Current Pharmaceutical Design - Volume 20, Issue 14, 2014

While conventional chemotherapy regimens aim to be cytotoxic against proliferating cells, molecular targeted therapies are directed at specific cancer-associated pathways. To optimize cancer care, an early evaluation of treatment response is warranted for any tumor type - and for any treatment – by using conventional imaging modalities such as ultrasound, CT and MR, FDG-PET or specific radiotracer. FDG-PET is one of the most extensively and successfully used imaging modalities to achieve an early response evaluation. A high SUV-value is a surrogate for malignancy in terms of cancer care and a decrease in FDG-uptake after therapy is associated with treatment response and a favorable clinical outcome. Anyhow, the potential of PET reaches further. By providing metabolic information PET (with or without CT) can help to select patients for targeted therapy and to adapt treatment protocols. PET with FDG and maybe other, more specific PET tracers, promises to direct in a better way personalized cancer care and thus promote translational research. An interesting aspect of molecular imaging is the ability to achieve knowledge on distribution and expression levels of a given receptor. Hereby, imaging could help in guiding systemic treatment given a broad spectrum of radiotracers, detecting specific mutations at molecular level in vivo. From an oncologists point of view the concept of ‘personalized medicine’ should evolve to include ‘personalized imaging’ as well as ‘personalized treatment’ in order to optimize cancer care, reduce side effects and improve quality of life for cancer patients.

Radiolabelled peptides and proteins have recently gained great interest as theranostics, due to their numerous and considerable advantages over small (organic) molecules. Developmental procedures of these radiolabelled biomolecules start with the radiolabelling process, greatly defined by the amino acid composition of the molecule and the radionuclide used. Depending on the radionuclide selection, radiolabelling starting materials are whether or not essential for efficient radiolabelling, resulting in direct or indirect radioiodination, radiometal-chelate coupling, indirect radiofluorination or 3H/14C-labelling. Before preclinical investigations are performed, quality control analyses of the synthesized radiopharmaceutical are recommended to eliminate false positive or negative functionality results, e.g. changed receptor binding properties due to (radiolabelled) impurities. Therefore, radionuclidic, radiochemical and chemical purity are investigated, next to the general peptide attributes as described in the European and the United States Pharmacopeia. Moreover, in vitro and in vivo stability characteristics of the peptides and proteins also need to be explored, seen their strong sensitivity to proteinases and peptidases, together with radiolysis and trans-chelation phenomena of the radiopharmaceuticals. In vitro biomedical characterization of the radiolabelled peptides and proteins is performed by saturation, kinetic and competition binding assays, analyzing KD, Bmax, kon, koff and internalization properties, taking into account the chemical and metabolic stability and adsorption events inherent to peptides and proteins. In vivo biodistribution can be adapted by linker, chelate or radionuclide modifications, minimizing normal tissue (e.g. kidney and liver) radiation, and resulting in favorable dosimetry analyses. Finally, clinical trials are initiated, eventually leading to the marketing of radiolabelled peptides and proteins for PET/SPECT-imaging and therapy of different clinical diseases.

This review describes several aspects required for the development of small molecule PET-tracers. Design and selection criteria are important to consider before starting to develop novel PET-tracers. Principles and latest trends in 11C and 18F-radiochemistry are summarized. In addition an update of some new developments in regulatory aspects is supplied.

Receptor tyrosine kinases (RTK) are transmembrane receptors regulating cellular proliferation, differentiation, apoptosis, motility and recruitment of the vasculature. Aberrant expression and/or function of RTK have been detected in many malignant tumors and are considered to be a part of the transformed phenotype. The action of several classes of anti-cancer drugs is based on specific recognition of RTK. Monoclonal antibodies target extracellular binding domains, while tyrosine kinase inhibitors (TKI) bind to intracellular kinase domains to suppress RTK signaling. The issues regarding the efficient use of RTK targeting are the inter- and intra-patient heterogeneity of RTK expression and the changes of expression levels during the course of disease and in response to therapy. Radionuclide molecular imaging of RTK expression may aid in selecting patients who would benefit from RTK-targeting therapy and in identifying non-responders. Therefore, the therapy would be more personalized. Currently, radiolabeled proteins (monoclonal antibodies and their fragments, natural peptides ligands to RTK and de novo selected affinity proteins) and TKI and their analogues are under development for the visualization of RTK. In this review, we discuss the advantages and disadvantages of these approaches.

Angiogenesis is essential for tumor growth and inhibiting angiogenesis has become an important therapeutic strategy in clinical oncology. Nonetheless, the mechanisms behind anti-angiogenic therapeutics as well as resistance to these drugs remain unclear. With a lack of validated genetic or molecular biomarkers for anti-angiogenic responsiveness, novel methods to identify responsive patients are required. Non-invasive nuclear imaging would allow the elucidation of the basic drug mechanisms as well as resistance routes and aid the personalization of anti-angiogenic therapy by enabling target expression quantification prior to and during treatment. This review focuses on the development of radiolabeled probes to image four key proteins expressed during angiogenesis, namely vascular endothelial growth factor and its receptor, integrin αv β3, the extracellular domain of fibronectin and matrix metalloproteases, and how these probes can be utilized for personalized anti-angiogenic therapy.

Hypoxia is a characteristic feature of many solid tumors which has been described in a wide range of tumor types. Its presence impairs the effectiveness of common anti-cancer therapies and accordingly, tumor hypoxia has been associated with an aggressive tumor phenotype, poor response to radio- and chemotherapy, and worse prognosis. In order to predict outcome and identify patients with a worse prognosis and/or patients that would benefit from appropriate treatments, in vivo measurement of tumor hypoxia is required. Given the difficulties associated with invasive methods, a non-invasive method is of major clinical interest. Although several candidate molecules have been labeled with PET and SPECT labels, none of them is used in daily clinical routine due to a number of difficulties that complicate their use. This review aims to give an overview of the most important hypoxia tracers, their prognostic significance and how these tracers can play a role in tomorrows personalized medicine.

Evasion of apoptosis is one of the hallmarks of cancer and any effective therapy primarily attempts to induce apoptosis. The evaluation of the degree of success of cancer therapy is currently mainly based on clinical and laboratory parameters and in a later stage on tumor shrinkage. However, none of these parameters provide an objective and early analysis of a therapeutic effect. Molecular imaging may provide a tool for this purpose by using not only pathophysiological but also biochemical effects of the therapy. First in the field, FDG-PET has been explored and demonstrated to offer insight in the amount of viable cells, even though false positives are commonly due to the lack of specificity of this particular radiopharmaceutical. More specific markers target the dying cells instead of those remaining alive. Specific apoptosis markers have been developed of which the radiolabeled Annexin A5 is the most intensely studied probe. Site-specific labeling strategies have improved this imaging probe with good results both in pre-clinical studies and in clinical trials, with promises for clinical applications. Caspase sensitive probes, such as the isatines, can also effectively image apoptosis but are limited due to the high background activities. More recent discoveries of small apoptosis sensitive probes, such as 18F-ML10, are currently being explored. In this review, the most important apoptosis sensitive probes are described from both a pre-clinical and a clinical perspective, highlighting their potential but also their limitations as an early marker for therapeutic success. It seems that apoptosis imaging can help to guide therapy, not by replacing the current methodology but by providing additional and useful information.

The G-protein coupled receptor system is involved in a range of cell types and actions and as such has a universal potential in identifying cell functions. The most widely explored system is that of the somatostatin receptors which has been exploited for both imaging and therapy. However, even with this fairly simple system, variation is seen in the behaviour of cells between patients and within different cell population within the patient. Newer work will exploit different ligands in a wider range of both tumour types and non-oncological processes such as inflammation.

Inflammatory and infectious diseases include many different clinical conditions not often well recognised and characterized with conventional radiology and biochemical tests. Radiological techniques (TC, MRI, US) show anatomical changes that usually occur in chronic stages of the disease leading to a delayed diagnosis and therapy. The possibility of Nuclear Medicine imaging to detect biological and biochemical changes in the earliest phases of diseases, allow the clinician not only to promptly identify the infective or inflammatory focus, but also to establish the best therapeutic approach for the patient. The recent availability of different monoclonal antibodies and analogues of growth and signalling factors offers physicians a wide spectrum of promising radiopharmaceuticals as markers for different pathological events. Therefore, NM may help in therapy decision making, management and follow-up through the evaluation of the expression of these specific molecules, leading to the development of personalized therapies. The appeal to Nuclear Medicine imaging is becoming, indeed, more and more widespread not only for diagnostic purposes, but also for monitoring drug efficacy. Several advances have been observed in this field, and they seem to be very promising for a tailored medicine.

MicroRNAs are small noncoding RNAs that have emerged as important regulators of many biological and pathological processes, including those relevant to the development of the heart and cardiovascular disease. Several recent studies using genetic models and profiling of microRNAs have established the important role of these novel molecules in a number of conditions of the heart. These studies have led to a flurry of research focussing on the identification of new therapeutic targets for the treatment of cardiac disease, as well as the identification of potential biomarkers for early diagnosis of heart disease. These early reports have stimulated much interest in microRNAs and indeed other non-coding RNAs in the broader context of cardiovascular disease. This work has been further investigated as a result of ease with which the levels of these molecules can be modulated both in vitro but also in animal disease models. Furthermore, a number of studies have specifically looked at the prognostic potential of these microRNAs as biomarkers of cardiovascular disease. This review is focused on highlighting some of the novel aspects of recent research in the area of the development of new therapeutics and better diagnostics for cardiovascular disease.

Inhibition of the renin-angiotensin system (RAS) has been shown to have beneficial effects in cardiovascular disease prognosis and therapy.Discovery of (pro)renin receptor [(P)RR] revealed that (P)RR upon binding to both renin or prorenin in their proenzyme inactive form made them enzymatically active, thus aiding the catalytic conversion of angiotensinogen (AGT) to angiotensin (Ang) I. This binding also transduces intracellular signal to the nucleus via various pathways. Our recent research elucidated the physiological roles of (P)RR in cell life, wherein it acts as an essential accessory protein of vacuolar H+-ATPase (V-ATPase) as well as an adaptor protein of Wnt signaling. The present review provides insights into a novel approach to cardiovascular diseases, which will open the gates to new therapeutic approaches for treating cardiovascular diseases.

The metabolic syndrome is strongly associated with insulin resistance and visceral obesity and consists of a constellation of factors such as diabetes, hypertension, dyslipidemia and non-alcoholic steatohepatits, which could in concert increase the risk for cardiovascular diseases (CVD). CVD, including myocardial infarction and stroke, is one of the leading causes of morbidity and mortality in the developed countries. Atherothrombosis, characterized by atherosclerotic plaque disruption and subsequent thrombus formation, contributes to the pathogenesis of CVD. Although therapeutic strategy for CVD has been progressed with anti-platelet and anti-thrombotic therapy, statins, and inhibitors of renin-angiotensin system, current therapeutic options may have therapeutic limitations because a substantial number of patients still experience CVD. Therefore, to develop novel therapeutic strategies that specifically target CVD is intensely desired. We and the others, have recently found that pigment epithelium-derived factor (PEDF), one of the serpins with neuronal differentiative activity, has insulin-sensitizing actions in the liver and adipose tissues, and exerts anti-inflammatory, anti-thrombogenic and vasculoprotective properties in vivo, thereby playing a protective role against the development and progression of the metabolic syndrome and CVD. In addition, serum levels of PEDF have been shown to increase in patients with visceral obesity, insulin resistance, diabetes, chronic kidney disease and CVD, thus being a novel biomarker of various cardiometabolic disorders. This paper discusses not only the role of PEDF, but also the clinical utility of measuring its levels in patients with various cardiometabolic disorders.

Dipeptidyl peptidases 4 (DPP4) inhibitors are a new class of oral anti-hyperglycemic drugs for the treatment of type 2 diabetes (T2DM). They are also called “incretins” because they act by inhibiting the degradation of endogenous incretin hormones, in particular GLP-1, that mediates their main metabolic effects. DPP4 is an ubiquitous protease that regulates not only glucose and lipid metabolism, but also exhibits several systemic effects at different site levels. DPP4 inhibition improves endothelial function, reduces the pro-oxidative and the pro-inflammatory state, and exerts renal effects. These actions are mediated by different DPP4 ligands, such as cytokines, growth factors, neuotransmitters etc. Clinical and experimental studies have demonstrated that DPP4 inhibitors are efficient in protecting cardiac, renal and vascular systems, through antiatherosclerotic and vasculoprotective mechanisms. For these reasons DDP4 inhibitors are thought to be “cardiovascular protective” as well as anti-diabetic drugs. Clinical trials aimed to demonstrate the efficacy of DPP4 inhibitors in reducing cardiovascular events, independent of their anti-hyperglycemic action, are ongoing. These trials will also give necessary information on their safety.

Advanced glycation end products (AGEs) are a heterogenous group of molecules formed during a non-enzymatic reaction between proteins and sugar residues. Recently, AGEs and their receptor (receptor for AGEs; RAGE) play a central role in the pathogenesis of cardiovascular disease (CVD), which accounts for disability and high mortality rate in patients with diabetes. AGEs initiate diabetic micro- and macrovascular complications through the structural modification and functional alteration of the extracellular matrix proteins as well as intracellular signaling molecules. Engagement of RAGEs with AGEs elicits intracellular reactive oxygen species (ROS) generation and subsequently activates mitogen-activated protein kinase (MAPK) and nuclear factor kappa-B (NF-κB) signaling, followed by production of several inflammatory and/or profibrotic factors such as vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), plasminogen activator inhibitor-1 (PAI-1) and monocyte chemoattractant protein-1 (MCP-1), thereby being involved in the progression of atherosclerosis. Administration of soluble form of RAGE (sRAGE) could work as a decoy receptor for AGEs and might inhibit the binding of AGEs to RAGE, preventing the development and progression of atherosclerosis in animal models. Furthermore, AGEs/high mobility group box-1 (HMGB-1)-RAGE interaction is involved in heart failure, abdominal aortic aneurysm (AAA) and vascular calcification as well. Thus, blockade of the AGEs/HMGB-1-RAGE system may be a promising therapeutic target for preventing diabetes- and/or age-related CVD. We review here the pathological role of the AGEs/HMGB-1-RAGE system in various types of CVD.

Nonalcoholic fatty liver disease (NAFLD) is among the most common causes of chronic liver disease in the westernized world and now represents a worldwide public health problem. NAFLD encompasses a broad spectrum of conditions, ranging from simple steatosis (nonalcoholic fatty liver) to nonalcoholic steatohepatitis (NASH). The latter is recognized as a potentially progressive disease that could lead to cirrhosis, liver failure, and hepatocellular carcinoma. The recent rise in obesity likely explains the NAFLD epidemic worldwide. Recognition of the importance of NAFLD and its strong association with metabolic syndrome has stimulated interest in its putative role in the development of cardiovascular disease (CVD). Recently, accumulating evidence suggests that NAFLD is associated with a significant greater overall mortality, as well as with increased prevalence of CVD, both of which are independent of classical atherosclerotic risk factors. Furthermore, observation studies of natural history of NAFLD have shown that increased age-related mortality of NAFLD patients is attributable to CVD and liver-related diseases such as liver failure and hepatocellular carcinoma. In this paper, we review clinical data to support a strong association between NAFLD and CVD, and discuss possible underlying mechanisms for accelerated atherosclerosis in NAFLD.

Chronic kidney disease carries a very high mortality risk, in particular from cardiac diseases. Often heart failure and renal failure coincide, a phenomenon referred to as the cardio renal syndrome. In recent years, it has become clear that not only fibrotic repair but also restoration of damaged kidney and heart can occur and the use of cell therapy has been advanced as a means to activate endogenous repair mechanisms or even to re-introduce repairing tissue. In this perspective, mesenchymal stromal cells are of particular interest, since these cells have both immune modulating and reparative functions and are on the brink of entering the clinical arena. Indeed, MSCs can trigger numerous therapeutic biologic processes that contribute to both renal and cardiac repair; however exact mechanisms of actions are largely unknown. In the present review we have made a critical appraisal of the data available with respect to origin and function of MSCs, and we discuss both preclinical as well as clinical evidence on their therapeutic potential in kidney and heart disease.

Endothelial cell injury is considered to play a critical role for development and progression of atherosclerosis as well as for complications after percutaneous coronary artery interventions in patients with coronary disease. Through the course of human life, the endothelium is constantly replaced and exposure to endothelial cell damaging stimuli, such as cardiovascular risk factors, requires a substantially faster repair and replacement response in order to maintain endothelial integrity and function. Moreover, after coronary interventions, the induced vascular injury requires a fast and efficient re-endothelialization in order to prevent thrombotic events. The promotion of endothelial repair and re-endothelialization responses in patients with cardiovascular disease is therefore a therapeutic target of high interest. In this review we will critically summarize novel insights into the vascular repair process, as well as the tightly linked mechanisms of adverse vascular remodeling. We will address the roles of resident vascular cell types, as well as circulating mononuclear cell populations, microvesicles and soluble mediators for the vascular repair response. A better understanding of the mechanisms limiting vascular repair in patients with cardiovascular disease may provide novel opportunities for therapeutic interventions aiming to promote the maintenance of vascular integrity.

Atherosclerosis and its thrombotic complications represent the major cause of morbidity and mortality in the industrialized countries. Despite recent advances in the diagnosis and management of cardiovascular disease, a substantial number of patients still die from acute coronary syndromes. Recently, atherosclerotic plaque composition rather than the degree of arterial stenosis has been shown to reflect the plaque vulnerability, thus contributing to the pathogenesis of cardiovascular disease. Vulnerable plaques have a large lipidrich necrotic core, a thin-fibrous cap and numerous inflammatory cells. Among them, macrophage activation plays a central role in vascular inflammation and plaque instability within the atherosclerosis, being strongly involved in acute coronary syndromes. Various morphologic features of plaque vulnerability have been described by computed tomography angiography, magnetic resonance imaging, intravascular ultrasound, and optical coherence tomography. Molecular imaging is the tool best suited for identifying metabolically active macrophages. Indeed, positron emission tomography (PET) imaging with 18F-fluorodeoxyglucose (FDG) is capable of identifying and quantifying vascular inflammation characterized by macrophage activation within the atherosclerotic plaques. So, FDG-PET might be a feasible clinical tool for detecting vulnerable plaques and evaluating the efficacy of drugs in plaque instability. In this paper, we review the clinical utility of FDG-PET imaging in identifying patients at risk of plaque rupture and resultantly prone to cardiovascular disease.