Assessing the risk of drug crystallization in vivo.

INTRODUCTION: Low intrinsic solubility leading to poor oral bioavailability is a common challenge in drug discovery that can often be overcome by formulation strategies, however, it remains a potential limitation that can pose challenges for early risk assessment and represent a significant obstacle to drug development. We identified a selective inhibitor (BMS-986126) of the IL-1 receptor-associated kinase 4 (IRAK4) with favorable properties as a lead candidate, but with unusually low intrinsic solubility of <1 µg/mL. METHODS: Conventional histopathology identified the issue of crystal formation in vivo. Subsequent investigative work included confocal Raman micro-spectroscopy, MALDI-MS, polarized light microscopy of fresh wet-mount tissue scrapings and transmission electron microscopy. RESULTS: BMS-986126 was advanced into a 2-week toxicology study in rats. The main finding in this study was minimal granulomatous inflammation in the duodenum, associated with the presence of birefringent crystals at the highest dosage of 100 mg/kg/day. Considering the safety margin, and the single location of the lesion, BMS-986126 was further progressed into IND-enabling toxicology studies where tolerability deteriorated with increasing dosing duration. Birefringent crystals and granulomatous inflammation were detected in multiple organs at dosages ≥20 mg/kg/day. Raman spectroscopy confirmed the identity of the crystals as BMS-986126. Therefore, follow up investigations were conducted to further characterize drug crystallization and to evaluate detection methods for their potential to reliably detect in vivo crystallization early. DISCUSSION: The purpose of our efforts was to identify critical factors influencing in vivo drug crystallization and to provide a preliminary assessment (based on one compound) which method would be best suited for identifying crystals. Results indicated a combination of methods was required to provide a complete assessment of drug crystallization and that a simple technique, scraping of freshly collected tissue followed by evaluation under polarizing light was suitable for detecting crystals. However, dosing for 2 weeks was required for crystals to grow to a clearly detectable size.

Moisture-Induced Amorphous Phase Separation of Amorphous Solid Dispersions: Molecular Mechanism, Microstructure, and Its Impact on Dissolution Performance.

Amorphous phase separation (APS) is commonly observed in amorphous solid dispersions (ASD) when exposed to moisture. The objective of this study was to investigate: (1) the phase behavior of amorphous solid dispersions composed of a poorly water-soluble drug with extremely low crystallization propensity, BMS-817399, and PVP, following exposure to different relative humidity (RH), and (2) the impact of phase separation on the intrinsic dissolution rate of amorphous solid dispersion. Drug-polymer interaction was confirmed in ASDs at different drug loading using infrared (IR) spectroscopy and water vapor sorption analysis. It was found that the drug-polymer interaction could persist at low RH (≤75% RH) but was disrupted after exposure to high RH, with the advent of phase separation. Surface morphology and composition of 40/60 ASD at micro-/nano-scale before and after exposure to 95% RH were also compared. It was found that hydrophobic drug enriched on the surface of ASD after APS. However, for the 40/60 ASD system, the intrinsic dissolution rate of amorphous drug was hardly affected by the phase behavior of ASD, which may be partially attributed to the low crystallization tendency of amorphous BMS-817399 and enriched drug amount on the surface of ASD. Intrinsic dissolution rate of PVP decreased resulting from APS, leading to a lower concentration in the dissolution medium, but supersaturation maintenance was not anticipated to be altered after phase separation due to the limited ability of PVP to inhibit drug precipitation and prolong the supersaturation of drug in solution. This study indicated that for compounds with low crystallization propensity and high hydrophobicity, the risk of moisture-induced APS is high but such phase separation may not have profound impact on the drug dissolution performance of ASDs. Therefore, application of ASD technology on slow crystallizers could incur low risks not only in physical stability but also in dissolution performance.

A novel approach to measuring macrophage-specific reverse cholesterol transport in vivo in humans.

Reverse cholesterol transport (RCT) is thought to be an atheroprotective function of HDL, and macrophage-specific RCT in mice is inversely associated with atherosclerosis. We developed a novel method using 3H-cholesterol nanoparticles to selectively trace macrophage-specific RCT in vivo in humans. Use of 3H-cholesterol nanoparticles was initially tested in mice to assess the distribution of tracer and response to interventions known to increase RCT. Thirty healthy subjects received 3H-cholesterol nanoparticles intravenously, followed by blood and stool sample collection. Tracer counts were assessed in plasma, nonHDL, HDL, and fecal fractions. Data were analyzed by using multicompartmental modeling. Administration of 3H-cholesterol nanoparticles preferentially labeled macrophages of the reticuloendothelial system in mice, and counts were increased in mice treated with a liver X receptor agonist or reconstituted HDL, as compared with controls. In humans, tracer disappeared from plasma rapidly after injection of nanoparticles, followed by reappearance in HDL and nonHDL fractions. Counts present as free cholesterol increased rapidly and linearly in the first 240 min after nadir; counts in cholesteryl ester increased steadily over time. Estimates of fractional transfer rates of key RCT steps were obtained. These results support the use of 3H-cholesterol nanoparticles as a feasible approach for the measurement of macrophage RCT in vivo in humans.

Pre-absorption physicochemical compatibility assessment of 8-drug metabolic cocktail.

A comprehensive 8-drug metabolic cocktail was designed to simultaneously target 6 Cytochrome P450 enzymes and 2 membrane transporters. This study aimed to assess the pre-absorption risk of this new metabolic cocktail which contained metoprolol, caffeine, midazolam, pravastatin, flurbiprofen, omeprazole, digoxin and montelukast. This paper describes a systematic approach to understand whether the co-administration of the 8 selected drug products, i.e., the physical mixing of these products in the human gastro-intestinal environment, will create any issue that may interfere with the individual drug dissolution which in turns modify the total amount or timing of their availability for absorption. The evaluation consisted of two steps. An initial evaluation was based on theoretical understanding of the physicochemical properties of the drugs and the gastro intestinal environment, followed by in vitro dissolution tests. The results indicated that the designer 8-drug cocktail has acceptable pre-absorption compatibility when dosed simultaneously, and recommended the progression of the cocktail into clinical validation study.