Axl molecular targeting counteracts aggressiveness but not platinum-resistance of ovarian carcinoma cells

Ovarian carcinoma, the most common gynaecological cancer, is characterized by high lethality mainly due to late diagnosis and treatment failure. The efficacy of platinum drug-based therapy in the disease is limited by the occurrence of drug resistance, a phenomenon often associated with increased metastatic potential. Because the Tyr-kinase receptor Axl can be deregulated in ovarian carcinoma and plays a pro-metastatic/anti-apoptotic role, the aim of this study was to examine if Axl inhibition modulates drug resistance and aggressive features of ovarian carcinoma cells, using various pairs of cisplatin-sensitive and -resistant cell lines. We found that mRNA and protein levels of Axl were increased in the platinum-resistant IGROV-1/Pt1 and IGROV-1/OHP cell lines compared to the parental IGROV-1 cells. IGROV-1/Pt1 cells displayed increased migratory and invasive capabilities. When Axl was silenced, these cells exhibited reduced growth and invasive/migratory capabilities compared to control siRNA-transfected cells, associated with decreased p38 and STAT3 phosphorylation. In keeping with this evidence, pharmacological inhibition of p38 and STAT3 decreased IGROV-1/Pt1 invasive capability. Molecular inhibition of Axl did not sensitize IGROV-1/Pt1 cells to cisplatin, but enhanced ErbB3 activation in IGROV-1/Pt1 cells and suppressed the clonogenic capability of various ovarian carcinoma cell lines. The combination of cisplatin and AZD8931, a small molecule which inhibits ErbB3, produced a synergistic effect in IGROV-1/Pt1 cells. Thus, Axl targeting per se reduces invasive capability of drug-resistant cells, but sensitization to cisplatin requires the concomitant inhibition of additional survival pathways.