Oncogenic MST1R activity in pancreatic and gastric cancer represents a valid target of HSP90 inhibitors.

Aim: To evaluate the effects of HSP90 blockade by EC154 on the oncogenic receptor tyrosine kinase macrophage-stimulating 1 receptor (MST1R) in gastric and pancreatic cancer.
Materials and Methods: Impact of EC154 on signaling pathways was investigated by western blotting. Cancer cell migration was evaluated in Boyden chambers. Transcriptional regulation of MST1R was examined by using promoter-luciferase reporter constructs. Effects on MST1R expression, and tumor growth were investigated in in vivo tumor models.
Results: MST1R was expressed by cancer cells without evidence of MST1R mutations. EC154 led to an effective inhibition of cancer cell growth, down-regulated MST1R, diminished its promoter activity, and disrupted oncogenic macrophage-stimulating protein 1 (MSP1) signaling. Moreover, pro-migratory activities of cancer cells were dramatically inhibited. In vivo, treatment with EC154 significantly reduced tumor growth, while MST1R expression was down-regulated.
Conclusion: Wild-type MST1R is an HSP90 client protein that can be targeted in gastrointestinal cancer using HSP90 inhibitors.