J. D. Geratz

Novel pentamidine analogs in the treatment of experimental Pneumocystis carinii pneumonia.

We have recently demonstrated that substitution of imidazoline moieties for the amidine groups of pentamidine produces a molecule that is effective against rat Pneumocystis carinii pneumonia and that is apparently less toxic than pentamidine. For this reason, 10 novel imidazoline substituted compounds were evaluated for their effect against rat P. carinii pneumonia. While several of the new compounds were observed to have advantages over pentamidine in the treatment of disease in the rat model, only one compound stood out as a potential new clinical agent. Treatment for 2 weeks with intravenous (i.v.) doses of 1,3-di(4-imidazolino-2-methoxyphenoxy)propane (DIMP) at 1 mg/kg per day produced an anti-P. carinii pneumonia effect equivalent to i.v. doses of pentamidine at 10 mg/kg per day. Although pentamidine and one of the test drugs, 1,3-di(4-imidazolinophenoxy)propane, showed no activity against P. carinii pneumonia when administered per os, DIMP exhibited potent anti-P. carinii pneumonia activity when given by daily gavage doses of 40 and 25 mg/kg. DIMP retained significant activity when given every other day by a gavage dose of 25 mg/kg. No toxicity was observed with the drug at any of the dose levels or by either of the routes of administration. However, the low solubility of the drug prevented testing at higher i.v. doses. Our conclusion is that DIMP has the potential of providing a safer and more effective alternative to pentamidine for the treatment of P. carinii pneumonia.

Inhibition of respiratory syncytial virus-host cell interactions by mono- and diamidines.

Several aromatic mono- and diamidines were found to block cell fusion induced by respiratory syncytial virus. The best inhibitors were able to achieve complete suppression of syncytium formation at a concentration of 1.0 microM. Inhibition occurred in respiratory syncytial virus-infected HEp-2 and CV-1 cells, but the same inhibitors were ineffective in preventing fusion induced by parainfluenza virus type 3. The fusion inhibitors did not reduce single-cycle virus yields, but did reduce multiple-cycle yields. In addition, the active compounds caused a significant retardation of respiratory syncytial virus penetration. The mechanism by which amidines interfere with respiratory syncytial virus-host cell interactions is unknown, but parallels can be drawn between antiviral activity and the ability of the compounds to inhibit certain trypsin-like proteases. Images

Suppression of respiratory syncytial virus infection in cotton rats by bis(5-amidino-2-benzimidazolyl)methane.

Intraperitoneal administration of bis(5-amidino-2-benzimidazolyl)methane at well-tolerated daily doses of 25 mg/kg subsequent to challenge and for 3 days thereafter effected over a 1-log reduction in the amount of virus recovered from lungs of cotton rats inoculated intratracheally with respiratory syncytial virus. When animals were immunosuppressed to prolong virus shedding, the reduction in recovered virus achieved with a 7-day dosing schedule of bis(5-amidino-2-benzimidazolyl)methane exceeded 2 logs.

Effect of synthetic protease inhibitors of the amidine type on cell injury by Rickettsia rickettsii.

To evaluate the importance of proteolytic activity in the pathogenesis of cell injury by Rickettsia rickettsii, a series of four aromatic amidine inhibitors of trypsin-like proteases were introduced into the plaque model. The compounds were shown to be active toward plaque reduction with their order of effectiveness parallel to their antitrypsin activity. One of the compounds, bis(5-amidino-2-benzimidazolyl)-methane, at a concentration of 10(-5) M demonstrated complete inhibition of plaque formation on day 6. Bis(5-amidino-2-benzimidazolyl)methane at the same concentration reduced cell injury even when added to the system after 72 h of rickettsial infection. The reduction in morbidity in guinea pigs experimentally infected with R. rickettsii and treated with bis(5-amidino-2-benzimidazolyl)methane as compared with morbidity in infected, untreated animals, comprised delay in the onset of fever and slightly fewer febrile animals. Because bis(5-amidino-2-benzimidazolyl)methane had no effect on phospholipase A2, the enzyme activity associated with penetration-induced cell injury, it is likely that a trypsin-like protease also plays an essential role either in the physiology of R. rickettsii or as its pathogenic mechanism.

Inhibitory effect of amidino-substituted heterocyclic compounds on the amidase activity of plasmin and of high and low molecular weight urokinase and on urokinase-induced plasminogen activation

Abstract A number of heterocyclic mono- and diamidines were examined for their inhibitory effect on urokinase and on plasmin. Interaction with both enzymes was competitive in nature, and a comparison of the inhibition constants revealed similarities as well as differences in the binding conditions between the two active sites. The most potent inhibitor in the series was represented by bis (5-amidino-2-benzimidazolyl)methane with K i values of 2.3 × 10 −6 M and 2.6 × 10 −6 M for high molecular weight urokinase and plasmin, respectively. The high and low molecular weight forms of urokinase were very similar in their susceptibility to inhibition by amidines. In plasminogen activation assays the inhibitory influence of the compounds did not parallel antiurokinase potency as expressed by the K i values. This paradoxical behavior is still unexplained, but additional interaction of the compounds with plasminogen has to be considered.