Synthesis, structure-affinity relationships, and biological activities of ligands binding to retinoic acid receptor subtypes

Article abstract of DOI:10.1021/jm00026a006

The retinoic acid receptors (RARs) transduce retinoid dependant gene regulation, and many biological effects of retinoids are mediated through binding and activation of three closely related receptor subtypes (RARα, RARβ, and RARγ). In order to investigate the role of receptor subtypes, we have carried out a chemical synthesis program to seek selective retinoids for these receptors. We measured receptor binding affinity using recombinant RARα, -β, and -γ proteins and assessed cellular differentiating activity in F9 murine teratocarcinoma cells (F9 cells). This research has identified the 4-substituted-3-(1-adamantyl)phenyl moiety as a new pharmacophore which can replace the β-cyclogeranylidene ring of the naturally ocurring all- trans-retinoic acid. Two chemical series derived from the general structures 6-(3-tertioalkyl-phenyl)-2-naphthoic acid (series I) and 4-[(E)-2-(3- tertioalkylphenyl)propenyl]benzoic acid (series II) were developed. In particular, we have obtained the RARγ selective derivatives 6-[3-(1- adamantyl)-4-hydroxyphenyl]-2-naphthoic acid (7) [K(i)(RARα) = 6500 nM, Ki(RARβ) = 2480 nM, K(i)(RARγ) = 77 nM] and 4-[(E)-2-[3-(1-adamantyl)-4- hydroxyphenyl]propenyl]benzoic acid (19) [K(i)(RARα) = 1 144 nM, K(i)(RARβ) = 1245 nM, K(i)(RARγ) = 53 nM]. In series I, the presence of a phenol group, irrespective of the nature of tertioalkyl group, imparted at least partial RARγ selectivity, whereas in series II, the presence of both adamantyl and phenol groups is needed to confer RARγ selectivity. The RARγ selective ligands induce differentiation in F9 cells (7, AC₅₀ = 33 nM; 19, AC₅₀ = 66 nM). From series I, a mixed RARβ-γ agonist with potent cellular differentiating activity was selected for development as a topical antiacne agent, 6-[3-(1-adamantyl)-4-methoxyphenyl]-2-naphthoic acid (5, CD 271) [K(i)(RARα) = 1100 nM, K(i)-(RARβ) = 34 nM, K(i)(RARγ) = 130 nM, AC₅₀(F9) = 37 nM]. Finally, from series II, we have obtained a weak antagonist in the F9 cellular differentiation assay, 4-[(E)-2-(3-tert-butyl- 4-hydroxyphenyl)propenyl]benzoic acid (15, IC₅₀ = 700 nM).