11β-HSD1-mediated cortisol conversion promotes immune suppression and tumor cell migration in canine mammary...

Canine mammary carcinoma (CMC) is a common malignancy for which effective chemotherapy regimens remain limited. While recent studies have shown that tumor-derived glucocorticoids (GCs) produced via 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) promote metastasis in mice, their autonomous capacity in CMC is unknown. Here, we investigated 11β-HSD1-mediated cortisol conversion and its functional significance using the CMC cell lines EMC1, CTBp, and CHMp. Quantitative reverse transcription-polymerase chain reaction revealed that 11β-HSD1 expression was approximately 21.8-1520-fold higher in these CMC cell lines versus the control Madin-Darby canine kidney cells. CMC cell lines efficiently converted inactive cortisone to active cortisol, a process significantly inhibited by the non-selective 11β-HSD1 inhibitor carbenoxolone, demonstrating that they possess the capacity for 11β-HSD1-mediated cortisol conversion. To evaluate the functional impact of tumor-derived cortisol, we used a conditioned medium from EMC1 cells treated with various cortisone concentrations (0, 100, and 500 nM designated as conditioned medium (CM)0.0, CM.100, and CM.500, respectively). CM.100 and CM.500 significantly suppressed CD8⁺ T-cell activity and enhanced tumor cell migration compared with CM.0. Importantly, both immunosuppression and increased migration were reversed by the GC receptor antagonist mifepristone. These findings represent the first report of autonomous cortisol conversion in CMC, suggesting that tumor-derived GCs contribute to metastatic niche formation through immune evasion and enhanced motility. Our results identify the 11β-HSD1-GC axis as a potential novel therapeutic target for CMC.