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Page 518<br />

The differences between mice and men should be obvious to the casual reader. Enterovirus-induced<br />

paralytic illnesses are systemic infections, and the virus must at some point move through the body and<br />

be subject to circulating drug. Upper respiratory infections resulting from rhino-or enteroviruses tend to<br />

be localized to the pharynx, which would require that drug titers remain high in this region of the body.<br />

In spite of these difficulties, there have been some dramatic successes in clinical trials of antirhinovirals,<br />

although clearly there are still obstacles to overcome. Two different classes of antipicornavirus<br />

compounds have been shown to be successful at inhibiting at least some types of infection when<br />

administered prophylactically. The WIN compound 54954, given orally, has been shown to inhibit<br />

Coxsackie virus A21 in humans [6]. The Jaansen compound R77975 has been shown to inhibit HRV9<br />

when administered intranasally 6 times daily [95,96], but R77975 has not been shown to inhibit<br />

infection when used therapeutically (after symptoms occur). Further clinical trials with WIN 54954 were<br />

suspended due to the developments of side effects. More recently VP 63843 has been shown to have<br />

dramatically improved effect when compared with WIN 54954 in the prophylactic treatment of<br />

Coxsackie virus A21 infection in humans and it will be tested therapeutically.<br />

The inability of R77975 to show a therapeutic effect is more likely due to poor pharmacodynamics<br />

rather than a fundamental inability for this compound to inhibit an established infection. The<br />

pharmacodynamic problem was witnessed in the R77975 study, which showed that administration<br />

intranasally 3 times a day did not yield prophylactic protection. Yet if administered 6 times daily the<br />

prophylaxis occurs. Therefore if more potent and metabolically stable compounds are found, more<br />

positive clinical results would be expected.<br />

VII. Future Directions<br />

The structures of the picornaviruses (native, with receptor bound, in the presence of acid, with a myriad<br />

of compounds bound, and of acid- and drug-resistant mutants) have yielded valuable information about<br />

possible molecular mechanisms for their uncoating. These same studies have suggested the mechanism<br />

<strong>by</strong> which these uncoating inhibitors work. A <strong>by</strong>-product of this research is the hypothesis that these<br />

compounds may mimic naturally occurring factors that occupy the VP1 pocket. The hunt for these<br />

natural compounds and their significance is underway.<br />

This understanding of the mechanism of action, as well as the structure-activity studies, have also<br />

yielded valuable information for future development of antipicornaviral drugs. The determination of<br />

compound's size, shape, and other physical requirements for activity will also be of assistance.<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_518.html [4/9/2004 12:45:50 AM]

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