P-glycoprotein is positively correlated with p53 in human oral pre-malignant and malignant lesions and is associated with poor prognosis.

P-glycoprotein (Pgp) encoded by the MDR1 gene, a predictor of chemoresistance, may also serve as a prognosticator of clinical outcome in cancer patients. The mutant tumour-suppressor p53 protein has been shown to activate the MDR1 promoter, whereas the wild-type p53 represses this activity in cultured cells. We have described the differential expression of Pgp and p53 proteins in betel- and tobacco-related oral tumorigenesis in the Indian population. Herein, Pgp expression was analysed in relation to p53 protein accumulation in pre-malignant and malignant oral lesions by immunohistochemical and flow-cytometric analyses. The relationship between Pgp and p53 protein accumulation and clinicopathological parameters as well as prognosis was determined. Expression of Pgp was observed in 81% of oral squamous cell carcinomas (SCCs) and 71% of pre-malignant lesions. Sixty-five of 75 p53-positive oral SCCs and 21/24 p53-positive pre-malignant lesions showed expression of Pgp. Significant correlation between Pgp and p53 expression was found not only in oral SCCs but also in pre-malignant lesions. Co-expression of Pgp and p53 proteins was indicative of poor prognosis. Follow-up studies of 35 patients showed that 7 of 10 oral SCCs with accumulation of Pgp and p53 proteins also exhibited shorter disease-free survival (recurrence/metastases). Our findings provide clinical evidence for a significant association between Pgp and p53 protein expression in oral tumorigenesis and may account for the aggressive nature of the tumour and poor prognosis.