Encyclopedia of Signaling Molecules

2018 Edition
| Editors: Sangdun Choi

HGF (Hepatocyte Growth Factor)

  • Hiroki Sato
  • Shunsuke Aoki
  • Takashi Kato
  • Kunio Matsumoto
Reference work entry
DOI: https://doi.org/10.1007/978-3-319-67199-4_101701

Synonyms

Historical Background

In 1984, hepatocyte growth factor (HGF) was first reported as a potent mitogen of rat hepatocytes in a primary culture. The primary structure of HGF became evident with cDNA cloning in 1989, and HGF was simultaneously identified as a novel growth factor (Nakamura et al. 1989; Miyazawa et al. 1989). Meanwhile, scatter factor was identified from fibroblast-cultured media as a scattering-inducible factor toward epithelial cells. The biological activities of HGF and scatter factor seemed unrelated, but subsequent biochemical analysis has revealed that HGF and scatter factor are identical.

Initially, a transforming Met fusion protein, translocated promoter region (TPR)–Met, was discovered in a human osteosarcoma cell line as an active oncogene (Cooper et al. 1984). The proto-oncogene c-Met was later found to encode the transmembrane protein with intracellular tyrosine kinase domain in 1987. Therefore, Met was predicted to be a novel growth factor receptor, but its ligand had not been identified at that time. In 1991, Bottaro and a colleague reported that Met tyrosine kinase is a cell signaling receptor for HGF (Bottaro et al. 1991). Co-transfection of Met and its ligand HGF into murine cells induced the transformation of these cells via an autocrine mechanism, suggesting involvement of the HGF–Met signaling pathway in tumorigenesis. Furthermore, molecular biological and biochemical approaches revealed that the HGF–Met signaling pathway is essential in developmental and physiological processes. Recombinant HGF has been used therapeutically in clinical trials. Elucidation of the roles of the HGF–Met pathway in tumor biology has facilitated the clinical development of different types of inhibitors of the HGF–Met axis.

Structure of HGF and Met

The HGF gene locus has been mapped on chromosome 7q21.1 where a gene is composed of 18 exons and 17 intron spans. Mature HGF is composed of 697 amino acids and is a heterodimer composed of disulfide-linked α- and β-chains (Fig. 1a). The α-chain contains an N-terminal hairpin domain and four kringle domains (K1–K4), and the β-chain contains a serine proteinase homology (SPH) domain (Nakamura et al. 1989; Miyazawa et al. 1989). HGF is biosynthesized as an inactive single chain (728 amino acids), and cleavage of inactive HGF occurs between Arg494 and Val495 by several serine proteinases, such as HGF-activator, matriptase, and hepsin (Kawaguchi and Kataoka 2014). The α-chain of HGF provides a high-affinity binding site to Met, while the β-chain provides a low-affinity binding site. The simultaneous binding of two interfaces between the α-chain and Met and the β-chain and Met induces the activation of Met and biological responses.
HGF (Hepatocyte Growth Factor), Fig. 1

Structures of HGF and Met. Binding of HGF to the Met receptor triggers various biological effects on cellular behaviors via Met tyrosine phosphorylation and the docking of signaling molecules. (a) Schematic structures of single-chain pro-HGF and two-chain mature HGF. (b) Domain structure of Met and recruitment of typical cytoplasmic adaptor molecules

Naturally occurring variants of HGF such as those produced through the alternative splicing of HGF mRNA have been identified. These variants have different biological functions. A variant that lacks five amino acids in the first kringle domain was discovered as the second major form of HGF. This molecule retains all the biological activities of full-length HGF. Smaller N-terminal variants consisting of the N-terminal hairpin and the first (designated NK1) and second kringle domains (designated NK2) are naturally biosynthesized variants of HGF. NK1 serves a minimum set of domains that are responsible for the high affinity of HGF to the Met receptor. NK1 and NK2 bind the Met receptor and exhibit antagonistic activity on HGF-induced mitogenesis, while they function as agonists in terms of cell motility activity.

The Met proto-oncogene is located on the chromosome 7q21–q31 in humans. Met receptor consists of a 50 kDa extracellular α-chain and a transmembrane 140 kDa β-chain. The two subunits are disulfide linked to form a 185 kDa heterodimeric complex. The Met receptor is composed of structural domains that include extracellular SEMA, PSI (a similar structure is found in the plexins, semaphorins, and integrins), IPT (a similar structure is found in the plexins and transcriptional factor), the transmembrane, the intracellular juxtamembrane, and tyrosine kinase (Fig. 1b) (Trusolino et al. 2010; Gherardi et al. 2012). HGF exhibits a 50% homology to an amino acid sequence in HGF-like protein. HGF and HGF-like protein contain four kringle domains in the α-chain. HGF-like protein specifically binds and activates Ron receptor tyrosine kinase, a family of the Met receptor. Thus, the sole receptor of HGF is Met, while the sole ligand of Met is HGF; HGF and Met have a “one-to-one relationship.”

The crystal structures of HGF (NK1 and β-chain) and Met (Sema, PSI, and tyrosine kinase domain) have been partially revealed (Chirgadze et al. 1999; Schiering et al. 2003; Wang et al. 2006; Stamos et al. 2004). The complex structures for NK1 and heparin, the β-chain of HGF and Sema, and the PSI domains of Met have also been determined. The crystal structures for the NK1 dimer, the complex structures of β-chain and Sema + PSI domains, and tyrosine kinase domains are shown in Fig. 2. The NK1 dimer structure is assumed to engage two Met molecules for receptor dimerization (Birchmeier et al. 2003), whereas it has yet to be determined whether the same structural dimerization interfaces are responsible for natural Met activation. How the entire HGF molecule structurally activates Met is unknown, but the full activation of Met receptor by the bivalent macrocyclic peptides in an equivalent potency to HGF indicates that the stable dimerization of Met with an appropriate length provides a fundamental structural base for the optimum activation of Met by HGF (Ito et al. 2015).
HGF (Hepatocyte Growth Factor), Fig. 2

Crystal structures of HGF and Met domains. (a) The dimer complex of the NK1 domains of HGF, (b) the complex between the β-chain of HGF and Sema + PSI domains of Met (PDB number: 1SHY), and (c) the Met tyrosine kinase domain (PDB number 1ROP) are indicated. Displayed images were created with UCSF Chimera software (http://www.rbvi.ucsf.edu/chimera)

Physiological Roles

The binding of HGF to Met induces the phosphorylation of tyrosine kinase residues (Tyr1230, Tyr1234, and Tyr1235) in the cytoplasmic kinase domain of Met, which leads to the activation of tyrosine kinase and to the autophosphorylation of the carboxyl-terminal multi-substrate-binding site (Tyr1349 and Tyr1356). Various cytoplasmic adaptor proteins, including Gab1, Grb2, phospholipase C (PLC)-γ, Src homology 2 domain-containing phosphatase 2 (Shp2; also known as PTPN11), PI3K, and STAT-3, are either directly or indirectly recruited to this site, and these proteins become frequently phosphorylated on tyrosine residues. Association of the adaptor protein Gab-1 (Grb2-associated binding protein 1) with Met provides docking platforms for the further binding of signaling molecules, which leads to unique biological responses in the HGF–Met pathway.

Biological Functions

HGF exhibits multiple biological activities, such as the stimulation of cell growth, the promotion of cell migration, and the inhibition of apoptosis, in a wide variety of cells (Matsumoto et al. 2014; Sakai et al. 2015). Among the multifunctional characteristics of HGF, its morphogenic activity is notably unique. HGF stimulation of spherical cysts induces branching tubulogenesis in epithelial cells, including renal tubular cells, mammary gland epithelial cells, and hepatic bile duct epithelial cells in collagen gels. HGF also induces or upregulates the expression of uPA and matrix metalloproteinases (MMPs) such as membrane-type MMP and MMP-9. These proteinases are known to play important roles in the branching of tubulogenesis, as well as in the migration and invasion of cells. These HGF activities imply that endogenous HGF contributes to morphogenesis, particularly tubulogenesis, during developmental processes.

The crucial role of stromal fibroblasts in the invasion of cancer cells through the 3D collagen matrix was first demonstrated using human oral squamous cell carcinoma. The fibroblast-derived factor responsible for the 3D invasion was identified as HGF. The profound action of HGF on cancer invasion has been demonstrated in a variety of cell types. Therefore, HGF is also known as a molecular mediator in the interactions between epithelial (or tumor) cells and stromal cells. These interactions mediate crucial aspects of normal development, affecting tissue induction, morphogenesis, and organogenesis. In organ cultures, the neutralizing anti-HGF antibody inhibits both the morphogenesis of developing lung epithelia and the branching tubulogenesis of developing epithelia in the kidneys and mammary glands.

Developmental and Physiological Functions

Full knockout mice of HGF or Met are embryonically lethal due to impaired organogenesis of the placenta and liver (Schmidt et al. 1995; Uehara et al. 1995; Bladt et al. 1995). In the placenta, the number of epithelial trophoblasts in the labyrinthine layer is markedly reduced. This placental defect causes an impaired exchange of oxygen and nutrients between the maternal and embryonic bloodstreams. The embryonic liver is reduced in size and shows extensive apoptotic cell death, indicating that HGF is required for liver development via hepatoblasts/hepatocytes proliferation and/or survival. Likewise, skeletal muscles of the limb and diaphragm are not formed in Met−/− mice (Bladt et al. 1995). In the mouse embryo, HGF expression is observed in the limb bud mesenchyme and septum transversum (which develops into the diaphragm) and the migration of Met-positive myogenic precursor cells from dermomyotome in the somite to limb buds. Thus, HGF functions as a chemoattractant-like motogenic factor for the myogenic precursor cells. A similar function of HGF was noted in the migration of myogenic precursor cells into the tongue.

Transgenic mice experiments have revealed the critical role of HGF in the development of the nervous systems. Endogenous HGF derived from the limb bud mesenchyme also functions as an axonal chemoattractant for spinal motor neurons and for the projection of motor neurons to limb muscle. The developmental and morphogenic roles of HGF are summarized in Table 1.
HGF (Hepatocyte Growth Factor), Table 1

Developmental and physiological roles of HGF

Developmental roles

 Growth and morphogenesis of the liver and placenta

 Morphogenesis of the kidney (tubulogenesis), lung, mammary gland, and tooth germ

 Migration of myogenic precursor cells from the dermomyotome to the limb, diaphragm, and tongue

 Attraction and/or axon guidance of motor neurons to the limb cranial motor neurons

Physiological roles

 Liver regeneration following partial hepatectomy, ischemia, or administration of hepatotoxins

 Renal regeneration following unilateral nephrectomy, ischemia, or administration of nephrotoxins

 Lung regeneration following partial pneumonectomy or chemical injury

 Cardiac protection following ischemia

 Promotion of epithelial wound healing in the stomach, intestine, and skin

 Angiogenesis

 Enhancement of insulin secretion and anti-apoptosis in pancreatic β cells

HGF–Met signaling also contributes to tissue regeneration and protection in several organs. In a 70% resection of the liver, the remaining hepatocytes rapidly proliferate via the paracrine and/or endocrine effects of HGF, and the original liver mass is restored within a week. In pathological conditions, HGF levels in sera or tissue fluid are known to increase in patients with different types of diseases, including acute hepatitis, fulminant hepatitis, acute renal rejection after transplantation, pneumonia, cardiac infarction, severe acute pancreatitis, and Crohn’s, Huntington’s, Parkinson’s, and Alzheimer’s diseases. The symptoms of these conditions reflect physiological responses to tissue and cellular damage. A conditional knockout of the Met gene in mice has helped to define the roles of the HGF–Met pathway in tissue protection and repair.
  • Liver regeneration and protection: Loss of liver mass can be induced in rodents by administering hepatotoxic chemicals or by surgical resection. Shortly after partial hepatectomy, HGF mobilization from the extracellular matrix results in Met activation in hepatocytes, which leads to DNA synthesis and cytokinesis, as well as impaired proliferation and incomplete liver regeneration. Hepatocytes subjected to selective loss of functional Met are highly susceptible to cell death even after mild liver injury, indicating that the anti-apoptotic activity of HGF plays a role in protecting the liver.

  • Skin repair: In mice with conditional knockout of Met in keratinocytes, only cells that had escaped recombination and that continued to express functional Met could contribute to regeneration and wound healing. This result indicates that growth factors of the EGF and fibroblast growth factor (FGF) families are also involved in reepithelialization but cannot compensate for a lack of HGF–Met signaling in the skin.

  • Kidney development: A loss of functional Met in renal tubules resulted in no appreciable defect in renal function, but when tubular cell-specific Met−/− mice were subjected to renal injury, they displayed a higher serum creatinine, more severe morphologic lesions, and increased cell death compared with control mice. A recent study demonstrated cooperative signaling between Met and the epidermal growth factor receptor (EGFR) during kidney development, providing genetic evidence for the role of HGF in kidney-branching morphogenesis that was assumed from earlier experiments with cell and organ cultures. The absence of Met during renal development caused reduced branching of the ureteric bud and a decreased number of nephrons, and the defect was particularly severe in mice in which both Met and EGFR signaling were impaired.

These findings using transgenic mice clearly indicate that the physiological effect of endogenous HGF plays important roles for tissue protection and regeneration in vivo, which cannot be replaced by other growth factors, cytokines, or bioactive molecules. The phenotypes of conditional knockout or mutant mice of the Met gene are summarized in Table 2.
HGF (Hepatocyte Growth Factor), Table 2

Phenotypes of genetically modification of HGF/Met signaling

Treatment

Target cells

Outcomes

References

Conditional Met KO mice (Cre-LoxP system)

Liver

Mx1-Cre

Hepatocytes

Impaired liver regeneration. Decreased hepatocyte proliferation

Proc Natl Acad Sci USA 101: 10608 (2004)

Alb-Cre and Alfp-Cre

Hepatocytes

Enhancement of liver damage and fibrosis in chronic injury

Gastroenterology 137: 297 (2009)

Alb-Cre

Hepatocytes

Impaired liver regeneration. Impaired hepatocyte migration

Proc Natl Acad Sci USA 101: 4477 (2004)

Alb-Cre

Hepatocytes

Defects in redox regulation. Increase of apoptosis

J Biol Chem 283: 14581 (2008)

Alb-Cre

Hepatocytes

Suppression of hepatocarcinogenesis. Increased oxidative stress

Cancer Res 67: 9844 (2007)

Alb-Cre and Mx1-Cre

Hepatocytes

Defects of cell cycle progression

PLoS ONE 5: e12739 (2010)

Alb-Cre and Mx1-Cre

Oval cells

Impaired liver regeneration. Failure of hepatic stem cell mobilization

Hepatology 55: 1215 (2012)

Alb-Cre

Hepatocytes

Progression of nonalcoholic fatty liver disease

J Hepatol 61: 883 (2014)

Alb-Cre

Hepatocytes (donor)

Deficiency of repopulation in unmodified recipient livers

Gut 61: 1209 (2012)

Alb-Cre

Hepatocytes (recipient)

Enhanced expansion of unmodified donor cells

Gut 61: 1209 (2012)

Lung

SP-C-Cre

Alveolar type II cells

Suppression of alveogenesis (E18.5)

Yamamoto et al., Dev. Biol. 308: 43 (2007)

SPC-rtta/+; otet-Cre

Alveolar type II cells

Impaired airspace formation marked by a reduction in AEC abundance and survival, truncation of the pulmonary vascular bed, and enhanced oxidative stress

PLoS Genetics 9: e1003228 (2013)

Kidney

Podocin-Cre

Podocytes

Enhancement of podocyte injury, proteinuria

Kidney Int 77: 962 (2010)

HoxB7-Cre

Tubular cells (collecting duct)

Decrease of uretic bud branching, Nephron loss

Development 136: 337 (2009)

HoxB7-Cre

Tubular cells (collecting duct)

Reduction of tubular cell proliferation, kidney regeneration. Increase of interstitial fibrosis, infiltration, acute tubular necrosis

Kidney Int 76: 868 (2009)

Ksp-Cre

Tubular cells

Increase of tubular cell apoptosis and renal inflammation

Kidney Int 84:509 (2013)

gGT-Cre

Tubular cells (proximal)

Increase of tubular injury and cell apoptosis after ischemia/reperfusion

J Am Soc Nephrol 25:329 (2014)

Pancreas

RIP-Cre

β cells

Impairment of glucose tolerance and glucose-dependent insulin secretion

Diabetes 65: 2090 (2005)

RIP-Cre

β cells

Impairment of glucose tolerance and glucose-dependent insulin secretion

Am J Pathol 167: 429 (2005)

Pdx-Cre

β cells

Sensitive to multiple low-dose streptozotocin (MLDS)-induced diabetes

Diabetes 60: 525 (2011)

Pdx-Cre

β cells

Decrease of β-cell replication after post-pancreatectomy and MLDS treatment

Diabetes 63: 216 (2014)

Pdx-Cre

β cells

Incomplete maternal β cell adaptation and development of gestational diabetes mellitus

Diabetes 61: 1143 (2014)

Heart

a-MHC-Cre

Cardiomyocytes

Cardiomyocyte hypertrophy associated with interstitial fibrosis and systolic cardiac dysfunction

Biochim Biophys Acta 1832: 2204 (2013)

Breast

MMTV-Cre

Mammary epithelium

Defects in secondary and ductal side branching in mammary gland

Dev Biol 355: 394 (2011)

Skin

K14-Cre

Keratinocytes

Reepithelization of skin wound

J Cell Biol 177: 151 (2007)

Muscle

Pax7-CreERT2 allele for tamoxifen inducible

Satellite cells

Defect in muscle regeneration in response to acute muscle injury

PLoS ONE 8; e81757 (2013)

Eye

AAV-Cre (subretinal injection)

Retinal pigment epithelium

Reduction of retinal pigment epithelium migration into the outer retina of laser-injured eyes

PLoS ONE 7; e40771 (2012)

Neuron

Emx1-Cre

Neurons arising in the dorsal pallium

Alteration of neocortical neuron architecture

J Comp Neurol 518: 4463 (2010)

Emx1-Cre

Neurons arising in the dorsal pallium

Excitatory hyperconnectivity in specific anterior frontal cortex microcircuits

J Neurosci 31: 5855 (2011)

Emx1-Cre

Neurons arising in the dorsal pallium

Precocious maturation of excitatory synapse and a faster GluN2A subunit switch, an enhanced acquisition of AMPA receptors

J Neurosci 34: 16166 (2014)

Emx1-Cre

Neurons arising in the dorsal pallium

Hypoactivity in the activity chamber and in the T-maze

J Neurodev Disord 7: 35 (2015)

Nestin-Cre

All neural cells

Deficit in contextual fear condition

J Neurodev Disord 7: 35 (2015)

Wnt1-Cre

Myenteric plexus neurons

Loss and reduced length of myenteric plexus Met-immunoreactive (Met-IR) neurite

J Neurosci 35: 11543 (2015)

Enhancement of bowel injury and reduction of epithelial cell proliferation

Immunity

Mx1-Cre

Dendritic cells

Failure to emigrate toward lymph nodes upon inflammation-induced activation

J Immunol 189, 1699–1707 (2012)

Impaired contact hypersensitivity reaction to contact allergens

Mrp8-Cre

Neutrophil

Enhancement of tumor growth and metastasis

Nature 522: 349 (2015)

CD4-Cre

T cells

Acieration of age-related thymic involution

Immunology 144:245 (2015)

Conditional KO mice (partial mutation)

Met(D/D)

 

Embryonic lethal, defects of placenta, liver, and limb muscle

Cell 87: 531 (1996)

Met(DGrb2/DGrb2)

 

Embryonic lethal. Limb muscle defects

Cell 87: 531 (1996)

Reduction of sensory nerves, Postnatal cerebellar impairment

Genes Dev 11: 3341 (1997)

Conditional mutant mice (including specific binding motif)

Met(2P/2P)

 

Defects of the liver, placenta, myoblast proliferation, and migration

Mol Cell 7: 1293 (2001)

Met(2S/2S)

 

Defects of the liver, myoblast migration, axon outgrowth

Mol Cell 7: 1293 (2001)

Met(2G/GS)

 

Developmentally normal

Mol Cell 7: 1293 (2001)

Conditional KO mice (partial mutation using Cre-LoxP system)

Met(grb2/grb2neo+)

 

Embryonic lethal. Limb muscle defects

Proc Natl Acad Sci USA 99: 15200 (2002)

Met(grb2/grb2neo-)

 

Reduction of cerebellum, foliation defects, declined proliferation of granule precursors

Proc Natl Acad Sci USA 99: 15200 (2002)

Tumorigenesis and Malignant Progression

Aberrant activation of Met is associated with tumorigenesis or malignant characteristics of several types of carcinomas. For instance, breast cancer, glioblastoma, and non-small cell lung cancers frequently express both HGF and Met. Although many types of carcinomas also express Met, the ligand is expressed by adjacent, noncancerous tissue rather than by tumor cells. In these cases, therefore, Met activation could occur in a paracrine manner. Ligand-independent activation of tyrosine kinase receptor is typically observed in cells that express high levels of receptor. Overexpression of Met by gene amplification has been found in cancers with highly invasive and malignant characteristics, including gastric and esophageal carcinomas, medulloblastoma, and non-small cell lung carcinomas (NSCLC). Moreover, Missense mutations in the Met gene are causative genetic disorders in inherited and in some sporadic, papillary renal carcinomas. Mutations found in papillary renal carcinomas are located in the tyrosine kinase domain of the Met receptor, and these Met mutations are likely to be caused by function mutations. In addition to papillary renal carcinoma, missense mutations in the Met gene have been found in different types of cancers, including lung cancer, hepatocellular carcinoma, and gastric cancer in the Sema, IPT, juxtamembrane, and tyrosine kinase domains.

Cancer cell migration is typically regulated by integrins, matrix-degrading enzymes, cell–cell adhesion molecules, and cell–cell communication. The HGF–Met signaling pathway affects these processes through cooperative integrin signaling, promotion of matrix metalloproteinases (MMPs) expression, and regulation of cadherin endocytosis processes. Similarly, in the tumor metastatic phase, HGF–Met axis is important for distant metastasis via the inducement of angiogenesis, chemokine-induced homing, and inhibition of tumor anoikis, which suggests that the HGF–Met pathway plays important roles in various tumor microenvironments.

Some growth factors, as represented by HGF, have all been shown to cause drug resistance by reactivating either or both of the PI3K–AKT and MEK–ERK pathways. Inhibition of their corresponding RTKs was able to overcome the growth factor-mediated drug resistance but was ineffective as a monotherapy. In NSCLC, Met gene amplification has been detected in ~20% of patients with acquired resistance to gefitinib or erlotinib, which are selective inhibitors for EGFR tyrosine kinase (Engelman et al. 2007). HGF induces resistance to EGFR tyrosine kinase inhibitors in EGFR mutant lung cancer. High-level expression of HGF has been noted in 60% and 19% of patients with acquired and intrinsic resistance to EGFR tyrosine kinase inhibitors, respectively. In addition to EGFR tyrosine kinase inhibitors, HGF induces resistance to vemurafenib in BRAFV600E melanoma models and to the ERBB2 inhibitor lapatinib in ERBB2-amplified breast cancer cell lines. Clinically, circulating levels of HGF before treatment have been correlated with lessened incidences of progression-free status and with diminished overall survival in patients.

An important implication in the cancer stem cell concept is that therapeutic success depends on the eradication of the elusive tumor cell subpopulation, because only this population is capable of generating or regenerating tumors and metastasis even after a prolonged period of remission. The HGF–Met pathway plays an important role in regulating the stemness and invasiveness of cancer stem cells. In colon adenocarcinomas, Wnt activity is thought to be supported by myofibroblast-secreted HGF. Indeed, HGF secreted from tumor-associated cells increases CD44v6, which is a typical marker of cancer stem cells, and also increases expression in colorectal cancer stem cells by activating the Wnt/β-catenin pathway that promotes migration and metastasis. Therefore, the potential use of new molecules that inhibit the HGF/Met: axis is one of therapeutic targets for the targeting of cancer stem cells.

Therapeutic Approaches with HGF

Based on the evidence that activation of the Met receptor leads to tissue protection and repair against tissue injury, but also to invasive and metastatic progression of cancer cells in tumor tissues, two distinct therapeutic approaches can be considered: one is compensation of HGF such as Met agonist, for the treatment of organ injuries; the other is as inhibitory molecules against the HGF–Met pathway for suppression of cancer invasion and metastasis.

As mentioned above, endogenous HGF is required for self-repair of the injured livers, kidneys, lungs, and so on. Experiments to explore the therapeutic potential of HGF in the treatment of diseases have been performed in various disease models in different tissues (Table 3) (Matsumoto et al. 2014). When recombinant human HGF was administrated into hepatectomy or hepatotoxins in mice, hepatocyte proliferation and duplication were enhanced. Inversely, administration of anti-HGF antibody diminished the regenerative responses of hepatocytes after liver injury. In these forms of tissue regeneration and anti-apoptotic actions, HGF has been used to abrogate the onset of acute hepatitis and fulminant hepatic failure. Regenerative and/or tissue-protective effects of HGF have been observed in other organs. HGF is also required for repair during acute renal failure caused by the administration of nephrotoxic drugs or renal ischemia. Likewise, in a murine model of cardiac ischemia/reperfusion injury, HGF has reduced the infarcted area via the protection of cardiac myocytes from apoptotic cell death.
HGF (Hepatocyte Growth Factor), Table 3

Therapeutic approaches with recombinant HGF protein in various disease models

Tissues and disease/injury models

References

Liver

 Acute hepatitis

Hepatology 16: 1227–1235 (1992)

 Cholestasis

Am. J. Physiol. 292: G639–G646 (2007)

 Fulminant hepatitis

Biochem. Biophys. Res. Commun. 244: 683–690 (1998)

 Liver fibrosis/cirrhosis

J. Biochem. 118: 643–649 (1995)

 Liver cirrhosis + surgery

Hepatology 28: 756–760 (1998)

 Alcoholic steatohepatitis

J. Clin. Investig. 1999: 103, 313–320 (1999)

Gastrointestinal

 Ulcerative colitis

J. Pharmacol. Exp. Ther. 307: 146–151 (2003)

 Gastric ulcer

Gastroenterology 113: 1858–1872 (1997)

 Gastric injury

Biochem. Biophys. Res. Commun. 341: 897–903 (2006)

Kidney

 Acute kidney injury

Proc. Natl. Acad. Sci. USA 91: 4357–4361 (1994)

 Acute renal inflammation

Kidney Int. 69: 1166–1174 (2006)

 Septic acute renal failure

Biochem. Biophys. Res. Commun. 380: 333–337 (2009)

 Diabetic nephropathy

Am. J. Physiol. 286: F134–F143 (2004)

 Chronic kidney disease

J. Clin. Investig. 101: 1827–1834 (1998)

 Glomerulonephritis

Am. J. Physiol. 284: F1171–F1180 (2003)

 Chronic allograft nephropathy

J. Am. Soc. Nephrol. 12: 1280–1292 (2001)

Cardiovascular

 Critical limb ischemia

Circulation 97: 381–390 (1998)

 Neointimal hyperplasia

Circulation 101: 2546–2549 (2000)

 Coronary artery disease

Surg. Today 35: 855–860 (2005)

 Myocardial infarction

J. Clin. Investig. 106: 1511–1519 (2000)

 Cardiac allograft vasculopathy

Circulation 110: 1650–1657 (2004)

 Dilated cardiomyopathy

Am. J. Physiol. 288: H2131–H2139 (2005)

Respiratory

 Acute lung injury

Am. J. Physiol. 270: L1031–L1039 (1996)

 Ischemia/reperfusion

J. Heart Lung Transplant. 26: 935–943 (2007)

 Lung fibrosis

Am. J. Resp. Crit. Care Med. 156: 1937–1944 (1997)

 Pulmonary emphysema

Biochem. Biophys. Res. Commun. 324: 276–280 (2004)

 Left pneumonectomy

Am. J. Respir. Cell Mol. Biol. 26: 525–533 (2002)

 Allergic airway inflammation

Am. J. Respir. Cell Mol. Biol. 32: 268–280 (2005)

 Vocal fold scarring

Ann. Otol. Rhinol. Laryngol. 116: 762–769 (2007)

Skin

 Wounding

J. Pathol. 203: 831–838 (2004)

Nervous system(s)

 Cerebral ischemia

J. Celebral. Blood Flow Metab. 18: 345–348 (1998)

 Peripheral nerve injury

Eur. J. Neurosci. 11: 4130–4144 (1999)

 Amyotrophic lateral sclerosis

J. Neuropathol. Exp. Neurol. 66: 1037–1044 (2007)

 Hydrocephalus

Neurobiol. Disease 21: 576–586 (2006)

 Retinal injury

Invest. Ophthalmol. Vis. Sci. 43: 528–536 (2002)

 Photoreceptor degeneration

Curr. Eye Res. 31: 347–355 (2006)

 Difficulty in hearing

Acta Otolaryngol. 129: 453–457 (2009)

Musculoskeletal

 Articular cartilage injury

Acta Orthop. Stand. 68: 474–480 (1997)

 Skeletal muscle injury

Am. J. Physiol. 278: C174–C181 (2000)

 Rheumatoid arthritis

J. Immunol. 175: 4745–4753 (2005)

 Ligament injury

Arthroscopy 26: 84–90 (2010)

Chronic inflammatory diseases are characterized by fibrotic changes in tissues, including liver cirrhosis, chronic renal failure, lung fibrosis, and cardiomyopathy. These fibrotic diseases are progressive and currently incurable, with the exception of organ transplantation. Administration of HGF into rats with liver cirrhosis has induced uPA expression and the degradation of hepatic extracellular matrix components, thereby abrogating the mortality rate due to hepatic dysfunction. When used in mouse models of nephrotic syndrome, HGF has also been useful for restoring renal dysfunction through the tubular repair and resolution of fibrosis. Although the mechanisms responsible for the anti-fibrotic action of HGF are not fully understood, HGF is known to suppress the expression of transforming growth factor-β (TGF-β), a key growth factor during the onset of tissue fibrosis. Reciprocal balance between tissue levels of HGF and TGF-β is involved in determining the prognosis of chronic inflammatory diseases. Thus, HGF compensation could produce therapeutic outcomes to enhance the proteinase activities responsible for the degradation of extracellular matrix components, including matrix metalloproteinases. The neurotrophic actions of HGF have been expanded to include therapeutic approaches for the treatment of congenital neural disorders and regeneration of neural tissues lost as a result of neurodegenerative diseases and injuries. An infusion of HGF into the brain has been used to prevent neuronal death in the hippocampus, cerebral cortex, and spinal cord. Intrathecal administration of HGF has suppressed disease progression and prolonged the life span in rat models for amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder characterized by the progressive loss of motor neurons and the degeneration of motor axons. Likewise, the intrathecal administration of HGF has been used to promote functional recovery after spinal cord injury in the common marmoset.

The efficacy and safety of the intramuscular injection of a naked plasmid encoding the human HGF gene were investigated in patients with critical limb ischemia in a multicenter, randomized, double-blind, placebo-controlled trial. HGF achieved an improvement rate that was significantly higher than that of the placebo, including the improvement of resting pain and a reduction in ulcer size. In this instance, HGF gene therapy improved the quality of life, without major safety problems. Thus, HGF gene therapy is determined to be safe and effective for critical limb ischemia. A phase I clinical trial of recombinant HGF protein for the treatment of patients with acute kidney injury has been completed. More recently, phase II clinical trials of recombinant human HGF for the treatment of patients with ALS and spinal cord injury are ongoing.

Drug Development of HGF–Met Inhibitors

With a comprehensive understanding of the roles of the HGF–Met pathway in carcinogenesis, its pathway has been targeted by novel therapeutic agents, including small molecular inhibitors of Met kinase activities, ribozymes, small interfering RNA, monoclonal antibodies, soluble forms of Met, and HGF antagonists. Among them, the development of small synthetic Met tyrosine kinase inhibitors and humanized monoclonal antibodies against HGF or Met has either progressed to clinical development or is already being marketed (Table 4) (Cecchi et al. 2012).
HGF (Hepatocyte Growth Factor), Table 4

HGF–Met inhibitors in clinical development

Classification and name

Target(s)

Stage

Clinical application

Small synthetic

AMG 208

Met

Phase I

Advanced solid tumors

Tivantinib (ARQ197)

Met

Phase II

Advanced/metastatic pancreatic cancer

Phase III

Advanced/metastatic non-small cell lung cancer

BMS-777607

Met

Phase I/II

Advanced/metastatic squamous cell carcinoma (head and neck)

Advanced/metastatic papillary renal cell carcinoma

E7050

Met, VEGFR2

Phase I/II

Advanced solid malignancies, glioblastoma, unresectable stage III/IV melanoma

Foretinib (GSK1363089)

Met, Ron, VEGFR1–3, PDGFR, Kit, Flt-3, Tie-2

Phase II

Recurrent/metastatic squamous cell carcinoma (head and neck), advanced/metastatic gastric cancer

Phase I/II

Papillary renal carcinoma,

Amuvatinib (MP470)

Met, Ret, Kit, PDGFR, Flt-3

Phase II

Small cell lung cancer

MGCD265

Met

Phase I/II

Advanced malignancies, non-small cell lung cancer

MK-2461

Met, Tie-2, Ron

Phase I/II

Advanced solid malignancies

Crizotinib (PF-02341066)

Alk, Met

Phase I/II

Non-small cell lung cancer

Phase I/II

Relapsed/refractory solid malignancies

Approved

Alk-mutated non-small cell lung cancer

PF-04217903

Met

Phase I

Advanced solid malignancies

Cabozantinib (XL184)

Met, VEGFR1–3, Ret, Kit, Flt-3, Tie-2

Phase II

Glioblastoma multiforme, carcinoid/pancreatic neuroendocrine tumor, metastatic castrate-resistant prostate cancer

Grade IV astrocytic tumor

Phase III

Medullary thyroid cancer

MK-8033

Met

Phase I/II

Advanced/metastatic solid malignancies and gastric cancer, recurrent/metastatic squamous cell carcinoma (head and neck), advanced/metastatic hepatocellular carcinoma

Antibody

Rilotumumab (AMG102)

HGF

Phase I/II

Advanced malignant glioma, prostate cancer, metastatic gastric, and esophageal adenocarcinoma

Phase II

Renal cell cancer, advanced malignant glioma

MetMAb

Met

Phase III

Non-small cell lung cancer

SCH900105

HGF

Phase II

Non-small cell lung cancer

For more current and details: http://clinicaltrials.gov/ct2/show/NCT01357395

Crizotinib (PF02341066) inhibits ALK, ROS1, and Met and is an FDA-approved TKI for NSCLC patients with EML–ALK fusion oncoprotein. Moreover, crizotinib showed a high efficacy in NSCLC patients with de novo Met amplification and splicing mutations in the Met exon 14, which is relevant since these mutations have been found with a relatively high frequency in NSCLC. MetMAb (onartuzumab) is a humanized monovalent monoclonal antibody against Met receptor that blocks the binding of HGF to the Met, while rilotumumab (AMG102) and SCH900105 are humanized monoclonal antibodies that inhibit downstream Met signaling. Rilotumumab has been studied in a phase II trial of advanced gastric or esophagogastric cancer and has demonstrated efficacy in patients with Met high expression. Development of onartuzumab and rilotumumab was terminated. Effectiveness, target cancer, and advantages/disadvantages of each of these therapeutic tools (small molecule Met tyrosine kinase inhibitors, anti-HGF, or anti-Met antibody) will be clarified in further clinical trials.

Summary

HGF exhibits multiple biological functions such as motogenic and morphogenic factors via the Met transmembrane receptor tyrosine kinase. Met activation induces autophosphorylation of cytoplasmic multi-substrate-binding sites. Cytoplasmic adaptor proteins are directly or indirectly recruited to this site and provide docking platforms for the further binding of signaling molecules, which leads to multiple biological responses unique to the HGF–Met pathway. HGF plays essential roles in developmental, physiological, and therapeutic processes. In particular, conditional knockout mice lack functional HGF or Met in selective cells/tissues, which has helped clarify many unpredicted functions such as the embryonic development of the liver and the placenta, the migration of myogenic precursor cells, and epithelial morphogenesis. Under physiological and pathological conditions, HGF–Met signaling contributes to tissue regeneration and protection in a variety of organs. Therefore, compensation and/or augmentation of HGF–Met signaling by administration of recombinant HGF or HGF genes has shown therapeutic value, and clinical trials are ongoing for treatments of diseases such as spinal cord injury and amyotrophic lateral sclerosis. Inversely, several HGF–Met inhibitors are in clinical trials for the treatment of patients with malignant tumors. Clinical study on abnormal HGF–Met function in the pathogenesis of malignant tumors will explore further therapeutic use of HGF–Met inhibitors for the treatment of patients with malignant tumors.

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Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  • Hiroki Sato
    • 1
  • Shunsuke Aoki
    • 2
  • Takashi Kato
    • 3
  • Kunio Matsumoto
    • 1
  1. 1.Division of Tumor Dynamics and Regulation, Cancer Research InstituteKanazawa UniversityKanazawaJapan
  2. 2.Department of Bioscience and Bioinformatics, Graduate School of Computer Science and Systems EngineeringKyushu Institute of TechnologyIizuka-shiJapan
  3. 3.Department of Pharmacology, Faculty of MedicineKinki UniversitySayamaJapan