Improved Delivery through Biological Membranes. Synthesis and Antiviral Activity of a Series of Ribavirin Chemical Delivery Systems: 2′ and 3′ Derivatives

Ribavirin was chemically manipulated to provide a number of derivatives in which a 1,4-dihydrotrigonellinate species was attached to either the 2′ or 3′-position. In addition, a variety of other modifications was used to augment the lipophilicity and stability of the ribavirin redox systems. Prepared compounds were tested in a murine model of viral encephalitis. Intravenous administration of an isomeric pair of derivatives (1-[3′-O-(N-methyl-3-carbonyl-1,4-dihydropyridine)-2′-O-benzoyl-β-D-ribofuranosyl]-1,2,4-triazole-3-carboxamide/1-[2′-O-(N-methyl-3-carbonyl-1,4-dihydropyridine)-3′-O-benzoyl-β-D-ribofuranosyl]-1,2,4-triazole-3-carboxamide) resulted in 43% survival compared with 0% for vehicle treatment and resulted in a decrease in brain viral titres by 10-fold.

Improved Delivery through Biological Membranes. Synthesis, Characterization and Antiviral Activity of a Series of Ribavirin Chemical Delivery Systems: 5 and Carboxamide Derivatives

A number of 1-methyl-1,4-dihydrotrigonellinate derivatives of ribavirin and various ribavirin esters were prepared as potential brain-targeting delivery forms. Systemic administration of a model system (1-[5′-(1-methyl-3-carbonyl-1,4-dihydropyridine)-2′,3′-bis-O-isobutyrate-β-D-ribofuranosyl]1,2,4-triazol-3-carboxamide) resulted in a significant brain concentration of the corresponding pyridinium salt. Antiviral testing accomplished with the aid of a mouse model, in which a Phlebovirus (Punta Toro virus) was intracranially inoculated, showed that while ribavirin itself was without effect, several ribavirin chemical delivery systems (CDS) exerted significant activity. These responses included increased number of survivors and increased mean survival time. It is suggested that the CDS approach may improve the efficacy of ribavirin towards various RNA viral encephalitis diseases.

SCFMO Study of the Tautomerism of Anilino-Thiazole and Related Compounds

SCFMO study of the tautomerism of anilino-thiazole, anilino-oxazole, and anilino-oxadiazole shows that amino form predominates.

Recent advances in the design and development of soft drugs

This paper summarizes recent developments in the field of soft drug development as collected and reviewed for the 9th Retrometabolism-Based Drug Design and Targeting Conference. Soft drugs are still often confused with prodrugs because they both require metabolic transformations; however, they are conceptual opposites: whereas, prodrugs are pharmacologically inactive and are converted by a predictable mechanism to the active drug, soft drugs are active therapeutic agents as such and are designed to undergo a predictable and controllable metabolic deactivation after exerting their desired therapeutic effect. Several rationally designed soft drug examples including clinically approved ones (e.g., clevidipine, esmolol, landiolol, loteprednol etabonate, and remifentanil) as well as others that have reached clinical investigations within different therapeutic areas (e.g., budiodarone, naronapride, remimazolam, tecarfarine) are briefly summarized. Anesthesiology, which requires a high degree of pharmacologic control during the surgical procedure to maintain the anesthetic state together with a quick return to responsiveness at the end of this procedure, is a particularly well-suited area for soft drug development. Several new initiatives (e.g., MOC-etomidate, AZD3043) are focused in this area; they are also briefly reviewed. Finally, just as there are many 'accidental' prodrugs, there are 'accidental' soft drugs too: i.e., therapeutics that were not intentionally designed to be soft drugs, but turned out to be essentially soft drugs. Some examples, such as articaine or methylphenidate, are briefly reviewed.

Soft Drugs VI. The Application of the Inactive Metabolite Approach for Design of Soft β-Blockers1?2

The "inactive metabolite approach" was used to design β-blockers. The acidic inactive metabolite of metoprolol [4-(2-hydroxy-3-isopropylamino) propoxyphenylacetic acid] was used as the lead compound. Its esters (alkyl and cycloalkyl) were found active in vivo while reverting quantitatively to the same inactive metabolite in plasma. The cyclohexyl ester showed the best activity, which was cardioselective, similar to the parent compound metoprolol. Although most esters had a plasma half-life of approximately 1 min, their activity (antagonism of isoproterenol induced increase in heart rate) following intravenous administration lasted 45-90 minutes, and the maximum β-blockade was observed at 45-60 minutes in both rats and dogs.

The effects of delta1-cortienic acid on skin blanching, pharmacokinetics and stability of loteprednol etabonate

The effect of delta1-cortienic acid (delta1-CA) on human skin blanching activity of the soft corticosteroid, loteprednol etabonate (LE), has been studied. Ten volunteers had applied to their forearms a dose of LE ranging from 0.1 to 1 mM, or LE from 0.1 to 1 mM in combination with 2-times the concentration of delta1-CA (0.2 - 2mM). The results indicate that delta1-CA increased LE's effect on human vasoconstriction/skin blanching activity, both in the intensity and duration. This enhancing effect of delta1-CA was also observed in other blanching studies with other corticosteroids, such as hydrocortisone. The enhancement may occur through the displacement of LE bound to transcortin (also known as corticosteroid-binding globulin, or CBG) by delta1-CA as delta1-CA has a higher affinity for CBG than that for glucocorticoid receptor (GR), resulting in more free-LE to act on GR, and increased skin blanching. In rat studies, intravenous injection of delta1-CA (5-50 mg/kg) did not affect the pharmacokinetics of LE (5 mg/kg), indicating that delta1-CA is safe for combined use with LE. In stability studies, the presence of delta1-CA at the same concentrations as LE in aqueous suspension (0.1 and 0.2%) significantly increased the stability of LE. Thus, the combination of delta1-CA with LE serves an enhancing and stabilizing role while not impacting the pharmacokinetic properties of LE.

Recent advances in retrometabolic drug design (RMDD) and development

As a general review for the 7th Retrometabolism-Based Drug Design and Targeting Conference, recent developments within this field are briefly reviewed with various illustrative examples from different therapeutic areas. Retrometabolic drug design incorporates two major systematic approaches: the design of soft drugs and of chemical delivery systems (CDS). Both aim to design new, safe drugs with an improved therapeutic index by integrating structure-activity and structure-metabolism relationships; however, they achieve it by different means: whereas soft drugs are new, active therapeutic agents that undergo predictable metabolism to inactive metabolites after exerting their desired therapeutic effect, CDSs are biologically inert molecules that provide enhanced and targeted delivery of an active drug to a particular organ or site through a designed sequential metabolism that involves several steps.

Feasibility of localized immunosuppression: 1. Exploratory studies with glucocorticoids in a biohybrid device designed for cell transplantation

Emerging biotechnologies, such as the use of biohybrid devices for cellular therapies, are showing increasing therapeutic promise for the treatment of various diseases, including type 1 diabetes mellitus. The functionality of such devices could be greatly enhanced if successful localized immunosuppression regimens could be established, since they would eliminate the many otherwise unavoidable side effects of currently used systemic immunosuppressive therapies. The existence of local immune privilege at some specialized tissues, such as the eye, CNS, or pregnant uterus, supports the feasibility of localized immunomodulation, and such an approach is particularly well-suited for cell transplant therapies where all transplanted tissue is localized within a device. Following the success of syngeneic transplantation in a subcutaneous prevascularized device as a bioartificial pancreas in a rodent model, we now report the first results of exploratory in vivo islet allograft studies in rats using locally delivered glucocorticoids (dexamethasone phosphate and the soft steroid loteprednol etabonate). Following in vitro assessments, in silico drug distribution models were used to establish tentative therapeutic dose ranges. Sustained local delivery was achieved via implantable osmotic mini-pumps through a central sprinkler, as well as with a sustained-delivery formulation for loteprednol etabonate using poly(D,L-lactic) acid (PLA) microspheres. Doses delivered locally were approximately hundred-fold smaller than those typically used in systemic treatments. While several solubility, stability, and implantation problems still remain to be addressed, both compounds showed promise in their ability to prolong graft survival after tapering of systemic immunosuppression, compared to control groups.

Feasibility of localized immunosuppression: 2. PLA microspheres for the sustained local delivery of a soft immunosuppressant

While biohybrid therapy shows promise, their further development into an "artificial pancreatic" system in diabetics also requires the management of the related immuneresponse triggered by such cellular therapies. Ideally this should be on a local level within the biohybrid device. This study relates to the design of sustained release formulations of the glucocorticoid soft drug loteprednol etabonate (LE) that are intended to locally suppress the immune response within the biohybrid devices, thereby warranting high local activity and reduced systemic side effects. Poly(D,L-lactic) acid (PLA) and poly(D,L-lactic glycolic acid (PLGA) microspheres of the soft corticosteroid loteprednol etabonate (LE) were prepared by solvent evaporation. A range of particles differing in particle size, nature of the polymer, emulsification method, and emulsifier were prepared and characterized. These results showed that the approach is able to customize slow release particles with predictable release characteristics over a period of days to month. Preliminary studies were performed with particles of a drug loading of 3.9 (+/- 0.2) %, and a mean particle diameter of 5 microm. In-vitro release studies indicated that these particles released drug over a period of three months. In vitro cell toxicity studies suggested that at higher concentrations (> 1 microM), unencapsulated LE showed some effect on the viability of the MIN-6 insuloma cell line, while the sustained release microspheres showed no cytotoxicity. The ability of these microspheres to provide localized immunosuppression has been evaluated in a set of early exploratory experiments with diabetic rats receiving islet transplantation. Animals treated using a biohybrid device loaded with microspheres showed improved results compared to those treated by delivery in solution form with an osmotic mini-pump. These results show the promise of localized glucocorticoid treatment by sustained release microspheres as a possible form of localized immunosuppression regimen. However, further confirmation is required before use in cell or organ transplantation.

Pharmacokinetics and delta1-cortienic acid excretion after intravenous administration of prednisolone and loteprednol etabonate in rats

Detailed pharmacokinetic (PK) studies in rats were performed (i)to compare the PK of prednisolone (PRN) and loteprednol etabonate (LE, a soft corticosteroid) as well as their common inactive metabolite delta1-cortienic acid (delta1-CA), (ii) to investigate the excretion of delta1-CA after PRN and LE administration, and (iii) to investigate the effect of delta1-unsaturation on the excretion of delta1-CA versus CA. Following a 10 mg x kg(-1) intravenous bolus dose, the total clearance (CL(tot)) of PRN (27.0 +/- 1.4 mL x min(-1) kg(-1)) was significantly lower than that of LE (67.4 +/- 11.6 mL x min(-1) kg(-1)) or delta1-CA (53.8 +/- 1.4 mL x min(-1) kg(-1)) indicating that the metabolism/elimination of PRN in the liver (primarily, conjugation) may be less efficient than that of LE (primarily, hydrolysis) or delta1-CA (unchanged). The volume of distribution (Vd(ss)) of PRN (823 +/- 78 mL x kg(-1)) was significantly lower than that of LE (3078 +/- 79 mL x kg(-1)) indicating that LE is more distributed to lipophilic tissues. Excretion studies have confirmed that delta1-CA is indeed a metabolite of PRN. After intravenous injection of 10 mg x kg(-1), less than 1% of the administered PRN was excreted as delta1-CA by 4 h (0.38 +/- 0.10% in bile and 0.18 +/- 0.04% in urine), significantly less than for LE (17.01 +/- 2.09% in bile and 2.53 +/- 1.17% in urine) indicating that extent of this metabolic transformation can indeed be affected by molecular design. At doses of 100 mg/kg, the proportion of delta1-CA excreted after PRN administration (0.12 +/- 0.03% in bile and 0.19 +/- 0.03% in urine) was similar to that of CA excreted after hydrocortisone administration (0.11 +/- 0.03% in bile and 0.22 +/- 0.04% in urine) indicating that the presence of the delta1 double bond (delta1-unsaturation) does not affect significantly this metabolic conversion.

Synthesis and pharmacological effects of new, N-substituted soft anticholinergics based on glycopyrrolate

To reduce the possibility of systemic side-effects in locally administered anticholinergics, two new N-substituted glycopyrrolate analogues designed using soft drug design approaches have been synthesized and evaluated in vitro and in vivo. Because stereospecificity is known to be important at muscarinic receptors, the new compounds SGM and SGE also have been prepared as their pure 2R isomers, 2R-SGM and 2R-SGE, by starting from optically pure (-)-cyclopentylmandelic acid, and the corresponding isomers were indeed found to be more active. The new soft glycopyrrolates were chemically more stable under acidic conditions, and the ethyl esters SGE were more stable than the methyl esters SGM. The new compounds were also found to be quite susceptible to extrahepatic metabolism, having half-lives of 20–30 min in rat plasma (in vitro), consistent with their soft nature. Binding studies at human muscarinic receptors (M1−M4) and guinea-pig ileum assays found 2R-SGM and 2R-SGE to have potencies somewhat less than, but close to, those of glycopyrrolate and N-methylscopolamine. They caused pupil dilation in rabbit eyes, but their mydriatic effects lasted for considerably less time than that of glycopyrrolate, and they did not induce dilation of the pupil in the contralateral, water-treated eyes, indicating that, in agreement with their soft nature, they are locally active, but safe and with a low potential to cause systemic side-effects.

Novel, cell-penetrating molecular transporters with flexible backbones and permanently charged side-chains

Various cell-penetrating peptides have been discovered recently that can translocate across plasma membranes and can even carry large cargo molecules into the cells. Because under physiological conditions most of these peptides carry considerable positive charges due to the presence of basic amino acids such as arginine, we decided to investigate whether molecular transporters composed of permanently charged side-chains also possess such cell penetrating ability. Arginine-rich oligomers that have a backbone with increased flexibility due to incorporation of non-α-amino acids (ε-aminocaproic acid) have been found to be effective molecular transporters. Here, we report the preparation of analogue structures by replacing the arginine residues with the quaternary form of a novel redox amino acid (Nys+) that contain a trigonelline moiety; it has already been shown possible to replace the original basic amino acid side-chain of neuropeptides without significant activity-loss due to the sufficiently close steric and electronic analogy between the new Nys+ and the original side-chains (in their protonated form, e.g., Arg+, Lys+). A nonamer analogue showed transporter activity resulting in increased cellular uptake in human carcinoma (HeLa) cells.

Stereoisomers of N-substituted soft anticholinergics and their zwitterionic metabolite based on glycopyrrolate--syntheses and pharmacological evaluations

PURPOSE

In this study, isomers of two N-substituted soft anticholinergics based on glycopyrrolate, SGM (PcPOAGP_NA.Me) and SGE (PcPOAGP_NA.Et) [3'-(2-cyclopentyl-2-phenyl-2-hydroxyacetoxy)-1'-methyl-1'-alkoxycarbonylpyrrolidinium bromide] and their zwitterionic metabolite, SGa (PcPOAGP_NA.H) [3'-(2-cyclopentyl-2-phenyl-2-hydroxyacetoxy)-1'-methyl-1'-carboxymethylpyrrolidinium inner salt] were synthesized and their pharmacological activities were evaluated in vitro and in vivo.

METHODS

The isomers of SGM and SGE were synthesized with both optically pure methyl-cyclopentylmandelate and 3-hydroxy-N-methylpyrrolidine. Trans-esterification followed by quarternization with alkyl bromoacetate gave four isomers of SGM or SGE with the nitrogen chiral center unresolved (2R3'S-SGM, 2R3'R-SGM, 2S3'S-SGM, 2S3'R-SGM or 2R3'S-SGE, 2R3'R-SGE, 2S3'S-SGE, 2S3'R-SGE). The hydrolysis of these four isomers followed by HPLC separation resulted in eight fully resolved isomers of SGa (2R3'R1'R, 2R3'S1'R, 2R3'R1'S, 2R3'S1'S, 2S3'R1'R, 2S3'S1'R, 2S3'R1'S, and 2S3'S1'S). Pharmacological activities were assessed by using in vitro receptor-binding assay and guinea pig ileum pA2-assay, and by evaluating the in vivo rabbit mydriatic effects. Results were compared to those obtained with conventional anticholinergic agents, such as glycopyrrolate, N-meythylscopolamine, and tropicamide, as well as those obtained with previously prepared racemic mixtures and 2R isomers.

RESULTS

Receptor binding pKi values at cloned human muscarinic receptors (M1-M4 subtypes) were in the 6.0-9.5 range for the newly synthesized SGM and SGE isomers, and in the 5.0-8.6 range for the SGa isomers. In all cases, 2R isomers were significantly more active than 2S isomers (27 to 447 times for SGM isomers, and 6 to 4467 times for SGa isomers). Among the four SGM isomers with unresolved 1' (N) chiral center, the 3'R isomers were more active than the corresponding 3'S isomers (1.5-12.9 times), whereas, among the SGa isomers, the 3'S isomers were not always more active than the corresponding 3'R isomers indicating that activity determined based on configuration at chiral center 3' is significantly affected by the configuration of the other two chiral centers, 2 and 1'. Among the completely resolved eight SGa isomers (all three chiral centers resolved), 1'S isomers were always more active than the corresponding 1'R isomers (1.8-22.4 times). Results also indicate that some isomers showed good M3/M2 muscarinic-receptor subtype-selectivity (about 3-5 times), and 2R and 3'S were the determining configurations for this property. Guinea pig ileum assays and rabbit mydriasis tests on SGa isomers further confirmed the stereospecificity. In rabbit eyes, some 2R-SGa isomers showed mydriatic potencies similar to glycopyrrolate and exceeded tropicamide, but their mydriatic effects lasted considerably shorter, and they did not induce dilation of the pupil in the contralateral, water-treated eye. These results indicate that these compounds are locally active, but safe and have a low potential to cause systemic side effects. The pharmacological potency of the eight SGa isomers was estimated as 2R3'S1'S approximately equal to 2R3'R1'S approximately equal to 2R3'S1'R > 2R3'R1'R > 2S3'R1'S > 2S3'S1'S approximately equal to 2S3'R1'R > 2S3'S1'R (p < 0.05).

CONCLUSIONS

The stereospecificity and M3/M2 muscarinic-receptor subtype-selectivity of soft anticholinergics, SGM, SGE, and SGa have been demonstrated. In agreement with previous results, the potential for their effective and safe use has been confirmed.

Determination of estredox, a compound with sustained estradiol function, and its impurity profile by HPLC

The HPLC methods described here for the assay and purity test of Estredox (E2CDS), a molecule with a redox-based, brain-targeted chemical delivery system for estradiol, allow reliable conclusions to be made on the potency and purity of API and E2CDS/HPCD complex samples. Extensive work was done to isolate and characterize the major, potential contaminants, and ensure the required stability of solutions of E2CDS, an inherently labile compound by design. Both the sample solvent and the eluent were thoroughly tested to avoid unwanted changes in sample solutions during analyses. The 12 minute isocratic assay method at 220 or 360 nm is simple, well-founded, highly precise and accurate. Purity profiling of E2CDS raised several problems in detection, stability and accuracy, owing to the fact that the pattern of the UV spectra and the stability of the compound and those of the potential contaminants often differed greatly. As a result of meticulous analysis of the UV spectra and the factors influencing the behaviour, in solution, of the compounds concerned, the 20 minute gradient method developed for the purity test, at 220 nm, of E2CDS and E2CDS/HPCD complex samples has proved to be a reliable means of adequately resolving 15-20 peaks of known and unknown compounds, and establishing the purity of various E2CDS samples. Sample impurity can be expressed as area % at 220 nm, and/or as approximate w/w % (if needed), since the relative response factors, at 220 nm, of the 6 major, potential contaminants have also been determined.

Soft corticosteroids for local immunosuppression: exploring the possibility for the use of loteprednol etabonate for islet transplantation

Transplantation of pancreatic islets into subcutaneous, neovascularized devices is one of the possibilities explored as part of our search for a cure of diabetes. We have recently reported that syngeneic transplantation in a subcutaneous prevascularized device can restore euglycemia and sustain long-term function in rats and that explanted grafts showed preserved islets and intense vascular networks. Because all of the transplanted tissue is localized within the device, if such a bioartificial pancreas approach is used, localized immunosuppression might provide sufficient protection against rejection to achieve long-term function, while also avoiding the serious systemic side effects and the susceptibility for opportunistic infections that are commonly associated with systemic immunosuppressive therapies as only much smaller and localized doses are needed. Soft steroids are obvious candidates because soft drugs are specifically designed to produce targeted local activity, but no systemic side effects due to prompt metabolic (preferably extrahepatic, e.g., hydrolytic) inactivation. However, local concentrations that are effective for immunosuppression, but non-toxic to insulin-producing beta-cells have to be found, and nontrivial difficulties related to long-term local deliverability have to be addressed. Here, we report preliminary results obtained using in vitro studies with human islets used to establish a tentative therapeutic concentration range together with fully scaled three-dimensional finite element method (FEM)-based Comsol multiphysics computational models that were used to explore various possibilities to achieve and maintain these concentration levels within the device.

Comparative evaluation of Estredox, a brain-targeted estradiol delivery system versus traditional estrogen replacement therapy

Estredox is a novel brain-targeted delivery system for estradiol (E2). The mechanism of this estradiol-chemical delivery system (E2-CDS) is based on an interconvertible dihydropiridine <--> pyridinium salt carrier (targetor) attached to E2. After administration of the E2-CDS, the targetor moiety is oxidized to a quaternary pyridinium salt (E2-Q+). Here we demonstrate that a single i.v. injection with E2-CDS (3 mg/kg) resulted in sustained presence of E2-Q+ in three various brain regions. The sustained and gradual release of estradiol from E2-Q+ is reflected by the time-course of plasma estrogen level. At the end of repeated administration of E2-CDS (daily once 0.3 mg/kg i.v. for 10 consecutive days) we found a sharp decrease in the levels of plasma estradiol followed by a gradual decrease. The levels of E2-Q+ in the investigated brain regions decreased gradually from the first post-treatment day, however, a detectable amount of E2-Q+ was still present in the hypothalamus, striatum, and cortex even on the 24th post-treatment day. Strikingly different plasma estradiol levels were found in the groups of orchidectomized rats that received daily i.v. injections of estradiol benzoate (E2-BZ). The plasma estradiol levels in these animals were much higher compared to E2-CDS-treated animals throughout the treatment period but the level sharply dropped immediately after the treatments. In contrast to the E2-CDS-treated animals there was no estradiol in any of the brain regions of E2-BZ-treated rats on the 1st and 2nd post-treatment day. All of these data are in line with the long-lasting pharmacological effects of E2-CDS-treatment on estrogen-mediated functions in castrated rats and give further experimental support for brain-targeting estrogen-treatment approach as opposed to the traditional estrogen replacement therapy.

Pharmacological effects of some newly developed soft anticholinergics and a receptor-binding QSAR study

Receptor-binding studies using cloned human muscarinic receptors (M1-M4 subtypes) were performed on newly synthesized soft anticholinergics (F-828, F-838, SGM, SGE, SA-A) that are isosteric/ isoelectronic analogs of glycopyrrolate. The receptor binding pK(i) values of the new soft drugs were in the 5.5-9.5 range; with the majority being in the 7.0-8.5 range. As previously observed for similar structures, the pK(i) values tended to decrease with increasing molecular size, and with the introduction of three structural indicator variables, a QSAR equation accounting for close to 75% of the variability could be established. Confirming the known stereospecificity of these receptors, pure 2R isomers were found more active than the corresponding isomeric mixtures. In agreement with soft drug design principles, acid metabolites (SA-A) were found considerably less active than their parent esters. The more active, 2R isomer of SA-A showed some muscarinic subtype selectivity (M3/M2), which was not observed for the parent compounds of this zwitterionic metabolite. Guinea pig ileum assay pA2 values have also been determined, and they were found to be in good agreement with the pK(i), values obtained from the binding study (r2 = 0.72). SGM and SGE caused pupil-dilation in rabbit eyes, but their mydriatic effects lasted considerably shorter than that of glycopyrrolate, and they did not induce dilation of the pupil in the contralateral, water-treated eyes, indicating that they are locally active and safe, with a low potential to cause systemic side effects.

Preparation and biological effects of pure stereoisomeric novel soft anticholinergics

A series of pure stereoisomeric soft glycopyrrolate analogues 3, 4 and 5 was synthesized using chiral intermediates and by careful separation of the stereoisomers formed during the last quaternization step of the synthesis. The stereochemistry of the products was elucidated using various 1D and 2D NMR techniques. Anticholinergic activity of the new compounds was determined by receptor binding studies and performing tests on isolated organs and by in vivo tests. Receptor binding revealed that in the higher alkyl ester series the (2R, 1'R, 3'R) and the (2R, 1'S, 3'S) isomers were the compounds showing the highest receptor affinity furthermore it demonstrated the confines of the length of the alkyl chain. In vitro isolated organ experiments correlated well with the receptor binding results, and in vivo investigations indicated the soft character of the compounds.

Influence of the N-acetylation polymorphism on the metabolism of talampanel: an investigation in fasted and fed subjects genotyped for NAT2 variants

Talampanel is a 2,3-benzodiazepine-type allosteric (noncompetitive) AMPA-antagonist currently being developed as an orally active, broad-spectrum anticonvulsant. Here, a detailed study of its N-acetylation in humans is presented using plasma concentration data of both TLP and its N-acetyl metabolite obtained from healthy volunteers (n = 28) genotyped for N-acetyltansferase NAT2 isozymes. Plasma samples were obtained for up to 48 h after a single oral dose of 75 mg TLP both in fasted and in fed subjects. A perfect correspondence could be established between the phenotype inferred before the study from genotyping and that determined after the study by using plasma metabolite-to-parent molar ratios confirming that this route of metabolism is indeed mediated by NAT2. Analysis of the data has been performed using both noncompartmental analysis and a custom-built, unified parent-metabolite PK model, which incorporates three different acetylation rates according to the genotype-based classification of each subject as slow, intermediate, or fast acetylator to simultaneously fit plasma levels for both TLP and its metabolite. This suggest that for TLP in humans, (i) N-acetylation represents only a relatively small fraction of its total elimination (about one-fourth in fast acetylators and much less in slow acetylators), (ii) acetylation is about eight-twelve times faster in fast and three-six times faster in intermediate acetylators than in slow acetylators, and (iii) the N-acetyl metabolite is eliminated faster than the parent TLP.

HPLC separation of related impurities in etiprednol dicloacetate, a novel soft corticosteroid

Etiprednol dicloacetate (ethyl 17alpha-dichloroacetoxy-11beta-hydroxy-androsta-1,4-diene-3-one-17beta-carboxylate, code-named: BNP-166) has been prepared in a 3-step synthesis from prednisolone as starting material. The primary aim of the present work was to develop HPLC methods for the separation of all the impurities found in experimental pilot plant batches of BNP-166 at concentrations > or = 0.10 area %. Besides BNP-166, a total of 19 compounds, eight of them potential impurities, were involved in the HPLC studies in which several HPLC systems were examined and tested to optimize the separation. Of the parameters influencing chromatographic behaviour column type, the nature and composition of the mobile phase and column temperature were varied, while the pH of the eluent was kept constant at 4.5, a pH value at which stability of the BNP-166 ester bonds was found to be the highest. A comparison of the RRT values obtained allowed some conclusions to be drawn concerning the physico-chemical forces governing separation. The isocratic reversed-phase HPLC system (V02) chosen to be used for various GXP studies on BNP-166 affords baseline separation of nearly all the compounds concerned, and also the quantitation of the drug candidate (BNP-166). By means of this system, it was shown that the target compound prepared by the standardized synthesis method on a pilot plant scale, never contained more than 2-3 impurities with area % values higher than 0.10.

Metabolic properties of phosphonate esters

The object of the present work was to investigate the difference in the metabolism of the phosphonate derivatives of primary or secondary hydroxyl groups. To study the phosphorolytic cleavage of such P-O bonds, zidovudine (AZT) hexanoyloxymethyl-methylphosphonate (HOM-AZT-P), an ester of a primary OH functionality, and methyl-pivaloyloxymethyl-testosterylphosphonate (POM-T-P), an ester of a secondary OH functionality, were prepared. The actions of pure enzymes such as alkaline phosphatase and phosphodiesterase on the corresponding phosphonate compounds (AZT-P and T-P) were investigated at various pH values. The phosphonate derivative of the secondary hydroxyl group of testosterone proved completely resistant to such phosphorolytic attacks, and release of free testosterone could not be detected. The phosphonate derivative of the primary hydroxyl group of zidovudine proved resistant to phosphodiesterase, but not to alkaline phosphatase, and in this second case, release of free zidovudine could be detected.

Etiprednol dicloacetate, a new soft glucocorticoid drug candidate. Development of chemistry

During development of chemistry of the soft drug candidate etiprednol dicloacetate (BNP-166) 1) optimization studies on the three-step chemical synthesis resulted in a process that could be scaled-up to the kg level, 2) the impurity profile was determined, 3) synthetic routes were developed for the preparation of the radiolabeled target compound, and 4) a series of hydroxylated metabolites was prepared.

Soft glucocorticoid design: structural elements and physicochemical parameters determining receptor-binding affinity

Following rational, retrometabolism-based drug design strategies, already two generations of cortienic acid-based soft corticosteroids have been designed. During their development, a large number of receptor-binding affinity (RBA) data for the glucocorticoid receptor (GR) were determined. RBA is a major determinant of therapeutic potential for corticosteroids, because GRs from different tissues and even from different species seem to be essentially the same. A quantitative analysis of these RBA data obtained from more than sixty structures was performed. Within both generations of soft steroids, good receptor-binding affinity could be achieved with adequate substitution at the sensitive 17alpha or 17beta pharmacophores. For soft steroids that satisfy the main binding criteria at the glucocorticoid receptor, an indicator variable for a structural element (6alpha- or 9alpha-halogenation) and a physicochemical parameter (lipophilicity as measured by log P(o/w)) account for a large portion of the variability in RBA. Following a classical, regression-type analysis, a QSAR model that accounts for close to 80% of the variability in the log RBA data could be built using only these two descriptors. According to these data, receptor binding affinity at the GR is dramatically increased by 6alpha- or 9alpha-halogenation and it also tends to increase with increasing lipophilicity.

Anti-inflammatory effect and soft properties of etiprednol dicloacetate (BNP-166), a new, anti-asthmatic steroid

In vitro and in vivo anti-inflammatory properties and soft characteristics of etiprednol dicloacetate (BNP-166) a new steroid, which has been developed for the treatment of asthma, were investigated in this study. The compound effectively decreased cytokine production in lipopolysaccharide stimulated lymphocytes and attenuated lectin-induced proliferation of blood mononuclear cells in tissue culture. In an animal model of allergen sensitized and challenged Brown Norway rats, using topical treatment, etiprednol dicloacetate substantially attenuated the extent of allergen induced bronchoalveolar fluid eosinophilia. At every examined parameter its pharmacological effects were comparable to those of budesonide. By means of in vitro biological and analytical methods the soft character of BNP-166 was also investigated. The anti-inflammatory effect of etiprednol dicloacetate in vitro was shown to be the function of the quantity of serum components, present in the assay. This loss of activity was most likely the result of the fast metabolism of etiprednol dicloacetate, which in the presence of sera could have been demonstrated by LC/MS/MS. Our data indicate that the significant local effect of the compound will very likely be accompanied with a drastically reduced systemic activity indicating an encouraging selectivity of the pharmacological action of etiprednol dicloacetate.

Studies on a soft glycopyrrolate analog, SG-1

A short-acting soft drug analog (SG-1) of glycopyrrolate (G) was developed by retrometabolic design in order to minimize systemic side effects and optimize the therapeutic index. SG-1,3-(1'-hydroxycyclopentyl)phenylacetoxy-1-methyl-1- methoxycarbonylpyrrolidinium bromide, was synthesized by: (a) esterification of phenylacetic acid with N-methyl-3-pyrrolidinol by DCC to obtain N-methyl-3-pyrrolidinyl phenylacetate; (b) reaction of lithium salt of above phenylacetates with cyclopentanone to obtain N-methyl-3-pyrrolidinyl 3-(1'-hydroxycyclopentyl)phenylacetate; and (c) quarternization with methyl bromoacetate in acetonitrile to give the designed product. To evaluate the pharmacological effect of SG-1, its mydriatic activity in rabbit eyes was compared to that of glycopyrrolate. At the pharmacodynamically equivalent doses (the lowest dose that induces the maximum response) of SG-1 (1%) and glycopyrrolate (0.1%), the mydriatic activities lasted for 5 and 100 h, respectively. Compared to glycopyrrolate, the intrinsic pupil dilation potency of SG-1 was lower (approximately 1/10th) but the duration of action was much shorter (< 1/20th) as SG-1 is susceptible to facile enzymatic hydrolysis/deactivation in the rabbit eyes. In vitro metabolism and stability investigations further supported this finding. In vitro half lives of SG-1 in rat plasma, blood, and 20% liver and lung tissue homogenates were 15.62, 53.86, 263.43, and 318.35 min, respectively. In human plasma and blood, half-lives were 19.93 and 88.32 min, respectively. SG-1 was relatively stable under acidic conditions (pH 5 and lower). SG-1 is a promising, clinically useful short acting anticholinergic.

Physicochemical aspects of the enzymatic hydrolysis of carboxylic esters

Considering the important role played by enzymatic hydrolysis in the metabolism of therapeutic agents designed by retrometabolic approaches (soft drugs and chemical delivery systems), the present article offers a review of a number of issues related to the enzymatic hydrolysis of carboxylic esters. Current knowledge regarding interorgan- and interspecies variability, stereospecificity, activation energy, proposed mechanism, and quantitative structure-metabolism relationship is summarized. The effects of chain-length and branching in the alcohol or acyl substituent on the rate of hydrolysis in congener series are also summarized. Available in vitro human blood data suggest that shortest half-lives are achieved with sterically non-hindered chains that are neither too short nor too long and are of around four carbon-atom long.

Design, pharmacokinetic, and pharmacodynamic evaluation of soft anticholinergics based on tropyl alpha-phenylcyclopentylacetate

Four new soft anticholinergic agents based on tropyl alpha-phenylcyclopentylacetate, 15a, 15b, 18a, and 18b, were designed and synthesized. Receptor binding studies on the cloned human muscarinic receptors indicated that the new soft anticholinergic agents possessed moderate potency as pKi ranged from 6.7 to 7.6. Mydriatic studies in rabbit eyes revealed that the duration of the action of the new soft anticholinergics (8.5-11.0 h) were shorter than that of atropine (about 24 h) under pharmacodynamic equivalent dose, and one of them, 18a, showed even shorter than that of tropicamide. In addition, after unilateral administration, significant dilation of pupil in the control eyes was observed with tropicamide and atropine but not with soft drugs, suggesting the systemic activity of soft drugs was minimal. With their soft nature, the new soft anticholinergics displayed much shorter protective effect against carbachol-induced bradycardia (about 30 min) than atropine (at least 60 min) in rats. In vitro and in vivo pharmacokinetic studies demonstrated that the soft anticholinergics were rapidly hydrolyzed into the corresponding inactive metabolites once they were introduced into the systemic circulation.

28-day oral toxicity study with soft corticosteroid BNP-166 in rats and dogs, followed by a 14-day recovery period

The aim of the present study was to evaluate the soft corticosteroid BNP-166 in rats and dogs treated orally with 0.2, 2.0, and 20.0 mg/kg for 28 days and the reversibility of any abnormalities during a 14-day post-dosing period. The test substance, BNP-166, was well tolerated during the 28-day treatment period. The observed changes were all characteristic for the pharmacological actions of a glucocorticoid. Treatment related changes occurred in the adrenals and thymus, and, to a lesser extent, in the lymph nodes, spleen and liver. There were no statistically significant reductions in the cortisol levels of all groups in the 0.2 and 2 mg/kg treatments. Significant reductions were observed in the high-dose group (20 mg/kg), but levels returned to normal by the end of the 14-day recovery period. Based on the results, the No Observable Adverse Effect Level (NOAEL) of BNP-166 soft corticosteroid in rat and dog after 28-day oral administration is 2 mg/kg. This value is approximately 40 times higher than that of budesonide. Pharmacodynamic and receptor binding studies have shown BNP-166 to have a similar potency to budesonide; therefore, BNP-166 can be considered safer when administered orally than other corticosteroids such as prednisolone or budesonide.

Soft cannabinoid analogues as potential anti-glaucoma agents

Cannabinoids are able to reduce elevated intraocular pressure; however, their use in glaucoma treatment is not approved due to severe systemic side effects. New cannabinoid derivatives have been designed based on a retrometabolic/soft drug approach; they were expected to have local effect, but not systemic side effects. Lead compounds and soft analogues were prepared using Pechmann condensation. In agreement with the SAR hypothesis used for the present soft drug design, all the compounds that were successfully synthesized had IOP lowering effect, but the common metabolite of soft analogues that was found to be inactive. Accordingly, when the soft analogue 8 was administered i.v., its biological effect lasted just for 15 minutes; nevertheless, when administered topically, its effect lasted significantly longer. Its metabolite, though, was inactive when applied either i.v. or topically. Thus, the designed soft analogues proved to be good candidates for topical control of glaucoma without producing systemic side effects. The preliminary i.v. experimental data could be successfully described by an indirect response PK/PD model.

Targeted drug delivery to the central nervous system via phosphonate derivatives (anionic delivery system for testosterone)

An anionic chemical delivery system (aCDS) has been developed and applied to deliver testosterone (T) to the central nervous system (CNS). The delivery of a target compound is achieved through the use of a specific targetor moiety which is an (acyloxy)alkyl-phosphonate-type functional group. The T-aCDS readily penetrates biological membranes by passive transport due to its increased lipophilicity and enters the target organ. Hydrolytic cleavage by esterases provides a negatively charged, hydrophilic intermediate phosphonate compound (TP-), which is "locked in" the CNS and should provide sustained, site-specific release of the drug. In vitro and in vivo investigations in rats showed that methyl-pivaloyloxymethyl-17-testosterylphosphonate (T-aCDS) might function as an anionic chemical delivery system of testosterone. The concentration of T-aCDS decreased fairly rapidly in vitro. The half-lives (t1/2) in different organs are as follows: blood 4.48 min (r = 0.9388), lung 5.53 min (r = 0.9661), liver 2.82 min (r = 0.9498), and brain 7.37 min (r = 0.9972). Simultaneously with the disappearance of T-aCDS, testosterone-phosphonate (TP-) appeared as a main metabolite in increasing concentration. In vivo evaluations (tail vein 11.3 mg/kg in DMSO) found maximum T-aCDS brain levels 5-10 min after administration; they fell under the borderline of detectability (< 0.1 microgram/g) after 60 min. Maximum concentration of the decomposition product (TP-) was obtained at 30 min after administration; it did not decrease significantly during the study. Even if the phosphonate derivative of the secondary, hindered hydroxyl group in this product was fairly resistant to phosphorolytic attack, the design principle can work for other compounds.

Effect of 2-hydroxypropyl-beta-cyclodextrin on the solubility, stability, and pharmacological activity of the chemical delivery system of TRH analogs

To improve the aqueous solubility and stability of the chemical delivery system (CDS) of the thyrotropin-releasing hormone (TRH) analogs, 2-hydroxypropyl-beta-cyclodextrin (HPBCD) has been attempted. TRH analogs were [Leu2]-TRH, [Nva2]-TRH and [Nva2, Pip3]-TRH. Excess amount of CDS was added in various HPBCD in water solutions (0%-50%, pH 6.5). The mixture was saturated by ultra-sonication for 1 h at 15 degrees C and filtered. The concentration of CDS in the filtrate (solubility) was determined with UV detector, and subsequently the stability was investigated. By HPBCD complexation, the aqueous solubility and stability (half-life) of CDS were significantly improved from undetectable levels to about 15 mg/ml and 30 h, respectively. In pH 6.5 and 7.4 HPBCD solution, the degradation of CDS was mainly via acid catalyzed water addition reaction, thus, e.g. [Leu2]-TRH-CDS was more stable in pH 7.4 than in pH 6.5 aqueous solutions. After lyophilizing the saturated CDSs in 50% HPBCD complex solutions, the amount of CDS in the complex was determined as 26.22, 26.79, and 30.34 mg/g for [Leu2]-TRH, [Nva2]-TRH and [Nva2, Pip3]-TRH, respectively. The half-life of [Leu2]-TRH-CDS/HPBCD solid complex at 25 degrees C, 4 degrees C and -15 degrees C was about 100 days, 440 days and no detectable change in three months, respectively. Argon protected condition did not improve the stability of lyophilized [Leu2]-TRH-CDS/HPBCD complex. Dimethyl sulfoxide although increased the solubility of [Leu2]-TRH-CDS in the 50% HPBCD solution by 1.3 times, significantly decreased its stability by 6.6 times. After intravenous administration of CDS (in 30% HPBCD) at a dose of 10 mumole/kg in mice, compared to the vehicle control or the same dose of [Leu2]-TRH (in 30% HPBCD), a significant increase in pharmacological effect (decrease in barbiturate-induced sleeping time) was observed. These results demonstrate the usefulness of cyclodextrin in the formulation of the CDSs of TRH analogs.

Retrometabolic drug design--novel aspects, future directions

A brief overview of the general, retrometabolic drug design principles, including soft drug and chemical delivery system design, is presented. Selected recent developments within these fields are also summarized, including results related to the design of soft bufuralol and amiodarone analogues, to the airway activity of loteprednol etabonate, a soft corticosteroid, and to the brain targeted delivery of some neuropeptides.

A simple, predictive, structure-based skin permeability model

By an extension of our simple, molecular size-based model recently developed to describe octanol-water partition coefficients, we were able to obtain an entirely structure-based model that seems well suited to describe human skin permeability data. The corresponding equations not only eliminate the physicochemical interrelatedness of the parameters of the original Potts & Guy approach that was obtained from similar considerations, but also maintain its elegant simplicity and are consistent with a basic physicochemical model of the related phenomena. As the new model is structure based and fully computerized, it allows direct estimation of skin permeability for any molecule of known structure without the need to obtain octanol-water partition coefficients or other experimental data.

A tryptamine analog with high affinity to the heart tissues is a potential antiarrhythmic agent

A novel tryptamine analog, 1-methyl-3-[N-(3-indolyl)ethyl]carbamoyl-1,4-dihydropyridine (T-CDS) was synthesized and converted into a stable, solid complex with 2-hydroxypropyl-beta-cyclodextrin. An aqueous solution of the complex was given intravenously to dogs and the concentration of T-CDS and its corresponding quaternary (T-Q+) forms were monitored in the blood for 50 min. The effect of the drug on vital heart parameters was monitored throughout the studies. At the end of the experiment the dogs were sacrificed and the concentration of the quaternary pyridinium form (T-Q+) was determined in the different heart tissues, as well as in the kidney, liver, lung, brain, urine and cerebrospinal fluid. The compound was found to be selectively bound to the heart muscles and showed different concentrations in different heart tissues. The T-Q+ concentrations were much higher in the heart after administration of the dihydro form (T-CDS), than after administering T-Q+ directly. The compound was found to be active on certain vital signs of the cardiovascular system and could be an effective and safe antiarrhythmic agent.

Targeting drugs to the brain by redox chemical delivery systems

Chemical delivery systems (CDSs) based on the redox conversion of a lipophilic dihydropyridine to an ionic, lipid-insoluble pyridinium salt have been developed to improve the access of therapeutic agents to the central nervous system. A dihydropyridinium-type CDS or a redox analog of the drug is sufficiently lipophilic to enter the brain by passive transport, then undergoes an enzymatic oxidation to an ionic pyridinium compound, which promotes retention in the CNS. At the same time, peripheral elimination of the entity is accelerated due to facile conversion of the CDS in the body. This review discusses chemical, physicochemical, biochemical, and biological aspects in relation to the principles and practical implementation of the redox brain-targeting approach to various classes of drugs. Representative examples to the brain-enhanced delivery of neurotransmitters, steroids, anticonvulsants, antibiotics, antiviral, anticancer and antidementia agents, and neuropeptides and their analogs are presented in detail. In vivo and in vitro studies and preliminary clinical data of several novel derivatives have been promising, which could lead to a practical use of the redox CDSs after proper pharmaceutical development. The investigations accentuate the need for considering physicochemical, metabolic, and pharmacokinetic properties in designing of carrier systems that are able to target drugs into the central nervous system.

Brain-targeted chemical delivery of [Leu2, Pip3]-TRH: synthesis and biological evaluation

A chemical targeting system for [Leu2, Pip3]-TRH (Gln,Leu,Pip) was synthesized in order to allow its specific delivery to the central nervous system (CNS). Sequential metabolism of the obtained 'packaged' chemical delivery system, (CDS), DHT-Pro-Pro-Gln-Leu-Pip-OCh, should yield a 'locked-in' precursor following the oxidative conversion of the dihydrotrigonellyl (DHT) to the trigonellyl (T+) moiety, followed by removal of the cholesteryl function and cleavage of the T+-Pro-Pro by prolyl endopeptidase. The antagonism of barbiturate-induced sleeping time was used to assess the activity of the CDS. The sleeping time after administration of vehicle and [Leu2]-TRH was 100.5 +/- 6.3 min, and 78.2 +/- 4.7 min, respectively. The [Leu2, Pip3]-TRH-CDS showed a significant decrease in sleeping time (58.2 +/- 3.4 min) compared to the vehicle or [Leu2]-TRH. These results indicate successful brain delivery of the precursor construct, and an effective release of the active GlnLeuPip in the brain.

Soft drugs. 12. Design, synthesis, and evaluation of soft bufuralol analogues

In the search for more potent but still short-acting beta-blockers (BB), the methyl, ethyl, isopropyl, tert-butyl, cyclohexyl, 2-(1-adamantyl)ethyl, and methylthiomethyl esters of the acidic inactive metabolite of bufuralol were synthesized based on the "inactive metabolite" approach. The cleavage of the ester bond by blood and tissue esterases rapidly deactivates these compounds, resulting in an ultrashort duration of action. The beta-antagonist potencies and time courses of actions of the new "soft" BBs were characterized by recording ECG and intra-arterial blood pressure (BP) in rats. In the isoproterenol-induced tachycardia model, while bufuralol at an iv dose of 1 mg/kg (3.8 micromol/kg) diminished heart rate (HR) for at least 2 h, the effects of the soft drugs lasted for only 10-30 min at equimolar dose. The inactive metabolite did not decrease HR significantly. The first four members of this series of compounds showed the highest beta-blocking potencies, ranging between 25% and 50% of that of bufuralol. Next, the effects of these most active compounds on resting HR and BP were evaluated in comparison to esmolol. Infused for 10 min at a rate of 20 micromol/kg/min, esmolol decreased HR and mean arterial pressure (MAP) by 40% and 60%, respectively. The soft drugs at doses ranging only between 2 and 4 micromol/kg/min resulted in a 20-40% decrease in HR and a 30-50% reduction in MAP. However, the time courses of both the bradycardic and hypotensive effects of the soft drugs were superimposable to that of esmolol, diminishing within 60 min after the discontinuation of the infusions.

Synthesis and pharmacological evaluation of prodrugs of valproic acid

We report the synthesis of (+/-)-3,6-Di-O-valproil-1,2:4,5-di-O-isopropylidene-myo-inositol (5) as well as (+/-)-3,6-Di-O-valproil-4,5-O-isopropylidene-myo-inositol (6) and (+/-)-3,6-Di-O-valproil-myo-inositol (7), which results from acid hydrolysis of the formers. The anticonvulsant activity of the compound 7 (MES test) expressed as ED50 is four times higher than that reported for valproic acid.

Soft cannabinoid analogues as potential anti-glaucoma agents

Cannabinoids have intraocular pressure (IOP) lowering effects, thus, they have a therapeutic potential in the treatment of glaucoma. Unfortunately, in the same time, they show CNS and cardiovascular effects as well. Our aim was to develop a safer, cannabinoid type anti-glaucoma agent, a topically applied soft analogue, that has local, but no systemic effect. The lead compound chosen was a nitrogen-containing cannabinoid analogue that was shown to have IOP lowering activity. A full library of possible soft drugs was generated and the structures were ranked based on the closeness of calculated properties to those of the lead compound. The lead compound has been synthesized, and a preliminary pharmacological study was performed. The structure-activity relationship and pharmacological results indicate a good possibility for the development of a safe, soft anti-glaucoma agent.

Design, synthesis, and pharmacological evaluation of soft glycopyrrolate and its analog

Glycopyrrolate is a quaternary anticholinergic drug. Like for other anticholinergics, the usefulness of this agent is limited by its side effects. In this study, based on the structure of glycopyrrolate, we designed a soft drug, methoxycarbonylphenyl-cyclopentylacetoxy-N,N-dimethyl-3-p yrrolidinium methyl sulfate (SG), and its analog, methoxycarbonylphenylcyclopentyl-acetoxyethyl-N,N,N-trimethylammon ium methyl sulfate (SGA). These soft drugs are expected to be locally active, but systemically inactive in order to increase therapeutic index. SG and SGA were synthesized by (i) carboxylation of methyl phenylcyclopentylacetate, (ii) esterification with N-methyl-3-pyrrolidinol (for SG) or 2-chloro-N,N-dimethylaminoethane (for SGA), and (iii) quarternization with dimethyl sulfate. Receptor binding studies demonstrate that SG has muscarinic subtype selectivity (m3/m2). Guinea pig ileum pA2 assay indicates that activity of SG is moderate, and SG is about ten times more potent than SGA. The in vivo characterization of SG and SGA, both in mydriasis tests and in prevention of carbachol induced bradycardia, supported its soft nature. Applying SG or SGA into rabbit eyes, the dilation of the contralateral (water-treated) pupils was not observed. Glycopyrrolate application, however, caused dilation of the contralateral pupil, indicating a systemic effect of this drug. Cardiac studies were carried out by evaluating the protective effect of soft anticholinergics against carbachol induced bradycardia. The results indicate that SG and SGA were as potent as atropine-MeBr in preventing carbachol induced bradycardia in the rat; however, their durations of action were significantly shorter. In conclusion, the newly synthesized SG and SGA showed soft nature in the body. They are anticholinergics with subtype selectivity and moderate potency, and can be used as topical antiperspirants.

Effect of cyclodextrins on the solubility and stability of a novel soft corticosteroid, loteprednol etabonate

To increase the aqueous solubility and stability of the soft corticosteroid loteprednol etabonate (LE), drug complexation using various cyclodextrins (CDs), such as gamma-cyclodextrin (gamma-CD), 2-hydroxypropyl-beta-cyclodextrin (HPBCD), maltosyl-beta-cyclodextrin (MBCD), mixture of glucosyl/maltosyl-alpha-, beta-, and gamma-cyclodextrin (GMCD), and heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DMCD), were attempted. The solubilizing and stabilizing effects of CD by itself or combined with various co-solvents were also investigated. Micronized (5 micron) LE was mixed in various aqueous CD or CD with cosolvent solutions. After equilibration and filtration at 23 degrees C, the solubility of LE was determined by HPLC. Subsequently, the stability of LE in the solutions was also determined by following the LE concentration change in the solution for an appropriate period. CD complexation significantly increased the aqueous solubility and stability of LE. The increase in solubility displayed a concentration dependency on CDs (0-50%). Among the five CDs used, DMCD showed the highest effects on the solubility (4.2-18.3 mg/ml in 10-50% DMCD) and stability (t90 > 4 years at 4 degrees C, when LE 0.5 mg/ml was dissolved in 10% DMCD solution) of LE. By adding co-solvents, such as glycerol, propylene glycol (PG), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP-10), the solubility of LE in DMCD solutions was further increased. Degradation of LE to the corresponding metabolites, delta 1-cortienic acid etabonate (AE) and delta 1-cortienic acid (A), in aqueous CD solutions appeared to be a predicted, two-step kinetics. Differential Scanning Calorimetry (DSC) was used to assist explaining the solubilizing and stabilizing activity differences between CDs. LE/CD mixture or lyophilized LE/CD complex was scanned at a rate of 20 degrees C/min. The exothermic peak found in the DSC diagram with LE/DMCD sample, but not with LE/HPBCD samples, suggests a stronger complex formed between LE and DMCD, resulting in higher solubility and stability of LE in DMCD than in HPBCD.