High susceptibility of five axenic Entamoeba histolytica strains to gossypol.

The antiamoebic potency of gossypol was tested against 5 axenic Entamoeba histolytica strains, in logarithmic phase growth in PEHPS medium. All of the strains were moderately susceptible to this polyphenolic drug. The 50% inhibitory concentration (IC50) was of the same order of magnitude in all strains: 0.015 microM (for strain HM-1) to 0.067 microM (for HM-38). The difference between the IC50 of HM-1 and the remaining 4 strains (HM-38, HK-9, HM-2 and HM-3) was significant, although it was greater between HM-1 and HM-38 (P less than 0.005) than between HM-1 and the other 3 strains (P less than 0.05), for which the IC50 was 0.03 microM, 0.049 microM and 0.38 microM respectively. Gossypol is more toxic in vitro for amoebae than other drugs widely used clinically, its pharmacological effects and safe dosage in humans are well known because of its antifertilizing effect, and it is accumulated mainly in the liver and colon. Accordingly, this compound could be a good antiamoebic agent if it is as potent in vivo as it is in vitro.