Abstract
The synthetic retinoid 6-[3-(adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437), which can bind to and activate the nuclear retinoic acid receptors β and γ (RARβ/γ), is a potent inducer of apoptosis in various cancer cell lines. However, this effect was reported to be independent of RARs. In this study, we compared and contrasted the potencies and mechanisms of action of CD437 and several other receptor-selective retinoids in induction of apoptosis and modulation of squamous differentiation in UMSCC22B human head and neck squamous cell carcinoma cell line. CD437 and the structurally related retinoid CD2325 exhibited almost equal potency in inducing apoptosis, whereas several other retinoids failed to induce apoptosis. The RAR-specific pan antagonist AGN193109 failed to suppress CD437-induced apoptosis, indicating that the induction of apoptosis by CD437 was RAR-independent. c-Fos expression was induced by CD437 and CD2325 that induced apoptosis in the cell line but not by other retinoids that failed to induce apoptosis, suggesting a role for c-Fos in CD437-induced apoptosis. At low concentration (0.01 μM), CD437 shared with several other receptor-selective retinoids the ability to suppress the mRNA levels of the squamous differentiation markers Spr1, involucrin, and cytokeratin 1. This effect of CD437 could be blocked by AGN193109. We conclude that CD437 can exert its effects in UMSCC22B human human head and neck squamous cell carcinoma cells by at least two mechanisms: RAR-mediated suppression of squamous differentiation and RAR-independent induction of apoptosis.
Footnotes
- Received February 14, 2000.
- Accepted June 12, 2000.
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Send reprint requests to: Dr. Shi-Yong Sun or Dr. Reuben Lotan, Department of Thoracic/Head and Neck Medical Oncology, Box 80, The University of Texas, M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030. E-mail: ssun{at}notes.mdacc.tmc.edu orrlotan{at}notes.mdacc.tmc.edu
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This study was supported by U.S. Public Health Service Program Project Grant PO1 CA52051 from the National Cancer Institute and P50 DE11906 from the National Institute of Dental and Craniofacial Research. W.K.H. is an American Cancer Society Clinical Research Professor. R.L. is the incumbent of the Irving and Nadine Mansfield and Robert David Levitt Cancer Research Chair.
- The American Society for Pharmacology and Experimental Therapeutics
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