Radiosensitizing Drugs Research Articles

Renal elimination of the hypoxic cell radiosensitizer misonidazole in Wistar rats: influence of some drugs on its excretion.

The hypoxic cell radiosensitizing drug, misonidazole (Miso) (Ro 07-0582) and its demethylated metabolite were administered to Wistar rats at different dose levels to examine their renal elimination. The data were consistent with a model in which Miso is eliminated mainly after biotransformation into desmethylmisonidazole (Demiso) which is eliminated according to its renal clearance. The study of Miso renal elimination process shows a tubular reabsorption. So we analyzed the interaction of various drugs on urinary 24 hours elimination of this radiosensitizer. Following results were observed: Furosemide and acetazolamide do not change the rate of renal elimination of the drug; Soludactone increases the elimination level of unmetabolized Miso (p less than 0.01); Under probenecid treatment, the elimination of Miso and its O-demethylated derivative are increased; On the other hand, after a pretreatment with phenobarbital, the urinary level of desmethylmisonidazole is strongly increased (p less than 0.001).

Inhibition of glycolysis of mammalian cells by misonidazole and other radiosensitizing drugs: Prevention by thiols

Prolonged anaerobic incubation of Ehrlich ascites tumor cells and Chinese hamster V79–379A cells with misonidazole, desmethylmisonidazole, or niridazole led to inhibition of both glucose consumption and lactate formation. This effect was measured in cells washed free of the nitro compounds and resuspended in fresh buffer or medium. The degree of inhibition of glucose utilization was related to drug concentration, and to the rate of metabolic reduction, as measured under aerobic conditions by KCN-insensitive oxygen consumption. Misonidazole-induced inhibition of glycolysis developed concurrently with depletion of intracellular non-protein thiol (NPSH) and was protected against by the presence of cysteamine, cysteine and, to some extent, GSH in the cell incubate. These findings suggest reaction of reduced drug intermediates with thiol-containing enzymes. The glutathione-reactive agent diethyl maleate was used to deplete 90% of the endogenous NPSH, but this depletion did not alter the effects of misonidazole on glycolysis.

Radiation therapy, local tumor control, and prognosis in bronchogenic carcinoma: Current status and future prospects

While the overall prognosis for cure of bronchogenic carcinoma remains poor for most patients, there is a growing body of evidence suggesting that rationally optimized local therapy may benefit a significant subset of patients. Local therapy in this context includes any systemic therapy (such as chemotherapy or immunotherapy) that enhances local tumor control in the chest. Compared with many other human epithelial cancers, the total local tumor burden is large for many nonresectable lung cancers and not within the tolerance for control by radiation alone. Thus there is growing evidence that combined surgery and radiation treatment will improve results, especially in the differentiated tumors. Proper selection of patients is important and must include histologic stratification in addition to conventional TNM staging. It is projected that much useful research can be conducted during this decade using clinical tools now available and those that are being tested in early clinical trials throughout the world. Likely candidates for such improvements are both oxic and hypoxic radiosensitizing drugs that should decrease the death rate from uncontrolled local cancer in the chest.

Non-protein thiols and cellular response to drugs and radiation

Our results have enabled us to make a number of observations concerning the reactivity of nitrocompounds and non-nitrocompounds with glutathione (GSH) and cellular nonprotein thiols (NPSH), which may be as much as 90 % GSH. We have summarized our observations as follows with respect to the different types of reactions responsible for part or all of the cellular NPSH depletion by hypoxic cell radiosensitizing drugs. (A) Some nitrocompounds, such as 4-nitroimidazoles containing a 5-sulfonamide group, react spontaneously with GSH; (B) A number of hypoxic cell radiosensitizing drugs such as chlorodinitrobenzene (CDNB), dimethylfumarate (DMF) and diethylmaleate (DEM) are substrates for the enzyme glutathione-S-transferase and form covalent bonds with GSH; (C) NPSH may be oxidized by diamide; (D) form covalent bonds with N-ethylmaleimide; (E) or be converted by thiol-reactive drug intermediates formed under anaerobic conditions. The latter reaction occurs with misonidazole, Ro-05–9963, SR 2508 and SR 255:5; its mechanism is still unknown. It is obvious from the above that there are a variety of means by which radiosensitiizing drugs can alter cellular metabolism as reflected by changes in the NPSH. It remains to be determined whether a relationship exists between altered NPSH, metabolism and the radiosensitizing capacity of nitrocompounds when used alone or in combination with other drugs. Our studies strongly suggest that potential new sensitizers be routinely examined for their capacity to react spontaneously with GSH or to remove cellular NPSH under aerobic as well as anaerobic conditions. This is especially true for radiosensitizing drugs showing anomalous behavior, i.e., better sensitization than predicted by their one-electron reduction potentials. Such screening would pay dividends insofar as drugs that are too reactive could be excluded from further in vivo study.

The penetration of misonidazole into a mature structural cartilage.

Mature cartilage may be expected to contain populations of hypoxic cells as a result of the tissues lack of direct vascularization and structure; it may therefore be at risk from possible radiosensitization. The hypoxic-cell radiosensitizing drug misonidazole Ro-07-0582 (MISO) was administered i.v. to mature New Zealand White rabbits at a dose of 100 mg/kg, and the resulting drug concentrations in both blood and ear-cartilage samples measured by HPLC. Samples were taken at regular intervals up to 4 h after administration of MISO. Blood concentrations of MISO rose rapidly to 240 microgram/ml within 5 min of administration, before falling steadily, with a t1/2 of 45 min. Cartilage levels reached a peak of 70% of the blood levels approximately 30 min after administration. The levels of MISO then fell, with a t1/2 of 44 min.

A biochemical assessment of the neurotoxicity of the radiosensitizing drug misonidazole in the rat.

We have obtained biochemical evidence that misonidazole when administered in large doses to rats produces a sparse dying-back peripheral neuropathy and degenerative changes in the trigeminal ganglia and cerebellum. In our experience these neurotoxic effects of misonidazole cannot be detected reliably by the use of simple behavioural and functional tests, e.g., inclined plane and narrowing bridge tests (Rose and Dewar, unpublished results). Therefore, these methods would be of limited use in the neurotoxicity screening of misonidazole analogues. On the other hand, the biochemical approach provides a convenient quantitative method which could be used as the basis for comparing the neurotoxicity of other candidate radiosensitizing drugs.

The Pharmacokinetics and Tumor and Neural Tissue Penetrating Properties of SR-2508 and SR-2555 in the Dog-Hydrophilic Radiosensitizers Potentially Less Toxic than Misonidazole

The behavior of three 2-nitroimidazole drugs of similar electron affinity to misonidazole but with varying octanol: water partition coefficients has been compared in normal and tumor-bearing dogs. In particular the pharmacokinetic behavior, urinary excretion, and tumor and neural tissue penetrating properties of the three drugs have been studied. Peak plasma concentrations and plasma clearance rates increased with decreasing lipophilicity. Penetration into both the central and peripheral nervous system was significantly slower for the more polar drugs, and as a result of this and the increased plasma clearance rates, the drug exposure to these sites of potential neurotoxicity was reduced. Peak tumor concentrations increased with decreasing lipophilicity, and those for the two SR drugs were more than twice those for equimolar iv doses of misonidazole. It would seem on the basis of the increased plasma clearance rates, improved peak tumor concentrations, and reduced drug exposure to neural tissue that lowering lipophilicity may be an important means of designing radiosensitizing drugs which are less toxic than and superior to misonidazole.

A biochemical method for assessing the neurotoxic effects of misonidazole in the rat.

A proven biochemical method for assessing chemically induced neurotoxicity has been applied to the study of the toxic effects of misonidazole (MISO) in the rat. This involves the fluorimetric measurement of beta-glucuronidase and beta-galactosidase activities in homogenates of rat nervous tissue. The tissues analysed were sciatic/posterior tibial nerve (SPTN) cut into 4 sections, trigeminal ganglia and cerebellum. MISO administered i.p. to Wistar rats in doses greater than 300 mg/kg/day for 7 consecutive days produced maximal increases in both beta-glucuronidase and beta-galactosidase activities in th SPTN at 4 weeks (140-180% of control values). The highest increases were associated with the most distal secretion of the nerve. Significant enzyme-activity changes were also found in the trigeminal ganglia and cerebellum of MISO-dosed rats. The greatest activity occurred 4-5 weeks after dosing, and was dose-related. It is concluded that, in the rat, MISO can produce biochemical changes consistent with a dying-back peripheral neuropathy, and biochemical changes suggestive of cerebellar damage. This biochemical approach would appear to offer a convenient quantitative method for the detection of neurotoxic effects of other potential radio-sensitizing drugs.

The effect of hypoxic cell radiosensitizing drugs on cellular oxygen utilization

Various heterocyclic nitrocompounds ( nitroimidazoles, nitrofurans, nitropyrroles, nitrobenzenes) and thiol reactants (such as diamide and N- ethylmaleimide) that have been studied as anoxic cell radiosensitizers, alter cellular oxygen utilization. The effects are dependent upon the electron affinity and concentration of the drug, as well as on glucose and endogenous reducing substrates. Some of the drugs alter oxygen uptake by direct inhibition of electron transport, while others stimulate cellular oxygen utilization by forming oxygen-reactive nitro-intermediates. The production of these intermediates may be demonstrated with cyanide-inhibited cells or with purified microsomes. Ascorbate, in buffered solution, mimics cyanide-inhibited cells and purified microsomes by also producing oxygen-reactive nitro-intermediates. The importance of the drug effects on oxygen consumption is discussed with respect to radiation sensitization of multi-cellular systems in vitro and in vivo.

The effect of nitroheterocyclic drugs on DNA: An in vitro model of cytotoxicity

Electrolytic reduction of several nitroheterocyclic drugs was carried out at controlled potentials under anoxic (anaerobic) conditions in the presence of Esherichia coli DNA. The DNA was examined during the reduction process by viscometry, determination of T m values, and thermal renaturation of DNA; its single strand content was determined using hydroxyapatite chromatography and its electrophoretic migration characteristics in acridine-impregnated agarose gels. All the drugs examined decreased the viscosity, thermal renaturation and T m value, and increased the single strand content and migration distance of DNA. The results indicate that the drugs cause strand breakage of DNA as a primary mechanism of action, resulting in extensive loss of helix formation and a concomitant decrease in molecular weight. The method of drug reduction and the techniques to assess DNA damage may be used as a model to determine the relative cytotoxicities and the potential of such agents as antimicrobial and radiosensitizing drugs.

The effects of single and fractionated doses of X-rays and neutrons on the oesophagus

Damage to the oesophagus of mice after irradiation with single doses, 2, 5 or 10 equal fractions of X-rays or fast neutrons was measured by estimating ld 50 values for death between 10 and 40 days post-irradiation of the thorax. The slope of the isoeffect curve for X-irradiation was 0.40 and for neutrons was 0.29. RBE values obtained for oesophaged damage are close to those previously observed for intestinal injury and are among the highest observed with normal tissues. If, therefore, the RBE for oesophaged tumours follows that of the tissue of origin then oesophageal tumours would respond well to neutron therapy. However, the high RBE for the normal oesophageal damage may limit treatment at this site. Irradiation with single doses of X-rays of animals breathing oxygen or in normal air breathing conditions but after administration of the anoxic radiosensitizing drug misonidazole (Roche Products Ltd. Ro- 07-0582) both gave enhancement of damage relative to air breathing anaesthetised mice, indicating that hypoxia in these anaesthetised animals affects the sensitivity of the oesophagus to large doses of radiation.

Mechanism of Action of Nitroimidazole Antimicrobial and Antitumour Radiosensitizing Drugs

Electrolytic reduction of the hypoxic tumour cell radiosensitizing drug misonidazole was carried out at a controlled potential under anaerobic conditions in the presence of Escherichia coli DNA. During the reduction process the DNA was examined by viscometry, thermal hyperchromicity, melting and renaturation profiles, hydroxyapatite chromatography, agarose gel electrophoresis and alkaline sucrose density gradient centrifugation. The reduced drug decreases the viscosity, hyperchromicity and renaturation of DNA. These effects are consistent with strand breakage of the molecule which was corroborated by finding an increase in the single-strand content of DNA, increased migration and loss of fluorescence intensity on agarose gels and sedimentation to a less dense region in alkaline sucrose density gradients. The results are discussed in relation to postulated mechanisms of the selective toxicity of the drug towards anaerobes and cytotoxicity of electron affinic radiosensitizers of hypoxic tumour cells.

In Vitro Studies on the Radioresistance of Oxic and Hypoxic Cells in the Presence of Both Radioprotective and Radiosensitizing Drugs

In vitro studies, involving CHO monolayers, have demonstrated that the oxygenation status of the cells determines whether radioprotection or radiosensitization will be observed when both Ro-07-0582 (6 mM) and cysteine (8 mM) are present in the medium. This combination sensitizes hypoxic cells yet protects well-oxygenated ones. A comparison of individual drug effects on radiation resistance with those of the combination indicates that the latter can yield a larger therapeutic gain than either alone through reduction of drug toxicity and/or by improving relative tumor response.

The reaction of hypoxic cell radiosensitizing drugs with vitamin C

Hypoxic cell radiosensitizing drugs are oxygen-mimicking chemicals that will increase the radiation response of hypoxic cells in vitro and in vivo (Fowler et al., 1976). In addition to their oxygen-mimicking properties these drugs may also sensitize the cells to radiation by removing or binding intracellular biochemicals such as reduced pyridine nucleotides (NAD(P)H) and glutathione (GSH), capable of repairing radiation damage (Chapman et al., 1973). More recently it was found that metronidazole or “Flagyl” may inhibit cellular oxygen consumption and that this inhibition may cause reoxygenation of tumour tissue in vivo (Biaglow et al., 1974; Durand et al., 1976; Haynes and Inch, 1976).

Combined Use of Radioprotective and Radiosensitizing Drugs in Experimental Radiotherapy

The application of both radioprotective and radiosensitizing drugs in clinical radiotherapy is limited by the large drug doses required to obtain significant therapeutic gains. A potential means of circumventing these toxicity problems, while retaining significant therapeutic gains, would be to use small doses of both types of drugs. This possibility has been tested, using the specific drug combination WR-2721 and Ro-07-0582 with the following results: The two drugs are not additive in terms of lethal toxicity in the mouse; WR-2721 does not interfere with the ability of Ro-07-0582 to sensitize tumors in vivo; and Ro-07-0582 does not interfere with the ability of WR-2721 to protect mouse skin. While the therapeutic gains depend on the radiation dose and endpoints considered, the combination proved to be superior to either drug alone in all cases. The success of these preliminary investigations would appear to warrant further study.

Optimum fractionation of the C3H mouse mammary carcinoma using X-rays, the hypoxic-cell radiosensitizer Ro-07-0582, or fast neutrons

Experiments extending over several years have now been completed in which local control of mammary tumors in C3H mice was compared with acute skin reactions in other mice for a number of fractionated X-ray and fast neutron schedules. This paper presents the latest results, summarizes the previously published results, and discusses the pattern which has now emerged. Two types of fractionated treatment have been investigated: short overall times of up to 4 days and longer overall times of 9–18 days. The effectiveness of each schedule was estimated by comparing the local tumor control that could be achieved for a given skin reaction. In the short treatment schedules, the extent of tumor control was very variable, ranging from poor to good. It was critically dependent on fraction size and on the interval between fractions in a way that was consistent with reozygenation in the tumor bring the crucial factor. In the longer treatment schedules, fraction size and interval were not so critical end overall time was the governing factor; too long overall dam yielded poor results because proliferation in the tumor was faster then in skin. In the short, variable, type of treatment it was shown that poor results using X-rays could be improved, to about the same level as the best X-ray results, by using either the specific hypoxic-cell radiosensitizing drug Ro-07-0582 with X-rays, or by using cyclotron-produced fast neutrons. These observations support the concept of hypoxia and reoxygenation being the crucial factors in short treatment schedules.

The effect of nitroimidazole and nitroxyl radiosensitizers on the post-irradiation synthesis of DNA.

The modification of DNA damage by three radiosensitizing drugs, present during gamma-irradiation of hypoxic Chinese hamster cells, was investigated. Both 2-methyl-5-nitroimidazole-1-ethanol (metronidazole) and 1-(2-nitro-1-imidazole)-3-methoxy-2-propranol (Ro-07-0582) were found to cause large increases in the yield of DNA single-strand breaks (SSB); triacetoneamine-N-oxyl (TAN) was found to have only a small effect on SSB production. The three drugs tested did not inhibit the rejoining of SSB. A pulse label and chase procedure was used to examine post-irradiation DNA synthesis. TAN present during irradiation under hypoxia was found to cause interruptions in subsequent DNA synthesis. Metronidazole and Ro-07-0582 had no effect on post-irradiation DNA synthesis. In addition, the effects of pre- and post-irradiation exposure to TAN were investigated, since these treatments have shown increased cell-killing in survival studies. TAN pre- and post-treatments were found to have no significant effect on subsequent DNA synthesis.

Metronidazole (Flagyl): iron catalysed reaction with sulphydryl groups and tumour radiosensitisation.

THE possibility of using hypoxic cell radiosensitising drugs as adjuncts in the radiotherapy of some forms of cancer has received renewed attention1–4. In particular administration of metronidazole (Flagyl, May and Baker Ltd) to tumour bearing mice before exposure to X rays, has been found to reduce the radiation dose required to control 50% of the tumours by a factor of 1.2–1.3 (refs 5 and 6). Preliminary clinical trials are now in progress7. The drug was originally chosen for study because of its constituent nitro group (which suggested it was a strong radical oxidant) and its extremely favourable pharmacological and toxicological properties8. Previously the activity of a large number of radiosensitisers had been attributed to their ability to react with intracellular sulphydryl compounds9,10. The ability of the cell to repair radiation-induced free radical lesions by hydrogen11 or electron donation12 would thus be lowered. Measurements13 of anoxic solutions over a period of 2 h did not, however, show any appreciable reaction between metronidazole (8 × 10−4 M) and the sulphydryl groups of cysteamine (8 ×10−4 M) or dithiothreitol (4 ×10−4 M). Recent associated pharmacological studies with rat intestinal contents have prompted us to re-examine the reaction of metronidazole with sulphydryl compounds and to investigate the possibility of catalysis by ferrous ions. We now report experiments which show that the drug reacts with an iron–cysteine complex over time scales of the order of a second. A drug–iron–cysteine complex is formed which is subsequently reduced over a period of minutes.

Book reviewsRadiation Protection and Sensitization. Proceedings of the Second International Symposium on Radiosensitizing and Radioprotective Drugs, Rome, 1969. Eds. MorosonH. L. and QuintilianiM., pp. xvi + 522, Subject and author indexes, (illus.). 1970 (London, Taylor and Francis Ltd), £8·00.

Book reviewsRadiation Protection and Sensitization. Proceedings of the Second International Symposium on Radiosensitizing and Radioprotective Drugs, Rome, 1969. Eds. MorosonH. L. and QuintilianiM., pp. xvi + 522, Subject and author indexes, (illus.). 1970 (London, Taylor and Francis Ltd), £8·00.

Radiation Protection and Sensitization. Proceedings of the Second International Symposium on Radiosensitizing Drugs, Rome, 1969

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRadiation Protection and Sensitization. Proceedings of the Second International Symposium on Radiosensitizing Drugs, Rome, 1969Alfred BurgerCite this: J. Med. Chem. 1971, 14, 2, 177Publication Date (Print):February 1, 1971Publication History Published online7 January 2004Published inissue 1 February 1971https://doi.org/10.1021/jm00284a901RIGHTS & PERMISSIONSArticle Views17Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (184 KB) Get e-Alerts Get e-Alerts