Combining Neratinib with CDK4/6, mTOR, and MEK Inhibitors in Models of HER2-positive Cancer

Abstract

Purpose: Neratinib is an irreversible, pan-HER tyrosine kinase inhibitor that is FDA-approved for HER2-overexpressing/amplified (HER2⁺) breast cancer. In this preclinical study, we explored the efficacy of neratinib in combination with inhibitors of downstream signaling in HER2⁺ cancers in vitro and in vivo. Experimental Design: Cell viability, colony formation assays, and western blotting were used to determine effect of neratinib in vitro. In vivo efficacy was assessed with patient-derived xenografts (PDXs): two breast, two colorectal and one esophageal cancer; two with HER2 mutations. Four PDXs were derived from patients who received previous HER2-targeted therapy. Proteomics were assessed through Reverse Phase Protein Arrays (RPPA) and network level adaptive responses were assessed through Target Score algorithm. Results: In HER2⁺ breast cancer cells, neratinib was synergistic with multiple agents, including mTOR inhibitors everolimus and sapanisertib, MEK inhibitor trametinib, CDK4/6 inhibitor palbociclib, and PI3Ka inhibitor alpelisib. We tested efficacy of neratinib with everolimus, trametinib, or palbociclib in five HER2⁺ PDXs. Neratinib combined with everolimus or trametinib led to a 100% increase in median event-free survival (EFS; tumor doubling time) in 25% (1 of 4) and 60% (3 of 5) models respectively while neratinib with palbociclib increased EFS in all five models. Network analysis of adaptive responses demonstrated upregulation of EGFR and HER2 signaling in response to CDK4/6, mTOR and MEK inhibition, possibly providing an explanation for the observed synergies with neratinib. Conclusion: Taken together, our results provide strong preclinical evidence for combining neratinib with CDK4/6, mTOR and MEK inhibitors for the treatment of HER2⁺ cancer.