title: Potential efficacy of p16 gene therapy for EBV-positive nasopharyngeal carcinoma.
abstract: The p16 cell cycle inhibitory gene is a potentially critical molecular abnormality in nasopharyngeal carcinoma (NPC). Its expression is silenced through either deletion or promoter methylation in the vast majority of NPC. This in turn is associated with absent or reduced protein expression, which has been previously demonstrated by our group to correlate with inferior clinical outcome. Therefore, we were interested in evaluating the potential of adenoviral mediated p16 gene therapy (adv.p16) in an EBV-positive NPC model (C666-1). We confirm that under basal conditions, p16 protein is undetectable in C666-1 cells, which, in turn, is associated with retention of retinoblastoma protein (pRb) expression. P16 expression was observed as early as 4 hr after infection of C666-1 cells with adv.p16 (10 pfu/cell) with no discernible perturbation in pRb for up to 24 hr. At 48 hr post-infection, p16 expression continued to increase, but at this point, pRb expression started to decline significantly. Cell viability decreased in a dose-dependent manner, down to 20% using 50 pfu/cell of adv.p16. The addition of radiation therapy (RT) administered 24 hr post-infection achieved only a slightly additive cytotoxicity. Adv.p16 therapy resulted in multiple mechanisms of cytotoxicity, including cell cycle arrest at the G0/G1 phase, induction of senescence, along with apoptosis. Ex vivo infection of C666-1 cells with adv.p16 (25 pfu/cell) with subsequent implantation into scid mice completely prevented tumor formation, followed for up to 51 days. Our study demonstrates the potential efficacy of adv.p16 gene therapy for NPC, mediated through multimodal mechanisms of cytotoxicity. Future evaluations will examine strategies to increase in vivo tumor transduction with a view towards future clinical applications.
authors.affiliation: Ontario Cancer Institute, University Health Network, Ontario, Canada.
authors.forename: Anna Aihua
authors.initials: AA
authors.lastname: Li
authors.forename: Emily
authors.initials: E
authors.lastname: Ng
authors.forename: Wei
authors.initials: W
authors.lastname: Shi
authors.forename: Andrew
authors.initials: A
authors.lastname: Lee
authors.forename: Marie
authors.initials: M
authors.lastname: Chia
authors.forename: Ta-Jen
authors.initials: TJ
authors.lastname: Liu
authors.forename: Dolly
authors.initials: D
authors.lastname: Huang
authors.forename: Brian
authors.initials: B
authors.lastname: O'Sullivan
authors.forename: Pat
authors.initials: P
authors.lastname: Gullane
authors.forename: Fei-Fei
authors.initials: FF
authors.lastname: Liu
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002277:Carcinoma / Q000628:therapy* / Q000821:virology*; D002453:Cell Cycle; D002470:Cell Survival; D016922:Cellular Senescence; D004396:Coloring Agents / Q000494:pharmacology; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D016193:G1 Phase; D020868:Gene Silencing; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors; D006367:HeLa Cells; D004854:Herpesvirus 4, Human / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D009303:Nasopharyngeal Neoplasms / Q000628:therapy* / Q000821:virology*; D009368:Neoplasm Transplantation; D016192:Resting Phase, Cell Cycle; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013997:Time Factors; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D004396:Coloring Agents; D019941:Cyclin-Dependent Kinase Inhibitor p16; D013778:Tetrazolium Salts; D013844:Thiazoles; D001616:beta-Galactosidase; C022616:thiazolyl blue