Mesenchymal stem cells (MSCs) critically influence tumorigenesis within the tumor microenvironment. B7H3 is a known mediator of chemoresistance. But the mechanisms by which Gastric cancer mesenchymal stem cells (GCMSCs) modulate B7H3 to confer resistance in gastric cancer cells are undefined. This study aims to investigate how GCMSCs modulate B7H3 expression in gastric cancer cells to confer chemotherapeutic resistance and elucidate the underlying molecular mechanisms. GCMSCs were isolated from fresh gastric cancer tissues using the adherent separation method. GCMSCs were identified by flow cytometry and adipogenic and osteogenic differentiation assays. In vitro, chemoresistance-related proteins and apoptosis markers in gastric cancer cells were analyzed by Western blot, while proliferative capacity was assessed via CCK-8 assays and colony formation experiments. In vivo, subcutaneous tumor xenografts were established in BALB/c nude mice, with tumor growth monitored by volume measurement and weight analysis. Protein expression in xenograft tissues was evaluated by Western blot and immunohistochemistry. Our results showed that GCMSCs were successfully isolated from gastric cancer tissue samples and identified to have the ability of adipogenic and osteogenic differentiation. The cell surface was positive for CD105, CD90 and CD29 molecules, but negative for CD45, CD34 and CD19 molecules. Conditioned medium of GCMSCs (GCMSCs- CM) enhances the oxaliplatin (OXA) resistance of gastric cancer cells, which is manifested as the increased survival rate and colony formation level of gastric cancer cells after OXA treatment, the decreased level of apoptosis, accompanied by the decreased expression levels of cleaved caspase-3 and Bax, and the increased expression levels of Bcl-2, MDR1 and B7H3. In vivo results showed that GCMSCs-CM inhibited the sensitivity of tumor to chemotherapy drugs, while the chemoresistance of gastric cancer was improved after B7H3 knockdown. This study shows that GCMSCs-CM up-regulates B7H3 to induce OXA resistance of gastric cancer, which provides a new idea for improving chemotherapy resistance of gastric cancer.

Gastric Cancer, MSCs, B7H3, Chemoresistance