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Targeting Blood Clot in the Stroma of Genitourinary Cancer.
The presence of blood clot in the tumor stroma and around metastatic tumor cells has been recognized for many years. However, our knowledge about the contribution of blood clot to the function of the tumor extracellular matrix is still very limited. The research of my laboratory is aimed at (i) improving our understanding about the role of clot formation for the progression of genitourinary cancer and (ii) exploiting the presence of clot in these malignancies for targeted delivery of anti-tumor therapeutics and imaging agents.
Molecular analysis of the tumor homing peptides CLT1 and CLT2.
The tumor extracellular matrix is different from the normal connective tissue in that it contains clotted plasma proteins. The presence of clotted plasma (fibrin + cross-linked plasma proteins) in the tumor extracellular matrix is functionally connected to vascular endothelial growth factor, which causes hyperpermeability of tumor blood vessels. As a consequence, blood plasma leaks into tumor interstitial spaces where the plasma begins to clot in a manner similar to wounds. To identify small peptides that bind to the tumor extracellular matrix, we screened a phage library on clotted plasma in vitro and identified two peptides with the amino acid sequence CGLIIQKNEC (CLT1) and CNAGESSKNC (CLT2). Injected into mice, CLT1 and CLT2 accumulate strongly in the interstitial spaces of breast, prostate, kidney and skin tumors, but not in the connective tissue of normal organs. Both CLT peptides associate with fibrin-fibronectin in tumors and cease to home to tumors grown in fibrinogen and plasma fibronectin-deficient mice. In addition, we found that CLT1 is cytotoxic for tumor and proliferating endothelial cells while CLT2 has no such effects. We hypothesize that CLT1 is useful for the detection and treatment of genitourinary cancer. The objective of this project is to (1) identify amino acid residues within CLT1 critical for tumor homing and cytotoxicity; (2) identify receptor(s) on endothelial and tumor cells that mediate(s) CLT1 cytotoxicity; (3) test if CLT1 has anti-angiogenic and anti-tumor function in vivo; and (4) determine if CLT1 improves detection of genitourinary cancer by magnet resonance imaging.
Role of fibrin-fibronectin complexes for tumor metastasis.
Tumor metastasis is aided by blood clotting factors that form a thrombus consisting of platelets and clotted plasma around circulating tumor cells. We recently found that absence of plasma fibronectin (pFN), a major component of clotted plasma, leads to reduced lung metastasis by supporting adhesive interactions of tumor cell integrin αvβ3 with clotted plasma. In vitro studies showed that fibrin-fibronectin (FibFN) complexes, but not purified fibrin, support tumor cell attachment and invasion. FibFN also stimulates adhesion of monocytes, which served as a model for FibFN-mediated activation of integrin αvβ3. Paralleling these results in vivo, we found that pFN promotes co-localization of myeloid cells with circulating tumor cells. We hypothesize that FibFN binds to a novel receptor on tumor and myeloid cells and that the interaction of FibFN with its receptor promotes cell adhesion and invasion in vitro and tumor metastasis in vivo. The objective of this project is to (1) identify the FibFN binding site on tumor and myeloid cells that mediates cell adhesion, invasion and metastasis; (2) determine signaling pathways that mediate tumor cell invasion and metastasis downstream of FibFN; and (3) determine if FibFN mediates the recruitment of myeloid cells to metastatic tumor cells.
1. Gunjan Malik, Lynn M. Knowles, Rajiv Dhir, Shuping Xu, Shuting Yang, Erkki Ruoslahti and Jan Pilch. Plasma fibronectin promotes lung metastasis by contributions to fibrin clots and tumor cell invasion. Cancer Research, 70(11):4327-34, 2010.
2. D. Simberg, T. Duza, J.H. Park, M. Essler, J. Pilch, L. Zhang, A.M. Derfus, M. Yang, R.M. Hoffman, S. Bhatia, M.J. Sailor, E. Ruoslahti: Biomimetic amplification of nanoparticle homing to tumors. Proc Natl Acad Sci U S A, 104(3): 932-936, 2007.
3. J. Pilch, D.M. Brown, M. Komatsu, T.A.H. Jarvinen, M. Yang, D. Peters, R.M. Hoffman, E. Ruoslahti: Peptides selected for binding to clotted plasma accumulate in tumor stroma and wounds. Proc Natl Acad Sci U S A, 103(8): 2800-2804, 2006.
4. J. Pilch, C.M. Franzin, L.M. Knowles, F.J. Ferrer, F.M. Marassi, E. Ruoslahti: The anti-angiogenic peptide anginex disrupts the cell membrane. J Mol Biol, 356(4): 876-85, 2006.
5. M.E. Akerman*, J. Pilch*, D. Peters, E. Ruoslahti: Angiostatic peptides use plasma fibronectin to home to angiogenic vasculature. Proc Natl Acad Sci U S A, 102(6): 2040-2045, 2005.
*M.E. Akerman and J. Pilch contributed equally