title: Flavonol and imidazole derivatives block HPV16 E6 activities and reactivate apoptotic pathways in HPV⁺ cells.
abstract: High-risk human papillomaviruses (HR-HPVs) cause nearly all cases of cervical cancer, as well as approximately 30% of head and neck cancers. HPV 16 E6, one of two major viral oncogenes, protects cells from apoptosis by binding to and accelerating the degradation of several proteins important in apoptotic signaling, including caspase 8 and p53. We proposed that blocking the interactions between HPV E6 and its partners using small molecules had the potential to re-sensitize HPV(+) cells to apoptosis. To test this idea, we screened libraries of small molecules for candidates that could block E6/caspase 8 binding and identified several candidates from different chemical classes. We tested hits for dose-dependency and specificity in vitro and for toxicity in a cell-based assay and then used this information to select the two best candidates for further testing: myricetin, a flavonol, and spinacine, an imidazole amino-acid derivative of histidine. Both compounds clearly inhibited the ability of E6 to bind in vitro to both caspase 8 and E6AP, the protein that mediates p53 degradation. In addition, both compounds were able to increase the level of caspase 8 and p53 in SiHa cervical cancer cells, resulting in an increase of caspase 3/7 activity. Finally, both myricetin and spinacine sensitized HPV(+) cervical and oral cancer cells, but not HPV(-) cervical and oral cancer cells, to apoptosis induced by the cancer-specific ligand TRAIL, as well as the chemotherapeutic agents doxorubicin and cisplatin. New therapies based on this work may improve treatment for HPV(+) cancer patients.
authors.affiliation: Department of Basic Sciences, Loma Linda University School of Medicine, 11021 Campus Street, 101 Alumni Hall, Loma Linda, CA 92354, USA.
authors.forename: C-H
authors.initials: CH
authors.lastname: Yuan
authors.affiliation: Department of Basic Sciences, Loma Linda University School of Medicine, 11021 Campus Street, 101 Alumni Hall, Loma Linda, CA 92354, USA.
authors.forename: M
authors.initials: M
authors.lastname: Filippova
authors.affiliation: KGI School of Pharmacy, 535 Watson Drive, Claremont, CA 91711, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Krstenansky
authors.affiliation: Department of Basic Sciences, Loma Linda University School of Medicine, 11021 Campus Street, 101 Alumni Hall, Loma Linda, CA 92354, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Duerksen-Hughes
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000473:pathology / Q000821:virology; D002460:Cell Line; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000008:administration & dosage / Q000494:pharmacology; D004317:Doxorubicin / Q000008:administration & dosage / Q000494:pharmacology; D004357:Drug Synergism; D005419:Flavonoids / Q000008:administration & dosage / Q000494:pharmacology; D044948:Flavonols / Q000008:administration & dosage / Q000494:pharmacology*; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000821:virology; D006801:Humans; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D009856:Oncogene Proteins, Viral / Q000037:antagonists & inhibitors* / Q000378:metabolism; D027383:Papillomaviridae / Q000187:drug effects* / Q000378:metabolism*; D030361:Papillomavirus Infections / Q000188:drug therapy / Q000821:virology; D011725:Pyridines / Q000008:administration & dosage / Q000494:pharmacology; D012097:Repressor Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000077195:Squamous Cell Carcinoma of Head and Neck; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: C068651:E6 protein, Human papillomavirus type 16; D005419:Flavonoids; D044948:Flavonols; D007093:Imidazoles; D009856:Oncogene Proteins, Viral; D011725:Pyridines; D012097:Repressor Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C055336:spinacine; C040015:myricetin; D004317:Doxorubicin; D002945:Cisplatin