RECOMBINANT E1-DELETED ADENOVIRUS-MEDIATED GENE-THERAPY FOR CANCER - EFFICACY STUDIES WITH P53 TUMOR-SUPPRESSOR GENE AND LIVER HISTOLOGY INTUMOR XENOGRAFT MODELS

Type 5 adenoviral (Ad) vectors have been the ''vector-of-choice'' for preclinical studies on p53 tumor suppressor gene therapy of cancer. Pr evious studies have examined the in vivo efficacy of p53 Ad when given intratumorally. However published information does little to guide cl inicians in the design of intraperitoneal (i.p.) dosing trials for i.p . tumors, e.g., ovarian, or clinical trials using regional organ perfu sion, e.g., for lung tumors. Therefore, we examined several parameters with special significance for these routes of administration. Lung me tastases from p53(mut) MDA-MB-231 mammary xenografts were treated with therapeutic levels of intravenous buffer, beta-galactosidase (beta-Ga l) Ad, or p53 Ad. Treatment with intravenous p53 Ad significantly redu ced the number of metastases per lung and there was a dramatic reducti on in the surface area occupied by these tumors as compared to control groups. Two types of i.p. tumor xenografts were used for preclinical modeling of i.p. gene therapy, the p53(null) SK-OV-3 ovarian and the p 53(mut) DU-145 prostate human cancers. In a study examining the effect of different vehicle volumes on the efficacy of a constant drug dose, all mice treated with p53 Ad had reduced tumor burden compared to con trols. Dosing volumes between 0.2 and 1 mi were equally effective and all were more effective than a dosing volume of 0.1 mi. However, reduc ed efficacy was observed when a volume of 1.5 mi was used. When the ef fect of dosing frequency on antitumor efficacy was examined, fractiona ted doses of p53 Ad had somewhat greater efficacy than fewer, bolus in jections. One of the significant elements in the emerging toxicology a ssociated with recombinant adenoviruses is the hepatocyte pathology ca used by high systemic concentrations of adenovirus. For recombinant Ad used in this study, there was a pronounced dose-dependence for the li ver response, with very high, repeated doses causing significant hepat ocellular insult. Expression of cytoplasmic beta-Gal protein coincided with areas of greatest damage in mice treated with high doses of beta -Gal Ad. Ultrastructural examination of hepatocyte intranuclear inclus ions revealed moderately electron-dense, tightly packed granular mater ial interspersed with more electron-dense nuclear material. Human tumo r xenografts, but not mouse tissues, expressed viral hexon protein. In summary, hepatic toxicity caused by high concentrations of recombinan t adenovirus was observed in murine cancer models. However, therapeuti c levels of p53 Ad could be achieved which had dramatic efficacy witho ut significant pathology.