Abstract 5080: Antibody drug conjugate trastuzumab deruxtecan suppresses leptomeningeal brain metastasis cells and is potentiated by addition of immune check point inhibitor

Abstract Leptomeningeal disease (LMD) is defined by dissemination of metastatic cancer cells into the subarachnoid space with subsequent involvement of the cerebrospinal fluid and leptomeninges. LMD is an aggressive, late-stage development of cancer, which is increasing in prevalence as improved treatments for systemic malignancies are discovered. It leads to significant neurological morbidity and mortality, and outcomes remain poor despite improving cancer treatment strategies. There is a large population of patients with human epidermal growth factor receptor 2 (HER2) expressing cancers, such as breast and lung cancers, who suffer from leptomeningeal metastasis. There has been evolving research looking at antibody drug conjugates for treatment of these primary pathologies, such as Trastuzumab Deruxtecan (TDxd), which shows improved progression free survival and overall survival in those with HER2 expressing primary cancers, as well as in intraparenchymal brain metastasis. However, as of yet there has been no study of its utility in LMD. Additionally, use of immune check point inhibitors (ICI) for treatment of LMD has been studied, showing some efficacy, but less robust response than that in intraparenchymal brain metastasis. Given the significant population of patients who continue to be affected by leptomeningeal metastasis, there is significant need for an improved treatment regimen. We hypothesize that TDxd will have a killing effect on HER2 expressing LMD cells, which can be further potentiated by the addition of ICIs. To test this hypothesis, we developed breast and lung cancer cell lines (SKBrM-LMD, and H2030BrM-LMD) that express HER2 and preferentially metastasize to leptomeningeal space. These cell lines were also labeled with luciferase. We then treated these cell lines with TDxd and found that TDxd had significant growth inhibitory effect on these cells in vitro when compared to the control. Furthermore, we educated human T Cells against the SkBrM-LMD cells and treated these cells with the aforementioned T cells plus the ICI Anti-PD1. Our results showed that ICI had significant killing effect when compared to the control. We have also created an in vivo LMD model by performing intraventricular injection of HER2 expressing tumor cells into a mouse model, which can be used for testing the efficacy of TDxd and ICI by intrathecal injection. In conclusion, our results indicate that TDxd and ICI have significant killing activity against HER2 expressing LMD cells, and therefore intrathecal administration of these drugs is a promising treatment modality that will be demonstrated using a mouse LMD model. Citation Format: Eleanor C. Smith, Shih-Ying Wu, Ravindra P. Deshpande, Abhishek Tyagi, Kounosuke Watabe. Antibody drug conjugate trastuzumab deruxtecan suppresses leptomeningeal brain metastasis cells and is potentiated by addition of immune check point inhibitor abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5080.