The Development and Characterization of an scFv-Fc Fusion-Based Gene Therapy to Reduce the Psychostimulant Effects of Methamphetamine Abuse.

Methamphetamine (METH) continues to be among the most addictive and abused drugs in the United States. Unfortunately, there are currently no Food and Drug Administration-approved pharmacological treatments for METH-use disorder. We have previously explored the use of adeno-associated viral (AAV)-mediated gene transfer of an anti-METH monoclonal antibody. Here, we advance our approach by generating a novel anti-METH single-chain variable fragment (scFv)-Fc fusion construct (termed 7F9-Fc) packaged into AAV serotype 8 vector (called AAV-scFv-Fc) and tested in vivo and ex vivo. A range of doses [1 × 1010, 1 × 1011, and 1 × 1012 vector copies (vcs)/mouse] were administered to mice, eliciting a dose-dependent expression of 7F9-Fc in serum with peak circulating concentrations of 48, 1785, and 3831 µg/ml, respectively. Expressed 7F9-Fc exhibited high-affinity METH binding, IC50 = 17 nM. Between days 21 and 35 after vector administration, at both 1 × 1011 vc/mouse and 1 × 1012 vc/mouse doses, the AAV-7F9-Fc gene therapy significantly decreased the potency of METH in locomotor assays. On day 116 post-AAV administration, mice expressing 7F9-Fc sequestered over 2.5 times more METH in the serum than vehicle-treated mice, and METH concentrations in the brain were reduced by 1.2 times the value for vehicle mice. These data suggest that an AAV-delivered anti-METH Fc fusion antibody could be used to persistently reduce concentrations of METH in the central nervous system. SIGNIFICANCE STATEMENT: In this manuscript, we describe the testing of a novel antimethamphetamine (METH) single-chain variable fragment-Fc fusion protein delivered in mice using gene therapy. The results suggest that the gene therapy delivery system can lead to the production of significant antibody concentrations that mitigate METH's psychostimulant effects in mice over an extended time period.

FVIII activity following FVIII protein infusion or FVIII gene transfer predicts the bleeding risk in hemophilia A rats.

BACKGROUND: Prophylactic replacement therapy in hemophilia A (HA) patients does not adequately prevent bleeds and arthropathic complications. A more refined understanding of the relationship between coagulation factor VIII (FVIII) levels and bleeding risk during protein prophylaxis, or with gene therapy, is needed to improve patient care. OBJECTIVES: Investigate this relationship in the HA rat, a model exhibiting spontaneous bleeds and development of arthropathy similar to HA patients. METHODS: Human B domain-deleted FVIII was delivered to HA rats via adeno-associated virus (AAV)-mediated gene transfer or multiple intravenous protein injections. RESULTS AND CONCLUSIONS: After 12 weeks of observation, both approaches significantly reduced bleeds per animal and increased the proportion of bleed-free animals compared with controls (43% vs 0%, respectively [AAV]; 75% vs 8%, respectively [injection]). Both approaches resulted in an anti-FVIII inhibitory response in 20% to 37% of treated animals, similar to HA patients. Inhibitory antibodies were refractory to clinical improvement (reduction of bleeds) only in the AAV-based prophylaxis. An integrated model-based analysis of data on FVIII exposure and bleeding events was performed. This predicted the bleeding risk at any given circulating FVIII activity. Specifically, 4.8 or 10 IU/dL FVIII (0.048 and 0.1 IU/mL, respectively) were predicted to reduce bleeding risk by 90% or 95%, respectively, compared with untreated controls. Our data establish the utility of the HA rat model in FVIII prophylaxis studies and describe how FVIII activity affects bleeding risk in this setting. These enable further studies on FVIII prophylaxis focusing on disease complications for an optimized treatment of HA patients.

Rotational thromboelastometry can predict the probability of bleeding events in a translational rat model of haemophilia A following gene-based FVIIa prophylaxis.

INTRODUCTION: Monitoring of clinical effectiveness of bypassing agents in haemophilia patients is hampered by the lack of validated laboratory assays. Thromboelastography (TEG) and rotational thromboelastometry (ROTEM) have been evaluated for predicting clinical effectiveness of bypassing agents, however, with limited success. AIM: Application of a longitudinal model-based approach may allow for a quantitative characterization of the link between ROTEM parameters and the probability of bleeding events. METHODS: We analyse longitudinal data from haemophilia A rats receiving gene-based FVIIa prophylaxis in terms of total circulatory levels of FVII/FVIIa, clotting time (CT) measured using ROTEM and the probability of bleeding events. RESULTS: Using population pharmacokinetic-pharmacodynamic (PKPD) modelling, a PK-CT-repeated time-to-event (RTTE) model was developed composed of three submodels (a) a FVII/FVIIa PK model, (b) a PK-CT model describing the relationship between predicted FVIIa expression and CT and (c) a RTTE model describing the probability of bleeding events as a function of CT. The developed PK-CT-RTTE model accurately described the vector dose-dependent plasma concentration-time profile of total FVII/FVIIa and the exposure-response relationship between AAV-derived FVIIa expression and CT. Importantly, the developed model accurately described the occurrence of bleeding events over time in a quantitative manner, revealing a linear relationship between predicted change from baseline CT and the probability of bleeding events. CONCLUSION: Using PK-CT-RTTE modelling, we demonstrated that ROTEM parameters can accurately predict the probability of bleeding events in a translational animal model of haemophilia A.

Gene-based FVIIa prophylaxis modulates the spontaneous bleeding phenotype of hemophilia A rats.

A sizable proportion of hemophilia inhibitor patients fails immune tolerance induction and requires bypass agents for long-term bleed management. Recombinant human-activated coagulation Factor VII (rhFVIIa) is an on-demand bypass hemostatic agent for bleeds in hemophilia inhibitor patients. Prophylactic use of rhFVIIa may enable sustained hemostatic management of inhibitor patients, but the critical relationship of rhFVIIa circulating levels and clinical outcome in that setting remains unclear. To address this in vivo, we used the rat hemophilia A (HA) model that exhibits spontaneous bleeds and allows longitudinal studies with sufficient statistical power. We simulated activated Factor VII (FVIIa) prophylaxis by adeno-associated virus (AAV) gene transfer of a rat FVIIa transgene. Compared with naive HA animals, rat FVIIa continuous expression affected the overall observed bleeds, which were resolved with on-demand administration of recombinant rat FVIIa. Specifically, although 91% of naive animals exhibited bleeds, this was reduced to 83% and 33% in animals expressing less than 708 ng/mL (<14 nM) and at least 708 ng/mL (≥14 nM) rat FVIIa, respectively. No bleeds occurred in animals expressing higher than 1250 ng/mL (>25 nM). Rat FVIIa expression of at least 708 ng/mL was also sufficient to normalize the blood loss after a tail vein injury. Continuous, AAV-mediated rat FVIIa transgene expression had no apparent adverse effects in the hemostatic system of HA rats. This work establishes for the first time a dose dependency and threshold of circulating FVIIa antigen levels for reduction or complete elimination of bleeds in a setting of FVIIa-based HA prophylaxis.

A Phenome-Wide Association Study Uncovers a Pathological Role of Coagulation Factor X during Acinetobacter baumannii Infection.

Coagulation and inflammation are interconnected, suggesting that coagulation plays a key role in the inflammatory response to pathogens. A phenome-wide association study (PheWAS) was used to identify clinical phenotypes of patients with a polymorphism in coagulation factor X. Patients with this single nucleotide polymorphism (SNP) were more likely to be hospitalized with hemostatic and infection-related disorders, suggesting that factor X contributes to the immune response to infection. To investigate this, we modeled infections by human pathogens in a mouse model of factor X deficiency. Factor X-deficient mice were protected from systemic Acinetobacter baumannii infection, suggesting that factor X plays a role in the immune response to A. baumannii Factor X deficiency was associated with reduced cytokine and chemokine production and alterations in immune cell population during infection: factor X-deficient mice demonstrated increased abundance of neutrophils, macrophages, and effector T cells. Together, these results suggest that factor X activity is associated with an inefficient immune response and contributes to the pathology of A. baumannii infection.

Development and testing of AAV-delivered single-chain variable fragments for the treatment of methamphetamine abuse.

Methamphetamine (METH) substance abuse disorders have major impact on society, yet no medications have proven successful at preventing METH relapse or cravings. Anti-METH monoclonal antibodies can reduce METH brain concentrations; however, this therapy has limitations, including the need for repeated dosing throughout the course of addiction recovery. An adeno-associated viral (AAV)-delivered DNA sequence for a single-chain variable fragment could offer long-term, continuous expression of anti-METH antibody fragments. For these studies, we injected mice via tail vein with 1 x 10(12) vector genomes of two AAV8 scFv constructs and measured long-term expression of the antibody fragments. Mice expressed each scFv for at least 212 days, achieving micromolar scFv concentrations in serum. In separate experiments 21 days and 50 days after injecting mice with AAV-scFvs mice were challenged with METH in vivo. The circulating scFvs were capable of decreasing brain METH concentrations by up to 60% and sequestering METH in serum for 2 to 3 hrs. These results suggest that AAV-delivered scFv could be a promising therapy to treat methamphetamine abuse.

8(th) Symposium on Hemostasis: Translational and Basic Science Discoveries.

It has been 14 years since the first symposium on hemostasis at UNC Chapel Hill that focused primarily on the tissue factor (TF) and Factor VIIa (FVIIa) biology, biochemistry and translational work for the treatment of bleeding. Concepts, mechanistic data and therapeutic agents have since emerged that permeate not only aspects of the TF and FVIIa functions, but also broader processes in hemostasis and thrombosis. These processes involve circulating proteins, receptors, cells and cellular components that interact within the coagulation system as well as with additional systems that are dysregulated in disorders seemingly unrelated to bleeding/thrombosis. The reviews in this symposium provide the research background to understand such interactions and integrations.

Sustained correction of FVII deficiency in dogs using AAV-mediated expression of zymogen FVII.

Factor VII (FVII) deficiency is a rare autosomal recessive bleeding disorder treated by infusion of fresh-frozen plasma, plasma-derived FVII concentrates and low-dose recombinant activated FVII. Clinical data suggest that a mild elevation of plasma FVII levels (>10% normal) results in improved hemostasis. Research dogs with a G96E missense FVII mutation (FVII-G96E) have <1% FVII activity. By western blot, we show that they have undetectable plasmatic antigen, thus representing the most prevalent type of human FVII deficiency (low antigen/activity). In these dogs, we determine the feasibility of a gene therapy approach using liver-directed, adeno-associated viral (AAV) serotype 8 vector delivery of a canine FVII (cFVII) zymogen transgene. FVII-G96E dogs received escalating AAV doses (2E11 to 4.95E13 vector genomes [vg] per kg). Clinically therapeutic expression (15% normal) was attained with as low as 6E11 vg/kg of AAV and has been stable for >1 year (ongoing) without antibody formation to the cFVII transgene. Sustained and supraphysiological expression of 770% normal was observed using 4.95E13 vg/kg of AAV (2.6 years, ongoing). No evidence of pathological activation of coagulation or detrimental animal physiology was observed as platelet counts, d-dimer, fibrinogen levels, and serum chemistries remained normal in all dogs (cumulative 6.4 years). We observed a transient and noninhibitory immunoglobulin G class 2 response against cFVII only in the dog receiving the highest AAV dose. In conclusion, in the only large-animal model representing the majority of FVII mutation types, our data are first to demonstrate the feasibility, safety, and long-term duration of AAV-mediated correction of FVII deficiency.

The endothelial protein C receptor enhances hemostasis of FVIIa administration in hemophilic mice in vivo.

Recombinant activated human factor VII (rhFVIIa) is an established hemostatic agent in hemophilia, but its mechanism of action remains unclear. Although tissue factor (TF) is its natural receptor, rhFVIIa also interacts with the endothelial protein C receptor (EPCR) through its γ-carboxyglutamic acid (Gla) domain, with unknown hemostatic consequences in vivo. Here, we study whether EPCR facilitates rhFVIIa hemostasis in hemophilia using a mouse model system. Mouse activated FVII (mFVIIa) is functionally homologous to rhFVIIa, but binds poorly to mouse EPCR (mEPCR). We modified mFVIIa to gain mEPCR binding using 3 amino acid changes in its Gla domain (L4F/L8M/W9R). The resulting molecule mFVIIa-FMR specifically bound mEPCR in vitro and in vivo and was identical to mFVIIa with respect to TF affinity and procoagulant functions. In macrovascular injury models, hemophilic mice administered mFVIIa-FMR exhibited superior hemostatic activity compared with mFVIIa. This was abolished by blocking mEPCR and was absent in ex vivo whole blood coagulation assays, implicating a specific mFVIIa-FMR and endothelial mEPCR interaction. Because mFVIIa-FMR models the TF-dependent and EPCR binding properties of rhFVIIa, our data unmask a novel contribution of EPCR on the action of rhFVIIa administration in hemophilia, prompting the rational design of improved and safer rhFVIIa therapeutics.

Cellular localization and characterization of cytosolic binding partners for Gla domain-containing proteins PRRG4 and PRRG2.

The genes encoding a family of proteins termed proline-rich γ-carboxyglutamic acid (PRRG) proteins were identified and characterized more than a decade ago, but their functions remain unknown. These novel membrane proteins have an extracellular γ-carboxyglutamic acid (Gla) protein domain and cytosolic WW binding motifs. We screened WW domain arrays for cytosolic binding partners for PRRG4 and identified novel protein-protein interactions for the protein. We also uncovered a new WW binding motif in PRRG4 that is essential for these newly found protein-protein interactions. Several of the PRRG-interacting proteins we identified are essential for a variety of physiologic processes. Our findings indicate possible novel and previously unidentified functions for PRRG proteins.

Gene-based continuous expression of FVIIa for the treatment of hemophilia.

Qualitative or quantitative defects in the genes for coagulation factors VIII (FVIII) or IX (FIX) result in a life-threatening, bleeding phenotype (hemophilia A (HA) or B (HB), respectively). Although hemophilia treatment by clotting factor replacement is effective, a proportion of patients develop neutralizing antibodies (inhibitors) to the infused factor that complicate the disease management. For inhibitor patients, recombinant human activated coagulation Factor VII (rhFVIIa), when administered at therapeutic doses, has been shown to bypass the deficiency in FVIII or FIX and result in hemostasis. As an alternative to this protein infusion therapy, a gene-based approach for the treatment of hemophilia with inhibitors has been developed, using continuous expression of a transgene coding for FVIIa following viral-mediated delivery. This approach was validated in hemophilic mice and, notably, in dogs as a model that closely resembles the human disease. In particular, liver-directed FVIIa gene delivery in hemophilic dogs resulted in multi-year transgene expression that ameliorated the bleeding phenotype, without thrombotic complications. These data support the gene-based FVIIa expression as a novel bypass therapy for hemophilia with inhibitors.

A zymogen-like factor Xa variant corrects the coagulation defect in hemophilia.

Effective therapies are needed to control excessive bleeding in a range of clinical conditions. We improve hemostasis in vivo using a conformationally pliant variant of coagulation factor Xa (FXa(I16L)) rendered partially inactive by a defect in the transition from zymogen to active protease. Using mouse models of hemophilia, we show that FXa(I16L) has a longer half-life than wild-type FXa and does not cause excessive activation of coagulation. Once clotting mechanisms are activated to produce its cofactor FVa, FXa(I16L) is driven to the protease state and restores hemostasis in hemophilic animals upon vascular injury. Moreover, using human or murine analogs, we show that FXa(I16L) is more efficacious than FVIIa, which is used to treat bleeding in hemophilia inhibitor patients. FXa(I16L) may provide an effective strategy to enhance blood clot formation and act as a rapid pan-hemostatic agent for the treatment of bleeding conditions.

ARFI ultrasound monitoring of hemorrhage and hemostasis in vivo in canine von Willebrand disease and hemophilia.

A validated method for assessing hemostasis in vivo is critical for testing the hemostatic efficacy of therapeutic agents designed for patients with bleeding disorders such as von Willebrand disease (VWD) and hemophilia A. We hypothesize that rate of bleeding and time to hemostasis can be monitored in vivo by acoustic radiation force impulse (ARFI) ultrasound. We performed ARFI imaging following 12-gauge needle puncture of hind limb muscle encompassing an ∼2 mm vein in six normal, eight naïve hemophilia A before and after infusing canine factor VIII, three hemophilia A expressing canine factor VIIa following gene transfer, and two naïve VWD dogs. Serial data sets were processed with custom software to (1) estimate the rate of hemorrhage and (2) estimate the time of hemostasis onset. The rate of hemorrhage during the first 30 min following puncture was markedly increased in the VWD dogs relative to normal but was not significantly different between normal, naïve hemophilia A or hemophilia A expressing cFVIIa. ARFI-derived times to hemostasis were significantly longer in naïve hemophilia A dogs than in normal dogs and were shortened by canine coagulation factors VIII and VIIa. These data support our hypothesis that rate of hemorrhage and time to hemostasis in vivo in response to a standardized hemostatic challenge can be detected by ARFI ultrasound in canine models of VWD and hemophilia. These data also suggest that the ARFI-monitored hemostatic challenge is relevant for in vivo testing of the hemostatic efficacy of therapeutic clotting factor replacement products used to treat inherited bleeding disorders.

Mutation in the factor VII hepatocyte nuclear factor 4α-binding site contributes to factor VII deficiency.

Severe coagulant factor VII (FVII) deficiency in postpubertal dizygotic twin males results from two point mutations in the FVII gene, a promoter region T→C transition at -60 and a His-to-Arg substitution at amino acid 348; both mutations prevent persistence of plasma functional FVII. This report documents longitudinal laboratory measurements from infancy to adulthood of FVII coagulant activity (FVII:C) in the twin FVII-deficient patients; it also details specific biochemical analyses of the -60 T→C mutation. The results revealed FVII:C levels of less than 1% in infancy that remain severely decreased through puberty and into adulthood. In-vitro analyses utilizing hepatocyte nuclear factor 4α (HNF4α) co-transfection and a chromatin immunoprecipitation assay indicate that the -60 T→C mutation severely diminishes functional interaction between the FVII promoter and transcription factor HNF4α. The importance of interaction between the FVII gene and HNF4α in normal FVII expression provides an in-vivo illustration of the regulated expression of an autosomal gene encoding a coagulation protein. The constancy of FVII:C and peripubertal patient symptomatology reported here illustrates androgen-independent expression in contrast to expression with an analogous mutation in the promoter region of the gene encoding coagulation FIX.

Catalytic domain modification and viral gene delivery of activated factor VII confers hemostasis at reduced expression levels and vector doses in vivo.

Catalytic domain variants of activated factor VII (FVIIa) with enhanced hemostatic properties are highly attractive for the treatment of bleeding disorders via gene-based therapy. To explore this in a hemophilic mouse model, we characterized 2 variants of murine activated FVII (mFVIIa-VEAY and mFVIIa-DVQ) with modified catalytic domains, based on recombinant human FVIIa (rhFVIIa) variants. Using purified recombinant proteins, we showed that murine FVIIa (mFVIIa) and variants had comparable binding to human and murine tissue factor (TF) and exhibited similar extrinsic coagulant activity. In vitro in the absence of TF, the variants showed a 6- to 17-fold enhanced proteolytic and coagulant activity relative to mFVIIa, but increased inactivation by antithrombin. Gene delivery of mFVIIa-VEAY resulted in long-term, effective hemostasis at 5-fold lower expression levels relative to mFVIIa in hemophilia A mice or in hemophilia B mice with inhibitors to factor IX. However, expression of mFVIIa-VEAY at 14-fold higher than therapeutic levels resulted in a progressive mortality to 70% within 6 weeks after gene delivery. These results are the first demonstration of the hemostatic efficacy of continuous expression, in the presence or absence of inhibitors, of a high-activity gene-based FVIIa variant in an animal model of hemophilia.

Long-term expression of canine FVIIa in hemophilic dogs.

The traditional treatment for hemophilia has been by protein replacement. This is complicated by the development of inhibitory antibodies to the infused factor (Factor VIII [FVIII] or Factor IX [FIX]). High-dose infusion of recombinant activated Factor VII (rFVIIa) has a long track record of success in such patients but its short-half life limits its use in prophylaxis. We have developed an alternative strategy by continuous expression of activated FVII from a transgene that is introduced into the host by means of gene transfer. For this, we modified the FVII cDNA to introduce a cleavage site between the light and heavy chain that would generate a FVII molecule secreted in the two-chain, activated form. Using viral-mediated delivery and expression from a liver-specific promoter (or as a transgenic approach) we demonstrated the long-term hemostatic efficacy of this approach in hemophilic mice. Subsequently, we used the canine version of our modified FVII and via gene transfer, showed multi-year phenotypic correction in hemophilic dogs, clearly evident by the absence of spontaneous bleeds that are characteristic in this animal model. No adverse events were observed throughout the study. Remarkably, clinical benefit was also observed in one treated dog despite the lack of hemostatic effect by in vitro assays. Overall, the results in this large animal model of hemophilia indicate the potential of gene-based continuous expression of activated FVII as a therapeutic strategy for hemophilia or other coagulation defects currently treated by rFVIIa.

Successful treatment of canine hemophilia by continuous expression of canine FVIIa.

Continuous expression of activated factor VII (FVIIa) via gene transfer is a potential therapeutic approach for hemophilia patients with or without inhibitory antibodies to human factor VIII (FVIII) or IX (FIX). Here, we investigate whether gene transfer of an engineered canine FVIIa (cFVIIa) transgene can affect hemostasis in a canine model of hemophilia, a good predictor of efficacy of hemophilia treatments. Purified recombinant cFVIIa exhibited 12-fold higher tissue factor-dependent activity than purified recombinant zymogen cFVII. Subsequently, we generated a serotype 8 recombinant adeno-associated viral vector expressing cFVIIa from a liver-specific promoter. Vector delivery via the portal vein in hemophilia A and B dogs was well tolerated, and long-term expression of cFVIIa resulted in a shortening of the prothrombin time, partial correction of the whole blood clotting time and thromboelastography parameters, and a complete absence of spontaneous bleeding episodes. No evidence of hepatotoxicity, thrombotic complications, or inhibitory immune response was found. These data provide the first evidence for in vivo efficacy and safety of continuously expressed FVIIa as a FVIII/FIX-bypassing agent in a large animal model of hemophilia, avoiding the risk of inhibitor formation associated with bolus FVIII or FIX infusion.

Over-expression of factor VIIa in vivo.

Although recombinant factor VIIa has been shown to bypass the deficiency in factor VIII or factor IX, efforts to reduce factor consumption and subsequently treatment cost have been focused on continuous infusion regimens with variable success. Using an engineered factor VII that can be secreted as factor VIIa, viral-mediated delivery of this transgene in the mouse liver resulted in phenotypic correction of murine hemophilia B, at expression levels of approximately 1 microg/ml. This model of factor VIIa continuous infusion can be further used to address the potential risk of thrombosis, in a transgenic model approach. The relative contribution of the extrinsic and/or intrinsic pathways in such risk can be dissected by crossing over-expressing FVIIa mice to recently described models of low expression of tissue factor or factor X. Our current data support the potential of factor VIIa gene transfer as a therapeutic alternative to bolus dosing but effective monitoring and modulation of factor VIIa expression will most likely be required.