Abstract
There is considerable evidence that DNA intercalating drugs fail to penetrate tumor tissue efficiently. This study used the multicellular layer (MCL) experimental model, in conjunction with computational modeling, to test the hypothesis that a DNA intercalator in phase II clinical trial,N-[2-(dimethylamino)-ethyl]acridine-4-carboxamide (DACA), has favorable extravascular transport properties. Single cell uptake and metabolism of DACA and the related but more basic aminoacridine 9-[3-(dimethylamino)propylamino]acridine (DAPA), and penetration through V79 and EMT6 MCL, were investigated by high-performance liquid chromatography. DACA was accumulated by cells to a lesser extent than DAPA and was metabolized to the previously unreported acridan by V79 but not EMT6 cells. Despite this metabolism, flux of DACA through MCL was much faster than that of DAPA. Modeling MCL transport as diffusion with reaction (metabolism and reversible binding) showed that the faster flux of DACA was due to a 3-fold higher free drug diffusion coefficient and 10-fold lower binding site density. The MCL transport parameters were used to develop a spatially resolved pharmacokinetic model for the extravascular compartment in tumors, which provided a reasonable prediction of measured average tumor concentrations from plasma pharmacokinetics in mice. Area under the curve was essentially independent of distance from blood vessels, although the combined pharmacokinetic/pharmacodynamic model predicted a modest decrease in cytotoxicity (from 1.8 to 1.1 logs of cell kill) across a 125-μm region. In conclusion, this study demonstrates that it is possible to design DNA intercalators that diffuse efficiently in tumor tissue, and that there is little impediment to DACA transport over distances required for its antitumor action.
Footnotes
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Send reprint requests to: Dr. Kevin O. Hicks, Experimental Oncology Group, Auckland Cancer Society Research Center, The University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: k.hicks{at}auckland.ac.nz
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This study was supported by Fellowships from the New Zealand Lottery Grants Board (to K.O.H.) the Health Research Council of New Zealand (to W.R.W.), and a grant from the Cancer Society of New Zealand. The LC/MS system was purchased with funds from the Wellcome Trust and New Zealand Lottery Health Grants Board.
- Abbreviations:
- MCL
- multicellular layer
- HPLC
- high-performance liquid chromatography
- DAPA
- 9-[3-(dimethylamino)propylamino]acridine
- DACA
- N-[2-(dimethylamino)-ethyl]acridine-4-carboxamide
- DACA-2H
- N-[2-(dimethylamino)ethyl]-9,10-dihydroacridine-4-carboxamide
- LC/MS
- liquid chromatography/mass spectrometry
- PK
- pharmacokinetic
- AUC
- area under the curve
- Rt
- retention time
- Df
- the diffusion coefficient of the free drug
- Dm
- Df in the MCL
- Ds
- Dfin the Teflon support membrane
- c1,0
- initial concentration in the donor compartment at time 0
- c0
- initial concentration in single cell uptake and metabolism experiments
- ce
- extracellular concentration
- ci
- intracellular concentration
- cf
- cb1,cb2 are the concentrations of free, nonsaturably bound and saturably bound drug, respectively
- k1 and k−1
- forward (association) and reverse (dissociation) rate constants for nonsaturable binding
- k2 and k−2
- the forward and reverse rate constants for saturable binding
- Bmax
- the total concentration of saturable binding sites
- kmet
- the first order metabolic rate constant
- khydr
- the rate constant for hydrolysis
- K1
- the equilibrium association constant for nonsaturable binding
- K2
- the equilibrium dissociation constant for saturable binding
- φi
- intracellular volume fraction
- A and B are the coefficients and α
- β and Ka are the absorption, distribution and elimination rate constants in the DACA PK model for mouse plasma
- a
- K, m, and n are constants in the model for DACA cytotoxicity in single cells
- Received November 6, 2000.
- Accepted February 1, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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