208 F. L. HORSFALL, JR. 



halogen atoms present in the benzenoid ring but also on the structure of the 

 carbohydrate moiety (Tamm, 1956b; Tamm et al., 1956). a-Linked ribofurano- 

 sides of halogenated benzimidazoles are much less inhibitory than the 

 corresponding /3-linked derivatives. For highest inhibitory activity against 

 influenza virus, which contains RNA (Ada and Perry, 1954), the carbo- 

 hydrate moiety must not only be ribose but also a ribofuranose in ^-linkage 

 (Tamm, 1958). 



Not only is DRB a potent inhibitor of the multiplication of influenza B 

 virus (LEE and MB strains) in the chorioallantoic membrane in vitro, but also 

 it inhibits the multiplication of influenza A virus (PR8 and FM1 strains) to 

 the same extent in this host tissue (Tamm et al., 1954). In addition, it inhibits 

 the multiplication of the LEE strain in the intact chick embryo and in mice 

 without causing significant signs of toxicity in either host species (Tamm et 

 al., 1954). Moreover, DRB, as well as the corresponding trichloro compound 

 (TRB), inhibit the reproduction of mumps virus in the allantoic sac of the 

 chick embryo (Tamm, 1954b). 



b. Inhibition of Poliovirus Multiplication. DRB inhibits the multiplication 

 of poliovirus, type 2, in monkey kidney cells in vitro (Tamm and Nemes, 1957). 

 In single-cycle multiplication experiments (Nemes and Tamm, 1958), the 

 compound at 0.03 mg. per milliliter effectively inhibited reproduction when 

 added at 2 hours, but had little or no effect when added at 4 hours. The latent 

 period of poliovirus virus in monkey kidney cells in vitro is about 4 to 5 

 hours (Lwoff et al., 1955; Fogh, 1955). The compound, therefore, is effective 

 only in the early part of the latent period, and becomes much less effective 

 as the later part of the period is approached. 



DRB does not inactivate the infectivity of poliovirus in vitro (Tamm and 

 Nemes, 1957) and probably does not affect attachment or penetration of the 

 virus, for inhibition was no more marked when it was added with the virus 

 than at 2 hours after (Nemes and Tamm, 1958). 



Poliovirus contains RNA (Schwerdt and Schaffer, 1955), and the inhibition 

 of RNA synthesis caused by DRB in monkey kidney cells (Nemes and Tamm, 

 1958) may be correlated with the inhibitory effect of the compound on the 

 multiplication of the virus during the early part of the latent period. DRB 

 has only a slight effect on protein synthesis by monkey kidney cells in vitro 

 (Nemes and Tamm, 1958). 



As with inhibitory activity against influenza virus, any departure from the 

 jS-D-ribofuranose structure in the carbohydrate moiety of gylcosides of 

 chlorobenzimidazoles reduced inhibitory activity relative to poliovirus 

 virus multiplication (Tamm and Nemes, 1957). Because of the similarity in 

 the nucleic acids of the two viruses and the demonstration that DRB inhibits 

 RNA sythesis in the host cells used for both agents, correspondence between 

 the results was anticipated (Tamm and Nemes, 1957). 



