Chemopreventive Role of Preferential COX-2 Inhibitor Diclofenac in 9, 10- Dimethybenz(a)anthracene Induced Experimental Lung Carcinogenesis

Lung cancer was induced in female Wistar rats by a single intratracheal instillation of 9, 10Dimethybenz(a)anthracene (DMBA). To evaluate the chemopreventive potential of Diclofenac, which is a preferential cyclooxygenase-2 (COX-2) inhibitor, animals were divided into four groups. Group 1 received normal saline intratracheally, Group 2 DMBA (20 mg/kg), Group 3 a daily oral dose of Diclofenac (8 mg/kg) in addition to the DMBA while group 4 received Diclofenac alone. Animals were sacrificed after 6 and 12 weeks. Presence of tumors was confirmed by morphological and histological analysis. COX-2 expression was studied by immunohistochemistry (IHC) and Western immunoblot, which showed higher expression in DMBA treated animals but much lower in DMBA+Diclofenac. EtBr/AO co-staining of alveolar macrophages under fluorescence microscope showed that Diclofenac was able to induce apoptosis in DMBA treated animals. DNA fragmentation and TUNEL assay also showed similar results. To explore the apoptotic pathway further, Caspase-3 expression was studied by Western immunoblot which showed its absence in DMBA treated animals while present in the DMBA+Diclofenac group. Nitric oxide and citrulline levels were also quantitated which were lowered in the DMBA+Diclofenac group. The results indicate that Diclofenac might have beneficial effects in lung cancer chemoprevention and its action is mediated by COX2 inhibition and caspase-3 activation.