Roles of cylooxygenase-2 and caspase-3 expression in pathogenesis of lung carcinoma: An experiment with rats

Objective: To investigate the dynamic expression of cyclooxygenase-2 (COX-2) and caspase-3 during the carcinogenesis, invasion and metastasis of 3-methylcholanthrene (MCA) and diethyinitrosamine (DEN)-induced rat lung cancer and its significance. Methods: Iodized oil with MCA and DEN was instilled into the left bronchi of 80 Wistar rats to induce squamous cell lung carcinoma. Iodized oil without MCA and DEN was instilled into the left bronchi of 10 rats as control group. Sixteen rats in the experimental group and 2 rats in the control group were killed 10, 15, 35, 60, and 270 days after experiment respectively to undergo pathological examination. Immunohistochemistry was used to detect the protein expression of COX-2 and caspase-3 in the bronchial endothelial cells. Immunohistochemical scores (IHS) were calculated. Results: Pathological changes of different phases, such as hyperplasia of bronchial mucosal endothelial cells (14 cases), squamous metaplasia (25 cases), atypical proliferation (35 cases), carcinoma in situ (12 cases), infiltrative carcinoma (54 cases), and metestatic carcinoma (15 cases) appeared successively in the left lung mucosal endothelium of the experimental group. Weak expression of COX-2 protein was occasionally seen in the normal bronchial mucosal endothelium. COX-2 protein expression was becoming stronger and the IHS was becoming higher along with the development of carcinoma (P < 0.01). Caspace-2 protein expression was positive in 8 of the 10 (80%) of the control rats with an HIS of 5.92 ± 0.9. And caspace-2 protein expression was becoming weaker along with the development of carcinoma (P < 0.01 or P < 0.05). Significant negative correlation was found between the COX-2 protein expression and caspase-3 expression (P < 0.01). Conclusion: COX-2 and caspase-3 play important roles in the carcinogenesis of MCA and DEN-induced rat lung squamous cell carcinoma. COX-2 may take part in blocking cell apoptosis by inhibiting caspase-3 activity, thereby promoting the carcinogenesis of lung cancer. The imbalance between COX-2 and caspase-3 may be a critical factor affecting the biologic behavior of lung carcinogenesis, invasion and metastasis.