Thesis Format

Integrated Article

PU.1 Inhibition Appears to Restrain Murine Melanoma Growth by Promoting the CXCL9/10/11 - CXCR3 Network in Tumor-Associated Macrophages

Author

Nichita Sleapnicov, Western UniversityFollow

Degree

Master of Science

Program

Microbiology and Immunology

Supervisor

Kim, Sung Ouk

Abstract

The tumor microenvironment is essential in tumor growth/development. Tumor-associated-macrophages (TAMs) are often the most abundant immune cells in the microenvironment with a predominantly immunosuppressive phenotype, assisting tumor growth. Due to this, TAMs are an ideal immunotherapy target, but TAM-selective reagents are still to be discovered. Here, I used a small molecule inhibitor which likely blocks PU.1 (critical macrophage transcription factor) binding, modulating TAM activity in murine melanoma. PU.1 inhibitor DB2313 restrained syngeneic mouse tumor growth, increased natural killer cell and T-cell recruitment/tumor cell-specific T-cell infiltration, along with cytotoxic markers in tumors. Depleting TAMs blocked this recruitment. PU.1 inhibition increased mRNA expression of chemokines CXCL9/CXCL10 in TAMs. Blocking CXCL9 and its receptor CXCR3 seemed to silence the effect of PU.1 inhibition on tumor growth and T-cell/natural killer cell recruitment, suggesting the anti-tumor effect of PU.1 inhibition is dependent on the CXCL9/10/11-CXCR3 network. This study evaluates and explores a novel immunotherapy’s mechanism.

Summary for Lay Audience

Within solid tumors, the tumor microenvironment consists of tumor cells, extracellular components, and immune cells. Macrophages are immune cells that act to uptake damaged cell parts, microorganisms, and debris. They can also release signaling molecules for other cells upon stimulation. In tumors, they are known as tumor-associated macrophages and serve a pro-tumor role by the release of signaling molecules, creating a microenvironment suited for tumor growth. A crucial part of macrophage development is the transcription factor PU.1. Transcription factors are nuclear proteins that can enhance or reduce gene expression in cells, and PU.1 is most important in the life cycle of macrophages. In this study, I interfered with PU.1 activity using a small molecule inhibitor in mice to modulate tumor-associated macrophage activity, evaluating and examining the effect this has on melanoma tumors. PU.1 inhibition reduced tumor growth and brought more immune cells which are responsible for tumor cell destruction, T cells and Natural Killer cells, to the tumor sites. When tumor-associated macrophages were depleted, PU.1 inhibition had no effect on tumor growth and immune recruitment. In these macrophages, inhibiting PU.1 increased the expression of CXCL9 and CXCL10 genes. These genes encode for two proteins which share a receptor, CXCR3, and function as homing signals for immune effector cells to the site where they were secreted. Blocking CXCL9 and CXCR3 also blocked the anti-tumor and immune recruitment effects of PU.1 inhibition, indicating that they are likely the agents which are driving this effect. This study evaluated the efficacy and examined the mechanism of PU.1 inhibition in murine melanoma.

Recommended Citation

Sleapnicov, Nichita, "PU.1 Inhibition Appears to Restrain Murine Melanoma Growth by Promoting the CXCL9/10/11 - CXCR3 Network in Tumor-Associated Macrophages" (2024). Electronic Thesis and Dissertation Repository. 10639.
https://ir.lib.uwo.ca/etd/10639

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 License.