Studies of the Effectiveness of Bisphosphonate and Vanadium-Bisphosphonate Compounds In Vitro against Axenic Leishmania tarentolae

Abstract

Leishmaniasis is a disease that is a significant problem for people, especially in tropical regions of the world. Current drug therapies to treat the disease are expensive, not very effective, and/or of significant side effects. A series of alkyl bisphosphonate compounds and one amino bisphosphonate compound, as well as alendronate and zoledronate, were tested as potential agents against Leishmania tarentolae. Also, two polyoxometalates (POMs) with nitrogen-containing bisphosphonate ligands, vanadium/alendronate (V5(Ale)2) and vanadium/zoledronate (V3(Zol)3), were tested against L. tarentolae and compared to the results of the alendronate and zoledronate ligands alone. Of the compounds evaluated in this study, the V5(Ale)2 and V3(Zol)3 complexes were most effective in inhibiting the growth of L. tarentolae. The V5(Ale)2 complex had a larger impact on cell growth than either alendronate or orthovanadate alone, whereas zoledronate itself has a significant effect on cell growth, which may contribute to the activity of the V3(Zol)3 complex.

Figure 1

Bisphosphonate compounds. Compounds 1–5 are expected to be doubly deprotonated at the experimental pH (7.5) resulting in a net negative charge.

Figure 2

Cell growth curve (absorbance using MTT reagent versus day in culture) of Leishmania tarentolae with and without 1-aminodecane-1,1,-bisphosphonate (5). (a) and (b) are data from two representative experiments. Compound is added on day 2.

Figure 3

Leishmania cells one hour after 10.0 mM 1,4-butyl bisphosphonate addition (2) (400x).

Figure 4

MTT cell viability assay of day 3 cells incubated 3 hours with test compounds (mean ± SD, n = 4).

Figure 5

Microscopic observation of day 2 after addition of Leishmania tarentolae (a) control cells and cells incubated with representative test compounds (b) 1,4-butyl bisphosphonate (2, 10.0 mM), (c) V₅(Ale)₂ (6, 1.0 mM), and (d) V₃(Zol)₃ (7, 1.0 mM) for 24 hours (400x). See Figure 1 for structures.

Figure 6

MTT cell viability assay of cells incubated with test compounds after 27 hours (mean ± SD, n = 4).

Figure 7

Microscopic evaluation of day 2 after addition of Leishmania tarentolae incubated with (b) 1,4-butyl bisphosphonate (2, 10 mM) and V₅(Ale)₂ (6, 1.0 mM) compared to (a) control cells (400x).

Figure 8

MTT cell viability of Leishmania tarentolae incubated with 1,4-butyl bisphosphonate (2, Figure 1) compared to control cells.

Figure 9

MTT data of Leishmania tarentolae incubated with V₅(Ale)₂ (6) compared to control cells.