Biomedical subjects
Publications and source records attributed to P Workman.
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The hypoxic cell-radiosensitizing drug misonidazole (1-(2-nitroimidazol-1-yl)-3-methoxypropan -2 -ol, Ro 07-0582, MIS) was administered at a dose of 150 mg/kg i.v. to 6 dogs bearing spontaneous tumours, and the resulting tumour concentrations were measured to HPLC analysis. In 4 dogs it was possible to obtain serial biopsy specimens up to 5 h. With the exception of a brain tumour, the tumour concentrations ranged between 47% and 95% of the plasma concentration, most of the values falling within the range 50--70%. Concentrations in the brain tumour were markedly lower. Barbiturate anaesthesia was necessary for the removal of the serial biopsy specimens, and the effects of sodium pentobarbitone anaesthesia on the pharmacokinetics of MIS were investigated in 2 dogs. After barbiturate anaesthesia peak plasma concontrations were raised and the availability of MIS was increased, although the biological half-life remained unaltered. The metabolism of MIS to the O-demethylated metabolite, Ro 05-9963, was delayed initially. The concentrations of MIS AND Ro 05-9963 in cerebrospinal fluid were also recorded in these dogs; MIS concentrations were found to approach those of the plasma, whereas the metabolite concentrations were considerably lower (0--58% of the plasma concentration).
Concentrations of the hypoxic cell radiosensitizer misonidazole (MIS) and its O-demethylated metabolite Ro 05-9963 were determined in plasma (or blood), brain and tumour after injection of 1 g/kg MIS i.p. to control mice or mice pretreated with 4-6 daily injections of phenobarbitone or phenytoin. Analysis was by high-performance liquid chromatography (HPLC). Phenobarbitone and phenytoin did not alter the peak MIS concentration in plasma, brain or tumor. However, the apparent elimination half-life (t 1/2) for MIS was reduced by 20-67%, and the area under the curve (AUC) was decreased by 23-49% in plasma, brain and tumour. The decrease in MIS t 1/2 was associated with an initially increased Ro 05-9963 metabolite concentration. However, the AUC for total 2-nitromidazole (MIS + Ro 05-9963) in plasma, tumour and brain was reduced by 20-50%. Urinary excretion of MIS and its metabolites accounted for 15-42% of the injected dose, and was unaltered by pretreatment with phenobarbitone or phenytoin. Tumour/plasm and brain/plasma concentration ratios for MIS, and tumour/plasma ratios for Ro 05-9963 were very similar, but the brain/tumour ratios for Ro 05-9963 were considerably lower. Tissue/plasma ratios were unaltered by pretreatment with phenobarbitone or phenytoin. The acute LD50 for MIS was increased from 1.54 to 1.90 g/kg after phenobarbitone pretreatment and 1.78 g/kg after phenytoin pretreatment. In addition, pretreatment with either compound shortened the duration of the MIS-induced decrease in body temperature. These data suggest that pretreatment with microsomal-enzyme-inducing agents may reduce the toxicity of MIS without affecting the radiosensitization. The significance of these findings for the mechanism of MIS toxicity is also discussed.
Bilateral kidney ligation of mice immediately before injection of misonidazole (MIS) prolongs the plasma half-life of this radiosensitizer from about 2 h (in normal mice) to 10-11 h, similar to that in man. Kidney ligation does not, however, change the relative proportions of MIS and its O-demethylated metabolite, Ro-05-9963, for the first 12 h after MIS injection. Kidney ligation was used with the two radiosensitizers, MIS and Ro-05-9963, to investigate the influence of plasma half-life both on peak plasma levels and on the tumour/plasma ratio of sensitizer concentration in the EMT6 mouse tumour. Although the acute LD50 of Ro-05-9963 in normal mice was twice that of MIS, this apparent advantage was offset by peak tumour levels 50% or less of those achieved by equimolar injected doses of MIS. However, by comparing the plasma and tumour levels in mice in which the drug half-lives were prolonged by bilateral kidney ligation, it was concluded that the lower plasma and tumour levels of Ro-05-9963 were a result of its shorter plasma half-life, rather than of an intrinsic barrier to tumour penetration. Because of this rapid clearance, the radiosensitization produced by Ro-05-9963 was less than that produced by equimolar injected doses of MIS. As this difference did not occur in kidney-ligated mice, and hence would not be expected to occur in man, the comparison of MIS and Ro-05-9963 in mice produces an artificially low radiosensitization for Ro-05-9963 and possibly also for other compounds with short plasma half-lives. Although the short plasma half-life of Ro-05-9963 appeared to be responsible for its low peak plasma concentration, it did not produce a low tumour/plasma ratio. Within the limits of plasma nitroimidazole half-lives investigated (0.5-10 h) the tumour/plasma ratio was insensitive to plasma half-life, being 50-70% for both MIS and Ro-05-9963 in both normal and kidney-ligated mice. It is concluded that the common assumption that tumour/plasma ratios of MIS in the mouse are less than those in man is unjustified.
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Potent inhibition of human prostatic carcinoma tissue acid phosphatase by N,N-d-di-2-chloroethylaminophenol (AMOH) and N,N-p-di-2-chloroethylaminophenyl phosphate (AMPh) is described. Certain other difunctional nitrogen mustards were also inhibitory but N,N-p-di-2hydroxyethylaminophenol, the non-alkylating fully hydrolysed product from AMOH, was not. Inactivation of the enzyme by AMPh was progressive with time, showed apparent first order reaction kinetics and was not reversed by extensive dialysis. The results suggest that the inability of the enzyme to catalyse the hydrolysis of AMPh was due to inhibition in the presence of AMPh, possibly involving an alkylating mechanism. The implications for possible chemotherapy with AMPh are discussed.
Concentrations of misonidazole and its O-demethylated metabolite Ro 05-9963 in the plasma and saliva of 10 patients with malignant disease have been determined. A good linear correlation was established between plasma and saliva misonidazole concentration, and salivary sampling was found to be suitable for the estimation of a number of pharmacokinetic parameters. Data are also presented for serial tumour cencentrations of misonidazole and Ro 05-9963 in 3 of the 10 patients. Monitoring of salivary misonidazole concentration appears to be a useful alternative to plasma monitoring, particularly for those patients in whom plasma sampling is unsuitable or impossible.
The reaction rates of enzymes hydrolysing fluorescein diacetate have been studied in populations of intact tissue-culture EMT6, cells using flow cytofluorimetric techniques. It was found that the activity of these enzymes increased in plateau phases and that this correlated inversely with plating efficiency. Highly abnormal substrate-dependent reaction velocity kinetics were found in 14-, 21-, 28- and 35-day cultures.
The preliminary details of a randomized clinical trial of misonidazole for the radiotherapy of Grades 3 and 4 cerebral astrocytoma are described. Plasma concentrations of misonidazole and its O-demethylated metabolite, determined by high-pressure liquid chromatography analysis, are reported for 8 patients with astrocytoma, 1 with carcinoma of the bronchus and 1 with carcinoma of the breast. In the latter case, tumour concentrations are also presented.
Latent antitumour agents require spontaneous or enzyme-catalysed activation to cytotoxic species in vivo. Activation may occur principally in normal tissues or in the target tumour. Agents of this type are discussed and mechanisms of drug action and selectivity are described, with reference to appropriate examples. The comparatively poor therapeutic activity of many agents designed for selective activation in tumours is attributed to the often unfavourable distribution of activating enzymes between normal and neoplastic tissues. Factors to be considered in the design of new enzyme-activated agents are discussed and possible artefacts involved in the assay of tumour enzymes are described. Some novel approaches to the design of latent antitumour agents are also discussed.
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