Re-evaluation of the molecular pharmacology of mitomycin C

Enhancement of human bladder carcinoma cell chemosensitivity to Mitomycin C through quasi-monochromatic blue light (λ = 453 ± 10 nm)

Human urothelial bladder carcinoma (uBC) is the second most tumor entity of the urogenital tract. As far as possible, therapy for non-muscle invasive uBC takes place as resection of the tumor tissue, followed by intravesical chemotherapy or immunotherapy. Because of the high recurrence rate of uBC, there is a need for improved efficiency in the treatment. In the present in vitro study we have evaluated a new approach to enhance the cytotoxic efficiency of Mitomycin C (MMC), which is commonly used for intravesical treatment of uBC on the relevant urothelial cancer cell line RT112. For that we used quasi-monochromatic blue light (453 ± 10 nm) at its non-toxic dose of 110 J/cm2 as an additive stimulus to enhance the therapeutic efficiency of MMC (10 μg/ml). We found, that blue light exposure of RT112 cells led to a very strong increase in intracellular production of reactive oxygen species (ROS) and to a significant reduction (p < 0.05) of all function parameters of mitochondrial respiration, including basal activity and ATP production. Although not being toxic when used as a single impact, together with MMC blue light strongly enhanced the therapeutic efficiency of MMC in the form of significantly enhanced cytotoxicity via apoptosis and secondary necrosis. Our results clearly show that blue light, most likely due to its ability to increase intracellular ROS production and reduce mitochondrial respiration, increased the cytotoxic efficiency of MMC and therefore might represent an effective, low-side-effect, and success-enhancing therapy option in the local treatment of bladder cancer.

Topical versus interlesional mitomycin C in auricular keloids

BACKGROUND

The Keloid is an elevated fibrous scar that may extend beyond the borders of the original wound.

OBJECT

To compare between topical and intralesional mitomycin C in the treatment of auricular keloids.

PATIENTS AND METHODS

Prospective randomized study in which 40 patients with auricular keloids were included. The patients were divided into 2 groups, Group I included 32 patients who underwent topical mitomycin C application after the surgical removal of the auricular keloids, while Group II included 8 cases who underwent intra-lesional injection of mitomycin C after surgical removal of the auricular keloids.

RESULTS

The two groups showed no significant difference regarding patient or lesion criteria (p>.05). VSS decreased significantly from 10.63 and 11.0 down to 1.38 and 3.0 after treatment in the topical and intra-lesional groups respectively (p<.001). However, greater improvement and satisfaction was detected in the topical group.

CONCLUSION

Both topical and intra-lesional mitomycin C injection are effective methods in managing auricular keloids. However, better VSS scores and patient satisfaction are reported with topical administration.

Translesion DNA Synthesis and Reinitiation of DNA Synthesis in Chemotherapy Resistance

Many chemotherapy drugs block tumor cell division by damaging DNA. DNA polymerases eta (Pol η), iota (Pol ι), kappa (Pol κ), REV1 of the Y-family and zeta (Pol ζ) of the B-family efficiently incorporate nucleotides opposite a number of DNA lesions during translesion DNA synthesis. Primase-polymerase PrimPol and the Pol α-primase complex reinitiate DNA synthesis downstream of the damaged sites using their DNA primase activity. These enzymes can decrease the efficacy of chemotherapy drugs, contribute to the survival of tumor cells and to the progression of malignant diseases. DNA polymerases are promising targets for increasing the effectiveness of chemotherapy, and mutations and polymorphisms in some DNA polymerases can serve as additional prognostic markers in a number of oncological disorders.

Coupling High-Performance Thin-Layer Chromatography with Bacterial Genotoxicity Bioreporters

We present an innovative technological platform for monitoring the direct genotoxicity of individual components in complex environmental samples, based on bioluminescent Escherichia coli genotoxicity bioreporters, sprayed onto the surface of a high-performance thin-layer chromatography (HPTLC) plate. These sensor strains harbor plasmid-borne fusions of selected gene promoters of the E. coli SOS DNA repair system to the Photorhabdus luminescens luxABCDE gene cassette, and mark by increased luminescence the presence of potentially DNA-damaging sample components separated on the plate. We demonstrate an "on plate" quantifiable dose-dependent response to several model genotoxicants (without metabolic activation). We further demonstrate the applicability of the system by identifying as genotoxic specific components of HPTLC-separated influent and effluent samples of wastewater treatment plants, thereby alleviating the need for a comprehensive chemical analysis of the sample.

Sequential intravesical mitomycin plus Bacillus Calmette-Guérin for non-muscle-invasive urothelial bladder carcinoma: translational and phase I clinical trial

PURPOSE

To determine the safety and toxicities of sequential MMC (mitomycin C) + BCG (bacillus Calmette-Guérin) in patients with non-muscle-invasive bladder cancer (NMIBC) and explore evidence for potentiation of BCG activity by MMC.

EXPERIMENTAL DESIGN

A 3 + 3 phase I dose-escalation trial of six weekly treatments was conducted in patients with NMIBC. MMC (10, 20, or 40 mg) was instilled intravesically for 30 minutes, followed by a 10-minute washout with gentle saline irrigation and then instillation of BCG (half or full strength) for 2 hours. Urine cytokines were monitored and compared with levels in a control cohort receiving BCG only. Murine experiments were carried out as described previously.

RESULTS

Twelve patients completed therapy, including 3 patients receiving full doses. The regimen was well tolerated with no treatment-related dose-limiting toxicities. Urinary frequency and urgency, and fatigue were common. Eleven (91.7%) patients were free of disease at a mean (range) follow-up of 21.4 (8.4-27.0) months. Median posttreatment urine concentrations of IL2, IL8, IL10, and TNFα increased over the 6-week treatment period. A greater increase in posttreatment urinary IL8 during the 6-week period was observed in patients receiving MMC + BCG compared with patients receiving BCG monotherapy. In mice, intravesical MMC + BCG skewed tumor-associated macrophages (TAM) toward a beneficial M1 phenotype.

CONCLUSIONS

Instillation of sequential MMC + BCG is safe tolerable up to 40-mg MMC plus full-strength BCG. This approach could provide improved antitumor activity over BCG monotherapy by augmenting beneficial M1 TAMs.

Canonical and new generation anticancer drugs also target energy metabolism

Significant efforts have been made for the development of new anticancer drugs (protein kinase or proteasome inhibitors, monoclonal humanized antibodies) with presumably low or negligible side effects and high specificity. However, an in-depth analysis of the side effects of several currently used canonical (platin-based drugs, taxanes, anthracyclines, etoposides, antimetabolites) and new generation anticancer drugs as the first line of clinical treatment reveals significant perturbation of glycolysis and oxidative phosphorylation. Canonical and new generation drug side effects include decreased (1) intracellular ATP levels, (2) glycolytic/mitochondrial enzyme/transporter activities and/or (3) mitochondrial electrical membrane potentials. Furthermore, the anti-proliferative effects of these drugs are markedly attenuated in tumor rho (0) cells, in which functional mitochondria are absent; in addition, several anticancer drugs directly interact with isolated mitochondria affecting their functions. Therefore, several anticancer drugs also target the energy metabolism, and hence, the documented inhibitory effect of anticancer drugs on cancer growth should also be linked to the blocking of ATP supply pathways. These often overlooked effects of canonical and new generation anticancer drugs emphasize the role of energy metabolism in maintaining cancer cells viable and its targeting as a complementary and successful strategy for cancer treatment.

Differential toxicity of DNA adducts of mitomycin C

The clinically used antitumor agent mitomycin C (MC) alkylates DNA upon reductive activation, forming six covalent DNA adducts in this process. This review focuses on differential biological effects of individual adducts in various mammalian cell cultures, observed in the authors' laboratories. Evidence is reviewed that various adducts are capable of inducing different cell death pathways in cancer cells.This evidence is derived from a parallel study of MC and its derivatives 2,7-diaminomitosene (2,7-DAM) which is the main metabolite of MC and forms two mono-adducts with DNA, and decarbamoyl mitomycin C (DMC), which alkylates and cross-links DNA, predominantly with a chirality opposite to that of the DNA adducts of MC. 2,7-DAM is not cytotoxic and does not activate the p53 pathway while MC and DMC are cytotoxic and able to activate the p53 pathway. DMC is more cytotoxic than MC and can also kill p53-deficient cells by inducing degradation of Checkpoint 1 protein, which is not seen with MC treatment of the p53-deficient cells. This difference in the cell death pathways activated by the MC and DMC is attributed to differential signaling by the DNA adducts of DMC. We hypothesize that the different chirality of the adduct-to-DNA linkage has a modulating influence on the choice of pathway.

Protective effect of melatonin against mitomycin C-induced genotoxic damage in peripheral blood of rats

Mitomycin C (MMC) generates free radicals when metabolized. We investigated the effect of melatonin against MMC-induced genotoxicity in polychromatic erythrocytes and MMC-induced lipid peroxidation in brain and liver homogenates. Rats (N = 36) were classified into 4 groups: control, melatonin, MMC, and MMC + melatonin. Melatonin and MMC doses of 10 mg/kg and 2 mg/kg, respectively, were injected intraperitoneally. Peripheral blood samples were collected at 0, 24, 48, 72, and 96 hours posttreatment and homogenates were obtained at 96 hours posttreatment. The number of micronucleated polychromatic erythrocytes (MN-PCE) per 1000 PCE was used as a genotoxic marker. Malondialdehyde (MDA) plus 4-hydroxyalkenal (4-HDA) levels were used as an index of lipid peroxidation. The MMC group showed a significant increase in MN-PCE at 24, 48, 72, and 96 hours that was significantly reduced with melatonin begin coadministrated. No significant differences were found in lipid peroxidation. Our results indicate that MMC-induced genotoxicity can be reduced by melatonin.

Melatonin as antioxidant, geroprotector and anticarcinogen

The effect of the pineal indole hormone melatonin on the life span of mice, rats and fruit flies has been studied using various approaches. It has been observed that in female CBA, SHR, SAM and transgenic HER-2/neu mice long-term administration of melatonin was followed by an increase in the mean life span. In rats, melatonin treatment increased survival of male and female rats. In D. melanogaster, supplementation of melatonin to nutrient medium during developmental stages produced contradictory results, but and increase in the longevity of fruit flies has been observed when melatonin was added to food throughout the life span. In mice and rats, melatonin is a potent antioxidant both in vitro and in vivo. Melatonin alone turned out neither toxic nor mutagenic in the Ames test and revealed clastogenic activity at high concentration in the COMET assay. Melatonin has inhibited mutagenesis and clastogenic effect of a number of indirect chemical mutagens. Melatonin inhibits the development of spontaneous and 7-12-dimethlbenz(a)anthracene (DMBA)- or N-nitrosomethylurea-induced mammary carcinogenesis in rodents; colon carcinogenesis induced by 1,2-dimethylhydrazine in rats, N-diethylnitrosamine-induced hepatocarcinogenesis in rats, DMBA-induced carcinogenesis of the uterine cervix and vagina in mice; benzo(a)pyrene-induced soft tissue carcinogenesis and lung carcinogenesis induced by urethan in mice. To identify molecular events regulated by melatonin, gene expression profiles were studied in the heart and brain of melatonin-treated CBA mice using cDNA gene expression arrays (15,247 and 16,897 cDNA clone sets, respectively). It was shown that genes controlling the cell cycle, cell/organism defense, protein expression and transport are the primary effectors for melatonin. Melatonin also increased the expression of some mitochondrial genes (16S, cytochrome c oxidases 1 and 3 (COX1 and COX3), and NADH dehydrogenases 1 and 4 (ND1 and ND4)), which agrees with its ability to inhibit free radical processes. Of great interest is the effect of melatonin upon the expression of a large number of genes related to calcium exchange, such as Cul5, Dcamkl1 and Kcnn4; a significant effect of melatonin on the expression of some oncogenesis-related genes was also detected. Thus, we believe that melatonin may be used for the prevention of premature aging and carcinogenesis.

Effect of sulforaphane on micronucleus induction in cultured human lymphocytes by four different mutagens

Isothiocyanates (ITCs) are commonly found in cruciferous vegetables. A variety of biological activities have been ascribed to ITCs, such as inhibition of cytochrome P450 enzymes and induction of phase II enzymes in animal models. ITCs are also able to block cell-cycle progression and induce apoptosis in human cancer cells in vitro. In this study, we evaluated the ability of the ITC sulforaphane to protect cultured human lymphocytes from micronucleus (MN) induction by four different mutagens: ethyl methanesulfonate (EMS), vincristrine (VIN), H(2)O(2) and mitomycin C (MMC). To understand the mechanisms of action of sulforaphane, the cultures were treated with the compound before, during and after treatment with the mutagens; in addition, the cultures were evaluated for the induction of apoptosis. Up to 10 microM, sulforaphane was non-genotoxic by itself, while 30 microM sulforaphane reduced the replicative index of the cells by more than 60%. Moreover, 1-10 microM sulforaphane reduced the MN frequency induced by EMS, VIN, H(2)O(2) and MMC in at least one of the treatment protocols; it had no effect on H(2)O(2)-MN induction in the post-treatment protocol, and it increased MN induction by MMC in the pre-treatment protocol. Apoptosis was produced in the cultures treated with sulforaphane alone. The fraction of apoptotic cells was increased after co- or post-treatment with sulforaphane and EMS and MMC, suggesting that sulforaphane-mediated apoptosis may remove highly damaged cells induced by these agents. Other mechanisms are involved in the anti-genotoxic activity of sulforaphane against VIN and H(2)O(2). Taken together, our findings indicate that under certain conditions sulforaphane possesses anti-genotoxic activity in vitro and that further studies are warranted to characterize this property in vivo.

Synthesis, antitumour activity and structure–activity relationships of 5H-benzo[b]carbazoles

A series of novel 5H-benzo[b]carbazoles related to the ellipticines was obtained from the reactions of p-benzoquinones with 2-aminomethylene-1-indanones. Most of the compounds were evaluated for their antitumour activity in the National Cancer Institute's in vitro human tumour cell line screening panel. Among them, particularly derivative 15c bearing a p-quinone methide moiety in ring C of the heterocycle was found to show in vitro activity comparable to clinically well established anticancer agents such as amsacrine or mitomycin C. Compounds 9d, 9e and 12k showed increased potency to distinct cell lines like the leukemia or melanoma subpanel of cell lines. Based on the test results, structure-activity relationships for this series of compounds were developed. For instance, it was found that a quinonoid substructure in ring C leads to a noticeable increase in activity. The same observation was made for a 2-hydroxyl substituent at the ring system. 2-Acetoxy and 2-methoxy derivatives as well as 2-unsubstituted 5H-benzo[b]carbazoles either had a decreased potency or were found to be inactive. A COMPARE analysis with some of these compounds showed poor or no correlation with anticancer drugs of the NCI's standard agents database indicating a novel mechanism of action. Additionally, UV-vis titrations in the series of 5H-benzo[b]carbazoles indicated interactions with calf thymus DNA only for the highly active quinone methide 15c.

Anti-clastogenic activity of two structurally related pterocarpans purified from Bituminaria bituminosa in cultured human lymphocytes

Plant-derived isoflavones are currently receiving much attention because of their phyto-estrogenic, antioxidant, anti-mutagenic, and anti-tumor activities. In this study we have evaluated the clastogenic and anti-clastogenic activities in human lymphocytes of two structurally related pterocarpans, iso-flavonoid derivatives, termed erybraedin C and bitucarpin A, recently purified from Bituminaria bituminosa and chemically characterized. Mitomycin C (MMC) and the radio-mimetic bleomycin (BL) were used as reference clastogens. The end point studied was micronucleus formation. The results obtained in this study indicate that erybraedin C and bitucarpin A, when assayed alone, do not affect either the mitotic index or the cell-proliferation index of human lymphocytes. Interestingly, both compounds appear to be non-clastogenic in the range of concentrations used. In contrast, both substances seem to affect significantly the clastogenic effects induced by BL and MMC. A 1-h pre-exposition of the cell culture to erybraedin C was necessary to display its anti-clastogenic potential against BL, whereas bitucarpin A was inactive in this respect, with a structure-activity relationship. In contrast, the clastogenic activity of MMC was significantly reduced by both erybraedin C and bitucarpin A, using either a pre-incubation schedule or simultaneous treatment. These results suggest that the protective effects displayed by the two anti-clastogenic compounds against MMC could be due to the induction or inhibition of cellular reductive metabolic enzymes.

Electrochemical genosensor for Mitomycin C–DNA interaction based on guanine signal

The interaction of mitomycin C (MC) with fish sperm or calf thymus DNA immobilized onto carbon screen-printed electrodes (CSPE) and carbon paste electrode (CPE) have been studied by using electrochemical techniques as square wave voltammetry (SWV) and differential pulse voltammetry (DPV). After the interaction was occurred between DNA and MC on electrode surface, it was observed that the guanine signal was higher with bare electrode than DNA-modified one. The changes in the experimental parameters such as the concentration of MC, and the accumulation time of MC were studied by using SWV and DPV. In addition, reproducibility, and detection limit parameters were determined using both electrodes. The partition coefficient of MC was also calculated before and after interaction of MC with dsDNA at CPE surface. These results showed that these two different DNA biosensors could be used for the sensitive, rapid and cost effective detection of MC-DNA interaction.

Effects of exogenous melatonin--a review

The results of studies on the effect of pineal indole hormone melatonin on the life span of mice, rats, fruit flies, and worms are critically reviewed. In mice, long-term administration of melatonin was followed by an increase in their life span in 12 experiments and had no effect in 8 of 20 different experiments. In D. melanogaster, the supplementation of melatonin to the nutrient medium during developmental stages gave contradictory results, but when melatonin was added to food throughout the life span, an increase in the longevity of fruit flies has been observed. Melatonin decreased the survival of C. elegans but increased the clonal life span of planaria Paramecium tertaurelia. Available data suggest antioxidant and atherogenic effects of melatonin. Melatonin alone turned out to be neither toxic nor mutagenic in the Ames test and revealed clastogenic activity in high concentration in the COMET assay. Melatonin inhibits mutagenesis induced by irradiation and by indirect chemical mutagens and inhibits the development of spontaneous and chemical-induced tumors in mice and rats. Further studies and clinical trials are needed to verify that melatonin is both safe and has geroprotector efficacy for humans.

Studies on the mechanisms of activation of indolequinone phosphoramidate prodrugs

Previously a series of 2- and 3-substituted indolequinone phosphoramidate prodrugs was synthesized, and the compounds were shown to be nanomolar inhibitors of cell proliferation. The activation of these compounds following both one- and two-electron reduction has been investigated. (31)P NMR experiments demonstrated that both series of compounds undergo rapid activation following two-electron reduction. Additionally, the 3-series of compounds undergo rapid activation following one-electron reduction, while activation of the 2-series of compounds via this mechanism is very slow. The activation of these prodrugs by direct displacement using sulfur nucleophiles such as glutathione has been examined. Activation via this route is rapid for the 3-regioisomers, but is considerably slower for the 2-substituted analogues under similar conditions. Together these findings suggest that drug delivery via two-electron reduction from the 2-position is the more selective prodrug strategy.

Relationship between NAD(P)H:quinone oxidoreductase 1 (NQO1) levels in a series of stably transfected cell lines and susceptibility to antitumor quinones 1 2 1In accordance with the policy of the University of Colorado Health Sciences Center, D.R., R.H.J.H., and J.B. declare a patent interest in RH1. 2Abbreviations: MMC, mitomycin C; NQO1, NAD(P)H:quinone oxidoreductase 1 or DT-diaphorase; MeDZQ, 2,5-diaziridinyl-3,6-dimethyl-1,4-benzoquinone; DCPIP, 2,6-dichlorophenol-indophenol; MTT, thiazolyl blue; P450R, NADPH:cytochrome P450 reductase; b5R, NADH:cytochrome b5 reductase; NSCLC, non-small cell lung cancer; SCLC, small cell lung cancer; FBS, fetal bovine serum; and MEM, Eagle’s minimum essential medium

To investigate the importance of NAD(P)H:quinone oxidoreductase 1 (or DT-diaphorase; NQO1) in the bioactivation of antitumor quinones, we established a series of stably transfected cell lines derived from BE human colon adenocarcinoma cells. BE cells have no NQO1 activity due to a genetic polymorphism. The new cell lines, BE-NQ, stably express wild-type NQO1. BE-NQ7 cells expressed the highest level of NQO1 and were more susceptible [determined by the thiazolyl blue (MTT) assay] to known antitumor quinones and newer clinical candidates. Inhibition of NQO1 by pretreatment with an irreversible inhibitor, ES936 [5-methoxy-1,2-dimethyl-3-[(4-nitrophenoxy)methyl]indole-4,7-dione], protected BE-NQ7 cells from toxicity induced by streptonigrin, ES921 [5-(aziridin-1-yl)-3-(hydroxymethyl)-1,2-dimethylindole-4,7-dione], and RH1 [2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone]. RH1 was evaluated further by clonogenic assay for cytotoxic response and was more cytotoxic to BE-NQ7 cells than to BE cells. Cytotoxicity was abrogated by inhibition of NQO1 with ES936 pretreatment. Using a comet assay to evaluate DNA cross-linking, BE-NQ7 cells demonstrated significantly higher DNA cross-links than did BE cells in response to RH1 treatment. DNA cross-linking in BE-NQ7 cells was observed at very low concentrations of RH1 (5 nM), confirming that NQO1 activates RH1 to a potent cross-linking species. Further studies using streptonigrin, ES921, and RH1 were undertaken to analyze the relationship between NQO1 activity and quinone toxicity. Toxicity of these compounds was measured in a panel of BE-NQ cells expressing a range of NQO1 activity (23-433 nmol/min/mg). Data obtained suggest a threshold for NQO1-induced toxicity above 23 nmol/min/mg and a sharp dose-response curve between the no effect level of NQO1 (23 nmol/min/mg) and the maximal effect level (>77 nmol/min/mg). These data provide evidence that NQO1 can bioactivate antitumor quinones in this system and suggest that a threshold level of NQO1 activity is required to initiate toxic events.

The role of NAD(P)H oxidoreductase (DT-Diaphorase) in the bioactivation of quinone-containing antitumor agents: a review

Bioactivation of quinone-containing anticancer agents has been studied extensively within the context of the chemistry and structure of the individual quinones which may result in various mechanisms of bioactivation and activity. In this review we focus on the two electron enzymatic reduction/activation of quinone-containing anticancer agents by DT Diaphorase (DTD). This enzyme has become important in oncopharmacology because its activity varies with tissues and it has been found to be elevated in tumors. Thus, a selective tumor cell kill can exist for agents that are good substrates for this enzyme. In addition, the enzyme can be induced by a variety of agents, a fact that can be used in chemotherapy. That is induction by a nontoxic agent followed by treatment with a good DT-Diaphorase substrate. A wide variety of anticancer drugs are discussed some of which are not good substrates such as Adriamycin, and some of which are excellent substrates. The latter category includes a variety of quinone containing alkylating agents.

The role of reductive enzymes in cancer cell resistance to mitomycin C

Mitomycin C (MMC) is bioreductively activated to DNA binding species via complex chemical pathways involving a common hydroquinone intermediate. A recent publication by Belcourt et al. (1999) has revealed that the bacterial mitomycin C resistance protein (MCRA) acts as a unique hydroquinone oxidase converting this reactive intermediate back to the parent drug in the presence of molecular oxygen, preventing the formation of cytotoxic interstrand DNA crosslinks. It was argued that a mechanism analogous to MCRA may be responsible for the often observed phenomenon of aerobic drug resistance that develops in vitro to MMC in human cancer cell lines. Altered expression of activating reductase enzymes, which usually accompanies aerobic drug resistance, was claimed to be of lesser importance. Therefore, the role of reductases in MMC drug resistance has been reviewed. While it is clear from numerous studies that lowered reductase expression can in certain situations produce drug resistance, simple correlations between a specific enzyme and chemosensitivity generally do not hold due to the complex functional and regulatory interplay that exists among the different activating enzymes and detoxification systems. Copyright 2000 Harcourt Publishers Ltd.

Pharmacological determinants of the antitumour activity of mitomycin C

Recent investigations into bioreductive anticancer drugs have focused on profiling reductase enzymes and relating their expression to therapeutic activity in an approach referred to as enzyme directed drug development. However, few studies have attempted to validate this approach in vivo and even less is known about how the expression of reductases relates quantitatively and qualitatively to metabolic activation. In the present study, the antitumour activity, pharmacokinetics and metabolism of mitomycin C (MMC) has been determined in vivo in two murine adenocarcinomas of the colon, MAC 16 (high DT-diaphorase activity) and MAC 26 (low DT-diaphorase activity) after intra-tumoural injection of drug. Over a broad range of drug concentrations (50-250 microg), MAC 16 proved to be consistently the more sensitive tumour (e.g. 75 microg of MMC, T/C 11% for MAC 16 and 31% for MAC 26). Higher levels of parent drug (peak concentration 103 microg/tumour compared to 58 microg/tumour) were maintained over 45 min in MAC 16 after which time clearance was rapid from both tumours. Four metabolites were detected in both tumours characteristic of different pathways of metabolism. However, by far the major metabolite was 2,7-diaminomitosene (2,7-DM), an accurate indicator of metabolic activation of MMC. Despite higher reductase levels and greater sensitivity to the drug, there was 4-fold less production of 2,7-DM in MAC 16. These results indicate a lack of a simple relationship in vivo between reductase expression and metabolic activation and suggest factors other than pharmacological determinants being responsible for the chemosensitivity of the MAC tumours to MMC.

Current issues in the enzymology of mitomycin C metabolic activation

1. Mitomycin C (MMC) is considered to be the prototype bioreductive drug undergoing activation to toxic species preferentially under hypoxic conditions. Therefore a proper understanding of the enzymology of bioreduction in tumor tissue is of great importance. 2. DT-diaphorase and NADPH:cytochrome P-450 reductase (quinone reductases) are believed to have established roles in this activation pathway, but these roles are now undergoing revision. 3. It is emerging, however, that different reductases prevail under different physiological conditions. Indeed, DT-diaphorase has been found to protect cells from the hypoxic cytotoxicity of MMC in cell lines expressing high levels of the enzyme. 4. A novel mitochondrial reductase(s) has been identified in solid tumor tissue and is active only under hypoxic conditions and is more efficient at metabolizing MMC than are the other reductases identified. 5. Thus, this newly identified mitochondrial reductase(s) is a potential new target for enzyme-directed bioreductive drug therapy if tumor hypoxia can be achieved. However, because most tumors overexpress DT-diaphorase, this enzyme may prove optimal for MMC drug therapy.

Modulatory effects of melatonin on genotoxic response of reference mutagens in the Ames test and the comet assay

The effect of a potent endogenous antioxidant, the pineal gland indole melatonin (MLT) on the mutagenicity of twelve well-known mutagens and carcinogens has been investigated using two in vitro tests the Ames test and the single cell gel electrophoresis assay (SCGE assay or COMET assay). The 12 mutagens used were 7, 12-dimethylbenz(a)anthracene (DMBA), benzo(a)pyrene (BP), 2-aminofluorene (AF), 1,2-dimethylhydrazine (DMH), bleomycin, cyclophosphamide (CP), 4-nitroquinoline-N-oxide (NQO), 2,4, 7-trinitro-9-fluorenone (TNF), 9-aminoacridine (AA), N-nitrosomethylurea (NMU), mitomycin C and sodium azide tested in the absence or in the presence of S9 mix. MLT alone turned out neither toxic nor mutagenic in the Ames test and revealed clastogenic activity at the highest concentration tested (100 microM) in the SCGE assay. In four Salmonella typhimurium tester strains TA 97, TA 98, TA 100 and TA 102 MLT significantly reduced the mutagenicity of chemicals which require S9 activation. In the SCGE assay performed on CHO cells, preincubation with MLT led to a strong inhibition of clastogenic activities of DMBA and CP, and in a lesser extent with BP and NMU. With mitomycin C, MLT exacerbated responses in both tests. The possible mechanisms of MLT's inhibitory action are discussed.

Suppository administration of chemotherapeutic drugs with concomitant radiation for rectal cancer

PURPOSE

Preoperative radiation with combined chemotherapy is effective in shrinking advanced rectal cancer locally and facilitating subsequent surgery. Suppository delivery of 5-fluorouracil is associated with less toxicity and higher rectal tissue concentrations than intravenous administration. This prompted us to evaluate suppository and intravenous administration of 5-fluorouracil and mitomycin C with concomitant radiation to determine associated toxicity.

METHODS

Rectal, liver, lymph node, and lung tissue and systemic and portal blood were collected serially from male Sprague Dawley rats to determine drug concentrations following suppository or intravenous delivery of 5-fluorouracil or mitomycin C. Thirty-six animals were randomly assigned to treatment groups and received 5-fluorouracil suppositories, mitomycin C suppositories, or an equivalent intravenous dose of 5-fluorouracil or mitomycin C 30 minutes before radiation therapy. Before and 3, 6, 10, and 15 days following this treatment, blood was collected, colonoscopy was performed, and rectal tissue was harvested for histologic examination.

RESULTS

Mitomycin C suppository was significantly less toxic compared with intravenous delivery, and higher rectal tissue concentrations were observed from 10 to 30 minutes (P < 0.05). Compared with intravenous 5-fluorouracil administration and radiation, 5-fluorouracil suppository and radiation resulted in additive myelosuppression at day 6 (P < 0.05) with rapid recovery.

CONCLUSIONS

5-Fluorouracil and mitomycin C suppository delivery combined with radiation causes less systemic toxicity and is more effective than intravenous administration.

Mitomycin C-DNA adducts generated by DT-diaphorase. Revised mechanism of the enzymatic reductive activation of mitomycin C

Mitomycin C (MC) was reductively activated by DT-diaphorase [DTD; NAD(P)H:quinone oxidoreductase] from rat liver carcinoma cells in the presence of Micrococcus lysodeicticus DNA at pH 5.8 and 7.4. The resulting alkylated MC-DNA complexes were digested to the nucleoside level and the covalent MC-nucleoside adducts were separated, identified, and quantitatively analyzed by HPLC. In analogous experiments, two other flavoreductases, NADH-cytochrome c reductase and NADPH-cytochrome c reductase, as well as two chemical reductive activating agents Na2S2O4 and H2/PtO2 were employed as activators for the alkylation of DNA by MC. DTD as well as all the other activators generated the four known major guanine-N2-MC adducts at both pHs. In addition, at the lower pH, the guanine-N7-linked adducts of 2,7-diaminomitosene were detectable in the adduct patterns. At a given pH all the enzymatic and chemical reducing agents generated very similar adduct patterns which, however, differed dramatically at the acidic as compared to the neutral pH. Overall yield of MC adducts was 3-4-fold greater at pH 7.4 than at 5. 8 except in the case of DTD when it was 4-fold lower. Without exception, however, cross-link adduct yields were greater at the acidic pH (2-10-fold within the series). The ratio of adducts of bifunctional activation to those of monofunctional activation was 6-20-fold higher at the acidic as compared to the neutral pH. A comprehensive mechanism of the alkylation of DNA by activated MC was derived from the DNA adduct analysis which complements earlier model studies of the activation of MC. The mechanism consists of three competing activation pathways yielding three different DNA-reactive electrophiles 11, 12, and 17 which generate three unique sets of DNA adducts as endproducts. The relative amounts of these adducts are diagnostic of the relative rates of the competing pathways in vitro, and most likely, in vivo. Factors that influence the relative rates of individual pathways were identified.

Induction intraarterial chemotherapy for T4 breast cancer through an implantable port-catheter system

Eleven patients with T4 breast cancer received induction intraarterial chemotherapy (IACT) as the first step in multidisciplinary therapy. The IACT agents (epirubicin and mitomycin C), were delivered weekly in the outpatient department by bolus injection through an implantable port-catheter system. A modified technique of port-catheter system implantation was used. The precise localization of the catheter was dually confirmed by angiography and dye test. The effectiveness of the treatment was evaluated by clinical appearance, image study, and microscopic examination. A 91% response rate was obtained, and the lesions were resectable in < or = 8 weeks. No obvious systemic toxicity resulted from the IACT. Our results show that weekly IACT by bolus injection through a port-catheter system for treating locally advanced T4 breast cancer is feasible and efficacious.

The mitomycin bioreductive antitumor agents: cross-linking and alkylation of DNA as the molecular basis of their activity

This review focuses on the chemical and enzymatic aspects of the reductive activation of mitomycin C, its disulfide analogs KW-2149 and BMS-181174, and, in less detail, FR66979 and FR900482, newly discovered antitumor antibiotics related to mitomycins. Furthermore, structural aspects of DNA damage induced by these drugs in vitro and in vivo are described, including the chemical and conformational characteristics of DNA interstrand and intrastrand cross-links and monofunctional alkylation products, with emphasis on DNA adducts of mitomycin C. The DNA sequence specificity of the damage and its mechanism is reviewed. The relationship between the chemical and structural properties of the DNA damage on the one hand, and the antitumor and other biological activities of the mitomycins on the other, is discussed.

Enzymatic activation of DNA cleavage by dynemicin A and synthetic analogs

Dynemicin A (1), a member of the enediyne family of natural products, binds to double-stranded DNA (K(B) approximately 10(4) M(-1)) and in the presence of millimolar concentrations of a reducing cofactor such as NADPH or GSH reacts to cleave DNA. In this work, we show that the two flavin-based enzymes ferredoxin-NADP+ reductase and xanthine oxidase catalyze the reductive activation of 1 by NADPH and NADH, respectively. The enzyme-catalyzed reductive activation of 1 leads to more rapid and efficient cleavage of DNA, even with 10-20-fold lower concentrations of the stoichiometric reductant. Significantly, the enzymatic systems are also found to activate the tight-binding (K(B) > or = 10(6) M(-1)) synthetic dynemicin analogs 3 and 5 toward DNA cleavage. These same analogs do not undergo reductive activation with NADPH or NADH alone, where evidence has been obtained to support the proposal that the DNA-bound drugs are protected from reductive activation. The new enzymatic activation processes described may have important implications for chemistry occurring with 1 and synthetic analogs in vivo, as well as for the future development of dynemicin-based anticancer agents.

Enzymology of mitomycin C metabolic activation in tumour tissue. Characterization of a novel mitochondrial reductase

In this study, the enzymology of mitomycin C (MMC) bioactivation in two murine colon adenocarcinomas, MAC 16 and MAC 26, was examined. Subcellular quinone reductase assessment via cytochrome c reduction confirmed a number of active enzymes. MAC 16 exhibited 22-fold greater levels of cytosolic DT-diaphorase than MAC 26, while microsomal NADPH:cytochrome P-450 reductase levels were similar in both tumour types. Metabolism of MMC by subcellular fractions isolated from both MAC 16 and MAC 26 was quantitated by monitoring the formation of the principle metabolite 2,7-diaminomitosene (2,7-DM) via high-performance liquid chromatography (HPLC). In MAC 16 only, activity displaying the properties of cytosolic DT-diaphorase and microsomal NADPH:cytochrome P-450 reductase was detected and confirmed, using the enzyme inhibitors dicoumarol and cytochrome P-450 reductase antiserum, respectively. The highest level of MMC metabolism was associated with the mitochondrial fraction from both tumours and was the sole enzyme activity detected in MAC 26. The greatest mitochondrial drug metabolism was achieved in the presence of NADPH as cofactor and hypoxia (MAC 16-specific activity, 3.67 +/- 0.58 nmol/30 min/mg; MAC 26 specific-activity, 3.87 +/- 0.71 nmol/30 min/mg) and was unaffected by the addition of the inhibitors dicoumarol and cytochrome P-450 reductase antiserum. NADH-dependent mitochondrial activity was only observed in MAC 16 at approximately 4-fold less than that seen with NADPH. MAC 26 homogenate incubations displayed enhanced metabolism under hypoxia, presumably due to the presence of the identified mitochondrial enzyme. MAC 16 homogenates showed no increase in metabolism under hypoxia, suggesting that other enzyme(s) may be predominant. These data indicate the presence of a novel mitochondrial one-electron reductase capable of metabolising MMC in MAC 16 and MAC 26.