Blockade of MMP14 Activity in Murine Breast Carcinomas: Implications for Macrophages, Vessels, and Radiotherapy

Matrix metalloproteinases (MMPs) facilitate cancer progression (1–3). However, broad-spectrum MMP inhibitors failed in part because MMPs mediate both pro- and anticancer effects (4–7) and because off-target, dose-limiting toxicity impeded efficacy (7). To counter these deficiencies, agents targeting specific MMPs have been developed. For breast cancer (BC), MMP14 (membrane type 1-MMP; MT1-MMP) is an especially attractive target (2,8). Genetic knockdown of MMP14 in BC cells impedes their migration and metastases but does not affect their in vitro viability or primary tumor growth (3,8). In contrast, antibody inhibition—which blocks both cancer and stromal MMP14 activity—slows primary tumor growth (9,10). Indeed, a considerable number of reactive stromal cells also express MMP14 (2), illustrating the potential importance of stromal MMP14. MMP14 facilitates angiogenesis (11–13), and MMP14 blockade can inhibit tumor angiogenesis (9,10). Various antiangiogenic agents, however, can also transiently normalize the tumor vasculature, improving tumor perfusion and oxygenation, leading to enhanced efficacy of chemo- and/or radiation-therapy (14–16). In preclinical models, blockade of MMP14 could enhance the response to cytotoxic therapies (9,10). These findings prompted us to determine a potential improvement in tumor vascular function by MMP14 blockade. The antiangiogenic effect of MMP14 inhibition is thought to result from reduced activation of MMP2 by MMP14 (9). However, other MMP14 targets have not been studied, including transforming growth factor β (TGFβ), a mediator of vascular response and a potent immunosuppressor. TGFβ is associated with poor clinical outcome in BC (17). TGFβ has proangiogenic activities and mediates vessel stabilization (18–20). TGFβ inhibitors increase antitumor immunity associated with increasing interferon (IFN)-γ and granzyme B production from natural killer (NK) cells and cytotoxic CD8+ T cells, reducing T regulatory cells, and shifting macrophages toward an inducible nitric oxide synthase (iNOS)–expressing antitumor M1-like phenotype and away from tumor-supportive M2-type (21–27). In this study we investigated if DX-2400 (9), a highly selective MMP14 inhibitory antibody, could decrease TGFβ levels and alter the macrophage phenotype in tumors. We also aimed to determine if DX-2400 could improve tumor vessel function and thus provide additional benefits when combined with radiation therapy.