Pexmetinib

Patients with tumors that do not respond to immune-checkpoint inhibition often harbor a non-T cell-inflamed tumor microenvironment, characterized by the absence of IFN-γ-associated CD8⁺ T cell and dendritic cell activation. Understanding the molecular mechanisms underlying immune exclusion in non-responding patients may enable the development of novel combination therapies. p38 MAPK is a known regulator of dendritic and myeloid cells however a tumor-intrinsic immunomodulatory role has not been previously described. Here we identify tumor cell p38 signaling as a therapeutic target to potentiate anti-tumor immunity and overcome resistance to immune-checkpoint inhibitors (ICI). Molecular analysis of tumor tissues from patients with human papillomavirus-negative head and neck squamous carcinoma reveals a p38-centered network enriched in non-T cell-inflamed tumors. Pan-cancer single-cell RNA analysis suggests that p38 activation may be an immune-exclusion mechanism across multiple tumor types. P38 knockdown in cancer cell lines increases T cell migration, and p38 inhibition plus ICI in preclinical models shows greater efficacy compared to monotherapies. In a clinical trial of patients refractory to PD1/L1 therapy, pexmetinib, a p38 inhibitor, plus nivolumab demonstrated deep and durable clinical responses. Targeting of p38 with anti-PD1 has the potential to induce the T cell-inflamed phenotype and overcome immunotherapy resistance.

Breast cancer metastases to the bone can lead to a series of bone-related events that seriously affect the quality of life. Pexmetinib, a novel p38 mitogen-activated protein kinase (p38) inhibitor that has been evaluated in phase I clinical trials for myelodysplastic syndrome, but the effects of Pexmetinib on breast cancer induced osteolysis haven't been explored. Here, we found that Pexmetinib inhibited receptor activator of nuclear factor-κB ligand-induced osteoclast formation and bone resorption in vitro. Pexmetinib suppressed p38-mediated signal transducer and activator of transcription 3 (STAT3), which direct regulated transcription of the nuclear factor of activated T cells 1 (NFATc1), leading to reduced osteoclast formation. Moreover, Pexmetinib exerted anti-tumor effects in breast cancer cells in vitro via suppressing p38-mediated STAT3 activation and matrix metalloproteinases (MMPs) expression. Furthermore, Pexmetinib suppressed breast cancer-associated osteolysis in vivo. These results suggest that Pexmetinib may be a promising drug for the treatment of breast cancer-induced osteolysis.