(W1030-05-29) Topical Cream Formulation of Integrated Stress Response Inhibitor (ISRIB) for the Potential Treatment of Chemical Warfare Skin Injury: Effect of Chemical Enhancers, Concentration, and pH

Purpose: Lewisite and other similar arsenic-derived chemicals were developed as chemical weapons during World War I and II because of their extremely toxic effects. Such warfare vesicant chemicals, soon after skin exposure, activate the cellular defense integrated stress response (ISR) that causes severe cutaneous blistering, erythema, inflammation, and pain, and can lead to systemic toxicity causing a significant threat to human health. ISRIB, a potent ISR inhibitor, has the potential to mitigate such cutaneous injuries by reducing the stress granules generated in keratinocytes upon arsenicals exposure. Therefore, topical application of ISRIB (MW 451.3 g/mol and logP 4.8) could be effective in local tissue recovery that can further minimize the chances of systemic injury. However, the lipophilic (logP 4.8) nature of ISRIB poses a significant challenge in effective dermal delivery. This can be overcome using chemical enhancers which reversibly reduce the skin barrier resistance by lipid or protein modification and improve drug solubility and partitioning. In this study, we formulated a novel topical cream formulation by incorporating different chemical enhancers and explored the delivery of ISRIB in the skin. Further, we have explored the effect of pH changes and increasing drug concentration in the skin delivery of ISRIB.

Methods: In vitro permeation test (IVPT) studies were performed on vertical Franz diffusion cells using dermatomed porcine ear skin. Samples (300 µL) were withdrawn at predetermined time points, and at the end of 24 h, the unabsorbed formulation was removed, and the permeation area was extracted in isopropanol to determine skin delivery of ISRIB. All the samples were analyzed using the validated HPLC method and analyzed statistically using one-way ANOVA. For combinations of the chemical enhancers group (Figure 1), a 90% saturated solution of ISRIB in the chemical enhancers with propylene glycol as vehicle was used. These chemical enhancers included different combinations and concentrations of N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), azone, 5-methyl-3-phenylisoxazole-4-carboxylic acid, oleic acid, Labrafac™, ethanol, 1,3 Dimethyl-2-Imidazolidinone, and transcutol. An oil-in-water cream was formulated by the addition of the oil phase to the aqueous phase under homogenization at 8000 rpm for 20 min. Different concentrations of selected chemical enhancers, ranging from 30% to 60%, were integrated into the cream to evaluate their impact on the drug delivery into the skin. The oil phase consisted of ISRIB, stearic acid, NMP, and azone, while the aqueous phase consisted of glycerol, hydroxyethyl cellulose, poloxamer, and DMSO. Further, the initial cream formulation (pH 6.2) was modified at two different pH of 4.5 and 5.5 with citric acid and citrate buffer with an increase in drug concentration.

Results: The saturation solubility of ISRIB with chemical enhancers showed that the presence of higher concentrations of DMSO, NMP, and azone in combination showed higher solubility of ISRIB. IVPT results showed that a combination of DMSO + azone + NMP had a significantly higher delivery (348.28 ± 22.96 µg/cm²) compared to other combinations (p ≤ 0.05) (Figure 1). This suggests that NMP, DMSO, and azone may have contributed to enhancing the skin delivery of ISRIB, and thus was incorporated into the cream formulation. Further, the concentration of chemical enhancers in the cream formulation (30-60%) was formulated with a minimum drug loading of 0.7% w/w. The F1 (30%) cream formulation had a significantly higher delivery (32.87 ± 3.97 µg/cm²) when compared to, F2 (40%) (18.93 ± 1.46 µg/cm²), F3 (45%) (21.12 ± 1.79 µg/cm²), and F4 (50%) ( 19.18 ± 0.13 µg/cm²) chemical enhancers. No significant difference was found between F1 and F5 (60%) and among the remaining groups with each other. F1 exhibited the lowest pH value (6.29 ± 0.01) among the five formulation groups which played a role in increasing the solubility of ISRIB (21.43 ± 0.43 mg/mL) and also improved its permeation into the skin. Based on this, we subjected F1 to two pH changes, 4.5 and 5.5, and increased the drug loading to 1.4% to evaluate the impact on drug delivery. IVPT results indicated that F1 (pH 5.5) had the highest skin delivery (62.49 ± 8.11 µg/cm²), followed by F1 (pH 4.5) (48.33 ± 1.15 µg/cm²), and F1 (pH 6.2) (32.45 ± 3.24 µg/cm²). It was also observed that an increase in drug concentration did not have any effect on the permeation of ISRIB. Thus, the optimum pH for improved skin permeation was found to be 5.5. Moreover, this slightly acidic nature of F1(pH 5.5) may accelerate the cutaneous healing of injured skin from chemical warfare exposure.

Conclusion: The current study successfully identified the potential chemical enhancers that improved the permeation of a lipophilic molecule, ISRIB. Further, a novel effective cream formulation was developed, utilizing various concentrations of these enhancers and altering the pH and drug concentration to optimize the delivery of ISRIB into the skin. Therefore, this study establishes cream formulation of ISRIB formation for its potential use in the treatment of chemical warfare skin injury.


Amount of ISRIB delivered to the skin with different combinations of chemical enhancers


Amount of ISRIB delivered to the skin with a different cream composition


Amount of ISRIB delivered to the skin by altering pH and drug concentration in F1 cream formulation