Alzheimer's Disease: A Suitable Case for Treatment with Precision Medicine?

Alzheimer's disease (AD) is the most common cause of neurodegenerative impairment in elderly people. Clinical characteristics include short-term memory loss, confusion, hallucination, agitation, and behavioural disturbance. Owing to evolving research in biomarkers AD can be discovered at early onset, but the disease is currently considered a continuum, which suggests that pharmacotherapy is most efficacious in the preclinical phase, possibly 15 - 20 years before discernible onset. Present developments in AD therapy aim to respond to this understanding and go beyond the drug families that relieve clinical symptoms. Another important factor in this development is the emergence of precision medicine that aims to tailor treatment to specific patients or patient subgroups. This relatively new platform would categorize AD patients on the basis of parameters like clinical aspects, brain imaging, genetic profiling, clinical genetics and epidemiological factors. This review enlarges on recent progress in the design and clinical use of antisense molecules, antibodies, antioxidants, small molecules and gene editing to stop AD progress and possibly reverse the disease on the basis of relevant biomarkers.

Friends and Foes in Alzheimer's Disease

Alzheimer's disease (AD) is a disabling neurodegenerative disease. The prognosis is poor, and currently there are no proven effective therapies. Most likely, the etiology is related to cerebral inflammatory processes that cause neuronal damage, resulting in dysfunction and apoptosis of nerve cells. Pathogens that evoke a neuroinflammatory response, collectively activate astrocytes and microglia, which contributes to the secretion of pro-inflammatory cytokines. This leads to the deposit of clustered fragments of beta-amyloid and misfolded tau proteins which do not elicit an adequate immune reaction. Apart from the function of astrocytes and microglia, molecular entities such as TREM2, SYK, C22, and C33 play a role in the physiopathology of AD. Furthermore, bacteria and viruses may trigger an overactive inflammatory response in the brain. Pathogens like Helicobacter pylori, Chlamydia pneumonia, and Porphyromonas gingivalis (known for low-grade infection in the oral cavity) can release gingipains, which are enzymes that can damage and destroy neurons. Chronic infection with Borrelia burgdorferi (the causative agent of Lyme disease) can co-localize with tau tangles and amyloid deposits. As for viral infections, herpes simplex virus 1, cytomegalovirus, and Epstein-Barr virus can play a role in the pathogenesis of AD. Present investigations have resulted in the development of antibodies that can clear the brain of beta-amyloid plaques. Trials with humanized aducanumab, lecanemab, and donanemab revealed limited success in AD patients. However, AD should be considered as a continuum in which the initial preclinical phase may take 10 or even 20 years. It is generally thought that this phase offers a window for efficacious treatment. Therefore, research is also focused on the identification of biomarkers for early AD detection. In this respect, the plasma measurement of neurofilament light chain in patients treated with hydromethylthionine mesylate may well open a new way to prevent the formation of tau tangles and represents the first treatment for AD at its roots.

Parkinson's Disease: A Tale of Many Players

In 2020, more than 9 million patients suffering from Parkinson's disease (PD) were reported worldwide, and studies predict that the burden of this disease will grow substantially in industrial countries. In the last decade, there has been a better understanding of this neurodegenerative disorder, clinically characterized by motor disturbances, impaired balance, coordination, memory difficulties, and behavioral changes. Various preclinical investigations and studies on human postmortem brains suggest that local oxidative stress and inflammation promote misfolding and aggregation of alpha-synuclein within Lewy bodies and cause nerve cell damage. Parallel to these investigations, the familial contribution to the disease became evident from studies on genome-wide association in which specific genetic defects were linked to neuritic alpha-synuclein pathology. As for treatment, currently available pharmacological and surgical interventions may improve the quality of life but do not stop the progress of neurodegeneration. However, numerous preclinical studies have provided insights into the pathogenesis of PD. Their results provide a solid base for clinical trials and further developments. In this review, we discuss the pathogenesis, the prospects, and challenges of synolytic therapy, CRISPR, gene editing, and gene- and cell-based therapy. We also throw light on the recent observation that targeted physiotherapy may help improve the gait and other motor impairments.

Pharmacological, Cell, and Gene Therapy Strategies to Promote Spinal Cord Regeneration

In this review, recent studies using pharmacological treatment, cell transplantation, and gene therapy to promote regeneration of the injured spinal cord in animal models will be summarized. Pharmacological and cell transplantation treatments generally revealed some degree of effect on the regeneration of the injured ascending and descending tracts, but further improvements to achieve a more significant functional recovery are necessary. The use of gene therapy to promote repair of the injured nervous system is a relatively new concept. It is based on the development of methods for delivering therapeutic genes to neurons, glia cells, or nonneural cells. Direct in vivo gene transfer or gene transfer in combination with (neuro)transplantation (ex vivo gene transfer) appeared powerful strategies to promote neuronal survival and axonal regrowth following traumatic injury to the central nervous system. Recent advances in understanding the cellular and molecular mechanisms that govern neuronal survival and neurite outgrowth have enabled the design of experiments aimed at viral vector-mediated transfer of genes encoding neurotrophic factors, growth-associated proteins, cell adhesion molecules, and antiapoptotic genes. Central to the success of these approaches was the development of efficient, nontoxic vectors for gene delivery and the acquirement of the appropriate (genetically modified) cells for neurotransplantation. Direct gene transfer in the nervous system was first achieved with herpes viral and E1-deleted adenoviral vectors. Both vector systems are problematic in that these vectors elicit immunogenic and cytotoxic responses. Adeno-associated viral vectors and lentiviral vectors constitute improved gene delivery systems and are beginning to be applied in neuroregeneration research of the spinal cord. Ex vivo approaches were initially based on the implantation of genetically modified fibroblasts. More recently, transduced Schwann cells, genetically modified pieces of peripheral nerve, and olfactory ensheathing glia have been used as implants into the injured spinal cord.

Interpretation of cloud-climate feedback as produced by 14 atmospheric general circulation models

Understanding the cause of differences among general circulation model projections of carbon dioxide-induced climatic change is a necessary step toward improving the models. An intercomparison of 14 atmospheric general circulation models, for which sea surface temperature perturbations were used as a surrogate climate change, showed that there was a roughly threefold variation in global climate sensitivity. Most of this variation is attributable to differences in the models' depictions of cloud-climate feedback, a result that emphasizes the need for improvements in the treatment of clouds in these models if they are ultimately to be used as climatic predictors.

Neuroregenerative effects of lentiviral vector-mediated GDNF expression in reimplanted ventral roots

Traumatic avulsion of spinal nerve roots causes complete paralysis of the affected limb. Reimplantation of avulsed roots results in only limited functional recovery in humans, specifically of distal targets. Therefore, root avulsion causes serious and permanent disability. Here, we show in a rat model that lentiviral vector-mediated overexpression of glial cell line-derived neurotrophic factor (GDNF) in reimplanted nerve roots completely prevents motoneuron atrophy after ventral root avulsion and stimulates regeneration of axons into reimplanted roots. However, over the course of 16 weeks neuroma-like structures are formed in the reimplanted roots, and regenerating axons are trapped at sites with high levels of GDNF expression. A high local concentration of GDNF therefore impairs long distance regeneration. These observations show the feasibility of combining neurosurgical repair of avulsed roots with gene-therapeutic approaches. Our data also point to the importance of developing viral vectors that allow regulated expression of neurotrophic factors.

Lentiviral vector-mediated reporter gene expression in avulsed spinal ventral root is short-term, but is prolonged using an immune "stealth" transgene

PURPOSE

Spinal root avulsions result in paralysis of the upper and/or lower extremities. Implanting a peripheral nerve bridge or reinsertion of the avulsed roots in the spinal cord are surgical strategies that lead to some degree of functional recovery. In the current study lentiviral (LV) vector-mediated gene transfer of a green fluorescent protein (GFP) reporter gene was used to study the feasibility of gene therapy in the reimplanted root to further promote regeneration of motor axons.

METHODS

A total of 68 female Wistar rats underwent unilateral root avulsion of the L4, L5 and L6 ventral lumbar roots. From 23 rats intercostal nerves were dissected before ventral root avulsion surgery, injected with a lentiviral vector encoding GFP (LV-GFP) and inserted between the spinal cord and avulsed rootlet. In the remaining 45 rats, the avulsed ventral root was injected with either LV-GFP or a lentiviral vector encoding a fusion between a GlyAla repeat and GFP (LV-GArGFP), and reinserted into the spinal cord. Expression of GFP was evaluated at 1,2, 4 and 10 weeks, and one group at 4 months.

RESULTS

LV-GFP transduction of either nerve implants or reimplanted ventral roots revealed high GFP expression during the first 2 post-lesion weeks, but virtually no expression at 4 weeks. Since this reduction coincided with the appearance of mononuclear cells at the repair site, an immune response against GFP may have occurred. In a subsequent experiment reimplanted ventral roots were transduced with a vector encoding GFP fused with the GlyAla repeat of Epstein-Barr virus Nuclear Antigen 1 known to prevent generation of antigenic peptides from transgene products. Expression of this "stealth" gene persisted for at least 4 months in the reimplanted root.

CONCLUSION

Thus persistent transgene expression can be achieved with non-immunogenic transgene products in reimplanted ventral roots. This demonstrates the feasibility of combining neurosurgical repair with LV vector-mediated gene therapy. The current approach will be used in future experiments with LV vectors encoding neurotrophic factors to enhance the regeneration of spinal motor neurons after traumatic avulsion of spinal nerve roots.

Gene transfer to the spinal cord neural scar with lentiviral vectors: predominant transgene expression in astrocytes but not in meningeal cells

Viral vector-mediated overexpression of neurotrophins in cells constituting the neural scar may represent a powerful approach to rendering scar tissue of a central nervous system (CNS) lesion permissive for neuronal regrowth. In this study a lentiviral vector encoding green fluorescent protein (LV-GFP) was injected in and around the neural scar 2 weeks after a dorsal column lesion in the rat spinal cord in order to analyze transduction characteristics of the neural scar after 4, 7, and 14 days. GFP expression was found at all points after injection and increased from 4 to 7 days, with no apparent difference observed between 7 and 14 days. The core of the lesion was virtually devoid of GFP signal despite direct vector injections in this area. The colocalization of GFP with specific cell markers (GFAP, vimentin, Raldh2, NeuN, OX-42, ED-1, and NG-2) indicated that the predominant cells transduced in the rim of the lesion were astrocytes, with neurons, microglia, oligodendrocyte precursors, and macrophages transduced to a lesser extent. None of the Raldh2-positive meningeal cells, present in the core of the scar, expressed GFP. In vitro meningeal cells were readily transduced, indicating that in vivo the formation of an extracellular matrix might prevent LV particles from transducing cells in the core of the scar. Because astrocytes are important cellular constituents of the glial scar after CNS injury, transduction of astrocytes with LV vectors encoding neurotrophic factors like BDNF or NT-3 may be used to enhance regeneration of severed axonal tracts through or along boundaries of a CNS lesion.

Profound Differences in Spontaneous Long-Term Functional Recovery after Defined Spinal Tract Lesions in the Rat

The purpose of this study was to compare spontaneous functional recovery after different spinal motor tract lesions in the rat spinal cord using three methods of analysis, the BBB, the rope test, and the CatWalk. We transected the dorsal corticospinal tract (CSTx) or the rubrospinal tract (RSTx) or the complete dorsal half of the spinal cord (Hx) at thoracic level T8. Functional recovery was monitored for 31 weeks. We found no recovery of consistent inter limb coordination in any experimental group over time using the BBB locomotor rating scale. Quantitative CatWalk analysis revealed significant differences between experimental groups for inter limb coordination (RI). RSTx and Hx animals showed a significant decrease in the RI, and only in the RSTx group did the RI improve from 6 weeks post-lesion onward. Significant differences between experimental groups in step sequence patterns and base of support were also observed. In the rope test all experimental groups had significantly higher error percentages compared to control animals. Tracing of the CST revealed enhanced collateral formation rostral to the lesion in the CSTx group, not in other groups. The results presented here show that locomotor function in all, but CSTx groups gradually improved over time. This is important for studies that employ pharmacological, cell-, and/or gene therapy- based interventions to improve axonal regeneration and functional recovery after spinal cord injury.

Rescue and sprouting of motoneurons following ventral root avulsion and reimplantation combined with intraspinal adeno-associated viral vector-mediated expression of glial cell line-derived neurotrophic factor or brain-derived neurotrophic factor

Following avulsion of a spinal ventral root, motoneurons that project through the avulsed root are axotomized. Avulsion between, for example, L2 and L6 leads to denervation of hind limb muscles. Reimplantation of an avulsed root directed to the motoneuron pool resulted in re-ingrowth of some motor axons. However, most motoneurons display retrograde atrophy and subsequently die. Two neurotrophic factors, glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF), promote the survival of motoneurons after injury. The long-term delivery of these neurotrophic factors to the motoneurons in the ventral horn of the spinal cord is problematic. One strategy to improve the outcome of the neurosurgical reinsertion of the ventral root following avulsion would involve gene transfer with adeno-associated viral (AAV) vectors encoding these neurotrophic factors near the denervated motoneuron pool. Here, we show that AAV-mediated overexpression of GDNF and BDNF in the spinal cord persisted for at least 16 weeks. At both 1 and 4 months post-lesion AAV-BDNF- and -GDNF-treated animals showed an increased survival of motoneurons, the effect being more prominent at 1 month. AAV vector-mediated overexpression of neurotrophins also promoted the formation of a network of motoneuron fibers in the ventral horn at the avulsed side, but motoneurons failed to extent axons into the reinserted L4 root towards the sciatic nerve nor to improve functional recovery of the hind limbs. This suggests that high levels of neurotrophic factors in the ventral horn promote sprouting, but prevent directional growth of axons of a higher number of surviving motoneurons into the implanted root.

Adeno-associated viral vector-mediated gene transfer of brain-derived neurotrophic factor reverses atrophy of rubrospinal neurons following both acute and chronic spinal cord injury

Rubrospinal neurons (RSNs) undergo marked atrophy after cervical axotomy. This progressive atrophy may impair the regenerative capacity of RSNs in response to repair strategies that are targeted to promote rubrospinal tract regeneration. Here, we investigated whether we could achieve long-term rescue of RSNs from lesion-induced atrophy by adeno-associated viral (AAV) vector-mediated gene transfer of brain-derived neurotrophic factor (BDNF). We show for the first time that AAV vectors can be used for the persistent transduction of highly atrophic neurons in the red nucleus (RN) for up to 18 months after injury. Furthermore, BDNF gene transfer into the RN following spinal axotomy resulted in counteraction of atrophy in both the acute and chronic stage after injury. These novel findings demonstrate that a gene therapeutic approach can be used to reverse atrophy of lesioned CNS neurons for an extended period of time.

Viral vector-mediated gene transfer of neurotrophins to promote regeneration of the injured spinal cord

Injuries to the adult mammalian spinal cord often lead to severe damage to both ascending (sensory) pathways and descending (motor) nerve pathways without the perspective of complete functional recovery. Future spinal cord repair strategies should comprise a multi-factorial approach addressing several issues, including optimalization of survival and function of spared central nervous system neurons in partial lesions and the modulation of trophic and inhibitory influences to promote and guide axonal regrowth. Neurotrophins have emerged as promising molecules to augment neuroprotection and neuronal regeneration. Although intracerebroventricular, intrathecal and local protein delivery of neurotrophins to the injured spinal cord has resulted in enhanced survival and regeneration of injured neurons, there are a number of drawbacks to these methods. Viral vector-mediated transfer of neurotrophin genes to the injured spinal cord is emerging as a novel and effective strategy to express neurotrophins in the injured nervous system. Ex vivo transfer of neurotrophic factor genes is explored as a way to bridge lesions cavities for axonal regeneration. Several viral vector systems, based on herpes simplex virus, adenovirus, adeno-associated virus, lentivirus, and moloney leukaemia virus, have been employed. The genetic modification of fibroblasts, Schwann cells, olfactory ensheathing glia cells, and stem cells, prior to implantation to the injured spinal cord has resulted in improved cellular nerve guides. So far, neurotrophic factor gene transfer to the injured spinal cord has led to results comparable to those obtained with direct protein delivery, but has a number of advantages. The steady advances that have been made in combining new viral vector systems with a range of promising cellular platforms for ex vivo gene transfer (e.g., primary embryonic neurons, Schwann cells, olfactory ensheating glia cells and neural stem cells) holds promising perspectives for the development of new neurotrophic factor-based therapies to repair the injured nervous system.

Adeno-associated viral vector-mediated neurotrophin gene transfer in the injured adult rat spinal cord improves hind-limb function

To foster axonal growth from a Schwann cell bridge into the caudal spinal cord, spinal cells caudal to the implant were transduced with adeno-associated viral (AAV) vectors encoding for brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (AAV-NT-3). Control rats received AAV vectors encoding for green fluorescent protein or saline. AAV-BDNF- and AAV-NT-3-transduced 293 human kidney cells produced and secreted BDNF or NT-3, respectively, in vitro. The secreted neurotrophins were biologically active; they both promoted outgrowth of sensory neurites in vitro. In vivo, transgene expression was observed predominantly in neurons for at least 16 weeks after injection. Compared with controls, a modest though significant improvement in hind-limb function was found in rats that received AAV-BDNF and AAV-NT-3. Retrograde tracing demonstrated that twice as many neurons with processes extending toward the Schwann cell graft were present in the second lumbar cord segment of AAV-BDNF- and AAV-NT-3-injected animals compared with controls. We found no evidence, however, for growth of regenerated axons from the Schwann cell implant into the caudal cord. Our results suggest that AAV vector-mediated overexpression of BDNF and NT-3 in the cord caudal to a Schwann cell bridge modified the local lumbar axonal circuitry, which was beneficial for locomotor function.

Ex vivo adenoviral vector-mediated neurotrophin gene transfer to olfactory ensheathing glia: effects on rubrospinal tract regeneration, lesion size, and functional recovery after implantation in the injured rat spinal cord

The present study uniquely combines olfactory ensheathing glia (OEG) implantation with ex vivo adenoviral (AdV) vector-based neurotrophin gene therapy in an attempt to enhance regeneration after cervical spinal cord injury. Primary OEG were transduced with AdV vectors encoding rat brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or bacterial marker protein beta-galactosidase (LacZ) and subsequently implanted into adult Fischer rats directly after unilateral transection of the dorsolateral funiculus. Implanted animals received a total of 2 x 105 OEG that were subjected to transduction with neurotrophin-encoding AdV vector, AdV-LacZ, or no vector, respectively. At 4 months after injury, lesion volumes were smaller in all OEG implanted rats and significantly reduced in size after implantation of neurotrophin-encoding AdV vector-transduced OEG. All OEG grafts were filled with neurofilament-positive axons, and AdV vector-mediated expression of BDNF by implanted cells significantly enhanced regenerative sprouting of the rubrospinal tract. Behavioral analysis revealed that OEG-implanted rats displayed better locomotion during horizontal rope walking than unimplanted lesioned controls. Recovery of hind limb function was also improved after implantation of OEG that were transduced with a BDNF- or NT-3-encoding AdV vector. Hind limb performance during horizontal rope locomotion did directly correlate with lesion size, suggesting that neuroprotective effects of OEG implants contributed to the level of functional recovery. Thus, our results demonstrate that genetic engineering of OEG not only resulted in a cell that was more effective in promoting axonal outgrowth but could also lead to enhanced recovery after injury, possibly by sparing of spinal tissue.

[Comments on the Dutch Institute for Health Care Improvement's standard code of practice entitled, "Donation of fetal tissue"]

Under the auspices of the Kwaliteitsinstituut voor de Gezondheidszorg CBO [Dutch Institute for Healthcare Improvement] a standard code of practice was developed as a template for local institutional codes to implement the Law on Foetal Tissue. It is a useful model code, but arguments should have been outlined more explicitly, notably in instances where the code adopts a somewhat stricter position than the Law. The following remarks pertain to the model code: 1. It may be argued that the inclusion or exclusion of 12-15-year-old pregnant girls should be relative to the privacy-related sensitivity of the use of foetal tissue. 2. Transplantation requires additional tests for the safety of the recipient, including testing for HIV/AIDS. A pregnant woman's permission for such testing should not be taken for granted. 3. The abortion technique may be modified in view of the subsequent use of foetal tissue if the woman consents to the modification, with the prerequisites that the modification does not harm the woman and that any potential sensation of pain by the foetus must be minimised.

Pharmacological, cell, and gene therapy strategies to promote spinal cord regeneration

In this review, recent studies using pharmacological treatment, cell transplantation, and gene therapy to promote regeneration of the injured spinal cord in animal models will be summarized. Pharmacological and cell transplantation treatments generally revealed some degree of effect on the regeneration of the injured ascending and descending tracts, but further improvements to achieve a more significant functional recovery are necessary. The use of gene therapy to promote repair of the injured nervous system is a relatively new concept. It is based on the development of methods for delivering therapeutic genes to neurons, glia cells, or nonneural cells. Direct in vivo gene transfer or gene transfer in combination with (neuro)transplantation (ex vivo gene transfer) appeared powerful strategies to promote neuronal survival and axonal regrowth following traumatic injury to the central nervous system. Recent advances in understanding the cellular and molecular mechanisms that govern neuronal survival and neurite outgrowth have enabled the design of experiments aimed at viral vector-mediated transfer of genes encoding neurotrophic factors, growth-associated proteins, cell adhesion molecules, and antiapoptotic genes. Central to the success of these approaches was the development of efficient, nontoxic vectors for gene delivery and the acquirement of the appropriate (genetically modified) cells for neurotransplantation. Direct gene transfer in the nervous system was first achieved with herpes viral and El-deleted adenoviral vectors. Both vector systems are problematic in that these vectors elicit immunogenic and cytotoxic responses. Adeno-associated viral vectors and lentiviral vectors constitute improved gene delivery systems and are beginning to be applied in neuroregeneration research of the spinal cord. Ex vivo approaches were initially based on the implantation of genetically modified fibroblasts. More recently, transduced Schwann cells, genetically modified pieces of peripheral nerve, and olfactory ensheathing glia have been used as implants into the injured spinal cord.

Adeno-associated viral vectors as agents for gene delivery: application in disorders and trauma of the central nervous system

The use of viral vectors as agents for gene delivery provides a direct approach to manipulate gene expression in the mammalian central nervous system (CNS). The present article describes in detail the methodology for the injection of viral vectors, in particular adeno-associated virus (AAV) vectors, into the adult rat brain and spinal cord to obtain reproducible and successful transduction of neural tissue. Surgical and injection procedures are based on the extensive experience of our laboratory to deliver viral vectors to the adult rat CNS and have been optimized over the years. First, a brief overview is presented on the use and potential of viral vectors to treat neurological disorders or trauma of the CNS. Next, methods to deliver AAV vectors to the rat brain and spinal cord are described in great detail with the intent of providing a practical guide to potential users. Finally, some data on the experimental outcomes following AAV vector-mediated gene transfer to the adult rat CNS are presented as is a brief discussion on both the advantages and limitations of AAV vectors as tools for somatic gene transfer.

Clinical neurotransplantation: core assessment protocol rather than sham surgery as control

Basic neurotransplantation research evoked clinical trials of restorative brain surgery. Parkinson's disease was the first and primary test bed for this putative new therapeutic method. Various centers performed the grafting surgery and the behavioral evaluations in different ways, and observed a varying degree of symptomatic relief. This led to a plea for double blind placebo-controlled clinical trials, which have since been performed and of which the first outcomes were recently published. In the present paper this approach of experimental neurotransplantation in brain diseases is discussed and rejected. Neural grafting in the central nervous system is irreversible and is therefore not suitable for experimental approaches originally designed for and best suited to drug studies. For Parkinson's disease in particular, the technique is far from optimized to perform large-scale studies at this stage. Moreover, previous negative results of adrenal medulla tissue implantation in the brain of patients make placebo effects rather unlikely. Moral arguments concerning the validity of the informed consent, therapeutic misconception, and the risk/benefit ratio can be added in the plea against this control surgery. Finally, a recommendation is made for study designs that apply a disease-dedicated core assessment protocol (CAP) that can evaluate the period from pre-operative to post-convalescent stages quantitatively, and therefore, unbiased. The strength of these CAPs is that they allow comparisons of different grafting techniques, of results between centers and of other types of interventions and invasive treatments such as deep brain stimulation. On ethical grounds, it is unacceptable not to use a study design that circumvents sham or imitation surgery. It is a challenge for the neuroscience community to develop CAPs for brain diseases that are eligible for neurotransplantation in the future.

Intravitreal injection of adeno-associated viral vectors results in the transduction of different types of retinal neurons in neonatal and adult rats: a comparison with lentiviral vectors

Replication-deficient viral vectors encoding the marker gene green fluorescent protein (GFP) were injected into the vitreous of newborn, juvenile (P14), and adult rats. We tested two different types of modified virus: adeno-associated viral-2-GFP (AAV-GFP) and lentiviral-GFP vectors (LV-GFP). The extent of retinal cell transduction in different-aged animals was compared 7, 21, and 70 days after eye injections. At all postinjection times, LV-GFP transduction was mostly limited to pigment epithelium and cells in sclera and choroid. In contrast, transduction of large numbers of neural retinal cells was seen 21 and 70 days after AAV-GFP injections. AAV-GFP predominantly transduced neurons, although GFP-positive Müller cells were seen. All neuronal classes were labeled, but the extent of transduction for a given class varied depending on injection age. After P0 injections about 50% of transduced cells were photoreceptors and 30-40% were amacrine or bipolar cells. After adult injections 60-70% of transduced cells were retinal ganglion cells. In adults many GFP-positive retinal axons were traced through the optic nerve/tract and terminal arbors were visualized in central targets.

[A European discussion about stem cells for therapeutic use]

Stem cells as a source material for growing cellular transplants to repair dysfunctional organs appear to be a new challenge for medical science. Though stem cells are also present in foetal and adult organs, embryonic stem cells from the pre-implantation embryo in particular have the potency to proliferate easily in vitro and the capacity to differentiate into all the body's organ-specific cells. Therefore, these are the ideal cells for developing new cell transplantation therapies for diseases such as Parkinson's disease, diabetes mellitus and heart failure. The use of spare in vitro fertilization (IVF) embryos or pre-implantation embryos specially created to harvest human embryonic stem cells is, however, controversial and an ethical problem. In a European discussion platform organised by the European Commission Research Directorate-General, the status quo of the progress was presented and subsequently commented upon and discussed in terms of medical-ethical, social, industrial and patient interests. The expectations of this new medical technology were high, but clinical trials seem only acceptable once the in vitro differentiation of stem cells can be adequately controlled and once it is known how in vitro prepared stem cells behave after implantation. The ethical justification of the use of in vitro pre-implantation embryos remains controversial. The prevailing view is that the interests of severely ill patients for whom no adequate therapy exists, surmounts the interest of protection of a human in vitro pre-implantation embryo, regardless of whether it was the result of IVF or of transplantation of a somatic cell nucleus of the patient in an enucleated donor egg cell (therapeutic cloning).

Ethical guidance on human embryonic and fetal tissue transplantation: a European overview

This article presents an overview of regulations, guidelines and societal debates in eight member states of the EC about a) embryonic and fetal tissue transplantation (EFTT), and b) the use of human embryonic stem cells (hES cells) for research into cell therapy, including 'therapeutic' cloning. There appears to be a broad acceptance of EFTT in these countries. In most countries guidance has been developed. There is a 'strong' consensus about some of the central conditions for 'good clinical practice' regarding EFTT. International differences concern, amongst others, some of the informed consent issues involved, and the questions whether an intermediary organisation is necessary, whether the methods of abortion may be influenced by the possible use of EFT, and whether EFTT should only be used for the experimental treatment of rare disorders. The potential use of hES cells for research into cell therapy has given a new impetus to the debate about (human) embryo research. The therapeutic prospects with regard to the retrieval and research use of hES cells appear to function as a catalyst for the introduction of less restrictive regulations concerning research with spare embryos, at least in some European countries. It remains to be seen whether the prospect of treating patients suffering from serious disorders with transplants produced by therapeutic cloning will decrease the societal and moral resistance to allowing the generation of embryos for 'instrumental' use.

Viral vector-mediated gene expression in olfactory ensheathing glia implants in the lesioned rat spinal cord

Implantation of olfactory ensheathing glia (OEG) is a promising strategy to augment long-distance regeneration in the injured spinal cord. In this study, implantation of OEG following unilateral hemisection of the dorsal cervical spinal cord was combined with ex vivo gene transfer techniques. We report, to our knowledge for the first time, that purified cultures of primary OEG are capable of expressing a foreign gene following adenoviral (AdV) and lentiviral (LV) vector-mediated gene transfer. OEG implants subjected to AdV vector-mediated gene transfer expressed high levels of transgenic protein in both intact and lesioned spinal cord at 7 days after implantation. However, the levels of transgene expression gradually declined between 7 and 30 days after implantation in lesioned spinal cord. Infection with LV vectors resulted in stable transduction of primary OEG cultures and transgene expression persisted for at least 4 months after implantation. Genetic engineering of OEG opens the possibility of expressing additional neurotrophic genes and create optimal 'bridging' substrates to support spinal axon regeneration. Furthermore, stable transduction of OEG allows us to reliably study the behaviour of implanted cells and to obtain better understanding of their regeneration supporting properties.

Adenoviral Vector-Mediated Expression of Neurotrophin-3 Increases Neuronal Survival in Suprachiasmatic Nucleus Grafts

To improve transplantation results of fetal suprachiasmatic nucleus (SCN) in SCN-lesioned (SCNX) rats, grafts were ex vivo transduced with an adenoviral vector encoding for neurotrophin-3 (AdNT-3) before implantation. Mock- and AdLacZ-transduced grafts were used as controls. First, transplants were evaluated microscopically and by image analysis for the presence of vasopressinergic (VPergic) and vasoactive intestinal polypeptidergic (VIPergic) SCN neurons at 10 weeks or later postgrafting. Ex vivo AdNT-3-transduced transplants displayed increased volume areas of VPergic and VIPergic SCN cells in comparison with those in mock- and AdLacZ-transduced transplants, but significantly improved graft-to-host VPergic and VIPergic SCN fiber growth was not reached (though AdNT-3-transduced transplants tended to grow more VPergic fibers into the brain of VP-deficient SCNX Brattleboro rat recipients, which were chosen as recipients to circumvent the presence of non-SCN VP fiber staining). Second, a small group of arrhythmic Wistar rats received AdNT-3- or control-treated SCN grafts while continuously on-line for the monitoring of overt circadian activities in the pre- and postgrafting periods. The results indicated that ex vivo transduced SCN grafts can still restore arrhythmia, but that the NT-3-mediated anatomical improvements of the grafting results were not sufficient to enhance efficacy of reinstatement of circadian rhythm in SCN-lesioned rats. However, in this group VIP staining volume area, not VP staining volume area, correlated significantly with reinstatement of circadian rhythm.

The suprachiasmatic nucleus and the circadian time-keeping system revisited

Many physiological and behavioral processes show circadian rhythms which are generated by an internal time-keeping system, the biological clock. In rodents, evidence from a variety of studies has shown the suprachiasmatic nucleus (SCN) to be the site of the master pacemaker controlling circadian rhythms. The clock of the SCN oscillates with a near 24-h period but is entrained to solar day/night rhythm by light. Much progress has been made recently in understanding the mechanisms of the circadian system of the SCN, its inputs for entrainment and its outputs for transfer of the rhythm to the rest of the brain. The present review summarizes these new developments concerning the properties of the SCN and the mechanisms of circadian time-keeping. First, we will summarize data concerning the anatomical and physiological organization of the SCN, including the roles of SCN neuropeptide/neurotransmitter systems, and our current knowledge of SCN input and output pathways. Second, we will discuss SCN transplantation studies and how they have contributed to knowledge of the intrinsic properties of the SCN, communication between the SCN and its targets, and age-related changes in the circadian system. Third, recent findings concerning the genes and molecules involved in the intrinsic pacemaker mechanisms of insect and mammalian clocks will be reviewed. Finally, we will discuss exciting new possibilities concerning the use of viral vector-mediated gene transfer as an approach to investigate mechanisms of circadian time-keeping.

Intercostal nerve implants transduced with an adenoviral vector encoding neurotrophin-3 promote regrowth of injured rat corticospinal tract fibers and improve hindlimb function

Following injury to central nervous tissues, damaged neurons are unable to regenerate their axons spontaneously. Implantation of peripheral nerves into the CNS, however, does result in axonal regeneration into these transplants and is one of the most powerful strategies to promote CNS regeneration. In the present study implantation of peripheral nerve bridges following dorsal hemisection is combined with ex vivo gene transfer with adenoviral vectors encoding neurotrophin-3 (Ad-NT-3) to examine whether this would stimulate regeneration of one of the long descending tracts of the spinal cord, the corticospinal tract (CST), into and beyond the peripheral nerve implant. We chose to use an adenoviral vector encoding NT-3 because CST axons are sensitive to this neurotrophin and Schwann cells in peripheral nerve implants do not express this neurotrophin. At 16 weeks postimplantation of Ad-NT-3-transduced intercostal nerves, approximately three- to fourfold more of the anterogradely traced corticospinal tract fibers had regrown their axons through gray matter below the lesion site when compared to control animals. Regrowth of CST fibers occurred over more than 8 mm distal to the lesion site. No regenerating CST fibers were, however, observed into the transduced peripheral implant. Animals with a peripheral nerve transduced with Ad-NT-3 also exhibited improved function of the hindlimbs when compared to control animals treated with an adenoviral vector encoding LacZ. Thus, transient overexpression of NT-3 in peripheral nerve tissue bridges is apparently sufficient to stimulate regrowth of CST fibers and to promote recovery of hindlimb function, but does not result in regeneration of CST fibers into such transplants. Taken together, combining an established neurotransplantation approach with viral vector-gene transfer promotes the regrowth of injured CST fibers through gray matter and improves the recovery of hindlimb function.

The use of adenoviral vectors and ex vivo transduced neurotransplants: towards promotion of neuroregeneration

Regeneration of injured axons following injury depends on a delicate balance between growth-promoting and growth-inhibiting factors. Overexpression of neurotrophin genes seems a promising strategy to promote regeneration. Trophic genes can be overexpressed at the site of injury at the axonal stumps, or at the perikaryal level of the injured neuron. Transduction of the neural cells can be achieved by applying adenoviral vectors, either directly in vivo or-in the case of neurotransplantation as an ex vivo approach. In both cases it would create a more permissive environment for axonal growth and therefore in functional regeneration. In this article, the feasibility of the use of adenoviral vectors in several neuroregeneration models--in particularly in spinal cord lesion models and the biological clock transplantation model--is illustrated. The results show that the adenoviral vectors can be a powerful tool to study the effects of overexpression of genes in an in vivo paradigm of nerve regeneration or nerve outgrowth. The potential use of adenoviral vectors and ex vivo transduced neurotransplants is discussed.

Adenoviral vector-mediated expression of a foreign gene in peripheral nerve tissue bridges implanted in the injured peripheral and central nervous system

Axons of the CNS do normally not regenerate after injury, in contrast to axons of the PNS. This is due to a different microenvironment at the site of the lesion as well as a particular intrinsic program of axonal regrowth. Although transplantation of peripheral nerve tissue bridges is perhaps the most successful approach to promoting regeneration in the CNS, ingrowth of CNS nerve fibers with such transplants is limited. Genetic modification of peripheral nerve bridges to overexpress outgrowth-promoting proteins should, in principle, improve the permissive properties of peripheral nerve transplants. The present study shows that pieces of peripheral intercostal nerve, subjected to ex vivo adenoviral vector-mediated gene transfer and implanted as nerve bridges in transected sciatic nerve, avulsed ventral root, hemi-sected spinal cord and intact brain, are capable of expressing a foreign gene. In vitro studies showed expression of the reporter gene LacZ up to 30 days in Schwann cells. After implantation, LacZ expression could be detected at 7 days postimplantation, but had virtually disappeared at 14 days. Schwann cells of the transduced nerve bridges retained the capacity of guiding regenerative peripheral and central nerve fiber ingrowth. Transduction of intercostal nerve pieces prior to implantation should, in principle, enable enhanced local production of neurotrophic factors within the transplant and has the potential to improve the regeneration of injured axons into the graft.

Ethical issues in neurografting of human embryonic cells

During the last decade neurotransplantation has developed into a technique with the possible potential to repair damaged or degenerating human brain. Effective neurotransplantation has so far been based on the use of fetal brain tissue derived from aborted embryos or fetuses. The ethical issues related to this new therapeutic approach therefore not only concern the possible adverse side effects for a neural graft-receiving patient, but also the relationship between the requirements for fetal tissue and the decision-making process for induced abortion. Although for decades human embryos and fetuses have been the subject of biomedical studies, and, in principle, their use has therefore not been seen as ethically objectionable, the above points made it necessary to reconsider the moral issues. The present paper points out several of these issues, both from the donor and acceptor (patient) point of view. The conclusion is that under a series of restrictions intended to prevent the use of grafts from encouraging induced abortions and to maintain high standards of respect for life and human dignity, neurotransplantation using embryonic or fetal brain tissue parts cannot be rejected on moral grounds.

Ontogeny of neurotrophin receptor trkC expression in the rat forebrain and anterior hypothalamus with emphasis on the suprachiasmatic nucleus

There is little information about neurotrophic regulation in the developing rat hypothalamus. In the present study, we therefore examined the expression of neurotrophin receptor TrkC in the developing forebrain and hypothalamus. In situ hybridization of coronal sections revealed that on the 15th day of gestation, trkC messenger RNA expression is homogeneously distributed over the neocortex, septum, thalamus, hypothalamus, hippocampus, rhinencephalon and the amygdala. Exceptions were the anteroventral nucleus of the hypothalamus and the striatum, which showed higher levels of trkC messenger RNA expression, and the germinal zones which were devoid of trkC messenger RNA. After birth, the homogeneous staining pattern changes into a heterogeneous staining pattern like that found in adulthood. TrkC expression is observed in the area of the suprachiasmatic nucleus as early as E17 and continues until adulthood. The presence of the TrkC receptor in the E17 suprachiasmatic nucleus suggests that neurotrophin-3 plays a role in development of this structure and that application of neurotrophin-3 could stimulate neuronal survival and neuritic outgrowth in a suprachiasmatic nucleus transplantation model.

Vasopressin-deficient suprachiasmatic nucleus grafts re-instate circadian rhythmicity in suprachiasmatic nucleus-lesioned arrhythmic rats

It was investigated whether grafts of the suprachiasmatic nucleus could re-instate circadian rhythmicity in the absence of its endogenous vasopressin production and whether the restored rhythm would have the long period length of the donor. Grafts of 17-days-old vasopressin-deficient homozygous Brattleboro rat fetuses, homotopically placed in arrhythmic suprachiasmatic nucleus-lesioned Wistar rats, re-instated circadian drinking rhythm within 20-50 days similar as seen for grafts of heterozygous control fetuses. Period length of the recovered rhythm revealed a similar difference (average 24.3 vs. 23.8 h) as reported for the rhythm between the adult Brattleboro genotypes. In all transplants, also those of the two-third non-recovery rats, a surviving suprachiasmatic nucleus was visible as a vasoactive intestinal polypeptide-positive neuronal cell cluster, whereas heterozygous transplants also revealed the complementary vasopressinergic cell part. Explanation of the absence of recovery failed since no undisputable correlation emerged between recovery of rhythm and vasoactive intestinal polypeptide, vasopressin and/or somatostatin immunocytochemical characteristics of the suprachiasmatic nucleus of the transplant. Special focus on the somatostatinergic neurons revealed their presence only occasionally near or in between the vasoactive intestinal polypeptidergic and (in the case of heterozygous grafts) vasopressinergic cell cluster. However their aberrant cytoarchitectural position appeared not to have affected the possibility to restore drinking rhythm of the suprachiasmatic nucleus-lesioned arrhythmic rat. It was concluded that grafted Brattleboro fetal suprachiasmatic nucleus develop their intrinsic rhythm conform their genotype and that vasopressin is not a crucial component in the maintenance nor in the transfer of circadian activity of the biological clock for drinking activity. Vasopressin of the suprachiasmatic nucleus may instead serve modulation within the circadian system.

Circadian rhythmicity of vasopressin levels in the cerebrospinal fluid of suprachiasmatic nucleus-lesioned and -grafted rats

Transplantation of the fetal suprachiasmatic nucleus (SCN) in arrhythmic SCN-lesioned rats can reinstate circadian drinking rhythms in 40% to 50% of the cases. In the current article, it was investigated whether the failure in the other rats could be due to the absence of a circadian rhythm in the grafted SCN, using a circadian vasopressin (VP) rhythm in the cerebrospinal fluid (CSF) as the indicator for a rhythmic SCN. CSF was sampled in continuous darkness from-intact control rats and SCN-lesioned and -grafted rats. VP could be detected in all samples, with concentrations of 15 to 30 pg/ml in the control rats and 5 to 15 pg/ml in the grafted rats. A circadian VP rhythm with a two- to threefold difference between peak and nadir values was found in all 7 control rats but in only 4 of 13 experimental rats, despite the presence of a VP-positive SCN in all grafts. A circadian VP rhythm was present in 2 drinking rhythm-recovered rats (6 of 13) and in 2 nonrecovery rats. Apparently, in these latter rats, the failure of the grafted SCN to restore a circadian drinking rhythm cannot be attributed to a lack of rhythmicity in the SCN itself. Thus, the presence of a rhythmic grafted SCN, as is deduced from a circadian CSF VP rhythm, appears not to be sufficient for restoration of a circadian drinking rhythm in SCN-lesioned arrhythmic rats.

New iodinated progestins as potential ligands for progesterone receptor imaging in breast cancer. Part 2: In vivo pharmacological characterization

On the basis of the observed high selective binding to both the human and rat progesterone receptor (PR) in vitro, three 17alpha-iodovinyl-substituted nortestosterone derivatives, i.e., the Z-isomer of 17alpha-iodovinyl-19-nortestosterone (Z-IVNT; Z-IPG1) and both the stereoisomers of 17alpha-iodovinyl-18-methyl-11-methylene-19-nortestosterone (E- and Z-IPG2), were selected for radio-iodination and subsequently evaluated as potential radioligands for PR imaging in human breast cancer. Their target tissue uptake, retention, and uptake selectivity were studied in female rats. The distribution studies revealed that PR-mediated uptake in the uterus and ovaries could only be demonstrated for Z-[123I]IPG2. The target tissue uptake selectivity was, however, low, with the highest uterus-to-nontarget tissue uptake ratios observed at 2-4 h postinjection (p.i.), being 4.4, 1.8, and 7.4 for the uterus-to-blood, -fat, and -muscle ratio, respectively. For Z-[123I]IPG2, distribution was also studied in dimethylbenzanthracene (DMBA)-induced mammary tumour-bearing rats and in normal rabbits. Mammary tumour uptake of Z-[123I]IPG2 in the mammary tumour-bearing rat was also found to be PR-specific. In rabbits, higher selective target tissue uptake of Z-[123I]IPG2 was observed than in rats, resulting in uterus-to-blood, -fat, and -muscle ratios of 6.6, 2.2, and 21.3 at 2-4 h p.i., respectively. In conclusion, Z-[123I]IPG2, which displayed high binding affinity for both the human and rat PR in vitro, showed specific PR-mediated target tissue uptake in rats and rabbits in vivo, the uptake selectivity being highest in the latter. Because the binding characteristics appeared to vary between species, a pilot study in breast cancer patients may be needed to decide whether Z-[123I]IPG2 can be of potential use as PR imaging agent in breast cancer.

Cellular requirements of suprachiasmatic nucleus transplants for restoration of circadian rhythm

Fetal neurografts containing the suprachiasmatic nucleus (SCN) can restore the circadian locomotor and drinking rhythm of SCN-lesioned (SCNX) rat and hamster. This functional outcome finally proves that the endogenous biological clock autonomously resides in the SCN. Observations on the cellular requirements of the "new" SCN for restoration of the arrhythmic SCNX animals have led to some new insights and confirmed findings from other studies. A critical mass of SCN neurons appeared necessary for functional effects, whereas the temporal profile of reinstatement of rhythm correlated with the delayed maturation of the grafted SCN. Cytoarchitectonically, the grafted SCN does not seem to develop normally for all anatomical aspects. Complementary clusters of vasoactive intestinal polypeptide(VIP)- and vasopressin(VP)ergic neurons are formed, but somatostatin(SOM)ergic neurons do not always "join" this group, as is normally seen in situ. Nevertheless, these new SCNs can restore the ablated functions. As the period length of restored rhythms tends to vary, it might be that the grafted SCN underwent an altered or impaired maturation that resulted in a different setting of its clock mechanism. A prominent role of VIPergic neurons seems indicated by their presence in all functional grafts, but, although they may be required, these cells do not appear to be a sufficient condition for restoration of rhythm. Many grafts exhibit the presence of VIPergic cells without counteracting the arrhythmia, whereas VP- and SOMergic SCN neurons are usually present as well. Findings with VP-deficient Brattleboro rat grafts indicated that VP is not the primary obligatory signal of circadian activity. It is argued that perhaps the role of SOMergic neurons in the clock function of the (grafted) SCN has been insufficiently considered. However, one should keep in mind that the peptides of the various types of SCN neurons may function only as cofactors, mutually modulating molecular or bioelectrical cellular activities within the nucleus or the message of the main transmitter gamma-aminobutyric acid.

Synthesis, estrogen receptor binding, and tissue distribution of a new iodovinylestradiol derivative (17alpha,20E)-21-[123I]Iodo-11beta-nitrato-19-norp regna-1,3,5 (10),20-tetraene-3,17-diol (E-[123I]NIVE)

We have synthesized and evaluated E-11beta-nitrato-17alpha-iodovinylestradiol (E-NIVE; E-3c) and its 123I-labelled form, as a new potential radioligand for imaging of estrogen receptor (ER)-positive human breast tumors. E-[123I]NIVE was prepared by stereospecific iododestannylation of the E-tri-n-butylstannylvinyl precursor (E-2c), obtained from reaction of 11beta-nitrato-estrone (8) with E-tributylstannylvinyllithium. In competitive binding studies, E-NIVE proved to have high binding affinity for both the rat and the human ER (Ki 280-730 pM), without significant binding to human sex hormone binding globulin. Distribution studies in normal and mammary tumor-bearing rats showed specific ER-mediated uptake of E-[123I]NIVE in the estrogen target tissues, i.e., uterus, ovaries, pituitary, and hypothalamus, but not in the mammary tumors. Selective retention in these target tissues, including tumor tissue, resulted in significant increases over time for the target tissue-to-muscle uptake ratios, but not for the target tissue-to-fat uptake ratios. The tumor-to-fat uptake ratio even appeared constantly below 1. In the primary estrogen target tissues, E-[123I]NIVE displayed high specific ER-mediated uptake and retention, which resulted in moderate target-to-nontarget tissue uptake ratios. In contrast, in tumor tissue, E-[123I]NIVE uptake appeared to be rather low and not ER-specific. As a consequence, E-[123I]NIVE appears to be a less favorable radioligand for ER imaging in breast cancer than the previously studied stereoisomers of 11beta-methoxy-17alpha-[123I]iodovinylestradiol (E- and Z-[123I]MIVE; [123I]E- and [123I]Z-3b).

Transgene expression in rat fetal brain grafts is maintained for 7 months after ex vivo adenoviral vector-mediated gene transfer

Fetal brain tissue fragments containing the suprachiasmatic nucleus were infected with an adenoviral vector containing the marker gene LacZ encoding for beta-galactosidase, and subsequently cultured or transplanted in the third ventricle of SCN-lesioned adult Wistar rats. In previous studies we optimized the infection procedure and characterized the immunological response directed against the viral vector in this model. The present study reports on beta-gal expression for at least 7 months in neuronal and glial cells. Maturation of the transplanted fetal SCN with respect to immunoreactivity for vasoactive intestinal polypeptide and C-terminal propressophysin was not hampered by the viral infection.

[123I]FP-CIT binds to the dopamine transporter as assessed by biodistribution studies in rats and SPECT studies in MPTP-lesioned monkeys

[123I]FP-CIT (N-omega-fluoropropyl-2 beta-carbomethoxy-3 beta-(4-iodophenyl)-tropane), a radioiodinated cocaine analogue, was evaluated as an agent for the in vivo labeling of dopamine (DA) transporters by biodistribution studies in rats and by single photon emission computed tomography (SPECT) studies in unilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned monkeys. In rats, intravenous injection of [123I]FP-CIT resulted in high accumulation of radioactivity in the striatum. Less pronounced uptake was seen in brain areas with high densities of serotonergic uptake sites. While striatal uptake of radioactivity after injection of [123I]FP-CIT was displaced significantly by GBR12,909 but not by fluvoxamine, the opposite was observed in brain areas known to be rich of serotonin transporters. Monkeys which were unilaterally treated with neurotoxic doses of MPTP showed severe loss of striatal [123I]FP-CIT uptake at the side of treatment. The results of this study indicate that [123I]FP-CIT, although not being a selective radioligand, binds specifically to the striatal DA transporter in vivo and thus suggest that [123I]FP-CIT promises to be a suitable radioligand for SPECT imaging of DA transporters in humans.

Imaging of estrogen receptors in primary and metastatic breast cancer patients with iodine-123-labeled Z-MIVE

PURPOSE

To evaluate the feasibility of noninvasive imaging of estrogen receptors (ERs) in primary and metastatic breast cancer with the iodine-123-labeled ER-specific ligand cis-11beta-methoxy-17alpha-iodovinylestradiol-17beta (Z-[123I]MIVE) using conventional nuclear medicine techniques.

PATIENTS AND METHODS

Z-[123I]MIVE planar scintigraphy and single-photon emission computed tomography (SPECT) were performed in 12 patients with proven primary breast cancer and 13 patients with proven or from other imaging modalities evident bone, liver, lung, pleura and/or lymph node metastases. The results were compared with those of ER immunohistochemistry (IHC). Blocking studies with the antiestrogen tamoxifen were performed to test whether Z-[123I]MIVE tumor uptake was ER-mediated.

RESULTS

Planar imaging showed uptake in 11 of 12 primary carcinomas. ER IHC performed for nine of these was positive. For the planar scintigraphy-negative patient, SPECT was faintly positive, but ER IHC negative (agreement, 90%). In nine of 13 metastatic patients, planar scintigraphy was positive. The agreement between the results of ER IHC on the original primary tumor and of Z-[123I]MIVE scintigraphy was 82%. Specificity of tumor Z-[123I]MIVE uptake was established by complete blockade of uptake by tamoxifen, except in two patients who showed progressive disease. Z-[123I]MIVE scintigraphy also enabled discriminating metastases from confounding nonmalignant abnormalities of the bone scan.

CONCLUSION

Z-[123I]MIVE scintigraphy shows high sensitivity and specificity for the detection of ER-positive breast cancer. This may have impact on diagnostic possibilities and therapeutic management. Since ER imaging shows the functional status, addressing known intratumoral and intertumoral ER heterogeneity, it may improve the characterization of disease and the selection of patients who may benefit from hormonal therapy.

Long-term transgene expression in fetal rat suprachiasmatic nucleus neurografts following ex vivo adenoviral vector-mediated gene transfer

Ex vivo gene transfer to fetal suprachiasmatic nucleus (SCN)-containing solid piece neurografts was explored using a first-generation prototype adenoviral vector containing the reporter gene LacZ (Ad-LacZ). Transgene expression was examined at different intervals following grafting in the IIIrd ventricle of rat brain and was compared to that of explant cultures. Large numbers of beta-galactosidase-positive cells were observed 8 days postgrafting. The number of stained cells had decreased considerably at 21 days but transduced cells were still present at 70 days. In vitro culturing of infected SCN tissue revealed high expression up to 21 days, indicating that the in vivo and in vitro fates of Ad-LacZ-infected cells were different. The main reason for this difference appeared to be cell loss by necrosis in the initial phase after transplantation, a phenomenon not related to the infection with Ad-LacZ since it similarly occurred in control grafts. In vivo inflammatory responses, observed after immunostaining for macrophages and T-lymphocytes, were also comparable in control and Ad-LacZ-treated transplants, except that cytotoxic T-cells were observed in the Ad-LacZ-treated transplants and not in controls. The recruitment of these cells was, however, minor and primarily observed at 8 days postgrafting, indicating that a major immunological rejection of the transduced graft did not occur. In both control and Ad-LacZ-infected transplants similar survival and intraimplant neuritic growth of SCN cells were visible. Ex vivo gene transfer of solid piece fetal SCN grafts with adenoviral vectors therefore appeared to be a nontoxic long-term gene-introducing procedure. This would in principle enable the local production of neurotrophic factors within the transplant and has the potential to improve functional SCN neurografting.

[123I]FP-CIT SPECT shows a pronounced decline of striatal dopamine transporter labelling in early and advanced Parkinson's disease

OBJECTIVES

The main neuropathological feature in Parkinson's disease is a severe degeneration of the dopaminergic neurons in the substantia nigra resulting in a loss of dopamine (DA) transporters in the striatum. [123I]beta-CIT single photon emission computed tomography (SPECT) studies have demonstrated this loss of striatal DA transporter content in Parkinson's disease in vivo. However, studies with this radioligand also showed that an adequate imaging of the striatal DA transporter content could only be performed on the day after the injection of radioligand, which is not convenient for outpatient evaluations. Recently, a new radioligand [123I]FP-CIT, with faster kinetics than beta-CIT, became available for imaging of the DA transporter with SPECT, and the applicability of this ligand was tested in patients with early and advanced Parkinson's disease, using a one day protocol.

METHODS

[123I]FP-CIT SPECT was performed in six patients with early and 12 patients with advanced Parkinson's disease, and in six age matched healthy volunteers.

RESULTS

Compared with an age matched control group striatal [123I]FP-CIT uptake in patients with Parkinson's disease was decreased, and this result was measurable three hours after injection of the radioligand. In the Parkinson's disease group the uptake in the putamen was reduced more than in the caudate nucleus. The contralateral striatal uptake of [123I]FP-CIT was significantly lower than the ipsilateral striatal uptake in the Parkinson's disease group. Specific to non-specific striatal uptake ratios correlated with the Hoehn and Yahr stage. A subgroup of patients with early Parkinson's disease also showed significantly lower uptake in the putamen and lower putamen:caudate ratios than controls.

CONCLUSION

[123I]FP-CIT SPECT allows a significant discrimination between patients with Parkinson's disease and age matched controls with a one day protocol, which will be to great advantage in outpatient evaluations.

Development of radioligands for the imaging of cardiac beta-adrenoceptors using SPECT. Part I: Asymmetric synthesis and structural characterization of five new iodine-containing beta-adrenoceptor antagonist derivatives

The asymmetric synthesis of a series of iodinated beta-adrenoceptor ligands is described. One ligand, (S)-(-)-[1-(2-iodophenoxy)]-3'-(tert-butylamino)-2'-propanol (CYBL3), is based on the beta-adrenoceptor antagonist penbutolol. The other ligands are N-iodovinyl and N-iodoaryl analogues of the beta-adrenoceptor antagonist CGP12177. These have been synthesized from 2-amino-3-nitrophenol. Furthermore, radioiodinated [123I]CYBL3 and [123I](2'S,2"E)-[4-(3'-(1",1"-dimethyl-3"-iodo-2" propenylamino)-2'-hydroxy propoxy)]-benzimidazol-2-one have been prepared by radiolabelling the corresponding trialkyltin precursors using [123I]-NaI in the presence of hydrogen peroxide.

Practical benefit of [123I]FP-CIT SPET in the demonstration of the dopaminergic deficit in Parkinson's disease

Loss of striatal dopamine (DA) transporters in Parkinson's disease (PD) has been accurately assessed in vivo by single-photon emission tomography (SPET) studies using [123I]beta-CIT. However, these studies have also shown that adequate imaging of the striatal DA transporter content can be performed only 20-30 h following the injection of [123I]beta-CIT, which is not convenient for routine out-patient evaluations. Recently, a new ligand, N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl) tropane (FP-CIT), became available for in vivo imaging of the DA transporter. The faster kinetics of [123I]FP-CIT have been shown to allow adequate acquisition as early as 3 h following injection. In the present study, loss of striatal DA transporters in five non-medicated PD patients was assessed on two consecutive SPET scans, one with [123I]beta-CIT (24 h following injection) and one with [123I]FP-CIT (3 h following injection). The ratios of specific to non-specific [123I]FP-CIT uptake in the caudate nucleus and putamen were consistently 2.5-fold lower than those of [123I]beta-CIT. However, when the uptake ratio of both ligands in these brain regions of patients was expressed as a percentage of the uptake ratio found in healthy controls, both the decrease and the variation of the data were similar. It is concluded on the basis of these findings that [123I]FP-CIT seems as good as [123I]beta-CIT for the assessment of the dopaminergic deficit in PD. The faster kinetics of [123I]FP-CIT are a clear advantage.

The Z-isomer of 11 beta-methoxy-17 alpha-[123I]iodovinylestradiol is a promising radioligand for estrogen receptor imaging in human breast cancer

The potential of both stereoisomers of 11 beta-methoxy-17 alpha-[123I] iodovinylestradiol (E- and Z-[123I]MIVE) as suitable radioligands for imaging of estrogen receptor (ER)-positive human breast tumours was studied. The 17 alpha-[123I]iodovinylestradiol derivatives were prepared stereospecifically by oxidative radioiododestannylation of the corresponding 17 alpha-tri-n-butylstannylvinylestradiol precursors. Both isomers of MIVE showed high in vitro affinity for dimethylbenzanthracene-induced rat and fresh human mammary tumour ER, that of Z-MIVE however being manyfold higher than that of E-MIVE. In vivo distribution studies with E- and Z-[123I]MIVE in normal and tumour-bearing female rats showed ER-mediated uptake and retention in uterus, ovaries, pituitary, hypothalamus and mammary tumours, again the highest for Z-[123I]MIVE. The uterus- and tumour-to-nontarget tissue (far, muscle) uptake ratios were also highest for Z-[123I]MIVE. Additionally, planar whole body imaging of two breast cancer patients 1-2 h after injection of Z-[123I]MIVE showed increased focal uptake at known tumour sites. Therefore, we conclude that Z-[123I]MIVE is a promising radioligand for the diagnostic imaging of ER in human breast cancer.

Development of radioligands for the imaging of cardiac beta-adrenoceptors using SPECT. Part II: Pharmacological characterization in vitro and in vivo of new 123I-labeled beta-adrenoceptor antagonists

Cardiac beta-adrenoceptors are assumed to play a key role in chronic heart failure. Although several radioligands labeled with 11C or 18F have been synthesized for imaging purposes with positron emission tomography (PET), so far no optimal ligands are available to image cardiac beta-adrenoceptors using single photon emission tomography (SPECT). In the present study, we characterized four new synthesized analogues of the nonselective beta-adrenoceptor antagonist 4-(3-t-butylamino-2-hydroxypropoxy)-benzimidazol-2-one (CGP12177) and one analogue of the nonselective beta-adrenoceptor antagonist penbutolol. Using classical in vitro displacement studies with left ventricular tissue of New Zealand White rabbits and [125I]iodocyanopindolol as a radioligand, binding affinity to the receptor was determined. From the four analogues, only (2'S,2"E)- [4-(3'-(1",1"-dimethyl-3"-Iodo-2" propenylamino)-2'-hydroxypropoxy)]-benzimidazol-2-one proved to have a high affinity, with Ki = 1.25 +/- 0.09 nM, n = 3. The other analogues showed relatively low affinity, with Ki-values > 1 nM. The analogue of penbutolol ((S)-(-)-[1-(2-Iodophenoxy)]-3'-(tert-butylamino)-2'-propanol) also showed a Ki value of 0.64 +/- 0.26 nM, n = 3. Subsequently, (2'S,2"E)-[4-(3'-(1",1"-dimethyl-3"-Iodo-2" propenylamino)-2'-hydroxypropoxy)]-benzimidazol-2-one and (S)-(-)-[1-(2-Iodophenoxy)]-3'-(tert-butylamino)-2'-propanol were radioactively labeled with 123I to study their biodistribution in New Zealand White rabbits and to determine specific binding. Significant uptake was observed in both lungs and left ventricles. However, both compounds showed high nonspecific binding in vivo because uptake of the radioligand could not be inhibited by preinjection of different (selective- and nonselective-adrenoceptor antagonists and hydrophilic and lipophilic antagonists) antagonists. In conclusion, although two analogues showed reasonable affinity in vitro for the receptor, their binding in vivo proved to be largely nonspecific, suggesting that these two compounds are unsuitable for imaging purposes. However, because marked differences in affinity for the receptor were observed with only little structural changes between compounds, the present results offer future perspectives for the synthesis of a more specific radioligand.