In vivo fate and therapeutic efficacy of PF‐4/CTF microspheres in an orthotopic human glioblastoma model

Development of Intratumoral Drug Delivery Based Strategies for Antitumor Therapy

Research for tumor treatment with significant therapy effects and minimal side-effects has been widely carried over the past few decades. Different drug forms have received a lot of attention. However, systemic biodistribution induces efficacy and safety issues. Intratumoral delivery of agents might overcome these problems because of its abundant tumor accumulation and retention, thereby reducing side effects. Delivering hydrogels, nanoparticles, microneedles, and microspheres drug carriers directly to tumors can realize not only targeted tumor therapy but also low side-effects. Furthermore, intratumoral administration has been integrated with treatment strategies such as chemotherapy, enhancing radiotherapy, immunotherapy, phototherapy, magnetic fluid hyperthermia, and multimodal therapy. Some of these strategies are ongoing clinical trials or applied clinically. However, many barriers hinder it from being an ideal and widely used option, such as decreased drug penetration impeded by collagen fibers of a tumor, drug squeezed out by high density and high pressure, mature intratumoral injection technique. In this review, we systematically discuss intratumoral delivery of different drug carriers and current development of intratumoral therapy strategies.

Targeted Therapy for Glomerulonephritis Using Arterial Delivery of Encapsulated Etanercept

Complex immunosuppressive therapy is prescribed in medical practice to patients with glomerulonephritis to help them overcome symptoms and prevent chronic renal failure. Such an approach requires long-term systemic administration of strong medications, which causes severe side effects. This work shows the efficiency of polymer capsule accumulation (2.8 ± 0.4 µm) containing labeled etanercept (100 μg per dose) in the kidneys of mice. The comparison of injection into the renal artery and tail vein shows the significant superiority of the intra-arterial administration strategy. The etanercept retention rate of 18% and 8% ID in kidneys was found 1 min and 1 h after injection, respectively. The capsules were predominantly localized in the glomeruli after injection in mice using a model of acute glomerulonephritis. Histological analysis confirmed a significant therapeutic effect only in animals with intra-arterial administration of microcapsules with etanercept. The proposed strategy combines endovascular surgery and the use of polymer microcapsules containing a high molecular weight drug that can be successfully applied to treat a wide range of kidney diseases associated with glomerular pathology.

Strategies to better treat glioblastoma: antiangiogenic agents and endothelial cell targeting agents

Glioblastoma multiforme (GBM) is the most prevalent and aggressive form of glioma, with poor prognosis and high mortality rates. As GBM is a highly vascularized cancer, antiangiogenic therapies to halt or minimize the rate of tumor growth are critical to improving treatment. In this review, antiangiogenic therapies, including small-molecule drugs, nucleic acids and proteins and peptides, are discussed. The authors further explore biomaterials that have been utilized to increase the bioavailability and bioactivity of antiangiogenic factors for better antitumor responses in GBM. Finally, the authors summarize the current status of biomaterial-based targeting moieties that target endothelial cells in GBM to more efficiently deliver therapeutics to these cells and avoid off-target cell or organ side effects.

Encapsulated Carbenoxolone Reduces Lung Metastases

Carbenoxolone is an anti-inflammatory compound and a derivate of a natural substance from the licorice plant. We previously showed that carbenoxolone reduces the metastatic burden in the lungs of mice through its antagonistic effect on high mobility group box 1 (HMGB1). To further enhance carbenoxolone's activity and localization in the lungs, thereby reducing the potential adverse side effects resulting from systemic exposure, we developed a poly(lactic-co-glycolic acid) (PLGA) slow-release system for pulmonary delivery which maintains drug activity in-vitro, as demonstrated in the anoikis assay. Both systemic and intranasal administrations of carbenoxolone effectively minimize metastatic formation in a lung colonization model in mice. Our results show a decrease in the metastatic burden in the lung tissue. Notably, the therapeutic effect of a single intranasal administration of 25 mg/kg carbenoxolone, in the form of drug-loaded particles, had a similar effect in reducing metastatic lesions in the lungs to that of a 10-fold dose of the free drug via intraperitoneal injections, three times per week over the course of four weeks. These data offer new means to potentiate the anti-cancer activity of carbenoxolone and simultaneously reduce the requirement for high dosage administration; the upshot substantially improves therapeutic effect and avoidance of side effects.

Nanocarriers and nonviral methods for delivering antiangiogenic factors for glioblastoma therapy: the story so far

Angiogenesis, the formation of new blood vessels, is an essential component of glioblastoma (GB) progression. The development of angiogenesis inhibitor therapy, including treatments targeting vascular endothelial growth factor (VEGF) in particular, raised new hopes for the treatment of GB, but no Phase III clinical trial to date has reported survival benefits relative to standard treatment. There are several possible reasons for this limited efficacy, including VEGF-independent angiogenesis, induction of tumor invasion, and inefficient antiangiogenic factor delivery to the tumor. Efforts have been made to overcome these limitations by identifying new angiogenesis inhibitors that target angiogenesis through different mechanisms of action without inducing tumor invasion, and through the development of viral and nonviral delivery methods to improve antiangiogenic activity. Herein, we describe the nonviral methods, including convection-enhanced delivery devices, implantable polymer devices, nanocarriers, and cellular vehicles, to deliver antiangiogenic factors. We focus on those evaluated in intracranial (orthotopic) animal models of GB, the most relevant models of this disease, as they reproduce the clinical scenario of tumor progression and therapy response encountered in GB patients.

Local strategies and delivery systems for the treatment of malignant gliomas

Glioma is one of the most common type of malignant tumours with high morbidity and mortality rates. Due to the particular features of the brain, such as blood-brain barrier or blood-tumour barrier, therapeutic agents are ineffective by systemic administration. The tumour inevitably recurs and devitalises patients. Herein, an overview of the localised gliomas treatment strategies is provided, including direct intratumoural/intracerebral injection, convection-enhanced delivery, and the implant of biodegradable polymer systems. The advantages and disadvantages of each therapy are discussed. Subsequently, we have reviewed the recent developments of therapeutic delivery systems aimed at transporting sufficient amounts of antineoplastic drugs into the brain tumour sites while minimising the potential side effects. To treat gliomas, localised and controlled delivery of drugs at their desired site of action is preferred as it reduces toxicity and increases treatment efficiency. Simultaneously, various drug delivery systems (DDS) have been used to enhance drug delivery to the brain. Use of non-conventional DDS for localised therapy has greatly expanded the spectrum of drugs available for the treatment of malignant tumours. Use smart DDS via localised delivery strategies, in combination with radiotherapy and multiple drug loading would serve as a promising approach to treat gliomas.

Microwave-assisted synthesis of TEMPO-labeled hydrogels traceable with MRI

Polymer functionalization strategies have recently attracted considerable attention for several applications in biomaterials science. In particular, technological advancements in medical imaging have focused on the design of polymeric matrices to improve non-invasive approaches and diagnostic accuracy. In this scenario, the use of microwave irradiation of aqueous solutions containing appropriate combinations of polymers is gaining increasing interest in the synthesis of sterile hydrogels without using monomers, eliminating the need to remove unreacted species. In this study, we developed a method for the in situ fabrication of TEMPO-labeled hydrogels based on a one-pot microwave reaction that can then be tracked by magnetic resonance imaging (MRI) without using toxic compounds that could be hostile for the target tissue. Click chemistry was used to link TEMPO to the polymeric scaffold. In an in vivo model, the system was able to preserve its TEMPO paramagnetic activity up to 1 month after hydrogel injection, showing a clear detectable signal on T₁-weighted MRI with a longitudinal relaxivity value of 0.29 mM s^-1, comparable to a value of 0.31 mM s^-1 characteristic of TEMPO application. The uncleavable conjugation between the contrast agent and the polymeric scaffold is a leading point to record these results: the use of TEMPO only physically entrapped in the polymeric scaffold did not show MRI traceability even after few hours. Moreover, the use of TEMPO-labeled hydrogels can also help to reduce the number of animals sacrificed being a longitudinal non-invasive technique.

Visual in vivo degradation of injectable hydrogel by real-time and non-invasive tracking using carbon nanodots as fluorescent indicator

Visual in vivo degradation of hydrogel by fluorescence-related tracking and monitoring is crucial for quantitatively depicting the degradation profile of hydrogel in a real-time and non-invasive manner. However, the commonly used fluorescent imaging usually encounters limitations, such as intrinsic photobleaching of organic fluorophores and uncertain perturbation of degradation induced by the change in molecular structure of hydrogel. To address these problems, we employed photoluminescent carbon nanodots (CNDs) with low photobleaching, red emission and good biocompatibility as fluorescent indicator for real-time and non-invasive visual in vitro/in vivo degradation of injectable hydrogels that are mixed with CNDs. The in vitro/in vivo toxicity results suggested that CNDs were nontoxic. The embedded CNDs in hydrogels did not diffuse outside in the absence of hydrogel degradation. We had acquired similar degradation kinetics (PBS-Enzyme) between gravimetric and visual determination, and established mathematical equation to quantitatively depict in vitro degradation profile of hydrogels for the predication of in vivo hydrogel degradation. Based on the in vitro data, we developed a visual platform that could quantitatively depict in vivo degradation behavior of new injectable biomaterials by real-time and non-invasive fluorescence tracking. This fluorescence-related visual imaging methodology could be applied to subcutaneous degradation of injectable hydrogel with down to 7 mm depth in small animal trials so far. This fluorescence-related visual imaging methodology holds great potentials for rational design and convenient in vivo screening of biocompatible and biodegradable injectable hydrogels in tissue engineering.

Non-invasive in vitro and in vivo monitoring of degradation of fluorescently labeled hyaluronan hydrogels for tissue engineering applications

Tracking of degradation of hydrogels-based biomaterials in vivo is very important for rational design of tissue engineering scaffolds that act as delivery carriers for bioactive factors. During the process of tissue development, an ideal scaffold should remodel at a rate matching with scaffold degradation. To reduce amount of animals sacrificed, non-invasive in vivo imaging of biomaterials is required which relies on using of biocompatible and in situ gel forming compounds carrying suitable imaging agents. In this study we developed a method of in situ fabrication of fluorescently labeled and injectable hyaluronan (HA) hydrogel based on one pot sequential use of Michael addition and thiol-disulfide exchange reactions for the macromolecules labeling and cross-linking respectively. Hydrogels with different content of HA were prepared and their enzymatic degradation was followed in vitro and in vivo using fluorescence multispectral imaging. First, we confirmed that the absorbance of the matrix-linked near-IR fluorescent IRDye® 800CW agent released due to the matrix enzymatic degradation in vitro matched the amount of the degraded hydrogel measured by classical gravimetric method. Secondly, the rate of degradation was inversely proportional to the hydrogel concentration and this structure-degradation relationship was similar for both in vitro and in vivo studies. It implies that the degradation of this disulfide cross-linked hyaluronan hydrogel in vivo can be predicted basing on the results of its in vitro degradation studies. The compliance of in vitro and in vivo methods is also promising for the future development of predictive in vitro tissue engineering models.

STATEMENT OF SIGNIFICANCE

The need for engineered hydrogel scaffolds that deliver bioactive factors to endogenous progenitor cells in vivo via gradual matrix resorption and thus facilitate tissue regeneration is increasing with the aging population. Importantly, scaffold should degrade at a modest rate that will not be too fast to support tissue growth nor too slow to provide space for tissue development. The present work is devoted to longitudinal tracking of a hydrogel material in vivo from the time of its implantation to the time of complete resorption without sacrificing animals. The method demonstrates correlation of resorption rates in vivo and in vitro for hydrogels with varied structural parameters. It opens the possibility to develop predictive in vitro models for tissue engineered scaffolds and reduce animal studies.

Spatial distribution and antitumor activities after intratumoral injection of fragmented fibers with loaded hydroxycamptothecin

There was only a small percentage of drug delivered to tumors after systemic administration, and solid tumors also have many barriers to prevent drug penetration within tumors. In the current study, intratumoral injection of drug-loaded fiber fragments was proposed to overcome these barriers, allowing drug accumulation at the target site to realize the therapeutic efficacy. Fragmented fibers with hydroxycamptothecin (HCPT) loaded were constructed by cryocutting of aligned electrospun fibers, and the fiber lengths of 5 (FF-5), 20 (FF-20), and 50μm (FF-50) could be easily controlled by adjusting the slice thickness. Fragmented fibers were homogeneously dispersed into 2% sodium alginate solution, and could be smoothly injected through 26G1/2 syringe needles. FF-5, FF-20 and FF-50 fiber fragments indicated similar release profiles except a lower burst release from FF-50. In vitro viability tests showed that FF-5 and FF-20 fiber fragments caused higher cytotoxicity and apoptosis rates than FF-50. After intratumoral injection into murine H22 subcutaneous tumors, fragmented fibers with longer lengths indicated a higher accumulation into tumors and a better retention at the injection site, but showed less apparent diffusion within tumor tissues. In addition to the elimination of invasive surgery, HCPT-loaded fiber fragments showed superior in vivo antitumor activities and fewer side effects than intratumoral implantation of drug-loaded fiber mats. Compared with FF-5 and FF-50, FF-20 fiber fragments indicated optimal spatial distribution of HCPT within tumors and achieved the most significant effects on the animal survival, tumor growth inhibition and tumor cell apoptosis induction. It is suggested that the intratumoral injection of drug-loaded fiber fragments provided an efficient strategy to improve patient compliance, allow the retention of fragmented fibers and spatial distribution of drugs within tumor tissues to achieve a low systemic toxicity and an optimal therapeutic efficacy.

Drug encapsulated polymeric microspheres for intracranial tumor therapy: A review of the literature

Despite intensive surgical excision, radiation therapy, and chemotherapy, the current life expectancy for patients diagnosed with glioblastoma multiforme is only 12 to 15months. One of the approaches being explored to increase chemotherapeutic efficacy is to locally deliver chemotherapeutics encapsulated within degradable, polymeric microspheres. This review describes the techniques used to formulate drug encapsulated microspheres targeted for intracranial tumor therapy and how microsphere characteristics such as drug loading and encapsulation efficiency can be tuned based on formulation parameters. Further, the results of in vitro studies are discussed, detailing the varied drug release profiles obtained and validation of drug efficacy. Finally, in vivo results are summarized, highlighting the study design and the effectiveness of the drug encapsulated microspheres applied intracranially.

Real-time, non-invasive monitoring of hydrogel degradation using LiYF4:Yb(3+)/Tm(3+) NIR-to-NIR upconverting nanoparticles

To design a biodegradable hydrogel as cell support, one should know its in vivo degradation rate. A technique commonly used to track gel degradation is fluorescence spectroscopy. However, the fluorescence from conventional fluorophores quickly decays, and the fluorophores are often moderately cytotoxic. Most importantly, they require ultraviolet or visible (UV-Vis) light as the excitation source, which cannot penetrate deeply through biological tissues. Lanthanide-doped upconverting nanoparticles (UCNPs) are exciting alternatives to conventional fluorophores because they can convert near-infrared (NIR) to UV-Vis-NIR light via a sequential multiphoton absorption process referred to as upconversion. NIR light can penetrate up to few cm inside tissues, thus making these UCNPs much better probes than conventional fluorophores for in vivo monitoring. Also, UCNPs have narrow emission bands, high photoluminescence (PL) signal-to-noise ratio, low cytotoxicity and good physical and chemical stability. Here, we show a nanocomposite system consisting of a biodegradable, in situ thermogelling injectable hydrogel made of chitosan and hyaluronic acid encapsulating silica-coated LiYF4:Yb(3+)/Tm(3+) UCNPs. We use these UCNPs as photoluminescent tags to monitor the gel degradation inside live, cultured intervertebral discs (IVDs) over a period of 3 weeks. PL spectroscopy and NIR imaging show that NIR-to-NIR upconversion of LiYF4:Yb(3+)/Tm(3+)@SiO2 UCNPs allows for tracking of the gel degradation in living tissues. Both in vitro and ex vivo release of UCNPs follow a similar trend during the first 5 days; after this time, ex vivo release becomes faster than in vitro, indicating a faster gel degradation ex vivo. Also, the amount of released UCNPs in vitro increases continuously up to 3 weeks, while it plateaus after 15 days inside the IVDs showing a homogenous distribution of UCNPs throughout the IVD tissue. This non-invasive optical method for real time, live tissue imaging holds great potential for tissue analysis, biomapping and bioimaging applications.

Real-time and non-invasive fluorescence tracking of in vivo degradation of the thermosensitive PEGlyated polyester hydrogel

The real-time monitoring of materials degradation is crucial to determine the in vivo retention time and the design or screening of degradable biomaterials. However, in vivo performance cannot always be predicted through the traditional determination of in vitro erosion and current standard methods sacrifice samples or animals, preventing the sequential measurement of the same specimen. Herein, a non-invasive fluorescence imaging method was developed to sequentially follow in vivo loss of fluorescence signal to simultaneously characterize the hydrolytic and enzymatic degradation of PEGlyated polyester hydrogel. Rhodamine B was conjugated to thermosensitive amphiphilic triblock copolymer based on cyclic ether modified PCL and PEG (abbreviated as PECT) and no obvious influence on gelation time or gel strength was observed with the conjugation content under 0.121% (w/w). Both in vitro and in vivo degradation profiles followed linear fittings while in vivo and in vitro hydrogel degradation rates correlated in an exponential mathematical model, enabling the general prediction of in vivo erosion trends of new biomaterial formulations from in vitro data. This methodology possibly enabled rational design and rapid in vitro screening of degradable materials, and might be potentially extended to simultaneously determine the material erosion and speculate the drug release from a drug-incorporated scaffold, or the cell growth profile in tissue-engineering formulations.

Anti-angiogenic peptides for cancer therapeutics

Peptides have emerged as important therapeutics that are being rigorously tested in angiogenesis-dependent diseases due to their low toxicity and high specificity. Since the discovery of endogenous proteins and protein fragments that inhibit microvessel formation (thrombospondin, endostatin) several peptides have shown promise in pre-clinical and clinical studies for cancer. Peptides have been derived from thrombospondin, collagens, chemokines, coagulation cascade proteins, growth factors, and other classes of proteins and target different receptors. Here we survey recent developments for anti-angiogenic peptides with length not exceeding 50 amino acid residues that have shown activity in pre-clinical models of cancer or have been tested in clinical trials; some of the peptides have been modified and optimized, e.g., through L-to-D and non-natural amino acid substitutions. We highlight technological advances in peptide discovery and optimization including computational and bioinformatics tools and novel experimental techniques.

In vivo and in vitro tracking of erosion in biodegradable materials using non-invasive fluorescence imaging

The design of erodible biomaterials relies on the ability to program the in vivo retention time, which necessitates real-time monitoring of erosion. However, in vivo performance cannot always be predicted by traditional determination of in vitro erosion, and standard methods sacrifice samples or animals, preventing sequential measures of the same specimen. We harnessed non-invasive fluorescence imaging to sequentially follow in vivo material-mass loss to model the degradation of materials hydrolytically (PEG:dextran hydrogel) and enzymatically (collagen). Hydrogel erosion rates in vivo and in vitro correlated, enabling the prediction of in vivo erosion of new material formulations from in vitro data. Collagen in vivo erosion was used to infer physiologic in vitro conditions that mimic erosive in vivo environments. This approach enables rapid in vitro screening of materials, and can be extended to simultaneously determine drug release and material erosion from a drug-eluting scaffold, or cell viability and material fate in tissue-engineering formulations.

Platelet factor-4 and its p17-70 peptide inhibit myeloma proliferation and angiogenesis in vivo

Background

Angiogenesis plays an important role in the development of multiple myeloma (MM). The interaction between MM cells and the bone marrow microenvironment stimulates the proliferation and migration of endothelial progenitor cells (EPCs). Vascular endothelial growth factor (VEGF) contributes to the formation of new blood vessels by actively recruiting circulating EPCs. The production of proangiogenic and antiangiogenic factors is also dysregulated in MM. Platelet factor 4 (PF4) is a potent angiostatic cytokine that inhibits angiogenesis and tumor growth in several animal models.

Methods

In this study, we stably transfected human myeloma cell lines with the PF4 gene or the sequence encoding its more potent p17-70 peptide and investigated the effects of PF4 and p17-70 on angiogenesis and tumor growth in vitro and in a SCID-rab myeloma model.

Results

PF4 and p17-70 significantly attenuated VEGF production, both in vitro and in vivo. In a migration study using a Transwell system, PF4 or p17-70 markedly suppressed the migration of co-cultured human endothelial progenitor cells. PF4 or p17-70 also caused a significant reduction in microvessel densities in myeloma xenografts and markedly reduced the tumor volume in the SCID mice. Kaplan-Meier analysis demonstrated that PF4 and p17-70 significantly extended the overall survival of SCID mice bearing human myeloma xenografts.

Conclusions

Our findings indicate that PF4 or p17-70 could be valuable in combating multiple myeloma by disrupting tumor angiogenesis.

Design of a composite drug delivery system to prolong functionality of cell-based scaffolds

Cell encapsulation technology raises hopes in medicine and biotechnology. However, despite important advances in the field in the past three decades, several challenges associated with the biocompatibility are still remaining. In the present study, the effect of a temporary release of an anti-inflammatory agent on co-administered encapsulated allogeneic cells was investigated. The aim was to determine the biocompatibility and efficacy of the approach to prevent the inflammatory response. A composite delivery system comprised of alginate-poly-l-lysine-alginate (APA)-microencapsulated Epo-secreting myoblasts and dexamethasone (DXM)-releasing poly(lactic-co-glycolic acid) (PLGA) microspheres was implanted in the subcutaneous space of Balb/c mice for 45 days. The use of independently co-implanted DXM-loaded PLGA microspheres resulted in an improved functionality of the cell-based graft, evidenced by significantly higher hematocrit levels found in the cell-implanted groups by day 45, which was found to be more pronounced when higher cell-doses (100 μL) were employed. Moreover, no major host reaction was observed upon implantation of the systems, showing good biocompatibility and capability to partially avoid the inflammatory response, probably due to the immunosuppressive effects related to DXM. The findings of this study imply that DXM-loaded PLGA microspheres show promise as release systems to enhance biocompatibility and offer advantage in the development of long-lasting and effective implantable microencapsulated cells by generating a potential immunopriviledged local environment and an effective method to limit the structural ensheathing layer caused by inflammation.

Angiopoietin-4 promotes glioblastoma progression by enhancing tumor cell viability and angiogenesis

Glioblastoma multiforme (GBM) is a highly invasive and vascularized aggressive brain tumor. Less than 10% of GBM patients survive >5 years after diagnosis. Angiogenesis plays an important role in GBM growth, and antiangiogenesis-based therapies have shown clinical efficacy for GBM patients. Unfortunately, therapeutic resistance often develops in these patients, suggesting that GBM cells are capable of switching their dependency on one proangiogenic signaling pathway to an alternative one. Therefore, it is important to identify novel angiogenic factors that play essential roles in tumor angiogenesis and GBM progression. Angiopoietins (Ang-1, Ang-2, and Ang-4) are the ligands of the Tie-2 receptor tyrosine kinase (RTK). The roles of Ang-1 and Ang-2 in tumor angiogenesis have been established. However, little is known about how Ang-4 affects tumor angiogenesis and GBM progression and the mechanism underlying its effects. In our current study, we establish that Ang-4 is upregulated in human GBM tissues and cells. We show that, like endothelial cells, human GBM cells express Tie-2 RTK. We first establish that Ang-4 promotes in vivo growth of human GBM cells by promoting tumor angiogenesis and directly activating extracellular signal-regulated kinase 1/2 (Erk1/2) in GBM cells. Our results establish the novel effects of Ang-4 on tumor angiogenesis and GBM progression and suggest that this pro-GBM effect of Ang-4 is mediated by promoting tumor angiogenesis and activating Erk1/2 kinase in GBM cells. Together, our results suggest that the Ang-4-Tie-2 functional axis is an attractive therapeutic target for GBM.

The COOH-terminal peptide of platelet factor-4 variant (CXCL4L1/PF-4var47-70) strongly inhibits angiogenesis and suppresses B16 melanoma growth in vivo

Chemokines influence tumor growth directly or indirectly via both angiogenesis and tumor-leukocyte interactions. Platelet factor-4 (CXCL4/PF-4), which is released from alpha-granules of activated platelets, is the first described angiostatic chemokine. Recently, it was found that the variant of CXCL4/PF-4 (CXCL4L1/PF-4var) could exert a more pronounced angiostatic and antitumoral effect than CXCL4/PF-4. However, the molecular mechanisms of the angiostatic activities of the PF-4 forms remain partially elusive. Here, we studied the biological properties of the chemically synthesized COOH-terminal peptides of CXCL4/PF-4 (CXCL4/PF-4(47-70)) and CXCL4L1/PF-4var (CXCL4L1/PF-4var(47-70)). Both PF-4 peptides lacked monocyte and lymphocyte chemotactic activity but equally well inhibited (25 nmol/L) endothelial cell motility and proliferation in the presence of a single stimulus (i.e., exogenous recombinant fibroblast growth factor-2). In contrast, when assayed in more complex angiogenesis test systems characterized by the presence of multiple mediators, including in vitro wound-healing (2.5 nmol/L versus 12.5 nmol/L), Matrigel (60 nmol/L versus 300 nmol/L), and chorioallantoic membrane assays, CXCL4L1/PF-4var(47-70) was found to be significantly (5-fold) more angiostatic than CXCL4/PF-4(47-70). In addition, low (7 microg total) doses of intratumoral CXCL4L1/PF-4var(47-70) inhibited B16 melanoma growth in mice more extensively than CXCL4/PF-4(47-70). This antitumoral activity was predominantly mediated through inhibition of angiogenesis (without affecting blood vessel stability) and induction of apoptosis, as evidenced by immunohistochemical and fluorescent staining of B16 tumor tissue. In conclusion, CXCL4L1/PF-4var(47-70) is a potent antitumoral and antiangiogenic peptide. These results may represent the basis for the design of CXCL4L1/PF-4var COOH-terminal-derived peptidomimetic anticancer drugs.

Design and development of polymer conjugates as anti-angiogenic agents

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, is one of the central key steps in tumor progression and metastasis. Consequently, it became an important target in cancer therapy, making novel angiogenesis inhibitors a new modality of anticancer agents. Although relative to conventional chemotherapy, anti-angiogenic agents display a safer toxicity profile, the vast majority of these agents are low-molecular-weight compounds exhibiting poor pharmacokinetic profile with short half-life in the bloodstream and high overall clearance rate. The "Polymer Therapeutics" field has significantly improved the therapeutic potential of low-molecular-weight drugs and proteins for cancer treatment. Drugs can be conjugated to polymeric carriers that can be either directly conjugated to targeting proteins or peptides or derivatized with adapters conjugated to a targeting moiety. This approach holds a significant promise for the development of new targeted anti-angiogenic therapies as well as for the optimization of existing anti-angiogenic drugs or polypeptides. Here we overview the innovative approach of targeting tumor angiogenesis using polymer therapeutics.

Novel technologies for antiangiogenic drug delivery in the brain

Antiangiogenic therapies aimed at inhibiting the formation of tumor vasculature hold great promise for cancer therapy, with multiple compounds currently undergoing clinical trials. As with many forms of chemotherapy, antiangiogenic drugs face numerous hurdles in their translation to clinical use. Many such promising agents exhibit a short half-life, low solubility, poor bioavailability and multiple toxic side effects. Furthermore, when targeting malignant brain tumors the blood-brain barrier represents a formidable obstacle, preventing drugs from penetrating into the central nervous system (CNS). In this review, we discuss several preclinical antiangiogenic therapies and describe issues related to the unique conditions in the brain with regard to cancer treatment and neurotoxicity. We focus on the limitations of antiangiogenic drugs in the brain, along with numerous solutions that involve novel biomaterials and nanotechnological approaches. We also discuss an example in which modifying the properties of an antiangiogenic compound enhanced its clinical efficacy in treating tumors while simultaneously mitigating undesirable neurological side-effects.

Cell microencapsulation technology: towards clinical application

The pharmacokinetic properties of a drug can be significantly improved by the delivery process. Scientists have understood that developing suitable drug delivery systems that release the therapeutically active molecule at the level and dose it is needed and during the optimal time represents a major advance in the field. Cell microencapsulation is an alternative approach for the sustained delivery of therapeutic agents. This technology is based on the immobilization of different types of cells within a polymeric matrix surrounded by a semipermeable membrane for the long-term release of therapeutics. As a result, encapsulated cells are isolated from the host immune system while allowing exchange of nutrients and waste and release of the therapeutic agents. The versatility of this approach has stimulated its use in the treatment of numerous medical diseases including diabetes, cancer, central nervous system diseases and endocrinological disorders among others. The aim of this review article is to give an overview on the current state of the art of the use of cell encapsulation technology as a controlled drug delivery system. The most important advantages of this type of "living" drug release strategy are highlighted, but also its limitations pointed out, and the major challenges to be addressed in the forthcoming years are described.

The role of CXC chemokines and their receptors in cancer

Chemokines, or chemotactic cytokines, and their receptors have been discovered as essential and selective mediators in leukocyte migration to inflammatory sites and to secondary lymphoid organs. Besides their functions in the immune system, they also play a critical role in tumor initiation, promotion and progression. There are four subgroups of chemokines: CXC, CC, CX(3)C, and C chemokine ligands. The CXC or alpha subgroup is further subdivided in the ELR(+) and ELR(-) chemokines. Members that contain the ELR motif bind to CXC chemokine receptor 2 (CXCR2) and are angiogenic. In contrast, most of the CXC chemokines without ELR motif bind to CXCR3 and are angiostatic. An exception is the angiogenic ELR(-)CXC chemokine stromal cell-derived factor-1 (CXCL12/SDF-1), which binds to CXCR4 and CXCR7 and is implicated in tumor metastasis. This review is focusing on the role of CXC chemokines and their receptors in tumorigenesis, including angiogenesis, attraction of leukocytes to tumor sites and induction of tumor cell migration and homing in metastatic sites. Finally, their therapeutic use in cancer treatment is discussed.