Mixed Lineage Kinase Suppression in Triple-Negative Breast Cancer: Identification of a Dual Inhibitor Targeting MLK3 and NAMPT.

Triple-negative breast cancer (TNBC) is aggressive and lacks targeted therapeutic options. Mixed lineage kinase 3 (MLK3) plays a key role in TNBC progression. To enhance the therapeutic impact of MLK3 inhibition in TNBC, a novel MLK3 inhibitor scaffold was optimized to incorporate inhibition of NAMPT, often upregulated in TNBC to meet the increased demand for NAD+. Cell-free and cell-based assays for MLK3 and NAMPT inhibition drove the design and optimization of GR2-128, a dual inhibitor with matched nanomolar inhibition for MLK3 and NAMPT, antiproliferative in TNBC cell lines, with acceptable metabolic stability and bioavailability. GR2-128 attenuated tumorigenesis in a syngeneic mouse breast cancer model, increasing apoptosis via inhibition of MLK3 and NAMPT, attenuating macrophage and neutrophil infiltration and increasing tumor T-cell markers without change in B-cell count. These data support the dual inhibition of MLK3/NAMPT as a therapeutic approach to TNBC, with the potential for tumor immuno-sensitization.