Abstract A36: Unveiling biomarker and mechanism of drug resistance to molecular targeted therapeutics in renal cell carcinoma

Abstract

Abstract Introduction and Objective: Renal cell carcinoma (RCC) is the most lethal of the urologic malignancies and it is largely incurable when it becomes metastatic. Recent development of molecular targeted agents such as tyrosine kinase inhibitors (TKIs) and mammalian target of rapamycin (mTOR) inhibitors have provided some survival benefit for a subset of RCC patients. Overall, only 30% patients exhibit a response to these agents, however, almost all patients eventually develop drug resistance. Currently, there is no reliable biomarker(s) for predicting drug response for individual patients and the mechanism(s) of drug resistance is largely unknown. It is known that DAB2IP, a novel member of the Ras GTPase-activating protein gene family, is associated with cell proliferation, apoptosis, metastasis and chemo- or radio-resistance in several cancer types. In the present study, we decided to investigate the association between DAB2IP expression and therapeutic response to molecular targeted agents in RCC patients and explored the possible mechanism of DAB2IP in regulating drug response of RCC cells. Methods: DAB2IP expression was evaluated by immunohistochemistry (IHC) in a cohort of RCC patients who had received targeted therapies. Correlation between DAB2IP expression and patients' survival was analyzed. The effect of DAB2IP on RCC cells was examined using a panel of knockdown (KD) or overexpression cells generated by gene transfection and also determined for their in vitro and in vivo (xenograft model) responses to targeted agents treatment. The mechanism of drug resistance was delineated by signaling cascade profiling with a variety of molecular biologic techniques such as cDNA array, ChIP, reporter gene assay, real-time PCR and Western blot. Results: The levels of DAB2IP expression in RCC specimens determined by IHC positively correlate with the survival of patients receiving targeted therapies. DAB2IP KD RCC cells exhibit drug resistance to mTOR inhibitor Temsirolimus (Tem) treatment compared with the control from both in vitro and in vivo experiments. In contrast, increased DAB2IP in RCC cells by gene transfection can sensitize their response to Tem. Mechanistically, loss of DAB2IP was able to activate both the PI3K/mTOR pathway and the ERK/RSK1 pathway that further led to increased expression of hypoxia-inducible factor (HIF)-2α protein. Inhibitor(s) of either the mTOR pathway or the ERK pathway only partially suppressed growth of DAB2IP KD cells. However, the combination of both inhibitors achieved a synergistic growth inhibition in resistant cells. In this event, HIF-2α, but not HIF-1α, appeared to be a key converging factor and we further demonstrated that silencing of HIF-2α expression with specific shRNA was able to reverse the resistant phenotype in DAB2IP KD cells. Conclusions: DAB2IP represents a new predictive biomarker for the therapeutic response of RCC patients to targeted therapy. Most importantly, its functional role in RCC provides new therapeutic strategies in combating this lethal disease. Citation Format: Jiancheng Zhou, Kaijie Wu, Eunjin Yun, Payal Kapur, Rey-Chen Pong, Dalin He, Jer-Tsong Hsieh. Unveiling biomarker and mechanism of drug resistance to molecular targeted therapeutics in renal cell carcinoma. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr A36.