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netLibrary - eBook Summary Structure-based Drug Design by ...

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Page 517<br />

than the wild-type virus. At the optimal drug concentration for growth, the pH-stability of these<br />

mutations is equivalent to that of native HRV1A in the absence of drug. Increasing drug concentration<br />

beyond that which is optimal for growth further increases the acid-stability of these mutant viruses so<br />

that they are more acid-stable than native virus without drug (Daniel Pevear, personal communication).<br />

C. Clinical Resistance and Virulence<br />

The clinical importance of these mutations has not been clearly demonstrated. In at least one case a drugresistant<br />

mutant was able to grow in vitro in single-cycle growth experiments as well as wild-type<br />

HRV14 [28]. Frequently, however, drug-resistant or acid-stable mutants will not grow as well in cell<br />

culture as native virus [93].<br />

The final analysis of the clinical importance of resistant mutants awaits the results of clinical trails. In<br />

the one study published to date, HRV2 mutants of the compensation type (resistant to the capsid-binding<br />

compound chalcone) were tested in healthy human volunteers [65]. The drug-resistant mutants caused<br />

significantly fewer colds than the normal virus. Mutants that require the presence of drug to grow did<br />

not cause any apparent disease. In this single case it appears that the mutant viruses were not as virulent<br />

as the parent strain.<br />

VI. Animal and Clinical Studies<br />

The idea that an inhibitor that binds to a nonenzymatic, nonreceptor site of a virion could inhibit viral<br />

replication in vivo would a priori be considered to be an unlikely scenario <strong>by</strong> most in the field of<br />

structure-<strong>based</strong> design. If this idea were proposed knowing only the structure of the native virus<br />

(especially HRV14, which has a closed-pocket conformation) skepticism would abound. This type of<br />

project arose not from a structure-<strong>based</strong> approach, but from the tried-and-true screening approach. The<br />

compounds were first shown to be effective in inhibiting viral replication in vitro [52]. This was<br />

followed <strong>by</strong> an experiment showing that these compounds could inhibit at least one enterovirus in a<br />

mouse model [94].<br />

In this study, suckling mice were inoculated with an echovirus and if untreated they developed a fatal<br />

paralytic illness. When treated either prophylactically or within a few days of the viral inoculation,<br />

virtually all of the mice were protected. This is dramatic proof of the concept that these compounds can<br />

inhibit picornaviral infection in vivo.<br />

There are important differences between mice and men and between enteroviral paralytic illness and<br />

rhinoviral upper respiratory tract infections.<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_517.html [4/9/2004 12:45:48 AM]

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