Current Pharmaceutical Design - Volume 18, Issue 25, 2012

The blood-brain barrier (BBB) has been considered as an important regulator of brain homeostasis, and its disturbance has been implicated in the onset and/or evolution of many pathological manifestations of neurodegenerative and inflammatory diseases [1, 2]. In particular, BBB breakdown has been closely associated with the primary insult, as well as the secondary cell death of stroke. Here, we review the pioneering contributions of leading scientists who have vested interest in advancing our understanding of the pivotal role of BBB in stroke, but also exploiting this knowledge in developing novel BBB-based therapeutic regimens to abrogate stroke symptoms. The study of BBB as a fundamental research theme and as a target for clinical applications in stroke can be approached in three main themes namely, basic science research, translational and clinical research, and emerging therapies for BBB repair in stroke. This minireview captures cutting-edge discoveries establishing BBB as a central target for abetting neuroprotection and neurorestoration in stroke.

The blood-brain barrier (BBB) is a critical regulator of brain homeostasis. Additionally, the BBB is the most significant obstacle to effective CNS drug delivery. It possesses specific charcteristics (i.e., tight junction protein complexes, influx and efflux transporters) that control permeation of circulating solutes including therapeutic agents. In order to form this “barrier,” brain microvascular endothelial cells require support of adjacent astrocytes and microglia. This intricate relationship also occurs between endothelial cells and other cell types and structures of the CNS (i.e., pericytes, neurons, extracellular matrix), which implies existence of a “neurovascular unit.” Ischemic stroke can disrupt the neurovascular unit at both the structural and functional level, which leads to an increase in leak across the BBB. Recent studies have identified several pathophysiological mechanisms (i.e., oxidative stress, activation of cytokinemediated intracellular signaling systems) that mediate changes in the neurovascular unit during ischemic stroke. This review summarizes current knowledge in this area and emphasizes pathways (i.e., oxidative stress, cytokine-mediated intracellular signaling, glial-expressed receptors/targets) that can be manipulated pharmacologically for i) preservation of BBB and glial integrity during ischemic stroke and ii) control of drug permeation and/or transport across the BBB. Targeting these pathways present a novel opportunity for optimization of CNS delivery of therapeutics in the setting of ischemic stroke.

Blood-brain barrier (BBB) leakage and brain edema is a critical part of stroke pathophysiology. In this mini-review, we briefly survey the potential role of matrix metalloproteinases (MMPs) in BBB dysfunction. A large body of data in both experimental models as well as clinical patient populations suggests that MMPs may disrupt BBB permeability and interfere with cell-cell signaling in the neurovascular unit. Hence, ongoing efforts are underway to validate MMPs as potential biomarkers in stroke as well as pursue MMP blockers as therapeutic opportunities. Because BBB perturbations may also occur in neurodegeneration, MMPs and associated neurovascular unit mechanisms may also be potential targets in a broader range of CNS disorders.

Recent evidence indicates that circulating endothelial progenitor cells can play an important role, not only in endothelium homeostasis of the pre-stroke brain, but also in angiogenesis of the post-stroke brain. Circulating endothelial progenitor cells are considered to repair endothelial cells by incorporating them into newly formed vessels, or by releasing pro-angiogenic factors. The number or function of circulating endothelial progenitor cells can be modulated by various kinds of factors. For example, elevated serum cholesterol, hypertension, diabetes and smoking decreased the number whereas vascular endothelial growth factor (VEGF), exercise, and statins can increase it. In this review, we discuss the present knowledge of endogenous mechanisms for the repair of endothelial cells, and how to enhance their possible capacity to remodel vascular units as neuronal self-repair strategies.

Central nervous system pericytes have critical and complex inductive, structural, and regulatory roles interacting with other cell types of the neurovascular unit, especially endothelial cells and astrocytes. Pericyte-endothelial interactions are particularly prominent for blood-brain barrier (BBB) maintenance, with profound effects on basement membrane and endothelial tight junction structure and function. Under experimental conditions of hypoxia-ischemia mimicking stroke, pericytes migrate from their usual microvascular location and influence, directly or indirectly, BBB permeability. The contractile properties of pericytes provide the capacity to regulate capillary blood flow, but this may have detrimental effects on ischemic injury. Stem cell characteristics of pericytes imply an important regenerative role following stroke. Pericytes thus appear to orchestrate multiple critical functions in stroke, involving blood flow, permeability, and repair of the neurovascular unit.

Stroke remains a major cause of death in the US and around the world. Despite major scientific advances in our understanding of stroke pathology, the only FDA-approved drug for ischemic stroke is tissue plasminogen activator (tPA). Moreover, the therapeutic window for tPA is confined to the acute phase of stroke, thereby greatly limiting its benefits to less than 3% of ischemic stroke patients. Many treatment strategies for stroke have targeted the subacute or chronic phase in an effort to abrogate the secondary cell death that ensues after the initial stroke insult. Here, we advance the hypothesis that blood vessel disruption, or aneurysm, in the brain is an exacerbating factor for stroke, especially in the evolution of the penumbra or peri-infarct area. A better understanding of aneurysm, specifically its dynamic onset and juxtaposition to the ischemic brain tissue should facilitate the development of novel strategies for attenuating the secondary cell death associated with stroke. To this end, we discuss the laboratory and clinical evidence implicating aneurysm formation in stroke and also provide insights on how stem cell therapy may prove efficacious in combating aneurysm and stroke.

Cell therapy has been shown as a potential treatment for stroke and other neurological disorders. Human umbilical cord blood (HUCB) may be a promising source of stem cells for cell therapy. The most desired outcomes occur when stem cells cross the blood brain barrier (BBB) and eventually reach the injured brain site. We propose, from our previous studies, that mannitol is capable of disrupting the BBB, allowing the transplanted cells to enter the brain from the periphery. However, when the BBB is compromised, the inflammatory response from circulation may also be able to penetrate the brain and thus may actually exacerbate the stroke rather than afford therapeutic effects. We discuss how an NF-kB decoy can inhibit the inflammatory responses in the stroke brain thereby reducing the negative effects associated with BBB disruption. In this review, we propose the combination of mannitol-induced BBB permeation and NF-kB decoy for enhancing the therapeutic benefits of cell therapy in stroke.

Thrombolytic therapy with tissue plasminogen activator (tPA) remains the most effective treatment for acute ischemic stroke, but can cause vascular damage leading to edema formation and hemorrhagic transformation (HT). In this review, we discuss how tPA contributes to the pathogenesis of vascular damage and highlight evidence to support combination therapy of tPA with pharmacological agents that are vascular protective. There is an unmet need to develop therapeutic interventions which target the underlying mechanisms of vascular damage after acute ischemic stroke in order to prevent HT and improve the safety and impact of tPA.

Stem cell transplantation has emerged as a promising treatment strategy for stroke. The development of effective ways to monitor transplanted stem cells is essential to understand how stem cell transplantation enhances stroke recovery and ultimately will be an indispensable tool for advancing stem cell therapy to the clinic. In this review, we describe existing methods of tracking transplanted stem cells in vivo, including optical imaging, magnetic resonance imaging (MRI), and positron emission tomography (PET), with emphasis on the benefits and drawbacks of each imaging approach. Key considerations such as the potential impact of each tracking system on stem cell function, as well as its relative applicability to humans are discussed. Finally, we describe multi-modal imaging strategies as a more comprehensive method to track transplanted stem cells in the stroke-injured brain.

Stroke is the 4th leading cause of death and disability in adults in the USA. However, in the majority of patients, the detrimental effects of an ischemic insult go untreated because of the lack of efficacious neuroprotective compounds. Using naturally occurring compounds as a building block to create efficacious neuroprotective compounds that cross the blood brain barrier may eventually benefit the stroke patients. However, historically, the development of novel compounds has been fraught with problems including lack of significant pleiotropic activity, inability to effectively cross the blood brain barrier and poor bioavailability. This article details, in a stepwise manner, the synthesis and in vitro screening steps used to produce new flavonoids that have increased neuroprotective activity compared to the parent compound fisetin. Moreover, as a preliminary de-risking step, select compounds have been screened in a transfected Madin Darby canine kidney cell assay as a measure of blood brain barrier penetration. Initial de-risking steps have allowed us to identify a series of BBB-penetrating neuroprotective candidates for further development.

Stroke is a devastating disease with few therapeutic options. Despite our growing understanding of the critical mechanistic events in post-stroke brain injury, the clinical translation of these findings has been less effective. A monumental hurdle to the field has been the inability of many systemically applied therapies to efficiently cross the blood brain barrier (BBB) and enter brain cells. Over the last two decades, however, significant technological achievements have overcome this obstacle to facilitate central nervous system (CNS) drug delivery. Noninvasive drug carriers, especially cell penetrating peptide (CPP) show great potential to deliver neurotherapeutics across the BBB for the treatment of ischemic brain injury. This review begins with a brief introduction to the BBB in relation to drug delivery and then provides an overview of the development of drug carriers for neurotherapeutics, with a focus on CPP-mediated transduction. We discuss recent advances and limitations in this field, as well as mechanisms underlying CPP-mediated brain targeting. We also summarize the application of CPPs in stroke research. Continuing modifications and improvements of CPPs are expected to enhance both their feasibility in clinical stroke management and their specificity towards particular cell types.

Stroke pathology involves multifactorial pro-death responses, including inflammation, oxidative stress, vascular dysfunction, and activation of necrotic and apoptotic pathways. The interruption of a single specific pathway in defined stroke model systems has not been sufficient to address the multifactorial nature of stroke-induced injuries in the human population. CD36 is a class B scavenger receptor that functions in regulating normal physiological and pathological functions. CD36 pathways are activated by several distinct ligands. Convergence of these pathways results in inflammatory responses and endothelial dysfunction, which may be an underlying cause of cardio- and cerebrovascular diseases. The current review describes receptor CD36-ligand interactions relevant to endothelial function and discusses how targeting CD36 may have therapeutic utility in stroke.

Endothelial progenitor cells (EPCs) correspond to a population of cells with novel properties capable of angiogenesis and vasculogenesis, thus they are likely to display unique role in the reconstitution of the blood brain barrier (BBB) after stroke. Laboratory evidence supports safety and efficacy of cell therapy for stroke, with limited clinical trials recently initiated. This lab-to-clinic ascent of cellbased therapeutics has been aided by the establishment of consortium consisting of thought-leaders from academia, industry, National Institutes of Health (NIH) and the United States Food and Drug Administration (FDA). However, there remain unanswered questions prior to realization of large-scale application of cell transplantation in patients. This review article discusses translational challenges associated in cell therapy, emphasizing the need for optimizing both safety and efficacy profiles for advancing the clinical applications of EPC transplantation for stroke patients.

Ovarian cancer is the most lethal gynecological cancer in women in the western world with a 5-year survival of 49.7%. Advanced stage ovarian cancer is treated both surgically and with chemotherapy, but despite initial high response rates of 60- 75%, many women experience disease recurrence with a dismal prognosis, 5 year overall survival for FIGO stage IIIc and IV disease being only 32 and 18%. In an attempt to improve outcome for both primary and recurrent disease, dose-intense and dose-dense chemotherapy regimens have been investigated. This overview summarizes these results in first and second-line treatment. In first-line treatment, no benefit was found of dose-intense regimes in the majority of the studies, only toxicity was increased. However, results are conflicting with the recent Japanese Gynecologic Oncology Group (JGOG) trial showing an improved progression free and overall survival in patients treated with dose-dense weekly paclitaxel combined with standard 3-weekly carboplatin. For recurrent disease dose-dense weekly combination chemotherapy seems to be very effective in patients with platinum-resistant ovarian cancer. Several phase II studies showed an increase in response rate, progression free survival and overall survival for dose-dense paclitaxel and carboplatin, compared to results of nonplatinum chemotherapy. In platinum-sensitive ovarian cancer, on contrary, the results of weekly paclitaxel and carboplatin seem to be comparable with standard 3-weekly regimens.

Trabectedin (ET-743, Yondelis®) is a novel marine antineoplastic alkaloid with a unique mechanism of action. The active substance trabectedin, a tetrahydroisoquinoline alkaloid, is a natural product originally isolated from the Caribbean sea squirt, Ecteinascidia turbinata and is currently manufactured by total synthesis. Trabectedin is licensed by the Spanish pharmaceutical drug company, PharmaMar and co-developed by Johnson & Johnson Pharmaceutical Research and Development, L.L.C., pursuant to a licensing agreement with PharmaMar. Trabectedin is the first anticancer marine-derived drug to be approved by the European Union. In 2007, trabectedin obtained marketing authorization from the European Commission and in many other countries worldwide for the treatment of patients with advanced soft tissue sarcoma (STS) after failure of anthracyclines and ifosfamide, or for those patients who are unsuitable to receive these agents. Based on the recently reported results of a large phase III study (OVA-301) comparing pegylated liposomal doxorubicin (PLD) alone with a combination of PLD and trabectedin in patients with recurrent ovarian cancer, in 2009 the European Commission granted marketing authorization for trabectedin combined with PLD for the treatment of patients with relapsed platinum-sensitive ovarian cancer. The results from OVA-301 showed that the combination of trabectedin and PLD improves progression-free survival and overall response rate over PLD alone with acceptable tolerance in the second-line treatment of recurrent ovarian cancer. In addition, an enhanced activity of trabectedin combined with PLD was observed in platinum sensitive patients, especially in those with a platinum-free interval ranging from 6 to 12 months. Overall, trabectedin-induced toxicities are mainly hematological and hepatic, with grade 3/4 neutropenia and thrombocytopenia observed in approximately 50% and 13% of patients, respectively, and grade 3/4 elevation of liver aminotransferases observed in 40-50% of patients treated with trabectedin. Current efforts are focused on the evaluation of the role of trabectedin in prolonging the platinum-free interval and the identification of predictive factors for patients treated with trabectedin as well as in the development of new trabectedin-based combinations.

Homologous recombination (HR), a key mechanism of DNA double strand break (DSB) repair, is commonly defective in high grade serous carcinomas (HGSC) of the ovary. BRCA1/2 mutations, as well as many other molecular and genetic defects, can lead to impaired HR. Treatment of HR-defective tumours with poly-ADP ribose polymerase (PARP) inhibitors, which block the key mechanism of single strand DNA breaks (SSB), exploits a therapeutic concept called “synthetic lethality”. Early experiences with PARP inhibitors in germline BRCA mutation carriers and sporadic HGSCs of the ovary have been promising. The development of PARP inhibitors for ovarian cancer is an area of active research. This article provides an overview of the molecular rationale for the use of PARP inhibitors and summarizes some of the key early clinical data of their use in ovarian cancer.

Background: There is a strong rationale for usage of anti-angiogenic agents in epithelial ovarian cancer. Bevacizumab is the most widely investigated anti-VEGF agent and has shown promising results in recent clinical trials. Objective: To review the rationale and usage of bevacizumab in advanced epithelial ovarian cancer; as mono-therapy, in combination with chemotherapy both as first line and for recurrent ovarian cancer as well as in combination with other targeted therapies. Results: In epithelial ovarian cancer, angiogenesis promotes tumor growth, ascites formation and metastasis. Targeting VEGF in ovarian cancer patients may have indirect and direct cytotoxic effects. Results of placebo controlled phase III trials, the GOG-218 and ICON7, of carboplatin-paclitaxel alone or combined with bevacizumab in chemo-naive patients and the OCEAN trial comparing carboplatin-gemcitabine with or without bevacizumab in women with recurrent platinum-sensitive epithelial ovarian cancer all suggest a benefit for the addition of bevacizumab on progression free survival. Additionally, bevacizumab in combination with other targeted therapies, such as sorafenib and everolimus are under investigation in phase II trials and the current knowledge of molecular predictors is discussed. In Conclusion: Until now no survival benefit has been observed, but bevacizumab is the first anti-angiogenic agent demonstrating a progression free survival benefit in addition to standard chemotherapy regimens in advanced epithelial ovarian cancer, both in the upfront and recurrent setting. Mature overall survival data and the search for predictive biomarkers are important for the future role of bevacizumab in epithelial ovarian cancer.

Objective: Insight into the expression of multiple vascular endothelial growth factor (VEGF) family members can support the implementation of anti-angiogenic therapy. This study aimed to assess VEGF family member expression in ovarian cancers and related omental metastases. Methods: Tissue microarrays encompassing 270 primary cancers and 112 paired metastases were immunostained for VEGF-A, VEGF-B, VEGF-C and VEGF-D. Staining intensities were categorized as absent, weak, moderate or strong. Expression was related to clinicopathological characteristics and survival. Results: Immunohistochemical positivity (defined as moderate or strong expression) was observed for VEGF-A in 90%, VEGF-B in 4%, VEGF-C in 41% and VEGF-D in 55% of the primary ovarian cancers. VEGF-A expression correlated with VEGF-C and VEGF-D expression (P < 0.01). Simultaneous positivity for VEGF-A and VEGF-C or VEGF-D was observed in 38% and 54% of the cancers, respectively. Metastases showed positivity for VEGF-A in 78%, VEGF-B in 5%, VEGF-C in 26% and VEGF-D in 45% of cases. VEGF family member expression showed no independent prognostic significance in multivariate survival analysis. Conclusion: VEGF-A, VEGF-C and VEGF-D are widely and often simultaneously expressed in ovarian cancer, which may contribute to bevacizumab resistance. Measuring their expression could support a rational, individualized choice of anti-angiogenic therapy and might be of predictive value. Studies are warranted to determine whether combinatorial analysis of VEGF family member expression can be used to predict anti-angiogenic drug efficacy.

The standard treatment for advanced ovarian cancer consists in complete cytoreductive surgery (CRS) and intravenous combination chemotherapy with a platinum compound and a taxane. Although response rates to initial therapy are high, many patients will recur and die of peritoneal carcinomatosis. The addition of Hyperthermic IntraPEritoneal Chemotherapy (HIPEC) to the standard therapy aims at increasing survival by reducing peritoneal recurrence. This review describes the survival results of HIPEC at the different time-points of the treatment of ovarian cancer: at upfront CRS, at interval CRS, at consolidation CRS after complete response to initial therapy, at secondary CRS after incomplete response, at salvage CRS for recurrence and as palliative treatment without CRS for unresectable ovarian cancer with chemotherapy resistant ascites. The available evidence suggests that a potential survival benefit of adding HIPEC may be largest in the settings of secondary CRS for stage III ovarian cancer and salvage CRS for recurrent ovarian cancer, two time-points representing failure of initial standard therapy. There is much less evidence for a potential benefit of HIPEC for less advanced stages (I-II) and for earlier time-points in the treatment of ovarian cancer (upfront, interval and consolidation). Postoperative mortality is not higher after CRS and HIPEC (0.7%) than after CRS only (1.4%). Four randomised trials are ongoing and their results are eagerly awaited. Palliative HIPEC without CRS might be used more in patients with incapacitating ascites due to recurrent ovarian cancer which has become resistant to systemic chemotherapy.

Immunotherapy for ovarian cancer is one of the new treatment strategies currently investigated in epithelial ovarian cancer. This review discusses the results of different immunization strategies, identifies possible drawbacks in study design and provides potential solutions for augmentation of clinical efficacy. A potential target for cancer immunotherapy is p53, as approximately 50% of ovarian cancer cells carry p53 mutations. Therefore we review the immunological and clinical responses observed in ovarian cancer patients vaccinated with p53 targeting vaccines in particular. In most studies antigen-specific vaccine-induced immunological responses were observed. Unfortunately, no clinical responses with significant reduction of tumor-burden have been reported. Based on the currently available results we emphasize the necessity of multimodality treatment of ovarian cancer, combining classical cytoreductive surgery, (neo) adjuvant chemotherapy, immunotherapy and/or targeted therapy.

Epithelial ovarian cancer (EOC) is the most lethal of the gynecologic malignancies, largely due to the advanced stage at diagnosis in most patients. Standard treatment for EOC is surgical debulking followed by platinum-based chemotherapy. While the majority of ovarian cancer patients will respond to initial chemotherapy, most will ultimately relapse. The major focus of current clinical trials for treatment of recurrent ovarian cancer is the use of targeted biologic agents. Folate receptor alpha (FRα) is upregulated in majority of EOC and correlated with tumor stage and grade. It is hypothesized that the presence of overexpressed FRα correlates with the propagation rate of the tumors. FRα is largely absent from normal tissue, making it an attractive therapeutic target. Farletuzumab (MORAb-003), a humanized monoclonal antibody against FRα, has shown antitumor activity in preclinical xenograft models. A Phase 1 dose escalation study did not demonstrate dose-limiting toxicities, or severe adverse effects. A phase 2 efficacy and safety study of farletuzumab with carboplatin and taxane in patients with platinum-sensitive EOC in first relapse, have shown an improved response rate and time to progression compared with historical controls. Recently, preliminary safety data from a phase 1 trial reported that the combination of farletuzumab, carboplatin and PLD has an acceptable safety profile in patients with platinum- sensitive EOC following first or second relapse. Two randomized, double-blind, placebo-controlled Phase 3 studies with farletuzumab plus chemotherapy have been done. A trial of: farletuzumab with weekly paclitaxel in platinum-resistant EOC closed in December 2011 with full report pending. A second trial of farletuzumab with carboplatin and taxane in platinum-sensitive EOC in first relapse is slated to complete accrual in early 2012. Results from these trials will help define the role of farletuzumab in EOC.

Epithelial ovarian cancer is a major problem as about 75% of patients develop recurrence after initial primary treatment and tumors are often chemoresistant. This article reviews the role of the interleukin-6 (IL-6) in chemoresistance and suppression of tumor immunity in ovarian cancer and provides the rationale for modulating the IL-6/ IL-6 receptor (IL-6R) induced pathway as a potential new target for the treatment of ovarian cancer. IL-6 is elevated in serum and ascites of ovarian cancer patients and increased IL-6 levels correlate with chemoresistance and poor prognosis in these patients. IL-6 induced Jak/Stat3, Ras/MEK/ERK and PI3K/Ras signaling pathways lead to cell survival, proliferation, angiogenesis, and confers resistance to apoptosis induced by conventional therapies. Furthermore, IL-6 induces tumor-promoting macrophages which are known to foster tumor growth and suppress local immunity. However, direct proof of the clinical impact of IL-6 blocking on disease progression is missing necessiting further studies in which the IL-6(R) pathway is modulated and its clinical impact on (epithelial) ovarian cancer is tested.