Novel mechanisms of ovarian cancer growth inhibition, via microRNA downregulation and oxidative damage, by a rationally designed histone deacetylase inhibitor.

2475

Hydroxamate-based histone deacetylase inhibitors (HDACIs) have demonstrated promise in the therapy of hematologic malignancies. One such HDACI, suberoylanilide hydroxamic acid (SAHA, vorinostat, Zolinza), was recently approved by the Food and Drug Administration for the treatment of cutaneous T-cell lymphoma. In solid tumors, however, these agents are less well characterized and many have displayed variable potency. Our group has now developed a novel hydroxamate-tethered phenylbutyrate derivative, known as “HDAC42,” that possesses greater histone deacetylase activity than other HDACIs. Previously, we demonstrated that HDAC42 elicits potent antigrowth effects, equal to or greater than SAHA, against a number of ovarian cancer cell lines. In this project, we specifically examined possible mechanisms of the antiproliferative action of HDAC42, as compared to SAHA. Using cisplatin-resistant CP70 ovarian cancer cells, we identified a polycistronic cluster of microRNAs (miRs), encoded on 4q25, which is distinctly downregulated by 48-hr HDAC42 treatment, but not by the identical treatment with SAHA. This specific cluster, originally characterized as overexpressed in embryonic stem cells, includes the miRs 302a, 302b, 302c, 302d, and 367, as designated by the miRNA Registry (Sanger Institute, Cambridge, UK). Using miRBase (Sanger Institute), we identified several candidate genes that are potentially regulated by those five mature miRs. Notably, we demonstrated that one of these, miR302a, possesses homology to several putative tumor suppressor genes, including PDCD8, CFLAR, and DOC1, the latter two of which we are currently further analyzing. In an additional mechanistic study of HDAC42-mediated growth inhibition, we demonstrated oxidative damage as a strong contributing factor, as antiproliferative activity was completely abrogated by treatment with the antioxidant N-acetyl-cysteine (IC50 increase from 1.4 µM to 69 µM, a 49-fold decrease in drug potency). To further investigate the precise contribution of oxidative damage to HDAC42-mediated growth arrest, we are currently performing quantitative assessments of that phenomenon; we are also comparing HDAC42 mechanistic determinations to modes of action of SAHA. Finally, to assess the generality of these findings, we are also examining HDAC42-specific antigrowth mechanisms of action in other ovarian cancer cell lines. In summary, we believe that this novel histone deacetylase inhibitor holds promise for the therapy of ovarian cancer, and its route of action may allow for a greater understanding of possible factors involved in this devastating disease.