: Inhalational anthrax, caused by inhaled Bacillus anthracis spores, has a ~50% fatality rate even when treated with antibiotics. Pathogenesis is mediated by two toxic non-covalent complexes - edema toxin and lethal toxin. An essential component of both complexes, protective antigen (PA), binds to the major mammalian receptor which mediates toxin lethality in vivo, capillary morphogenesis protein-2 (CMG2). We have produced a fusion of the extracellular domain of human CMG2 and human IgG Fc, using a tobacco expression system, and demonstrated its effectiveness in treating inhalational anthrax in rabbits, both prophylactically and therapeutically. Our recombinant protein, PBI-220, binds to PA, blocks it from binding to cell-surface CMG2 and thus blocks toxicity. Significantly, PBI-220 neutralizes engineered PA variants that are poorly neutralized by anti-PA monoclonal antibodies in an in vitro assay, making it potentially superior to other anthrax therapeutics under development. We are developing PBI-220 as a passive immunotherapy to complement the use of antibiotics during treatment of inhalational anthrax. We have already completed pilot toxicology studies of PBI-220 in rats and cynomolgus macaques, and are developing a cGMP manufacturing process. We are collaborating with researchers at the Galveston National Laboratory and the Tulane National Primate Research Center to evaluate the benefits of combining PBI-220 and antibiotic treatment in late stages of disease in rabbits and to evaluate PBI-220 as a treatment in a cynomolgus macaque model of inhalational anthrax. This grant will advance our Product Development Plan for PBI-220 by completing the manufacturing and pre-clinical animal studies required for preparing an Investigational New Drug (IND) application, thus enabling human safety trials. Grant objectives include: 1) Develop a quantitative assay for contaminating plant proteins, to assure a minimal level of these proteins in the drug product, as required for human therapeutics;2) Conduct GLP safety studies in two animal species (rats and monkeys) with drug product of the same quality as will be used in the first human clinical trial;3 Produce PBI-220 under cGMP for Phase 1 clinical trial(s);4) Develop immunoassays for clinical sample analyses (quantification of drug and anti-drug antibodies) and 5) Complete required benchmarks for successful submission of an IND application to FDA.
This application focuses on GLP pre-clinical studies of our lead biodefense countermeasure, PBI-220, an immunoadhesin therapy for patients symptomatic for inhalational anthrax caused by Bacillus anthracis, a Category A pathogen. We are developing PBI-220 as a passive immunotherapy to complement the use of approved antibiotics such as Ciprofloxacin during treatment of the infection. We will manufacture PBI-220 under GMP for GLP toxicology and safety pharmacology studies in two animal species, thus advancing towards Biologic License Application (BLA) approval, under the Animal Rule (21 CFR 601.90 (Subpart H), which will allow PBI-220 to be supplied to the Strategic National Stockpile as a countermeasure against traditional, enhanced and advanced anthrax strains.