Kasiram Katneni

Drug transport across the blood-brain barrier and the impact of breast cancer resistance protein (ABCG2).

With the discovery of novel therapeutic targets within the central nervous system (CNS), there has been a significant effort to synthesize a multitude of drug molecules with increasing potency and selectivity. However, the impact of the blood-brain barrier (BBB) in limiting effective concentrations of drug candidate from reaching the brain parenchyma is often ignored, resulting in a lack of efficacy when administered to animal models or humans. Intercellular drug transport across the BBB is negligible due to the impermeable tight junctions formed by interconnecting endothelial cells. Furthermore, drug permeability via the transcellular route cannot be assumed for all molecules due to the high expression of drug efflux transport proteins, which effectively extrude compounds from the brain endothelial cell back into the cerebral vasculature. In addition to the extensively-studied P-glycoprotein (P-gp, ABCB1), the brain endothelial cells also express multidrug resistance associated proteins (MRP, ABCC) and breast cancer resistance protein (BCRP, ABCG2), amongst other efflux transporters. While more research has focussed on the impact of P-gp and MRP on drug transport across the BBB, the role of ABCG2 in limiting exposure of drug molecules to the CNS is now becoming more clearly understood. The purpose of this review, therefore, is to summarise the findings of the various studies assessing the expression profile of ABCG2 at the BBB, to provide an overview on the current research being undertaken to identify specific ABCG2 inhibitors with therapeutic benefit, and to critically assess the functional role of ABCG2 on drug transport across the BBB.

3-alkylthio-1,2,4-triazine dimers with potent antimalarial activity.

We report on the discovery of 3-alkylthio-1,2,4-triazine dimers that are potently toxic to Plasmodium falciparum, with single digit nanomolar activity, and up to several thousand-fold lower toxicity to mammalian cells. They are equipotent against chloroquine-resistant strains of P. falciparum.

An evaluation of the relative roles of the unstirred water layer and receptor sink in limiting the in-vitro intestinal permeability of drug compounds of varying lipophilicity.

The roles of the unstirred water layer (UWL) and receptor sink on the in‐vitro transmembrane permeability of an increasingly lipophilic series of compounds (mannitol (MAN), diazepam (DIA) and cinnarizine (CIN)) have been assessed. Altered carbogen bubbling rates were used as a means to change the UWL thickness and polysorbate‐80 (PS‐80), bovine serum albumin (BSA) and α‐1‐acid glycoprotein (AAG) were employed to alter sink conditions. After correction for solubilisation, Papp data for MAN, DIA and CIN were consistent across varying donor PS‐80 concentrations suggesting that for the drugs examined here, the donor UWL did not limit in‐vitro permeability. Similarly, altered bubbling rates and receptor sink conditions had no impact on the permeability of MAN. In contrast, decreasing the size of the receptor UWL or adding solubilising agents to the receptor sink resulted in modest enhancements to the permeability of the more lipophilic probe DIA. For the most lipophilic compound, CIN, very significant changes to measured permeability (>30 fold) were possible, but were most evident only after concomitant changes to both the UWL and sink conditions, suggesting that the effectiveness of enhanced sink conditions were dependent on a decrease in the width of the UWL.

Preclinical comparison of intravenous melphalan pharmacokinetics administered in formulations containing either (SBE)7 m‐β‐cyclodextrin or a co‐solvent system

The aim of this work was to evaluate the impact of sulfobutyl ether β-cyclodextrin ((SBE)(7u2009m)-β-CD; Captisol(®)) on the in vivo pharmacokinetics of melphalan in rats. Melphalan is a chemically unstable antineoplastic drug which in the current commercial formulation (Alkeran(®) for Injection) has some limitations with regard to solubility, stability and biocompatibility. Melphalan formulations containing (SBE)(7u2009m)-β-CD have previously been evaluated in vitro and shown to significantly reduce the rate of degradation and to simplify the reconstitution procedure for lyophilised melphalan. In this study, melphalan was administered intravenously in rats in formulations that either contain (SBE)(7u2009m)-β-CD or a co-solvent system (i.e. the commercial formulation). Pharmacokinetic parameters, including half-life, volume of distribution, clearance and extent of renal elimination of melphalan were essentially unchanged between the two formulations. These findings indicate that the pharmacokinetics of melphalan are not altered in the presence of (SBE)(7u2009m)-β-CD consistent with a rapid shift in the equilibrium to the fully dissociated drug from the fraction associated with the cyclodextrin host molecule upon intravenous administration.

Impact of Chlorpromazine Self-Association on Its Apparent Binding Constants With Cyclodextrins: Effect of SBE7-β-CD on the Disposition of Chlorpromazine in the Rat

Chlorpromazine is an antipsychotic agent with poor aqueous solubility. Complexation with SBE(7)-beta-CD can aid intravenous delivery through increasing the apparent solubility of chlorpromazine. However, chlorpromazine has also been known to self-associate. This self-association can influence its capacity to interact with other chemical species, such as cyclodextrins. This study aimed to characterise the self-association and cyclodextrin binding properties of chlorpromazine, and the effect on pharmacokinetic parameters in rats when dosed with a SBE(7)-beta-CD containing formulation. Pharmacokinetic studies of chlorpromazine in the presence and absence of SBE(7)-beta-CD were undertaken in rats. The binding constant of SBE(7)-beta-CD and chlorpromazine was studied relative to chlorpromazine concentration via fluorescence. The self-association of chlorpromazine was studied by fluorescence and UV-visible spectrophotometry. Urinary excretion of intact chlorpromazine increased in the presence of SBE(7)-beta-CD. The SBE(7)-beta-CD binding constant of chlorpromazine is highly concentration dependent and the variation can be attributed to the self-association of chlorpromazine. The apparent binding constant of chlorpromazine is highest at pharmacologically relevant concentrations, providing an explanation for the significant increase in renal chlorpromazine excretion observed in rats.

Pharmacokinetics and brain uptake of AM-36, a novel neuroprotective agent, following intravenous administration to rats

The plasma pharmacokinetics and brain uptake of the novel neuroprotective agent AM‐36 (1‐(2‐(4‐chlorophenyl)‐2‐hydroxy)ethyl‐4‐(3,5‐bis‐(1, 1dimethylethyl)‐4‐hydroxyphenyl) methylpiperazine) were assessed over 72 h following i.v. administration to male Sprague‐Dawley rats. At nominal i.v. doses of 0.2, 1 and 3 mg kg−1, AM‐36 exhibited an extremely large volume of distribution (18.2–24.6 L kg−1) and a long terminal elimination half‐life, ranging from 25.2 to 37.7 h. Over this dose range, AM‐36 exhibited linear pharmacokinetics, with no apparent change in clearance, volume of distribution or dose‐normalised area under the plasma concentration‐time curve. AM‐36 was very highly bound to plasma proteins (> 99.6%); however, this did not appear to affect the ability of AM‐36 to permeate the blood‐brain barrier. Following a single i.v. dose of AM‐36 at 3 mg kg−1 to rats, brain concentrations were detected for up to 72 h, and the brain‐to‐plasma ratios were high at all time points (ranging from 8.2 at 5 min post‐dose to 0.9 at 72 h post‐dose). The very high brain uptake of AM‐36 supports previous in‐vivo efficacy studies demonstrating the neuroprotective effects of this compound when administered to rats with middle cerebral artery occlusion.

Oral bioavailability and pharmacokinetics of the new insulin sensitizer DRF-2189 in Wistar rats.

The pharmacokinetics of the new insulin sensitizing agent, DRF-2189 ([5-[4-[2-(1-indolyl) ethoxy]phenyl]methyl]thiazolidine-2,4-dione, CAS 172647-53-9) were studied in male Wistar rats following oral doses of 1, 3 and 10 mg/kg as suspension in 0.25% carboxymethylcellulose. Drug was extracted from plasma samples using a solvent mixture containing ethylacetate and dichloromethane (3:2) and analyzed by high-performance liquid chromatography with fluorescence detection. DRF-2189 was absorbed slowly, attaining maximum levels at 2-3 h, and was eliminated with a half-life (t1/2) of about 3 h. The Cmax and AUC(0-infinity) increased linearly (r2 = 0.99) with the dose, while the elimination half-life (t1/2) was independent of the dose. An intravenous pharmacokinetic study of DRF-2189 was carried out in Wistar rats at a dose of 3.0 mg/kg. The pharmacokinetic parameters AUC(0-infinity), t1/2, plasma clearance (Cl) and volume of distribution (Vd) were found to be 49.52 micrograms x h/ml, 2.99 h, 16.31 ml/h and 45.11 ml. respectively. Oral bioavailability (f) of DRF-2189 in Wistar rats was 44%. Based on pharmacokinetic studies, DRF-2189 is a good choice for further development.