Abstract 2244: Pharmacological TLR4 antagonism using topical resatorvid blocks solar UV-induced skin tumorigenesis in SKH-1 mice (2017)

Abstract An urgent need exists for the development of more efficacious molecular strategies targeting non-melanoma skin cancer (NMSC), the most common malignancy worldwide. Inflammatory signaling downstream of Toll-like receptor 4 (TLR4) is a causative factor in several forms of tumorigenesis, yet its role in solar UV-induced skin carcinogenesis remains undefined. In our recently published work based upon immunohistochemical (IHC) analysis of NMSC tissue microarrays and proteomic analysis of reverse-phase protein microarrays (RPPA) from banked human tissue, we observed increased TLR4 expression in association with tumorigenic progression from normal skin to actinic keratosis and cutaneous squamous cell carcinoma. In immortalized keratinocytes expressing luciferase reporter constructs, resatorvid potently inhibits UV-induced AP-1 and NF-κB signaling, associated with downregulation of inflammatory mediators (IL-6, IL-8, IL-10) and MAP Kinase phosphorylation. In a subsequent acute exposure model in SKH-1 mice, topical resatorvid efficiently antagonized UV-induced stress signaling while potentiating UV-induced epidermal apoptosis. In the current report, we show for the first time that pharmacological inhibition of TLR4 using the specific antagonist resatorvid (TAK-242) blocks UV-induced tumorigenesis in SKH-1 mice. After assessing photostability, efficient cutaneous delivery, and skin residence time of topical resatorvid, we then tested the feasibility of TLR4-directed inhibition of UV-induced tumorigenesis. To this end, SKH-1 mice were split into three groups (n = 20). Each group was exposed to solar-simulated UV (three times a week; 15 weeks duration), followed by another 10 weeks in the absence of UV exposure (sacrifice at week 25). The control group received topical vehicle (acetone) on their backs 1 hour prior to UV exposure (three times a week until sacrifice). The “Prevention” group received topical resatorvid following an analogous dosing regimen. The “Intervention” group received vehicle 1hr prior to each UV treatment but switched to topical resatorvid three times a week only after UV was terminated. In the Prevention model, topical treatment with resatorvid significantly inhibited both tumor area (66% reduction, p = 0.0052) and tumor multiplicity (32% reduction, p = 0.0329; cross sectional Kruskal-Wallis test). In the Intervention model, a marked inhibition of both measures of tumor yield was observed, yet they did not reach statistical significance. Likewise, suppression of UV-induced TLR4-driven signaling was also confirmed in murine skin harvested at week 14 (prior to tumor onset), as assessed by IHC and RPPA analysis. Taken together, these data generated using resatorvid in a murine photocarcinogenesis model suggest that pharmacological TLR4 antagonism may represent a novel molecular strategy for topical prevention of solar UV-induced NMSC. Citation Format: Sally E. Dickinson, Karen Blohm-Mangone, Nichole B. Burkett, Shekha Tahsin, Paul B. Myrdal, Kelly L. Karlage, Jaroslav Janda, Kathylynn Saboda, Denise J. Roe, Zigang Dong, Ann M. Bode, Emanuel F. Petricoin, Valerie S. Calvert, Clara Curiel-Lewandrowski, David S. Alberts, Georg T. Wondrak. Pharmacological TLR4 antagonism using topical resatorvid blocks solar UV-induced skin tumorigenesis in SKH-1 mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2244. doi:10.1158/1538-7445.AM2017-2244