Mass Spectrometry Improves Osteoporosis Drug Design

Osteoporosis has been a long-standing issue in our population. Current drug therapies are available but can cause unwanted off target effects that may result in severe side effects and even ironically cause bone weakening. Using advanced mass spectrometry technology, scientists from the Florida campus of The Scripps Research Institute (TSRI) have developed a molecular model that may provide a new framework for improving the design of osteoporosis treatments. This work was recently featured in our news items. 

We spoke to Professor Patrick Griffin (PG), the paper's last author and Co-Chair of Molecular Medicine at The Scripps Research Institute in Florida, to learn more about the new approach and how technological advances have facilitated the research.

KS How did you come to work in this area of research? 

PG I have been working in the area of nuclear receptors (NRs) from my days at Merck. The difficultly in developing ligands for nuclear receptors is that independent of binding potency, small changes in the chemical structure of the ligand can lead to big changes in how the target gene program is modulated. This is due to the conformational plasticity of the ligand binding domain of NRs. Given that my background was in protein mass spectrometry we became very interested in using the technique called hydrogen/deuterium exchange mass spectrometry (HDX-MS) as a way to map conformational changes induced by ligand binding to NRs, these NRs included the vitamin D receptor (VDR).

KS How much of a significant problem is osteoporosis becoming in our population and what do you think are the main contributory factors?

PG Osteoporosis is a significant problem with aging especially in woman and especially if a person is pre-diabetic or diabetic. These folks are at increased risk for fractures, and this of course leads to loss of mobility and increase hospitalization. Both of which contribute to poor health outcomes. 

KS Would this study have been possible 10 years ago, and if not how have advances in mass spectroscopy enabled this work? What advantages over previous strategies has your approach afforded?

PG We were doing similar studies 10 years ago, but with the types of mass specs available then (low resolution) we were limited in the size of the protein we could study. The new current state of the art high resolution mass specs have significant improvements in sensitivity, mass accuracy, and mass resolving power, all of which extend the utility of HDX to very large protein complexes such as that in this study – the full length VDR/RXR heterodimer. The approach used here allowed us to do comprehensive conformational mapping of the receptor complex in the presence of DNA with ligands that were structurally similar, but had very different biological responses. The high precision and high reproducibility of the new HDX platform allowed us to generate very high-quality data that gave the ability to see small but significant changes in regions throughout the heterodimer that appear to correlation with the functional selectivity of the ligands we were comparing.

KS Whilst your work looks to avoid activation of one pathway that is known to produce unwanted side effects in conventional osteoporosis treatments, is there potential for alternative pathways to be adversely affected? Are there still any challenges that need to be overcome in realizing a potential ligand?

PG Yes, these are essentially tool compounds. Much more profiling for off target effects will need to be done. However, the study proves the point that we can rapidly assess any backup compound should these or other ligands run into issues with off target effects.

KS How significant do you think the development of this “mapping” technique is and can you foresee wider applications for this technology beyond osteoporosis?

PG The applications are essentially limitless. In fact we have applied this approach in the areas of cancer, metabolic disease, autoimmune disorders, and many others. We have applied HDX to look at compound/ligand interactions with enzymes, cell surface receptors, and motor proteins, many of these studies have been published.

Prof. Patrick Griffin was speaking to Dr Karen Steward, Science Writer for Technology Networks.