TY - JOUR T1 - Nitrogen-Bisphosphonates Block Retinoblastoma Phosphorylation and Cell Growth by Inhibiting the Cholesterol Biosynthetic Pathway in a Keratinocyte Model for Esophageal Irritation JF - Molecular Pharmacology JO - Mol Pharmacol SP - 193 LP - 202 DO - 10.1124/mol.59.2.193 VL - 59 IS - 2 AU - Alfred A. Reszka AU - Judit Halasy-Nagy AU - Gideon A. Rodan Y1 - 2001/02/01 UR - http://molpharm.aspetjournals.org/content/59/2/193.abstract N2 - The surprising discovery that nitrogen-containing bisphosphonates (N-BPs) act via inhibition of the mevalonate-to-cholesterol pathway raised the possibility that esophageal irritation by N-BPs is mechanism-based. We used normal human epidermal keratinocytes (NHEKs) to model N-BP effects on stratified squamous epithelium of the esophagus. The N-BPs alendronate and risedronate inhibited NHEK growth in a dose-dependent manner without inducing apoptosis. N-BPs (30 μM) caused accumulation of cells in S phase and increased binucleation (inhibited cytokinesis). Consistent with N-BP inhibition of isoprenylation, geranylgeraniol or farnesol prevented accumulation in S phase. Binucleation was also induced by the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor lovastatin and by the squalene synthase inhibitor zaragozic acid A and was prevented by adding low-density lipoprotein. At 300 μM, N-BPs reduced expression of cyclin-dependent kinase (cdk) 2 and cdk4 and enhanced expression of p21waf1 and p27kip1 and their binding to cdks with corollary hypophosphorylation of retinoblastoma. Lovastatin and zaragozic acid A produced similar effects, except that p21waf1 expression and binding to cdks was not induced. Growth inhibition, but not binucleation, was also caused by the geranylgeranyl transferase I inhibitor, GGTI-298, which also enhanced cdk2 and cdk4 association with p27kip1. These findings are consistent with suppression of epithelial cell growth by N-BPs via inhibition of the mevalonate pathway and the consequent reduction in cholesterol synthesis, which blocks cytokinesis, and in geranylgeranylation, which interferes with progression through the cell cycle. ER -