Anti-colchicine Fab fragments prevent lethal colchicine toxicity in a porcine model: a pharmacokinetic and clinical study.

BACKGROUND: Colchicine poisoning is commonly lethal. Colchicine-specific Fab fragments increase rat urinary colchicine clearance and have been associated with a good outcome in one patient. We aimed to develop a porcine model of colchicine toxicity to study the pharmacokinetics and efficacy of ovine Fab. METHODS: A Göttingen minipig critical care model was established and serial blood samples taken for colchicine and Fab pharmacokinetics, clinical chemistry, and haematology. Animals were euthanised when the mean arterial pressure fell below 45 mmHg without response to vasopressor, or at study completion. RESULTS: Initial studies indicated that oral dosing produced variable pharmacokinetics and time-to-euthanasia. By contrast, intravenous infusion of 0.25 mg/kg colchicine over 1 h produced reproducible pharmacokinetics (AUC0-20 343 [SD = 21] µg/L/h), acute multi-organ injury, and cardiotoxicity requiring euthanasia a mean of 22.5 (SD = 3.2) h after dosing. A full-neutralising equimolar Fab dose given 6 h after the infusion (50% first hour, 50% next 6 h [to reduce renal-loss of unbound Fab]) produced a 7.35-fold increase in plasma colchicine (AUC0-20 2,522 [SD = 14] µg/L/h), and removed all free plasma colchicine, but did not prevent toxicity (euthanasia at 29.1 [SD = 3.4] h). Earlier administration over 1 h of the full-neutralising dose, 1 or 3 h after the colchicine, produced a 12.9-fold (AUC0-20 4,433 [SD = 607] µg/L/h) and 6.0-fold (AUC0-20 2,047 [SD = 51] µg/L/h) increase in plasma colchicine, respectively, absence of free plasma colchicine until 20 h, and survival to study end without marked cardiotoxicity. CONCLUSIONS: Colchicine-specific Fab given early, in equimolar dose, bound colchicine, eliciting its movement into the blood, and preventing severe toxicity. Clinical studies are now needed to determine how soon this antidote must be given to work in human poisoning.

Post-exposure treatment of non-human primates lethally infected with Ebola virus with EBOTAb, a purified ovine IgG product.

Despite sporadic outbreaks of Ebola virus (EBOV) over the last 4 decades and the recent public health emergency in West Africa, there are still no approved vaccines or therapeutics for the treatment of acute EBOV disease (EVD). In response to the 2014 outbreak, an ovine immunoglobulin therapy was developed, termed EBOTAb. After promising results in the guinea pig model of EBOV infection, EBOTAb was tested in the cynomolgus macaque non-human primate model of lethal EBOV infection. To ensure stringent therapeutic testing conditions to replicate likely clinical usage, EBOTAb was first delivered 1, 2 or 3 days post-challenge with a lethal dose of EBOV. Results showed a protective effect of EBOTAb given post-exposurally, with survival rates decreasing with increasing time after challenge. Viremia results demonstrated that EBOTAb resulted in a decreased circulation of EBOV in the bloodstream. Additionally, assay of liver enzymes and histology analysis of local tissues identified differences between EBOTAb-treated and untreated groups. The results presented demonstrate that EBOTAb conferred protection against EBOV when given post-exposure and should be explored and developed further as a potential intervention strategy for future outbreaks, which are likely to occur.

Post-exposure treatment of Ebola virus disease in guinea pigs using EBOTAb, an ovine antibody-based therapeutic.

Ebola virus (EBOV) is highly pathogenic, with a predisposition to cause outbreaks in human populations accompanied by significant mortality. An ovine polyclonal antibody therapy has been developed against EBOV, named EBOTAb. When tested in the stringent guinea pig model of EBOV disease, EBOTAb has been shown to confer protection at levels of 83.3%, 50% and 33.3% when treatment was first started on days 3, 4 and 5 post-challenge, respectively. These timepoints of when EBOTAb treatment was initiated correspond to when levels of EBOV are detectable in the circulation and thus mimic when treatment would likely be initiated in human infection. The effects of EBOTAb were compared with those of a monoclonal antibody cocktail, ZMapp, when delivered on day 3 post-challenge. Results showed ZMapp to confer complete protection against lethal EBOV challenge in the guinea pig model at this timepoint. The data reported demonstrate that EBOTAb is an effective treatment against EBOV disease, even when delivered late after infection.

Development of a Cost-effective Ovine Polyclonal Antibody-Based Product, EBOTAb, to Treat Ebola Virus Infection.

The highly glycosylated glycoprotein spike of Ebola virus (EBOV-GP1,2) is the primary target of the humoral host response. Recombinant EBOV-GP ectodomain (EBOV-GP1,2ecto) expressed in mammalian cells was used to immunize sheep and elicited a robust immune response and produced high titers of high avidity polyclonal antibodies. Investigation of the neutralizing activity of the ovine antisera in vitro revealed that it neutralized EBOV. A pool of intact ovine immunoglobulin G, herein termed EBOTAb, was prepared from the antisera and used for an in vivo guinea pig study. When EBOTAb was delivered 6 hours after challenge, all animals survived without experiencing fever or other clinical manifestations. In a second series of guinea pig studies, the administration of EBOTAb dosing was delayed for 48 or 72 hours after challenge, resulting in 100% and 75% survival, respectively. These studies illustrate the usefulness of EBOTAb in protecting against EBOV-induced disease.

Immunological cross-reactivity and neutralisation of European viper venoms with the monospecific Vipera berus antivenom ViperaTAb.

Medically important cases of snakebite in Europe are predominately caused by European vipers of the genus Vipera. The mainstay of snakebite therapy is polyclonal antibody therapy, referred to as antivenom. Here we investigate the capability of the monospecific V. berus antivenom, ViperaTAb®, to cross-react with, and neutralise lethality induced by, a variety of European vipers. Using ELISA and immunoblotting, we find that ViperaTAb® antibodies recognise and bind to the majority of toxic components found in the venoms of the Vipera species tested at comparably high levels to those observed with V. berus. Using in vivo pre-clinical efficacy studies, we demonstrate that ViperaTAb® effectively neutralises lethality induced by V. berus, V. aspis, V. ammodytes and V. latastei venoms and at much higher levels than those outlined by regulatory pharmacopoeial guidelines. Notably, venom neutralisation was found to be superior to (V. berus, V. aspis and V. latastei), or as equally effective as (V. ammodytes), the monospecific V. ammodytes "Zagreb antivenom", which has long been successfully used for treating European snake envenomings. This study suggests that ViperaTAb® may be a valuable therapeutic product for treating snakebite by a variety of European vipers found throughout the continent.

Single-reagent one-step procedures for the purification of ovine IgG, F(ab')2 and Fab antivenoms by caprylic acid.

Antivenoms are typically produced in horses or sheep and often purified using salt precipitation of immunoglobulins or F(ab')2 fragments. Caprylic (octanoic) acid fractionation of antiserum has the advantage of not precipitating the desired antibodies, thereby avoiding potential degradation that can lead to the formation of aggregates, which may be the cause of some adverse reactions to antivenoms. Here we report that when optimising the purification of immunoglobulins from ovine antiserum raised against snake venom, caprylic acid was found to have no effect on the activity of the enzymes pepsin and papain, which are employed in antivenom manufacturing to digest immunoglobulins to obtain F(ab')2 and Fab fragments, respectively. A "single-reagent" method was developed for the production of F(ab')2 antivenom whereby whole ovine antiserum was mixed with both caprylic acid and pepsin and incubated for 4h at 37°C. For ovine Fab antivenom production from whole antiserum, the "single reagent" comprised of caprylic acid, papain and l-cysteine; after incubation at 37°C for 18-20h, iodoacetamide was added to stop the reaction. Caprylic acid facilitated the precipitation of albumin, resulting in a reduced protein load presented to the digestion enzymes, culminating in substantial reductions in processing time. The ovine IgG, F(ab')2 and Fab products obtained using these novel caprylic acid methods were comparable in terms of yield, purity and specific activity to those obtained by multi-step conventional salt fractionation with sodium sulphate.

Long-term physicochemical and immunological stability of a liquid formulated intact ovine immunoglobulin-based antivenom.

An antivenom should be stable under the conditions that it will be both transferred and stored. Thus instability may lead to a loss of efficacy and an increased incidence and severity of adverse effects. Stability is a particular problem in countries where the temperatures and humidity are high. Here we investigate the stability of a liquid-formulated, intact ovine immunoglobulin-based antivenom, EchiTAbG™, which is used extensively in Nigeria to treat envenoming by the West African saw-scaled viper, Echis ocellatus. Ampoules of antivenom were assessed as to their specific antibody content by small scale affinity chromatography and their purity by size exclusion gel filtration and turbidity. Three different batches of the antivenom revealed no significant changes, using these assessment techniques, during 42 months storage at 4 °C or at ambient temperature, followed by one month at 37 °C. These real-time studies indicate that the antivenom remains stable for a minimum of 3.5 years and that it can be exposed to tropical temperatures without any loss in immunoglobulin binding activity. This further highlights the clinical utility of liquid formulated ovine IgG antivenoms by demonstrating their retention of potency in the event of a short term failing in the cold chain.

Development and evaluation of an ovine antibody-based platform for treatment of Clostridium difficile infection.

Treatment of Clostridium difficile is a major problem as a hospital-associated infection which can cause severe, recurrent diarrhea. The currently available antibiotics are not effective in all cases and alternative treatments are required. In the present study, an ovine antibody-based platform for passive immunotherapy of C. difficile infection is described. Antibodies with high toxin-neutralizing titers were generated against C. difficile toxins A and B and were shown to neutralize three sequence variants of these toxins (toxinotypes) which are prevalent in human C. difficile infection. Passive immunization of hamsters with a mixture of toxin A and B antibodies protected them from a challenge with C. difficile spores in a dose-dependent manner. Antibodies to both toxins A and B were required for protection. The administration of toxin A and B antibodies up to 24 h postchallenge was found to reduce significantly the onset of C. difficile infection compared to nonimmunized controls. Protection from infection was also demonstrated with key disease isolates (ribotypes 027 and 078), which are members of the hypervirulent C. difficile clade. The ribotype 027 and 078 strains also have the capacity to produce an active binary toxin and these data suggest that neutralization of this toxin is unnecessary for the management of infection induced by these strains. In summary, the data suggest that ovine toxin A and B antibodies may be effective in the treatment of C. difficile infection; their potential use for the management of severe, fulminant cases is discussed.

Formulation of a liquid ovine Fab-based antivenom for the treatment of envenomation by the Nigerian carpet viper (Echis ocellatus).

Most antivenoms are required for use in tropical or sub-tropical countries where temperatures may be high and refrigerated storage unavailable or unreliable. Although freeze-dried products can be expected to have maximal storage stability, many antivenoms are manufactured in liquid form to lower their cost and ease their use. We developed a liquid formulation of an existing freeze-dried antivenom against the carpet viper (Echis ocellatus) for use in Nigeria. When Fab fragments, prepared from antisera raised in sheep, were exposed to pH between 3.0 and 8.0, time and temperature dependent precipitation of some populations of the Fab product occurred over the range 4.5-7.0. Formulation of the Fab fragments in acetate buffer (20 mM) at pH 4.0 provided a clear, colourless, particle-free and stable product which retained neutralising potency for at least one year at 4 degrees C and room temperature. An accelerated study indicated stability for at least 4 weeks at 37 degrees C which may be considered equivalent to four years at 4 degrees C. The presence of sugars (sorbitol at 20 g/l or mannitol at 50 g/l) or sodium chloride (153 mM) had no effect in stabilising Fab at high temperature (37 degrees C) and, in agreement with the prediction of these accelerated studies, no beneficial effect of mannitol was found in real-time studies after one year.