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Deficient TP53 Expression, Function, and Cisplatin Sensitivity Are Restored by Quinacrine in Head and Neck Cancer

Authors' Affiliation: Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, Maryland

Requests for reprints: Carter Van Waes, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders/NIH, 10/5D55, MSC-1419, Bethesda, MD 20892-1419. Phone: 301-402-4216; Fax: 301-402-1140; E-mail: vanwaesc{at}nidcd.nih.gov.

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 p21 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 inducible TP53 on function and cellular proliferation was confirmed using selective TP53 inhibitor pifithrin- 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 p21 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- 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.