Evaluation of poly (ADP-ribose) polymerase inhibitor ABT-888 combined with radiotherapy and temozolomide in glioblastoma
© Barazzuol et al.; licensee BioMed Central Ltd. 2013
Received: 9 November 2012
Accepted: 12 March 2013
Published: 19 March 2013
The cytotoxicity of radiotherapy and chemotherapy can be enhanced by modulating DNA repair. PARP is a family of enzymes required for an efficient base-excision repair of DNA single-strand breaks and inhibition of PARP can prevent the repair of these lesions. The current study investigates the trimodal combination of ABT-888, a potent inhibitor of PARP1-2, ionizing radiation and temozolomide(TMZ)-based chemotherapy in glioblastoma (GBM) cells.
Four human GBM cell lines were treated for 5 h with 5 μM ABT-888 before being exposed to X-rays concurrently with TMZ at doses of 5 or 10 μM for 2 h. ABT-888′s PARP inhibition was measured using immunodetection of poly(ADP-ribose) (pADPr). Cell survival and the different cell death pathways were examined via clonogenic assay and morphological characterization of the cell and cell nucleus.
Combining ABT-888 with radiation yielded enhanced cell killing in all four cell lines, as demonstrated by a sensitizer enhancement ratio at 50% survival (SER50) ranging between 1.12 and 1.37. Radio- and chemo-sensitization was further enhanced when ABT-888 was combined with both X-rays and TMZ in the O6-methylguanine-DNA-methyltransferase (MGMT)-methylated cell lines with a SER50 up to 1.44. This effect was also measured in one of the MGMT-unmethylated cell lines with a SER50 value of 1.30. Apoptosis induction by ABT-888, TMZ and X-rays was also considered and the effect of ABT-888 on the number of apoptotic cells was noticeable at later time points. In addition, this work showed that ABT-888 mediated sensitization is replication dependent, thus demonstrating that this effect might be more pronounced in tumour cells in which endogenous replication lesions are present in a larger proportion than in normal cells.
This study suggests that ABT-888 has the clinical potential to enhance the current standard treatment for GBM, in combination with conventional chemo-radiotherapy. Interestingly, our results suggest that the use of PARP inhibitors might be clinically significant in those patients whose tumour is MGMT-unmethylated and currently derive less benefit from TMZ.
Glioblastoma (GBM), or WHO grade IV glioma, is the most common and malignant of all primary brain tumours, accounting for the most years of human life lost, per patient, than any other form of adult cancer . Despite recent advances in combined modality treatment with surgery, radiotherapy and temozolomide (TMZ) chemotherapy, the outlook for patients is bleak with a median survival of 12–14 months .
The key cytotoxic and mutagenic lesion induced by TMZ is considered to be the formation of O6-methylguanine (O6-MeG). Transcriptional silencing of the repair protein encoded by the O6-methylguanine-DNA-methyltransferase (MGMT) gene allows genotoxic damage induced by TMZ to persist, and is predictive of treatment outcome and patient survival . Only 5% of all DNA methylation induced by TMZ occurs at the O6 position of guanine. N7-methylguanine and N3-methyladenine account for 60-70% and 10-20% of the total methyl adducts, respectively. These lesions, together with radiation induced single stranded breaks (SSBs), are recognised and processed by the base excision repair (BER) pathway. The enzyme poly(ADP-ribose) polymerase (PARP) plays a key role in BER, by binding to processed SSBs, and facilitating recruitment of X-ray repair cross-complementing 1 (XRCC1). XRCC1 intervenes as a scaffold protein recruiting other DNA polymerases and DNA ligases.
Recent data suggest that defects in the BER system may have particular impact on the response to both ionizing radiation and TMZ . On this basis, PARP inhibition has been extensively explored as a potential approach to derive additional cytotoxicity from radiotherapy and DNA-methylating agents.
ABT-888 (Veliparib) is a novel, orally bioavailable, and potent PARP inhibitor developed by Abbott laboratories from a modification of a benzimidazole ring. ABT-888 inhibits both PARP-1 and PARP-2 enzymes with an inhibitory constant, Ki, of 5.2 and 2.9 nmol/l, respectively . Preclinical pharmacokinetic studies reported oral bioavailabilty values between 56 to 92% and, more importantly, ABT-888′s ability to cross the blood brain barrier (BBB) with plasma to brain ratio of 3:1 as evaluated in tumour-bearing rats .
This study investigates the sensitizing effects of ABT-888 in combination with ionizing radiation and TMZ on four human GBM cell lines. It is the first in vitro study to investigate possible synergy between these three agents, and to assess the influence of MGMT promoter methylation status on tumour response.
Four human GBM cell lines (T98G, LN18, U87 and U251) were used in this study. T98G cells were provided by Mick Woodcock, Gray Institute for Radiation Oncology and Biology, Oxford, UK; U87 and U251 cells were obtained from the Health Protection Agency Culture Collections (HPACC, Wiltshire, UK) and LN18 from the American Type Culture Collection (ATCC, Middlesex, UK). All cell lines were confirmed Mycoplasma free before use. The cells were cultured as previously described in Barazzuol et al. .
MGMT Western blot analysis
Whole cell lysates were prepared in assay buffer (20 mM Tris, 100 mM NaCl, 5 mM EDTA, 1 mM EGTA, 5 mM β-mercaptoethanol; pH 7.5) and passed repeatedly through a 21-gauge needle for lysis. The cell lysate was then centrifuged at 13,000 g for 20 min at 4°C. Protein concentration was measured using the Bradford assay (Thermo Scientific, Northumberland, UK). Whole-cell lysates (30 μg) were mixed with 5 × SDS loading buffer and boiled for 5 min prior to SDS-PAGE on Bio-Rad precast gel (Bio-Rad, Hertfordshire, UK), run at a constant voltage of 125 V for 1.5 h. Semi-dry transfer was done to PVDF membrane for 30 min, using the Bio-Rad Trans-Blot Turbo transfer system. After blocking in 5% skimmed milk in TBST (20 mM Tris–HCl, 150 Mm NaCl, 0.1% Tween 20; pH 7.6) for 5 h, the membrane was incubated at 4°C overnight with primary antibody against MGMT (2739; Cell Signaling Technology, Danvers, US) at 1:250 dilution in TBST. Bound antibodies were visualised with peroxidase-conjugated goat anti-rabbit IgG (1:2000 in TBST) using the Bio-Rad Immun-Star Western C chemiluminescence kit according to the manufacturer’s instructions.
TMZ was provided by Fluka (Sigma-Aldrich, Dorset, UK) and reconstituted in dimethylsulfoxide (DMSO) to a final concentration not exceeding 0.1% (at this concentration, DMSO alone had no effect on cell viability). TMZ was administered at different concentrations and exposure times according to the type of experiment. For single-agent TMZ cytotoxicity, cells were exposed continuously to increasing concentrations of TMZ according to the MGMT status. For combined TMZ, ABT-888 and radiation, TMZ was administered in 5 μM for the MGMT-methylated cells and 10 μM for the MGMT-unmethylated cells for a total exposure time of 2 h, including 1 h before irradiation. After 2 h with TMZ, the medium was replaced.
ABT-888 was supplied by Enzo Life Sciences (Farmingdale, US) and reconstituted in Milli-Q water. For single ABT-888 cytotoxicity, cells were incubated continuously with increasing concentrations of ABT-888 from 0.002 to 50 μM. For the combined experiments with TMZ and radiation, ABT-888 was used at 5 μM and administered for 5 h prior to TMZ treatment and irradiation (2 h exposure time for TMZ).
X-ray irradiation was performed using a Gulmay machine operating at 250 kVp with a dose rate of 0.65 Gy/min (Royal Surrey County Hospital, Guildford, UK). Cells were grown in 6- well plates and incubated for 5 h before irradiation. Cells were then exposed at room temperature to doses between 1 to 6 Gy.
Clonogenic survival assay
Clonogenic assay was used to evaluate single drug cytotoxicity (TMZ and ABT-888) and combined treatments (ABT-888, TMZ and X-rays). Cells were grown in 6-well plates and after treatment incubated for up to 14 days. Colonies were fixed with 50% ethanol in PBS and then stained with 5% crystal violet in PBS (Sigma-Aldrich, Dorset, UK). The colonies with more than 50 cells were counted and the survival fractions were determined taking into consideration the plating efficiency for all treatment modalities based on three separate experiments.
pADPr immunofluorescence quantification
Cells were grown in polystyrene dishes at a concentration of 5 × 105 cells/ml, and pre-treated with 5 μM ABT-888 for 2 h before treatment with 20 mM hydrogen peroxide (H2O2) for 10 min with or without 5 μM ABT-888. Cells were then washed with ice-cold PBS and fixed with ice-cold methanol/acetone (50:50) for 5 min. Samples were then washed twice with ice-cold PBS and incubated with 1% BSA in PBS for 30 min, before being probed for pADPr adding an anti-pADPr antibody (ab14459; Abcam, Cambridge, UK) at a dilution of 1:400 in 1% BSA in PBS for 1 h at room temperature. Cells were then washed three times with PBS before adding FITC-conjugated goat anti-mouse IgG secondary antibody (Millipore, Watford, UK) at a dilution of 1:400 in 1% BSA in PBS for 1 h protected from light. Cells were washed three times with PBS before adding 2.5 μg/ml 4′,6-diamidino-2-phenylindole dilactate (DAPI; Invitrogen, Oregon, US) in PBS for 1 min. Finally, round coverslips were mounted with 10 μl of ProLong Gold anti-fade reagent (Invitrogen, Oregon, US). Samples were analysed using the microscope described in a separate paper  at ×40 magnification. Image processing was performed using ImageJ (v1.44p, National Institutes of Health, Bethesda, US) and the pADPr signal intensity was measured as the mean gray value within selected regions of interest (ROI) corresponding to the relative DAPI-stained nuclei.
Cell death analysis
Cells were treated as described above and collected at different time points after irradiation (1, 5, 10, 24, 48 and 72 h for 3 Gy; and, 24 and 48 h for 2 and 4 Gy) and fixed in 1% formaldehyde (Sigma-Aldrich, Dorset, UK). Samples were stained with 10 μg/ml acridine orange and 8.3 μg/ml Hoechst 33342 (Invitrogen, Oregon, US). The morphological characterization of cell death included apoptosis, necrosis and mitotic catastrophe (Additional file 1). Between 200 and 400 cells were scored for each sample.
where dx%(no drug) is the radiation dose (Gy) required to produce ×% cell survival without drug and dx%(drug) in presence of drug (i.e. TMZ and/or ABT-888). SER was calculated at doses related to surviving fractions of 37 and 50%.
Statistical significance was determined using a two-sample t-test and a p value less than 0.05 was considered significant.
Cell sensitivity to TMZ and ABT-888
Evaluation of pADPr synthesis in the presence of ABT-888
Clonogenic survival after treatment with X-rays, TMZ and ABT-888
Radiobiological parameter values
0.08 ± 0.02
0.04 ± 0.01
0.04 ± 0.02
0.05 ± 0.01
0.15 ± 0.04
0.04 ± 0.01
0.01 ± 0.02
0.06 ± 0.01
X-rays + 5/10 μM TMZ
0.13 ± 0.02
0.04 ± 0.01
0.02 ± 0.01
0.05 ± 0.01
0.12 ± 0.05
0.05 ± 0.01
0.04 ± 0.03
0.06 ± 0.01
X-rays + 5 μM ABT-888
0.18 ± 0.02
0.04 ± 0.01
0.12 ± 0.02
0.04 ± 0.01
0.21 ± 0.02
0.04 ± 0.01
0.12 ± 0.02
0.07 ± 0.01
X-rays + 5 μM ABT-888 + 5/10 μM TMZ
0.16 ± 0.01
0.05 ± 0.01
0.15 ± 0.01
0.04 ± 0.01
0.33 ± 0.02
0.02 ± 0.01
0.20 ± 0.01
0.05 ± 0.01
The combination of X-rays and ABT-888 led to a substantial radiosensitizing effect with SER50 ranging between 1.13 and 1.37, and SER37 between 1.12 and 1.31. This was also accompanied by an increase in α parameter of the LQ model (Table 1). The highest radiosensitization was found in LN18 and U251 cell lines, as demonstrated by SER50 values above 1.28. T98G and U87 cell lines displayed only a modest effect of ABT-888 on the radiation survival curve (p = 0.16-0.24 Figures 6b and 6c). Importantly, the radiosensitizing effect of ABT-888 was independent of the MGMT methylation status.
The triple combination of X-rays, TMZ and ABT-888 was more effective than single agents in all four cell lines and appeared to be more pronounced in the two MGMT-methylated cell lines. Higher levels of ABT-888-mediated sensitization to X-rays and TMZ were observed in both U87 and U251 cell lines with SER50 of 1.30 and 1.44, respectively. Further sensitization was also observed in the MGMT-unmethylated T98G cell line with SER50 of 1.30 for all three agents compared to 1.16 with the dual combination of X-rays and ABT-888. However, no additional enhancement was observed with LN18 cells after trimodal treatment compared to X-rays and ABT-888 (SER50 of 1.28 compared to SER50 of 1.25; Table 1).
Induction of apoptosis by X-rays, TMZ and ABT-888
In MGMT-unmethylated LN18 cells, a single early apoptotic peak was observed 5 h after treatment with X-rays, TMZ and ABT-888, as demonstrated by the amount of apoptotic cells that was greater (8.27%) than with X-rays alone (5.89%). However, this disproportion was not statistically significant (p = 0.23 Figure 7a). This peak was not seen in the MGMT-methylated U87 cells. Apoptotic responses for U87 cells were very similar for the different treatment combinations (p > 0.05 Figure 7a).
In addition, dose–response measurements were performed at 24 and 48 h after irradiation with 2, 3 and 4 Gy (Figure 7). Both LN18 and U87 cells showed a dose-dependent increase in radiation-induced apoptotic cells. At 48 h, the trimodal treatment seemed to be more effective than single modalities. In particular, in U87 there was a significant difference in apoptosis after treatment with 4 Gy, TMZ and ABT-888 as compared with radiation alone (p < 0.04 Figure 7f).
The sensitizing effect of ABT-888 to TMZ and X-rays may involve other cell death pathways distinct from apoptosis. Therefore, mitotic catastrophe and necrosis were evaluated at 72 h after treatment with 3 Gy X-rays, TMZ and ABT-888. A minimal amount of cells (< 3%) undergoing mitotic catastrophe and necrosis was seen in both LN18 and U87 cells for all treatment combinations (data not shown).
PARP inhibition is a promising mechanism for enhancing efficacy of chemoradiation therapy. A number of PARP inhibitors are currently being assessed in clinical trials, including ABT-888 for which six phase I-II clinical trials exist in patients with brain or central nervous system (CNS) tumours .
To date, only one preclinical study has looked at the trimodal combination of PARP inhibitor ABT-888 with TMZ and X-rays in GBM xenografts . The present in vitro study suggests that ABT-888 enhances the effects of radiation. A further sensitization has also been shown when ABT-888 was added to both TMZ and X-rays. Although the maximum enhancement in cell killing was obtained in MGMT-methylated cell lines, MGMT expression did not prevent ABT-888-mediated sensitization. This study also indicates that PARP inhibition has an effect on the apoptotic cell death pathway.
ABT-888 is a potent inhibitor of PARP
Our study confirmed ABT-888′s favourable pharmacokinetic profile and effective attenuation of pADPr formation at a non-cytotoxic concentration of 5 μM in all four GBM cell lines. These results concur with previously reported data by Albert et al.  on H460 lung carcinoma cells and Horton et al.  on leukaemia cells, in which an optimal dose of 5 μM ABT-888 was determined for in vitro models. Importantly, phase 0-I clinical trials have established the achievable area under the plasma concentration time curve for ABT-888 to be 1.46 μM at an initial dose of 10 mg administered orally twice a day (BID) showing that μM concentrations are clinically achievable [12, 13].
The EC50 values for ABT-888 did not show strong variations among the cell lines, except for the MGMT-methylated, p53 wild-type U87 cell line (EC50 = 6.44 μM). It would be of interest to elucidate the relationship between PARP and p53 as all the other cell lines (LN18, T98G and U87) were mutant for p53. Previous reports suggest that PARP-1 is a critical regulator of the p53 response to DNA damage [14, 15]. This observation might be relevant to the clinical treatment of GBM as about a third of GBMs have p53 mutations .
ABT-888 enhances radiation response regardless of the MGMT status
The results demonstrated that exposure to 5 μM ABT-888 for 5 h before irradiation resulted in significant radiosen-sitization of all four cell lines (SER50 = 1.12-1.37), regardless of the MGMT methylation status (Figure 6). The radiosensitizing effect of ABT-888 seemed to be inversely related to the cell population doubling time. Indeed, this effect was more pronounced in LN18 and U251 cells with SER50 of 1.28 and 1.37, respectively, and doubling times of 24 h. This is relevant in the case of brain tumours as the surrounding normal tissue is composed of cells which proliferate slowly or not at all [17–19].
Consistent with the current study, Albert et al.  found that 6 h exposure to 5 μM ABT-888 sensitizes lung cancer H460 cells to radiation with a SER25 of 1.27. This was also accompanied by a delay in the resolution of γ-H2AX foci at 6 h after irradiation. Similarly, Efimova et al.  noted that ABT-888 markedly enhances persistence of γ-H2AX foci in breast cancer cells up to 24 h after irradiation. Liu et al.  also showed that ABT-888 impairs the resolution of DSBs remaining at 24 h in the malignant prostate cancer 22RV1 cell line. Altogether, these data suggest that the radiosensitizing effect of ABT-888 is likely to be the consequence of an interaction between unrepaired SSBs and collapsed DNA replication forks . Collapsed replication forks are recognized by the cell cycle checkpoint system which in turn initiates cell cycle arrest, DNA repair or cell death .
In vivo, one study using an HCT-116 colon model reported that ABT-888 is an effective radio-sensitizer . However, Clarke et al.  reported no effect of ABT-888 addition on survival relative to radiotherapy alone on two primary GBM xenografts.
ABT-888 further enhances response to TMZ plus X-rays in MGMT-methylated cell lines
Stratification of clinical treatment response by MGMT-methylation status demonstrates poorer outcomes for patients with MGMT-unmethylated tumours. An agent capable of enhancing radiation response in this group would be a valuable new treatment. Our study suggests that trimodal treatment with ABT-888, TMZ and X-rays seems to mostly enhance cell killing in the MGMT-methylated U87 and U251 cell lines (Figure 6). The relative SER50 increased from 1.13 and 1.37 with ABT-888 plus X-rays to 1.3 and 1.44 with ABT-888, TMZ and X-rays for U87 and U251 cell lines, respectively. These SER values lie in the range of those obtained with platinum- and taxane-based chemotherapy for different tumour types and end points [22, 23].
An increase in SER50 was also noted in the MGMT-unmethylated T98G cells. This observation suggests that the MGMT methylation status is not an absolute predictor of response to trimodal treatment. However, there is disagreement in the literature on whether ABT-888-mediated sensitization to TMZ is independent of the MGMT. Palma et al.  reported that neither MGMT nor mismatch repair (MMR) precluded sensitivity to ABT-888 plus TMZ in several tumour types. Likewise, Horton et al.  suggested that ABT-888 chemo-potentiation in leukaemia and colon cancer cells might not depend on MGMT activity. However, the authors acknowledged that ABT-888 was less effective in the presence of elevated MGMT levels. In contrast, Clarke et al.  showed that not all GBM tumours respond equally to ABT-888 plus TMZ, suggesting that ABT-888 may not overcome tumour resistance to TMZ.
Furthermore, it would be of interest to explore different treatment schedules, in particular a different duration of ABT-888 and TMZ exposure before irradiation, and whether TMZ might further sensitize the cells to radiation. To date, a growing number of preclinical studies have looked at the effects of TMZ on the radiosensitivity of GBM cell lines reporting opposing results. While some studies support a synergistic effect between concurrent TMZ and radiation in favour of radiosensitization [25–28], other papers reported independent cell killing [29–32]. It is likely that the optimal schedule of drug administration for TMZ-mediated radiosensitization is the one that will also result in an increased efficiency of ABT-888.
ABT-888 has an effect on apoptotic response
Apoptosis is an energy dependent form of cell death, and as such, it requires adenosine-5′-triphosphate (ATP). The principal substrate of PARP is nicotinamide adenine dinucleotide (NAD+), which is required to catalyse pADPr in the presence of DNA damage. In turn, a reduction in NAD+ leads to a depletion of ATP. By preventing ATP loss, inhibition of PARP should enhance the apoptotic response to genotoxic damage. Our results confirm that the combination of ABT-888 with either radiation or radiation plus TMZ had an effect on the apoptotic response, noticeable at later time points after treatment (Figure 7).
Similarly, Albert et al.  assessed apoptosis after treatment with 5 μM ABT-888 and radiation on a lung cancer H460 cell line, reporting a 2.8-fold increase in apoptosis compared to control. Additionally, in vivo TUNEL analysis on sections of H460 tumour models showed a 65% increase in apoptosis when ABT-888 was added to radiotherapy. In a separate study, Liu et al.  showed that 5 μM ABT-888 co-treatment with the DNA alkylating agent N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) induced activation of caspase-9 and caspase-3 and increased apoptosis in cervical cancer HeLa cells by preventing ATP loss. Nowsheen et al.  reported a significant increase in apoptosis when head and neck cancer cells were treated with cetuximab and ABT-888. They hypothesized that apoptosis by PARP inhibition was due to intracellular stress signals, which resulted in the activation of the apoptotic intrinsic pathway. More recently, Huehls et al.  reported that ABT-888 promoted apoptosis in ovarian cancer cells treated with 5-fluorodeoxyuridine (FdUrd) but not with 5-fluorouracil (5-FU).
In summary, this study showed that modulating DNA repair by selectively inhibiting PARP is a potential therapeutic approach to enhance standard treatment in patients with GBM. The most attractive use of PARP inhibitors might be in those patients whose tumour is MGMT-unmethylated and currently derive less benefit from chemo-radiotherapy.
We are grateful to the Royal Surrey County Hospital for providing the time and supervision in the X-ray experiments. The research leading to these results has received funding from the European Community’s Seventh Framework Programme ([FP7/2007-2013] under grant agreement no 215840–2). NGB is supported by the National Institute of Health Research Cambridge Biomedical Research Centre, UK.
- Burnet NG, Jefferies SJ, Benson RJ, Hunt DP, Treasure FP: Years of life lost (YLL) from cancer is an important measure of population burden and should be considered when allocating research funds. Br J Cancer 2005, 92: 241-245.PubMedPubMed CentralGoogle Scholar
- Stupp R, Mason WP, van den Bent MJ, Weller M, Fisher B, Taphoorn MJ, Belanger K, Brandes AA, Marosi C, Bogdahn U, Curschmann J, Janzer RC, Ludwin SK, Gorlia T, Allgeier A, Lacombe D, Cairncross JG, Eisenhauer E, Mirimanoff RO: European Organisation for Research and Treatment of Cancer Brain Tumor and Radiotherapy Groups; National Cancer Institute of Canada Clinical Trials Group: Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. N Engl J Med 2005, 352: 987-996. 10.1056/NEJMoa043330View ArticlePubMedGoogle Scholar
- Hegi ME, Diserens AC, Gorlia T, Hamou MF, de Tribolet N, Weller M, Kros JM, Hainfellner JA, Mason W, Mariani L, Bromberg JE, Hau P, Mirimanoff RO, Cairncross JG, Janzer RC, Stupp R: MGMT gene silencing and benefit from temozolomide in glioblastoma. N Engl J Med 2005, 352: 997-1003. 10.1056/NEJMoa043331View ArticlePubMedGoogle Scholar
- Helleday T, Petermann E, Lundin C, Hodgson B, Sharma RA: DNA repair pathways as targets for cancer therapy. Nat Rev Cancer 2008, 8: 193-204.View ArticlePubMedGoogle Scholar
- Donawho CK, Luo Y, Luo Y, Penning TD, Bauch JL, Bouska JJ, Bontcheva-Diaz VD, Cox BF, DeWeese TL, Dillehay LE, Ferguson DC, Ghoreishi-Haack NS, Grimm DR, Guan R, Han EK, Holley-Shanks RR, Hristov B, Idler KB, Jarvis K, Johnson EF, Kleinberg LR, Klinghofer V, Lasko LM, Liu X, Marsh KC, McGonigal TP, Meulbroek JA, Olson AM, Palma JP, Rodriguez LE, Shi Y, Stavropoulos JA, Tsurutani AC, Zhu GD, Rosenberg SH, Giranda VL, Frost DJ: ABT-888, an orally active poly(ADPribose) polymerase inhibitor that potentiates DNA-damaging agents in preclinical tumor models. Clin Cancer Res 2007, 13: 2728-2737. 10.1158/1078-0432.CCR-06-3039View ArticlePubMedGoogle Scholar
- Barazzuol L, Jena R, Burnet NG, Jeynes JC, Merchant MJ, Kirkby KJ, Kirkby NF: In vitro evaluation of combined temozolomide and radiotherapy using X rays and high-linear energy transfer radiation for glioblastoma. Radiat Res 2012, 177: 651-662. 10.1667/RR2803.1View ArticlePubMedGoogle Scholar
- Kirkby KJ, Grime GW, Webb RP, Kirkby NF, Folkard M, Prise K, Vojnovic B: A scanning focussed vertical ion nanobeam: A new UK facility for cell irradiation and analysis. Nucl Instrum Meth B 2007, 260: 97-100. 10.1016/j.nimb.2007.01.281View ArticleGoogle Scholar
- Clinical trial registry. http://clinicaltrials.gov/
- Clarke MJ, Mulligan EA, Grogan PT, Mladek AC, Carlson BL, Schroeder MA, Curtin NJ, Lou Z, Decker PA, Wu W, Plummer ER, Sarkaria JN: Effective sensitization of temozolomide by ABT-888 is lost with development of temozolomide resistance in glioblastoma xenograft lines. Mol Cancer Ther 2009, 8: 407-414. 10.1158/1535-7163.MCT-08-0854View ArticlePubMedPubMed CentralGoogle Scholar
- Albert JM, Cao C, Kim KW, Willey CD, Geng L, Xiao D, Wang H, Sandler A, Johnson DH, Colevas AD, Low J, Rothenberg ML, Lu B: Inhibition of poly(ADP-ribose) polymerase enhances cell death and improves tumor growth delay in irradiated lung cancer models. Clin Cancer Res 2007, 13: 3033-3042. 10.1158/1078-0432.CCR-06-2872View ArticlePubMedGoogle Scholar
- Horton TM, Jenkins G, Pati D, Zhang L, Dolan ME, Ribes-Zamora A, Bertuch AA, Blaney SM, Delaney SL, Hegde M, Berg SL: Poly(ADP-ribose) polymerase inhibitor ABT-888 potentiates the cytotoxic activity of temozolomide in leukemia cells: influence of mismatch repair status and O6-methylguanine-DNA methyltransferase activity. Mol Cancer Ther 2009, 8: 2232-2242. 10.1158/1535-7163.MCT-09-0142View ArticlePubMedPubMed CentralGoogle Scholar
- Kummar S, Kinders R, Gutierrez ME, Rubinstein L, Parchment RE, Phillips LR, Ji J, Monks A, Low JA, Chen A, Murgo AJ, Collins J, Steinberg SM, Eliopoulos H, Giranda VL, Gordon G, Helman L, Wiltrout R, Tomaszewski JE, Doroshow JH: Phase 0 Clinical Trial of the Poly (ADP-Ribose) Polymerase Inhibitor ABT-888 in Patients With Advanced Malignancies. J Clin Oncol 2009, 27: 2705-2111. 10.1200/JCO.2008.19.7681View ArticlePubMedPubMed CentralGoogle Scholar
- Kummar S, Chen A, Ji J, Zhang Y, Reid JM, Ames M, Jia L, Weil M, Speranza G, Murgo AJ, Kinders R, Wang L, Parchment RE, Carter J, Stotler H, Rubinstein L, Hollingshead M, Melillo G, Pommier Y, Bonner W, Tomaszewski JE, Doroshow JH: Phase I Study of PARP Inhibitor ABT-888 in Combination with Topotecan in Adults with Refractory Solid Tumors and Lymphomas. Cancer Res 2011, 71: 5626-5634. 10.1158/0008-5472.CAN-11-1227View ArticlePubMedPubMed CentralGoogle Scholar
- Valenzuela MT, Guerrero R, Núñez MI, Ruiz De Almodóvar JM, Sarker M, de Murcia G, Oliver FJ: PARP-1 modifies the effectiveness of p53-mediated DNA damage response. Oncogene 2002, 21: 1108-1116. 10.1038/sj.onc.1205169View ArticlePubMedGoogle Scholar
- Wieler S, Gagné JP, Vaziri H, Poirier GG, Benchimol S: Poly(ADPribose) polymerase-1 is a positive regulator of the p53-mediated G1 arrest response following ionizing radiation. J Biol Chem 2003, 278: 18914-18921. 10.1074/jbc.M211641200View ArticlePubMedGoogle Scholar
- The Cancer Genome Atlas (TCGA) Research Network: Comprehensive genomic characterization defines human glioblastoma genes and core pathways. Nature 2008, 455: 1061-1068. 10.1038/nature07385View ArticleGoogle Scholar
- Chalmers AJ: Overcoming resistance of glioblastoma to conventional cytotoxic therapies by the addition of PARP inhibitors. Anticancer Agents Med Chem 2010, 10: 520-533. 10.2174/187152010793498627View ArticlePubMedGoogle Scholar
- Noël G, Godon C, Fernet M, Giocanti N, Mégnin-Chanet F, Favaudon V: Radiosensitization by the poly(ADP-ribose) polymerase inhibitor 4-amino-1,8-naphthalimide is specific of the S phase of the cell cycle and involves arrest of DNA synthesis. Mol Cancer Ther 2006, 5: 564-574. 10.1158/1535-7163.MCT-05-0418View ArticlePubMedGoogle Scholar
- Dungey FA, Lӧ ser DA, Chalmers AJ: Replication-dependent radiosensitization of human glioma cells by inhibition of poly (ADP-Ribose) polymerase: mechanisms and therapeutic potential. Int J Radiat Oncol Biol Phys 2008, 72: 1188-1197. 10.1016/j.ijrobp.2008.07.031View ArticlePubMedGoogle Scholar
- Efimova EV, Mauceri HJ, Golden DW, Labay E, Bindokas VP, Darga TE, Chakraborty C, Barreto-Andrade JC, Crawley C, Sutton HG, Kron SJ, Weichselbaum RR: Poly(ADP-ribose) polymerase inhibitor induces accelerated senescence inirradiated breast cancer cells and tumors. Cancer Res 2010, 70: 6277-6282. 10.1158/0008-5472.CAN-09-4224View ArticlePubMedPubMed CentralGoogle Scholar
- Liu SK, Coackley C, Krause M, Jalali F, Chan N, Bristow RG: A novel poly(ADP-ribose) polymerase inhibitor, ABT-888, radiosensitizes malignant human cell lines under hypoxia. Radiother Oncol 2008, 88: 258-268. 10.1016/j.radonc.2008.04.005View ArticlePubMedGoogle Scholar
- Wilson GD, Bentzen SM, Harari PM: Biologic basis for combining drugs with radiation. Semin Radiat Oncol 2006, 16: 2-9. 10.1016/j.semradonc.2005.08.001View ArticlePubMedGoogle Scholar
- Hei TK, Piao CQ, Geard CR, Hall EJ: Taxol and ionizing radiation: interaction and mechanisms. Int J Radiat Oncol Biol Phys 1994, 29: 267-271. 10.1016/0360-3016(94)90273-9View ArticlePubMedGoogle Scholar
- Palma JP, Wang YC, Rodriguez LE, Montgomery D, Ellis PA, Bukofzer G, Niquette A, Liu X, Shi Y, Lasko L, Zhu GD, Penning TD, Giranda VL, Rosenberg SH, Frost DJ, Donawho CK: ABT-888 confers broad in vivo activity in combination with temozolomide in diverse tumors. Clin Cancer Res 2009, 15: 7277-7290. 10.1158/1078-0432.CCR-09-1245View ArticlePubMedGoogle Scholar
- van Rijn J, Heimans JJ, van den Berg J, van der Valk P, Slotman BJ: Survival of human glioma cells treated with various combination of temozolomide and X-rays. Int J Radiat Oncol Biol Phys 2000, 47: 779-784. 10.1016/S0360-3016(99)00539-8View ArticlePubMedGoogle Scholar
- Chakravarti A, Erkkinen MG, Nestler U, Stupp R, Mehta M, Aldape K, Gilbert MR, Black PM, Loeffler JS: Temozolomide-mediated radiation enhancement in glioblastoma: a report on underlying mechanisms. Clin Cancer Res 2006, 12: 4738-4746. 10.1158/1078-0432.CCR-06-0596View ArticlePubMedGoogle Scholar
- van Nifterik KA, van den Berg J, Stalpers LJ, Lafleur MV, Leenstra S, Slotman BJ, Hulsebos TJ, Sminia P: Differential radiosensitizing potential of temozolomide in MGMT promoter methylated glioblastoma multiforme cell lines. Int J Radiat Oncol Biol Phys 2007, 69: 1246-1253. 10.1016/j.ijrobp.2007.07.2366View ArticlePubMedGoogle Scholar
- Kil WJ, Cerna D, Burgan WE, Beam K, Carter D, Steeg PS, Tofilon PJ, Camphausen K: In vitro and in vivo radiosensitization induced by the DNA methylating agent temozolomide. Clin Cancer Res 2008, 14: 931-938. 10.1158/1078-0432.CCR-07-1856View ArticlePubMedGoogle Scholar
- Wedge SR, Porteous JK, Glaser MG, Marcus K, Newlands ES: In vitro evaluation of temozolomide combined with X-irradiation. Anti-cancer drugs 1997, 8: 92-97. 10.1097/00001813-199701000-00013View ArticlePubMedGoogle Scholar
- Hermisson M, Klumpp A, Wick W, Wischhusen J, Nagel G, Roos W, Kaina B, Weller M: O6-methylguanine DNA methyltransferase and p53 status predict temozolomide sensitivity in human malignant glioma cells. J Neurochem 2006, 96: 766-776. 10.1111/j.1471-4159.2005.03583.xView ArticlePubMedGoogle Scholar
- Combs SE, Schulz-Ertner D, Roth W, Herold-Mende C, Debus J, Weber KJ: In vitro responsiveness of glioma cell lines to multimodality treatment with radiotherapy, temozolomide, and epidermal growth factor receptor inhibition with cetuximab. Int J Radiat Oncol Biol Phys 2007, 68: 873-882. 10.1016/j.ijrobp.2007.03.002View ArticlePubMedGoogle Scholar
- Chalmers AJ, Ruff EM, Martindale C, Lovegrove N, Short SC: Cytotoxic effects of temozolomide and radiation are additive- and schedule-dependent. Int J Radiat Oncol Biol Phys 2009, 75: 1511-9. 10.1016/j.ijrobp.2009.07.1703View ArticlePubMedGoogle Scholar
- Liu X, Shi Y, Guan R, Donawho C, Luo Y, Palma J, Zhu GD, Johnson EF, Rodriguez LE, Ghoreishi-Haack N, Jarvis K, Hradil VP, Colon-Lopez M, Cox BF, Klinghofer V, Penning T, Rosenberg SH, Frost D, Giranda VL, Luo Y: Potentiation of temozolomide cytotoxicity by poly(ADP)ribose polymerase inhibitor ABT-888 requires a conversion of single-stranded DNA damages to doublestranded DNA breaks. Mol Cancer Res 2008, 6: 1621-1629.PubMedGoogle Scholar
- Nowsheen S, Bonner JA, Lobuglio AF, Trummell H, Whitley AC, Dobelbower MC, Yang ES: Cetuximab augments cytotoxicity with poly (ADPribose) polymerase inhibition in head and neck cancer. PLoS One 2011, 6: 1-11.View ArticleGoogle Scholar
- Huehls AM, Wagner JM, Huntoon CJ, Geng L, Erlichman C, Patel AG, Kaufmann SH, Karnitz LM: Poly(ADP-ribose) polymerase inhibition synergizes with 5-fluorodeoxyuridine but not 5-fluorouracil in ovarian cancer cells. Cancer Res 2011, 71: 4944-4954. 10.1158/0008-5472.CAN-11-0814View ArticlePubMedPubMed CentralGoogle Scholar
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