A Small Molecule CCR2 Antagonist Depletes Tumor Macrophages and Synergizes with Anti–PD-1 in a Murine Model of Cutaneous T-Cell Lymphoma (CTCL)

Tumor-associated macrophages (TAMs) recruited from blood monocytes are key in establishing an immunosuppressive tumor microenvironment (TME) for the support of tumor growth. We hypothesize that blocking monocyte trafficking (through the inhibition of specific chemokine receptors) into skin can positively affect tumor development. Herein, the authors examined the effects of oral administration of a small molecule inhibitor for CCR2, CCR2i, which blocks CCR2-mediated chemotaxis of monocytes in a syngeneic mouse T-cell lymphoma in skin. Following CCR2i administration, the depletion of macrophages was achieved as early as 2 days after tumor initiation in ear TME. Quantitative real-time PCR detected an increase in the levels of immune stimulatory inflammatory cytokines, for example, IFN-γ and IL-12, in CCR2i- versus vehicle-treated mice. Within 2 weeks, the tumors from the control groups attained the maximum size, whereas CCR2i-treated mice exhibited much smaller tumor sizes and weights. Immunohistochemistry revealed that CCR2i-treated tumors possessed considerably more CD8+ T cells, which demonstrated their essential role in CCR2i-induced tumor inhibition. Finally, the combination of anti-programmed cell death protein 1 with CCR2i considerably increased the efficacy of tumor eradication related to the activation of IFN-γ–producing CD8 T cells. Our findings provide strong evidence that the CCR2i, particularly in combination with an immune checkpoint inhibitor, reduces tumor growth and is a potential future treatment option for cutaneous T-cell lymphomas.