Abstract B72: Combination therapy by Toll-like receptor 3 activation and chemotherapeutics synergistically induces cancer cell death.

Abstract

Abstract Toll-like receptors (TLRs) recognize molecular motifs of microbial origin and initiate innate immune response. TLR agonists are already being used in clinical studies because of their ability to induce apoptosis and activate the immune system. We have previously shown that TLR3 activation by synthetic dsRNA [poly (I:C)] in the pharyngeal cancer cell line Detroit 562 induced caspase-dependent apoptosis. Additionally, when combined with chemotherapeutics this treatment acts synergistically by enhancing cancer cell death. In this study we tried to decipher the mechanism of poly (I:C) and chemotherapeutics synergy. Cell survival was determined by using cytotoxicity assay and colony formation assay while protein expression was obtained by western blot. We demonstrated that combination of poly (I:C) and cisplatin is TLR3-dependent while methotrexate and hydroxyurea act through other dsRNA receptors (RIG-I and MDA5). Subsequently, we showed that poly (I:C) had more complex effects on Detroit 562 cells than previously thought: while it induces pro-apoptotic events it also triggers anti-apoptotic mechanisms, for example an increase in the expression of c-IAP2. Combined treatment by poly (I:C) and c-IAP inhibitor significantly decreased cell survival even at low concentrations. However, poly (A:U), which stimulates only TLR3 and not other dsRNA receptors, when combined with c-IAP inhibitor induced cell death only at high concentrations suggesting that RIG-I and MDA5 are also involved. Conversely, the combination of c-IAP inhibitors with poly (I:C) and chemotherapeutics did not result in a stronger cytotoxic effect against malignant cells. One explanation seems to be the fact that cisplatin abrogated c-IAP2 expression induced by poly (I:C) in the Detroit 262 cells thus shifting the balance towards apoptosis. Our conclusion is that future investigations should explore combinations of poly (I:C) with either cisplatin or c-IAP inhibitors. When we used laryngeal cell line SQ20B stably transfected with inducible shRNA for TLR3, we confirmed that synergistic effect of poly (A:U) and cisplatin on cell death is TLR3-dependent. Additionally, as SQ20B is radiation resistant cell line, we have shown here that they can be sensitized to radiotherapy by treatment with poly (I:C). In conclusion, synthetic dsRNAs like poly (I:C) have the potential to help overcoming the resistance of some human malignant cells to classical modalities of radiotherapy and chemotherapy. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B72. Citation Format: Tanja Matijevic Glavan, Benjamin Verillaud, Pierre Busson, Jasminka Pavelic. Combination therapy by Toll-like receptor 3 activation and chemotherapeutics synergistically induces cancer cell death. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B72.