Nocturnal blood pressure non-dipping, posttraumatic stress disorder, and sleep quality in women

Women with posttraumatic stress disorder (PTSD) have poor sleep quality and increased risk of cardiovascular disease (CVD). Non-dipping of nocturnal blood pressure may be an explanatory factor for the relationship between sleep and CVD found in previous research. The current study was designed to determine if non-dipping nocturnal blood pressure was associated with trauma exposure, PTSD diagnosis, PTSD symptoms, and sleep quality in a sample of women. Participants completed 24 hours of ABPM and self-report questionnaires. Non-dipping was defined as less than 10% reduction in blood pressure during sleep. The frequency of non-dippers did not differ by diagnostic status (d = .15). However, non-dippers endorsed more traumatic event categories (d = .53), more PTSD hyperarousal symptoms (d = .53), poorer overall sleep quality (d = .59), more frequent use of sleep medication (d = .62), greater sleep-related daytime dysfunction (d = .58), and longer sleep onset latencies (d = .55) than dippers. Increased attention to nocturnal blood pressure variation may be needed to improve blood pressure control in trauma-exposed women.

Smoking in help-seeking veterans with PTSD returning from Afghanistan and Iraq

Past research has shown that veterans and individuals with posttraumatic stress disorder (PTSD) have increased rates of smoking. However, the rates of smoking in younger help-seeking veterans returning from Afghanistan and Iraq, and possible correlates of smoking among this population are unknown. In this study, we evaluated the rate of lifetime and current smoking among a sample of 90 returning male veterans diagnosed with PTSD. Fifty-nine percent reported a lifetime history of smoking including 32% that were current smokers. Current smokers were significantly younger than non-smokers. Current smokers (mean age=31) reported a mean age of smoking onset as 15.86 with a pack year history of 8.89. These smokers reported on average five previous quit attempts. According to a stages of change model, one-half of the smokers were in the contemplation phase of stopping smoking (50%), 29% were in the pre-contemplation phase and 21% were in the preparation phase. The results are placed in the context of non-psychiatric and psychiatric smokers.

Combretastatin A-4 phosphate as a tumor vascular-targeting agent: early effects in tumors and normal tissues

The potential for tumor vascular-targeting by using the tubulin destabilizing agent disodium combretastatin A-4 3-0-phosphate (CA-4-P) was assessed in a rat system. This approach aims to shut down the established tumor vasculature, leading to the development of extensive tumor cell necrosis. The early vascular effects of CA-4-P were assessed in the s.c. implanted P22 carcinosarcoma and in a range of normal tissues. Blood flow was measured by the uptake of radiolabeled iodoantipyrine, and quantitative autoradiography was used to measure spatial heterogeneity of blood flow in tumor sections. CA-4-P (100 mg/kg i.p.) caused a significant increase in mean arterial blood pressure at 1 and 6 h after treatment and a very large decrease in tumor blood flow, which-by 6 h-was reduced approximately 100-fold. The spleen was the most affected normal tissue with a 7-fold reduction in blood flow at 6 h. Calculations of vascular resistance revealed some vascular changes in the heart and kidney for which there were no significant changes in blood flow. Quantitative autoradiography showed that CA-4-P increased the spatial heterogeneity in tumor blood flow. The drug affected peripheral tumor regions less than central regions. Administration of CA-4-P (30 mg/kg) in the presence of the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester, potentiated the effect of CA-4-P in tumor tissue. The combination increased tumor vascular resistance 300-fold compared with less than 7-fold for any of the normal tissues. This shows that tissue production of nitric oxide protects against the damaging vascular effects of CA-4-P. Significant changes in tumor vascular resistance could also be obtained in isolated tumor perfusions using a cell-free perfusate, although the changes were much less than those observed in vivo. This shows that the action of CA-4-P includes mechanisms other than those involving red cell viscosity, intravascular coagulation, and neutrophil adhesion. The uptake of CA-4-P and combretastatin A-4 (CA-4) was more efficient in tumor than in skeletal muscle tissue and dephosphorylation of CA-4-P to CA-4 was faster in the former. These results are promising for the use of CA-4-P as a tumor vascular-targeting agent.

Peroxidase-catalyzed effects of indole-3-acetic acid and analogues on lipid membranes, DNA, and mammalian cells in vitro

This study aimed to explore the mechanisms and molecular parameters which control the cytotoxicity of derivatives of indole-3-acetic acid (IAA) when oxidatively activated by horseradish peroxidase (HRP). Lipid peroxidation was measured in liposomes, damage to supercoiled plasmid DNA assessed by gel electrophoresis, free radical intermediates detected by EPR following spin trapping, binding of IAA-derived products demonstrated by 3H labelling, stable products measured by HPLC, and cytotoxicity in hamster fibroblasts measured by clonogenic survival. IAA, and nine analogues more easily oxidized by HRP, caused lipid peroxidation in liposomes, but not detectably in membranes of hamster fibroblasts, and were cytotoxic after HRP activation to varying degrees. Cytotoxicity was not correlated with activation rate. The hydrophilic vitamin E analogue, Trolox, inhibited cytotoxicity, whereas loading fibroblasts with vitamin E was ineffective, consistent with an oxidative mechanism in which radical precursors to damage are intercepted by Trolox in the aqueous phase. However, two known oxidation products were nontoxic (the 3-carbinol and 3-aldehyde, both probably produced from 3-CH2OO* peroxyl radicals via the 3-CH*2 [skatolyl] radical following decarboxylation of the radical cation). The skatolyl radical from IAA was shown by EPR with spin trapping to react with DNA; electrophoresis showed binding to occur. Treatment of hamster fibroblasts with 5-3H-IAA/HRP resulted in intracellular bound 3H. Together with earlier results, the new data point to unknown electrophilic oxidation products, reactive towards intracellular targets, being involved in cytotoxicity of the IAA/HRP combination, rather than direct attack of free radicals, excited states, or membrane lipid peroxidation.

Determination of combretastatin A-4 and its phosphate ester pro-drug in plasma by high-performance liquid chromatography

High-performance liquid chromatography with both absorbance and fluorescence detection has been applied to the determination of the potential anti-tumour agent combretastatin A-4 and its phosphate ester in murine and human plasma. The presence of different interfering peaks in the two species makes absorbance detection at 295 nm the method of choice for the mouse, and fluorescence detection (295 nm/390 nm) for human plasma. The calibration was linear over the range studied (0.01-50 microM for combretastatin A-4, 0.02-200 microM for combretastatin A-4 phosphate), with quantitation limits of 0.05 microM for both drugs in the mouse, and 0.05 microM and 0.0125 microM for the phosphate ester and free drug, respectively, in human plasma. The method should be useful for pharmacokinetic studies in the forthcoming Phase I clinical trial of combretastatin A-4 phosphate.

Pharmacokinetics of nicotinamide in cancer patients treated with accelerated radiotherapy: the experience of the Co-operative Group of Radiotherapy of the European Organization for Research and Treatment of Cancer

BACKGROUND

The EORTC has initiated studies to combine nicotinamide with carbogen in accelerated fractionation schedules (ARCON), since for some tumour types, acute and chronic hypoxia as well as treatment protraction may prejudice the outcome of radiotherapy. The tolerable dose of nicotinamide and the optimal interval for administration need to be ascertained.

AIM

Full pharmacokinetic profiles of nicotinamide concentrations in plasma were analyzed repeatedly in 15 patients to determine the inter- and intra-patient variability in peak plasma concentrations and the optimum times for administering nicotinamide as a radiosensitizer.

METHODS

Nicotinamide (Nicobion) was administered in tablet form to patients with advanced head and neck and non-small cell lung carcinomas. A standard 6 g dose was given regardless of body weight after an overnight fast and at least 30 min before breakfast. In 15 patients, blood samples were taken prior to and 1, 2, 4, 6, 8, 12 and 24 h after administration of the drug. This full profile was determined on two to four occasions for the head and neck cancer patients and on two occasions for the lung cancer patients. For each profile, the maximum concentration of nicotinamide (Cmax), time to peak plasma concentration (Tmax), elimination half-lives (t1/2) and area under the curve (AUC) were determined. Compliance was recorded and nausea and vomiting were graded on a 0-3 scale. Complete profiles of the five major metabolites were also obtained.

RESULTS

In the 48 complete sets of blood samples, peak plasma concentrations ranged from 787 to 2312 nmol/ml with a median value of 1166 nmol/ml. The peak plasma concentration was achieved at 1 h in only 54% of the pharmacokinetic profiles, but at this time 92% of the profiles had already exceeded the target concentration of 700 nmol/ml, the level required in the mouse for tumour radiosensitization. The median t1/2 for all 15 cases was 9.3 h, with minimum and maximum values of 4.2 and 26.8 h. The highest concentrations of nicotinamide metabolites were found to be the N-oxide, 2-pyridone and 1-methylnicotinamide. The toxicity (nausea and vomiting) was scored and found not to be correlated with any of the pharmacokinetic parameters.

CONCLUSIONS

The plasma concentrations considered necessary to radiosensitize can easily be exceeded with a dose of 6 g taken as 12 x 500 mg in tablet form; 700 nmol/ml was achieved in all patients and apparently would have been achieved in most even with a considerable reduction in dose. An adequate time between administration and radiotherapy appeared to be 1 h with this drug formulation for 92% of the profiles.

Indolequinone antitumor agents: reductive activation and elimination from (5-methoxy-1-methyl-4,7-dioxoindol-3-yl)methyl derivatives and hypoxia-selective cytotoxicity in vitro

A series of indolequinones bearing a variety of leaving groups at the (indol-3-yl)methyl position was synthesized by functionalization of the corresponding 3-(hydroxymethyl)indolequinone, and the resulting compounds were evaluated in vitro as bioreductively activated cytotoxins. The elimination of a range of functional groups-carboxylate, phenol, and thiol-was demonstrated upon reductive activation under both chemical and quantitative radiolytic conditions. Only those compounds which eliminated such groups under both sets of conditions exhibited significant hypoxia selectivity, with anoxic:oxic toxicity ratios in the range 10-200. With the exception of the 3-hydroxymethyl derivative, radiolytic generation of semiquinone radicals and HPLC analysis indicated that efficient elimination of the leaving group occurred following one-electron reduction of the parent compound. The active species in leaving group elimination was predominantly the hydroquinone rather than the semiquinone radical. The resulting iminium derivative acted as an alkylating agent and was efficiently trapped by added thiol following chemical reduction and by either water or 2-propanol following radiolytic reduction. A chain reaction in the radical-initiated reduction of these indolequinones (not seen in a simpler benzoquinone) in the presence of a hydrogen donor (2-propanol) was observed. Compounds that were unsubstituted at C-2 were found to be up to 300 times more potent as cytotoxins than their 2-alkyl-substituted analogues in V79-379A cells, but with lower hypoxic cytotoxicity ratios.

Involvement of oxygen free radicals in ischaemia-reperfusion injury to murine tumours: role of nitric oxide

Ischaemia-reperfusion (I/R) injury is a model system of oxidative stress and a potential anti-cancer therapy. Tumour cytotoxicity follows oxygen radical damage to the vasculature which is modulated by tumour production of the vasoactive agent, nitric oxide (NO.). In vivo hydroxylation of salicylate, to 2,3- and 2,5-dihydroxybenzoate (DHBs), was used to measure the generation of hydroxyl radicals (OH.) following temporary vascular occlusion in two murine tumours (with widely differing capacity to produce NO.) and normal skin. Significantly greater OH. generation followed I/R of murine adenocarcinoma CaNT tumours (low NO. production) compared to round cell sarcoma SaS tumours (high NO. production) and normal skin. These data suggest that tumour production of NO. confers resistance to I/R injury, in part by reducing production of oxygen radicals and oxidative stress to the vasculature. Inhibition of NO synthase (NOS), during vascular reperfusion, significantly increased OH. generation in both tumour types, but not skin. This increase in cytotoxicity suggests oxidative injury may be attenuation by tumour production of NO.. Hydroxyl radical generation following I/R injury correlated with vascular damage and response of tumours in vivo, but not skin, which indicates a potential therapeutic benefit from this approach.

Oxidative denitrification of the antitumour drug hydroxyguanidine

The oxidative denitrification of the antitumour agent hydroxyguanidine (HOG) has been investigated by radiolysis methods and EPR spectroscopy. The azide radical (N3.), a model one-electron oxidant, reacts with HOG with the rate constant 5.1 x 10(9) dm3 mol(-1) s(-1) to yield the guanidino carbon-centred radical (HOG.) which rapidly eliminates nitric oxide (k = 3.1 x 10[3] s[-1]) with the concomitant formation of urea. The HOG. undergoes conjugation with molecular oxygen to form a peroxyl radical (HOGOO.) with a rate constant 8.8 x 10(8) dm3 mol(-1) s(-1). The HOGOO. radical also eliminates nitric oxide but may act as a precursor to the peroxynitrite (ONOO-) ion. The oxidation of HOG by the dibromide radical (Br2.-) was found to release nitric oxide with a yield of 95% relative to Br2.- as determined from the combined yields of inorganic nitrite, nitrate and a HOG/nitric oxide-adduct. This study provides a possible mechanistic basis for the oxidative denitrification of HOG which may contribute to the observed toxicity of the drug both in vitro and in vivo and for the oxidation of nonphysiological hydroxyguanidines to NO. via nitric oxide synthase-independent pathways.

Accelerated radiotherapy, carbogen and nicotinamide (ARCON) in locally advanced head and neck cancer: a feasibility study

BACKGROUND AND PURPOSE

ARCON (Accelerated Radiotherapy, CarbOgen, Nicotinamide) achieves a large therapeutic gain in rodents. A phase I/II study was therefore undertaken to determine its feasibility in patients with locally advanced head and neck cancer.

MATERIALS AND METHODS

The accelerated regime CHART was used in 35 patients given carbogen and/or nicotinamide with 11 small volume fractions. Eight patients received carbogen, 12 received nicotinamide and 15 were treated with ARCON. Treatment compliance, side-effects and acute mucositis were monitored in all cases.

RESULTS

All patients underwent CHART as intended. In the 23 patients receiving carbogen, two failed to complete treatment. Compliance with nicotinamide was much lower. Out of 25 patients, only 52% received 10-11 doses of the 80 mg/kg/day of the drug. The most common side-effect was nausea and vomiting, which responded to standard anti-emetics in almost half of the patients. Historical comparisons with the CHART head and neck trials indicate that there was no increase in the severity of acute mucositis in any of these patients. Although the observation period is not sufficiently long to be definitive (median 20 months) there is no evidence of an increase in late normal tissue reactions.

CONCLUSIONS

ARCON using CHART as the radiotherapy protocol is feasible in patients with advanced head and neck cancer. However, we are concerned about the low compliance rate in our patients, which is far lower than that reported elsewhere. The implications are discussed together with identifying strategies for increasing compliance.

The role of nitric oxide in cancer. Improved methods for measurement of nitrite and nitrate by high-performance ion chromatography

The short lifetime of nitric oxide (NO) in vivo impedes its quantitation directly; however, the determination of nitrite and nitrate ions as the end-products of NO oxidation has proven a more practical approach. High-performance ion chromatographic analysis of nitrite in biological fluids is hampered by the large amount of chloride ion (up to approximately 100 mmol/l) which results in insufficient peak resolution when utilizing conductimetric detection. Analysis of both anions in small sample volumes is also constrained by the need to minimise sample handling to avoid contamination by environmental nitrate. We report a means to remove Cl- ions from small sample volumes using Ag+ resin which facilitates quantitation of either nitrite and nitrate anions in biological samples, using silica or polymer based ion-exchange resins with conductimetric or electrochemical and spectrophotometric detection. Including a reversed-phase guard column before the anion-exchange guard and analytical column also greatly extends column lifetime.

Administration of nicotinamide during a five- to seven-week course of radiotherapy: pharmacokinetics, tolerance, and compliance

BACKGROUND AND PURPOSE

Nicotinamide was administered daily as a liquid formulation to head and neck cancer patients receiving a 5- to 7-week course of radiotherapy. The pharmacokinetics, compliance, and tolerance of this drug formulation were studied.

MATERIALS AND METHODS

Blood samples were drawn and nicotinamide levels determined in 40 head and neck cancer patients. On the first treatment day serial samples were obtained followed by daily samples at the time of irradiation during the first and last full weeks of the treatment. Side-effects of nicotinamide were monitored.

RESULTS

In all patients peak concentrations greater than 700 nmol/ml could be obtained 0.25-3 h (mean 0.83 +/- 0.73 h) after drug intake. During the first week of treatment plasma levels at the time of irradiation were adequate in 82% of the samples. This decreased to 59% in the last week of treatment which can be partly attributed to reduced compliance. The most important side-effect of nicotinamide was nausea with or without vomiting occurring in 65% of the patients. Severe side-effects were associated with high plasma concentrations over subsequent days. Tolerance improved after a 25% reduction of dose in six of seven patients but plasma levels at the time of irradiation fell below 700 nmol/ml in four out of six of these patients.

CONCLUSIONS

Peak plasma concentrations above the 700 nmol/ml level were obtained in all patients but these concentrations could not be reproduced during the entire course of the treatment in a significant portion of the subjects. Side-effects of nicotinamide are associated with plasma concentrations and tolerance can be improved by a moderate reduction of dose.

Metabolic and clonogenic consequences of ischaemia reperfusion insult in solid tumours

Tumour cell survival is intimately related to blood vessel function and so the tumour vasculature represents a novel target for cancer therapy. We have investigated a murine tumour model in which a metal clamp was used to occlude the vascular supply temporarily and then removed to allow reperfusion. This allows the study of ischaemia-reperfusion as a model system for investigating tumour response to metabolic and oxidative stress. Recent studies have shown that prolonged reduction of tumour blood flow results in a deterioration of the hypoxic and acidic microenvironment found within tumours which leads to cytotoxicity. This cytotoxicity is dramatically enhanced if these cells are subsequently reperfused. It was the aim of the present study to determine the relative contribution of cytotoxicity occurring during the ischaemic period and that occurring during reperfusion. Although significant reductions in tumour energy status were induced during the clamping period itself, these were poorly correlated with the degree of tumour cytotoxicity. Relative vascular perfusion, measured using a radiolabelled tracer, remained significantly depressed below the control value following clamp removal. The degree of recovery of perfusion was also dependent upon the clamp duration. Relative tumour perfusion at 1 h after clamp removal was 70.1 +/- 14.6 and 50.5 +/- 6.3% of control values after a 1 or 3 h clamp, respectively, and showed no significant further increase when measured at 24 h after clamp removal. Tumour cytotoxicity following ischaemia reperfusion insult was modulated by administering the anti-oxidant enzymes superoxide dismutase or catalase intravenously just before clamp removal. These enzymes are restricted to the vascular compartment, where it is proposed that they modulate the concentration of oxygen free radicals released during reperfusion and by neutrophil oxidative burst. Reperfusion injury to the tumour was enhanced by administration of an inhibitor of nitric oxide synthase, nitro-L-arginine, probably owing to enhanced neutrophil adhesion and oxidative burst. Conversely, reperfusion injury to the tumour was reduced by administration of a nitric oxide donor, diethylamine nitric oxide. The murine model reported in this paper shows that ischaemia-reperfusion damage mediated by oxygen free radical formation provides a model system for investigating tumour response to oxidative stress at the level of the vascular endothelium.

The relationship between extracellular lactate and tumour pH in a murine tumour model of ischaemia-reperfusion

We have studied the relationship between extracellular lactate (LACTe) and extracellular pH (pHe) in murine tumours after vascular occlusion (clamping) followed by reperfusion. In tumours occluded at ambient room temperature, LACTe, measured by microdialysis, increased linearly with time and correlated strongly with the acidification of the extracellular compartment (r=0.97, P<0.03, n=4). Significant decrease in LACTe was evident following removal of occlusion at room temperature and is consistent with vascular reperfusion. Occlusion at 35 degrees C, i.e. to maintain tumour temperature during occlusion, resulted in an initial increase in LACTe, which mirrored a rapid reduction in pHe. However further reductions in pHe occurred without increase in LACTe. During vascular occlusion, tumour adenine nucleotide pool decreased and AMP accumulated. AMP subsequently decreased in the 35 degrees C group and this may contribute to the observed differences in accumulation of LACTe, and capacity to recover from vascular occlusion, between the two treatment groups. These data show that extracellular lactate concentration is a good predictor for tumour pH when adequate energy sources are available within the tumour. However, under conditions of more severe stress, resulting in abolition of primary energy stores and cell death, the pHe continues to decline in the absence of a corresponding accumulation of extracellular lactate. This emphasizes the fact that other processes, apart from lactate production, can contribute to reduction in extracellular pH.

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.

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.

Scavenging of nitrogen dioxide, thiyl, and sulfonyl free radicals by the nutritional antioxidant beta-carotene

Mechanisms of free radical scavenging by the nutritional antioxidant beta-carotene have been investigated by pulse radiolysis. Free radicals, which can initiate the chain of lipid peroxidation, including nitrogen dioxide (NO2.), thiyl (RS.), and sulfonyl (RSO2.) radicals, are rapidly scavenged by beta-carotene. Absolute rate constant k[NO2. + beta-carotene] = (1.1 +/- 0.1) x 10(8) m-1 s-1 and for the glutathione thiyl radical k[GS. + beta-carotene] = (2.2 +/- 0.1) x 10(8) m-1 s-1 have been determined. The mechanisms however are mutually exclusive, the former involving electron transfer to generate the radical-cation [ beta-carotene]+. and the latter by radical-addition to generate an adduct-radical [RS... beta-carotene].. Rate constants for thiyl radical-addition reactions vary from 10(6) to 10(9) m-1 s-1 and correlate with the lipophilicity of the thiyl radical under study. Sulfonyl radicals undergo both electron abstraction, [ beta-carotene]+. and radical-addition, [RSO2... beta-carotene]. in an approximate 3:1 ratio. The beta-carotene radical-cation and adduct-radicals are highly resonance stabilized and undergo slow bimolecular decay to non-radical products. These carotenoid-derived radicals react differently with oxygen, a factor which is expected to influence the antioxidant activity of beta-carotene within tissues of varying oxygen tension in vivo.

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.

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.

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).

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.

Extracellular: intracellular and subcellular concentration gradients of thiols

Chinese hamster V79 cells in Eagle's minimum essential medium in vitro at room temperature were incubated with the aminothiol, WR-1065, or glutathione (GSH) at extracellular concentrations of approximately 1 mmol dm-3. Average intracellular concentrations of GSH, cysteine, and WR-1065 were measured by high performance liquid chromatography, and the effective reducing environment near DNA probed by staining the cells with acridine orange (AO) and measuring the delayed fluorescence. Exposure to either thiol resulted in a rapid, 10-fold increase in average intracellular cysteine concentrations (to about 1 mmol dm-3). Adding extracellular GSH after prior depletion of GSH by treatment with L-buthionine sulfoximine (BSO) did not restore intracellular GSH, but intracellular cysteine was elevated 10-fold. These results are ascribed to thiol/disulfide exchange with cystine in the medium. WR-1065 slowly concentrated intracellularly to approximately 160% of the extracellular concentration. Chemical conjugation of GSH in cells decreased the reducing environment near DNA, but BSO treatment altered the uptake of AO. The electrostatic attraction of WR-1065 toward isolated DNA was markedly affected by ionic strength.

Measurement of incorporation of bromodeoxyuridine into DNA by high performance liquid chromatography using a novel fluorescent labelling technique

5'-Bromo-2-deoxyuridine (BUdR) is a halogenated pyrimidine analogue that is an efficient radiosensitizer through its incorporation into DNA in place of thymidine. Radiosensitization is proportional to percentage replacement and we present here a novel derivatization technique that specifically labels the thymidine and BUdR with 4-bromomethyl-7-methoxycoumarin (BrMMC) to give the highly fluorescent coumarin derivatives which are quantitated using high performance liquid chromatography (HPLC). This allows for a simple single-stage DNA hydrolysis and sensitive peak detection. Data are presented showing the incorporation with time of BUdR into the DNA of Chinese hamster V79 cells. Attention is also drawn to the care needed in the selection of enzymes required for DNA digestion.

Radiosensitization by misonidazole, pimonidazole and azomycin and intracellular uptake in human tumour cell lines

The radiosensitization of two human tumour in vitro cell lines, HT-1080 and LoVo, has been compared with that of the Chinese hamster cell line V79-379A. Although the two human tumour cell lines were more radiosensitive than the V79 cell line sensitizer, enhancement ratios for misonidazole, pimonidazole and azomycin were similar (relative to extracellular concentration) for all three cell lines. Average intracellular concentrations of radiosensitizer were measured by high-performance liquid chromatography. In all three cell lines the uptake of misonidazole and azomycin was extremely rapid whereas that of pimonidazole was initially much slower before reaching a plateau. The ratios of intracellular concentration of radiosensitizer to extracellular concentration (Ci to Ce) for misonidazole were 0.8 (HT-1080) and 0.7 (LoVo and V79); for azomycin 0.9 (HT-1080 and LoVo) and 0.8 (V79). In contrast Ci/Ce for pimonidazole varied with cell line, the values being 1.8 (LoVo), 2.6 (HT-1080) and 3.3 (V79). Intracellular amounts of non-protein sulphydryl (NPSH) varied between cell lines by about a factor of three. However, when the average cell volume was taken into consideration the concentrations of NPSH were very similar, being 4.2 (HT-1080), 5.6 (LoVo) and 5.7 (V79) mmol dm-3. NPSH levels expressed as nmol per mg protein were also similar.

Increase in intracellular cysteine after exposure to dithiothreitol: implications in radiobiology

Dithiothreitol reduces cystine in tissue-culture medium, and the resulting cysteine is accumulated in Chinese hamster V79 cells to an extent which should be taken into account in evaluating models of radiosensitivity and the effects of thiol radioprotectors.

A probe for intracellular concentrations of drugs: delayed fluorescence from acridine orange

The aim of this work is to develop fluorescent probes that will indicate effective concentrations of therapeutic agents, or endogenous protectors, at important cellular sites. Acridine orange associates with nucleic acids and emits a 'delayed' fluorescence signal. This signal is quenched by oxidants such as oxygen, nitroaryl radiosensitizers, adriamycin and mitomycin-c, and reductants such as thiols, ascorbate and other radioprotectors. The quenching of the acridine orange delayed fluorescence reflects the effective concentration of these therapeutically-important oxidants and reductants near DNA. The relative concentration of basic radiosensitizers such as pimonidazole (Ro 03-8799) near the DNA is greater than that of misonidazole. Thiols quench the delayed fluorescence signal according to the degree of ionization of the thiol function; this may model the reactivity of thiols with guanine radical sites in DNA. Ascorbate and aminopyrine do not quench the delayed fluorescence from cells stained with acridine orange as these compounds are taken up by cells very inefficiently.

Radiosensitizer-DNA interactions in relation to intracellular uptake

We have studied the intracellular uptake of a number of neutral, acidic, and basic radiosensitizers. For neutral sensitizers, we observed a correlation between the measured intracellular concentration and sensitization, but for bases, a large change in average intracellular concentration results in only a small change in sensitization. In addition, by modifying the intralysosomal pH, we have altered the measured average intracellular concentration of the weak base pimonidazole by a factor of two, although this had no detectable effect upon sensitization. Using spin filtration of solutions of sensitizers with naked calf thymus DNA or chromatin we have assessed the affinity of DNA for sensitizers with different prototropic and lipophilic properties. We have also shown that this anomalous behavior of the basic sensitizers could be partly explained on the basis of intracellular localization adjacent to the DNA due to ionic interactions. Thus, intracellular localization needs to be considered when interpreting average intracellular uptake data.

A comparison of the intracellular uptake and radiosensitization efficiency in different media of uncharged 2-nitroimidazoles of varying lipophilicity

The effect of varying octanol: water partition coefficients, P, (range 0.026-260) on the uptake of uncharged 2-nitroimidazoles into Chinese hamster V79 379A cells has been studied. Average intracellular concentrations were measured by high performance liquid chromatography after centrifuging cells through oil or an aqueous medium. The ratio of intracellular concentration of radiosensitizer to extracellular concentration (Ci/Ce) for misonidazole (P = 0.43) was 0.85 for the oil method and 0.68 for the aqueous method. For values of P less than about 0.05 uptake was initially very slow and Ci was always less than Ce. When P greater than or equal to 0.1 uptake was rapid and then remained unchanged for times up to 3 h; for P greater than or equal to 10, Ci/Ce increased rapidly as P increased. Ro 31-1405 (P = 260) concentrated by a factor of 7 inside the cell. Although uptake was identical for cells suspended in full growth medium and PBS, radiosensitization was greater for cells in PBS: 1 mmol dm-3 misonidazole produced an enhancement ratio of 1.6 in full growth medium and 1.9 in PBS. This increase in radiosensitization could not be accounted for by protein binding. However, measurements on cellular non-protein sulphydryl (NPSH) demonstrated the levels to be reduced to about 60 per cent for cells in PBS. Similar reductions in NPSH levels have previously been shown not to increase the radiosensitivity of control cells but to increase greatly the effectiveness of nitroimidazole radiosensitizers.

Glutathione-reactive nitro compounds as radiosensitizers: mechanistic and therapeutic implications

The "extra" radiosensitization seen with GSH-reactive nitro compounds is too large to be accounted for by GSH-depletion acting independently--there must be competition. The GS-conjugate leaks out of cells slowly and is trapped at high concentrations. Its properties, such as concentration trapped and reduction potential, must be considered. Limited therapeutic exploitation of the glutathione conjugate trapping and concomitant GSH depletion may be possible if intratumor injection is permitted.

Cellular uptake of misonidazole and analogues with acidic or basic functions

Average intracellular concentrations of five radiosensitizers in hamster fibroblast-like V79-379A cells in vitro were measured by high performance liquid chromatography, varying the extracellular pH (pHe) and estimating the apparent intracellular pH from the distribution of 5,5-dimethyloxazolidine-2,4-dione. The intracellular: extracellular concentration ratio for the 2-nitroimidazole, misonidazole was constant at about 0.7 for pHe = 6.6-7.6, whereas the weak base, Ro 03-8799 (1-(2-nitro-1-imidazolyl)-3-N-piperidino-2-propanol) was concentrated intracellularly at pHe = 7.3-7.4 by a factor of 3.3, the factor increasing from about 0.8 at pHe = 6.0, to 7.5 at pHe = 7.85. The weak acid, azomycin (2-nitroimidazole) showed approximately constant uptake (factor 1.1) between pHe = 6.0-7.0, decreasing to 0.8 at pHe = 7.3 and 0.4 at pHe = 7.8. Measurements of intracellular uptake of Ro 31-0052 (the more hydrophilic and less basic 3'-hydroxypiperidino analogue of Ro 03-8799) and of Ro 31-0258 (3-(2-nitro-1-imidazolyl)propionic acid, a stronger acid than azomycin) were made for comparison. The results were compared with theoretical calculations of pH-induced concentration gradients; the time dependence of the uptake of the bases is not at present clearly understood. These measurements of uptake are broadly consistent with the distribution of misonidazole and Ro 03-8799 in human and animal tissues and provide a useful insight into the likely intracellular concentrations in the clinical use of Ro 03-8799 or other basic radiosensitizers. The measurements also resolve the apparent discrepancy in radiosensitizer efficiency for weak bases in vitro and in vivo which has been previously noted.