Molecular-Targeted Immunotherapeutic Strategy for Melanoma <i>via</i> Dual-Targeting Nanoparticles Delivering Small Interfering RNA to Tumor-Associated Macrophages

TLDR

Tumor‑associated macrophages (TAMs) are a key immunotherapy target, yet delivering drugs specifically to the tumor‑promoting M2‑like TAMs remains difficult. The authors designed dual‑targeting nanoparticles (M2NPs) that combine an SR‑B1‑binding α‑peptide with an M2‑macrophage‑binding M2pep to selectively engage M2‑like TAMs. By conjugating anti‑CSF‑1R siRNA to M2NPs, the platform blocks the survival signal of M2‑like TAMs, leading to their depletion from melanoma tumors. In mouse melanoma models, M2NP‑siRNA treatment eliminated 52 % of M2‑like TAMs, reduced tumor size by 87 %, prolonged survival, suppressed IL‑10/TGF‑β, boosted IL‑12/IFN‑γ and CD8⁺ T‑cell infiltration, and restored T‑cell function by down‑regulating PD‑1/Tim‑3 and increasing IFN‑γ secretion.

Abstract

Tumor-associated macrophages (TAMs) are a promising therapeutic target for cancer immunotherapy. Targeted delivery of therapeutic drugs to the tumor-promoting M2-like TAMs is challenging. Here, we developed M2-like TAM dual-targeting nanoparticles (M2NPs), whose structure and function were controlled by α-peptide (a scavenger receptor B type 1 (SR-B1) targeting peptide) linked with M2pep (an M2 macrophage binding peptide). By loading anti-colony stimulating factor-1 receptor (anti-CSF-1R) small interfering RNA (siRNA) on the M2NPs, we developed a molecular-targeted immunotherapeutic approach to specifically block the survival signal of M2-like TAMs and deplete them from melanoma tumors. We confirmed the validity of SR-B1 for M2-like TAM targeting and demonstrated the synergistic effect of the two targeting units (α-peptide and M2pep) in the fusion peptide (α-M2pep). After being administered to tumor-bearing mice, M2NPs had higher affinity to M2-like TAMs than to tissue-resident macrophages in liver, spleen, and lung. Compared with control treatment groups, M2NP-based siRNA delivery resulted in a dramatic elimination of M2-like TAMs (52%), decreased tumor size (87%), and prolonged survival. Additionally, this molecular-targeted strategy inhibited immunosuppressive IL-10 and TGF-β production and increased immunostimulatory cytokines (IL-12 and IFN-γ) expression and CD8+ T cell infiltration (2.9-fold) in the tumor microenvironment. Moreover, the siRNA-carrying M2NPs down-regulated expression of the exhaustion markers (PD-1 and Tim-3) on the infiltrating CD8+ T cells and stimulated their IFN-γ secretion (6.2-fold), indicating the restoration of T cell immune function. Thus, the dual-targeting property of M2NPs combined with RNA interference provides a potential strategy of molecular-targeted cancer immunotherapy for clinical application.