Quantification and In Silico Toxicity Assessment of Tazarotene and its Impurities for a Quality and Safe Drug Product Development

'In silico' toxicology methods in drug safety assessment

While experimental animal investigation has historically been the most conventional approach conducted to assess drug safety and is currently considered the main method for determining drug toxicity, these studies are constricted by cost, time, and ethical approvals. Over the last 20 years, there have been significant advances in computational sciences and computer data processing, while knowledge of alternative techniques and their application has developed into a valuable skill in toxicology. Thus, the application of in silico methods in drug safety assessment is constantly increasing. They are very complex and are grounded on accumulated knowledge from toxicology, bioinformatics, biochemistry, statistics, mathematics, as well as molecular biology. This review will summarize current state-of-the-art scientific data on the use of in silico methods in toxicity testing, taking into account their shortcomings, and highlighting the strategies that should deliver consistent results, while covering the applications of in silico methods in preclinical trials and drug impurities toxicity testing.

Photostability Testing of a Third-Generation Retinoid-Tazarotene in the Presence of UV Absorbers

Exposure of a drug to UV irradiation could affect its physicochemical properties. Hence, photostability testing is essential for topically administered drugs. Tazarotene, a receptor-selective, third-generation retinoid, is commonly used to treat acne vulgaris and psoriasis. In the present study, an in-depth analysis of the photostability of tazarotene in ethanolic solution in the presence of zinc oxide and/or titanium dioxide as well as benzophenone-type UV filters was performed. Eleven presumed products were derived from the photocatalytic degradation of tazarotene using ultra-performance liquid chromatography–tandem mass spectrometry, and transformation pathways were proposed. The degradation process mainly affected the 4,4-dimethyl-3,4-dihydro-2H-thiopyran moiety. The fragments most susceptible to oxidation were the methyl groups and the sulfur atom. Moreover, in the presence of sulisobenzone, under UV irradiation, tazarotene was subjected to a degradation process, which resulted in two photodecomposition products. In silico studies performed by OSIRIS Property Explorer demonstrated that five of the degradation products could be harmful in terms of the reproductive effects, which are associated with 3,4-dihydro-6-methyl-2H-1-benzothiopyran 1,1-dioxide, while one of them demonstrated potential irritant activity. The cytotoxic properties of the degradation products of tazarotene were assessed by MTT assay on a panel of human adherent cancer cells. Time- and concentration-dependent growth inhibition was evidenced in ovary (A2780) and breast (MDA-MB-231) cancer cell lines. The potential implication of the outcomes of the present research requires further studies mainly concerning the photostability of tazarotene in the topical formulations.

Insights into the degradation chemistry of tazarotene, a third generation acetylenic retinoid: LC-HRMS (Orbitrap), LC-MSn and NMR characterization of its degradation products, and prediction of their physicochemical and ADMET properties

Tazarotene is a prodrug that belongs to the acetylenic class of retinoids. The drug was subjected to hydrolytic, oxidative and photolytic stress testing to establish its comprehensive degradation chemistry. The drug proved to be unstable under acidic and basic hydrolytic conditions, yielding tazarotenic acid, which is a known major degradation product (DP) and an active metabolite. Additionally, two DPs each were generated upon interaction of drug and tazarotenic acid with HCl, used as an acid stressor. These were experimentally proven as pseudo DPs, as they did not originate when H₂SO₄ was employed as the stressor. The drug was also unstable under oxidative and photolytic conditions, yielding six DPs. All the products were separated on reversed phase (C18) column, using mobile phase composed of 10 mM ammonium formate (pH 3.5) and acetonitrile, which was run in a gradient mode. The separated DPs were subjected to LC-HRMS and LC-MSⁿ studies for their initial characterization. Seven hydrolytic and oxidative DPs that could be isolated using semi-preparative column were subjected to extensive 1D (¹H, ¹³C and DEPT-135) and 2D (COSY, HSQC and HMBC) NMR studies to confirm their structures. In total, five novel DPs were characterized, apart from two previously reported DPs, viz., tazarotenic acid and tazarotene sulfoxide, and four additional pseudo DPs. The complete degradation pathway of the drug was established. In silico ADMET properties of the drug and its DPs were evaluated using ADMET Predictor™.