EP-100 is a targeted anti-cancer drug comprised of Luteinizing Hormone Releasing Hormone (LHRH) fused to a lytic peptide. EP-100 is currently being investigated in human clinical trials. EP-100 seeks and destroys LHRH receptor positive cancer cells via a novel mechanism of action involving direct membrane disruption. Studies were conducted to determine the cytotoxic effects of combining EP-100 with paclitaxel using multi-drug resistant LHRH receptor positive ovarian (OVCAR-3), breast (MDA-MB-231), uterine sarcoma (MES-SA-Dx5), prostate (PC-3) and LHRH receptor negative ovarian (SKOV-3) cancer cells. Cells were cultured in the presence of EP-100 (0.005 nM-50µM, N=8) or paclitaxel (0.0025-500 nM, N=8) alone or in combination for 48 to 72 hours in non-constant and constant ratio formats (N=6). Cell viability was measured by luminometric assays. Data for IC50 values were obtained using the GraphPad Prism and GraphPad Software for the Hill Equation. The synergistic effects of EP-100 and paclitaxel were expressed as Combination Index (CI) using the CompuSyn Software analysis program. EP-100 alone killed LHRH receptor positive OVCAR-3, MDA-MB-231, MES-SA-Dx5 and PC-3 cells at low micromolar concentrations after 48 to 72 h incubation(IC50 values 2.189 ± 0.027 µM, 2.092 ± 0.114 µM, 1.419 ± 0.133 µM and 1.9 ± 0.071 µM respectively). As expected, SKOV-3 cells did not respond well to EP-100 (IC50= 10.3 ±0.36 µM) because they lack LHRH receptors on their surfaces. OVCAR-3, MDA-MB-231, MES-SA-Dx5 and SKOV-3 cells were resistant to paclitaxel (IC50 values = 13.6 ± 0.7 nM 86.2 ± 5.9 nM, 94.1 ± 0.3 nM and 48.52 ± 4.5 nM, for OVCAR-3, MDA-MB-231, MES-SA-Dx5 and SKOV-3, respectively) and PC-3 cells were very sensitive to paclitaxel with IC50 of 5.2 ± 1.1 nM. The combination of EP-100 at 50 nM and paclitaxel at 500 nM resulted in 3620 and 6720- fold increased sensitivity when compared to paclitaxel alone. The median CI values were 0.18, 0.05, 0.25, and 0.6 for for MES-SA-Dx5, OVCAR-3, MDA-MB-231 and PC-3, respectively indicating synergistic responses in the cell lines. No synergy was observed in the LHRH receptor negative SKOV-3 cell line (CI=8.4). These results indicate that a combination of EP-100 and paclitaxel results synergistic responses in LHRH-receptor positive and multi-drug resistant cancer cells.

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 3715. doi:1538-7445.AM2012-3715