TY - JOUR
T1 - Selective modulation of thyroid hormone receptor action
AU - Baxter, John D.
AU - Dillmann, Wolfgang H.
AU - West, Brian L.
AU - Huber, Russ
AU - Furlow, J. David
AU - Fletterick, Robert J.
AU - Webb, Paul
AU - Apriletti, James W.
AU - Scanlan, Thomas S.
N1 - Funding Information:
This work was supported by grants from the NIH (RJF and JDB). Dr. Baxter has proprietary interests in, and serves as a consultant and Deputy Director to Karo Bio AB, which has commercial interests in this area of research.
PY - 2001
Y1 - 2001
N2 - Thyroid hormones have some actions that might be useful therapeutically, but others that are deleterious. Potential therapeutically useful actions include those to induce weight loss and lower plasma cholesterol levels. Potential deleterious actions are those on the heart to induce tachycardia and arrhythmia, on bone to decrease mineral density, and on muscle to induce wasting. There have been successes in selectively modulating the actions of other classes of hormones through various means, including the use of pharmaceuticals that have enhanced affinities for certain receptor isoforms. Thus, there is reason to pursue selective modulation of thyroid hormone receptor (TR) function, and several agents have been shown to have some β-selective, hepatic selective and/or cardiac sparring activities, although development of these was largely not based on detailed understanding of mechanisms for the specificity. The possibility of selectively targeting the TRβ was suggested by the findings that there are α- and β-TR forms and that the TRα-forms may preferentially regulate the heart rate, whereas many other actions of these hormones are mediated by the TRβ. We determined X-ray crystal structures of the TRα and TRβ ligand-binding domains (LBDs) complexed with the thyroid hormone analog 3,5,3′-triiodithyroacetic acid (Triac). The data suggested that a single amino acid difference in the ligand-binding cavities of the two receptors could affect hydrogen bonding in the receptor region, where the ligand's 1-position substituent fits and might be exploited to generate β-selective ligands. The compound GC-1, with oxoacetate in the 1-position instead of acetate as in Triac, exhibited TRβ-selective binding and actions in cultured cells. An X-ray crystal structure of the GC-1-TRβ LBD complex suggests that the oxoacetate does participate in a network of hydrogen bonding in the TR LBD polar pocket. GC-1 displayed actions in tadpoles that were TRβ-selective. When administered to mice, GC-1 was as effective in lowering plasma cholesterol levels as T3, and was more effective than T3 in lowering plasma triglyceride levels. At these doses, GC-1 did not increase the heart rate. GC-1 was also less active than T3 in modulating activities of several other cardiac parameters, and especially a cardiac pacemaker channel such as HCN-2, which may participate in regulation of the heart rate. GC-1 showed intermediate activity in suppressing plasma thyroid stimulating hormone (TSH) levels. The tissue/plasma ratio for GC-1 in heart was also less than for the liver. These data suggest that compounds can be generated that are TR-selective and that compounds with this property and/or that exhibit selective uptake, might have clinical utility as selective TR modulators.
AB - Thyroid hormones have some actions that might be useful therapeutically, but others that are deleterious. Potential therapeutically useful actions include those to induce weight loss and lower plasma cholesterol levels. Potential deleterious actions are those on the heart to induce tachycardia and arrhythmia, on bone to decrease mineral density, and on muscle to induce wasting. There have been successes in selectively modulating the actions of other classes of hormones through various means, including the use of pharmaceuticals that have enhanced affinities for certain receptor isoforms. Thus, there is reason to pursue selective modulation of thyroid hormone receptor (TR) function, and several agents have been shown to have some β-selective, hepatic selective and/or cardiac sparring activities, although development of these was largely not based on detailed understanding of mechanisms for the specificity. The possibility of selectively targeting the TRβ was suggested by the findings that there are α- and β-TR forms and that the TRα-forms may preferentially regulate the heart rate, whereas many other actions of these hormones are mediated by the TRβ. We determined X-ray crystal structures of the TRα and TRβ ligand-binding domains (LBDs) complexed with the thyroid hormone analog 3,5,3′-triiodithyroacetic acid (Triac). The data suggested that a single amino acid difference in the ligand-binding cavities of the two receptors could affect hydrogen bonding in the receptor region, where the ligand's 1-position substituent fits and might be exploited to generate β-selective ligands. The compound GC-1, with oxoacetate in the 1-position instead of acetate as in Triac, exhibited TRβ-selective binding and actions in cultured cells. An X-ray crystal structure of the GC-1-TRβ LBD complex suggests that the oxoacetate does participate in a network of hydrogen bonding in the TR LBD polar pocket. GC-1 displayed actions in tadpoles that were TRβ-selective. When administered to mice, GC-1 was as effective in lowering plasma cholesterol levels as T3, and was more effective than T3 in lowering plasma triglyceride levels. At these doses, GC-1 did not increase the heart rate. GC-1 was also less active than T3 in modulating activities of several other cardiac parameters, and especially a cardiac pacemaker channel such as HCN-2, which may participate in regulation of the heart rate. GC-1 showed intermediate activity in suppressing plasma thyroid stimulating hormone (TSH) levels. The tissue/plasma ratio for GC-1 in heart was also less than for the liver. These data suggest that compounds can be generated that are TR-selective and that compounds with this property and/or that exhibit selective uptake, might have clinical utility as selective TR modulators.
KW - Thyroid hormone analogs
KW - Thyroid hormone receptor
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U2 - 10.1016/S0960-0760(01)00052-8
DO - 10.1016/S0960-0760(01)00052-8
M3 - Article
C2 - 11384861
AN - SCOPUS:0034987037
SN - 0960-0760
VL - 76
SP - 31
EP - 42
JO - Journal of Steroid Biochemistry and Molecular Biology
JF - Journal of Steroid Biochemistry and Molecular Biology
IS - 1-5
ER -