John P. Dekker

Protective Immunization against Inhalational Anthrax: A Comparison of Minimally Invasive Delivery Platforms

A new anthrax vaccine under clinical investigation is based on recombinant Bacillus anthracis protective antigen (rPA). Here, we investigated microneedle-based cutaneous and nasal mucosal delivery of rPA in mice and rabbits. In mice, intradermal (id) delivery achieved up to 90% seroconversion after a single dose, compared with 20% after intramuscular (im) injection. Intranasal (inl) delivery of a liquid formulation required 3 doses to achieve responses that were comparable with those achieved via the id or im routes. In rabbits, id delivery provided complete protection against aerosol challenge with anthrax spores; in addition, novel powder formulations administered inl provided complete protection, whereas a liquid formulation provided only partial protection. These results demonstrate, for the first time, that cutaneous or nasal mucosal administration of rPA provides complete protection against inhalational anthrax in rabbits. The novel vaccine/device combinations described here have the potential to improve the efficacy of rPA and other biodefense vaccines.

Microneedle-Based Intradermal Delivery of the Anthrax Recombinant Protective Antigen Vaccine

ABSTRACT The recombinant protective antigen (rPA) of Bacillus anthracis is a promising anthrax vaccine. We compared serum immunoglobulin G levels and toxin-neutralizing antibody titers in rabbits following delivery of various doses of vaccine by microneedle-based intradermal (i.d.) delivery or intramuscular (i.m.) injection using conventional needles. Intradermal delivery required less antigen to induce levels of antibody similar to those produced via i.m. injection during the first 2 weeks following primary and booster inoculation. This dose-sparing effect was less evident at the later stages of the immune response. Rabbits immunized i.d. with 10 μg of rPA displayed 100% protection from aerosol spore challenge, while i.m. injection of the same dose provided slightly lower protection (71%). Groups immunized with lower antigen doses were partially protected (13 to 29%) regardless of the mode of administration. Overall, our results suggest rPA formulated with aluminum adjuvant and administered to the skin by a microneedle-based device is as efficacious as i.m. vaccination.

Potentiation of 2,6-dinitrotoluene genotoxicity in fischer 344 rats by pretreatment with pentachlorophenol

Abstract The organochlorine pesticide, pentachlorophenol, a potent sulfotransferase inhibitor, reportedly reduces the binding of 2,6-dinitrotoluene, an industrial hepatocarcinogen to hepatic DNA by 95% after a single i.p. injection. Activation of 2,6-dinitrotoluene to genotoxic metabolites involves enzymes in both the liver and the intestinal flora. Since pentachlorophenol also has bactericidal activity and induces hepatic mixed function oxidase activity after longer treatment, the effect of pentachlorophenol on intestinal enzyme activity and the biotransformation of 2,6-dinitrotoluene to genotoxic metabolites was studied after 1, 2, 4, and 5 weeks of treatment. Male Fischer 344 rats were dosed daily, by gavage, with either 20 mg/kg pentachlorophenol or the peanut oil vehicle. After 1, 2, 4, and 5 weeks, select control and treated animals were injected p.o. with 75 mg/kg 2,6-dinitrotoluene and transferred to metabolism cages, where urine was collected for 24 hr and tested for mutagenic activity by the Ames Salmonella typhimurium reversion assay. At 2 and 4 weeks, six control and six treated animals were sacrificed and nitroreductase, azo reductase, β-glucuronidase, dechlorinase, and dehydrochlorinase activities were analyzed in homogenates of the small intestine, large intestine, and cecum. At 5 weeks, hepatic DNA adduct formation was assayed by the 32 P-postlabeling of DNA. Results from this study indicated that pentachlorophenol accelerated the biotransformation of 2,6-dinitrotoluene to genotoxic metabolites and potentiated the formation of 2,6-dinitrotoluene-induced DNA adducts in the liver. This is the first report of a chemical interaction leading to increased DNA adduct formation and indicates that chemical interactions could be important to risk assessment since they alter the relationship between exposure, dose, and the effect of genotoxicants.

Comparative gastrointestinal enzyme activity and activation of the promutagen 2,6-dinitrotoluene in male CD-1 mice and male Fischer 344 rats.

Comparative intestinal nitroreductase, azo reductase, beta-glucuronidase, dechlorinase and dehydrochlorinase activities in young male Fischer 344 rats and young male CD-1 mice were measured in vitro while the comparative biotransformation of 2,6-dinitrotoluene to mutagenic metabolites was determined in vivo. The mice, which exhibit a high spontaneous incidence of hepatomas, had markedly greater nitroreductase activity and metabolized significantly more 2,6-dinitrotoluene to mutagenic metabolites than did Fischer 344 rats, which show a low incidence of liver tumors. Results of this study indicate that species differences in the incidence of hepatomas may be influenced by microbial flora and/or the biotransformation of xenobiotics in the G.I. tract.