Blocking SHH/Patched Interaction Triggers Tumor Growth Inhibition through Patched-Induced Apoptosis

Abstract

The Sonic Hedgehog (SHH) pathway plays a key role in cancer. Alterations of SHH canonical signaling, causally linked to tumor progression, have become rational targets for cancer therapy. However, Smoothened (SMO) inhibitors have failed to show clinical benefit in patients with cancers displaying SHH autocrine/paracrine expression. We reported earlier that the SHH receptor Patched (PTCH) is a dependence receptor that triggers apoptosis in the absence of SHH through a pathway that differs from the canonical one, thus generating a state of dependence on SHH for survival. Here, we propose a dual function for SHH: its binding to PTCH not only activates the SHH canonical pathway but also blocks PTCH-induced apoptosis. Eighty percent, 64%, and 8% of human colon, pancreatic, and lung cancer cells, respectively, overexpressed SHH at transcriptional and protein levels. In addition, SHH-overexpressing cells expressed all the effectors of the PTCH-induced apoptotic pathway. Although the canonical pathway remained unchanged, autocrine SHH interference in colon, pancreatic, and lung cell lines triggered cell death through PTCH proapoptotic signaling. In vivo, SHH interference in colon cancer cell lines decreased primary tumor growth and metastasis. Therefore, the antitumor effect associated to SHH deprivation, usually thought to be a consequence of the inactivation of the canonical SHH pathway, is, at least in part, because of the engagement of PTCH proapoptotic activity. Together, these data strongly suggest that therapeutic strategies based on the disruption of SHH/PTCH interaction in SHH-overexpressing cancers should be explored. SIGNIFICANCE: Sonic Hedgehog-overexpressing tumors express PTCH-induced cell death effectors, suggesting that this death signaling could be activated as an antitumor strategy.