Conclusions
RhoA signaling promotes CSC phenotypes in DGA cells. Increased RhoA activity is correlated with worse overall survival in DGA patients, and RhoA inhibition can reverse chemotherapy resistance in DGA CSC and in tumor xenografts. Thus, the RhoA pathway is a promising new target in DGA patients.
Purpose
The Lauren diffuse type of gastric adenocarcinoma (DGA), as opposed to the intestinal type (IGA), often harbors mutations in RHOA, but little is known about the role of RhoA in DGA. Experimental design: We examined RhoA activity and RhoA pathway inhibition in DGA cell lines and in two mouse xenograft models. RhoA activity was also assessed in patient tumor samples.
Results
RhoA activity was higher in DGA compared with IGA cell lines and was further increased when grown as spheroids to enrich for cancer stem-like cells (CSCs) or when sorted using the gastric CSC marker CD44. RhoA shRNA or the RhoA inhibitor Rhosin decreased expression of the stem cell transcription factor, Sox2, and decreased spheroid formation by 78% to 81%. DGA spheroid cells had 3- to 5-fold greater migration and invasion than monolayer cells, and this activity was Rho-dependent. Diffuse GA spheroid cells were resistant in a cytotoxicity assay to 5-fluorouracil and cisplatin chemotherapy, and this resistance could be reversed with RhoA pathway inhibition. In two xenograft models, cisplatin inhibited tumor growth by 40% to 50%, RhoA inhibition by 32% to 60%, and the combination by 77% to 83%. In 288 patient tumors, increased RhoA activity correlated with worse overall survival in DGA patients (P = 0.017) but not in IGA patients (P = 0.612). Conclusions: RhoA signaling promotes CSC phenotypes in DGA cells. Increased RhoA activity is correlated with worse overall survival in DGA patients, and RhoA inhibition can reverse chemotherapy resistance in DGA CSC and in tumor xenografts. Thus, the RhoA pathway is a promising new target in DGA patients.