The Discovery and Characterization of HBS-101, a Novel Inhibitor of Midkine, as a Therapeutic Agent for the Treatment of Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with a poor clinical outcome. There is a dire need for the development of new targeted therapies for TNBC. Midkine (MDK), a multifunctional cytokine/growth factor, functions as an oncoprotein, and its expression is elevated in various cancers. The absence of small-molecule inhibitors targeting MDK represents a significant knowledge gap for translation. In this study, we identified HBS-101 as a potent MDK inhibitor with high specificity. Our modeling studies revealed that the interaction of HBS-101 with MDK is primarily driven by hydrophobic forces, and this interaction disrupted MDK's binding to its endogenous receptors. Microscale thermophoresis, cellular thermal shift assay, and biotin pull-down studies confirmed the direct interaction of HBS-101 with MDK. Therapeutically, HBS-101 treatment significantly reduced cell viability (IC50 0.3-2.8 µmol/L), clonogenic survival, invasiveness, and increased apoptosis. The underlying mechanism of HBS-101 involves suppression of the Akt/mTOR, STAT3, and NF-κB pathways. Importantly, HBS-101 exhibits distinct pharmacologic advantages, including oral bioavailability, blood-brain barrier penetration, and in vivo stability. Histologically, doses of up to 10 mg/kg showed no observable organ toxicity and had no effect on the mice's body weight. Dose range studies identified 5 mg/kg as the minimal effective dose, achieving more than a 50% tumor reduction. HBS-101 treatment led to a significant reduction in the growth of xenograft tumors derived from patients with TNBC in vivo and markedly reduced TNBC brain metastatic tumor growth and prolonged mice survival. Collectively, our studies identified a first-in-class MDK inhibitor, HBS-101, that can be used to treat MDK-driven cancers.