Abstract 5272: Molecular analysis of Sunitinib resistant renal cell carcinoma after sequential application of Cabozantinib

Abstract

Abstract Introduction: The tyrosine kinase inhibitors Sunitinib and Pazopanib have been established in firstline treatment of metastatic renal cell carcinoma (mRCC) patients especially in the good prognosis group. Despite the primary response many patients become resistant. Resistance mechanisms include activation of MET and AXL - downstream pathways have been reported. Cabozantinib (Cbz), a MET/AXL/VEGFR inhibitor, showed clinical benefits as second-line agent. However, why the therapy becomes ineffective and how the long-term administration with Sunitinib influences sensitivity of tumor cells towards Cbz remain to be answered. Methods: We referred to previously generated Sunitinib -resistant cells (786-O/S) and their untreated counterpart (786-O/WT) to test effect of Cbz in vitro. Drug sensitivity was determined via WST-1 cell proliferation assay, whereas cell pathways analysis in response to Cbz was evaluated at different time points by means of immunoblotting. Results: By challenging the two cell phenotypes with different concentrations of Cbz we found that the 786-O/WT cells were more sensitive to the drug in comparison to 786-O/S (IC50 value of 9.9 µM versus 12.2 µM, respectively). The 786-O/WT cells responded to short-term incubation with Cbz by decreasing the expression of the receptor MET and its downstream intracellular pathways: the activated Src (pSrc) and p38 MAPK (p-p38 MAPK). Besides, Erk protein showed a slight increased activity (pErk) after 8 and 24h drug exposure. In contrast, no significant regulation of MET, nor pSrc and p-p38 MAPK kinase expression was reported in the 786-O/S cells. Remarkably, pErk level was induced after Cbz incubation in a time-dependent manner. Finally, phosphorylated S6 (pS6) was used as a marker of PI3K/Akt/mTOR pathway. Cbz decreased the level of pS6 in 786-O/WT, while enhancing it in the 786-O/S cells. Conclusions: Our work provides a preclinical model for sequential therapy in mRCC. The initial in vitro data confirmed Cbz as a potent tool to contrast the progress of RCC in the first-line setting. Still, switching to Cbz after Sunitinb resistance resulted in Erk and mTOR pathways activation and might be interpreted as overlapping survival mechanism. This ongoing work will provide a better knowledge of the protein expression patterns of possible cross-resistance in RCC by analyzing additional cell lines including Pazopanib-resistant ones. Citation Format: Angela Zaccagnino, Bozhena Vynnytska-Myronovska, Michael Stockle, Kerstin Junker. Molecular analysis of Sunitinib resistant renal cell carcinoma after sequential application of Cabozantinib [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5272.