Deregulation of cell cycle progression is the hallmark of cancer; to this effect, several small molecules (AG-024322, AT7519, E7070, P1446A-05 and Flavopiridol) against cell cycle kinases are being developed to regulate cell cycle machinery that resulted in inhibition of tumor growth. The present study examined the effect of 3, 9-dihydroxy-2-prenylcoumestan-a furanocoumarin (Pso) on castration resistant prostate cancer cells (CRPC) cells. Treatment of CRPC (PC-3 and C4-2B) cells with Pso significantly caused irreversible G0-G1 cell cycle arrest that resulted in inhibition of cell proliferation. Protein analysis suggested that the expression of cdk inhibitors (CDKI) p21cip1 and p27kip1 were upregulated in both CRPC cell lines by Pso treatment. Studies using real-time reverse transcription-polymerase chain reaction analysis suggest that Pso transcriptionally regulates p21cip1 and p27kip1 in CRPC cells. Our immunofluorescence analysis pointed out that both p21cip1 and p27kip1 accumulated in the nucleus upon the treatment as compared to untreated CRPC cells. In addition, the cell cycle arrest was associated with decreased levels of both cyclins and cyclin-dependent kinases. However, cdk-4 appears to be more significantly downregulated when compared with either cyclins (D1, D2, D3 and Cyclin E) or other Cdk's (cdk2/6). Also, we noted an increased hypophosphorylated level of retinoblastoma (Rb) with a decreased in Rb phosphorylation resulted in inhibition of E2F1 function. Further, transient over expression of Cdk4 overcomes the Pso-induced G0-G1 arrest in CRPC cells. Also, knockdown of p21cip1 and p27kip1 expression with small interfering RNA significantly abrogated the Pso-induced G0-G1 cell cycle arrest suggested that induction of p21cip1 and p27kip1 is required for G0-G1 cell cycle arrest by Pso. Altogether our results strongly suggest that Pso could be a potential candidate for prevention and therapy against CRPC. Our ongoing studies using xenograft models of CRPC in nude mice may reveal the in vivo efficacy of Pso.

Citation Format: Thippeswamy Gulappa, Rama S. Reddy, Suman Suman, Chendil Damodaran. The molecular kinetics of p21 and Cdk4 dictates irreversible G0/G1 phase cell cycle arrest in CRPC cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 559. doi:10.1158/1538-7445.AM2013-559