title: Cisplatin-induced GADD34 upregulation potentiates oncolytic viral therapy in the treatment of malignant pleural mesothelioma.
abstract: BACKGROUND
  NV1066, a replication-competent oncolytic herpes simplex virus type 1 (HSV-1) attenuated by a deletion in the gene gamma(1)34.5, preferentially replicates in and kills malignant cells. gamma(1)34.5 encodes ICP34.5, a viral protein essential for productive replication, which has homology with mammalian stress response induced GADD34 (growth arrest and DNA damage-inducible protein). We hypothesized that cisplatin upregulates GADD34 expression, which enhances NV1066 replication and oncolysis.
  
  
  METHODS
  Ten human malignant pleural mesothelioma (MPM) cell lines were infected with NV1066 at multiplicities of infection (MOI; ratio of viral particles per tumor cell) 0.005 to 0.8 in vitro, with and without cisplatin (1 to 4 microM). In the MPM cell line VAMT, viral replication was determined by plaque assay, cell kill by lactate dehydrogenase assay, and GADD34 induction by quantitative RT-PCR and Western blot. Synergistic efficacy was confirmed by the isobologram and combination index methods of Chou-Talalay. GADD34 upregulation by cisplatin was inhibited with GADD34 siRNA to further confirm the synergistic efficacy dependence with GADD34.
  
  
  RESULTS
  Combination therapy with NV1066 and cisplatin showed strong synergism in epithelioid (H-2452, H-Meso), sarcomatoid (H-2373, H-28), and biphasic (JMN, Meso-9, MSTO-211H) MPM cell lines, and an additive effect in others. In VAMT cells combination therapy enhanced viral replication 4 to 11-fold (p < 0.01) and cell kill 2 to 3-fold (p < 0.01). Significant dose reductions for both agents (2 to 600-fold) were achieved over a wide range of therapeutic-effect levels (LD50-LD99) without compromising cell kill. Synergistic cytotoxicity correlated with GADD34 upregulation (2 to 4-fold, p < 0.01) and was eliminated following transfection with GADD34 siRNA.
  
  
  CONCLUSIONS
  Cisplatin-induced GADD34 expression selectively enhanced the cytotoxicity of the gamma(1)34.5-deficient oncolytic virus, NV1066. This provides a cellular basis for combination therapy with cisplatin and NV1066 to treat MPM and achieve synergistic efficacy, while minimizing dosage and toxicity.
authors.affiliation: Department of Surgery, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Prasad S
authors.initials: PS
authors.lastname: Adusumilli
authors.forename: Mei-Ki
authors.initials: MK
authors.lastname: Chan
authors.forename: Yun Shin
authors.initials: YS
authors.lastname: Chun
authors.forename: Michael
authors.initials: M
authors.lastname: Hezel
authors.forename: Ting-Chao
authors.initials: TC
authors.lastname: Chou
authors.forename: Valerie W
authors.initials: VW
authors.lastname: Rusch
authors.forename: Yuman
authors.initials: Y
authors.lastname: Fong
mesh_terms: D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002945:Cisplatin / Q000627:therapeutic use*; D003131:Combined Modality Therapy; D017353:Gene Deletion; D018259:Herpesvirus 1, Human / Q000235:genetics; D006801:Humans; D008654:Mesothelioma / Q000188:drug therapy / Q000628:therapy*; D050130:Oncolytic Virotherapy; D010997:Pleural Neoplasms / Q000188:drug therapy / Q000628:therapy*; D054645:Protein Phosphatase 1; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D015854:Up-Regulation; D014764:Viral Proteins / Q000235:genetics; D014779:Virus Replication / Q000187:drug effects / Q000235:genetics
chemical_list: D000943:Antigens, Differentiation; D018797:Cell Cycle Proteins; D034741:RNA, Small Interfering; D014764:Viral Proteins; C087519:PPP1R15A protein, human; D054645:Protein Phosphatase 1; D002945:Cisplatin