Combination of docetaxel and vandetanib in docetaxel-sensitive or resistant PC3 cell line

To examine the anti-proliferative effect of the combination of docetaxel, the cornerstone of modern chemotherapy for prostate cancer, and vandetanib, a potent inhibitor of VEGFR-2 tyrosine kinase, applied to the representative hormone-refractory human prostate cancer cell line PC3. The aim is to analyze if a supra-additive/synergic effect of the combined treatment on cell viability exists and to understand the molecular key-factors involved. We first hypothesized an effect of vandetanib in modulation the function of MDR1, leading to a longer retention of docetaxel inside the cell. It may also be possible that vandetanib could modulate the docetaxel-induced changes in expression of prosurvival and proapoptotic proteins, leading to a positive balance forward cell death.

We used PC3 cells either wild type (PC3wt) or with acquired resistance to docetaxel (PC3R), characterized by a higher expression of MDR1. We studied both mRNA and protein, the expression of EGF and VEGF receptors at a basal level and after each treatment, as well as the expression of cell cycle and apoptosis related genes.

Cell proliferation data suggested a supra-additive cytotoxic effect of the combination of docetaxel plus vandetanib, when given together or with the sequence vandetanib followed by docetaxel. We did not observe any effect of vandetanib on MDR1, in the PC3R cell lines, characterized by a higher pump expression than PC3wt. On the other side, we defined a number of key factors involved in the pro- and anti-survival balance, which regulation, by single drugs and/or by combined treatment, could explain the effect on cell cytotoxicity; also where there are apparently contradictory results.

Our data suggest that combined treatment with vandetanib and docetaxel alters the balance of proapoptotic and prosurvival proteins, ultimately leading to potentiation of docetaxel-induced apoptosis in human prostate cancer cells in vitro, irrespective of cells being sensitive or resistant to docetaxel.