Dose-dependent pharmacokinetics of 1-(2-Deoxy-?-D- ribofuranosyl)-2,4-difluoro-5-iodobenzene: A potential mimic of 5-iodo-2?-deoxyuridine

Biodistribution and imaging of 1-(2-deoxy-beta-d-ribofuranosyl)-2,4-difluoro-5-[123/125I]iodobenzene (dRF[(123/125)I]IB), a nonpolar thymidine-mimetic nucleoside, in rats and tumor-bearing mice

1-(2-Deoxy-beta-D-ribofuranosyl)-2,4-difluoro-5-iodobenzene (dRFIB) is a putative bioisostere of iododeoxyuridine (IUdR). The advantages of dRFIB over IUdR for in vivo studies include resistance to both phosphorolytic cleavage of the nucleoside bond and de-iodination. dRFIB was radioiodinated (dRF(123/125)IB) by copper-catalyzed exchange using commercial sodium [(123/125)I]iodide. The in vivo biodistribution of dRF[(125)I]IB in BALBc mice and imaging of dRF[(123)I]IB in Sprague-Dawley rats are reported. In vivo data for rats show rapid clearance of radioactivity from blood (>95%ID in 15 minutes), extensive excretion in urine (56%ID/24 hours), concentration in the hepatobiliary-small intestine system and very little fecal excretion (approximately 3%ID/24 hours). Pharmacokinetic data for dRF[(125)I]IB (i.v. 48.7 ug/kg) in rats (t(1/2)[h] = 0.51 +/- 0.14, AUC(inf)[microg.min/mL] = 3.7 +/- 0.4, Cl[L/kg/h] = 0.75 +/- 0.12, Vss[L/kg] = 0.96 +/- 0.18) confirm previously reported dose-dependent pharmacokinetics. Scintigraphic images of rats dosed with dRF[(123)I]I were compatible with rapid soft-tissue clearance and extensive accumulation of radioactivity in bladder/urine and liver/small intestine. In tumor-bearing mice, thyroid and stomach radioactivity was indicative of moderate deiodination. An unidentified polar radioactive metabolite was detected in serum.

Pharmacokinetics of the diastereomers of arteether, a potent antimalarial drug, in rats

The pharmacokinetics of alpha- and beta- diastereomers of arteether, a potent erythrocytic schizontocidal agent, and their active metabolite dihydroartemisinin were studied in male Sprague-Dawley rats after oral, intramuscular and intravenous administrations. Oral and intramuscular studies were carried out at three dose levels at 9, 17.5 and 30 mg kg(-1). The ratio of alpha- and beta-isomers was maintained at 30:70% w/w in the formulations used for the study. The average oral bioavailabilities of alpha-and beta-isomers, relative to intramuscular administration, were 9.6% and 3.8%, respectively, and the average in vivo alpha- to beta- ratio was 2.5. Following intravenous and intramuscular administrations the in vivo alpha- to beta- ratios were 0.7 and 0.9, respectively. The beta-isomer of arteether was characterized by a longer elimination half-life and a relatively larger volume of distribution than the alpha-isomer, suggesting that beta-arteether may be responsible for the prolonged in vivo schizontocidal activity. The alpha-isomer was absorbed rapidly after oral and intramuscular administrations and showed higher peak plasma concentrations but possessed a relatively shorter half-life. There was an apparent lack of linearity observed in terms of dose and AUCs for both alpha- and beta-arteether after oral and intramuscular administrations, suggesting nonlinear dose dependent pharmacokinetics at the dose levels studied. The rate and extent of conversion of arteether isomers to dihydroartemisinin was highest with oral and intravenous administration and least with intramuscular indicating that the intramuscular route of administration of the isomeric mixture may be more beneficial for malarial chemotherapy.

Phosphorylation of isocarbostyril- and difluorophenyl-nucleoside thymidine mimics by the human deoxynucleoside kinases

The thymidine mimics isocarbostyril nucleosides and difluorophenyl nucleosides were tested as deoxynucleoside kinase substrates using recombinant human cytosolic thymidine kinase (TK1) and deoxycytidine kinase (dCK), and mitochondrial thymidine kinase (TK2) and deoxyguanosine kinase (dGK). The isocarbostyril nucleoside compound 1-(2-deoxy-beta-D-ribofuranosyl)-isocarbostyril (EN1) was a poor substrate with all the enzymes. The phosphorylation rates of EN1 with TK1 and TK2 were <1% relative to Thd, where as the phosphorylation rates for EN1 were 1.4% and 1.1% with dCK and dGK relative to dCyd and dGuo, respectively. The analogue 1-(2-deoxy-beta-D-ribofuranosyl)-7-iodoisocarbostyril (EN2) showed poor relative-phosphorylation efficiencies (kcat/Km) with both TK1 and dGK, but not with TK2. The kcat/Km value for EN2 with TK2 was 12.6% relative to that for Thd. Of the difluorophenyl nucleosides, 5-(1'-(2'-deoxy-beta-D-ribofuranosyl))-2,4-difluorotoluene (JW1) and 1-(1'-(2'-deoxy-beta-D-ribofuranosyl))-2,4-difluoro-5-iodobenzene (JW2) were substrates for TK1 with phosphorylation efficiencies of about 5% relative to that for Thd. Both analogues were considerably more efficient substrates for TK2, with kcat/Km values of 45% relative to that for Thd. 2,5-Difluoro-4-[1-(2-deoxy-beta-L-ribofuranosyl)]-aniline (JW5), a L-nucleoside mimic, was phosphorylated up to 15% as efficiently as deoxycytidine by dCK. These data provide a possible explanation for the previously reported lack of cytotoxicity of the isocarbostyril- and difluorophenyl nucleosides, but potential mitochondrial effects of EN2, JW1 and JW2 should be further investigated.