Deficient TP53 expression, function, and cisplatin sensitivity are restored by quinacrine in head and neck cancer

Purpose: To determine the nature and potential pharmacologic reversibility of deficient TP53 expression and function in head and neck squamous cell carcinomas (HNSCC) with wild-type TP53, previously associated with decreased sensitivity to cisplatin therapy. Experimental Design: TP53 genotype, mRNA and protein expression, TP53-induced p2l expression, and TP53 DNA-binding and reporter gene function were determined in a panel of nine previously characterized HNSCC cell lines from the University of Michigan squamous cell carcinoma (UM-SCC) series. The genotoxic drug doxorubicin and the anti-inflammatory and antimalarial drug quinacrine, previously identified as inducers of TP53, were used to examine the nature and potential reversibility of deficient TP53 expression and function. The specific role of inducibleTP53 on function and cellular proliferation was confirmed using selectiveTP53 inhibitor pifithrin-alpha or short hairpin RNA knockdown. The capability of quinacrine to sensitize HNSCC to the cytotoxic effects of cisplatin was assessed. Results: UM-SCC cell lines with wild-type TP53 genotype underexpressed TP53 mRNA and protein when compared with normal human keratinocytes or UM-SCC with mutant TP53. Although doxorubicin failed to induce TP53 expression or functional activity, quinacrine induced TP53 mRNA and protein expression, increased TP53 reporter activity and p2l protein expression, and induced growth inhibition in these wild-type TP53 cell lines. Quinacrine-induced TP53 reporter activity and growth suppression were attenuated by pifithrin-alpha and TP53 short hairpin RNA knockdown. Furthermore, quinacrine sensitized UM-SCC to cisplatin in vitro. Conclusions: Deficient TP53 mRNA and protein expression underlies decreased function in a subset of HNSCC with wild-type TP53 and can be restored together with cisplatin sensitization by quinacrine.