Targeting Neuropilin-1 to Enhance Immunotherapy in Melanoma: Reducing Peripheral Treg-Mediated Immunosuppression and Tumour Progression

Melanoma, the most aggressive type of skin cancer with a high mutation rate, is the fifth most common cancer among Caucasians. Despite advancements in treatments like immune checkpoint inhibitors and targeted therapies, over 40% of patients experience immune-related side effects, presenting significant challenges. Neuropilin-1 (NRP1) has become an essential target in cancer therapy due to its overexpression in various cancers, where it enhances regulatory T cell (Treg) function and supports tumor growth, often leading to poor outcomes.

This study investigated the effects of NRP1 inhibition in B16-F10 melanoma and its impact on immune responses regulated by Tregs. NRP1 was overexpressed in several cancers, including B16-F10 cells, compared to non-cancerous NIH-3T3 cells. Inhibiting NRP1 selectively caused apoptosis in B16-F10 cells without affecting NIH-3T3 cells. It also reversed the immunosuppression of splenic T cells induced by B16-F10-conditioned media, reducing Treg markers (NRP1, NKG2A, FOXP3), Treg activity, and the production of immunosuppressive cytokines (IL-10, IL-17A). Furthermore, NRP1 inhibition increased T cell proliferation and boosted the release of effector cytokines (TNF, IFN-γ, IL-6, IL-2). NRP1 inhibition also suppressed the STAT, ERK MAPK, and Smad2/3 pathways while activating the PI3K/AKT pathway. In splenic T cells from B16-F10 tumor-bearing mice treated with an NRP1 inhibitor, there was a decrease in Treg markers and activity, along with enhanced T cell proliferation. Additionally, NRP1 inhibitor treatment reduced lung metastasis, decreased tumor size, and improved survival in these mice.

This study shows that inhibiting NRP1 may slow B16-F10 melanoma progression and reduce Treg-mediated immunosuppression. This suggests its potential as a promising approach in future cancer immunotherapies, especially in combination with other treatments.