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At least 883 records · Page 49Linked to original sources
PubMed2005

Antiproliferative effect of beta-elemene in chemoresistant ovarian carcinoma cells is mediated through arrest of the cell cycle at the G2-M phase.

Elemene is a natural antitumor plant drug. However, the effect of elemene on cell growth in ovarian cancer is unknown. In this study, we show that beta-elemene inhibited the proliferation of cisplatin-resistant human ovarian cancer cells and their parental cells, but had only a marginal effect in human ovary cells, indicating differential inhibitory effects on cell growth between ovarian cancer cells and normal ovary cells. We also demonstrated for the first time that beta-elemene markedly enhanced cisplatin-induced growth inhibition in resistant cells compared to sensitive cells. In addition, cell cycle analysis revealed a synergistic effect of beta-elemene and cisplatin on the induction of cell cycle G2-M arrest in our resistant ovarian carcinoma cells. Furthermore, we showed that treatment of these cells with both drugs downregulated cyclin B1 and Cdc2 expression, but elevated the levels of p53, p21waf1/cip1, p27kip1 and Gadd45. Finally, the combination of beta-elemene and cisplatin was found to increase the phosphorylation of Cdc2 and Cdc25C, which leads to a reduction in Cdc2-cyclin B1 activity. These novel findings suggest that beta-elemene sensitizes chemoresistant ovarian carcinoma cells to cisplatin-induced growth suppression partly through modulating the cell cycle G2 checkpoint and inducing cell cycle G2-M arrest, which lead to blockade of cell cycle progression.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2000

Centrosome-centriole abnormalities are markers for abnormal cell divisions and cancer in the transgenic adenocarcinoma mouse prostate (TRAMP) model.

We utilized the transgenic adenocarcinoma mouse prostate (TRAMP) model to study the formation of abnormal mitosis in malignant tumors of the prostate. The results presented here are focused on centrosome and centriole abnormalities and the implications for abnormal cell divisions, genomic instability, and apoptosis. Centrosomes are microtubule organizing organelles which assemble bipolar spindles in normal cells but can organize mono-, tri-, and multipolar mitoses in tumor cells, as shown here with histology and electron microscopy in TRAMP neoplastic tissue. These abnormalities will cause unequal distribution of chromosomes and can initiate imbalanced cell cycles in which checkpoints for cell cycle control are lost. Neoplastic tissue of the TRAMP model is also characterized by numerous apoptotic cells. This may be the result of multipolar mitoses related to aberrant centrosome formations. Our results also reveal that centrosomes at the poles in mitotic cancer cells contain more than the regular perpendicular pair of centrioles which indicates abnormal distribution of centrioles during separation to the mitotic poles. Abnormalities in the centriole-centrosome complex are also seen during interphase where the complex is either closely associated with the nucleus or loosely dispersed in the cytoplasm. An increase in centriole numbers is observed during interphase, which may be the result of increased centriole duplication. Alternatively, these centrioles may be derived from basal bodies that have accumulated in the cell's cytoplasm, after the loss of cell borders. The supernumerary centrioles may participate in the formation of abnormal mitoses during cell division. These results demonstrate multiple abnormalities in the centrosome-centriole complex during prostate cancer that result in abnormal mitoses and may lead to increases in genomic instability and/or apoptosis.

Adenocarcinoma↗
PubMed2002

Induction of thymidylate synthase as a 5-fluorouracil resistance mechanism.

Thymidylate synthase (TS) is a key enzyme in the de novo synthesis of 2'-deoxythymidine-5'-monophosphate (dTMP) from 2'-deoxyuridine-5'-monophosphate (dUMP), for which 5,10-methylene-tetrahydrofolate (CH(2)-THF) is the methyl donor. TS is an important target for chemotherapy; it is inhibited by folate and nucleotide analogs, such as by 5-fluoro-dUMP (FdUMP), the active metabolite of 5-fluorouracil (5FU). FdUMP forms a relatively stable ternary complex with TS and CH(2)THF, which is further stabilized by leucovorin (LV). 5FU treatment can induce TS expression, which might bypass dTMP depletion. An improved efficacy of 5FU might be achieved by increasing and prolonging TS inhibition, a prevention of dissociation of the ternary complex, and prevention of TS induction. In a panel of 17 colon cancer cells, including several variants with acquired resistance to 5FU, sensitivity was related to TS levels, but exclusion of the resistant variants abolished this relation. For antifolates, polyglutamylation was more important than the intrinsic TS level. Cells with low p53 levels were more sensitive to 5FU and the antifolate raltitrexed (RTX) than cells with high, mutated p53. Free TS protein down-regulates its own translation, but its transcription is regulated by E2F, a cell cycle checkpoint regulator. Together, this results in low TS levels in stationary phase cells. Although cells with a low TS might theoretically be more sensitive to 5FU, the low proliferation rate prevents induction of DNA damage and 5FU toxicity. TS levels were not related to polymorphisms of the TS promoter. Treatment with 5FU or RTX rapidly induced TS levels two- to five-fold. In animal models, 5FU treatment resulted in TS inhibition followed by a two- to three-fold TS induction. Both LV and a high dose of 5FU not only enhanced TS inhibition, but also prevented TS induction and increased the antitumor effect. In patients, TS levels as determined by enzyme activity assays, immunohistochemistry and mRNA expression, were related to a response to 5FU. 5FU treatment initially decreased TS levels, but this was followed by an induction, as seen with an increased ratio of TS protein over TS-mRNA. The clear retrospective relation between TS levels and response now forms the basis for a prospective study, in which TS levels are measured before treatment in order to determine the treatment protocol.

Animals↗
PubMed1999

C-1027-induced alterations in Epstein-Barr viral DNA replication in latently infected cultured human Raji cells: relationship to DNA damage.

This study is the first detailing drug-induced changes in EBV DNA replication intermediates (RIs). Both EBV replication inhibition and damage induction were studied in latently infected human Raji cells treated with the enediyne DNA strand-scission agent C-1027. Analysis of RIs on two-dimensional agarose gels revealed a rapid loss in the EBV bubble arc. When elongation of nascent chains was blocked by aphidicolin, this loss was inhibited, suggesting that C-1027-induced disappearance of RIs was related to maturation of preformed replication molecules in the absence of initiation of new RIs. C-1027 damage to EBV DNA was limited at concentrations where loss of the bubble arc was nearly complete, and none was detected within the replicating origin (ori P)-containing fragment, indicating that replication inhibition occurred in trans. By contrast, the non-nuclear mitochondrial genome was insensitive to replication inhibition but highly sensitive to damage induced by C-1027. C-1027-induced trans inhibition of nuclear but not mitochondrial DNA replication is consistent with a cell cycle checkpoint response to a DNA-damaging agent. EBV replication and Raji cell growth were inhibited at equivalent C-1027 doses.

Aminoglycosides↗
PubMed2006

Depletion of CHK1, but not CHK2, induces chromosomal instability and breaks at common fragile sites.

Common fragile sites are specific regions of the genome that form gaps and breaks on metaphase chromosomes when DNA synthesis is partially inhibited. Fragile sites and their associated genes show frequent deletions and other rearrangements in cancer cells, and may be indicators of DNA replication stress early in tumorigenesis. We have previously shown that the DNA damage response proteins ATR, BRCA1 and FANCD2 play critical roles in maintaining the stability of fragile site regions. To further elucidate the pathways regulating fragile site stability, we have investigated the effects of depletion of the cell cycle checkpoint kinases, CHK1 and CHK2 on common fragile site stability in human cells. We demonstrate that both CHK1 and CHK2 are activated following treatment of cells with low doses of aphidicolin that induce fragile site breakage. Furthermore, we show that depletion of CHK1, but not CHK2, using short-interfering RNA (siRNA) leads to highly destabilized chromosomes and specific common fragile site breakage. In many cells, CHK1 depletion resulted in extensive chromosome fragmentation, which was distinct from endonucleolytic cleavage commonly associated with apoptosis. These findings demonstrate a critical role for the CHK1 kinase in regulating chromosome stability, and in particular, common fragile site stability.

Cells, Cultured↗
PubMed2001

The p53-regulated cyclin-dependent kinase inhibitor, p21 (cip1, waf1, sdi1), is not required for global genomic and transcription-coupled nucleotide excision repair of UV-induced DNA photoproducts.

The p53 tumor suppressor gene is a transcriptional activator involved in cell cycle regulation, apoptosis, and DNA repair. We have shown that p53 is required for efficient nucleotide excision repair of UV-induced DNA photoproducts from global genomic DNA but has no effect on transcription-coupled repair. In order to evaluate whether p53 influences repair indirectly through cell cycle arrest following DNA damage or plays a direct role, we examined repair in vivo in human cells genetically altered to disrupt or regulate the function of p53 and p21. Both primary human fibroblasts and HCT116 colon carcinoma cells wild type for p53 but in which the p21 gene was inactivated through targeted homologous recombination showed no decrease in global repair of UV photoproducts. Human bladder carcinoma cells mutant for p53 and containing a tetracycline-regulated p21 cDNA showed no significant enhancement of repair upon induction of p21 expression. All of the cell lines, including the mismatch repair-deficient, MLH1 mutant HCT116 cells, were proficient for transcription-coupled repair. Clonogenic survival of HCT116 cells following UV irradiation showed no dependence on p21. Therefore, our results indicate that p53-dependent nucleotide excision repair does not require the function of the p21 gene product and is independent of p53-regulated cell cycle checkpoints.

Cell Line↗
PubMed2002

The second largest subunit of mouse DNA polymerase epsilon, DPE2, interacts with SAP18 and recruits the Sin3 co-repressor protein to DNA.

DNA polymerase epsilon is essential for cell viability and chromosomal DNA replication in budding yeast. In addition, DNA polymerase epsilon may be involved in DNA repair and cell-cycle checkpoint control. The enzyme consists of at least four subunits in mammalian cells as well as in yeast. The largest subunit of DNA polymerase epsilon is responsible for polymerase activity. To date, the functions of the other subunits have remained unknown. With a view to elucidating the functions of the second largest subunit of mouse DNA polymerase epsilon (DPE2), yeast two-hybrid screening was performed to identify mouse proteins that interact with this subunit. SAP18, a polypeptide associated with co-repressor protein Sin3, was identified as an interacting protein. A part of the N-terminal region of DPE2 (comprising amino acids 85-250) was found to be responsible for the interaction with SAP18. The interaction induced repression of transcription in reporter plasmid assays, which was inhibited by trichostatin A. These results indicate that DPE2 may recruit histone deacetylase (HDAC) to the replication fork to modify the chromatin structure.

Animals↗
PubMedDate not supplied

Unbalanced growth in mouse cells with amplified dhfr genes.

When grown in the absence of methotrexate, cells carrying unstably amplified dihydrofolate reductase (dhfr) genes have a growth disadvantage that is a function of their level of gene amplification. Although this growth disadvantage is thought to drive the loss of unstably amplified dhfr genes in the absence of methotrexate, its mechanism is not understood. The present studies of murine cell lines with different levels of dhfr gene amplification demonstrate that such cells experience increased unbalanced growth (excess RNA and protein content relative to DNA content) with increased levels of dhfr gene amplification. Stathmokinetic analysis of a cell line with unstably amplified dhfr genes showed that the unbalanced growth was associated with a very low rate of G1/S transit, which suggests that amplified DNA sequences may activate a cell cycle checkpoint at the G1/S boundary. Hydroxyurea, which is known to induce rapid elimination of amplified genes at sub-cytotoxic concentrations, also inhibits the cell cycle at the G1/S transition and causes unbalanced growth. Earlier work has shown that hydroxyurea selectively targets those cells within the heterogeneous drug resistant cell populations which have the highest amplified gene dosage. The finding that unstable gene amplification and hydroxyurea have similar effects on the cell suggests that hydroxyurea may achieve this selective targeting by pushing those cells with the highest levels of gene amplification over a critical stress threshold to cause growth arrest or cell death.

3T3 Cells↗
PubMed2000

Threonine 68 phosphorylation by ataxia telangiectasia mutated is required for efficient activation of Chk2 in response to ionizing radiation.

Eukaryotic cells activate an evolutionarily conserved set of proteins that rapidly induce cell cycle arrest to prevent replication or segregation of damaged DNA before repair is completed. In response to ionizing radiation (IR), the cell cycle checkpoint kinase, Chk2 (hCds1), is phosphorylated and activated in an ataxia telangiectasia mutated (ATM)-dependent manner. Here we show that the ATM protein kinase directly phosphorylates T68 within the SQ/TQ-rich domain of Chk2 in vitro and that T68 is phosphorylated in vivo in response to IR in an ATM-dependent manner. Furthermore, phosphorylation of T68 was required for full activation of Chk2 after IR. Together, these data are consistent with the model that ATM directly phosphorylates Chk2 in vivo and that this event contributes to the activation of Chk2 in irradiated cells.

Amino Acid Sequence↗
PubMed2002

The novel surveillance mechanism of the Trp53-dependent s-phase checkpoint ensures chromosome damage repair and preimplantation-stage development of mouse embryos fertilized with x-irradiated sperm.

Cell cycle checkpoints and apoptosis function as surveillance mechanisms in somatic tissues. However, some of these mechanisms are lacking or are restricted during the preimplantation stage. Previously, we reported the presence of a novel Trp53-dependent S-phase checkpoint that suppresses pronuclear DNA synthesis in mouse zygotes fertilized with X-irradiated sperm (sperm-irradiated zygotes) (Shimura et al., Mol. Cell. Biol. 22, 2220-2228, 2002). Here we studied the role of the Trp53-dependent S-phase checkpoint in the early stage of development of sperm-irradiated zygotes. In the Trp53(+/+) genetic background, all of the sperm-irradiated zygotes cleaved successfully to the two-cell stage despite the fact that half of them carried a sub-2N amount of DNA. These zygotes progressed normally to the eight-cell stage and then implanted, but the subsequent fetal development was suppressed in a dose-dependent manner. In contrast, sperm-irradiated Trp53(-/-) embryos lacking an S-phase checkpoint exhibited an abnormal segregation of chromosomes at the first cleavage, even though they carried an apparently normal 2N amount of DNA. They were morphologically abnormal with numerous micronuclei, and they degenerated before reaching the eight-cell stage. As a consequence, no implants were observed for sperm-irradiated Trp53(-/-) embryos. These results suggest that the Trp53-dependent S-phase checkpoint is a surveillance mechanism involved in the repair of chromosome damage and ensures the preimplantation-stage development of sperm-irradiated embryos.

Animals↗
PubMed2002

GADD45-induced cell cycle G2-M arrest associates with altered subcellular distribution of cyclin B1 and is independent of p38 kinase activity.

In response to DNA damage, the cell cycle checkpoint is an important biological event in maintaining genomic fidelity. Gadd45, a p53-regulated and DNA damage inducible protein, has recently been demonstrated to play a role in the G2-M checkpoint in response to DNA damage. In the current study, we further investigated the biochemical mechanism(s) involved in the GADD45-activated cell cycle G2-M arrest. Using the tetracycline-controlled system (tet-off), we established GADD45-inducible lines in HCT116 (wild-type p53) and Hela (inactivated p53 status) cells. Following inducible expression of the Gadd45 protein, cell growth was strongly suppressed in both HCT116 and Hela cells. Interestingly, HCT116 cells revealed a significant G2-M arrest but Hela cells failed to arrest at the G2-M phases, indicating that the GADD45-activated G2-M arrest requires normal p53 function. The GADD45-induced G2-M arrest was observed independent of p38 kinase activity. Importantly, induction of Gadd45 protein resulted in a reduction of nuclear cyclin B1 protein, whose nuclear localization is critical for the completion of G2-M transition. The reduced nuclear cyclin B1 levels correlated with inhibition of Cdc2/cyclin B1 kinase activity. Additionally, overexpression of cyclin B1 substantially abrogated the GADD45-induced cell growth suppression. Therefore, GADD45 inhibition of Cdc2 kinase activity through alteration of cyclin B1 subcellular localization may be an essential step in the GADD45-induced cell cycle G2-M arrest and growth suppression.

Checkpoint Kinase 1↗
PubMed2005

Mitotic instability in cancer: is there method in the madness?

It has been known for more than a century that neoplastic cells often exhibit disturbances of the mitotic process, but the causes have only recently been thoroughly explored. In many cancers, a combination of cell cycle checkpoint deficiency and abnormal shortening of telomeres predisposes to unbalanced chromosome segregation at cell division and the development of complex genomic rearrangements. Shortening of telomeric repeats beyond normal limits leads to fusion of chromosome ends and the formation of chromatin bridges at anaphase. In turn, these bridges may trigger at least three types of chromosomes mutation: (1) structural rearrangements of chromosomes through extensive chromatin fragmentation beyond the centromeric sequences, typically leading to the formation of isochromosomes and whole-arm translocations, (2) loss of whole chromosomes through mechanical detachment from the mitotic spindle machinery, and (3) failure of cytokinesis, leading to polyploidisation and supernumerary centrosomes, which may in turn orchestrate multipolar spindle configurations at a subsequent mitosis. Anaphase bridging rarely hinders further survival of tumor daughter cells. In contrast, multipolar mitoses may lead to extensive reshuffling of chromosome copies that compromise further clonal expansion. The telomere-dependent instability can be partly counteracted by expression of telomerase during tumor progression, but genomic stabilisation is rarely, if ever, complete.

Anaphase↗
PubMed2005

Inhibition of lung cancer cell growth by quercetin glucuronides via G2/M arrest and induction of apoptosis.

Lung cancer is the leading cause of cancer death in many developed countries, including Taiwan. Quercetin, a widely distributed bioflavonoid, is well known to induce growth inhibition in a variety of human cancer cells. Quercetin glucuronides are the main circulating metabolites after dietary supplements with quercetin in humans. However, there is little information available as to how quercetin glucuronides affect human cancer cells. We investigated the effects of quercetin glucuronides in a human lung cancer cell line NCI-H209. We checked the cell viability, cell cycle checkpoint proteins, pro- and antiapoptotic proteins, caspase-3 activity, and gene expression by flow cytometry and Western blot. The viability of cells decreased in a dose- and time-dependent manner. Cell cycle analysis revealed a significant increase of the proportion of cells in G2/M phase and subG0/G1 phase (corresponding to apoptotic cells). Moreover, quercetin glucuronides increased the expressions of cyclin B, Cdc25c-ser-216-p, and Wee1 proteins, indicating the G2/M arrest. We also demonstrated a concurrent decrease of the mitochondrial membrane potential, release of cytochrome c, up-regulation of Bax, down-regulation of Bcl-2, and activation of caspase-3, and subsequently, cleavage of poly(ADP-ribose) polymerase. In addition, quercetin glucuronide-induced apoptosis was totally blocked by the broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone. Taken together, we demonstrated that quercetin glucuronides inhibited proliferation through G2/M arrest of the cell cycle and induced apoptosis via caspase-3 cascade in the human lung cancer cell line NCI-H209. Delineation of the biological effects of specific major quercetin metabolites on chemotherapeutic potential or chemoprevention of human cancers warrants further investigation.

Animals↗
PubMed2004

The extracellular matrix, p53 and estrogen compete to regulate cell-surface Fas/Apo-1 suicide receptor expression in proliferating embryonic cerebral cortical precursors, and reciprocally, Fas-ligand modifies estrogen control of cell-cycle proteins.

BACKGROUND: Apoptosis is important for normal cerebral cortical development. We previously showed that the Fas suicide receptor was expressed within the developing cerebral cortex, and that in vitro Fas activation resulted in caspase-dependent death. Alterations in cell-surface Fas expression may significantly influence cortical development. Therefore, in the following studies, we sought to identify developmentally relevant cell biological processes that regulate cell-surface Fas expression and reciprocal consequences of Fas receptor activation. RESULTS: Flow-cytometric analyses identified two distinct neural sub-populations that expressed Fas on their cell surface at high (FasHi) or moderate (FasMod) levels. The anti-apoptotic protein FLIP further delineated a subset of Fas-expressing cells with potential apoptosis-resistance. FasMod precursors were mainly in G0, while FasHi precursors were largely apoptotic. However, birth-date analysis indicated that neuroblasts express the highest levels of cell-surface Fas at the end of S-phase, or after their final round of mitosis, suggesting that Fas expression is induced at cell cycle checkpoints or during interkinetic nuclear movements. FasHi expression was associated with loss of cell-matrix adhesion and anoikis. Activation of the transcription factor p53 was associated with induction of Fas expression, while the gonadal hormone estrogen antagonistically suppressed cell-surface Fas expression. Estrogen also induced entry into S-phase and decreased the number of Fas-expressing neuroblasts that were apoptotic. Concurrent exposure to estrogen and to soluble Fas-ligand (sFasL) suppressed p21/waf-1 and PCNA. In contrast, estrogen and sFasL, individually and together, induced cyclin-A expression, suggesting activation of compensatory survival mechanisms. CONCLUSIONS: Embryonic cortical neuronal precursors are intrinsically heterogeneous with respect to Fas suicide-sensitivity. Competing intrinsic (p53, cell cycle, FLIP expression), proximal (extra-cellular matrix) and extrinsic factors (gonadal hormones) collectively regulate Fas suicide-sensitivity either during neurogenesis, or possibly during neuronal migration, and may ultimately determine which neuroblasts successfully contribute neurons to the differentiating cortical plate.

Animals↗
PubMed2004

HIF-1alpha induces cell cycle arrest by functionally counteracting Myc.

Hypoxia induces angiogenesis and glycolysis for cell growth and survival, and also leads to growth arrest and apoptosis. HIF-1alpha, a basic helix-loop-helix PAS transcription factor, acts as a master regulator of oxygen homeostasis by upregulating various genes under low oxygen tension. Although genetic studies have indicated the requirement of HIF-1alpha for hypoxia-induced growth arrest and activation of p21(cip1), a key cyclin-dependent kinase inhibitor controlling cell cycle checkpoint, the mechanism underlying p21(cip1) activation has been elusive. Here we demonstrate that HIF-1alpha, even in the absence of hypoxic signal, induces cell cycle arrest by functionally counteracting Myc, thereby derepressing p21(cip1). The HIF-1alpha antagonism is mediated by displacing Myc binding from p21(cip1) promoter. Neither HIF-1alpha transcriptional activity nor its DNA binding is essential for cell cycle arrest, indicating a divergent role for HIF-1alpha. In keeping with its antagonism of Myc, HIF-1alpha also downregulates Myc-activated genes such as hTERT and BRCA1. Hence, we propose that Myc is an integral part of a novel HIF-1alpha pathway, which regulates a distinct group of Myc target genes in response to hypoxia.

Adenoviridae↗
PubMed2006

Resveratrol and propolis extract: an insight into the morphological and molecular changes induced in DU145 cells.

In the Western world cancer is the second leading cause of mortality, and prostate carcinoma represents in men the second most important type of cancer-causing death. We have already shown that resveratrol (200 microM) triggers in DU145, an androgen-resistant prostate cancer cell line, a necrotic-like cell death, while propolis ethanolic extract (100 microg/ml) causes an apoptotic-like cell demise. The present research is aimed to better elucidate the molecular mechanisms activated by the two micronutrients. Vinorelbine bitartrate, a drug widely used in prostate cancer therapy, was utilized as a reference drug, because it is known to induce apoptosis. The combined treatments between the micronutrients and vinorelbine have been studied to test a possible vinorelbine dose reduction, avoiding its side effects without altering its cytotoxic action. In this investigation SEM and TEM analyses were performed to examine the morphological modifications induced; our observations confirmed necrotic cell features after treatment with resveratrol, and apoptotic modifications after propolis. We also measured cell cycle progression to study a correlation with p21 and p53, two well-known cell cycle checkpoints. The levels of HSP27 and HSP70, two chaperones also exerting antioxidant/antiapoptotic functions, were been also analyzed. Our data indicate that the two micronutrients modulate cell cycle distribution, increasing p53 levels, without the induced HSPs being able to rescue DU145 from death. The results presented suggest chemotherapy based on resveratrol and propolis, alone or in combination with vinorelbine, as a potential useful tool for prostate cancer therapy; the increase in cell cycle control and the modulation of HSPs expression reinforce this suggestion.

Antineoplastic Agents, Phytogenic↗
PubMed2002

UCN-01 (7-hydroxystaurosporine) inhibits DNA repair and increases cytotoxicity in normal lymphocytes and chronic lymphocytic leukemia lymphocytes.

Elevated DNA repair processes represent resistance mechanisms to the treatment of malignancies with alkylating agents. Recently, the cell cycle checkpoint abrogator, UCN-01, was reported to inhibit nucleotide excision repair in cell-free systems. We hypothesized that if UCN-01 was combined with DNA-damaging agents, UCN-01 might inhibit the damage repair processes, thereby enhancing cytotoxicity in quiescent cells. Here, we investigated the effect of UCN-01 on DNA repair and viability of quiescent normal lymphocytes and chronic lymphocytic leukemia lymphocytes treated with UV or the cyclophosphamide prodrug 4-hydroperoxycyclophosphamide (4-HC). DNA damage repair kinetics were determined as DNA single strand breaks by the alkaline single cell gel electrophoresis (comet) assay and by [3H]thymidine incorporation. Pretreatment with UCN-01 inhibited DNA repair initiated by UV or 4-HC in normal lymphocytes as well as chronic lymphocytic leukemia lymphocytes in a concentration-dependent manner at clinically relevant levels (50-300 nM). This inhibition was demonstrated by the decreases in incision capability, DNA resynthesis, and in rejoining, suggesting that UCN-01 inhibits the multiple sites of the repair processes. The higher UCN-01 concentration (300 nM) maximized the inhibitory effects and enhanced the UV- or 4-HC-induced cytotoxicity, as determined by annexin V binding or Hoechst 33342 staining. This enhancement was not obtained by the lower concentrations that incompletely inhibited the repair, suggesting the close association between the inhibition of the repair and the enhancement of the cytotoxicity. Our findings suggest that UCN-01 may be a good candidate for combination strategies of cancer treatment.

Alkaloids↗