Abstract 4417: Vatalanib targets ABCG2-overexpressing multidrug resistant colon cancer cells under hypoxia

Abstract

Abstract Cancer microenvironment is characterized by significantly lower oxygen concentration. This hypoxic condition is known to reduce drug responsiveness to cancer chemotherapy via multiple mechanisms, among which the upregulation of an efflux transporter ABCG2 confers resistance to a wide variety of structurally unrelated anticancer drugs. Vatalanib (PTK787) is a multitargeted tyrosine kinase inhibitor for VEGFR2, Flt and c-Kit, which exhibit potent anticancer activity in vitro and in vivo. We investigated the potentiation effect of vatalanib on the anticancer activity of conventional cytotoxic drugs in colon cancer cell lines under both normoxic and hypoxic growth conditions. More significant synergistic anticancer activity was observed under hypoxic condition. Mechanistically, vatalanib was found to inhibit ABCG2 and P-gp efflux activity, probably by acting as an uncompetitive inhibitor and interfering with their ATPase activity. Under hypoxic growth condition, ABCG2-overexpressing cells sorted out by FACS technique as side population cells (SP) were found to be significantly more responsive to irinotecan (an ABCG2 substrate anticancer drug) in the presence of vatalanib. The colony formation capactiy of these SP cells was remarkably reduced upon treatment with a combination of irinotecan and vatalanib, compared to irinotecan alone. However, vatalanib, at concentrations that produced the circumvention of ABCG2-mediated resistance, did not appreciably alter ABCG2 mRNA or protein expression levels or the phosphorylation of Akt and extracellular signal-regulated kinase 1/2 (ERK1/2). Vatalanib was also evaluated for potential interference with the cytochrome P450 metabolic enzymes by a rapid N-in-one in vitro interaction screening assay. The result indicates that vatalanib is only a mild inhibitor of both CYP34A and CYP2D, two major drug-metabolizing P450 enzymes, which presumably may avoid the undesirable drug-drug interactions in combination therapy. Our study thus advocates the further investigation of vatalanib for use in combination chemotherapy to circumvent hypoxia-mediated drug resistance. Citation Format: Kenneth K. To, Daniel C. Poon, Yuming Wei, Fang Wang, Ge Lin, Li-wu Fu. Vatalanib targets ABCG2-overexpressing multidrug resistant colon cancer cells under hypoxia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4417. doi:10.1158/1538-7445.AM2015-4417