Oncologic Trogocytosis Figure 7. Expression and functionality of MDR proteins in hospicells. A, B and C. Immunofluorescence staining of P- Glycoprotein (P-gp) (A), Lung Resistance Protein (LRP) (B), and Breast Cancer Resistance Protein (BCRP) (C) in Hospicells isolated from ascitic fluid from 5 patients (Multidrug Resistance protein (MRP)). D. Expression of MDR proteins (mean fluorescence intensity (mfi)) assessed by FACS (mfi (+SD)). E. Flow cytometry of functionality of P-gp1 expressed by Hospicells: control, e.g. rhodamine incorporation (green curve – mfi = 22), rhodamine excretion (dashed curve - mfi = 35); inhibition of excretion by cyclosporine (red curve - mfi = 25) and GG918 (blue curve- mfi 26). F. Intercellular transfer of labelled P-gp on co- culture of hospicells and OVCAR3 cells for 1 hour, 5 hours and 18 hours. doi:10.1371/journal.pone.0003894.g007 cells. Noteworthy, Karnoub et al. have recently provided evidence that bone-marrow-derived human mesenchymal stem cells caused, through paracrine mechanism, weakly metastatic human breast carcinoma cells to increase their metastatic potency [32]. Interestingly, this enhanced metastatic ability was reversible and dependent on intercellular contact and CCL5 signalling through the chemokine receptor CCR5, the most potent mesenchymal cells in their study were CD10+ cells. Recently, Kaplan et al. have described the role of bone marrow VEGF-R1 progenitors as pre- metastatic niches in a model of lung cancer [33]. Following modification of the extracellular environment in host organs by secreted tumoral factors, bone marrow progenitors were able to constitute a pre-metastatic niche and subsequently attract cancer cells and facilitate the growth of metastasis [34]. The pre- PLoS ONE | www.plosone.org 8 December 2008 | Volume 3 | Issue 12 | e3894