(CANCER RESEARCH 50. 503-508, February 1, 1989] Disposition of Amsacrine and Its Analogue 9-({2-Methoxy-4-[(methylsulfonyl)- amino]phenyl}amino)-Ar,5-dimethyl-4-acridinecarboxamide (CI-921) in Plasma, Liver, and Lewis Lung Tumors in Mice1 Philip Kestell,2 James W. Paxton, Pandora C. Evans, Deborah Young, Jeffrey L. Juriina, Iain G. C. Robertson, and Bruce C. Baguley Cancer Research Laboratory ¡P.K., J. L. J., B. C. B.] and Department of Pharmacology and Clinical Pharmacology [J. W. P., P. C. E., D. Y., I. G. C. R.J, University of Auckland Medical School, Private Bag, Auckland, New Zealand ABSTRACT 9-(|2-Methoxy-4-((methylsuIfonyl)amino|phenyljamino)-Ar,5-di- methyl-4-acridinecarboxamide (CI-921), an analogue of the clinical an- tileukemia drug amsacrine with improved solid tumor activity in mice, is currently being evaluated in patients. In order to determine whether CI- 921 possesses any advantages over amsacrine in terms of tissue delivery, the pharmacokinetics of amsacrine and CI-921 were determined following i.v. injection in male B6D2F] mice. Plasma kinetics in normal mice were measured following administration of 14.4, 28.9, and 57.7 ftmol/kg. The kinetics in s.c. Lewis lung tumors, and in plasma and livers of normal and tumor-bearing mice were measured following administration of 57.7 «imol/kg. CI-921 and amsacrine were quantitated by high-performance liquid chrontatography after extraction from plasma and from liver and tumor homogenates. In experiments with appropriate 'I I-lahelcd com pounds, both total and covalenti) bound radioactivity (determined after precipitation and washing with acetonitrile) were measured in plasma and in liver homogenates. Over this dose range, nonlinear kinetics were observed in plasma for unchanged CI-921 and amsacrine, and a reason able fit was obtained with Michaelis-Menten kinetics to a one-compart ment model for CI-921 (#„3.7 »imol/liter;Vm, 18 ^mol/h/kg; V,, 3.3 liter/kg) and a two-compartment model for amsacrine (K„3.6«imol/liter; ' m.» 76 Mmol/h/kg; V,, 4.8 liter/kg). The area under the concentration- time curve (AUC) for plasma following a dose of 57.7 «imol/kgwas 31 Minol•¿ h/liicr for CI-921 and 6.3 *<mol •¿ h/liter for amsacrine. However, equilibrium dialysis measurements indicated high plasma protein binding with free drug fractions for CI-921 and amsacrine of 0.63 and 6.7%, respectively. In the liver, unchanged drug concentrations and total radio activity for both compounds were approximately 10-fold those in plasma, and the tissue half-life of CI-921 was approximately 4-fold longer for CI- 921 than for amsacrine. Plasma and liver kinetics in mice with s.c. Lewis lung tumors were similar to those in normal mice. Tumor half-lives of unchanged CI-921 and amsacrine were 3.9 and 2.7 h, respectively, considerably longer than those for plasma (1.2 and 0.30 h respectively) or liver (1.2 and 0.28 h, respectively). Tumor AUC values for CI-921 and amsacrine were 68 and 37 ¿iniol •¿ h/liter, respectively, as compared to the calculated AUC values for free drug in plasma of 0.19 and 0.42 «imol-h/ liter, respectively. It is concluded that the uptake into tumors from the plasma free drug fraction is more efficient for CI-921 than for amsacrine. INTRODUCTION Amsacrine (Fig. 1) is a 9-aminoacridine derivative first syn thesized by Cain and Atwell (1) and now used in the treatment of acute leukaemia, particularly in combination with agents such as cytosine arabinoside (2). Amsacrine was developed and selected predominantly on the basis of testing with murine leukemias (1). Its narrow clinical spectrum of action raised the question of whether the use of a preclinical screening protocol Received 5/8/89: revised 9/11/89; accepted 10/10/89. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1Supported by the Auckland Division of the Cancer Society of New Zealand, the Medical Research Council of New Zealand and a Warner-Lambert Fellowship. 2To whom requests for reprints should be addressed, at Cancer Research Laboratory, University of Auckland Medical School. Private Bag, Auckland, New Zealand. employing a solid tumor would have resulted in the selection of a different compound in this series. The Lewis lung carci noma, only slightly sensitive to treatment by amsacrine, was thus used in this laboratory to search for more active analogues of amsacrine (3). A disubstituted derivative, CI-9213 (Fig. 1), found to be curative against i.v. inoculated Lewis lung tumors (4) was selected for further development and has now completed Phase I clinical trials (5, 6). CI-921 and amsacrine both bind by intercalation to double- stranded DNA, with CI-921 having a 16-fold higher association constant (4). Both compounds appear to act by inducing the formation of covalent links between DNA and the enzyme topoisomerase II (7). In continuous drug-exposure growth- inhibitory assays, carried out with a number of human and mouse cell lines, CI-921 requires approximately 4-fold lower concentrations than does amsacrine to inhibit growth (4, 8-9). However, these results do not explain why CI-921 has superior solid tumor activity to amsacrine in vivo. We have therefore investigated whether pharmacokinetics plays a role in deter mining the superiority of CI-921 over amsacrine, using the advanced s.c. Lewis lung tumor in mice which is known to be more sensitive to CI-921 than to amsacrine (10). We have also determined whether the presence of a s.c. tumor modifies the pharmacokinetics of these drugs. MATERIALS AND METHODS Materials. The hydrochloride salts of amsacrine and [acridinyl-G- 3H]amsacrine (406 mCi/mmol; 99% radiochemical purity), and the 2- hydroxethanesulfonate salts of CI-921 and [acridinyl-G-3H]C\-92l (4.1 mCi/mmol; 97% radiochemical purity) and [carboxamide-ltC]Cl-92l (specific activity, 59.9 mCi/mmol; >99% radiochemical purity) were kindly provided by Dr. Lloyd Whitfield, Parke-Davis Division of the Warner-Lambert Company, MI. Radiochemical purity was confirmed by TLC (chloroform:methanol, 10:1 v/v or 4:1 v/v) and by HPLC. All other chemicals and solvents used were either analytical or HPLC grade. Animals. Male B6D2F, mice (20-25 g) were used for all experiments. They were bred and maintained in the laboratory under constant temperature and humidity with sterile bedding and food (3) according to institutional guidelines. For studies with tumor-bearing mice, groups of animals were inoculated s.c. with IO6Lewis lung cells into the right flank and the experiments were performed after approximately 14 days when the tumors were palpable (5-10-mm diameter, weight 0.42 ± 0.24 g SD). Drug Formulation and Administration. CI-921 solutions (10 HIM) were prepared by sonication in sterile water and amsacrine solutions (200 mM) were prepared in TV.A'-dimethylacetamide. Solutions were diluted with water (CI-921) or 34 mM lactic acid (amsacrine) to the 3The abbreviations used are: CI-921,9-({2-methoxy-4-((methylsulfonyl)amino] phenyl|amino)-A',5-dimethyl-4-acridinecarboxamide; GSH, glutathione: HPLC, high-performance liquid chromatography; TLC, thin-layer chromatography; tn, elimination half-life; K„, steady-state volume of distribution; Cm„, maximum concentration; AUC, area under the concentration-time curve extrapolated to infinity; CV, coefficient of variation. 503 on May 18, 2017. © 1990 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from