We report the activities of 62 bisphosphonates as inhibitors of the Leishmania major mevalonate/isoprene biosynthesis pathway enzyme, farnesyl pyrophosphate synthase. The compounds investigated exhibit activities (IC(50) values) ranging from approximately 100 nM to approximately 80 microM (corresponding to K(i) values as low as 10 nM). The most active compounds were found to be zoledronate (whose single-crystal X-ray structure is reported), pyridinyl-ethane-1-hydroxy-1,1-bisphosphonates or picolyl aminomethylene bisphosphonates. However, N-alicyclic aminomethylene bisphosphonates, such as incadronate (N-cycloheptyl aminomethylene bisphosphonate), as well as aliphatic aminomethylene bisphosphonates containing short (n = 4, 5) alkyl chains, were also active, with IC(50) values in the 200-1700 nM range (corresponding to K(i) values of approximately 20-170 nM). Bisphosphonates containing longer or multiple (N,N-) alkyl substitutions were inactive, as were aromatic species lacking an o- or m-nitrogen atom in the ring, or possessing multiple halogen substitutions or a p-amino group. To put these observations on a more quantitative structural basis, we used three-dimensional quantitative structure-activity relationship techniques: comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA), to investigate which structural features correlated with high activity. Training set results (N = 62 compounds) yielded good correlations with each technique (R(2) = 0.87 and 0.88, respectively), and were further validated by using a training/test set approach. Test set results (N = 24 compounds) indicated that IC(50) values could be predicted within factors of 2.9 and 2.7 for the CoMFA and CoMSIA methods, respectively. The CoMSIA fields indicated that a positive charge in the bisphosphonate side chain and a hydrophobic feature contributed significantly to activity. Overall, these results are of general interest since they represent the first detailed quantitative structure-activity relationship study of the inhibition of an expressed farnesyl pyrophosphate synthase enzyme by bisphosphonate inhibitors and that the activity of these inhibitors can be predicted within about a factor of 3 by using 3D-QSAR techniques.

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 µM) versus E. histolytica growth in vitro. The most active compounds (IC 50 ∼ 4-9 µM) 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 ∼ 10-20 µM), 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 µM 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 µM. 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.