Mechanism of acquired resistance to lapatinib via Src and RUNX3 in breast cancer

Abstract

Background: Lapatinib is an effective EGFR and HER2 targeting small molecular tyrosine kinase inhibitor, which is one of the standard of care medicine for HER2 positive metastatic breast cancer patients. Primary and acquired resistance to lapatinib developed. Despite several mechanisms of resistance to lapatinib have been suggested, still the mechanisms of developing lapatinib resistant remain as a question to solve. Thus, I tried to find out there is a novel mechanism which related to lapatinib resistant, and any specified molecules were involved in this process. Methods: Acquired resistant SK-BR-3 cells were established by chronic exposure to lapatinib. Lapatinib and saracatinib sensitivity were confirmed by MTT assay. Western blotting was used to determine signal transduction molecule changes. Wound healing assay and Boyden chamber assay were conducted for verifying invasive ability. Whole exome sequencing (WES) and siRNA knock-down system were used for further analysis. Results: Generation of Laptinib resistant (LR) cell lines confirmed by MTT assay. LR cell lines showed down-regulation of pHER2, pAkt, and pERK. The activity of Src family kinase was increased in LR cells. Vimentin, an EMT marker, is also up-regulated in LR cells. Migration and invasion were significantly increased in LR cells. Saracatinib inhibited activation of Src family kinase, cell migration and cell invasion in LR cells. Correlated with a missense mutation of RUNX3, which identified by WES, expression of RUNX3 was decreased in LR cells. Moreover, si-RUNX3 knock-down parental cells showed more resistance to lapatinib. Conclusion: The increase of Src activation, cell migration, and invasion was observed in LR cells. RUNX3, which identified by WES, affected to lapatinib sensitivity in SK-BR-3 cells. Based on our data, activation of Src contributes resistance to lapatinib and RUNX3 might be a potential marker, which partially contributes resistance to lapatinib.