title: The molecular mechanism of nitrogen-containing bisphosphonates as antiosteoporosis drugs.
abstract: Osteoporosis and low bone mass are currently estimated to be a major public health risk affecting >50% of the female population over the age of 50. Because of their bone-selective pharmacokinetics, nitrogen-containing bisphosphonates (N-BPs), currently used as clinical inhibitors of bone-resorption diseases, target osteoclast farnesyl pyrophosphate synthase (FPPS) and inhibit protein prenylation. FPPS, a key branchpoint of the mevalonate pathway, catalyzes the successive condensation of isopentenyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. To understand the molecular events involved in inhibition of FPPS by N-BPs, we used protein crystallography, enzyme kinetics, and isothermal titration calorimetry. We report here high-resolution x-ray structures of the human enzyme in complexes with risedronate and zoledronate, two of the leading N-BPs in clinical use. These agents bind to the dimethylallyl/geranyl pyrophosphate ligand pocket and induce a conformational change. The interactions of the N-BP cyclic nitrogen with Thr-201 and Lys-200 suggest that these inhibitors achieve potency by positioning their nitrogen in the proposed carbocation-binding site. Kinetic analyses reveal that inhibition is competitive with geranyl pyrophosphate and is of a slow, tight binding character, indicating that isomerization of an initial enzyme-inhibitor complex occurs with inhibitor binding. Isothermal titration calorimetry indicates that binding of N-BPs to the apoenzyme is entropy-driven, presumably through desolvation entropy effects. These experiments reveal the molecular binding characteristics of an important pharmacological target and provide a route for further optimization of these important drugs.
authors: Structural Genomics Consortium, University of Oxford, Oxford OX3 7LD, United Kingdom. kate.kavanagh@sgc.ox.ac.uk
authors: Kathryn L
authors: KL
authors: Kavanagh
authors: Kunde
authors: K
authors: Guo
authors: James E
authors: JE
authors: Dunford
authors: Xiaoqiu
authors: X
authors: Wu
authors: Stefan
authors: S
authors: Knapp
authors: Frank H
authors: FH
authors: Ebetino
authors: Michael J
authors: MJ
authors: Rogers
authors: R Graham G
authors: RG
authors: Russell
authors: Udo
authors: U
authors: Oppermann