Selective agonists for nuclear retinoic receptor gamma inhibit growth of HCS-2/8 chondrosarcoma cells.

Chondrosarcoma is the second most common primary bone sarcoma. Treatment of chondrosarcoma is limited to surgery due to radiation and chemotherapy resistance of this cancer. An ideal treatment for chondrosarcoma would be a well-tolerated, minimally invasive local or systemic treatment modality to halt or slow tumor growth prior to resection of local, unresectable local, or metastatic disease. Palovarotene, an agonist of nuclear retinoic acid receptor gamma (RAR gamma) has shown therapeutic action for treatment of heterotopic ossification and osteochondroma without serious adverse effects in animal models. We hypothesized that selective agonists of RAR gamma would have an inhibitory effect on chondrosarcoma. All human chondrosarcoma specimens expressed RAR gamma as determined by immunohistochemical staining. The Eta CS-2/8 chondrosarcoma cell line, established from low-grade human chondrosarcoma, was used to examine the actions of RAR gamma agonists. In Eta CS2/8 pellet cultures, RAR gamma agonist treatment reduced the mass size and significantly decreased total glycosaminoglycan, protein amounts, and gene expression levels of cartilage matrix molecules when compared with control groups. Systemic treatment with RAR gamma agonists significantly inhibited the growth of Eta CS-2/8 cell transplants in vivo. Furthermore, local injection of RAR gamma agonist-loaded poly-lactic acid nanoparticles induced regression of the mass size of the transplants. Histologic analysis demonstrated that RAR gamma agonist treatment inhibited cell proliferation activity and stimulated encapsulation of the tumor. These findings indicate that RAR gamma agonists, including palovarotene, may have an anti-tumor effect on low-grade chondrosarcomas. (C) 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.