Rational for targeted polytherapy in sarcoma: Get the genie out of the bottle.

Abstract

e13519 Background: While a change of paradigm occurred in the last decade from chemotherapy to targeted therapy for cancer treatment, this work investigates the optimal combination of targeted agents with doxorubicin in sarcoma. Methods: Three sarcoma cell lines were studied RD18 (rhabdomyosarcoma), A204 (undifferentiated sarcoma) and TC 71 (Ewing's sarcoma) and exposed to increasing concentrations of vorinostat (HDAC inhibitor), 17-DMAG (Hsp90 inhibitor), abacavir (anti-telomerase) and sorafenib (tyrosine kinase inhibitor) alone, combined 2 by 2, then with doxorubicin. Viability was assessed by MTS assay. The Chou and Talalay combination index (CI) was used to determine additive (CI=1), synergistic (CI<1) or antagonistic effect (CI>1). Cell cycle analysis, measure of apoptosis by Annexin V and caspase 3/7 activity were studied using flow cytometry analysis and luminescent assay. Results: In monotherapy, the agents showed 30% to 90% decrease in viability but abacavir, which remained less active. Combination therapies with vorinostat, sorafenib and 17-DMAG showed strong synergism. Abacavir was found antagonistic with each drug. Either vorinostat or 17DMAG synergized with doxorubicin, achieving 60% cell killing compared to doxorubicin alone 12% (p=0.007). However, no synergy was observed for sorafenib with doxorubicin. The triple therapy vorinostat, 17DMAG and Doxorubicin did not show synergism but transiently increased the subG1 population at 24H, 70% compared to 30% in monotherapy with an increase in early caspase-independent apoptosis (11% to 36%, p= 0.0008). Conclusions: This work provides evidence of synergism of dual combinations of vorinostat, 17DMAG and sorafenib. In adjunction to doxorubicin, these combinations enhance doxorubicin cytotoxicity at therapeutically relevant concentrations. [Table: see text]