Simon Chen

THE EFFECT OF HIGH AND LOW ULTRAVIOLET-B DOSE EXPOSURE ON THE DEGREE OF HAIRLESS MOUSE SKIN WRINKLING

Abstract— Chronic exposure of hairless mice to ultraviolet light (UVB 290‐320 nm) causes degradative changes in the dermal matrix and wrinkle production. We compared the effects of two different UVB dosing regimens on wrinkle production and dermal damage in female Skh:HR‐1 hairless mice using a bank of unfiltered FS‐40 lamps. One group of mice, the low dose group, was exposed to a suberythemal UVB dose of 12 mJ/cm2 (1 MED = 14 mJ/cm2), 3 times per week for 20 weeks (total dose = 0.72 J/cm2). A second group, the high dose group, was exposed also 3 times per week for 15 weeks to a UVB dose which started with the sub‐erythemal dose of 12 mJ/cm3 at Week 1. and J MED at week 2. The dose was then increased weekly by 1 MED until reaching 4 MED at week 5. The animals were then dosed at 4 MED for 10 additional weeks (total dose = 2.1 J/cm2). Visual results indicate that, as expected, within the same group, the degree of wrinkling was generally dependent on the total UVB dose administered. However, comparison between the low dose and high dose groups shows that equal cumulative UVB doses did not always result in identical wrinkle grades. For example. at a cumulative dose of 0.5 J/cm2, the mean wrinkle grade for the low dose group was 1.75 compared to that of 1.2 for the high dose group (age‐matched = 0). This observation may suggest that there are other factors in addition to total cumulative dose which are important for the appearance of wrinkling in this model.

Role of Retinoic Acid Receptor Gamma in the Rhino Mouse and Rabbit Irritation Models of Retinoid Activity

The three retinoic acid receptors (RAR alpha, RAR beta and RAR gamma) are known to modulate the transcription of target genes through interaction of the individual receptors with their naturally occurring ligand, retinoic acid (RA). Since RA has multiple effects in vivo, considerable effort has recently been devoted to finding selective compounds to elucidate the functions of individual receptors and to relate these functions to specific in vivo effects. The racemic synthetic retinoid 6-[(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthyl)hydroxy-methyl]-2- naphthalene carboxylic acid has recently been identified as an RAR gamma-selective agonist. A synthetic method involving lipase-mediated transformation has been developed to prepare the individual enantiomers. Discrimination between the two enantiomers is seen in both transcriptional activity and binding to recombinant receptors with the (S)-enantiomer being the more active. Differences between the two compounds are also seen in the Rhino mouse utriculi reduction assay and the rabbit irritation model. In both animal models, the (S)-enantiomer consistently gave a greater response. Taken together, these results suggest that the activity and irritation seen with RA and related compounds is receptor mediated. Further, the strong selectivity of the compounds reported here for RAR gamma suggests that this receptor plays an important role in these in vivo biological activities. The discrimination between these enantiomers may be useful in the design of novel retinoids with uniquely defined biological properties.

Structural modifications of 6-naphthalene-2-carboxylate retinoids

Abstract The keto linker of 2-naphthoate retinoid 1 has been found nonessential for RAR transactivation activity and can be replaced with heteroatoms such as S, O, N without significant reduction of the activity. On the other hand, substitutions on the aromatic rings of retinoids 1 and 2 resulted in analogs with reduced potentcy and RAR selectivity.

APPLICATION OF THE HECK REACTION IN THE SYNTHESIS OF TRUNCATED NAPHTHOIC ACID RETINOIDS

Abstract A series of truncated naphthoic acid retinoids have been prepared using the Heck reaction. These retinoids were evaluated in the RAR transactivation assay in vitro and in the utriculi reduction assay in vivo. It has been found that the naphthalene ring of the retinoids is crucial for their retinoid activity and receptor selectivity.

Gene expression of retinoic acid receptors and cellular retinoic acid-binding proteins in rhino and hairless mouse skin.

The rhino mouse comedolytic model and the hairless mouse photoaging model are established animal models for screening the in vivo activity of retinoids. However, the expression of the retinoic acid receptors (RARs) and cellular retinoic acid-binding proteins (CRABPs), known to regulate retinoid activity, is not completely understood in these mouse mutants. For this purpose, mRNA was isolated from rhino and hairless mouse skin and the gene expression of the RARs and CRABPs was measured by Northern blot hybridization. Results showed that RARγ was the predominantly expressed RAR in both mouse strains. Two isoforms of RARγ, RARγ1 and RARγ2, were detected with RARγ1 being the more strongly expressed. RARα was also detected, but to a lesser degree than RARγ. RARβ expression was not detectable by our methodology. Additionally, topical treatment of these mice with 0.1% all-trans-retinoic acid (tRA) cream resulted in no significant alteration in the expression of the RAR genes. By contrast, CRABP-II was induced 2–4 fold by topical tRA treatment. CRABP-I, expressed to a lesser degree than CRABP-II, was not inducible. The relative expression of the RARs, CRABPs, and inducibility of CRABP-II by tRA in both rhino and hairless mouse skin paralleled that reported for human and mouse skin. These observations suggest that the altered phenotype observed in the rhino mouse most likely does not result from an altered expression level of these genes. The results also support these two animals as models for evaluating the therapeutic potential of retinoids.

The Pharmacology of a Novel Topical Retinoid, BMY 30123: Comparison with Tretinoin

Abstract— Preclinical studies pertaining to the pharmacology and toxicology of BMY 30123 (4‐acetamidophenyl retinoate) are reported. BMY 30123 is a novel compound which has topical retinoid activity. This compound exhibits lower toxicity, both local and systemic, than other clinically used topical retinoids such as tretinoin (all‐trans retinoic acid) in animal models. BMY 30123 is effective in a number of retinoid sensitive skin models including the rhino mouse utriculi reduction assay, the mouse epidermal hyperplasia model and in the suppression of DNA synthesis in mouse skin stimulated with phorbol ester. BMY 30123 was equipotent with tretinoin in these topical models. In the rhino mouse model the ED30 values for BMY 30123 and tretinoin were 0·037 and 0·015 Mm, respectively. In addition, BMY 30123 was active in the UVB‐induced photodamaged mouse model, another retinoid sensitive model. One of the problems associated with topically applied tretinoin is local irritation. Therefore, for topical therapy to be optimal, it is important to reduce or minimize local irritation. Repeated applications of BMY 30123 to rabbit skin resulted in low skin irritation. The first perceptible signs of skin irritation produced by BMY 30123 occurred at a dose 10 times higher than that observed for tretinoin. BMY 30123 also exhibits low retinoid activity after oral or i.p. administration in mice and produced no signs of hypervitaminosis A‐related toxicity at twenty times the no effect dose of tretinoin. Because retinoids are effective modulators of epidermal growth and differentiation, this compound should be useful for the treatment of cutaneous disorders that exhibit altered epidermal differentiation such as acne, psoriasis, ichthyosis and epithelial tumours. While BMY 30123 and tretinoin are shown here to be equipotent in animal efficacy models, the low skin irritation activity gives BMY 30123, at a minimum, a 10‐fold enhancement in the therapeutic index relative to tretinoin and suggests that retinoid efficacy and skin irritation are separable phenomena.

In-vivo activity of retinoid esters in skin is related to in-vitro hydrolysis rate.

BMS‐181163 (4‐acetamidophenyl retinoate, previously reported as BMY‐30123), the acetamidophenyl ester of all‐trans‐retinoic acid (tRA), is topically active in various retinoid‐sensitive animal models, but was recently shown to be ineffective for the treatment of acne in patients. To determine whether BMS‐181163 functions as a prodrug of tRA in mice but not in man, the relative rates of ester hydrolysis in mouse and human skin homogenates were determined.

Synthesis of Nitrone Analogues of Rar α Selective Retinoid AM580

Abstract Synthesis of nitrone analogues of RAR α-selective retinoid Am 580 in which the amide linker is replaced with a nitrone moiety is discribed. The nitrone segment was constructed by oxidizing the corresponding amine using MCPBA or dimethyldioxirane. The resulting nitrone derivatives were found unstable in acidic and basic conditions. The stability limitations of using this nitrone moiety as an amide surrogate are briefed.