Vascular endothelial growth factor secreted by breast cancer cells plays a critical role in the formation of pre-metastatic niche in the mouse lung / 中华肿瘤杂志

ABSTRACT

<p><b>OBJECTIVE</b>To explore the formation of pre-metastatic niche in the mouse lung and to study the underlying molecular mechanisms whereby primary breast carcinoma-derived factors mediate recruitment of bone marrow-derived cells (BMDCs) and affect the formation of pre-metastatic lung environment before the arrival of tumor cells.</p><p><b>METHODS</b>Mammary carcinoma 4T1 cells were inoculated into the mammary gland to construct mouse model of breast cancer. Confocal microscopy was used to detect the recruitment of BMDCs in the pre-metastatic lungs. The expression of factors in the mouse sera and 4T1 cell culture media was assayed using RayBio Custom mouse cytokine antibody array kit. The mice were injected daily with recombinant VEGF for 7 consecutive days to observe the effect of VEGF on BMDCs recruitment in the mouse lung.</p><p><b>RESULTS</b>No BMDCs were observed in the lungs of control and 4T1-tumor-bearing mice on day 0. On day 7 and 14, clusters of BMDCs observed in the lungs of 4T1-tumor-bearing mice were 8.7±2.2/objective field and 48.8±3.2/objective field, respectively, significantly higher than those in the control mice (1.1±0.8/objective field and 3.1±1.7/objective field) (P<0.05 for both). Confocal microscopic observation found that metastatic breast cancer cells preferentially facilitate BMDCs recruitment sites in the pre-metastatic mouse lungs. The levels of VEGF, GM-CSF, and IL-6 in the serum of 4T1-tumor-bearing mice were significantly increased compared with those in the control group (P<0.05 for all). However, VEGF was detected only in the culture media of 4T1 cells. The amount of BMDCs in the mouse lung tissue was (22.8±3.6)/objective field in the VEGF group and (3.1±0.4)/objective field in the control group (P<0.05). There were 36.8±5.4 metastatic foci in the lung tissue of VEGF group and 12.6±2.2 in the control group (P<0.05).</p><p><b>CONCLUSIONS</b>The results of this study demonstrate that primary breast cancer cells can alter the lung microenvironment during the pre-metastatic phase and induce the formation of pre-metastatic niche. Primary tumor cell-derived VEGF may be a crucial factor responsible for the formation of pre-metastatic niche.</p>