title: Synergistic growth inhibition of squamous cell carcinoma of the head and neck by erlotinib and epigallocatechin-3-gallate: the role of p53-dependent inhibition of nuclear factor-kappaB.
abstract: We have previously reported that the green tea polyphenol epigallocatechin-3-gallate (EGCG) and the epidermal growth factor receptor-tyrosine kinase inhibitor erlotinib had synergistic growth-inhibitory effects in cell culture and a nude mouse xenograft model of squamous cell carcinoma of the head and neck. However, the mechanism of their antitumor synergism is not fully understood. In the current study, we investigate the mechanism of their synergistic growth-inhibitory effects. The treatment of squamous cell carcinoma of the head and neck cell lines with erlotinib time-dependently increased the expression of cell cycle regulatory proteins p21 and p27 and apoptosis regulatory protein Bim. EGCG alone had very little or no effect on the expression of these proteins among the cell lines. However, simultaneous treatment with EGCG and erlotinib strongly inhibited erlotinib-induced expression of p21 and p27 without affecting the expression of Bim. Moreover, erlotinib increased the expression of p53 protein, the ablation of which by short hairpin RNA strongly inhibited EGCG- and erlotinib-mediated growth inhibition and the expression of p21, p27, and Bim. In addition, combined treatment with erlotinib and EGCG inhibited the protein level of p65 subunit of nuclear factor-kappaB and its transcriptional target Bcl-2, but failed to do so in cells with ablated p53. Taken together, our results, for the first time, suggest that erlotinib treatment activates p53, which plays a critical role in synergistic growth inhibition by erlotinib and EGCG via inhibiting nuclear factor-kappaB signaling pathway. Characterizing the underlying mechanisms of EGCG and erlotinib synergism will provide an important rationale for chemoprevention or treatment trials using this combination.
authors.affiliation: Department of Hematology and Medical Oncology, Winship Cancer Institute, Emory University, Atlanta, Georgia 30322, USA.
authors.forename: A R M Ruhul
authors.initials: AR
authors.lastname: Amin
authors.forename: Fadlo R
authors.initials: FR
authors.lastname: Khuri
authors.forename: Zhuo Georgia
authors.initials: ZG
authors.lastname: Chen
authors.forename: Dong M
authors.initials: DM
authors.lastname: Shin
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D045744:Cell Line, Tumor / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D000069347:Erlotinib Hydrochloride; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006258:Head and Neck Neoplasms / Q000473:pathology*; D006801:Humans; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D051996:Transcription Factor RelA / Q000037:antagonists & inhibitors* / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D018797:Cell Cycle Proteins; D016328:NF-kappa B; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D034741:RNA, Small Interfering; D051996:Transcription Factor RelA; D016159:Tumor Suppressor Protein p53; D002392:Catechin; C045651:epigallocatechin gallate; D000069347:Erlotinib Hydrochloride