6'-substituted naphthalene-2-carboxylic acid analogs, a new class of retinoic acid receptor subtype-specific ligands.

The biological response to retinoic acid (RA) and synthetic derivatives (retinoids) is mediated by three nuclear retinoic acid receptors, RAR alpha, beta and gamma. To explore the potential of retinoids as receptor subtype selective activators, we employed a transcriptional activation assay. Hybrid receptors that recognize an estrogen response element were used to avoid measuring activities of endogenous retinoic acid receptors. In response to retinoic acid, the three hybrid receptors ER-RAR alpha, ER-RAR beta and ER-RAR gamma exhibited the same induction profile as the corresponding wild type receptors RAR alpha, RAR beta, and RAR gamma. Three different retinoids, analogs of 6'-substituted naphthalene-2-carboxylic acid, elicited strong transcriptional activation of gamma receptor while no activation of alpha receptor was observed. Conversely, two retinobenzoic acid analogs showed a limited alpha selectivity. We conclude that retinoids with unique profiles of retinoic acid receptor subtype selectivity can be defined and tested for their impact on cellular differentiation and for therapeutical applications.