In cancer, increased infiltration of macrophages within and surrounding the tumor mass correlates with increased tumor invasiveness and growth. In addition, presence of tumor-associated macrophages (TAMs) has been shown to correlate with poor prognosis, particularly in breast, prostate, ovarian and cervical cancer. TAM proliferation, differentiation and survival is dependent on Colony Stimulating Factor - 1 Receptor (CSF-1R) activation, a type III integral membrane tyrosine kinase receptor selectively expressed on cells of the mononuclear phagocyte lineage. Given that TAMs enhance tumor growth and that activation of the CSF-1R pathway is required for TAM function, an antibody against mouse CSF-1R was generated for proof-of-principle studies. CS7, a monoclonal anti-mouse CSF-1R antibody inhibited both CSF-1 and IL-34 binding to mouse CSF-1R, leading to inactivation of the receptor and downstream signaling molecules. In addition, CS7 prevented monocyte proliferation and macrophage differentiation with IC50s of 0.1 nM and 0.75 nM, respectively. In murine models of breast cancer using CSF-1-secreting MDA-MB-231, Hcc1954, 4T1 or EMT6 tumor cells, CS7 treatment led to a marked reduction in TAMs and an associated decrease in tumor growth. In contrast, breast tumor xenografts with CSF-1 non-secreting breast tumor cell lines JimT1 and MCF-7 had limited or no decrease in tumor volume following CS7 treatment. In prostate models, DU145 tumor cell line xenografts (CSF-1-secreting) but not PC3 (CSF-1 non-secreting) tumor growth was inhibited by CS7, recaptitulating the results seen with breast xenografts. Thus, in breast and prostate preclinical models, CSF-1 secretion by tumor cells is a prerequisite for sensitivity to anti-CSF-1R treatment. Taken together, targeting CSF-1R with a monoclonal antibody inhibits CSF-1R signaling via CSF-1 and IL-34, prevents monocytic to macrophage differentiation, and reduces tumor volume in preclinical models, validating CSF-1R as a target for therapeutic application in cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3539. doi:1538-7445.AM2012-3539