Therapeutic targeting with DABIL-4 depletes myeloid suppressor cells in 4T1 triple-negative breast cancer model.

In many solid tumors including triple-negative breast cancer (TNBC), upregulation of the IL-4 receptor (IL-4R) has been shown to promote cancer cell proliferation, apoptotic resistance, metastatic potential and a Th2 response in the tumor microenvironment (TME). Since immunosuppressive cells in the TME and spleen including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) also express the IL4-R, we hypothesized that selective depletion of IL4-R bearing cells in TNBC would result in the direct killing of tumor cells as well as the depletion of immunosuppressive cells and lead to an enhanced anti-tumor response. To selectively target IL-4R+ cells, we employed DABIL-4, a fusion protein toxin consisting of the catalytic and translocation domains of diphtheria toxin fused to murine IL-4. As anticipated, DABIL-4 has potent cytotoxic activity against TNBC cells both in vitro and in vivo. We demonstrate in the murine 4T1 TNBC model that DABIL-4 significantly reduces tumor growth, splenomegaly and lung metastases. Importantly, we also show that administration of DABIL-4 results in the selective depletion of MDSCs, TAMs and regulatory T cells in treated mice, with a concomitant increase of IFNγ+ CD8 effector T-cells in the tumor microenvironment. Since the 4T1 anti-tumor activity of DABIL-4 was largely diminished in IL-4R KO mice, we postulate that DABIL-4 functions primarily as an immunotherapeutic by depletion of MDSCs, TAMs, and Tregs. NanoString analysis of control and treated tumors confirmed and extended these observations by showing a marked decline of mRNA transcripts that are associated with tumorigenesis and metastasis. In conclusion, we demonstrate that DABIL-4 targeting of both tumor and immunosuppressive host cells likely represents a novel and effective treatment strategy for 4T1 TNBC and warrants further study.