Systemic administration of poly(I:C) and resiquimod reprograms tumor-associated macrophages and prevents tumor progression and metastasis in murine cancer models.

Abstract

Tumor-associated macrophages (TAMs) drive the immunosuppressive tumor microenvironment (TME), promoting oncogenic progression, metastasis and treatment resistance. While we previously established that intratumoral administration of poly(I:C) and R848 (TLR3 and TLR7/8 agonists) has strong therapeutic efficacy and triggers STAT1-mediated TAM reprogramming superior to monotherapies, this study evaluates the translational potential, systemic tolerability and immunological impact of their combined systemic (intravenous) delivery. Across diverse syngeneic murine models of solid tumors, including lung adenocarcinoma, triple-negative breast cancer (TNBC), fibrosarcoma and glioblastoma, systemic poly(I:C)+R848 administration significantly inhibited primary tumor growth and spontaneous lung metastasis. The treatment exhibited good tolerability under the conditions tested, with no body weight loss or histopathological damage to major organs. Treatment triggered a transient trend toward elevation of pro-inflammatory cytokines (TNF-α, IFN-γ, CXCL10, CCL5), while anti-inflammatory markers (IL-10, IL-4) remained unchanged. In primary tumors, treatment-induced TAM reprogramming was evidenced by upregulated M1-like markers (Irf7, Ccl5) and decreased M2-like markers (Arg1), accompanied by enhanced Cd8 and Cd4 T cell markers and cytotoxic effectors (Prf-1 and Gzmb). Multispectral immunophenotyping confirmed this shift toward an antitumor macrophage phenotype, characterized by increased CD86 and decreased ARG1 across all primary tumors. Furthermore, treatment significantly prevented lung metastasis and tumor-induced splenomegaly, shifting splenic macrophages toward an elevated M1/M2 ratio in both fibrosarcoma and TNBC models. These findings demonstrate that intravenous administration of the poly(I:C)+R848 combination effectively reprograms TAMs, suppressing tumor progression and preventing metastasis across a variety of preclinical models of difficult-to-treat solid tumors.