Mechanisms of cell death in cutaneous melanoma

PROJECT SUMMARY
The incidence of cutaneous melanoma is rising. While small molecule targeted inhibitors and immune
checkpoint antibodies have increased long-term survival in advanced-stage cutaneous melanoma, many
patients still do not benefit and regimens are associated with high toxicity. We are studying the determinants
of treatment response and mechanisms of resistance in melanoma. From our studies, we aim to generate pre-
clinical data for new combinations that delay/prevent the onset of acquired resistance while minimizing patient
toxicities in order to improve patient survival and quality of life. Multiple clinical trials have emanated from our
work (NCT03580382, NCT02012231, NCT02683395). Tumor immunogenicity, defined as the ability of the
tumor itself to trigger an anti-tumor adaptive immune response, is one of the most important determinants of
successful anti-cancer therapy. The immunogenicity of a tumor depends on its antigenicity, conferred by neo-
antigens, and also by adjuvant effects triggered by damage-associated molecular patterns (DAMPs) released
from stressed or dying tumor cells during a process called immunogenic cell death (ICD). We recently
discovered a signaling pathway that allows efficient release of DAMPs from dying cells by switching apoptosis
into a potentially immunogenic form of cell death called pyroptosis. Mechanistically, activation of caspase-3
during apoptosis leads to cleavage of gasdermin E (GSDME), generating a pore-forming GSDME-N fragment.
GSDME-N pores allow release of intracellular DAMPs such as HMGB1, DNA, and ATP. The ability of this
novel pathway to switch apoptosis into pyroptosis suggests that GSDME-induced pyroptosis is likely a key
effector of cancer cell immunogenicity and may determine their successful response to various anti-cancer
therapies. Supporting this hypothesis, our preliminary data revealed that efficient BRAFi + MEKi-induced anti-
tumor immune responses in melanoma cells are dependent, at least in part, on the pyroptotic activity of
GSDME. The goals of this application are to define mechanisms underlying BRAFi + MEKi regulation of
GSDME and pyroptosis in melanoma and to investigate how GSDME-induced pyroptosis alters the effects of
immune checkpoint inhibitors. The standard of care for melanomas is immune checkpoint inhibition, specifically
anti-PD-1 (pembrolizumab and nivolumab) and anti-CTLA-4 (ipilimumab). Immune checkpoint inhibitors are
efficacious in some melanoma patients; however, many do not respond. Other patients who initially respond,
ultimately progress. This proposal is designed to utilize targeted therapies to optimize up-front immune
checkpoint inhibitors as well as invigorating the immune system in resistant tumors. Thus, we aim to develop
new therapeutic strategies that will address clinical unmet needs in the melanoma field.

Grant Number: 5R01CA256945-05
NIH Institute/Center: NIH
Principal Investigator: Andrew Aplin