Topically Applied Hsp90 Inhibitor 17AAG Inhibits UVR-Induced Cutaneous Squamous Cell Carcinomas

We present here that heat-shock protein 90 (Hsp90) inhibitor 17-(allylamino)-17-demethoxygeldanamycin (17AAG), when topically applied to mouse skin, inhibits UVR-induced development of cutaneous squamous cell carcinoma (SCC). In these experiments, DMSO:acetone (1:40 v/v) solution of 17AAG (500 nmol) was applied topically to mouse skin in conjunction with each UVR exposure (1.8 kJ m(-2)). The UVR source was Kodacel-filtered FS-40 sun lamps (approximately 60% UVB and 40% UVA). In independent experiments with three separate mouse lines (SKH-1 hairless mice, wild-type FVB, and protein kinase C epsilon (PKC epsilon)-over-expressing transgenic FVB mice), 17AAG treatment increased the latency and decreased both the incidence and multiplicity of UVR-induced SCC. Topical 17AAG alone or in conjunction with UVR treatments elicited neither skin nor systemic toxicity. 17AAG-caused inhibition of SCC induction was accompanied by a decrease in UVR-induced (1) hyperplasia, (2) Hsp90 beta-PKC epsilon interaction, and (3) expression levels of Hsp90 beta, Stat3, pStat3Ser727, pStat3Tyr705, pAktSer473, and matrix metalloproteinase (MMP). The results presented here indicate that topical Hsp90 inhibitor 17AAG is effective in prevention of UVR-induced epidermal hyperplasia and SCC. One may conclude from the preclinical data presented here that topical 17AAG may be useful for prevention of UVR-induced inflammation and cutaneous SCC either developed in UVR-exposed or organ transplant population.