Characterization of a polymorphism in NAD(P)H: quinone oxidoreductase (DT-diaphorase)

NAD(P)H:quinone oxidoreductase (NQO1, EC 1.6.99.2) is an obligate two-electron reductase that can either bioactivate or detoxify quinones and has been proposed to play an important role in chemoprevention. We have previously characterized a homozygous point mutation in the BE human colon carcinoma cell line that leads to a loss of NQO1 activity. Sequence analysis showed that this mutation was at position 609 of the NQO1 cDNA, conferring a proline to serine substitution at position 187 of the NQO1 enzyme. Using polymerase chain reaction (PCR) analysis, we have found that the H596 human non-small-cell lung cancer (NSCLC) cell line has elevated NQO1 mRNA, but no detectable enzyme activity. Sequencing of the coding region of NQO1 from the H596 cells showed the presence of the identical homozygous point mutation present in the BE cell line. Expression and purification of recombinant wild-type and mutant protein from E. coli showed that mutant protein could be detected using immunoblot analysis and had 2% of the enzymatic activity of the wild-type protein. PCR and Northern blot analysis showed moderate to low levels of expression of the correctly sized transcript in the mutant cells. Immunoblot analysis also revealed that recombinant mutant protein was immunoreactive; however, the mutant protein was not detected in the cytosol of either BE or H596 cells, suggesting that the mutant proteins were either not translated or were rapidly degraded. The absence of any detectable, active protein, therefore, appears to be responsible for the lack of NQO1 activity in cells homozygous for the mutation. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis for the mutation at position 609 conducted on 90 human lung tissue samples (45 matched sets of tumour and uninvolved tissue) revealed a 7% incidence of individuals homozygous for the mutation, and 42% heterozygous for the mutation. These data suggest that the mutation at position 609 represents a polymorphism in an important xenobiotic metabolizing enzyme, which has implications for cancer therapy, chemoprevention and chemoprotection.

Radiotherapy for treatment of localized gastrointestinal non-Hodgkin's lymphoma

BACKGROUND

The study analyses a standardized, risk-adapted radiotherapy for stage IE-IIE primary extranodal lymphoma of the stomach and bowel.

METHODS

Sixty eight patients (31 females, 37 males, median age 56 years) were treated from 1987-1992 in 15 centers. Fifty six patients had gastric and 12 patients had bowel lymphomas. Gastric lymphomas (low or intermediate grade stage I-II: 38 patients/high grade stage I: 18 patients) were treated by whole abdominal irradiation (25/30 Gy), booster dose to involved field (30/40 Gy) and additional boost to macroscopic residual lymphoma (40/50 Gy). Surgery consisted of gastrectomy (19 patients), partial gastric resection (30) or biopsy (7). In 8/18 stage II patients, supradiaphragmal irradiation was added. In 10/12 patients with bowel lymphoma, segment resection was performed, two received biopsy only. Radiation doses equalled those used for gastric lymphoma:

RESULTS

In 51/56 patients (91%) with gastric lymphoma, the recommended dose for whole abdominal irradiation was given. A total of 40/56 patients (71%) received the required dose to the upper abdominal region, in 22/56 patients (39%) a booster dose for residual disease was applied. Five-year overall survival was 87%, 5-year disease-free survival 84%. Of nine relapses, two were in the gastric stump of low grade patients after reinfection with Helicobacter pylori. Three infield, intraabdominal relapses were observed in intermediate and high grade lymphoma, all other relapses were outfield. Eleven patients experienced late toxicity (bowel obstruction after laparatomy and irradiation, four patients; chronic gastritis, three patients; asymptomatic left kidney atrophy, two patients; asymptomatic hepathopathia, two patients). In bowel lymphoma, 5-year disease-free survival was 65%.

CONCLUSION

This study demonstrates the high efficacy of risk-adapted radiotherapy in gastric lymphoma. In low grade gastric lymphoma, whole abdominal irradiation may be reduced in dose or omitted. Total gastrectomy does not improve results and should therefore be avoided if possible.

Cell-specific activation and detoxification of benzene metabolites in mouse and human bone marrow: identification of target cells and a potential role for modulation of apoptosis in benzene toxicity

The role of cell-specific metabolism in benzene toxicity was examined in both murine and human bone marrow. Hemopoietic progenitor cells and stromal cells are important control points for regulation of hemopoiesis. We show that the selective toxicity of hydroquinone at the level of the macrophage in murine bone marrow stroma may be explained by a high peroxidase/nicotanimide adenine dinucleotide phosphate, reduced [NAD(P)H]:quinone oxidoreductase (NQO1) ratio. Peroxidases metabolize hydroquinone to the reactive 1,4-benzoquinone, whereas NQO1 reduces the quinones formed, resulting in detoxification. Peroxidase and NQO1 activity in human stromal cultures vary as a function of time in culture, with peroxidase activity decreasing and NQO1 activity increasing with time. Peroxidase activity and, more specifically, myeloperoxidase, which had previously been considered to be expressed at the promyelocyte level, was detected in murine lineage-negative and human CD34+ progenitor cells. This provides a metabolic mechanism whereby phenolic metabolites of benzene can be bioactivated in progenitor cells, which are considered initial target cells for the development of leukemias. Consequences of a high peroxidase/NQO1 ratio in HL-60 cells were shown to include hydroquinone-induced apoptosis. Hydroquinone can also inhibit proteases known to play a role in induction of apoptosis, suggesting that it may be able to inhibit apoptosis induced by other stimuli. Modulation of apoptosis may lead to aberrant hemopoiesis and neoplastic progression. This enzyme-directed approach has identified target cells of the phenolic metabolites of benzene in bone marrow and provided a metabolic basis for benzene-induced toxicity at the level of the progenitor cell in both murine and human bone marrow.

The pulmonary autograft: history and basic techniques

The pulmonary autograft introduced in 1967 evolved from the homograft aortic valve, which had been in place 5 years by the time it showed structural deterioration. The strength of the autograft cusps was an initial anxiety, but clinical and experimental studies have shown that they are well able to withstand aortic pressures. The right side reconstruction has been with homografts, first aortic and later pulmonary. Other forms of reconstruction, including autogenous fascia lata and pericardium, have not been satisfactory. Clinical results have been rewarding and suggest a permanent valve replacement. Additionally, there is accumulating evidence that the autograft will grow in young patients. Most surgeons favor root replacement, but there is some anxiety about possible dilatation of the root. This probably relates to technical inadequacies, but subcoronary and inclusion or cylinder insertion remain valid options. There are few contraindications to the use of an autograft, and it has an increasing application in infective and post prosthetic endocarditis.

Expression of human NAD(P)H: quinone oxidoreductase (DT-diaphorase) in Chinese hamster ovary cells: effect on the toxicity of antitumor quinones

Previous studies have indicated that NAD(P)H: quinone oxidoreductase [DT-diaphorase (NQO1)] plays an important role in the bioreductive activation of quinone-containing antitumor agents. Although these studies demonstrated that purified NQO1 can reduce these compounds in vitro, the importance of NQO1 in the intracellular activation of quinone-containing antitumor agents remains controversial. In our study, we transfected human NQO1 into Chinese hamster ovary cells that do not normally express NQO1 activity and obtained stable clones that expressed NQO1 activity of 19-3527 nmol of 2,6-dichlorophenolindophenol reduced/min/mg of protein. The level of NQO1 expression correlated with an increased killing by streptonigrin, EO9 (3-hydroxymethyl-5-aziridinyl-1-methyl-2-(1H-indole-4,7-dione)-propen ol), and 2,5-diaziridinyl-3,6-dimethyl-1,4-benzoquinone, but mitomycin C sensitivity was independent of this activity. NQO1 expression also led to a slight decrease in the sensitivity of cells to menadione. Our data demonstrate that compounds that are efficient substrates for NQO1 in vitro are also bioactivated in cultured mammalian cells when they are transfected with human NQO1. These results are consistent with the relative abilities of mitomycin C, streptonigrin, EO9, and 2,5-diaziridinyl-3,6-dimethyl-1,4-benzoquinone to serve as substrates for bioreduction by human NQO1, and show that NQO1 levels are not necessarily predictive in terms of sensitivity to mitomycin C.

Induction of apoptosis by benzene metabolites in HL60 and CD34+ human bone marrow progenitor cells

Two cell types, HL60 human promyelocytic leukemia cells and CD34+ human bone marrow progenitor cells, were used as model systems to explore a possible role for apoptosis in the myelotoxicity of the phenolic metabolites of benzene. HL60 cells were treated with either phenol, catechol, hydroquinone, or 1,2,4-benzenetriol and then stained with Hoechst 33342 and propidium iodide and subjected to fluorescent microscopy. Cells with nuclear condensation and fragmentation were scored as apoptotic, and etoposide (40 microM) was used as a positive control. Catechol, 1,2,4-benzenetriol, and hydroquinone induced marked time- (0-24 hr) and concentration- (25-100 microM) dependent apoptosis, whereas phenol (750 microM) did not. Under these conditions, no significant necrosis was observed. The induction of apoptosis was confirmed by internucleosomal cleavage of DNA, assessed by agarose gel electrophoresis. CD34+ cells treated with etoposide (40 microM) or hydroquinone (50 microM) for 18 hr were stained and subjected to fluorescent microscopy as above. The percentage of cells exhibiting nuclear condensation and/or fragmentation as well as high intensity staining significantly increased in both cases. The induction of apoptosis was confirmed using a terminal deoxynucleotidyl transferase assay. These data show that apoptosis can be induced in both HL60 and CD34+ human bone marrow progenitor cells by benzene metabolites. The ability of phenolic metabolites of benzene to induce apoptosis in human bone marrow progenitor cells may contribute to benzene myelotoxicity.

Autologous breast reconstruction with endoscopic latissimus dorsi musculosubcutaneous flaps in patients choosing breast-conserving therapy: mammographic appearance

OBJECTIVE

The objective of this study was to define and evaluate mammographic changes in patients treated with breast-conserving therapy and a new reconstructive technique that uses autologous tissue from a latissimus dorsi musculosubcutaneous flap.

MATERIALS AND METHODS

Of 20 patients who underwent either immediate or delayed endoscopic latissimus dorsi muscle flap reconstruction after lumpectomy, 13 also had postsurgery mammograms available for review. Radiographic findings assessed included skin thickening, density or radiolucency at the reconstruction site, density around the flap, fat necrosis, calcifications, and the presence of surgical clips.

RESULTS

Mammograms for three patients (23%) revealed thickening that we believed was attributable to radiation therapy. No patient had increased density in the flap itself; all flaps were relatively radiolucent centrally (13/13; 100%). Mammograms revealed density around the rim of the flap in four patients (31%). This density was most likely secondary to latissimus dorsi muscle fibers and did not limit radiographic evaluation. One patient had calcifications, probably secondary to fat necrosis. No oil cysts were seen. In the majority of patients (11/13; 85%), surgical clips were visible.

CONCLUSION

Endoscopic latissimus dorsi muscle flap reconstruction, previously used only for mastectomy patients, is now being used for improved esthetic outcome in selected patients who desire breast conservation. Our results indicate that the mammographic findings are predictable. The most common findings are relative radiolucency centrally, with or without density from muscle fibers around the edges of the area of tissue transfer. The transplanted musculosubcutaneous flap does not interfere with mammographic evaluation.

Cytotoxic properties of iron-hydroxynaphthoquinone complexes in rat hepatocytes

The mechanisms of toxicity to isolated rat hepatocytes of Fe(II) and Fe(III) complexes of two structurally related naphthoquinones have been studied. All complexes were found to show a dose-dependent toxicity which precedes cell death. Within the naphthoquinone series the order of toxicity is Fe(II) > parent naphthoquinone > Fe(III). The iron complexes of 5-OH-1,4 naphthoquinone (5-OH-1,4 NQ; Juglone) are more toxic than the iron complexes of 2-OH-1,4 naphthoquinone (2-OH-1,4 NQ; Lawsone) indicating that the mechanisms of toxicity are different. Electrochemical studies on these complexes shows that 5-OH-1,4 NQ facilitates formation of stable semiquinone species while 2-OH-1,4 NQ does not. The low redox potential of 2-OH-1,4 NQ makes it a poor substrate for metabolism by reductases.

Immortalisation of a human diploid fibroblast cell strain: a DT-diaphorase paradox

Transfection of a normal human diploid fibroblast cell strain, GM38, with a simian virus 40 (SV40) large T antigen containing plasmid, yielded an immortal cell line, G38-8X, which had a similar sensitivity as the parental cell strain to the quinone-containing chemotherapeutic agent mitomycin C (MMC), under both aerobic and hypoxic exposure conditions. The activity level of DT-diaphorase was similar in both the parental GM38 and G38-8X cells. Although DT-diaphorase could be detected by Western blot analysis, using two mouse anti-human monoclonal antibodies, in GM38 cells, it was not detected in the G38-8X cells. G38-8X cells have a slightly increased P450R activity (2-fold), and have elevated P-glycoprotein levels compared with the parental GM38 cell strain. The immortal G38-8X cell line is 2-fold more resistant to ionising radiation than the parental GM38 cell strain (D10 approximately 5 Gy). Although these SV40 large T antigen immortalised human diploid fibroblasts behaved similarly to their parental cell strain in terms of MMC sensitivity and DT-diaphorase activity, careful characterisation revealed that these cells had enhanced P-glycoprotein activity and had a decreased sensitivity to ionising radiation.