Bortezomib Aqueous Solubility in the Presence and Absence of D-Mannitol: A Clarification With Formulation Implications.

The solubility of bortezomib, a boronic acid, in water and normal saline is often misquoted in the literature. Here we confirm that bortezomib equilibrium solubility in water and normal saline is 0.59 ± 0.07 and 0.52 ± 0.11 mg/mL, respectively. The aqueous solubility is significantly enhanced, 1.92 ± 0.14 and 3.40 ± 0.21 mg/mL, respectively, in the presence of 55 mM and 137 mM D-mannitol in normal saline, as in the commercial formulation, Velcade®, after reconstitution. This is due to reversible ester formation between bortezomib and D-mannitol. Based on the pH-solubility profile curve for bortezomib in the absence of added D-mannitol, bortezomib's pKa value is estimated to be 8.8 ± 0.2. Boric acid, glycine and a combination of the two, used in an alternative formulation to that of Velcade® do not enhance the equilibrium aqueous solubility of bortezomib.

Prodrugs: My Initial Exploration and Where It Led.

This review presents my early exploration in the area of prodrugs and specifically prodrugs of the anticonvulsant, phenytoin, also called diphenylhydantoin. My journey started in graduate school with an introduction to the prodrug concept and continued for much of my career as I remain fascinated by the topic/technique. I have also included some backstories that the reader might find noteworthy. Prodrug intervention is now recognized as one of the better tools for taking a challenging small molecule drug from un-developable to developable.

Boric Acid, a Lewis Acid With Unique and Unusual Properties: Formulation Implications.

This review provides insight into the use of boric acid as a pharmaceutical, a buffer, and an adjuvant/excipient in pharmaceutical formulations. Boric acid is a Lewis acid with a pKa of 8.92-9.24 that is sensitive to temperature, ionic strength, and concentration. The pKa varies with concentration because of polymerization above 0.02 M. Boric acid reacts reversibly with alcohols, especially 1,2-diols including carbohydrates, with carboxylic acids, thiols, and amines. These esters/adducts, are also Lewis acids with lower pKa values. Boric acid can stabilize some materials while catalyzing the degradation of others. Boric acid is used in various dermal and women's hygiene products because of its mild antibacterial and antifungal activity. In ophthalmic products, it is used as a buffer and in combination with other preservatives to broaden the prservative spectrum. Boric acid has been used reluctantly in parenteral products but appears to be quite safe at low doses. However, at high exposure, toxicity, including death, has been reported in humans, especially in children. Animal toxicities have also been noted, including reductions in male sperm counts. Boric acid is well absorbed on oral dosing. Its biological half-life is about 21 h in humans and has an affinity for some tissues, especially bone.

Sulfobutylether-ß-cyclodextrin.

This review presents the early history, the motivation, the research and some of the backstories behind the discovery and development of sulfobutylether-ß-cyclodextrin as a novel parenterally safe solubilizer and stabilizer. A specific sulfobutylether-ß-cyclodextrin with an average degree of 6.5 sulfobutyl-groups variably substituted on the 2-, 3- and 6-hydroxyls of the seven glucopyranose (dextrose) units of ß-cyclodextrin, is known by its commercial name, Captisol®. Today it is in 13 FDA approved injectables and numerous clinical candidates. It is also an example of a novel product discovered and initially preclinically developed at an academic institution.

Some Preformulation Studies of Pyruvic Acid and Other α-Keto Carboxylic Acids in Aqueous Solution: Pharmaceutical Formulation Implications for These Peroxide Scavengers.

The purpose of this study is to assess some of the variables determining the aldol-like condensation of pyruvic acid (1), a peroxide scavenger, in aqueous solution to parapyruvic acid and higher oligomers. Its stability is compared to 3 other α-keto carboxylic acids, 2 with sterically hindered methylene groups alpha to the keto functionality (2-3) and phenylglyoxylic acid (4) with no methylene group. High-performance liquid chromatography, nuclear magnetic resonance, and liquid chromatography mass spectroscopy techniques are used in the kinetics and product analyses. 1 condensation is concentration dependent and base catalyzed above pH 7, consistent with the reaction mechanism proceeding through the attack of the fraction of the methylene group, alpha to the keto group, in its anionic form, at the keto group of a second molecule of 1. The major product is confirmed to be parapyruvic acid, but higher-order oligomers are also observed. All 3 of the other α-keto carboxylic acids 2-4 are considerably less reactive, with 4 being completely stable. Stable solutions of 1 can be prepared by the use of relatively dilute solutions maintained at slightly acidic pH values. 1 prevents the oxidation of methionine on addition of hydrogen peroxide.

Routine splenic flexure mobilization may increase compliance with pathological quality metrics in patients undergoing low anterior resection.

AIM: Mandatory splenic flexure mobilization (SFM) has been debated for rectal cancers. Proponents argue that additional mobilization facilitates a tension-free anastomosis; however, this must be weighed against heightened morbidity. Little is known about the impact of specific techniques on pathology quality metrics. We aim to determine the impact of SFM on pathology quality metrics for patients undergoing rectal resections for colorectal adenocarcinoma. METHOD: Patients were selected by querying the University of Kansas electronic medical records and the American College of Surgeons National Surgical Quality Improvement Program database based on Current Procedural Terminology codes. Patients were categorized as SFM or non-SFM. Primary outcomes were node yield less than 12 and margin length. RESULTS: There were 146 patients who met the inclusion criteria for chart review and 7369 included from the national database. Splenic flexure mobilization was associated with wider margins (3.52 vs 2.51 cm in low anterior resection, P < 0.01) and a decreased rate of inadequate nodal staging in patients undergoing low anterior resection (3.7% vs 19.3% P < 0.01). CONCLUSIONS: SFM may affect surgical quality metrics in patients undergoing resection for distal colon and rectal adenocarcinoma. Further study is warranted to determine whether these differences in quality and pathology translate into differences in oncological outcomes.

Origins, and formulation implications, of the pKa difference between boronic acids and their esters: A density functional theory study.

The purpose of this study is to try to identify the etiology and formulation implications of the significant pKa drop in aqueous solution that occurs when boronic acids are reversibly esterified by reaction with alcohols, especially 1,2-diols. Experimental studies have shown that conversion of a boronic acid to a boronic acid ester, both Lewis acids, is accompanied by an increase in the acidity, that is, a lowering of the pKa value in aqueous solution. The drop in pKa value has significant implications for the formulation of boronic acid-based drugs. Specifically, in the presence of 1,2-diols, a ΔpKa, a drop, of about 3 pKa units has been observed for several boronic acids, including boron-based drugs that have demonstrated value as active pharmaceutical ingredients. Boric acid itself shows an even larger drop of about 4 units. Here, electronic structure calculations are used to investigate the origins of this pKa change. Specifically, density functional theory (DFT) is used to predict the ΔpKa for a model boronic acid, methylboronic acid, to two of its esters, the dimethyl ester and the cyclic ester with ethylene glycol. The approach is validated by accurately predicting the experimentally observed increased acidity of the cyclic boronic acid ester relative to the corresponding boronic acid. The origins of the acidity difference are examined in detail. Analysis shows that the primary origin is an electronic effect with a smaller contribution due to the reduced structural flexibility of the boronic ester.

Novel prodrug PRX-P4-003, selectively activated by gut enzymes, may reduce the risk of iatrogenic addiction and abuse.

OBJECTIVES: Prescription stimulants are vulnerable to oral and parenteral abuse. Intravenous forms of abuse may be most detrimental due to an enhanced risk of dependence, overdose, and infectious diseases. Our objective was to discover an orally active prodrug of a stimulant that would not be easily converted to its parent when injected, thus hindering intravenous abuse. METHODS: Following an initial analysis of stimulant structures, the fencamfamine isomer [(-)-FCF; (N-ethyl-3-phenylbicyclo[2.2.1]heptan-2-amine)] was chosen as a parent drug due to its favorable biochemical properties. Subsequently, PRX-P4-003 {(-)-N-(Octadecanoyloxymethoxycarbonyl)-N-ethyl-3-phenylbicyclo[2.2.1]heptan-2-amine} qualified for further development. Experimental testing of PRX-P4-003 included radioligand binding assays, stability studies, and rodent pharmacokinetic and locomotor assays. RESULTS: Prodrug PRX-P4-003 is a pharmacologically inactive, hydrophobic compound, whereas its parent (-)-FCF is a dopamine reuptake inhibitor with weaker effects on norepinephrine reuptake (Ki = 0.07 and 0.80 µM, respectively). PRX-P4-003 is metabolized to (-)-FCF in simulated intestinal fluid (with pancreatin) but not in simulated gastric fluid (with pepsin). Finally, PRX-P4-003 shows a significant oral but no intravenous increase in locomotion, correlating with its pharmacokinetics by these different routes of administration. CONCLUSIONS: PRX-P4-003 is a novel prodrug stimulant enzymatically activated in the gut. Our data suggest a pancreatic, lipase-based mechanism of activation and as only 1% of this enzyme is found in the systemic circulation, PRX-P4-003 is unlikely to be bioactive if injected intravenously. Enzymatic release of (-)-FCF is needed prior to its systemic absorption, which may discourage oral abuse (e.g., by chewing). PRX-P4-003 is being developed for apathy in Alzheimer's disease and binge eating disorder.

Early operative outcomes and learning curve of robotic assisted giant paraesophageal hernia repair.

BACKGROUND: We have previously described our technique of robotic-assisted giant paraesophageal hernia repair (RA-GPEHR). The purpose of this study was to report our initial experience, early outcomes and learning curve with RA-GPEHR using a four-arm robotic platform. METHODS: 24 consecutive patients presenting with symptomatic giant paraesophageal hernias (GPEH) underwent RA-GPEHR from April 2011 to February 2014. Peri-operative data and short-term patient outcomes were assessed by retrospective review of a prospectively maintained database. RESULTS: Median age was 62 years (range 44-84). 15 (63%) patients underwent fundoplication and 9 (37%) gastropexy. Median procedure time was 277 min (range: 185-485) and decreased steadily over the experience. There were no intra-operative complications or surgical mortality. No patients experienced dysphagia in the early post-operative period. CONCLUSIONS: RA-GPEHR is safe, with reported short-term operative and functional outcomes similar to conventional laparoscopic approaches. The initial learning curve appears relatively short for experienced minimally invasive esophageal surgeons. Copyright © 2016 John Wiley & Sons, Ltd.

Isolation, Solubility, and Characterization of D-Mannitol Esters of 4-Methoxybenzeneboronic Acid.

The purpose of this study was to determine the aqueous solubility of a model phenyl boronic acid, 4-methoxybenzeneboronic acid, as a function of pH both in the absence and in the presence of varying D-mannitol concentration. Solid isolated D-mannitol esters were characterized by differential scanning calorimetry, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray studies, and the boronic acid-to-D-mannitol ratio was quantified by HPLC. Hydrolysis of the monoester was studied using UV spectral differences between the monoester and the parent boronic acid. Two D-mannitol esters of 4-methoxybenzeneboronic acid were isolated. The triboronate ester was very insoluble whereas a symmetrical monoboronate monohydrate was also less soluble than the parent. Both esters were crystalline. The monoboronate monohydrate was, however, more soluble than the parent at alkaline pH values due to its lower pKa value (6.53) compared to the parent acid (9.41). Hydrolysis of the monoboronate was extremely fast when even small amount of water was added to dry acetonitrile solutions of the ester. The hydrolysis was buffer concentration dependent and apparent pH sensitive with hydrolysis accelerated by acid. Implications affecting the formulation of future boronic acid drugs are discussed.

Mechanism of Degradation of an α-Keto-Epoxide, a Model for the Warhead for Various Proteasome Inhibitor Anticancer Agents.

The anticancer agent, carfilzomib, has a unique α-keto-epoxide warhead. The model α-keto-epoxide, N-((S)-1-((R)-2-methyloxiran-2-yl)-1-oxo-3-phenylpropan-2-yl)pivalamide (1), along with a few of its degradation products was synthesized and studied. The kinetics of hydrolysis and identification of some of the degradation products of 1 were performed at pH values 2, 4, 5, 7, and 8 at 25°C, 40°C, and 60°C and followed by HPLC and liquid chromatography-mass spectroscopy, respectively. 1 degraded independent of pH between pH values 4-7 but showed some acid catalysis at pH 2 and base catalysis at pH 8. Energy of activation, Ea, values progressed from 16.8 ± 0.1 at pH 2 to 20.3 ± 0.1 kcal/mole at pH 8. The major initial degradation products in the pH range 4-5 were the S,R diol (hydrolysis of the epoxide), and S,R chlorohydrin (in the presence of chloride ions). At pH 7-8, the major products were the R,R diastereomer and the S,R and R,R diols. At pH 2, additional unidentified products were seen with relative retention times of 0.28, 0.30, 0.33, and 0.35 and masses equivalent to the diols. The study of 1 provides insight into the degradation of future drugs that use an α-keto-epoxide functional group.

Effect of Molecular Structure on the Relative Hydrogen Peroxide Scavenging Ability of Some α-Keto Carboxylic Acids.

The α-keto carboxylic acid, pyruvic acid (1) was found to be a very effective peroxide scavenger but is subject to an aldol-like self-condensation/polymerization reaction. The purpose of this study was to evaluate the hydrogen peroxide, H2O2, scavenging ability of 3-methyl-2-oxobutanoic acid (2), 4-methyl-2-oxopentanoic acid (3), and 2-oxo-2-phenylacetic acid (phenylglyoxylic acid, 4) in the pH range 2-9 at 25°C and the effect of molecular structure on the relative reactivity. The reaction with H2O2 was followed by UV spectrophotometry at 220 or 260 nm and high-performance liquid chromatography. Pseudo-first order, buffer-independent decarboxylation kinetics were observed in the presence of molar excess H2O2. The second-order rate constants for 2-4 followed a sigmoidal shape and mechanism similar to pyruvic acid. Pyruvic acid was a superior H2O2 scavenger to 2-4 over the pH range 2-9 but 4 was more reactive than 2 and 3 at pH values above 6. There was a qualitative correlation between the degree of keto-group hydration and reactivity of the acids in the pH range 4-6 while the data above pH 7 suggested that the intrinsic decarboxylation step for 4 was faster than for pyruvic acid. Differences in reactivity to molecular structure were analyzed.

Mechanism of Decarboxylation of Pyruvic Acid in the Presence of Hydrogen Peroxide.

The purpose of this work was to probe the rate and mechanism of rapid decarboxylation of pyruvic acid in the presence of hydrogen peroxide (H2O2) to acetic acid and carbon dioxide over the pH range 2-9 at 25 °C, utilizing UV spectrophotometry, high performance liquid chromatography (HPLC), and proton and carbon nuclear magnetic resonance spectrometry ((1)H, (13)C-NMR). Changes in UV absorbance at 220 nm were used to determine the kinetics as the reaction was too fast to follow by HPLC or NMR in much of the pH range. The rate constants for the reaction were determined in the presence of molar excess of H2O2 resulting in pseudo first-order kinetics. No buffer catalysis was observed. The calculated second-order rate constants for the reaction followed a sigmoidal shape with pH-independent regions below pH 3 and above pH 7 but increased between pH 4 and 6. Between pH 4 and 9, the results were in agreement with a change from rate-determining nucleophilic attack of the deprotonated peroxide species, HOO(-), on the α-carbonyl group followed by rapid decarboxylation at pH values below 6 to rate-determining decarboxylation above pH 7. The addition of H2O2 to ethyl pyruvate was also characterized.

Determination of pKa and Hydration Constants for a Series of α-Keto-Carboxylic Acids Using Nuclear Magnetic Resonance Spectrometry.

The determination of the acid-base dissociation constants, and thus the pKa values, of α-keto acids such as pyruvic acid is complex because of the existence of these acids in their hydrated and nonhydrated or oxo state. Equilibria involved in the hydration and dehydration of the α-keto group of pyruvic acid and three other α-keto acids, 3-methyl-2-oxobutanoic acid, 4-methyl-2-oxopentanoic acid, and 2-oxo-2-phenylacetic acid, were investigated by proton and carbon nuclear magnetic resonance spectrometry, at constant ionic strength, 0.15, and 25 °C. Dissociation constants for the oxo (pKa(oxo)) and hydrated (pKa(hyd)) acids of each compound were estimated from the change in the degree of hydration with changes in pH and directly from the changes in chemical shifts of various hydrogen and carbons nuclei with pH. α-Keto acids showed greater hydration in their acidic forms than their carboxylate forms. The degree of hydration was sensitive to steric and electronic/resonance factors. As expected, the oxo forms of the acids were stronger acids compared with their hydrated analogs, and their dissociation constants were also sensitive to steric and electronic factors.

Interaction of model aryl- and alkyl-boronic acids and 1,2-diols in aqueous solution.

The goal of this work was to quantitate ester formation between alkyl and aryl boronic acids and vicinal-diols or 1,2-diols in aqueous solution. As used here, 1,2-diols includes polyols with one or more 1,2-diol pairs. Multiple techniques were used including apparent pKa shifts of the boronic acids using UV spectrophotometry (for aryl acids) and titration (for aryl and alkyl acids). Isothermal microcalorimetry was also used, with all reactions being enthalpically favored. For all the acids and 1,2-diols and the conditions studied, evidence only supported 1:1 ester formation. All the esters formed were found to be significantly more acidic, as Lewis acids, by 3-3.5 pKa units than the corresponding nonesterified boronic acid. The equilibrium constants for ester formation increased with increasing number of 1,2-diol pairs but stereochemistry may also play a role as sorbitol with five possible 1,2-diol pairs and five isomers (taking into account the stereochemistry of the alcohol groups) was twice as efficient at ester formation compared with mannitol, also with five possible 1,2-diol pairs but only three isomers. Alkyl boronic acids formed esters to a greater extent than aryl acids. Although some quantitative differences were seen between the various techniques used, rank ordering of the structure/reactivity was consistent. Formulation implications of ester formation between boronic acids and 1,2-diols are discussed.

Targeted delivery of a model immunomodulator to the lymphatic system: comparison of alkyl ester versus triglyceride mimetic lipid prodrug strategies.

A lipophilic prodrug approach has been used to promote the delivery of a model immunomodulator, mycophenolic acid (MPA), to the lymphatic system after oral administration. Lymphatic transport was employed to facilitate enhanced drug uptake into lymphocytes, as recent studies demonstrate that targeted drug delivery to lymph resident lymphocytes may enhance immunomodulatory effects. Two classes of lymph-directing prodrugs were synthesised. Alkyl chain derivatives (octyl mycophenolate, MPA-C8E; octadecyl mycophenolate, MPA-C18E; and octadecyl mycophenolamide, MPA-C18AM), to promote passive partitioning into lipids in lymphatic transport pathways, and a triglyceride mimetic prodrug (1,3-dipalmitoyl-2-mycophenoloyl glycerol, 2-MPA-TG) to facilitate metabolic integration into triglyceride deacylation-reacylation pathways. Lymphatic transport, lymphocyte uptake and plasma pharmacokinetics were assessed in mesenteric lymph and carotid artery cannulated rats following intraduodenal infusion of lipid-based formulations containing MPA or MPA prodrugs. Patterns of prodrug hydrolysis in rat digestive fluid, and cellular re-esterification in vivo, were evaluated to examine the mechanisms responsible for lymphatic transport. Poor enzyme stability and low absorption appeared to limit lymphatic transport of the alkyl derivatives, although two of the three alkyl chain prodrugs - MPA-C18AM (6-fold) and MPA-C18E (13-fold) still increased lymphatic drug transport when compared to MPA. In contrast, 2-MPA-TG markedly increased lymphatic drug transport (80-fold) and drug concentrations in lymphocytes (103-fold), and this was achieved via biochemical incorporation into triglyceride deacylation-reacylation pathways. The prodrug was hydrolysed rapidly to 2-mycophenoloyl glycerol (2-MPA-MG) in the presence of rat digestive fluid, and 2-MPA-MG was subsequently re-esterified in the enterocyte with oleic acid (most likely originating from the co-administered formulation) prior to accessing the lymphatics and lymphocytes. Importantly, after administration of 2-MPA-TG, the concentrations of free MPA in the mesenteric lymph nodes were significantly enhanced (up to 28 fold) when compared to animals administered equimolar quantities of MPA, suggesting the efficient conversion of the esterified prodrug back to the pharmacologically active parent drug. The data suggest that triglyceride mimetic prodrugs have potential as a means of enhancing immunotherapy via drug targeting to lymphocytes and lymph nodes.

Hydrolysis of the quinone methide of butylated hydroxytoluene in aqueous solutions.

Butylated hydroxytoluene or BHT is an antioxidant commonly used in pharmaceutical formulations. BHT upon oxidation forms a quinone methide (QM). QM is a highly reactive electrophilic species that can undergo nucleophilic addition. Here, the kinetic reactivity of QM with water at various apparent pH values in a 50% (v/v) water-acetonitrile solution at constant ionic strength of I = 0.5 (NaCl)4 , was studied. The hydrolysis of QM in the presence of added acid, base, sodium chloride, and phosphate buffer resulted in the formation of only one product--the corresponding 3,5-di-tert-butyl-4-hydroxybenzyl alcohol (BA). The rate of BA formation was catalyzed by the addition of acid and base, but not chloride and phosphate species. Nucleophilic excipients, used in the pharmaceutical formulation, or nucleophilic groups on active pharmaceutical ingredient molecule may form adducts with QM, the immediate oxidative product of BHT degradation, thus having implications for drug product impurity profiles. Because of these considerations, BHT should be used with caution in formulations containing drugs or excipients capable of acting as nucleophiles.

Chemical drug stability in lipids, modified lipids, and polyethylene oxide-containing formulations.

To critique the stability complications seen in formulating poorly water-soluble, problematic drugs in lipids, modified lipids, and polyethylene oxide solvents and surfactants in hard and soft gelatin capsules as well as some parenterals, a literature search was performed and personal experiences, and those of colleagues, collated. The literature is replete with examples of molecules undergoing rapid oxidative degradation in the presence of polyethylene oxide based solvents and surfactants as well as in the presence of unsaturated lipids. More recently appreciated is instability caused by the reaction of amine and amide drugs, with formaldehyde, formic acid found in many of these solvents as impurities and other degradation byproducts of the solvents themselves. One would expect acylation and transacylation reactions to be more common than reported but the literature has some good examples. An added complexity is occasionally seen with the use of hard and soft gelatin capsules with these solvents. The chemical stability of drugs in liquid and semi-solid formulations in the presence of lipids, modified lipids, and polyoxyethylene oxide-based solvents and surfactants can be complex, further exacerbated by the use of gelatin capsules, and can lead to a plethora of degradation pathways often not seen when the same drugs are formulated in solid dosage forms.

Dissolution of weak acids under laminar flow and rotating disk hydrodynamic conditions: application of a comprehensive convection-diffusion-migration-reaction transport model.

A steady-state mass transfer model that incorporates convection, diffusion, ionic migration, and ionization reaction processes was extended to describe the dissolution of weak acids under laminar flow and a rotating disk hydrodynamics. The model accurately predicted the experimental dissolution rates of benzoic acid, 2-naphthoic acid, and naproxen in unbuffered and monoprotic buffers within the physiological pH range for both hydrodynamic systems. Simulations at various flow rates indicated a cube root dependency of dissolution rate on the flow rate for a given bulk pH value for the laminar hydrodynamic system, as proposed earlier by Shah and Nelson (1975. J Pharm Sci 64(9):1518-1520) for neutral compounds. The model has limitations in its ability to accurately predict the dissolution of weak acids under certain conditions that imposed steep concentration gradients, such as high pH values, and for polyprotic buffer systems that caused the numerical solution to be unstable, suggesting that alternative numerical techniques may be required to obtain a stable numerical solution at all conditions. The model presents many advantages, most notably the ability to successfully predict the complex process under physiological conditions without simplifying assumptions, and therefore accurately representing the system in a comprehensive manner.

Properties of a model aryl boronic acid and its boroxine.

Many boronic acid-containing molecules are currently under investigation as possible therapeutics. An increase in the knowledge of the physical and chemical properties of these compounds will lead to their improved formulation into usable dosage forms. The current study describes the formation and characterization of a boronic acid anhydride, called a boroxine. The model boronic acid, 4-methoxybenzeneboronic acid is used. The current study demonstrates the utility of thermal (differential scanning calorimetry and thermogravimetric analysis) and spectral (solid-state nuclear magnetic resonance and ultraviolet spectroscopy) methods to quantitate and characterize the boronic acid and its boroxine, validated against definitive structures solved by single-crystal X-ray diffraction. The present work also demonstrates that the hydrolysis of the boroxine in the presence of water is very rapid in a time scale relative to drug substance manufacture and product formulation.