Abstract PO3-26-08: Genetic modification of tumor associated macrophages using CRISPR lipid nanoparticle platform altered tumor microenvironment and induced cancer cell elimination

Abstract More than half of patients with stage IV breast cancer will eventually develop liver metastasis. Due to their nature, liver metastases are hard to treat, and the five-year survival rate for stage IV breast cancer is very low (~11%). In the recent years, vital roles macrophages play in cancer progression and immune evasion have become increasingly clear, making them an appealing target for therapeutic intervention. As one of the most abundant cell populations recruited to the tumor microenvironment, tumor-associated macrophages (TAM) are typically immunosuppressive Arg1+ M2-like macrophages, which support cancer growth, metastasis progression, and drug resistance. Numerous studies, including from our laboratory, have shown that reversal of the macrophage phenotype to the classical inflammatory CD80+ M1-like macrophages is very promising for cancer eradication. In this study, we used CRISPR loaded into lipid nanoparticles (CRISPR-LNP) to modulate macrophage polarization in breast cancer metastasis in vivo. We hypothesize that CRISPR-mediated gene editing through lipid nanoparticle (LNP) delivery of CRISPR enzyme and target gRNA (CRISPR-LNP) is a highly effective and safe approach. Using our CRISPR-LNP platform, we screened multiple genes with significant roles in macrophage polarization and found that targeting the RICTOR gene alone enabled reprograming of pro-tumorigenic M2 TAMs to anti-tumorigenic M1 phenotype in vitro and in vivo. We administered the CRISPR-LNP targeting RICTOR (CRISPR-RIC-LNP) on a syngeneic liver metastasis mouse model via intravenous injection. Single dose studies were conducted to determine biodistribution, treatment efficacy, and shift in immune landscape of the tumor after treatment via immunofluorescence staining, Imaging Mass Cytometry, and single cell RNA sequencing. A spatial map was built using digital pathology analysis for investigation of the interactions amongst immune and tumor cells within the tumor immune microenvironment. In 4T1 breast cancer liver metastatic model, we observed that CRISPR-RIC-LNP treatment: (i) accumulated in the liver metastases lesions in vivo 24 hours after injection. ~0.5% of total injected dose, which corresponds to ~75% of fluorescence from the whole body at 24h time point was confined only in the metastatic regions; (ii) led to modest increase of macrophage number, and (iii) significant shift of macrophage phenotype from immunosuppressive, pro-tumorigenic Arg1+, CD206+ macrophages to inflammatory, anti-tumor CD80+ phenotype (from ~5 to ~9% of total cell in the tumor lesions) 24 hours after injection; (iv) reduced the cancer cell number by almost 80%; and (v) dramatically reduced exhausted T-cell and regulatory T-cell population, as determined by single cell RNA sequencing analysis. We plan to validate our preliminary finding with flow cytometry analysis of metastatic lesions, and evalute the efficacy of CRISPR-RIC-LNP as single and in combinatorial therapies in survival studies. These data showed that reprograming macrophages from cancer-supporting to cancer-eliminating phenotype is a promising tool to suppress cancer cell growth and increase the presence of cytotoxic CD8+ T-cells. We propose that this approach can be efficiently used as single therapy or as combination with immune checkpoint inhibitors to obtain synergistic effects and efficiently eradicate cancer cells. We will assess the safety, optimize the accumulation in TME, and devise methods to limit exposure to healthy cells. In the future, we also aim to expand scope of our candidate therapy as therapeutics for other types of breast cancer metastases. Citation Format: Fransisca Leonard, Tyler Galbraith, Nourhan Abdelfattah, Arturas Ziemys, Chihiro Hashimoto, Harlan Cook, Yitian Xu, Shu-Hsia Chen, Roberto Rosato, Kyuson Yun. Genetic modification of tumor associated macrophages using CRISPR lipid nanoparticle platform altered tumor microenvironment and induced cancer cell elimination 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 PO3-26-08.