Abstract 3643: Manipulation of HuR expression alters the efficacy of PARP-inhibitors in pancreatic and ovarian cancer cells

Abstract

Abstract PARP-inhibitors (PARPi) are a novel class of agents that target cancer cells deficient in DNA repair. Early phase trials show promising success with PARP-inhibitors, yet drug resistance mechanisms and off-target pathways affected by drug exposure have not been explored. HuR (ELAV1) is a protein that binds and stabilizes mRNA transcripts upon certain stress stimuli. These HuR mRNA targets result in an increase in protein expression; and thus, protein function. Recently, we demonstrated that HuR binds and regulates deoxycytidine kinase, the gemcitabine metabolizing enzyme. Thus, HuR expression enhances gemcitabine efficacy against pancreatic cancer cells. We subsequently screened other chemotherapeutics that may stimulate the HuR stress response. In isogenic pancreatic cancer cell lines, stable HuR overexpression rendered cells up to 2-fold more sensitive to PARPi compared to control cells. Accordingly, siRNA knock down of HuR expression in both pancreatic and ovarian cancer cell lines caused PARPi resistance compared to a scramble-sequence control siRNA. In a pancreatic cancer cell line, MiaPaCa2, a 2.5-fold siRNA knock down of HuR mRNA expression detected by qPCR rendered cells approximately 4-fold more resistant to PARPi. Similarly, a modest siRNA knock down of HuR in an ovarian cancer cell line, A2780, rendered cells more resistant to PARPi. Immunofluorescence studies indicate that a 5 hour treatment with 75 µM PARPi directly caused HuR to transport from the nucleus to the cytoplasm, presumably moving ARE-rich mRNA cargoes after drug exposure. Focused gene expression analysis on HuR bound, immunoprecipitated RNA defined functional HuR downstream targets (including deoxycytidine kinase). Current studies will reveal and validate the importance of these downstream mRNA targets in PARP-inhibitor metabolism and efficacy. We hypothesize that HuR may be central to PARPi effectiveness and may be useful in understanding PARPi de novo drug resistance mechanisms. Future work will reveal whether HuR status can be utilized as a predictive marker for PARP-inhibitor-based therapy and if all clinically available PARP-inhibitors engage HuR's regulation of unique mRNA cargoes in cancer cells upon treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3643.