Melanoma often metastasizes to bone where it is exposed to high concentrations of TGF-β. Constitutive Smad signaling occurs in human
melanoma. Because TGF-β promotes
metastases to bone by several types of solid
tumors including
breast cancer, we hypothesized that pharmacologic blockade of the TGF-β signaling pathway may interfere with the capacity of
melanoma cells to metastasize to bone. In this study, we tested the effect of a small molecule inhibitor of TGF-β receptor I
kinase (TβRI),
SD-208, on various parameters affecting the development and progression of
melanoma, both in vitro and in a mouse model of human
melanoma bone
metastasis. In
melanoma cell lines,
SD-208 blocked TGF-β induction of Smad3 phosphorylation, Smad3/4-specific transcription,
Matrigel invasion and expression of the TGF-β target genes
PTHrP,
IL-11, CTGF, and RUNX2. To assess effects of
SD-208 on
melanoma development and
metastasis, nude mice were inoculated with 1205Lu
melanoma cells into the left cardiac ventricle and
drug was administered by oral gavage on prevention or treatment protocols.
SD-208 (60 mg/kg/d), started 2 days before
tumor inoculation prevented the development of osteolytic bone
metastases compared with vehicle. In mice with established bone
metastases, the size of osteolytic lesions was significantly reduced after 4 weeks treatment with
SD-208 compared with vehicle-treated mice. Our results demonstrate that therapeutic targeting of TGF-β may prevent the development of
melanoma bone
metastases and decrease the progression of established osteolytic lesions.