Abstract 5371: Repurposing erbb2 (HER2/neu) as a neoantigen target for neu-negative tumors using a novel erbb2-encoding lentivirus

Abstract

Abstract INTRODUCTION: HER2/neu is a potent biomarker for which anti-HER2/neu antibodies offer significant responses. However, many cancers, such as melanoma, have less than 5% expression of HER2/neu. The purpose of this study was to determine whether induced expression of erbb2 (mouse HER2/neu analogue) could function as a neoantigen target for anti-erbb2 antibody. METHODS: RT-PCR was used to construct a rat erbb2-encoding vector using the live, non-replicating lentivirus pLenti6.3. erbb2-encoding pLenti6.3 was transfected in vitro into the B16 mouse melanoma cell line, which has less than 5% endogenous expression of erbb2. The generated erbb2+ B16 cell line was designated B16/neu. Anti-erbb2 antibody (7.16.4) was used to treat C57Bl/6 male and female mice bearing B16/neu (200 ug intraperitoneally three times per week for 3 weeks). To confirm activity of 7.16.4, this antibody (100 ug per T75 flask) was co-cultured with B16/neu in vitro, and cell growth/confluence was measured. RESULTS: The novel B16/neu cell line expressed approximately 50% erbb2 in vitro on flow cytometry analysis, compared to 2% errb2 expression in naïve B16. Erbb2/neu expression was confirmed on fluorescent Western blot. Anti-erbb2 antibody (7.16.4) slowed the growth of B16/neu in vitro, confirming the suppressive effects of 7.16.4. In B16/neu-bearing mice, 7.16.4 resulted in effective control of tumor growth and a complete tumor response rate of 35.7%, (5/14 mice) compared to placebo controls (p < 0.01). Interestingly, B16/neu tumors demonstrated slower growth kinetics compared to naïve B16 tumors (p = 0.013), suggesting immune recognition of erbb2 in naïve C57Bl/6 mice as a neoantigen target. No adverse reactions were observed with 7.16.4. In vivo inoculation of erbb2-encoding pLenti6.3 in naïve B16 tumors and treatment of in vivo transfected B16/neu tumors with 7.16.4 comprise ongoing experiments. CONCLUSIONS: erbb2 expression on B16 melanoma was successfully achieved using a novel erbb2-encoding lentivirus. Induced erbb2 served as a neoantigen target for anti-erbb2 antibody. This preclinical study provides translational evidence that induced HER2/neu expression may be utilized to repurpose anti-HER2 antibodies for human malignancies that do not normally express high levels of HER2/neu. Citation Format: Emmanuel M. Gabriel, Brian Necela, Deborah Bahr, Jamie Kaplan, Kristopher Attwood, Keith Knutson. Repurposing erbb2 (HER2/neu) as a neoantigen target for neu-negative tumors using a novel erbb2-encoding lentivirus [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5371.