The non‐tumorigenic prostate epithelial cell line RWPE‐1, the AR‐null PC cell line PC‐3, the androgen‐dependent cell line LNCaP, and the CRPC cell lines C4‐2B and 22Rv1 were treated for 72 h with vehicle (DMSO), DOX [100 ng/ml (184 nM)], N‐9 [200 ng/ml (613 nM)], or the combination of DOX [100 ng/ml (184 nM)] and N‐9 [200 ng/ml (613 nM)]. C4‐2B and 22Rv1 cells were kept in 10% CSS media, and the other cell lines were kept in 10% FBS. Cell confluence was monitored using the Incucyte Zoom System. Data represent two independent experiments, with four to six replicates each, showing the mean ± s.e.m., and normalized to vehicle controls. Kruskal–Wallis test, (P‐value < 0.0001, two‐tailed) and Dunn's multiple comparisons test were performed. *P‐value < 0.05, **P‐value < 0.01, ***P‐value < 0.001.