apaziquone and Colonic-Neoplasms

Anti-tumor quinone, including mitomycin C (MMC), needs to be activated by bioreduction to exert its cytotoxic activities. The enzymes underlying this bioreductive activation have been the subject of extensive research on Mitomycin C. Cytochrome P450 reductase, cytochrome b5 reductase, xanthine oxidase, xanthine dehydrogenase and DT-diaphorase (DTD) have been shown to be involved in the reduction of MMC. The relationship between bioreductive enzymes and the cytotoxicity of quinone, however, has not been analyzed yet. In this study, we investigated the relationship between the bioreductive enzymes and the cytotoxicity of MMC. We carried out the following experiments and the following results were obtained. I) We isolated an MMC-resistant variant. This cell showed five-fold resistance to MMC as compared with the parental cell line. DTD was deficient in this resistant cell. II) We have examined the bioreductive enzyme activities of DTD and cytochrome P450 reductase and IC50's of MMC in 13 colon and gastric carcinoma cell lines. A positive correlation was not found between the enzyme activities and MMC sensitivities, but the cells with little or no DTD activity showed higher IC50 values compared to the other cell lines. III) To elucidate directly the role of DTD in MMC sensitivity, we introduced NQO1 gene into St-4 cells. NQO1 gene encodes DTD and St-4 cells have no DTD activity. All of the transfectants showed five- to ten-fold higher sensitivity to MMC as compared to the parental St-4 cells. The above data indicate that DTD is a critical determinant of sensitivity to MMC in aerobic conditions.

Topics: Antibiotics, Antineoplastic; Aziridines; Colonic Neoplasms; Cytochrome Reductases; Cytochrome-B(5) Reductase; Drug Screening Assays, Antitumor; Humans; Indolequinones; Indoles; Mitomycin; Mitomycins; NAD(P)H Dehydrogenase (Quinone); NADH, NADPH Oxidoreductases; NADPH-Ferrihemoprotein Reductase; Stomach Neoplasms; Tumor Cells, Cultured; Xanthine Dehydrogenase; Xanthine Oxidase

EO9 is a novel bioreductive drug which has recently undergone extensive clinical evaluation. Its mechanism of action remains to be clearly defined. Antitumour activity of EO9 has been determined in 2 human colon cancer xenografts (HT-29 and BE) and 2 murine colon adenocarcinomas (MAC 16 and 26) after intratumoural injection of 250 microg of drug. Levels of the major bioreductive enzymes (DT-diaphorase, cytochrome P-450 reductase and cytochrome b5 reductase) were measured in tumours using cytochrome c reduction and menadione as the intermediate electron acceptor. There was no correlation between chemosensitivity (T/C: HT-29, 15%; BE, 27%; MAC 16, 33% and MAC 26, 60%) and enzyme activity (r2 = 0.47 for DT-diaphorase, r2 = 0.1 for cytochrome P-450 reductase and r2 = 0.52 for cytochrome b5 reductase). Drug metabolism was followed in vitro using tumour homogenates incubated under aerobic and anaerobic conditions. Four metabolites were identified by HPLC and characterised bv UV-visible spectroscopy. With the exception of the hydrolysis product EO5A, all other metabolites appeared to be drug adducts. No correlation was observed between the kinetics of metabolite formation and antitumour activity. A good correlation (r2 = 0.86) was found with the rate of disappearance of parent drug and antitumour activity. These data show that the overall capacity of a tumour to metabolise EO9 is the most important determinant of antitumour activity rather than the expression of the major bioreductive enzymes and that the parent drug rather than a metabolite leads to the active form of the drug.

Topics: Adenocarcinoma; Animals; Antineoplastic Agents; Aziridines; Colonic Neoplasms; Humans; Indolequinones; Indoles; Mice; Mice, Nude; Tumor Cells, Cultured

The poor blood supply to solid tumours introduces many factors that affect the outcome of chemotherapy, one of which is the problem of drug delivery to poorly vascularized regions of tumours. Whereas poor drug penetration has been recognized as a contributing factor to the poor response of many solid tumours, the question of drug penetration through multicell layers has not been thoroughly addressed, largely because of restrictions imposed upon these studies by the requirement for either radiolabelled or naturally fluorescent compounds. The aim of this study is to describe modifications made to a recently published assay that broadens the scope for assessing drug penetration during the early stages of drug development and to characterize the ability of various drugs to penetrate multicell layers. DLD-1 human colon carcinoma cells were cultured on Transwell-COL plastic inserts placed into 24-well culture plates so that a top and bottom chamber were established, the two chambers being separated by a microporous membrane. Drugs were added to the top chamber at doses equivalent to peak plasma concentrations in vivo and the rate of appearance of drugs in the bottom chamber determined by high-performance liquid chromatography (HPLC). Both 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine) and 7-[4'-(2-nitroimidazol-1-yl)-butyl]-theophylline (NITP) rapidly penetrated DLD-1 multicell layers (50.9 +/- 12.1 microm thick) with t(1/2) values of 1.36 and 2.38 h respectively, whereas the rate of penetration of 5-aziridino-3-hydroxymethyl-1-methyl-2-[1H-indole-4,7-dione] prop-beta-en-alpha-ol (EO9) and doxorubicin through multicell layers was significantly slower (t(1/2) = 4.62 and 13.1 h respectively). Inclusion of dicoumarol increases the rate of EO9 penetration, whereas reducing the oxygen tension to 5% causes a reduction in tirapazamine penetration through multicell layers, suggesting that the extent of drug metabolism is one factor that determines the rate at which drugs penetrate multicell layers. The fact that EO9 does not readily penetrate a multicell layer, in conjunction with its rapid elimination in vivo (t(1/2) < 10 min), suggests that EO9 is unlikely to penetrate more than a few microm from a blood vessel within its pharmacokinetic lifespan. These results suggest that the failure of EO9 in the clinic is due to a combination of poor drug penetration and rapid elimination in vivo.

Topics: Antibiotics, Antineoplastic; Antineoplastic Agents; Aziridines; Carcinoma; Cell Division; Chromatography, High Pressure Liquid; Colonic Neoplasms; Dicumarol; Doxorubicin; Humans; Indolequinones; Indoles; Oxygen; Tirapazamine; Triazines; Tumor Cells, Cultured

DT-diaphorase (DTD) is an important enzyme for the bioreductive activation of the new alkylating indoloquinone EO9. In preclinical studies, EO9 has shown selective anti-tumour activity against solid tumours and under hypoxic conditions. The levels of three reductive enzymes have been determined in three types of human solid tumours, together with corresponding normal tissues and normal liver. DTD enzyme activities were measured in tumour extracts using 2,6-dichlorophenolindophenol (DCPIP) and NADH as substrates; cytochrome P450 reductase or cytochrome b5 reductase activities were assessed with cytochrome c and NADPH or NADH respectively. DTD activity was highest in non-small-cell lung (NSCLC)-tumours (mean 123 nmol DCPIP min-1 mg-1), followed by colon carcinoma (mean 75 nmol min-1 mg-1) and squamous cell carcinoma of the head and neck (6-fold lower than NSCLC). DTD activity was very low in normal liver and normal lung (4-6 nmol min-1 mg-1), while the levels in normal colon mucosa or normal mucosa of the head and neck region were in the same range as the corresponding tumours. The levels of the two other reductive enzymes, cytochrome P450 reductase (CP450R) and cytochrome b5 reductase (Cb5R), were 5 to 25-fold lower than those of DTD in all the tissues, except for normal liver, in which DTD was 2 to 4-fold lower. The degree of variation found for DTD (range 4-250 nmol min-1 mg-1), was not observed for these enzymes (CP450R, 0.8-7.8 nmol cytochrome c min-1 mg-1; Cb5R, 3.5-27.6 nmol min-1 mg-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Antineoplastic Agents; Aziridines; Carcinoma, Non-Small-Cell Lung; Colonic Neoplasms; Humans; Indolequinones; Indoles; Lung Neoplasms; NAD(P)H Dehydrogenase (Quinone); Neoplasms

Twenty-three human tumour cell lines (lung, breast, and colon) and eight rodent cell lines were evaluated for their sensitivity to the quinone-based anticancer drug EO9 [3-hydroxymethyl-5-aziridinyl-1-methyl-2-(1H indole-4,7-dione)prop-beta-en-alpha-o1]. Sensitivity was compared with the intracellular levels of DT-diaphorase, and cell lines showing highest enzyme activity tended to be the most sensitive to EO9. The role of DT-diaphorase in determining drug sensitivity was confirmed by using the enzyme inhibitor dicoumarol, which protects cells containing high levels of DT-diaphorase from the cytotoxic action of EO9. Hypoxia increased the cytotoxicity of cells containing low but not high levels of DT-diaphorase, implying that both 1- and 2-electron reductive activation processes can be important for expression of EO9 toxicity. It is concluded that EO9 is a potentially useful agent in the enzyme directed approach to the use of bioreductive drugs in cancer therapy.

Topics: Animals; Antineoplastic Agents; Aziridines; Breast Neoplasms; Colonic Neoplasms; Cricetinae; Humans; Hypoxia; Indolequinones; Indoles; Lung Neoplasms; Mammary Neoplasms, Animal; NAD(P)H Dehydrogenase (Quinone); Oxygen; Tumor Cells, Cultured

Studies with purified DT-diaphorase have shown that the enzyme is capable of catalyzing a two-electron reduction of the novel indoloquinone EO9 to a DNA-damaging alkylating species. The aim of this study was to determine to what extent DT-diaphorase may be involved in the metabolic activation of EO9 and mitomycin C in both aerobic and hypoxic conditions. Two human colon-carcinoma cell lines were used; HT29 has high levels of DT-diaphorase whilst BE lacks this activity because of a point mutation in the NQOI gene. In aerobic conditions the 2 cell lines show similar sensitivities to a number of cytotoxic drugs including cisplatin, doxorubicin and etoposide. They are equally sensitive to the benzotriazine di-N-oxide SR 4233 but HT29 is more sensitive than BE to mitomycin C and EO9. Sensitivity to SR 4233 is increased by about 100-fold for both cell lines in hypoxic conditions. DT-diaphorase-deficient BE cells show markedly increased sensitivity to mitomycin C and particularly EO9 in hypoxic conditions, whereas DT-diaphorase-rich HT29 cells show little hypoxic sensitization to these agents unless exposed in the presence of dicoumarol. These results suggest that DT-diaphorase can reduce EO9 and mitomycin C to potent cytotoxic species in aerobic conditions, and this activity predominates over the one-electron-reducing enzymes even in hypoxic conditions. In the absence of DT-diaphorase activity, EO9 and mitomycin C are reduced in hypoxic conditions, presumably by one-electron-reducing enzymes, to a similar or greater extent than is achieved with DT-diaphorase.

Topics: Aerobiosis; Antineoplastic Agents; Aziridines; Cell Hypoxia; Colonic Neoplasms; Dose-Response Relationship, Drug; Drug Screening Assays, Antitumor; Humans; Indolequinones; Indoles; Mitomycin; NAD(P)H Dehydrogenase (Quinone); Tumor Cells, Cultured

EO9 is a novel and fully synthetic bioreductive alkylating indoloquinone. Although structurally-related to mitomycin C, EO9 exhibits a distinct preclinical antitumour profile and there are also differences in its biochemical activation. In this study, EO9 was found to demonstrate preferential cytotoxicity against solid tumours in vitro as compared to leukaemia cell lines both in the Corbett two-tumour assay and in the disease-oriented human tumour cell line panel of the U.S. National Cancer Institute. In the latter system activity was particularly apparent in colon, melanoma and central nervous system lines, together with some renal and non-small cell lung lines. Preferential cytotoxicity towards hypoxic versus aerobic EMT6 mouse mammary tumour cells was observed. In vivo, EO9 was inactive against the P388 murine leukaemia, while exerting significant antiproliferative effects against several murine and human solid tumours, including the generally resistant MAC mouse colon tumours and gastric, ovarian and breast xenografts. These results confirmed in vitro observations of preferential solid tumour activity. In animal toxicology studies, EO9 induced vascular congestion in the gastrointestinal tract, but no significant bone marrow toxicity. The LD10 value of EO9 after a single intravenous injection into mice was 9 mg/kg (27 mg/m2). A dose of one-tenth of the mouse equivalent LD10 (2.7 mg/m2), the recommended starting dose for clinical phase I studies, was found to be safe in rats. Considering its distinct mechanism of bioactivation as compared to mitomycin C, its preferential solid tumour activity, its excellent activity against hypoxic cells, and lack of significant bone marrow toxicity in animals studies, EO9 has been selected for clinical evaluation within the framework of the EORTC.

Topics: Adenocarcinoma; Animals; Antineoplastic Agents; Aziridines; Bone Marrow; Cell Survival; Colonic Neoplasms; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Female; Humans; Indolequinones; Indoles; Leukemia P388; Male; Mice; Neoplasm Transplantation; Rats; Tumor Cells, Cultured

The indoloquinone EO9 exhibits promising in vitro and in vivo antitumour activity. EO9 is metabolised to DNA damaging species by DT-diaphorase in vitro. In the present study DT-diaphorase specific activity was 16 fold higher in the mouse adenocarcinoma MAC 16, a tumour which is quite responsive to EO9 in vivo, compared with levels in the more resistant mouse adenocarcinoma MAC 26. This order of responsiveness is the reverse of that seen with the most active of the clinically used agents in these tumours [chloroethylnitrosoureas and 5-fluorouracil (5-FU)]. In addition, when the in vitro sensitivity of two human colon carcinoma cell lines was compared, EO9 was 15-30 fold more active in the DT-diaphorase rich HT29 line than in the enzyme-deficient BE cell line counterpart. These results are consistent with the hypothesis that DT-diaphorase expression may be a major determinant of the sensitivity of tumours to EO9. This should be considered in the clinical development of the drug.

Topics: Adenocarcinoma; Animals; Antineoplastic Agents; Aziridines; Cell Line; Colonic Neoplasms; Dose-Response Relationship, Drug; Female; Humans; Indolequinones; Indoles; Mice; Mice, Inbred Strains; NAD(P)H Dehydrogenase (Quinone); Tumor Cells, Cultured

DT-diaphorase is a unique two electron (2e) donating reductase catalyzing either bioactivation or bioprotection reactions. Using human and rodent DT-diaphorase preparations (cell extracts and purified enzyme) we have characterized the reductive metabolism of the hypoxic cell cytotoxins EO9, mitomycin C (MMC), CB 1954, and SR 4233 in vitro. Drug metabolism was assayed spectrophotometrically or by HPLC, with dicoumarol as a selective inhibitor. DNA damage was measured using an agarose gel mobility technique with plasmid pBR322 DNA. The developmental indoloquinone, EO9, was metabolized by both rat Walker and human HT29 tumor DT-diaphorases. Reduction proceeded 5-fold more efficiently with the rat than the human tumor enzyme and resulted in single-strand breaks in plasmid DNA. The structurally related MMC was metabolized much more slowly than EO9 by the rat Walker tumor enzyme and there was no detectable reaction with the human HT29 tumor DT-diaphorase. No DNA damage was seen with MMC for either enzyme. The dinitrophenylaziridine CB 1954 was reduced by both human and rat enzymes forming, preferentially, the highly toxic 4-hydroxylamine as a 4e reduction product. Rates were 3-fold lower than for the human tumor enzyme. SR 4233 was also reduced by the rat tumor enzyme predominantly via 4e reduction to the benzotriazine SR 4330, in a novel reaction mechanism. This appears to be a bioprotection pathway that bypasses the toxic 1e radical formed by other reductases. Such information may be valuable in the selection of hypoxic cell cytoxins to treat human tumors high or low in DT-diaphorase and should facilitate 'enzyme-directed' analogue development.

Topics: Animals; Antineoplastic Agents; Aziridines; Carcinoma 256, Walker; Cell Hypoxia; Colonic Neoplasms; Humans; In Vitro Techniques; Indolequinones; Indoles; Mitomycin; NAD(P)H Dehydrogenase (Quinone); Oxidation-Reduction; Prodrugs; Rats; Tirapazamine; Triazines

EO9 [3-hydroxymethyl-5-aziridinyl-1-methyl-2-(H-indole-4, 7-indione)-propenol] is a novel indoloquinone structurally related to mitomycin C, a quinone anticancer drug that requires reductive bioactivation. NAD(P)H: (quinone-acceptor) oxidoreductase (quinone reductase, DT-diaphorase, EC 1.6.99.2) is an obligate 2-electron donating enzyme that can reduce a variety of quinones resulting either in bioactivation or bioprotection. Using quinone reductase (QR) preparations from rat Walker 256 mammary tumor cells and human HT29 colon carcinoma cells, we have characterized the role of this enzyme in EO9 reductive metabolism. QR activity was assayed under optimal conditions by following cytochrome c reduction at 550 nm in the presence of enzyme, quinone substrate, NADH, and bovine albumin, and confirmed by loss of EO9 absorbance at 550 nm. Both the rat and human tumor cell enzymes catalyzed reduction of the benchmark quinone menadione with a similar Km of 1.4-3.1 microM, although the Vmax was 7 to 8-fold lower for the human preparation. EO9 was readily reduced by the rat Walker QR. The mean Km was about 5-fold higher than for menadione at around 15 microM and the Vmax was 6-fold lower at around 2.5 mumol of cytochrome c reduced mg-1 of protein. EO9 was also metabolized by QR from HT29 human colon carcinoma cells but rather less efficiently than by the rat tumor enzyme. For example, the rate was 6-fold lower than that for the Walker tumor enzyme at 100 microM substrate concentration after correcting for the 7- to 8-fold difference in specific activity for the two preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Antineoplastic Agents; Aziridines; Biotransformation; Carcinoma 256, Walker; Colonic Neoplasms; Dicumarol; DNA Damage; DNA, Bacterial; Humans; Indolequinones; Indoles; Kinetics; Mitomycin; Mitomycins; NAD(P)H Dehydrogenase (Quinone); Oxidation-Reduction; Quinone Reductases; Quinones; Rats; Superoxide Dismutase; Tumor Cells, Cultured; Vitamin K