Histological changes during regression induced by retinoic acid in a transplantable rat chondrosarcoma

Selective Agonists of Nuclear Retinoic Acid 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 γ (RARγ) has shown therapeutic action for treatment of heterotopic ossification and osteochondroma without serious adverse effects in animal models. We hypothesized that selective agonists of RARγ would have an inhibitory effect on chondrosarcoma. All human chondrosarcoma specimens expressed RARγ as determined by immunohistochemical staining. The ΗCS-2/8 chondrosarcoma cell line, established from low-grade human chondrosarcoma, was used to examine the actions of RARγ agonists. In ΗCS2/8 pellet cultures, RARγ 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 RARγ agonists significantly inhibited the growth of ΗCS-2/8 cell transplants in vivo. Furthermore, local injection of RARγ agonist-loaded poly-lactic acid nanoparticles induced regression of the mass size of the transplants. Histologic analysis demonstrated that RARγ agonist treatment inhibited cell proliferation activity and stimulated encapsulation of the tumor. These findings indicate that RARγ agonists, including palovarotene, may have an anti-tumor effect on low-grade chondrosarcomas. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1045-1051, 2020.

13-Cis-retinoic acid: pharmacology, toxicology, and clinical applications for the prevention and treatment of human cancer

Retinoids, particularly 13-cis-retinoic acid, have shown great promise against a number of benign, but serious dermatological conditions. In animal models, 13-cis-retinoic acid functions is a potent antipromoter whether a cancer has been initiated by chemical, physical, or viral agents. Additionally, substantial antiproliferative activity of this compound has been demonstrated in vitro in many culture systems. Clinical activity noted against several types of skin malignancies has led to several investigations to determine the anticancer activity of 13-cis-retinoic acid. Response of a variety of preneoplastic and neoplastic lesions of epithelial histology has been demonstrated. The toxicity of 13-cis-retinoic acid largely reflects its tissue distribution with skin and subcutaneous side-effects limiting dose escalation. The pharmacology and pharmacokinetics of 13-cis-retinoic acid has been explored in a number of patients and a long terminal half-life demonstrated. This review will discuss 13-cis-retinoic acid as a good model for a biological response modifier.

Retinoic acid-induced cartilage resorption: induction of specific changes in protein synthesis and inhibition by tunicamycin

The addition of retinoic acid to fetal rat bones in culture induces the release of proteoglycans followed by cartilage resorption. In this system retinoic acid markedly suppressed 3H-leucine and 3H-mannose incorporation into acid-precipitable macromolecules, and specifically changed the 3H-leucine incorporation pattern as revealed by gel electrophoresis. Tunicamycin, which selectively inhibits glycosylation of the asparagine residues in proteins, prevented the cartilage cell degradation in response to retinoic acid. Inhibitors of DNA synthesis did not affect the retinoic acid-induced changes indicating that cell division was not required for the cartilage degradation processes induced by retinoic acid. In consideration of our previous and present demonstrations that retinoic acid-induced cartilage resorption required RNA, protein, and glycoprotein synthesis and specifically changed the protein synthesis pattern, we suggest that retinoic acid may exert its action by altering gene expression.