COX-2 Inhibitors Decrease Expression of PD-L1 in Colon Tumors and Increase the Influx of Type I Tumor-infiltrating Lymphocytes

Cancer Prev Res (Phila). 2022 Apr 1;15(4):225-231. doi: 10.1158/1940-6207.CAPR-21-0227.


Colon cancer is initiated under inflammatory conditions associated with upregulation of immune checkpoint proteins. We evaluated immune modulation induced by nonsteroidal anti-inflammatory agents used for colon cancer prevention. Both celecoxib and naproxen inhibited polyp growth in APC Min mice. Treatment of mice with either drug significantly decreased PD-L1 expression on polyps in a dose-dependent manner (P < 0.0001 for both). The decrease in PD-L1 was associated with an influx of CD8+ T cells into polyps (P < 0.0001, celecoxib; P = 0.048, naproxen) compared with lesions from untreated animals and correlated with disease control. Naproxen is a nonselective inhibitor of both COX-1 and COX-2, and we questioned the role of the different cyclooxygenases in PD-L1 regulation. Silencing either COX-2 or COX-1 RNA in the murine colon cancer cell line MC38, reduced PD-L1 expression by 86% in COX-2-silenced cells (P < 0.0001) while there was little effect with COX-1 siRNA compared with control. Naproxen could inhibit the growth of MC38 in vivo. Naproxen-treated mice demonstrated a significant reduction in MC38 growth as compared with control (P < 0001). Both Tbet+ CD4 and CD8 tumor-infiltrating lymphocytes (TIL) were significantly increased (P = 0.04 and P = 0.038, respectively) without a concurrent increase in GATA3+ TIL (P > 0.05). CD8+ TIL highly expressed the activation marker, CD69. Not only was PD-L1 expression decreased on tumors, but LAG3+CD8+ T cells and PD-1 and LAG3 expression on regulatory T cells was also reduced (P = 0.008 and P = 0.002, respectively). These data demonstrate COX-2 inhibitors significantly decrease PD-L1 in colonic lesions and favorably impact the phenotype of tumor-infiltrating lymphocytes to control tumor growth.

Prevention relevance: Nonsteroidal anti-inflammatories (NSAID) are an essential component of any combination chemoprevention of colon cancer. We show NSAID treatment reduces PD-L1 expression on intestinal tumor cells. NSAID regulation of PD-L1 is dependent on COX-2 expression. These data underscore an important immunologic mechanism of action for NSAID in colon cancer prevention. See related Spotlight, p. 209.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • B7-H1 Antigen / metabolism
  • CD8-Positive T-Lymphocytes
  • Colonic Neoplasms* / drug therapy
  • Colonic Neoplasms* / metabolism
  • Colonic Neoplasms* / prevention & control
  • Cyclooxygenase 2 Inhibitors / pharmacology
  • Lymphocytes, Tumor-Infiltrating*
  • Mice


  • B7-H1 Antigen
  • Cyclooxygenase 2 Inhibitors