Richard L. Beard

Differential teratogenic response of mouse embryos to receptor selective analogs of retinoic acid

Early events that initiate teratogenesis by Accutane or other retinoids in mammalian embryos remain unknown. It would be helpful for mechanistic considerations to know whether or not retinoids act through retinoid receptor-dependent pathways, and if they do, which of the two families of receptors (retinoic acid receptors - RARalpha, beta, gamma or retinoid X receptors - RXRalpha, beta, gamma) are more likely involved. We previously used an in vitro bioassay to demonstrate that those retinoid analogs with binding affinity and transactivational activity limited only to the RXRs have a low potential as teratogens. Here, we have extended the study to examine teratogenicity, in pregnant mice, of a number of synthetic retinoids with varying degrees of receptor selectivity. The ability of each compound to induce fetal limb and craniofacial defects after a single exposure on day 11 of gestation was assessed and compared to that of all-trans retinoic acid (RA). The highest dose selected was 100 mg/kg maternal body weight since such a regimen of all-trans RA affects virtually every exposed embryo without any indication of maternal toxicity. We found that although all RAR agonists were strong teratogens, their potencies varied over a wide magnitude. The teratogenic potencies and receptor transactivation profiles of RAR agonists were not directly correlated since compounds with similar receptor activities presented major differences in potencies. Three compounds were exclusively RXR agonists, and these were not teratogenic under our experimental conditions. Two additional compounds which turned out to be non-teratogenic were distinguished by the fact that they activated neither RARs nor RXRs. These data indicate that although RAR-dependent mechanisms are likely involved in retinoid-induced teratogenesis, there are additional factors which determine teratogenic potency. The absence of teratogenic response in the case of RXR agonists suggests that risk-benefit analyses of such receptor-selective compounds may be fruitful in further studies.

Synthesis and biological activity of retinoic acid receptor-α specific amides

Abstract Retinoids are analogues of all- trans -retinoic acid, a powerful hormone that mediates many fundamental biological processes. Cancer and other serious hyperproliferative diseases are attractive therapeutic targets for retinoids, but the therapeutic use of retinoids is limited due to severe toxicity. We report here the design of retinoid receptor-α specific ligands with growth inhibitory activity in breast cancer cell lines, and which do not cause the cutaneous toxicity associated with the currently available nonselective retinoid agonists.

Diminished teratogenicity of retinoid X receptor-selective synthetic retinoids.

One feature that contraindicates the wide therapeutic use of retinoids is their teratogenicity. Synthetic retinoids are distinguishable from each other on the basis of their partial or exclusive preference in binding and activation of all-trans retinoic acid receptors (RARs) or retinoid X receptors (RXRs). Using mouse embryo limb bud cells in micromass cultures as a bioassay, we examined the inhibitory activities of a number of standard and novel retinoids on chondrogenic cell differentiation. Transient cotransfection of HeLa cells was used to measure the ability of each retinoid to induce transcription of a reporter gene by activating RAR alpha, RAR beta, RAR gamma, or RXR alpha chimeric constructs. All retinoids in this study that activated RARs to any degree in the cotransfection assay also inhibited chondrogenesis in vitro, whereas retinoids that were either specific for RXR or inactive in the cotransfection assay did not. The activity of RAR-selective agonists and the inactivity of RXR-specific agonists in the cotransfection assay correlated well with the relative teratogenicity of six of the representative retinoids studied when orally administered at day 11 to pregnant ICR mice.

Structural basis for the differential RXR & RAR activity of stilbene retinoid analogs

Abstract Retinoids elicit their biological actions by activating nuclear receptors that regulate gene transcription. There are six known retinoid receptors which belong to the retinoic acid receptor (RAR) and retinoid X receptor (RXR) families. We report RXR-active stilbene retinoid analogs and discuss the structural features that impart RAR and RXR activation properties to compounds of this class.

Differential RXR & RAR activity of stilbene retinoid analogs bearing thiazole and imidazole carboxylic acids

Retinoids are hormones which activate two distinct families of nuclear receptors: the retinoic acid receptors (RARα,β,γ) and the retinoid X receptors (RXRα,β,γ). We report thiazole and imidazole substituted stilbene analogs that have RXR specific or pan-agonist activity and discuss the structural features that impart these differential activation properties to compounds of this class.

Synthesis and biological activity of 1,2,3,4-tetrahydroquinoline and 3,4-(1H)-dihydroquinolin-2-one analogs of retinoic acid

Abstract Retinoids are natural and synthetic analogs of the hormone retinoic acid. Retinoids are currently being investigated clinically as drugs in several areas, including dermatology and oncology. We report the synthesis and biological activity of a new series of potent, RAR-specific retinoids substituted with a 1,2,3,4-tetrahydroquinoline or a 3,4-(1H)-dihydroquinolin-2-one group.

Phenylcyclohexene and phenylcyclohexadiene substituted compounds having retinoid antagonist activity.

Retinoids are natural and synthetic analogues of the hormone retinoic acid. Systemic retinoid agonist therapy is usually associated with toxic side effects, such as mucocutaneous toxicity, which may be alleviated by the use of topical retinoid antagonists. We report the synthesis and biological activity of a new series of potent, RAR-specific antagonists substituted with phenylcyclohexene and phenylcyclohexadiene groups.