Triple-negative breast cancer (TNBC) has the lowest 5-year survival rate of invasive breast carcinomas, and currently there are no approved targeted therapies for this aggressive form of the disease. The androgen receptor (AR) is expressed in up to one third of TNBC and we find that all AR+ TNBC primary tumors tested display nuclear localization of AR, indicative of transcriptionally active receptors. While AR is most abundant in the “luminal AR (LAR)” molecular subtype of TNBC, here, for the first time, we use both the new-generation anti-androgen enzalutamide and AR knockdown to demonstrate that the other non-LAR molecular subtypes of TNBC are critically dependent on AR protein. Indeed, AR inhibition significantly reduces baseline proliferation, anchorage-independent growth, migration, and invasion and increases apoptosis in four TNBC lines (SUM159PT, HCC1806, BT549, and MDA-MB-231), representing three non-LAR TNBC molecular subtypes (mesenchymal-like, mesenchymal stem–like, and basal-like 2). In vivo, enzalutamide significantly decreases viability of SUM159PT and HCC1806 xenografts. Furthermore, mechanistic analysis reveals that AR activation upregulates secretion of the EGFR ligand amphiregulin (AREG), an effect abrogated by enzalutamide in vitro and in vivo. Exogenous AREG partially rescues the effects of AR knockdown on proliferation, migration, and invasion, demonstrating that upregulation of AREG is one mechanism by which AR influences tumorigenicity. Together, our findings indicate that non-LAR subtypes of TNBC are AR dependent and, moreover, that enzalutamide is a promising targeted therapy for multiple molecular subtypes of AR+ TNBC.

Immunosuppressive entities in the tumor microenvironment (TME) remain a major impediment to immunotherapeutic approaches for a majority of patients with cancer. While the immunosuppressive role of transforming growth factor-β (TGF-β) in the TME is well known, clinical studies to date with anti-TGF-β agents have led to limited success. The bifunctional agent bintrafusp alfa (previously designated M7824) has been developed in an attempt to address this issue. Bintrafusp alfa consists of an IgG1targeting programmed death ligand 1 (PD-L1) moiety fused via peptide linkers to the extracellular domain of two TGF-β receptor II molecules designed to ‘trap’ TGF-β in the TME. This agent is able to bring the TGF-β trap to the TME via its anti-PD-L1 component, thus simultaneously attacking both the immunosuppressive PD-L1 and TGF-β entities. A number of preclinical studies have shown bintrafusp alfa capable of (1) preventing or reverting TGF-β-induced epithelial-mesenchymal transition in human carcinoma cells; this alteration in tumor cell plasticity was shown to render human tumor cells more susceptible to immune-mediated attack as well as to several chemotherapeutic agents; (2) altering the phenotype of natural killer and T cells, thus enhancing their cytolytic ability against tumor cells; (3) mediating enhanced lysis of human tumor cells via the antibody-dependent cell-mediated cytotoxicity mechanism; (4) reducing the suppressive activity of Tregcells; (5) mediating antitumor activity in numerous preclinical models and (6) enhancing antitumor activity in combination with radiation, chemotherapy and several other immunotherapeutic agents. A phase I clinical trial demonstrated a safety profile similar to other programmed cell death protein 1 (PD-1)/PD-L1 checkpoint inhibitors, with objective and durable clinical responses. We summarize here preclinical and emerging clinical data in the use of this bispecific and potentially multifunctional agent.

BackgroundDespite the success of immune checkpoint blockade therapy in the treatment of certain cancer types, only a small percentage of patients with solid malignancies achieve a durable response. Consequently, there is a need to develop novel approaches that could overcome mechanisms of tumor resistance to checkpoint inhibition. Emerging evidence has implicated the phenomenon of cancer plasticity or acquisition of mesenchymal features by epithelial tumor cells, as an immune resistance mechanism.MethodsTwo soluble factors that mediate tumor cell plasticity in the context of epithelial-mesenchymal transition are interleukin 8 (IL-8) and transforming growth factor beta (TGF-β). In an attempt to overcome escape mechanisms mediated by these cytokines, here we investigated the use of a small molecule inhibitor of the IL-8 receptors CXCR1/2, and a bifunctional agent that simultaneously blocks programmed death ligand 1 (PD-L1) and traps soluble TGF-β.ResultsWe demonstrate that simultaneous inhibition of CXCR1/2, TGF-β, and PD-L1 signaling synergizes to reduce mesenchymal tumor features in murine models of breast and lung cancer, and to markedly increase expression of tumor epithelial E-cadherin while reducing infiltration with suppressive granulocytic myeloid-derived suppressor cells, significantly enhancing T-cell infiltration and activation in tumors, and leading to improved antitumor activity.ConclusionsThis study highlights the potential benefit of combined blockade of CXCR1/2 and TGF-β signaling for modulation of tumor plasticity and potential enhancement of tumor responses to PD-L1 blockade. The data provide rationale for the evaluation of this novel approach in the clinic.