P3–142 - DS12079 Displays Anticancer Activity Through Dual Inhibition on Topoisomerase and Hdac in PC-3 Cancer Cells

Abstract

Hormone refractory prostate cancers (HRPCs) are resistant to androgen deprivation therapy and are highly metastatic that explains the major clinical obstacle. Topoisomerase I and HDAC are two potential targets for anticancer strategy. Topoisomerase I inhibitors are developed as anticancer agents with the action targeted on interrupting DNA replication. HDAC inhibitors disrupt the normal function of HDACs, which in turn causes hyperacetylation of histones and affects gene expression. Both topoisomerase inhibitors and HDAC inhibitors may eventually result in apoptotic cell death. DS12079 is a small molecule which was synthesized based on the rationale to block both topoisomerase activity and HDAC activity. The sulforhodamine B assay revealed that DS12079 was effective against the cell growth of PC-3, a HRPC cell line, with an IC50 of 0.5 µM. DS12079 induced an arrest of the cell cycle at both G1 (at lower concentrations) and G2 phase (at higher concentration) using flow cytometric analysis of propidium iodide staining. The HDAC activity assay demonstrated that DS12079 was a pan HDAC inhibitor. The ICE (in vivo complex of enzyme) bioassay showed that DS12079 induced the formation of topoisomerase I-DNA cleavage complex, suggesting an inhibition on topoisomerase I activity. Furthermore, DS12079 induced the phosphorylation of Chk1 and Chk2 at Ser345 and Thr68, respectively, indicating the activation of both kinases and the occurrence of DNA damage response. DS12079 also dramatically increased the levels of histone H3 acetylation and phosphorylation, confirming the inhibitory effect on HDAC activity. Moreover, the combination between DS12079 and the proteasome inhibitor MG-132 caused a synergistic effect on cell apoptosis. In summary, the data suggest that DS12079 is a dual inhibitor against topoisomerase I and HDAC activity. It induces phosphorylation and acetylation of histone H3 and DNA-damage response signaling, leading to apoptotic cell death in PC-3 cells.