HER-Family Ligands Promote Acquired Resistance to Trastuzumab in Gastric Cancer.

Despite the clinical benefit of trastuzumab, eventually all HER2-amplified gastric cancer tumors develop drug resistance. We aimed to identify molecular mechanisms of acquired resistance to trastuzumab in gastric cancer by using well-established cell line-based preclinical models, as well as samples from patients with HER2-positive gastric cancer treated with trastuzumab. We studied trastuzumab resistance in NCI-N87 and OE19, two gastric cancer cell lines that overexpress HER2 receptor and are trastuzumab sensitive. Differences at protein, DNA, and RNA levels between the parental and resistant cells were characterized and functional studies were performed. Paired pre- and post-trastuzumab blood and tissue samples from patients with gastric cancer treated with trastuzumab were analyzed. We found that resistant cells were associated with increased activation of MAPK/ERK and PI3K/mTOR pathways driven by SRC activation. Upstream, resistant cells showed increased coexpression of multiple HER-family ligands that allowed for compensatory activation of alternative HER receptors upon HER2 blockade. Simultaneous inhibition of EGFR, HER2, and HER3 by the novel antibody mixture, Pan-HER, effectively reverted trastuzumab resistance

©2019 American Association for Cancer Research.