Abstract 2705: Hyaluronic acid impairs NK killing towards breast tumor spheroids despite elevated cytotoxicity

Abstract The tumor microenvironment (TME) is often regarded as a critical component in tumor progression and metastasis. Among the main structural components of the TME, such as collagen and glycosaminoglycans (GAGs), hyaluronic acid (HA) is highly elevated in the breast TME, and is associated with poor prognosis. In recent years, immunotherapy has gained tremendous success in the battle against hematological cancers. Yet, solid tumors have remained a significant clinical challenge for immunotherapy due to the physical constraints they impose on immune cells. Mechanically, our previous work has shown that the abundance of high molecular weight (HMW) HA significantly reduces matrix pore sizes and softens the collagen and HA cogel, and impairs breast tumor invasion. However, it is still unclear how modulating tumor invasion through the mechanics of the TME may correlate with the efficacy of immunotherapy. In this study, we aim to investigate the effect of HMW HA on natural killer (NK) cell-based immunotherapy using a tumor spheroid model (GFP-labeled MCF-7). We introduced NK-92 MI cells into tumor spheroid embedded collagen gels with or without HA, and followed spheroid-NK cell interactions through live cell imaging. Preliminary data shows that while tumor spheroids were still able to invade in the collagen only gel, they underwent apoptosis in the presence of NK cells. More importantly, the presence of HA within the ECM reduced NK cells’ ability to kill tumor spheroids. Specifically, when surrounded by NK cells, tumor spheroids remained intact and viable in the collagen-HA cogel, while they underwent apoptosis in collagen only gels. In a parallel experiment, multicolor flow cytometry data showed that HA increased NK activation and certain cytotoxic markers (interferon-gamma, perforin, and granzyme-B), despite the fact that spheroids appeared to be more resistant towards NK cells in the presence of HA. Taken together, we speculate that the presence of HMW HA in the TME may protect solid tumors from immune attacks by modulating the mechanical environment. Citation Format: Brian C. Cheung, Alan T. Li, Jeffrey E. Segall, Mingming Wu. Hyaluronic acid impairs NK killing towards breast tumor spheroids despite elevated cytotoxicity 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 2705.