Abstract 1913: Epithelial mesenchymal transition: A mechanism of resistance to VEGF pathway inhibition in genitourinary cancers

Background: Targeting tumor angiogenesis by inhibiting the VEGF pathway is now an established treatment modality for several solid tumors. Especially in renal cell carcinoma, sunitinib has significantly improved progression-free survival and impacted overall survival. However, resistance to sunitinib develops in virtually all patients. Emerging clinical evidence suggests that epithelial to mesenchymal transition (EMT), a cellular phenotype observed with aggressive malignancy and metastasis, is associated with resistance to angiogenesis inhibitors. To better study and characterize this clinical observation we set out to generate well-defined preclinical kidney and prostate cancer models of EMT mediated resistance to the angiogenesis inhibitor sunitinib. Approach: Two genitourinary cancer cell lines, ACHN (kidney) and DU145 (prostate), which regress on sunitinib treatment, were forced to stably overexpress the EMT activators Twist1, Snail or ZEB1. All these cells demonstrated EMT phenotype by in vitro studies, and were xenografted subcutaneously into immunocompromised mice (NOD/SCID) for in vivo studies. Mice were treated with sunitinib once the tumors reached a size of 0.5mm3 or larger, and the tumor response was assessed. Correlative studies for microvascular density and blood vessel maturation were performed. Mechanism of resistance was studied by evaluating the ability of cancer cells to induce pericyte and endothelial cell migration. Results: E-cadherin downregulation, a hallmark of EMT, was seen in all the Twist, Snail, or ZEB1 overexpressed cells. Compared with the wild type cells, the EMT cells showed mesenchymal morphology. Functionally, all the EMT cells showed an increased ability to proliferate and migrate, as well as the ability to grow in an anchorage independent manner. The in vivo growth of all the EMT tumors was accelerated; importantly, tumors of ACHN-Twist and DU145-ZEB1 continued to grow under sunitinib treatment while the other tumors shrunk. In addition, ACHN-Twist and ACHN-ZEB1 cancer cells spontaneously metastasized to the lung. Intriguingly, although immunohistochemistry studies showed no difference in resistant tumor vasculature between sunitinib treated and untreated mice, the pericyte coverage was markedly reduced in sunitinib sensitive tumors. The Boyden chamber assay showed the resistant cancer cells (ACHN-Twist and DU145-ZEB1) induced significant pericyte and endothelial cell migrating toward cancer cells. Conclusions: Our stud