Background: Oncolytic herpes simplex virus-1 (oHSV-1) vectors are promising new therapeutic agents for cancer. For the nuerovirulence of ICP34.5 protein, the encoding gene named γ34.5 is deleted in all oHSV-1 mutants currently in clinical trials. However, the deletion of γ34.5 also promotes the interferon-induced shutoff of virual protein synthesis, and attenuates the virus replication in cancer cells at the same time. Previous studies reported that the carboxyl-terminus of MyD116/GADD34 was homologous to that of γ34.5 gene; hence, it might substitute for γ34.5 gene to enhance the replication and cytotoxicity of the virus. Objective: To reconstruct a novel oHSV-1 mutant named GD116 by inserting γ34.5-MyD116 chimeric gene into G47Δ genome, and to investigate whether the carboxyl-terminus of murine MyD116 can enhance the antitumour efficacy of GD116 on human breast cancer cell line in vitro and in vivo. Methods: Using G47Δ genome and bacterial artificial chromesome (BAC) as the backbone, the GD116 virus expressing γ34.5-MyD116 was reconstructed via Cre/loxp and FLP/FRT recombinase systems. A GD-empty virus mutant containing only the CMV sequence was also constructed as a control at the same time. Then, the replication and cytotoxicity of these two virus mutants in MDA-MB-231 humanbreast cancer cell line was evaluated in vitro. Meanwhile, the subcutaneous tumor model was also generated by injecting MDA-MB-231 cells into the right flank of BALB/c mice. Then, the antitumor efficacy of GD116 on breast cancer in vivo was evaluated by intratumoral injection. Results: Compared with GD-empty, GD116 possessed an enhanced replication capability and oncolytic efficacy in MDA-MB-231 cell line. On the fifth day after infection with GD116 at MOIs of 0.1 and 0.3, 35.0% and 50.2% of MDA-MB-231 cells were killed respectively, which were higher than that with GD-empty (24.3% and 37.8%). Additionally, GD116 exhibited enhanced antitumor efficacy on subcutaneous tumor xenografts of human breast cancer cells in vivo compared with GD-empty. On day 21 after treatment, the average tumor volume of mice was 585.5 mm3, 289.0 mm3 and 121.9 mm3 in Control, GD-empty and GD116 group respectively. Conclusion: Our findings indicate that the carboxyl-terminus of the murine MyD116 can substitute for the corresponding domain of the γ34.5 gene in oHSV-1 to promote the replication of the virus in infected cancer cells; and the mutant GD116 armed with γ34.5-MyD116 chimaera has enhanced oncolytic effect on MDA-MB-231 breast cancer cells in vitro and in vivo.

Citation Format: Cheng L, Wang J, Liu R. A novel oncolytic herpes simplex virus, GD116, has enhanced antitumour efficacy in human breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-04-01.