Salt form selection and characterization of LY333531 mesylate monohydrate

Determination of Ruboxistaurin analysis in rat plasma utilizing LC–MS/MS technique

Background

Ruboxistaurin (RBX) used to treat retinopathy in diabetic patients which caused by microvascular damage and leakage which contributes to visual loss. There are no published studies on the use of liquid chromatography-tandem mass spectrometry for development and validation of a simple, sensitive, and accurate method for measuring RBX in rat plasma.

Method

Chromatographic separation of RBX was achieved using ultra-performance liquid chromatography. Multiple-reaction monitoring quantification used RBX [M + H] + ion at m/z 469.18 and daughter ions at m/z 84, 58.12, and 98.10. Atorvastatin was used as internal standard (IS), has a single daughter ion, and was identified using m/z 559.6 → 249.9. Validation of the liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for RBX in rat plasma for linearity (greater than0.997) was carried out at 25-1000 ng/mL.

Results

In rat plasma, the accuracy was within 3.4%, and the intra- and inter-day precision was within 11.8%. Stability, recovery, and matrix effect were all within acceptable limits. The drug retention time (0.85 ± 0.03 min) was remarkably short.

Conclusion

The method developed in the current study is suitable to quantify RBX in plasma or bulk doses.

Estimating the maximal solubility advantage of drug salts

Salt formation can enable the development of poorly water-soluble drugs containing at least one ionizable moiety. Not only can salts offer a solubility enhancement that can sometimes far exceed that of other commonly used solubilization strategies applied across the pharmaceutical industry, they can simultaneously bestow additional benefits such as providing low-cost formulation options. The goal of this work is to put forth a simple methodology to enable one to accurately predict the maximal solubility advantage of acidic and basic drugs whose unionized conjugate (neutral parent molecule) is poorly soluble. While published equations leveraging the Henderson-Hasselbalch/H-H relationship reasonably estimate the thermodynamic solubility limit (in systems where there is no supersaturation), under physiologically relevant conditions the maximal/kinetic solubility can play an important role in determining oral bioavailability, as in the case of amorphous drugs. Under these circumstances, a higher solubility can be maintained for short durations through drug supersaturation provided that the precipitation is slow, thereby causing deviations from H-H predictions. It is possible also that, in some instances, supersaturation could coincide with behavior previously attributed to drug aggregation in solution. The proposed methodology utilizes speciation across the pH range to allow one to determine the maximal amount of ionized and unionized drug in solution at each pH. The calculation is easily extended to cases where the counterion serves as a competing weak acid, weak base, or as a common ion. Additionally, a more thorough assessment of the Gibbs free energy change associated with the solubilization of salts is also presented, as this energy describes the key driving force for the recrystallization of the neutral parent by triggering its nucleation. Lastly, to demonstrate applicability to real-world compounds containing multiple ionizable moieties, the complex pH-solubility profile of a drug maleate salt taken from the literature is simulated.

Synthesis and Characterization of the Selective, Reversible PKCβ Inhibitor (9 S)-9-[(Dimethylamino)methyl]-6,7,10,11-tetrahydro-9 H,18 H-5,21:12,17-dimethenodibenzo[ e,k]pyrrolo[3,4- h][1,4,13]oxadiazacyclohexadecine-18,20(19 H)-dione, Ruboxistaurin (LY333531)

The demonstrated role of PKC_β in  mediating amphetamine-stimulated dopamine efflux, which regulates amphetamine-induced dopamine transporter trafficking and activity, has promoted the research use of the selective, reversible PKC_β inhibitor (9 S)-9-[(dimethylamino)methyl]-6,7,10,11-tetrahydro-9 H,18 H-5,21:12,17-dimethenodibenzo[ e,k]pyrrolo[3,4- h][1,4,13]oxadiazacyclohexadecine-18,20(19 H)-dione, ruboxistaurin. Despite the interest in development of ruboxistaurin as the mesylate monohydrate (Arxxant) for the treatment of diabetic retinopathy, macular edema, and nephoropathy, several crucial details in physicochemical characterization were erroneous or missing. This report describes the synthesis and full characterization of ruboxistaurin free base (as a monohydrate), including X-ray crystallography to confirm the absolute configuration, and of the mesylate salt, isolated as a hydrate containing 1.5 mol of water per mole.

Preparation, characterization, and in vitro/vivo evaluation of polymer-assisting formulation of atorvastatin calcium based on solid dispersion technique

Due to low solubility and bioavailability, atorvastatin calcium is confronted with challenge in conceiving appropriate formulation. Solid dispersion of atorvastatin calcium was prepared through the solvent evaporation method, with Poloxamer 188 as hydrophilic carriers. This formulation was then characterized by scanning electron microscopy, differential scanning calorimetry, powder X-ray diffraction and fourier transform infrared spectroscopy. Moreover, all these studies suggested the conversion of crystalline atorvastatin calcium. In addition, the drug solubility studies as well as dissolution rates compared with bulk drug and market tablets Lipitor were also examined. Furthermore, the study investigated the pharmacokinetics after oral administration of Lipitor and solid dispersion. And the AUC_0–8 h and C_max increased after taking ATC-P188 solid dispersion orally compared with that of Lipitor. All these could be demonstrated that ATC-P188 solid dispersions would be prospective means for enhancing higher oral bioavailability of ATC.

Assessment of spiramycin-loaded chitosan nanoparticles treatment on acute and chronic toxoplasmosis in mice

Toxoplasmosis is a zoonotic parasitic disease with worldwide distribution. Chitosan is a natural polymer which is commonly used in the production of nanomedicines. It is known to enable higher drug permeation, being biocompatible and has very low toxicity, besides its antimicrobial effects. Our study aimed to assess the effect of spiramycin-loaded chitosan nanoparticles (SLCNs) in treatment of acute and chronic toxoplasmosis in mice. 200 male Swiss albino mice were included in our study, divided to two main groups; Toxoplasma gondii RH strain infected group and ME49 strain infected group, each main group was subdivided into four subgroups; subgroup I: infected control, subgroup II: infected and received chitosan nanoparticles (CS NPs); 20 µg of CS NPs in 100 µl of PBS/mouse/dose, subgroup III: infected and treated with spiramycin (Rovamycin); 100 mg/kg/day, subgroup IV: infected and treated with 100 mg/kg/day spiramycin-loaded chitosan nanoparticles. Effect of treatment was assessed parasitologically and histopathologically. It was noticed that SLCNs significantly decreased the mortality rate of infected mice with both strains compared to high mortality rate of mice in the infected control subgroups. Moreover, there was a significant decrease in the number of organisms of SLCNs treated subgroup as compared to the other subgroups. Histopathological studies showed a marked improvement of the pathological pictures of brain, liver, spleen and eye in the subgroup received SLCNs as opposed to other groups. In conclusion, the present study revealed that loading of spiramycin on chitosan nanoparticles increased its antiparasitic effect on acute and chronic T. gondii infection.

The effect of microcrystalline cellulose crystallinity on the hydrophilic property of tablets and the hydrolysis of acetylsalicylic acid as active pharmaceutical ingredient inside tablets

The crystal structures of active pharmaceutical ingredients and excipients should be strictly controlled because they influence pharmaceutical properties of products which cause the change in the quality or the bioavailability of the products. In this study, we investigated the effects of microcrystalline cellulose (MCC) crystallinity on the hydrophilic properties of tablets and the hydrolysis of active pharmaceutical ingredient, acetylsalicylic acid (ASA), inside tablets by using tablets containing 20% MCC as an excipient. Different levels of grinding were applied to MCC prior to tablet formulation, to intentionally cause structural variation in the MCC. The water penetration and moisture absorbability of the tablets increased with decreasing the crystallinity of MCC through higher level of grinding. More importantly, the hydrolysis of ASA inside tablets was also accelerated. These results indicate that the crystallinity of MCC has crucial effects on the pharmaceutical properties of tablets even when the tablets contain a relatively small amount of MCC. Therefore, controlling the crystal structure of excipients is important for controlling product qualities.

Physicochemical properties of novel protein kinase inhibitors in relation to their substrate specificity for drug transporters

INTRODUCTION

Small molecule tyrosine and serine-threonine kinase inhibitors (TKIs and STKIs) are emerging drugs that interfere with downstream signaling pathways involved in cancer proliferation, invasion, metastasis and angiogenesis. The understanding of their pharmacokinetics, the identification of their transporters and the modulating activity exerted on transporters is pivotal to predict therapy efficacy and to avoid unwarranted drug treatment combinations.

AREAS COVERED

Experimental or in silico data were collected and summarized on TKIs and STKIs physico-chemical properties, which influence their transport, metabolism and efficacy, and TKIs and STKIs as influx transporter substrates and inhibitors. In addition, the uptake by tumor cell influx transporters and some factors in the tumor microenvironment affecting the uptake of TKIs and STKIs by cancer cells are briefly covered.

EXPERT OPINION

Membrane transporters play an important role in the pharmacokinetics and hence the efficacy of anticancer drugs, including TKIs and STKIs. These drugs are substrates and inhibitors of various transporters. Drug resistance may be bypassed not only by identifying the proper transporter but also by selective combinations, which may either downregulate or increase transporter activity. However, care has to be taken because this profile might be disease, drug and patient specific.

Novel organic salts based on fluoroquinolone drugs: synthesis, bioavailability and toxicological profiles

In order to overcome the problems associated with low water solubility, and consequently low bioavailability of active pharmaceutical ingredients (APIs), novel organic salts containing fluoroquinolones (e.g. ciprofloxacin and norfloxacin) were prepared, using an optimized synthetic procedure based on direct protonation, with different biocompatible counter ions such as mesylate, gluconate and glycolate. All the prepared organic salts were characterized by spectroscopic techniques, mass spectrometry and thermal analysis. Solubility studies in water and simulated biological fluids at 25°C and 37°C were also performed. Additionally, octanol-water and phospholipid-water partition coefficients were measured at 25°C. The cytotoxicity and anti-inflammatory efficacy using an human cell model of intestinal epithelia (Caco-2 cells) were also evaluated and compared to those of the parent APIs. The adequate selection of the biocompatible anions allows the tuning of important physical, thermal and toxicological properties.

An effect of cellulose crystallinity on the moisture absorbability of a pharmaceutical tablet studied by near-infrared spectroscopy

In this study, we investigated molecular-level variation of tablets caused by grinding and its effect on their actual moisture absorbability. Model tablets contained acetaminophen as an active pharmaceutical ingredient and microcrystalline cellulose (MCC) as an excipient. Different levels of grinding were applied during the tablet formulation to intentionally cause the structural variation of the MCC. The moisture absorbability of tablets showed obvious variation depending on the grinding time, and the corresponding change in near-infrared spectra was readily captured. The detailed analysis of the variation of the band frequencies (i.e., wavenumber) revealed that the grinding process substantially disintegrates the crystalline and generates a glassy amorphous structure of MCC, which is a requirement to absorb water molecules. Consequently, it is very likely that the change of the moisture absorbability of the tablets is closely related to the development of the amorphous structure. These results indicate that the pharmaceutical product performances can be influenced by the physical properties of the excipient, which in turn can be controlled by the grinding process.

Incorporation of physiologically based pharmacokinetic modeling in the evaluation of solubility requirements for the salt selection process: a case study using phenytoin

In the pharmaceutical industry, salt is commonly used to improve the oral bioavailability of poorly soluble compounds. Currently, there is a limited understanding on the solubility requirement for salts that will translate to improvement in oral exposure. Despite the obvious need, there is very little research reported in this area mainly due to the complexity of such a system. To our knowledge, no report has been published to guide this important process and salt solubility requirement still remains unanswered. Physiologically based pharmacokinetic (PBPK) modeling offers a means to dynamically integrate the complex interplay of the processes determining oral absorption. A sensitivity analysis was performed using a PBPK model describing phenytoin to determine a solubility requirement for phenytoin salts needed to achieve optimal oral bioavailability for a given dose. Based on the analysis, it is predicted that phenytoin salts with solubility greater than 0.3 mg/mL would show no further increases in oral bioavailability. A salt screen was performed using a variety of phenytoin salts. The piperazine and sodium salts showed the lowest and highest aqueous solubility and were tested in vivo. Consistent with our analysis, we observed no significant differences in oral bioavailability for these two salts despite an approximate 60 fold difference in solubility. Our study illustrates that higher solubility salts sometimes provide no additional improvements in oral bioavailability and PBPK modeling can be utilized as an important tool to provide guidance to the salt selection and define a salt solubility requirement.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Impact of preformulation on drug development

INTRODUCTION

Preformulation assists scientists in screening lead candidates based on their physicochemical and biopharmaceutical properties. This data is useful for selection of new chemical entities (NCEs) for preclinical efficacy/toxicity studies which is a major section under investigational new drug application. A strong collaboration between discovery and formulation group is essential for selecting right NCEs in order to reduce attrition rate in the late stage development.

AREAS COVERED

This article describes the significance of preformulation research in drug discovery and development. Various crucial preformulation parameters with case studies have been discussed.

EXPERT OPINION

Physicochemical and biopharmaceutical characterization of NCEs is a decisive parameter during product development. Early prediction of these properties helps in selecting suitable physical form (salt, polymorph, etc.) of the candidate. Based on pharmacokinetic and efficacy/toxicity studies, suitable formulation for Phase I clinical studies can be developed. Overall these activities contribute in streamlining efficacy/toxicology evaluation, allowing pharmacologically effective and developable molecules to reach the clinic and eventually to the market. In this review, the magnitude of understanding preformulation properties of NCEs and their utility in product development has been elaborated with case studies.

Effect of counterions on physicochemical properties of prazosin salts

This study evaluated the effect of counterions on the physicochemical properties of prazosin salts. Salt forms of prazosin, namely, mesylate, besylate, tosylate, camsylate, oxalate, and maleate, were prepared and compared with the marketed anhydrous and polyhydrate forms of prazosin hydrochloride. Physicochemical characterization was performed in the order of crystallinity, hygroscopicity, solubility, and stability to select the optimal salt(s). Permeability study in Caco-2 cell lines and in vivo bioavailability study in rat model were investigated to ascertain their biopharmaceutical advantage. All salt forms were crystalline, nonhygroscopic (except the anhydrous hydrochloride salt), and had solubility in the range of 0.2 to 1.6 mg/ml. All salts were physically and chemically stable at 40°C/75% relative humidity, but degraded in UV-visible light, except the anhydrous hydrochloride salt. Prazosin mesylate was selected as the optimal salt, as it possessed higher solubility, permeability, and bioavailability, compared to the commercial hydrochloride salts. Hydrochloride salt is reported to have poor bioavailability that is partially attributed to its low solubility and extensive common-ion effect in the gastric region. Factors like hydrophilicity of the counterion, hydration state of the salt, and melting point of the salt contribute to the physicochemical properties of the salts. This study has implications in the selection of an optimal salt form for prazosin, which is suitable for further development.

Solution-mediated phase transformation: significance during dissolution and implications for bioavailability

Solubility improvement of poorly soluble drug compounds is a key approach to ensuring the successful development of many new drugs. Methods used to improve the solubility of drug compounds include forming a salt, cocrystal, or amorphous solid. These methods of improving solubility can often lead to a phenomenon called solution-mediated phase transformation, a phase change that is facilitated through exposure to solution. Solution-mediated phase transformation occurs in three steps: dissolution to create a supersaturated solution followed by nucleation of less soluble phase and the growth of that phase. When the growth of the less soluble phase occurs on the surface of the metastable solid, this phenomenon can cause a marked decrease in dissolution rate during in vitro dissolution evaluation, and ultimately in vivo. Therefore, transformation to a less soluble solid during dissolution is an important aspect to consider when evaluating approaches to increase the solubility of a poorly soluble drug. Identification of solution-mediated phase transformation during dissolution is reviewed for powder dissolution, rotating disk method, and channel flow-through apparatus. Types of solution-mediated phase transformation are described in this report, including those involving salts, polymorphs, amorphous solids, and cocrystals. Many experimental examples are provided. Evidence of potential solution-mediated phase transformation in vivo is discussed to better understand the relationship between in vitro dissolution evaluation and in vivo performance.

Preformulation evaluation of AZD1305, an oxabispidine intended for oral and intravenous treatment

AIM

AZD1305 is a novel, water-soluble investigational antiarrhythmic agent for restoration and maintenance of sinus rhythm in atrial fibrillation patients. The present studies were performed to evaluate the possibility for further development of the compound.

METHODS

A set of technical approaches were used, including X-ray powder diffractometry, differential scanning calorimetry, thermogravimetrical analysis, dynamic vapor sorption, scanning electron microscopy, salt screen, and liquid chromatography.

RESULTS

AZD1305 is a crystalline oxabispidine and its neutral form is a base with a pK(a) of 9.9. The substance degrades with higher temperature and lower pH. The free base of the solid substance is stable at 25°C (closed container), 40°C/75% relative humidity (open container), and at 50°C (closed container) for at least 3 months. The free base of AZD1305 is polymorphic with two known forms. Both forms are non-hygroscopic ansolvates with melting points of approximately 90°C. No salt was found with overall improved properties. The substance had a strong odor, which was reduced by increased particle size.

CONCLUSIONS

The free base of AZD1305 seemed to be the most suitable agent for product development even though it has a fairly low melting point and occurred as two different crystal forms. Form B was the most stable thermodynamically in the temperature interval of interest.

The complex world of oligodendroglial differentiation inhibitors

Myelination is a central nervous system (CNS) process wherein oligodendrocyte-axon interactions lead to the establishment of myelin sheaths that stabilize, protect, and electrically insulate axons. In inflammatory demyelinating diseases such as multiple sclerosis (MS), the degeneration and eventual loss of functional myelin sheaths slows and blocks saltatory conduction in axons, which results in clinical impairment. However, remyelination can occur, and lesions can be partially repaired, resulting in clinical remission. The recruitment and activation of resident oligodendrocyte precursor cells (OPCs) play a critical role in the repair process because these cells have the capacity to differentiate into functional myelinating cells. Mature oligodendrocytes, however, are thought to have lost the capacity to develop new myelin sheaths and frequently undergo programmed cell death in MS. The endogenous capacity to generate new oligodendrocytes in MS is limited, and this is predominantly due to the presence of inhibitory components that block OPC differentiation and maturation. Here, we present an overview of recently identified negative regulators of oligodendroglial differentiation and their potential relevance for CNS repair in MS. Because currently available immunomodulatory drugs for MS mainly target inflammatory cascades outside the brain and fail to repair existing lesions, achieving more efficient lesion repair constitutes an important goal for future MS therapies.

Ruboxistaurin: PKC-beta inhibition for complications of diabetes

Diabetes mellitus is the most common cause of blindness among working-age adults, with a prevalence of 7 - 8% of adults in the USA, and is one of the most common causes of renal failure requiring kidney transplant and the most common cause of non-traumatic lower limb amputation in developed nations [1] . The role of the intracellular signaling enzyme protein kinase C (PKC) in the development of diabetic complications has become a field of intense research interest. An inhibitor of the PKC-beta isoform ruboxistaurin (RBX) has in vitro and in vivo benefits in ameliorating disturbances of cell regulation and blood flow related to hyperglycemia. The benefit of RBX for peripheral neuropathy has not been successfully demonstrated in Phase III trials. Although there was a beneficial effect of RBX on nephropathy in a pilot study, there has been no further clinical development for this indication. The major cause of visual disability - diabetic macular edema - seems to respond to RBX treatment with both anatomic and functional benefits. The manufacturer, Eli Lilly Co., has received an approvable letter from the FDA for the prevention of vision loss in patients with diabetic retinopathy with RBX, pending results of additional clinical trials for this indication.

Initial salt screening procedures for manufacturing ibuprofen

The aim of this paper is to design initial salt screening procedures for manufacturing ibuprofen. Salt forms of a pharmaceutical acid racemic (R,S)-(+/-)-ibuprofen and their "developable" synthetic routes were ferreted out simultaneously through the screening of seven bases of sodium hydroxide, potassium hydroxide, L-arginine, L-histidine, L-lysine, diethanolamine, and tris(hydroxymethyl)aminomethane (THAM), and the match with the use of nine organic solvents of methanol, dimethyl sulfoxide, ethanol, N, N-dimethylformamide, acetonitrile, isopropyl alcohol, 1,4-dioxane, acetone, and tetrahydrofuran mainly in the presence of water in 20 mL scintillation vials. Racemic (R,S)-(+/-)-sodium ibuprofen dihydrate, a well-known ibuprofen salt and the newly discovered racemic (R,S)-(+/-)-THAM ibuprofen, appeared as white-squared powders with a molecular weight of 327.42 g/mol, a melting point of 160.17 degrees C, and the apparent solubility product, K'(sp), of 6.0 x 10(-4) M(2) at 25 degrees C were successfully synthesized by the initial salt screening methods. The new amine salt of ibuprofen was monoclinic and had a space group of P2(1)/c and lattice parameters of a = 17.578(8) degrees, b = 10.428(4) degrees, c = 9.991(4) A, alpha = 90.00 degrees , beta = 97.17(1) degrees, gamma = 90.00 degrees, and V = 1,817.05(244) A(3). The aspect ratio of the amine salt crystals of ibuprofen of approximately 1.0 implied that the crystals had a better flowability than the sodium salt counterparts. This amine salt of ibuprofen was more stable in moist or dried atmospheres and was more hydrophobic than the sodium salt of ibuprofen. Moreover, the slow dissolution of this amine salt of ibuprofen might have made it less bitter and more suitable as a sustained release drug than the sodium salt of ibuprofen. The future work is to search for the different polymorphs of this amine salt of ibuprofen and to extend the initial salt screening working logics to the formation of co-crystals.

Chemical biology of natural indolocarbazole products: 30 years since the discovery of staurosporine

Staurosporine was discovered at the Kitasato Institute in 1977 while screening for microbial alkaloids using chemical detection methods. It was during the same era that protein kinase C was discovered and oncogene v-src was shown to have protein kinase activity. Staurosporine was first isolated from a culture of Actinomyces that originated in a soil sample collected in Mizusawa City, Japan. Thereafter, indolocarbazole compounds have been isolated from a variety of organisms. The biosynthesis of staurosporine and related indolocarbazoles was finally elucidated during the past decade through genetic and biochemical studies. Subsequently, several novel indolocarbazoles have been produced using combinatorial biosynthesis. In 1986, 9 years since its discovery, staurosporine and related indolocarbazoles were shown to be nanomolar inhibitors of protein kinases. They can thus be viewed as forerunners of today's crop of novel anticancer drugs. The finding led many pharmaceutical companies to search for selective protein kinase inhibitors by screening natural products and through chemical synthesis. In the 1990s, imatinib, a Bcr-Abl tyrosine kinase inhibitor, was synthesized and, following human clinical trials for chronic myelogenous leukemia, it was approved for use in the USA in 2001. In 1992, mammalian topoisomerases were shown to be targets for indolocarbazoles. This opened up new possibilities in that indolocarbazole compounds could selectively interact with ATP-binding sites of not only protein kinases but also other proteins that had slight differences in ATP-binding sites. ABCG2, an ATP-binding cassette transporter, was recently identified as an important new target for indolocarbazoles.

Preparation and characterization of salt forms of enalapril

Selection of an optimal salt form of a drug candidate is a vital component of preformulation stage of drug development. In this study, six salts of enalapril--citrate, mesylate, tartrate, malate, besylate and tosylate--were prepared and characterized by Mass Spectroscopy, Differential Scanning Calorimetry, Thermogravimetric Analysis, Microscopy, Powder X-ray Diffraction, Karl Fischer Titration, High Performance Liquid Chromatography, Fourier-Transform Infra-red Spectroscopy and Head Space Gas Chromatography. All the six salts were subjected to a tiered screening involving five stages in the following order: crystallinity, hygroscopicity, solubility, stability and flow/compactability. Enalapril malate showed encouraging profile because of its lower hygroscopicity, higher solubility, good solid state stability, and better flow and compactability, in comparison to the marketed maleate salt.

Increased Dissolution Rate and Bioavailability Through Comicronization with Microcrystalline Cellulose

Micronization is a commonly used enabling technology to improve the bioavailability of compounds where absorption is dissolution rate limited. However, decreasing particle size often results in increased Van der Waals' interactions and electrostatic attraction between particles. This causes agglomeration of particles, thereby compromising the increase in surface area gained by micronization. Comicronization with excipients has been reported to offer significant advantages over neat micronization. The present work describes the comicronization of a model compound CI-1040 at a high drug load that shows an increase in the dissolution rate and bioavailability in male Wistar rats. Physicochemical characterization of the comicronized and neat micronized material is presented to help explain the in-vitro and in-vivo data.

Protein kinase C isozymes and their selectivity towards ruboxistaurin

Protein kinase C (PKC) isozymes are an important class of enzymes in cell signaling and as drug targets. They are involved in specific pathways and have selectivity towards certain ligands, despite their high sequence similarities. Ruboxistaurin is a specific inhibitor of PKC-beta. To understand the molecular determinants for the selectivity of ruboxistaurin, we derived the three-dimensional structures of the kinase domains of PKC-alpha, -betaI, and -zeta using homology modeling. Several binding orientations of ruboxistaurin in the binding sites of these PKC catalytic domains were analyzed, and a putative alternative binding site for PKC-zeta was identified in its kinase domain. The calculated free energy of binding correlates well with the IC(50) of the inhibitor against each PKC isozyme. A residue-based energy decomposition analysis attributed the binding free energy to several key residues in the catalytic sites of these enzymes, revealing potential protein-ligand interactions responsible for ligand binding. The contiguous binding site revealed in the catalytic domain of PKC-zeta provides avenues for selective drug design. The details of structural nuances for specific inhibition of PKC isozymes are presented in the context of the three-dimensional structures of this important class of enzymes.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.

Physicochemical properties and oral bioavailability of amorphous atorvastatin hemi-calcium using spray-drying and SAS process

The objective of the study was to prepare amorphous atorvastatin hemi-calcium using spray-drying and supercritical antisolvent (SAS) process and evaluate its physicochemical properties and oral bioavailability. Atorvastatin hemi-calcium trihydrate was transformed to anhydrous amorphous form by spray-drying and SAS process. With the SAS process, the mean particle size and the specific surface area of amorphous atorvastatin were drastically changed to 68.7+/-15.8nm, 120.35+/-1.40m2/g and 95.7+/-12.2nm, 79.78+/-0.93m2/g from an acetone solution and a tetrahydrofuran solution, respectively and appeared to be associated with better performance in apparent solubility, dissolution and pharmacokinetic studies, compared with unprocessed crystalline atorvastatin. Oral AUC0-8h values in SD rats for crystalline and amorphous atorvastatin were as follow: 1121.4+/-212.0ngh/mL for crystalline atorvastatin, 3249.5+/-406.4ngh/mL and 3016.1+/-200.3ngh/mL for amorphous atorvastatin from an acetone solution and a tetrahydrofuran solution with SAS process, 2227.8+/-274.5 and 2099.9+/-339.2ngh/mL for amorphous atorvastatin from acetone and tetrahydrofuran with spray-drying. The AUCs of all amorphous atorvastatin significantly increased (P<0.05) compared with crystalline atorvastatin, suggesting that the enhanced bioavailability was attributed to amorphous nature and particle size reduction. In addition, the SAS process exhibits better bioavailability than spray-drying because of particle size reduction with narrow particle size distribution. It was concluded that physicochemical properties and bioavailability of crystalline atorvastatin could be improved by physical modification such as particle size reduction and generation of amorphous state using spray-drying and SAS process. Further, SAS process was a powerful methodology for improving the physicochemical properties and bioavailability of atorvastatin.