Hedgehog pathway inhibition in chondrosarcoma using the smoothened inhibitor IPI-926 directly inhibits sarcoma cell growth.

Hedgehog (Hh) pathway inhibition in cancer has been evaluated in both the ligand-independent and ligand-dependent settings, where Hh signaling occurs either directly within the cancer cells or within the nonmalignant cells of the tumor microenvironment. Chondrosarcoma is a malignant tumor of cartilage in which there is ligand-dependent activation of Hh signaling. IPI-926 is a potent, orally delivered small molecule that inhibits Hh pathway signaling by binding to Smoothened (SMO). Here, the impact of Hh pathway inhibition on primary chondrosarcoma xenografts was assessed. Mice bearing primary human chondrosarcoma xenografts were treated with IPI-926. The expression levels of known Hh pathway genes, in both the tumor and stroma, and endpoint tumor volumes were measured. Gene expression profiling of tumors from IPI-926-treated mice was conducted to identify potential novel Hh target genes. Hh target genes were studied to determine their contribution to the chondrosarcoma neoplastic phenotype. IPI-926 administration results in downmodulation of the Hh pathway in primary chondrosarcoma xenografts, as demonstrated by evaluation of the Hh target genes GLI1 and PTCH1, as well as inhibition of tumor growth. Chondrosarcomas exhibited autocrine and paracrine Hh signaling, and both were affected by IPI-926. Decreased tumor growth is accompanied by histopathologic changes, including calcification and loss of tumor cells. Gene profiling studies identified genes differentially expressed in chondrosarcomas following IPI-926 treatment, one of which, ADAMTSL1, regulates chondrosarcoma cell proliferation. These studies provide further insight into the role of the Hh pathway in chondrosarcoma and provide a scientific rationale for targeting the Hh pathway in chondrosarcoma.

Modulating hedgehog signaling can attenuate the severity of osteoarthritis.

Osteoarthritis is associated with the irreversible degeneration of articular cartilage. Notably, in this condition, articular cartilage chondrocytes undergo phenotypic and gene expression changes that are reminiscent of their end-stage differentiation in the growth plate during skeletal development. Hedgehog (Hh) signaling regulates normal chondrocyte growth and differentiation; however, the role of Hh signaling in chondrocytes in osteoarthritis is unknown. Here we examine human osteoarthritic samples and mice in which osteoarthritis was surgically induced and find that Hh signaling is activated in osteoarthritis. Using several genetically modified mice, we found that higher levels of Hh signaling in chondrocytes cause a more severe osteoarthritic phenotype. Furthermore, we show in mice and in human cartilage explants that pharmacological or genetic inhibition of Hh signaling reduces the severity of osteoarthritis and that runt-related transcription factor-2 (RUNX2) potentially mediates this process by regulating a disintegrin and metalloproteinase with thrombospondin type 1 motif-5 (ADAMTS5) expression. Together, these findings raise the possibility that Hh blockade can be used as a therapeutic approach to inhibit articular cartilage degeneration.