Engineering and Preclinical Evaluation of Western Reserve Oncolytic Vaccinia Virus Expressing A167Y Mutant Herpes Simplex Virus Thymidine Kinase.

Viral replication of deleted () vaccinia virus (VV) is attenuated in resting normal cells, enabling cancer selectivity, however, replication potency of VV appears to be diminished in cancer cells. Previously, we found that wild-type herpes simplex virus (HSV () disappeared in most of the recombinant VV after multiple screenings, and only a few recombinant VV containing naturally mutated remained stable. In this study, VV of western reserve (WR) VV was replaced by A167Y mutated (), to alter nucleoside selectivity from broad spectrum to purine exclusive selectivity. WOTS-418 remained stable after numerous passages. WOTS-418 replication was significantly attenuated in normal cells, but cytotoxicity was almost similar to that of wild type WR VV in cancer cells. WOTS-418 showed no lethality following a 5 × 10 PFU intranasal injection, contrasting WR VV, which showed 100% lethality at 1 × 10 PFU. Additionally, ganciclovir (GCV) but not BvdU inhibited WOTS-418 replication, confirming specificity to purine nucleoside analogs. The potency of WOTS-418 replication inhibition by GCV was > 10-fold higher than that of our previous truncated recombinant OTS-412. Overall, WOTS-418 demonstrated robust oncolytic efficacy and pharmacological safety which may delegate it as a candidate for future clinical use in OV therapy.