title: Bcl-2 antisense oligonucleotide overcomes resistance to E1A gene therapy in a low HER2-expressing ovarian cancer xenograft model.
abstract: We are currently conducting clinical trials of E1A gene therapy for patients with ovarian cancer. The adenovirus type 5 E1A gene suppresses growth of ovarian cancer cells that overexpress HER-2/neu (HER2) and growth of some--but not all--that express low HER2. In HER2-overexpressing cells, suppression by E1A is predominantly by down-regulation of HER2, but the mechanism in low HER2-expressing cells is not fully understood. The adenoviral E1B protein has sequential and functional homology to Bcl-2 and prolongs the viability of adenovirus host cells by inhibiting E1A-induced apoptosis. Bcl-2 is overexpressed in ovarian cancer and participates in chemoresistance; we hypothesized that Bcl-2 inhibits E1A-induced apoptosis leading to resistance to E1A gene therapy. E1A suppressed colony formation of ovarian cancer cells that express low levels of Bcl-2 and HER2 (OVCAR-3 and OVCA 433), but enhanced colony formation in low HER2-, high Bcl-2-expressing ovarian cancer cells (2774 and HEY). Treating 2774 or HEY cells with antisense oligonucleotide Bcl-2 (Bcl-2-ASO) did not reduce cell viability. E1A combined with Bcl-2-ASO led to significant decreases in cell viability resulting from increased apoptosis relative to cells treated with E1A alone (P < 0.05). The increase in apoptosis was partly due to cytochrome c release and subsequently caspase-9 activation by Bcl-2-ASO. Finally, in an ovarian cancer xenograft model, treatment with Bcl-2-ASO did not prolong survival, but E1A plus Bcl-2-ASO did (P < 0.001). In conclusion, ovarian tumors overexpressing Bcl-2 may not respond well to E1A gene therapy, but treatment with a combination of E1A and Bcl-2-ASO may overcome this resistance.
authors.affiliation: Breast Cancer Translational Research Laboratory, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: Chandra
authors.initials: C
authors.lastname: Bartholomeusz
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Itamochi
authors.forename: Linda X H
authors.initials: LX
authors.lastname: Yuan
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Esteva
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Wood
authors.forename: Naoki
authors.initials: N
authors.lastname: Terakawa
authors.forename: Mien-Chie
authors.initials: MC
authors.lastname: Hung
authors.forename: Naoto T
authors.initials: NT
authors.lastname: Ueno
mesh_terms: D017501:Adenovirus E1B Proteins / Q000235:genetics*; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D015316:Genetic Therapy / Q000379:methods*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D016376:Oligonucleotides, Antisense; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism / Q000628:therapy*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis* / Q000235:genetics; D013873:Thionucleotides / Q000096:biosynthesis / Q000235:genetics*; D014162:Transfection; D023041:Xenograft Model Antitumor Assays
chemical_list: D017501:Adenovirus E1B Proteins; D053453:Caspase 9; D020169:Caspases; D045304:Cytochromes c; D016376:Oligonucleotides, Antisense; D018719:Erb-b2 Receptor Tyrosine Kinases; D013873:Thionucleotides; C408162:oblimersen; C506433:CASP9 protein, human; C506434:Casp9 protein, mouse