AMG 706, an oral, multikinase inhibitor that selectively targets vascular endothelial growth factor, platelet-derived growth factor, and kit receptors, potently inhibits angiogenesis and induces regression in tumor xenografts

The growth of solid tumors is dependent on the continued stimulation of endothelial cell proliferation and migration resulting in angiogenesis. The angiogenic process is controlled by a variety of factors of which the vascular endothelial growth factor (VEGF) pathway and its receptors play a pivotal role. Small-molecule inhibitors of VEGF receptors (VEGFR) have been shown to inhibit angiogenesis and tumor growth in preclinical models and in clinical trials. A novel nicotinamide, AMG 706, was identified as a potent, orally bioavailable inhibitor of the VEGFR1/Flt1, VEGFR2/kinase domain receptor/Flk-1, VEGFR3/Flt4, platelet-derived growth factor receptor, and Kit receptors in preclinical models. AMG 706 inhibited human endothelial cell proliferation induced by VEGF, but not by basic fibroblast growth factor in vitro, as well as vascular permeability induced by VEGF in mice. Oral administration of AMG 706 potently inhibited VEGF-induced angiogenesis in the rat corneal model and induced regression of established A431 xenografts. AMG 706 was well tolerated and had no significant effects on body weight or on the general health of the animals. Histologic analysis of tumor xenografts from AMG 706-treated animals revealed an increase in endothelial apoptosis and a reduction in blood vessel area that preceded an increase in tumor cell apoptosis. In summary, AMG 706 is an orally bioavailable, well-tolerated multikinase inhibitor that is presently under clinical investigation for the treatment of human malignancies.

Role of anti-angiogenesis agents in treating NSCLC: focus on bevacizumab and VEGFR tyrosine kinase inhibitors

OPINION STATEMENT

Successful inhibition of angiogenesis with the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab has improved the efficacy seen with standard cytotoxic therapy in NSCLC. The addition of bevacizumab to first-line chemotherapy improved response rate and progression free survival and added 2 months to median overall survival for those patients with advanced stage NSCLC on the treatment arm of E4599. Bevacizumab is now a standard agent to add to frontline carboplatin and paclitaxel for patients with newly diagnosed NSCLC who meet the eligibility criteria from the landmark E4599 trial. Unfortunately about half of all patients are not eligible either because they have squamous histology, brain metastases, or are on anti-coagulation. Ongoing trials are further exploring the safety of bevacizumab in these patient populations, as well as in combination with other cytotoxic regimens. Exploration of other applications of bevacizumab in the second-line and adjuvant setting are ongoing as well. The largest class of drugs that block angiogenesis are the multi-targeted tyrosine kinase inhibitors (TKIs) that target the VEGF receptor (VEGFR). These drugs are still in development, and though two are now on the market for treating other malignancies, their role in NSCLC is under investigation. These agents have the advantages of hitting multiple targets, convenient oral administration, and potential for lower cost. Their lack of target specificity leads to unexpected toxicity, but also promising efficacy. For example, the overall objective response rate of 9.5% with single agent sunitinib compares similarly to that of pemetrexed or docetaxel in previously treated NSCLC patients, but toxicity, notably fatigue, lead to discontinuation in 38% of patients. Hypertension, hemorrhage and cavitation are common toxicities amongst this class of agents. Rash, fatigue, myalgia, and hand-foot syndrome are more specifically seen with TKIs. These compounds may also be synergistic or additive with traditional cytotoxic chemotherapy drugs and other novel compounds. In early trials sorafenib as a single agent has shown no clinical response in previously treated NSCLC patients, whereas clinical benefit in combination with erlotinib or chemotherapy has been seen in early studies. Vandetanib has demonstrated objective responses as a single agent and in combination with chemotherapy in previously treated NSCLC patients. A phase I trial of AZD2171 with carboplatin and paclitaxel in newly diagnosed advanced stage NSCLC also demonstrated promising results with 6 of 15 patients achieving partial responses. NSCLC specific trials are also underway, or in development for pazopanib, axitinib, AMG 706, XL647, enzastaurin, and other TKIs. Other anti-angiogenesis agents with different mechanisms of action include thalidomide and its derivatives, monoclonal antibodies to the VEGFRs, and VEGF Trap, a chimeric molecule which combines extracellular portions of VEGFR1 and VEGFR2 with the Fc portion of immunoglobulin G1 to form a molecule that binds and "traps" VEGF. Despite modest improvements, prognosis continues to be poor for patients with advanced NSCLC. Bevacizumab is a first step into the world of angiogenesis inhibitors for NSCLC and though it only offers a modest survival benefit in a limited patient population, it paves the way for the development of the next generation of anti-angiogenesis inhibitors. We can hope that further improvements in survival will follow.

Imaging tumor vascular heterogeneity and angiogenesis using dynamic contrast-enhanced magnetic resonance imaging

This article reviews the application of dynamic contrast-enhanced magnetic resonance imaging in both clinical studies and early-phase trials of angiogenesis inhibitors. Emphasis is placed on how variation in image acquisition and analysis affects the meaning and use of derived variables. We then review the potential for future developments, with particular reference to the application of dynamic contrast-enhanced magnetic resonance imaging to evaluate the heterogeneity of tumor tissues.

A review of the latest clinical compounds to inhibit VEGF in pathological angiogenesis

Angiogenesis plays an important role in the formation of new blood vessels and is crucial for tumour development and progression. Imbalance between pro- and antiangiogenesis factors regulates the biological process of angiogenesis. The best characterised of the proangiogenic factors and the most potent is vascular endothelial growth factor (VEGF). The binding of VEGF to one of its transmembrane tyrosine kinase receptors, which are predominantly found on endothelial cells, results in receptor dimerisation, activation and autophosphorylation of the tyrosine kinase domain. This triggers a cascade of complex downstream signalling pathways. Several strategies targeting the VEGF signalling pathway have been developed. These include neutralising antibodies to VEGF (bevacizumab) or VEGF receptors (VEGFRs) (DC101), soluble VEGFR/VEGFR hybrids (VEGF-Trap), and tyrosine kinase inhibitors of VEGFRs (BAY43-9006, SU11248, ZD6474, AZD2171, PTK/ZK and others). Several of these agents are now being investigated in clinical trials.

DCE-MRI biomarkers in the clinical evaluation of antiangiogenic and vascular disrupting agents

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is now frequently used in early clinical trial assessment of antiangiogenic and vascular disrupting compounds. Evidence of drug efficacy and dose-dependent response has been demonstrated with some angiogenesis inhibitors. This review highlights the critical issues that influence T₁-weighted DCE-MRI data acquisition and analysis, identifies important areas for future development and reviews the clinical trial findings to date.

Therapeutic options to target angiogenesis in human malignancies

The critical role of angiogenesis in tumour growth and metastasis is now well established in the literature. Growing tumours stimulate neovascularisation through the secretion of pro-angiogenic growth factors, in particular, basic fibroblast growth factor and VEGF. Several lines of evidence have implicated VEGF in tumourigenesis, and understanding the role of VEGF in tumour angiogenesis has facilitated the development of novel targeting agents that specifically interfere with angiogenesis. Different approaches to disrupting tumour-induced angiogenesis encompass tyrosine kinase inhibitor, monoclonal antibodies, small-molecule inhibitors and transcription inhibitors. However, monoclonal antibody and tyrosine kinase inhibitors are the most advanced drug classes currently being investigated in clinical trials. So far, three anti-VEGF inhibitors, bevacizumab, sunitinib and sorafenib, have been approved for the treatment of solid human malignancies including colorectal cancer, gastrointestinal stromal tumours and renal cell carcinoma. Other antiangiogenic drugs are being investigated in various types of cancer. This review summarises the current literature on the use of these agents to interfere with VEGF, VEGF receptor, the matrix breakdown or other mechanisms involved in angiogenesis.

The second annual symposium on the future of lung cancer: a translational focus

Lung cancer continues to be a leading cause of death in the US, and in its most advanced stages remains incurable. Cytotoxic chemotherapies have been the standard of care for the treatment of unresectable disease. However, recent advances in the development of epidermal growth factor receptor (EGFR) inhibitors have led the way to a new generation of targeted biological agents. During the second annual symposium entitled 'the future of lung cancer: a translational focus', which was sponsored by the Physician s Education Resource, new strategies for the treatment of lung cancer were discussed. Besides the role of EGFR inhibitors, potential targets include the angiogenesis pathway; other growth factor pathways, such as phosphoinositol-3 kinase/Akt and Raf-MEK; the 26S proteasome, the histone deacetylase mechanism; and the TNF-related apoptosis-inducing factor receptors. Agents that are directed against these targets are all in varying stages of clinical development. As more is learned about their mechanisms of action and clinical spectrum of activity, the author anticipates their incorporation into novel regimens with enhanced activity against lung cancer.

Targeting Angiogenesis in Lung Cancer

The prognosis for the majority of patients with lung cancer remains poor, and treatment strategies including newer generation chemotherapeutics have not improved survival. New approaches are required to further improve patient outcome and survival. Recently, key molecules involved in signal transduction pathways that contribute to tumor growth have been identified as therapeutic targets, particularly molecules involved in cellular proliferation and angiogenesis. Novel therapeutics that specifically target angiogenesis have shown promise as single agents and in combination with standard chemotherapy. The results of recent studies validate the use of this class of targeted therapeutics as an important new treatment modality in cancer therapy. This review will focus on a discussion of antiangiogenic therapeutic monoclonal antibodies in development for the treatment of non-small cell lung cancer.