Abstract PO3-25-05: Eribulin Induces Chromosomal Instability and Enhances cGAS Expression in the Nucleus of Triple-Negative Breast Cancer
Authors: Yamada Hideyuki , Takada Mamoru , Suzuki Aussie , Muhan Yu , Nagashima Takeshi , Fujimoto Hiroshi , Sakakibara Junta , Kasuya Masaharu , Kawate Takahiko , Miura Daishu , Suzuki Masato , Miyashita Masaru , Narui Kazutaka , Hasegawa Yoshie , Ishikawa Takashi , Otsuka Masayuki 
Published: May 2024

Abstract
Background: Eribuliln (ERI), a microtubule polymelization, is approved for locally advanced or metastatic breast cancer. However, its effects on drug-naive cancers are not well understood. In EMBRACE trial, ERI improves overall survival (OS) of the patients with metastatic breast cancer. This result might suggest that ERI could be involved in the immune system. In particular, there are a few reports on the effects of ERI on the innate immune system. This study aimed to investigate how ERI influences the innate immune system, focusing on the cyclic-GMP-AMP synthase (cGAS), a DNA sensor that triggers the production of type-I interferons. Methods: Clinical samples from the JONIE-3 trial were analyzed using immunohistochemistry (IHC). 121 patients were assigned to 2 different neoadjuvant chemotherapy (NAC) groups receive ERI (Group E) or paclitaxel (Group P) followed by FEC. The patients of both groups were performed biopsy before and after chemotherapy. We performed IHC on 56 samples and examined for association with pathological complete response (pCR), which was defined as no invasive redidual tumor tissue in the breast.
Additionally, 5 different cell lines were established to evaluate the acute and chronic effects of ERI treatment.
The cell lines were as follows: no treatment (control), PTX for short time (PTX short), PTX for long time (PTX long), ERI for short time (ERI short) and ERI for long time (ERI long).
We evaluated the acute effects of short-term dosing, while the chronic effects of long-term dosing, which mimic resistance to treatment. Protein expression of the cGAS-STING pathway was examined, along with cGAS and IFNβ expression levels and their impact on cell division in the above cell lines. Then at the cellular level, each cell lines were evaluated for differences in cGAS and IFNβ expression and their effects on cell division. The differences in cGAS expression between cytoplasmic and nuclear fractions were verified by the cell fractuation assay. In addition, mitotic abnormalities and cell proliferation were also assessed. Results: In the clinical trial, ERI did not significantly differ from paclitaxel in terms of pathological complete response (pCR). However, high cGAS expression in Group E (ERI) correlated with increased pCR rates, while no such correlation was observed in Group P (PTX) (Figure). Additionally, High IFNβ expression in Group E also correlated with increased pCR rates, differed from Group P. In vitro, ERI upregulated cGAS, STING, pIRF3, and IFNβ protein expression compared to PTX. Notably, ERI induced elevated cGAS expression in the nucleus, as confirmed by immunofluorescence and cell fracturation assays. Additionally, PTX and ERI differed in their ability to cause mitotic abnormalities. PTX induced more micronuclei cells than ERI, on the other hand ERI induced more micronuclei cells and mitotic slippage. These results were also verified by live cell imaging. Finally, the knockdown of cGAS resulted in accelerated cell proliferation. Conclusion: ERI promoted chromosomal instability, leading to increased cGAS expression, particularly in the nucleus. These findings contribute to our understanding of ERI's effects on the innate immune response in triple-negative breast cancer, potentially paving the way for improved therapeutic strategies.
The differences in intensity scores between GroupP and GroupE in the immunostaining of cGAS

High cGAS expression in Group E correlated with increased pCR rates (p=0.0375), while no such correlation was observed in Group P (p=0.2983).
Citation Format: Hideyuki Yamada, Mamoru Takada, Aussie Suzuki, Yu Muhan, Takeshi Nagashima, Hiroshi Fujimoto, Junta Sakakibara, Masaharu Kasuya, Takahiko Kawate, Daishu Miura, Masato Suzuki, Masaru Miyashita, Kazutaka Narui, Yoshie Hasegawa, Takashi Ishikawa, Masayuki Otsuka. Eribulin Induces Chromosomal Instability and Enhances cGAS Expression in the Nucleus of Triple-Negative Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-25-05.