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Correlation between immune modulation of macrophage recruitment and new blood vessel formation in a subcutaneous murine mouse model of colorectal cancer

Shelby N. Bess, Timothy J Muldoon

University of Arkansas, Fayetteville, AR 72701

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Background

  • Colorectal cancer is the fourth most common cancer in the United States
    • > 500,000 deaths annually

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  • Standard treatment: 5-fluorouracil (5-FU) based chemotherapy
    • Disadvantage: tumors become resistant to treatment

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Immunotherapy

  • Modulation of the immune system has become an emerging strategy in overcoming treatment resistance and recurrence rates
  • Types
    • Adoptive cell transfer (ACT) therapy
    • Cancer vaccines
    • Monoclonal antibody therapy: Immune checkpoint inhibitors or cytokine therapy

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CCL2

  • CCL2: monocyte chemoattractant protein-1
    • Cytokine that recruits circulating monocytes to the tumor microenvironment
    • Monocytes differentiate into tumor-associated macrophages (TAMs), which promote immunosuppression, tumor growth and angiogenesis

anti-CCL2 has been linked to reduced tumor burden and recurrence risk in various cancers (i.e., breast and prostate). However, it has not been studied in CRC.

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Research Question

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How does anti-CCL2 immunotherapy affect tumor associated macrophage recruitment and new blood vessel formation when combined with 5-FU chemotherapy?

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Mouse Model

  • Nine-week-old Balb/c mice (n=13)
    • CT26 cell injection (SQ) into left flank
    • When tumors reached 75mm3, mice were divided into five treatment groups:
      • Control
      • Isotype control
      • anti-CCL2
      • 5-FU
      • Combination (anti-CCL2 + 5-FU)

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Treatment Timeline

  • Dosing:
    • anti-CCL2 (5.0 mg/kg/dose)
    • 5-FU (15 mg/kg/dose)

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Tumor Associated Macrophages

**** p < 0.0001

*** p = 0.0001

The addition of anti-CCL2 to 5-FU has shown a significant reduction in TAMs over time.

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Blood Vessel Formation

The addition of anti-CCL2 to 5-FU has shown a reduction in new blood vessel formation.

** p = 0.001

 

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Correlations between TAMs and vessel formation

There is a slightly positive correlation between the number of TAMs and the density of blood vessels.

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Conclusions

  • The blockade of CCL2 in combination with a 5-FU based chemotherapy
    • Reduced the area of new blood vessel formation
    • Decreased the number of TAMs being recruited into the tumor microenvironment

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  • There is a small correlation between the number of TAMs being recruited into the tumor microenvironment and the density of blood vessels within a tumor

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Acknowledgements

  • Translational Biophotonics and Imaging Laboratory
    • Current Members
      • Timothy Muldoon, M.D., Ph.D.
      • Ariel Mundo
      • Kathryn Priest
    • Lab Alumni
      • Gage Greening, Ph.D.
  • Narasimhan Rajaram, Ph.D.
  • University of Arkansas

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