Abstract
BackgroundNitrogen-containing bisphosphonates (N-BPs) have been designed to inhibit osteoclast-mediated bone resorption. However, it is now accepted that part of their anti-tumor activities is related to interference with the mevalonate pathway.MethodsWe investigated the effects of zoledronic acid (ZOL), on cell proliferation and protein isoprenylation in two tumoral (LnCAP, PC-3,), and one normal established (PNT1-A) prostatic cell line. To assess if inhibition of geranyl-geranylation by ZOL impairs the biological activity of RhoA GTPase, we studied the LPA-induced formation of stress fibers. The inhibitory effect of ZOL on geranyl geranyl transferase I was checked biochemically. Activity of ZOL on cholesterol biosynthesis was determined by measuring the incorporation of 14C mevalonate in cholesterol.ResultsZOL induced dose-dependent inhibition of proliferation of all the three cell lines although it appeared more efficient on the untransformed PNT1A. Whatever the cell line, 20 μM ZOL-induced inhibition was reversed by geranyl-geraniol (GGOH) but neither by farnesol nor mevalonate. After 48 hours treatment of cells with 20 μM ZOL, geranyl-geranylation of Rap1A was abolished whereas farnesylation of HDJ-2 was unaffected. Inhibition of Rap1A geranyl-geranylation by ZOL was rescued by GGOH and not by FOH. Indeed, as observed with treatment by a geranyl-geranyl transferase inhibitor, treatment of PNT1-A cells with 20 μM ZOL prevented the LPA-induced formation of stress fibers. We checked that in vitro ZOL did not inhibit geranyl-geranyl-transferase I. ZOL strongly inhibited cholesterol biosynthesis up to 24 hours but at 48 hours 90% of this biosynthesis was rescued.ConclusionAlthough zoledronic acid is currently the most efficient bisphosphonate in metastatic prostate cancer management, its mechanism of action in prostatic cells remains unclear. We suggest in this work that although in first intention ZOL inhibits FPPsynthase its main biological actitivity is directed against protein Geranylgeranylation.
Highlights
Nitrogen-containing bisphosphonates (N-BPs) have been designed to inhibit osteoclast-mediated bone resorption
Some studies confirmed the hypothesis of an inhibition of FPP synthase because apoptosis [7,8,9] and caspase activation [7] induced by several N-BPs were reversed by addition of FPP and GGPP or of cell-permeable analogs, farnesol (FOH) and geranyl-geraniol (GGOH)
Zoledronic acid inhibits proliferation of LNCap, PC-3 and PNT1-A cells The effect of ZOL on cell growth was assessed in the three prostatic cell lines: the cells were treated from day 1 (D1) to D5 with ZOL from 5 to 20 μM
Summary
Nitrogen-containing bisphosphonates (N-BPs) have been designed to inhibit osteoclast-mediated bone resorption. The lategeneration BPs have a nitrogen-containing aliphatic side chain (pamidronate, alendronate, ibandronate) or heterocyclic ring (zoledronate) Their anti-resorptive potency is up to 1000-fold greater than that of non-amino BPs and they exert their cellular effects by interference with the mevalonate (MVA) pathway [2]. Whatever the enzymatic target(s) of N-BPs most previous reports agree to suggest that the action of N-BPs results in the impairment of protein isoprenylation in osteoclasts or bone explants [4,5,8,10,13,14] as well as in tumoral cell lines [9,12,15,16,17] It remains unclear whether protein farnesylation and geranyl-geranylation are affected by N-BPs. Some recent data suggest that geranyl-geranylation, especially of Rho GTPases, may be the main target of ELFNfifgeCuctarPeof1zoledronate on proliferation of PC-3, PNT1-A and Effect of zoledronate on proliferation of PC-3, PNT1A and LNCaP. Error bars indicate inter-assay mean ± 1 SD. * indicates a significant difference versus non-treated cells (p < 0.01)
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