Farnesyl pyrophosphate synthase (FPPS)

Class

nitrogen-containing bisphosphonate; inhibits the mevalonate-pathway enzyme FPPS, blocking protein prenylation in osteoclasts

Pathway

inhibition of FPPS in the mevalonate pathway prevents prenylation of small GTPases required for osteoclast function, inducing osteoclast apoptosis and suppressing osteoclastic bone resorption, including tumor-induced bone resorption

Farnesyl pyrophosphate synthase (FPPS) is an enzyme in the mevalonate pathway, the metabolic route cells use to synthesize cholesterol and a family of lipid molecules called isoprenoids. Isoprenoids are attached to certain intracellular signaling proteins, small GTPases, in a modification called prenylation that anchors them to cell membranes so they can function. Osteoclasts, the cells responsible for breaking down bone tissue, depend heavily on properly prenylated GTPases to organize their cytoskeleton and carry out resorption. Nitrogen-containing bisphosphonates inhibit FPPS, depleting the isoprenoid intermediates needed for this modification. Without prenylation, osteoclasts lose their functional machinery and undergo programmed cell death, reducing bone breakdown. Because bisphosphonates bind avidly to bone mineral, this inhibition is concentrated where bone turnover is highest. This mechanism is broadly relevant wherever excessive osteoclast activity drives disease, including osteoporosis, Paget's disease of bone, and skeletal complications arising from cancers that metastasize to bone or from bone marrow malignancies that stimulate resorption. Suppressing osteoclast-driven bone loss in these settings can reduce fractures, bone pain, and other skeletal-related events, making FPPS inhibition a foundational mechanism in skeletal pharmacology.