Targeting RAS/RAF/PI3K pathway for CD40 induction in melanoma cells to overcome resistance to anti-PD1 immunotherapies

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Presentation Time: 11:30 AM - 12:45 PM
Poster Board Number: B137
Abstract ID: 4969

Presenting Author:
Chi Yan , Assistant Professor (Research) at Vanderbilt Univ. Sch. of Med., VA Tennessee Valley Healthcare Sys.

Abstract:

The first-line treatment for metastatic melanoma is immune checkpoint blockade (ICB), but it fails in many patients and may have serious adverse events. We showed that rigosertib (RGS), a RAS-pathway inhibitor, promotes CD40 upregulation on melanoma cells and synergizes with ICB in preclinical melanoma models. However, residual disease still occurred with uncontrolled ERK activation. Our present study explores the efficacy of RGS plus trametinib (T), a MEK1/2 inhibitor, to overcome ICB resistance. The concurrent RGS+T+αPD1 resulted in an additive effect to suppress ICB-resistant NRAS^mut 1014 tumor growth, and 44.4% (4/9) tumors completely regressed after 2 weeks of treatment. The RGS+T regimen promoted CD8⁺ T cell responses in the tumor microenvironment (TME) and extended the time to αPD1 resistance (p<0.0001). Combining RGS+T with agonist CD40 (aCD40) resulted in increased CD8⁺ T cells, natural killer cells, and M1 macrophages in the TME, with a reduction of myeloid-like CD11b⁺PD-L1⁺ regulatory B cells in the tumors (~70%, p<0.0001) and tumor-draining lymph nodes (~40%, p<0.0001). CRISPR/dCas9-based overexpression of CD40 (CD40-OE) in 1014 melanoma cells reduced in vivo tumor growth and successfully turned the ICB-resistant tumors into responders to αPD1 (p=0.025), which further regressed with aCD40+αPD1 (p<0.001). Our preclinical data support the therapeutic use of RAS/RAF/PI3K inhibition plus CD40 agonism for metastatic melanoma patients who do not respond to ICB.