Abstract 2080: Novel molecularly targeted combination for renal cell carcinoma

Abstract

Abstract INTRODUCTION: Despite many available treatments, >90% of metastatic renal cell carcinoma (mRCC) patients die within 5 years. Due to its modest efficacy, Sorafenib (SF) is a second line treatment for mRCC. Molecular basis for SF failure is unknown. Hymecromone (HC) is a non−toxic orally bioavailable agent used in Europe for improving liver health. We examined the molecular basis of SF failure in clinical specimens and provided mechanistic evidence for why SF+HC could be a potent therapeutic combination against mRCC. METHODS: UGT1A9 (A9) levels and SF glucuronidation were measured in kidney specimens (45 normal; 86 tumor) by qPCR and a glucuronidation assay using tumor microsomes. Response to SF+HC combination in vector-only (EV), A9-overexpressing (A9) and A9-knockdown (A9-KO) 786-0 and Caki-1 transfectants, primary RCC spheroids, and endothelial cells was examined by proliferation, apoptosis, motility and invasion assays. Target analysis was performed by immunoblot. Treatment efficacy was evaluated in Caki−1 s.c. and orthotopic xenograft models, with bioluminescence imaging. RESULTS: A9 has been shown to glucuronidate and inactivate SF. A9 levels were 8-10-fold elevated in mRCC patients’ tumors compared to non-mRCC patients and normal kidney tissues. A9 levels were an independent predictor of metastasis (P=0.022; efficacy: 73%; sensitivity: 93.8%). Tumor microsomes from mRCC patients’ glucuronidated SF 5-fold higher than from non-mRCC patients. In RCC cells, HC treatment downregulated A9 levels, A9 promoter activity and inhibited SF-glucuronidation. SF (5 µM) and HC (20-40 µg/ml) combination inhibited RCC cell and primary tumor spheroid proliferation (>90%), motility/invasion (>80%), and induced apoptosis (5-fold). While A9 transfectants were resistant to SF+HC treatment, A9-KO cells were sensitive to SF alone. Endothelial cells co-cultured with A9 transfectants were resistant to SF+HC treatment. SF+HC upregulated apoptosis effectors, but downregulated CD44, RHAMM, and phospho-Met levels in EV but not A9 transfectants. HC (100 or 200 mg/kg) and SF (30 mg/kg) oral combination abrogated Caki−1 tumor growth (>80%) without serum/tissue toxicity. HC+SF treatment decreased A9 levels, Ki67 index and microvessel density. A9-overexpressing tumors were resistant to treatment. CONCLUSION: This is the first study to demonstrate that A9 overexpression in mRCC is likely a mechanism of SF failure and A9 downregulation can re-sensitize cells. HC+SF is an orally bioavailable and non-toxic combination that may be an effective therapeutic strategy for mRCC. Citation Format: Andre R. Jordan, Jiaojiao Wang, Luis E. Lopez, Daley S. Morera, Vinata B. Lokeshwar. Novel molecularly targeted combination for renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2080.