(+)-2-(1-Hydroxyl-4-oxocyclohexyl) ethyl caffeate suppresses solar UV-induced skin carcinogenesis by targeting PI3K, ERK1/2, and p38.

For decades, skin cancer incidence has increased, mainly because of oncogenic signaling pathways activated by solar ultraviolet (UV) irradiation (i.e., sun exposure). Solar UV induces multiple signaling pathways that are critical in the development of skin cancer, and therefore the development of compounds capable of targeting multiple molecules for chemoprevention of skin carcinogenesis is urgently needed. Herein, we examined the chemopreventive effects and the molecular mechanism of (+)-2-(1-hydroxyl-4-oxocyclohexyl) ethyl caffeate (HOEC), isolated from Incarvillea mairei var. grandiflora (Wehrhahn) Grierson. HOEC strongly inhibited neoplastic transformation of JB6 Cl41 cells without toxicity. PI3K, ERK1/2, and p38 kinase activities were suppressed by direct binding with HOEC in vitro. Our in silico docking data showed that HOEC binds at the ATP-binding site of each kinase. The inhibition of solar UV-induced PI3K, ERK1/2, and p38 kinase activities resulted in suppression of their downstream signaling pathways and AP1 and NF-κB transactivation in JB6 cells. Furthermore, topical application of HOEC reduced skin cancer incidence and tumor volume in SKH-1 hairless mice chronically exposed to solar UV. In summary, our results show that HOEC exerts inhibitory effects on multiple kinase targets and their downstream pathways activated by solar UV in vitro and in vivo. These findings suggest that HOEC is a potent chemopreventive compound against skin carcinogenesis caused by solar UV exposure.