The Role of Hedgehog Signaling in the Melanoma Tumor Bone Microenvironment

Abstract A crucial regulator in melanoma progression and treatment resistance is the tumor microenvironment, and Hedgehog (Hh) signals activated in a tumor bone microenvironment are a potential new therapeutic target. The mechanism of bone destruction by melanomas involving Hh /Gli signaling in the tumor microenvironment is unknown. Here, we analyzed surgically resected oral malignant melanoma specimens and observed that Sonic hedgehog, Gli1, and Gli2 were highly expressed in tumor cells, vasculatures and osteoclasts. We established a tumor bone destruction mouse model by inoculating B16 cells into the bone marrow space of the right tibial metaphysis of 5-week-old female C57BL mice. An intraperitoneal administration of GANT61 (40 mg/kg), a small molecule inhibitor of Gli1 and Gli2, caused bone destruction of cortical bone, TRAP-positive osteoclasts, and a significant suppression of endomucin-positive tumor vessels. A gene set enrichment analysis suggested that genes involved in the apoptosis, angiogenesis, and PD-L1 expression pathway in cancer were significantly altered by GANT61 treatment. A flow cytometry analysis revealed that PD-L1 expression was significantly decreased in cells in which apoptosis was induced by GANT61 treatment. These results suggest that Hh signaling plays an important role in the melanoma bone microenvironment through normalization and remodeling of the tumor bone microenvironment.