LTX-315

Malignant melanoma is the most aggressive and deadliest form of skin cancer due to its highly metastatic potential, which calls for new and improved therapies. Cationic antimicrobial peptides (CAPs) are naturally occurring molecules found in most species, in which they play a significant role in the first line of defense against pathogens, and several CAPs have shown promising potential as novel anticancer agents. Structure-activity relationship studies on the CAP bovine lactoferricin allowed us to de novo design short chemically modified lytic anticancer peptides. In the present study, we investigated the in vivo antitumor effects of LTX-315 against intradermally established B16 melanomas in syngeneic mice. Intratumoral administration of LTX-315 resulted in tumor necrosis and the infiltration of immune cells into the tumor parenchyma followed by complete regression of the tumor in the majority of the animals. LTX-315 induced the release of danger-associated molecular pattern molecules such as the high mobility group box-1 protein in vitro and the subsequent upregulation of proinflammatory cytokines such as interleukin (IL) 1β, IL6 and IL18 in vivo. Animals cured by LTX-315 treatment were protected against a re-challenge with live B16 tumor cells both intradermally and intravenously.

LTX-315 is a cationic amphilytic peptide that preferentially permeabilizes mitochondrial membranes, thereby causing partially BAX/BAK1-regulated, caspase-independent necrosis. Based on the observation that intratumorally injected LTX-315 stimulates a strong T lymphocyte-mediated anticancer immune response, we investigated whether LTX-315 may elicit the hallmarks of immunogenic cell death (ICD), namely (i) exposure of calreticulin on the plasma membrane surface, (ii) release of ATP into the extracellular space, (iii) exodus of HMGB1 from the nucleus, and (iv) induction of a type-1 interferon response. Using a panel of biosensor cell lines and robotized fluorescence microscopy coupled to automatic image analysis, we observed that LTX-315 induces all known ICD characteristics. This conclusion was validated by several independent methods including immunofluorescence stainings (for calreticulin), bioluminescence assays (for ATP), immunoassays (for HMGB1), and RT-PCRs (for 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 as caspase-3 activation in a fraction of the cells.