# M2-type tumor-associated macrophages promote invasion of canine breast cancer through ADAM9 upregulation

## TL;DR

This study shows that M2-type tumor-associated macrophages promote canine breast cancer invasion by increasing ADAM9 levels, which could be a new target for treatment.

## Contribution

The study identifies ADAM9 as a novel effector of TAM-driven tumor invasion across species.

## Key findings

- ADAM9 is enriched in M2-polarized TAMs and enhances tumor migration and invasion.
- ADAM9 knockdown reduces ECM degradation and F-actin remodeling in tumor cells.
- CSC-conditioned medium increases ADAM9 expression, linking it to macrophage crosstalk.

## Abstract

Tumor-associated macrophages (TAMs) represent the most abundant immune cell population within the tumor microenvironment and play a critical role in cancer progression. However, the molecular mediators underlying TAM-driven tumor invasion remain incompletely defined. This study investigated whether ADAM9 functions as a key effector of pro-invasive TAM polarization using a canine mammary tumor model integrated with human transcriptomic datasets.

Transcriptomic analyses were performed using canine and publicly available human datasets. Single-cell RNA sequencing was used to determine cellular localization of ADAM9. IL-4–induced M2 macrophages were evaluated for ADAM9 expression, tumor migration and invasion capacity, extracellular matrix (ECM) degradation, cytoskeletal remodeling, and spheroid destabilization. ADAM9 knockdown and cancer stem cell (CSC)–conditioned medium experiments were conducted to assess mechanistic involvement.

ADAM9 was consistently enriched in M2-polarized TAMs across species and was confirmed to be expressed in TAM populations by single-cell RNA sequencing. IL-4–induced M2 macrophages upregulated ADAM9 and significantly enhanced tumor migration and invasion. ADAM9 knockdown attenuated ECM degradation, reduced MMP9 expression, and disrupted F-actin remodeling. CSC-conditioned medium further induced ADAM9 expression, suggesting its role as a convergent mediator of CSC–macrophage crosstalk. In spheroid models, ADAM9 depletion prevented TAM-mediated spheroid destabilization and suppressed collective invasion.

These findings identify ADAM9 as a key effector of TAM-driven tumor invasion through ECM remodeling and cytoskeletal regulation, and highlight ADAM9 as a promising therapeutic target within the tumor immune microenvironment.