GGTI-2166 is a geranylgeranyl transferase I inhibitor. GGTI-2166 inhibit the pOC formation induced by RANKL or TNF-alpha in cultures of both mouse marrow-derived macrophage-colony-stimulating factor (M-CSF) dependent monocytes (MD cells) and the mouse monocyte cell line RAW 264.7 (RAW cells). GGTI-2166 inhibited TRAP activity induced by RANKL or TNF-alpha in both cell cultures and prevented the incorporation of [3H]all-trans geranylgeraniol into prenylated proteins in RAW cells.