Sister Chromatid Exchange Levels Research Articles

Human Polynucleotide Kinase Participates in Repair of DNA Double-Strand Breaks by Nonhomologous End Joining but not Homologous Recombination

Human polynucleotide kinase (hPNK) is a bifunctional enzyme possessing a 5'-DNA kinase activity and a 3'-phosphatase activity. Studies based on cell extracts and purified proteins have indicated that hPNK can act on single-strand breaks and double-strand breaks (DSB) to restore the termini to the chemical form required for further action by DNA repair polymerases and ligases (i.e., 5'-phosphate and 3'-hydroxyl termini). These studies have revealed that hPNK can bind to XRCC4, and as a result, hPNK has been implicated as a participant in the nonhomologous end joining (NHEJ) pathway for DSB repair. We sought to confirm the role of hPNK in NHEJ in the cellular setting using a genetic approach. hPNK was stably down-regulated by RNA interference expression in M059K glioblastoma cells, which are NHEJ positive, and M059J cells, which are NHEJ deficient due to a lack of DNA-PK catalytic subunit (DNA-PKcs). Whereas depletion of hPNK significantly sensitized M059K cells to ionizing radiation, no additional sensitization was conferred to M059J cells, clearly implying that hPNK operates in the same DNA repair pathway as DNA-PKcs. On the other hand, depletion of hPNK did not increase the level of sister chromatid exchanges, indicating that hPNK is not involved in the homologous recombination DSB repair pathway. We also provide evidence that the action of hPNK in the repair of camptothecin-induced topoisomerase 1 "dead-end" complexes is independent of DNA-PKcs and that hPNK is not involved in the nucleotide excision repair pathway.

XRCC1 down‐regulation in human cells leads to DNA‐damaging agent hypersensitivity, elevated sister chromatid exchange, and reduced survival of BRCA2 mutant cells

Previous studies using rodent cells indicate that a deficiency in XRCC1 results in reduced single-strand break repair, increased sensitivity to DNA-damaging agents, and elevated levels of sister chromatid exchange (SCE). Epidemiological studies have suggested an association of certain human XRCC1 polymorphisms with genetic instability and cancer susceptibility. However, investigations on the molecular functions of XRCC1 in human cells are limited. To determine the contributions of this nonenzymatic scaffold protein, we suppressed XRCC1 levels in several human cell lines using small interfering RNA (siRNA) technology. We report that XRCC1 down-regulation in HeLa cells leads to a concomitant decrease in the DNA ligase 3 protein level and an impaired nick ligation capacity. In addition, depletion of XRCC1 resulted in a significantly increased sensitivity to the alkylating agent methyl methanesulfonate and the thymidine base analog 5-hydroxymethyl-2'-deoxyuridine, a slightly increased sensitivity to ethyl methanesulfonate and 1,3-bis(2-chloroethyl)-1-nitrosourea, and no change in the response to camptothecin. We also discovered that a 70-80% reduction in XRCC1 protein leads to an elevated level of SCE in both HeLa cells and normal human fibroblasts, but does not affect chromosome aberrations in the diploid fibroblasts. Last, XRCC1 siRNA transfection led to an approximately 40% decrease in the survival of BRCA2-deficient cells, supporting a model whereby the accumulation of unrepaired SSBs leads to the accumulation of cytotoxic DNA double strand breaks following replication fork collapse in cells defective in homologous recombination.

Chromosome fragility in cattle with chronic enzootic haematuria

Chronic enzootic haematuria (CEH) is a severe syndrome due to prolonged ingestion of toxic principles of bracken fern, such as quercetin and ptaquiloside. Little information is available on chromosomal instability of cattle with access to bracken fern and suffering from CEH. In the present study, 45 cattle, aged from 7 to 12 years and pastured in the south of Italy, were cytogenetically investigated for the first time in search of both chromosomal aberrations (aneuploidy, gaps, chromatid breaks, chromosome breaks and fragments) and sister chromatid exchanges (SCEs). Of these animals, 30 (group 1) had access to bracken fern and showed signs of CEH, and 15 (group 2; control) did not. Percentage of abnormal cells (aneuploidy, chromatid breaks, chromosome breaks and fragments) was higher in animals affected by CEH (34.7%, group 1) than that (24.3%) reached in the control (group 2). The same results were achieved when including gaps. Indeed, the mean number of cells with structural aberrations excluding gaps (chromatid breaks, chromosome breaks and fragments) per cell was higher (P<0.001) in animals affected by CEH (0.16+/-0.36) than that (0.09+/-0.29) found in the control. Chromosome fragility in cells of animals affected by CEH was also confirmed when applying the SCE test: statistically higher levels (P<0.001) of SCEs were observed in animals with CEH (7.35+/-3.59 SCE/cell, group 1) than those in the control (5.40+/-2.68 SCE/cell).

Efforts to Ensure Safety of Hospital Pharmacy Personnel Occupationally Exposed to Antineoplastic Drugs during a Preparation Task

Purpose Antineoplastic drugs are often detected in the plasma and urine of medical staff, despite the adoption of safety measures. This study involves ambulatory chemotherapy, which was prepared on a rotating schedule at the Department of Pharmacy. The first objective of this study was to evaluate occupational exposure by measuring epirubicin in the urine and plasma and sister chromatid exchanges (SCE) in the peripheral lymphocytes of the involved pharmacists. The second, to improve a previously reported method for ease of occupational exposure evaluation. The third, to determine environmental contamination. Methods Pharmacists were categorized into three groups based on three patterns, depending on the other tasks they performed. They were alternately responsible for the preparation in each group with the recommended protections. Samples were collected at the end of each work day. High-performance liquid chromatography (HPLC) analysis along with fluorescence detection was performed at a flow rate of 200 mcL/min using 0.1% formic acid, methanol, and acetonitrile (75:5:20). Epirubicin in the samples was extracted by solid-phase extraction. Chromosomes were prepared according to a standard protocol. Results A final concentration of 2 ng/mL was the lower quantification limit. Epirubicin was not detected in the urine and plasma, and the SCE levels were within the normal limits for all the subjects. However, epirubicin was detected in samples collected from the preparation gloves. Conclusions For personnel safety, it is important to periodically evaluate protective measures. Pharmacists on a rotating schedule who work less than 6 hours per week on preparatory tasks were not unduly exposed to antineoplastics.

White blood cell sister chromatid exchange among a sample of Thai subjects exposed to toluene, an observation

There is a particular concern with toluene because some research has indicated that toluene exposure could result in chronic toxicity including mutagenesis and carcinogenesis. This study aimed to determine the rate of sister chromatid exchanges (SCE), a marker for genotoxicity, and its correlation to the classical urine biomarker for toluene exposure, urine hippuric acid, among a sample of Thai exposed subjects. A total of 26 police (all males) were included in this study. The average (mean +/- SD) urine hippuric acid level in these police was 0.8 +/- 0.4 mg/g creatinine. The average (mean +/- SD) SCE level in these police was 4.5 +/- 1.0/cell. The average SCE among the police with high urine hippuric acid levels was non-significantly higher than the average SCE level of those without (P = 0.41). This implies that the cytogenetic response to toluene was not different between the subjects with and without high toluene exposure. High exposure to toluene seems not to be related to high SCE.

Influence of polymorphisms in xenobiotic‐metabolizing genes and DNA‐repair genes on diepoxybutane‐induced SCE frequency

Analysis of the combined effects of polymorphisms in genes encoding xenobiotic metabolizing enzymes (XMEs) and DNA repair proteins may be a key to understanding the role of these genes in the susceptibility of individuals to mutagens. In the present study, we performed an in vitro experiment on lymphocytes from 118 healthy donors that measured the frequency of diepoxybutane (DEB) induced sister chromatid exchanges (SCEs) in relation to genetic polymorphisms in genes coding for XMEs (CYP1A1, CYP2E1, GSTT1, EPHX, and NAT2), as well as DNA repair proteins (XRCC1, XRCC2, XRCC3, XPD, XPA, XPC, XPG, XPF, ERCC1, BRCA1, NBS1, and RAD51). We found that GSTT1(-) and CYP2E1 c1/c2 polymorphisms were associated with higher DEB-induced SCE frequencies, and that NAT2 G(590)A was associated with lower SCE induction by DEB. Analysis of the effect of pairs of genes showed that for a fixed GSTT1 genotype, the SCE level increased with an increasing number of Tyr alleles in EPHX codon 113. We found that among GSTT1(+) individuals the DEB-induced SCE level was significantly lower when the EPHX 139 codon was His/Arg rather than His/His. An interaction between polymorphisms in CYP2E1 and at EPHX codon 113 was also observed. The results of our study confirm observations in cancer patients and in people exposed to xenobiotics indicating that sensitivity to mutagens depends upon a combined effect of a variety of "minor impact" genes. Moreover, our results indicate that polymorphisms in genes coding for XMEs have a greater influence on the genotoxic activity of DEB, measured by DEB-induced SCE frequency, than polymorphisms in genes encoding DNA repair proteins.

MPS1-dependent mitotic BLM phosphorylation is important for chromosome stability

Spindle assembly checkpoint (SAC) ensures bipolar attachment of chromosomes to the mitotic spindle and is essential for faithful chromosome segregation, thereby preventing chromosome instability (CIN). Genetic evidence suggests a causal link between compromised SAC, CIN, and cancer. Bloom syndrome (BS) is a genetic disorder that predisposes affected individuals to cancer. BS cells exhibit elevated rates of sister chromatid exchange, chromosome breaks, and CIN. The BS gene product, BLM, is a member of the RecQ helicases that are required for maintenance of genome stability. The BLM helicase interacts with proteins involved in DNA replication, recombination, and repair and is required for the repair of stalled-replication forks and in the DNA damage response. Here we present biochemical evidence to suggest a role of BLM phosphorylation during mitosis in maintaining chromosome stability. BLM is associated with the SAC kinase MPS1 and is phosphorylated at S144 in a MPS1-dependent manner. Phosphorylated BLM interacts with polo-like kinase 1, a mitotic kinase that binds to phosphoserine/threonine through its polo-box domain (PBD). Furthermore, BS cells expressing BLM-S144A show normal levels of sister chromatid exchange but fail to maintain the mitotic arrest when SAC is activated and exhibit a broad distribution of chromosome numbers. We propose that MPS1-dependent BLM phosphorylation is important for ensuring accurate chromosome segregation, and its deregulation may contribute to cancer.

A biomonitoring study on the workers from textile dyeing plants

We evaluated the genotoxic risk of workers from textile dyeing plants in Kahramanmaras, Turkey. Sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) were investigated in peripheral blood lymphocyte cultures of 40 workers and compared to those of 32 age-sex- and habit-matched healthy controls. Groups were selected after a questionnaire administration. Use of Maras powder (a kind of smokeless tobacco) was considered as modulating factor. The SCEs level did not show significant differences between workers and controls. The frequency of CA was significantly higher in workers than in controls. Use of Maras powder was a significant factor to increase the frequencies of SCE and CA in control group. The level of SCE and CA did not correlate with the age whereas there was a significant correlation between years of exposure and CA frequency. The results of this study revealed the genotoxic risk of textile dyers. Protective measures such as masks and gloves are desirable for preventing or minimizing the occupational exposure.

Biomarkers of environmental contaminants in field population of green mussel (Perna viridis) from Karnataka–Kerala coast (South West coast of India)

The green mussel Perna viridis was sampled from relatively clean and contaminated sites along the Kartanata-Kerala coast (south west coast of India) to study the tissue concentration of trace metals and biological responses to stress (biomarkers) such as sister chromatid exchange (SCE), chromosomal aberration, micronucleus (MN) test, hemic neoplasia (HN), Chromotest (Ames test) and comet assay. In general, mean tissue concentrations of toxic trace metals collected from 25 sampling sites were found to be below the World Health Organisation (WHO) permissible concentration given for seafood. The digestive gland extract of mussels from all 25 sampling sites showed negative reaction for mutagenic activity (Ames test) in the absence of metabolic activation. Very low levels of chromosomal aberration, SCE, MN, HN and comet cells were observed in mussels collected from both the urban associated and relatively clean sites. This study seems to indicate that that the coastal waters of Karnataka and Kerala are minimally contaminated with genotoxic and carcinogenic chemicals.

The sister-chromatid exchange and acetylcholine esterase enzyme levels among patients with insecticide intoxication in the Çukurova region, Turkey

This study included 45 patients with intentional insecticide intoxication and 21 with accidental intoxication who were treated at the First-Aid and Emergency Department of Balcali Hospital at the Faculty of Medicine in the Cukurova University, Adana, Turkey, while the control group consisted of 25 people selected from university personnel known to be healthy. Patients with a history of X-ray exposure in the last 6 months or of any virus disease as well as continuous drug users and smokers were excluded, leaving a total of 49 patients. Acetylcholine esterase (Pseudocholinesterase) enzyme (AchE), sister-chromatid exchanges (SCE), the mitotic index (MI), and the replication index (RI) were evaluated. Blood samples were cultured for SCE evaluation and sera separated for AchE levels. Insecticide exposure was generally intentional for suicide in adolescents and at older ages, but accidental for children. AchE levels were found to be significantly lower in organophosphorus (OP) and carbamated (CB) insecticide poisoning groups in comparison with the control group (p<0.001), while the pyrethroid (PY) group was not statistically different for the AchE effect (p>0.05). SCE was found to be significantly higher in OP and CB groups (p<0.001), while the PY and control groups were statistically similar for SCE levels (p>0.05). This study showed an increase in SCE in response to orally ingested insecticides. These findings indicate that insecticide exposure results in cell abnormalities, with resulting impediments to the division and replication of cells, as suggested by MI decreases and RI increases, while the speed of the division cycles of stimulated cells increases.

DNA interstrand crosslinks are induced in cells prelabelled with 5-bromo-2′-deoxyuridine and exposed to UVC radiation

It has been observed previously that 5-bromo-2′-deoxyuridine (BrdU) potentiates the effect of UVC radiation on the level of sister chromatid exchanges. It is not known which type of DNA damage is responsible for this enhancing effect and we have proposed this to be the DNA interstrand crosslink (ICL) which, theoretically, may arise in cells that are labelled with BrdU for one round of replication and exposed to UVC radiation. The aim of the present investigation was to verify if ICLs are indeed formed during this irradiation scenario. CHO-K1 cells were prelabelled with BrdU and exposed to UVC. ICLs were detected by a modified version of the comet assay that relies on the reduction of induced DNA migration in the agarose gel. Carboplatin was used as a positive control. We found that BrdU + UVC treatment indeed results in a reduction of the damage induced by gamma-radiation. Furthermore, we observed that CL-V4B cells exposed to BrdU + UVC, but not to UVC alone, showed a very high level of chromosomal damage. These cells have a deficient Rad51C paralog that renders them extremely sensitive towards ICLs. Interestingly, the cytogenetic results did not correlate with cell survival, where it was found that the CL-V4B cells tolerate BrdU + UVC better than the wild type cells. The possible reasons are discussed. Taken together our results indicate that ICLs are formed in DNA that was prelabelled with BrdU and exposed to UVC radiation.

Chromosomal damage and atherosclerosis. A protective effect from simvastatin

In uremic patients, the frequency of sister chromatid exchanges appears markedly higher than in the general population. Statins are well known for their pleiotropic effects, which are independent of any reduction in cholesterol circulating levels. The aim of the present study was to determine the effects of exposure to escalating doses of simvastatin on the sister chromatid exchange rate in cultured lymphocytes in order to identify the influence of statin on genomic damage. Peripheral lymphocytic samples for culture were obtained from 25 healthy volunteers, 20 patients with documented carotid atherosclerosis and 30 atherosclerotic patients on maintenance regular acetate-free biofiltration. Hemodialyzed patients had a greater percentage of high frequency cells (50%) than healthy controls (3%) and a significantly higher average number of sister chromatid (9.82 ± 2.1 vs. 4.65 ± 2.18). The subgroup of hemodialyzed patients with high plaque score values was characterized by significantly greater values for both sister chromatid exchanges rate and high frequency cells percentage. Our findings demonstrate that there is an association between sister chromatid exchanges and high frequency cells rate and atherosclerosis in acetate-free biofiltration patients. In cultures with added simvastatin, high frequency cells percentages and mean sister chromatid exchanges levels were significantly lower than in cultures with an added vehicle alone, the reduction occurring in a dose-dependent fashion, above all in cultures from end stage renal disease patients. The findings, moreover, demonstrate new effects of simvastatin, which appeared to mitigate the expression of genomic damage in our model. However, it is not yet clear whether this effect is due to the prevention of genomic damage or to the potentiation of the DNA repair capacity. Statins may therefore have an anti-atherogenic action partly ascribable to their ability to provide protection against the development of atherosclerotic plaque.

The genotoxic risk of underground coal miners from Turkey

A cytogenetic monitoring study was carried out on a group of workers from a bituminous coal mine in Zonguldak province of Turkey, to investigate the genotoxic risk of occupational exposure to coal mine dust. Cytogenetic analysis, namely sister chromatid exchanges (SCEs), chromosomal aberrations (CAs) and micronucleus (MN) tests were performed on a strictly selected group of 39 workers and compared to 34 controls matched for gender, age, and habit. Smoking and age were considered as modulating factors. Both SCE and CA frequencies in coal miners appeared significantly higher than in controls. Similarly, there was a significant increase in the frequency of total micronuclei in exposed group as compared to control group. The effect of smoking on the level of SCE and MN was significant in the control group. A positive correlation between the age and the level of SCE was also found in controls. The frequencies of both SCE and CA were significantly enhanced with the years of exposure. The results of this study demonstrated that occupational exposure to coal mine dust leads to a significant induction of cytogenetic damage in peripheral lymphocytes of workers engaged in underground coal mining.

Lack of genotoxic effect in workers exposed to very low doses of 1,3-butadiene

1,3-Butadiene (BD), a probable carcinogen to humans, has been shown to have an ill-defined genotoxicity in occupationally exposed workers. In the present study, the influence of exposure to very low doses of BD and to cigarette smoking was investigated on some cytogenetic endpoints, namely, sister chromatid exchanges (SCE), chromosomal aberrations (CA) and cells with a high frequency of SCE (HFC), in peripheral blood lymphocytes. Twenty-seven male workers employed in a petrochemical plant and 26 matched controls were included in the study. As regards the airborne BD values, there was a significant difference between exposed (median BD value 1.5, min-max 0.2-69.0 microg/m3) and non-exposed workers (median BD value 0.4, min-max <0.1-3.8 microg/m3). Genotoxic biomarkers were not able to distinguish between the two groups. The frequency of SCE was higher in smokers than in non-smokers (p=0.001), with a positive correlation between the number of cigarettes smoked per day and both SCE (r=0.4; p=0.004) and HFC frequency (r=0.3; p=0.04). Multiple regression analysis confirmed the influence of cigarette smoking on the level of SCE and HFC, while these parameters were not affected by personal exposure to BD. Overall, the biomarkers of genotoxic effect investigated in our study were not able to discriminate between workers with a very low exposure to BD and controls, while it was possible to distinguish between smokers and non-smokers on the basis of SCE.

Children's exposure to environmental pollutants and biomarkers of genetic damageII. Results of a comprehensive literature search and meta-analysis

The present review is based on findings from 178 publications retrieved through an extensive search of the MedLine/PubMed database for a 25 years time period (1980-2004) and 10 manually identified papers. Among the cytogenetic biomarkers that are frequently used in field studies, chromosome aberrations (CA) and micronuclei (MN) but not sister chromatid exchanges (SCE) were found consistently increased in children exposed to environmental pollutants. Meta-analysis of the studies reporting SCE in cord blood showed similar levels of SCE in exposed and in non-exposed newborns. Exposure to airborne pollutants, soil and drinking water contaminants, mostly increased CA and, to a lesser extent, MN levels in children. The effect of exposure to airborne urban pollutants was consistently reported by field studies measuring DNA, albumin and hemoglobin adducts. Prenatal (in utero) and postnatal exposure (environmental tobacco smoke, ETS) to tobacco smoke compounds were associated with increased frequencies of DNA and hemoglobin adducts and CA. The limited number of field studies measuring DNA fragmentation (Comet assay), hypoxanthine-guanine phosphoribosyltransferase (HPRT) and the glycophorinA (GPA) mutation frequency in environmentally exposed children precluded a meaningful evaluation of the usefulness of these assays. Meta-analyses performed in children exposed to ETS and in newborns exposed in utero to their mothers' smoke showed 1.3 and 7 times higher levels of hemoglobin adducts compared to referent subjects, respectively. These increases are consistent with the epidemiological evidence of higher lung cancer risks reported in adults who had never smoked and were exposed to ETS during childhood and with 7-15 times higher lung cancer risks reported in smokers than in non-smokers. Higher levels of PAH-DNA adducts were found in fetal than in maternal tissue, suggesting a specific susceptibility of the fetus to this class of ubiquitous environmental pollutants. According to these findings, future research and biomonitoring programs on children would greatly benefit from the inclusion of selected biomarkers that could provide biologically based evidence for the identification of intervention priorities in environmental health.

Multiple Roles of Vertebrate REV Genes in DNA Repair and Recombination

In yeast, Rev1, Rev3, and Rev7 are involved in translesion synthesis over various kinds of DNA damage and spontaneous and UV-induced mutagenesis. Here, we disrupted Rev1, Rev3, and Rev7 in the chicken B-lymphocyte line DT40. REV1-/- REV3-/- REV7-/- cells showed spontaneous cell death, chromosomal instability/fragility, and hypersensitivity to various genotoxic treatments as observed in each of the single mutants. Surprisingly, the triple-knockout cells showed a suppressed level of sister chromatid exchanges (SCEs), which may reflect postreplication repair events mediated by homologous recombination, while each single mutant showed an elevated SCE level. Furthermore, REV1-/- cells as well as triple mutants showed a decreased level of immunoglobulin gene conversion, suggesting participation of Rev1 in a recombination-based pathway. The present study gives us a new insight into cooperative function of three Rev molecules and the Polzeta (Rev3-Rev7)-independent role of Rev1 in vertebrate cells.

The HRDC domain of BLM is required for the dissolution of double Holliday junctions

Bloom's syndrome is a hereditary cancer-predisposition disorder resulting from mutations in the BLM gene. In humans, BLM encodes one of five members of the RecQ helicase family. One function of BLM is to act in concert with topoisomerase IIIalpha (TOPO IIIalpha) to resolve recombination intermediates containing double Holliday junctions by a process called double Holliday junction dissolution, herein termed dissolution. Here, we show that dissolution is highly specific for BLM among human RecQ helicases and critically depends upon a functional HRDC domain in BLM. We show that the HRDC domain confers DNA structure specificity, and is required for the efficient binding to and unwinding of double Holliday junctions, but not for the unwinding of a simple partial duplex substrate. Furthermore, we show that lysine-1270 of BLM, which resides in the HRDC domain and is predicted to play a role in mediating interactions with DNA, is required for efficient dissolution.

Die Wirkung von Sevofluran auf Zellteilung, Mitoseindex (MI) und Austausch der Schwesterchromatide (Sister Chromatide Exchange SCE)

Purpose of the study was to investigate the mitotic index (MI) and sister chromatid exchange (SCE) levels to identify the mutagenic and carcinogenic effects of sevoflurane (sevoflurane). 42 non-smoking male and female turkish patients of ASA-risk I and II were included. The patients received an anaesthesia induction with 8 % sevoflurane in 100 % oxygen ("tidal volume methode") and 0.1 mg/kg BW vecuronium for neuromuscular block and endotracheal intubation. Anaesthesia was maintained with 2.0 - 2.5 sevoflurane in 60 % N(2)O and 40 % O(2). Four 5 ml venous blood samples werde taken: before induction (control), 60 minutes, 24 hours and 5 days after sevoflurane anesthesia. Samples were prepared according to the periferic blood culture assay, modified by Morhead and co-workers, and levels of MI and SCE were examined. 60 minutes after sevoflurane-anaesthesia a significant decrease of MI was found compared to controls (p < 0.01). This depression was lower after 24 hours (p < 0.05) and reversible after 5 days. SCE increased significantly during 60 minutes of anaesthesia (p < 0.001), was also lower after 24 hours (5.6 +/- 2.4 vs. 4.4 +/- 1.7) and returned to normal levels after 5 days (p > 0.05). The application of sevoflurane for anaesthesia may influence the cell division in humans and may have a mutagenic effect on DNA at the cell level, which is reversible.

BLAP75, an essential component of Bloom's syndrome protein complexes that maintain genome integrity

Bloom's syndrome (BS) is a rare human genetic disorder characterized by dwarfism, immunodeficiency, genomic instability and cancer predisposition. We have previously purified three complexes containing BLM, the helicase mutated in this disease. Here we demonstrate that BLAP75, a novel protein containing a putative OB-fold nucleic acid binding domain, is an integral component of BLM complexes, and is essential for their stability in vivo. Consistent with a role in BLM-mediated processes, BLAP75 colocalizes with BLM in subnuclear foci in response to DNA damage, and its depletion impairs the recruitment of BLM to these foci. Depletion of BLAP75 by siRNA also results in deficient phosphorylation of BLM during mitosis, as well as defective cell proliferation. Moreover, cells depleted of BLAP75 display an increased level of sister-chromatid exchange, similar to cells depleted of BLM by siRNA. Thus, BLAP75 is an essential component of the BLM-associated cellular machinery that maintains genome integrity.

Preclinical studies on NSC290205 aza‐steroid alkylator activity in combination with adriamycin against lymphoid leukaemia

Summary NSC290205 (A) is an hybrid synthetic antineoplastic ester that is a combination of a d-lactam derivative of androsterone and an alkylating derivative of N,N-bis(2-chloroethyl)aniline. We tested NSC290205 for synergistic antileukaemic activity with adriamycin (ADR), (i) in vitro against the human lymphoid leukaemia cell lines: CCRF-CEM, MOLT-4, and RPMI-8226, (ii) in vivo against P388 lymphocytic and L1210 lymphoid murine leukaemias (at incipient and advanced phase). Our results indicated significant cytostatic and cytotoxic synergy of NSC290205 and ADR in vitro. We further examined these results in vivo by replacing cyclophosphamide in the standard CHOP (cyclophosphamide, hydroxydaunomycin, Oncovin, prednisone) regimen with NSC290205 (AHOP) and comparing the efficiency of these two regimens in vivo. Although treatment of P388 and L1210 with cyclophosphamide or NSC290205 alone yielded equivalent results, AHOP produced a clear benefit for survival compared with CHOP against advanced leukaemias, confirming the in vitro observations [higher percentage increase in median lifespan of treated animals over the untreated (control): 188% and 239% in L1210, 308% and 353% in P388, P < 0.01, for CHOP and AHOP respectively]. AHOP also proved to be more genotoxic and cytostatic than CHOP, inducing higher sister chromatid exchange levels and cell division delays on P388 cells in vivo. NSC290205 showed superior antineoplastic potential against lymphoid leukaemia and significant synergy with ADR, producing an excellent therapeutic outcome.