title: Purine Nucleoside Phosphorylase mediated molecular chemotherapy and conventional chemotherapy: a tangible union against chemoresistant cancer.
abstract: BACKGROUND
  Late stage Ovarian Cancer is essentially incurable primarily due to late diagnosis and its inherent heterogeneity. Single agent treatments are inadequate and generally lead to severe side effects at therapeutic doses. It is crucial to develop clinically relevant novel combination regimens involving synergistic modalities that target a wider repertoire of cells and lead to lowered individual doses. Stemming from this premise, this is the first report of two- and three-way synergies between Adenovirus-mediated Purine Nucleoside Phosphorylase based gene directed enzyme prodrug therapy (PNP-GDEPT), docetaxel and/or carboplatin in multidrug-resistant ovarian cancer cells.
  
  
  METHODS
  The effects of PNP-GDEPT on different cellular processes were determined using Shotgun Proteomics analyses. The in vitro cell growth inhibition in differentially treated drug resistant human ovarian cancer cell lines was established using a cell-viability assay. The extent of synergy, additivity, or antagonism between treatments was evaluated using CalcuSyn statistical analyses. The involvement of apoptosis and implicated proteins in effects of different treatments was established using flow cytometry based detection of M30 (an early marker of apoptosis), cell cycle analyses and finally western blot based analyses.
  
  
  RESULTS
  Efficacy of the trimodal treatment was significantly greater than that achieved with bimodal- or individual treatments with potential for 10-50 fold dose reduction compared to that required for individual treatments. Of note was the marked enhancement in apoptosis that specifically accompanied the combinations that included PNP-GDEPT and accordingly correlated with a shift in the expression of anti- and pro-apoptotic proteins. PNP-GDEPT mediated enhancement of apoptosis was reinforced by cell cycle analyses. Proteomic analyses of PNP-GDEPT treated cells indicated a dowregulation of proteins involved in oncogenesis or cancer drug resistance in treated cells with accompanying upregulation of apoptotic- and tumour- suppressor proteins.
  
  
  CONCLUSIONS
  Inclusion of PNP-GDEPT in regular chemotherapy regimens can lead to significant enhancement of the cancer cell susceptibility to the combined treatment. Overall, these data will underpin the development of regimens that can benefit patients with late stage ovarian cancer leading to significantly improved efficacy and increased quality of life.
authors.affiliation: Oncology Research Centre, Prince of Wales Hospital, Randwick, Sydney, NSW, 2031, Australia.
authors.forename: Preetinder P
authors.initials: PP
authors.lastname: Singh
authors.forename: Swapna
authors.initials: S
authors.lastname: Joshi
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Russell
authors.forename: Sham
authors.initials: S
authors.lastname: Nair
authors.forename: Aparajita
authors.initials: A
authors.lastname: Khatri
mesh_terms: D000256:Adenoviridae / Q000235:genetics*; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D024201:Bystander Effect; D016190:Carboplatin / Q000494:pharmacology / Q000627:therapeutic use; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D000077143:Docetaxel; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000628:therapy*; D011355:Prodrugs / Q000378:metabolism; D040901:Proteomics; D011683:Purine-Nucleoside Phosphorylase / Q000235:genetics* / Q000378:metabolism; D043823:Taxoids / Q000494:pharmacology / Q000627:therapeutic use; D014161:Transduction, Genetic
chemical_list: D000970:Antineoplastic Agents; D011355:Prodrugs; D043823:Taxoids; D000077143:Docetaxel; D016190:Carboplatin; D011683:Purine-Nucleoside Phosphorylase