TMET-01. Synergistic potential of Tucatinib and Dichloroacetate in HER2+ breast cancer: an in vitro analysis

Abstract BACKGROUND: Tucatinib is a selective, orally available HER2-targeted tyrosine kinase inhibitor (TKI) approved for HER2-positive metastatic breast and colorectal cancers. Synergistic drug combinations have been explored in breast cancer with promising results in brain metastases. Dichloroacetate (DCA), a pyruvate dehydrogenase kinase (PDK) inhibitor, shifts metabolism from glycolysis toward oxidative phosphorylation, reversing the Warburg effect. Given that EGFR/ERBB2 signaling contributes to HIF1 activation and subsequent PDK1 upregulation, DCA may enhance EGFR/HER2 targeted therapy. However, previous in vitro studies used DCA concentrations exceeding human plasma levels (10–40 mM vs. 1 mM). This study evaluates potential synergy between tucatinib and DCA at pharmacokinetically relevant concentrations in HER2+ breast cancer cells. METHODS: BT474 breast cancer cells were seeded at 25,000 cells/mL in 96-well plates and grown for 24h. Cells were treated with tucatinib (1:5 or 1:3 serial dilutions), DCA (1.0 mM), their combination, or left untreated. Following 72h incubation, cellular proliferation was assessed using Presto Blue resazurin-based assays (570 nm). IC50 curves were compared to evaluate whether the addition of DCA improved the efficacy of Tucatinib. RESULTS: DCA alone at 1.0 mM modestly attenuated cellular proliferation, while tucatinib exhibited the expected antiproliferative effects with increasing doses. The addition of DCA reduced the IC50 of tucatinib from 24.15 nM (95% CI: 9.5, 58.7) to 18.16 nM (6.378, 46.81) with a p-value of 0.03. CONCLUSION: The addition of DCA at 1mM improves the antiproliferative effects of Tucatinib in HER2+ BT474 breast cancer cells. Further studies investigating additional drug combinations and cell lines are ongoing.