Xina Nair

Evaluation of retinoids as therapeutic agents in dermatology.

Evaluation of 13-cis-12-substituted analogues of retinoic acid in a series of dermatologic screens has revealed that structural modifications can lead to selectivity and specificity. An analogue, 11-cis,13-cis-12-hydroxymethylretinoic acid, δ-lactone, has been found to have good activity and to be devoid of topical and systemic toxicity.

The Yucatan miniature swine as an in vivo model for screening skin depigmentation

The usefulness of the Yucatan miniature pig as a screen for skin dipigmenting activity by topical application was evaluated with standard compounds. This is a naturally occurring breed of swine with light brown to dark brown skin that is relatively hairless. The skin morphology, including the pattern of pigment distribution, in this breed of swine closely resembles the human skin. Test compounds examined in this study included the three standard compounds with known clinical depigmenting activity, hydroquinone (HQ), 4-hydroxyanisole (4HA) and tert-butyl catechol (TBC), each at a 5% concentration. Test materials in 25 microliters of propylene glycol/ethanol (50:50) were applied topically twice daily, 7 days a week for 90 days to test sites on each side of the dorsal mid-line. Test sites were graded weekly for variation in pigmentation and local irritation. After 90 days of test material application, skin biopsies of the test sites were taken for histological evaluation. Topical application of HQ, 4HA and TBC promoted marked skin depigmentation which was substantiated by reductions of pigment and melanocytes observed on microscopic examination. While both HQ and TBC produced marked local irritation, 4HA was only mildly irritating. These results suggest that the Yucatan pig, could be a potentially useful model for screening compounds with skin depigmenting activity.

UVB-Induced Pigmentation in Hairless Mice as an in vivo Assay for Topical Skin-Depigmenting Activity

Several reports have demonstrated that exposure to ultraviolet light elicits increased pigmentation in the skin of the Skh:HR2 mouse. We have reexamined this model to assess its potential as a screen for compounds with skin-depigmenting activity. The application of the previously reported ultraviolet light-B (UVB) doses led to marked necrotic damage to the skin which greatly diminished the usefulness of the model for drug testing. We have modified this model by exposing the mice to a progressively increasing dose of UVB that promotes pigmentation with a marked reduction of skin irritation. Furthermore, for compound evaluation, we preselected only those mice which developed signs of increased pigmentation after the first week of UVB exposure. This was critical for any meaningful compound evaluation, since only about 50% of the mice eventually showed signs of increased pigmentation with UVB. Our modifications make it possible to use this model for evaluating new compounds with skin-depigmenting activity. The validity of this method has been examined with a number of compounds including hydroquinone, 4-hydroxyanisole, kojic acid and all-trans retinoic acid, all with known depigmenting activity.

Novel mimics of sialyl Lewis X: design, synthesis and biological activity of a series of 2- and 3-malonate substituted galactoconjugates.

A series of potent inhibitors of P-selectin as potential anti-inflammatory agents is reported. These compounds are derivatives of galactocerebrosides bearing a malonate side chain in positions 2 and 3 of the galactose moiety. Based on the binding mode of sialyl Lewis X, the two acidic groups of the malonate are designed to form ionic interactions with two important lysines in the active site of P-selectin, Lys113 and Lys111. On the other hand, the 4- and 6-hydroxy groups on the galactose ring are arranged to chelate the calcium ion in the P-selectin active site. The synthesis and the biological activity of this series of compounds are described. Lead compounds having a greater potency than sialyl Lewis X are identified.

Biochemical and pharmacological properties of a new topical anti-inflammatory compound, 9-phenylnonanohydroxamic acid (BMY 30094)

Drugs which block the biosynthesis of leukotrienes and prostaglandins may have potential in the treatment of psoriasis and other skin diseases. The biochemical and anti-inflammatory activity of 9-phenylnonanohydroxamic acid (BMY 30094) is described. BMY 30094 inhibited human neutrophil 5-lipoxygenase with an IC50 of 5.7 μM. BMY 30094 also blocked human platelet cyclooxygenase and lipoxygenase with IC50 values of 15.2 and 15.0 μM, respectively. Topical application of this compound blocked arachidonic acid and 12-O-tetradecanoylphorbol ester-induced mouse skin inflammation with activity comparable to that observed for lonapalene. The topical ED50 for BMY 30094 in the arachidonic acid-induced inflammation model is 2.2 μmoles/ear. In the sub-cutaneous carrageenan sponge assay in rats, BMY 30094 blocked LTB4 and PGE2 production and inhibited neutrophil migration. This compound would be a useful tool to determine the role of arachidonic acid metabolites in the etiology of inflammatory dermatoses.

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.

Effects of retinoids on phorbol ester-stimulated epidermal DNA synthesis and hyperplasia in hairless mice

We investigated the effects of the retinoids, all-trans retinoic acid (t-RA), 13-cis retinoic acid, etretinate, and arotinoid ethyl ester, on 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced DNA synthesis, and epidermal hyperplasia in hairless mouse skin. Topical application of these retinoids produced dose-dependent inhibition of the TPA-induced epidermal DNA synthesis as measured by [3H]thymidine incorporation at 15 h after TPA application. However, this inhibition was only transient and did not affect the corresponding increase in epidermal cell layers measured at 40 or 70 h after TPA application. Fluocinonide also inhibited the epidermal DNA synthesis and failed to block TPA-induced epidermal hyperplasia. However, fluocinonide did effectively suppress the inflammation caused by TPA. In this paper we have shown that the suppression of TPA-stimulated DNA synthesis is a general property of topically applied retinoids. The biologic significance of a temporary suppression of TPA-stimulated epidermal DNA synthesis by the retinoids and fluocinonide is not understood at this time.

Evaluation of Retinoid Lactones as Topical Therapeutic Agents in Dermatology

AbstractPurpose. Optimization of the therapeutic ratio of analogs of the topically active 11-cis,13-cis-12-hydroxymethylretinoic acid, δ-lactone (1) relative to antihyperproliferation and antihyperkeratinization vs. toxicity. Methods. Nine analogs of 1, in which variations were made in the lipophilic cyclohexenyl moiety or in the lactone ring, were evaluated for topical activity against hyperkeratinization, inhibition of TPA-induced DNA synthesis and for skin irritation. Results. Although more potent lactones than the parent lactone 1 were identified, none possessed the favorable therapeutic ratio associated with 1.Conclusions. The δ-lactone 1 possesses unique molecular features responsible for its desirable therapeutic ratio as an anti-hyperproliferative and antihyperkeratotic agent. In view of its very low systemic retinoid toxicity and the absence of any systemic toxicity, this lactone may be a good candidate for use in the topical treatment of acne.