Inter-species variation in the metabolism and inhibition of N-[(2'-dimethylamino)ethyl]acridine-4-carboxamide (DACA) by aldehyde oxidase.

N-[(2'-Dimethylamino)ethyl]acridine-4-carboxamide (DACA) is a new anticancer agent currently undergoing clinical trials. The metabolism of DACA to acridone metabolites by aldehyde oxidase (AO) (EC 1.2.3.1) appears to play a major role in its elimination in human patients and rodents. The aim of this study was to compare the ability of human, guinea pig, and rat AO preparations to metabolise DACA, and to determine if either animal model was appropriate for predicting AO-mediated DACA-drug interactions in humans. Both human and rodent liver samples were homogenised in buffer before sequential centrifugation to produce the cytosol fraction. Human supernatant underwent an additional ammonium sulphate precipitation procedure, which produced a 2-fold increase in enzyme activity per milligram of protein. After incubations with DACA (range, 0-200 microM), DACA-9(10H)-acridone formation was determined by HPLC analysis. Michaelis-Menten parameters, Km and Vmax, were determined from the best fit curves by nonlinear regression. Three of the four human liver preparations had similar DACA intrinsic clearance values (Vmax/Km) ranging from 0.27 to 0.35 mL/min/mg protein, whereas both the rat and guinea pig had approximately 7- and 160-fold greater intrinsic clearances, due to lower Km values in rats (4.5 +/- 0.7 microM) and guinea pigs (0.15 +/- 0.1 microM) compared with humans (28.3 +/- 8.3 microM, N = 4). Amsacrine, menadione, and 7-hydroxy-DACA were potent inhibitors of DACA metabolism in all three species, but 10-fold differences in IC50 values were apparent between species. In addition, SKF-525A was a potent inhibitor of the metabolism of DACA in rat cytosol but caused minimal inhibition in the guinea pig or human preparations. These results suggest that neither rat nor guinea pig AO preparations are suitable for predicting AO-mediated DACA-drug interactions in humans.

Metabolism of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in cancer patients undergoing a phase I clinical trial.

N-[2-(Dimethylamino)ethyl]acridine-4-carboxamide (DACA) is an experimental antitumour agent that has just completed phase I clinical trials in New Zealand and the United Kingdom. Urine (0-72 h) was analysed from 20 patients receiving DACA infused over 3 h (dose range 60-1000 mg/m2, the latter being the highest dose achieved in the trial). Aliquots were analysed for DACA and its metabolites by high-performance liquid chromatography (HPLC). Over 72 h, 44+/-5% (range 20-60%) of the dose was recovered in the urine, with 0.8+/-0.3% (range 0-3.1%) occurring as DACA. The major urinary metabolite was DACA-N-oxide-9(10H)acridone, accounting for 34+/-3% of the dose. Minor metabolites were identified as N-monomethyl-DACA-9(10H)acridone (2.0+/-0.5%), DACA-9(10H)acridone (3.3+/-0.5%), N-monomethyl-DACA (0.2+/-0.1%) and DACA-N-oxide (0.5+/-0.1%). No ring-hydroxylated metabolite was detected. The urinary excretion of metabolites was greatest over 0-6 h in most patients. The composition of urinary metabolites was also independent of the delivered dose. Plasma was sampled at intervals throughout the infusion and at time points up to 48 h post-administration. The major plasma metabolites observed were DACA-9(10H)acridone and DACA-N-oxide-9(10H)acridone. These results indicate that, based on urinary excreted metabolites, the major biotransformation reactions for DACA in humans involve N-oxidation of the tertiary amine side chain and acridone formation, both of which appear to be detoxication reactions.

Evaluation of potential health effects of 10 kHz magnetic fields: a rodent reproductive study.

New technology involving the use of high-frequency inductive power distribution (HID) has recently been developed for use in materials handling and personnel transfer. Sinusoidal magnetic fields at a frequency of 10 kHz with field intensities of approximately 0.2 mT are generated directly between the current-carrying coils of this equipment. Effects of 10 kHz magnetic fields on cell division, migration, and differentiation have never been previously investigated. To evaluate potential effects on these parameters, a rodent reproductive study was undertaken using Wistar rats. Exposures were at 0.095, 0.24, and 0.95 mT with a background exposure of 5-10 microT. Three sets of parental rats were exposed continuously for 20-23.5 h/day to the fields: maternal rats during gestation, paternal rats for at least 45 days prior to mating and maternal rats 1 month prior to mating. Exposure phases thus covered spermatogenesis, maturation of the ovum and ovulation, fertilization, implantation, embryogenesis, organogenesis, and maturation of the fetus immediately prior to parturition. In all experiments pregnancy outcome was assessed. These studies failed to demonstrate any reproductive toxicity resulting from maternal or fetal exposure during gestation or following paternal or maternal exposure for several weeks prior to mating. No quantitative or qualitative effects on spermatogenesis occurred after exposure, and no effects on the estrous cycle or ovulation could be demonstrably linked to the 10 kHz magnetic field exposure at 0.095, 0.25, or 0.95 mT. Where possible, parental clinical chemistry and hematology were also examined. As in mouse toxicology studies previously reported, minor differences were observed between control and treated groups. These were regarded as statistically, but not biologically, significant and could not categorically be attributed to magnetic field exposure.

Effect of substituents on the metabolism of nitracrine in rat.

1. Male Wistar rats were treated with either the antitumour agent nitracrine (1-nitro-9-(3'-dimethylamino-N-propylamino)-acridine; NC), 4-methoxy-NC, NC-aliphatic-N-oxide, 4-methoxy-NC-aliphatic-N-oxide, or NC-aromatic-N-oxide (30 mumol/kg, via the femoral vein) and the major biliary and urinary metabolites analysed by hplc. 2. No NC or 4-methoxy-NC were detected in bile or urine of rat treated with NC or 4-methoxy-NC respectively, whereas the aliphatic N-oxides of NC and 4-methoxy-NC were recovered largely unchanged in both bile and urine. 3. NC-aromatic-N-oxide was rapidly and extensively converted to a major polar biliary product. This product was also synthesised enzymatically from NC-aromatic-N-oxide using rat liver cytosol and has been identified by mass and 1H-nmr spectrometry as 1-(S-glutathionyl)-9-(3'-dimethylamino-N-propylamino)-acridine-N(10)-oxi de. 4. The equivalent 1-(S-glutathionyl) conjugate appears to be formed from NC, and excreted in bile as a minor product, but not from 4-methoxy-NC. Further experiments with cytosol indicate that direct displacement of the nitro group by GSH is mediated by GSH transferase. 5. Finally, the major biliary metabolite of NC has been provisionally identified as a glucuronide of 1-nitro-2-hydroxy-NC. 6. It is concluded that, for at least a significant fraction of NC, nitroreduction does not occur. Further, N-oxidation of the aliphatic (but not the aromatic ring) nitrogen, plus 4-methoxy substitution, decreases the overall metabolism of NC in the rat.

Evaluation of potential health effects of 10 kHz magnetic fields: a short-term mouse toxicology study.

A high-frequency inductive power distribution (HID) technology has been developed that generates sinusoidal magnetic fields at a frequency of 10 kHz. In typical industrial applications, field intensities in the order of 0.2 mT can be expected between the current-carrying coils. Because the possible health effects of 10 kHz sinusoidal magnetic fields of this type had never been investigated, a broad evaluation of possible effects on animal health was made in a preliminary 14 day acute study and in a 90 day subchronic study using male and female B6C3F1 mice. Exposures were at 0.08, 0.28, and 1.0 mT vs. a background exposure of 3.7 microT and were essentially continuous. These studies failed to demonstrate any health effects that can be clearly related to the magnetic field exposure. No changes in animal behaviour or indications of morbidity were detected during the initial exposure to the fields. There were no significant differences in body weight between exposed and unexposed (control) mice at any time in the study, and the clinical chemistry and hematology parameters were essentially unchanged. Although minor differences in some clinical chemistry and hematology parameters were seen between control and exposure groups, the lack of exposure dependence, the lack of consistency between sexes, and the lack of correspondence with the results of the two studies all suggest that these were chance associations. Even if the changes were real, the magnitude of the changes was very small and does not indicate serious biological effects. Finally, all organs were macroscopically and microscopically normal except for isolated, generally mild, histological lesions and lesions that were ascribed to fighting among males. There was no obvious association with field intensity.

Methadone: a potent inhibitor of rat liver aldehyde oxidase.

Several drugs with structural similarities to SKF-525A were tested for their ability to inhibit rat liver aldehyde oxidase using the experimental antitumour agent N-[(2'-dimethylamino)ethyl]acridine-4-carboxamide (AC; NSC 601316; acridine carboxamide) as substrate. The antihistamine D-chlorpheniramine, and the antiarrhythmics disopyramide, procainamide and lignocaine were ineffective in inhibiting this reaction. The antihistamines diphenhydramine, pheniramine, doxylamine, orphenadrine, methapyrilene and pyrilamine, gave IC50 values of 100-500 microM. The narcotic analgesics D-propoxyphene and, in particular, methadone were potent inhibitors of acridine formation with IC50 values of 15.5 and 0.31 microM, respectively. Further analysis indicates mixed non-competitive type inhibition by methadone with inhibition constants (Kis and Kii, respectively) of 0.03 +/- 0.01 (SE) and 0.57 +/- 0.12 microM.

Plasma protein binding of the experimental antitumour agent acridine-4-carboxamide in man, dog, rat and rabbit.

The plasma binding of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (AC) was investigated in-vitro by equilibrium dialysis for 3 h at 37 degrees C against isotonic phosphate buffer (pH 7.35) using [3H]AC. There were significant species differences with the smallest % free fraction (mean +/- s.d.) occurring in human plasma (3.4 +/- 0.2), followed by dog (8.1 +/- 0.4), mouse (14.8 +/- 0.8), rat (16.3 +/- 0.9) and rabbit (20.2 +/- 0.7). In plasma from healthy individuals (n = 5), the % free fraction ranged from 2.7 to 3.8. In physiological solutions of human proteins, the greatest binding was observed for alpha 1-acid glycoprotein (AAG) (0.75 g L-1) with a mean free fraction of 24.1 +/- 2.2%, followed by albumin (40 g L-1) with 31.6 +/- 0.7 and 39.8 +/- 2.5% for fatty-acid-free and globulin-free, respectively. There was also some binding to globulins (5 g L-1) with a mean % free fraction of 70.3 +/- 1.6 and 84.8 +/- 2.2 for Cohn's fraction I and IV, respectively. Binding data from the displacement of [3H]AC by increasing concentrations of AC in human AAG (0.75 g L-1) or albumin solution (40 g L-1) indicated that AAG had 10-fold greater binding affinity for AC (Ka, 7.8 x 10(4) M-1) compared with albumin (Ka, 6.8 x 10(3) M-1). In human plasma enriched with AAG there was a significant negative linear correlation (r = 0.932; P < 0.001) between % AC free fraction and increasing AAG concentration over the range 0.6-4.5 g L-1.(ABSTRACT TRUNCATED AT 250 WORDS)

The characterization of two biliary glutathione conjugates of amsacrine using liquid secondary ion mass spectrometry.

An additional biliary glutathione (GSH) conjugate of the anilinoacridine anti-tumour agent amsacrine (4'-(9-acridinylamino)methanesulphon-m-anisidide, NSC 249992) has been identified in bile collected from male Wistar rats by cannulation of the common bile duct and from male BDF1 mice by removal of the gall bladder after treatment with amsacrine. The presence of this conjugate, at the 6'-position of the anilino ring, has been confirmed by liquid secondary ion (LSI) mass spectrometric analysis of selected biliary metabolites separated by high-performance liquid chromatography. The two major metabolites each gave a daughter ion spectrum which was diagnostic for either 5'- or 6'-GSH conjugation. This pattern was confirmed by comparison with LSI mass spectral data obtained from authentic chemical standards formed on reaction of the quinone diimine derivative of amsacrine with methanethiol or mercaptoethanol.

Metabolism of the experimental antitumor agent acridine carboxamide in the mouse.

The metabolism of the experimental antitumor agent acridine carboxamide (AC) has been examined in the male BDF1 mouse. [3H]AC was administered at the optimal single intraperitoneal dose for antitumor activity (410 mumol/kg body weight) and the metabolites in urine, bile, and feces characterized using reversed-phase HPLC. In urine (0-24 hr) the main product appears to be a glucuronide, also present in bile, with lesser amounts of AC, AC-N-oxide, and at least 10 minor products. Biliary excretion of AC metabolites (examined after removal of the gallbladder at the appropriate times) is greatest at 1-2 hr after treatment when at least 14 products are detected, including AC, AC-N-oxide, and other products with UV/visible spectra characteristic of ring hydroxylated and/or acridone derivatives. In feces (0-24 hr) no AC-N-oxide is detected, the major metabolites being two polar species and AC. These polar species are both present in urine and bile where they are increased on incubation with crude beta-glucuronidase. These aglycones have been identified as the 7-hydroxy-9(10H)acridone derivatives of AC and N-monomethyl-AC by [1H]NMR and mass spectrometry. Thus the main pathways of elimination of AC appear to be 1) N-oxidation and 2) 9(10H)acridone formation plus 7-hydroxylation of both AC and its N-demethylated product followed by glucuronidation. Reduction of AC-N-oxide in the gut may allow reabsorption of AC. Both the back-reduction and reabsorption of AC, and enterohepatic circulation of the 7-hydroxyacridone derivatives may contribute to the slow elimination of AC metabolites.

Inhibition by SKF-525A of the aldehyde oxidase-mediated metabolism of the experimental antitumour agent acridine carboxamide.

Oxidation of the experimental anti-tumour agent N-[(2'-dimethylamino)ethyl]acridine-4-carboxamide (AC; NSC 601316; acridine carboxamide) to the 9(10H)acridone, followed by ring hydroxylation and glucuronidation, appears to be the main pathway of detoxication of AC in the rat and mouse. The acridone formation has been further characterized in vitro using an enzyme-enriched fraction where activity per milligram protein is increased approximately 10-fold compared with the cytosolic fraction. Inhibition by amsacrine [4'-(9-acridinylamino)methanesulphon-m-anisidide; NSC 249992] and menadione (50% inhibition at 6.4 and 1.8 microM, respectively) but not allopurinol (to 30 microM) indicates that the activity is due to aldehyde oxidase, without the involvement of xanthine oxidase. Interestingly, acridone formation in both the cytosolic and enzyme-enriched fractions is highly sensitive to the classical cytochrome P450 inhibitor SKF-525A [proadifen hydrochloride; 2'-(diethylamino)ethyl 2,2-diphenylpentenoate] (50% inhibition at 9.2 and 1.9 microM, respectively). Further analysis indicates mixed non-competitive type inhibition by SKF-525A (K(is), 0.3 microM; K(ii), 4.9 microM). Little or no inhibition was seen with cimetidine, metyrapone or methimazole. No NADPH-dependent acridone formation was observed with the microsomal fraction. These data indicate that acridone formation previously observed in isolated rat hepatocytes and in vivo is most likely due to aldehyde oxidase rather than cytochrome P450.

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.

Oxidative metabolism of amsacrine by the neutrophil enzyme myeloperoxidase.

Oxidative metabolism of the anti-cancer drug amsacrine 4'-(9-acridinylamino) methane-sulphan-m-anisidide has been suggested to account for its cytotoxicity. However, enzymes capable of oxidizing it in non-hepatic tissue have yet to be identified. A potential candidate, that may be relevant to the metabolism of amsacrine in blood and its action in myeloid leukaemias and myelosuppression, is the haem enzyme myeloperoxidase. We have found that the purified human enzyme oxidizes amsacrine to its quinone diimine, either directly or through the production of hypochlorous acid. In comparison, the 4-methyl-5-methylcarboxamide derivative of amsacrine, CI-921 9-[[2-methoxy-4[(methylsulphonyl)-amino]phenyl]amino)-N, 5-dimethyl-4-acridine carboxamide, reacted poorly with myeloperoxidase, although it was oxidized by hypochlorous acid. Detailed studies of the mechanism by which myeloperoxidase oxidizes amsacrine revealed that the semiquinone imine free radical is a likely intermediate in this reaction. Oxidation of amsacrine analogues indicated that factors other than their reduction potential determine how readily they are metabolized by myeloperoxidase. Both amsacrine and CI-921 inhibited production of hypochlorous acid by myeloperoxidase. CI-921 acted by trapping the enzyme as the inactive redox intermediate compound II. Amsacrine inhibited by a different mechanism that may involve conversion of myeloperoxidase to compound III, which is also unable to oxidize Cl-. The susceptibility of amsacrine to oxidation by myeloperoxidase indicates that this reaction may contribute to the cytotoxicity of amsacrine toward neutrophils, monocytes and their precursors.

Differences in the metabolism of the antitumour agents amsacrine and its derivative CI-921 in rat and mouse.

1. Rats and mice were treated with the antitumour agent CI-921 (I), and parent compound amsacrine, with all biliary metabolites being analysed. 2. In both rat and mouse the major biliary metabolites of amsacrine are the 5'- and 6'-glutathione (GSH) conjugates, with no C9-GSH conjugate being detected. 3. 5'- and 6'-GSH conjugates of I are also formed in both species. However, two additional products were detected and their structures confirmed by liquid secondary ion mass spectrometry and 1H-n.m.r. spectrometry, and by comparison with synthetic standards. 4. Additional metabolites of I are the C9-GSH conjugate and the 4-hydroxymethyl derivative which, either as the aglycone or glucuronide, is the predominant product in rat bile (comprising 56% of the dose eliminated over 3.5 h). 5. Relative amounts of the C9-GSH conjugate to the 5'- and 6'-GSH conjugates to the 4-hydroxymethyl derivatives, were 24:65:10 in mouse bile and 2:8:90 in rat bile. 6. These differences indicate first, likely enzyme involvement in the formation of the C9-GSH conjugate of I, and second, in comparison with amsacrine, alternative pathways which may decrease formation of the reactive quinone diimine intermediate of I and consequent hepatotoxicity.

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.

Cytosol mediated metabolism of the experimental antitumor agent acridine carboxamide to the 9-acridone derivative.

The acridine antitumor agent N-[2'-(dimethylamino)ethyl]acridine-4-carboxamide (AC; NSC 601316; acridine carboxamide) is oxidized efficiently in vitro by rat and mouse hepatic cytosolic fractions. Under these conditions the oxidase activity has an apparent Km of 11 microM towards AC. A single product is formed which has been identified as the corresponding 9(10H)-acridone carboxamide by 1H-NMR and mass spectrometry. Inhibition with menadione and amsacrine, but not allopurinol, indicates that this reaction is most likely to be catalysed by aldehyde oxidase (EC 1.2.3.1). Several AC analogues with modifications to the side chain (the N-oxide, N-monomethyl-, and amino-derivatives) are also metabolized to the equivalent acridone product but the 7-hydroxylated and 4-carboxylic acid acridine derivatives are not.

Fetal phenytoin exposure, hypoplastic nails, and jitteriness.

In a prospective study infants born to mothers with epilepsy (n = 61) were found to have an unexpectedly high incidence of congenital anomalies (26/61, 43%) and neonatal conditions (26/61, 43%) compared with controls (0/62, and 6/62, 10%, respectively). There were two neonatal deaths in the study group but none among the controls. Hypoplasia of the finger or toenails was a common congenital anomaly in those infants whose mothers had received phenytoin alone or in combination with other anticonvulsant drugs (11 of 40, 28%). The mean serum phenytoin concentration was higher among mothers of infants with hypoplastic nails than among those with normal nails. Jitteriness was a common neonatal condition affecting infants of epileptic mothers (11 of 61, 18%) but not controls The mean cord serum phenytoin concentrations were similar among jittery and non-jittery infants. At follow up (after excluding one infant with Down's syndrome from the study group) the infants seemed to have developed normally, though one had serious learning difficulties at school. We suggest that hypoplasia of the nails is related to high maternal serum concentrations of phenytoin, and though 18% of infants born to epileptic mothers were jittery compared with no control infants this may not be the result of withdrawal of the drug in all cases.