To identify suitable host cells permissive for virus growth but resistant to the triterpenoid compound cicloxolone sodium (CCX), 18 eel/lines were studied for tolerance to treatment for 48 h with increasing drug concentrations. IC 5 0 values and replication indices of the IC 5o , at 300 f1M CCX and in the absence of drug, were determined. Eight eel/lines proved resistant, six sensitive and four intermediate in sensitivity to CCX. Four of the resistant eel/ lines were then selected as appropriate hosts for investigating the antiviral effect of CCX. Infectious yield dose-response experiments were carried out with viruses from eight different families comprising enveloped and non-enveloped DNA and RNA viruses. The RNA viruses included some with genomes that were segmented or non-segmented, positive-stranded, negative-stranded or doublestranded. No consistent relationship between sensitivity to CCX and any of these characteristics was found. Three classes of response were obtained: class 1 [VSV (Indiana), Influenza A, EHV-1 and BHV-1] showed a consistent, progressive CCX dose-dependent 10~100000-fold reduction in infectious virus yield; class 2 (Bunyamwera and Germiston, PoIi0-1, Reovirus-3 and Adenovirus-5) eXhibited initial sensitivity (1Q-1OO-fold) but increasing the dose had minimal further effect on yield, with plateau values reached between 100 and 200 f1M CCX; class 3 (SFV) appeared to be unaffected by CCX treatment. Plaque reduction assays revealed that HCMV and VZV are also highly sensitive to CCX inhibition.
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