Intravenous glial-derived neurotrophic factor gene therapy of experimental Parkinson's disease with Trojan horse liposomes and a tyrosine hydroxylase promoter

Neurotrophic factors and neurodegenerative diseases: a delivery issue

Neurotrophic factors (NTFs) represent one of the most stimulating challenge in neurodegenerative diseases, due to their potential in neurorestoring and neuroprotection. Despite the large number of proofs-of-concept and evidences of their activity, most of the clinical trials, mainly regarding Parkinson's disease and Alzheimer's disease, demonstrated several failures of the therapeutic intervention. A large number of researches were conducted on this hot topic of neuroscience, clearly evidencing the advantages of NTF approach, but evidencing the major limitations in its application. The inability in crossing the blood-brain barrier and the lack of selectivity actually represent some of the most highlighted limits of NTFs-based therapy. In this review, beside an overview of NTF activity versus the main neuropathological disorders, a summary of the most relevant approaches, from invasive to noninvasive strategies, applied for improving NTF delivery to the central nervous systems is critically considered and evaluated.

Positive autoregulation of GDNF levels in the ventral tegmental area mediates long-lasting inhibition of excessive alcohol consumption

Glial cell line-derived neurotrophic factor (GDNF) is an essential growth factor for the survival and maintenance of the midbrain dopaminergic (DA-ergic) neurons. Activation of the GDNF pathway in the ventral tegmental area (VTA), where the GDNF receptors are expressed, produces a long-lasting suppression of excessive alcohol consumption in rats. Previous studies conducted in the DA-ergic-like cells, SHSY5Y, revealed that GDNF positively regulates its own expression, leading to a long-lasting activation of the GDNF signaling pathway. Here we determined whether GDNF activates a positive autoregulatory feedback loop in vivo within the VTA, and if so, whether this mechanism underlies the long-lasting suppressive effects of the growth factor on excessive alcohol consumption. We found that a single infusion of recombinant GDNF (rGDNF; 10 μg) into the VTA induces a long-lasting local increase in GDNF mRNA and protein levels, which depends upon de novo transcription and translation of the polypeptide. Importantly, we report that the GDNF-mediated positive autoregulatory feedback loop accounts for the long-lasting inhibitory actions of GDNF in the VTA on excessive alcohol consumption. Specifically, the long-lasting suppressive effects of a single rGDNF infusion into the VTA on excessive alcohol consumption were prevented when protein synthesis was inhibited, as well as when the upregulation of GDNF expression was prevented using short hairpin RNA to focally knock down GDNF mRNA in the VTA. Our results could have implications for the development of long-lasting treatments for disorders in which GDNF has a beneficial role, including drug addiction, chronic stress and Parkinson's disease.

Novel and emerging strategies in drug delivery for overcoming the blood-brain barrier

Two decades of molecular research have revealed the presence of transporters and receptors expressed in the brain vascular endothelium that provide potential novel targets for the rational design of blood-brain barrier-penetrating drugs. In this review, we briefly introduce the reader to the molecular characteristics of the blood-brain barrier that make this one of the most important obstacles towards the development of efficacious CNS drugs. We highlight recent attempts to rationally target influx and bidirectional transport systems expressed on the brain endothelial cell and avoid the important obstacle presented in the form of efflux transporters. Many of these approaches are highly innovative and show promise for future human application. Some of these approaches, however, have revealed significant limitations and are critiqued in this review. Nonetheless, these combined efforts have left the field of CNS drug delivery better positioned for developing novel approaches towards the rational design of CNS-penetrating drugs.

A comparative study of transfection efficiency between liposomes, immunoliposomes and brain-specific immunoliposomes

This study investigated the transfection ability and efficiency of liposomes and immunoliposomes for exogenous gene delivery into the brain via the venous system. Four groups of rats underwent tail vein injection with one of the following: liposomes encapsulating pCMV (human cytomegalovirus promoter)-LacZ plasmid 80 microg (low dose) or 300 microg (high dose); general immunoliposomes encapsulating 80 microg transferrin receptor antibodies (OX26)-pCMV-LacZ plasmid; or brain-specific immunoliposomes encapsulating 80 microg OX26-pGFAP (glial fibrillary acidic protein promoter)-LacZ plasmid. A control group received no injected agent. The LacZ mRNA levels (1 h post-injection) and beta-galactosidase activity (48 h post-injection) in the brain and peripheral organs were assayed using real-time reverse transcription-polymerase chain reaction and histochemical staining, respectively. Both immunoliposomes delivered exogenous DNA containing the LacZ gene into the brain after venous injection, resulting in extensive LacZ expression in the brain. Furthermore, the brain-specific OX26-pGFAP-LacZ immunoliposome decreased the non-specific expression of LacZ in peripheral organs without affecting transfection efficiency in the brain. Thus, brain-specific immunoliposomes are an efficient and brain-specific targeting vector.

Brain-targeting mechanisms of lactoferrin-modified DNA-loaded nanoparticles

Ligand-mediated brain-targeting drug delivery is one of the focuses at present. Elucidation of exact targeting mechanisms serves to efficiently design these drug delivery systems. In our previous studies, lactoferrin (Lf) was successfully exploited as a brain-targeting ligand to modify cationic dendrimer-based nanoparticles (NPs). The mechanisms of Lf-modified NPs to the brain were systematically investigated in this study for the first time. The uptake of Lf-modified vectors and NPs by brain capillary endothelial cells (BCECs) was related to clathrin-dependent endocytosis, caveolae-mediated endocytosis, and macropinocytosis. The intracellular trafficking results showed that Lf-modified NPs could rapidly enter the acidic endolysosomal compartments within 5 mins and then partly escape within 30 mins. Both Lf-modified vectors and NPs showed higher blood-brain barrier-crossing efficiency than unmodified counterparts. All the results suggest that both receptor- and adsorptive-mediated mechanisms contribute to the cellular uptake of Lf-modified vectors and NPs. Enhanced brain-targeting delivery could be achieved through the synergistic effect of the macromolecular polymers and the ligand.

Receptor-mediated therapeutic transport across the blood–brain barrier

The blood–brain barrier (BBB) hinders drug delivery to the brain parenchyma. The ultimate goal of brain drug targeting technology is to deliver therapeutics across the BBB with a diverse collection of molecular transport systems. Receptor-mediated transcytosis (RMT) is one such class of transport system. Insulin and transferrin, as well as other endogenous peptides, employ the vesicular trafficking machinery of the endothelium to transport substances between the blood and the brain. In addition to vector development, strategies for coupling drugs to the vector that give high-efficiency coupling are the other important element for RMT. After the BBB-targeting vector–therapeutic conjugates have crossed the BBB, there may still be a need to target them to a specific population of cells in the brain. This review will focus on two major aspects of RMT brain drug delivery: new advances of existing RMT systems and development of new BBB transport vectors and specific RMT targets.

Transcriptional targeting to brain cells: Engineering cell type-specific promoter containing cassettes for enhanced transgene expression

Transcriptional targeting using a mammalian cellular promoter to restrict transgene expression to target cells is often desirable for gene therapy. This strategy is, however, hindered by relatively weak activity of some cellular promoters, which may lead to low levels of gene expression, thus declining therapeutic efficacy. Here we outline the advances accomplished in the area of transcriptional targeting to brain cells, with a particular focus on engineering gene cassettes to augment cell type-specific expression. Among the effective approaches that improve gene expression while retaining promoter specificity are promoter engineering to change authentic sequences of a cellular promoter and the combined use of a native cellular promoter and other cis-acting elements. Success in achieving high level and sustained transgene expression only in the cell types of interest would be of importance in allowing gene therapy to have its impact on patient treatment.

Differential receptor-mediated drug targeting to the diseased brain

The brain is not directly accessible for intravenously administered macro- and most small molecular drugs because of the presence of the blood-brain barrier (BBB). In this respect the BBB functions as a physical and metabolic barrier which is presented by the endothelial cells in brain capillaries. In order to overcome the BBB, therapeutic compounds have been targeted to internalizing receptors at the BBB. In this review we summarize the different approaches that have been described in current literature, including the possible difficulties for clinical application. Particularly, we focus on the possible impact of brain diseases on receptor-mediated transport to the BBB/brain and how this may affect various targeting strategies. Moreover, it is our opinion that a differential drug targeting/delivery approach should be applied to treat central nervous system (CNS) diseases that are related to the BBB alone, and for CNS diseases that are related to both the brain and the BBB.

Hexa-arginine enhanced uptake and residualization of selective high affinity ligands by Raji lymphoma cells

Background

A variety of arginine-rich peptide sequences similar to those found in viral proteins have been conjugated to other molecules to facilitate their transport into the cytoplasm and nucleus of targeted cells. The selective high affinity ligand (SHAL) (DvLPBaPPP)₂LLDo, which was developed to bind only to cells expressing HLA-DR10, has been conjugated to one of these peptide transduction domains, hexa-arginine, to assess the impact of the peptide on SHAL uptake and internalization by Raji cells, a B-cell lymphoma.

Results

An analog of the SHAL (DvLPBaPPP)₂LLDo containing a hexa-arginine peptide was created by adding six D-arginine residues sequentially to a lysine inserted in the SHAL's linker. SHAL binding, internalization and residualization by Raji cells expressing HLA-DR10 were examined using whole cell binding assays and confocal microscopy. Raji cells were observed to bind two fold more ¹¹¹In-labeled hexa-arginine SHAL analog than Raji cells treated with the parent SHAL. Three fold more hexa-arginine SHAL remained associated with the Raji cells after washing, suggesting that the peptide also enhanced residualization of the ¹¹¹In transported into cells. Confocal microscopy showed both SHALs localized in the cytoplasm of Raji cells, whereas a fraction of the hexa-arginine SHAL localized in the nucleus.

Conclusion

The incorporation of a hexa-D-arginine peptide into the linker of the SHAL (DvLPBaPPP)₂LLDo enhanced both the uptake and residualization of the SHAL analog by Raji cells. In contrast to the abundant cell surface binding observed with Lym-1 antibody, the majority of (DvLPBaPPP)₂LArg6AcLLDo and the parent SHAL were internalized. Some of the internalized hexa-arginine SHAL analog was also associated with the nucleus. These results demonstrate that several important SHAL properties, including uptake, internalization, retention and possibly intracellular distribution, can be enhanced or modified by conjugating the SHALs to a short polypeptide.

Near complete rescue of experimental Parkinson's disease with intravenous, non-viral GDNF gene therapy

PURPOSE

Rats with experimental Parkinson's disease (PD) are treated with intravenous glial-derived neurotrophic factor (GDNF) plasmid DNA and non-viral gene therapy using Trojan horse liposomes (THLs) targeted with a monoclonal antibody (MAb) to the rat transferrin receptor (TfR). The GDNF transgene expression is under the influence of the rat tyrosine hydroxylase (TH) promoter.

METHODS

The GDNF expression plasmid is designated pTHproGDNF. Rats were treated with 3 weekly injections of THLs starting 1 week after the intra-cerebral injection of 6-hydroxydopamine. The dose of the pTHproGDNF was 10 mICROg/rat/weekly injection. Rats were tested with three assays of neurobehavior, and terminal striatal TH enzyme activity was measured at 6 weeks following toxin administration, which is 3 weeks following the last administration of THLs.

RESULTS

Apomorphine-induced contralateral rotation was reduced 87% by THL gene therapy; amphetamine-induced ipsilateral rotation was reduced 90% by THL gene therapy; whisker-induced forelimb placement abnormalities were reduced 77% with THL gene therapy. The improvement in neurobehavior correlated with a lasting 77% increase in striatal TH enzyme activity, relative to saline treated rats.

CONCLUSIONS

Near complete abrogation of the neurotoxin effects are achieved with multiple intravenous dosing of GDNF plasmid DNA gene therapy, using receptor-targeted THLs, and a region-specific promoter.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.