Bishomoisoprenoid triazole bisphosphonates as inhibitors of geranylgeranyl diphosphate synthase

Abstract

Protein geranylgeranylation reactions are dependent on the availability of geranylgeranyl diphosphate (GGDP), which serves as the isoprenoid donor. Inhibition of GGDP synthase (GGDPS) is of interest from a drug development perspective as GGDPS inhibition results in impaired protein geranylgeranylation, which in multiple myeloma, disrupts monoclonal protein trafficking and induces apoptosis. We have recently reported a series of isoprenoid triazole bisphosphonates and have demonstrated that a 3:1 mixture of homogeranyl and homoneryl isomers potently, and in a synergistic manner, inhibits GGDPS. We now present the synthesis and biological evaluation of a novel series of bishomoisoprenoid triazoles which furthers our understanding of the structure-function relationship of this class. These studies demonstrate the importance of chain length and olefin stereochemistry on inhibitory activity.

Keywords: Bishomoisoprenoids; Bisphosphonate; GGDP synthase; Inhibition; Isoprenoid biosynthesis; Triazole.

Figure 1

Triazole bisphosphonates and their activity in enzyme (GGDPS) and cellular assays.

Figure 2. Effects of the bishomoisoprenoid triazole bisphosphonates on protein geranylgeranylation

RPMI-8226 cells were incubated for 48 hours in the presence or absence of lovastatin (Lov, 10 μM) or varying concentrations of the test compounds. A) Immunoblot analysis of Rap1a (antibody detects only unmodified protein) and β-tubulin (as a loading control). B) Intracellular lambda light chain concentrations were determined via ELISA. Data are expressed as a percentage of control (mean + SD, n=3). The * denotes p < 0.05 per unpaired two-tailed t-test. C) Immunoblot analysis of the detergent fraction from Triton X-114 lysis of Rab6 and calnexin (loading control). Densitometric analysis of Rab6 (normalized to calnexin) for the treated cells normalized to untreated (control) cells is shown (relative intensity, Rel Int).

Scheme 1

Synthesis of bromides 13a–c.

Scheme 2

Synthesis of the bishomoallylic compounds 17a–c.