Bi-functional IgG-lysosomal enzyme fusion proteins for brain drug delivery.

Most lysosomal storage disorders affect the central nervous system. However, lysosomal enzymes do not cross the blood-brain barrier (BBB), and intravenous enzyme infusion is not effective for the brain. Lysosomal enzymes can be re-engineered for BBB transport as IgG-enzyme fusion proteins, where the IgG domain is a monoclonal antibody (MAb) against an endogenous BBB receptor/transporter, and which acts as a molecular Trojan horse to deliver the enzyme to brain. However, the problem is retention of high enzyme activity following enzyme fusion to the IgG. The present investigation shows this is possible with a versatile approach that employs fusion of the enzyme to either the IgG heavy chain or light chain using a long flexible linker. The model IgG is a chimeric monoclonal antibody (MAb) against the human insulin receptor (HIR). The enzyme activity of the HIRMAb-enzyme fusion protein is preserved for hexosaminidase A, which is mutated in Tay Sachs disease, for protein palmitoylthioesterase-1, which is mutated in Batten disease type 1, acid sphingomyelinase, which is mutated in Niemann Pick disease type A, and beta galactosidase-1, which is mutated in GM1 gangliosidosis.

Blood-Brain Barrier Transport, Plasma Pharmacokinetics, and Neuropathology Following Chronic Treatment of the Rhesus Monkey with a Brain Penetrating Humanized Monoclonal Antibody Against the Human Transferrin Receptor.

A monoclonal antibody (mAb) against the blood-brain barrier (BBB) transferrin receptor (TfR) is a potential agent for delivery of biologic drugs to the brain across the BBB. However, to date, no TfRMAb has been tested with chronic dosing in a primate model. A humanized TfRMAb against the human (h) TfR1, which cross reacts with the primate TfR, was genetically engineered with high affinity (ED50 = 0.18 ± 0.04 nM) for the human TfR type 1 (TfR1). For acute dosing, the hTfRMAb was tritiated and injected intravenously (IV) in the Rhesus monkey, which confirmed rapid delivery of the humanized hTfRMAb into both brain parenchyma, via transport across the BBB, and into cerebrospinal fluid (CSF), via transport across the choroid plexus. For chronic dosing, a total of 8 adult Rhesus monkeys (4 males, 4 females) were treated twice weekly for 4 weeks with 0, 3, 10, or 30 mg/kg of the humanized hTfRMAb via a 60 min IV infusion for a total of 8 doses prior to euthanasia and microscopic examination of brain and peripheral organs. A pharmacokinetics analysis showed the plasma clearance of the hTfRMAb in the primate was nonlinear, and plasma clearance was increased over 20-fold with chronic treatment of the low dose, 3 mg/kg, of the antibody. Chronic treatment of the primates with the 30 mg/kg dose caused anemia associated with suppressed blood reticulocytes. Immunohistochemistry of terminal brain tissue showed microglia activation, based on enhanced IBA1 immuno-staining, in conjunction with astrogliosis, based on increased GFAP immuno-staining. Moderate axonal/myelin degeneration was observed in the sciatic nerve. Further studies need to be conducted to determine if this neuropathology is induced by the antibody effector function, or is an intrinsic property of targeting the TfR in brain. The results indicate that chronic treatment of Rhesus monkeys with a humanized hTfRMAb may have a narrow therapeutic index, with associated toxicity related to microglial activation and astrogliosis of the brain.

Reduction in Brain Heparan Sulfate with Systemic Administration of an IgG Trojan Horse-Sulfamidase Fusion Protein in the Mucopolysaccharidosis Type IIIA Mouse.

Mucopolysaccharidosis Type IIIA (MPSIIIA), also known as Sanfilippo A syndrome, is an inherited neurodegenerative disease caused by mutations in the lysosomal enzyme, N-sulfoglucosamine sulfohydrolase (SGSH), also known as sulfamidase. Mutations in the SGSH enzyme, the only mammalian heparan N-sulfatase, cause accumulation of lysosomal inclusion bodies in brain cells comprising heparan sulfate (HS) glycosaminoglycans (GAGs). Treatment of MPSIIIA with intravenous recombinant SGSH is not possible because this large molecule does not cross the blood-brain barrier (BBB). BBB penetration by SGSH was enabled in the present study by re-engineering this enzyme as an IgG-SGSH fusion protein, where the IgG domain is a chimeric monoclonal antibody (mAb) against the mouse transferrin receptor (TfR), designated the cTfRMAb. The IgG domain of the fusion protein acts as a molecular Trojan horse to deliver the enzyme into brain via transport on the endogenous BBB TfR. The cTfRMAb-SGSH fusion protein bound to the mouse TfR with high affinity, ED50 = 0.74 ± 0.07 nM, and retained high SGSH enzyme activity, 10 043 ± 1003 units/mg protein, which is comparable to recombinant human SGSH. Male and female MPSIIIA mice, null for the SGSH enzyme, were treated for 6 weeks with thrice-weekly intraperitoneal injections of vehicle, 5 mg/kg of the cTfRMAb alone, or 5 mg/kg of the cTfRMAb-SGSH fusion protein, starting at the age of 2 weeks, and were euthanized 1 week after the last injection. Brain and liver HS, as determined by liquid chromatography-mass spectrometry, were elevated 30-fold and 36-fold, respectively, in the MPSIIIA mouse. Treatment of the mice with the cTfRMAb-SGSH fusion protein caused a 70% and 85% reduction in brain and liver HS, respectively. The reduction in brain HS was associated with a 28% increase in latency on the rotarod test of motor activity in male mice. The mice exhibited no injection related reactions, and only a low titer end of study antidrug antibody response was observed. In conclusion, substantial reductions in brain pathologic GAGs in a murine model of MPSIIIA are produced by chronic systemic administration of an IgG-SGSH fusion protein engineered to penetrate the BBB via receptor-mediated transport.

Very High Plasma Concentrations of a Monoclonal Antibody against the Human Insulin Receptor Are Produced by Subcutaneous Injection in the Rhesus Monkey.

Brain penetration of recombinant protein drugs is possible following the re-engineering of the drug as an IgG fusion protein. The IgG domain is a monoclonal antibody (mAb) against an endogenous blood-brain barrier (BBB) receptor transporter, such as the insulin receptor. One such mAb targets the human insulin receptor (HIR) and is active in Rhesus monkeys. Prior work has measured the plasma pharmacokinetics of HIRMAb-derived fusion proteins following intravenous (IV) infusion. However, an alternative method of administration for chronic treatment of brain disease is the subcutaneous (SQ) route. The extent to which an antibody against the insulin receptor undergoes systemic distribution and clearance is unknown. Therefore, in the present study, the rate of plasma clearance of the HIRMAb is measured in Rhesus monkeys following IV or SQ administration of 3, 10, and 30 mg/kg doses of the antibody. The HIRMAb is readily absorbed into the systemic circulation following SQ injection with a 42% plasma bioavailability. The rate of plasma clearance of the antibody, 0.04-0.06 mL/min/kg, is the same following either IV or SQ administration. Owing to the slow rate of plasma clearance of the antibody, high concentrations of the HIRMAb are sustained in plasma for days after the SQ injection. The plasma concentration of the HIRMAb exceeds 0.8 mg/mL, which is 9% of the entire plasma IgG pool in the primate, after the SQ injection of the high dose, 30 mg/kg, of the antibody. In summary, the pharmacokinetics of plasma clearance of the HIRMAb are such that HIRMAb-derived fusion proteins can be developed as protein therapeutics for the brain with chronic SQ administration on a weekly or twice-weekly regimen.

Insulin Receptor Antibody-α-N-Acetylglucosaminidase Fusion Protein Penetrates the Primate Blood-Brain Barrier and Reduces Glycosoaminoglycans in Sanfilippo Type B Fibroblasts.

Mucopolysaccharidosis Type IIIB (MPSIIIB) is caused by mutations in the gene encoding the lysosomal enzyme, α-N-acetylglucosaminidase (NAGLU). MPSIIIB presents with severe disease of the central nervous system, but intravenous NAGLU enzyme replacement therapy has not been developed because the NAGLU enzyme does not cross the blood-brain barrier (BBB). A BBB-penetrating form of the enzyme was produced by re-engineering NAGLU as an IgG-enzyme fusion protein, where the IgG domain is a monoclonal antibody (mAb) against the human insulin receptor (HIR). The HIRMAb traverses the BBB via transport on the endogenous insulin receptor and acts as a molecular Trojan horse to ferry the fused NAGLU across the BBB from blood. The NAGLU was fused to the carboxyl terminus of each heavy chain of the HIRMAb via an extended 31-amino acid linker, and the fusion protein is designated HIRMAb-LL-NAGLU. The fusion protein retains high affinity binding to the HIR, and on a molar basis has an enzyme activity equal to that of recombinant human NAGLU. Treatment of MPSIIIB fibroblasts with the fusion protein normalizes intracellular NAGLU enzyme activity and reduces sulfate incorporation into intracellular glycosoaminoglycan. The fusion protein is targeted to the lysosomal compartment of the cells as shown by confocal microscopy. The fusion protein was radiolabeled with the [(125)I]-Bolton-Hunter reagent and injected intravenously in the adult Rhesus monkey. The fusion protein was rapidly cleared from plasma by all major peripheral organs. The high brain uptake of the fusion protein, 1% injected dose/brain, enables normalization of brain NAGLU enzyme activity with a therapeutic dose of 1 mg/kg. The HIRMAb-LL-NAGLU fusion protein is a new treatment of the brain in MPSIIIB, which can be administered by noninvasive intravenous infusion.

Insulin receptor antibody-sulfamidase fusion protein penetrates the primate blood-brain barrier and reduces glycosoaminoglycans in Sanfilippo type A cells.

Mutations in the lysosomal enzyme, N-sulfoglucosamine sulfohydrolase (SGSH), also called sulfamidase, cause accumulation of lysosomal inclusion bodies in the brain of children born with mucopolysaccharidosis type IIIA, also called Sanfilippo type A syndrome. Enzyme replacement therapy with recombinant SGSH does not treat the brain because the enzyme is a large molecule drug that does not cross the blood-brain barrier (BBB). A BBB-penetrating form of SGSH was produced by re-engineering the enzyme as an IgG fusion protein, where the IgG domain is a monoclonal antibody (mAb) against the human insulin receptor (HIR). The HIRMAb domain of the HIRMAb-SGSH fusion protein acts as a molecular Trojan horse to ferry the fused enzyme across the BBB. The HIRMAb-SGSH was produced in stably transfected host cells and purified to homogeneity by protein A chromatography. The fusion protein reacted with antibodies against either human IgG or SGSH on Western blotting. High affinity binding to the HIR was retained following SGSH fusion to the HIRMAb, with an EC50 of 0.33 ± 0.05 nM in an HIR binding ELISA. The SGSH enzyme activity of the HIRMAb-SGSH fusion protein was 4712 ± 388 units/mg protein based on a two-step fluorometric enzyme assay. The HIRMAb-SGSH was taken up by lysosomes in MPSIIIA fibroblasts, and treatment of these cells with the fusion protein caused an 83% reduction in sulfate incorporation into lysosomal glycosoaminoglycans. The HIRMAb-SGSH fusion protein was radiolabeled with the [(125)I]-Bolton-Hunter reagent and injected intravenously in the Rhesus monkey. The brain uptake of the fusion protein was high, ∼1% injected dose/brain. Calculations, based on this level of brain uptake, suggest normalization of brain SGSH enzyme activity is possible following administration of therapeutic doses of the fusion protein. These studies describe a novel IgG-SGSH fusion protein that is a new noninvasive treatment of the brain in MPS type IIIA.

Insulin receptor antibody-iduronate 2-sulfatase fusion protein: pharmacokinetics, anti-drug antibody, and safety pharmacology in Rhesus monkeys.

Mucopolysaccharidosis (MPS) Type II is caused by mutations in the gene encoding the lysosomal enzyme, iduronate 2-sulfatase (IDS). The majority of MPSII cases affect the brain. However, enzyme replacement therapy with recombinant IDS does not treat the brain, because IDS is a large molecule drug that does not cross the blood-brain barrier (BBB). To enable BBB penetration, IDS has been re-engineered as an IgG-IDS fusion protein, where the IgG domain is a monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb crosses the BBB via receptor-mediated transport on the endogenous BBB insulin receptor, and the HIRMAb domain of the fusion protein acts as a molecular Trojan horse to ferry the fused IDS into brain from blood. The present study reports on the first safety pharmacology and pharmacokinetics study of the HIRMAb-IDS fusion protein. Juvenile male Rhesus monkeys were infused intravenously (IV) weekly for 26 weeks with 0, 3, 10, or 30 mg/kg of the HIRMAb-IDS fusion protein. The plasma clearance of the fusion protein followed a linear pharmacokinetics profile, which was equivalent either with measurements of the plasma concentration of immunoreactive HIRMAb-IDS fusion protein, or with assays of plasma IDS enzyme activity. Anti-drug antibody (ADA) titers were monitored monthly, and the ADA response was primarily directed against the variable region of the HIRMAb domain of the fusion protein. No infusion related reactions or clinical signs of immune response were observed during the course of the study. A battery of safety pharmacology, clinical chemistry, and tissue histopathology showed no signs of adverse events, and demonstrate the safety profile of chronic treatment of primates with 3-30 mg/kg weekly IV infusion doses of the HIRMAb-IDS fusion protein.

Blood-brain barrier molecular trojan horse enables imaging of brain uptake of radioiodinated recombinant protein in the rhesus monkey.

Recombinant proteins are large molecule drugs that do not cross the blood-brain barrier (BBB). However, BBB-penetration of protein therapeutics is enabled by re-engineering the recombinant protein as IgG fusion proteins. The IgG domain is a monoclonal antibody (mAb) against an endogenous BBB receptor-mediated transport system, such as the human insulin receptor (HIR), and acts as a molecular Trojan horse to ferry the fused protein across the BBB. In the present study, a recombinant lysosomal enzyme, iduronate 2-sulfatase (IDS), is fused to the HIRMAb, and BBB penetration of the IDS alone vs the HIRMAb-IDS fusion protein is compared in the Rhesus monkey. Recombinant IDS and the HIRMAb-IDS fusion protein were radiolabeled with indirect iodination with the [(125)I]-Bolton-Hunter reagent and with direct iodination with Iodogen/[(125)I]-idodine. IDS and the HIRMAb-IDS fusion protein have comparable plasma pharmacokinetics and uptake by peripheral organs. IDS does not cross the BBB. The HIRMAb-IDS fusion protein crosses the BBB and the brain uptake is 1% of injected dose/brain. Brain imaging shows HIRMAb-IDS penetration to all parts of brain, and immunoprecipitation of brain radioactivity shows intact fusion protein in brain. The use of BBB molecular Trojan horses enables brain imaging of recombinant proteins that are re-engineered for BBB transport.

Disaggregation of amyloid plaque in brain of Alzheimer's disease transgenic mice with daily subcutaneous administration of a tetravalent bispecific antibody that targets the transferrin receptor and the Abeta amyloid peptide.

Anti-amyloid antibodies (AAA) are under development as new therapeutics that disaggregate the amyloid plaque in brain in Alzheimer's disease (AD). However, the AAAs are large molecule drugs that do not cross the blood-brain barrier (BBB), in the absence of BBB disruption. In the present study, an AAA was re-engineered for receptor-mediated transport across the BBB via the endogenous BBB transferrin receptor (TfR). A single chain Fv (ScFv) antibody form of an AAA was fused to the carboxyl terminus of each heavy chain of a chimeric monoclonal antibody (mAb) against the mouse TfR, and this produced a tetravalent bispecific antibody designated the cTfRMAb-ScFv fusion protein. Unlike a conventional AAA, which has a plasma half-time of weeks, the cTfRMAb-ScFv fusion protein is cleared from plasma in mice with a mean residence time of about 3 h. Therefore, a novel protocol was developed for the treatment of one year old presenilin (PS)-1/amyloid precursor protein (APP) AD double transgenic PSAPP mice, which were administered daily subcutaneous (sc) injections of 5 mg/kg of the cTfRMAb-ScFv fusion protein for 12 consecutive weeks. At the end of the treatment, brain amyloid plaques were quantified with confocal microscopy using both Thioflavin-S staining and immunostaining with the 6E10 antibody against Abeta amyloid fibrils. Fusion protein treatment caused a 57% and 61% reduction in amyloid plaque in the cortex and hippocampus, respectively. No increase in plasma immunoreactive Abeta amyloid peptide, and no cerebral microhemorrhage, was observed. Chronic daily sc treatment of the mice with the fusion protein caused no immune reactions and only a low titer antidrug antibody response. In conclusion, re-engineering AAAs for receptor-mediated BBB transport allows for reduction in brain amyloid plaque without cerebral microhemorrhage following daily sc treatment for 12 weeks.

Pharmacokinetics and brain uptake of an IgG-TNF decoy receptor fusion protein following intravenous, intraperitoneal, and subcutaneous administration in mice.

Tumor necrosis factor (TNF)-α is a proinflammatory cytokine active in the brain. Etanercept, the TNF decoy receptor (TNFR), does not cross the blood-brain barrier (BBB). The TNFR was re-engineered for BBB penetration as a fusion protein with a chimeric monoclonal antibody (mAb) against the mouse transferrin receptor (TfR), and this fusion protein is designated cTfRMAb-TNFR. The cTfRMAb domain of the fusion protein acts as a molecular Trojan horse and mediates transport via the endogenous BBB TfR. To support future chronic treatment of mouse models of neural disease with daily administration of the cTfRMAb-TNFR fusion protein, a series of pharmacokinetics and brain uptake studies in the mouse was performed. The cTfRMAb-TNFR fusion protein was radiolabeled and injected into mice via the intravenous, intraperitoneal (IP), or subcutaneous (SQ) routes of administration at doses ranging from 0.35 to 10 mg/kg. The distribution of the fusion protein into plasma following the IP or SQ routes was enhanced by increasing the injection dose from 3 to 10 mg/kg. The fusion protein demonstrated long circulation times with high metabolic stability following the IP or SQ routes of injection. The IP or SQ routes produced concentrations of the cTfRMAb-TNFR fusion protein in the brain that exceed by 20- to 50-fold the concentration of TNFα in pathologic conditions of the brain. The SQ injection is the preferred route of administration, as the level of cTfRMAb fusion protein produced in the brain is comparable to that generated with intravenous injection, and at a much lower plasma area under the concentration curve of the fusion protein as compared to IP administration.

Pharmacokinetics and brain uptake in the rhesus monkey of a fusion protein of arylsulfatase a and a monoclonal antibody against the human insulin receptor.

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder of the brain caused by mutations in the gene encoding the lysosomal sulfatase, arylsulfatase A (ASA). It is not possible to treat the brain in MLD with recombinant ASA, because the enzyme does not cross the blood-brain barrier (BBB). In the present investigation, a BBB-penetrating IgG-ASA fusion protein is engineered and expressed, where the ASA monomer is fused to the carboxyl terminus of each heavy chain of an engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb crosses the BBB via receptor-mediated transport on the endogenous BBB insulin receptor, and acts as a molecular Trojan horse to ferry the ASA into brain from blood. The HIRMAb-ASA is expressed in stably transfected Chinese hamster ovary cells grown in serum free medium, and purified by protein A affinity chromatography. The fusion protein retains high affinity binding to the HIR, EC50 = 0.34 ± 0.11 nM, and retains high ASA enzyme activity, 20 ± 1 units/mg. The HIRMAb-ASA fusion protein is endocytosed and triaged to the lysosomal compartment in MLD fibroblasts. The fusion protein was radio-labeled with the Bolton-Hunter reagent, and the [(125) I]-HIRMAb-ASA rapidly penetrates the brain in the Rhesus monkey following intravenous administration. Film and emulsion autoradiography of primate brain shows global distribution of the fusion protein throughout the monkey brain. These studies describe a new biological entity that is designed to treat the brain of humans with MLD following non-invasive, intravenous infusion of an IgG-ASA fusion protein.

IgG-enzyme fusion protein: pharmacokinetics and anti-drug antibody response in rhesus monkeys.

The chronic administration of recombinant fusion proteins in preclinical animal models may generate an immune response and the formation of antidrug antibodies (ADA). Such ADAs could alter the plasma pharmacokinetics of the fusion protein, and mask any underlying toxicity of the recombinant fusion protein. In the present study, a model IgG-enzyme fusion protein was evaluated with chronic dosing of rhesus monkeys. The IgG domain of the fusion protein is a genetically engineered monoclonal antibody (mAb) against the human insulin receptor (HIR), which is shown to cross-react with the primate insulin receptor. The enzyme domain of the fusion protein is human iduronidase (IDUA), the lysosomal enzyme mutated in Mucopolysaccharidosis Type I (MPSI). MPSI affects the brain, but enzyme replacement therapy is not effective for the brain, because IDUA does not cross the blood-brain barrier (BBB). The HIRMAb domain of the fusion protein acts as a molecular Trojan horse to deliver the IDUA across the BBB. The HIRMAb-IDUA fusion protein was administered to rhesus monkeys with weekly intravenous infusions of 3-30 mg/kg for 6 months, and the pharmacokinetics, immune response, and tissue toxicology were assessed. The pharmacokinetics of plasma clearance of the fusion protein was determined with measurements of plasma IDUA enzyme activity. ADAs formed during the course of the 6 months of treatment, as determined by a sandwich ELISA. However, the plasma clearance of the fusion protein at the start and end of the 6-month study was comparable at all drug doses. Fusion protein administration for 6 months showed no evidence of chronic tissue toxicity. These studies demonstrate that the immune response produced with chronic treatment of primates with an IgG-enzyme fusion protein has no effect on the pharmacokinetics of plasma clearance of the fusion protein.

Glycemic control and chronic dosing of rhesus monkeys with a fusion protein of iduronidase and a monoclonal antibody against the human insulin receptor.

Hurler's syndrome, or mucopolysaccharidosis type I, is a lysosomal storage disorder caused by mutations in the gene encoding the lysosomal enzyme iduronidase (IDUA). The disease affects both peripheral tissues and the central nervous system (CNS). Recombinant IDUA treatment does not affect the CNS, because IDUA does not cross the blood-brain barrier (BBB). To enable BBB penetration, human IDUA was re-engineered as an IgG-IDUA fusion protein, where the IgG domain is a genetically engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb penetrates the brain from the blood via transport on the endogenous BBB insulin receptor and acts as a molecular Trojan horse to deliver the fused IDUA to the brain. Before human testing, the HIRMAb-IDUA fusion protein was evaluated in a 6-month weekly dosing toxicology study at doses of 0, 3, 9, and 30 mg/kg/week of the fusion protein administered to 40 rhesus monkeys. The focus of the present study is the effect of chronic high dose administration of this fusion protein on plasma glucose and long-term glycemic control. The results show that the HIRMAb has weak insulin agonist activity and causes hypoglycemia at the high dose, 30 mg/kg, after intravenous infusion in normal saline. When dextrose is added to the saline infusion solution, no hypoglycemia is observed at any dose. An intravenous glucose tolerance test performed at the end of the 6 months of chronic treatment showed no change in glucose tolerance at any dose of the HIRMAb-IDUA fusion protein.

Brain-penetrating IgG-iduronate 2-sulfatase fusion protein for the mouse.

Mucopolysaccharidosis (MPS) type II (Hunter's syndrome) is caused by mutations in the iduronate 2-sulfatase (IDS) fusion protein. MPS-II affects the brain, and enzyme replacement therapy is not effective in the brain, because the enzyme does not cross the blood-brain barrier. To treat mouse models of MPS-II with brain-penetrating IDS, the lysosomal enzyme was reengineered as an IgG-IDS fusion protein. The mature human IDS was fused to the carboxyl terminus of both heavy chains of the chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and the fusion protein is designated cTfRMAb-IDS. The purity and identity of the fusion protein was confirmed by electrophoresis and Western blotting with antibodies to mouse IgG and human IDS. The EC50 of binding of the cTfRMAb-IDS fusion protein to the mouse TfR (0.85 ± 0.15 nM) was comparable to the EC50 of binding of the cTfRMAb (0.78 ± 0.05 nM). The IDS enzyme activity of the cTfRMAb-IDS fusion protein was 126 ± 1 nmol · h⁻¹ · µg⁻¹ protein. After intravenous injection in the mouse, the cTfRMAb-IDS fusion protein was rapidly removed from plasma and distributed to tissues, including brain and spinal cord. The uptake of the fusion protein by brain or spinal cord was 1.3 ± 0.1 and 2.2 ± 0.2% injected dose/g, respectively, which is 100-fold greater than the brain uptake of IDS alone. This work shows that a lysosomal sulfatase can be reengineered as an IgG-enzyme fusion protein that rapidly penetrates the brain after intravenous administration.

Neuroprotection with a brain-penetrating biologic tumor necrosis factor inhibitor.

Biologic tumor necrosis factor (TNF)-α inhibitors do not cross the blood-brain barrier (BBB). A BBB-penetrating TNF-α inhibitor was engineered by fusion of the extracellular domain of the type II human TNF receptor (TNFR) to the carboxyl terminus of the heavy chain of a mouse/rat chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and this fusion protein is designated cTfRMAb-TNFR. The cTfRMAb-TNFR fusion protein and etanercept bound human TNF-α with high affinity and K(D) values of 374 ± 77 and 280 ± 80 pM, respectively. Neuroprotection in brain in vivo after intravenous administration of the fusion protein was examined in a mouse model of Parkinson's disease. Mice were also treated with saline or a non-BBB-penetrating TNF decoy receptor, etanercept. After intracerebral injection of the nigral-striatal toxin, 6-hydroxydopamine, mice were treated every other day for 3 weeks. Treatment with the cTfRMAb-TNFR fusion protein caused an 83% decrease in apomorphine-induced rotation, a 67% decrease in amphetamine-induced rotation, a 82% increase in vibrissae-elicited forelimb placing, and a 130% increase in striatal tyrosine hydroxylase (TH) enzyme activity. In contrast, chronic treatment with etanercept, which does not cross the BBB, had no effect on neurobehavior or striatal TH enzyme activity. A bridging enzyme-linked immunosorbent assay specific for the cTfRMAb-TNFR fusion protein showed that the immune response generated in the mice was low titer. In conclusion, a biologic TNF inhibitor is neuroprotective after intravenous administration in a mouse model of neurodegeneration, providing that the TNF decoy receptor is reengineered to cross the BBB.

Delivery of a peptide radiopharmaceutical to brain with an IgG-avidin fusion protein.

The genetic engineering, host cell expression, purity, identity, and in vivo brain drug targeting properties are described for a new IgG-fusion protein, designated the cTfRMAb-AV fusion protein. Avidin (AV) is fused to the carboxyl terminus of the heavy chain of the genetically engineered chimeric monoclonal antibody (mAb) against the mouse transferrin receptor (TfR). The TfRMAb binds the endogenous TfR on the blood-brain barrier (BBB), which triggers transport into brain from blood. The cTfRMAb-AV fusion protein is produced in stably transfected Chinese hamster ovary cells, which are grown in serum free medium under conditions of biotin starvation. Following affinity purification, the purity and identity of the cTfRMAb-AV fusion protein were verified by electrophoresis and Western blotting. The affinity of the cTfRMAb for the murine TfR is high, K(I) = 4.6 ± 0.5 nM, despite fusion of avidin to the antibody heavy chain. The model peptide radiopharmaceutical used in this study is the Aß(1-40) amyloid peptide of Alzheimer's disease (AD), which in a brain-penetrating form could be used to image the amyloid plaque in brain in AD. The BBB transport and brain uptake of the [(125)I]-Aß(1-40) peptide was measured in mice injected intravenously (IV) with the peptide either free or conjugated to the cTfRMAb-AV fusion protein. The brain uptake of the free Aß(1-40) peptide was very low, 0.1% of injected dose (ID)/gram brain following i.v. injection, and is comparable to the brain uptake of a brain blood volume marker. However, the brain uptake of the Aß(1-40) peptide was high, 2.1 ± 0.2% ID/gram brain, following attachment of the biotinylated peptide to the cTfRMAb-AV fusion protein. Capillary depletion analysis showed the peptide penetrated the brain parenchyma from blood. The cTfRMAb-AV fusion protein is a new drug delivery system that can target to mouse brain monobiotinylated peptide or antisense radiopharmaceuticals.

Reversal of lysosomal storage in brain of adult MPS-I mice with intravenous Trojan horse-iduronidase fusion protein.

A mouse model of mucopolysaccharidosis (MPS) type I, which is null for the lysosomal enzyme, α-L-iduronidase (IDUA), is treated with intravenous, receptor-mediated enzyme replacement therapy of the brain. Murine IDUA, which does not cross the blood-brain barrier, is re-engineered for targeting to the brain as an IgG-enzyme fusion protein. The amino terminus of mature IDUA is fused to the carboxyl terminus of the heavy chain of a chimeric monoclonal antibody (mAb) against the murine transferrin receptor (TfR), and this fusion protein is designated cTfRMAb-IDUA. The cTfRMAb part of the fusion protein acts as a molecular Trojan horse to ferry the fused IDUA across the BBB and neuronal cell membrane via transport on the TfR. The IDUA enzyme activity of the fusion protein, 776 ± 79 units/µg protein, is comparable to recombinant IDUA. MPSI null mice, 6-8 months of age, were treated iv twice a week for 8 weeks with either saline or 1 mg/kg cTfRMAb-IDUA. The glycosoaminoglycan levels in liver, spleen, heart, and kidney were reduced by >95%, 80%, 36%, and 20%, respectively. Lysosomal inclusion bodies in the brain were quantitated from semithin sections stained with o-toluidine blue and normalized per 100 nucleoli per brain section. Treatment of the MPSI mice with the cTfRMAb-IDUA reduced intracellular lysosomal inclusion bodies by 73% in brain, as compared to the MPSI mice treated with saline. In conclusion, the reversal of pre-existing neural pathology in the brain of MPSI mice is possible with receptor-mediated enzyme replacement therapy of the brain.

Chronic dosing of mice with a transferrin receptor monoclonal antibody-glial-derived neurotrophic factor fusion protein.

Glial-derived neurotrophic factor (GDNF) is a potential neurotrophic factor treatment of brain disorders, including Parkinson's disease. However, GDNF does not cross the blood-brain barrier (BBB). A brain-penetrating form of GDNF, which is a fusion protein of human GDNF and a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), has been engineered for the mouse and is designated the cTfRMAb-GDNF fusion protein. The present study examined the potential toxic side effects and immune response after treatment of mice with twice-weekly cTfRMAb-GDNF fusion protein at a dose of 2 mg/kg i.v. for 12 consecutive weeks. Chronic treatment with the fusion protein caused no change in body weight, no change in 23 serum chemistry measurements, and no histologic changes in brain and cerebellum, kidney, liver, spleen, heart, or pancreas. Chronic treatment caused a low-titer immune response against the fusion protein, which was directed against the variable region of the antibody part of the fusion protein, with no immune response directed against either the constant region of the antibody or against GDNF. A pharmacokinetics and brain uptake study was performed at the end of the 12 weeks of treatment. There was no change in clearance of the fusion protein mediated by the TfR in peripheral organs, and there was no change in BBB permeability to the fusion protein mediated by the TfR at the BBB. The study shows no toxic side effects from chronic cTfRMAb-GDNF systemic treatment and the absence of neutralizing antibodies in vivo.

Brain penetrating IgG-erythropoietin fusion protein is neuroprotective following intravenous treatment in Parkinson's disease in the mouse.

Parkinson's disease (PD) is caused by oxidative stress, and erythropoietin (EPO) reduces oxidative stress in the brain. However, EPO cannot be developed as a treatment for PD, because EPO does not cross the blood-brain barrier (BBB). A brain penetrating form of human EPO has been developed wherein EPO is fused to a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), which is designated as the cTfRMAb-EPO fusion protein. The TfRMAb acts as a molecular Trojan horse to transport the fused EPO into brain via transport on the BBB TfR. Experimental PD was induced in adult mice by the intra-striatal injection of 6-hydroxydopamine, and PD mice were treated with 1mg/kg of the cTfRMAb-EPO fusion protein intravenously (IV) every other day starting 1 h after toxin injection. Following 3weeks of treatment mice were euthanized for measurement of striatal tyrosine hydroxylase (TH) enzyme activity. Mice treated with the cTfRMAb-EPO fusion protein showed a 306% increase in striatal TH enzyme activity, which correlated with improvement in three assays of neurobehavior. The blood hematocrit increased 10% at 2weeks, with no further changes at 3weeks of treatment. A sandwich ELISA showed the immune reaction against the cTfRMAb-EPO fusion protein was variable and low titer. In conclusion, the present study demonstrates that a brain penetrating form of EPO is neuroprotective in PD following IV administration with minimal effects on erythropoiesis.

Expression in CHO cells and pharmacokinetics and brain uptake in the Rhesus monkey of an IgG-iduronate-2-sulfatase fusion protein.

Sulfatases are potential therapeutic biopharmaceuticals, as mutations in sulfatase genes leads to inherited disease. Mucopolysaccharidosis (MPS) Type II is caused by mutations in the lysosomal enzyme, iduronate-2-sulfatase (IDS). MPS-II affects the brain and enzyme replacement therapy is ineffective for the brain, because IDS does not cross the blood-brain barrier (BBB). To deliver IDS across the human BBB, the sulfatase has been re-engineered as an IgG-sulfatase fusion protein with a genetically engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb part of the HIRMAb-IDS fusion protein acts as a molecular Trojan horse to ferry the fused IDS across the BBB. Chinese hamster ovary (CHO) cells were stably transfected to produce the HIRMAb-IDS fusion protein. The fusion protein was triaged to the lysosomal compartment of MPS-II fibroblasts based on confocal microscopy, and 300 ng/mL medium concentrations normalized IDS enzyme activity in the cells. The HIRMAb-IDS fusion protein was tritiated and injected intravenously into the adult Rhesus monkey at a low dose of 0.1 mg/kg. The IDS enzyme activity in plasma was elevated 10-fold above the endogenous level, and therapeutic plasma concentrations were generated in vivo. The uptake of the HIRMAb-IDS fusion protein in the brain was sufficiently high to produce therapeutic concentrations of IDS in the brain following IV administration of the fusion protein.