Obiltoxaximab Prevents Disseminated Bacillus anthracis Infection and Improves Survival during Pre- and Postexposure Prophylaxis in Animal Models of Inhalational Anthrax.

The Centers for Disease Control and Prevention recommend adjunctive antitoxins when systemic anthrax is suspected. Obiltoxaximab, a monoclonal antibody against protective antigen (PA), is approved for treatment of inhalational anthrax in combination with antibiotics and for prophylaxis when alternative therapies are not available. The impact of toxin neutralization with obiltoxaximab during pre- and postexposure prophylaxis was explored, and efficacy results that supported the prophylaxis indication are presented here. New Zealand White rabbits and cynomolgus macaques received obiltoxaximab as a single intramuscular or intravenous dose of 2 to 16 mg/kg of body weight at various times relative to Bacillus anthracis aerosol spore challenge. The primary endpoint was survival, and effect of treatment timing was explored. In rabbits, obiltoxaximab administration 9 h postchallenge singly or combined with a 5-day levofloxacin regimen protected 89% to 100% of animals compared to 33% with levofloxacin monotherapy. In cynomolgus macaques, a single intramuscular dose of 16 mg/kg obiltoxaximab led to 100% survival when given 1 to 3 days preexposure and 83% to 100% survival when given 18 to 24 h postexposure and prior to systemic bacteremia onset. Obiltoxaximab administration after bacteremia onset resulted in lower (25% to 50%) survival rates reflective of treatment setting. Prophylactic administration of obiltoxaximab before spore challenge or to spore-challenged animals before systemic bacterial dissemination is efficacious in promoting survival, ameliorating toxemia, and inhibiting bacterial spread to the periphery.

Efficacy Projection of Obiltoxaximab for Treatment of Inhalational Anthrax across a Range of Disease Severity.

Inhalational anthrax has high mortality even with antibiotic treatment, and antitoxins are now recommended as an adjunct to standard antimicrobial regimens. The efficacy of obiltoxaximab, a monoclonal antibody against anthrax protective antigen (PA), was examined in multiple studies conducted in two animal models of inhalational anthrax. A single intravenous bolus of 1 to 32 mg/kg of body weight obiltoxaximab or placebo was administered to New Zealand White rabbits (two studies) and cynomolgus macaques (4 studies) at disease onset (significant body temperature increase or detection of serum PA) following lethal challenge with aerosolized Bacillus anthracis spores. The primary endpoint was survival. The relationship between efficacy and disease severity, defined by pretreatment bacteremia and toxemia levels, was explored. In rabbits, single doses of 1 to 16 mg/kg obiltoxaximab led to 17 to 93% survival. In two studies, survival following 16 mg/kg obiltoxaximab was 93% and 62% compared to 0% and 0% for placebo (P = 0.0010 and P = 0.0013, respectively). Across four macaque studies, survival was 6.3% to 78.6% following 4 to 32 mg/kg obiltoxaximab. In two macaque studies, 16 mg/kg obiltoxaximab reduced toxemia and led to survival rates of 31%, 35%, and 47% versus 0%, 0%, and 6.3% with placebo (P = 0.0085, P = 0.0053, P = 0.0068). Pretreatment bacteremia and toxemia levels inversely correlated with survival. Overall, obiltoxaximab monotherapy neutralized PA and increased survival across the range of disease severity, indicating clinical benefit of toxin neutralization with obiltoxaximab in both early and late stages of inhalational anthrax.

Development of angiotensin IV analogs as hepatocyte growth factor/Met modifiers.

The 6-AH family [D-Nle-X-Ile-NH-(CH(2))(5)-CONH(2); where X = various amino acids] of angiotensin IV (Ang IV) analogs binds directly to hepatocyte growth factor (HGF) and inhibit HGF's ability to form functional dimers. The metabolically stabilized 6-AH family member, D-Nle-Tyr-Ile-NH-(CH(2))(5)-CONH(2,) had a t(1/2) in blood of 80 min compared with the parent compound norleual [Nle-Tyr-Leu-Ψ-(CH(2)-NH(2))(3-4)-His-Pro-Phe], which had a t(1/2) in blood of <5 min. 6-AH family members were found to act as mimics of the dimerization domain of HGF (hinge region) and inhibited the interaction of an HGF molecule with a (3)H-hinge region peptide resulting in an attenuated capacity of HGF to activate its receptor Met. This interference translated into inhibition of HGF-dependent signaling, proliferation, and scattering in multiple cell types at concentrations down into the low picomolar range. We also noted a significant correlation between the ability of the 6-AH family members to block HGF dimerization and inhibition of the cellular activity. Furthermore, a member of the 6-AH family with cysteine at position 2, was a particularly effective antagonist of HGF-dependent cellular activities. This compound suppressed pulmonary colonization by B16-F10 murine melanoma cells, which are characterized by an overactive HGF/Met system. Together, these data indicate that the 6-AH family of Ang IV analogs exerts its biological activity by modifying the activity of the HGF/Met system and offers the potential as therapeutic agents in disorders that are dependent on or possess an overactivation of the HGF/Met system.

Mimics of the dimerization domain of hepatocyte growth factor exhibit anti-Met and anticancer activity.

The angiotensin IV analog norleual [Nle-Tyr-Leu-ψ-(CH(2)-NH(2))-Leu-His-Pro-Phe] has been shown recently to act as a hepatocyte growth factor (HGF)/Met antagonist capable of blocking the binding of HGF to the Met receptor, inhibiting HGF-dependent activation of Met, and attenuating HGF-dependent cellular activities. In addition, norleual exhibited marked anticancer activity. Homology between norleual and the dimerization domain (hinge region) of HGF led to the hypothesis that norleual acts by interfering with HGF dimerization/multimerization and functions as a dominant-negative hinge region mimic. To test this hypothesis we investigated the ability of norleual to bind to and inhibit the dimerization of HGF. To further evaluate the idea that norleual was acting as a hinge region mimic, we synthesized a hexapeptide representing the HGF hinge sequence and established its capacity to similarly block HGF-dependent activation of Met and HGF-dependent cellular functions. The hinge peptide not only bound with high affinity directly to HGF and blocked its dimerization but it also inhibited HGF-dependent Met activation, suppressed HGF-dependent cellular functions, and exhibited anticancer activity. The major implication of this study is that molecules targeting the dimerization domain of HGF may represent novel and viable anticancer therapeutic agents; the development of such molecules should be feasible using norleual and the hinge peptide as synthetic templates.

Angiotensin receptor subtype mediated physiologies and behaviors: new discoveries and clinical targets.

The renin-angiotensin system (RAS) mediates several classic physiologies including body water and electrolyte homeostasis, blood pressure, cyclicity of reproductive hormones and sexual behaviors, and the regulation of pituitary gland hormones. These functions appear to be mediated by the angiotensin II (AngII)/AT(1) receptor subtype system. More recently, the angiotensin IV (AngIV)/AT(4) receptor subtype system has been implicated in cognitive processing, cerebroprotection, local blood flow, stress, anxiety and depression. There is accumulating evidence to suggest an inhibitory influence by AngII acting at the AT(1) subtype, and a facilitory role by AngIV acting at the AT(4) subtype, on neuronal firing rate, long-term potentiation, associative and spatial learning, and memory. This review initially describes the biochemical pathways that permit synthesis and degradation of active angiotensin peptides and three receptor subtypes (AT(1), AT(2) and AT(4)) thus far characterized. There is vigorous debate concerning the identity of the most recently discovered receptor subtype, AT(4). Descriptions of classic and novel physiologies and behaviors controlled by the RAS are presented. This review concludes with a consideration of the emerging therapeutic applications suggested by these newly discovered functions of the RAS.