(12f) Dynamic Biochemical Tissue Analysis Detects Functional Selectin Ligands on Colon Cancer Tissues

A growing body of evidence suggests that the selectin family of cell adhesion molecules, comprised of E-, P-, and L-selectin, engage  ligands presented on colon cancer cells to mediate the adhesion of cancer cells to blood vessel walls at the secondary site during metastasis. This adhesion is a rolling adhesion in which selectin/selectin ligand bonds repeatedly form and dissociate under forces generated by hemodynamic blood flow. Currently, standard tissue analyses, such as immunohistochemistry (IHC), do not functionally assay for those molecules that mediate rolling. Recently, our lab developed a novel tissue analysis assay, termed dynamic biochemical tissue analysis (DBTA), which detects functional selectin ligands by probing tissues with selectin-coated microspheres. The selectin microspheres are delivered to tissues under hydrodynamic flow conditions, and if selectin ligands are present, the selectin microspheres will roll on tissues presenting ligands that form functional bonds under the applied force conditions of the assay.  When colon cancer tissues of distinct histological classifications were assayed using DBTA, significantly greater quantities of selectin microspheres specifically adhered to cancer tissues relative to noncancerous tissues, and the adhesion patterns of all three types of selectin microspheres demonstrated a heterogeneous presentation of functional selectin ligands on cancer tissues. Furthermore, the rolling velocities of selectin microspheres were a function of the hydrodynamic shear stress and demonstrated the force-dependent nature of selectin/selectin ligand interactions, which are governed by catch-slip bonds. Specifically, microsphere rolling velocities were stabilized at 0.5-0.75 dyn/cm², yet outside this range the microsphere rolling velocities became erratic as the rate of bond dissociation exceeded the rate of bond formation. Remarkably, when colon cancer tissues were probed with selectin molecules using IHC and DBTA, the two assays disparately detected selectin ligands such that, in certain regions of tissue, selectin ligands were detected using DBTA but not IHC.  These results demonstrate that DBTA yields a tissue characterization that is distinct from standard methods of tissue analysis, thereby illustrating the relevance of assays that functionally detect target molecules.