This dissertation presents an investigation of the impact of Multidrug Resistance-associated Protein 2/ATP-binding cassette superfamily C member 2 (Mrp2/Abcc2) and 3 (Mrp3/Abcc3) on the pharmacokinetics (PKs) of methotrexate (MTX) using gene knockout murine models. MTX is a substrate for numerous human ATP-binding cassette (ABC) efflux transporters, yet the impact of these transporters on the pharmacokinetics of MTX over a large dose range has not been examined. To investigate the effects of two transporters, Abcc2 (Mrp2) and Abcc3 (Mrp3), involved in MTX hepatobiliary disposition in vivo, MTX plasma, urine and feces concentrations were analyzed after 10, 50, and 200 mg/kg intravenous (IV) doses to groups of wild type (WT), Abcc2-/- and Abcc3-/- mice. The absence of Abcc2 caused a decrease in total clearance of MTX relative to WT mice at all dose levels yet was accompanied by compensatory increases in renal excretion and metabolism to 7-hydroxymethotrexate (7OH-MTX). In Abcc3-/- mice total clearance was elevated at the two lower dose levels that was attributed to stimulation of biliary excretion and confirmed by elevated fecal excretion; however at the high 200 mg/kg dose clearance was severely retarded and could be attributed to hepatotoxicity as conversion to 7OH-MTX was diminished. We also sought to characterize the effects of Abcc2 and Abcc3, on the PKs of MTX after oral dosing. Plasma, urine, and fecal concentrations of MTX were measured after 10, 50, and 200 mg/kg oral doses to cohorts of WT, Abcc2-/- and Abcc3-/- mice mouse strains. The absence of Abcc2 caused an approximate 2-fold increase in system exposure and a slight increase in oral bioavailability of MTX relative to WT mice at all dose levels. These elevations were accompanied by compensatory increases in conversion to 7OH-MTX, and based on AUC7OH-MTX/AUCMTX (area under the curve ratio of metabolite and parent drug) that ranged from 3% to 9% in WT mice increased to a range of 16% to 26% in Abcc2-/- mice. Renal excretion of unchanged MTX was unaltered in the Abcc2-/- strain; fraction urinary excretion (fr) ranged from about 4% to 11% in WT mice, whereas in Abcc2-/- mice fr ranged from about 7% to 23%. Abcc3-/- mice exhibited more than a 2-fold decrease in Cmax and significant reductions in AUCMTX when compared to WT mice at all dose levels. There were no compensatory increases in either metabolism or in renal and biliary excretion, which suggests future studies for investigating a potential unknown mechanism. Regardless of the mouse strain, increases in the MTX dose were not accompanied by proportional increases in AUCMTX. The PKs of MTX in different mouse strains was successfully modeled by a nonlinear semi-mechanistic 3-compartmental conditional model incorporating key efflux transporters. The model employed population-based analysis and conditional transport terms to well capture the nonlinear properties of MTX systemic disposition for a wide dose range of 10 - 200 mg/kg in WT and knockout strains. The model correlates the mechanistic nature of the nonlinear phenomenon with the key efflux transporters effects on MTX PKs and provides insight for preclinical therapeutic study design. Overall, the information obtained in this investigation underscores the significance of efflux transporters, Abcc2 and Abcc3, for they significantly influence the pharmacokinetics of MTX and their impact can be reflected by a nonlinear semi-mechanistic 3-compartmental conditional model. The studies also provide implication in the preclinical therapeutic study design and insights on the source of inter-patient variability as well as on the combination drug regimens to maximize drug activity yet without toxicity. / Pharmaceutical Sciences

Proton MR spectroscopy is a tool that provides quantified brain bioprofiles. Two methods exist: single- and multi-voxel spectroscopy. No studies compare their clinical validity in vivo. Gadolinium based MR contrast agents are used to improve lesional conspicuity. Adverse events are reported. Brain deposition occurs following administration in people and murine models. In dogs, doses are anecdotal and deposition is not described. Eight normal dogs underwent MRI at 3 Tesla with two methods of spectroscopy and were administered varying doses of gadodiamide. No differences were seen between single- and multi-voxel spectroscopy when interrogating identical regions of interest. Brains were harvested and evaluated for gadolinium depots using inductively coupled plasma mass spectrometry. Gadolinium was found in the brains of all dogs with dose dependency. Further, adequate normal brain conspicuity was seen at a dose of 0.5 mmol/kg. Thus, clinical trials of gadolinium chelated contrast agents at this dose are recommended.

No / A series of analogues of cryptolepine (1) have been synthesized and evaluated for their in vitro antiplasmodial and cytotoxic properties. The IC50 values of several compounds (11a, 11k¿m, 11o, 13) against Plasmodium falciparum (strain K1) were <0.1 ¿M, 5¿10-fold lower than that of 1 but their cytotoxicities were only 2¿4 times greater than that of 1. Compounds with a halogen in the quinoline ring and a halogen or a nitro group in the indole ring have enhanced antiplasmodial activity. In mice infected with P. berghei, the 7-bromo-2-chloro (11k) and 2-bromo-7-nitro (13) derivatives of 1 suppressed parasitemia by >90% at doses of 25 mg kg-1 day-1 with no apparent toxicity to the mice. 2,7-Dibromocryptolepine (15) was evaluated at several dose levels, and a dose-dependent suppression of parasitemia was seen (ED90 = 21.6 mg kg-1 day-1). The antimalarial mode of action of 1 appears to be similar to that of chloroquine and involves the inhibition of hemozoin formation. A number of analogues were assessed for their effects on the inhibition of ß-hematin (hemozoin) formation, and the results were compared with their antiplasmodial activities having taken account of their predicted accumulation into the acidic parasite food vacuole. No correlation was seen (r2 = 0.0781) suggesting that the potent antimalarial activity of compounds such as 15 involves other mechanisms in addition to the inhibition of hemozoin formation.