Targeting the HGF/Met signalling pathway in cancer

Under normal conditions, hepatocyte growth factor (HGF)-induced Met tyrosine kinase (TK) activation is tightly regulated by paracrine ligand delivery, ligand activation at the target cell surface, and ligand activated receptor internalisation and degradation. Despite these controls, HGF/Met signalling contributes to oncogenesis and tumour progression in several cancers and promotes aggressive cellular invasiveness that is strongly linked to tumour metastasis. The prevalence of HGF/Met pathway activation in human malignancies has driven rapid growth in cancer drug development programmes. Pathway inhibitors can be divided broadly into biologicals and low molecular weight synthetic TK inhibitors; of these, the latter now outnumber all other inhibitor types. We review here the basic properties of HGF/Met pathway antagonists now in preclinical and clinical development as well as the latest clinical trial results. The main challenges facing the effective use of HGF/Met-targeted antagonists for cancer treatment include optimal patient selection, diagnostic and pharmacodynamic biomarker development, and the identification and testing of optimal therapy combinations. The wealth of basic information, analytical reagents and model systems available concerning HGF/Met oncogenic signalling will continue to be invaluable in meeting these challenges and moving expeditiously toward more effective disease control.

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.

Metastatic renal cell carcinoma: recent advances in the targeted therapy era

CONTEXT

The treatment of metastatic renal cell carcinoma (mRCC) has recently evolved from being predominantly cytokine based to being grounded in the use of targeted agents.

OBJECTIVE

To analyse current evidence on the medical management of mRCC.

EVIDENCE ACQUISITION

The PubMed and Medline databases were searched for articles published as of 15 July 2009. Only articles published in English were considered. The search terms were metastatic renal cell cancer, targeted therapy, and immunotherapy. Proceedings from the 2000-2009 conferences of the American Society of Clinical Oncology, the American Urological Association, and the European Association of Urology were also searched for relevant abstracts.

EVIDENCE SYNTHESIS

Sunitinib has recently emerged as a front-line standard of care in mRCC. Temsirolimus is considered a first-line therapy for patients with poor risk features. Bevacizumab/interferon is likely to be the next U.S. Food and Drug Administration-approved first-line treatment. The use of sorafenib has moved toward second-line and later therapy. Everolimus was the first agent to show clinical benefit post-tyrosine kinase inhibitor failure in a phase 3 study and is considered the standard of care in this setting. Temsirolimus provided benefit to patients with non-clear-cell histology. In preliminary results, a favourable risk-benefit ratio has been shown with pazopanib and axitinib as first- and second-line treatment. Until combination therapy is clearly shown to be superior to monotherapy, it should be used in the context of a clinical trial. Deciding which is the best sequence to use in mRCC patients remains up to the best judgement of the treating physician. Cytoreductive nephrectomy in the presence of metastatic disease is often indicated as part of an integrated management strategy.

CONCLUSIONS

Given considerable advances in understanding the biology of mRCC, several new drugs have recently been developed, offering an increasing number of treatment options. A treatment algorithm based on the best available evidence so far can be therefore postulated, though it continues to evolve as data from ongoing trials become available.

Targeted therapy for malignant glioma patients: lessons learned and the road ahead

Molecularly targeted therapies are transforming the care of patients with malignant gliomas, including glioblastoma, the most common malignant primary brain tumor of adults. With an arsenal of small molecule inhibitors and antibodies that target key components of the signal transduction machinery that are commonly activated in gliomas, neuro-oncologists and neurosurgeons are poised to transform the care of these patients. Nonetheless, successful application of targeted therapies remains a challenge. Strategies are lacking for directing kinase inhibitor or other pathway-specific therapies to individual patients most likely to benefit. In addition, response to targeted agents is determined not only by the presence of the key mutant kinases, but also by other critical changes in the molecular circuitry of cancer cells, such as loss of key tumor suppressor proteins, the selection for kinase-resistant mutants, and the deregulation of feedback loops. Understanding these signaling networks, and studying them in patients, will be critical for developing rational combination therapies to suppress resistance for malignant glioma patients. Here we review the current status of molecular targeted therapies for malignant gliomas. We focus initially on identifying some of the insights gained to date from targeting the EGFR/PI3K/Akt/mTOR signaling pathway in patients and on how this has led toward a reconceptualization of some of the challenges and directions for targeted treatment. We describe how advances from the world of genomics have the potential to transform our approaches toward targeted therapy, and describe how a deeper understanding of the complex nature of cancer, and its adeptness at rewiring molecular circuitry to evade targeted agents, has raised new challenges and identified new leads.

Novel therapeutics for metastatic renal cell carcinoma

The treatment of metastatic renal cell carcinoma (RCC) has changed dramatically during the past few years. Sunitinib malate, sorafenib tosylate, bevacizumab with interferon alpha, temsirolimus, and everolimus have improved clinical outcomes in randomized phase 3 trials by inhibiting the vascular endothelial growth factor and related pathways. Combinations and sequences of these agents are being evaluated. Other novel agents are in clinical development, some of which target novel pathways not yet exploited as therapy for RCC. Recently reported and ongoing clinical trials will help further define the role of these agents as therapy for metastatic RCC.

Nonclinical antiangiogenesis and antitumor activities of axitinib (AG-013736), an oral, potent, and selective inhibitor of vascular endothelial growth factor receptor tyrosine kinases 1, 2, 3

PURPOSE

Axitinib (AG-013736) is a potent and selective inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases 1 to 3 that is in clinical development for the treatment of solid tumors. We provide a comprehensive description of its in vitro characteristics and activities, in vivo antiangiogenesis, and antitumor efficacy and translational pharmacology data.

EXPERIMENTAL DESIGN

The potency, kinase selectivity, pharmacologic activity, and antitumor efficacy of axitinib were assessed in various nonclinical models.

RESULTS

Axitinib inhibits cellular autophosphorylation of VEGF receptors (VEGFR) with picomolar IC(50) values. Counterscreening across multiple kinase and protein panels shows it is selective for VEGFRs. Axitinib blocks VEGF-mediated endothelial cell survival, tube formation, and downstream signaling through endothelial nitric oxide synthase, Akt and extracellular signal-regulated kinase. Following twice daily oral administration, axitinib produces consistent and dose-dependent antitumor efficacy that is associated with blocking VEGFR-2 phosphorylation, vascular permeability, angiogenesis, and concomitant induction of tumor cell apoptosis. Axitinib in combination with chemotherapeutic or targeted agents enhances antitumor efficacy in many tumor models compared with single agent alone. Dose scheduling studies in a human pancreatic tumor xenograft model show that simultaneous administration of axitinib and gemcitabine without prolonged dose interruption or truncation of axitinib produces the greatest antitumor efficacy. The efficacious drug concentrations predicted in nonclinical studies are consistent with the range achieved in the clinic. Although axitinib inhibits platelet-derived growth factor receptors and KIT with nanomolar in vitro potencies, based on pharmacokinetic/pharmacodynamic analysis, axitinib acts primarily as a VEGFR tyrosine kinase inhibitor at the current clinical exposure.

CONCLUSIONS

The selectivity, potency for VEGFRs, and robust nonclinical activity may afford broad opportunities for axitinib to improve cancer therapy.

Recent advances in the treatment of renal cell carcinoma and the role of targeted therapies

Immunotherapy confers a small but significant overall survival advantage in metastatic renal cell carcinoma (RCC) but only for the minority of patients, i.e. the 20% with good prognostic features. Recent developments in the molecular biology of renal cell carcinoma have identified multiple pathways associated with the development of this cancer. Several strategies have been investigated targeting these pathways, with significant clinical benefits shown in early studies. New agents including the small molecule targeted inhibitors sunitinib, sorafenib and temsirolimus, and the monoclonal antibody bevacizumab have shown anti-tumour activity in randomised clinical trials and have become the standard of care for most patients. Sunitinib and temsirolimus have shown significant improvements in progression-free survival (sunitinib) and overall survival (temsirolimus) in separate phase III studies in the first-line setting when compared with interferon-alpha. Sorafenib has demonstrated prolonged progression-free survival in a phase III study in comparison with placebo in the second-line setting. More recently two phase III studies have compared bevacizumab and interferon-alpha with interferon-alpha alone. Both studies showed a statistically significant improvement in progression-free survival for the combination arm. Additional studies are needed to optimise the use of these agents by identifying those patients who most benefit and elucidating the best way of delivering them, either in combination or as sequential single agents.

MET as a target for treatment of chest tumors

The receptor tyrosine kinase MET has been studied of a large variety of human cancers, including lung and mesothelioma. The MET receptor and its ligand HGF (hepatocyte growth factor) play important roles in cell growth, survival and migration, and dysregulation of the HGF-MET pathway leads to oncogenic changes including tumor proliferation, angiogenesis and metastasis. In small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), and malignant pleural mesothelioma (MPM), MET is dysregulated via overexpression, constitutive activation, gene amplification, ligand-dependent activation, mutation or epigenetic mechanisms. New drugs targeted against MET and HGF are currently being investigated in vitro and in vivo, with promising results. These drugs function at a variety of steps within the HGF-MET pathway, including MET expression at the RNA or protein level, the ligand-receptor interaction, and tyrosine kinase function. This paper will review the structure, function, mechanisms of tumorigenesis, and potential for therapeutic inhibition of the MET receptor in lung cancer and mesothelioma.

c-Met targeted therapy of cholangiocarcinoma

Cholangiocarcinoma continues to be a challenging disease to treat. Systemic therapy is used in unresectable disease, disease progression after surgery, and in the palliative setting. Unfortunately, results of multiple phase II trials have rarely yielded positive results. As data on the molecular carcinogenesis of cholangiocarcinoma is developing, we are more able to understand the disease process and can use this understanding to create unique targeted therapies. We reviewed the role of c-Met/hepatocyte growth factor (HGF) in the development of cholangiocarcinoma. Furthermore, we explored the use of the c-Met guided cascade as a target to treat cholangiocarcinoma. We reviewed the current use and options for future development of c-Met agents to treat this disease.