C-Met Proto-Oncogene Expression in Benign and Malignant Human Renal Tissues

A novel combination therapy with Cabozantinib and Honokiol effectively inhibits c-Met-Nrf2-induced renal tumor growth through increased oxidative stress

Receptor tyrosine kinase (RTK), c-Met, is overexpressed and hyper active in renal cell carcinoma (RCC). Most of the therapeutic agents mediate cancer cell death through increased oxidative stress. Induction of c-Met in renal cancer cells promotes the activation of redox-sensitive transcription factor Nrf2 and cytoprotective heme oxygenase-1 (HO-1), which can mediate therapeutic resistance against oxidative stress. c-Met/RTK inhibitor, Cabozantinib, has been approved for the treatment of advanced RCC. However, acquired drug resistance is a major hurdle in the clinical use of cabozantinib. Honokiol, a naturally occurring phenolic compound, has a great potential to downregulate c-Met-induced pathways. In this study, we found that a novel combination treatment with cabozantinib + Honokiol inhibits the growth of renal cancer cells in a synergistic manner through increased production of reactive oxygen species (ROS); and it significantly facilitates apoptosis-and autophagy-mediated cancer cell death. Activation of c-Met can induce Rubicon (a negative regulator of autophagy) and p62 (an autophagy adaptor protein), which can stabilize Nrf2. By utilizing OncoDB online database, we found a positive correlation among c-Met, Rubicon, p62 and Nrf2 in renal cancer. Interestingly, the combination treatment significantly downregulated Rubicon, p62 and Nrf2 in RCC cells. In a tumor xenograft model, this combination treatment markedly inhibited renal tumor growth in vivo; and it is associated with decreased expression of Rubicon, p62, HO-1 and vessel density in the tumor tissues. Together, cabozantinib + Honokiol combination can significantly inhibit c-Met-induced and Nrf2-mediated anti-oxidant pathway in renal cancer cells to promote increased oxidative stress and tumor cell death.

cMET - a prognostic marker in papillary renal cell carcinoma?

BACKGROUND

The tyrosine-protein kinase c-Met plays a decisive role in numerous cellular processes, as a proto-oncogene that supports aggressive tumor behavior. It is still unknown whether c-Met could be relevant for prognosis of papillary RCC (pRCC).

PATIENTS AND METHODS

Specimen collection were a collaboration of the PANZAR consortium. Patients' medical history and tumor specimens were collected from n=197 and n=110 patients with type 1 and 2 pRCC, respectively. Expression of cMET was determined by immunohistochemistry (IHC).

RESULTS

In total, cMET staining was evaluable in of 97/197 type 1 and 63/110 type 2 of pRCC cases. Five-years overall survival reviled no significant difference in dependence of cMET positivity (cMET^- vs. cMET⁺: pRCC type 1: 84.8 % vs. 80.3 %, respectively (p=0.303, log-rank); type 2: 71.4 % vs. 64.4 % respectively (p= 0.239, log-rank)). Interestingly, the subgroup analyses showed a significant difference for cMET expression in T stage and metastases of the pRCC type 2 (p=0.014, p=0.022, chi-square). The cMET positive type 2 collective developed more metastases compared to the cMET negative cohort (pRCC Typ 2 M+: cMET^-: 2 (4.3%) vs. cMET⁺: 12 (19%)).

CONCLUSION

CMET expression did not qualify as a prognostic marker in pRCC for overall survival.

C-Met as a Key Factor Responsible for Sustaining Undifferentiated Phenotype and Therapy Resistance in Renal Carcinomas

C-Met tyrosine kinase receptor plays an important role under normal and pathological conditions. In tumor cells’ overexpression or incorrect activation of c-Met, this leads to stimulation of proliferation, survival and increase of motile activity. This receptor is also described as a marker of cancer initiating cells. The latest research shows that the c-Met receptor has an influence on the development of resistance to targeted cancer treatment. High c-Met expression and activation in renal cell carcinomas is associated with the progression of the disease and poor survival of patients. C-Met receptor has become a therapeutic target in kidney cancer. However, the therapies used so far using c-Met tyrosine kinase inhibitors demonstrate resistance to treatment. On the other hand, the c-Met pathway may act as an alternative target pathway in tumors that are resistant to other therapies. Combination treatment together with c-Met inhibitor reduces tumor growth, vascularization and pro-metastatic behavior and results in suppressed mesenchymal phenotype and vascular endothelial growth factor (VEGF) secretion. Recently, it has been shown that the acquirement of mesenchymal phenotype or lack of cell differentiation might be related to the presence of the c-Met receptor and is consequently responsible for therapy resistance. This review presents the results from recent studies identifying c-Met as an important factor in renal carcinomas being responsible for tumor growth, progression and metastasis, indicating the role of c-Met in resistance to antitumor therapy and demonstrating the pivotal role of c-Met in supporting mesenchymal cell phenotype.

Clinicopathological impacts of high c-Met expression in renal cell carcinoma: a meta-analysis and review

c-Met overexpression has been observed in renal cell carcinoma (RCC). However, its clinicopathological impacts remain uncertain. We performed this meta-analysis to evaluate the pathologic and prognostic impacts of high c-Met expression in patients with RCC. A systematic computerized search of the electronic databases PubMed and Embase was performed. From 12 studies, 1,724 patients with RCC were included in the meta-analysis. Compared with RCCs showing low c-Met expression, tumors with high c-Met expression showed significantly higher nuclear grade (odds ratio = 2.45 [95% CI: 1.43-4.19], P = 0.001) and pT stage (odds ratio = 2.18 [95% CI: 1.27-3.72], P = 0.005). In addition, patients with c-Met-high RCC showed significantly worse overall survival than those with c-Met-low tumor (hazard ratio = 1.32 [95% CI: 1.12-1.56], P = 0.0009). In conclusion, this meta-analysis demonstrates that high c-Met expression correlate with significantly worse pathological features and overall survival, indicating c-Met overexpression is a potential adverse prognostic marker for patients with RCC.

The role of c-Met in prognosis and clinicopathology of renal cell carcinoma: Results from a single-centre study and systematic review

BACKGROUND AND OBJECTIVES

The c-Met proto-oncogene pathway plays an important role in the progression of various cancers. However, the effect of the c-Met pathway on renal cell carcinoma (RCC) remains controversial. We decided to clarify the role of c-Met in prognosis and clinicopathology of RCC.

METHODS

A total of 10 pairs of tumour and adjacent tissues were obtained from patients with primary RCC between 2013 and 2014 and tissue microarrays to assess c-Met expression in tumour tissues from 90 patients with RCC by Western blot and immunohistochemical staining. We also presented a meta-analysis to explore the correlation between c-Met and pathological grade and stage of RCC. The two-tailed Pearson's χ² and Fischer exact tests were used to compare categorical variables. Multivariate analysis was performed using the multivariate Cox proportional hazards model.

RESULTS

C-Met protein levels were increased in 8 of 10 RCC tissue samples compared with their adjacent normal tissue and c-Met expression levels were positively associated with a high nuclear grade (P = 0.008) and pT stage (P = 0.002). Multivariate analysis showed that a high expression of c-Met was an independent predictor of disease-specific survival (P = 0.017). A meta-analysis found that increased c-Met expression in RCC tissues was closely correlated with high tumour grade (P<0.001) and high pT stage (P = 0.001). Most importantly, c-Met expression was significantly correlated with disease-specific survival (P<0.001).

CONCLUSIONS

Because c-Met is strongly associated with pathological grade, stage and disease-specific survival, c-Met levels may have potential to predict patient prognosis and to guide clinical diagnosis and treatment.

c-Met in chromophobe renal cell carcinoma

c-Met plays a role as a prognostic marker in clear cell renal cell carcinoma. In addition, recently the tyrosine kinase inhibitor cabozantinib targeting c-Met was approved for the treatment of advanced renal cell carcinoma (RCC). In contrast to clear cell RCC, little is known about c-Met expression patterns in rarer RCC subtypes. The aim of this study was to evaluate the prevalence, distribution and prognostic impact of c-Met expression on chromophobe (ch)RCC. Patients who underwent renal surgery due to chRCC were retrospectively evaluated. Tumor specimens were analyzed for c-Met expression by immunohistochemistry. Expression data were associated with clinicopathological parameters including patient survival. Eighty-one chRCC patients were eligible for analysis. Twenty-four (29.6%) patients showed a high c-Met expression (c-Met^high, staining intensity higher than median). Our results showed an association between c-Met^high expression and the existence of lymph node metastasis (p = 0.007). No further significant clinicopathological associations with c-Met were identified, also regarding c-Met expression and overall survival. In conclusion, to our knowledge this is the first study evaluating the prognostic impact of c-Met in a considerably large cohort of chRCC. High c-Met expression is associated with the occurrence of lymph node metastasis. This indicates that c-Met might be implicated into metastatic progression in chRCC.

The evolving role of monoclonal antibodies in the treatment of patients with advanced renal cell carcinoma: a systematic review

INTRODUCTION

While the majority of the vascular endothelial growth factor (VEGF) and mammalian target of rapamycin (mTOR) inhibitors currently used for the therapy of metastatic renal cell carcinoma (mRCC) are small molecule agents inhibiting multiple targets, monoclonal antibodies are inhibitors of specific targets, which may decrease off-target effects while preserving on-target activity. A few monoclonal antibodies have already been approved for mRCC (bevacizumab, nivolumab), while many others may play an important role in the therapeutic scenario of mRCC.

AREAS COVERED

This review describes emerging monoclonal antibodies for treating RCC. Currently, bevacizumab, a VEGF monoclonal antibody, is approved in combination with interferon for the therapy of metastatic RCC, while nivolumab, a Programmed Death (PD)-1 inhibitor, is approved following prior VEGF inhibitor treatment. Other PD-1 and PD-ligand (L)-1 inhibitors are undergoing clinical development.

EXPERT OPINION

Combinations of inhibitors of the PD1/PD-L1 axis with VEGF inhibitors or cytotoxic T-lymphocyte antigen (CTLA)-4 inhibitors have shown promising efficacy in mRCC. The development of biomarkers predictive for benefit and rational tolerable combinations are both important pillars of research to improve outcomes in RCC.

The renal effects of ALK inhibitors

Anaplastic lymphoma kinase 1 (ALK-1) is a member of the insulin receptor tyrosine kinase family. In clinical practice, three small molecule inhibitors of ALK-1 are used, namely crizotinib, ceritinib and alectinib. Several more agents are in active pre-clinical and clinical studies. Crizotinib is approved for the treatment of advanced ALK-positive non-small cell lung cancer (NSCLC). According to the package insert and published literature, treatment with crizotinib appears to be associated with kidney failure as well as an increased risk for the development and progression of renal cysts. In addition, this agent is associated with development of peripheral edema and rare electrolyte disorders. This review focuses on the adverse renal effects of Crizotinib in clinical practice.

Imaging features of renal complications after crizotinib treatment for non-small-cell lung cancer: a case report

Crizotinib has been approved for the treatment of advanced ALK-positive non–small cell lung cancer. Its use is associated with the development of complex renal cysts. However, there is limited literature regarding imaging features of renal cystic disease during crizotinib therapy and its complications or progression. Here, we describe a case of a patient with ALK-positive advanced non–small cell lung cancer who developed complex renal cyst during crizotinib treatment. The renal cyst is complicated by infection and abscess formation. Subsequent renal biopsy, antibiotics treatment, and open drainage of loculated renal abscess showed no malignant cells and contributed to the diagnosis. The imaging features should be recognized as renal cystic disease of crizotinib treatment and not to be mistaken as new metastasis and disease progression.

Development of renal cysts after crizotinib treatment in advanced ALK-positive non-small-cell lung cancer

INTRODUCTION

The development of complex renal cysts after crizotinib treatment for non-small-cell lung cancer (NSCLC) is a reported side effect. However, its occurrence and characteristics have not been reported.

METHODS

Medical records and computed tomography images of crizotinib-treated patients in three prospective clinical trials were reviewed. The size and Bosniak category of the renal cysts before and after crizotinib treatment were determined. Patients' clinical characteristics, tumor stage, treatment response, renal function, and outcomes were analyzed.

RESULTS

During December 2010 to March 2013, we enrolled 32 patients who received crizotinib. There were 23 patients who had renal cysts before crizotinib. The median follow-up time was 493 days. Seven patients (22%, six with baseline renal cyst and one without baseline renal cyst) had significant renal cyst change. Four (13% of all) had new complex renal cysts. The median time from crizotinib treatment to first recognization of significant renal cyst change was 77 days. After stopping crizotinib, complex renal cysts regressed significantly. Patients with significant renal cyst change received more previous anticancer therapy (median, 5 lines versus 3 lines, p = 0.04) and received crizotinib for longer duration (median, 956 days versus 248 days, p = 0.007) compared with those without significant renal cyst change.

CONCLUSIONS

Change of renal cysts after crizotinib treatment is not uncommon. Development of complex renal cysts reverses after stopping crizotinib.

Targeting the hepatocyte growth factor/c-Met signaling pathway in renal cell carcinoma

The product of a proto-oncogene, the c-Met protein is a transmembrane receptor tyrosine kinase. Its only known ligand, hepatocyte growth factor/scatter factor, regulates cell growth, motility, migration, invasion, proliferation, and angiogenesis. Dysregulation of c-Met and hepatocyte growth factor have been observed in both clear cell and non-clear cell renal cell carcinomas (RCCs), although only papillary RCCs harbor activating mutations in the MET gene. In clear cell RCC, there is evidence of a direct link between loss of von Hippel-Lindau and up-regulation of c-Met. As in other cancers, high expression of c-Met correlates with worse outcomes in RCC. In vitro and in vivo preclinical RCC models demonstrate cancer control with small molecule and antibodies against c-Met. Given these findings, the c-Met pathway is a logical therapeutic target in RCC, and several agents are in clinical testing with early signs of efficacy.

Mutant p53 cooperates with knockdown of endogenous wild-type p53 to disrupt tubulogenesis in Madin-Darby canine kidney cells

Mutation of the p53 gene is the most common genetic alteration in human malignances and associated clinically with tumor progression and metastasis. To determine the effect of mutant p53 on epithelial differentiation, we developed three-dimensional culture (3-D) of Madin-Darby canine kidney (MDCK) cells. We found that parental MDCK cells undergo a series of morphological changes and form polarized and growth-arrested cysts with hollow lumen, which resembles branching tubules in vitro. We also found that upon knockdown of endogenous wild-type p53 (p53-KD), MDCK cells still form normal cysts in 3-D culture, indicating that p53-KD alone is not sufficient to disrupt cysts formation. However, we found that ectopic expression of mutant R163H (human equivalent R175H) or R261H (human equivalent R273H) in MDCK cells leads to disruption of cyst polarity and formation of invasive aggregates, which is further compounded by knockdown of endogenous wild-type p53. Consistently, we found that expression of E-cadherin, β-catenin, and epithelial-to-mesenchymal transition (EMT) transcription factors (Snail-1, Slug and Twist) is altered by mutant p53, which is also compounded by knockdown of wild-type p53. Moreover, the expression level of c-Met, the hepatocyte growth factor receptor and a key regulator of kidney cell tubulogenesis, is enhanced by combined knockdown of endogenous wild-type p53 and ectopic expression of mutant R163H or R261H but not by each individually. Together, our data suggest that upon inactivating mutation of the p53 gene, mutant p53 acquires its gain of function by altering morphogenesis and promoting cell migration and invasion in part by upregulating EMT and c-Met.

Onartuzumab (MetMAb): using nonclinical pharmacokinetic and concentration-effect data to support clinical development

PURPOSE

We characterized the pharmacokinetics of onartuzumab (MetMAb) in animals and determined a concentration-effect relationship in tumor-bearing mice to enable estimation of clinical pharmacokinetics and target doses.

EXPERIMENTAL DESIGN

A tumor growth inhibition model was used to estimate tumoristatic concentrations (TSC) in mice. Human pharmacokinetic parameters were projected from pharmacokinetics in cynomolgus monkeys by the species-invariant time method. Monte Carlo simulations predicted the percentage of patients achieving steady-state trough serum concentrations (Ctrough ss) ≥TSC for every 3-week (Q3W) dosing.

RESULTS

Onartuzumab clearance (CL) in the linear dose range was 21.1 and 12.2 mL/d/kg in mice and cynomolgus monkeys with elimination half-life at 6.10 and 3.37 days, respectively. The estimated TSC in KP4 pancreatic xenograft tumor-bearing mice was 15 μg/mL. Projected CL for humans in the linear dose range was 5.74 to 9.36 mL/d/kg with scaling exponents of CL at 0.75 to 0.9. Monte Carlo simulations projected a Q3W dose of 10 to 30 mg/kg to achieve Ctrough ss of 15 μg/mL in 95% or more of patients.

CONCLUSIONS

Onartuzumab pharmacokinetics differed from typical bivalent glycosylated monoclonal antibodies with approximately 2-times faster CL in the linear dose range. Despite this higher CL, xenograft efficacy data supported dose flexibility with Q1W to Q3W dose regimens in the clinical setting with a TSC of 15 μg/mL as the Ctrough ss target. The projected human efficacious dose of 10 to 30 mg/kg Q3W should achieve the target TSC of 15 μg/mL. These data show effective pharmacokinetic/pharmacodynamic modeling to project doses to be tested in the clinic.

Expression of the c-Met Proteins in Malignant Skin Cancers

BACKGROUND

The expression of c-Met is substantially elevated in most malignant human cancers. We therefore searched for c-Met expression and compared the expression level among malignant skin cancers.

OBJECTIVE

The aim of this study was to determine the c-Met expression pattern and the protein expression level in selected malignant cutaneous tumors.

METHODS

G361 cells (malignant melanoma cell line) and A431 cells (squamous cell carcinoma cell line) were cultured and analyzed, using immunoprecipitation and Western blot analysis, for expression of c-Met. Additionally, 16 separate specimens of malignant melanomas (MMs), 16 squamous cell carcinomas (SCCs), 16 basal cell carcinomas (BCCs) and 16 normal tissues were analyzed for the expression of c-Met using immunohistochemical studies.

RESULTS

Based on cultured cell immunoprecipitation and Western blot analysis, both A431 cells and G361 cells expressed c-Met, however, c-Met was expressed substantially more in G361 cells. Immunohistochemical examination of c-Met showed that it was over-expressed in all malignant skin cancers. In addition, c-Met expression was more increased in MM compared to other cancers.

CONCLUSION

In our study, c-Met is involved in malignant skin cancer development and the level of its expression is thought to be related to the degree of malignancy in melanoma cancers.

A phase II study of the efficacy and safety of AMG 102 in patients with metastatic renal cell carcinoma

OBJECTIVE

• To evaluate the efficacy and safety of single-agent AMG 102, an investigational, fully human monoclonal antibody to hepatocyte growth factor/scatter factor (HGF/SF), in renal cell carcinoma (RCC).

PATIENTS AND METHODS

• This open-label phase II study included patients ≥ 18 years old with histologically confirmed, advanced or metastatic RCC (mRCC) and Eastern Cooperative Oncology Group performance status 0 to 2. AMG 102 was administered i.v. at 10 or 20 mg/kg once every 2 weeks. • A two-stage design was used at each dose level and the primary endpoint was objective best confirmed response (by Response Evaluation Criteria in Solid Tumours) at any time.

RESULTS

• Sixty-one patients with mRCC enrolled and received AMG 102 (40 at 10 mg/kg; 21 at 20 mg/kg). Overall, 70.5% were men, median age was 59 years (range, 39 to 84 years), and 92% had received previous anti-vascular endothelial growth factor therapy. RCC histologies were: clear cell (75.4%), papillary (11.5%), chromophobe (4.9%) and unclassified (8.2%). • One confirmed partial response occurred at 10 mg/kg, maintained for over 2.5 years; 26 patients (43%) had stable disease, 10 (16%) for ≥ 32 weeks. The median profression-free survival was 3.7 months at 10 mg/kg and 2.0 months at 20 mg/kg. The commonest adverse events were oedema (45.9%), fatigue (37.7%) and nausea (27.9%). Grade 3 or 4 adverse events occurred in 33% of patients, the most common being oedema (9.8%). • Baseline levels of plasma HGF/SF and soluble c-Met as well as archival-tumour c-Met did not correlate with measures of efficacy.

CONCLUSION

• Single-agent AMG 102 was tolerable, but it is unclear if AMG 102 was growth inhibitory in this population of patients with mRCC.

Selection criteria for c-Met-targeted therapies: emerging evidence for biomarkers

Extensive development of targeted therapies emphasize the critical need for biomarkers and major efforts have been engaged to identify screening, prognostic, stratification and therapy-monitoring markers. One of the challenges in translating preclinical studies into effective clinical therapies remains the accurate identification of a responsive subsets of patients. Studies on trastuzumab demonstrated that patient response could be specifically correlated with the amplification of the Her2 gene. However, for the EGF receptor, it has been more difficult to find the right stratification biomarker and recent data demonstrate that genetic alterations for the EGF receptor have to be considered. Taken together, these data underline the need for a deeper understanding of both targeted receptor and human disease to determine pathways that might be investigated during early clinical trials in order to define relevant biomarkers for patient selection. This article, dealing with the c-Met tyrosine kinase receptor, provides an overview of c-Met alterations observed in cancer and proposes approaches for stratification biomarker selection.

Expression of hepatocyte growth factor and its receptor met in Wilms' tumors and nephrogenic rests reflects their roles in kidney development

PURPOSE

Hepatocyte growth factor (HGF) and its receptor Met are known to play diverse roles in both organogenesis and cancer. Wilms' tumor (WT) is a prototype for the link between abrogated development and neoplasia, with dysregulation of growth factor/receptor pathways playing key roles. Despite this, an understanding of the HGF/Met axis in the process is lacking.

EXPERIMENTAL DESIGN

Observing copy number alterations at the loci for these genes in WTs and their precursor lesions nephrogenic rests, we examined protein expression by immunohistochemistry and investigated the effects of HGF on an in vitro model of kidney development.

RESULTS

HGF was preferentially expressed in the blastemal cells of nephrogenic rests but not WTs. Met expression was infrequent and restricted to well-differentiated epithelial cells and stroma in both lesions. In an independent cohort of favorable histology WTs on a tissue microarray, HGF was expressed in 15 of 193 (8%) cases and correlated with a predominance of epithelial cells, whereas Met expression was observed in 25 of 179 (14%) cases and was associated with stromal subtypes. In a mouse mesonephric cell line model, we observed Met expression in culture conditions reflecting both mesenchymal and epithelial differentiation, whereas HGF was up-regulated in association with acquisition of a more epithelial-like phenotype. This could be mimicked by exogenous exposure of mesenchymal-like cells to recombinant HGF.

CONCLUSIONS

These data show that the relatively infrequent expression of HGF and Met in WT tumorigenesis reflects their roles in nephrogenesis, particularly the mesenchymal-to-epithelial transition, rather than a dependence on oncogenic signaling pathways.

Phase II randomized study of Plitidepsin (Aplidin), alone or in association with L-carnitine, in patients with unresectable advanced renal cell carcinoma

This randomized phase II study evaluated two schedules of the marine compound Plitidepsin with or without co-administration of L-carnitine in patients with renal cell carcinoma. Patients had adequate performance status and organ function. The primary endpoint was the rate of disease control (no progression) at 12 weeks (RECIST). Other endpoints included the response rate and time dependent efficacy measures. The trial also assessed the efficacy of L-carnitine to prevent Plitidepsin-related toxicity. The two regimes given as 24 hour infusion every two weeks showed hints of antitumoral activity. Disease control at 12 weeks was 15.8% in Arm A (5mg/m2, no L-carnitine) and 11,1% in Arm B (7 mg/m2 with L-carnitine). Two partial responses were observed in Arm A (19 patients), none in Arm B (20 patients). Both schedules had the same progression-free interval (2.1 months). The median overall survival was 7.0 and 7.6 months. The safety profile was similar in both arms of the trial and adverse events were mainly mild to moderate (NCI CTC version 2.0). Increasing the dose to 7 mg/m2 did not increase the treatment efficacy but the incidence of transaminase and CPK elevations and serious AEs. Coadministration of L-carnitine did not prevent muscular toxicity or CPK-elevation associated with Plitidepsin.

Scatter Factors in renal disease: Dr. Jeckyll and Mr. Hyde?

The Scatter Factors are two homologous proteins, named Scatter Factor/Hepatocyte Growth Factor and Macrophage Stimulating Protein. Their receptors are the products of two oncogenes, Met and Ron, respectively. The Scatter Factors induce movement, stimulate proliferation, regulate apoptosis and are morphogenic, i.e. operate an integrated program that seems tailored to drive organ development and to regenerate injured tissues. On the other hand, Scatter Factors may be responsible for pathologic tissue remodeling, infiltration of inflammatory cells, and tumor growth and diffusion. The review describes the involvement of Scatter Factors in renal disease, including acute renal failure, glomerulonephritis, chronic fibrosing nephropathies, dialysis, renal transplantation and renal tumors, and discusses the double-faced role of Scatter Factors, that play either a protective or a pathogenic role.

Origin of renal cell carcinomas

Cancer is a heritable disorder of somatic cells: environment and heredity are both important in the carcinogenic process. The primal force is the "two hits" of Knudson's hypothesis, which has proved true for many tumours, including renal cell carcinoma. Knudson et al. [1, 2] recognised that familial forms of cancer might hold the key to the identification of important regulatory elements known as tumour-suppressor genes. Their observations (i.e., that retinoblastoma tend to be multifocal in familial cases and unifocal in sporadic presentation) led them to propose a two-hit theory of carcinogenesis. Furthermore, Knudson postulated that patients with the familial form of the cancer would be born with one mutant allele and that all cells in that organ or tissue would be at risk, accounting for early onset and the multifocal nature of the disease. In contrast, sporadic tumours would develop only if a mutation occurred in both alleles within the same cell, and, as each event would be expected to occur with low frequency, most tumours would develop late in life and in a unifocal manner [3, 4]. The kidney is affected in a variety of inherited cancer syndromes. For most of them, both the oncogene/tumour-suppressor gene involved and the respective germline mutations have been identified. Each of the inherited syndromes predisposes to distinct types of renal carcinoma. Families with hereditary predisposition to cancer continue to provide a unique opportunity for the identification and characterisation of genes involved in carcinogenesis. A surprising number of genetic syndromes predispose to the development of renal cell carcinoma, and genes associated with five of these syndromes have been already identified: VHL, MET, FH, BHD and HRPT2. Few cancers have as many different types of genetic predisposition as renal cancer, although to date only a small proportion of renal cell cancers can be explained by genetic predisposition.

Prognostic significance of serum hepatocyte growth factor in clear cell renal cell carcinoma: comparison with serum vascular endothelial growth factor

No adequate serum predictive biomarker currently exists, which can identify the activity of renal cell carcinoma (RCC). We investigate the association of serum hepatocyte growth factor (HGF) and serum vascular endothelial growth factor (VEGF) levels with clinicopathologic parameters in untreated clear cell RCC patients. We measured serum levels of HGF and VEGF in 45 patients with untreated clear cell RCC and 45 healthy controls using an enzyme-linked immunosorbent assay (ELISA). Patients with clear cell RCC had significantly higher serum HGF and VEGF concentrations than healthy subjects: median, 1070.7 versus 728.3 pg/ml (p<0.0001) for HGF; and median, 397.5 versus 245.6 pg/ml (p=0.0003) for VEGF. We found a significant correlation between serum level of HGF and clinical stage and tumor grade. Survival of patients with high serum HGF (>1150 pg/ml) was significantly reduced compared to patients with low serum HGF concentrations (p=0.0044). In patients with nuclear grade 2 or high stage RCC, the higher serum HGF group exhibited significantly lower cause-specific survival (p=0.0087 and p< 0.05, respectively). No significant difference was observed between serum VEGF levels and cause-specific survival rate. Serum HGF might be a diagnostic and prognostic indicator in clear cell RCC, especially for patients with grade 2 or high stage RCC.

Molecular cancer therapy: can our expectation be MET?

Altered regulation of tyrosine kinase receptors (RTKs) is frequent in solid tumours and it is often associated with the acquisition of an aggressive phenotype. Thus, therapies targeting these receptors have been proposed as molecular approaches to treat human cancers. The MET proto-oncogene, encoding the tyrosine kinase receptor for hepatocyte growth factor (HGF), controls genetic programmes leading to cell growth, invasion and protection from apoptosis. Germ-line mutations of MET in patients affected by hereditary papillary renal carcinomas (HPRC) have provided strong genetic evidences for its role in human malignancies; moreover, constitutive activation of this receptor, as a consequence of different mechanisms such as over-expression, autocrine stimulation or point mutations, is frequent in sporadic cancers. Several strategies to block the activation of MET are under development, such as the use of tyrosine kinase inhibitors or monoclonal antibodies and some of these compounds have already been used in clinical trials. In this review, we will discuss the molecular mechanisms underlying MET involvement in tumourigenesis and present pre-clinical and clinical data obtained with compounds aimed at targeting MET in the frame of cancer therapy.

Nuclear E-cadherin and VHL immunoreactivity are prognostic indicators of clear-cell renal cell carcinoma

The loss of functional von Hippel-Lindau (VHL) tumor suppressor gene is associated with the development of clear-cell renal cell carcinoma (CC-RCC). Recently, VHL was shown to promote the transcription of E-cadherin, an adhesion molecule whose expression is inversely correlated with the aggressive phenotype of numerous epithelial cancers. Here, we performed immunohistochemistry on CC-RCC tissue microarrays to determine the prognostic value of E-cadherin and VHL with respect to Fuhrman grade and clinical prognosis. Low Fuhrman grade and good prognosis associated with positive VHL and E-cadherin immunoreactivity, whereas poor prognosis and high-grade tumors associated with a lack of E-cadherin and lower frequency of VHL staining. A significant portion of CC-RCC with positive VHL immunostaining correlated with nuclear localization of C-terminally cleaved E-cadherin. DNA sequencing revealed in a majority of nuclear E-cadherin-positive CC-RCC, subtle point mutations, deletions and insertions in VHL. Furthermore, nuclear E-cadherin was not observed in chromophobe or papillary RCC, as well as matched normal kidney tissue. In addition, nuclear E-cadherin localization was recapitulated in CC-RCC xenografts devoid of functional VHL or reconstituted with synthetic mutant VHL grown in SCID mice. These findings provide the first evidence of aberrant nuclear localization of E-cadherin in CC-RCC harboring VHL mutations, and suggest potential prognostic value of VHL and E-cadherin in CC-RCC.

Presence of phosphorylated hepatocyte growth factor receptor/c-Met is associated with tumor progression and survival in patients with conventional renal cell carcinoma

PURPOSE

Hepatocyte growth factor receptor (HGFR/c-Met) signaling is associated with tumor progression in various cancers. The clinical significance and pathologic roles of phosphorylated HGFR/c-Met in renal cell carcinoma (RCC) are not fully understood; therefore, this study sought to clarify the possible role of two tyrosine residues (pY1234/pY1235 and pY1349) in HGFR/c-Met.

EXPERIMENTAL DESIGN

The kinetics of tyrosine phosphorylation at these two residues was examined in a human renal carcinoma cell line, ACHN cells. In addition, phosphorylated HGFR/c-Met expression (using phosphorylation site-specific antibodies for pY1234/pY1235 and pY1349) was examined in 114 tumor sections of conventional RCC patients by immunohistochemistry. The relationships between these expressions and clinicopathologic features and survival were also investigated.

RESULTS

Although phosphorylation of Y1349 HGFR/c-Met was observed for 120 minutes after HGF treatment of ACHN cells, maximal phosphorylation of Y1234/Y1235 was observed at 30 minutes followed by a rapid inactivation. Median rates (range) of cancer cells immunopositive for pY1234/pY1235 HGFR/c-Met and pY1349 HGFR/c-Met in the tumor sections were 0% (0-5.2%) and 14.3% (0-64.3%), respectively. Positive expression of pY1349 HGFR/c-Met was significantly associated with high pT stage, presence of metastasis, and high-grade carcinoma. Multivariate Cox analysis revealed that the positive expression of pY1349 HGFR/c-Met was a significant and an independent predictor of cause-specific survival (odds ratio, 2.94; 95% confidence interval, 1.12-7.72; P = 0.028).

CONCLUSIONS

Phosphorylated HGFR/c-Met may be important in the tumor progression of RCC. Expression of pY1349 HGFR/c-Met is a useful predictor for metastasis and survival of conventional RCC patients.

MET expression in sporadic renal cell carcinomas

Although germline mutations of met proto-oncogene on human chromosome 7q31-34 have been known as useful molecular markers of hereditary papillary renal cell carcinoma (RCC), the expression of MET, a product of met proto-oncogene, has not been fully studied in sporadic RCC, along with its clinical significance. We investigated the expression of MET by immunohistochemistry in 182 cases of renal neoplasm encompassing 145 RCC, 25 urothelial carcinomas of renal pelvis, and 12 oncocytomas. MET was diffusely and strongly expressed in 90% of papillary RCC, all collecting duct carcinomas, and 92% of urothelial carcinomas of renal pelvis. On the contrary, clear cell RCC, chromophobe RCC, and oncocytomas were negative or focally positive for MET expression. In clear cell RCC, MET expression was positively correlated with high nuclear grade, presence of infiltrative growth, tumoral necrosis, papillary architecture, sarcomatoid component, tumoral involvement of the renal pelvis or ureter, involvement of the calyx, and lymphatic invasion. In conclusion, diffuse and strong expression of MET in papillary RCC and collecting duct carcinoma might be helpful in discriminating from the other subtypes of RCC with tubular or papillary growth. In case of MET expression observed in clear cell RCC, it might correlate with those clinicopathological parameters implying aggressive behavior.

Inactivation of von Hippel-Lindau gene induces constitutive phosphorylation of MET protein in clear cell renal carcinoma

It is well known that inactivation of von Hippel-Lindau (VHL) gene predisposes for human clear cell renal carcinoma (CCRC). However, details about critical roles of VHL inactivation during tumorigenesis are still unknown. MET protein is a tyrosine kinase receptor for hepatocyte growth factor/scatter factor (HGF/SF), which regulates cell growth, cell morphology, and cell motility. We showed that MET protein overexpressed in CCRC cells was phosphorylated without HGF/SF. This constitutive phosphorylation of MET protein in CCRC cells was inhibited by the rescue of exogenous wild-type VHL gene without a decrease in expression level of MET protein. Interestingly, wild-type VHL gene suppressed the phosphorylation of MET protein only under high cell density conditions. Additionally, MET protein activated by the inactivation of VHL gene modified cell adherence, including N-cadherin and beta-catenin. When activation of MET protein in CCRC cells was inhibited by the MET inhibitor K252a, the growth of CCRC cells in vitro and the tumorigenesis induced by CCRC cells in nude mice were suppressed. From these results, we concluded that inactivation of VHL gene induced constitutive phosphorylation of MET protein and modified intercellular adherence structure to trigger the cell growth released from contact inhibition, finally resulting in tumorigenesis. This is one of the mechanisms of CCRC oncogenesis, and MET protein has potential as a molecular target for novel CCRC therapies.

Expression of the c-Met in advanced epithelial ovarian cancer and its prognostic significance

The purpose of this study was to evaluate the prognostic significance of c-Met expression in advanced cases of epithelial ovarian carcinoma. Paraffin-embedded tissues from 41 stage IIIC primary ovarian adenocarcinoma were stained immunohistochemically for c-Met expression. The expression of c-Met was correlated with conventional clinicopathologic parameters and with overall survival of the patients. c-Met expression was found in 60.9% of cases. This clinicopathologic study showed that epithelial ovarian carcinomas with c-Met expression had higher histologic tumor grade and were more frequently associated with para-aortic lymph node metastasis (P < 0.05). In multivariate analysis, c-Met expression remained as a statistically significant predictor for survival with histologic grade. The patients with stage IIIC epithelial ovarian cancers whose tumors expressed c-Met were more likely to have high-grade tumors, have more para-aortic lymph node involvement, and have a significantly worse overall survival than those whose tumors were c-Met negative. In conclusion, c-Met expression might be a potential prognostic marker for patients with advanced-stage epithelial ovarian cancers.

Expression of hepatocyte growth factor and its receptor C-met in acquired renal cystic disease associated with renal cell carcinoma

PURPOSE

The development of renal cell carcinoma (RCC) is a critical problem in acquired renal cystic disease (ARCD) in patients with end stage renal disease, particularly males on chronic hemodialysis. We examined the expression of hepatcyte growth factor (HGF) and its receptor c-met in ARCD associated with RCC to elucidate the role of the HGF/c-met pathway in renal cyst development and subsequent tumor transformation.

MATERIALS AND METHODS

Immunohistochemical expression of HGF, c-met and Bcl-2 was examined in 15 normal tissue samples of kidneys obtained from nephrectomy for localized RCC and 19 with ARCD associated with RCC from 16 patients on dialysis. The expression of HGF mRNA was examined by reverse transcriptase-polymerase chain reaction.

RESULTS

In normal kidneys immunostaining for HGF was scarcely detected in renal tubular cells. Bcl-2 and c-met immunostaining was observed mainly in distal tubular cells. In nontumor areas of kidneys with ARCD associated RCC the expression of HGF and c-met was up-regulated in tubular and the cyst epithelial cells. Hyperplastic cysts with multilayer epithelium and micropapillary projection were the predominant cysts stained with HGF and c-met. Immunostaining for HGF and c-met was also detected in RCC regions. The Bcl-2 immunostaining pattern was similar to that of HGF and c-met in nontumor and RCC regions. On reverse transcriptase-polymerase chain reaction HGF mRNA expression was up-regulated in nontumor areas and RCC regions in ARCD.

CONCLUSIONS

These results suggest that up-regulation of HGF and its receptor c-met may be involved in renal cyst formation and subsequent tumor transformation in patients with end stage renal disease. Increased Bcl-2 expression may promote this process through the inhibition of apoptosis.

Hepatocyte growth factor activator inhibitor types 1 and 2 are expressed by tubular epithelium in kidney and down-regulated in renal cell carcinoma

PURPOSE

Hepatocyte growth factor (HGF) and its receptor MET have been implicated in kidney development and renal cell carcinoma (RCC) progression. HGF is secreted as an inactive proform and it must be activated to initiate MET signaling. HGF activator (HGFA) activates pro-HGF in injured tissue. We evaluated the expression of HGFA and its endogenous inhibitors HAI-1 and HAI-2 in normal kidney and RCC.

MATERIALS AND METHODS

We examined the gene expression of HGFA, HAI-1, HAI-2, HGF and MET in a normal kidney by laser captured microdissection, followed by reverse transcriptase-polymerase chain reaction. We also quantified the mRNA levels of these proteins in 14 RCC cases by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

HAI-1 and HAI-2 were abundant in the normal kidney. The uriniferous tubules showed the highest levels of HAI-1 and HAI-2 mRNA. HGFA was hardly detectable in the normal kidney. However, in the kidney with RCC a low but distinct level of HGFA mRNA became detectable in the tumor and adjacent renal tissue. The HAI-1 mRNA level was significantly and consistently down-regulated in RCC relative to normal tissue. HAI-2 mRNA was also significantly low in the advanced stage of RCC. MET was up-regulated in most cases of RCC.

CONCLUSIONS

HAI-1 and HAI-2 were expressed in renal tubular epithelial cells. The expression of the 2 HAIs was significantly down-regulated in RCC, whereas HGFA expression was enhanced in the diseased kidney, suggesting an imbalance between HAI and its target proteinases, including HGFA, in favor of proteinase activities in RCC.

Overexpression of c-met as a prognostic indicator for transitional cell carcinoma of the urinary bladder: a comparison with p53 nuclear accumulation

PURPOSE

The c-met proto-oncogene encodes a receptor tyrosine kinase (Met) and has been shown to play a role in oncogenesis. Given that high titers of hepatocyte growth factor, the specific ligand for Met, are excreted in the urine and tend to reflect disease activity of bladder cancer, we performed this study to examine the clinical significance of Met in human bladder cancer.

MATERIALS AND METHODS

We studied the mRNA expression and genomic alteration of c-met in five bladder cancer cell lines. Significance of Met overexpression was then compared with p53 nuclear accumulation (TP53) in primary bladder cancer (n = 142 patients).

RESULTS

Expression of c-met mRNA tended to positively correlate with differentiation of cancer cell lines in the absence of point mutation. High expression of Met was found in seven cases (4.9%), low expression in 32 cases (22.5%), and negative expression in 103 cases (72.5%). Expression of Met was positively associated with histologic grade, stage classification, tumor size, and nodular tumor growth (P <.05, respectively); however, it was not related to TP53 status. Factors that predicted disease progression were tumor stage, Met status, and TP53 accumulation (P <.05, respectively). Indicators for poor long-term survival were invasive cancer, multiple tumors, and Met overexpression (P =.0006,.01, and.04, respectively).

CONCLUSION

The c-met proto-oncogene plays a more important role in the progression of bladder carcinogenesis than p53. Evaluation of Met expression could identify a subset of bladder cancer patients who may require a more intensive treatment strategy.

Expression of HGF/SF and Met protein is associated with genetic alterations of VHL gene in primary renal cell carcinomas

We analyzed the genetic alterations of VHL, HGF/SF, and Met genes and the expression pattern of HGF/SF and Met protein in 26 renal cell carcinomas (RCCs). We found five mutations of the VHL gene and frequent LOH (50%) only in non-papillary clear cell RCC. We found six cases in which the CpG island of VHL was methylated. In addition, one missense mutation of the HGF/SF gene was detected in clear cell RCC. HGF/SF and Met protein were expressed in 84.6% and 80.7% of RCCs, respectively. All of the cases with the genetic alterations of VHL or HGF/SF demonstrated strong expression of HGF/SF and Met protein in RCC cells. Statistically, genetic alterations of VHL and HGF/SF were significantly correlated with HGF/SF and Met expression (Fisher's exact test, p=0.022 and p=0.0070). Thus, these results strongly suggest that the expression of HGF/SF and Met protein is closely associated with the genetic alterations of VHL and HGF/SF in primary RCCs.

Biology of kidney cells: ontogeny-recapitulating phylogeny

Biology of kidney cells can be used as a model for further understanding of ontogeny-recapitulating phylogeny. The common and species-specific structural and functional relationship between blood capillaries and the environment via a filtration barrier of nephrons is a biological phenomenon resulting from renal cell memory acquired through evolution. Genetically programmed development, a subsequent series of gene expression, and inductive interactions played a key role in differentiation and maintenance of specific activities of kidneys in birds and mammals. Various environmental factors may alter kidney development and specific activities at the levels of gene expression, repression, or derepression, and defensive mechanisms involved in reaction to risk factors are developed. Autoimmunity and cancerogenesis are closely dependent on a variety of environmental agents, such as antigens originating from infections with some viruses and toxins, or irradiation, advanced industrialization, and progress of civilization. As a result of gene mutation, delation, rearrangement, and/or susceptibility to different agents, renal cell memory is altered. Instead of cell-specific activities, the abilities for regeneration, and other genetically programmed activities, the genesis of kidney diseases are common. Balkan endemic nephropathy, as regional disease, is an important example of the role, of environmental agents, at the level of genes. Research programs on molecular genetics will contribute to our efforts both to prevent infections and to elucidate the genesis, diagnosis, prognosis, prevention, and therapy of kidney diseases.

Expression of c-met and WT-1

Protooncogenes and tumor-suppressor genes are two types of genes associated with cancer development.

Enhancement of retrovirus-mediated gene transfer to rat liver in vivo by infusion of hepatocyte growth factor and triiodothyronine

BACKGROUND/AIMS

Gene transfer using recombinant Moloney murine leukemia viruses (rMoMuLV) requires mitosis of the target cell. Previously, we and others have used partial hepatectomy for induction of hepatocellular proliferation for gene transfer to the liver in vivo by exsanguineous perfusion with rMo-MuLV. We hypothesized that induction of hepatocellular proliferation by combined administration of two hepatocellular mitogens, hepatocyte growth factor (HGF) and triiodothyronine (T3), should permit rMo-MuLV-mediated gene transfer into liver without invasive approaches.

METHODS

HGF (1 mg/kg) was perfused continuously into the portal vein of Wistar male rats and T3 (2 mg/kg) was injected subcutaneously. Twenty-four hours after injecting HGF and T3, the state of proliferation of hepatocytes was estimated from the incorporation of 5'-bromo-2'-deoxy-uridine (BrdU). The amphotropic retroviral receptor (Ram-1) expression of liver was evaluated at different time points after injecting HGF and T3 by means of Northern blotting using Ram-1 cDNA probe. In order to evaluate the role of hormone treatment on gene transfer, the liver was perfused exsanguineously with rMoMuLV 24 h after injection with hormones.

RESULTS

Rats treated with a combination of HGF and T3 expressed BrdU and beta-galactosidase in 8.3% and 0.7% of hepatocytes, respectively. On the other hand, there was near absence of gene transfer in untreated rats perfused with rMoMuLV Twenty-four hours after the initial manipulation, abundant expression of Ram-1 mRNA was observed in rat hepatocytes treated with HGF plus T3.

CONCLUSIONS

Stimulation of hepatocellular mitosis and upregulation of Ram-1 expression by HGF and T3 augment retrovirus-mediated gene transfer into hepatocytes.

Hepatocyte growth factor (HGF) induces invasion of endometrial carcinoma cell lines in vitro

OBJECTIVES

The overall goal of this study was to investigate the role of the hepatocyte growth factor (HGF)/Met pathway in the pathophysiology of invasive endometrial carcinoma. Our objectives were (1) to examine expression of HGF and Met in surgical endometrial carcinoma specimens and endometrial carcinoma cell lines, and (2) to determine if HGF would stimulate invasion of endometrial carcinoma cell lines in vitro.

METHODS

Using RT-PCR and Western immunoblotting, endometrial carcinoma specimens and the endometrial carcinoma cell lines KLE, HEC-1A, HEC-1B, and RL-95 were examined for expression of HGF and Met. A Boyden chamber invasion assay using collagen type I coated 8-microm porous membranes was then used to determine if HGF would stimulate cell invasion. Last, we assessed the capacity of endometrial stromal cells, isolated from normal human endometrium, to produce HGF as determined by an enzyme-linked immunosorbent assay and to stimulate invasion of the KLE cell line.

RESULTS

All of the endometrial carcinoma tissue samples were found to express Met mRNA, and two of four samples expressed HGF mRNA. However, the endometrial carcinoma cell lines expressed only Met and not HGF mRNA. Both the endometrial carcinoma tissue specimens and the endometrial carcinoma cell lines expressed the 140-kDa Met protein. HGF induced the invasion of the KLE and HEC-1A cells through the collagen-coated membranes in a dose-dependent fashion. The optimal concentration of HGF was between 10 and 100 ng/ml. HGF (10 ng/ml) stimulated KLE invasion 1.8-fold (P < 0.05) and HEC-1A invasion 6.5-fold (P < 0.05). During exposure to endometrial stromal cell conditioned medium containing HGF as determined by ELISA, invasion of the KLE cell line was stimulated 2.5-fold (P < 0.05).

CONCLUSION

These results demonstrate that HGF stimulates the invasion of endometrial carcinoma cells in vitro. Since endometrial adenocarcinoma specimens express Met, these findings suggest that the HGF/Met pathway may play a role in the invasive progression of endometrial carcinoma.

Hepatocyte growth factor and the kidney: it is not just for the liver

Mesenchymal-epithelial interactions are important for many biological processes in epithelial organs such as the kidney. Hepatocyte growth factor (HGF) is a mesenchymally derived polypeptide cytokine that acts through its tyrosine kinase c-met receptor and is an important mediator of these interactions. This article reviews data showing the in vitro actions of HGF on renal epithelial cells that result in such diverse responses as mitogenesis, motogenesis, and morphogenesis. It also examines the in vivo evidence linking HGF and the c-met receptor to kidney development, regeneration following injury, and renal disease. Elucidating cellular mechanisms underlying the coordinated control of diverse HGF-induced phenotypic changes in renal epithelia in vitro should contribute to a clearer understanding of complex biological processes such as organogenesis, regeneration, and carcinogenesis in epithelial organs such as the kidney.