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Title:  Methods for modulation of the effects of aging on the primate brain
United States Patent: 
January 2, 2007

Tuszynski; Mark H. (La Jolla, CA), Blesch; Armin (San Diego, CA)
 The Regents of the University of California (Oakland, CA)
Appl. No.: 
December 5, 2000


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The invention provides a clinically useful protocol for delivery of recombinant nervous system growth factors into the aging mammalian brain. The invention is particularly useful in tempering and reversing the loss of neurological function in the aging mammalian brain, by (a) correlating loss of cortical fiber density to impairment of neurological function in the normal, aging brain; and (b) providing minimally invasive means by which such losses may be reversed. To these ends, a method is provided by which a growth factor-encoding transgene is delivered to, and expressed in, preselected sites within the brain, to stimulate growth of neurons at, and at a distance from, each delivery site.


The invention provides a clinically useful protocol for delivery of recombinant nervous system growth factors into the aging mammalian brain. The invention is particularly useful in tempering and reversing the loss of neurological function in the aging mammalian brain, by (a) correlating loss of cortical fiber density to impairment of neurological function in the normal, aging brain; and (b) providing means by which such losses may be reversed.

More specifically, the invention consists of methods for intraparenchymal delivery of a recombinant growth factor or other growth-promoting gene growth factor(generically, molecules which act on neuronal tissue to stimulate axonal growth) to the mammalian brain. Delivery of the growth factors to targeted cells is achieved by in vivo transduction of neurons targeted for treatment, by transfection of cells neighboring these target neurons (neurons or glia) with a recombinant expression vector for expression of the desired growth factor in situ, and/or by ex vivo grafting of transgene expressing host cells to targeted tissue.

Growth factors delivered according to the invention exert a trophic effect at or near the delivery site (along chemotropic gradients stemming from the delivery site). Startlingly, such growth factors also exert non-chemotropic effects on distant axonal termini. Thus, the invention provides an opportunity to improve neuronal function over relatively expansive sectors of the brain while minimizing surgical invasion into brain tissue.


I. Primates Suffer Structural Alterations in Cholinergic Innervation of the Brain during Aging

The invention provides proof, not previously established, that normal aging in the non-human primate brain is associated with a significant reduction in cholinergic innervation of the cortex, as evidenced by losses of cortical cholinergic axonal terminals. Cholinergic systems contribute only a small fraction to the total number of axons and synapses in the cortex, yet exert an important role in modulating neuronal excitability throughout the neocortex and hippocampus. Thus, alterations in this system can exert wide-ranging effects on various aspects of cognition, including attention and memory.

For example, as described in greater detail in the Examples, aged monkeys who received grafts of beta-galactosidase expressing host cells did not differ significantly from aged non-operated animals in cholinergic innervation of the various cortical fields examined. Such animals were collectively utilized as controls ("aged controls").

Aged control monkeys exhibited a significant 24.8.+-.2.6% decline in AChE axon terminal density averaged across all cortical regions compared to non-aged subjects (p<0.0001, post-hoc Fischer's). These differences were consistent and significant across several individual cortical regions when analyzed independently, including the insular cortex, cingulate cortex and frontal cortex regions. Strong trends toward similar age-related differences in cholinergic innervation were present in inferior temporal cortex and in the hippocampal formation (id.).

II. Reversal of Age-Related Neuronal Loss in the Brain

A. Improved Cholinergic Innervation Extends from the Delivery Site

Age-related changes in cortical cholinergic innervation in diverse cortical regions were substantially reversed by cellular gene delivery of NGF. For example, aged monkeys that received grafts of NGF-secreting cells exhibited a substantial and significant reversal of age-related declines in cortical cholinergic innervation. When averaged across all cortical regions examined, NGF-grafted animals had levels of cholinergic innervation that were significantly greater than values of aged control monkeys (p<0.0001, post-hoc Fischer's) and were equal to intact young monkeys (p=0.89, post-hoc Fischer's).

Further, cortical regions (insular and inferior temporal cortices) receiving innervation primarily from the intermediate division of Ch4, the cholinergic subdivision targeted for grafting, demonstrated levels of cholinergic innervation significantly exceeding those of normal young monkeys (overall 13.4.+-.4.5% increase relative to young monkeys; p=0.01, post-hoc Fischer's. Levels of cholinergic innervation in these regions also significantly exceeded control-aged monkeys (overall 43.6.+-.3.0% increase; p <0.0001, post-hoc Fischer's). Cholinergic fiber densities in cortical regions (cingulate and frontal cortex, hippocampus) not heavily innervated by the targeted Ch4i cell population also exhibited reversal of age-related losses after NGF cell grafting, although the magnitude of the reversal (20.6.+-.4.1% increase; p=0.01, post-hoc Fischer's) was more modest than that observed in temporal and insular cortex.

These effects of cellularly-delivered NGF on cortical cholinergic innervation were exerted at a distance, since the growth factor was presented to the cholinergic soma yet influenced terminal axon density in the distant cortex. Remarkably, reversal of age-related axonal attenuation in both the soma and the cortex was achieved after only three months of NGF delivery to the primate brain soma. Thus, practice of the invention significantly and efficiently ameliorates neuronal loss accompanying the normal aging process in the primate brain.

From a clinical perspective, a significant advantage provided by the invention is the ability to introduce exogenous growth factor to discrete regions of identified neuronal loss (to induce local chemotropic sprouting of axons into growth factor-secreting grafts, as shown in), while at the same time inducing a significant increase in the number or complexity of neuronal terminals via non-chemotropic influence by the growth factors in regions of the brain distant from the delivery sites. While not limiting of the scope of the invention, it can be surmised from these results that the mechanism through which growth factors influence axonal morphology at a distance may involve activation of diverse intracellular downstream signaling pathways, including PI-3 kinase and ras/erk, leading to increases in cellular transport of growth-related proteins.

B. Growth Factor Delivery: Site Selection and Dosing

To use both the local chemotropic and distant non-chemotropic effects of growth factors delivered according to the invention to advantage, specific delivery sites are preferably selected so as to cluster in an area of neuronal atrophy or loss, or likely neuronal atrophy or loss (such regions may include, but are not limited to, the cholinergic basal forebrain in normal aging, the entorhinal cortex in normal aging, and any cortical region in normal aging; the cholinergic basal forebrain or entorhinal cortex in patients with a significant history of Alzheimer's Disease, the substantia nigra in patients with Parkinson's disease, or motor neurons in patients with amyotrophic lateral sclerosis). Once areas of neuronal loss (or likely neuronal loss) are identified, delivery sites are selected for stereotaxic distribution so each unit dosage of growth factor composition is delivered into the brain at the target site, or within diffusion reach of a chemotropic (concentration) gradient leading to the target site (generally, within 500 .mu.m of a targeted neuron).

The terms "unit dosage" and "dosage" refer to concentration of growth factor or similarly-encoding transgene delivered via recombinant expression vector or donor cell in a pharmaceutically acceptable composition ("growth factor delivery composition"). One of ordinary skill in the art will be able to adjust dosage as appropriate to the patient and his or her condition. However, depending on whether the growth factor expressing transgene is introduced by an in vivo approach (via a viral or non-viral expression vector), or by an ex vivo approach (via grafting of transgene expressing host cells to target tissue), the preferred dosing parameters vary.

For ex vivo delivery, a unit dosage of growth factor delivery composition contains a concentration of donor cells of at least 1.times.10.sup.5 cells/.mu.l. Each graft made at a delivery site is comprised of between 2 and 20 .mu.l of a donor cell composition.

For in vivo delivery, a unit dosage of growth factor delivery composition consists of 2.5 to 10 .mu.l of such composition, wherein the composition provides from 10.sup.10 up to 10.sup.12 growth factor expressing viral particles per ml.

Each unit dosage of growth factor delivery composition is preferably delivered to each grafting site in the target tissue through a surgical incision over a period of about 5 10 minutes (depending on the total volume of cell suspension to be delivered). The rate of delivery of the cells may therefore vary from about 0.2 .mu.l cell suspension/minute to about 4 .mu.l cell suspension/minute.

III. Materials for Use in Practicing the Invention

Materials useful in the methods of the invention include donor cells, recombinant expression vectors, packaging cell lines, helper cell lines, synthetic in vivo gene therapy vectors, regulatable gene expression systems, encapsulation materials, pharmaceutically acceptable carriers and polynucleotides coding for growth factors of interest.

A. Nervous System Growth Factors

Known nervous system growth factors include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5), neurotrophin-6 (NT-6), ciliary neurotrophic factor (CNTF), glial cell line-derived neurotrophic factor (GDNF), the fibroblast growth factor family (FGF's 1 15), leukemia inhibitory factor (LIF), certain members of the insulin-like growth factor family (e.g., IGF-1), the neurturins, persephin, the bone morphogenic proteins (BMPs), the immunophilins, the transforming growth factor (TGF) family of growth factors, the neuregulins, epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and others. NGF and NT-3 in particular have been tested with promising results in clinical trials and animal studies (see, e.g., Hefti and Weiner, Ann Neurol., 20:275 281 (1986); Tuszynki and Gage, Ann. Neurol., 30:625 636 (1991); Tuszynski, et al., Gene Therapy, 3:305 314 (1996) and Blesch and Tuszynski, Clin.Neurosci., 3:268 274 (1996)). Of the known nervous system growth factors, human NGF ,BDNF, NT-3 and GDNF are preferred for use in the invention for their relatively low immunogenicity as compared to allogenic growth factors.

Coding polynucleotides for hNGF ,BDNF, NT-3 and GDNF are known, as are coding sequences for growth factors of other mammalian species (e.g., mouse, in which the coding sequence for NGF is highly homologous to the human coding sequence). For example, a cDNA including the coding sequence for hNGF is reported in GenBank at E03015 (Kazuo, et al., Japanese Patent Application No. JP19911175976-A, while the nucleotide sequence of genomic hNGF (with putative amino acid sequence) is reported in GenBank at HSBNGF (Ullrich, Nature, 303:821 825 (1983)) and the mRNA sequence is reported in GenBank at Accession No. X52599; locus HSBNGFAC (Borsani, et al., Nucleic Acids Res., 18:4020 (1990)). The genomic nucleotide sequence of hNT3 is reported in GenBank at E07844 (Asae, et al., JP Patent Application No. 1993189770-A4). These references are incorporated herein to illustrate knowledge in the art concerning nucleotide and amino acid sequences for use in synthesis of growth factor.

B. In Vivo And Ex Vivo Recombinant Expression Vectors

1. Identity.

The strategy for preparing genes for transfer into target cells in the brain includes the following basic steps: (1) selection of an appropriate growth factor expressing transgene; (2) selection and development of suitable and efficient vectors for gene transfer; (3) in vivo transduction of target cells, or grafting of donor cells to target tissue; (4) demonstration that transgene expression occurs stably and efficiently; (5) demonstration that the delivery procedure caused no serious deleterious effects; and (6) demonstration of a desired phenotypic effect in the host animal.

For either in vivo or ex vivo delivery, because adult mammalian brain cells are non-dividing, the recombinant expression vector chosen must be able to transduce and be expressed in non-dividing cells. At present, vectors known to have this capability include DNA viruses such as adenoviruses and certain RNA viruses such as HIV-based lentiviruses and feline immunodeficiency virus (FIV). Other vectors with this capability include herpes simplex virus (HSV). A HIV-based lentiviral vector has recently been developed which, like other retroviruses, can insert a transgene into the nucleus of host cells (enhancing the stability of expression) but, unlike other retroviruses, can make the insertion into the nucleus of non-dividing cells. This lentiviral vector has been shown to stably transduce brain cells after direct injection and stably express a foreign transgene without detectable pathogenesis from viral proteins (see, Naldini, et al., Science, 272:263 267 (1996), the disclosure of which is incorporated by reference). Following the teachings of the researchers who first constructed the HIV-1 retroviral vector, those of ordinary skill in the art will be able to construct lentiviral vectors suitable for use in the methods of the invention (for more general reference concerning retrovirus construction, see, e.g., Kriegler, Gene Transfer and Expression, A Laboratory Manual, W. Freeman Co. (NY 1990) and Murray, E J, ed., Methods in Molecular Biology, Vol. 7, Humana Press (NJ 1991)).

Adenoviruses and AAV have been shown to be quite safe for in vivo use and have been shown to result in long-term gene expression in vivo; they are therefore a preferred choices for use in the in vivo methods of the invention, where safety and long-term expression of growth factor encoding transgenes is necessary. Those of ordinary skill in the art are familiar with the techniques used to construct adenoviral and AAV vectors and can readily employ them to produce vector compositions useful in the claimed invention (for reference, see, e.g., Straus, The Adenovirus, Plenum Press (NY 1984), pp. 451 496; Rosenfeld, et al., Science, 252:431 434 (1991); U.S. Pat. No. 5,707,618 [adenovirus vectors for use in gene therapy]; and U.S. Pat. No. 5,637,456 [method for determining the amount of functionally active adenovirus in a vector stock], the contents of each of which is incorporated herein to illustrate the level of skill in the art).

Herpesviruses, alpha viruses and pox viruses are also well-characterized virus vectors which may be applied to the methods of the invention. Of these vectors, adeno-associated vectors are an especially attractive choice for their lack of pathogenicity and ability to insert a transgene into a host genome.

Non-viral delivery methods are also an option for use in the in vivo methods of the invention. In particular, the plasmid (in a "naked" or lipid-complexed form), lipoplexes (liposome complexed nucleic acids), amino acid polymer complexes with nucleic acids and artificial chromosomes are all non-viral gene delivery agents which are demonstrably able to transduce cells and deliver a foreign transgene. Synthetic in vivo gene therapy vectors are also an option for use in the methods of the invention.

For ex vivo use, retroviral vectors (especially those of murine origin) offer an efficient, useful, and presently the best-characterized means of introducing and expressing foreign genes efficiently in mammalian cells. These vectors have very broad host and cell type ranges, integrate by reasonably well understood mechanisms into random sites in the host genome, express genes stably and efficiently, and under most conditions do not kill or obviously damage their host cells.

2. Construction.

Construction of vectors for recombinant expression of nervous system growth factors for use in the invention may be accomplished using conventional techniques which do not require detailed explanation to one of ordinary skill in the art. For review, however, those of ordinary skill may wish to consult Maniatis et al., in Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, (NY 1982).

Briefly, construction of recombinant expression vectors employs standard ligation techniques. For analysis to confirm correct sequences in vectors constructed, the ligation mixtures may be used to transform a host cell and successful transformants selected by antibiotic resistance where appropriate. Vectors from the transformants are prepared, analyzed by restriction and/or sequenced by, for example, the method of Messing, et al., (Nucleic Acids Res., 9:309, 1981), the method of Maxam, et al., (Methods in Enzymology, 65:499, 1980), or other suitable methods which will be known to those skilled in the art. Size separation of cleaved fragments is performed using conventional gel electrophoresis as described, for example, by Maniatis, et al., (Molecular Cloning, pp. 133 134, 1982).

Expression of a gene is controlled at the transcription, translation or post-translation levels. Transcription initiation is an early and critical event in gene expression. This depends on the promoter and enhancer sequences and is influenced by specific cellular factors that interact with these sequences. The transcriptional unit of many prokaryotic genes consists of the promoter and in some cases enhancer or regulator elements (Banerji et al., Cell 27:299 (1981); Corden et al., Science 209:1406 (1980); and Breathnach and Chambon, Ann. Rev. Biochem. 50:349 (1981)). For retroviruses, control elements involved in the replication of the retroviral genome reside in the long terminal repeat (LTR) (Weiss et al., eds., The molecular biology of tumor viruses: RNA tumor viruses, Cold Spring Harbor Laboratory, (NY 1982)). Moloney murine leukemia virus (MLV) and Rous sarcoma virus (RSV) LTRs contain promoter and enhancer sequences (Jolly et al., Nucleic Acids Res. 11:1855 (1983); Capecchi et al., In: Enhancer and eukaryotic gene expression, Gulzman and Shenk, eds., pp. 101 102, Cold Spring Harbor Laboratories (NY 1991). Other potent promoters include those derived from cytomegalovirus (CMV) and other wild-type viral promoters.

Promoter and enhancer regions of a number of non-viral promoters have also been described (Schmidt et al., Nature 314:285 (1985); Rossi and de Crombrugghe, Proc. Natl. Acad. Sci. USA 84:5590 5594 (1987)). Methods for maintaining and increasing expression of transgenes in quiescent cells include the use of promoters including collagen type I (1 and 2) (Prockop and Kivirikko, N. Eng. J. Med. 311:376 (1984); Smith and Niles, Biochem. 19:1820 (1980); de Wet et al., J. Biol. Chem., 258:14385 (1983)), SV40 and LTR promoters.

In addition to using viral and non-viral promoters to drive transgene expression, an enhancer sequence may be used to increase the level of transgene expression. Enhancers can increase the transcriptional activity not only of their native gene but also of some foreign genes (Armelor, Proc. Natl. Acad. Sci. USA 70:2702 (1973)). For example, in the present invention collagen enhancer sequences are used with the collagen promoter 2(I) to increase transgene expression. In addition, the enhancer element found in SV40 viruses may be used to increase transgene expression. This enhancer sequence consists of a 72 base pair repeat as described by Gruss et al., Proc. Natl. Acad. Sci. USA 78: 943 (1981); Benoist and Chambon, Nature 290:304 (1981), and Fromm and Berg, J. Mol. Appl. Genetics, 1:457 (1982), all of which are incorporated by reference herein. This repeat sequence can increase the transcription of many different viral and cellular genes when it is present in series with various promoters (Moreau et al., Nucleic Acids Res. 9:6047 (1981).

Transgene expression may also be increased for long term stable expression using cytokines to modulate promoter activity. Several cytokines have been reported to modulate the expression of transgene from collagen 2(I) and LTR promoters (Chua et al., connective Tissue Res., 25:161 170 (1990); Elias et al., Annals N.Y. Acad. Sci., 580:233 244 (1990)); Seliger et al., J. Immunol. 141:2138 2144 (1988) and Seliger et al., J. Virology 62:619 621 (1988)). For example, transforming growth factor (TGF), interleukin (IL)-1, and interferon (INF) down regulate the expression of transgenes driven by various promoters such as LTR. Tumor necrosis factor (TNF) and TGF1 up regulate, and may be used to control, expression of transgenes driven by a promoter. Other cytokines that may prove useful include basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF).

Collagen promoter with the collagen enhancer sequence (Coll(E)) can also be used to increase transgene expression by suppressing further any immune response to the vector which may be generated in a treated brain notwithstanding its immune-protected status. In addition, anti-inflammatory agents including steroids, for example dexamethasone, may be administered to the treated host immediately after vector composition delivery and continued, preferably, until any cytokine-mediated inflammatory response subsides. An immunosuppression agent such as cyclosporin may also be administered to reduce the production of interferons, which downregulates LTR promoter and Coll(E) promoter-enhancer, and reduces transgene expression.

It is also useful to be able to regulate the secretion of the genetically engineered gene product after grafting. The release of a gene product such as acetylcholine (ACh), a transmitter that is greatly decreased through degeneration of cholinergic neuron populations, from cultured cells infected with a MLV vector expressing the choline acetyltransferase cDNA can be augmented using choline, a precursor for acetylcholine. This suggests a means for dietary regulation of intracerebral gene therapy.

C. Pharmaceutical Preparations of Gene Vectors

Growth factor delivery compositions may consist of expression vectors or donor cells placed into a pharmaceutically acceptable suspension, solution or emulsion. Suitable mediums include saline and may, for those embodiments which do not rely on antigen presenting cells for delivery of the growth factor transgenes into target tissue, liposomal preparations.

More specifically, pharmaceutically acceptable carriers may include sterile aqueous of non-aqueous solutions, suspensions, and emulsions. Examples of non-aqueous solvents are propylene glycol, polyethylene glycol, vegetable oils such as olive oil, and injectable organic esters such as ethyl oleate. Aqueous carriers include water, alcoholic/aqueous solutions, emulsions or suspensions, including saline and buffered media. Parenteral vehicles include sodium chloride solution, Ringer's dextrose, dextrose and sodium chloride, lactated Ringer's or fixed oils. Intravenous vehicles include fluid and nutrient replenishers, electrolyte replenishers (such as those based on Ringer's dextrose), and the like. Preservatives and other additives may also be present such as, for example, antimicrobials, antioxidants, chelating agents, and inert gases and the like. Further, a composition of growth factor transgenes may be lyophilized using means well known in the art, for subsequent reconstitution and use according to the invention.

A colloidal dispersion system may also be used for targeted gene delivery. Colloidal dispersion systems include macromolecule complexes, nanocapsules, microspheres, beads, and lipid-based systems including oil-in-water emulsions, micelles, mixed micelles, and liposomes. The preferred colloidal system of this invention is a liposome.

IV. Methods for Delivery of Transgene Delivery Composition

The most effective mode and timing of injection of the growth factor delivery compositions of the invention will vary with the patient's health, response to treatment, and the judgment of the treating health professional.

Direct delivery of the growth factor delivery compositions of the invention may be achieved by means familiar to those of skill in the art, including microinjection (see, e.g., Capecchi, Cell, 22:479 488 (1980); electropotation (see, e.g., Andreason and Evans, Biotechniques, 6:650 660 (1988); infusion, chemical complexation with a targeting molecule or co-precipitant (e.g., liposome, calcium), and microparticle bombardment (Tang, et al., Nature, 356:152 154 (1992)).

V. Animal Models and Clinical Evaluation

Data demonstrating the use and efficacy of the methods of the invention in an aged, non-human primate model (used to best approximate the size requirements of the primate brain) are provided in the Examples.

Clinical evaluation and monitoring of treatment can be performed using the in vivo imaging techniques described above as well as through biopsy and histological analysis of treated tissue. In the latter respect, basal forebrain cholinergic neuronal numbers can be quantified in a tissue sample using, for example, anti-growth factor antibody (for immunoassay of secreted growth factor) or NGF-receptor (p75) and choline acetyltransferase (ChAT) for labeling of neurons. A sample protocol for in vitro histological analysis of treated and control tissue samples is described in the Examples.

Claim 1 of 21 Claims

1. A method for ameliorating neuronal atrophy and loss in the mammalian brain, the method comprising directly delivering a neurotrophin-encoding transgene composition comprising a recombinant expression vector containing said neurotrophin-encoding trnasgene to preselected delivery sites in the brain for expression of the neurotrophin at, or within diffusion distance of, targeted cholinergic or dopaminergic neurons, wherein the neurotrophin is nerve growth factor (NGF) or glial derived nerve growth factor (GDNF) and stimulates non-chemotrophic axonal growth by, or activity in, the targeted neurons.

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