Abstract 1594: Lipid-laden macrophages are associated with KRAS therapy resistance in pancreatic cancer

Our recent discovery in pancreatic ductal adenocarcinoma (PDAC) demonstrates that tumor-associated macrophages (TAMs) are pivotal in driving resistance to KRAS-targeted therapy. Using a genetically engineered mouse (GEM) model of PDAC with doxycycline-inducible KRASG12D, pancreas-specific p48-Cre, and conditional p53 knockout (known as "iKPC"), we found that myeloid cell remodeling from a neutrophil-rich to a macrophage-rich phenotype occurred after KRAS depletion. TAMs were sufficient and essential for PDAC cells to bypass KRAS dependency. Consistent with our findings, KRAS inhibition (KRASi) rewired the tumor microenvironment (TME) with increased TAM presence in several cancer models, including those of the pancreas, colon, and lung. However, the exact role of TAMs in promoting or impairing KRASi resistance remains controversial. Considering the heterogeneous, plastic, and multi-functional features of TAMs, we performed single-cell RNA sequencing (scRNA-seq) to compare KRAS on and off tumors from iKPC GEM. We identified two major subclusters of TAMs: Siglecf+ and Apoe+, with only Apoe+ TAMs expressing high levels of Ccr2, indicating their origin from circulating macrophages. Both subclusters express immune regulatory genes, but genes related to cholesterol homeostasis are upregulated in Apoe+ TAMs compared to other cell types. Notably, lipid metabolism regulatory gene signatures are significantly enriched in TAMs from KRAS off tumors versus KRAS on tumors. Specifically, we observed upregulation of genes encoding scavenger receptors, lysosome enzymes, lipid binding proteins, galectins, and complement factors in TAMs from KRAS off tumors versus KRAS on tumors, resembling the characteristics of lipid-laden macrophages. Lipidomic profiling comparing tumor-educated macrophages (TEMs) exposed to conditional media from KRASi pre-treated KPC (p48-Cre, p53Lox/+, LSL-KRASG12D) PDAC cells (KRASi CM) and DMSO control (DMSO CM) revealed that the most significantly increased lipids were phospholipids, very long chain fatty acids, and ultra-long chain fatty acids. After examination of the expression of rate-limiting enzymes and key receptors involved in fatty acid synthesis, breakdown, and transportation, we found that Elovl1 and Abcd1 were significantly upregulated in TEMs exposed to KRASi CM compared to those exposed to DMSO control CM. Consistently, lipid content was higher in KRASi CM-treated TEMs compared to controls, as shown by BODIPY staining. Additionally, we observed an increased number of peroxisomes in KRASi CM-treated TEMs compared to control TEMs. These data collectively indicate that macrophages associated with KRASi-treated tumors exhibit aberrant accumulation of fatty acids. Citation Format: Pingping Hou, Ting-yu Chu, Yuemeng Huang, Daiyong Deng, Habeebunnisa Begum. Lipid-laden macrophages are associated with KRAS therapy resistance in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1594.