A novel bis-indole destabilizes Microtubules and displays potent in vitro and in vivo antitumor activity in prostate cancer

Purpose: Microtubules are one of the most useful subcellular targets in chemotherapy. We identified a novel indole, (3-(1H-indol-2-yl)phenyl)(1H-indol- 2-yl)methanone (15), that inhibits tubulin action and exhibits potent antitumor activity in various preclinical models. Methods: In vitro cancer cell growth inhibition was measured by SRB or MTT assay in human cancer cell lines. Apoptosis induced by 15 was examined in LNCaP and PC-3 cells. Effects of 15 on cell cycle distribution and tubulin were investigated via in vitro models. In vivo toxicity and xenograft efficacy studies were conducted in mice. Results: Indole 15 inhibited the in vitro growth of a number of human cancer cell lines, including drug-resistant cell lines that over-express P-glycoprotein, multidrug resistance-associated proteins, and breast cancer resistance protein with IC ₅₀ values in the range of 34-162 nM. Nanomolar concentrations of the compound caused downregulation of bcl-2, induced PARP cleavage, and induced apoptosis in both LNCaP and PC-3 prostate cancer cells, as confirmed by anti-histone ELISA and DNA laddering. In vitro studies revealed that the compound inhibited polymerization of purified tubulin and induced a strong and concentration-dependent G ₂M arrest in PC-3 cells. In vivo studies in immunodeficient mice bearing PC-3 tumor xenografts showed that the compound effectively inhibited tumor growth. Conclusions: The potent in vitro and in vivo antitumor activities of this novel indole suggest that drugs with this novel chemical scaffold might be developed for treatment of drug-resistant prostate cancer.