Figure 1.

Metastatic human breast cancer cells use αvβ3 to interact with platelets and arrest during blood flow. (A) Primary metastatic human breast cancer cells (PE02JA) and MDA-MB 435 cell variants derived from mammary fat pad (mfp) tumors or metastases to bone, lungs, lymph node (LN), or the pleural cavity in mice, but not the parental MDA-MB 435 cell population at large, bind to activated platelets and thereby arrest during blood flow. Tumor cells stained with hydroethidine (red fluorescence) were suspended in human blood (containing mepacrine, green fluorescence) and perfused over a thrombogenic collagen I matrix at a venous wall shear rate (50 s⁻¹, 4 dynes/cm²) (10). Platelets adhere to the matrix, become activated, and form thrombi, to which arrest-competent tumor cells attach (monitored by video microscopy and image acquisition at predefined positions with filter settings to discern platelet- and tumor cell-specific signals). None of the tumor cells attached directly to the matrix. Thrombus formation was not affected by tumor cell type. (B) Arrest-competent breast cancer cells use integrin αvβ3 for attachment. Tumor cells in blood were perfused and analyzed as in A in the absence (open bars) or presence (hatched bars) of function-blocking anti-αvβ3 mAb VNR1 27.1 (18). Columns represent the means of triplicate runs (±SD) with blood from the same donor. (C) Projection of confocal sections through a heteroaggregate of platelets and primary metastatic breast cancer cells, PE02JA (images acquired during perfusion). Attaching to a thrombus, tumor cells extend pseudopods for continued anchorage.