Functional Genetic Approach Identifies MET, HER3, IGF-1R, INSR Pathways as Determinants of Lapatinib Unresponsiveness in HER2-positive Gastric Cancer
Menée in vitro, cette étude identifie des mécanismes permettant de rendre compte, via l'activation de plusieurs voies de signalisation (MET, HER3, IGF-AR et INSR), d'une absence de réponse au lapatinib dans le traitement des patients atteints d'un cancer avancé de l'estomac HER2+
Purpose: Targeting HER2 therapy is currently considered as the standard treatment for HER2-positive advanced gastric cancer (GC). However, as seen in recent clinical trails, most of HER2-positive GC are actually unresponsive to HER2-targeted agents, including lapatinib. The aim of the present study is to identify the responsible RTKs potentially conferring lapatinib unresponsiveness in HER2-positive GC and elucidate the molecular mechanism underlying this RTKs-induced resistance. Experimental Design: A functional RNAi screen targeting human RTKs and related growth factors was used to identify candidate RTKs conferring lapatinib unresponsiveness in HER2+ GC cells. Independent siRNAs transfection and corresponding ligands supplement were performed to validate the effects of candidate RTKs on lapatinib sensitivity. Cross-talks of pathways involved were analyzed via western blot. Cell apoptosis and cell motility were detected using FACs system and transwell assay. Immunohistochemistry was used to analyze protein expression in clinical samples. Results: MET, HER3, IGF-1R and INSR were identified to mediate lapatinib unresponsiveness in HER2-positive GC cells. Activation of these bypass RTKs attenuated lapatinib-induced apoptosis and suppression of cell motility, mechanistically due to re-stimulating the shared downstream AKT or ERK signaling, as well as re-stimulating WNT signaling and epithelial to mesenchymal transition (EMT) like process. Patients specimens revealed that these unresponsiveness-conferring RTKs were particularly enriched in the majority of HER2-positive GC patients. Conclusions: MET, HER3, IGF-1R and INSR pathways activation represent novel mechanism underlying lapatinib unresponsiveness in HER2-positive GC. Combination strategy may be recommended in treating HER2-positive GC patients with these pathways activation.