Preclinical evidence of multiple mechanisms underlying trastuzumab resistance in gastric cancer

Abstract

// Chiara Arienti 1 , Michele Zanoni 1 , Sara Pignatta 1 , Alberto Del Rio 2, 3 , Silvia Carloni 1 , Michela Tebaldi 1 , Gianluca Tedaldi 1 , Anna Tesei 1 1 Biosciences Laboratory, Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori (IRST) IRCCS, Meldola, Italy 2 Institute of Organic Synthesis and Photoreactivity (ISOF), National Research Council (CNR), Bologna, Italy 3 Innovamol Srls, Modena, Italy Correspondence to: Chiara Arienti, e-mail: chiara.arienti@irst.emr.it Anna Tesei, e-mail: anna.tesei@irst.emr.it Keywords: trastuzumab resistance, gastric cancer, HER family receptors, HER signaling pathways, IQGAP1 Received: October 19, 2015      Accepted: February 11, 2016      Published: February 22, 2016 ABSTRACT HER2-positive advanced gastric cancer patients frequently develop resistance to trastuzumab through mechanisms still poorly understood. In breast cancer, other members of the HER-family are known to be involved in trastuzumab-resistance, as is overexpression of the scaffold protein IQGAP1. In the present work, we investigated acquired resistance to trastuzumab in gastric cancer experimental models. Trastuzumab-resistant (HR) subclones derived from 3 HER2-overexpressing gastric cancer cells were generated and characterized for alterations in HER2-signaling mechanisms by next-generation sequencing, immunohistochemical, western blot and qRT-PCR techniques, and molecular modeling analysis. All subclones showed a reduced growth rate with respect to parental cell lines but each had a different resistance mechanism. In NCI N87 HR cells, characterized by a marked increase in HER2-signaling pathways with respect to the parental cell line, trastuzumab sensitivity was restored when IQGAP1 expression was silenced. AKG HR subclone showed higher HER3 protein expression than the parental line. High nuclear HER4 levels were observed in KKP HR cells. In conclusion, our study revealed that high IQGAP1 expression leads to resistance to trastuzumab in gastric cancer. Furthermore, 2 new mutations of the HER2 gene that may be involved in acquired resistance were identified in AKG HR and KKP HR subclones.