Non-steroidal anti-inflammatory drugs (NSAIDs) display anti-inflammatory, antipyretic and analgesic properties by inhibiting cyclooxygenases and blocking prostaglandin production. Previous studies, however, suggested that some NSAIDs also modulate peroxisome proliferator activated receptors (PPARs), raising the possibility that such off target effects contribute to the spectrum of clinically relevant NSAID actions. In this study, we set out to understand how peroxisome proliferator activated receptor-γ (PPARγ/PPARG) interacts with NSAIDs using X-ray crystallography and to relate ligand binding modes to effects on receptor activity. We find that several NSAIDs (sulindac sulfide, diclofenac, indomethacin and ibuprofen) bind PPARγ and modulate PPARγ activity at pharmacologically relevant concentrations. Diclofenac acts as a partial agonist and binds to the PPARγ ligand binding pocket (LBP) in typical partial agonist mode, near the β-sheets and helix 3. By contrast, two copies of indomethacin and sulindac sulfide bind the LBP and, in aggregate, these ligands engage in LBP contacts that resemble agonists. Accordingly, both compounds, and ibuprofen, act as strong partial agonists. Assessment of NSAID activities in PPARγ-dependent 3T3-L1 cells reveals that NSAIDs display adipogenic activities and exclusively regulate PPARγ-dependent target genes in a manner that is consistent with their observed binding modes. Further, PPARγ knockdown eliminates indomethacin activities at selected endogenous genes, confirming receptor-dependence of observed effects. We propose that it is important to consider how individual NSAIDs interact with PPARγ to understand their activities, and that it will be interesting to determine whether high dose NSAID therapies result in PPAR activation.

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Sobetirome binds selectively to the main hepatic form of thyroid hormone (TH) receptor, TRβ1, compared to TRα1, which is principally responsible for thyrotoxic effects on heart, muscle and bone. Sobetirome also preferentially accumulates in liver. It was originally envisaged that sobetirome could be used to stimulate hepatic pathways that lower cholesterol without harmful side effects and might be used in conjunction with statins. Indeed, sobetirome progressed through preclinical animal studies and Phase I human clinical trials with excellent results and without obvious harmful side effects. Despite the fact that cardiovascular disease remains a major cause of mortality and that new therapies are desperately needed, it is unlikely that sobetirome will progress in further human clinical trials in the near future. The emergence of alternative cholesterol-lowering therapeutics may render selective thyromimetics redundant. Further, fears of thyrotoxic effects in the heart and emergence of cartilage defects in dogs after long-term use of eprotirome, a similar though not identical compound, has reduced enthusiasm for this strategy. We argue that it is nevertheless important to explore uses of sobetirome in humans; more treatment strategies would help patients with hard-to-treat dyslipidemias. Sobetirome may also have additional applications in orphan indications and short-term controlled weight loss.