Pharmacokinetics and metabolite identification of a novel VEGFR-2 and Src dual inhibitor 6-chloro-2-methoxy-N-(2-methoxybenzyl) acridin-9-amine in rats by liquid chromatography tandem mass spectrometry.

A novel VEGFR-2 and Src dual inhibitor, 6-Chloro-2-methoxy-N-(2-methoxybenzyl) acridin-9-amine (MBAA), is a 9-aminoacridine derivative, but its pharmacokinetics and metabolism in body remain unknown. Using liquid chromatography tandem electrospray ionization mass spectrometry with the multiple reaction monitoring modes, we developed and validated a simple, rapid, sensitive and accurate technology for analyses of MBAA in the rat plasma, urine and bile. The micro samples were quickly prepared by 96-well plate. Chromatographic separation was performed on a C(18) column with gradient elution. High-quality linearity calibration curves were achieved over a concentration range of 1.00-3000 ng mL(-1). Intra- and inter-day precisions (RSD) were less than 8.5%, and accuracy (RE%) ranged from -2.9% to 12%. Extraction recoveries of MBAA were consistent with an average of 82.2-111.4% at three QC concentrations. When administered intravenously at a single dose of 2.0 mg kg(-1) to male SD rats, MBAA was rapidly eliminated with a T(1/2) of 0.9 ± 0.1h and AUC(0-t) of 369 ± 44.7 ng mL(-1). We identified four direct phase I and phase II metabolites by mass difference of molecular ions between metabolites and the parent compound. Various fragmentation patterns of MBAA were used to identify and characterize its metabolites. This LC-MS/MS analysis provides a useful approach to the pharmacokinetic and metabolic study of MBAA.

The imidazoacridinone antitumor drug, C-1311, is metabolized by flavin monooxygenases but not by cytochrome P450s.

5-Diethylaminoethylamino-8-hydroxyimidazoacridinone (C-1311) is an antitumor agent that is also active against autoimmune diseases. The intention of the present studies was to elucidate the role of selected liver enzymes in metabolism of C-1311 and the less active 8-methyl derivative, 5-diethylaminoethylamino-8-methoxyimidazoacridinone (C-1330). Compounds were incubated with rat liver microsomal fraction, with a set of 16 human liver protein samples, and with human recombinant isoenzymes of cytochrome P450, flavin monooxygenases (FMO), and UDP-glucuronosyltransferase (UGT). Our results showed that C-1311 and C-1330 were metabolized with human liver microsomal enzymes but not with any tested human recombinant cytochromes P450 (P450s). Two of these, CYP1A2 and CYP3A4, were inhibited by both compounds. In addition, results of C-1311 elimination from hepatic reductase-null mice, in which liver NADPH-P450 oxidoreductase has been deleted indicated that liver P450s were slightly engaged in drug transformation. In contrast, both compounds were good substrates for human recombinant FMO1 and FMO3 but not for FMO5. The product of FMO metabolism, P(FMO), which is identified as an N-oxide derivative, was identical to P3(R) of liver microsomes. P3(R) was observed even in the presence of the P450 inhibitor, 1-aminobenzotriazole, and it disappeared after heating. Therefore, FMO enzymes could be responsible for microsomal metabolism to P3(R) = P(FMO). Glucuronidation on the 8-hydroxyl group of C-1311 was observed with liver microsomes supported by UDP-glucuronic acid and with recombinant UGT1A1, but it was not the case with UGT2B7. Summing up, we showed that, whereas liver P450 isoenzymes were involved in the metabolism of C-1311 to a limited extent, FMO plays a significant role in the microsomal transformations of this compound, which is also a specific substrate of UGT1A1.

Nanoparticle coated emulsions as novel dermal delivery vehicles.

The dermal delivery characteristics of hydrophilic silica nanoparticle coated medium chain triglyceride oil-in-water emulsions are reported and correlated with the physicochemical and interfacial properties of the emulsion based drug carriers. The synergistic drug/stabiliser/nanoparticle interactions are demonstrated to be a function of the charge and concentration of the initial emulsion stabiliser; charge and initial loading phase of nanoparticles and physicochemical properties of the drug molecule. The improved physical stability of the emulsions and the chemical stability of two model lipophilic agents (all-trans-retinol and acridine orange 10-nonyl bromide) confirm that engineered nanoparticle layers can enhance the shelf-life of liable lipophilic agents. Nanoparticle coatings are shown to control the in-vitro release of active agents from emulsions and significantly promote skin retention. The lipophilic agents distributed into the deeper viable skin layers without permeation through full-thickness skin and hence systemic exposure. Nanoparticle-coated submicron oil-in-water emulsions can serve as novel dermal carriers with controlled release kinetics and targeted drug delivery.

Metabolic transformations of antitumor imidazoacridinone, C-1311, with microsomal fractions of rat and human liver.

The imidazoacridinone derivative C-1311 is an antitumor agent in Phase II clinical trials. The molecular mechanism of enzymatic oxidation of this compound in a peroxidase model system was reported earlier. The present studies were performed to elucidate the role of rat and human liver enzymes in metabolic transformations of this drug. C-1311 was incubated with different fractions of liver cells and the reaction mixtures were analyzed by RP-HPLC. We showed that the drug was more sensitive to metabolism with microsomes than with cytosol or S9 fraction of rat liver cells. Incubation of C-1311 with microsomes revealed the presence of four metabolites. Their structures were identified as dealkylation product, M0, as well as a dimer-like molecule, M1. Furthermore, we speculate that the hydroxyl group was most likely substituted in metabolite M3. It is of note that a higher rate of transformation was observed for rat than for human microsomes. However, the differences in metabolite amounts were specific for each metabolite. The reactivity of C-1311 with rat microsomes overexpressing P450 isoenzymes, of CYP3A and CYP4A families was higher than that with CYP1A and CYP2B. Moreover, the M1 metabolite was selectively formed with CYP3A, whereas M3 with CYP4A. In conclusion, this study revealed that C-1311 varied in susceptibility to metabolic transformation in rat and human cells and showed selectivity in the metabolism with P450 isoenzymes. The obtained results could be useful for preparing the schedule of individual directed therapy with C-1311 in future patients.

Similarity between enzymatic and electrochemical oxidation of 2-hydroxyacridinone, the reference compound of antitumor imidazoacridinones.

The present work is part of a wide research project aimed to elucidate the mechanism of the metabolic activation of the antitumor imidazoacridinone agent C-1311 selected for clinical trials. The objectives of the investigations presented here were: (i) to examine the enzymatic transformation of the reference compound 2-hydroxyacridinone and (ii) to test the similarity between enzymatic and electrochemical oxidation of acridinone compounds. This similarity was searched with respect to the usefulness of the electrochemical results for further studies on the metabolic oxidation of imidazoacridinone antitumor drugs. The enzymatic oxidation of 2-hydroxyacridinone was performed with a model system containing various amounts of horseradish peroxidase and hydrogen peroxide and was followed by UV-VIS spectroscopy and by HPLC. One product of the reaction was isolated and its chemical structure was identified. It was shown that 2-hydroxyacridinone was transformed by the studied system in a manner dependent on the amount of the enzyme and on the compound/H(2)O(2) ratio. While under mild reaction conditions the transformation ran slowly to yield only one product, p1, independently of the reaction time, higher enzyme concentration resulted in several steps of transformation. Product p1 turned out to be a dimer: 1,1-bi(2-hydroxyacridinone). A comparison of the results of the enzymatic transformations of 2-hydroxyacridinone presented here with studies on the electrochemical oxidation reported earlier allowed us to show both transformations to be similar as far as the reaction pathway and two reaction products are concerned.

Cellular uptake, cytotoxicity and DNA-binding studies of the novel imidazoacridinone antineoplastic agent C1311.

C1311 is a novel therapeutic agent with potent activity against experimental colorectal cancer that has been selected for entry into clinical trial. The compound has previously been shown to have DNA-binding properties and to inhibit the catalytic activity of topoisomerase II. In this study, cellular uptake and mechanisms by which C1311 interacts with DNA and exerts cytotoxic effects in intact colon carcinoma cells were investigated. The HT29 colon cancer cell line was chosen to follow cellular distribution of C1311 over a time course of 24 h at drug concentrations that just inhibited cell proliferation by 50% or 100%. Nuclear uptake of C1311 and co-localization with lysosomal or mitochondrial dyes was examined by fluorescence microscopy and effects on these cellular compartments were determined by measurement of acid phosphatase levels, rhodamine 123 release or DNA-binding behaviour. The strength and mode of DNA binding was established by thermal melting stabilization, direct titration and viscometric studies of host duplex length. The onset of apoptosis was followed using a TUNEL assay and DNA-fragmentation to determine a causal relationship of cell death. Growth inhibition of HT29 cells by C1311 was concomitant with rapid drug accumulation in nuclei and in this context we showed that the compound binds to duplex DNA by intercalation, with likely A/T sequence-preferential binding. Drug uptake was also seen in lysosomes, leading to lysosomal rupture and a marked increase of acid phosphatase activity 8 h after exposure to C1311 concentrations that effect total growth inhibition. Moreover, at these concentrations lysosomal swelling and breakdown preceded apoptosis, which was not evident up to 24 h after exposure to drug. Thus, the lysosomotropic effect of C1311 appears to be a novel feature of this anticancer agent. As it is unlikely that C1311-induced DNA damage alone would be sufficient for cytotoxic activity, lysosomal rupture may be a critical component for therapeutic efficacy.

In vivo metabolism of the antitumor imidazoacridinone C1311 in the mouse and in vitro comparison with humans.

C1311 has emerged as the lead compound from a novel group of anticancer agents, the imidazoacridinones, and will be entering clinical trials shortly. Previous murine pharmacokinetic studies have shown C1311 to be rapidly and extensively distributed into tissues including tumor. This study has identified two major metabolites of C1311 and describes their pharmacokinetics in mice. M1 is a glucuronide of the parent compound with high concentrations in both plasma and liver. Calculated area under the plasma concentration versus time curve values were 6-fold and 2-fold greater, respectively, than C1311. Based on these studies, we propose M2 to be a nonfluorescent oxidation product because electrospray ionization-mass spectroscopy/mass spectroscopy analysis gave a molecular ion at m/z 367, 16 U greater than the parent compound. It formed rapidly in liver preparations in vitro, both murine and human, by a cytosolic process in the presence of NADPH and in vivo was detected in liver tissues at concentrations equivalent to those of C1311 but was not detectable in plasma. Preliminary in vitro toxicity studies showed M2 to be as potent as C1311 against MAC15A tumor cells. Over the first 24 h, 39% of the administered dose is eliminated via the bile (28%) mostly as C1311 or the kidneys (11%) as the glucuronide (M1). This study has given valuable information as to the likely metabolic pathway to occur in humans, and the cytotoxic metabolite M2 may play a role in the antitumor activity or toxicity of C1311 in the clinic.

The relevance of enzymatic oxidation by horseradish peroxidase to antitumour potency of imidazoacridinone derivatives.

The presented study concentrated on the oxidative enzymatic transformation of six imidazoacridinone derivatives exhibiting different antitumour activity. Horseradish peroxidase was applied as an enzymatic model system. The investigations aimed to evaluate: (1) whether the studied compounds can undergo oxidative biotransformation; (2) whether the susceptibility to such biotransformation relates to the structure and antitumour activity of these compounds; and (3) which elements of imidazoacridinone structure are involved in this kind of transformation. The reaction courses were followed by three methods: UV-VIS spectroscopy, electron paramagnetic resonance and high-performance liquid chromatography. It was shown that all the imidazoacridinones studied underwent enzymatic oxidation resulting in the formation of several products, spectra of which revealed that imidazoacridinone chromophore as well as alkylamino side-chain were involved in these biotransformations. The susceptibility to enzymatic oxidation turned out to be well correlated with antitumour activity of these compounds. It was demonstrated that the highly active antitumour 8-hydroxy derivatives underwent oxidative transformation far more readily than the less active 8-methoxy derivatives and analogues without substituent in position 8. The results indicated that the oxidation pathway of 8-hydroxy compounds was different from those observed for the remaining imidazoacridinones studied. It also differed from the pathway proposed earlier for mitoxantrone. Moreover, it was find out that not only the rate but also the mechanism of horseradish oxidation of 8-hydroxy derivatives depended on the reaction conditions. In the presence of excess of hydrogen peroxide, the drugs were exceptionally reactive giving rise to the mixture of many unstable products, among which compounds with both changed and unchanged chromophore structure were formed. However, the equimolar ratio of drug and hydrogen peroxide led to stable products, which resulted from the oxidation in aminoalkyl side-chain. The possible structures of products of imidazoacridinone enzymatic oxidation are discussed. In conclusion, the results presented in this paper indicate that the oxidative metabolic activation of imidazoacridinones may represent the crucial step in their biological action.

Pharmacokinetics and tissue distribution of the imidazoacridinone C1311 in tumour-bearing mice.

C1311 is the most active member of a new series of rationally designed anti-cancer agents, the imidazoacridinones, which has shown promising pre-clinical anti-tumour activity in vitro and in vivo against a variety of human colon cancers and is a strong candidate for clinical trials. Data are not available on the pharmacokinetic properties of this compound; therefore, the main aim of this project was to study the plasma pharmacokinetics and tissue and tumour distribution of C1311 in mice and to assess, prior to potential clinical application, whether these pharmacokinetics were linear with respect to the dose. The distribution of C1311 in whole blood was also studied. NMRI or NCR-Nu mice were used throughout the study. C1311 was given i.p. at doses of 15, 50, 100 and (the maximum tolerated dose, (MTD) 150 mg kg(-l) i.p. Plasma, tissue and tumour levels were monitored over a 24-h period using high-performance liquid chromatography (HPLC) with fluorescence detection. The distribution of C1311 in murine and human whole blood was studied using both HPLC and fluorescence microscopy. C1311 was quickly cleared from the plasma (47410 ml min kg(-1)) and rapidly distributed into the tissues at all doses. Tissue-to-plasma ratios were large, ranging from 8 in the liver (15 mg kg(-l)) to 600 (50 mg kg(-1)) in the spleen. Overall concentrations were ranked in the order of plasma << liver < kidney < fat < small intestine < spleen. Tumour concentrations were similar to those measured in the liver and kidney, with AUCs being 186 (MAC15A) and 94.4 microg h ml(-l)(HT-29). Plasma pharmacokinetics were linear at doses of 15-100 mg kg(-1), but disproportionate increases were seen in plasma and tissue concentrations at doses above 100 mg kg(-l). C1311 distributed unevenly in both mouse and human blood, with higher concentrations occurring in the cellular fraction than in plasma. Nucleated cells accounted for a large proportion of this localised drug. In conclusion, C1311 is quickly cleared from the plasma and rapidly distributed into the tissues, with tissue concentrations being far higher than plasma levels. The plasma pharmacokinetics are linear up to but not above doses of 100 mg kg(-1). Concentrations of C1311 are greater in the cellular fraction of the blood than in the plasma, with disproportionately high concentrations occurring in the nucleated fraction.

Decreased mitochondrial function in quiescent cells isolated from multicellular tumor spheroids.

Cells in the inner region of multicellular spheroids markedly reduce their oxygen consumption rate, presumably in response to their stressful microenvironment. To determine the mechanism behind this metabolic adaptation, we have investigated relative mitochondrial mass and mitochondrial function in cells isolated from different regions of tumor spheroids by using a combination of mitochondrial-specific fluorescent stains and flow cytometric analysis. Uptake of rhodamine 123 (R123) is driven by the mitochondrial membrane potential and thus reflects mitochondrial activity. Uptake of 10-nonyl-acridine orange (NAO) reflects total mitochondrial mass independently of activity because this compound binds to cardiolipin in the inner mitochondrial membrane. NAO fluorescence per unit cell volume only decreased 10-20% for cells from the inner spheroid region compared with those near the surface. There was greater than a twofold reduction in R123 fluorescence in the inner region cells, however. Thus, tumor cells in spheroids alter their rate of respiration predominately by downregulating mitochondrial function as opposed to degradation of mitochondria. There was a correlation between R123 staining per unit cell volume and the growth fraction of the cells from spheroids, but not for monolayer cultures. We also show a linear correlation between R123 staining and the rate of oxygen consumption for both monolayer- and spheroid-derived cells. After separating the inner region cells from the spheroid and replating them in monolayer culture, the R123 uptake recovered to normal levels prior to entry of the cells into S-phase. This reduction in mitochondrial function in quiescent cells from spheroids can explain the long period required for these cells to re-enter the cell cycle and may have important implications for the regulation of tumor cell oxygenation in vivo.

Uptake of acridinecarboxamide derivatives by L1210 cells.

The uptake of six 9-aminoacridinecarboxamide derivatives by L1210 cells in relation to their lipophilicity and cytotoxic activity was studied. The amount of acridines taken up by cells was estimated by fluorimetric measurements. It was found that the uptake efficiency of this class of compounds by cells depends on the size of carboxamide residue as well as on position of the substituent. The increase of size of carboxamide chain resulted in the loss of capability of acridines to penetrate cell membrane. Cytotoxic effects of acridines were well correlated with the level of drugs accumulated by cells, whereas no clear correlation between uptake and lipophilicity was observed. It is concluded that uptake of 9-aminoacridinecarboxamides is the most important factor determining their antiproliferative activity.

Preclinical evaluation of novel imidazoacridinone derivatives with potent activity against experimental colorectal cancer.

Novel imidazoacridinone derivatives, C1310 and C1311, have been evaluated for their potential to inhibit tumour cell growth in vitro and in vivo. A cell line panel, including seven human and murine colon carcinoma cell lines and three in vivo models, was used. The compounds were found to be potent inhibitors of tumour cell growth with IC50 values ranging between 10 nM and 2 microM in human colon cancer cell lines. Statistically significant tumour growth delay (P < 0.01) was observed after a single intraperitoneal (i.p.) dose of C1311 (100 mg kg-1 body weight) in MAC15A, MAC29 murine and HT29 human adenocarcinomas of the colon. Rapid accumulation of fluorescence of both C1310 and C1311 was seen in the nuclei of HT29 human colon tumour cells in culture. C1311 was also found to bind into calf thymus DNA as shown by spectrophotometric titration and thermal denaturation and to cause early inhibition of thymidine incorporation in HT29 cells in vitro. The results of this study suggest that C1311 should be considered as a candidate for clinical development.

9-[3-(2-Nitro-1-imidazolyl)propylamino]-1,2,3,4-tetrahydroacridine hydrochloride. A novel DNA-affinic hypoxic cell cytotoxin and radiosensitizer. Comparison with NLA-1.

Electron-affinic compounds with strong DNA intercalating properties have demonstrated less than the expected radiosensitization due to restriction of their mobility along the DNA backbone and their lower extravascular diffusion in tumors. A 2-nitroimidazole linked 1,2,3,4-tetrahydroacridine derivative (THNLA-1) has been synthesized as a hypoxia-selective cytotoxin and radiosensitizer with presumably lower DNA-binding affinity due to the perturbation of the planarity in the acridine ring. THNLA-1 is a good hypoxia-selective cytotoxin with a differential toxicity of approximately equal to 11 in V79 cells, but it is approximately equal to 2 times less potent on a concentration basis than NLA-1 (the 2-nitroimidazole linked acridine analog). However, THNLA-1 is a very efficient radiosensitizer, showing a sensitization enhancement ratio (SER) of 3.04 +/- 0.05 at 100 microM at 25 degrees C, and the concentration giving an SER of 1.6(C1.6) is 19.0 +/- 0.5 microM. The therapeutic index, defined as the ratio of the clonogenic IC50 under aerobic conditions for 1-h exposure (IC50A,1h) to the C1.6 value, is 20 for THNLA-1 vs. 11 for NLA-1. THNLA-1's partition coefficient in octanol/water is 0.14 +/- 0.02. Topoisomerase I and II interaction studies with THNLA-1 showed that topoisomerase I-mediated relaxation of supercoiled DNA was inhibited at relatively high THNLA-1 concentrations (> or = 1000 microM), while topoisomerase II-mediated decatenation of kinetoplast DNA remained unaffected even in concentrations toxic in vitro under aerobic conditions. Uptake studies under aerobic conditions showed high intracellular drug concentrations, compatible with the required ones for topoisomerase I inhibition.

Rat hepatocyte-mediated metabolism of the experimental anti-tumour agent N-[2'-(dimethylamino)ethyl]acridine-4-carboxamide.

1. Metabolism of the experimental antitumour agent N-[2'-(dimethylamino)-ethyl]acridine-4-carboxamide (AC) has been studied in isolated rat hepatocytes using 3H-AC. 2. The major primary metabolites of AC (150 microM) are the 9(10H)acridone, N-oxide and N-monomethyl derivatives. The equivalent 9(10H)acridone derivatives are also formed from AC-N-oxide and N-monomethyl-AC followed by formation of the 7-hydroxy-9(10H)acridone derivatives of AC and N-monomethyl-AC. A similar pattern of metabolism was observed on incubation of AC-N-oxide. 3. Inhibition studies with SKF 525A (250 microM) and methimazole (250 microM) indicate that N-demethylation is mainly catalysed by cytochrome P450 whereas N-oxidation is mediated mainly by flavin-containing monooxygenases. Both primary and secondary acridone formation were also inhibited by SKF 525A as was the back-reduction of AC-N-oxide to AC. 4. These results show that the rat hepatocyte system is a suitable model for further characterization of the metabolism of AC.

Tumour profile of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide after intraperitoneal administration in the mouse.

N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (AC) is an experimental antitumour agent that is being considered for phase I trials. After i.p. administration of 150 mg/kg [3H]-AC to tumour-bearing mice, AC was absorbed rapidly into the plasma and tissues such as the heart, liver, kidney and brain but more slowly into the s.c. tumour. The maximal AC concentration (86 +/- 36 mumol/kg) in the tumour occurred at 35-60 min and was 3-fold the maximal plasma concentration, which occurred at 15 min. Although higher maximal concentrations were observed in other tissues, these concentrations fell rapidly in parallel with plasma concentrations. In contrast, AC concentrations in the tumour remained elevated, the t1/2 value (16.3 h) and mean residence time (MRT, 9.5 h) being prolonged in comparison with those in the plasma and other tissues (t1/2 range, 1.0-2.9 h; MRT, 1.2-1.4 h). AC concentrations were not detectable by our high-performance liquid chromatographic (HPLC) method (limit of detection, 0.02 mumol/l) in the plasma or other tissues at 24 or 48 h after administration but were measurable in the tumour (1.6 +/- 0.8 and 0.6 +/- 0.3 mumol/kg, respectively). Radioactivity concentrations in the plasma, tissues and tumour were very variable but were greater than the corresponding levels of unchanged parent AC. By 24 h, radioactivity concentrations in the plasma, tissues and tumour had fallen to similar levels with prolonged elimination profiles. Thus, the exposure of the s.c. implanted tumour to a threshold AC concentration for a prolonged time (> 24 h) tumour, whereas the shorter period of exposure of blood and other tissues may explain its low haematological toxicity.

Pharmacokinetics of acridine-4-carboxamide in the rat, with extrapolation to humans.

The pharmacokinetics of N-[2-(dimethyl-amino)ethyl]acridine-4- carboxamide (AC) were investigated in rats after i.v. administration of 18, 55 and 81 mumol/kg [3H]-AC. The plasma concentration-time profiles of AC (as measured by high-performance liquid chromatography) typically exhibited biphasic elimination kinetics over the 8-h post-administration period. Over this dose range, AC's kinetics were first-order. The mean (+/- SD) model-independent pharmacokinetic parameters were: clearance (Cl), 5.3 +/- 1.1 1 h-1 kg-1; steady-state volume of distribution (Vss), 7.8 +/- 3.0 l/kg; mean residence time (MRT), 1.5 +/- 0.4 h; and terminal elimination half-life (t1/2Z), 2.1 +/- 0.7 h (n = 10). The radioactivity levels (expressed as AC equivalents) in plasma were 1.3 times the AC concentrations recorded at 2 min (the first time point) and remained relatively constant for 1-8 h after AC administration. By 6 h, plasma radioactivity concentrations were 20 times greater than AC levels. Taking into account the species differences in the unbound AC fraction in plasma (mouse, 16.3%; rat, 14.8%; human, 3.4%), allometric equations were developed from rat and mouse pharmacokinetic data that predicted a Cl value of 0.075 (range, 0.05-0.10; 95% confidence limits) 1 h-1 kg-1 and a Vss value of 0.63 (range, 0.2-1.1) l/kg for total drug concentrations in humans.

Comparison of the blood-brain barrier and liver penetration of acridine antitumor drugs.

The blood-brain barrier penetration of amsacrine and its analogs 9-([2-methoxy-4-[(methylsulfonyl)-amino]phenyl]amino)-,5-dimethyl- 4-acridine carboxamide (CI-921) and M-[2-(dimethylamino)ethyl]-acridine-4-carboxamide (AC) was measured in the barbiturate-anesthetized mouse. After intracarotid administration, AC was almost completely extracted (90%) in a single transit through the brain capillaries, whereas CI-921 (20%) and amsacrine (15%) were moderately extracted. AC is retained in the brain; no loss of AC from the brain was apparent at 1, 2, 4, or 8 min after injection. In contrast, after intraportal administration, 75% of the AC, 94% of the CI-921, and 57% of the amsacrine was extracted in a single transit through the hepatic vasculature. Rather than being retained in the mouse liver, these acridine antitumor agents show time-dependent loss (t1/2 = 10 min for amsacrine and AC, 24 min for CI-921). We conclude that unlike most antitumor agents, these acridine drugs appear to penetrate the blood-brain barrier readily.

Pharmacokinetics and toxicity of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide after i.v. administration in the mouse.

The pharmacokinetics, tissue distribution and toxicity of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide(AC) were studied after i.v. administration to mice. Over the dose range of 9-121 mumol/kg (3-40 mg/kg), AC displayed linear kinetics with the following model-independent parameters: clearance (C), 21.0 +/- 1.9 1 h-1 kg-1; steady-state volume of distribution (Vss), 11.8 +/- 1.4 l/kg; and mean residence time (MRT), 0.56 +/- 0.02 h. The plasma concentration-time profiles for AC fitted a two-compartment model with the following parameters: Cc, 19.4 +/- 2.3 1 h-1 kg-1; Vc, 7.08 +/- 1.06 l/kg; t1/2 alpha 13.1 +/- 3.5 min; and t1/2Z, 1.60 +/- 0.65 h. AC displayed moderately high binding in healthy mouse plasma, giving a free fraction of 15.9%-25.3% over the drug concentration range of 1-561 microM. After the i.v. administration of 30 mumol/kg [3H]-AC, high radioactivity concentrations were observed in all tissues (especially the brain and kidney), showing a high t1/2c value (37-59 h). At 2 min (first blood collection), the AC concentration as measured by high-performance liquid chromatography (HPLC) comprised 61% of the plasma radioactivity concentration (expressed as AC equivalents/l). By 48 h, 73% of the dose had been eliminated, with 26% and 47% of the delivered drug being excreted by the urinary and faecal routes, respectively; less than 1% of the total dose was excreted as unchanged AC in the urine. At least five distinct radiochemical peaks were distinguishable by HPLC analysis of plasma extracts, with some similar peaks appearing in urine. The 121-mumol/kg dose was well tolerated by mice, with sedation being the only obvious side effect and no significant alterations in blood biochemistry or haematological parameters being recorded. After receiving a dose of 152 mumol/kg, all mice experienced clonic seizures for 2 min (with one death occurring) followed by a period of sedation that lasted for up to 2 h. No leucopenia occurred, but some mild anaemia was noted. There was no significant change in blood biochemistry. A further 20% increase in the i.v. dose (to 182 mumol/kg) resulted in mortality, with death occurring within 2 min of AC administration.

Intraperitoneal administration of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in the mouse: bioavailability, pharmacokinetics and toxicity after a single dose.

The pharmacokinetics, tissue distribution and toxicity of the antitumour agent N-[2-(dimethylamino)-ethyl]acridine-4-carboxamide (AC) were studied after i.p. administration of [3H]-AC (410 mumol/kg) to mice. The latter is the optimal single dose for the cure of advanced Lewis lung tumours. AC was rapidly absorbed into the systemic circulation after i.p. administration, with the maximal concentration (Cmax) occurring at the first time point (5 min). There was no reduction in bioavailability as compared with previous i.v. studies, but the shape of the plasma concentration-time profile was considerably different, reflecting a 3-fold lower Cmax value (20.9 +/- 3.6 mumol/l) and a longer t1/2 value (2.7 +/- 0.3 h) as compared with that observed after i.v. administration (1.6 +/- 0.6 h). Model independent pharmacokinetic parameters after i.p. administration were: clearance (C), 17.5 l h-1 kg-1; steady-state volume of distribution (Vss), 14.1 l/kg; and mean residence time (MRT), 1.46 h. High but variable tissue uptake of AC was observed, with tissue/plasma AUC ratios being 5.7 for heart, 8.4 for brain, 18.9 for kidney and 21.0 for liver but with similar elimination t1/2 values ranging from 1.3 to 2.7 h. All radioactivity profiles in plasma and tissues were greater than the respective parent AC profiles and showed prolonged elimination t1/2 values ranging from 21 h in liver to 93 h in brain. However, tissue/plasma radioactivity AUC ratios were near unity, ranging from 0.7 to 1.57, with the exception of the gallbladder (15.6), which contained greater amounts of radioactivity. By 48 h, approximately 70% of the total dose had been eliminated, with the faecal to urinary ratio being approximately 2:1. This i.p. dose was well tolerated by mice, with sedation being the only obvious side effect. No major change was observed in blood biochemistry or haematological parameters. Comparisons of Cmax, tmax and AUC values determined for AC in brain after its i.p. and i.v. administration suggest that the reduction in acute toxicity after i.p. administration is not due to reduced exposure of the brain to AC as measured by AUC but may be associated with the lower Cmax value or the slower rate of entry of AC into the brain after i.p. administration.

Quantitation of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in plasma by high-performance liquid chromatography.

N-[2-(Dimethylamino)ethyl]acridine-4-carboxamide is a new experimental antitumour agent which has excellent in vivo activity against the Lewis lung tumour in mice. A reversed-phase high-performance liquid chromatographic method is described for the measurement of this agent in plasma. The internal standard was N-[2-(diethylamino)ethyl]acridine-4-carboxamide. The compounds of interest were extracted from plasma (0.2 ml) with acetonitrile and further purified on C18 solid-phase extraction Bond Elut columns. After elution with acetonitrile-ammonium acetate buffer and evaporation, the final separation was carried out on a C18 muBondapak column with fluorimetric detection. Over the plasma concentration range 100-5000 nM, the intra- and inter-assay coefficients of variation were less than 4.1 and 7.7%, respectively. The accuracy of the method varied from 97 to 105% of the theoretical values. The lowest concentration which could be measured with acceptable accuracy (+/- 10%) and precision (coefficient of variation less than 10%) was 10 nM. The method was sufficiently sensitive to allow pharmacokinetic analyses of 30 mumol/kg doses for more than six half-lives (t1/2) in rabbits (t1/2 = 4) and mice (t1/2 = 1.3 h).