Impact of human neutralizing antibodies on antitumor efficacy of an oncolytic adenovirus in a murine model.

PURPOSE: The purpose of this study was to assess the impact of anti-adenovirus neutralizing antibodies (AdNAbs) on the distribution, tolerability, and efficacy of intravenously administered oncolytic adenovirus. A translational model was developed to evaluate the impact of humoral immunity on intravenous administration of oncolytic adenovirus in humans. EXPERIMENTAL DESIGN: Initially, severe combined immunodeficient (SCID)/beige mice were passively immunized with various amounts of human sera to establish a condition of preexisting humoral immunity similar to humans. A replication-deficient adenovirus encoding beta-galactosidase (rAd-betagal) was injected intravenously into these mice. An AdNAb titer that mitigated galactosidase transgene expression was determined. A xenograft tumor-bearing nude mouse model was developed to assess how a similar in vivo titer would impact the activity of 01/PEME, an oncolytic adenovirus, after intravenous administration. RESULTS: In SCID/beige mice, there was a dose dependence between AdNAbs and galactosidase transgene expression; 90% of transgene expression was inhibited when the titer was 80. A similar titer reconstituted in the nude mice with human serum, as was done in the SCID/beige mice, did not abrogate the antitumor efficacy of the replicating adenovirus after intravenous administration. Viral DNA increased in tumors over time. CONCLUSIONS: In intravenous administration, preexisting AdNAb titer of 80 significantly attenuated the activity of a 2.5 x 10(12) particles per kilogram dose of nonreplicating adenovirus; the same titer had no affect on the activity of an equivalent dose of replicating adenovirus. Our results suggest that a majority of patients with preexisting adenovirus immunity would be candidates for intravenous administration of oncolytic adenovirus.

Pharmacologic indicators of antitumor efficacy for oncolytic virotherapy.

Central to the development of oncolytic virotherapies for cancer will be a better understanding of the parameters that influence the outcome of virotherapy to treat disseminated cancer by i.v. administration versus regional disease by local treatment. Intratumoral administration of 01/PEME, an oncolytic adenovirus, required approximately 1000-fold less dose than i.v. administration to induce similar tumor growth inhibition. Despite the short (<10 min) circulating half-life of the virus DNA, we could monitor virus distribution to the tumor site and observed virus replication by >1000-fold increase in virus DNA copies over time. There were doses of 01/PEME for which the virus DNA concentration in the tumor increased over time but did not result in antitumor efficacy. Oncolytic virus replication at a tumor site may not be a relevant indication of antitumor efficacy. Efficient distribution to the tumor site may be one of the most critical parameters for antitumor efficacy with oncolytic virotherapy.

Tumor growth inhibition by interferon-alpha using PEGylated protein or adenovirus gene transfer with constitutive or regulated expression.

Inducible synthesis and secretion of therapeutic proteins following gene transfer could be a viable strategy to deliver biopharmaceuticals that currently require parenteral administration. Evaluating the protein pharmacokinetics and biological responses generated by different delivery modalities will provide a better understanding of the advantages and disadvantages of each strategy. The interferon-alpha (IFN-alpha) family of proteins, used clinically for infectious and malignant diseases, has a short half-life, and IFN-alpha therapy requires frequent administration of the drug by injection. Subcutaneous xenograft tumors were inhibited by weekly administration of polyethylene glycol modified (PEGylated) IFN-alpha protein or by a single administration of an adenovirus constitutively expressing IFN-alpha (IACB). Both treatment modalities inhibited tumor growth in a dose-dependent manner, suggesting that increasing exposure to IFN-alpha could result in effective tumor control. A single adenovirus that encodes the components necessary for tetracycline induction (IADR) expressed IFN-alpha in a ligand-dependent manner. Adding doxycycline to the drinking water of mice treated intravenously with the inducible adenovirus IADR inhibited tumor growth by 85% compared with mice that were not given doxycycline. The correlation between serum IFN-alpha concentration and the degree of tumor growth inhibition did not depend on the delivery technology used. It is likely that it will be feasible to control expression of IFN-alpha by oral administration of small molecule drugs after gene delivery to induce therapeutic concentrations of proteins.