The team of researchers led by Simone Cenci, Director of the Genetics and Cell Biology Division, group leader of the Age Related Diseases lab at IRCCS Ospedale San Raffaele and Professor at Vita-Salute San Raffaele University, and by Doctor Matteo Bellone, group leader of the Cellular Immunology Lab at IRCCS Ospedale San Raffaele, has identified the mitochondrial protease ClpP as a novel potential target for the treatment of multiple myeloma (MM). The results of the work have been published in this week’s issue of the journal Blood.

ClpP silencing reduces multiple myeloma cell growth

The authors analyzed published RNA-seq datasets of plasma cells derived from the bone marrow of patients with MM and found that ClpP mRNA is upregulated specifically in malignant cells, as compared to healthy counterparts, and that its expression increases with disease progression. Moreover, analysis of public expression data from the Cancer Cell Line Encyclopedia showed that MM ranks first among human cell cancers for the expression of ClpP.

These findings identified the high expression of ClpP as a possible tumor-specific vulnerability that the authors set out to investigate to design new therapeutic strategies against MM.

To investigate the role of ClpP in tumor growth and survival, the authors knocked down its expression by engineering stable and inducible short hairpin RNAs against ClpP in several human MM cell lines. ClpP knock down resulted in reduced MM cell growth in vitro.

Additionally, subcutaneous injections in immunodeficient mice of human MM cells in which ClpP had been knocked down led to delayed tumor appearance and delayed tumor growth in vivo. MM cell growth was reduced also by pharmacological blockade of ClpP, in vitro and in vivo.

Finally, the authors showed that ClpP promotes MM cell growth and survival by degrading the enzyme ornithine aminotransferase, thereby ensuring the supply of ornithine for the cytoplasmic biosynthesis of polyamines, which are essential to plasma cells.

These experiments identified ClpP as a novel tumor cell-intrinsic metabolic vulnerability, whose inhibition can reduce and delay MM growth.

ClpP silencing triggers anti-multiple myeloma immune response

Transcriptomic analyses revealed that ClpP knock down not only reduced MM cell growth, but also resulted in the induction of an immunostimulatory type I interferon (IFN) response in MM cells in vitro and in vivo.

As a result, the supernatant collected from ClpP silenced MM cells activated human dendritic cells in culture, which, in turn, were able to induce the release of IFN-γ from co-cultured T cells. Moreover, immunocompetent mice injected with ClpP-silenced MM cells revealed significantly lower tumor growth, associated with higher proportions in the bone marrow of relevant T cell subpopulations, namely, IFN-γ-producing CD4⁺ and CD8⁺ T cells, and central and effector memory CD4⁺ T cells, and with lower representation of exhausted CD4⁺ T cells.

Finally, further attesting to therapeutic relevance, ClpP knock down in vivo increased the efficacy of pharmacological treatment with the immune checkpoint PD-L1 inhibitor against MM.

These findings reveal that inhibiting ClpP holds potential as a strategy to trigger effective anti-myeloma immunity and to enhance the efficacy of currently available immunotherapies.

Future perspectives

The clinical management of MM remains challenging; thus, the identification of novel targets is crucial for developing new therapeutic strategies against this still incurable cancer.

In this context, the role of mitochondria in regulating cell homeostasis and metabolism could point to new therapeutic avenues, as also witnessed by the repurposing of FDA-approved mitochondria-targeting agents in the treatment of tumors.

“In this work, we identified the mitochondrial protease ClpP as a single target whose silencing provides a twofold advantage against multiple myeloma. By knocking down the expression of this enzyme in MM cells, it was indeed possible not only to reduce tumor growth, but also to trigger effective antitumor immune response”, says Tommaso Perini, who shares with Doctor Paola Zordan co-first authorship of the study.

“This work provides a novel immunogenic chemotherapy framework of potential great relevance to treat multiple myeloma, a prototypical immunologically “cold” tumor, and points to mitochondria as a powerful source of pleiotropic targets for anti-cancer therapies”, concludes Professor Simone Cenci.

Written by Laura  Celotto
Published on 12/09/2025