Inhibition of prostaglandin synthase by pirprofen. Studies with sheep seminal vesicle enzyme.

1. Pirprofen, racemic 2-[3-chloro-4(3-pyrrolinyl) phenyl] propionic acid, was evaluated for its ability to inhibit the conversion of arachidonic acid into prostaglandin E2 by sheep seminal vesicle prostaglandin synthase in vitro. 2. The compound proved to be a potent inhibitor with a Ki value of about 1.2 muM. Like indomethacin, aspirin and certain other non-steroidal anti-inflammatory drugs, pirprofen inhibited the enzyme competively with respect to substrate. Unlike most non-steroidal anti-inflammatory drugs, however, pirprofen did not promote time-dependent inactivation of the enzyme. It behaved as a competitive, reversible inhibitor, whereas most of the other agents acted as competitive, irreversible inhibitors. 3. The results suggest that inhibition of prostaglandin synthesis accounts in large part for the pharmacological effects of pirprofen.

Demonstration of potent lipid-lowering activity by a thyromimetic agent devoid of cardiovascular and thermogenic effects.

A potent lipid-lowering thyromimetic (CGS 26214) devoid of cardiac and thermogenic activity was identified based on its ability to preferentially access and bind the nuclear fraction of hepatocytes over that of myocytes in culture. The difference in access achieved with CGS 26214 was at least 100-fold better for hepatocytes than for myocytes. This in vitro hepatoselectivity resulted in a compound with unprecedented in vivo lipid-lowering potency with a minimal effective dose of 1 microgram/kg in rats and dogs (approximately 25x that of L-T3). At the same time, CGS 26214 was free of any cardiovascular effects up to the highest dose tested of 25 mg/kg and 100 micrograms/kg in rats and dogs, respectively.

Synthesis and structure-activity relationships of oxamic acid and acetic acid derivatives related to L-thyronine.

Aryloxamic acids 7 and 23, (arylamino)acetic acids 29, arylpropionic acids 33, arylthioacetic acids 37, and (aryloxy)acetic acid 41 related to L-triiodothyronine (L-T3) were prepared and tested in vitro for binding to the rat liver nuclear L-T3 receptor and the rat membrane L-T3 receptor. The structure-activity relationships for these compounds are described, with 7f, 23a, 29c, 33a, 37b, and 41 showing excellent potency (IC50's of 0.19, 0.16, 1.1, 0.11, 3.5, and 0.10 nM, respectively) to the nuclear receptor and significantly lower binding affinity to the membrane receptor (IC50's > 5 microM). Some of these compounds, especially in the oxamic acid series 7 and 23, showed an unprecedented potency for methyl-substituted derivatives such as 7f and 23a. Compounds 7f and 23a showed good lipid lowering effects in rats with ED50's of 20 and 5 micrograms/kg po, respectively, and a lack of cardiac side effects in rats at doses as high as 10 and 25 mg/kg po, respectively.

Reduction of cardiovascular and thyroxine-suppressing activities of L-T3 by liver targeting with cholic acid.

This study was designed to determine whether the conjugation product of L-T3 with cholic acid would result in a liver-targeted compound (CGH 509A) with hypocholesterolemic (HC) activity significantly dissociable from cardiovascular (CV) and thyroxine-suppressing (TS) effects normally observed with thyroid hormone. Evaluation of HC activity in lipemic rats showed that CGH 509A was 6 times less potent than L-T3 with ED25 values estimated at 150 and 25 nmol/kg, respectively. CV function measured as changes in atrial rate, atrial tension and heart weight was determined in euthyroid rats. CGH 509A was at least 64 times less cardio-stimulant than L-T3 with minimum effective doses estimated at 2350 and 37 nmol/kg, respectively. TS activity was assessed in euthyroid rats as the potency of any compound to reduce plasma T4 levels. CGH 509A was 50 times less potent than-L-T3 with ED50 values estimated at 900 and 18 nmol/kg, respectively. From these results, it is clear that, while L-T3 was equally potent on HC, CV and TS activities, the HC potency of CGH 509A was at least 15 and 6 times greater than its CV and TS potencies, respectively.

In vitro and in vivo studies demonstrating potent and selective estrogen inhibition with the nonsteroidal aromatase inhibitor CGS 16949A.

CGS 16949A inhibited the conversion of [4-14C]androstenedione (A) to [4-14C]estrone by human placental microsomes in a competitive manner (Ki = 1.6 nM). Aminoglutethimide, also a competitive inhibitor, had a Ki = 0.7 microM in this assay system. The Km for the aromatization of A was 0.11 microM. Using ovarian microsomes from immature rats primed with pregnant mare's serum gonadotrophin and using [4-14C]testosterone conversion to [4-14C]estradiol as a measure of aromatase activity, the Km was 42 nM. At a substrate concentration 3-fold the Km, CGS 16949A was 180 times more potent as an inhibitor than aminoglutethimide, exhibiting half-maximal inhibition at 1.7 nM as compared to 0.3 microM. In vivo CGS 16949A lowered ovarian estrogen synthesis by gonadotropin-primed, androstenedione treated, immature rats by 90% at a dose of 260 micrograms/kg (PO). A dose of 100 mg/kg of aminoglutethimide was needed to produce this same effect. CGS 16949A at a dose of 4 mg/kg (PO) induced uterine atrophy (aromatase inhibition) without inducing adrenal hypertrophy - indicating a lack of inhibition of corticosterone secretion, while aminoglutethimide at 40 mg/kg (PO) induced adrenal hypertrophy without inducing uterine atrophy. CGS 16949A was neither androgenic nor estrogenic in rats using standard bioassays. The data suggest that CGS 16949A may serve as a potent and selective agent for modulating estrogen-dependent functions.

Synthesis and biological activity of phenoxyphenyl oxamic acid derivatives related to L-thyronine.

The synthesis of substituted phenoxyphenyl oxamic acid derivatives related to L-thyronine (L-T3) is described. The in vitro and in vivo cholesterol lowering and cardiovascular effects of these compounds are presented and discussed.