Pharmacokinetic properties of newly synthesized retinoid X receptor agonists possessing a 6-[N-ethyl-N-(3-alkoxy-4-isopropylphenyl)amino]nicotinic acid skeleton in rats.

OBJECTIVE: The pharmacokinetic properties of three newly synthesized retinoid X receptor (RXR) agonists were evaluated in rats to elucidate the structural factor influencing their pharmacokinetic properties. MATERIAL AND METHODS: Three RXR agonists possessing a common 6-[N-ethyl-N-(3-alkoxy-4-isopropylphenyl)amino]nicotinic acid skeleton and side chain structures that are slightly different from each other were prepared as we previously reported (Takamatsu et al., ChemMedChem, 2008; 3:780-787). The plasma concentration profiles of these compounds were evaluated following the intravenous and intra-intestinal administrations. Their hepatic metabolism was characterized using rat liver microsomes. RESULTS: Based on the plasma concentration profile, NEt-3IP (3-isopropoxy) was shown to have a distribution volume of 4.53 L/kg, and to be cleared from the body with an elimination half-time of 0.95 h. The bioavailability of NEt-3IP is 16.4%, whereas those of the isobutoxy analog NEt-3IB and the cyclopropylmethoxy analog NEt-3cPM are 46.5% and 22.6%, respectively. Subsequently, in the experiments using rat liver microsomes, the K(m) and V(max) values of NEt-3IP were determined as 7.85 µM and 0.48 nmol/min/mg protein, respectively. This K(m) value is nearly the same as those of NEt-3IB and NEt-3cPM, but the V(max) value is noticeably smaller. Additionally, it was revealed that the CYP family mainly metabolizing NEt-3IP is different from those metabolizing the other analogs. CONCLUSION: Based on these findings, the pharmacokinetic properties of the compounds possessing this type of the skeleton seem to be largely influenced by a slight modification of the side chain structure.

Replacing alkyl sulfonamide with aromatic sulfonamide in sulfonamide-type RXR agonists favors switch towards antagonist activity.

Retinoid X receptor (RXR) ligands are attractive candidates for clinical application because of their activity against tamoxifen-resistant breast cancer, taxol-resistant lung cancer, metabolic syndrome, and allergy. Though several RXR ligands, especially RXR antagonists, have been reported, the rational molecular design of such compounds is not well advanced. 4-[N-Methanesulfonyl-N-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthyl)amino]nicotinic acid (5a) is a moderately RXRalpha-preferential agonist, and we examined the feasibility of replacing the methyl group on the sulfonamide with a longer alkyl chain or an aromatic ring as an approach to produce new RXR antagonists. Several of the resulting benzenesulfonanilide-type compounds showed RXR antagonist activity. This design strategy should be a useful approach for addressing the lack of structure diversity of RXR antagonists.

Mechanism of retinoid X receptor partial agonistic action of 1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-1H-benzotriazole-5-carboxylic acid and structural development to increase potency.

We have reported that retinoid X receptor (RXR) partial agonist 1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-1H-benzotriazole-5-carboxylic acid (CBt-PMN, 4a) shows a significant antidiabetes effect in the KK-A(y) type 2 diabetes model mice, with reduced side effects compared to RXR full agonists. To elucidate the mechanism of the RXR partial agonist activity of 4a, we synthesized derivatives of 4a, evaluated their RXR agonist activity, and performed structure-activity relationship analysis. Reporter gene assay revealed that though 6b, which possesses an amino group at the 2-position of 5-carboxybenzimidazole, showed RXR full-agonist activity, compounds 6d and 6e, which possess an oxygen atom and a sulfur atom at the corresponding position, respectively, showed weak RXR agonist activity. On the other hand, 6c, which has a trifluoromethyl group at the corresponding position, acts as an RXR partial agonist, having similar Emax (67 ± 2%) and lower EC50 (15 ± 0 nM) compared to those of 4a (Emax = 75 ± 4%, EC50 = 143 ± 2 nM). A fluorescence polarization assay of cofactor recruitment confirmed that fluorescein-labeled D22 coactivator peptide was less efficiently recruited to RXR by 4a and 6c than by LGD1069 (1), a known RXR full agonist. Electrostatic potential field calculations and computational docking studies suggested that full agonists show an electrostatic attraction, which stabilizes the holo structure and favors coactivator recruitment, between the side chain at the benzimidazole 2-position and the α-carbonyl oxygen of asparagine-306 in helix 4 (H4) of the RXR receptor. However, RXR partial agonists 4a and 6c lack this interaction. Like 4a, 6c showed a significant antidiabetes effect in KK-A(y) type 2 diabetes model mice with reduced levels of the side effects associated with RXR full agonists. These findings should aid the design of new RXR partial agonists as antitype 2 diabetes drug candidates.

RXR Partial Agonist CBt-PMN Exerts Therapeutic Effects on Type 2 Diabetes without the Side Effects of RXR Full Agonists.

Treating insulin resistance and type 2 diabetes in rodents, currently known retinoid X receptor (RXR) agonists induce significant adverse effects. Here we introduce a novel RXR partial agonist CBt-PMN (11b), which shows a potent glucose-lowering effect and improvements of insulin secretion and glucose tolerance without the serious adverse effects caused by RXR full agonists. We suggest that RXR partial agonists may be a new class of antitype 2 diabetes drug candidates.

The first potent subtype-selective retinoid X receptor (RXR) agonist possessing a 3-isopropoxy-4-isopropylphenylamino moiety, NEt-3IP (RXRalpha/beta-dual agonist).

Retinoid X receptor (RXR) agonists (rexinoids) are attracting much attention for their use in treatment of cancers, including tamoxifen-resistant breast cancer and taxol-resistant lung cancer, and metabolic disease. However, known RXR agonists have a highly lipophilic character. In addition, no subtype-selective RXR agonists have been found. We previously reported an RXRalpha-preferential agonist 4-[N-methanesulfonyl-N-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthyl)amino]benzoic acid (6 a). The RXR agonistic activity is much less than that of well-known RXR agonists. To develop potent, less-lipophilic, and subtype-selective RXR agonists, we created new RXR agonists possessing alkoxy and isopropyl groups as a lipophilic domain of the common structure of well-known RXR agonists. As a result, compounds possessing branched alkoxy groups, 6-[N-ethyl-N-(3-isopropoxy-4-isopropylphenyl)amino]nicotinic acid (NEt-3IP: 7 a) and 6-[N-ethyl-N-(3-isobutoxy-4-isopropylphenyl)amino]nicotinic acid (NEt-3IB: 7 c), showed RXR agonistic activity as potent as, or more potent than, the activities of representative RXR agonists. Moreover, NEt-3IP (7 a) was found to be the first RXRalpha/beta-selective (or RXRalpha/beta-dual) agonist. Being potent, less lipophilic, and having RXR subtype-selective activity, NEt-3IP (7 a) is expected to become a new drug candidate and to be a useful biological tool for clarifying each RXR subtype function.

Reduction of lipophilicity at the lipophilic domain of RXR agonists enables production of subtype preference: RXRalpha-preferential agonist possessing a sulfonamide moiety.

Retinoid X receptor agonists (RXR agonists, rexinoids) are interesting candidates for the treatment of cancers such as tamoxifen-resistant breast cancer and taxol-resistant lung cancer. However, well-known RXR agonists possess a strong lipophilic character. In addition, although RXR has three subtypes, no subtype-selective RXR agonists are known. Thus we aimed to produce less-lipophilic and subtype-selective RXR agonists. By designing sulfonamide-type RXR agonists, 4-[N-methanesulfonyl-N-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthyl)amino]benzoic acid (8 a) was found to prefer RXRalpha over RXRbeta and RXRgamma, although the potency is less than the potencies of well-known RXR pan-agonists. Moreover, our results suggest that the reduction of lipophilicity at the hydrophobic interaction region of RXR agonists enables production of RXR subtype preference. Our finding will be useful for the creation of more potent and less-lipophilic subtype-selective RXR agonists aimed at the reduction of undesirable side effects.