Abstract 516: The mechanism associated with radio-resistant renal cell carcinoma and its targeting strategy

Introduction and Purpose: Although ionizing radiation (IR) represents an effective regimen for most solid tumors, renal cell carcinoma (RCC) is known to be highly radio-resistant and the underlying mechanisms associated with IR-resistance remained elusive. In this study, we unveiled the factors associated with IR-resistance and the potential targeting strategy. Experimental procedures: Several RCC sublines were generated with different genetic manipulation and cells were irradiated with different doses and the surviving fractions were evaluated in 7 days. To investigate the underlying mechanism, various biochemical and molecular biologic methods, such as quantitative real-time PCR, mass-spectroscopy (MS), immunoprecipitation (IP), western blot, and ELISA were performed. Results: DAB2IP (DOC-2/DAB2 interactive protein) known as a tumor suppressor that functions as a scaffold protein modulating many signal pathways associated cell growth/survival, apoptosis/autophage, and cell migration/invasiveness. In RCC, the status of DAB2IP has not been characterized. We found DAB2IP was frequently lost in RCC; more than 50% in every subtype of RCC. We observed that DAB2IP-deficient RCC cells exhibited IR-resistance whereas re-introduction of DAB2IP could sensitize RCC cells to IR. From MS and IP, it appeared that DAB2IP could directly interact with poly (ADP-ribose) polymerase-1 (PARP-1). In the presence of DAB2IP, PARP-1 activities were suppressed because DAB2IP was able to induce PARP-1 protein degradation via unique proteasome pathway. Since PARP-1 is commonly involved in many cellular functions such as DNA damage repair or transcription modulation, which is also considered as a therapeutic target particularly IR therapy. In this study, elevated PARP-1 led to rapid DNA repairing and IR resistance in DAB2IP-expressing RCC cells. In contrast, by knocking-down PARP-1 in DAB2IP-deficient RCC cells can sensitize cells to IR, suggesting that PARP-1 inhibitors can be a potential radio-sensitizer. Conclusion: In summary, this study demonstrates a new functional role of DAB2IP in IR-resistant RCC cells via modulating PARP-1 expression and activities. Therefore, targeting PARP-1 by small molecular inhibitor or gene therapy becomes a potential therapeutic strategy to overcome IR resistant RCC. Citation Format: Eun-Jin Yun, Chun-Jung Lin, Debabrata Saha, Jer-Tsong Hsieh. The mechanism associated with radio-resistant renal cell carcinoma and its targeting strategy. [abstract]. I