Growth factors maintain intratumoral heterogeneity and drive therapeutic resistance in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) shows considerable intratumoral heterogeneity, which contributes to therapeutic resistance. Recent studies show that targeted therapeutics can steer TNBC toward homogeneous, drug-resistant states, but little is understood about how the microenvironment modulates these responses. We report studies to determine how components of the microenvironment impact response to trametinib and cellular heterogeneity. We find that multiple microenvironmental factors, including HGF and neuregulin 1, can drive therapeutic resistance and that treatment with hepatocyte growth factor (HGF) inhibitors restores trametinib sensitivity. Interestingly, treatment with these ligands reverses trametinib-induced homogeneity, restoring heterogeneity to levels comparable to baseline both in vitro and in vivo. Analysis of patient data demonstrates that TNBC with high HGF expression levels has a poor outcome and increased expression of basal and mesenchymal state markers. Our data suggest that common growth factors drive therapeutic resistance and maintain tumor heterogeneity in TNBC, and that co-targeting these factors may improve therapeutic response.