Christopher G. Thanos

Nanotechnology and medicine

Nanotechnology, or systems/device manufacture at the molecular level, is a multidisciplinary scientific field undergoing explosive development. The genesis of nanotechnology can be traced to the promise of revolutionary advances across medicine, communications, genomics and robotics. On the surface, miniaturisation provides cost effective and more rapidly functioning mechanical, chemical and biological components. Less obvious though is the fact that nanometre sized objects also possess remarkable self-ordering and assembly behaviours under the control of forces quite different from macro objects. These unique behaviours are what make nanotechnology possible, and by increasing our understanding of these processes, new approaches to enhancing the quality of human life will surely be developed. A complete list of the potential applications of nanotechnology is too vast and diverse to discuss in detail, but without doubt one of the greatest values of nanotechnology will be in the development of new and effective medical treatments (i.e., nanomedicine). This review focuses on the potential of nanotechnology in medicine, including the development of nanoparticles for diagnostic and screening purposes, artificial receptors, DNA sequencing using nanopores, manufacture of unique drug delivery systems, gene therapy applications and the enablement of tissue engineering.

Targeted nanoparticle-based drug delivery and diagnosis

Nanotechnology, or systems/device manufacture at sizes generally ranging between 1 and 100 nm, is a multidisciplinary scientific field undergoing explosive development. The genesis of nanotechnology can be traced to advances in medicine, communications, genomics and robotics. One of the greatest values of nanotechnology will be in the development of new and effective medical treatments (i.e. nanomedicine). This review focuses on the potential of nanomedicine as it relates to the development of nanoparticles for enabling and improving the targeted delivery of therapeutic and diagnostic agents. We highlight the use of nanoparticles for specific intra-compartmental analysis using the examples of delivery to malignant cancers, to the central nervous system, and across the gastrointestinal barriers.

Transplants of encapsulated rat choroid plexus cells exert neuroprotection in a rodent model of Huntington's disease.

Choroid plexus (CP) epithelial cells secrete several neurotrophic factors and have been used in transplantation studies designed to impart neuroprotection against central nervous system (CNS) trauma. In the present study, CP was isolated from adult rats, encapsulated within alginate microcapsules, and transplanted unilaterally into the rat striatum. Three days later, unilateral injections of quinolinic acid (QA; 225 nmol) were made into the ipsilateral striatum to mimic the pathology observed in Huntingtons disease (HD). After surgery, animals were tested for motor function using the placement test. Rats receiving CP transplants were significantly less impaired on this test. Nissl-stained sections demonstrated that CP transplants significantly reduced the volume of the striatal lesion produced by QA. Quantitative analysis of striatal neurons further demonstrated that choline acetyltransferase-immunoreactive, but not diaphorase-positive, neurons were protected by CP transplants. These data demonstrate that transplanted CP cells can be used to protect striatal neurons from excitotoxic damage and that the pattern of neuroprotection varies across specific neuronal populations.

Characterization of soluble, salt-loaded, degradable PLGA films and their release of tetracycline

A local drug delivery system has been designed to release tetracycline over a period of 30 days from poly (lactide-co-glycolide) films. Incorporation of either soluble salt excipients or low molecular weight polymeric species has been found to modulate the release kinetics of the system. The following research describes the fabrication of the delivery system, monitors tetracycline release from the system, and fully characterizes the degradation of the polymer films via scanning electron microscopy, gel permeation chromatography, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and X-ray diffraction techniques. Results show that the modulation via use of salts occurs without changing the inherent degradation rate of the system. We suggest that this phenomenon may be due to the increased amount of swelling and uptake of buffer by the films loaded with soluble salt. Uptake, therefore, may be creating microscopic pores that permit further diffusion of tetracycline from the polymer matrix as well as allow the free monomers to leave the system, thereby preventing autocatalysis within the system.

Encapsulated cell therapy for neurodegenerative diseases: From promise to product☆

Delivering therapeutic molecules, including trophic factor proteins, across the blood brain barrier to the brain parenchyma to treat chronic neurodegenerative diseases remains one of the great challenges in biology. To be effective, delivery needs to occur in a long-term and stable manner at sufficient quantities directly to the target region in a manner that is selective but yet covers enough of the target site to be efficacious. One promising approach uses cellular implants that produce and deliver therapeutic molecules directly to the brain region of interest. Implanted cells can be precisely positioned into the desired region and can be protected from host immunological attack by encapsulating them and by surrounding them within an immunoisolatory, semipermeable capsule. In this approach, cells are enclosed within a semiporous capsule with a perm selective membrane barrier that admits oxygen and required nutrients and releases bioactive cell secretions while restricting passage of larger cytotoxic agents from the host immune defense system. Recent advances in human cell line development have increased the levels of secreted therapeutic molecules from encapsulated cells, and membrane extrusion techniques have led to the first ever clinical demonstrations of long-term survival and function of encapsulated cells in the brain parenchyma. As such, cell encapsulation is capable of providing a targeted, continuous, de novo synthesized source of very high levels of therapeutic molecules that can be distributed over significant portions of the brain.

Aging reduces the neuroprotective capacity, VEGF secretion, and metabolic activity of rat choroid plexus epithelial cells.

Delivery of neurotrophic molecules to the brain has potential for preventing neuronal loss in neurodegenerative disorders. Choroid plexus (CP) epithelial cells secrete numerous neurotrophic factors, and encapsulated CP transplants are neuroprotective in models of stroke and Huntingtons disease (HD). To date, all studies examining the neuroprotective potential of CP transplants have used cells isolated from young donor animals. Because the aging process significantly impacts the cytoarchitecture and function of the CP the following studies determined whether age-related impairments occur in its neuroprotective capacity. CP was isolated from either young (3–4 months) or aged (24 months) rats. In vitro, young CP epithelial cells secreted more VEGF and were metabolically more active than aged CP epithelial cells. Additionally, conditioned medium from cultured aged CP was less potent than young CP at enhancing the survival of serum-deprived neurons. Finally, encapsulated CP was tested in an animal model of HD. Cell-loaded or empty alginate capsules (control group) were transplanted unilaterally into the rat striatum. Seven days later, the animals received an injection of quinolinic acid (QA; 225 nmol) adjacent to the implant site. Animals were tested for motor function 28 days later. In the control group, QA lesions severely impaired function of the contralateral forelimb. Implants of young CP were potently neuroprotective as rats receiving CP transplants were not significantly impaired when tested for motor function. In contrast, implants of CP from aged rats were only modestly effective and were much less potent than young CP transplants. These data are the first to directly link aging with diminished neuroprotective capacity of CP epithelial cells.

Encapsulated porcine islet transplantation: an evolving therapy for the treatment of Type I diabetes

Background: Allogeneic tissue-based therapies for Type I diabetes have demonstrated efficacy but are limited due to tissue-sourcing constraints, as the number of patients exceeds that of tissue donors. Porcine islets derived from designated pathogen-free sources could be an alternative, particularly if delivered in a way that evades the host immune systems rejection. Methods: This review focuses on approaches designed to protect xenogeneic islets from immune rejection by provision of perm-selective barriers. Results: Designated pathogen-free herds could provide a supply of wild-type porcine islets that are well tolerated when administered in a suitable protective delivery vehicle. Such barrier systems have enabled amelioration of diabetes in a variety of animal models and preliminary evidence suggests that similar results could be attained in humans. Conclusion: With advances in biomaterial design, source tissue selection, and the evolution of critical cell processing techniques, contemporary encapsulated porcine islet therapies offer a new level of clinical promise.

Improving relative bioavailability of dicumarol by reducing particle size and adding the adhesive poly(fumaric-co-sebacic) anhydride.

AbstractPurpose. This study was carried out to show the effect of particle size reduction and bioadhesion on the dissolution and relative bioavailability of dicumarol. Methods. Formulations were produced by a variety of methods including a novel technique to reduce particle size as well as phase inversion with poly(fumaric-co-sebacic)anhydride p(FA:SA) to create nanospheres. Drug was administered to groups of pigs and rats via oral gavage of a suspension, and dicumarol concentration in the blood was measured using a double extraction technique.Results. In vitro results showed improved dissolution in both the micronized formulation and the encapsulated p(FA:SA) nanospheres. In vivo, relative bioavailability of a spray-dried formulation was increased by 17% in the rat and 72% in the pig by further reduction in particle size. The bioadhesive p(FA:SA) formulation also improved relative bioavailability over the spray-dried drug, increasing it by 55% in the rat and 96% in the pig. Additionally, the p(FA:SA) formulation prolonged Tmax and decreased Cmax in both species. Conclusion. This work demonstrates the importance of particle size and bioadhesion to improve oral bioavailability of ducumarol.

Unique insights into the intestinal absorption, transit, and subsequent biodistribution of polymer-derived microspheres

Polymeric microspheres (MSs) have received attention for their potential to improve the delivery of drugs with poor oral bioavailability. Although MSs can be absorbed into the absorptive epithelium of the small intestine, little is known about the physiologic mechanisms that are responsible for their cellular trafficking. In these experiments, nonbiodegradable polystyrene MSs (diameter range: 500 nm to 5 µm) were delivered locally to the jejunum or ileum or by oral administration to young male rats. Following administration, MSs were taken up rapidly (≤5 min) by the small intestine and were detected by transmission electron microscopy and confocal laser scanning microscopy. Gel permeation chromatography confirmed that polymer was present in all tissue samples, including the brain. These results confirm that MSs (diameter range: 500 nm to 5 µm) were absorbed by the small intestine and distributed throughout the rat. After delivering MSs to the jejunum or ileum, high concentrations of polystyrene were detected in the liver, kidneys, and lungs. The pharmacologic inhibitors chlorpromazine, phorbol 12-myristate 13-acetate, and cytochalasin D caused a reduction in the total number of MSs absorbed in the jejunum and ileum, demonstrating that nonphagocytic processes (including endocytosis) direct the uptake of MSs in the small intestine. These results challenge the convention that phagocytic cells such as the microfold cells solely facilitate MS absorption in the small intestine.

Intracompartmental delivery of CNTF as therapy for huntingtons disease and retinitis pigmentosa

Ciliary neurotrophic factor (CNTF) is a cytokine with neurotrophic activity across a broad spectrum of peripheral and central nervous system (CNS) cells. While its therapeutic potential for CNS diseases has been clear for sometime, the blood brain barrier (BBB) hinders the systemic delivery of CNTF and direct bolus injections are not suitable due to the short half-life of CNTF. One means of overcoming the BBB while providing continuous delivery of CNTF is with immunoisolated cellular implants that produce and deliver CNTF directly to the region of interest. Cells can be protected from host rejection by encapsulating, or surrounding, them within an immunoisolatory, semipermeable membrane that admits oxygen and required nutrients and releases bioactive cell secretions, but restricts passage of larger cytotoxic agents from the host immune defense system. The selective membrane eliminates the need for chronic immunosuppression of the host and allows the implanted cells to be obtained from nonhuman sources. In this review we discuss cell immunoisolation for Huntingtons disease and retinitis pigmentosa. These two indications are highlighted because of extensive pre-clinical data supporting the general concept and recent clinical data that both strengthens the theoretical role of CNTF for treating neurodegeneration and justifies additional clinical evaluation in these and other diseases.