Abstract LB-080: Reactivating RBL2/p130 oncosuppressive function as a new, possible antitumoral strategy

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Deregulation of cell cycle control is the leading cause of cancer. The retinoblastoma (Rb) family members, including RB1/p105, RBL1/p107 and RBL2/p130, are crucial to restrain cell cycle progression and their inactivation, either direct or indirect, is a hallmark of most human tumors. In particular, RBL2/p130 emerging role in senescence and apoptosis, seems to contribute importantly to its tumor suppressor function. Furthermore, many studies largely contributed to establish RBL2/p130 as an important cancer target, which is inactivated by cell cycle kinases and whose deregulation underlies various cancer types. In this regard, we set out to restore RBL2/p130 function in tumors and exploit its tumor suppressive potential for cancer therapy. In particular, we have identified, through computational chemistry and molecular modeling studies, a small molecule able to act as a specific inhibitor of the CDK2-CycA complex and to reactivate the tumor suppressive function of RBL2/p130 in cancer. We analyzed by MTS assay the cytotoxic effect of our compound on a panel of different tumor cell lines and determined its IC50 values. We evaluated its effects on cell cycle and apoptosis by FACS and dissected its molecular mechanism of action by Western blot and RT-PCR. We found that our compound effectively inhibited proliferation of lung cancer and mesothelioma cell lines by specifically inhibiting CDK2-CycA activity towards RBL2/p130. The decrease in RBL2/p130 phosphorylation led to stabilization of its complex with the E2F4 transcriptional factor and consequent repression of their targets necessary for cell cycle progression, including CDK2 itself. Consistently, our compound arrested cell cycle and triggered apoptosis. Interestingly, apoptosis seemed to be mediated by RBL2/p130 itself because it was repressed in RBL2/p130-silenced cells. Furthermore, our compound proved to be active in an A549 xenograft model of lung cancer. Overall our findings indicate that the pharmacological reactivation of RBL2/p130 induces its cell-cycle restraining and pro-apoptotic functions, the latter being still largely unexplored, and identify a new possible therapeutic strategy for cancer treatment. Citation Format: Francesca Pentimalli, Luca Esposito, Iris Maria Forte, Carmelina Antonella Iannuzzi, Flavio Rizzolio, Tiziano Tuccinardi, Paola Indovina, Silvia Boffo, Antonio Giordano. Reactivating RBL2/p130 oncosuppressive function as a new, possible antitumoral strategy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-080. doi:10.1158/1538-7445.AM2015-LB-080