Tixocortol pivalate, a corticosteroid with no systemic glucocorticoid effect after oral, intrarectal, and intranasal application

Physicochemical property trends of marketed prodrugs

Many prodrug reviews describe specific examples of the successful application of prodrug technology to produce blockbuster drugs, such as simvastatin, omeprazole, acyclovir and enalapril. These reviews are helpful to understand the previous success stories and case histories of prodrug technology. The aim of the current review seeks to more clearly define quantitative trends in the changes in the physicochemical property parameters between the successful prodrug and the active parent molecule. This information can serve to guide medicinal chemists toward more successful pharmaceutical prodrugs in the future.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

Comparative tolerability of treatments for inflammatory bowel disease

Despite limited understanding of therapeutic aetiopathogenesis of ulcerative colitis and Crohn's disease, there is a strong evidence base for the efficacy of pharmacological and biological therapies. It is equally important to recognise toxicity of the medical armamentarium for inflammatory bowel disease (IBD). Sulfasalazine consists of sulfapyridine linked to 5-aminosalicylic acid (5-ASA) via an azo bond. Common adverse effects related to sulfapyridine 'intolerance' include headache, nausea, anorexia, and malaise. Other allergic or toxic adverse effects include fever, rash, haemolytic anaemia, hepatitis, pancreatitis, paradoxical worsening of colitis, and reversible sperm abnormalities. The newer 5-ASA agents were developed to deliver the active ingredient of sulfasalazine while minimising adverse effects. Adverse effects are infrequent but may include nausea, dyspepsia and headache. Olsalazine may cause a secretory diarrhoea. Uncommon hypersensitivity reactions, including worsening of colitis, pancreatitis, pericarditis and nephritis, have also been reported. Corticosteroids are commonly prescribed for treatment of moderate to severe IBD. Despite short term efficacy, corticosteroids have numerous adverse effects that preclude their long term use. Adverse effects include acne, fluid retention, fat redistribution, hypertension, hyperglycaemia, psycho-neurological disturbances, cataracts, adrenal suppression, growth failure in children, and osteonecrosis. Newer corticosteroid preparations offer potential for targeted therapy and less corticosteroid-related adverse effects. Azathioprine and mercaptopurine are associated with pancreatitis in 3 to 15% of patients that resolves upon drug cessation. Bone marrow suppression is dose related and may be delayed. The adverse effects of methotrexate include nausea, leucopenia and, rarely, hypersensitivity pneumonia or hepatic fibrosis. Common adverse effects of cyclosporin include nephrotoxicity, hypertension, headache, gingival hyperplasia, hyperkalaemia, paresthesias, and tremors. These adverse effects usually abate with dose reduction or cessation of therapy. Seizures and opportunistic infections have also been reported. Antibacterials are commonly employed as primary therapy for Crohn's disease. Common adverse effects of metronidazole include nausea and a metallic taste. Peripheral neuropathy can occur with prolonged administration. Ciprofloxacin and other antibacterials may be beneficial in those intolerant to metronidazole. Newer immunosuppressive agents previously reserved for transplant recipients are under investigation for IBD. Tacrolimus has an adverse effect profile similar to cyclosporin, and may cause renal insufficiency. Mycophenolate mofetil, a purine synthesis inhibitor, has primarily gastrointestinal adverse effects. Biological agents targeting specific sites in the immunoinflammatory cascade are now available to treat IBD. Infliximab, a chimeric antibody targeting tumour necrosis factor-or has been well tolerated in clinical trials and early postmarketing experience. Additional trials are needed to assess long term adverse effects.

Novel steroid spiro enones: condensation of prednisolone derivatives with diethyl oxalate

In a continuing effort to discover potent anti-inflammatory steroids without systemic side effects, diethyl oxalate was condensed with the 17beta-ketol side chain of prednisolone derivatives. Prednisolone gave the most interesting result in forming a novel spiro enone with alpha-hydroxy and beta-carboxylic ester substitutions, and a facile one-pot procedure has been established for the synthesis of this highly functionalized spiro enone structure. The spiro products were tested for their binding potency to the RAW 264.7 macrophage glucocorticoid receptor, for their effect on LPS-induced nitric oxide generation in RAW 264.7 cells, and for their inhibition of rats ear edema induced by croton oil. The new compounds showed weak activities in all of the bioassays. Because the corresponding acid metabolites of two representative spiro enone esters gave no activity in either the binding assay or the nitric oxide generation test, the novel steroids are probably antedrugs. The reduced potency as compared to their parent compounds suggests that the rigid spiro structure is unfavorable to anti-inflammatory activities. Molecular modeling studies confirm that the spiro enones adopt a rigid planar geometry with the ester group in the plane.

Review article: issues in oral administration of locally acting glucocorticosteroids for treatment of inflammatory bowel disease

Inflammatory bowel diseases are treated in some cases by local administration of anti-inflammatory drugs. Local delivery of drugs in the colon following oral administration may lead to improved efficacy/side-effect profiles and may improve patient compliance. This review covers a number of issues important in the design of oral delivery systems of glucocorticosteroids for local therapy of colonic inflammation. The choice of specific glucocorticosteroids is based on the drug's physicochemical and pharmacological properties. The conditions under which an orally administered glucocorticosteroid (or other drug) must be delivered to treat ulcerative colitis are also discussed. These conditions include variations in local pH, transit throughout the gastrointestinal tract, the potential role of gut microflora, and drug dissolution in both the healthy and diseased large intestine. The effective delivery of topically-active glucocorticosteroids in ulcerative colitis and Crohn's colitis patients is complex, but if successful could improve their usefulness.

Prodrugs for nasal drug delivery

Recently, the delivery of xenobiotics via the nasal route has received increasing attention as this offers several advantages, i.e. high systemic availability, rapid onset of action. Both charged and uncharged forms of drugs can be transported across the nasal epithelium. This mucosa is rich in various metabolizing enzymes such as aldehyde dehydrogenase, glutathione transferases, epoxide hydrolases, cyt-P450-dependent monooxygenases. The presence of these enzymes may make it possible for pharmaceutical scientists to design prodrugs for better absorption and high systemic availability. Recent advances in peptide nasal delivery through prodrug modification has been thoroughly discussed in this paper. Finally, nasally delivered therapeutic agents targeted to various disease states have been examined.

New steroidal anti-inflammatory antedrugs: methyl 3,20-dioxo-9 alpha-fluoro-11 beta,17 alpha,21-trihydroxy-1,4-pregnadiene-16 alpha-carboxylate and methyl 21-acetyloxy-3,20-dioxo-11 beta, 17 alpha-dihydroxy-9 alpha-fluoro-1,4-pregnadiene-16 alpha-carboxylate

Focused efforts have been made to increase local-to-systemic activity ratios of potent anti-inflammatory steroids for local and/or topical applications. The approach taken in the present investigation is based upon the concept of "antedrug," defined as a locally active compound that exerts its action at the application site but rapidly undergoes a predictable biotransformation to an inactive metabolite that is readily excreted upon entry into the systemic circulation. In continuing efforts to synthesize potent, anti-inflammatory steroids without systemic glucocorticoid activities, 9 alpha-fluoro-methyl 11 beta, 17 alpha, 21-trihydroxy-3,20-dioxo-pregna-1,4-diene-16 alpha-carboxylate (FP16CM) and its 21-acetate derivative (FP16CMAc) have been synthesized and screened. Novel antedrugs were evaluated for antiinflammatory activity in the acute croton oil-induced ear edema bioassay, adverse systemic effects in the 5-day croton oil model, receptor binding, and concomitant L-tyrosine-2-oxoglutarate aminotransferase (EC 2.6.1.5) (TAT) enzyme induction in HTC cells in culture. Following a single topical application in the croton oil-induced ear edema bioassay, treatment with all compounds resulted in dose-dependent inhibition of edema. From these dose-response profiles, the following ID50 values (nmol resulting in a 50% reduction of edema) were calculated: 817, 540, 266, and 67 for hydrocortisone (HC), prednisolone (P), FP16CM, and FP16CMAc, respectively. Calculated relative potencies, setting HC = 1.0, were P, 1.5; FP16CM, 3.1, and FP16CMAc, 12.2. Results of the 5-day rat croton oil ear edema bioassay indicated that, in contrast to the parent compound P, the novel steroidal antedrugs did not significantly alter body weight gain, thymus weights, or plasma corticosterone levels. Relative binding potencies for cytosolic HTC glucocorticoid receptors were 1.0, 20.1, 5.4, and 2.5 for HC, P, FP16CM, and FP16CMAc, respectively. As predicted by the antedrug concept, FP16CM and FP16CMAc were very weak agonists for induction of TAT in HTC cells. Collectively, results of these investigations suggest that modification of P, which included addition of the 9-fluoro and 16-methoxycarbonyl group alone or in conjunction with a 21-acetoxy moiety, increase topical anti-inflammatory activity without significant adverse systemic effects. These new antedrugs may be useful as anti-inflammatory steroids for local applications.

Receptor binding affinity and antiproliferative activity of new antiinflammatory antedrugs: 6-methoxycarbonyl prednisolone and its derivatives

Systemic side effects of antiinflammatory steroids may be minimized by incorporation of a metabolically labile group which is metabolized to make the steroid inactive upon entry into the systemic circulation (antedrug concept). In continuing efforts to minimize systemic adverse effects of potent antiinflammatory steroids, we have recently synthesized methyl 11 beta, 17 alpha, 21-trihydroxy-3,20-dioxopregna-1,4-diene-6-carboxylate (P6CM), its 21-acetoxys (P6CMa, P6CMb) and 17,21-acetonide (P6CMacet) derivatives. Structure-activity relationships have now been assessed and compared with prednisolone (P) for glucocorticoid receptor affinity (P IC50 = 28 nM), gluconeogenic activity as induction of tyrosine aminotransferase (EC50 = 4.4 nM) in H4-II-C3 HTC cells and antiproliferative effects (P = 48% inhibition of [3H]thymidine incorporation at 1 microM). Relative potencies for receptor binding (P = 1) were 0.12, 0.03, 0.004, and 0.0008 for P6CM, P6CMa, P6CMb, and P6CMacet, respectively, and enzyme induction relative potencies were 0.13, 0.05, 0.01, and 0.008, respectively. Antiproliferative effects of all derivatives were also less than that of P. These decreases suggest that addition of the 6-carboxymethyl group to prednisolone results in the general reduction of glucocorticoid activities. Taken together with previously reported results demonstrating retention of topical antiinflammatory activity of these novel steroids, P6CM and its derivatives may represent new locally active antiinflammatory steroids with reduced propensity to cause gluconeogenic and antiproliferative adverse effects.

Review article: topical corticosteroids in inflammatory bowel disease

It would be ideal to treat inflammatory bowel disease with topical corticosteroids that are either not absorbed through the mucosa, or have a substantial first-pass hepatic metabolism. The topical use of hydrocortisone, prednisolone-21-phosphate or betamethasone is often associated with systemic side-effects. Newer corticosteroid preparations (prednisolone metasulphobenzoate, tixocortol pivalate, fluticasone propionate, beclomethasone dipropionate and budesonide) are usually associated with minimal systemic corticosteroid activity. This article reviews the clinical activity and safety of these newer preparations.

Food-dependent Cushing's syndrome mediated by aberrant adrenal sensitivity to gastric inhibitory polypeptide

BACKGROUND

Some patients with Cushing's syndrome have nodular adrenal hyperplasia. In most the disease is corticotropin-dependent, but in others it is corticotropin-independent. The cause of the adrenal hyperplasia in the latter patients is not known.

METHODS

We studied a 49-year-old woman with Cushing's syndrome and nodular adrenal hyperplasia in whom food stimulated cortisol secretion. Plasma cortisol concentrations were measured in response to the ingestion of mixed meals, glucose, protein, and fat and after the administration of various gastrointestinal and other types of hormones. We also studied the ability of the long-acting somatostatin analogue octreotide to prevent the food-induced increase in plasma cortisol concentrations and to ameliorate the clinical manifestations of Cushing's syndrome in this patient.

RESULTS

The patient's fasting plasma cortisol concentrations were subnormal, ranging from 3.0 to 7.5 micrograms per deciliter (83 to 207 nmol per liter), and they increased to as high as 16.5 micrograms per deciliter (455 nmol per liter) after a mixed meal. Her urinary cortisol excretion ranged from 164 to 250 micrograms per day (453 to 690 nmol per day) and could not be suppressed by a large dose of dexamethasone. Plasma corticotropin concentrations were virtually undetectable at all times. The ingestion of glucose, protein, and fat increased plasma cortisol concentrations to 3.6, 2.2, and 4 times the base-line value, respectively; the meal-induced and glucose-induced increases were inhibited by octreotide. The infusion of gastric inhibitory polypeptide (GIP) increased the patient's plasma cortisol concentration to 3.7 times the base-line value, but had no effect in normal subjects. The patient's fasting plasma GIP concentrations were normal both before and after a meal, and there was a close correlation between her plasma cortisol and GIP concentrations. Treatment with octreotide decreased urinary cortisol excretion and ameliorated the clinical manifestations of Cushing's syndrome.

CONCLUSIONS

The development of aberrant adrenal sensitivity to GIP can result in food-dependent adrenal hyperplasia and therefore in Cushing's syndrome.

Fluticasone propionate in Crohn's disease

Fluticasone propionate, a topically active corticosteroid of low systemic bioavailability after oral administration, has been used in a pilot study for the treatment of mild and moderately active Crohn's disease. Twelve patients received oral fluticasone propionate for three weeks, and the effects were monitored using the Crohn's disease activity index and by 111In granulocyte scanning, assessing inflammation from scan appearances, four day faecal excretion of radioactivity, and whole body excretion of radioactivity. All patients completed the trial. No serious side effects were reported. There was a significant fall in Crohn's disease activity index values over the three week treatment period (193 (84) v 122 (51), p less than 0.01). 111In leucocyte scan images were improved (seven patients) or unchanged (five patients). There was a significant fall in excretion of injected radioactivity calculated from whole body data (28 (21)% v 14 (0.7)%, p less than 0.05). There were no changes in plasma cortisol values, either basal or synacthen stimulated. Fluticasone propionate is a promising therapeutic agent for Crohn's disease that offers the possibility of controlling inflammation without inducing systemic corticosteroid side effects and which merits evaluation in a double blind trial versus conventional corticosteroids.

Direct inhibition of cyclooxygenase pathway in platelets by tixocortol 21-pivalate: comparison with related structures, steroidal and non steroidal anti-inflammatory drugs

Direct activity of the local anti-inflammatory steroid, tixocortol 21-pivalate (21 thioester derivative of cortisol) on metabolism of exogenous arachidonate by rabbit platelets was investigated in vitro. Tixocortol 21-pivalate inhibited generation of prostanoids from cyclooxygenase with an IC50 value of 19.6 microM without affecting the 12-lipoxygenase pathway. In this model, reference anti-inflammatory glucosteroids were ineffective, whereas indomethacin and aspirin inhibited the cyclooxygenase activity. Among tixocortol 21-pivalate related structures, tixocortol and its disulfide dimere or several other tixocortol esters exhibited a quite similar efficacy while S-methylation and subsequent S-oxydations of tixocortol abolished inhibitory activity. These results indicate that tixocortol 21-pivalate in contrast to other glucosteroids is able to act directly on cyclooxygenase pathway and that some specific chemical environment of the 21 thiol side chain are required for this inhibition.

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.

New enema treatments for inflammatory bowel disease

Two new preparations are under clinical trial for use in the treatment of ulcerative proctitis and left-sided colitis. One is 5-aminosalicylate, a component of sulfasalazine. This substance has virtually no immunomodulating capabilities. Evidence for efficacy equal to that of sulfasalazine in acute colitis has been obtained but its role in preventing recurrences is unknown. The other substance is tixocortol, a rapidly metabolized steroid, which has local antiinflammatory activity. Specific procedures of preparation and dosage remain to be established. Both preparations are administered as enemas.

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.

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.