The Targeting And Neutralization Of Circulating Cancer Cells With E-Selectin And Trail.

Abstract

The survival rate for patients with metastatic vs. localized cancer is dramatically reduced. Most cancer-related deaths are associated with the formation of secondary tumors. In order to form a secondary tumor, cancer cells must detach from the primary tumor, using a complex series of steps change the surrounding tissue making its way to the circulatory system, survive within the circulation and evade the immune system, and leave the circulatory system at a distal site to form a secondary tumor. While circulating, cancer cells interact with the endothelial lining of the vasculature via a series of adhesive interactions that facilitate tethering mediated via transient bond formation with the selectin group of glycoproteins. This ultimately leads to firm adhesion of cancer cells to vessels in the initial steps of metastasis. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), identified based on its homology to the TNF superfamily, holds promise as a tumorspecific cancer therapeutic agent. Unlike other TNF family members, TRAIL specifically induces a death signal in transformed cells while sparing non-cancerous cells via a caspase-dependent pathway. In the present work, we exploit this phenomenon to deliver a receptor-mediated apoptosis signal to cancer cells under flow conditions. My studies show that cancer cells exhibit shear-dependent rolling behavior over a selectin-coated microcapillary flow chamber and that the density of the selectin molecule, along with the shear force imposed by the flowing fluid on the cancer cell play an important role in regulating the rolling velocity. Further, I have demonstrated that flowing cancer cells through a microtube functionalized with TRAIL and E-selectin is capable of killing the captured cancer cells. This killing is time-dependent and is more efficient compared to static conditions with immobilized TRAIL and E-selectin. The functionalized microtubes do not kill healthy blood and bone marrow cells neither do they activate !2 integrin present on leukocytes. Studies suggest that many cancer cells that are resistant to TRAIL can be sensitized by chemotherapy and radiation. To this extent, the microtube device was tested for use as adjuvant therapy. When pre-treating cells with sublethal doses of chemotherapeutic agent, a super-additive (greater than the sum of kill by individual agent) increase in kill rate was seen. This represents the first demonstration of a novel biomimetic method to capture metastatic cells from circulation and deliver an apoptotic signal, thereby reducing the metastatic load with a hope to improve patient survival. Using a different approach, nanoscale lipid particles decorated with two proteins are developed that would bind circulating cancer cells and kill them. Results show that the lipid nanoparticles bind to cells under conditions of uniform shear with high efficiency and kill over 50% of cells in 2 hours. When cancer cells were spiked in blood, a kill of over 90% was seen when compared to control lipid nanoparticles. Before these modalities become therapies, further studies evaluating the efficacy in animal models are necessary. However, these results show promising possibilities in killing metastatic cancer cells, thereby improving chances for patient survival.