Down-Regulation of Toll-Like Receptor 5 (TLR5) Increased VEGFR Expression in Triple Negative Breast Cancer (TNBC) Based on Radionuclide Imaging.

In this study, GFP-tagged TNBC 4T1 cells with down-regulated TLR5 expression (TLR5 4T1) and normal TLR5 expression (TLR5 4T1) were constructed, respectively. RT-PCR and Western blot studies showed that down-regulation of TLR5 obviously increased the expression of VEGFR in 4T1 cells. Highly stable radio-probes I-anti-TLR5 mAb/I-VEGF/I-IgG were obtained with labeling rates over 85% and radiochemical purities above 90%. Among these three probes, I-anti-TLR5 mAb and I-VEGF were used for specifically imaging TNBC, while I-IgG was used for comparison. Whole-body phosphorus autoradiography showed clear imaging at 48 h after injection of I-anti-TLR5 mAb and I-VEGF also provided clear imaging at 24 h. Biodistribution study demonstrated a higher tumor uptake of I-anti-TLR5 mAb in TLR5 group compared with that in TLR5 group (P < 0.05), whereas tumor uptake of I-VEGF in TLR5 group was lower than that in the TLR5 group (P < 0.05). Immunohistochemical staining suggested that the expression of TLR5 was lower, whereas the expression of VEGFR, CD31, and MVD (microvessel density) was higher in TLR5 tumor-bearing mice. In summary, the down-regulation of TLR5 in TNBC promoted the VEGFR expression and angiogenesis, resulting in the proliferation of TNBC cells. TLR5/VEGF might be a better indicator for monitoring the development of TNBC.