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Roles of cyclooxygenase (COX) enzyme and intrinsic pathway of apoptosis have been explored for the chemopreventive effects of non-steroidal anti-inflammatory drugs (NSAIDs) on 9,10-dimethyl benz(a)anthracene (DMBA)-induced lung cancer in rat model. 16 weeks after the administration of DMBA, morphological analysis revealed the occurrences of tumours and lesions, which were regressed considerably with the co-administration of indomethacin and etoricoxib, the two NSAIDs under investigation. DMBA group was marked by hyperplasia and dysplasia as observed by histological examination, and these features were corrected to a large extent by the two NSAIDs. Elevated levels of COX-2 were seen in the DMBA group, the enzyme responsible for prostaglandin synthesis during inflammation and cancer, whilst the expression of the constitutive isoform, COX-1, was equally expressed in all the groups. Apoptosis was quantified by studying the activities of apaf-1, caspase-9, and 3 by immunofluorescence and western blots. Their activities were found to diminish in the DMBA-treated animals as compared to the other groups. Fluorescent co-staining of the isolated broncho-alveolar lavage cells showed reduced number of apoptotic cells in the DMBA group, indicating decrease in apoptosis after carcinogen administration. The present results thus suggest that the mechanism of cancer chemoprevention of NSAIDs may include the suppression of COX-2 and the induction of apoptosis.

9,10-Dimethyl benz(a)anthracene (DMBA), when injected intratracheally once at a dose of 20 mg/kg body weight, is found to induce lung cancer in rats. Two nonsteroidal anti-inflammatory drugs (NSAIDs), indomethacin and etoricoxib, are given orally daily as chemopreventive agents at a dose of 0.6 mg/kg body weight and 2 mg/kg body weight, respectively, along with DMBA. Morphologic and histologic analysis revealed the occurence of tumors and intense cellular proliferation in the DMBA-treated animals, whereas no such features were observed in the other groups. Nuclear factor κB, a nuclear transcription factor, and proliferating cell nuclear antigen, a cell proliferation antigen, were studied by immunoblotting and immunohistochemistry and their levels were markedly elevated in the DMBA group compared with the others. Oxidative stress parameters, as studied by the inducible nitric oxide synthase activity, and the levels of reactive oxygen and nitrogen species were found to be suppressed in the DMBA group. Furthermore, fluorescent staining of the isolated lung cells from bronchoalveolar lavage was performed to study apoptosis and alterations in the mitochondrial membrane potential, and the DMBA-induced lung cancer was found to be associated with high inner mitochondrial membrane potential and a suppressed level of apoptosis.