The human adenovirus E1B gene encodes a 55-kilodalton protein that inactivates the cellular tumor suppressor protein p53. Here it is shown that a mutant adenovirus that does not express this viral protein can replicate in and lyse p53-deficient human tumor cells but not cells with functional p53. Ectopic expression of the 55-kilodalton EIB protein in the latter cells rendered them sensitive to infection with the mutant virus. Injection of the mutant virus into p53-deficient human cervical carcinomas grown in nude mice caused a significant reduction in tumor size and caused complete regression of 60 percent of the tumors. These data raise the possibility that mutant adenoviruses can be used to treat certain human tumors.

The 55-kilodalton (kDa) protein from the E1B-region of adenovirus binds to and inactivates the p53 gene, which is mutated in half of human cancers. We have previously shown that the replication and cytopathogenicity of an E1B, 55-kDa gene-attenuated adenovirus, ONYX-015, is blocked by functional p53 in RKO and U20S carcinoma lines. We now report that normal human cells were highly resistant to ONYX-015-mediated, replication-dependent cytolysis. In contrast, a wide range of human tumor cells, including numerous carcinoma lines with either mutant or normal p53 gene sequences (exons 5-9), were efficiently destroyed. Antitumoral efficacy was documented following intratumoral or intravenous administration of ONYX-015 to nude mouse-human tumor xenografts; efficacy with ONYX-015 plus chemotherapy (cisplatin, 5-fluorouracil) was significantly greater than with either agent alone.

Replication-selective oncolytic viruses constitute a rapidly evolving and new treatment platform for cancer. Gene-deleted viruses have been engineered for tumor selectivity, but these gene deletions also reduce the anti-cancer potency of the viruses. We have identified an E1A mutant adenovirus, dl922-947, that replicates in and lyses a broad range of cancer cells with abnormalities in cell-cycle checkpoints. This mutant demonstrated reduced S-phase induction and replication in non-proliferating normal cells, and superior in vivo potency relative to other gene-deleted adenoviruses. In some cancers, its potency was superior to even wild-type adenovirus. Intravenous administration reduced the incidence of metastases in a breast tumor xenograft model. dl922-947 holds promise as a potent, replication-selective virus for the local and systemic treatment of cancer.

ONYX-015 is an E1B-deleted adenovirus that replicates in and causes lysis of p53-deficient cancer cells selectively. To study the efficiency of intratumoral (i.t.) spread by ONYX-015, we infected specific fractions of tumor cells (two p53-deficient tumor lines and one p53 functional line) in vitro before subcutaneous inoculation into nude mice. Infection of as few as 5% of p53 Ϫ tumor cells prevented tumor development in all cases; infection of 1% of p53 Ϫ tumor cells resulted in significant growth inhibition but did not prevent tumor formation. In contrast, infection with ONYX-015 had no significant effect on p53 ϩ tumor formation. These data suggested that replication-dependent tumor cell lysis and spread was occurring, but that tumor destruction might be improved by increasing i.t. virus distribution. Two treatment parameters were then varied to determine whether virus distribution, and consequently efficacy, could be improved. Divided i.t. injections of virus were more efficacious than a single injection of the same total dose. Likewise, increasing the volume of the viral suspension for i.t. injection allowed better distribution within the tumor mass and increased efficacy. These results have implications for the treatment of cancer patients with viral agents.