Spatial and seasonal variability of human and fish viruses in mussels inside and offshore of Ravenna's harbour (Adriatic Sea, Italy).

AIMS: This study aims to investigate the presence and spatial-seasonal variability of human and fish viruses in coastal marine systems using Ravenna's harbour area (Adriatic Sea, Italy) as a model. METHODS AND RESULTS: Human viruses (noroviruses and hepatitis A virus) and one of the most threatening finfish pathogens, the nervous necrosis virus (NNV), were investigated in mussels living inside and offshore Ravenna's harbour. Thirty-three and 36·7% of tested mussel samples resulted contaminated by human and fish viruses respectively. A different spatial-seasonal distribution was observed. Human viruses were detected mainly in inner port sites during colder months, while NNV was detected in both inside and offshore of Ravenna's harbour, mainly during warmer months. CONCLUSIONS: The presence of human viruses in the inner port close to the city centre could be attributed to wastewaters carrying pathogens in the port environment and this arises public health concerns, however, the presence of these viruses limited to the canal port during the winter can greatly reduce the risk to human health. Regarding NNV, the accumulation and release of viable virus by mussels, could represent a viral source for susceptible finfish. These findings reflect the different epidemiological features of these infections and indicate the importance to choose the correct indicator to monitor viral contaminations. SIGNIFICANCE AND IMPACT OF THE STUDY: The high frequency of viral contamination pointed out in the study stresses the imperative to monitor the viral presence in all coastal habitats where the high natural value meets several recreational and commercial activities such as the Ravenna's harbour area. Particularly, this study could represent a novel starting point for the development of a more structured bio-monitoring program, in order to ensure improved environmental management and safety of coastal areas.

Sediment metal enrichment and ecological risk assessment of ten ports and estuaries in the World Harbours Project.

Ten global harbours were assessed for sediment quality by quantifying the magnitude of anthropogenic change and ecological risk. Anthropogenic change (enrichment) was high for Derwent River and Sydney estuary, moderate for Santander Harbour, Rio de Janeiro and Dublin Port, slight for Hong Kong, minimal for Darwin. All 10 enrichment indices used showed similar results. Derwent River sediment was rated at high ecological risk, followed by Sydney and Santander estuaries with moderate risk. Auckland and Darwin sediments exhibited minimal ecological risk and sediment in the remaining harbours (Dublin, Hong Kong, Ravenna, Ria de Vigo and Rio de Janeiro) were assessed at slight ecological risk. The extraordinary variety of environments and types/quantities/qualities of data investigated resulted in as much a critique and development of methodology, as an assessment of human impact, including unique techniques for elemental normalisation and contaminant classification. Recommendations for an improved technical framework for sediment quality assessment are provided.

Identifying Frailty Levels and Associated Factors in a Population Living in the Context of Poverty and Social Vulnerability.

This study aimed to investigate a vulnerable population living in the context of poverty in a Brazilian municipality, in order to identify the factors that are associated with frailty syndrome in elderly people. From the total population living in the area, a random sample of 363 community-dwelling people, 60 years and older, age and gender-stratified, was selected to participate in the research. After losses, a sample of 304 older adults was classified as non-frail, pre-frail and frail. According to the Fried frailty criteria, the prevalence was 12.2% for non-frail individuals, 60.5% pre-frail and 27.3% frail. The main factors associated with frailty in the studied sample were low level of physical activity (OR: 5.2, 95%CI: 2.5-11.0), the occurrence of two or more falls within 12 months (OR: 3.1, 95%CI: 1.4-7.1), mobility deficits (OR: 3.0, 95%CI: 1.5-5.8), and depressive symptoms (OR: 1.9, 95%CI: 1.1-3.7). This study identified the most important factors that must be evaluated to identify frailty syndrome in a socially vulnerable population in the context of poverty. The data should help to encourage effective strategies concerning public health policies for this population.

Human trampling as short-term disturbance on intertidal mudflats: effects on macrofauna biodiversity and population dynamics of bivalves.

The effect of physical disturbance in the form of trampling on the benthic environment of an intertidal mudflat was investigated. Intense trampling was created as unintended side-effect by benthic ecologists during field experiments in spring and summer 2005, when a mid-shore area of 25 × 25 m was visited twice per month by on average five researchers for a period of 8 months. At the putatively-impacted location (I) (25 × 25 m) and two nearby control locations (Cs) (25 × 25 m each), three sites (4 × 4 m) were randomly selected and at each site, three plots (50 × 50 cm) were sampled after 18 and 40 days from the end of the disturbance. Multivariate and univariate asymmetrical analyses tested for changes in the macrofaunal assemblage, biomass of microphytobenthos and various sediment properties (grain-size, water content, NH4 and NO3 concentrations in the pore water) between the two control locations (Cs) and the putatively-impacted location (I). There were no detectable changes in the sediment properties and microphytobenthos biomass, but variability at small scale was observed. Microphytobenthos and NH4 were correlated at I to the number of footprints, as estimated by the percentage cover of physical depressions. This indicated that trampling could have an impact at small scales, but more investigation is needed. Trampling, instead, clearly modified the abundance and population dynamics of the clam Macoma balthica (L.) and the cockle Cerastoderma edule (L.). There was a negative impact on adults of both species, probably because footsteps directly killed or buried the animals, provoking asphyxia. Conversely, trampling indirectly enhanced recruitment rate of M. balthica, while small-sized C. edule did not react to the trampling. It was likely that small animals could recover more quickly because trampling occurred during the growing season and there was a continuous supply of larvae and juveniles. In addition, trampling might have weakened negative adult-juvenile interactions between adult cockles and juvenile M. balthica, thus facilitating the recruitment. Our findings indicated that human trampling is a relevant source of disturbance for the conservation and management of mudflats. During the growing season recovery can be fast, but in the long-term it might lead towards the dominance of M. balthica to the cost of C. edule, thereby affecting ecosystem functioning.

Impact of dredging in a shallow coastal lagoon: Microtox Basic Solid-Phase Test, trace metals and Corophium bioassay.

The aim of this work was to measure survival of the amphipod Corophium insidiosum and luminescence inhibition in the marine bacterium Vibrio fisheri on surface sediment samples collected from a shallow coastal lagoon (Pialassa Baiona, northern Adriatic Italian coast) before execution of dredging operations to deepen the main inner channel of the lagoon and restore the water circulation. Trace metal (Cd, Cu, Cr, Hg, Ni, Pb) concentrations, grain size and organic carbon matter content as loss of ignition were also measured. Toxicity testing with V. fisheri was carried out according to the Microtox Basic Solid-Phase Test (BSPT) protocol. The preliminary outcomes of this work show that: (a) the investigated area can be categorised as moderately degraded; (b) there is no evident spatial pattern in sediment toxicity and trace metal concentrations; (c) Microtox responses are not biased by sediment characteristics such as silt, clay and organic matter content.

Association of personal and familial suicide risk with low serum cholesterol concentration in male lithium patients.

OBJECTIVE: We sought to establish whether low cholesterol concentration may be associated with a personal history of attempted suicide or a family history of completed suicide in psychiatric out-patients on maintenance lithium treatment, who represent a population at risk for suicide. METHOD: We retrospectively reviewed charts regarding 783 out-patients consecutively admitted to a lithium clinic from 1976 to 1999. Individual age- and gender-specific quartile of serum cholesterol concentration were correlated against personal lifetime suicide attempts and completed suicide in first-degree relatives. RESULTS: The proportion of men with a personal lifetime history of attempted suicide, especially if violent, and that of men with history of completed suicide in a first-degree relative were significantly higher among the group with cholesterol concentration in the lowest quartile compared to the group with cholesterol levels above the 25th percentile. CONCLUSION: Low cholesterol concentration should be studied further as a potential biological/genetic marker of suicide risk.

Association between dopamine receptor genes and migraine without aura in a Sardinian sample.

BACKGROUND: Migraine seems to be caused by a combination of environmental and genetic factors. Clinical and pharmacologic evidence supports the hypothesis that dopaminergic transmission is involved in the pathogenesis of migraine. OBJECTIVE: The current report concerns a genetic study to test the involvement of genes for dopamine (DA) receptors D2 (DRD2), D3 (DRD3), and D4 (DRD4) in migraine without aura, particularly in a subgroup with enhanced DA sensitivity. METHODS: For the first time, a family-based association method--the Transmission Disequilibrium Test (TDT)--was used to examine an isolated population, such as Sardinians. We studied 50 nuclear families of patients affected by migraine without aura. The subgroup of dopaminergic migraineurs was selected based on the presence of both nausea and yawning immediately before or during the pain phase of migraine. RESULTS: No association was detected using the TDT between DRD3, DRD4, and migraine without aura either in the overall sample or in the subgroup. No difference was observed in DRD2 allelic distribution in the overall sample, although the allelic distribution at the DRD2 locus differed significantly in the subgroup of dopaminergic migraineurs (p = 0.004). Allele 1 of the TG dinucleotide intronic noncoding polymorphism of the DRD2 locus was the individual allele that appeared to be in disequilibrium with migraine without aura (p = 0.02). CONCLUSIONS: Our data suggest that a genetic approach could be useful in providing molecular support to the hypothesis that hypersensitivity of the dopaminergic system may represent the pathophysiologic basis of migraine, at least in a subgroup of patients.

A step forward in enzymatic measurement of creatinine.

We describe an improved enzymatic ultraviolet absorbance method for assaying creatinine in serum, plasma, and urine. Creatinine is hydrolyzed by creatinine iminohydrolase (EC 3.5.4.21) to ammonia and N-methylhydantoin. The ammonia produced combines with 2-oxoglutarate and NADPH in the presence of glutamate dehydrogenase to yield glutamate and NADP+. The consumption of NADPH, measured by a two-point fixed-time assay, is proportional to the amount of creatinine in the sample. The assay is carried out in two steps: The first step eliminates background absorbance in hyperlipemic samples and endogenous ammonia through a "clearing system" and an isocitrate dehydrogenase-based "ammonia scavenger system"; the second step starts creatinine measurement. The method affords a simple, rapid, and sensitive assay with good precision and extended linearity; it employs working solutions stable at least 4 months. Test results compare closely with those of the isotope dilution-mass spectrometry Definitive Method, the HPLC procedure, and the fuller's earth method. The proposed method is not subject to interference from several metabolites or from the 72 drugs tested. Because it is easily automated, the method is suitable for routine work in clinical laboratories.

Automatic quantitative evaluation of autoradiographic band films by computerized image analysis.

The present paper describes a new image processing method for automatic quantitative analysis of autoradiographic band films. It was developed in a specific image analysis environment (IBAS 2.0), but the algorithms and methods can be utilized elsewhere. The program is easy to use and presents some particularly useful features for evaluation of autoradiographic band films, such as the choice of whole film or single lane background determination; the possibility of evaluating bands with film scratch artifacts and the quantification in absolute terms or relative to reference values. The method was tested by comparison with laser-scanner densitometric quantifications of the same autoradiograms. The results show the full compatibility of the two methods and demonstrate the reliability and sensitivity of image analysis. The method can be used not only to evaluate autoradiographic band films, but to analyze any type of signal bands on other materials (e.g. electrophoresis gel, chromatographic paper, etc.).

Kinetic colorimetric assay of lipase in serum.

We describe a kinetic colorimetric method for assaying lipase (EC 3.1.1.3) activity in serum by using a natural long-chain fatty acid 1,2-diglyceride. In the presence of colipase, deoxycholate, and calcium ions, pancreatic lipase hydrolyzes the clear substrate solution to produce a 2-monoglyceride, which in turn releases glycerol by the action of a 2-monoglyceride lipase. Glycerol is then assayed by a sequence of enzymatic actions (glycerol kinase, glycerol phosphate oxidase, and peroxidase) that produce a violet quinone monoimine dye with peak absorption at 550 nm. The method features zero-order reaction kinetics, provides a simple and rapid assay with an extended dynamic range, is specific and precise, gives results that correlate well (r greater than or equal to 0.99) with those of methods in which emulsified triolein is the substrate, and lends itself readily to automation. For all these reasons, the method seems highly suitable for routine use in clinical laboratories.

DNA cross-linking and sequence selectivity of aziridinylbenzoquinones: a unique reaction at 5'-GC-3' sequences with 2,5-diaziridinyl-1,4-benzoquinone upon reduction.

Several bifunctional alkylating agents of the aziridinylbenzoquinone class have been evaluated as potential antitumor agents. 3,6-Bis[(2-hydroxyethyl)amino]-2,5- diaziridinyl-1,4-benzoquinone (BZQ), 2,5-diaziridinyl-1,4-benzoquinone (DZQ), 3,6-bis(carboxyamino)-2,5-diaziridinyl- 1,4-benzoquinone (AZQ), and six analogues of AZQ have been studied for their ability to induce DNA interstrand cross-linking, as measured by an agarose gel technique, and to determine whether they react with DNA in a sequence-selective manner, as determined by a modified DNA sequencing technique. At an equimolar concentration (10 microM), only DZQ and BZQ showed any detectable cross-linking at pH 7 without reduction. Cross-linking was enhanced in both cases at low pH (4). Reduction by ascorbic acid at both pH's increased the cross-linking, which was particularly striking in the case of DZQ. In contrast, AZQ and its analogues only produced a significant level of cross-linking under both low-pH and reducing conditions, the extent of cross-linking decreasing as the size of the alkyl end group increased. The compounds reacted with all guanine-N7 positions in DNA with a sequence selectivity similar to other chemotherapeutic alkylating agents, such as the nitrogen mustards, although some small differences were observed with BZQ. Nonreduced DZQ showed a qualitatively similar pattern of reactivity to the other compounds, but on reduction (at pH 4 or 7) was found to react almost exclusively with 5'-GC-3' sequences, and in particular, at 5'-TGC-3' sites. A model to explain this unique reaction is proposed.

Cis dichlorodiammine platinum induced DNA interstrand cross-links in primary cultures of human ovarian cancer.

We quantified and examined the kinetics of DNA interstrand cross links (DNA-ISC) caused by Cis dichlorodiammine platinum (DDP) using the method of alkaline elution in 58 highly purified human ovarian tumours growing in primary culture. A large heterogeneity in both the quantity and kinetics of DDP induced DNA-ISC was observed in cultures derived from neoplasms of different patients and from different lesions of the same patient. In the majority of cases. DNA-ISC lasted for prolonged time intervals after 1 h drug exposure, being significantly repaired only 48 or 72 h following drug washout. The persistence of DNA-ISC is probably due to a prolonged formation of these lesions for up to 24 h as assessed by the change in the repair kinetics that occurred after preventing new DNA-ISC formation by quenching of monoadducts with thiourea. The inefficient repair of DDP monoadducts appears therefore to be a possible reason for the permanence of DNA-ISC. These studies suggest that the long permanence of DNA-ISC in human ovarian cancer could be the basis for the high selectivity of DDP for this human malignancy.

Measurement of the sequence specificity of covalent DNA modification by antineoplastic agents using Taq DNA polymerase.

A polymerase stop assay has been developed to determine the DNA nucleotide sequence specificity of covalent modification by antineoplastic agents using the thermostable DNA polymerase from Thermus aquaticus and synthetic labelled primers. The products of linear amplification are run on sequencing gels to reveal the sites of covalent drug binding. The method has been studied in detail for a number of agents including nitrogen mustards, platinum analogues and mitomycin C, and the sequence specificities obtained accord with those obtained by other procedures. The assay is advantageous in that it is not limited to a single type of DNA lesion (as in the piperidine cleavage assay for guanine-N7 alkylation), does not require a strand breakage step, and is more sensitive than other primer extension procedures which have only one cycle of polymerization. In particular the method has considerable potential for examining the sequence selectivity of damage and repair in single copy gene sequences in genomic DNA from cells.

DNA interstrand crosslinking and sequence selectivity of dimethanesulphonates.

Members of the homologous series of alkanediol dimethanesulphonates of general formula H3C.SO2O.(CH2)n.O.SO2.CH3 have been tested for their ability to produce DNA interstrand crosslinking and DNA sequence selectivity of guanine-N7 alkylation. In a sensitive crosslinking gel assay the efficiency of DNA interstrand crosslink formation, dependent on the ability of the alkylating moiety to span critical nucleophilic distances within the DNA, was found at 6 h to be 1,6-hexanediol dimethanesulphonate (Hexa-DMS) (n = 6) greater than methylene dimethanesulphonate (MDMS) (n = 1) greater than 1,8-octanediol dimethanesulphonate (Octa-DMS) (n = 8) greater than Busulphan (n = 4). The DNA interstrand crosslinking produced by MDMS was not due to either of its hydrolysis products, formaldehyde or methanesulphonic acid (MSA). In contrast the extent of monoalkylation at guanine-N7 as determined by a modified DNA sequencing technique was found to be Busulphan much greater than Hexa-DMS = Octa-DMS, with a sequence selectivity somewhat less than that of other chemotherapeutic alkylating agents such as nitrogen mustards. MDMS at high levels induced a non-specific depurination as a result of the reduction in pH resulting from MSA release. More strikingly MDMS (and MSA) produced a single strong site of guanine reaction (depurination) in a guanine-rich 276 base pair fragment of pBR322 DNA in the sequence of 5'-ATGGTGG-3'. This was observed when non-specific depurination was negligible and was not seen with formic acid. Thus structurally similar alkylating agents can differ in their type and extent of DNA monoalkylation and interstrand crosslinking, and in some cases (e.g. MDMS/MSA) produce reactions with a high degree of selectivity.

Selective DNA interaction of the novel distamycin derivative FCE 24517.

N-Deformyl-N-(4-N-N,N-bis(2-chloroethylamino)benzoyl)distamy cin A (FCE 24517) is a novel cytotoxic and antitumor agent shortly to be investigated in phase I clinical trials. It was equally effective in inhibiting the growth of the murine L1210 line and of a subline (L1210/PAM) resistant to nitrogen mustards, whereas distamycin A was virtually inactive. The cellular uptake and retention of FCE 24517 and distamycin A were similar, thus excluding the possibility that this marked variation in cytotoxic activity was due to different intracellular concentrations of the two compounds. FCE 24517 did not appear to act as an inhibitor of macromolecule synthesis. As shown by radioactively labeled precursor incorporation only 24 h after drug treatment a significant inhibition of DNA synthesis was observed in L1210 or in L1210/PAM, when a marked proportion of cells was arrested in premitotic phase. FCE 24517 did not cause DNA breaks, DNA interstrand cross-links, or DNA-protein cross-links in L1210 cells exposed to active drug concentrations. A very low amount of radioactivity was found to be bound irreversibly to DNA in L1210 cells exposed for 1 h to [14C]FCE 24517. Using plasmid pBr322 DNA fragments in a modified version of the Maxam and Gilbert DNA sequencing technique we found no detectable binding of FCE 24517 to N-7-guanine (the major site of alkylation for classical alkylating agents), whereas some alkylations to adenine (presumably to N-3-adenine) were demonstrated. Thus it appears that FCE 24517 is a novel antitumor agent with a mode of action different from that of the drugs currently used in the clinic. In summary it is suggested that FCE 24517 acts by causing a few selective alkylations to adenines in the minor groove of DNA, although the precise base sequence necessary has yet to be elucidated.

DNA damage and sequence specificity of DNA binding of the new anti-cancer agent 1,4-bis(2'-chloroethyl)-1,4-diazabicyclo-[2.2.1] heptane dimaleate (Dabis maleate)

The DNA damage and the sequence specificity of guanine-N7 alkylation produced by the novel, positively charged, antineoplastic agent 1,4-bis(2'-chloroethyl)-1,4-diazabicyclo-[2.2.1] heptane dimaleate (Dabis maleate) and its uncharged tertiary amine analogue 1,4-bis(2'-chloroethyl)-1,4-diazacyclohexane (Dabis analogue) were investigated in L1210 cells and isolated DNA. Both compounds are cytotoxic in vitro causing an arrest of L1210 cells in G2/M phase of the cell cycle. In isolated DNA, Dabis maleate alkylates guanine at the N7-position with some differences in specificity compared to other alkylating agents (e.g. nitrogen mustard). Significant differences are also evident between Dabis maleate and Dabis analogue, suggesting that Dabis analogue is not the sole alkylating species of Dabis maleate. Using the alkaline elution technique a moderate number of DNA interstrand cross-links were detected in L1210 cells treated with both compounds, which were completely repaired within 24 h. Dabis maleate and Dabis analogue do not cause DNA single strand breaks or DNA protein cross-links at the doses at which DNA interstrand cross-links were detected.

Distamycins inhibit the binding of OTF-1 and NFE-1 transfactors to their conserved DNA elements.

We investigated the effects of the antiviral agent distamycin A and of a distamycin derivative (FCE 24517) which possesses antineoplastic activity on the binding of some regulatory proteins to DNA. Both compounds inhibited the binding to DNA of the ubiquitous octamer binding factor OTF 1 and of the erythroid specific GATAAG protein (NFE 1). This was shown using the electrophoretic mobility shift assay on a DNA fragment of human gamma-globin gene promoter (-156 to -201), on the same fragment with a point mutation (T to C mutation) known to have an increased affinity of binding for NFE 1, on a DNA fragment of human histone H2B promoter and on a DNA fragment of mouse alpha 1 globin promoter. The ability of distamycin or of FCE 24517 to inhibit the binding was specific for AT-rich sequences since neither drug inhibited the binding of nuclear protein factors to the sequence CCACACCC of the human beta globin gene. Binding to DNA was investigated by evaluating the drugs' ability to protect selected sequences from DNase I digestion (DNase footprinting). Distamycins binding was highly preferential for DNA sequences containing stretches of AT. These studies indicate that chemicals which have a high degree of DNA sequence-specific binding can selectively inhibit the binding of regulatory proteins to DNA. These effects might be responsible for modification of the transcription of specific genes and might to some extent account for these drugs' antiviral and antineoplastic activities. This approach offers potential for the investigation of new such drugs.

One-step protocol for assays of total and direct bilirubin with stable combined reagents.

We describe an improved colorimetric method for assays of total and direct bilirubin in serum. Bilirubin reacts with diazotized sulfanilic acid in an acidic medium to form a blue azopigment. Total bilirubin is assayed in the presence of reaction accelerators (caffeine, urea, and citric acid), direct bilirubin in their absence. The azo compound so formed is read at the same wavelength (570 nm) in both assays. A sample blank is run in parallel. Standard curves are linear for total and direct bilirubin concentrations up to 513.0 and 256.5 mumol/L, respectively. The method is characterized by (a) use of the same protocol for both assays, i.e., a one-step procedure with short reaction time (5 min at room temperature), and (b) use of a single working solution, which, refrigerated, is stable for one month. The method is reliable, yields results that compare closely with those of the classical Jendrassik--Gróf method, is suitable for routine use, and lends itself to automation.

DNA damage, cytotoxic effect and cell-cycle perturbation of Hoechst 33342 on L1210 cells in vitro.

This study was designed to evaluate the effects of vital dye Hoechst 33342 (HO 33342), at concentrations used to obtain a good DNA histogram resolution, on DNA integrity, cell growth, and cell-cycle phase distribution of L1210 cells. HO 33342 exposure for 2 h, at 37 degrees C produced DNA single-strand breaks as assessed by the method of alkaline elution. DNA single-strand breaks were concentration dependent (in the range .5-5 micrograms/ml) and increased significantly when HO 33342 (0.5-1.5 micrograms/ml) was associated with exposure in a flow cytometer to U.V. laser beam illumination. HO 33342 produced a cytotoxic effect on cell growth even at the concentration of 0.5 microgram/ml--a concentration ten-fold smaller than those required to obtain a good DNA histogram resolution. HO 33342 produced a severe block of the cells in the G2-M phase of the cell cycle already evident 24 h after stain exposure and continuing up to 144 h after start of recovery. A new polyploid cell population (with a 4 c DNA content) not present in the unstained cells was already evident 24 h after dye exposure. The data shown in the present paper would imply caution in using sorted cells stained with HO 33342 dye for biological, biomedical, and pharmacological studies.

In vitro and in vivo methazolastone-induced DNA damage and repair in L-1210 leukemia sensitive and resistant to chloroethylnitrosoureas.

DNA damage caused by methazolastone [an analogue of 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide which does not require metabolic activation] was investigated in L-1210 leukemia which is sensitive to this drug and in a L-1210 subline [L-1210/N,N-bis(2-chloroethyl)-N-nitrosourea (BCNU)] which is resistant to both chloroethylnitrosoureas and methyltriazenes. Both in vitro and in vivo metazolastone caused formation of DNA alkali-labile sites (assessed by alkaline elution techniques) which were present in similar amounts and repaired at a similar rate in L-1210 and L-1210/BCNU. This suggests that these lesions are not crucial to methyltriazenes activity. DNA alkali-labile sites may be due to the removal of 7-methylguanine by 7-methylguanine-DNA glycosylase which showed the same activity in L-1210 and L-1210/BCNU. Flow cytometry studies revealed that in L-1210 but not in L-1210/BCNU methazolastone induced an arrest of cells in SL-G2-M phases. This blockade was delayed, occurring after at least two cell divisions after drug treatment and therefore appeared temporally unrelated to the presence of DNA alkali-labile sites. There was three times more O6-methylguanine-DNA methyltransferase in L-1210/BCNU than in L-1210 suggesting that methylation of O6-guanine is an important lesion for methyltriazenes activity and resistance to this drug may be linked to its repair.