Triamcinolone acetonide 21-oic acid methyl ester: a potent local antiinflammatory steroid without detectable systemic...

There have been many previous attempts to prepare glucocorticoid analogs that would have high antiinflammatory activity at the site of application but minimal systemic side effects. In principle, esters of cortoic acids could fulfill these criteria, if they had sufficient affinity for the glucocorticoid receptors but were rapidly hydrolyzed to the inactive acids in the circulation. With this rationale, we have synthesized esters of the 21-oic acid of triamcinolone acetonide (TA, 9 alpha-fluoro-11 beta, 16 alpha, 17 alpha, 21-tetrahydroxy-pregna-1, 4-diene-3,20-dione 16,17-acetonide), a potent synthetic glucocorticoid, in both tritiated and unlabeled forms. The synthesis involves 1) oxidation to the 21-dehydro compound with methanolic cupric acetate, 2) further oxidation to the acid with methylene blue in the presence of KCN at pH 6.5, 3) esterification with diazomethane in the presence of methanol or ethanol, to produce the methyl ester of TA (TAme) or ethyl ester, respectively, and 4) purification of the products by TLC and HPLC. The molecular weights and structures of the esters were established by mass spectrometry and nuclear magnetic resonance. The binding of [3H]TAme to steroid receptors or serum steroid-binding proteins and the in vitro hydrolysis of the ester were evaluated simultaneously, by chromatography on Sephadex LH-20 columns in aqueous buffer. [3H]TAme is bound with high affinity by receptors from human leukemic cells and rat liver. The pattern of competition for this binding is characteristic of glucocorticoid receptors: TA approximately equal to TAme greater than R5020 (a synthetic progestin) approximately equal to aldosterone greater than 5 alpha-dihydrotestosterone. [3H]TAme is not bound detectably by serum steroid-binding proteins and is rapidly hydrolyzed during incubation with serum at 37 C. The acidic product has a very low affinity for the glucocorticoid receptor. Complexes of [3H]TAme with human and rat receptors have sedimentation coefficients of 9-10S in hypotonic buffer containing 20 mM Na2MoO4 and approximately 4S in hypertonic, molybdate-free buffer. These values of s20,w are similar to those of the oligomeric and monomeric forms, respectively, of the same receptors labeled with [3H]TA, and of mammalian steroid receptors, in general. The antiinflammatory activity of TAme in rats is comparable to that of prednisolone, but the ester is devoid of the side effects associated with prednisolone treatment (suppression of thymic weight and of serum corticosterone concentration). These bioassay data and the high affinity of the ester for human glucocorticoid receptors suggest that TAme may eventually be useful clinically, as a loc