Biomedical subjects

A M Rauth

Publications and source records attributed to A M Rauth.

At least 19 recordsLinked to original sources

PubMed1992

Depletion of intracellular glutathione by 1-methyl-2-nitrosoimidazole.

In addition to their ability to radiosensitize, nitroimidazoles are selectively toxic toward hypoxic cells. Reduction of the nitro group is required to observe cytotoxicity. One of the reduction products believed to play a role in this cytotoxicity is the nitroso-derivative. One-methyl-2-nitrosoimidazole (INO), chemically synthesized from one-methyl-2-nitroimidazole (INO2), has been used as a model to study the reactivity of 2-nitrosoimidazoles. The ability of INO to react rapidly with glutathione in Chinese hamster ovary cells treated with a sub-toxic and toxic level of the drug has been measured. The kinetics of GSH loss as well as oxidized GSH (GSSG) formation and loss were assessed at short times (0-15 min) after INO exposure using a high pressure liquid chromatography (HPLC) assay for GSH and GSSG. The results obtained were consistent with a model, based on previous chemical studies of the reaction of INO with GSH, whereby GSH reduces INO forming GSSG and as well reacts with a reduced form of INO to form an adduct (I-SG). These results suggest possible strategies for modifying the toxicity of reduction products of one-substituted-2-nitroimidazoles.

Animals↗

PubMed1992

Mode of interaction of 5-fluorouracil, radiation, and mitomycin C: in vitro studies.

An examination of the effects of radiation combined with either 5-fluorouracil, Mitomycin C, or both drugs in vitro has been made using a mouse squamous tumor cell line SCC VIITo and cell viability as an endpoint. Depending on how the survival endpoint was calculated, the interaction of 5-fluorouracil, Mitomycin C, or 5-fluorouracil plus Mitomycin C with radiation was greater than additive (plating efficiency) or only additive (viable cells per flask). These results suggest that the cytostatic effect of these drugs may be an important aspect of their action clinically.

Animals↗

PubMed1992

Mechanistic studies of enhanced in vitro radiosensitization and hypoxic cell cytotoxicity by targeting radiosensitizers to DNA via intercalation.

In an effort to increase the molar efficiency of 2-nitroimidazoles as hypoxic cell radiosensitizers and cytotoxins, they have been linked to a DNA intercalating group. The lead compound in this series, NLP-1, is a 2-nitroimidazole, linked at the one position to a phenanthridine ring system via a three carbon chain. Studies of the hypoxic cell specific radiosensitizing properties and hypoxic cell selective toxicity of NLP-1 toward CHO AA8-4 cells show the drug does have enhanced efficiency compared to the untargeted 2-nitroimidazole, misonidazole, based on external drug concentrations. To see if this enhanced efficiency was due to the proposed mechanism, targeting to DNA, or to a general increase in the intracellular concentration of the drug, its uptake and accumulation intracellularly were determined. Radioactive NLP-1 was synthesized labelled with 14C at the 2 position of the imidazole ring. Cells were incubated with the radioactive drug under aerobic and hypoxic exposure conditions, and intracellular levels of the drug were determined by a spin-through-oil technique. Results indicated that, at a drug concentration of 0.5 mM, there was no net accumulation of the drug over the external drug levels after aerobic exposure. Under hypoxic conditions, the drug did accumulate intracellularly, presumably because of hypoxia specific drug metabolism. Experiments with radioactive misonidazole labelled with 14C in the 2 position of the imidazole ring were run as controls. These results suggest that, under the conditions used, NLP-1 has an increased molar efficiency as a hypoxic cell radiosensitizer and cytotoxin, compared to misonidazole, based on intracellular drug concentrations.

Animals↗

PubMed1992

Use of a high frequency ultrasound microscope to image the action of 2-nitroimidazoles in multicellular spheroids.

A system was designed to allow imaging of control and drug treated multicellular spheroids with a high frequency backscatter ultrasound microscope. It allowed imaging of individual spheroids under good growth conditions. Since little data were available on cellular toxicity of ultrasound at these high frequencies (80 MHz), studies were undertaken to evaluate effects on cell survival, using a colony forming assay. No toxicity was observed on cell monolayers subjected to pulsed ultrasound at the intensities used for imaging experiments. Spheroids were also subjected to pulsed ultrasound and no growth delay was observed when exposed spheroids were compared with mock-exposed spheroids. Imaging studies were performed and pictures of untreated spheroids were obtained in which the necrotic and viable regions are clearly distinguishable. When the hypoxic cell cytotoxin 1-methyl-2-nitroimidazole (INO2) was added to the spheroid, dramatic changes were observed in the backscatter signal. The interior viable cells of the spheroid were selectively affected. Changes in the backscatter signal were also observed when the reduction product 1-methyl-2-nitrosoimidazole (INO) was added to spheroids. With INO however, the changes were located at the periphery of the spheroid, presumably due to the high reactivity of INO which limits diffusion of the drug into the spheroid. The present work demonstrates the potential usefulness of ultrasound backscatter microscopy in following the action of selected drugs in this in vitro tumour model.

Animals↗

PubMed1991

Effect of 1-methyl-2-nitrosoimidazole on intracellular thiols and calcium levels in Chinese hamster ovary cells.

The cellular reduction of 2-nitroimidazoles under hypoxic conditions can lead to cell killing. One of the postulated toxic intermediates is the two-electron reduction product, the nitrosoimidazole. 1-Methyl-2-nitrosoimidazole (INO) was used as a model to study the reactivity of 2-nitrosoimidazoles with sulfhydryls. INO reacted within minutes with bovine serum albumin (BSA) in a stoichiometric fashion as measured by the loss of its characteristic absorption at 360 nm. It appeared to react specifically with the SH group of BSA as demonstrated by the loss of 5,5'-dithiobis-2- nitrobenzoic acid (DTNB) reactive groups and by the loss of INO reactivity if BSA was previously reacted with DTNB. INO also depleted glutathione (GSH) and protein sulfhydryls (Pr-SH) in Chinese hamster ovary (CHO) cells in a concentration-dependent fashion. INO at 25 microM, a non-toxic concentration in terms of cell colony-forming ability, depleted GSH to 10-20% of control levels within 5 min after treatment. Pr-SH were depleted more slowly to 60% of control levels. GSH recovered to near control levels over 3-4 hr but Pr-SH remained depressed. The recovery of GSH was blocked by buthionine sulfoximine (BSO), suggesting that the recovery was due to de novo synthesis of GSH. At a toxic concentration of INO (45 microM), GSH was again depleted to 10-20% and Pr-SH to 50% of control levels. No recovery of either was observed up to 4 hr. The effect of this extensive oxidative stress on intracellular calcium (Ca2+i) levels was monitored using 1-[2-amino-5-(6-carboxyindole-2-yl)-phenoxyl]-2- (2'-amino-5'-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid pentaacetoxy methylester (INDO-1 AM). At toxic concentrations of INO, Ca2+i increased in a sustained, non-physiological manner starting at approximately 60 min after the addition of INO. No increase in Ca2+i was observed when cells were treated with nontoxic concentrations of INO. INO toxicity may be modulated by an uncontrolled influx of Ca2+ which can trigger the activation of cellular enzymes and lead to cell death.

Animals↗

PubMed1991

Studies on the mechanism of resistance to mitomycin C and porfiromycin in a human cell strain derived from a cancer-prone individual.

The mechanism of aerobic resistance to the quinone-containing anti-tumour agents mitomycin C (MMC) and porfiromycin (PM) has been investigated using non-transformed human cells. One of the cell strains used (3437T) was derived from an afflicted member of a cancer-prone family. This cell strain had been shown previously to be six times more resistant to the cytotoxic effects of these agents under aerobic but not hypoxic conditions when compared to a cell strain derived from an unrelated, normal donor (GM38). Differences could not be detected in the ability of cell sonicates prepared from either cell strain to produce alkylating species under aerobic conditions using a 4-(p-nitrobenzyl)pyridine assay. However, using 3H-labelled PM to monitor rapid drug uptake and subsequent accumulation due to drug metabolism, results were obtained indicating that the resistant cell strain (3437T) was deficient in an enzymatic pathway capable of metabolizing these compounds under aerobic but not hypoxic conditions. Dicumarol, an inhibitor of the quinone reductase DT-diaphorase (EC 1.6.99.2), decreased aerobic drug accumulation and cytotoxicity in the control cell strain, but did not alter the lack of accumulation noted in the resistant cell strain. Under hypoxic conditions, dicumarol increased cytotoxicity and drug accumulation in both cell strains. The mechanism of this enhanced cytotoxicity remains unclear. These results suggested that the resistant cells were deficient in the enzyme DT-diaphorase, a potential activator of PM. Enzymatic assays confirmed this and revealed no alterations in cytochrome P450 reductase (EC 1.6.2.4) activity or glutathione content. No protein characteristic of DT-diaphorase was detected in the resistant cell strain using a polyclonal rabbit-anti-rat antibody raised against this enzyme. Southern blot analysis using a rat DT-diaphorase cDNA probe demonstrated differences between the normal and resistant cell strains in the restriction fragment patterns. The present results are consistent with the hypothesis that decreased DT-diaphorase levels are causally associated with PM and MMC resistance in these cells under aerobic exposure conditions.

Cell Line↗

PubMed1991

DT-diaphorase activity and mitomycin C sensitivity in non-transformed cell strains derived from members of a cancer-prone family.

Non-transformed skin fibroblasts derived from five members of a cancer-prone family and three unrelated healthy volunteers were assayed for their levels of activity of the quinone reductase DT-diaphorase and for their sensitivity to the antitumor quinone mitomycin C (MMC). Previous studies of skin fibroblasts derived from one afflicted member of this family (3437T) demonstrated increased resistance to MMC under aerobic exposure conditions and a reduced level of DT-diaphorase. In the present study 3437T cells and a cell strain derived from another afflicted member of the cancer-prone family were found to be hyperresistant to the cytotoxic effects of MMC, and demonstrated negligible DT-diaphorase activity (30 +/- 10 nmol/min/mg protein). Cell strains derived from the three other family members demonstrated intermediate DT-diaphorase activity (400-800 nmol/min/mg protein). Enzyme activities of 1800-6000 nmol/min/mg protein were measured in the three control cell strains. A protein that was reactive with a rabbit polyclonal antibody raised against rat DT-diaphorase and corresponded to the known mol. wt of DT-diaphorase was clearly evident in the three control cell strains, but absent in the two MMC-hyperresistant cell strains. This protein was present in intermediate amounts in the remaining members of the cancer-prone family. Southern analysis of DNA isolated from all eight cell strains and restricted with EcoRI demonstrated the presence of a DNA sequence of approximately 15 kb which hybridized to a rat DT-diaphorase cDNA probe. Northern analysis revealed the presence of an RNA species approximately 1200 bp in size, consistent with that for a human DT-diaphorase mRNA, in all cell strains derived from family members. A post-transcriptional defect would, therefore, appear to be responsible for the decreased enzyme activity observed in the resistant cell strains. These results suggest a role for DT-diaphorase in MMC bioactivation and that reduced levels of the protein may be causally related to the cancer-prone tendency of this family.

Adolescent↗

PubMed1991

Targeting radiosensitizers to DNA by attachment of an intercalating group: nitroimidazole-linked phenanthridines.

The nitroimidazole-linked phenanthridine series of compounds (NLP-1, 2, and 3) were synthesized under the assumption that it should be possible to enhance the molar efficiency of 2-nitroimidazoles as hypoxic cell radiosensitizers and cytotoxins by targeting them to their likely site of action, DNA. The targeting group chosen was the phenanthridine moiety, the major component of the classical DNA intercalating compound, ethidium bromide. The sole difference between the compounds is the length of the hydrocarbon chain linking the nitroimidazole to the phenanthridine. The phenanthridine group with a three-carbon side chain, P-1, was also synthesized to allow studies on the effect of the targeting group by itself. The ability of the compounds to bind to DNA is inversely proportional to their linker chain length with binding constant values ranging from approximately 1 x 10(5) mol-1 for NLP-2 to 6 x 10(5) mol-1 for NLP-3. The NLP compounds show selective toxicity to hypoxic cells at 37 degrees C at external drug concentrations 10-40 times lower than would be required for untargeted 2-nitroimidazoles such as misonidazole in vitro. Toxicity to both hypoxic and aerobic cells is dependent on the linker chain: the shorter the chain, the greater the toxicity. In addition, the NLP compounds radiosensitize hypoxic cells at external drug concentrations as low as 0.05 mM with almost the full oxygen effect being observed at a concentration of 0.5 mM. These concentrations are 10-100 times lower than would be required for similar radiosensitization using misonidazole. Radiosensitizing ability is independent of linker chain length. The present compounds represent prototypes for further studies of the efficacy and mechanism of action of 2-nitroimidazoles targeted to DNA by linkage to an intercalating group.

Animals↗

PubMed1990

Differential cytotoxicity of diaziquone toward Chinese hamster ovary cells under hypoxic and aerobic exposure conditions.

Diaziquone [AZQ, 2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone] has been investigated for its toxicity toward Chinese hamster ovary cells AA8-4 under both aerobic and hypoxic conditions. Under acute (1-5 h) exposures to 2.5-10 microM AZQ in alpha-medium plus 10% fetal calf serum, AZQ showed an approximately linear concentration x time dependency for cell killing which was 3-4 times less under hypoxic compared to aerobic conditions. This selective toxicity toward hypoxic cells was prevented by low levels of oxygen. Under aerobic exposure conditions the toxicity of 2.5 microM AZQ was greatly increased by addition of 1-2 mM ascorbate. This ascorbate mediated toxicity of AZQ, presumably extracellular, could be prevented by the simultaneous addition of catalase. Under hypoxic exposure conditions there was no enhancement of AZQ toxicity by ascorbate or protection by catalase. The present results are consistent with two mechanisms for AZQ toxicity proposed earlier by others: toxicity due to (a) redox cycling and increased levels of oxidative stress and (b) reduction of the quinone leading to enhanced reactivity of the aziridines. The relative potency of AZQ as a hypoxic or aerobic cell selective toxin is determined by the balance between these two mechanisms.

Aerobiosis↗

PubMed1990

Spontaneous phenotypic and karyotypic progression in the SV40 transfected cell line SVG during prolonged passage in vitro.

Transfection of primary cultures of human cells with origin of replication deficient SV40 DNA has been carried out by others to generate in vitro models of malignant transformation in vivo. The present work describes progressive alterations in karyotype and phenotype in one such transfected (neuroglial) cell line (SVG). After repeated passage, recognisable marker chromosomes evolved. These may be related to karyotypic anomalies found in human glial tumors. Accompanying the evolution in karyotype were changes in phenotype. Although presaging malignant transformation, these stopped short of actual tumorigenicity.

Animals↗

PubMed1989

1-Methyl-2-nitrosoimidazole: cytotoxic and glutathione depleting capabilities.

We tested 1-methyl-2-nitrosoimidazole (INO), the two electron reduction product of 1-methyl-2-nitroimidazole (INO2) for its in vitro cytotoxicity and glutathione (GSH) depleting capabilities. The half life of INO was shown to be dependent on cell concentration above 10(5) cells/ml, decreasing with increasing cell concentration up to 2 X 10(6) cells/ml. For a 10-fold decrease in cell concentration, from 10(6) to 10(5) cells/ml, the toxicity curve shifted 10-fold towards lower concentrations. At 10(6) cells/ml, INO depleted GSH, in the range of concentrations where toxicity was observed, down to a plateau of 15% of the control level at a concentration of 100 microM INO. Oxidized glutathione (GSSG) levels were not elevated significantly above control cultures at this concentration. INO2, 1000 microM, did not deplete GSH under similar exposure conditions while 2-hydroxylamino-1-methylimidazole (INHOH) depleted GSH minimally at this same concentration. The nitroso intermediate may play a central role in the toxicity and GSH depleting capabilities of 2-nitroimidazoles in mammalian cells.

Animals↗

PubMed1989

NLP-1: a DNA intercalating hypoxic cell radiosensitizer and cytotoxin.

The 2-nitroimidazole linked phenanthridine, NLP-1 (5-[3-(2-nitro-1-imidazoyl)-propyl]-phenanthridinium bromide), was synthesized with the rationale of targeting the nitroimidazole to DNA via the phenanthridine ring. The drug is soluble in aqueous solution (greater than 25 mM) and stable at room temperature. It binds to DNA with a binding constant 1/30 that of ethidium bromide. At a concentration of 0.5 mM, NLP-1 is 8 times more toxic to hypoxic than aerobic cells at 37 degrees C. This concentration is 40 times less than the concentration of misonidazole, a non-intercalating 2-nitroimidazole, required for the same degree of hypoxic cell toxicity. The toxicity of NLP-1 is reduced at least 10-fold at 0 degrees C. Its ability to radiosensitize hypoxic cells is similar to misonidazole at 0 degrees C. Thus the putative targeting of the 2-nitroimidazole, NLP-1, to DNA, via its phenanthridine group, enhances its hypoxic toxicity, but not its radiosensitizing ability under the present test conditions. NLP-1 represents a lead compound for intercalating 2-nitroimidazoles with selective toxicity for hypoxic cells.

Animals↗

PubMed1989

Deficient activation by a human cell strain leads to mitomycin resistance under aerobic but not hypoxic conditions.

Two non-transformed human skin fibroblast strains, GM38 and 3437T, were found to be more sensitive to the bioreductive alkylating agents mitomycin C (MMC) and porfiromycin (PM) under hypoxic compared to aerobic conditions. One of these strains, 3437T, was 6-7 times more resistant to these agents under aerobic exposure conditions, but was identical in sensitivity to the normal strain, GM38, under hypoxic conditions. Aerobic 3437T cells demonstrated no increased resistance to cisplatin compared to the normal strain, arguing against enhanced ability to repair DNA interstrand cross-links as the underlying explanation for the mitomycin resistance. The aerobic resistance of 3437T was not altered by dicumarol, an inhibitor of the enzyme DT-diaphorase which is believed to be involved in aerobic activation of MMC and PM. Dicumarol did increase the resistance of GM38, but not to the same level of resistance demonstrated by 3437T. These results suggest that the aerobic MMC and PM resistance of 3437T may arise, in part, from a deficiency in DT-diaphorase activity. The identical sensitivities under hypoxic conditions indicate that drug activation pathways operative in the absence of oxygen are similar in both the normal and 3437T cells.

Biotransformation↗

PubMed1988

Oxygen and exposure kinetics as factors influencing the cytotoxicity of porfiromycin, a mitomycin C analogue, in Chinese hamster ovary cells.

Some factors affecting the cytotoxicity of porfiromycin (PM), an analogue of mitomycin C (MMC), were investigated in suspension cultures of wild-type (AA8-4) and repair-deficient (UV-20) Chinese hamster ovary cells. Oxygen was an important modulator of PM toxicity in AA8-4 cells. The aerobic toxicity was significantly less, and toxicity under extremely hypoxic conditions was significantly greater for PM than MMC. Porfiromycin cytotoxicity at intermediate O2 levels was similar to that observed previously for MMC. While the aerobic/hypoxic ratio was greater for PM than MMC, survival at intermediate oxygen concentrations could limit the therapeutic utility of these drugs as adjuncts to radiotherapy. Ascorbic acid was found to increase the aerobic, but not hypoxic, cytotoxicity of PM in AA8-4 cells, as was observed previously for MMC. Investigation of various exposure times and drug concentrations revealed that drug toxicity for both aerobic and hypoxic cells was dependent on the product of drug concentration and time, and that the aerobic/hypoxic differential observed in AA8-4 cells was constant over a broad range of exposure conditions. The sensitivity of UV-20 cells was also a linear function of concentration and time, but no aerobic/hypoxic differential was observed in these cells. It is suggested that the sensitivity of UV-20 to PM and MMC, and its lack of an hypoxic/aerobic differential could result from lethality being due to a different lesion than in wild-type cells.

Animals↗

PubMed1988

Preparation, toxicity and mutagenicity of 1-methyl-2-nitrosoimidazole. A toxic 2-nitroimidazole reduction product.

1-Methyl-2-nitrosoimidazole (INO), the 2-electron reduction product of 1-methyl-2-nitroimidazole (INO2), was prepared by electrochemical reduction of INO2 to 2-hydroxylamino-1-methyl-imidazole (INHOH), followed by back oxidation with iodine. Although stable in crystalline form, INO reacted in water, phosphate-buffered saline, and mammalian cell growth medium. Half-lives for decay were determined by UV-visible spectroscopy. INO was found to be highly toxic towards Chinese hamster ovary (CHO) cells, concentrations of 10-60 microM producing significant cytotoxicity. The rate of INO decay was found to be increased in the presence of CHO cells. INO was also toxic and mutagenic towards Salmonella typhimurium TA-100. When compared on a molar basis to the parent nitro compound INO2, and the 4- and 6-electron reduction products INHOH and 2-amino-1-methylimidazole (INH2), INO was by far (two orders of magnitude) the most toxic under aerobic conditions. These results suggest that the nitroso reduction product of 2-nitroimidazoles may be the reduced species responsible for hypoxic cell selective toxicity of 2-nitroimidazoles.

Animals↗

PubMed1988

Molecular mechanisms for the hypoxia-dependent activation of 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233).

The reduction of the hypoxic cell toxin 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233) was investigated using pulse radiolysis, radiation chemical reduction, and xanthine oxidase. Evidence was found that the one-electron reduction product of the parent compound is an oxidizing radical that caused single- and double-strand breaks in plasmid DNA and that produced a malondialdehyde-like thiobarbituric acid adduct from 2-deoxy-D-ribose. Possible forms of the reactive radical, either carbon- or nitrogen-centered, are suggested. The "natural" lifetime of the radical was sufficiently long that it could diffuse over significant distances within hypoxic cells and thus inflict oxidative damage on cellular targets. The radical reacted with O2 at a rate comparable to those of the nitroimidazoles misonidazole and metronidazole. Thus, the selectivity for hypoxic cells is probably due to the elimination of "futile" reduction when the cellular oxygen concentration is sufficiently low.

Carbon Dioxide↗

PubMed1987

5-Fluorouracil infusions and fractionated doses of radiation: studies with a murine squamous cell carcinoma.

The present investigation describes the effects on a murine squamous cell tumor of combined treatment using radiation and 5-Fluorouracil (5FU), with emphasis on 5FU infusions. The tumor, SCC VII/To, was grown intramuscularly in the hind legs of C3H mice. Radiation was given locally with 100 kVp X rays either alone or in combination with 5FU by i.p. bolus injections or 4-14 day infusions using subcutaneously implanted mini-osmotic pumps. Studies with radiation alone indicated regrowth delay increased with total dose. This increase was less for fractionated than single doses. The effects of 5FU alone were compared using i.p. injections or 4, 7 or 14 day infusions. Tumor response to single i.p. bolus injections or 4 day infusions were not significantly different. Up to total drug doses of 200 mg/kg, 14 day infusions were least effective on regrowth delay, 4 day infusions were intermediate and 7 day infusions were most effective. Above total drug doses of 200 mg/kg, effects of 14 day infusions on regrowth delay increased rapidly. The LD50 for single i.p. bolus injections and 7 day infusions were similar, 230 and a total drug dose of 270 mg/kg, respectively. When a 7 day infusion of 5FU (133 mg/kg) was combined with increasing total radiation doses (1 or 5 fractions), the increase in regrowth delay was additive. Combining a fractionated dose of 5 Gy per day for 5 days (5/5 Gy) with increasing total drug doses of 5FU (single i.p. bolus injections or 4, 7 or 14 day infusions) resulted in regrowth delays that were dependent on the total dose of 5FU. Administering a 133 mg/kg dose of 5FU (via a single i.p. bolus injection or 7 day infusion) starting 2 days before, during, or immediately after 5/5 Gy gave the same regrowth delay, indicating no effect of drug sequencing. In conclusion, the above data indicate that (a) 5FU infusions (greater than 4 days) are more effective than 5FU injections on regrowth delay and (b) combinations of 5FU and radiation, produce an additive tumor response, which occurs independent of mode, schedule, and time of 5FU administration, and is dependent on 5FU total dose.

Animals↗

PubMed1987

Mitomycin C pharmacokinetics in patients with recurrent or metastatic colorectal carcinoma.

The pharmacokinetics of mitomycin C as a single agent have been determined in 25 treatment courses given to 18 patients with recurrent or metastatic colorectal carcinoma using a high performance liquid chromatography (HPLC) assay to analyze plasma and urine samples. The plasma pharmacokinetics conformed to a two-compartment linear model in 21 of 25 courses monitored with a mean t1/2 lambda 1 of 9.8 +/- 1.2 (SEM) min and mean t1/2 lambda z of 64.1 +/- 8.9 (SEM) min. The large variation observed in t1/2 lambda z was not related to dose or treatment, but an interaction of these two factors approached significance (p = 0.057). Renal excretion in the 12 courses in which it was determined averaged only 2.3% of the total administered dose during the first 4 h monitored and no mitomycin C metabolites were detected in plasma or urine by the HPLC technique used. The most common toxicity, thrombocytopenia, did not correlate with t1/2 lambda z or the area under the curve. This may be due to a failure to monitor active metabolites of mitomycin C; other factors besides plasma drug concentrations that mediate toxicity towards marrow elements; or the small number of courses associated with thrombocytopenia (less than 100,000/mm3). Our study indicates that an interaction of drug dose and treatment course may be associated with increasing t1/2 lambda z; the renal clearance contributes a small component of mitomycin C elimination; metabolites of mitomycin C cannot be detected by the present HPLC technique; and routine monitoring of mitomycin C using present methods cannot be recommended for clinical use to predict toxicity.

Aged↗