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 (125)I-anti-TLR5 mAb/(125)I-VEGF/(125)I-IgG were obtained with labeling rates over 85% and radiochemical purities above 90%. Among these three probes, (125)I−anti−TLR5 mAb and (125)I-VEGF were used for specifically imaging TNBC, while (125)I-IgG was used for comparison. Whole-body phosphorus autoradiography showed clear imaging at 48 h after injection of (125)I-anti-TLR5 mAb and (125)I-VEGF also provided clear imaging at 24 h. Biodistribution study demonstrated a higher tumor uptake of (125)I-anti-TLR5 mAb in TLR5(+) group compared with that in TLR5(−) group (P < 0.05), whereas tumor uptake of (125)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.