Abstract 3052: Role of p53 in cdk inhibitor VMY-1-103-induced apoptosis in prostate cancer

Abstract

Abstract The mammalian cell cycle is a tightly regulated process that controls cell division and replication. The tumor suppressor p53 plays a crucial role in both the G1/S and mitotic checkpoints, as well as in apoptosis in response to DNA damage. P53 activates p21, which is an inhibitor of cdk/cyclin E complexes, to cause cell cycle arrest. P53 can also function as a mediator of apoptosis by activating either the instrinsic or extrinsic pathway of apoptosis by activating transcriptional targets such as Bax, Bid, and TRAIL R4/5. In prostate cancer (PCa), p53 mutations are frequently associated with advanced staged disease. We recently have developed a novel analog of the CDK inhibitor purvalanol B, termed VMY-1-103 (VMY) which functions as a potent inhibitor of proliferation. To assess the efficacy of this compound in vitro, we tested the ability of VMY to cause cell cycle arrest and apoptosis in LNCaP, DU145, and PC3 prostate cancer cell lines. VMY caused an increase in cells in G2/M in all cell lines tested. Additionally, VMY treatment resulted in a large amount of apoptosis in LNCaP cells, which are p53 wild-type. In contrast, DU145 cells, which are p53 mutant, and PC3 cells, which are p53 null, were significantly less susceptible to VMY-mediated apoptosis, strongly suggesting that functional p53 was required for VMY to induce apoptosis in PCa cells. In order to test this hypothesis, a series of experiments were carried out in these PCa cell lines. Knockdown of p53 by siRNA in LNCaP cells resulted in a decreased sensitivity to VMY, as these cells no longer underwent cell cycle arrest or apoptosis. Further modulation of p53 was performed by overexpressing a wild-type construct in PC3 cells, which greatly sensitized the cells to cell death following VMY treatment. Conversely, introduction of several mutant p53 constructs into LNCaP cells did not decrease sensitivity to the drug whatsoever. Importantly, in DU145 cells, which have two mutations of p53 on opposite alleles, apoptosis was significantly increased when cells were pre-treated with PRIMA-1 to restore WT p53 function. Therefore, our data establishes p53 plays a crucial regulator of sensitivity to VMY and its ability to induce apoptosis in prostate cancer cells. In addition we show that modification of mutant p53 by PRIMA in a p53 deficient cell lines, and the ensuing restoration of drug sensitivity, enhances the potential of VMY as a novel therapeutic for prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3052. doi:1538-7445.AM2012-3052