Resistance mechanism to Trastuzumab in HER2-positive cancer cells and its overcome by Src inhibition

Abstract

Background: Trastuzumab in combination with chemotherapy is a standard of care for patients with HER2-positive breast and gastric cancer. Resistance mechanism to trastuzumab, anti-HER2 therapy, includes multiple pathways. Among them, Src is not well known especially in HER2-positive gastric and biliary tract cancers. We investigated the role of Src involved in trastuzumab resistance and explored the potential of Src inhibition as a trastuzumab resistance overcoming strategy. Methods: Four trastuzumab-resistant (HR) cells (SNU216HR, N87HR, SNU2670HR, SNU2773HR) were established from 2 HER2-amplified gastric cancer cells (SNU216, NCI-N87) and 2 HER2-amplified biliary tract cancer cells (SNU2670, SNU2773). For Src inhibition, bosutinib was used. MTT assay, colony formation assay, cell cycle analysis by FACS Calibur flow cytometer, and cell migration assay were done. Animal experiments were conducted to test anti-tumor effect of bosutinib using SNU2670 and SNU2670HR xenograft models. Results: SNU2670HR/NCI-N87HR cells showed pSrc activation, in contrast, SNU216HR/SNU2773HR cells exhibited decreased pSrc expression. In these pSrc decreased HR cells, pFAK was elevated. Bosutinib downregulated Src-FAK signaling more obviously in Src activated HR cells than parental cells. In pSrc decreased HR cells, bosutinib reduced Src-dependent FAK phosphorylation to affect cell fate. Bosutinib inhibited the growth of both parental cells and HR cells, and induced apoptosis and G1 arrest in HR cells. Bosutinib suppressed HR cell migration more effectively compared with parental cells. Bosutinib exhibited potent tumor growth inhibition in both SNU2670 and SNU2670HR xenograft models and more significantly suppressed tumor growth in HR models. Conclusion: Src activation may contribute to trastuzumab resistance in part in HER2-positive gastric and biliary tract cancer cells. Targeting Src might be a candidate strategy to overcome trastuzumab resistance in HER2-positive cancers.