A NOVEL MULTIPLY-MUTATED HSV-1 STRAIN FOR THE TREATMENT OF HUMAN BRAIN-TUMORS

A promising approach for the therapeutic treatment of brain tumors uti lizes replication-competent, neuroattenuated herpes simplex virus-1 (H SV-1) mutants. This approach requires mutation of HSV-1 to eliminate k illing of normal, nondividing cells of the brain (e.g., neurons). We h ave generated a HSV-1 double-mutant, designated 3616UB, by interruptin g the uracil DNA glycosylase (UNG) gene in a previously studied ICP34. 5 mutant, R3616. The HSV-1-encoded UNG gene is required for efficient HSV-1 replication in nondividing cells, but is dispensable for replica tion in rapidly dividing cells. The specific function of the HSV-1 ICP 34.5 gene is not completely clear, but it is thought to be necessary f or viral replication in cells of the nervous system, because, when mut ated, the resultant viral strains are fully neuroattenuated. Strain 36 16UB did not replicate in primary neuronal cultures in vitro or in mou se brain, but efficiently killed six of six human tumor cell lines wit hin 6 days in vitro and successfully infected and replicated within br ain tumor xenografts. The potential safety of 3616UB for human use is enhanced by an unexpected hypersensitivity to the antiherpetic drug ga nciclovir. These data suggest that 3616UB may be effective for the tre atment of human brain tumors. Intratumoral injection of 3616UB into hu man medulloblastoma or angiosarcoma xenografts established in severe c ombined immunodeficient (SCID) mice produced significant growth arrest and some tumor regressions. Strain 3616UB was as effective as R3616 i n this therapy study and did not cause any obvious distress in the tre ated animals. Together, the data show that 3616UB is a very safe alter native to other HSV-1 mutants because the presence of two mutations re duces the possibility of recombinational events in situ that could lea d to the generation of virulent viral progeny during 3616UB therapy.