Farnesol and geranylgeraniol prevent activation of caspases by aminobisphosphonates: Biochemical evidence for two distinct pharmacological classes ofbisphosphonate drugs

Recently, advances have been made in understanding the molecular mechanisms by which bisphosphonate drugs inhibit bone resorption. Studies with the ma crophage-like cell line J774 have suggested that alendronate, an amino-cont aining bisphosphonate, causes apoptosis by preventing post-translational mo dification of GTP-binding proteins with isoprenoid lipids. However, clodron ate, a nonaminobisphosphonate, does not inhibit protein isoprenylation but can be metabolized intracellularly to a cytotoxic, beta-gamma-methylene (Ap pCp-type) analog of ATP. These observations raise the possibility that bisp hosphonates can be divided into two groups with distinct molecular mechanis ms of action depending on the nature of the R-2 side chain. We addressed th is question by directly comparing the ability of three aminobisphosphonates (alendronate, ibandronate, and pamidronate) and three nonaminobisphosphona tes (clodronate, etidronate, and tiludronate) to inhibit protein isoprenyla tion and activate caspase-3-like proteases or to be metabolized to AppCp-ty pe nucleotides by J774 cells. All three aminobisphosphonates inhibited prot ein isoprenylation and activated caspase-3-like proteases. Apoptosis and ca spase activation after 24-h treatment with the aminobisphosphonates could b e prevented by addition of famesol or geranylgeraniol, confirming that thes e bisphosphonates inhibit the metabolic mevalonate pathway. No AppCp-type m etabolites of the aminobisphosphonates could be detected by mass spectromet ry. The three nonaminobisphosphonates did not inhibit protein isoprenylatio n or cause activation of caspase-3-like proteases, but were incorporated in to AppCp-type nucleotides. Taken together, these observations clearly demon strate that bisphosphonate drugs can be divided into two pharmacological cl asses: the aminobisphosphonates, which act by inhibiting protein isoprenyla tion, and the less potent nonaminobisphosphonates, which act through the in tracellular accumulation of AppCp-type metabolites.