Enhancing the Oral Absorption of Kinase Inhibitors Using Lipophilic Salts and Lipid-Based Formulations.

The absolute bioavailability of many small molecule kinase inhibitors (smKIs) is low. The reasons for low bioavailability are multifaceted and include constraints due to first pass metabolism and poor absorption. For smKIs where absorption limits oral bioavailability, low aqueous solubility and high lipophilicity, often in combination with high-dose requirements have been implicated in low and variable absorption, food-effects, and absorption-related drug-drug interactions. The current study has evaluated whether preparation of smKIs as lipophilic salts/ionic liquids in combination with coadministration with lipid-based formulations is able to enhance absorption for examples of this compound class. Lipophilic (docusate) salt forms of erlotinib, gefitinib, ceritinib, and cabozantinib (as example smKIs demonstrating low aqueous solubility and high lipophilicity) were prepared and isolated as workable powder solids. In each case, the lipophilic salt exhibited high and significantly enhanced solubility in lipidic excipients (>100 mg/g) when compared to the free base or commercial salt form. Isolation as the lipophilic salt facilitated smKI loading in model lipid-based formulations at high concentration, increased in vitro solubilization at gastric and intestinal pH and in some cases increased oral absorption (∼2-fold for cabozantinib formulations in rats). Application of a lipophilic salt approach can therefore facilitate the use of lipid-based formulations for examples of the smKI compound class where low solubility limits absorption and is a risk factor for increased variability due to food-effects.

Dietary docosahexaenoic acid supplementation enhances expression of fatty acid-binding protein 5 at the blood-brain barrier and brain docosahexaenoic acid levels.

The cytoplasmic trafficking of docosahexaenoic acid (DHA), a cognitively beneficial fatty acid, across the blood-brain barrier (BBB) is governed by fatty acid-binding protein 5 (FABP5). Lower levels of brain DHA have been observed in Alzheimer's disease (AD), which is associated with diminished BBB expression of FABP5. Therefore, up-regulating FABP5 expression at the BBB may be a novel approach for enhancing BBB transport of DHA in AD. DHA supplementation has been shown to be beneficial in various mouse models of AD, and therefore, the aim of this study was to determine whether DHA has the potential to up-regulate the BBB expression of FABP5, thereby enhancing its own uptake into the brain. Treating human brain microvascular brain endothelial (hCMEC/D3) cells with the maximum tolerable concentration of DHA (12.5 µM) for 72 h resulted in a 1.4-fold increase in FABP5 protein expression. Associated with this was increased expression of fatty acid transport proteins 1 and 4. To study the impact of dietary DHA supplementation, 6- to 8-week-old C57BL/6 mice were fed with a control diet or a DHA-enriched diet for 21 days. Brain microvascular FABP5 protein expression was up-regulated 1.7-fold in mice fed the DHA-enriched diet, and this was associated with increased brain DHA levels (1.3-fold). Despite an increase in brain DHA levels, reduced BBB transport of 14 C-DHA was observed over a 1 min perfusion, possibly as a result of competitive binding to FABP5 between dietary DHA and 14 C-DHA. This study has demonstrated that DHA can increase BBB expression of FABP5, as well as fatty acid transporters, overall increasing brain DHA levels.

Reduced blood-brain barrier expression of fatty acid-binding protein 5 is associated with increased vulnerability of APP/PS1 mice to cognitive deficits from low omega-3 fatty acid diets.

Lower levels of the cognitively beneficial docosahexaenoic acid (DHA) are often observed in Alzheimer's disease (AD) brains. Brain DHA levels are regulated by the blood-brain barrier (BBB) transport of plasma-derived DHA, a process facilitated by fatty acid-binding protein 5 (FABP5). This study reports a 42.1 ± 12.6% decrease in the BBB transport of 14 C-DHA in 8-month-old AD transgenic mice (APPswe,PSEN1∆E9) relative to wild-type mice, associated with a 34.5 ± 6.7% reduction in FABP5 expression in isolated brain capillaries of AD mice. Furthermore, short-term spatial and recognition memory deficits were observed in AD mice on a 6-month n-3 fatty acid-depleted diet, but not in AD mice on control diet. This intervention led to a dramatic reduction (41.5 ± 11.9%) of brain DHA levels in AD mice. This study demonstrates FABP5 deficiency and impaired DHA transport at the BBB are associated with increased vulnerability to cognitive deficits in mice fed an n-3 fatty acid-depleted diet, in line with our previous studies demonstrating a crucial role of FABP5 in BBB transport of DHA and cognitive function.

Endosomal signaling of the receptor for calcitonin gene-related peptide mediates pain transmission.

G protein-coupled receptors (GPCRs) are considered to function primarily at the plasma membrane, where they interact with extracellular ligands and couple to G proteins that transmit intracellular signals. Consequently, therapeutic drugs are designed to target GPCRs at the plasma membrane. Activated GPCRs undergo clathrin-dependent endocytosis. Whether GPCRs in endosomes control pathophysiological processes in vivo and are therapeutic targets remains uncertain. We investigated the contribution of endosomal signaling of the calcitonin receptor-like receptor (CLR) to pain transmission. Calcitonin gene-related peptide (CGRP) stimulated CLR endocytosis and activated protein kinase C (PKC) in the cytosol and extracellular signal regulated kinase (ERK) in the cytosol and nucleus. Inhibitors of clathrin and dynamin prevented CLR endocytosis and activation of cytosolic PKC and nuclear ERK, which derive from endosomal CLR. A cholestanol-conjugated antagonist, CGRP8-37, accumulated in CLR-containing endosomes and selectively inhibited CLR signaling in endosomes. CGRP caused sustained excitation of neurons in slices of rat spinal cord. Inhibitors of dynamin, ERK, and PKC suppressed persistent neuronal excitation. CGRP8-37-cholestanol, but not unconjugated CGRP8-37, prevented sustained neuronal excitation. When injected intrathecally to mice, CGRP8-37-cholestanol inhibited nociceptive responses to intraplantar injection of capsaicin, formalin, or complete Freund's adjuvant more effectively than unconjugated CGRP8-37 Our results show that CLR signals from endosomes to control pain transmission and identify CLR in endosomes as a therapeutic target for pain. Thus, GPCRs function not only at the plasma membrane but also in endosomes to control complex processes in vivo. Endosomal GPCRs are a drug target that deserve further attention.

Correlating in Vitro Solubilization and Supersaturation Profiles with in Vivo Exposure for Lipid Based Formulations of the CETP Inhibitor CP-532,623.

Lipid based formulations (LBFs) are a promising formulation strategy for many poorly water-soluble drugs and have been shown previously to enhance the oral exposure of CP-532,623, an oral cholesteryl ester transfer protein inhibitor. In the current study, an in vitro lipid digestion model was used to probe the relationship between drug solubilization and supersaturation on in vitro dispersion and digestion of LBF containing long chain (LC) lipids and drug absorption in vivo. After in vitro digestion of LBF based on LC lipids, the proportion of CP-532,623 maintained in the solubilized state in the aqueous phase of the digest was highest in formulations containing Kolliphor RH 40, and in most cases outperformed equivalent formulations based on MC lipids. Subsequent administration of the LC-LBFs to beagle dogs resulted in reasonable correlation between concentrations of CP-532,623 measured in the aqueous phase of the in vitro digest after 30 min digestion and in vivo exposure (AUC); however, the LC-LBFs required greater in vitro drug solubilization to elicit similar in vivo exposure when compared to previous studies with MC-LBF. Although post digestion solubilization was enhanced in LC-LBF compared to MC-LBF, equilibrium solubility studies of CP-532,623 in the aqueous phase isolated from blank lipid digestion experiments revealed that equilibrium solubility was also higher, and therefore supersaturation lower. A revised correlation based on supersaturation in the digest aqueous phase and drug absorption was therefore generated. A single, linear correlation was evident for both LC- and MC-LBF containing Kolliphor RH 40, but this did not extend to formulations based on other surfactants. The data suggest that solubilization and supersaturation are significant drivers of drug absorption in vivo, and that across formulations with similar formulation composition good correlation is evident between in vitro and in vivo measures. However, across dissimilar formulations, solubilization and supersaturation alone are not sufficient to explain drug exposure and other factors also likely play a role.

In vitro-in vivo evaluation of lipid based formulations of the CETP inhibitors CP-529,414 (torcetrapib) and CP-532,623.

The present study investigated the use of lipid based drug delivery systems to enhance the oral bioavailability of the CETP inhibitors CP-532,623 and torcetrapib. A series of self-emulsifying lipid based drug delivery systems (SEDDS) were assembled and examined using an in vitro lipid digestion model to evaluate patterns of drug precipitation under simulated intestinal conditions. Drug exposure after oral administration of the same formulations was subsequently assessed in beagle dogs. CP-532,623 was maintained in a solubilised state during dispersion of most formulations in simulated intestinal fluid, however, solubilisation capacity was reduced to various degrees upon in vitro digestion. Administration of SEDDS formulations to beagle dogs resulted in moderate differences in plasma AUC when compared to the differences in solubilisation observed in vitro. Similar trends were observed for torcetrapib. In all cases, however, in vivo exposure of CP-532,623 was greatly enhanced by administration in lipid based drug delivery systems when compared to a powder formulation. Some correlation between in vitro solubilisation and in vivo drug exposure (AUC) was evident; however, this was not linear. The data suggest that for highly lipophilic drugs such as CP-532,623 in vitro digestion data may be a conservative in vitro indicator of utility and that good exposure may be evident even for formulations that result in significant drug precipitation during in vitro digestion.

Digestion of phospholipids after secretion of bile into the duodenum changes the phase behavior of bile components.

Bile components play a significant role in the absorption of dietary fat, by solubilizing the products of fat digestion. The absorption of poorly water-soluble drugs from the gastrointestinal tract is often enhanced by interaction with the pathways of fat digestion and absorption. These processes can enhance drug absorption. Thus, the phase behavior of bile components and digested lipids is of great interest to pharmaceutical scientists who seek to optimize drug solubilization in the gut lumen. This can be achieved by dosing drugs after food or preferably by formulating the drug in a lipid-based delivery system. Phase diagrams of bile salts, lecithin, and water have been available for many years, but here we investigate the association structures that occur in dilute aqueous solution, in concentrations that are present in the gut lumen. More importantly, we have compared these structures with those that would be expected to be present in the intestine soon after secretion of bile. Phosphatidylcholines are rapidly hydrolyzed by pancreatic enzymes to yield equimolar mixtures of their monoacyl equivalents and fatty acids. We constructed phase diagrams that model the association structures formed by the products of digestion of biliary phospholipids. The micelle-vesicle phase boundary was clearly identifiable by dynamic light scattering and nephelometry. These data indicate that a significantly higher molar ratio of lipid to bile salt is required to cause a transition to lamellar phase (i.e., liposomes in dilute solution). Mixed micelles of digested bile have a higher capacity for solubilization of lipids and fat digestion products and can be expected to have a different capacity to solubilize lipophilic drugs. We suggest that mixtures of lysolecithin, fatty acid, and bile salts are a better model of molecular associations in the gut lumen, and such mixtures could be used to better understand the interaction of drugs with the fat digestion and absorption pathway.

Silica-lipid hybrid (SLH) formulations enhance the oral bioavailability and efficacy of celecoxib: An in vivo evaluation.

This study is the first to demonstrate in canines the ability of silica-lipid hybrid (SLH) microparticles to enhance the bioavailability and efficacy of a poorly water-soluble drug after oral administration. Spray-dried SLH microparticles comprising Capmul MCM (mono-diglycerides of C8/C12 fatty acids) and silica nanoparticles (Aerosil® 380) were shown to significantly enhance the fasted state oral bioavailability of celecoxib (CEL) (6.5 fold, relative to an aqueous suspension and more than 2-fold higher relative to the fed state) after oral administration to beagle dogs. Comparable bioavailability was observed between the SLH microparticle formulation and a conventional Capmul lipid solution, however, plasma concentrations were observed to be higher (Cmax, 1.1±0.06 vs. 0.8±0.03µg/mL) (p≤0.05) with the SLH microparticle system. The enhanced bioavailability of CEL observed with the SLH microparticles was reflected in a subsequent efficacy study conducted in an adjuvant-induced arthritis model in the rat. Reduced clinical and histological severity was observed at a dose of 3mg/kg/day, with the progression of arthritic symptoms and tissue damage reduced to a similar degree to that of a higher dose administered at 5mg/kg/day and prepared in an aqueous suspension., The enhanced bioavailability and improved efficacy observed with the SLH microparticles were attributed to the maintenance of CEL in a solubilised form during digestion of the lipid vehicle. We hypothesise that the presence of silica in the formulation may have contributed to the prevention of drug precipitation in the intestinal lumen by providing an alternative binding site for CEL to adsorb to prior to re-solubilisation and absorption. The study highlights the potential utility of novel SLH microparticle formulations as stable dry powders that possess the properties of a lipid-based formulation for the enhanced delivery and efficacy of poorly water-soluble drugs.

In vitro digestion testing of lipid-based delivery systems: calcium ions combine with fatty acids liberated from triglyceride rich lipid solutions to form soaps and reduce the solubilization capacity of colloidal digestion products.

In vitro digestion testing is of practical importance to predict the fate of drugs administered in lipid-based delivery systems. Calcium ions are often added to digestion media to increase the extent of digestion of long-chain triglycerides (LCTs), but the effects they have on phase behaviour of the products of digestion, and consequent drug solubilization, are not well understood. This study investigates the effect of calcium and bile salt concentrations on the rate and extent of in vitro digestion of soybean oil, as well as the solubilizing capacity of the digestion products for two poorly water-soluble drugs, fenofibrate and danazol. In the presence of higher concentrations of calcium ions, the solubilization capacities of the digests were reduced for both drugs. This effect is attributed to the formation of insoluble calcium soaps, visible as precipitates during the digestions. This reduces the availability of liberated fatty acids to form mixed micelles and vesicles, thereby reducing drug solubilization. The use of high calcium concentrations does indeed force in vitro digestion of LCTs but may overestimate the extent of drug precipitation that occurs within the intestinal lumen.

Oral bioavailability assessment and intestinal lymphatic transport of Org 45697 and Org 46035, two highly lipophilic novel immunomodulator analogues.

Org 45697 (MW 600.7, clogP 7.92, soybean oil solubility 50 mg/g) and Org 46035 (MW 601.6, clog P 8.46, soybean oil solubility 40 mg/g) are two poorly water soluble (<0.1 microg/ml), highly lipophilic drug candidates with immunomodulator activity and highly analogous chemical structures. After oral administration to conscious ambulatory rats in an aqueous-based methylcellulose/Tween 80 suspension, the bioavailability of both compounds was low (< 2% of administered dose). However, bioavailability was significantly increased (> 5 fold) after oral administration in a long chain triglyceride lipid (olive oil) formulation. Subsequent studies have explored the potential for solubilising formulations, including lipid-based formulations, to enhance the oral bioavailability of Org 45697 and Org 46035 and secondly to explore the potential contribution of intestinal lymphatic transport to intestinal absorption. The experimental data show that solubilising formulations may provide for significant increases in oral bioavailability for Org 45697 and Org 46035 and that after co-administration with lipid, 35-50% of the absorbed dose may be transported to the systemic circulation via the intestinal lymph. Interestingly, the lymphatic transport of the less lipid soluble analogue, Org 46035 was approximately 40% lower than that of Org 45697 suggesting that relatively subtle differences in lipid solubility can have significant impact on the extent of lymphatic transport.

Increasing the proportional content of surfactant (Cremophor EL) relative to lipid in self-emulsifying lipid-based formulations of danazol reduces oral bioavailability in beagle dogs.

PURPOSE: To investigate the impact of a change in the proportions of lipid, surfactant and co-solvent on the solubilisation capacity of self-emulsifying formulations of danazol during in vitro dispersion and digestion studies and correlation with in vivo bioavailability in beagle dogs. METHODS: Formulations from within the phase diagram of the pseudo-ternary system composed of soybean oil:maisine 35-1 (1:1 w/w), Cremophor EL and ethanol were assessed in vitro on dispersion and digestion. The relative bioavailability of danazol after administration of a series of these formulations was also determined. RESULTS: All formulations formed microemulsions in the presence of water and no drug precipitation was observed on dispersion. In contrast, drug solubilisation was markedly affected by lipase-mediated digestion and a reduction in lipid (and increase in surfactant) content resulted in increased drug precipitation. Consistent with these data, the bioavailability of danazol decreased significantly when the lipid content in the formulations was reduced. CONCLUSION: A rank-order correlation was observed between the patterns of solubilisation obtained during in vitro digestion and the in vivo performance of self-emulsifying formulations of danazol. In general a decrease in the lipid content and an increase in the proportions of surfactant and co-solvent resulted in reduced danazol bioavailability.

A novel cubic phase of medium chain lipid origin for the delivery of poorly water soluble drugs.

The existence of a novel cubic liquid crystalline phase is described within the pseudo-ternary system comprising lauric acid, monolaurin, and simulated endogenous intestinal fluid (SEIF). This phase behaviour has been characterized using cross-polarizing light microscopy (CPLM), and the structure of the cubic phase identified by small angle X-ray scattering (SAXS). The presence of the cubic phase was found to be temperature sensitive within the 20-37 degrees C range making it putative material for in situ gelation purposes. The cubic phase was shown to have a high capacity to solubilise a model poorly water-soluble drug, cinnarizine, and initial in vitro release data highlight the potential of this phase to provide sustained release. Absorption of cinnarizine from the cubic phase was studied in an unconscious rat model via duodenal administration and blood sampling via the carotid artery. The rate of absorption was significantly reduced when compared to a simple suspension formulation, a likely combination of retarded erosion of the cubic phase together with hindered drug release from the cubic matrix. The results of this study suggest that this cubic phase may potentially be of benefit in the delivery of poorly water-soluble compounds due to its high loading capacity and potential for sustained release. The ability to manipulate this system using temperature may warrant further interest in delivery applications via other routes of administration.

Desbutylhalofantrine: evaluation of QT prolongation and other cardiovascular effects after intravenous administration in vivo.

Desbutylhalofantrine (Hfm) is an active and equipotent metabolite of halofantrine (Hf). Both compounds are effective in the treatment of sensitive and multidrug-resistant and In vitro data and interpretation of some clinical studies of Hf have suggested that, unlike Hf, Hfm may be devoid of adverse cardiac effects. The aim of these investigations was to provide the first in vivo examination of the intrinsic capacity of Hfm to affect repolarization in the heart, using an anesthetized rabbit model. Using a dose-rising regimen, Hfm was administered IV at doses of 1, 1, 2, 4, and 8 mg/kg and the baseline rate-corrected QT interval (QTc) value of 377 +/- 13 ms rose to 394 +/- 16, 396 +/- 12, 429 +/- 18, 433 +/- 16, and 489 +/- 15 ms, respectively. There were no significant changes in blood pressure, heart rate, or PR or QRS intervals. The Hfm plasma concentrations were quantitated after high-performance liquid chromatographic analysis, the results indicating a significant correlation between Hfm plasma concentration and QT(c) prolongation. The study also identified a concentration-dependent hemolysis of erythrocytes after administration of Hfm. The conclusions from this study are that IV administration of Hfm does cause a significant prolongation of the QT(c) interval in a rabbit model.

Evaluation of the in-vitro digestion profiles of long and medium chain glycerides and the phase behaviour of their lipolytic products.

An evaluation of the in-vitro digestion profile and phase behaviour of the common formulation lipids Miglyol 812 (medium chain triglyceride, MCT), Capmul MCM (C8/C10 monoglyceride/ diglyceride mixture), soybean oil (long chain triglyceride, LCT) and Maisine 35-1 (C18 monoglyceride/diglyceride mixture), is described. Experiments were conducted using titrimetric, high-performance thin-layer chromatographic (HPTLC) and ultracentrifugational techniques under model fasted and post-prandial intestinal conditions. The rate and extent of digestion of the medium chain lipids was greater than the corresponding long chain lipids, and independent of bile salt concentration, with complete conversion to monoglyceride and fatty acid occurring after 30 min digestion. The long chain lipid digests separated into an oily phase (containing undigested triglyceride and diglyceride), an aqueous phase (containing bile salt, fatty acid and monoglyceride) and a pellet phase (containing approximately 5 mm of fatty acid, presumably as an insoluble soap) after ultracentrifugation. Higher proportions of long chain fatty acid and monoglyceride were dispersed into the aqueous phase with increasing bile salt concentrations. In contrast, medium chain lipolytic products separated only into an aqueous phase and a pellet fraction in a bile-salt-independent manner. The digestion of both the C8/C10 and C18 monoglyceride/diglyceride lipid mixtures was more rapid than the corresponding triglyceride, especially at early time points. This investigation provides insight into the relative digestion kinetics of medium chain and long chain lipids and provides information regarding the phase behaviour of their lipolytic products under conditions modelled on those expected after oral administration. The data also provide a background for improved understanding of the potential utility of long chain and medium chain lipid-based formulations.