Continuous real time ex vivo epifluorescent video microscopy for the study of metastatic cancer cell interactions with microvascular endothelium

Recent studies suggest that only endothelium-attached malignant cells are capable of giving rise to hematogenous cancer metastases. Moreover, tumor cell adhesion to microvascular endothelium could be crucial in metastasis predilection to specific organs or tissues. However, the existing in vitro and in vivo techniques do not provide for sufficient delineation of distinct stages of a dynamic multi-step intravascular adhesion process. Here we report the development of an experimental system allowing for prolonged continuous ex vivo real-time observation of malignant cell adhesive interactions with perfused microvessels of a target organ in the context of its original tissue. Specifically, the vasculature of excised dura mater perfused with prostate cancer cells is described. An advantage of this technique is that selected fluorescently labeled tumor cells can be followed along identified vascular trees across the entire tissue specimen. The techniques provide for superior microvessel visualization and allow for uninterrupted monitoring and video recording of subsequent adhesion events such as rolling, docking (initial reversible adhesion), locking (irreversible adhesion), and flattening of metastatic cancer cells within perfused microvasculature on a single cell level. The results of our experiments demonstrate that intravascular adhesion of cancer cells differs dramatically from such of the leukocytes. Within dura microvessels perfused at physiological rate, non-interacting, floating, tumor cells move at velocities averaging 7.2 × 10³ μm/s. Some tumor cells, similarly to leukocytes, exhibit rolling-like motion patterns prior to engaging into more stable adhesive interactions. In contrast, other neoplastic cells became stably adhered without rolling showing a rapid reduction in velocity from 2 × 10³ to 0 μm/s within fractions of a second. The experimental system described herein, while developed originally for studying prostate cancer cell interactions with porcine dura mater microvasculature, offers great flexibility in adhesion experiments design and is easily adapted for use with a variety of other tissues including human.