Abstract P2-20-04: Vaccination against HIF1α/c-MET peptides overcome lapatinib resistance and inhibits tumor growth by immunomodulating in HER2 positive breast cancer

Abstract

Abstract Human Epidermal growth factor Receptor 2 (HER2) is overexpressed in 20% to 30% of breast cancers and is associated with poor prognosis. Patients with advanced HER2-type breast cancer are treated with HER2-directed tyrosine kinase inhibitors as well as antibodies, but many patients finally acquire therapeutic resistance. Therefore, it is important to develop new treatment strategies that circumvent HER2 positive resistant breast cancer. Among the suggested mechanisms of resistance to HER2-targeted therapeutics, tumor hypoxia and relevant biological factors are known as important players. In this study, we aimed to explore the role of tumor hypoxia in the development of resistance to HER2-targeted therapeutics, and whether the role of an immunological therapy targeting this could contribute to overcoming resistance. To this end, we established lapatinib-resistant HER2 positive breast cancer cells in vitro (SKBR3, BT-474 for human and MMC for murine cells). First, we examined if lapatinib-sensitivity is different according to oxygen concentration using lapatinib-resistant cell lines (LR-SKBT3, LR-BT-474, LR-MMC) compared with parent cell lines. Resistant cells were resistant both in normoxic and hypoxic conditions, but parent cells were highly sensitive in both of the oxygen concentration. In the Western blot analysis, HIF1α and c-MET were overexpressed in the resistant cells compared with parent cell lines in both normoxic and hypoxic condition. Interestingly, treatment with lapatinib had reduced HIF1α and c-MET expression at normoxia in parent cell lines but not in resistant cell lines. Under the hypoxic conditions, the difference in expression of HIF1α and c-MET was more pronounced between parent cell lines and resistant cell lines treated with lapatinib. These results indicate that the expression of HIF1α and c-MET was involved in lapatinib-resistant. In a previous study, we have identified epitopes from HIF1α/c-MET and demonstrated effect of delayed bone metastasis in triple negative breast cancer model when used as peptide vaccine. Herein, we evaluated whether the immunization using HIF1α/c-MET peptide vaccine is effective in inhibition of lapatinib-resistant HER2 positive breast cancer growth in vivo. MMTVneu-transgenic mouse model was used and 6- 8 weeks old mice were injected with LR-MMC subcutaneously. Immunization using the HIF1α/c-MET peptide vaccine significantly inhibited growth of LR-MMC cells in MMTVneu-transgenic mice compared with controls. HIF1α/c-MET specific IFN-γ-secreting T cell responses in the splenocytes were significantly higher in the immunized group than controls. Immunohistochemical staining of T cells revealed that expression of tumor HIF1α and c-MET was significantly decreased, while the number of CD8+ T cell was increased in the tumors from immunized animals compared with control tumors. In conclusion, our study demonstrated that the vaccine targeting HIF1α/c-MET might be a promising cancer immunotherapy in lapatinib-resistant HER2 positive breast cancer. In vivo study to evaluate efficacy of combination therapy (lapatinib and HIF1α/c-MET vaccine) is ongoing. Citation Format: Ji Min Lee, Jin Hwa Hong, Soon Young Lim, Ju Won Kim, Ah Reum Lim, Myung Han Hyun, Kyong Hwa Park. Vaccination against HIF1α/c-MET peptides overcome lapatinib resistance and inhibits tumor growth by immunomodulating in HER2 positive breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-20-04.