Extracellular Targeting of Cell Signaling in Cancer

Strategies Directed at MET and RON Receptor Tyrosine Kinase Pathways

James W. Janetka, Roseann M. Benson, James W. Janetka, Roseann M. Benson

• Publisher: Wiley
• Year: 2018
• Print ISBN:
  9781119300182
• eBook ISBN:
  9781119300212
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

International experts present innovative therapeutic strategies to treat cancer patients and prevent disease progression

Extracellular Targeting of Cell Signaling in Cancer highlights innovative therapeutic strategies to treat cancer metastasis and prevent tumor progression. Currently, there are no drugs available to treat or prevent metastatic cancer other than non-selective, toxic chemotherapy.  With contributions from an international panel of experts in the field, the book integrates diverse aspects of biochemistry, molecular biology, protein engineering, proteomics, cell biology, pharmacology, biophysics, structural biology, medicinal chemistry and drug development.

A large class of proteins called kinases are enzymes required by cancer cells to grow, proliferate, and survive apoptosis (death) by the immune system. Two important kinases are MET and RON which are receptor tyrosine kinases (RTKs) that initiate cell signaling pathways outside the cell surface in response to extracellular ligands (growth factors.) Both kinases are oncogenes which are required by cancer cells to migrate away from the primary tumor, invade surrounding tissue and metastasize. MET and RON reside on both cancer cells and the support cells surrounding the tumor, called the microenvironment. MET and RON are activated by their particular ligands, the growth factors HGF and MSP, respectively. Blocking MET and RON kinase activation and downstream signaling is a promising therapeutic strategy for preventing tumor progression and metastasis. Written for cancer physicians and biologists as well as drug discovery and development teams in both industry and academia, this is the first book of its kind which explores novel approaches to inhibit MET and RON kinases other than traditional small molecule kinase inhibitors. These new strategies target key tumorigenic processes on the outside of the cell, such as growth factor activation by proteases. These unique strategies have promising potential as an improved alternative to kinase inhibitors, chemotherapy, or radiation treatment. 

1
Discovery and Function of the HGF/MET and the MSP/RON Kinase Signaling Pathways in Cancer

Silvia Benvenuti, Melissa Milan and Paolo M. Comoglio

Candiolo Cancer Institute, Italy

1.1 Introduction

MET and RON oncogenes encoding two related tyrosine kinase receptors are among the most important genes involved in the control of the invasive growth genetic program. Under physiological conditions, such as embryonic development and organ regeneration, the invasive growth program controls the normal tissue development by coordinating, in time and space, several biological events including cellular proliferation, disruption of intercellular junctions, migration through the extracellular matrix (ECM), and protection from programmed cell death (apoptosis). In transformed tissues, MET or RON deregulation results in cancer formation and metastatic dissemination. Upon either ligand stimulation or constitutive receptor activation, cancer cells are induced to leave the primary tumor, degrade the basal membrane, move towards different organs and generate metastasis (1,2). The two sibling receptors exert a dual role: they are necessary oncogenes for those tumors that rely on MET activity for growth and survival (oncogene addiction) and adjuvant, pro‐metastatic genes for other tumors, where MET activation is a secondary event that exacerbates the malignant properties of already transformed cells (oncogene expedience). In this complex scenario, MET and RON become very attractive candidates for targeted therapeutic intervention.

1.2 MET Tyrosine Kinase Receptor and its Ligand HGF: Structure

MET oncogene, positioned on chromosome 7q21‐31, is composed of 21 exons encoding a transmembrane tyrosine kinase receptor made of a disulphide‐linked heterodimer (190 kDa), which originates from the proteolytic cleavage, in the post‐Golgi compartment, of a single chain precursor. The heterodimer is formed by a single‐pass transmembrane β chain (145 kDa) and a completely extracellular α chain (45 kDa). The extracellular portion contains a SEMA (semaphorin) domain, an atypical motif made by over 500 amino acids, which has a low affinity binding activity for the ligand and is involved in receptor dimerization; a plexin, SEMA and integrin cysteine‐rich (PSI) domain, which encompasses about 50 residues and contains 4 disulphide bonds; and 4 immunoglobulin‐plexin‐transcription structures (IPT domain), a characteristic protein‐protein interaction region. A single pass hydrophobic membrane‐spanning domain is followed by the intracellular portion made of a juxtamembrane section followed by a catalytic site and a C‐terminal regulatory tail (Figure 1.1). The juxtamembrane segment is essential for receptor down‐regulation (2). It contains a serine residue (Ser985) that, upon phosphorylation, is responsible for inhibition of receptor kinase activity, and a tyrosine (Tyr1003) capable of binding the E3‐ubiquiting ligase CBL (cellular homologue of Cas NS‐1 oncogene), that promotes receptor degradation (3,4). The catalytic site contains two tyrosines (Tyr1234 and Tyr1235) that regulate the enzymatic activity. Finally, the C‐terminal tail encompasses two tyrosines (Tyr1349 and Tyr1356) that, when phosphorylated, generate a docking site able to recruit a vast cohort of intracellular molecules and adaptor proteins responsible for transducing the signaling triggered by the ligand‐receptor interaction (5).The latter two tyrosines have shown to be essential and sufficient to execute MET physiological functions (5), and to elicit MET oncogenic potential (6).

Figure 1.1 MET tyrosine kinase receptor and its ligand HGF: structure.MET is a transmembrane tyrosine kinase receptor made of a disulphide‐linked heterodimer formed by a single‐pass transmembrane β chain and a completely extracellular α chain. The extracellular portion contains a SEMA domain, involved in ligand binding and receptors dimerization; a PSI domain, encompassing four disulphide bonds; and four IPT domains, a protein–protein interaction region. A single pass transmembrane domain is followed by the intracellular portion made of a juxtamembrane section, a catalytic site and a C‐terminal regulatory tail. The juxtamembrane segment contains a serine (serine 985) and a tyrosine (tyrosine 1003) responsible to inhibit receptor kinase activity and promote receptor down‐regulation. The catalytic site contains the ‘catalytic’ tyrosines 1234 and 1235 that regulate the enzymatic activity, while the C‐terminal tail encompasses the ‘docking’ tyrosines 1349 and 1356 that, upon phosphorylation, generate a docking site able to recruit a vast cohort of intracellular adaptors and molecules responsible of triggering the signal transduction cascade.HGF: hepatocyte growth factor; HL: hairpin loop; IPT: immunoglobulin‐plexin transcription domain; K: kringle; PSI: plexin‐semaphorin‐integrin domain; SEMA: semaphorin domain; SPH: serine‐protease domain.

MET high affinity ligand is known as the scatter factor (SF) or hepatocyte growth factor (HGF). SF is a factor capable of inducing scatter of epithelial cells, a complex phenomenon that consists of a first step in which cells dissociate one from another and a second phase in which the released cells begin to move (7,8). While HGF is a potent growth stimulator for primary hepatocytes kept in culture (9), the two molecules were later shown to be identical (10). SF/HGF belongs to the plasminogen family of peptidases; it contains an amino terminal hairpin loop (HL), followed by four Kringle domains, flanked by an activation portion and a serine‐protease domain (SPH) devoid of proteolytic activity (Figure 1.1). This ligand, synthesized and secreted as a single chain inactive precursor (pro‐HGF) by stromal cells (i.e. fibroblasts), is present in the extracellular environment of almost all tissues. Its activation occurs locally upon proteolytic cleavage by proteases that cleave the bond between Arg494 and Val495.

To date, several proteases (present either in the serum or within cells) have been proposed as HGF/SF activators, including HGF activator (HGFA) (11), plasma kallikrein and coagulation factors XIIa and XIa (12), matriptase and hepsin (13,14), TMPRSS2 (15), TMPRSS13 (16), urokinase‐type plasminogen activator (uPA), and tissue‐type plasminogen activator (tPA) (17). Among them, HGFA and matriptase, synthesized in turn as inactive precursors, show the most efficient pro‐HGF/SF processing activity (18). Mature HGF is a heterodimer made of a 69 kDa α chain and a 34 kDa β chain linked by a disulfide bond. HGF contains two binding sites with differential affinity for the MET receptor: a high‐affinity site located within the α chain and a low affinity site in the β chain. The low affinity site in the β chain becomes accessible only after pro‐HGF activation, which is essential for receptor dimerization and subsequent activation. Cells of mesenchymal origin are the primary producers and source of HGF in the pericellular environment, which acts on cells expressing the MET receptor (cells of epithelial origin) ...

Table of contents

• Cover
• Table of Contents
• List of Contributors
• Preface
• Chapter 1: Discovery and Function of the HGF/MET and the MSP/RON Kinase Signaling Pathways in Cancer
• Chapter 2: The Role of HGF/MET and MSP/RON Signaling in Tumor Progression and Resistance to Anticancer Therapy
• Chapter 3: HGF Activator (HGFA) and its Inhibitors HAI-1 and HAI-2: Key Players in Tissue Repair and Cancer
• Chapter 4: Physiological Functions and Role of Matriptase in Cancer
• Chapter 5: The Cell-Surface, Transmembrane Serine Protease Hepsin: Discovery, Function and Role in Cancer
• Chapter 6 Targeting HGF with Antibodies as an Anti-Cancer Therapeutic Strategy
• Chapter 7: MET and RON Receptor Tyrosine Kinases as Therapeutic Antibody Targets for Cancer
• Chapter 8: Inhibitory Antibodies of the Proteases HGFA, Matriptase and Hepsin
• Chapter 9 Inhibitors of the Growth-Factor Activating Proteases Matriptase, Hepsin and HGFA: Strategies for Rational Drug Design and Optimization
• Chapter 10: Cyclic Peptide Serine Protease Inhibitors Based on the Natural Product SFTI-1
• Chapter 11: Screening Combinatorial Peptide Libraries in Protease Inhibitor Drug Discovery
• Chapter 12: Chemical Probes Targeting Proteases for Imaging and Diagnostics in Cancer
• Chapter 13: Cancer Diagnostics of Protease Activity and Metastasis
• Chapter 14: Roles of Pericellular Proteases in Tumor Angiogenesis: Therapeutic Implications
• Index
• End User License Agreement