Abstract 5583: Decrease in expression of Gadd45 is associated with gemcitabine and hydroxyurea resistance in human head and neck squamous-cell carcinoma
Authors: Zhang Keqiang , Kim Charles , Wu Xiwei , Wang Yafan , Loera Sofia , Shibata Stephen , Yen Yun 
Published: August 2012

Abstract
Gemcitabine (2′, 2′-difluorodeoxycytidine) is a new nucleoside analogue to block DNA replication. Another target of gemcitabine is the enzyme ribonucleotide reductase (RNR). The diphosphate analogue binds to RNR active site and inactivates the enzyme irreversibly. Hydroxyurea can also decrease production of deoxyribonucleotides via inhibition of the enzyme ribonucleotide reductase by scavenging tyrosyl free radicals as they are involved in the reduction NDPs. Gemcitabine and hydroxyurea have demonstrated a broad spectrum anti-tumor and favorable toxicity profile. In 2006, we conducted a small phase-2 study to evaluate the therapeutic effect of the combination of gemcitabine and hydroxyurea on 14 patients with recurrent locally persistent squamous-cell carcinoma of head and neck cancers (SCCHN). The outcomes of this trial demonstrated that 4 of patients displayed a complete/partial remission and/or stable diseases and 10 of progressive diseases. Since, the molecular mechanisms for the drug-resistant of this combinational treatment in advanced head and neck patients were poorly understood; therefore, we investigated difference in the gene expression profile between stable and progressive diseases. According to their clinical response to the treatments, patients were sorted into either stable disease or progressive disease group. Total RNA was extracted from biopsies of pre-treated patients of these two groups, and then subjected to cDNA microarray analysis. The cDNA microarray analysis indicated that a set of 116 gene transcripts were significant different between stable and progressive diseases. We focused on genes in the set with known roles in drug-resistant of gemcitabine and hydroxyurea such as two subunits of RNR: RRM1 and RRM2, and also on these genes, which are involved in DNA synthesis and DNA damage repair such as, Fos, BNIP3, PITX1, GADD45-alpha and GADD45-gamma. Q-PCR analysis showed that mRNA of FOS, BNIP3 and PITX1 were significantly higher in progressive diseases than that in stable diseases, whereas GADD45-alpha and GADD45-gamma were significantly decreased in stable group than in progressive group. Immunohistochemistry analysis further identified a significant decrease of GADD45-alpha and GADD45-gamma staining and increase of RRM1 and RRM2 staining in tissues of progressive diseases. Our data indicates that, beside increase of RRM1/M2, decrease of GADD45-alpha and GADD45-gamma in SCCHN may be also associated with drug-resistant of gemcitabine and hydroxyurea. Moreover, statistic algorithm indicates that these top-10 genes in the 116-gene list may be sufficient for accurately predicting the outcome of stable and progressive diseases of SCCHN, if patients are subjected to gemcitabine and hydroxyurea treatment.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5583. doi:1538-7445.AM2012-5583