A new arylbenzofuran derivative functions as an anti-tumour agent by inducing DNA damage and inhibiting PARP activity

(1) Background: Lung cancer (LC) is a major leading cause of death worldwide. Poly (ADP-ribose) polymerase (PARP)-1 and PARP-2 are key players in cancer. We aimed to assess PARP-1 and PARP-2 expression and activity and DNA damage in tumors and non-tumor lungs from patients with/without chronic obstructive pulmonary disease (COPD). (2) Methods: Lung tumor and non-tumor specimens were obtained through video-assisted thoracoscopic surgery (VATS) in LC patients with/without underlying COPD (two groups of patients, n = 15/group). PARP-1 and PARP-2 expression (ELISA), PARP activity (PARP colorimetric assay kit) and DNA damage (immunohistochemistry) levels were identified in all samples. (3) Results: Both PARP-1 and PARP-2 expression levels were significantly lower in lung tumors (irrespective of COPD)compared to non-tumor specimens, while DNA damage and PARP activity levels significantly increased in lung tumors compared to non-tumor specimens only in LC-COPD patients. PARP-2 expression was positively correlated with smoking burden in LC-COPD patients. (4) Conclusions: In lung tumors of COPD patients, an overactivation of PARP enzyme was observed. A decline in PARP-1 and PARP-2 protein expression was seen in lung tumors irrespective of COPD. Other phenotypic features (airway obstruction) beyond cancer may account for the increase in PARP activity seen in the tumors of patients with underlying COPD.

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Increased activity of poly(ADP-ribose)-polymerase in PML-depleted cells - novel perspectives for cancer therapy

Kazan medical journal ◽

10.17816/kmj1775 ◽

2013 ◽

Vol 94 (1) ◽

pp. 75-79

Author(s):

S V Boichuk ◽

B R Ramazanov ◽

I G Mustafin ◽

Gjoerup O

Keyword(s):

Dna Damage ◽

Ionizing Radiation ◽

Genotoxic Stress ◽

Dna Double Strand Breaks ◽

Compensatory Response ◽

Strand Breaks ◽

Fetal Bovine ◽

Parp Activity ◽

The Relationship ◽

Increased Activity

Aim. To investigate the relationship between PML expression and poly(ADP-ribose)-polymerase (PARP) activity in physiological conditions and at genotoxic stress induced by chemotherapy and ionizing radiation. Methods. The study was conducted on BJ fibroblasts cultured in DMEM/199 medium supplemented with fetal bovine serum, L-glutamine and antibiotics. PML down-regulation was achieved by short interfering ribonucleic acid transfection. To induce deoxyribonucleic acid (DNA) damage in BJ fibroblasts, doxorubicin and hydroxyurea or ionizing radiation were used. PARP activity, formation of DNA double-strand breaks and DNA damage response were examined by Western blotting and immunofluorescence microscopy. Results. PML knockdown was accomplished with an increased PARP activity, confirmed by an increased expression of poly-ADP-ribose (PAR) polymers. At PML knockdown ant DNA damage caused by chemotherapy and ionizing radiation, there is a significant increase in PAR polymers expression as well as increase in the number of cells containing PAR foci. Conclusion. Increased activity of poly(ADP-ribose)-polymerase at PML knockdown and DNA damaging conditions indicates the compensatory response due to insufficiency of the homologous recombination mechanisms. The phenomenon found widens the spectrum of malignancies that might be potentially sensitive to the therapy with poly(ADP-ribose)-polymerase inhibitors.

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DNA Excision Repair and DNA Damage-Induced Apoptosis Are Linked to Poly(ADP-Ribosyl)ation but Have Different Requirements for p53

Molecular and Cellular Biology ◽

10.1128/mcb.20.18.6695-6703.2000 ◽

2000 ◽

Vol 20 (18) ◽

pp. 6695-6703 ◽

Cited By ~ 39

Author(s):

Ralph Beneke ◽

Christoph Geisen ◽

Branko Zevnik ◽

Thomas Bauch ◽

Wolfgang-Ulrich Müller ◽

...

Keyword(s):

Dna Damage ◽

Cell Death ◽

Dna Repair ◽

Zinc Finger Protein ◽

Excision Repair ◽

Dna Breaks ◽

In Vivo Models ◽

P53 Expression ◽

Dna Excision Repair ◽

Parp Activity

ABSTRACT Poly(ADP-ribose) polymerase (PARP) is a DNA binding zinc finger protein that catalyzes the transfer of ADP-ribose residues from NAD+ to itself and different chromatin constituents, forming branched ADP-ribose polymers. The enzymatic activity of PARP is induced upon DNA damage and the PARP protein is cleaved during apoptosis, which suggested a role of PARP in DNA repair and DNA damage-induced cell death. We have generated transgenic mice that lack PARP activity in thymocytes owing to the targeted expression of a dominant negative form of PARP. In the presence of single-strand DNA breaks, the absence of PARP activity correlated with a strongly increased rate of apoptosis compared to cells with intact PARP activity. We found that blockage of PARP activity leads to a drastic increase of p53 expression and activity after DNA damage and correlates with an accelerated onset of Bax expression. DNA repair is almost completely blocked in PARP-deficient thymocytes regardless of p53 status. We found the same increased susceptibility to apoptosis in PARP null mice, a similar inhibition of DNA repair kinetics, and the same upregulation of p53 in response to DNA damage. Thus, based on two different experimental in vivo models, we identify a direct, p53-independent, functional connection between poly(ADP-ribosyl)ation and the DNA excision repair machinery. Furthermore, we propose a p53-dependent link between PARP activity and DNA damage-induced cell death.

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High Activity of Poly(ADP-Ribose) Polymerase in Chronic Lymphocytic Leukemia

Blood ◽

10.1182/blood.v120.21.1788.1788 ◽

2012 ◽

Vol 120 (21) ◽

pp. 1788-1788 ◽

Cited By ~ 1

Author(s):

Elaine Willmore ◽

Natalie Rodrigues ◽

Lisa Allinson ◽

Geoffrey P Summerfield ◽

Jonathan Wallis ◽

...

Keyword(s):

Oxidative Stress ◽

Dna Damage ◽

Clinical Trials ◽

Genomic Instability ◽

Parp Inhibitor ◽

Lymphocytic Leukemia ◽

Homologous Recombination Repair ◽

Patient Stratification ◽

Recombination Repair ◽

Parp Activity

Abstract Abstract 1788 Current treatment protocols for Chronic lymphocytic leukemia (CLL), including FCR (fludarabine, cyclophosphamide and rituximab) have improved response rates and newer approaches targeting the B-cell receptor show promise in early clinical trials. Despite these advances, CLL remains incurable, and since CLL patients are predominantly elderly, many cannot tolerate more aggressive therapies. Therefore, development of biomarkers to stratify subgroups of patients for personalised medicine is paramount to achieve the best therapeutic outcomes for these patients. Chemo-resistance in CLL frequently occurs due to loss of function of either p53 or ataxia telangiectasia mutated kinase (ATM) (del(17p) and del(11q) respectively). p53 and ATM mutation and/or deletion results in defective DNA double-strand break (DSB) response pathways, which confer greater genomic instability, poorer response and shorter overall survival (OS). ATM is a key DSB signaling kinase with roles in homologous recombination repair and cell cycle checkpoint activation, which facilitate DNA repair. We hypothesized that as well as defects in DSB-activated enzymes, genomic instability arising from unresolved single-strand DNA breaks may play a role in disease progression and resistance in CLL. Poly (ADP-ribose) polymerase (PARP) is activated by DNA damaging agents that induce single strand breaks (e.g. alkylating agents) and is pivotal in the signaling to direct repair of such DNA damage. Therefore, inhibitors of PARP sensitise cells to certain classes of chemotherapeutic agents by inhibiting DNA repair. PARP is also the first line of defence against oxidative stress, which is associated with poor prognosis in CLL. We developed the first clinically-used PARP inhibitor (PARPi) and subsequent studies identified the synthetic lethality of PARPi monotherapy in homologous recombination repair defective (HRD) cancer, which selectively kills HRD tumour cells, but is non-toxic to the HR-competent normal tissues. Importantly, PARP activity is reported to be higher in HRD cells, which may reflect increased genomic instability and oxidative stress in these cells. Currently, there are several PARPi undergoing clinical evaluation, including two studies in CLL patients. Here, we analysed the activity of PARP in CLL, to determine whether it could be used as a biomarker of response to conventional therapy and a means to stratify patients for novel therapies, including PARP inhibitor (PARPi) monotherapy. Using the clinically validated PARP activity assay, we found that PARP activity in PBMCs from healthy volunteers was in the same range as we had previously observed (Zaremba T, Biochem J 2011). However when we measured PARP activity in CLL cells (n=33 cases) it was up to 100-fold higher than the activity in PBMCs from healthy volunteers. Activity ranged from 100-50, 000 pmoL/106 cells and was higher in those patients with Binet stage C, or progressive disease. When patients were stratified according to ATM functional status (determined by measuring ATM activity) PARP activity was significantly higher in cases with confirmed ATM dysfunction (p=0.02), compared to those with functional ATM. We then designated cases as having PARP activity that was either higher than, or lower than the median (12,400 pmoL/106cells) and performed Kaplan Meier analysis. There was a trend towards high PARP activity being associated with shorter OS. These results could have significant ramifications: recent reports support the concept that ATM-defective CLL can call be selectively targeted by PARPi (Weston VJ, Blood 2010) and therefore current phase I clinical trials are investigating the use of PARPi in HRD (including ATM-defective) CLL.These trials are stratifying patients by del(11q) and ATM status (since ATM plays a key role in mediating successful HR) with the aim of selectively killing ATM-defective CLL cells with the PARPi. However, ATM status alone may not be sufficient for patient stratification. We propose that CLL cells with high PARP activity are “addicted” to PARP by virtue of its role protecting against increased DNA damage, and that PARP activity may be a key determinant of patient sensitivity to PARP inhibitors. Additionally, the underlying mechanism for high PARP activity in CLL requires further investigation, since this may reveal new therapeutic options, and strategies for patient stratification prior to clinical trial. Disclosures: No relevant conflicts of interest to declare.

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MacroH2A1 Regulation of Poly(ADP-Ribose) Synthesis and Stability Prevents Necrosis and Promotes DNA Repair

Molecular and Cellular Biology ◽

10.1128/mcb.00230-19 ◽

2019 ◽

Vol 40 (1) ◽

Cited By ~ 3

Author(s):

Penelope D. Ruiz ◽

Gregory A. Hamilton ◽

Jong Woo Park ◽

Matthew J. Gamble

Keyword(s):

Dna Damage ◽

Cell Death ◽

Dna Damage Response ◽

Oxidative Dna Damage ◽

Necrotic Cell Death ◽

Necrotic Cell ◽

Damage Response ◽

Parp Activity ◽

Kinetics Of

ABSTRACT Through its ability to bind the ends of poly(ADP-ribose) (PAR) chains, the function of the histone variant macroH2A1.1, including its ability to regulate transcription, is coupled to PAR polymerases (PARPs). PARP1 also has a major role in DNA damage response (DDR) signaling, and our results show that macroH2A1 alters the kinetics of PAR accumulation following acute DNA damage by both suppressing PARP activity and simultaneously protecting PAR chains from degradation. In this way, we demonstrate that macroH2A1 prevents cellular NAD+ depletion, subsequently preventing necrotic cell death that would otherwise occur due to PARP overactivation. We also show that macroH2A1-dependent PAR stabilization promotes efficient repair of oxidative DNA damage. While the role of PAR in recruiting and regulating macrodomain-containing proteins has been established, our results demonstrate that, conversely, macrodomain-containing proteins, and specifically those containing macroH2A1, can regulate PARP1 function through a novel mechanism that promotes both survival and efficient repair during DNA damage response.

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Automodified Poly(ADP-Ribose) Polymerase Analysis to monitor DNA Damage in Peripheral Lymphocytes of Floricoltorists occupationally exposed to Pesticides

10.20944/preprints201901.0019.v1 ◽

2019 ◽

Author(s):

Serena Imperato ◽

Carmela Mistretta ◽

Maria Marone ◽

Ilaria Migliaccio ◽

Ilaria Pulcinelli ◽

...

Keyword(s):

Dna Damage ◽

Genotoxic Stress ◽

Polymerase Activity ◽

Peripheral Blood Lymphocytes ◽

Activity Levels ◽

Strand Breaks ◽

Non Invasive ◽

Occupationally Exposed ◽

Parp Activity ◽

Dna Strand

Background: Increased DNA damage and the propension to cancer development, depend on the modulation of the mechanisms to control and maintain genomic integrity. Poly(ADP-Ribose)Polymerase activation and automodification are early responses to genotoxic stress. Upon binding to DNA strand breaks, the enzyme, a molecular DNA nick sensor, is hyperactivated: this is the first step in a series of events leading to either DNA repair or apoptosis. Enzyme hyperactivation and automodification can be easily measured and are widely used to look at DNA damage extent in the cell. We investigated whether these two markers (increased catalytic activity and auto modification), could help to monitor DNA damage in lymphocytes of flower growers from Southern Italy, occupationally exposed to pesticides. Methods: Peripheral lymphocyte lysates were analysed for Poly(ADP-Ribose) Polymerase activity, and by SDS-PAGE and anti-Poly(ADP-Ribose)Polymerase 1-antibody to measure automodified anti-Poly(ADP-Ribose) Polymerase levels by densitometry. Results: Poly(ADP-Ribose)Polymerase activity levels were consistent with those of enzyme auto-modification. Growers daily exposed to pesticides, showed both biomarkers very high, either in the presence or in the absence of pathologies. Conclusions: PARP activity and auto-modification in peripheral blood lymphocytes are possible,non-invasive, and routinar tools to monitor the healthy conditions of floricoltorists.

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Automodified Poly(ADP-Ribose) Polymerase Analysisto Monitor DNA Damagein Peripheral Lymphocytes of Floriculturists Occupationally Exposed to Pesticides

Cells ◽

10.3390/cells8020137 ◽

2019 ◽

Vol 8 (2) ◽

pp. 137 ◽

Cited By ~ 6

Author(s):

Serena Imperato ◽

Carmela Mistretta ◽

Maria Marone ◽

Ilaria Migliaccio ◽

Ilaria Pulcinelli ◽

...

Keyword(s):

Dna Damage ◽

Genotoxic Stress ◽

Polymerase Activity ◽

Peripheral Blood Lymphocytes ◽

Strand Breaks ◽

Non Invasive ◽

Sds Page ◽

Occupationally Exposed ◽

Parp Activity ◽

Dna Strand

Increased DNA damage and the propension to cancer development, depend on the modulation of the mechanisms to control and maintain genomic integrity. Poly(ADP-Ribose)Polymerase activation and automodification are early responses to genotoxic stress. Upon binding to DNA strand breaks, the enzyme, a molecular DNA nick sensor, is hyperactivated: this is the first step in a series of events leading to either DNA repair or apoptosis. Enzyme hyperactivation and automodification can be easily measured and are widely used to look at DNA damage extent in the cell. We investigated whether these two markers (increased catalytic activity and auto modification), could help to monitor DNA damage in lymphocytes of flower growers from Southern Italy, occupationally exposed to pesticides. Peripheral lymphocyte lysates were analyzed for Poly(ADP-Ribose)Polymerase activity, and by SDS-PAGE and anti-Poly(ADP-Ribose)Polymerase 1-antibodyto measure automodified Poly(ADP-Ribose)Polymerase levels bydensitometry. Poly(ADP-Ribose)Polymerase activity and PARP automodification followed the same trend. Growers daily exposed to pesticides, showed both biomarkers very high, either in the presence or in the absence of pathologies. PARP activity and auto-modification in peripheral blood lymphocytes are possible, non-invasive, androutinartools to monitor the healthy conditions of floricoltorists.

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PARP activity and expression in response to DNA damage in mice with lung cancer-induced cachexia

10.1183/13993003.congress-2021.pa1117 ◽

2021 ◽

Author(s):

JUN TANG ◽

Xuejie Wang ◽

Liyun Qin ◽

Coral Ampurdanés ◽

Xavier Duran ◽

...

Keyword(s):

Lung Cancer ◽

Dna Damage ◽

Parp Activity

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Spliceosome Mutant Myeloid Malignancies Are Preferentially Sensitive to PARP Inhibition

Blood ◽

10.1182/blood-2021-149688 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 322-322

Author(s):

Dang Hai Nguyen ◽

Zhiyan Silvia Liu ◽

Sayantani Sinha ◽

Maxwell Bannister ◽

Erica Arriaga-Gomez ◽

...

Keyword(s):

Dna Damage ◽

Cell Survival ◽

Dna Damage Response ◽

Myeloid Leukemia ◽

Research Funding ◽

Splicing Factor ◽

Leukemia Cells ◽

Damage Response ◽

Parp Activity ◽

Mutant Cells

Abstract Somatic heterozygous mutations in spliceosome genes SRSF2, U2AF1, and SF3B1 commonly occur in patients with myeloid malignancies such as myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Moreover, SRSF2 and U2AF1 mutations associate with poor survival and high risk of progression to AML, representing a unique genetic vulnerability for targeted therapy. We and others previously found that R-loops, a group of transcription intermediates containing RNA:DNA hybrids and displaced single-stranded DNA, are a source of genomic instability induced by different spliceosome mutants. We further showed that inhibition of ATR kinase activity preferentially kills spliceosome mutant cells in an R-loop-dependent manner. Inspired by ATR inhibition results, we performed a focused drug screen with inhibitors targeting additional DNA damage response pathways to identify novel therapeutic vulnerabilities generated by spliceosome mutations. We generated a murine leukemia model by overexpressing the MLL-AF9 fusion oncogene on an Srsf2 P95H/+background, a mutational combination that is found in ~10% of MLL-rearranged leukemias. Surprisingly, we found that Srsf2 P95H/+cells are more sensitive to five inhibitors targeting ADP-ribosyltransferases or PARP (olaparib, talazoparib, rucaparib, niraparib, veliparib) (Figs 1A-B). Olaparib (PARPi)-treated Srsf2 P95H/+cells exhibited increased apoptosis compared to Srsf2 +/+ cells as determined by AnnexinV (Fig 1C). PARPi sensitivity was also observed in isogenic murine MLL-AF9 U2af1 S34F/+cells compared to MLL-AF9 U2af1 +/+ cells (Fig 1D). These data highlight that both SRSF2 P95H and U2AF1 S34F mutations create a common vulnerability that is dependent on PARP activity for survival. To evaluate PARP activity in cells, we used isogenic K562 leukemia cells expressing SRSF2 P95H and U2AF1 S34F mutations from their endogenous loci and monitored PAR (poly(ADP-ribose)) chain levels, a marker of PARP activity. Both SRSF2 P95H and U2AF1 S34F cells exhibited elevated PAR levels compared to wildtype cells (Figs 1E-F). PARPi treatment significantly suppressed PAR signals in SRSF2 P95H and U2AF1 S34F cells. PARP inhibitors target both PARP1 and PARP2 enzymes, of which PARP1 plays a key role in DNA damage response. We used CRISPR-Cas9 to knockout PARP1 gene to determine the major PARP responsible for elevated PAR level in these leukemia cells. PARP1 deletion abrogated elevated PAR levels in U2AF1 S34F (Fig 1G) and SRSF2 P95H cells (data not shown). Altogether, we demonstrated that SRSF2 P95H and U2AF1 S34F cells trigger a PARP1 response critical for cell survival. To test whether increased PAR level arises from U2AF1 S34F-induced R-loops, we generated U2AF1 S34F cells that inducibly express RNaseH1, an enzyme that specifically cleaves the RNA moiety within RNA:DNA hybrids. Induction of RNaseH1 in U2AF1 S34F cells significantly reduced PAR levels, showing that U2AF1 S34F-induced PAR chains is R-loop-dependent (Fig 1H). Moreover, RNaseH1 overexpression suppressed the growth inhibition of PARPi-treated U2AF1 S34F cells (Fig 1I). Collectively, these results suggest that U2AF1 S34F mutants induce R-loop accumulation and elicit an R-loop-associated PARP1 signaling to promote cell survival. We next tested whether combining ATR inhibitor (ATRi) can further exacerbate PARPi sensitivity in spliceosome mutant cells. To examine ATR activity, we monitored phosphorylated RPA (Replication Protein A, or pRPA), a known ATR substrate. pRPA level was enhanced in PARPi-treated SRSF2 P95H cells compared to PARPi-treated SRSF2 WT cells but was suppressed when treated with ATRi (Fig 1J), suggesting that splicing factor mutant cells are more reliant on ATR function in the context of PARPi. Importantly, the combination of PARPi with ATRi, but not with ATMi, significantly promoted cell growth inhibition in SRSF2 P95H cells compared to SRSF2 WT cells or to SRSF2 P95H cells treated with individual compounds alone (Fig 1K). Collectively, these data provide a pre-clinical rationale that splicing factor mutant leukemias are preferentially sensitive to PARP1 modulation compared to their wildtype counterpart. Moreover, combining PARPi and ATRi may further sensitize spliceosome mutant cells and could represent a new therapeutic strategy in myeloid leukemia patients harboring these mutations (Fig 1L). Figure 1 Figure 1. Disclosures Graubert: Calico: Research Funding; Janssen: Research Funding; astrazeneca: Research Funding.

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Inhibition of Poly ADP Ribose Polymerase (PARP) Activity Exerts Cytotoxic Effects on Chromosomal Instability Syndrome and Leukaemic Cell Lines: Potential for Anti-Leukaemia Therapy.

Blood ◽

10.1182/blood.v108.11.2647.2647 ◽

2006 ◽

Vol 108 (11) ◽

pp. 2647-2647

Author(s):

Terry J. Gaymes ◽

S. Shall ◽

Farzin Farzaneh ◽

Ghulam J. Mufti

Keyword(s):

Cell Cycle ◽

Dna Damage ◽

Dna Repair ◽

Cell Survival ◽

Cell Lines ◽

Chromosomal Instability ◽

Parp Inhibitors ◽

Dna Breaks ◽

Leukaemic Cells ◽

Parp Activity

Abstract Recent reports suggest that BrCA1−/− and BrCA2−/− cells can be selectively targeted for cell death through abrogation of their PARP activity. It is postulated that as a result of PARP inhibition, accumulation of single strand DNA breaks (SSB) leads to the replication fork collapse and conversion of SSB to double strand DNA breaks (DSB). The inability of repair defective cells such as BrCA2−/− to repair the DSB would lead to cell death. Exploitation of DNA repair defects using PARP inhibitors (PI) thus represents a more specific and less toxic form of therapy for a number of haematological malignancies. Chromosomal instability (CI) syndromes that have inherent defects in double strand DNA repair also have a uniformly high incidence of transformation to acute leukaemia or lymphoma. In order to test the efficacy of PI therapy we analysed CI cell lines, myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML) cell lines and the potential for combination therapy with inhibitors of DNA methyltransferase (DNMTi) or histone deacetylase inhibitors (HDACi). We report that cells from CI syndromes; Blooms syndrome, Fanconi Anaemia (FancD2 and FancA), Ataxia telancgectasia and Nijmegen break syndrome display abnormal cell cycle profiles and excessive apoptosis in response to the PI’s PJ34 (3μM) and EB47 (45μM). In contrast, normal control cells displayed standard cell cycle profiles and no apoptosis in response to PI at equivalent concentrations. Clonogenic cytotoxicity assays showed that CI syndrome cells exhibit between 30–75% cell survival compared with 100% cell survival in control cells (p<0.05) in response to PI. The homologous recombination (HR) DNA repair component, rad51 forms foci in response to DNA damage. In HR compromised cells, rad51 foci fail to form. In response to PI, immunofluorescent studies show that CI syndrome cells demonstrate severely reduced rad51 foci formation (<5%) compared to control cells (15%). This confirms that PI targets the HR deficiencies in CI syndrome cells. Histone γH2AX, phosphorylated in response to DSB had greatly increased foci formation in CI syndrome cells compared to control cells as a result of unrepaired DNA damage (25.3 vs 9.3%)(p<0.05). CI syndromes have increased transformation potential to the MDS and AML. Addition of 3μM PJ34 to the myelomonocytoid leukaemic/myelodysplastic cell line, P39 exhibited significant apoptosis, with a cell survival fraction of 65% compared to 100% in control cells (p<0.01). Immunofluorescent studies revealed reduced rad51 foci formation (6.3 vs 15%) and increased γH2AX foci formation (17.6 vs 9.3%)(p<0.01). Strikingly, we were also able to reproduce similar PI responses in the Jurkat T-cell leukaemic cell line. We next explored the use of PI in combination with DNMTi or HDACi. Whilst 3μM PJ34 offered only additive effects on decitabine cytotoxicity, a sub-optimal concentration (1μM) of PJ34 behaved synergistically with HDACi potentiating the cytotoxic effect of 200nM MS275 by 55% compared to MS275 alone (p<0.05) in P39 cells. In conclusion, we have shown that in a panel of CI syndrome and leukaemic cells, PI demonstrates significant cytotoxic responses. We also show that PI acts synergistically in combination with HDACi. Parp inhibitors can potentially exploit DSB repair defects in leukaemic cells paving the way for a targeted therapy for MDS and leukaemia.

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