Interactions with Human Blood in Vitro and Pharmacokinetic Properties in Mice of Liposomal N-Octadecyl-1-b-D- arabinofuranosylcytosine, A New Anticancer Drug

The interactions of N-octadecyl-1-b-D-arabinofuranosylcytosine (NOAC), a lipophilic derivative of 1-b-D-arabinofuranosylcytosine (ara-C), were studied in vitro with human blood components. Binding of NOAC incorporated into liposomes to erythrocytes (Ec) was saturated at 63 nmol/10 Ec and binding analysis resulted in a weak affinity of 3 3 10 liters/mol and 4 3 10 binding sites per Ec. The Ec partition coefficient DEc was approximately 4, which demonstrates the high accumulation of NOAC in Ec membranes. The calculated fraction fb of drug bound to plasma proteins was 30%. Analysis of serum protein binding of NOAC was done by density gradient ultracentrifugation and agarose gel electrophoresis. Liposomal NOAC was distributed to low-density lipoproteins (LDL) at 36%, to highdensity lipoproteins at 21%, to albumin and other proteins at 12% and to very-low-density lipoproteins at 5%. Comparable results were obtained for the analog N-hexadecyl-1-b-D-arabinofuranosylcytosine and when the drugs were dissolved in dimethyl sulfoxide. The biodistribution of liposomal NOAC in ICR mice after intravenous application revealed a biphasic blood concentration versus time curve with a distribution halflife t1/2a of 23 min and an elimination half-life t1/2b of 7 h. The drug was distributed mainly into the liver with an organ load of 69% and with an elimination half-life of 8 h. The strong affinity of NOAC to LDL might be exploited for the enhanced uptake of the drug in tumor cells expressing high numbers of LDL receptor molecules. 1-b-D-Arabinofuranosylcytosine is an effective chemotherapeutic agent for the treatment of acute myelogenous leukemia (Gahrton, 1983; Keating et al., 1982; Plunkett and Gandhi, 1993). However, its usefulness is impaired by its rapid deamination to the biologically inactive metabolite ara-U (Ho and Frei, 1971). To increase the cytotoxic activity of ara-C numerous N-derivatives were synthesized to protect the drug from deamination and to alter its pharmacokinetic properties (Kanai and Ichino, 1974; Rosowsky et al., 1982; Wempen et al., 1968). Whereas short-chain modifications of ara-C at the N-amino group generally resulted in a weak enhancement of cytotoxicity (Aoshima et al., 1976), lipophilic derivatives with long-chain fatty acids had a strong antitumor activity in murine tumor models (Kataoka and Sakurai, 1980; Tsuruo et al., 1980). In a previous study, we reported that N-acyl derivatives of ara-C, incorporated into the membranes of small unilamellar liposomes, were active against murine L1210 leukemia and B16 melanoma at lower concentrations than unmodified ara-C (Rubas et al., 1986). However, the protection against enzymatic deamination to ara-U was only partially achieved with the N-acyl derivatives. Therefore we synthesized the N-alkyl-ara-C derivatives NHAC and NOAC shown in figure 1 (Schwendener et al., 1995a; Schwendener and Schott, 1992). These derivatives Received for publication November 11, 1996. 1 This work was supported by a grant from the E.G., G., G., and Ch. Sassella Foundation (to S.K.M.K.-L.) and in part by a grant from the Stiftung für angewandte Krebsforschung (to R.A.S.). ABBREVIATIONS: ara-C, 1-b-D-Arabinofuranosylcytosine; ara-U, 1-b-D-arabinofuranosyluracil; NOAC, N-octadecyl-1-b-D-arabinofuranosylcytosine; NHAC, N-hexadecyl-1-b-D-arabinofuranosylcytosine; SPC, soy phosphatidylcholine; PB, phosphate buffer; saline/EDTA, saline containing 0.01% EDTA; DMSO, dimethyl sulfoxyde; EDTA, ethylenediaminetetraacetic acid; Ec, erythrocytes; Bmax, maximal drug binding capacity; Kd, ligand concentration at half-maximal binding; r, binding rate; cu, unbound drug; AEc, drug bound to Ec; Ectot, total concentration of Ec; DEc, Ec partition coefficient; Ablood, total drug in whole blood; Aplasma, drug in the plasma fraction; H, hematocrit; fb, plasma protein-binding fraction; HDL, high-density lipoprotein; LDL, low-density lipoprotein; VLDL, very-low-density lipoprotein; KBr, potassium bromide; t1/2a, distribution half-life; t1/2b, elimination half-life; Vd(area), area-derived apparent volume of distribution; Vc, apparent volume of the central compartment; Vp, apparent volume of the peripheral compartment; Cltotal, systemic clearance; AUC(tr. 03`), area under the curve for time zero to infinity calculated modelindependently with the trapezoidal rule; AUMC, area under the moment curve; cblood, drug concentration in blood; cplasma, drug concentration in plasma; Vblood, total blood volume; MRT, mean residence time; Clin, tissue uptake rate index; T(t1), amount of drug in the tissue at time t1; Clorgan, organ clearance; Worgan, organ weight; HPLC, high-performance liquid chromatography. 0022-3565/97/2823-1572$03.00/0 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 282, No. 3 Copyright © 1997 by The American Society for Pharmacology and Experimental Therapeutics Printed in U.S.A. JPET 282:1572–1580, 1997 1572 at A PE T Jornals on M arch 0, 2017 jpet.asjournals.org D ow nladed from