Synthesis and biological activity of some novel, chemically reactive glucocorticoids

Local anti-inflammatory activities of tixocortol 21-pivalate, inhibition of prostaglandins and leukotrienes synthesis, in carrageenin-induced pleurisy. Reversion of effects by RU 486

Since a direct effect of tixocortol pivalate (TP) has been described on cyclooxygenase pathway, local anti-inflammatory activities of some 21 thiol derivatives of steroids were investigated on the carrageenin-induced pleurisy model in comparison with dexamethasone (Dex) or other anti-inflammatory drugs. LTC4/D4 contents in pleural fluid were assayed by RIA as well as PGE2 levels to characterize the effects on arachidonate pathways. After oral administration, TP was inactive up to 1 g/kg on exudate volume and leukocyte migration as expected for this strict local anti-inflammatory steroid contrary to Dex (ID50 = 0.05-0.41 mg/kg). When administered locally, TP and tixocortol (T) exerted a dose dependent inhibitory activity on exudate volume (ID30 = 12.4 micrograms or 13.1 micrograms/pleural cavity) and leukocyte count (ID30 = 83 or 230 micrograms); in the same conditions. Dex was more active (ID30 = 0.7 and 2.6 micrograms). All these steroids decreased PGE2 and LTC4/D4 contents in exudate fluids, respectively TP (50 micrograms/pleural cavity) by 28 and 63%; T (100 micrograms) by 33 and 31%; Dex (5 micrograms) by 43 and 40%. Local co-administration of RU 486 (50 micrograms) with either TP, T or Dex reversed the anti-inflammatory effects of all steroids, indicating in these conditions a local activity through glucosteroid receptor occupancy.

Glucocorticosteroid regulation of prostaglandin biosynthesis in human myometrial smooth muscle cells in monolayer culture

In the present investigation, we evaluated the production of prostaglandins by human myometrial smooth muscle cells maintained in monolayer culture in the absence or presence of glucocorticosteroids. In the presence of cortisol (10(-7) M) or dexamethasone (10(-8) M), the rate of production of prostacyclin (PGI2) by these cells was decreased significantly. The glucocorticosteroid-mediated inhibition of prostaglandin production was attenuated when cortisol-21-mesylate (10(-6) M), a glucocorticosteroid antagonist, was present in the culture medium. The rate of conversion of radiolabeled arachidonic acid to radiolabeled prostaglandins as determined by use of sonicates of myometrial cells and optimal assay conditions, however, was not affected significantly by treatment with cortisol or dexamethasone in concentrations sufficient to inhibit prostaglandin formation by more than 80%. These findings are suggestive that glucocorticosteroids act in human myometrial smooth muscle cells in culture to inhibit prostaglandin formation by way of a receptor-mediated process that does not involve inhibition of enzyme activities that are involved in the biosynthesis of prostaglandins, i.e. the conversion of arachidonic acid to prostaglandin.

Formation of a fluorescent glucocorticoid receptor-steroid complex in HTC cell cytosol

An intensely fluorescent rhodamine derivative of dexamethasone (i.e. Dex-C2-Rho) was synthesized. Dex-C2-Rho possessed high affinity for HTC cell glucocorticoid receptors in cell-free systems. Whole cell activity and receptor affinity of Dex-C2-Rho were both much lower, apparently due to problems with cell permeability and/or metabolism. A specific, fluorescent receptor-steroid complex at concentrations as low as 1 X 10(-9) M could readily be observed with crude HTC cell receptors after removal of the free Dex-C2-Rho. This appears to be the first report of a fluorescent glucocorticoid receptor-steroid complex.

Binding of dexamethasone to rat liver nuclei in vivo and in vitro: evidence for two distinct binding sites

The binding of [3H]dexamethasone (DEX) to rat liver nuclei in vitro and in vivo have been compared. In vitro, purified nuclei displayed a single class of specific glucocorticoid binding sites with a dissociation constant (Kd) of approximately 10(-7) M for [3H]DEX at 4 degrees C. The glucocorticoid agonists prednisolone, cortisol, and corticosterone and the antagonists progesterone and cortexolone competed avidly for this site, but the potent glucocorticoid triamcinolone acetonide (TA) competed poorly in vitro. Nuclei isolated from the livers of intact rats contained 1-2 X 10(4) [3H]DEX binding sites/nucleus. Up to 85% of the binding sites were recovered in the nuclear envelope (NE) fraction when NE were prepared either before or after labeling with [3H]DEX in vitro. After adrenalectomy, the specific [3H]DEX binding capacity of both nuclei and NE decreased to 15-20% of control values, indicating sensitivity of the binding sites to hormonal status of the animals. Efforts to restore the binding capacity by administration of exogenous glucocorticoids, however, were unsuccessful. After labeling of rat liver nuclei in vivo by intraperitoneal injection of [3H]DEX or [3H]TA into living animals, the steroid specificity and subnuclear localization of radiolabel were different. Both [3H]TA (which did not bind in vitro) and [3H]DEX became localized to nuclei in a saturable fashion in vivo. With either of these ligands, approximately 20% of the total nuclear radiolabel was recovered in the NE fraction. These results suggest the presence of two separate and distinct binding sites in rat liver nuclei, one which is localized to the NE and binds [3H]DEX (but not [3H]TA) in vitro, and another which is not localized to the NE but binds [3H]DEX and [3H]TA in vivo.

Affinity of tixocortol pivalate (JO 1016), tixocortol, cortisol acetate and cortisol for dexamethasone receptors of mouse thymus cells and rat renomedullary interstitial cells in culture. Correlation with their biological activities

Affinity for the dexamethasone binding sites of tixocortol pivalate, (the ester of the 21 thiol derivatives of cortisol), a steroid with local anti-inflammatory activity similar to cortisol acetate and with no systemic activity, was investigated in comparison with other steroids: tixocortol (the thiol derivative yielded by esterase hydrolysis), cortisol acetate and cortisol. The rank order of relative affinity for dexamethasone receptor of mouse thymocytes (37 degrees C) was: dexamethasone (1), cortisol (0.20), tixocortol pivalate (0.16), tixocortol (0.065), cortisol acetate (0.05). The corresponding 21 oxygenated ester (cortisol pivalate) was found less potent (0.080). Using rat renomedullary interstitial cells in culture, tixocortol pivalate showed also a higher receptor affinity than tixocortol. Cortisol acetate was as potent as tixocortol pivalate. The biological activity of tixocortol pivalate measured by the inhibition of PGE2 secretion on the same model, was similar to cortisol acetate and cortisol (10(-6) M, 24 h incubation, 38-55% inhibition). Tixocortol was less active (26%). These results with tixocortol pivalate are in good agreement with previously reported in vivo studies and show a good correlation between its binding ability and biological effect.

Dexamethasone 21-mesylate: an affinity label of glucocorticoid receptors from rat hepatoma tissue culture cells

We recently described the biological properties of an alpha-keto mesylate derivative of cortisol, cortisol-Mes. Cortisol-Mes exhibited long-term antiglucocorticoid activity, but there was no firm evidence that this activity was irreversible or receptor-mediated. Here we report that dexamethasone mesylate (Dex-Mes), which is the alpha-keto mesylate derivative of the more active glucocorticoid dexamethasone, is a candidate for a steroid-specific affinity label of glucocorticoid receptors. Dex-Mes is relatively stable, like cortisol-Mes, but possesses greater whole-cell antiglucocorticoid activity. However, Dex-Mes also possesses partial agonist activity, which is expressed at somewhat higher concentrations of Dex-Mes than the antagonist activity. Dex-Mes is more efficient than cortisol-Mes in competing for dexamethasone binding to glucocorticoid receptors. Furthermore, Dex-Mes is effective at lower concentrations than cortisol-Mes in causing long-term apparently irreversible antiglucocorticoid effects in whole and broken cells. The cell-free effect of Dex-Mes is specifically prevented by coincubation with an excess of cortisol. These facts argue that the apparently irreversible effects of Dex-Mes are steroid mediated. [3H]Dex-Mes has been used to identify a glucocorticoid-specific, covalently labeled fraction on sodium dodecyl sulfate/polyacrylamide gels with a molecular weight of approximately 85,000. Thus Dex-Mes appears to have been established as an affinity label for glucocorticoid receptors.

17-Ketosteroids via a base induced cleavage of C-17-dihydroxy acetone side chains

A new, base-catalyzed cleavage of C21-steroids to give 17-ketosteroids is described. This reaction is specific for those steroids containing the C-17-dihydroxy acetone side chain. In the presence of oxygen, these same reaction conditions readily degrade corticosterone to the 17 beta-carboxylic acid.

Unique long-acting antiglucocorticoid in whole and broken cell systems

The biological properties of cortisol 21-mesylate (CM), an alkylating derivative of cortisol, were investigated in a line of rat hepatoma tissue culture (HTC) cells. CM appears to bind to glucocoticoid receptors in cell-free extracts because CM inhibits the specific binding of [3H]dexamethasone. However, in whole cells CM not only fails to induce the enzyme tyrosine aminotransferase (TyrATase) but also inhibits the induction of TyrATase by dexamethasone. Thus CM is an antiglucocorticoid. This is not caused by cell death, because CM is relatively nontoxic up to concentrations of 10 microM. The concentration of CM needed for half maximal inhibition of TyrATase induction is an order of magnitude lower than that predicted from the apparent cell-free affinity of CM for the glucocorticoid receptors of HTC cells, which suggests that the cell-free binding data does not reflect an equilibrium situation. In fact, the reactive alpha-keto mesylate group was intentionally incorporated into cortisol in hopes of obtaining a steroid capable of undergoing irreversible reactions. When HTC cells were preincubated with either CM or the reversible antiglucocorticoid progesterone and then washed to remove free steroid, only the CM-treated cells failed to show subsequent induction of TyrATase by dexamethasone. Furthermore, preincubation of HTC-cell cytosol with CM blocked approximately 75% of the subsequent exchange binding of [3H]dexamethasone to glucocorticoid receptor sites. Thus, the actions of CM in whole and broken cells either require an exceptionally long time for reversal or are not reversible. Together, these results indicate that CM is a unique antagonist and could be an irreversible antiglucocorticoid in vitro.