Reduced capacity of tumour blood vessels to produce endothelium-derived relaxing factor: significance for blood flow modification

The effect of nitric oxide-dependent vasodilators on vascular resistance of tumours and normal tissue was determined with the aim of modifying tumour blood flow for therapeutic benefit. Isolated preparations of the rat P22 tumour and normal rat hindlimb were perfused ex vivo. The effects on tissue vascular resistance of administration of sodium nitroprusside (SNP) and the diazeniumdiolate (or NONO-ate) NOC-7, vasodilators which act via direct release of nitric oxide (NO), were compared with the effects of acetylcholine (ACh), a vasodilator which acts primarily via receptor stimulation of endothelial cells to release NO in the form of endothelium-derived relaxing factor (EDRF). SNP and NOC-7 effectively dilated tumour blood vessels after preconstriction with phenylephrine (PE) or potassium chloride (KCl) as indicated by a decrease in vascular resistance. SNP also effectively dilated normal rat hindlimb vessels after PE/KCl constriction. Vasodilatation in the tumour preparations was accompanied by a significant rise in nitrite levels measured in the tumour effluent. ACh induced a significant vasodilation in the normal hindlimb but an anomalous vasoconstriction in the tumour. This result suggests that tumours, unlike normal tissues are incapable of releasing NO (EDRF) in response to ACh. Capacity for EDRF production may represent a difference between tumour and normal tissue blood vessels, which could be exploited for selective pharmacological manipulation of tumour blood flow.

Electron transfer reactions in RB90745, a bioreductive drug having both aromatic N-oxide and nitroarene moieties

The bifunctional hypoxia-specific cytotoxin RB90745, has a nitroimidazole moiety attached to an imidazol[1,2-a]quinoxaline mono-N-oxide with a spacer/linking group. The reduction chemistry of the drug was studied by pulse radiolysis using the one electron reductant CO2.-. As N-oxides and nitro compounds react with CO2.- at diffusion controlled rates, initial reaction produced a mixture of the nitro radical (lambda max 410 nm) and the N-oxide radical (lambda max 550 nm) in a few microseconds. Subsequently an intramolecular electron transfer (IET) was observed (k = 1.0 +/- 0.25 x 10(3) s-1 at pH 5-9), from the N-oxide to the more electron-affinic nitro group. This was confirmed by the first order decay rate of the radical at 550 nm and formation at 410 nm, which was independent of both the concentration of the parent compound and the radicals. The rates of electron transfer and the decay kinetics of the nitro anion radicals were pH dependent and three different pKas could be estimated for the one electron reduced species: 5.6 (nitroimidazole group) and 4.3, and 7.6 (N-oxide function). The radicals react with oxygen with rate constants of 3.1 x 10(7) and 2.8 x 10(6) dm3 mol-1 s-1 observed at 575 nm and 410 nm respectively. Steady state radiolysis studies indicated four electron stoichiometry for the reduction of the compound.

Nitric oxide involvement in the toxicity of hydroxyguanidine in leukaemia HL60 cells

The free-radical intermediates and the stable products formed on one-electron oxidation of hydroxyguanidine (HOG) were investigated in order to suggest a mechanistic basis for HOG-induced cytotoxicity and cytostasis in leukaemia HL60 cells. The azide radical (generated radiolytically) reacted with HOG to produce a carbon-centred radical which in the absence of oxygen decays by a first-order process (k = 3.2 x 10(3) s-1) to yield nitric oxide (NO) and urea. Although the HOG radical reacts rapidly with oxygen (rate constant for O2 addition, k = 4.2 x 10(8) dm3 mol-1 s-1) this neither prevented the elimination of NO. nor generated alternative nitrogen oxides (e.g. peroxynitrite) capable of contributing to cellular oxidative stress. The detection of NO. in HL60 cells corroborated mechanistic studies that oxidative denitrification of HOG does not require catalysis by nitric oxide synthase. Quantitation of NO. by electron paramagnetic resonance (EPR) spectroscopy (utilising a NO. -selective probe) shows higher amounts of NO. under anoxic conditions, reflecting competition for NO. with molecular oxygen in oxic cells. Inhibition of cytochrome P450 and myeloperoxidase activity decreased NO. production thereby identifying these enzyme systems as capable of oxidizing HOG in vitro. A correlation exists between the intracellular levels of NO. with both the cytotoxic and cytostatic effects of HOG within HL60 cells. A higher toxicity was observed with hypoxic than with oxic cells. The lower levels of NO. associated with aerobic conditions caused a G1 --> S block in the cell cycle which under anoxia potentiated NO. -induced apoptotic cell death.

Nicotinamide pharmacokinetics in humans: effect of gastric acid inhibition, comparison of rectal vs oral administration and the use of saliva for drug monitoring

The effect of inhibiting gastric acid secretion on nicotinamide pharmacokinetics was studied in five volunteers with the intent of reducing the large variations observed previously in the time to and magnitude of peak plasma concentrations. Plasma levels were determined using a standard high-performance liquid chromatography (HPLC) method after an oral dose of 3 g of nicotinamide either alone or preceded by pretreatment with omeprazole. Suppression of gastric acid production had no significant effect on the rate of uptake or on the peak levels achieved. To bypass gastric acidity, the rectal route was also assessed using a suppository in four volunteers and one patient undergoing radiotherapy. Absorption was slow and variable and much lower plasma levels were observed than after oral dosing. Thus, no improvement in the pharmacokinetics of nicotinamide was observed using either of these two approaches. Parallel estimations were made using a novel and non-invasive method for monitoring nicotinamide pharmacokinetics in saliva. A large and variable fraction of the total amount of nicotinamide-related material in saliva was found to be nicotinic acid, a metabolite not normally found in human plasma. This conversion was inhibited by the use of a chlorhexidine mouthwash, indicating that the oral flora was responsible for its production. The time to peak levels of nicotinamide or of nicotinamide plus nicotinic acid in saliva correlated well with that in plasma. However, peak concentrations for nicotinamide alone were significantly lower than in plasma, and very variable, whereas for nicotinamide plus nicotinic acid saliva levels were 20-30% higher, but more consistent. Although there are some practical difficulties in quantitatively handling saliva, the method is very useful for monitoring nicotinamide pharmacokinetics and for assessment of compliance with nicotinamide treatment.

Oxidative denitrification of N omega-hydroxy-L-arginine by the superoxide radical anion

The superoxide radical anion (O2-.) produced during the catalytic activity of nitric oxide synthase (NOS) and cytochrome P-450 has been implicated in the oxidative denitrification of hydroxyguanidines ( > C = NOH). The reactivity of the radiolytically generated O2-. radical with N omega-hydroxy-L-arginine (NHA) is pH dependent and appears to parallel the prototropic equilibrium of the hydroxyguanidino group ( > C = NOH reversible > C = NO(-)+H+; pK = 8). The N omega-hydroxyguanidino group is more reactive towards O2-. when deprotonated but exhibits negligible reactivity when protonated. Based on a model, the rate constant for the reaction of the O2-. with NHA was estimated as kappa (O2-.+ > C = NO-) approximately 200-500 M-1.s-1, which is probably too low to compete with O2-. reactions with NO- or superoxide dismutase, which occur many orders of magnitude faster. The oxidative elimination of NO from NHA by O2-. was not accompanied by the formation of L-citrulline. Since only 21% of NHA will exist in the deprotonated > C = NO- form at physiological pH, it is unlikely that oxidative denitrification of NHA by cytochrome P-450 or NOS-derived O2-. radicals will prove a major free-radical pathway to NO. and L-citrulline.

Chemical properties which control selectivity and efficacy of aromatic N-oxide bioreductive drugs

Pulse radiolysis was used to generate radicals from one electron reduction of 1,2,4-benzotriazine-1,4-dioxides (derivatives of tirapazamine), and of imidazo [1,2-a]quinoxaline-4-oxides (analogues of RB90740), which have selective toxicity towards hypoxic cells. Radicals from the mono N-oxides (from the latter compounds) react with oxygen approximately 10-40 times faster than does the tirapazamine radical. Radicals from the tirapazamine analogues studied react with oxygen up to approximately 10 times slower than tirapazamine radicals. The quinoxaline N-oxide radicals are involved in prototropic equilibria with pK(a) values (5.5 to 7.4) spanning that reported for tirapazamine (6.0). Generation of radicals radiolytically in the presence of H donors (formate, 2-propanol, deoxyribose) indicate a chain reaction ascribed to H abstraction by the drug radical. The protonated drug radical is much more reactive than the radical anion (H abstraction rate constant approximately equal to 10(2) - 10(3) dm3 mol-1 s-1). Chain termination is ascribed to drug radical-radical reactions, i.e. radical stability in anoxia, with rate constants 2k approximately equal to 1 x 10(7) to 2 x 10(8) dm3 mol-1 s-1 at pH approximately 7.4. Estimates of the reduction potentials of the drug-radical couples in water at pH 7 for two of the mono-N-oxides were in the range-0.7 to 0.8 V vs NHE at pH 7.

Nicotinamide as a repair inhibitor in vivo: studies using single and fractionated X-ray doses in mouse skin and kidneys

Inhibitors of adenosine diphosphoribosyl transferase, like nicotinamide, 3-aminobenzamide and other analogues, can inhibit repair of radiation-induced sublethal and/or potentially lethal damage in some in vitro systems. Therefore, we have tested the effect of nicotinamide on repair parameters in vivo in two rodent normal tissues. In skin, the sensitivity to dose fractionation (1, 2, 5 or 10 X-ray fractions in 5 days) was monitored by defining the alpha/beta ratio in the presence or absence of nicotinamide (0.5 mg g-1) in air or carbogen. Pre- and postirradiation sensitization were investigated using an X-ray schedule of 5 fractions/5 days in carbogen alone or combined with nicotinamide given 1 h before, immediately after or 8 h after irradiation. Also, changes in the steepness of the underlying X-ray survival curve for the target skin clonogens, reflected by a change in the alpha/beta ratio, were investigated using the neutron top-up design. Underlying survival curves for oxygen +/- nicotinamide were obtained over the X-ray dose range 2.5 to 25 Gy, by administering single X-ray doses and following these with single top-up doses of d(4)-Be neutrons. Finally, in mouse kidney, recovery half-times (t1/2) were obtained by determining the time-dependent disappearance of X-ray damage using a split-dose design of two 6-Gy fractions separated by an interval which varied from 0 to 48 h and followed by two top-up doses from a neutron beam. No increase in alpha/beta for epidermal damage was seen with nicotinamide alone and, although sensitization was observed when the drug was given 1 h before irradiation, no postirradiation sensitization was detected. In kidney, there was no significant difference in the proportion of total repairable damage or in the half-life of recovery between treatments given with or without nicotinamide. Therefore, no decrease in normal tissue tolerance should be observed with the use of nicotinamide in clinical radiotherapy resulting either from reduced sparing with dose fractionation or from an increase in residual damage when shortening the interfraction interval. Finally, unless repair of radiation damage in normal tissues in vivo differs markedly from that of tumors, it is unlikely that the large sensitization seen in rodent tumors at 1.5 to 2 Gy per fraction, with carbogen and nicotinamide, can be attributed to nicotinamide acting as a repair inhibitor.

Nicotinamide pharmacokinetics in normal volunteers and patients undergoing palliative radiotherapy

The influence of nicotinamide formulation on absorption characteristics and incidence of adverse side-effects has been studied in normal volunteers and in patients undergoing radiotherapy. Escalating single or repeated oral doses of nicotinamide were administered in tablet or liquid form under fasting or non-fasting conditions. Drug absorption was slowed both by the presence of food in the stomach and by the administration of nicotinamide in tablet form compared with when it was dissolved in orange juice. Peak concentrations were generally slightly higher following the liquid preparation, but the incidence of adverse side-effects (chiefly nausea) was increased. A single dose of 9 g (88-97 mg/kg) nicotinamide in tablet form was well tolerated in two fasting normal volunteers, and in patients, doses of up to 133 mg/kg as tablets were tolerated twice/week for three weeks. Daily administration of 80 mg/kg nicotinamide was tolerated when given as tablets, but not in a liquid formulation. Neither the peak concentration nor the area under the concentration/time curve (AUC) of nicotinamide, nor the main metabolites of nicotinamide appeared to correlate with the incidence of toxicity.

Ischemia reperfusion injury in tumors: the role of oxygen radicals and nitric oxide

Oxidative stress is a key process involved in the action of several therapeutic modalities used in cancer treatment. Ischemia reperfusion insult provides a model system for investigating the processes involved in determining the sensitivity of tumor tissue to oxidative stress. We have investigated the response of the murine CaNT tumor to ischemia reperfusion injury and the role that oxygen radicals and nitric oxide may play in this phenomenon. Our results show that little or no cell kill is detected in tumors exposed to up to 3 h of ischemia if the tumors are excised immediately before reperfusion. However, if reperfusion is permitted, then extensive cell kill is evident 24 h later. i.v. administration of superoxide dismutase or catalase, at the time when vascular reperfusion occurred, resulted in a significant protection against tumor cell kill, suggesting that the damage was mediated by oxygen radicals. Conversely, administration of an inhibitor of nitric oxide synthase, N omega-nitro-L-arginine, resulted in potentiation of tumor cell damage. Administration of a nitric oxide (NO) donor, diethylamine NO, at the time when vascular reperfusion occurred resulted in significant protection against tumor damage. These results suggest that nitric oxide is a potent mediator in determining tumor damage after ischemia reperfusion injury. The role of intrinsic NO production by murine tumors was investigated by measuring the accumulation of nitrate in the medium of tumor explants cultured in vitro in two tumors with differing sensitivity to ischemia reperfusion damage. The clamp-insensitive tumor SaS showed a greater nitrate accumulation than the clamp-sensitive tumor CaNT, which may confer a greater capacity for preventing tumor and endothelial cell damage after oxidative stress.

Pharmacokinetics and binding of the bioreductive probe for hypoxia, NITP: effect of route of administration

The novel compound 7(-)[4'-(2-nitroimidazol-l-yl)-butyl]-theophylline (NITP) can be used as an immunologically detectable probe for hypoxic cells. Because of the limited water solubility of NITP, it has been administered dissolved in peanut oil with 10% dimethylsulphoxide (DMSO). A new aqueous formulation has been devised, based on a 50% solution of a modified beta-cyclodextrin (Molecusol HPB), which increases the water solubility of NITP 10-fold. The pharmacokinetics of NITP in plasma and tumours have been compared following oral and intraperitoneal (i.p.) administration of the NITP in Molecusol, i.p. administration of NITP dissolved in peanut oil + 10% DMSO and injection of a near-saturated aqueous solution of the drug intravenously via the tail vein or i.p. or directly into the tumours. Binding of the marker to hypoxic cells within tumours was also measured after the different routes of administration. The Molecusol vehicle was unexpectedly toxic when administered i.p., but there was no toxicity from NITP dissolved in Molecusol when administered orally. Binding of the drug within tumours was seen for both the peanut oil + 10% DMSO and Molecusol formulations and for both oral and intraperitoneal routes. Binding of NITP within tumours has also been observed following direct injection of the drug, with minimal whole-body exposure to NITP. However, the bound metabolites of NITP within tumours were localised to the injection site, suggesting that direct injection is unlikely to be a useful method of administering bioreductive hypoxia markers. The data in this paper demonstrate that bound metabolites of the hypoxia marker NITP can be detected in tumours following oral administration of an aqueous formulation of NITP, and suggest that oral administration could be a satisfactory administration route for clinical studies with NITP.

Radicals from one-electron reduction of nitro compounds, aromatic N-oxides and quinones: the kinetic basis for hypoxia-selective, bioreductive drugs

Drugs based on nitroarene, aromatic N-oxide or quinone structures are frequently reduced by cellular reductases to toxic products. Reduction often involves free radicals as intermediates which react rapidly with oxygen to form superoxide radicals, inhibiting drug reduction. The elevation of cellular oxidative stress accompanying oxygen inhibition of reduction is generally less damaging than drug reduction to toxic products, so the drugs offer selective toxicity to hypoxic cells. Since such cells are resistant to radiotherapy, these bioreductive drugs offer potential in tumour therapy. The basis for the selectivity of action entails kinetic competition involving the contesting reaction pathways. The reduction potential of the drug, radical pKa and nature of radical/radical decay kinetics all influence drug activity and selectivity, including the range of oxygen tensions over which the drug offers selective toxicity. These properties may be quantified using generation of radicals by pulse radiolysis, presenting a physicochemical basis for rational drug design.

Glutathione determination by the Tietze enzymatic recycling assay and its relationship to cellular radiation response

Large fluctuations in glutathione content were observed on a daily basis using the Tietze enzyme recycling assay in a panel of six human cell lines of varying radiosensitivity. Glutathione content tended to increase to a maximum during exponential cell proliferation, and then decreased at different rates as the cells approached plateau phase. By reference to high-performance liquid chromatography and flow cytometry of the fluorescent bimane derivative we were able to verify that these changes were real. However, the Tietze assay was occasionally unable to detect glutathione in two of our cell lines (MGH-U1 and AT5BIVA), although the other methods indicated its presence. The existence of an inhibitory activity responsible for these anomalies was confirmed through spiking our samples with known amounts of glutathione. We were unable to detect a direct relationship between cellular glutathione concentration and aerobic radiosensitivity in our panel of cell lines.

Administration of nicotinamide during chart: pharmacokinetics, dose escalation, and clinical toxicity

PURPOSE

To determine nicotinamide pharmacokinetics in patients undergoing accelerated radiotherapy with the CHART regimen (continuous, hyperfractionated, accelerated radiotherapy) and given nicotinamide on a daily basis. The aim was to establish the pharmacokinetic profiles and their reproducibility during repeated administration, the maximum tolerated dose with fractionated radiotherapy, whether such a dose achieves sufficiently high plasma levels for radiosensitization, the optimal time interval between nicotinamide and irradiation, and toxic side effects.

METHODS AND MATERIALS

Nicotinamide plasma concentrations were determined using high performance liquid chromatography in 11 patients with advanced carcinomas of the head and neck and rectum being treated with CHART (36 fractions in 12 days). Kinetic profiles on the first day of radiotherapy and residual 24-h values were obtained in 10 patients; in four of these, full profiles were repeated two or three times during the course of treatment. In one other, a single sample per day was taken four times over the 12-day period. Doses of 80, 90, or 100 mg/kg/day were given 90 min prior to the second radiotherapy fraction on each day.

RESULTS

A dose of 80 mg/kg/day was well tolerated by all the patients. However, an increase of 10-25% in dose led to significant drug accumulation and major clinical toxicity, and none of the patients in the dose-escalation arm completed the planned regimen. Large interpatient variations in absolute peak concentrations were seen from 0.4 to 1.4 mumol/ml (mean 0.9 +/- 0.3; standard deviation (SD)). Of the five samples with the lowest peak levels, four were obtained from one patient. The time taken to peak concentration was also very variable from 0.8 to 4 h (mean 2.1 +/- 1.3 h; SD). In 70% of the samples, absolute plasma levels > or = 0.7 mumol/ml were reached within 1-2 h after administration and maintained for up to 6 h (mean 2.8 +/- 1.8 h; SD). There was a small but nonsignificant increase in the half-life of nicotinamide when the dose was increased from 80 to 90 or 100 mg/kg (7.1 h and 8.6 h, respectively).

CONCLUSIONS

In an accelerated regimen such as CHART, 80 mg/kg/day of oral nicotinamide is feasible and clinically tolerated, giving no or few side effects, and a 2-h interval between its oral administration and radiotherapy should achieve effective plasma levels in most patients.

Analysis of the acidic microenvironment in murine tumours by high-performance ion chromatography

High-performance ion chromatography (HPIC) has been utilised to probe the biochemistry associated with changes in tumour pH following total vascular occlusion. Samples from the tumour extracellular compartment were obtained by insertion of a microdialysis probe and analysed by HPIC with conductivity detection. Separations were carried out by ion-exclusion chromatography using an IonPac ICE AS1 weak-acid column. The eluent (0.5 mM octanesulphonic acid) was chemically suppressed with 5 mM tetrabutylammonium hydroxide through a micromembrane suppressor. After complete vascular occlusion induced by a clamp, lactate levels increased in the extracellular compartment.

Nitric oxide in biological fluids: analysis of nitrite and nitrate by high-performance ion chromatography

The analysis of nitric oxide-derived nitrite and nitrate ions in biological fluids represents a proven strategy for determining nitric oxide participation in a diverse range of physiological and pathophysiological processes in vivo. In this article we describe a versatile method for the simultaneous measurement of NO2- and NO3- anions in both plasma and isolated tumour models based on anion-exchange chromatography with spectrophotometric detection (214 nm). This method compares well with the capillary electrophoresis technique, exhibiting an equivalent sensitivity for NO2-/NO3- anions and short run-times, i.e. not greater than 4 min. Comparisons are also made with two alternative but less satisfactory methods which employ ion-exchange or reversed-phase ion-pair chromatography with conductimetric as well as spectrophotometric detection. Technical problems associated with each method, particularly those arising from nitrate contamination, have been addressed.

Bioreductive markers for hypoxic cells: 2-nitroimidazoles with biotinylated 1-substituents

The interference by oxygen with the bioreductive metabolism and binding within cells of 2-nitroimidazoles has been used to identify hypoxic cells. Three novel compounds were synthesized with a 1-substituent containing a biotin moiety. Bound adducts of these compounds could be identified in hypoxic cells in vitro by the biotin binding proteins, avidin or streptavidin, labeled with fluorescein. The metabolism and discrimination of these compounds between well-oxygenated and hypoxic cells was evaluated by flow cytometry. Ester or amide links between the 2-nitroimidazole and the biotin were degraded in the presence of mouse serum, but a compound with a C5 hydrocarbon link was stable, and this compound was suitable for evaluation in an in vivo tumor model.

Determination of adenine nucleotides by fluorescence detection using high-performance liquid chromatography and post-column derivatisation with chloroacetaldehyde

A novel rapid method for the analysis of adenine nucleotides in cells and tissues using post-column derivatisation with chloroacetaldehyde (CAA) followed by fluorescence detection is described. The CAA is incorporated in the eluent, but only reacts post-column when the temperature is elevated to 100 degrees C. Samples are chromatographed following neutralisation of acid extracts. Examples are given using both trichloroacetic acid extraction for cells in culture, and perchloric acid for murine liver.

Formation of hydroxyl radicals on reaction of hypochlorous acid with ferrocyanide, a model iron(II) complex

Hypochlorous acid reacts with the model iron(II) complex, ferrocyanide (Fe(CN)6(4-)) in aqueous solution with the rate constant 220 +/- 15 dm3 mol-1 s-1. Free hydroxyl radicals are formed in this reaction in 27% yield as shown by the hydroxylation of benzoate to give a product distribution identical to that of free (radiolytically generated) hydroxyl radicals. This reaction is three orders of magnitude faster than the analogous reaction involving hydrogen peroxide (the Fenton reaction), suggesting that the hypochlorous acid generated by activated neutrophils may be a source of hydroxyl radicals.

Pharmacokinetics and biochemistry studies on nicotinamide in the mouse

Nicotinamide sensitizes murine tumours to the effect of radiation, but the pharmacokinetics are not well characterized at doses that are achievable in humans. In the mouse, nicotinamide given i.p. at doses of 100-500 mg/kg showed biphasic elimination with dose-dependent changes in half-life. The initial half-life increased significantly (P < 0.05) from 0.8 to 2 h and the terminal half-life increased from 3.4 to 5.6 h over the dose range studied. Clearance, however, decreased significantly from 0.3 to 0.24 l kg-1 h-1 only at the highest dose. Peak concentrations increased in a dose-dependent manner from 1,000 to 4,800 nmol/ml. The main plasma metabolite in the mouse is nicotinamide N-oxide, the peak concentration of which increased only from 80 to 160 nmol/ml. The N-oxide, which is also a weak radiosensitizer, is subject to reduction to the parent nicotinamide following administration at a dose of 276 mg/kg; peak concentrations of the N-oxide of 1900 nmol/ml were reached in 10 min, whereas concentrations of nicotinamide produced by reduction reached a maximum of 144 nmol/ml at 1 h. Elimination of the N-oxide was also biphasic, with initial and terminal half-lives being 0.39 and 1.8 h, respectively. The bioavailability of both drugs given via the i.p. as compared with the i.v. route was close to 100%. Tumour concentrations of nicotinamide paralleled those in the plasma after a short lag. Tumour nicotinamide adenine dinucleotide (NAD) concentrations were elevated by factors of 1.5 and 1.8 following doses of 100 and 500 mg/kg nicotinamide, respectively. Maximal concentrations were seen after 3-6 h, but levels remained elevated for 16 h. No change in tumour energy charge or in plasma 5-hydroxytryptamine was detected following a dose of 500 mg/kg nicotinamide.

Pharmacokinetics of varying doses of nicotinamide and tumour radiosensitisation with carbogen and nicotinamide: clinical considerations

Plasma concentrations, after administration of varying doses of nicotinamide, were measured in CBA male mice using a newly-developed high performance liquid chromatography assay. In all dose groups, peak levels were observed within the first 15 min after an i.p. administration of 0.1, 0.2, 0.3 or 0.5 mg g-1 of nicotinamide. There was a clear dose-dependent increase in plasma concentration with increasing dose, with almost a five-fold lower concentration (1.0 vs 4.9 mumol ml-1) achieved with a dose of 0.1 mg g-1 compared with 0.5 mg g-1, respectively. The half-life of nicotinamide increased from 1.4 h to 2.2 h over the dose range (P < 0.01). Comparisons with previous pharmacokinetic data in humans show that clinically-relevant oral doses of 6 and 9 g in humans give plasma levels slightly higher than those achieved at 1 h with doses of 0.1 to 0.2 mg g-1 in mice. Tumour radiosensitisation with carbogen alone, and with carbogen combined with varying doses of nicotinamide (0.05 to 0.5 mg g-1), was investigated using a 10-fraction in 5 days X-ray schedule. Relative to air-breathing mice, a statistically significant increase in sensitisation was observed with both a local tumour control and with an in vivo/in vitro excision assay (P < or = 0.007). With the local control assay, a trend was observed towards lower enhancement ratios (ERs) with decreasing nicotinamide dose (from 1.85 to 1.55); carbogen alone was almost as effective as when combined with 0.1 mg g-1 of nicotinamide. With the excision assay, ERs for carbogen combined with nicotinamide increased with decreased levels of cell survival. At a surviving fraction of 0.02, enhancement ratios of 1.39-1.48 were obtained for carbogen plus 0.1 to 0.3 mg g-1 of nicotinamide. These were lower than those seen with the two higher doses of 0.4 to 0.5 mg g-1 (ERs = 1.63-1.69).

Free hydroxyl radicals are formed on reaction between the neutrophil-derived species superoxide anion and hypochlorous acid

Superoxide anion reacts with hypochlorous acid to yield free hydroxyl radicals, as shown by the hydroxylation of benzoate. This reaction is analogous to the Haber-Weiss reaction but in the absence of metal ions is at least six orders of magnitude faster.

Flavone acetic acid (FAA) with recombinant interleukin-2 (rIL-2) in advanced malignant melanoma. IV: Pharmacokinetics and toxicity of flavone acetic acid and its metabolites

Flavone acetic acid (FAA) was administered at a dose of 4.8 g m-2 over 1 h to patients with advanced malignant disease in combination with Interleukin II. A new high performance liquid chromatography method is described to determine both the parent compound and eight drug-related products, and the conditions required to determine these components in plasma are discussed. The half-life over the first 8 h was 2.3 h, but the terminal clearance of the drug was extremely slow. Severe (WHO Grade 4) hypotension was observed in some patients. However, incidence of this did not appear to be associated with any differences in FAA plasma concentrations, nor were there differences in FAA clearance between those patients whose tumour responded to the drug combination and those who did not.

High-performance liquid chromatographic determination of nicotinamide and its metabolites in human and murine plasma and urine

A high-performance liquid chromatographic method is described which enables the determination of nicotinamide and eight of its possible metabolites in human and murine plasma and urine, using ion-pairing on a base-deactivated reversed-phase column. Calibration curves were linear up to 2 mumol/ml for nicotinamide and 200 nmol/ml for the metabolites; both the intra- and inter-assay relative standard deviations ranged between 1 and 8%. In murine plasma, the N-oxide was the major nicotinamide metabolite, but in man, formation of 1-methylnicotinamide and the 2- and 4-pyridones was also significant. In urine, nicotinuric acid was seen in the mouse, but no nicotinic acid metabolites were seen in man.

Pharmacokinetics of nicotinamide and its effect on blood pressure, pulse and body temperature in normal human volunteers

The pharmacokinetics of nicotinamide were studied in four human volunteers after oral doses of 1-6 g. Plasma concentrations and clearance rates of the vitamin were found to be dose-dependent, with a half-life of approximately 7-9 h for the two highest doses administered (4 and 6 g), approximately 4 h with 2 g and approximately 1.5 h with a 1-g dose. Peak concentrations ranged from 0.7 to 1.1 mumol.ml-1 after a 6-g dose. The time to reach peak plasma concentration was dose independent with a broad range from 0.73 to 3 h. In this study, nicotinamide had no detectable effect on blood pressure, pulse or body temperature.

Collagen metabolism in the murine colon following X irradiation

Female CBA mice, aged 16 weeks, were irradiated to the total pelvic region with either single doses (5-20 Gy) or two equal fractions (10- to 30-Gy total dose, 24-h interval) of 240 kV X rays. Total protein and collagen synthesis rates, collagen breakdown, and net collagen content of the colon were measured at various times postirradiation using a radioisotope incorporation method and HPLC analysis. Immunohistochemical staining and computerized image analysis were used to assess the relative amounts of collagen types I and III at various times postirradiation, in various regions of the colon. Total protein and collagen synthesis rates were elevated above control levels at 4 and 8 weeks postirradiation, as was collagen degradation. Values had returned to control levels by 16 weeks postirradiation, and there were no further changes up to 71 weeks postirradiation. The net amount of collagen in the colon did not change relative to controls at any time during the investigation. There was, however, increased immunohistochemical staining for collagen type I 52 weeks postirradiation in all regions of the colon and decreased staining of type III in the circular muscle layer and villi. Altered ratios of these two collagen isotypes are consistent with changes in mechanical properties of the tissue.