Breast cancer is the most common malignant tumor in women. Its incidence is associated with obesity and metabolic syndrome (MetS), which are highly prevalent world widely and have been identified as poorer prognosis factors in breast cancer including triple-negative breast cancer (TNBC), which has poorer response to chemotherapy, radiotherapy, and endocrine therapy. Programmed death ligand 1 (PD-L1) is one of the immune checkpoints ligands that facilitates tumor escape and progress. Obesity/MetS could cause systemic inflammation and immune disorders, however, whether and how obesity/MetS affect PD-L1 expression in breast cancer had not been clarified. In the present study, we examined the PD-L1 expression profile in breast cancer either in online database or cell lines. We found higher PD-L1 mRNA level but not DNA copy number in breast cancer than normal breast tissue, and higher PD-L1 expression in TNBC than other subtypes. Moreover, we found a positive relationship between PD-L1 expression in TNBC and metabolic complications in patients. Next, obesity/MetS related M1 macrophage was found to promote the expression of PD-L1 in breast cancer cells cocultured with polarized macrophages derived from either monocyte-like cell line THP-1 or Wistar rat models. IL6/JAK/STAT pathway was further identified to be involved in the process. In addition, we discovered that the PD-L1 expression promoted by obesity/MetS could be restored by telmisartan, one of the angiotensin II receptor blockers (ARBs) and could affect macrophage polarization, through its selective peroxisome proliferator-activated receptor-gamma (PPARG) activation and NFKB p65 inhibition and therefore downregulates IL6 secretion from M1 macrophage.
Keywords: Obesity/MetS; PD-L1; TNBC; macrophage; telmisartan.