Why an Osteoporosis Drug Works

Raloxifene is a U.S. Food and Drug Administration (FDA)-approved treatment for decreasing fracture risk in osteoporosis. While raloxifene is as effective at reducing fracture risk as other current treatments, the medication works only partially by suppressing bone loss. With the use of wide- and small-angle x-ray scattering (WAXS and SAXS, respectively), researchers carried out experiments at the U.S. Department of Energy’s (DOE’s) Advanced Photon Source (APS) at Argonne National Laboratory that revealed an additional mechanism underlying raloxifene action that provides an explanation for how this drug can achieve equivalent clinical benefit.

A release from the laboratory explains that Tthese data, together with complementary techniques, help define a novel mechanism by which raloxifene increases inherent bone toughness.

In osteoporosis, decreased bone density increases the risk of fracture. All current drugs for treatment of this disease act upon living cells within the bone matrix to either decrease bone resorption, a process by which the mineral components of bone are broken down and released into the bloodstream, or to increase net bone formation during remodeling, a process by which bone is also broken down but then reforms bone. In either case, treatment results in an overall increase in bone density, and therefore a reduction in fracture risk.

The release quotes David B. Burr of Indiana University School of Medicine and lead author of the August 2014 Bone article on this research as saying, “It has always been somewhat paradoxical that raloxifene suppresses bone loss less than other osteoporosis therapies, yet reduces fracture risk to about the same level.”

To uncover the density-independent mechanism by which raloxifene (marketed as Evista by Eli Lilly and Company) increases bone toughness, researchers in this study from the Indiana University School of Medicine; Purdue University; Indiana University–Purdue University at Indianapolis; the University of California, San Diego; Northwestern University; and Argonne National Laboratory assessed the effect of the drug on devitalized bone cleared of living cells that normally mediate resorption and remodeling.

In these bone samples, raloxifene prolonged the loading that the bone could bear before fracturing, indicating that the drug was acting upon the physical properties of the bone itself. Using ultra-short-echo-time nuclear magnetic resonance, researchers found that raloxifene-mediated water retention within the bone matrix is associated with the observed increase in toughness.