Abstract 1686: Synergistic combination of Trabectedin and Olaparib in breast cancer tumor cell lines

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Trabectedin (Yondelis, ET-743) is a marine-derived antitumor agent that is currently used for the treatment of sarcoma and, in combination with pegylated-liposomal doxorubicin, of platinum-sensitive ovarian cancer patients. After binding to the DNA minor groove, trabectedin induces a potent transcription inhibition on tumor cells and tumor-associated macrophages. The resolution of functional DNA adducts generated by the drug is known to occur through the coordinated action of multiple DNA repair pathways, including homologous recombination (HR), a process that gives rise to double-strand breaks (DSBs). Trabectedin treatment at nanomolar concentrations does indeed produce a high proportion of DSB-positive tumor cells with abundant γ-H2AX foci and an S-phase delay/arrest by activation of the DNA replication checkpoints. We had previously shown the synergism (CI < 1) of the combination of Trabectedin with Olaparib (AZD-2281) in the breast cancer cell lines HCC-1937, MCF-7, MDA-MB-231 and MDA-MB-436. In this work we have investigated the mechanism of this synergistic effect at the molecular level. While the treatment with either compound alone (0.05 nM Trabectedin or 5 μM Olaparib for 72 hours) induced only a mild antiproliferative effect, the combination of both compounds at the mentioned concentrations induced strong apoptosis in all the breast cancer cell lines. Exposure to 0.5 and 2.5 nM Trabectedin for 72 hours induced a clear accumulation of γ-H2AX foci. Exposure to Olaparib alone induced only a mild DNA damage at 72 hours with all the concentrations tested. Olaparib induced a clear inhibition of PARylation at concentrations from 1-2.5 μM of the compound. The combination of both drugs, keeping Olaparib at 5 μM and varying the concentrations of Trabectedin from 0.05 to 2.5 nM, demonstrated a synergistic effect on the accumulation of histone H2AX phosphorylation, as analyzed both by western blotting and immunofluorescence microscopy. When comparing all these results, it was clearly seen that, although Trabectedin or Olaparib generated a considerable amount of DSBs, the combination of both drugs induced a higher proportion of DNA damage that remained at very high levels even after 72 hours of treatment. Thus, the observed synergistic effect seems to be the result of higher accumulation of DSBs after the administration of the combination of Trabectedin with Olaparib. Citation Format: Sonia Avila, Marta Martinez, Victoria Moneo, Juan F. Martinez-Leal, Carmen Cuevas, Luis F. Garcia-Fernandez, Carlos M. Galamarini. Synergistic combination of Trabectedin and Olaparib in breast cancer tumor cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1686. doi:10.1158/1538-7445.AM2014-1686