High-dose mitomycin-C with autologous bone marrow transplantation in patients with refractory malignancies. Influence of dose schedule on pharmacokinetics and nonhematopoietic toxicities

Thirteen courses of high-dose mitomycin-C with autologous bone marrow transplantation (ABMT) were administered to 12 patients. Four dose schedules were evaluated: A) 60 mg/M2 X 1, 60-min infusion; B) 30 mg/M2/day X 2, 15-min infusion; C) 30 mg/M2/day X 2, 60-min infusion; D) 15 mg/M2/day X 4, 60-min infusion. Pharmacokinetic studies using HPLC technique were done in nine patients. All patients have since died and autopsies were performed in nine patients. Two major nonhematopoietic toxicities were encountered and were dose-schedule dependent: hemorrhagic colitis (six of six courses in Schedules A and B; two of seven in Schedules C and D), and hepatic dysfunction (five of six in Schedules A and B; two of seven in Schedules C and D). Histopathologic evidence of venocclusive disease of the liver was present in four of five autopsies in Schedules A and B, and two of four in Schedules C and D. One patient died as a result of liver failure associated with submassive hepatic necrosis. Saturation kinetics described by other investigators cannot be confirmed by our pharmacokinetic analyses in nine patients. Severe nonhematopoietic toxicities of mitomycin-C were found at three times the conventional dose; thus, this drug is assessed as not being clinically useful as a single agent in ABMT.

Characterization of a simian virus 40-transformed Fanconi anemia fibroblast cell line

We have characterized a SV40-transformed human fibroblast cell line (GM6914) derived from a patient with Fanconi anemia (FA) in order to establish its usefulness for biochemical and genetic experiments, including DNA-mediated gene transfer. GM6914 cells have a growth rate similar to that of SV40-transformed normal human fibroblasts and an indefinite lifespan in culture. As has been established for other FA cell types, GM6914 cells have an increased sensitivity to DNA-crosslinking agents such as mitomycin C (MMC). The D10 for GM6914 cells is 8 times lower than for equivalent controls. GM6914 cells also have an elevated frequency of spontaneous chromosome aberrations and this frequency can be increased by MMC concentrations which show no effect on control cells. Genetic complementation studies with lymphoblasts derived from two affected sibs of the donor of GM6914 cells show that GM6914 belongs to FA complementation group A. In DNA-transfection studies using plasmid pRSVneo, colonies of GM6914 cells resistant to the drug G-418 were observed at frequencies ranging from 1.7 to 16 X 10(-4), values similar to those observed with several other SV40-transformed human cell lines. GM6914 should be a useful recipient cell line in experiments using DNA-mediated gene transfer to clone the normal allele of the gene which is defective in FA complementation group A. GM6914 would also be an excellent cell line for studies on mutagenesis, recombination and repair using plasmid vectors.

Chromosome aberrations in rat liver cells and bone marrow cells following treatment in vivo with mitomycin C

The clastogenic potential of mitomycin C (MMC) was studied in rat liver cells and bone marrow cells. Male Sprague-Dawley rats were partially hepatectomized and treated with a single i.p. dose of MMC (3.5 mg/kg body weight) 7 or 24 h after the operation. Non-hepatectomized rats were also treated with the same dose of MMC 7 or 24 h after the mutagenic treatment; liver and bone marrow cells were isolated from hepatectomized rats (31 h after the operation) and bone marrow cells only from non-hepatectomized animals. The results show that, if MMC was administered 7 h before the isolation of cells, the induction was more efficient in liver cells than in bone marrow cells. At this sampling time, there was no consistent difference between the frequencies observed in bone marrow cells from hepatectomized and non-hepatectomized rats. An increase was observed in both tissues 24 h after the mutagenic treatment. At this sampling time, the effect was significantly higher in the bone marrow cells from non-hepatectomized animals than in the liver cells and bone marrow cells from hepatectomized animals. No significant difference between the two cell types from hepatectomized rats was observed. Different factors related to the cytostatic properties of MMC and/or to cell kinetics in the two cell types, probably affected by the surgical operation, may account for the differences in the yield of chromosomal damage.

Characterization of mitomycin C-induced gastrointestinal damage: changes in the gastric absorption of drugs in rats

The effect of mitomycin C (MMC) pre-administration intravenously on the absorption of drugs from rat stomach has been examined by means of the in-situ loop technique. 48 h after the MMC-treatment, the absorption of salicylic acid, aspirin and sulphanilic acid was not influenced but that of sulphanilamide was significantly increased compared with the control. At 96 h, a differential effect of MMC on the absorption of each drug was seen: the absorption of weakly acidic drugs was significantly decreased while that of bases and strong sulphonic acid increased. The decreased absorption of salicylic acid and aspirin correlated with the reduced gastric mucosal blood flow. At 96 h there were severe haemorrhagic lesions in the gastric mucosae. The increase in absorption of poorly absorbed drugs could be ascribed to the increased permeability of the blood-gastric epithelium barrier as was evidenced by leakage of Evans Blue.

Mitomycin C skin toxicity studies in mice: reduced ulceration and altered pharmacokinetics with topical dimethyl sulfoxide

A series of toxicologic and pharmacokinetic studies were performed in BALB/c mice administered intradermal (ID) mitomycin C (MMC) at doses of .015 to 0.25 mg. Dose-dependent skin ulcers were produced at clinically relevant MMC dose levels of .05 and .075 mg (3.6 to 10.7 mg/m2). These doses produced peak ulcers of 0.15 to 0.22 cm2, respectively, one to five days after injection. The integrated ulcer area X time values (area under the curve [AUC] ulceration) were 0.89 and 3.11 cm2 X d. A large number of local pharmacologic adjuvants were found to be ineffective at reducing MMC ulceration after proximal ID injection. These included diphenhydramine, catalase, heparin, hyaluronidase, hydrocortisone, cysteine, N-acetylcysteine, lidocaine, vitamin E, and superoxide dismutase. Also, neither topical heating nor cooling of skin reduced MMC ulcerations. In contrast, a single topical application of a 100% dimethyl sulfoxide (DMSO) solution completely prevented 0.025 mg MMC-induced skin ulceration and significantly reduced .075 mg MMC ulceration (P less than .05 by multiple range tests). Topical DMSO also altered the disposition of ID MMC in mouse skin but not in plasma. Unexpectedly, the DMSO applications slowed MMC elimination from the skin. DMSO significantly increased the AUC for MMC in skin from 0.89 to 2.25 ng/h/mL of tissue (P less than .05). DMSO did not alter the degree of protein binding in skin tissue nor the in vitro chemical stability of MMC in skin tissue homogenates. These results show that experimental MMC-induced skin ulcers in mice can be ameliorated with an immediate application of topical DMSO. This effect is not due to enhanced systemic drug uptake, but may be due to reduced reactivity of MMC with target cellular nucleophiles.

Fumaric acid enhances DNA synthesis of rat hepatocytes by counteracting the toxicities of mitomycin C and aflatoxin B1

The effect of fumaric acid was examined on DNA synthesis in hepatocytes or hepatoma cells from rats treated with toxic agents. Male Donryu rats were injected with mitomycin C or aflatoxin B1, singly or in combination with fumaric acid. After a specified period, hepatocytes were isolated from the liver by the collagenase perfusion method and placed in culture, and their activities for DNA synthesis were measured. The iv injection of rats with mitomycin C (0.5 mg/kg) reduced the semiconservative DNA synthesis of the hepatocytes, but simultaneous dosing of fumaric acid (40 mg/kg) enhanced the recovery of the DNA synthesis. The DNA synthesis of hepatoma cells, a 3'-methyl-4-(dimethylamino)azobenzene-induced transplantable cell line growing in the abdominal ascites of rats, was also reduced by the iv injection of mitomycin C but, in contrast to that of the hepatocytes, was little influenced by the simultaneous dosing of fumaric acid. The ip injection of fumaric acid also reduced the toxicity of aflatoxin B1 (0.25 mg/kg, ip), preventing the reduction of DNA synthesis as well as the occurrence of nuclear degenerative changes in the aflatoxin B1-exposed hepatocytes.

Sensitivity to DNA-damaging agents and mutation induction by UV light in UV-sensitive CHO cells

Three UV-sensitive (UVs) mutants isolated from a CHO cell line were analyzed for survival after exposure to H2O2, EMS, MMC, CCNU, X-rays and for mutation induction after UV-irradiation. The UVs mutants showed normal sensitivities to EMS and H2O2, whereas they were hypersensitive to the bifunctional alkylating agents MMC and CCNU and to hypoxic X-irradiation. Compared to parental cells, one of the UV-sensitive clones showed approximately 3- and 7-fold enhancement in the mutagenic response per unit UV dose for 6-thioguanine and ouabain resistance, respectively.

Effect of mitomycin C on the neural tube defects of the curly-tail mouse

Around 60% of the mouse mutants called curly-tail, have tail aberrations in the form of a coil or a kink, with or without lumbosacral spina bifida, and rarely, exencephaly. These neural tube defects (NTD) are the result of an incompletely penetrant recessive gene. A single injection of various doses (1-6 mg/kg) of the DNA inhibitor mitomycin C was given to pregnant curly-tail mice on day 7, 8, or 9 of gestation, and its effect on the NTD of the embryos was noted. No dose used was lethal to the embryo. When given on day 7 or day 8, mitomycin C markedly increased the number of exencephalics, and additionally, on day 8, it reduced the number of posterior abnormalities. However, on day 9, no exencephaly was produced, and there was a drastic reduction in the number of tail and spinal defects, the overall incidence of NTD being as low as 15% with 2 mg/kg. A twofold effect of mitomycin C on the curly-tail embryos was thus observed--according to the time in development it was administered, firstly, a teratogenic effect, and later, a "remedial" or preventive effect.

Inhibition of cyclophosphamide and mitomycin C-induced sister chromatid exchanges in mice by vitamin C

Ascorbic acid (vitamin C) is known to act as an antimutagen and anticarcinogen in several test systems. However, there is no report of its effect on carcinogen-induced chromosomal damage in vivo in animals. The present study was performed to determine whether or not ascorbic acid affects sister chromatid exchanges (SCEs) induced by cyclophosphamide (CPA) and mitomycin C (MMC) in bone marrow and spleen cells in mice. The results indicate that ascorbic acid per se did not cause a significant increase in SCEs in mice. However, increasing concentrations of ascorbic acid caused decreasing levels of CPA- and MMC-induced SCEs in both cell types in vivo. At the highest concentration of ascorbic acid, 6.68 g/kg, approximately 75 and 40% SCE inhibition in both cell types was noted for CPA and MMC, respectively. Likewise, under in vivo/in vitro conditions (exposure of animals to experimental chemicals followed by culturing of cells), ascorbic acid caused a dose-related decrease in CPA- and MMC-induced SCEs, up to a dose of 3.34 g/kg At this concentration, approximately 50% CPA- and MMC-induced SCE inhibition was observed in both cell types studied. Thus, ascorbic acid acts as an anti-SCE agent in both in vivo and in vivo/in vitro conditions in mice.

Treatment methods for extravasations of chemotherapeutic agents: a comparative study

A rat model was used to compare early surgical intervention with injectable and topical antidotes with regard to their effectiveness in preventing cutaneous ulcers that were caused by intradermal injections of vesicant chemotherapeutic agents. The (animals) rats received bilateral flank injections of doxorubicin, vincristine, actinomycin D, mitomycin C, or carmustine (BCNU) in concentrations that were comparable to concentrations used for human patients; after the injections they underwent debridement at various intervals or received immediate applications of selected antidotes. Many "antidotes" which were frequently used, were not effective in limiting the size of the ulcer and in producing rapid healing of ulcers that were caused by experimental vesicant extravasations. Early surgical debridement was the most effective method of decreasing vesicant ulcer size and facilitating rapid ulcer healing of all the interventions tested.

Adaptation-like response to the chemical induction of sister chromatid exchanges in human lymphocytes

Experiments have been performed to determine whether human lymphocytes in primary cultures can show an "adaptive" response to the induction of cellular lesions (manifested as a production of sister chromatid exchanges, SCEs) as previously found in bacteria and established human and mammalian cell lines. Human lymphocytes were pretreated with various subtoxic concentrations (5-50 ng/ml) of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) once every 6h for 72 h, and subsequently challenged by a high dose (4 micrograms/ml) of MNNG. The lymphocytes in MNNG-challenged cultures had the lowest frequency of SCEs when pretreated with 10 ng/ml MNNG. Further cross-resistance study revealed that repeated pretreatments of lymphocytes with 10 ng/ml MNNG for 72 h can render the cells resistant to the induction of SCEs by the following challenge with a high dose of MNNG, but not of mitomycin C or ethyl nitrosourea. The data also suggest variations in the degree of the adaptation-like response among individuals.

Carcinogenesis in mammalian urothelium: changes induced by non-carcinogenic substances and chronic indwelling catheters

Carcinogenesis in urinary bladders may not be represented by a continuum of pathological lesions beginning with papillary tumors or flat dysplasias/atypias. In a previous experiment, sterile water and saline continuously infused via catheters connected to ALZA mini-pumps were shown to induce papillary urothelial lesions indistinguishable from tumors considered to be carcinomas in most histological classification schemes. The animals in the initial experiment were followed for relatively brief periods which did not allow for determination of potential reversibility of the process and did not distinguish the effects of the catheters versus those of the infused substances. The present study was designed to control for these variables. Rats were divided into seven groups to examine the urothelial changes after: surgery alone, continuous infusion of the sterile water and mitomycin C, and chronic indwelling catheters with and without infusion. The results indicated that chronic irritation with indwelling catheters was a strong stimulus for the induction of urothelial neoplasms and that continuous infusion of certain substances, even sterile water, might play a small role in the process of carcinogenesis. Comparing the frequencies of papillary urothelial tumors appearing after brief exposure to sterile water and catheters in the initial experiment (75 per cent) and papillary lesions appearing long after removal of the sterile water and catheters in the current study (0 per cent) indicates that these lesions are reversible and probably not neoplastic.

Spontaneous and induced chromosomal aberrations and gene mutations in human lymphoblasts: mitomycin C, methylnitrosourea, and ethylnitrosourea

The concentration-dependent mutagenic, clastogenic, and cytocidal activities of mitomycin C (MC), methylnitrosourea (MNU), and ethylnitrosourea (ENU) were measured in the human lymphoblast cell line TK6. For treatments resulting in fewer than 2 lethal hits, MNU, ENU, and MC gave rise to apparently linear dose-response curves for gene mutations (hgprt and tk genes) as well as for chromosomal aberrations. The numbers of induced mutants at the tk and hgprt loci were similar between the two loci for each compound. However, the ratio of mutagenic activity relative to the clastogenic activity (aberrations/cell) was lowest for mitomycin C, intermediate for methylnitrosourea, and highest for ethylnitrosourea. These results confirm in human cells the general observation that the processes of mutagenesis and clastogenesis are nonidentical: compounds vary independently in their mutagenic and clastogenic potentials.

The influence of a protein synthesis inhibitor on sister-chromatid exchange in the plant Vicia faba

Cycloheximide strongly antagonizes the induction of sister-chromatid exchange by mitomycin C in Vicia faba root tips. This behavior is analogous to that previously observed in mammalian cells (Sono and Sakaguchi, 1981) and suggests that newly synthesized protein is also required for recombination between sister DNA molecules in plants. Conversely hydroxyurea is shown to increase the frequency of both spontaneous and induced sister-chromatid exchange. Based on these results, possible mechanisms underlying sister-chromatid exchange formation in plants are discussed with special emphasis on the absence of DNA polymerase beta in somatic tissues.

Effect of cancer chemotherapeutic drugs on radiation-induced lung damage in mice

The effect of adriamycin (ADM), bleomycin (BLM), cyclophosphamide (CTX), 5-fluorouracil (5-FU), methotrexate (MTX), mitomycin C (MM-C) and cis-diamminedichloroplatinum(II) (cis-DDP) on the radiation-induced lung damage in mice was assessed by the ventilation rate (VR) and the lethality. Single drug doses were administered 15 min before graded single doses of irradiation and at different intervals from 28 days before to 28 days after fixed radiation doses. ADM, BLM and CTX administered 15 min before irradiation enhanced the radiation response with dose effect factors (DEF) of 1.46, 1.56 and 2.35, respectively. The effect of MM-C presented a complex picture. The drug had no effect at administration 15 min before 14-20 Gy, but enhanced the radiation response if given 15 min before 6-12 Gy (DEF = 1.57). The radiation-modifying effect of ADM, BLM, CTX and MM-C was most pronounced when the drugs were given 15 min before irradiation. The effect of ADM was present when administered from 7 days before to 7 days after irradiation. BLM and CTX enhanced the radiation response at administration from 24 h before to 3 days after irradiation, and the effect of MM-C was observed when the drug was given from 24 h before to 24 h after irradiation. 5-FU, MTX and cis-DDP had no effect on the radiation response at any of the investigated intervals.

Mitomycin C-induced damage and repair in human and pig lymphocytes

Human and pig lymphocytes were used to compare the chromosomal sensitivity to MMC and the efficiency of repair of MMC-induced DNA adducts. No significant interspecies differences were found. The results obtained show that SCE frequencies are linearly correlated with MMC doses. During the G0 period there are indications that lymphocytes may half-repair the DNA-interstrand crosslinks transforming bi- into mono-adducts. SCEs induced by MMC decrease to near control levels in the second cell cycle. Therefore, most MMC lesions responsible for SCEs should be repaired between the moment in the first S phase in which they induce the exchanges and the onset of the second S period.

Mutual neoplastic promotion by instillation of mitomycin C and cauterization on rat bladder urothelium

The authors studied the effect of bladder instillation of mitomycin C (MMC), a potential carcinogen, on the duration and severity of the hyperplasia induced by transurethral fulguration. This experimental system may simulate closely the intravesical chemoprophylaxis of MMC after transurethral resection of bladder cancer. Physiologic saline or MMC was instilled into the rat bladder once on the day of, or 3 or 7 days after cauterization. In all groups instilled with physiologic saline the changes were reversed by day 14. On the other hand, five of nine MMC-instilled rats developed papillary lesions, and three of these had mild dysplastic epithelium on day 84. Under the scanning electron microscope, the animals of these groups showed pleomorphic microvilli on the luminal surface of the regenerative cells on days 10 and 14 after cauterization. These results may indicate the mutual neoplastic promotion by instillation of MMC and cauterization to a certain extent.

In vitro induction of sister chromatid exchanges and chromosomal aberrations in peripheral lymphocytes of the oyster toadfish and American eel

A series of experiments was conducted to characterize the proliferation of oyster toadfish lymphocytes in medium containing 5-bromodeoxyuridine (BrdUrd) and to determine the effectiveness of cytogenetic endpoints for assessing the genotoxic effects of in vitro exposure of toadfish and eel lymphocytes to known mammalian clastogens. Although the rate of proliferation of toadfish lymphocytes was low compared to that of mammalian lymphocytes, the effects of increasing BrdUrd concentrations were similar, in that proliferation exhibited a concentration-dependent inhibition for concentrations above 10 microM BrdUrd, and sister chromatid exchange (SCE) frequencies exhibited a concentration-dependent increase for concentrations above 100 microM BrdUrd. Mitomycin C (MMC) and ethylene dibromide (EDB) induced concentration-dependent increases in chromatid-type exchange and SCE frequencies with least effective concentrations (control SCE frequency divided by the slope of the least-squares line) for SCE induction by MMC (6.8 X 10(-9) M) and EDB (2.6 X 10(-4) M) that were comparable to or slightly lower than those that have been obtained with mammalian in vitro systems. In vitro exposure of toadfish lymphocytes to dimethoate (DIM) induced a concentration-dependent increase in SCE frequency with a least effective concentration of 2.8 X 10(-3) M that was much higher than that observed with mammalian in vitro systems. In vitro exposure of American eel lymphocytes to MMC also induced a concentration-dependent increase in the frequency of chromosomal aberrations and SCEs with a least effective concentration for SCE induction of 2.0 X 10(-9) M. These results indicate that cytogenetic endpoints can be effectively scored with cultured lymphocytes from these and perhaps other fish species with comparable karyotypes that contain an average of at least 0.07 pg DNA/chromosome.

Antitumor activity and toxicity in animals of BMY-25282, a new mitomycin derivative

BMY-25282, 7-N-(dimethylamino methylene)mitomycin C, is one of a novel series of amidino mitomycin derivatives. Some of these were discovered as intermediates in a synthetic program being conducted to find improved procedures for modifying the structure of mitomycin C (MMC). Markedly superior in vivo antitumor effects have been observed with BMY-25282 compared to MMC in initial tests against i.p.-implanted P388 leukemia and B16 melanoma. When administered i.v. to mice bearing s.c. B16 melanoma, BMY-25282 was also superior to MMC. The derivative was fully active against a line of L1210 leukemia which was partially resistant to MMC treatment but had little or no activity against a line of L1210 fully resistant to MMC. It is also 2 to 4 times more potent than MMC based on a comparison of doses required to achieve optimum antitumor effects. The superior antitumor efficacy of BMY-25282 over MMC against both i.p. and s.c. B16 melanoma was maintained when the drug was given in pluronic acid formulation. Against P-388 leukemia, however, the efficacy of the drugs was equivalent when BMY-25282 was administered in the pluronic vehicle. In an in vitro clonogenic assay involving freshly explanted human tumors, BMY-25282 was consistently more potent in cytotoxic effects than MMC. With human colorectal carcinoma samples, BMY-25282 was 13.8 times more potent than MMC. The i.v. 50% lethal dose values of BMY-25282 and MMC in C57BL/6 X DBA/2 F1 mice were 2.1 mg/kg and 8.6 mg/kg, respectively. Leukopenic effects of the drugs in mice were comparable at doses up to their respective 50% lethal dose values. Hematology studies in ferrets revealed a similar pattern of depression and recovery of lymphocytes, neutrophils, and platelets for BMY-25282 and MMC; however, with BMY-25282 there was earlier recovery of platelet counts. BMY-25282 is being further developed toward possible clinical trial.

Persistence of sister chromatid exchanges and in vitro morphological transformation of Syrian hamster fetal cells by chemical and physical carcinogens

The induction of neoplastic cell transformation is closely associated with DNA alterations which occur shortly after carcinogen exposure. Sister chromatid exchange (SCE) formation is a sensitive indicator of carcinogen-DNA interaction and correlates with the induction of morphological cell transformation. The persistence of lesions generating SCE produced by chemical and physical carcinogens and its relevance to the induction of morphologic transformation was evaluated in coordinated experiments with cultured Syrian hamster fetal cells (HFC). Exponentially growing HFC were exposed for 1 h to benzo[a]pyrene (BP), methyl-methanesulfonate (MMS), cis-platinum (II) diaminedichloride (cis Pt II), N-methyl-N'-nitrosourea (MNU), mitomycin C (MMC), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), N-acetoxy-2-fluorenyl-acetamide (AcAAF) or u.v. light irradiated. Cells were incubated for 24 h with 5-bromodeoxyuridine (BrdUrd) required for SCE visualization at 1, 24 and 48 h after carcinogen exposure. The induction of morphological transformation was determined on the quantitative colony assay at 6 days after carcinogen treatment. SCE analysis demonstrates that for a period of 48 h after carcinogen exposure, during which time the cells undergo at least four replicative cycles, DNA damage generating SCE induced by all chemical carcinogens either persisted or was partially removed, whereas u.v.-induced lesions were completely removed. An elevated SCE frequency persisted after two additional cell cycles after treatment with BP, AcAAF or MMC without increased cell lethality as compared to other carcinogens whose lesions were completely eliminated during the same period. Although a correlation between the persistence of SCE and the induction of transformation was not observed for all carcinogens, this study illustrates that DNA damage generating SCE can persist over several replicative cycles, thus raising the possibility that lasting DNA alterations are important for the induction of neoplastic cell transformation.

Sister-chromatid exchanges and cell-cycle kinetics in human lymphocyte cultures exposed to alkylating mutagens: apparent deformity in dose-response relationships

Experiments have been carried out using human whole-blood cultures to determine the effects of sampling times and of the duration of 5-bromodeoxyuridine (BrdUrd) treatment before fixation on sister-chromatid exchange (SCE) frequencies following exposure to mitomycin C (MMC). Cells were pulse treated for 1 h with 3 X 10(-6) M MMC at G1, and then sampled at 4-h intervals up to 88 h after stimulation of cultures with phytohemagglutinin (PHA). Results showed that this MMC treatment induced a 5-6 h proliferation delay per cell cycle, and that SCE frequencies first increased with time of fixation, peaking at 68 h, and then decreased. When cells were similarly treated with MMC, but subsequently exposed to BrdUrd for various times before fixation of cultures at 72 h, the SCE frequencies markedly increased with increasing durations of BrdUrd incubation times. These data indicate that, in mutagen-treated cultures, lymphocytes having relatively longer cell-cycle times show a higher mean frequency of SCEs. In a subsequent experiment, cells were treated for 1 h with increasing doses of MMC or 4-nitroquinoline 1-oxide (4NQO) at 0, 24, or 48 h, and then fixed at 72 h after PHA stimulation. Results showed that the optimal treatment times at which the agents could most efficiently produce SCEs were different for MMC and 4NQO, and that the dose-response curves tended to 'bend down' at very high doses; that is, treatments with very high doses induced smaller than expected numbers of SCEs. However, cells similarly treated with very high doses showed a higher, expected frequency of SCEs when sampled at 84 h, but again had a lower than expected SCE frequency when fixed at 96 h. The results indicate that there is an optimal time for sampling at which one can observe the maximum increase in SCE frequencies following mutagen exposure, and strongly suggest that the higher the dose, the later the optimal sampling time. Because of the apparent deformity of dose-response curves obtained after various treatments and sampling times, it seems necessary that extra fixation-time points be included in test protocols so as to avoid false negatives or confirm possible positives.

Mitomycin-induced hemolytic uremic kidney. An experimental model in the rat

Hemolytic uremic syndrome (HUS) reported in some patients treated for cancer with mitomycin is of unknown pathogenesis, and evidence implicating mitomycin is inconclusive. To determine whether mitomycin can induce direct renal damage, left kidneys in Lewis rats were perfused with mitomycin (60-4000 micrograms). Control rats received perfusions of saline only. Renal tissue was examined from 1 hour up to 1 month later. In 29 of 31 rats left renal disease developed: in 9 (mitomycin, 1000-4000 micrograms), severe cortical infarction; in 20 (mitomycin, 60-500 micrograms), lesions indistinguishable from human HUS. Glomerular endothelial damage was the earliest detectable abnormality, followed by platelet accumulation and later capillary wall splitting typical of microangiopathy. Some kidneys had interlobular artery necrosis and thrombosis. Right kidneys were normal. In no rats in the control group (10) did HUS develop. Thus, mitomycin directly produced renal lesions indistinguishable from human HUS, which suggested a mechanism for injury seen in mitomycin-treated patients and provided a new model of HUS.

pH dependence of mitomycin C-induced cross-linking activity in EMT6 tumor cells

Mitomycin C (MC), a quinone-containing bioreductive alkylating agent, is cytotoxic to aerobic EMT6 tumor cells despite the fact that little bioactivation of MC occurs in EMT6 cell homogenates in the presence of O2. Because spontaneous activation of MC at acidic pH has been reported in chemical systems, aerobic EMT6 tumor cells were incubated in serum-free 2-(N-morpholino)ethanesulfonic acid or N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer at pH 5.7, 6.4, and 7.5 and exposed to MC for 2 h. As the extracellular pH was lowered, MC-induced DNA-DNA cross-linking, as measured by alkaline elution techniques, was enhanced. This effect was dose dependent at the three pH values tested. Measurement of intracellular pH by flow cytometric analysis indicated that the decrease in extracellular pH was paralleled by a fall in intracellular pH. The alteration of the extracellular pH had no effect on the colony-forming ability of control cells. The survival of cells treated with MC, however, was decreased as the pH was lowered. These data suggest that the intracellular and/or the extracellular pH is an important determinant of MC activity in aerobic EMT6 tumor cells.