Effects of bisphosphonates on the growth of Entamoeba histolytica and Plasmodium species in vitro and in vivo.

The effects of a series of 102 bisphosphonates on the inhibition of growth of Entamoeba histolytica and Plasmodium falciparum in vitro have been determined, and selected compounds were further investigated for their in vivo activity. Forty-seven compounds tested were active (IC(50) < 200 microM) versus E. histolytica growth in vitro. The most active compounds (IC(50) approximately 4-9 microM) were nitrogen-containing bisphosphonates with relatively large aromatic side chains. Simple n-alkyl-1-hydroxy-1,1-bisphosphonates, known inhibitors of the enzyme farnesylpyrophosphate (FPP) synthase, were also active, with optimal activity being found with C9-C10 side chains. However, numerous other nitrogen-containing bisphosphonates known to be potent FPP synthase inhibitors, such as risedronate or pamidronate, had little or no activity. Several pyridine-derived bisphosphonates were quite active (IC(50) approximately 10-20 microM), and this activity was shown to correlate with the basicity of the aromatic group, with activity decreasing with increasing pK(a) values. The activities of all compounds were tested versus a human nasopharyngeal carcinoma (KB) cell line to enable an estimate of the therapeutic index (TI). Five bisphosphonates were selected and then screened for their ability to delay the development of amebic liver abscess formation in an E. histolytica infected hamster model. Two compounds were found to decrease liver abscess formation at 10 mg/kg ip with little or no effect on normal liver mass. With P. falciparum, 35 compounds had IC(50) values <200 microM in an in vitro assay. The most active compounds were also simple n-alkyl-1-hydroxy-1,1-bisphosphonates, having IC(50) values around 1 microM. Five compounds were again selected for in vivo investigation in a Plasmodium berghei ANKA BALB/c mouse suppressive test. The most active compound, a C9 n-alkyl side chain containing bisphosphonate, caused an 80% reduction in parasitemia with no overt toxicity. Taken together, these results show that bisphosphonates appear to be useful lead compounds for the development of novel antiamebic and antimalarial drugs.

Inhibition of geranylgeranyl diphosphate synthase by bisphosphonates and diphosphates: a potential route to new bone antiresorption and antiparasitic agents.

We report the inhibition of a human recombinant geranylgeranyl diphosphate synthase (GGPPSase) by 23 bisphosphonates and six azaprenyl diphosphates. The IC50 values range from 140 nM to 690 microM. None of the nitrogen-containing bisphosphonates that inhibit farnesyl diphosphate synthase were effective in inhibiting the GGPPSase enzyme. Using three-dimensional quantitative structure-activity relationship/comparative molecular field analysis (CoMFA) methods, we find a good correlation between experimental and predicted activity: R2 = 0.938, R(cv)2 = 0.900, R(bs)2 = 0.938, and F-test = 86.8. To test the predictive utility of the CoMFA approach, we used three training sets of 25 compounds each to generate models to predict three test sets of three compounds. The rms pIC50 error for the nine predictions was 0.39. We also investigated the pharmacophore of these GGPPSase inhibitors using the Catalyst method. The results demonstrated that Catalyst predicted the pIC50 values for the nine test set compounds with an rms error of 0.28 (R2 between experimental and predicted activity of 0.948).