231, DU145 and PC3 cell lines with the IC50 values of 3.8, 7.6 and 5.8 μM, respectively. It was also observed that the halogenated-benzyl substitution at N-9 position, C-3 Methyl and C-7 methoxy group on carbazole motif are favoured for anti-cancer activity. The detailed investigation was carried out with compound 3bg and its SEDDS (self-emulsifying drug delivery systems) formulation 3bgF. The in vivo drug release behavior study showed that the formulation enhanced slow release and better bioavailability at a tumor site. Compound 3bg and its formulation (3bgF) significantly inhibited cell proliferation and colony formation, induced G2/M arrest, reduced cellular ROS generation and induced caspase-dependent apoptosis in MDA-MB-231 cells. 3bg also induced significant alteration of Bax/Bcl expression ratio suggesting involvement of mitochondrial apoptosis. Additionally, 3bg caused down-regulation of mTOR/Akt survival pathway. 3bg do not bind to DNA, but interacts with tubulin as observed with in silico molecular docking studies. This interaction results in stabilization of tubulin polymerization similar to paclitaxel as detected in cell-free assay. Oral administration of 3bgF for 30 days at dose rate of 10 and 20 mg/kg body weight significantly reduced tumor growth in syngenic rat LA-7 mammary tumor model. These results indicated that the pyranocarbazole natural product based N-substituted analogues can act as potential anti-cancer lead.