Because the treatment of inhalational anthrax cannot be studied in human clinical trials, it is necessary to conduct efficacy studies using a rhesus monkey model. However, the half-life of levofloxacin was approximately three times shorter in rhesus monkeys than in humans. Computer simulations to match plasma concentration profile, area under the concentration-time curve (AUC), and time above MIC for a human oral dose of 500 mg levofloxacin once a day identified a dosing regimen in rhesus monkeys that would most closely match human exposure: 15 mg/kg followed by 4 mg/kg administered 12 h later. Approximately 24 h following inhalational exposure to approximately 49 times the 50% lethal doses of Bacillus anthracis (Ames strain), monkeys were treated daily with vehicle, levofloxacin, or ciprofloxacin for 30 days. Ciprofloxacin was administered at 16 mg/kg twice a day. Following the 30-day treatment, monkeys were observed for 70 days. Nine of 10 control monkeys died within 9 days of exposure. No clinical signs were observed in fluoroquinolone-treated monkeys during the 30 treatment days. One monkey died 8 days after levofloxacin treatment, and two monkeys from the ciprofloxacin group died 27 and 36 days posttreatment, respectively. These deaths were probably related to the germination of residual spores. B. anthracis was positively cultured from several tissues from the three fluoroquinolone-treated monkeys that died. MICs of levofloxacin and ciprofloxacin from these cultures were comparable to those from the inoculating strain. These data demonstrate that a humanized dosing regimen of levofloxacin was effective in preventing morbidity and mortality from inhalational anthrax in rhesus monkeys and did not select for resistance.Human inhalational anthrax resulting from exposure to aerosolized Bacillus anthracis is a rare disease in the natural setting but has the potential for causing epidemics as a result of bioterrorism, as recently seen in the United States. Based on predictions from animal models (9) and recent experiences (10), treatment of the disease with selected antibacterial agents appears to be successful but only if therapy is initiated shortly after infection. Inhalational anthrax cannot be studied in clinical trials and must be evaluated by using animal models. The U.S. Food and Drug Administration (FDA) has provided guidance in this area by recommending the use of a rhesus monkey disease and treatment model for inhalational anthrax (postexposure) as described previously by Friedlander et al. for ciprofloxacin, doxycycline, and penicillin G (3, 9). Other antibacterial drugs with favorable pharmacokinetics, good safety experience, and similar in vitro susceptibility profiles against B. anthracis isolates compared to the three approved agents may be candidates for evaluation using this model.Levofloxacin is a fluoroquinolone given once a day that has MICs similar to those of ciprofloxacin when tested against panels of natural isolates of B. anthracis (2, 16). In addition, the drug has a good safety profile...

We have investigated the mechanisms by which type 1 plasminogen activator inhibitor (PAI-1) is regulated by transforming growth factor beta (TGF-beta) and by epidermal growth factor (EGF) in CCL64 mink lung epithelial cells, BSC-1 monkey kidney epithelial cells, mouse embryo fibroblast (AKR-2B 84A) cells and normal rat kidney fibroblasts (NRK). TGF-beta increases PAI-1 expression in all four cell lines, and EGF acts synergistically with TGF-beta to increase PAI-1 expression in CCL64 cells but not in the other three cell lines. Here we show that PAI-1 expression can be regulated independently through two different signal transduction pathways. One pathway involves protein kinase C and is stimulated by the tumour promoter phorbol myristate acetate (PMA). Whereas preincubation with PMA completely eliminated PMA-induced PAI-1 synthesis and secretion in both CCL64 and BSC-1 cells, this treatment had no effect on TGF-beta- and EGF-induced PAI-1 levels. Therefore we conclude that protein kinase C does not mediate the effects of either EGF or TGF-beta on PAI-1 expression. The expression of PAI-1 was decreased by agents increasing intracellular cyclic AMP: (cAMP) cholera toxin, forskolin and dibutyryl cAMP lowered both the basal level and the TGF-beta- and PMA-induced levels of PAI-1 expression. These effects of cAMP-elevating agents and of TGF-beta on PAI-1 protein synthesis were also reflected in changes in TGF-beta-induced PAI-1 gene transcription, as measured by nuclear run-on. These results show that PAI-1 gene expression is sensitive to high levels of intracellular cAMP and that this effect occurs at the transcriptional level. Although increased intracellular cAMP concentrations decrease the absolute level of PAI-1 expression, the ability of TGF-beta and EGF to induce PAI-1 gene expression is unchanged. These results are discussed in relation to the observation that sensitivity to cAMP is a common feature of TGF-beta-regulated genes.

Background: TGF␤ and EGF co-regulate important cellular responses, including proliferation, EMT, and PAI-1 expression. Results: TGF␤ and EGF synergistically stimulate PAI-1 transcription through Smads and AP-1 combined with mRNA stabilization. Conclusion: TGF␤ and EGF coordinate multiple cellular responses to rapidly achieve large increases in PAI-1 expression. Significance: Synergism increases the sensitivity, precision, rapidity, and range of change in specific gene expression.

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