Smoking enhanced the expression of MDR-1 in rat prostatic carcinoma

Smoking is associated with the development of different malignancies, especially lung carcinoma. Considerably less interest has been devoted whether the outcome of cancer treatment can be affected by ongoing smoking. In the present study, the effects of ongoing smoking was evaluated on the expression of classical multidrug resistance (MDR-1) in a tumour tissue not usually related to smoking, prostatic carcinoma in rats. The expression of mdr1 was evaluated by quantitative RNA-RNA solution hybridisation and the distribution of the glycoprotein P-170 was examined by immunohistochemistry using the monoclonal antibodies C219 and C494. A group of animals was exposed to cigarette smoke in a nose-only exposure system for 1 h/day, 5 days/week for four weeks. The results demonstrated a significant enhanced expression of mdr1 RNA in the rumours from smoke exposed animals and the immunohistochemical analysis also displayed an increase of the positively stained cells following smoking. These results indicate that alteration at least at the level of transcription is involved in the overexpression of P-170 following smoking. An effect on translation or post-translation cannot be excluded. The observations might add to the experience of drug resistance seen in the clinical situation in tumours associated with carcinogens such as smoking.