David R. Taft

Phase I clinical trial of oral rigosertib in patients with myelodysplastic syndromes.

The multi‐kinase inhibitor rigosertib (ON 01910.Na) induces mitotic arrest and apoptosis in myeloblasts, while sparing normal cells. The purpose of this study was to determine the pharmacokinetic profile, maximum‐tolerated dose (MTD), safety, and clinical activity of an oral formulation of rigosertib in patients with myelodysplastic syndromes (MDS). For pharmacokinetic studies, patients received rigosertib in single escalating weekly doses. To determine the MTD, patient cohorts received escalating doses of rigosertib twice daily for 14 d of a 21‐d cycle. Overall, 37 patients were treated. Rigosertib exposure increased with escalating oral doses. Mean absolute oral bioavailability ranged from 13·9% (fed) to 34·8% (fasting) in 12 patients treated at the 560 mg b.i.d. dose level. Dose‐limiting toxicity (grade 3 dysuria and shortness of breath) occurred at the 700 mg b.i.d. dose. Five patients experienced grade 3 non‐haematological toxicity, including symptoms of urothelial inflammation, hypotension and syncope, fatigue and abdominal pain. Encouraging signs of clinical activity included two bone marrow complete remissions in refractory anaemia with excess blasts type 1 patients previously treated with azacitidine. In addition, four patients each achieved transfusion independence and haematological improvements. In conclusion, oral rigosertib is bioavailable and well tolerated, and has clinical activity in patients with MDS.

Renal Disposition and Drug Interaction Screening of (–)-2′-deoxy-3′-thiacytidine (3TC) in the Isolated Perfused Rat Kidney

AbstractPurpose. Dideoxynucleoside bases are used for the treatment of acquired immune deficiency syndrome (AIDS), acting by inhibiting reverse transcriptase and preventing human immunodeficiency virus (HIV) replication. Currently, AZT (zidovudine), ddC (zalcitibine), and ddI (didanosine) are available to the medical community to prevent the onset of AIDS in HIV-infected individuals. 3TC (–)-2′-deoxy-3′-thiacytidine, lamivudine), a new dideoxynucleoside base, is currently undergoing Phase II/III trials, and has exhibited anti-HIV replication activity, a favorable adverse event safety profile, and is eliminated via renal mechanisms. Concomitantly administered drugs could potentiate the effects of 3TC due to interaction in the kidney. Methods. An isolated perfused rat kidney (IPK) technique was used to screen several clinically relevant drugs for potential interaction with 3TC. The following perfusions were performed: baseline 3TC; and 500 ng/mL 3TC with clinically relevant concentrations of AZT, ddC, ddI, probenecid, trimethoprim, sulfamethoxazole, ranitidine, and cimetidine. Results. Renal clearance of 3TC was nonlinear between 500 and 5000 ng/mL, decreasing from 3.06 to 1.74 mL/min. Excretion ratio also decreased, from 3.67 (500 ng/mL) to 2.49 (5000 ng/mL), consistent with a decrease in 3TC secretion. AZT, ddI, and ddC elicited no or minimal effects on 3TC elimination at the concentrations studied. However, trimethoprim caused significant reductions in 3TC elimination parameters: clearance and excretion ratio decreased to 1.25 mL/min and 1.43, respectively. Conclusions. These results indicate that caution should be exercised when the combination of 3TC and trimethoprim are administered to AIDS patients.

Preclinical Drug Development

The Scope of Preclinical Drug Development: An Introduction and Framework Interspecies Differences in Physiology and Pharmacology: Extrapolating Preclinical Data to Human Populations Transgenic Animals for Preclinical Drug Development Pharmacokinetics/ADME of Small Molecules Pharmacokinetics/ADME of Large Molecules Preclinical Pharmacokinetic-Pharmacodynamic Modeling and Simulation Formulation and Route of Administration - Influencing Drug Assessment of Pharmacokinetics and Drug Activity: Isolated Organ Alternate Methods for Assessing Absorption, Metabolism and Routes of Toxicity Evaluations: ICH Guidelines and Current Practice Application of Pathology in Safety Assessment Principles of Toxicogenomics: Implications for Preclinical Drug Development Utilizing the Preclinical Database to Support Clinical Drug Development

The Isolated Perfused Rat Kidney Model: A Useful Tool for Drug Discovery and Development

Over the past three decades, the Isolated Perfused Rat Kidney (IPK) has been used to study numerous aspects of renal drug disposition. Among the available ex-vivo methods to study renal transport, the IPK allows for elucidation of the overall contributions of renal transport mechanisms on drug excretion. Therefore, IPK studies can provide a bridge between in vitro findings and in vivo disposition. This review paper begins with a detailed overview of IPK methodology (system components, surgical procedure, study design). Various applications of the IPK are then presented. These applications include characterizing renal excretion mechanisms, screening for clinically significant drug interactions, studying renal drug metabolism, and correlating renal drug disposition with drug-induced changes in kidney function. Lastly, the role of IPK studies in drug development is discussed. Demonstrated correlations between IPK data and clinical outcomes make the IPK model a potentially useful tool for drug discovery and evaluation.

Effects of Trimethoprim on the Clearance of Apricitabine, a Deoxycytidine Analog Reverse Transcriptase Inhibitor, and Lamivudine in the Isolated Perfused Rat Kidney

Apricitabine (ATC) is a novel deoxycytidine analog reverse transcriptase inhibitor in development for the treatment of human immunodeficiency virus infection. Studies were performed to characterize the excretion of ATC and its metabolite, BCH-335 (–1-(2-hydroxymethyl-[1,3]oxathiolan-4-yl)-1H-pyrimidine-2,4-dione), in the isolated perfused rat kidney (IPK). A second objective was to investigate the effect of trimethoprim on ATC excretion because trimethoprim inhibits the excretion of lamivudine, structurally similar to ATC, in the IPK. ATC excretion was nonlinear at doses of 80 to 1600 μg. The excretion ratio (ratio of clearance to glomerular filtration rate, assuming negligible protein binding) was greater than 1.0, indicating net tubular secretion. In contrast, the excretion of BCH-335 was independent of the dose of BCH-335. Concomitant administration of ATC and BCH-335 did not affect the excretion of either compound. Trimethoprim significantly inhibited the excretion of both ATC and BCH-335, with IC50 values of 0.45 and 0.54 μg/ml, respectively. In the presence of trimethoprim, the excretion ratios for both compounds were less than 1.0, indicating tubular reabsorption. Trimethoprim inhibited the excretion of ATC and lamivudine to similar extents. Following concomitant administration of ATC, lamivudine, and trimethoprim, there was no evidence of an interaction between ATC and lamivudine. These results suggest that ATC undergoes active tubular secretion in the kidney. Because the renal excretion of both ATC and lamivudine is inhibited by trimethoprim to similar extents, in clinical practice exposure to ATC, it would be expected to be increased in the presence of therapeutic concentrations of trimethoprim to a similar extent as has been shown previously for lamivudine.

Renal excretion of emtricitabine I: effects of organic anion, organic cation, and nucleoside transport inhibitors on emtricitabine excretion.

The excretion of emtricitabine (FTC) was characterized using isolated perfused rat kidney (IPK) model. Studies were performed to assess the dose-linearity of FTC excretion, to evaluate the effect of inhibitors of organic anion (probenecid, PBC), organic cation (tetraethylammonium, TEA; cimetidine, CMD) and nucleoside (uridine, URD) transport systems on FTC excretion, and to determine the potential interaction between FTC and trimethoprim (TMP). FTC excretion was studied over a range of doses (80-1600 microg), targeting concentrations encompassing the therapeutic range of FTC (1-20 microg/mL). FTC (2 microg/mL) was also coperfused with PBC (500 microM), TEA (500 microM), CMD (2 mM), URD (500 microM), and TMP (13.7 microM). FTC dose-linearity studies revealed that excretion parameters were not significantly different among dosing groups. Of the transport inhibitors tested, FTC XR decreased more than twofold in the presence of CMD (0.32 +/- 0.099). PBC, TEA, and URD had no observed effect on FTC excretion. TMP coadministration significantly inhibited FTC excretion (XR = 0.43 +/- 0.052). The results suggest that FTC renal transport is likely mediated by a CMD-sensitive organic cation transporter (OCT) in the kidney. TMP may inhibit the renal excretion of FTC when the two compounds are coadministered in vivo.

Aristolochic acid I metabolism in the isolated perfused rat kidney.

Aristolochic acids are natural nitro-compounds found globally in the plant genus Aristolochia that have been implicated in the severe illness in humans termed aristolochic acid nephropathy (AAN). Aristolochic acids undergo nitroreduction, among other metabolic reactions, and active intermediates arise that are carcinogenic. Previous experiments with rats showed that aristolochic acid I (AA-I), after oral administration or injection, is subjected to detoxication reactions to give aristolochic acid Ia, aristolactam Ia, aristolactam I, and their glucuronide and sulfate conjugates that can be found in urine and feces. Results obtained with whole rats do not clearly define the role of liver and kidney in such metabolic transformation. In this study, in order to determine the specific role of the kidney on the renal disposition of AA-I and to study the biotransformations suffered by AA-I in this organ, isolated kidneys of rats were perfused with AA-I. AA-I and metabolite concentrations were determined in perfusates and urine using HPLC procedures. The isolated perfused rat kidney model showed that AA-I distributes rapidly and extensively in kidney tissues by uptake from the peritubular capillaries and the tubules. It was also established that the kidney is able to metabolize AA-I into aristolochic acid Ia, aristolochic acid Ia O-sulfate, aristolactam Ia, aristolactam I, and aristolactam Ia O-glucuronide. Rapid demethylation and sulfation of AA-I in the kidney generate aristolochic acid Ia and its sulfate conjugate that are voided to the urine. Reduction reactions to give the aristolactam metabolites occur to a slower rate. Renal clearances showed that filtered AA-I is reabsorbed at the tubules, whereas the metabolites are secreted. The unconjugated metabolites produced in the renal tissues are transported to both urine and perfusate, whereas the conjugated metabolites are almost exclusively secreted to the urine.

In vitro evaluation of the release of albuterol sulfate from polymer gels: Effect of fatty acids on drug transport across biological membranes

ABSTRACT In this investigation, the diffusion of the beta2 agonist albuterol sulfate (ABS) across several membranes (cellulose, hairless mouse skin, human cadaver skin) from polymer gels was studied, and the effects of several fatty acids on drug permeation through skin were evaluated. The results were then used to predict whether transdermal delivery would be appropriate for ABS. All in vitro release studies were carried out at 37°C using modified Franz diffusion cells. In preliminary studies, ABS release through cellulose membranes was studied from two polymeric gels, Klucel® (hydroxypropylcellulose) and Methocel® (hydroxypropylmethylcellulose). Three polymer concentrations were used for each gel (0.5%, 1.0%, and 1.5%). From these experiments, Klucel 0.5% was selected as the optimal formulation to study ABS diffusion across hairless mouse skin. Experiments were conducted to evaluate the effects of capric acid, lauric acid, and myristic acid as penetration enhancers. The results suggested that lauric acid preferentially enhanced ABS diffusion compared to the other fatty acids studied, and follow-up studies were done to evaluate the release through human cadaver skin from a donor containing 2% ABS and lauric acid in 0.5% Klucel®. These experiments showed that a 2:1 (lauric acid:ABS) molar ratio gave the best ABS release rates. The release rate across human cadaver skin declined slowly over 24 hr, and an average flux over 24 hr of ˜0.09 mg/hr cm2 was measured. Using this value as a steady-state flux, extrapolations predicted that transdermal delivery can be used to maintain therapeutic ABS plasma levels (6–14 ng/mL) for extended periods. The results of this research suggest that ABS is a good candidate for transdermal drug delivery.

Renal excretion of emtricitabine II. Effect of trimethoprim on emtricitabine excretion: In vitro and in vivo studies

The potential interaction between the nucleoside analog emtricitabine (FTC) and trimethoprim (TMP) was assessed in the isolated perfused rat kidney (IPK) model and in vivo in rats. IPK experiments were performed with FTC alone (2 microg/mL) and in the presence of increasing concentrations of TMP (1-10 microg/mL). TMP inhibited FTC excretion in a concentration dependent manner. The IC(50) (TMP concentration associated with a 50% reduction in FTC excretion) was 1.86 +/- 0.37 microg/mL. The results were compared to whole animal studies in rats. Animals received an IV dose of FTC (1 mg/kg) with or without pretreatment with TMP (25 mg/kg). TMP coadministration significantly decreased FTC clearance (7.4 +/- 1.2 mL/min/kg to 2.7 +/- 0.53 mL/min/kg), and elimination half-life was significantly increased (58 +/- 12 min to 215 +/- 44 min). A good correlation was obtained between IPK findings and in vivo data, as FTC renal clearance was reduced approximately 60% in the presence of TMP in both studies. Based on this investigation, TMP would be expected to inhibit the renal excretion of FTC when the two compounds are coadministered, resulting in increased plasma exposure of FTC. However, the clinical significance of this finding remains to be elucidated.

Determination of methazolamide concentrations in human biological fluids using high performance liquid chromatography.

Methazolamide is a carbonic anhydrase inhibitor used to treat glaucoma. In vivo, methazolamide readily distributes into red blood cells. Therefore, both blood and plasma concentration data are needed in order to characterize the pharmacokinetics of methazolamide. In the present study, an analytical method using high performance liquid chromatography was validated for determination of methazolamide concentrations in several biological fluids. Through slight modification of a previously reported method for acetazolamide, another carbonic anhydrase inhibitor, methazolamide was readily quantitated in whole blood, plasma and urine. Sample preparation involved liquid-liquid extraction with ethyl acetate followed by a washing step using phosphate buffer (pH 8.0). After back extraction into glycine buffer (pH 10.0), samples were then washed with ether and injected onto the chromatograph. Chromatography was performed using a C-18, 5 microns reverse-phase column with UV detection at a wavelength of 285 nm. Mobile phase consisted of 0.05 M sodium acetate (pH 4.0) and acetonitrile (20%). The assay was validated over two standard concentration ranges from 1 to 100 micrograms ml-1, concentrations reflective of those expected in vivo, Calibration curves were linear for all biological fluids and coefficients of variation for interday and intraday reproducibility studies were less than 8% (range 3.1-7.9%). The method was used to measure methazolamide concentrations in blood, plasma and urine following oral administration to five human subjects.