Strategies in the design of solution-stable, water-soluble prodrugs II: properties of micellar prodrugs of methylprednisolone

Self-Assembly Properties of an Amphiphilic Phosphate Ester Prodrug Designed for the Treatment of COVID-19

PF-07304814 is a water-soluble phosphate ester prodrug of a small molecule inhibitor for the SARS CoV-2 3CL protease designed for the treatment of COVID-19. The amphiphilicity and self-assembly behavior of the prodrug was investigated computationally and experimentally via multiple orthogonal techniques to better design formulations for intravenous infusion. The self-assembly of PF-07304814 into micellar structures enabled an increase in the solubility of lipophilic impurities by up to 1900x in clinically relevant formulations. The observed solubilization could help extend the drug product shelf-life and in use stability through inhibition of precipitation, without the need for solubilizing excipients. The work presented in this manuscript provides a roadmap for the characterization of prodrug self-assembly and highlights the potential for prodrug modifications to enhance solubility of both active ingredients and impurities and to extend drug product shelf-life.

Albumin-Conjugated Lipid-Based Multilayered Nanoemulsion Improves Drug Specificity and Anti-Inflammatory Potential at the Spinal Cord Injury gSite after Intravenous Administration

Albumin-conjugated multilayered nanoemulsion (albumin-MNE) of methyl prednisolone (MP) was developed to ensure the specificity of the drug at the spinal cord injury (SCI) site. MNE was prepared by emulsification followed by ionic deposition of oppositely charged polymer followed by albumin conjugation using N-hydroxysuccinimide. Prepared nanoemulsion was characterized for particle size, polydispersity index (PDI), zeta potential (Zp), pH, viscosity, and entrapment efficiency. It was further evaluated for shape and morphological analysis, in vitro release, cell viability, and in vivo efficacy against post SCI-like conditions in terms of behavioral assessment, histopathological evaluation, and immunoflorescence assay of the histological sections showing Bax-driven apoptosis. Entrapment efficiency, particle size, PDI, and Zp of spherical-shaped, smooth-surfaced MNE droplets were found to be 68.9%, 83.2 ± 14.4 nm, 0.231, and + 62.7 mV, respectively. In vitro release of MP from MNE and albumin-MNE was observed to be 68.5 and 72.2% after 96th hour of the study. MNE showed higher viability of astrocytes than MP solution. Albumin-MNE improved behavior of SCI rat and histopathological conditions in a very effective manner when compared with MNE. Immunoflorescence assay reveals explicit decline in mitochondrial-mediated apoptosis by sub-cellular upregulation of Bax at spinal cord injury site. In conclusion, albumin-MNE delivered MP specifically at SCI site and avoided its instant availability inside astrocytes culture. On account of which the chitosan stabilized, lecithin-emulsified, multilayered nanoemulsion of MP depicts higher efficacy and safety than MNE and may offer safe and effective mean for the treatment of post SCI-like conditions in human.

Eudragit Coating of Chitosan-Prednisolone Conjugate Microspheres and In Vitro Evaluation of Coated Microspheres

Chitosan-prednisolone conjugate microspheres (Ch-SP-MS) were prepared, and Eudragit coating was applied in order to efficiently deliver the microspheres and drug to the intestinal disease sites. The Eudragit L100-coated microspheres (Ch-SP-MS/EuL100) were examined for particle characteristics and the release of drug and Ch-SP-MS in different pH media at 37 degrees C. Ch-SP-MS were spherical, with a mean size of 4.5 microm and prednisolone content of 3.3% (w/w). Ch-SP-MS/EuL100 were fairly spherical, with a mean size of 22. 5 microm and drug content of 0.32% (w/w). At pH 1.2, the release extent was less than 5% even at 48 h, and Eudragit coating tended to suppress the release. In contrast, at pH 6.8 and 7.4, Ch-SP-MS/EuL100 tended to show somewhat faster drug release than Ch-SP-MS. Ch-SP-MS/EuL100 displayed a release extent of 23 and 27% at pH 6.8 and 7.4, respectively. Ch-SP-MS aggregated at pH 1.2, but almost kept their initial size and shape at pH 6.8 and 7.4. Ch-SP-MS/EuL100 almost maintained their original shape and size at pH 1.2, and gradually released Ch-SP-MS at pH 6.8 and 7.4 due to dissolution of the Eudragit layer. Eudragit coating is suggested to be useful to efficiently deliver Ch-SP-MS to the intestinal disease sites.

Prodrug strategies to overcome poor water solubility

Drug design in recent years has attempted to explore new chemical spaces resulting in more complex, larger molecular weight molecules, often with limited water solubility. To deliver molecules with these properties, pharmaceutical scientists have explored many different techniques. An older but time-tested strategy is the design of bioreversible, more water-soluble derivatives of the problematic molecule, or prodrugs. This review explores the use of prodrugs to effect improved oral and parenteral delivery of poorly water-soluble problematic drugs, using both marketed as well as investigational prodrugs as examples. Prodrug interventions should be considered early in the drug discovery paradigm rather than as a technique of last resort. Their importance is supported by the increasing percentage of approved new drug entities that are, in fact, prodrugs.

Surface active drugs: self-association and interaction with membranes and surfactants. Physicochemical and biological aspects

Many pharmacologically active compounds are of amphiphilic (or hydrophobic) nature. As a result, they tend to self-associate and to interact with biological membranes. This review focuses on the self-aggregation properties of drugs, as well as on their interaction with membranes. It is seen that drug-membrane interactions are analogous to the interactions between membranes and classical detergents. Phenomena such as shape changes, vesiculation, membrane disruption, and solubilization have been observed. At the molecular level, these events seem to be modulated by lipid flip-flop and formation of non-bilayer phases. The modulation of physicochemical properties of drugs by self-association and membrane binding is discussed. Pathological consequences of drug-membrane interaction are described. The mechanisms of drug solubilization by surfactants are reviewed from the physicochemical point of view and in relation to drug carrying and absorption by the organism.

Calcium influx through calcium leak channels is responsible for the elevated levels of calcium-dependent proteolysis in dystrophic myotubes

To estimate calpain proteolysis, we measured the hydrolysis rate of a fluorogenic calpain substrate in individual resting normal and dystrophic mdx mouse myotubes in culture. Hydrolysis rates were high during myoblast and myotube alignment and fusion. After alignment and fusion ceased, hydrolysis rates declined. For normal myotubes, hydrolysis remained low after the development of contractile activity. In contrast, after the development of contractile activity, dystrophic mdx myotubes had abnormally high levels of hydrolysis that were dependent on external calcium and that could be abolished by calpeptin, an inhibitor of calpain. We eliminated the direct effects of contraction during measurements of hydrolysis by the addition of tetrodotoxin. Substrate hydrolysis by lysosomes or proteosomes was controlled for using NH(4)Cl and clasto-lactacystin beta-lactone, respectively. Increased activity of the calcium-activated protease in mature mdx myotubes was linked to the abnormal activity of calcium-specific leak channels because an antagonist of these channels reduced the higher levels of hydrolysis in dystrophic myotubes to nearly normal levels. The abnormal activity of these channels is linked to an increased frequency of transient sarcolemmal disruptions in the more fragile mdx myotubes (, ). Treatment of mdx myotubes with a pro-drug of methylprednisolone also reduced calpain substrate hydrolysis to nearly normal levels. However, this inhibition only required 2.5 h of pretreatment, which was not long enough to act by the known effects of prednisolone on calcium homeostasis.

Increased shelf-life of fosphenytoin: solubilization of a degradant, phenytoin, through complexation with (SBE)7m-beta-CD

Fosphenytoin, a water-soluble prodrug of phenytoin, degrades primarily to phenytoin at pH values <8 during long term storage; phenytoin readily precipitates when formed from fosphenytoin due to its limited aqueous solubility. The objective of this study was to develop stable formulations of fosphenytoin in the pH range of 7.4-8. 0 by inhibiting the phenytoin precipitation through complexation with a parenterally safe cyclodextrin, (SBE)7m-beta-CD. Phase solubility studies at 25 degreesC revealed that phenytoin could be effectively solubilized by (SBE)7m-beta-CD both in the presence and absence of 80.6 mg/mL fosphenytoin (as its dihydrate). The binding constants for the phenytoin/cyclodextrin complex were found to be 1073 and 792 M-1 at pH 7.4 and pH 8.0, respectively. Because of the competitive inclusion between fosphenytoin and phenytoin with (SBE)7m-beta-CD, the extent of solubilization of phenytoin was lower, as expected, in the presence of fosphenytoin than in the absence of fosphenytoin, even though the binding constants for the fosphenytoin/cyclodextrin complex were relatively small (41-45 M-1). Initial rates were used to follow the production of phenytoin from fosphenytoin. Zero-order kinetics were observed under all conditions investigated. Phenytoin production rates were followed at 25, 37, and 50 degreesC in the presence of 0.03 or 0.06 M (SBE)7m-beta-CD. It was projected from the solubility of phenytoin and the kinetic information that fosphenytoin shelf lives as high as nine years at 25 degreesC and pH 7.4 in the presence of 60 mM of (SBE)7m-beta-CD might be possible while longer shelf lives might be possible at pH 8.

Photodegradation products of methylprednisolone suleptanate in aqueous solution--evidence of a bicyclo[3.1.0]hex-3-en-2-one intermediate

Two major photodegradation products of methylprednisolone suleptanate (sodium 11 beta, 17 alpha-dihydroxy-6 alpha-methyl-21-[[8-[methyl(2-sulfoethyl)amino]-1,8-dioxooctyl+ ++]oxy]-pregna-1,4-diene-3,20-dione) in aqueous solution irradiated with white fluorescent light at 2000 lux for 28 days at 25 degrees C were isolated by preparative high-performance liquid chromatography and characterized. Structures of the photodegradation products were determined as sodium 11 beta,17 alpha-dihydroxy-5 alpha, 6 alpha-dimethyl-21-[[8-[methyl(2-sulfoethyl)amino]-1,8-dioxoocty l]-oxy]-19-norpregna-1(10),3-diene-2,20-dione and sodium 1 beta, 11 beta-epoxy-17 alpha-hydroxy-6 alpha-methyl-21-[[8-[methyl(2-sulfoethyl)amino]-1, 8-dioxooctyl]oxy]-19 alpha-pregn-4-ene-2.20-dione. Formation of these compounds, especially the 1,11-epoxy analogue, strongly supports the existence of the bicyclo[3.1.0]hex-3-en-2-one intermediate in the photorearrangement of steroidal cross-conjugated dienones. The intermediate can account for all the major ketonic and phenolic products; these products are generated from the intermediate after subsequent transformations and/or further skeletal rearrangements. The 1,11-epoxy analogues were obtained from the prednisolone steroids in high yields by irradiation with a high-pressure mercury lamp.

Effect of ionic strength on solution stability of PNU-67590A, a micellar prodrug of methylprednisolone

PURPOSE

PNU-67590A is a water-soluble micellar prodrug of methylprednisolone (MP). The major products of degradation of PNU-67590A are MP by hydrolysis and methylprednisolone 17-suleptanate (17-E) by 21-->17 acyl migration. The effect of ionic strength on micelle formation and stability of PNU-67590A in aqueous solution was examined.

METHODS

PNU-67590A solutions at pH 2 and 8 and ionic strength of 0.05, 0.1, 0.2, and 0.4 M were maintained at 25 degrees C in the dark to measure MP and 17-E levels over time.

RESULTS

The rate of degradation of micellar PNU-67590A at pH 8 was less than that of monomeric PNU-67590A, and vice versa at pH 2. Increase in ionic strength decreased both the critical micelle concentration of PNU-67590A and the degradation of micelle PNU-67590A at both pHs, resulting in improved overall stability of PNU-67590A.

CONCLUSIONS

Formulation of PNU-67590A in a concentrated solution with high ionic strength will maximize stability and shelf-life.

Risk factors for male breast cancer

Risk factors for male breast cancer were investigated in a case-control study of 21 cases and 82 controls admitted to hospital for acute, non-neoplastic, non-hormone-related diseases in the Greater Milan area between 1988 and 1994. More educated men tended to be at higher risk of breast cancer, with a multivariate odds ratio (OR) of 2.6 [95% confidence interval (CI) 0.7-9.4]. The OR was 3.2 (95% CI 1.1-9.6) for those in the higher social class. Men with no offspring were at higher risk than fathers, with an OR of 5.5 (95% CI 1.8-16.7). A history of breast cancer in female relatives was reported by two cases and one control, giving an OR of 8.5 (95% CI 1.1-69.0). Cases were somewhat heavier than controls, and significantly taller, with an OR of 5.7 (95% CI 1.6-19.9) for subjects taller than 170 cm vs shorter ones. The association with weight, however, decreased after allowance for height, and no difference was observed for body mass index. Socioeconomic correlates and family history are similar to well-assessed risk factors for female breast cancer. The associations with anthropometric measures and childlessness may find an explanation in chromosomal abnormalities, such as Klinefelter's syndrome, or other hormone-related disorders.

Marked antinephritic action and less adverse effects of methylprednisolone suleptanate by intermittent administration in rats

To establish the regimen for beneficial prolonged treatment with glucocorticoids on nephritis, we investigated the antinephritic effect of methylprednisolone suleptanate (MPS) and its influence on adrenal function by intermittent administration (IA) in comparison with daily administration (DA) in crescentic-type anti-GBM nephritic rats. In IA, MPS (0.25, 1.0 and 3.0 mg/kg) was injected for 3 successive days followed by a 3-day withdrawal during a 40-day period. MPS inhibited the elevation of urinary protein and serum cholesterol and glomerular alterations by both IA and DA. The effect of MPS on these parameters was more potent by IA than by DA. MPS significantly suppressed the increment of the number of ED-1(+) cells and TH-1(+) cells in nephritic glomeruli. DA, but not IA, caused atrophy of the adrenal glands. IA prevented the remarkable decrease in corticosterone level provoked in nephritic rats. In conclusion, for the treatment of nephritis, IA seems to be a better regimen for the administration of MPS. MPS may exert an antinephritic action by inhibiting mesangial cell proliferation and infiltration of monocytes/macrophages into glomeruli in addition inhibiting antibody production.

Immediate inhibitory effect of methylprednisolone suleptanate (U-67590A) on antigen-induced cutaneous and airway anaphylactic responses in guinea-pigs

1. Inhibitory effects of water-soluble glucocorticoids administered intravenously were examined on skin and airway reactions caused by antigen challenge or chemical mediators in guinea-pigs. 2. Methylprednisolone suleptanate (U-67590A) which is an analogue of methylprednisolone, produced immediate inhibition of 3-h and 7-day homologous passive cutaneous anaphylaxis (PCA) reactions, but not of histamine- or bradykinin-induced cutaneous vascular permeability, when administered 10 min before antigen challenge. In contrast, methylprednisolone succinate (MP) or dexamethasone (DXM) administered 10 min before antigen challenge failed to show an immediate inhibitory effect on the PCA or mediator-induced reactions. When administered 1 to 5 h before antigen challenge, all the steroids used in this study reduced both PCA and mediator-induced reactions. 3. Pretreatment with cycloheximide almost completely abolished the late inhibition of 3-h PCA and histamine reactions produced by U-67590A or MP, but it did not affect the immediate inhibition of 3-h PCA produced by U-67590A. 4. U-67590A also demonstrated immediate inhibitory effects on antigen-induced bronchoconstriction in guinea-pigs actively sensitized with ovalbumin even when administered 10 min before antigen challenge, whereas MP and DXM failed to show the immediate inhibitory effect. When administered 3 h before antigen challenge, all the steroids used in this study reduced the response to antigen. 5. The late inhibitory effect of U-67590A administered 3 h before antigen challenge was almost completely abolished by treatment with cycloheximide or 17 alpha-methyltestosterone, whereas the immediate inhibition produced by U-67590A administered 10 min before challenge was not affected by this treatment. 6. U-67590A administered 10 min or 3 h before challenge did not affect the bronchoconstriction induced by histamine or leukotriene D4.7. Release of histamine from lung fragments of sensitized guinea-pigs in vitro was inhibited by U-67590A.8. The present experiments indicate that U-67590A demonstrated dual, immediate and late, inhibitory effects. The former are independent of protein synthesis and may be associated with non-genomic direct action on the mediator-releasing process without affecting mediator-induced reactions. The latter share common inhibitory actions with other glucocorticoids which are dependent on protein synthesis through gene expression.

Water-soluble, solution-stable, and biolabile N-substituted (aminomethyl)benzoate ester prodrugs of acyclovir

Various N-substituted 3- or 4-(aminomethyl)benzoate esters of acyclovir were synthesized and evaluated as water-soluble prodrug forms with the aim of improving the delivery characteristics of acyclovir, in particular its parenteral administration. The esters showed a high solubility in weakly acidic solutions and, as demonstrated with the 3-(N,N-dipropylaminomethyl)benzoate ester, a high stability in such solutions, allowing storage for several years. The esters combine these properties with a high susceptibility to undergo enzymatic hydrolysis in plasma. The half-lives of hydrolysis in 80% human plasma ranged from 0.8 to 57 min, the rate being highly dependent on the position (3 or 4) of the aminomethyl group relative to the ester moiety. All esters were more lipophilic than acyclovir in terms of octanol-pH 7.4 buffer partition coefficients. These properties make N-substituted (aminomethyl)-benzoate esters a promising new prodrug type for acyclovir to enhance its delivery characteristics.

Self-association and solubility behaviors of a novel anticancer agent, brequinar sodium

To aid in the selection of appropriate excipients to formulate brequinar sodium [6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinolinecarboxyli c acid sodium salt; DuP 785], studies were initiated to characterize thoroughly its solubility behavior. The measured solubilities at RT (approximately 23 degrees C) agreed with the theoretical values in the pH range from 0.5 to 7.2, but became significantly greater than theoretical values at pH values above 7.2. This deviation was likely due to the vertical stacking-type self-association between brequinar molecules in water. The NMR and pH methods determined a critical association concentration of 15 mg/mL. Sodium salicylate, which has been proven to interfere with molecular self-association, reduced drug solubility from 116 to 10 mg/mL. But urea, another deaggregative agent, gave about a twofold increase rather than a decrease in solubility. Addition of sodium chloride caused a 226-fold decrease in solubility. The apparent solubility product did not remain constant but decreased as sodium chloride concentration increased, suggesting that the added salt decreased the degree of self-association between brequinar molecules. Among four surfactants examined (a bile salt with a rigid fused ring versus three ordinary surfactants with a flexible chain structure), only sodium cholate significantly increased the aqueous solubility of brequinar sodium.

Strategies in the design of solution-stable, water-soluble prodrugs III: influence of the pro-moiety on the bioconversion of 21-esters of corticosteroids

Succinate esters and many other carboxylic acid esters utilized as water-soluble prodrugs have limited utility due to their aqueous solution instability. In an earlier study, a strategy for the design of solution-stable 21-carboxylic acid esters of corticosteroids was developed from a consideration of various physical organic factors which influence ester hydrolysis. Several 21-esters of methylprednisolone were synthesized, and their stability in aqueous solution was monitored to demonstrate the feasibility of the approach. In this study, the bioconversion of representative examples of 21-esters of methylprednisolone exhibiting shelf lives of greater than or equal to 2 years at 25 degrees C was monitored to evaluate their utility as prodrugs in comparison to a commercially marketed sodium succinate ester. Ester hydrolysis studies conducted in human and rhesus monkey serum suggest that derivatives having an anionic solubilizing moiety (sulfonate or carboxylate) are not hydrolyzed in serum, while compounds having a cationic (tertiary amino) solubilizing moiety are hydrolyzed rapidly by serum esterases. In vivo pharmacokinetic studies in rhesus monkeys were also conducted to compare the bioconversion rates and overall bioavailability of several solution-stable prodrugs with the 21-succinate ester. Derivatives having solution stability exceeding 2 years at 25 degrees C with a faster bioconversion rate and an overall bioavailability equal to or higher than that of the succinate ester have been identified. Relative bioavailability appears to be highly sensitive to the charge of the solubilizing pro-moiety and pro-moiety chain length.