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1.  Intravital Microscopy Imaging Approaches for Image-Guided Drug Delivery Systems 
Current drug targets  2015;16(6):528-541.
Rapid technical advances in the field of non-linear microscopy have made intravital microscopy a vital pre-clinical tool for research and development of imaging-guided drug delivery systems. The ability to dynamically monitor the fate of macromolecules in live animals provides invaluable information regarding properties of drug carriers (size, charge, and surface coating), physiological, and pathological processes that exist between point-of-injection and the projected of site of delivery, all of which influence delivery and effectiveness of drug delivery systems. In this Review, we highlight how integrating intravital microscopy imaging with experimental designs (in vitro analyses and mathematical modeling) can provide unique information critical in the design of novel disease-relevant drug delivery platforms with improved diagnostic and therapeutic indexes. The Review will provide the reader an overview of the various applications for which intravital microscopy has been used to monitor the delivery of diagnostic and therapeutic agents and discuss some of their potential clinical applications.
PMCID: PMC5118947  PMID: 25901526
Biological barriers; drug delivery; therapeutic efficacy; intravital microscopy; vascular transport
2.  Immunomodulatory Drugs: Immune Checkpoint Agents in Acute Leukemia 
Current drug targets  2015;null.
Intrinsic immune responses to acute leukemia are inhibited by a variety of mechanisms, such as aberrant antigen expression by leukemia cells, secretion of immunosuppressive cytokines and expression of inhibitory enzymes in the tumor microenvironment, expansion of immunoregulatory cells, and activation of immune checkpoint pathways, all leading to T cell dysfunction and/or exhaustion. Leukemic cells, similar to other tumor cells, hijack these inhibitory pathways to evade immune recognition and destruction by cytotoxic T lymphocytes. Thus, blockade of immune checkpoints has emerged as a highly promising approach to augment innate anti-tumor immunity in order to treat malignancies. Most evidence for the clinical efficacy of this immunotherapeutic strategy has been seen in patients with metastatic melanoma, where anti-CTLA-4 and anti-PD-1 antibodies have recently revolutionized treatment of this lethal disease with otherwise limited treatment options. To meet the high demand for new treatment strategies in acute leukemia, clinical testing of these promising therapies is commencing. Herein, we review the biology of multiple inhibitory checkpoints (including CTLA-4, PD-1, TIM-3, LAG-3, BTLA, and CD200R) and their contribution to immune evasion by acute leukemias. In addition, we discuss the current state of preclinical and clinical studies of immune checkpoint inhibition in acute leukemia, which seek to harness the body’s own immune system to fight leukemic cells.
PMCID: PMC4729661  PMID: 25981611
Acute lymphoblastic leukemia; acute myeloid leukemia; co-inhibitory receptor; immune checkpoint pathway; immune evasion; immunotherapy; monoclonal antibody; T cells
3.  Safety of nanoparticles in medicine 
Current drug targets  2015;16(14):1671-1681.
Nanomedicine involves the use of nanoparticles for therapeutic and diagnostic purposes. During the past two decades, a growing number of nanomedicines have received regulatory approval and many more show promise for future clinical translation. In this context, it is important to evaluate the safety of nanoparticles in order to achieve biocompatibility and desired activity. However, it is unwarranted to make generalized statements regarding the safety of nanoparticles, since the field of nanomedicine comprises a multitude of different manufactured nanoparticles made from various materials. Indeed, several nanotherapeutics that are currently approved, such as Doxil and Abraxane, exhibit fewer side effects than their small molecule counterparts, while other nanoparticles (e.g. metallic and carbon-based particles) tend to display toxicity. However, the hazardous nature of certain nanomedicines could be exploited for the ablation of diseased tissue, if selective targeting can be achieved. This review discusses the mechanisms for molecular, cellular, organ, and immune system toxicity, which can be observed with a subset of nanoparticles. Strategies for improving the safety of nanoparticles by surface modification and pretreatment with immunomodulators are also discussed. Additionally, important considerations for nanoparticle safety assessment are reviewed. In regards to clinical application, stricter regulations for the approval of nanomedicines might not be required. Rather, safety evaluation assays should be adjusted to be more appropriate for engineered nanoparticles.
Graphical Abstract
This mini-review addresses the safety considerations for nanoparticles in medicine.
PMCID: PMC4964712  PMID: 26601723
nanomedicine; nanoparticle; nanosafety; nanotoxicity; safety; toxicity
4.  IL-17 Axis Driven Inflammation in Non-Alcoholic Fatty Liver Disease Progression 
Current drug targets  2015;16(12):1315-1323.
Obesity is a primary risk factor for the development of non-alcoholic fatty liver disease (NAFLD). NAFLD, the most common chronic liver disease in the world, represents a spectrum of disorders that range from steatosis (NAFL) to steatohepatitis (NASH) to cirrhosis. It is anticipated that NAFLD will soon surpass chronic hepatitis C infection as the leading cause for needing liver transplantation. Despite its clinical and public health significance no specific therapies are available. Although the etiology of NAFLD is multifactorial and remains largely enigmatic, it is well accepted that inflammation is a central component of NAFLD pathogenesis. Despite the significance, critical immune mediators, loci of immune activation, the immune signaling pathways and the mechanism(s) underlying disease progression remain incompletely understood. Recent findings have focused on the role of Interleukin 17 (IL-17) family of proinflammatory cytokines in obesity and pathogenesis of obesity-associated sequelae. Notably, obesity favors a Th17 bias and is associated with increased IL-17A expression in both humans and mice. Further, in mice, IL-17 axis has been implicated in regulation of both obesity and NAFLD pathogenesis. However, despite these recent advances several important questions require further evaluation including: the relevant cellular source of IL-17A production; the critical IL-17RA-expressing cell type; the critical liver infiltrating immune cells; and the underlying cellular effector mechanisms. Addressing these questions may aid in the identification and development of novel therapeutic targets for prevention of inflammation-driven NAFLD progression.
PMCID: PMC4929857  PMID: 26028039
IL-17; Inflammation; NAFLD; Obesity
5.  Adenosine monophosphate-activated protein kinase (AMPK) activators for the prevention, treatment and potential reversal of pathological pain 
Current drug targets  2016;17(8):908-920.
Pathological pain is an enormous medical problem that places a significant burden on patients and can result from an injury that has long since healed or be due to an unidentifiable cause. Although treatments exist, they often either lack efficacy or have intolerable side effects. More importantly, they do not reverse the changes in the nervous system mediating pathological pain, and thus symptoms often return when therapies are discontinued. Consequently, novel therapies are urgently needed that have both improved efficacy and disease-modifying properties. Here we highlight an emerging target for novel pain therapies, adenosine monophosphate-activated protein kinase (AMPK). AMPK is capable of regulating a variety of cellular processes including protein translation, activity of other kinases, and mitochondrial metabolism, many of which are thought to contribute to pathological pain. Consistent with these properties, preclinical studies show positive, and in some cases disease-modifying effects of either pharmacological activation or genetic regulation of AMPK in models of nerve injury, chemotherapy-induced peripheral neuropathy (CIPN), postsurgical pain, inflammatory pain, and diabetic neuropathy. Given the AMPK-activating ability of metformin, a widely prescribed and well-tolerated drug, these preclinical studies provide a strong rationale for both retrospective and prospective human pain trials with this drug. They also argue for the development of novel AMPK activators, whether orthosteric, allosteric, or modulators of events upstream of the kinase. Together, this review will present the case for AMPK as a novel therapeutic target for pain and will discuss future challenges in the path toward development of AMPK-based pain therapeutics.
PMCID: PMC4852160  PMID: 26521775
6.  Targeting the Eph System with Peptides and Peptide Conjugates 
Current drug targets  2015;16(10):1031-1047.
Eph receptor tyrosine kinases and ephrin ligands constitute an important cell communication system that controls development, tissue homeostasis and many pathological processes. Various Eph receptors/ephrins are present in essentially all cell types and their expression is often dysregulated by injury and disease. Thus, the 14 Eph receptors are attracting increasing attention as a major class of potential drug targets. In particular, agents that bind to the extracellular ephrin-binding pocket of these receptors show promise for medical applications. This pocket comprises a broad and shallow groove surrounded by several flexible loops, which makes peptides particularly suitable to target it with high affinity and selectivity. Accordingly, a number of peptides that bind to Eph receptors with micromolar affinity have been identified using phage display and other approaches. These peptides are generally antagonists that inhibit ephrin binding and Eph receptor/ephrin signaling, but some are agonists mimicking ephrin-induced Eph receptor activation. Importantly, some of the peptides are exquisitely selective for single Eph receptors. Most identified peptides are linear, but recently the considerable advantages of cyclic scaffolds have been recognized, particularly in light of potential optimization towards drug leads. To date, peptide improvements have yielded derivatives with low nanomolar Eph receptor binding affinity, high resistance to plasma proteases and/or long in vivo half-life, exemplifying the merits of peptides for Eph receptor targeting. Besides their modulation of Eph receptor/ephrin function, peptides can also serve to deliver conjugated imaging and therapeutic agents or various types of nanoparticles to tumors and other diseased tissues presenting target Eph receptors.
Graphical Abstract
Linear and cyclic peptides that bind to Eph receptors can be conjugated to imaging agents or drugs and incorporated into nanoparticles for targeted delivery to Eph receptor-positive diseased tissues.
PMCID: PMC4861043  PMID: 26212263
Angiogenesis; cancer; cyclic peptide; linear peptide; neural repair; neurodegenerative diseases; protein-protein interactions
7.  Identifying Novel Targets for Treatment of Liver Fibrosis: What Can We Learn from Injured Tissues which Heal Without a Scar? 
Current drug targets  2015;16(12):1332-1346.
The liver is unique in that it is able to regenerate. This regeneration occurs without formation of a scar in the case of non-iterative hepatic injury. However, when the liver is exposed to chronic liver injury, the purely regenerative process fails and excessive extracellular matrix proteins are deposited in place of normal liver parenchyma. While much has been discovered in the past three decades, insights into fibrotic mechanisms have not yet lead to effective therapies; liver transplant remains the only cure for advanced liver disease. In an effort to broaden the collection of possible therapeutic targets, this review will compare and contrast the liver wound healing response to that found in two types of wound healing: scarless wound healing of fetal skin and oral mucosa and scar-forming wound healing found in adult skin. This review will examine wound healing in the liver and the skin in relation to the role of humoral and cellular factors, as well as the extracellular matrix, in this process. While several therapeutic targets are similar between fibrotic liver and adult skin wound healing, others are unique and represent novel areas for hepatic anti-fibrotic research. In particular, investigations into the role of hyaluronan in liver fibrosis and fibrosis resolution are warranted.
PMCID: PMC4838187  PMID: 26302807
Extracellular matrix; fibrosis; hepatic stellate cell; inflammation; hyaluronan; macrophage
8.  HIV-1 Tat-Mediated Calcium Dysregulation and Neuronal Dysfunction in Vulnerable Brain Regions 
Current drug targets  2016;17(1):4-14.
Despite the success of combined antiretroviral therapy, more than half of HIV-1-infected patients in the USA show HIV-associated neurological and neuropsychiatric deficits. This is accompanied by anatomical and functional alterations in vulnerable brain regions of the mesocorticolimbic and nigrostriatal systems that regulate cognition, mood and motivation-driven behaviors, and could occur at early stages of infection. Neurons are not infected by HIV, but HIV-1 proteins (including but not limited to the HIV-1 trans-activator of transcription, Tat) induce Ca2+ dysregulation, indicated by abnormal and excessive Ca2+ influx and increased intracellular Ca2+ release that consequentially elevate cytosolic free Ca2+ levels ([Ca2+]in). Such alterations in intracellular Ca2+ homeostasis significantly disturb normal functioning of neurons, and induce dysregulation, injury, and death of neurons or non-neuronal cells, and associated tissue loss in HIV-vulnerable brain regions. This review discusses certain unique mechanisms, particularly the over-activation and/or upregulation of the ligand-gated ionotropic glutamatergic NMDA receptor (NMDAR), the voltage-gated L-type Ca2+ channel (L-channel) and the transient receptor potential canonical (TRPC) channel (a non-selective cation channel that is also permeable for Ca2+), which may underlie the deleterious effects of Tat on intracellular Ca2+ homeostasis and neuronal hyper-excitation that could ultimately result in excitotoxicity. This review also seeks to provide summarized information for future studies focusing on comprehensive elucidation of molecular mechanisms underlying the pathophysiological effects of Tat (as well as some other HIV-1 proteins and immunoinflammatory molecules) on neuronal function, particularly in HIV-vulnerable brain regions.
PMCID: PMC4772427  PMID: 26028040
neuroAIDS; cognition; medial prefrontal cortex; pyramidal neuron; over-excitation; neurotoxicity; electrophysiology
9.  CYLD-Mediated Signaling and Diseases 
Current drug targets  2015;16(4):284-294.
The conserved cylindromatosis (CYLD) codes for a deubiquitinating enzyme and is a crucial regulator of diverse cellular processes such as immune responses, inflammation, death, and proliferation. It directly regulates multiple key signaling cascades, such as the Nuclear Factor kappa B [NF-kB] and the Mitogen-Activated Protein Kinase (MAPK) pathways, by its catalytic activity on polyubiquitinated key intermediates. Several lines of emerging evidence have linked CYLD to the pathogenesis of various maladies, including cancer, poor infection control, lung fibrosis, neural development, and now cardiovascular dysfunction. While CYLD-mediated signaling is cell type and stimuli specific, the activity of CYLD is tightly controlled by phosphorylation and other regulators such as Snail. This review explores a broad selection of current and past literature regarding CYLD’s expression, function and regulation with emerging reports on its role in cardiovascular disease.
PMCID: PMC4418510  PMID: 25342597
Cardiovascular; CYLD; cylindromatosis; deubiquitination; K63; MAPK; NF-kB
10.  TNF Superfamily Protein–Protein Interactions: Feasibility of Small-Molecule Modulation 
Current drug targets  2015;16(4):393-408.
The tumor necrosis factor (TNF) superfamily (TNFSF) contains about thirty structurally related receptors (TNFSFRs) and about twenty protein ligands that bind to one or more of these receptors. Almost all of these cell surface protein-protein interactions (PPIs) represent high-value therapeutic targets for inflammatory or immune modulation in autoimmune diseases, transplant recipients, or cancers, and there are several biologics including antibodies and fusion proteins targeting them that are in various phases of clinical development. Small-molecule inhibitors or activators could represent possible alternatives if the difficulties related to the targeting of protein-protein interactions by small molecules can be addressed. Compounds proving the feasibility of such approaches have been identified through different drug discovery approaches for a number of these TNFSFR-TNFSF type PPIs including CD40-CD40L, BAFFR-BAFF, TRAIL-DR5, and OX40-OX40L. Corresponding structural, signaling, and medicinal chemistry aspects are briefly reviewed here. While none of these small-molecule modulators identified so far seems promising enough to be pursued for clinical development, they provide proof-of-principle evidence that these interactions are susceptible to small-molecule modulation and can serve as starting points toward the identification of more potent and selective candidates.
PMCID: PMC4408546  PMID: 25706111
CD40; costimulation; druggability; OX40; tumor necrosis factor
11.  Molecular Pathophysiology of Priapism: Emerging Targets 
Current drug targets  2015;16(5):474-483.
Priapism is an erectile disorder involving uncontrolled, prolonged penile erection without sexual purpose, which can lead to erectile dysfunction. Ischemic priapism, the most common of the variants, occurs with high prevalence in patients with sickle cell disease. Despite the potentially devastating complications of this condition, management of recurrent priapism episodes historically has commonly involved reactive treatments rather than preventative strategies. Recently, increasing elucidation of the complex molecular mechanisms underlying this disorder, principally involving dysregulation of nitric oxide signaling, has allowed for greater insights and exploration into potential therapeutic targets. In this review, we discuss the multiple molecular regulatory pathways implicated in the pathophysiology of priapism. We also identify the roles and mechanisms of molecular effectors in providing the basis for potential future therapies.
PMCID: PMC4430197  PMID: 25392014
Adenosine; Nitric Oxide; Opiorphins; Rho Kinase; Recurrent Ischemic Priapism Treatment; Testosterone
12.  Image-Guided Drug Delivery with Single-Photon Emission Computed Tomography: A Review of Literature 
Current drug targets  2015;16(6):592-609.
Tremendous resources are being invested all over the world for prevention, diagnosis, and treatment of various types of cancer. Successful cancer management depends on accurate diagnosis of the disease along with precise therapeutic protocol. The conventional systemic drug delivery approaches generally cannot completely remove the competent cancer cells without surpassing the toxicity limits to normal tissues. Therefore, development of efficient drug delivery systems holds prime importance in medicine and healthcare. Also, molecular imaging can play an increasingly important and revolutionizing role in disease management. Synergistic use of molecular imaging and targeted drug delivery approaches provides unique opportunities in a relatively new area called `image-guided drug delivery' (IGDD). Single-photon emission computed tomography (SPECT) is the most widely used nuclear imaging modality in clinical context and is increasingly being used to guide targeted therapeutics. The innovations in material science have fueled the development of efficient drug carriers based on, polymers, liposomes, micelles, dendrimers, microparticles, nanoparticles, etc. Efficient utilization of these drug carriers along with SPECT imaging technology have the potential to transform patient care by personalizing therapy to the individual patient, lessening the invasiveness of conventional treatment procedures and rapidly monitoring the therapeutic efficacy. SPECT-IGDD is not only effective for treatment of cancer but might also find utility in management of several other diseases. Herein, we provide a concise overview of the latest advances in SPECT-IGDD procedures and discuss the challenges and opportunities for advancement of the field.
PMCID: PMC4346511  PMID: 25182469
Cancer; Chemotherapy; Image-guided drug delivery; Molecular imaging; Single-photon emission computed tomography; Theranostics
13.  Cardiovascular complications in inflammatory bowel disease 
Current drug targets  2015;16(3):181-188.
Over the past years, a growing number of studies have indicated that patients suffering from inflammatory bowel disease (IBD) have an increased risk of developing cardiovascular disease. Both are chronic inflammatory diseases and share certain pathophysiological mechanisms that may influence each other. High levels of cytokines, C-reactive protein (CRP), and homocysteine in IBD patients may lead to endothelial dysfunction, an early sign of atherosclerosis. IBD patients, in general, do not show the typical risk factors for cardiovascular disease but changes in lipid profiles similar to the ones seen in cardiovascular events have been reported recently. Higher levels of coagulation factors frequently occur in IBD which may predispose to arterial thromboembolic events. Finally, the gut itself may have an impact on atherogenesis during IBD through its microbiota. Microbial products are released from the inflamed mucosa into the circulation through a leaky barrier. The induced rise in proinflammatory cytokines could contribute to endothelial damage, artherosclerosis and cardiovascular events. Although large retrospective studies favor a link between IBD and cardiovascular diseases the mechanisms behind still remain to be determined.
PMCID: PMC4366573  PMID: 25642719
Crohn’s disease; Ulcerative colitis; cardiovascular diseases; coronary artery disease; thromboembolism; endotoxins; LPS; dyslipidemia
14.  Biomedical Imaging in Implantable Drug Delivery Systems 
Current drug targets  2015;16(6):672-682.
Implantable drug delivery systems (DDS) provide a platform for sustained release of therapeutic agents over a period of weeks to months and sometimes years. Such strategies are typically used clinically to increase patient compliance by replacing frequent administration of drugs such as contraceptives and hormones to maintain plasma concentration within the therapeutic window. Implantable or injectable systems have also been investigated as a means of local drug administration which favors high drug concentration at a site of interest, such as a tumor, while reducing systemic drug exposure to minimize unwanted side effects. Significant advances in the field of local DDS have led to increasingly sophisticated technology with new challenges including quantification of local and systemic pharmacokinetics and implant-body interactions. Because many of these sought-after parameters are highly dependent on the tissue properties at the implantation site, and rarely represented adequately with in vitro models, new nondestructive techniques that can be used to study implants in situ are highly desirable. Versatile imaging tools can meet this need and provide quantitative data on morphological and functional aspects of implantable systems. The focus of this review article is an overview of current biomedical imaging techniques, including magnetic resonance imaging (MRI), ultrasound imaging, optical imaging, X-ray and computed tomography (CT), and their application in evaluation of implantable DDS.
PMCID: PMC4441594  PMID: 25418857
Biomaterials; drug delivery; fluorescence imaging; implant; MRI (magnetic resonance imaging); scaffold; ultrasound imaging; X-ray CT Imaging
15.  Protein Arginine Deiminases and Associated Citrullination: Physiological Functions and Diseases Associated with Dysregulation 
Current drug targets  2015;16(7):700-710.
Human proteins are subjected to more than 200 known post-translational modifications (PTMs) (e.g., phosphorylation, glycosylation, ubiquitination, S-nitrosylation, methylation, N-acetylation, and citrullination) and these PTMs can alter protein structure and function with consequent effects on the multitude of pathways necessary for maintaining the physiological homeostasis. When dysregulated, however, the enzymes that catalyze these PTMs can impact the genesis of countless diseases. In this review, we will focus on protein citrullination, a PTM catalyzed by the Protein Arginine Deiminase (PAD) family of enzymes. Specifically, we will describe the roles of the PADs in both normal human physiology and disease. The development of PAD inhibitors and their efficacy in a variety of autoimmune disorders and cancer will also be discussed.
PMCID: PMC4520219  PMID: 25642720
Apoptosis; autoimmune disease; citrullination; gene regulation; inflammatory disease; protein arginine deiminases
16.  Multistage Nanovectors Enhance the Delivery of Free and Encapsulated Drugs 
Current drug targets  2015;16(14):1582-1590.
Nanoparticles have considerable potential for cancer imaging and therapy due to their small size and prolonged circulation. However, biological barriers can impede the delivery of a sufficient dose of a drug to the target site, thereby also resulting in the accumulation of toxic compounds within healthy tissues, and systemic toxicity. Multistage nanovectors (MSV) preferentially accumulate on inflamed endothelium, and can thus serve as carriers for drugs and nanoparticles. Herein, we describe the loading of free (i.e., melittin) and nano-encapsulated (i.e., doxorubicin-loaded micelles) drugs into MSV, and report the impact of surface charge and pore size on drug loading. For both drug formulations, negatively charged MSV (i.e., oxidized) with larger pores were shown to retain higher concentrations of payloads compared to positively charged (i.e., APTES-modified) MSV with small pores. Treatment of human umbilical vein endothelial cells (HU-VEC) with melittin-loaded MSV (MEL@MSV) resulted in an 80% reduction in cell viability after 3 days. Furthermore, MEL@MSV conjugated with anti-vascular endothelial growth factor receptor 2 (VEGFR2) antibodies displayed preferential targeting and delivery of MEL to activated HUVEC expressing VEGFR2. Treatment of HUVEC and MCF7 cells with doxorubicin-loaded micelles (DOXNP@MSV) resulted in a 23% and 47% reduction in cell viability, respectively. Taken together, these results demonstrate increased loading of a payload in oxidized, large pore MSV, and effective delivery of free and nano-encapsulated drugs to endothelial and cancer cells.
PMCID: PMC4398589  PMID: 25316273
Doxorubicin; drug delivery; melittin; micelles; multistage nanovector; nanoparticles
17.  Proteomic Profiling of a Biomimetic Drug Delivery Platform 
Current drug targets  2015;16(13):1540-1547.
Current delivery platforms are typically designed for prolonged circulation that favors superior accumulation of the payload in the targeted tissue. The design of efficient surface modifications determines both a longer circulation time and targeting abilities of particles. The optimization of synthesis protocols to efficiently combine targeting molecules and elements that allow for an increased circulation time can be challenging and almost impossible when several functional elements are needed. On the other hand, in the last decade, the development of bioinspired technologies was proposed as a new approach with which to increase particle safety, biocompatibility and targeting, while maintaining the synthesis protocols simple and reproducible. Recently, we developed a new drug delivery system inspired by the biology of immune cells called leukolike vector (LLV) and formed by a nanoporous silicon core and a shell derived from the leucocyte cell membrane. The goal of this study is to investigate the protein content of the LLV. Here we report the proteomic profiling of the LLV and demonstrate that our approach can be used to modify the surface of synthetic particles with more than 150 leukocyte membrane-associated proteins that determine particle safety, circulation time and targeting abilities towards inflamed endothelium.
PMCID: PMC4426090  PMID: 25382209
Bio-mimetic camouflage; drug delivery; leukocyte; leukolike vector; membrane; nanotechnology; nanoparticles; proteomics
18.  FOXO1: A potential target for human diseases 
Current drug targets  2011;12(9):1235-1244.
The forkhead box O (FoxO) transcription factors are known to be involved in many physiological and pathological processes including apoptosis, cell cycle arrest, stress resistance, glucose metabolism, cellular differentiation and development, and tumor suppression. The environmental cues, such as growth factors, nutrients, oxidative stress and irradiation, can either positively or negatively modulate FoxO proteins’ activities, thereby ensuring distinctive transcription programs in the cell. The potent activities of FoxOs are tightly controlled by multiple mechanisms, which include posttranslational modification such as phosphorylation, acetylation, methylation and ubiquination, subcellular localization, and direct protein-protein interaction. Mounting evidence suggests that the human FOXO1 protein, a founding member of the FoxO family is likely involved in carcinogenesis, diabetes and other human diseases. Here we give an overview of most recent findings regarding the regulation and function of FoxO1, its potential role in human diseases and useful animal models for functional studies on FoxO1. Prospective ways in which the discoveries from the basic research of FoxO1 can be utilized for drug targeting and development of novel therapeutics for human diseases are also discussed.
PMCID: PMC4591039  PMID: 21443466
FoxO transcription factors; posttranslational modification; apoptosis; the cell cycle; glucose metabolism; cancer; diabetes; muscle atrophy
Current drug targets  2008;9(11):1013-1024.
Hepatocellular carcinoma (HCC) is a major cause of cancer death worldwide. As in many other types of cancer, aberrant activation of the canonical Wnt/β-catenin signaling pathway is an important contributor to tumorigenesis. In HCC this frequently occurs through mutations in the N-terminal region of β-catenin that stabilize the protein and permit an elevated level of constitutive transcriptional activation by β-catenin/TCF complexes. In this article we review the abundant evidence that Wnt/β-catenin signaling contributes to liver carcinogenesis. We also discuss what is known about the roles of Wnt signaling in liver development, regeneration, and stem cell behavior, in an effort to understand the mechanisms by which activation of the canonical Wnt pathway promotes tumor formation in this organ. The Wnt/β-catenin pathway presents itself as an attractive target for developing novel rational therapies for HCC, a disease for which few successful treatment strategies are currently available.
PMCID: PMC4446985  PMID: 18991612
20.  Hypoxia-Inducible Factor-1 (HIF-1): A Potential Target for Intervention in Ocular Neovascular Diseases 
Current drug targets  2013;14(8):919-935.
Constant oxygen supply is essential for proper tissue development, homeostasis and function of all eukaryotic organisms. Cellular response to reduced oxygen levels is mediated by the transcriptional regulator hypoxia-inducible factor-1 (HIF-1). It is a heterodimeric complex protein consisting of an oxygen dependent subunit (HIF-1α) and a constitutively expressed nuclear subunit (HIF-1β). In normoxic conditions, de novo synthesized cytoplasmic HIF-1α is degraded by 26S proteasome. Under hypoxic conditions, HIF-1α is stabilized, binds with HIF-1β and activates transcription of various target genes. These genes play a key role in regulating angiogenesis, cell survival, proliferation, chemotherapy, radiation resistance, invasion, metastasis, genetic instability, immortalization, immune evasion, metabolism and stem cell maintenance. This review highlights the importance of hypoxia signaling in development and progression of various vision threatening pathologies such as diabetic retinopathy, retinopathy of prematurity, age-related macular degeneration and glaucoma. Further, various inhibitors of HIF-1 pathway that may have a viable potential in the treatment of oxygen-dependent ocular diseases are also discussed.
PMCID: PMC4407697  PMID: 23701276
Age-related macular degeneration; diabetic retinopathy; hypoxia signaling; hypoxia-inducible factor-1 (HIF-1); ocular neovascularization; retinopathy of prematurity
21.  Triple Threat: The Na+/Ca2+ Exchanger in the Pathophysiology of Cardiac Arrhythmia, Ischemia and Heart Failure 
Current drug targets  2011;12(5):737-747.
The Na+/Ca2+ exchanger (NCX) is the main Ca2+ extrusion mechanism of the cardiac myocyte and thus is crucial for maintaining Ca2+ homeostasis. It is involved in the regulation of several parameters of cardiac excitation contraction coupling, such as cytosolic Ca2+ concentration, repolarization and contractility. Increased NCX activity has been identified as a mechanism promoting heart failure, cardiac ischemia and arrhythmia. Transgenic mice as well as pharmacological interventions have been used to support the idea of using NCX inhibition as a future pharmacological strategy to treat cardiovascular disease.
PMCID: PMC4406235  PMID: 21291388
22.  Sodium Dependent Multivitamin Transporter (SMVT): A Potential Target for Drug Delivery 
Current drug targets  2012;13(7):994-1003.
Sodium dependent multivitamin transporter (SMVT; product of the SLC5A6 gene) is an important transmembrane protein responsible for translocation of vitamins and other essential cofactors such as biotin, pantothenic acid and lipoic acid. Hydropathy plot (Kyte-Dolittle algorithm) revealed that human SMVT protein consists of 635 amino acids and 12 transmembrane domains with both amino and carboxyl termini oriented towards the cytoplasm. SMVT is expressed in various tissues such as placenta, intestine, brain, liver, lung, kidney, cornea, retina and heart. This transporter displays broad substrate specificity and excellent capacity for utilization in drug delivery. Drug absorption is often limited by the presence of physiological (epithelial tight junctions), biochemical (efflux transporters and enzymatic degradation) and chemical (size, lipophilicity, molecular weight, charge, etc.) barriers. These barriers may cause many potential therapeutics to be dropped from the preliminary screening portfolio and subsequent entry into the market. Transporter targeted delivery has become a powerful approach to deliver drugs to target tissues because of the ability of the transporter to translocate the drug to intracellular organelles at a higher rate. This review highlights studies employing SMVT transporter as a target for drug delivery to improve bioavailability and investigate the feasibility of developing SMVT targeted drug delivery systems.
PMCID: PMC4406285  PMID: 22420308
SMVT; tissue distribution; substrate specificity; transporter targeted drug delivery
23.  Therapeutic targeting of cancers with loss of PTEN function 
Current drug targets  2014;15(1):65-79.
Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is one of the most frequently disrupted tumor suppressors in cancer. The lipid phosphatase activity of PTEN antagonizes the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway to repress tumor cell growth and survival. In the nucleus, PTEN promotes chromosome stability and DNA repair. Consequently, loss of PTEN function increases genomic instability. PTEN deficiency is caused by inherited germline mutations, somatic mutations, epigenetic and transcriptional silencing, post-translational modifications, and protein-protein interactions. Given the high frequency of PTEN deficiency across cancer subtypes, therapeutic approaches that exploit PTEN loss-of-function could provide effective treatment strategies. Herein, we discuss therapeutic strategies aimed at cancers with loss of PTEN function, and the challenges involved in treating patients afflicted with such cancers. We review preclinical and clinical findings, and highlight novel strategies under development to target PTEN-deficient cancers.
PMCID: PMC4310752  PMID: 24387334
Phosphatase; cancer; tumor; targeted therapy; tumor suppressor; PI3K; mTOR; synthetic lethal
24.  Targeting Tumor Suppressor Networks for Cancer Therapeutics 
Current drug targets  2014;15(1):2-16.
Cancer is a consequence of mutations in genes that control cell proliferation, differentiation and cellular homeostasis. These genes are classified into two categories: oncogenes and tumor suppressor genes. Together, overexpression of oncogenes and loss of tumor suppressors are the dominant driving forces for tumorigenesis. Hence, targeting oncogenes and tumor suppressors hold tremendous therapeutic potential for cancer treatment. In the last decade, the predominant cancer drug discovery strategy has relied on a traditional reductionist approach of dissecting molecular signaling pathways and designing inhibitors for the selected oncogenic targets. Remarkable therapies have been developed using this approach; however, targeting oncogenes is only part of the picture. Our understanding of the importance of tumor suppressors in preventing tumorigenesis has also advanced significantly and provides a new therapeutic window of opportunity. Given that tumor suppressors are frequently mutated, deleted, or silenced with loss-of-function, restoring their normal functions to treat cancer holds tremendous therapeutic potential. With the rapid expansion in our knowledge on cancer over the last several decades, developing effective anticancer regimens against tumor suppressor pathways has never been more promising. In this article, we will review the concept of tumor suppression, and outline the major therapeutic strategies and challenges of targeting tumor suppressor networks for cancer therapeutics.
PMCID: PMC4032821  PMID: 24387338
tumor suppressors; RB; p53; BRCA1; BRCA2; gene therapy; small molecule inhibitors
25.  Targeting the LKB1 Tumor Suppressor 
Current drug targets  2014;15(1):32-52.
LKB1 (also known as serine-threonine kinase 11, STK11) is a tumor suppressor, which is mutated or deleted in Peutz-Jeghers syndrome (PJS) and in a variety of cancers. Physiologically, LKB1 possesses multiple cellular functions in the regulation of cell bioenergetics metabolism, cell cycle arrest, embryo development, cell polarity, and apoptosis. New studies demonstrated that LKB1 may also play a role in the maintenance of function and dynamics of hematopoietic stem cells. Over the past years, personalized therapy targeting specific genetic aberrations has attracted intense interests. Within this review, several agents with potential activity against aberrant LKB1 signaling have been discussed. Potential strategies and challenges in targeting LKB1 inactivation are also considered.
PMCID: PMC3899349  PMID: 24387336
LKB1 (serine-threonine kinase 11, STK11); AMP-activated protein kinase (AMPK); tumor suppression; mutations; targeting therapeutics

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