In Vitro Antiviral Activity of some Novel Isatin Derivatives against HCV and SARS-CoV Viruses

4-[(1,2-dihydro-2-oxo-3H-indol-3-ylidene)amino]-N(4,6-dimethyl-2-pyrimidiny)benzene sulphonamide and its derivatives were evaluated for antiviral activity against Pathogenic viruses such as Hepatitis C Virus and SARS-CoV in Vero and Huh 5-2 cells, respectively. The 5-fluoro derivative inhibited the HCV RNA synthesis at 6 μg/ml, without toxicity at a concentration up to 42 μg/ml in Huh 5-2 cells. Among the compounds tested SPIII-5F exhibits the 45% maximum protection against replication of SARS-CoV in Vero cells.

In the method adopted for antiviral activity against SARS-CoV in vero cells 10 . Vero E6 cells in 96-well tissue culture plates were used confluent. Culture medium was removed and 100 μL of minimum essential medium supplemented with 2% fetal bovine serum containing an appropriate concentration of antiviral compound was added. Inside a biosafety laboratory-3,25 μL of a SARS-CoV virus solution added. Five concentrations were tested for cytotoxicity of the antiviral compounds. After an incubation period of three days at 37º in 5% CO 2 , the inhibition of the cytopathic effect (CPE) by the compounds was measured in a spectrophotometer (at 492) by the reduction by cellular dehydrogenase of the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrzolium(MTS) dye (Cell titer 96 Aqueous One Solution kit, promega) (20 μL MTS for 3h at 37º) in to a water soluble coloured formazan product. The antiviral activity and cytotoxcity of the test compounds are presented in Table 1.
In view of the broad spectrum activities of isatin derivatives, we aimed at evaluating the antiviral activity of some novel 4-

Key words: Isatin, HCV, SARS-CoV, vero cells, huh 5-2 cells
essential amino acid (Life Technologies, DC); 100 IU/ml penicillin and 100 μg/ml streptomycin and 250 μg/ml G418 (Geneticin, Life Technologies Washington DC). Cells were seeded at a density of 7000 cells per well in 96 well view plate TM (Packard, CA) in medium containing the same compounds as described above, except for G418. Cells were allowed to adhere and proliferate for 24 h. At that time, culture was removed and serial dilution of test compounds were added in culture medium lacking G418. Interferon alfa 2a (500 IU) was added as a positive control. Plates were further incubated at 37º and 5% CO 2 for 72 h replication of HCV replicon in Huh-5 cells results in luciferase activity in the cells. Luciferase activity was measured by adding 50 μl of 1 × Gloysis buffer (Promega) for 15 min of followed by adding 50 μl Steady-Glo Luciferase assay reagent (promega). Luciferase activity was measured with luminometer and signal in each individual well was expressed as a percentage of the untreated culture. Parallel culture of Huh 5-2 cells, seeded at a density of 7000 cells/well of classical 96-well cell culture plates (Becton-Dicknson) were treated in a similar fashion except that no Glo-lysis buffer or Stady-Glo Luciferase reagent was added. Instead the density of the cluture was measured by means of the MTS method (Promega). The antiviral activity and cytotoxicity of the test compounds are prepared in Table 2.
The present study was aimed at investigating some novel isatin derivative for antiviral activities against HCV and SARS-CoV to identify potential bioactive agent in the series. From the results of biological activities it appeared that some of the derivatives showed antiviral activity against HCV virus in Huh 5-3 cells.SPIII-5H and bromo derivatives inhibited the synthesis of HCV RNA, but only at a relatively high concentration (17 and 19 μl/ml).
In the present study, the test compound SPIII-5F inhibited the HCV RNA synthesis in Huh 5-2 Cells (SI=7) and 45% maximum protection against the replication against the replication of acutely infected SARS-CoV in Vero cells (Table 1 and 2 ). Isatin lead molecule (5CI-IS-AC) did not inhibit the HCV RNA synthesis and replication of SARS-CoV. Presence of sulphonamide side chain in the 3 rd position was essential for antiviral activity (SPIII-5H, 5Br and 5F). Further modification in the series may help in optimizing antiHCV activity.