Sulindac is a nonsteroidal anti-inflammatory drug with demonstrated potency as a chemopreventive agent in animal models of carcinogenesis and in patients with familial adenomatous polyposis. Because tumor promotion is generally associated with exposure to pro-inflammatory stimuli, it is likely that anti-inflammatory agents may have potent antitumor effects. In human skin, sulindac reduces bradykinin-induced edema. In this study, we tested the hypothesis that the cyclooxygenase inhibitor sulindac can protect against ultraviolet (UVB)-induced injury that is crucial for the induction of cancer. Exposure of SKH-1 hairless mice to two consecutive doses of UVB (230 mJ/cm 2) induces various inflammatory responses including erythema, edema, epidermal hyperplasia, infiltration of polymorphonuclear leukocytes, etc. Topical application of sulindac (1.25-5.0 mg/0.2 ml acetone) to the dorsal skin of SKH-1 hairless mice either 1 h before or immediately after UVB exposure substantially inhibited these inflammatory responses in a dose-dependent manner. Oral administration of sulindac in drinking water (160 ppm) for 15 days before and during UVB irradiation similarly reduced these inflammatory responses. These potent anti-inflammatory effects of sulindac suggested the possibility that the drug could inhibit signaling processes that relate to carcinogenic insult by UVB. Accordingly, studies were conducted to assess the efficacy of sulindac in attenuating the expression of UVB-induced early surrogate molecular markers of photodamage and carcinogenesis. UVB exposure enhanced the expression of p53, c-fos, cyclins D1 and A, and PCNA 24 h after irradiation. Treatment of animals with either topical or oral administration of sulindac largely abrogated the expression of these UVB-induced surrogate markers. These results indicate that the cyclooxygenase inhibitor sulindac is effective in reducing UVB-induced events relevant to carcinogenesis and that this category of topically applied or orally administered drugs may prove to be effective chemopreventive agents for reducing the risk of photocarcinogenesis in human populations. © 2003 Elsevier Inc. All rights reserved.