title: A combination of a ribonucleotide reductase inhibitor and histone deacetylase inhibitors downregulates EGFR and triggers BIM-dependent apoptosis in head and neck cancer.
abstract: Head and neck squamous cell carcinomas (HNSCCs) are the sixth most common malignant neoplasm and more than 50% of patients succumb to this disease. HNSCCs are characterized by therapy resistance, which relies on the overexpression of anti-apoptotic proteins and on the aberrant regulation of the epidermal growth factor receptor (EGFR). As inherent and acquired resistance to therapy counteracts improvement of long-term survival, novel multi-targeting strategies triggering cancer cell death are urgently required. We investigated how induction of replicational stress by the ribonucleotide reductase inhibitor hydroxyurea (HU) combined with histone deacetylase inhibitors (HDACi) exerts anti-tumor activity. We treated HNSCC cell lines and freshly isolated tumor cells with HDACi, such as the clinically approved anti-epileptic drug valproic acid (VPA), in combination with HU. Our data demonstrate that at clinically achievable levels VPA/HU combinations efficiently block proliferation as well as clonogenic survival, and trigger apoptosis of HNSCC cells. In the presence of VPA/HU, such tumor cells increase expression of the pro-apoptotic BCL-2 family protein BIM, independent of wild-type p53 signaling and in the absence of increased expression of the p53 targets PUMA and BAX. The pro-apoptotic activity of BIM in HNSCCs was found critical for tumor cell death; ectopic overexpression of BIM induced HNSCC apoptosis and RNAi-mediated depletion of BIM protected HNSCC cells from VPA/HU. Also, significantly elevated BIM levels (p less than 0.01) were detectable in the apoptotic tumor centers versus proliferating tumor margins in HNSCC patients (n=31), underlining BIM's clinical relevance. Importantly, VPA/HU treatment additionally reduces expression and cell surface localization of EGFR. Accordingly, in a xenograft mouse model, VPA/HU efficiently blocked tumor growth (P less than 0.001) correlating with BIM induction and EGFR downregulation. We provide a molecular rationale for the potent anti-cancer activities of this drug combination. Our data suggest its exploitation as a potential strategy for the treatment of HNSCC and other tumor entities characterized by therapy resistance linked to dysregulated EGFR activation.
authors.affiliation: Molecular and Cellular Oncology/Mainz Screening Center, University Hospital of Mainz, Germany. rstauber@uni-mainz.de
authors.forename: Roland H
authors.initials: RH
authors.lastname: Stauber
authors.forename: Shirley K
authors.initials: SK
authors.lastname: Knauer
authors.forename: Negusse
authors.initials: N
authors.lastname: Habtemichael
authors.forename: Carolin
authors.initials: C
authors.lastname: Bier
authors.forename: Britta
authors.initials: B
authors.lastname: Unruhe
authors.forename: Simona
authors.initials: S
authors.lastname: Weisheit
authors.forename: Stephanie
authors.initials: S
authors.lastname: Spange
authors.forename: Frank
authors.initials: F
authors.lastname: Nonnenmacher
authors.forename: Verena
authors.initials: V
authors.lastname: Fetz
authors.forename: Torsten
authors.initials: T
authors.lastname: Ginter
authors.forename: Sigrid
authors.initials: S
authors.lastname: Reichardt
authors.forename: Claus
authors.initials: C
authors.lastname: Liebmann
authors.forename: Günter
authors.initials: G
authors.lastname: Schneider
authors.forename: Oliver H
authors.initials: OH
authors.lastname: Krämer
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000072224:Bcl-2-Like Protein 11; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000008:administration & dosage* / Q000494:pharmacology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D018773:Genes, erbB-1 / Q000187:drug effects*; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000473:pathology; D056572:Histone Deacetylase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012264:Ribonucleotide Reductases / Q000037:antagonists & inhibitors; D000077195:Squamous Cell Carcinoma of Head and Neck; D023041:Xenograft Model Antitumor Assays
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012264:Ribonucleotide Reductases