Photodegradation and stabilization of betamethasone-17 valerate in aqueous/organic solvents and topical formulations

Preformulation evaluation of selumetinib for topical application: skin distribution and photodegradation analysis using MALDI imaging and LC-MS/MS

Understanding drug behavior within the skin, especially for photosensitive compounds, is crucial for developing effective and safe topical therapies. This study employs Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI-MSI) and Liquid Chromatography-Mass Spectrometry (LC-MS/MS) to investigate the skin permeation and photostability of selumetinib, a MEK inhibitor used in treating type 1 neurofibromatosis (NF1). The highest amounts of selumetinib in the skin sections were obtained when using the gel formulation, suggesting that it is to be preferred to cream formulations to achieve higher permeation of the drug. Our study also revealed that selumetinib is amenable to photodegradation in ex vivo skin explants, and yields one main degradation product, whose degradation is likely triggered by hydrogen abstraction. MALDI-MSI results showed selumetinib and its degradation product concentrate in skin appendages, indicating these structures might serve as drug reservoirs, potentially prolonging retention and efficacy. This study demonstrates that combining MALDI-MSI with LC/MS-MS can highly contribute to the characterization of the fate of photosensitive compounds in the skin, an essential prerequisite to the development of compound-specific photoprotective measures. It will also pave the way for innovative topical delivery strategies for NF1 treatment.

Photolysis of tolfenamic acid in aqueous and organic solvents: a kinetic study

Tolfenamic acid (TA) is a non-steroidal anti-inflammatory drug that was studied for its photodegradation in aqueous (pH 2.0-12.0) and organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol). TA follows first-order kinetics for its photodegradation, and the apparent first-order rate constants (k obs) are in the range of 0.65 (pH 12.0) to 6.94 × 10-2 (pH 3.0) min-1 in aqueous solution and 3.28 (1-butanol) to 7.69 × 10-4 (acetonitrile) min-1 in organic solvents. The rate-pH profile for TA photodegradation is an inverted V (∧) or V-top shape, indicating that the cationic form is more susceptible to acid hydrolysis than the anionic form of TA, which is less susceptible to alkaline hydrolysis. The fluorescence behavior of TA also exhibits a V-top-shaped curve, indicating maximum fluorescence intensity at pH 3.0. TA is highly stable at a pH range of 5.0-7.0, making it suitable for formulation development. In organic solvents, the photodegradation rate of TA increases with the solvent's dielectric constant and solvent acceptor number, indicating solute-solvent interactions. The values of k obs decreased with increased viscosity of the solvents due to diffusion-controlled processes. The correlation between k obs versus ionization potential and solvent density has also been established. A total of 17 photoproducts have been identified through LC-MS, of which nine have been reported for the first time. It has been confirmed through electron spin resonance (ESR) spectrometry that the excited singlet state of TA is converted into an excited triplet state through intersystem crossing, which results in an increased rate of photodegradation in acetonitrile.

Molecular Mechanisms Involved in the Chemical Instability of ONC201 and Methods to Counter Its Degradation in Solution

Glioblastoma is one of the most common and aggressive forms of brain tumor, a rare disease for which there is a great need for innovative therapies. ONC201, a new drug substance, has been used in a compassionate treatment program where the choice of dosage form and regimen have yet to be justified. The prior knowledge needed to anticipate ONC201 stability problems has recently been partially addressed, by (i) showing that ONC201 is sensitive to light and oxidation and (ii) identifying the molecular structures of the main degradation products formed. The aim of the work presented here was to improve our understanding of the degradation pathways of ONC201 using data from ab initio calculations and experimental work to supplement the structural information we already published. The C-H bonds located αto the amine of the tetrahydropyridine group and those located alpha to the imine function of the dihydroimidazole group exhibit the lowest bond dissociation energies (BDEs) within the ONC201 molecule. Moreover, these values drop well below 90 kcal.mol-1 when ONC201 is in an excited state (S1; T1). The structures of the photoproducts we had previously identified are consistent with these data, showing that they would have resulted from radical processes following the abstraction of alpha hydrogens. Concerning ONC201's sensitivity to oxidation, the structures of the oxidation products matched the critical points revealed through mapped electrostatic potential (MEP) and average local ionization energy (ALIE). The data obtained from ab initio calculations and experimental work showed that the reactivity of ONC201 to light and oxidation conditions is highly dependent on pH. While an acidic environment (pH < 6) contributes to making ONC201 quantitatively more stable in solution in the face of oxidation and photo-oxidation, it nevertheless seems that certain chemical groups in the molecule are more exposed to nucleophilic attacks, which explains the variation observed in the profile of degradation products formed in the presence of certain antioxidants tested. This information is crucial to better understand the stability results in the presence of antioxidant agents and to determine the right conditions for them to act.

Photolytic fate of (E)- and (Z)-endoxifen in water and treated wastewater exposed to sunlight

Endoxifen is the main active metabolite of a common cytostatic drug, tamoxifen. Endoxifen has been recently detected in the final effluent of municipal wastewater treatment plants. The antiestrogenic activity of endoxifen could bring negative effects to aquatic life if released to the water environment. This study elucidated the fate and susceptibility of (E)- and (Z)-endoxifen (2 μg mL^-1, 1:1 wt ratio between the two easily interchangeable isomers) in wastewater and receiving surface water to sunlight. Phototransformation by-products (PBPs) and their toxicity were determined. Sunlight reduced at least 83% of endoxifen concentration in wastewater samples, whereas in surface water samples, 60% of endoxifen was photodegraded after 180 min of the irradiation. In ultrapure water samples spiked with endoxifen, PBPs were mainly generated via con-rotatory 6π-photocyclization, followed by oxidative aromatization. These PBPs underwent secondary reactions leading to a series of PBPs with different molecular weights. Eight PBPs were identified and the toxicity analysis via the Toxicity Estimation Software Tool revealed that seven of these PBPs are more toxic than endoxifen itself. This is likely due to the formation of poly-aromatic core in the PBPs due to exposure to sunlight. Therefore, highly toxic PBPs may be generated if endoxifen is present in water and wastewater exposed to sunlight. The presence, fates and activities of these PBPs in surface water especially at locations close to treated wastewater discharge points should be investigated.

Titanium Dioxide Nanoparticles: Prospects and Applications in Medicine

Metallic and metal oxide nanoparticles (NPs), including titanium dioxide NPs, among polymeric NPs, liposomes, micelles, quantum dots, dendrimers, or fullerenes, are becoming more and more important due to their potential use in novel medical therapies. Titanium dioxide (titanium(IV) oxide, titania, TiO₂) is an inorganic compound that owes its recent rise in scientific interest to photoactivity. After the illumination in aqueous media with UV light, TiO₂ produces an array of reactive oxygen species (ROS). The capability to produce ROS and thus induce cell death has found application in the photodynamic therapy (PDT) for the treatment of a wide range of maladies, from psoriasis to cancer. Titanium dioxide NPs were studied as photosensitizing agents in the treatment of malignant tumors as well as in photodynamic inactivation of antibiotic-resistant bacteria. Both TiO₂ NPs themselves, as well as their composites and combinations with other molecules or biomolecules, can be successfully used as photosensitizers in PDT. Moreover, various organic compounds can be grafted on TiO₂ nanoparticles, leading to hybrid materials. These nanostructures can reveal increased light absorption, allowing their further use in targeted therapy in medicine. In order to improve efficient anticancer and antimicrobial therapies, many approaches utilizing titanium dioxide were tested. Results of selected studies presenting the scope of potential uses are discussed in this review.

Photostability of Topical Agents Applied to the Skin: A Review

Topical treatment modalities have multiple advantages starting with the convenient application and non-invasive treatment and ending with the reduction of the risk of the systemic side effects. Active pharmaceutical substances must reach the desired concentration at the target site in order to produce a particular therapeutic effect. In contrast to other dosage forms topical agents applied to the skin may also be susceptible to photodegradation after application. That is why the knowledge of the susceptibility of these topical drugs to UV irradiation, which may contribute to their degradation or changes in chemical structure, is very important. Active pharmaceutical substances used in dermatology may differ both in chemical structure and photostability. Furthermore, various factors-such as light intensity and wavelength, pH, temperature, concentration-can influence the photodegradation process, which is reflected in particular in kinetics of photodegradation of active pharmaceutical substances as well as both the quantitative and qualitative composition of by-products. The aim of this study was to conduct a systematic review of the photostability of dermatological drugs, as well as of other substances commonly applied topically. The photostability of glucocorticosteroids, retinoids, and antifungal drugs as well as non-steroidal anti-inflammatory drugs applied topically and selected UV-filters have been discussed. Furthermore, the impact of photoinstability on the effectiveness of pharmacotherapy and some photostabilization strategies have been also included.

Photostability of Terbinafine Under UVA Irradiation: The Effect of UV Absorbers

The photostability of drugs administered topically on unprotected skin is a complex phenomenon that could be connected with the loss of activity or, rather rarely, the occurrence of toxic degradation products. In this study, an in-depth investigation of the photostability of terbinafine, in both solutions and formulations, was conducted, taking into account the presence of UV absorbers such as TiO₂ , ZnO, avobenzone, 3-(4-methylbenzylidene)camphor, octocrylene, benzophenone-1 and benzophenone-2. The clear photocatalytic degradation of terbinafine in ethanol solution was observed in the presence of TiO₂ and/or ZnO. In other cases, terbinafine was stable, with the exception of, in the presence of octocrylene. The presumed degradation products of terbinafine were identified for the first time using LC/MS/MS, and transformation pathways were proposed. In the case of a cream formulation, the percentage of initial terbinafine content was almost unchanged in the presence of the UV absorbers benzophenone-1, benzophenone-2 and 3-(4-methylbenzylidene)camphor. In vitro cytotoxicity risk assessment of terbinafine based on photostability under UVA irradiation was evaluated using the human skin fibroblast BJ (ATCC^® CRL-2522™), and this showed no statistically significant difference in cell viability for all samples analyzed.

Palm Olein Emulsion: a Novel Vehicle for Topical Drug Delivery of Betamethasone 17-Valerate

This study aims to investigate the use of palm olein as the oil phase for betamethasone 17-valerate (BV) emulsions. The physicochemical properties of the formulations were characterized. In vitro drug release study was performed with the Hanson Vertical Diffusion Cell System; the samples were quantified with HPLC and the results were compared with commercial products. Optimized emulsion formulations were subjected to stability studies for 3 months at temperatures of 4, 25, and 40°C; the betamethasone 17-valerate content was analyzed using HPLC. The formulations produced mean particle size of 2-4 μm, viscosities of 50-250 mPa.s, and zeta potential between -45 and -68 mV. The rheological analyses showed that the emulsions exhibited pseudoplastic and viscoelastic behavior. The in vitro release of BV from palm olein emulsion through cellulose acetate was 4.5 times higher than that of commercial products and more BV molecules deposited in rat skin. Less than 4% of the drug was degraded in the formulations during the 3-month period when they were subjected to the three different temperatures. These findings indicate that palm olein-in-water emulsion can be an alternative vehicle for topical drug delivery system with superior permeability.

Ionic strength effects on the photodegradation reactions of riboflavin in aqueous solution

A study of the effect of ionic strength on the photodegradation reactions (photoreduction and photoaddition) of riboflavin (RF) in phosphate buffer (pH7.0) has been carried out using a specific multicomponent spectrometric method. It has been found that the rates of photodegradation reactions of RF are dependent upon the ionic strength of the solutions at different buffer concentrations. The apparent first-order rate constants (kobs) for the photodegradation of riboflavin at ionic strengths of 0.1-0.5 (0.5M phosphate) lie in the range of 7.35-30.32 × 10(-3) min(-1). Under these conditions, the rate constants for the formation of the major products, lumichrome (LC) by photoreduction pathway, and cyclodehydroriboflavin (CDRF) by photoaddition pathway, are in the range of 3.80-16.03 and 1.70-6.07 × 10(-3) min(-1), respectively. A linear relationship has been observed between log kobs and √μ/1+√μ. A similar plot of log k/ko against √μ yields a straight line with a value of ~+1 for ZAZB showing the involvement of a charged species in the rate determining step. NaCl appears to promote the photodegradation reactions of RF probably by an excited state interaction. The implications of ionic strength on RF photodegradation by different pathways and flavin-protein interactions have been discussed.

Investigation of the stabilizing effects of antioxidants and benzophenone-3 on desonide photostability

Desonide is a topical corticoid used in the treatment of skin diseases and is marketed in different pharmaceutical dosage forms. Recently, the poor photostability of a commercially available hair solution after direct exposure to UVA light was verified. In this study, we investigated the ability of the antioxidants ascorbic acid, butylhydroxyanisole (BHA), butylhydroxytoluene (BHT), α-tocopherol, and the UV filter benzophenone-3 (BP-3) to prevent the photodegradation of desonide in hair solution (desonide 0.1%) and the stability of the proposed formulation under environmental conditions. The tested antioxidants were not able to prevent the photolysis of desonide, whereas the addition of 0.3% BP-3 enhanced the photostability of the drug. After 15 h of direct exposure to UVA radiation, the desonide remaining content in the hair solution with BP-3 was approximately 98%. Higher photostability was also verified under UVC radiation. Additionally, the results indicated that the formulation was stable under accelerated and room temperature conditions for 70 days, corresponding to the total period of the study.