(M0930-02-12) Intradermal Injection of a Thermoresponsive Polymeric Dexamethasone Prodrug (ProGel-Dex) Ameliorate Dermatitis in an Imiquimod (IMQ)-Induced Psoriasis-Like Mouse Model

Purpose: Psoriasis is a chronic immune-mediated inflammatory skin disease. It affects around 3% of the US population, significantly impacting their quality of life. [1, 2]. Currently, there is no cure for the disease. Among the most commonly used medications for psoriasis (e.g., retinoids, glucocorticoids (GC), phototherapies and biologics, etc.), GC is still one the most widely used effective treatment [3], albeit being hampered by different formulation limitations and systemic side effects. To improve the therapeutic efficacy and safety of GC, we have developed a N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-based thermoresponsive dexamethasone (Dex) prodrug (ProGel-Dex). Its aqueous solution is a free-flowing liquid at 4 °C but transition into a hydrogel at > 30 °C. We envision that upon intradermal injection, the prodrug solution will form a hydrogel to allow physical retention at the site of pathology, where it undergoes gradual dissolution, release and activation to exert its therapeutic functions. The focus of the present study is to assess the therapeutic efficacy and safety of ProGel-Dex in an imiquimod-induced psoriasis-like mouse model.

Methods: Female C57BL/6 mice aged 8 weeks were randomized into six groups: Healthy, ProGel-Dex (3 groups, dosing at 0.5, 1, 2 mg/kg/day Dex equivalent), Dex (1 mg/kg/day dexamethasone sodium phosphate Dex equivalent) and Saline group. For psoriasis induction, the back of the mice were shaved and completely dehaired with depilation cream. Imiquimod (IMQ, 62.5 mg of 5% cream) was applied daily on the exposed skin (2x3 cm2) starting on day 0 for 7 days. The ProGel-Dex formulation was injected intradermally as a single dose on day 1. For Dex group, dexamethasone sodium phosphate was topically applied daily 1 h before IMQ application. Body weight and PASI score (determined according to the severity of erythema, scaling, and skin thickening) of the mice were recorded daily[4]. Thickness of mouse skin was measured using a digital caliper. On day 7, mice were sacrificed with all major organs/tissues isolated, including the dorsal skin. Skin histology was performed to assess the therapeutic efficacy. Plasma of mice was collected for assessment of cytokine levels. For safety evaluation, organ weight, histology, white blood cell counting, and complete metabolic panel were analyzed.

Results: The appearance of psoriasis-like dermatitis following the application of IMQ was evident in the hematoxylin and eosin (H&E) stained skin sections, showing high inflammatory cell infiltration, acanthosis, and thickened prickle cell layer of epidermis (Figure 1A). The PASI scoring system for skin morphology change was employed to assess severity of dermatitis. Appearance of erythema, skin thickening, and scaling were visualized Figure 1B. Presence of ProGel-Dex in the dissected dorsal skin of psoriasis mice on day 7 post intradermal injection was shown in Figure 1C. And individual and calculative scores were shown in Figure 1D-G. Erythema scores were elevated in Saline group, which received daily IMQ and topical saline (P < 0.01) and were reduced in ProGel-Dex treatment group. Erythema score was higher in mice treated with Dex than those treated with ProGel-Dex low dose (P < 0.05). Mice treated with low dose ProGel-Dex were the only treatment group with significantly lower scaling score, skin thickness and total PASI score than the Saline group (P < 0.01). Levels of IL-6 in serum were up-regulated in IMQ psoriasis mice. Compared to Healthy group, level of IL-6 in Saline group was increased by more than 20-fold, indicating an enhanced immune inflammatory reaction. However, this increase of IL-6 in IMQ psoriasis mice was mostly diminished by low dose ProGel-Dex (P < 0.01) (Figure 2 A). The ratio of spleen to body weight was markedly increased in all psoriasis mice (regardless of treatment received) when compared to the Healthy mice, confirming the IMQ-induced immune activation (Figure 2B). Both ProGel-Dex high dose and Dex treatments seem to be able to slightly temper the immune response. Based on analysis of metabolic panel, levels of alanine aminotransferase, amylase and potassium were all upregulated in Dex treated group as shown in Figure 3 A-C. Body weight of Dex group was significantly lower than that of healthy group (P < 0.0001) and ProGel-Dex low dose group (P < 0.05) (Figure 3D).

Conclusion: In this study, we have validated the therapeutic efficacy and safety of a novel N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-based thermoresponsive dexamethasone (Dex) prodrug (ProGel-Dex) in an IMQ-induced psoriasis-like mouse model. ProGel-Dex effectively alleviated the severity of dermatitis, reducing erythema, scaling, skin thickness, and total PASI score, with low dose treatment group showing the most significant improvement. Moreover, ProGel-Dex could effectively dampen the IMQ-induced inflammatory response, as evident in the reduced IL-6 level and potential mitigation of splenomegaly. While Dex treatment was effective in mitigation of dermatitis, it was also found to be associated with significant side effects. Collectively, these findings support the development of intradermal ProGel-Dex as a promising alternative to conventional GC formulations for the treatment of psoriasis, offering improved efficacy, reduced systemic side effects, and improved patient’s compliance.

References: 1. Nestle FO, Kaplan DH, Barker J. Psoriasis. N Engl J Med. 2009 Jul 30;361(5):496-509. doi: 10.1056/NEJMra0804595. PMID: 19641206.
2. Griffiths CE, Barker JN. Pathogenesis and clinical features of psoriasis. Lancet. 2007 Jul 21;370(9583):263-271. doi: 10.1016/S0140-6736(07)61128-3. PMID: 17658397.
3. Rahman M, Alam K, Ahmad MZ, Gupta G, Afzal M, Akhter S, Kazmi I, Jyoti, Ahmad FJ, Anwar F. Classical to current approach for treatment of psoriasis: a review. Endocr Metab Immune Disord Drug Targets. 2012 Sep;12(3):287-302. doi: 10.2174/187153012802002901. PMID: 22463723.
4. Oji V, Luger TA. The skin in psoriasis: assessment and challenges. Clin Exp Rheumatol. 2015 Sep-Oct;33(5 Suppl 93):S14-9. Epub 2015 Oct 15. PMID: 26472560.

Acknowledgements:This study was supported in part by National Institutes of Health (R44DA051278). The content is solely the responsibility of the coauthors and does not necessarily represent the official views of the National Institutes of Health.

Figure 1. Treatment with ProGel-Dex ameliorated the morphological changes induced by IMQ. (A) Representative Hematoxylin-Erosin (H&E) staining of IMQ induced mice skin on day 7 of experiment. (B) Representative images of back skin damage including erythema, scaling and thickening. (C) The presence of ProGel-Dex in the dissected dorsal skin of psoriasis mice on day 7 post intradermal injection. (D-F) Individual scoring or measurement for scaling formation, redness and thickness. (G) PASI scoring. Data was expressed as mean ± SEM (n = 7); *P < 0.05, **P < 0.01, ***P < 0.001; Dex, Dexamethasone.

Figure 2. Treatment with ProGel-Dex ameliorated the inflammation by IMQ. (A) Serum IL-6 concentration of each group on day 7 was measured by ELISA. (B) The ratio of spleen weight to body weight. Data was expressed as mean ± SEM (n = 7); *P < 0.05, **P < 0.01, ***P < 0.001; Dex, Dexamethasone.

Figure 3. Dex treatment was associated with systemic adverse side effects. (A-C) Serum concentration of alkaline phosphatase, amylase and potassium of each group on day 7 was measured by blood chemistry analyzer. (B) Body weight on day 7. Data was expressed as mean ± SEM (n = 7); *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; Dex, Dexamethasone.