IDDF2023-ABS-0163 Targeting against highly plastic macrophages within tumor microenvironment reveals combinational targets at tumor transitions in mouse colorectal liver metastases

Background

The liver is the most common metastatic site for colorectal cancer (CRC); patients with liver metastases had significantly poor survival. Macrophages within the tumor microenvironment play indispensable roles in immune suppression, angiogenesis, metabolism, etc. In this study, by targeting at Kupffer cells- and/or monocytes- derived Tumor-associated macrophages (TAM), we aim to elucidate TAM function, transformation, and interaction with key tumor growth activities, and find optimal therapeutic strategies in a mouse colorectal liver metastasis (CRLM) model.

Methods

C57BL/6 mouse CRLM was established by splenic injection of MC38 CRC cells and separated into several phases including tumor initiation, local expansion/angiogenesis, medium- and high-volume metastases. Bulk and single-cell RNA sequencing was applied on varied CRLM-samples and cells. Data with Flow cytometry, immunohistochemistry, and in vitro co-culture experiments confirm the RNA-seq data analysis by varied bioinformatics methods. Clec4f-iDTR and LyZ2-iDTR mice were used to target the depletion of Kupffer cells or monocytes during CRLM. The HDAC inhibitor TMP195 or Clodronate liposomes were used to deplete macrophages or divert macrophage polarization in vivo.

Results

TAM is the most abundant immune cell, transformed from bone marrow-derived monocytes and Kupffer cells; Within medium tumors, T cells showed exhausted markers and interacted with TAMs. Targeted depletion of either Kupffer cells or monocytes did not affect tumor growth but changed the accumulation of T cells. Depletion of macrophages by liposomes or TMP195 treatment from the tumor transition of angiogenesis significantly distorted tumor vessels and resulted in greatly decreased tumor burdens. Liver lipid metabolism, glucosamine anabolism and glycogen catabolism, and nucleotide metabolism were active in order across tumor initiation, medium and high tumor stages, where TAM metabolic patterns overlapped with the latter two stages.

Conclusions

The combination therapies with targeting agents against TAM and anti-metabolic, anti-angiogenesis, or immune checkpoint inhibitors may achieve significant therapeutic efficacy in CRLM.