CDK4/6-MEK inhibition in MPNSTs causes plasma cell infiltration, sensitization to PD-L1 blockade, and tumor regression

ABSTRACT: Malignant peripheral nerve sheath tumors (MPNSTs) are lethal, Ras-driven sarcomas that lack effective therapies. Ras effectors, CDK4/6 and MEK, were identified as rational targets for combination therapy from patient tumor analyses and preclinical drug studies. In MPNST cells, low-dose combinations of CDK4/6 and MEK inhibitors synergistically reactivated the retinoblastoma (RB1) tumor suppressor, induced cell death, and decreased clonogenic survival. In immune-deficient mice, dual CDK4/6-MEK inhibition slowed growth but did not shrink MPNSTs in 4 of 5 patient-derived xenografts (PDXs). By comparison, combination therapy of de novo MPNSTs in immunocompetent mice caused tumors to regress, delayed resistant tumor outgrowth, and improved survival relative to monotherapies. While drug-resistant tumors adopted an immunosuppressive microenvironment enriched with MHC II-low macrophages, drug-sensitive tumors that regressed contained plasma cells and increased T cell clustering. In other cancers, intratumoral plasma cells are associated with better response to immune checkpoint blockade (ICB). Impressively, CDK4/6-MEK inhibition sensitized MPNSTs to anti-PD-L1 ICB therapy with some mice displaying complete tumor ablation. These results reveal a novel plasma cell-associated immune response and extended antitumor activity of combined CDK4/6-MEK inhibition in MPNSTs, which dramatically enhanced the efficacy of ICB therapy. This work highlights promising, potentially curative treatment options for MPNSTs.

ORGANISM(S): Mus musculus

PROVIDER: GSE224656 | GEO | 2023/06/29

REPOSITORIES: GEO