The mitochondrial protease ClpP is a metabolic vulnerability and an immunogenic trigger against multiple myeloma.

Abstract

Orchestrating key homeostatic functions, mitochondria likely entail cancer vulnerabilities. Moreover, due to their bacterial ancestry they can release potent immunogenic signals. Here we show that the mitochondrial protease ClpP is both a cell-intrinsic metabolic vulnerability and an actionable immunogenic trigger in multiple myeloma (MM). We found that ClpP mRNA is higher in bone marrow (BM)-purified malignant plasma cells (PC) than in normal or premalignant counterparts and that MM lines rank first for ClpP expression among human cancers. Moreover, we demonstrated that human MM cells are highly vulnerable to ClpP inhibition in vitro and in vivo. Surprisingly, MM cell dependence on ClpP was not accounted for by its acknowledged oxidative phosphorylation surveillance activity. Proteomic discovery of proteolytic targets, metabolomics, and metabolic tracing identified a critical control exerted by ClpP on ornithine aminotransferase abundance to sustain cytosolic biosynthesis of polyamines, essential to MM cells. Transcriptomics and targeted validation also revealed activation of a cyclic GMP-AMP synthase (cGAS)-dependent type-I interferon (IFN-I) response in ClpP-silenced MM cells, whose supernatants boosted dendritic cell activation and ability to stimulate IFNg production by T cells. In vivo, ClpP silencing re-shaped the BM immune environment in immunocompetent mice, significantly expanding IFNg-producing CD4+ and CD8+ T cells and CD4+ T memory cells, while containing exhausted CD4+ T cells and myeloid derived suppressor cells. Thus, ClpP is a novel addiction of MM cells, whose inhibition not only exerts cell-intrinsic toxicity, but also triggers otherwise indolent anti-tumoral immunity. Our findings yield a novel immunogenic chemotherapeutic framework of potential relevance against myeloma.