Professor Raj Suryanarayanan: Scientist, Educator, Mentor, Family Man and Giant in Pharmaceutical Research.

This special edition of the Journal of Pharmaceutical Sciences is dedicated to Professor Raj Suryanarayanan (Professor and William & Mildred Peters Endowed Chair, University of Minnesota, School of Pharmacy) and honors his extensive and distinguished career as a scientist, educator and mentor. The goal of this commentary is to provide an overview of Professor Suryanarayanan's noteworthy career path and summarize his key research contributions. The commentary concludes with the personal summaries by guest editors.

Application of resonant acoustic mixing in the synthesis of vitamin C-nicotinamide variable stoichiometry cocrystals.

The use of resonant acoustic mixing (RAM) to synthesize variable stoichiometry cocrystals of nicotinamide and vitamin C was investigated. Liquid assisted RAM (LA-RAM) was used to generate two polymorphs, Form I and II, of the 1 : 1 cocrystal of nicotinamide and vitamin C at a 700 mg scale using ethanol and methanol respectively as the liquid additives. LA-RAM was used to scale up polymorphs I and II of the 1 : 1 cocrystal to 20 grams. Finally, LA-RAM used was to produce a high purity 3 : 1 cocrystal of nicotinamide and vitamin C when either methanol or ethanol was used as the liquid additive. LA-RAM is demonstrated to be a scalable, environmentally friendly, ball-free method to make variable stoichiometry cocrystals.

Determination of BET Specific Surface Area of Hydrate-Anhydrate Systems Susceptible to Phase Transformation Using Inverse Gas Chromatography.

Specific surface area (SSA) is an important parameter in drug development that affects other downstream pharmaceutical properties of interest such as reactivity, stability, dissolution, and ultimately bioavailability. Traditionally, the Brunauer-Emmett-Teller (BET) SSA of pharmaceutical powders is measured via gas adsorption (nitrogen or krypton) that is preceded by a prolonged degassing step under low pressure. This degassing step may not be suitable for certain pharmaceutical hydrates that are susceptible to dehydration and phase transformation under reduced pressure and humidity conditions. Therefore, inverse gas chromatography (IGC) was explored as a reliable alternate technique for determining the SSA of model anhydrate-hydrate systems (trehalose and thiamine hydrochloride) that are prone to such phase transformation during SSA measurement. Both trehalose dihydrate and thiamine HCl non-stoichiometric hydrate were found to undergo partial phase transformation to anhydrous forms during BET analysis via degassing and gas adsorption. In contrast, these hydrates remained stable during surface area analysis using IGC owing to measurements under controlled relative humidity. Thus, IGC proved to be a viable technique for SSA measurement of pharmaceutical hydrates without compromising their physical stability.

Isothermal Crystallization Monitoring and Time-Temperature-Transformation of Amorphous GDC-0276: Differential Scanning Calorimetric and Rheological Measurements.

Cold crystallization of amorphous pharmaceuticals is an important aspect in the search to stabilize amorphous or glassy compounds used as amorphous pharmaceutical ingredients (APIs). In the present work, we report results for the isothermal crystallization of the compound GDC-0276 based on differential scanning calorimetric and rheometric measurements. The kinetics of isothermal crystallization from the induction time to the completion of crystallization can be described by the classic Johnson-Mehl-Avrami (JMA) equation. The time-temperature-transformation (TTT) diagrams were constructed for two time points-that of induction and that of completion of crystallization. The results show that the rheological measurement for GDC-0276 has a better overall sensitivity in detection of the early stage nucleation and, consequently, detects the onset of crystallization sooner than does the differential scanning calorimetry. Rheological measurements were also used to obtain the temperature dependence of the viscosity of GDC-0276 and the relevant parameters were used in a modified form of the JMA model to describe the temperature dependence of the crystal induction and completion times, that is, the TTT diagram for the material. In the modification, we assumed that the kinetics followed the viscosity to the 0.75 power as suggested by the recent work of Huang et al. (Huang, C., et al., J. Chem. Phys.2018,149, 054503). The relationship and the possible impact on crystallization kinetics of the break-down of the Stokes-Einstein relation in glass-forming liquids are discussed. From the crystallization kinetics modeling, the solid-liquid interfacial surface tension σSL was obtained for GDC-0276 and was compared with that obtained from the melting point depression measurements of the material confined in nanoporous glasses. The differences between the values from the two methods are discussed.

Using Supercritical Fluid Technology as a Green Alternative During the Preparation of Drug Delivery Systems.

Micro- and nano-carrier formulations have been developed as drug delivery systems for active pharmaceutical ingredients (APIs) that suffer from poor physico-chemical, pharmacokinetic, and pharmacodynamic properties. Encapsulating the APIs in such systems can help improve their stability by protecting them from harsh conditions such as light, oxygen, temperature, pH, enzymes, and others. Consequently, the API's dissolution rate and bioavailability are tremendously improved. Conventional techniques used in the production of these drug carrier formulations have several drawbacks, including thermal and chemical stability of the APIs, excessive use of organic solvents, high residual solvent levels, difficult particle size control and distributions, drug loading-related challenges, and time and energy consumption. This review illustrates how supercritical fluid (SCF) technologies can be superior in controlling the morphology of API particles and in the production of drug carriers due to SCF's non-toxic, inert, economical, and environmentally friendly properties. The SCF's advantages, benefits, and various preparation methods are discussed. Drug carrier formulations discussed in this review include microparticles, nanoparticles, polymeric membranes, aerogels, microporous foams, solid lipid nanoparticles, and liposomes.

Cyclodextrin Reduces Intravenous Toxicity of a Model Compound.

Solubilization of new chemical entities for toxicity assessment must use excipients that do not negatively impact drug pharmacokinetics and toxicology. In this study, we investigated the tolerability of a model freebase compound, GDC-0152, solubilized by pH adjustment with succinic acid and complexation with hydroxypropyl-ß-cyclodextrin (HP-ß-CD) to enable intravenous use. Solubility, critical micelle concentration, and association constant with HP-ß-CD were determined. Blood compatibility and potential for hemolysis were assessed in vitro. Local tolerability was assessed after intravenous and subcutaneous injections in rats. A pharmacokinetic study was conducted in rats after intravenous bolus administration. GDC-0152 exhibited pH-dependent solubility that was influenced by self-association. The presence of succinic acid increased solubility in a concentration-dependent manner. HP-ß-CD alone also increased solubility, but the extent of solubility enhancement was significantly lower than succinic acid alone. Inclusion of HP-ß-CD in the solution of GDC-0152 improved blood compatibility, reduced hemolytic potential by ∼20-fold in vitro, and increased the maximum tolerated dose to 80 mg/kg.

Understanding Phase Behavior of Nearly Energetically Equivalent Polymorphs To Achieve Controlled Crystallization for a Nav1.7 Pain Inhibitor Compound.

GENE-A, a Nav1.7 inhibitor compound with analgesic activity, was developed as a crystalline anhydrate, for which two polymorphic forms, I and II, were discovered. The two forms were found to possess very similar free energies as determined experimentally with Form II being thermodynamically stable above 25 °C based on solubility measurements. A detailed solid-state characterization was conducted to determine the relative stability of these solid forms, and both thermodynamic and kinetic pathways (slurry bridging and crystallization) were evaluated. Form II was obtained as the final form in competitive slurries at RT. The outcome of crystallization experiments in terms of the solid form obtained was complicated and yielded variable results depending on the form of the starting material and that of the seeds. Form II was reproducibly obtained as the end product in unseeded experiments and in those with Form II as seeds and starting material, while Form I was obtained in all other seeded experiments. On the basis of the experimental data, a controlled crystallization strategy was developed, wherein Form II was used both as starting material and seeds to reproducibly obtain the desired form upon scale-up.

Determination of Fragility in Organic Small Molecular Glass Forming Liquids: Comparison of Calorimetric and Spectroscopic Data and Commentary on Pharmaceutical Importance.

The fragility index ( m) and conversely the strength parameter ( D) are widely used to categorize glass forming liquids and are used to characterize temperature dependency of viscosity and relaxation time as the supercooled liquid approaches glass transition. The currently used calorimetric methods in pharmaceutical literature lead to wide variability in measured values of m. In this work, a modulated differential scanning calorimetry (DSC) method is introduced that can directly determine m with minimal variability. Although calorimetric fragility is easy to measure due to availability and ease of use of DSC, there is no correlation between calorimetric and dielectric fragility (calculated spectroscopically from relaxation times). In addition, there is also no correlation between calorimetric fragility and the so-called "thermodynamic fragility" that can be calculated using only thermodynamic parameters. No relationship can be found between the crystallization propensity in the supercooled liquid state and D. However, the crystallization propensity shows a reasonable correlation with the Kohlrausch distribution parameter ßk, which defines the breadth of the relaxation time distribution.

A rational approach towards development of amorphous solid dispersions: Experimental and computational techniques.

The purpose of this study was to determine the drug-polymer miscibility of GENE-A, a Genentech molecule, and hydroxypropyl methylcellulose-acetate succinate (HPMC-AS), a polymer, using computational and experimental approaches. The Flory-Huggins interaction parameter,χ, was obtained by calculating the solubility parameters for GENE-A and HPMC-AS over the temperature range of 25-100°C to obtain the free energy of mixing at different drug loadings (0-100%) using the Materials Studio modeling and simulation platform (thermodynamic approach). Solid-state nuclear magnetic spectroscopy (ssNMR) was used to measure the proton relaxation times for both drug and polymer at different drug loadings (up to 60%) at RT (kinetic approach). Thermodynamically, the drug and polymer were predicted to show favorable mixing as indicated by a negative Gibbs free energy of mixing from 25 to 100°C. ssNMR showed near identical relaxation times for both drug and polymer in the solid dispersion at RT and 40°C for a period up to 6 months showing phase mixing between the API and polymer on <10nm scale. Orthogonal computational and experimental approaches indicate phase mixing of the system components.

Probing the Distribution of Water in a Multi-Component System by Solid-State NMR Spectroscopy.

PURPOSE: To characterize the distribution of water among various components in a powder blend using solid-state NMR spectroscopy. METHODS: Water sorption behavior of theophylline anhydrate and excipients was determined by dynamic vapor sorption (DVS) and Karl Fischer Titration (KFT) after storing them in humidity chambers for 1 week at room temperature (RT) and calibration curves were generated for water content vs. (1)H T 1 relaxation times. Powder blends (either with microcrystalline cellulose or lactose as diluent) were stored at different relative humidity (RH) conditions and analyzed periodically using solid-state NMR, powder X-ray diffraction, and KFT. RESULTS: Anhydrous theophylline converted to the hydrate at ≥ 84% RH. Based on the calibration curves of water content vs. relaxation times, the distribution of water in the powder blends was estimated. The total water content calculated using ssNMR was in good agreement with values measured using KFT. In blends stored at 90% RH, theophylline anhydrate-to-hydrate conversion did not occur in 1 week. CONCLUSIONS: The distribution of water in multi-component powder blends was successfully determined using correlation between (1)H T 1 relaxation times and total water content. Excipient water sorption inhibited hydrate formation in theophylline at 90% RH. Water distribution was affected by excipient type. The extent of water sorbed by excipients in blends was found to be different than their standalone equilibrium water content.

Chemically Diverse Group I p21-Activated Kinase (PAK) Inhibitors Impart Acute Cardiovascular Toxicity with a Narrow Therapeutic Window.

p21-activated kinase 1 (PAK1) has an important role in transducing signals in several oncogenic pathways. The concept of inhibiting this kinase has garnered significant interest over the past decade, particularly for targeting cancers associated with PAK1 amplification. Animal studies with the selective group I PAK (pan-PAK1, 2, 3) inhibitor G-5555 from the pyrido[2,3-d]pyrimidin-7-one class uncovered acute toxicity with a narrow therapeutic window. To attempt mitigating the toxicity, we introduced significant structural changes, culminating in the discovery of the potent pyridone side chain analogue G-9791. Mouse tolerability studies with this compound, other members of this series, and compounds from two structurally distinct classes revealed persistent toxicity and a correlation of minimum toxic concentrations and PAK1/2 mediated cellular potencies. Broad screening of selected PAK inhibitors revealed PAK1, 2, and 3 as the only overlapping targets. Our data suggest acute cardiovascular toxicity resulting from the inhibition of PAK2, which may be enhanced by PAK1 inhibition, and cautions against continued pursuit of pan-group I PAK inhibitors in drug discovery.

Solid-State Characterization of Novel Propylene Glycol Ester Solvates Isolated from Lipid Formulations.

The purpose of this study was to identify and characterize precipitates obtained from a liquid formulation of GNE068.HCl, a Genentech developmental compound, and lipophilic excipients, such as propylene glycol monocaprylate, and monolaurate. Precipitates were characterized using powder X-ray diffractometry (PXRD), differential scanning calorimetry, thermogravimetry, microscopy, nuclear magnetic resonance spectroscopy (NMR; solution and solid-state) and water sorption analysis. PXRD and NMR revealed the precipitates to be crystalline solvates of propylene glycol esters. The solvates (capryolate and lauroglycolate) were isomorphic and stable up to 70 °C, beyond which melting of the lattice occurred with subsequent dissolution of the active ingredient in the melt (microscopy and variable temperature PXRD). They were found to be mechanically stable (no change in PXRD pattern upon compression) and were nonhygroscopic up to ∼70% RH (25 °C). Our results highlight the outcome of inadvertent drug-excipient interactions in two separate lipid solution formulations with good solid-state properties and, thus, potential for further development.

Characterization of a water-solid interaction in a partially ordered system.

GNE068-PC, a developmental compound, was previously characterized to be mesomorphous, i.e. having long-range order associated with significant local molecular disorder (Chakravarty et. al., Mol. Pharmaceutics, accepted). The compound was exposed to moisture under different relative humidity conditions ranging from 11% to 60% RH at room temperature (RT) for 7 days, and the resultant product phases were characterized. The partially ordered sample progressively lost crystallinity (long-range order) and birefringence (orientational order) upon exposure to increasing RH conditions, leading to the formation of a completely disordered amorphous phase at 60% RH (RT). Long-range positional order was irrecoverable even after moisture removal from the sample exposed to 60% RH. This was attributed to replacement of residual ethyl acetate by water, the former being critical for maintenance of long-range order in the material. In addition, water sorption appeared to irreversibly alter the molecular orientation, thereby affecting sample birefringence. Solid-state NMR revealed increases in (1)H and (13)C spin-lattice relaxation times (T1) going from the mesomorphous phase to the fully amorphous phase. This was indicative of reduction in lattice mobility, likely due to the decreased motion of the aromatic portions of the molecule, in particular C17, which showed the most dramatic increase in (13)C T1. This is likely due to decrease in available free volume upon water sorption. Drying of the hydrated disordered phase showed somewhat greater mobility than the hydrated phase, likely due to increased relative free volume through removal of water. A water-solid interaction therefore irreversibly changed the solid-state makeup of GNE068-PC.

Identification of a potential conformationally disordered mesophase in a small molecule: experimental and computational approaches.

GNE068, a small organic molecule, was obtained as an amorphous form (GNE068-A) after isolation from ethanol and as a partially disordered form (GNE068-PC) from ethyl acetate. On subsequent characterization, GNE068-PC exhibited a number of properties that were anomalous for a two phase crystalline-amorphous system but consistent with the presence of a solid state phase having intermediate order (mesomorphous). Modulated DSC measurements of GNE068-PC revealed an overlapping endotherm and glass transition in the 135-145 °C range. ΔH of the endotherm showed strong heating rate dependence. Variable temperature XRPD (25-160 °C) revealed structure loss in GNE068-PC, suggesting the endotherm to be an "apparent melt". In addition, gentle grinding of GNE068-PC in a mortar led to a marked decrease in XRPD peak intensities, indicating a "soft" crystalline lattice. Computational analysis of XRPD data revealed the presence of two noncrystalline contributions, one of which was associated with GNE068-A. The second was a variable component that could be modeled as diffuse scattering from local disorder within the associated crystal structure, suggesting a mesomorphous system. Owing to the dominance of the noncrystalline diffuse scattering in GNE068-PC and the observed lattice deformation, the mesomorphous phase exhibited properties consistent with a conformationally disordered mesophase. Because of the intimate association of the residual solvent (ethyl acetate) with the lattice long-range order, loss of solvent on heating through the glass transition temperature of the local disorder caused irrecoverable loss of the long-range order. This precluded the observation of characteristic thermodynamic mesophase behavior above the glass transition temperature.

Identification of C-2 hydroxyethyl imidazopyrrolopyridines as potent JAK1 inhibitors with favorable physicochemical properties and high selectivity over JAK2.

Herein we report on the structure-based discovery of a C-2 hydroxyethyl moiety which provided consistently high levels of selectivity for JAK1 over JAK2 to the imidazopyrrolopyridine series of JAK1 inhibitors. X-ray structures of a C-2 hydroxyethyl analogue in complex with both JAK1 and JAK2 revealed differential ligand/protein interactions between the two isoforms and offered an explanation for the observed selectivity. Analysis of historical data from related molecules was used to develop a set of physicochemical compound design parameters to impart desirable properties such as acceptable membrane permeability, potent whole blood activity, and a high degree of metabolic stability. This work culminated in the identification of a highly JAK1 selective compound (31) exhibiting favorable oral bioavailability across a range of preclinical species and robust efficacy in a rat CIA model.

Phase transformation in thiamine hydrochloride tablets: Influence on tablet microstructure, physical properties, and performance.

The objective of this article was to monitor phase transformation in thiamine hydrochloride, from a nonstoichiometric hydrate (NSH) to a hemihydrate (HH), in stored tablets, prepared both by direct compression and wet granulation, and to relate the storage-induced phase transformation with changes in tablet microstructure, physical properties, and performance. Raman spectroscopy revealed complete NSH → HH transformation in tablets, within 30 h of storage at 40°C/75% relative humidity. When the tablets were prepared by wet granulation of NSH alone, there was a marked increase in both tablet volume and hardness on storage. However, when microcrystalline cellulose (MCC) was included in granulation, the resulting stored tablets also exhibited a pronounced increase in disintegration time. In contrast, tablets prepared by dry processing via compression of a NSH-MCC physical mixture did not exhibit any changes in properties, despite the in situ solid form conversion. Scanning electron microscopy revealed growth of needle-like HH crystals in all stored tablets and mercury porosimetry revealed considerable changes in the pore size distribution during storage. Longer storage led to crystal growth (Ostwald ripening), causing further gradual but less dramatic changes in properties. The phase transformation and the complex interparticulate associations in the tablet influenced the changes in tablet microstructure, compact physical properties, and product behavior.

Investigation of solution and vapor phase mediated phase transformation in thiamine hydrochloride.

Thiamine hydrochloride (THCl) can exist as an anhydrate (AH), a hemihydrate (HH) and as a nonstoichiometric hydrate (NSH) where the water content can range between 0 and approximately 1 mole of water per mole of THCl. We have investigated the NSH --> HH phase transformation, in the presence of microcrystalline cellulose (MCC), following (i) wet massing, (ii) fluid-bed granulation, and (iii) exposure to water vapor (40 degrees C/75% RH). Based on Raman spectroscopy (40 degrees C), wet massing of NSH alone caused near complete transformation to HH in <100 min. In the presence of MCC, the transformation rate was decelerated. During fluid-bed granulation, approximately 20% of NSH was transformed to HH and the deceleratory effect of MCC was much less pronounced. Exposure to water vapor, of both NSH-MCC powder blends and granules (prepared by fluid-bed) resulted in complete HH formation within 6 days. Presence of MCC in the powder blend did not affect HH formation kinetics, but facilitated phase transformation in the granules. NSH --> HH conversion appeared to follow two-dimensional nucleation and growth model in powder blends, whereas the granules showed either three-dimensional diffusion controlled or a first-order kinetics. In a wet mass, polyvinyl pyrrolidone, a widely used binder, was much more effective than MCC in inhibiting HH formation during wet massing.

Insights into the dehydration behavior of thiamine hydrochloride (vitamin B1) hydrates: part II.

Thiamine hydrochloride (THCl) can exist as an anhydrate (AH) and as a hemihydrate (HH). AH sorbs water as a function of environmental water vapor pressure to form a nonstoichiometric hydrate (NSH). NSH dehydration is initiated at approximately 40 degrees C to yield AH, an isomorphic desolvate (ID) of NSH (Chakravaty et al., 2009, J Pharm Sci). Upon heating, dehydration of HH occurs only at elevated temperatures (>120 degrees C) and is accompanied by chemical decomposition. When heated at reduced temperature (60-90 degrees C) and pressure (20-760 mTorr), HH was incompletely dehydrated with partial loss of long-range lattice order. Complete dehydration of HH to AH was achieved through a solvent-mediated transformation in ethanol. The crystal structures of NSH and HH exhibit pronounced differences in the hydrogen bonding of water. The dehydration mechanism of NSH and HH can be explained by the "continuous and unified" dehydration model.