title: Systemic production of IL-12 by naked DNA mediated gene transfer: toxicity and attenuation of transgene expression in vivo.
abstract: BACKGROUND
  IL-12 is a potent antitumor cytokine for cancer gene therapy. Previously, we demonstrated that single systemic administration of naked DNA (encoding IL-12) could serve as a good model for in vivo evaluation of the antitumor effect of a candidate gene (unpublished data). In the present study, we propose that this gene delivery method could be a very useful model for in vivo evaluation of the toxicity of a given therapeutic gene (using IL-12 as an example). By comparing the toxicities and the effects of initial IL-12 administration on subsequent transgene expression, both IL-12 gene delivery and recombinant murine IL-12 protein (rmIL-12) administration showed similar toxicity profiles.
  
  
  METHODS
  Naked DNA encoding murine IL-12 (mIL-12) was delivered into mice by systemic administration. Toxicity profiles of mice treated with DNA or rmIL-12 were compared.
  
  
  RESULTS
  Systemic administration of naked DNA encoding mIL-12 resulted in very similar toxicity as rmIL-12 with respect to liver enzyme, hematological and immunological profiles. Repeated injection of mIL-12 gene did not recover a high level of mIL-12 production as the first injection. Moreover, initial mIL-12 administration resulted in inhibition of subsequent reporter gene expression with both viral and non-viral promoters (CMV, human alpha-antitrypsin or chicken beta-actin promoter). This transgene inhibition effect was entirely mediated by IFN-gamma as the transgene expression was fully recovered in IFN-gamma knockout mice.
  
  
  CONCLUSIONS
  Systemic IL-12 therapy, with either a protein or gene therapy approach, resulted in comparable liver and systemic toxicities. Refractoriness of mIL-12 production by subsequent administration of mIL-12 gene was observed. The transgene attenuation effect of IL-12 pre-dosing (either by IL-12 or rmIL-12), mediated by IFN-gamma, provided important insights for the design of IL-12 combination gene therapy and the improvement of gene vectors for IL-12 therapy. The present results show that simple injection of naked DNA could serve as a good model for in vivo evaluation of the toxicity of a candidate therapeutic gene.
authors.affiliation: Center for Pharmacogenetics, School of Pharmacy, University of Pittsburgh, PA 15213, USA.
authors.forename: V W
authors.initials: VW
authors.lastname: Lui
authors.forename: L D
authors.initials: LD
authors.lastname: Falo
authors.forename: L
authors.initials: L
authors.lastname: Huang
mesh_terms: D000818:Animals; D003587:Cytomegalovirus / Q000235:genetics; D006400:Hematocrit; D018664:Interleukin-12 / Q000235:genetics* / Q000633:toxicity; D007962:Leukocytes / Q000187:drug effects; D008099:Liver / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology*; D008111:Liver Function Tests; D051379:Mice; D008822:Mice, Transgenic; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000633:toxicity; D000515:alpha 1-Antitrypsin / Q000235:genetics
chemical_list: D011993:Recombinant Fusion Proteins; D000515:alpha 1-Antitrypsin; D018664:Interleukin-12