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

Discovery of a nasal spray steroid, tixocortol, as an inhibitor of SARS-CoV-2 main protease and viral replication

Coronaviruses rely on the viral-encoded chymotrypsin-like main protease (Mpro or 3CLpro) for replication and assembly. Our previous research on Mpro of SARS-CoV-2 identified cysteine 300 (Cys300) as a potential allosteric site of Mpro inhibition. Here, we identified tixocortol (TX) as a covalent modifier of Cys300 which inhibits Mpro activity in vitro as well as in a cell-based Mpro expression assay. Most importantly TX inhibited SARS-CoV-2 replication in ACE2 expressing HeLa cells. Biochemical analysis and kinetic assays were consistent with TX acting as a non-competitive inhibitor. By contrast, TX was a weaker inhibitor and modifier of C300S Mpro, confirming a role for Cys300 in inhibition of WT Mpro but also providing evidence for an additional Cys target. TX pivalate (TP), a prodrug for TX that was previously marketed as a nasal spray, also inhibited SARS-CoV-2 replication in HeLa-ACE2 cells at low micromolar IC50s. These studies suggest that TX and/or TP could possibly be repurposed for the prevention and/or treatment of SARS-CoV-2 infection.

Induction of the terminal differentiation of a human squamous cell carcinoma by steroids with glucocorticoid activity

SqCC/Y1, a human malignant squamous cell carcinoma, spontaneously differentiates when grown to confluence in delipidized serum-containing medium, as measured by the capacity to form detergent-insoluble cornified cell envelopes. Thus, 30% of SqCC/Y1 cells spontaneously attained the differentiated state after 6 days in culture. Exposure of SqCC/Y1 cells to 30, 100, or 300 nM hydrocortisone increased the number of mature cells, producing a 25, 100, and 225%, respective, increase in the number of differentiated cells over the spontaneous rate of maturation. Retinoic acid at levels of 3-300 nM was inhibitory, causing a 24-85% decrease in the number of differentiated cells. Simultaneous treatment with hydrocortisone and retinoic acid indicated mutual antagonism of the effects of these agents on the formation of cornified envelopes. Since hydrocortisone possesses antiangiogenic (AG), mineralocorticoid (MC) and glucocorticoid (GC) activities, steroids with different degrees of GC, MC, and AG potency were examined for their capacities to induce terminal differentiation. Only steroids with GC activity, such as dexamethasone, hydrocortisone, and RU-28362, were capable of increasing the degree of SqCC/Y1 differentiation and antagonizing the inhibitory effects of retinoic acid on the maturation process. In addition, the GC antagonist, RU-38486, reversed the stimulation of cellular differentiation produced by the glucocorticoids. The findings indicate that GC activity is required for the steroid-induced terminal differentiation of SqCC/Y1 cells.

Comparative pharmacokinetic studies of tixocortol pivalate and cortisol in the rat

Comparative pharmacokinetic studies of [14C]tixocortol pivalate ([14C]TP) and [14C]cortisol were carried out in rats. A 2.5 mg/kg i.v. dose (TP and cortisol) and oral doses of 1 and 25 mg/kg (cortisol), 25-250 and 1500 mg/kg (TP) were given separately to male and female rats. 14C-Radioactivity, [14C]cortisol, [14C]TP and [14C]T were determined in plasma samples, using TLC determinations and HPLC analysis. The results showed that plasma clearance and volume of distribution values of TP were respectively 6 and 10 times larger than those of cortisol (ClC = 4.7 l/h/kg and ClTP = 33.3 l/h/kg; VdC = 1.9 l/kg and VdTP = 21.7 l/kg). TP was rapidly converted into T whose plasma concentrations were close to those of TP. By the oral route, the bioavailability of cortisol was complete, whereas that of TP and T was 0.10-0.20. For the same 25 mg/kg p.o. dose, plasma Cmax values of TP and T were 100 times less than those of cortisol. It is concluded that a faster rate of metabolism combined with a larger volume of distribution and a low oral bioavailability all contribute to the lack of systemic activity of TP compared with cortisol.