Effect of the histone deacetylase inhibitor SNDX-275 on Fas signaling in osteosarcoma cells and the feasibility of its topical application for the treatment of osteosarcoma lung metastases. Patients with lung metastases from osteosarcoma (OS) have poor response to salvage therapy. Understanding the mechanisms involved in the metastatic process of OS may lead to new effective therapeutic approaches. The authors reported previously that up-regulation of the Fas receptor by transfecting OS cells with Fas plasmid inhibited the in vivo growth of metastases in the lungs.In the current study, the authors treated OS cells with the histone deacetylase inhibitor SNDX-275 and studied its cytotoxicity and its effect on Fas signaling in vitro and in vivo.Subtoxic doses of SNDX-275 were able to activate the Fas pathway in OS cells by increasing the expression of Fas messenger RNA; however, the increased expression was not always followed by increased levels of Fas receptor expression on the cell surface. The treatment of cells with a combination of SNDX-275 and Fas ligand (FasL) had a stronger cytotoxic effect on tested OS cells than either agent alone. Inhibition of the Fas pathway in cells by inhibition of the Fas-associated death domain (FADD) molecule eliminated this combination effect, indicating that activity of FADD is important for the efficacy of this agent in the FasL-expressing environment of the lungs. Intranasal administration of SNDX-275 in mice with OS lung metastases revealed that SNDX-275 may inhibit metastatic growth at a dose of 0.13 mg/kg, which is approximately 200-fold lower than the therapeutically effective oral dose reported previously.The current findings indicated that SNDX-275 can activate Fas signaling in OS cells in vitro and in vivo and that the administration of SDNX-275 by inhalation is feasible as a treatment for OS metastases and warrants its further investigation.Copyright © 2011 American Cancer Society.