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Biomedical subjects

P L Olive

Publications and source records attributed to P L Olive.

At least 19 recordsLinked to original sources
PubMed1999

Radioprotection of human cell nuclear DNA by polyamines: radiosensitivity of chromatin is influenced by tightly bound spermine.

The polyamines putrescine (PUT) and spermine (SPM) were examined for their ability to protect human cell DNA against the formation of radiation-induced double-strand breaks (DSBs). As observed previously, under conditions where polyamines were shown to be almost completely absent, association with nuclear matrix protein into a nucleoid, and organization into chromatin structure, protected DNA from induction of DSBs by factors of 4.5 and 95, respectively. At concentrations below 1 mM, PUT or SPM provided equivalent levels of protection to deproteinized nuclear DNA, consistent with their capacity to scavenge radiation-induced radicals. At constant ionic strength, 5 mM SPM protected deproteinized DNA and nucleoid DNA and DNA in nuclear chromatin by factors of 100 and 26, respectively. At 5 mM, SPM provided 15 times greater protection of deproteinized DNA than did PUT. Under physiologically relevant conditions, 5 mM SPM protected DNA in the intact nucleus from the induction of DSBs by a factor of 2 relative to DNA in the absence of SPM. Studies of SPM binding during cellular fractionation revealed that a significant fraction of the cellular SPM is tightly bound in the nucleus but can be removed by extended washing. Thus the association of SPM with nuclear chromatin appears to be a significant contributor to the resistance of the cell's DNA to the induction of DSBs.

Binding Sites↗
PubMed1998

Cell fusion studies to examine the mechanism for etoposide resistance in Chinese hamster V79 spheroids.

When exposed to etoposide, the outer cells from Chinese hamster V79 spheroids are about 10 times more resistant to DNA strand breaks and cell killing than V79 cells grown as monolayers. Previous results have shown that the outer cells of both spheroids and monolayers grow at the same rate and contain the same amount and activity of the target enzyme, topoisomerase II. In order to examine possible mechanisms for this resistance, cell fusion studies were conducted with fluorescent dye-tagged monolayer and spheroid cells. Fused cells were exposed for 30 min to 1.2 microg/ml etoposide and then separated using fluorescence-activated cell sorting into binucleate cells consisting of two monolayer cells, two spheroid cells, or a mixed doublet consisting of one cell of each type. Individual sorted cell doublets were examined for the presence of etoposide-induced DNA strand breaks using the alkaline comet assay. As expected, doublets of monolayer cells were sensitive to etoposide and doublets of spheroid cells were resistant. However, mixed doublets were as resistant to DNA damage by etoposide as spheroid doublets. In comparison, when etoposide- or adriamycin-resistant V79 monolayer cells were fused to the parent monolayer cells, the expected intermediate sensitivity to etoposide was observed for the mixed doublets. We conclude that etoposide resistance associated with the outer cells of spheroids can be "transferred" to produce resistance in monolayer cells. Rapid changes in phosphorylation that can affect topoisomerase II activity or localization, or that can alter chromatin structure, are suggested as possible mechanisms of resistance. In support of this hypothesis, topo IIalpha phosphorylation was at least 10 times greater in monolayers than in the outer cell layer of spheroids.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1998

Use of the comet assay for assessment of drug resistance and its modulation in vivo.

Drug resistance is generally considered to be a major impediment to successful cancer chemotherapy, yet it is generally not possible to predict the degree or timing of the emergence of tumour resistance in most chemotherapy protocols. Recent developments with the single-cell gel electrophoresis or 'comet' assay for DNA damage at the single-cell level suggest that this technique might provide a method for identifying and potentially monitoring tumour cell responsiveness to many anti-cancer agents in situ. In principle, this assay could be applied to any accessible tumour being treated with chemotherapeutic agents that cause overt DNA damage. We have investigated that supposition using several rodent and human tumour cell lines exhibiting a spectrum of resistance to the DNA strand-breaking drug, etoposide. By assessing cells grown as monolayers, spheroids and xenografted tumours in immunodeficient mice, we found that the comet assay can provide not only an index of sensitivity to etoposide, but, additionally, can demonstrate the efficacy (or lack thereof) of multidrug resistance (MDR) reversing agents for cells in vitro, and tumours in vivo.

Animals↗
PubMed1998

Rejoining of DNA single- and double-strand breaks in human white blood cells exposed to ionizing radiation.

PURPOSE: To characterize inter- and intra-individual differences in X-ray-induced DNA strand break rejoining kinetics in human peripheral white blood cells (WBC) obtained from 10 healthy volunteers. MATERIALS AND METHODS: The alkaline and neutral versions of the comet assay were used to measure the rate of rejoining of predominantly single-strand breaks (ssb) following exposure to 8 Gy and double-strand breaks (dsb) following 75 Gy. RESULTS: All cells within a population responded in a similar fashion to induction of ssb and dsb; however, a subset of the WBC appeared to rejoin ssb more rapidly. For the 10 individuals examined, the percentage of ssb rejoined by the rapid component(s) was 47 +/- 16% and the rejoining half-time for the slow component was 1.3 +/- 0.4 h. By 24 h after 8 Gy, 4.9 +/- 3.8% of the initial ssb remained. For dsb rejoining, 58 +/- 11% of the initial damage was still present 4h after 75 Gy and by 24 h 32% of the initial level of damage was still detected. Heavily damaged cells present 24 h after 75 Gy varied from 4% to 50% and were excluded from the analysis of repair rates. CONCLUSIONS: Inter-individual variability exceeded intra-individual variability for 2 of 4 endpoints examined for ssb repair, but not for dsb repair. It was concluded that DNA damage measured using the comet assay could identify a range in the X-ray repair responses of WBC from different normal individuals. Whether these differences correlate with differences in cell killing by radiation remains to be determined.

Adult↗
PubMed1998

Higher-order chromatin structure-dependent repair of DNA double-strand breaks: involvement of the V(D)J recombination double-strand break repair pathway.

Repair of DNA double-strand breaks (DSBs) is linked to the V(D)J recombination pathway through investigations of radiation-sensitive mutants. Here we report a possible association between the distribution of DSBs within higher-order chromatin structures and this pathway. Both murine severe combined immunodeficient (SCID) and Chinese hamster XR-1 cells exhibit defective DNA DSB repair and defective V(D)J recombination. The DSB repair defect is not complete, with only a subset of slowly repairing lesions affected by the mutations in these cell lines. We used a modified neutral filter elution procedure which retained elements of higher-order chromatin structures, namely nuclear matrix-DNA interactions. X-ray-induced DSBs that occurred as multiples within looped DNA structures were nonrepairable in SCID and XR-1 cells. In contrast, these lesions were repaired in radioresistant wild-type cells. Cell lines complemented with human DNA containing the respective complementing genes (XRCC7 and XRCC4) showed an increased rate of DSB repair. These results agree with previous findings with xrs5 cells (a member of the XRCC5 group). Xrs5 cells are defective for the Ku p80 subunit of the V(D)J recombination complex and show repair and V(D)J recombination defects similar to those of SCID and XR-1 cells.

Animals↗
PubMed1998

Higher-order chromatin structure-dependent repair of DNA double-strand breaks: factors affecting elution of DNA from nucleoids.

The nuclear matrix is increasingly identified with the processing of DNA damage. Previous work has suggested that association of DNA with the matrix can influence the repair of DNA double-strand breaks (DSBs) and the sensitivity of mammalian cells to ionizing radiation. By selectively examining DSBs that occur as multiples (multiple DSBs) within looped DNA structures, we have identified a subset of DSBs that repair with slow kinetics through the V(D)J recombination-associated DSB repair pathway. Enrichment of S-phase populations by centrifugal elutriation and selective examination of nascent DNA by pulse-labeling were used to demonstrate that elution of DNA from nucleoids is retarded by the presence of replicating DNA. Previously, application of a Poisson-based model of induction of multiple DSBs and DNA elution to a panel of mammalian cell lines indicated that the size of the looped chromatin domains varied between cell lines. The data presented here explain the range in domain sizes between cells as the result of differences in the percentage of cells actively replicating their DNA. Correction of the model to account for S-phase populations results in a looped domain size of 2.9 Mbp independent of cell type. Single-cell gel electrophoresis of nucleoids provides additional evidence for such sized structures. Stabilization of DNA to elution during S phase does not permit repair of DSBs in the DSB repair mutants xrs5 and St.SCID, both defective for the DSB repair pathway associated with V(D)J recombination.

Animals↗
PubMed1998

The role of DNA single- and double-strand breaks in cell killing by ionizing radiation.

Ionizing radiation produces many types of DNA lesions that have the potential of killing cells. The lethal lesion is probably an unrepaired or misrepaired double-strand break produced as part of a complex lesion. A variety of DNA damage assays have been applied in an effort to predict the sensitivity of cells to ionizing radiation. However, the relationships between initial DNA damage, rejoining of breaks and ultimate cell killing by radiation are not fully understood or predictable. While most repair-deficient cell lines can be identified based on slower strand break rejoining, controversy surrounds the ability of DNA damage assays to rank the radiosensitivity of tumor cells reliably in terms of results of clonogenic assays. Part of the difficulty may be that the most relevant lesions, those that are closely spaced locally or regionally, cannot be easily quantified. It is also possible that the DNA damage can be interpreted differently (in relation to repairability) depending on cell type and/or DNA damage assay. Repair itself does not always increase survival, and survival is the outcome of the actions of several pathways that can be both cell- and tissue-specific. Measurements of misrepair leading to chromosome damage and mutation have been helpful in ranking the radiosensitivity of cell lines, and may be a requirement for predictive assays. These concepts are illustrated with results from alkaline and neutral comet assays developed to detect single-strand breaks and double-strand breaks in individual cells.

Animals↗
PubMed1997

Multicell spheroid response to drugs predicted with the comet assay.

Multicell spheroids were exposed to DNA-damaging agents with the aim of determining whether prompt DNA damage could be predictive for cell killing and drug resistance. Chinese hamster V79 cells, SiHa human cervical carcinoma cells, and WiDr human colon carcinoma cells were grown as spheroids and exposed to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 4-nitroquinoline-1-oxide (4NQO), doxorubicin, etoposide, actinomycin D, 1-(2-nitro-1-imidazolyl)-3-aziridino-2-propanol (RSU 1069), 3-amino-1,2,4-benzotriazine-1,4-dioxide (tirapazamine), and nitrogen mustard. Average DNA damage measured using the alkali comet assay generally correlated with cell killing irrespective of exposure times or drug concentration. However, better predictive power was achieved by using DNA damage levels in individual cells to identify the fraction of cells containing sufficient numbers of DNA strand breaks to cause death. Using this concept of a "threshold" for DNA damage, cell survival could be predicted for exposure to 4NQO, tirapazamine, nitrogen mustard, RSU 1069, and actinomycin D and was largely independent of cell type. The threshold value varied for each drug. For 4NQO, tirapazamine, and RSU 1069, DNA damage equivalent to about 10,000 strand breaks/cell was not toxic to cells of any spheroid type. Conversely, for actinomycin D, any DNA damage above background levels (approximately 100 breaks) was toxic for all three cell types. For some DNA-damaging drugs, the lack of correlation between DNA damage and cell killing was also informative. For etoposide and doxorubicin, no common threshold for cell killing could be determined, consistent with the hypothesis that DNA damage is only one of the actions of these drugs leading to cell death. For MNNG, the tail moment threshold varied significantly for the different spheroid types, probably indicating differences in repair. Overall, for five of the eight drugs, DNA damage measured using the comet assay was an effective and quantitative method of predicting drug cytotoxicity in complex multicelled systems.

4-Nitroquinoline-1-oxide↗
PubMed1997

Radiation response of connexin43-transfected cells in relation to the "contact effect".

Some cell lines grown for only two cell doublings as multicell spheroids develop a form of resistance to killing by ionizing radiation that has been called the "contact" effect. While our previous results have implicated a role for higher order chromatin structure in the contact effect, another possible explanation is the presence of intercellular gap junctions that might facilitate communication between cells grown as spheroids and thereby enhance the ability of cells to resist or recover from radiation damage. To examine the role of gap junctions in the contact effect, rat glioma C6 and mouse EMT6 cell lines were transfected with a gene encoding the gap junctional protein connexin43. While C6 glioma cells are deficient in gap junctional communication, cells from spheroids were nonetheless more resistant than monolayers to killing by ionizing radiation, and the contact effect was present to a similar extent in the three transfected clones. For mouse EMT6 cells, radiosensitivity was similar whether cells were grown as monolayers or spheroids. Transfection of EMT6 cells with connexin43 increased gap junctional communication but did not promote development of a contact effect. Tumor volume doubling time in SCID mice increased significantly for one transfected clone; however, doubling time in vitro was also increased relative to the EMT6 parent. We conclude that extensive gap junctional communication is not a requirement for the increased radiation resistance observed when some cell lines are grown as spheroids.

Animals↗
PubMed1997

Detection of subpopulations resistant to DNA-damaging agents in spheroids and murine tumours.

Chinese hamster V79 monolayers, V79 spheroids, and SCCVII murine tumours were examined for DNA damage using the alkaline comet assay and for cell killing by measuring clonogenicity following a 1-h exposure to doxorubicin, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 4-nitroquinoline-N-oxide (4-NQO), etoposide, or 3-amino-1,2,4-benzotriazine-1,4-dioxide (tirapazamine). Greater heterogeneity in DNA damage was evident in spheroids compared to monolayers exposed to these drugs, and cell survival was correlated with the fraction of cells which lacked sufficient DNA damage following treatment with tirapazamine or doxorubicin. Cell sorting experiments verified that subpopulations of cells resistant to DNA damage were also more resistant to cell killing. Significant heterogeneity was observed in cells from SCCVII tumours exposed to tirapazamine and etoposide, and comet DNA content was used to independently assess DNA damage to aneuploid tumour cells and diploid host cells. These results suggest that, for some drugs, the comet assay may be an effective method of identifying drug-resistant cells in solid tumours.

Animals↗
PubMed1997

Physiologic and cytotoxic effects of tirapazamine in tumor-bearing mice.

Tirapazamine, a new bioreductive agent currently advancing through clinical trials, may have a valuable role to play in cancer therapy. In vitro, the drug shows markedly more toxicity to hypoxic cells than to aerobic cells, and preferential activity against hypoxic cells of solid tumors in vivo also can be inferred in many investigations. However, we have previously reported that tirapazamine has minimal activity against cells in the center of hypoxic spheroids, raising concerns with regard to whether the drug may be bioreductively inactivated before reaching chronically hypoxic tumor cells. We consequently examined the oxygen-dependent differential activity of tirapazamine in solid tumors in vivo by using fluorescence-activated cell sorting with clonogenicity assays for cell viability or with the comet assay for DNA damage. The preferential activity of tirapazamine against hypoxic vs. aerobic tumor cells in vivo was approximately threefold, much less than the factors of 50-500 typically seen in vitro. Interestingly, we also found that tirapazamine administration often modified tumor blood flow in the murine models, an effect that could be of clinical utility in sufficiently sensitive tumor cells. Taken together, our observations suggest that sequencing of tirapazamine with other agents requires careful consideration in the clinic.

Animals↗
PubMed1997

Impact of nicotinamide on human tumour hypoxic fraction measured using the comet assay.

BACKGROUND AND PURPOSE: Nicotinamide has been shown to reduce hypoxia in experimental tumours, but there are no data that measure the hypoxic fraction at the time of irradiation in humans. This study investigates whether nicotinamide with radiation can reduce human tumour hypoxia. MATERIALS AND METHODS: Twenty-two patients undergoing palliative radiotherapy for treatment of accessible metastatic tumours were exposed to two doses of radiation (3.5-8 Gy, median 6 Gy) separated by 1-6 days. Directly on completion of the first dose, two fine needle aspirate biopsies (FNAB) were taken and analyzed for hypoxic fraction using the alkaline comet assay. On the second day of radiation, 13 patients were given 80 mg/kg nicotinamide post-operatively on an empty stomach 2 h before treatment; the remaining nine patients acted as controls. A second comparative pair of aspirates were obtained immediately on completion of the second fraction. RESULTS: Sixteen tumours were suitable for analysis (nine nicotinamide and seven controls). Marked inter-tumour variations in hypoxic fraction were noted (0-67%). Both nicotinamide treated tumours and controls demonstrated a significant increase in the percentage of cells containing heavily damaged DNA following the second dose of radiation (P = 0.01). A significant reduction in mean hypoxic fraction after the second radiation treatment was noted (22 to 13%, P = 0.04). This reduction was predominantly due to the nicotinamide treated group, where mean hypoxic fraction fell from 25 to 11% (P = 0.08) compared to the much smaller change in the radiation only control group, 18 to 15% (P = 0.3). CONCLUSIONS: The decrease in hypoxic fraction suggests that nicotinamide can improve tumour hypoxia measured at the time of irradiation. Exposure to the first dose of radiation, or an effect of the first FNAB on microregional tumour blood flow may also contribute.

Administration, Oral↗
PubMed1997

Detection of hypoxic cells in a C3H mouse mammary carcinoma using the comet assay.

The comet assay was used to estimate radiobiological hypoxic fraction across a full range of tumour oxygenations in C3H mammary tumours implanted into the feet of female CDF1 mice. Tumours were either clamped before irradiation or mice were allowed to breath air, 100% oxygen, carbogen or carbon monoxide for 5-35 min before and during exposure to 15 Gy. For the alkaline comet assay, tumours were excised after irradiation and individual tumour cells were analysed for DNA single-strand breaks. Hypoxic cells were defined as those cells with approximately three times fewer single-strand breaks than aerobic cells. Radiobiological hypoxic fraction was calculated by fitting DNA damage histograms to two normal distributions, representing the response of the aerobic and hypoxic populations. The percentage of hypoxic cells estimated using the comet assay was then compared with hypoxic fraction measured using a clamped tumour control assay. Carbogen and oxygen breathing reduced the normal hypoxic fraction from 14% to 2-3% in this tumour, whereas 75-660 p.p.m. carbon monoxide progressively increased the hypoxic fraction from 18% to 82%. The slope of the line comparing the two methods was 1.23 with 95% confidence limits of 1.12-1.33 (r2 = 0.994). In the SCCVII squamous cell carcinoma growing subcutaneously in C3H mice, a similar correlation was observed between hypoxic fraction measured using the comet assay and hypoxic fraction measured in the same tumour cells using the paired survival curve assay (slope = 1.20 with 95% confidence limits of 1.03-1.37). These results confirm the ability of the comet assay to provide an accurate estimate of radiobiological hypoxic fraction over a wide range of tumour oxygenations and between two tumour types.

Animals↗
PubMed1997

Apoptosis: an indicator of radiosensitivity in vitro?

The mechanisms by which ionizing radiation kills cells was a topic of great interest to Dr Alper, and one suspects that she would have delighted in 'clarifying' the role of apoptosis. Indeed, clarification seems necessary in view of the abundance of often conflicting data currently emerging. However, given some simplifying assumptions, important patterns can be discerned. The following comments are thus framed in the context of haematopoietic cell lines, which generally undergo rapid apoptosis (within hours) following irradiation, in contrast to cells of non-haematopoietic origin, which are more likely to be characterized by delayed apoptosis (within days). Tolerance for DNA damage appears to be reduced in cells capable of rapid apoptosis, and those cells are sensitized to ionizing radiation when the apoptotic response mechanisms are fully functional. This rapid apoptotic response shows minor sensitivity to cell cycle position or radiation dose rate. Different considerations apply, however, for the delayed response. Delayed apoptosis appears to be triggered by chromosome damage, and evidence implicating delayed apoptosis as a modifier of cellular radiosensitivity is much less convincing at present.

Animals↗
PubMed1997

Influence of oxygen on radiation-induced DNA damage in testicular cells of C3H mice.

Radiation-induced DNA single-strand break (ssb) induction and rejoining were measured in murine testicular cells using the alkaline comet assay. Individual cells in different stages of differentiation were identified on the basis of DNA content. As expected, induction of DNA ssb in testis cells irradiated on ice was independent of ploidy, and the extent of damage was similar to that produced in cells from other normal tissues. However, in vivo irradiation of air-breathing mice produced more ssb in haploid than tetraploid germ cells, although their rates of rejoining were similar and comparable to repair rates of cells from other normal tissues. In addition, irradiation of testis in situ produced only half as much damage as irradiation in vitro, and this could be explained only in part by the rapid ssb rejoining occurring during irradiation and cell isolation. A lower cellular oxygenation was postulated to account for the apparent resistance of testis cells to induction of breaks and the difference in induction in relation to DNA content. This was confirmed when carbogen inhalation and treatment with nicotinamide not only increased the overall degree of ssb induction in all these cells, but also reduced differences between cells of different ploidies. Results using the hypoxic cell cytotoxin RSU 1069 confirmed that the extent of hypoxia was not as severe in the testis as in the SCCVII murine tumour. It can be concluded from these data that the oxygenation of all testis cells is low enough to confer radioresistance, and that haploid testis cells are less hypoxic than tetraploid spermatocytes.

Animals↗
PubMed1997

Higher-order chromatin structure-dependent repair of DNA double-strand breaks: modeling the elution of DNA from nucleoids.

A possible relationship between the repair of DNA double-strand breaks (DSBs) and their distribution within higher-order chromatin (Johnston and Bryant, Int. J. Radiat. Biol. 66, 531-536, 1994) has recently been demonstrated. Radiosensitive cells deficient for components of the DNA-dependent protein kinase DSB repair pathway exhibited a particular failure in the rejoining of DSBs occurring as multiples within looped DNA structures. Here, a Poisson-based model of induction of DSBs and elution of DNA from residual nuclear structures is presented. By applying this model to cells of a panel of human and rodent cell lines, a mean of 1.6 Mbp for the size of the relevant looped structures was obtained. Such large chromatin structures are of the same magnitude as those observed by functional mapping of interphase and mitotic chromosome structure, nucleoid sedimentation and the "replicon clusters" apparent during DNA replication. This work supports the hypotheses that (1) such structures are critical targets for induction of DSBs and (2) the distribution of damage within these domains may be a factor in the response and sensitivity of mammalian cells to ionizing radiation.

Animals↗
PubMed1997

DNA damage from oxidants: influence of lesion complexity and chromatin organization.

DNA damage by reactive oxygen species results in a spectrum of DNA lesions including single-strand breaks (ssb) and double-strand breaks (dsb). However, most damage is not lethal, and the location and nature of the DNA damage, in addition to total number of breaks, are likely to be critical in determining ultimate survival. Generally associated only with ionizing radiation, multiply damaged sites (i.e., complex lesions and clusters of complex lesions in DNA) are more likely to be lethal because they are less easily repaired. We examined five drugs known to cause DNA adducts, strand breaks, and reactive oxygen species for their ability to produce complex lesions: 4-nitroquinoline-1-oxide (4NQO), H2O2, doxorubicin, Tirapazamine, and etoposide. As indicators of lesion complexity we compared 1) the ratio of ssb to dsb, 2) the rate of rejoining of single-strand breaks, 3) the relative lethality of the breaks (number of breaks per mean lethal dose), and 4) the ability to produce complex lesions. Tirapazamine, etoposide, and doxorubicin gave dsb/ssb ratios similar to that for X-rays, whereas 4NQO and H2O2 showed dsb/ssb ratios of 200 and 3250, respectively. The number of dsb per LD50 varied from 2.5 to 500 for different drugs. There was no apparent relation between ssb rejoining half-time (3.5-85 min) and relative lethality or lesion complexity. A modified (nonionic detergent) filter elution method confirmed that tirapazamine, like ionizing radiation, produced multiple dsb within single chromatin domains. These data indicate that complex lesions can be produced by a number of different chemicals and suggest that the damage that results in killing by these drugs may be related to production of multiply damaged sites in DNA.

Animals↗