The experimental anticancer agent LTX-315 is an amphipathic cationic peptide that efficiently eradicates cancer cells in vitro and in vivo. Attracted by its efficacy we launched an in depth mechanistic study on LTX-315. First we focused on the mode of action of LTX-315 and found that the agent failed to induce morphological signs of apoptosis but evoked necrotic phenotypes. Accordingly, LTX-315 failed to stimulate the activation of caspases, and the pan-caspase inhibitor Z-VAD-fmk was unable to reduce cell killing. We then studied its subcellular localization by fractionation of LTX-315-treated cells, and revealed that the agent was enriched in mitochondria and caused an immediate arrest of mitochondrial respiration without any major uncoupling effect. LTX-315 disrupted the mitochondrial network, dissipated the mitochondrial inner transmembrane potential, and caused the release of mitochondrial intermembrane proteins into the cytosol. Cells lacking the two pro-death multidomain proteins BAX and BAK, were less susceptible to LTX-315-mediated killing. Moreover, cells engineered to lose their mitochondria were resistant against LTX-315, underscoring the importance of this organelle for LTX-315-mediated cytotoxicity. Further, we observed that LTX-315 induced all known characteristics of immunogenic cell death, including calreticulin exposure, ATP secretion, HMGB1 exodus and type-1 interferon induction. When injected into established cancers, LTX-315 caused a transiently hemorrhagic focal necrosis that was accompanied by massive release of HMGB1 (from close-to-all cancer cells), as well caspase-3 activation in a fraction of the cells. Collectively, these results support the idea that LTX-315 triggers unregulated necrosis, and kills cancer cells by virtue of its capacity to permeabilize mitochondrial membranes. In addition, LTX-315 can induce ICD, hence explaining its capacity to mediate immune-dependent therapeutic effects.

Citation Format: HENG ZHOU, Allan Sauvat, Sylvère Durand, Sabrina Forveille, Takahiro Yamazaki, Sylvie Souquere, Valentina Sica, Øystein Rekdal, Oliver Kepp, Guido Kroemer. Mode of action of LTX315-induced cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4309. doi:10.1158/1538-7445.AM2017-4309