scholarly journals A combination of PARP and CHK1 inhibitors efficiently antagonizes MYCN-driven tumors

Oncogene ◽  
2021 ◽  
Author(s):  
Stefano Di Giulio ◽  
Valeria Colicchia ◽  
Fabio Pastorino ◽  
Flaminia Pedretti ◽  
Francesca Fabretti ◽  
...  
Keyword(s):  
Parp Inhibitor ◽  
Primary Cultures ◽  
Neuroblastoma Cells ◽  
Parp Inhibitors ◽  
Mitotic Catastrophe ◽  
Clinical Settings ◽  
In Vivo Models ◽  
Chk1 Inhibitor

AbstractMYCN drives aggressive behavior and refractoriness to chemotherapy, in several tumors. Since MYCN inactivation in clinical settings is not achievable, alternative vulnerabilities of MYCN-driven tumors need to be explored to identify more effective and less toxic therapies. We previously demonstrated that PARP inhibitors enhance MYCN-induced replication stress and promote mitotic catastrophe, counteracted by CHK1. Here, we showed that PARP and CHK1 inhibitors synergized to induce death in neuroblastoma cells and in primary cultures of SHH-dependent medulloblastoma, their combination being more effective in MYCN amplified and MYCN overexpressing cells compared to MYCN non-amplified cells. Although the MYCN amplified IMR-32 cell line carrying the p.Val2716Ala ATM mutation showed the highest sensitivity to the drug combination, this was not related to ATM status, as indicated by CRISPR/Cas9-based correction of the mutation. Suboptimal doses of the CHK1 inhibitor MK-8776 plus the PARP inhibitor olaparib led to a MYCN-dependent accumulation of DNA damage and cell death in vitro and significantly reduced the growth of four in vivo models of MYCN-driven tumors, without major toxicities. Our data highlight the combination of PARP and CHK1 inhibitors as a new potential chemo-free strategy to treat MYCN-driven tumors, which might be promptly translated into clinical trials.

scholarly journals Targeting IDH1/2 mutant cancers with combinations of ATR and PARP inhibitors

NAR Cancer ◽  
2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Amrita Sule ◽  
Jinny Van Doorn ◽  
Ranjini K Sundaram ◽  
Sachita Ganesa ◽  
Juan C Vasquez ◽  
...  
Keyword(s):  
Kinase Inhibitors ◽  
Parp Inhibitor ◽  
Parp Inhibitors ◽  
Protein Kinase Inhibitors ◽  
Isocitrate Dehydrogenase 1 ◽  
Normal Product ◽  
Synthetic Lethal Interactions ◽  
Mutant Cells

Abstract Mutations in the isocitrate dehydrogenase-1 and -2 (IDH1/2) genes were first identified in glioma and acute myeloid leukemia (AML), and subsequently found in multiple other tumor types. These neomorphic mutations convert the normal product of enzyme, α-ketoglutarate (αKG), to the oncometabolite 2-hydroxyglutarate (2HG). Our group recently demonstrated that 2HG suppresses the high-fidelity homologous recombination (HR) DNA repair pathway, resulting in a state referred to as ‘BRCAness’, which confers exquisite sensitivity to poly(ADP-ribose) polymerase (PARP) inhibitors. In this study, we sought to elucidate sensitivity of IDH1/2-mutant cells to DNA damage response (DDR) inhibitors and, whether combination therapies could enhance described synthetic lethal interactions. Here, we report that ATR (ataxia telangiectasia and Rad3-related protein kinase) inhibitors are active against IDH1/2-mutant cells, and that this activity is further potentiated in combination with PARP inhibitors. We demonstrate this interaction across multiple cell line models with engineered and endogenous IDH1/2 mutations, with robust anti-tumor activity in vitro and in vivo. Mechanistically, we found ATR and PARP inhibitor treatment induces premature mitotic entry, which is significantly elevated in the setting of IDH1/2-mutations. These data highlight the potential efficacy of targeting HR defects in IDH1/2-mutant cancers and support the development of this combination in future clinical trials.

scholarly journals [18F]AZD2461, an Insight on Difference in PARP Binding Profiles for DNA Damage Response PET Imaging

2020 ◽  
Vol 22 (5) ◽  
pp. 1226-1234
Author(s):  
Florian Guibbal ◽  
Samantha L. Hopkins ◽  
Anna Pacelli ◽  
Patrick G. Isenegger ◽  
Michael Mosley ◽  
...  
Keyword(s):  
Pet Imaging ◽  
Parp Inhibitor ◽  
Parp Inhibitors ◽  
Cell Uptake ◽  
Pancreatic Cell ◽  
Anti Cancer ◽  
Damage Response ◽  
Automated Procedures

Abstract Background Poly (ADP-ribose) polymerase (PARP) inhibitors are extensively studied and used as anti-cancer drugs, as single agents or in combination with other therapies. Most radiotracers developed to date have been chosen on the basis of strong PARP1–3 affinity. Herein, we propose to study AZD2461, a PARP inhibitor with lower affinity towards PARP3, and to investigate its potential for PARP targeting in vivo. Methods Using the Cu-mediated 18F-fluorodeboronation of a carefully designed radiolabelling precursor, we accessed the 18F-labelled isotopologue of the PARP inhibitor AZD2461. Cell uptake of [18F]AZD2461 in vitro was assessed in a range of pancreatic cell lines (PSN-1, PANC-1, CFPAC-1 and AsPC-1) to assess PARP expression and in vivo in xenograft-bearing mice. Blocking experiments were performed with both olaparib and AZD2461. Results [18F]AZD2461 was efficiently radiolabelled via both manual and automated procedures (9 % ± 3 % and 3 % ± 1 % activity yields non-decay corrected). [18F]AZD2461 was taken up in vivo in PARP1-expressing tumours, and the highest uptake was observed for PSN-1 cells (7.34 ± 1.16 %ID/g). In vitro blocking experiments showed a lesser ability of olaparib to reduce [18F]AZD2461 binding, indicating a difference in selectivity between olaparib and AZD2461. Conclusion Taken together, we show the importance of screening the PARP selectivity profile of radiolabelled PARP inhibitors for use as PET imaging agents.

scholarly journals DNAzymes, Novel Therapeutic Agents in Cancer Therapy: A Review of Concepts to Applications

2021 ◽  
Vol 2021 ◽  
pp. 1-21
Author(s):  
I. B. K. Thomas ◽  
K. A. P. Gaminda ◽  
C. D. Jayasinghe ◽  
D. T. Abeysinghe ◽  
R. Senthilnithy
Keyword(s):  
Nucleic Acid ◽  
Cancer Therapy ◽  
Cancer Drug ◽  
Clinical Settings ◽  
Full Potential ◽  
In Vivo Models ◽  
Recent Advances ◽  
Catalytic Dna

The past few decades have witnessed a rapid evolution in cancer drug research which is aimed at developing active biological interventions to regulate cancer-specific molecular targets. Nucleic acid-based therapeutics, including ribozymes, antisense oligonucleotides, small interference RNA (siRNA), aptamer, and DNAzymes, have emerged as promising candidates regulating cancer-specific genes at either the transcriptional or posttranscriptional level. Gene-specific catalytic DNA molecules, or DNAzymes, have shown promise as a therapeutic intervention against cancer in various in vitro and in vivo models, expediting towards clinical applications. DNAzymes are single-stranded catalytic DNA that has not been observed in nature, and they are synthesized through in vitro selection processes from a large pool of random DNA libraries. The intrinsic properties of DNAzymes like small molecular weight, higher stability, excellent programmability, diversity, and low cost have brought them to the forefront of the nucleic acid-based therapeutic arsenal available for cancers. In recent years, considerable efforts have been undertaken to assess a variety of DNAzymes against different cancers. However, their therapeutic application is constrained by the low delivery efficiency, cellular uptake, and target detection within the tumour microenvironment. Thus, there is a pursuit to identify efficient delivery methods in vivo before the full potential of DNAzymes in cancer therapy is realized. In this light, a review of the recent advances in the use of DNAzymes against cancers in preclinical and clinical settings is valuable to understand its potential as effective cancer therapy. We have thus sought to firstly provide a brief overview of construction and recent improvements in the design of DNAzymes. Secondly, this review stipulates the efficacy, safety, and tolerability of DNAzymes developed against major hallmarks of cancers tested in preclinical and clinical settings. Lastly, the recent advances in DNAzyme delivery systems along with the challenges and prospects for the clinical application of DNAzymes as cancer therapy are also discussed.

The Nucleoside Analogue Acadesine Exerts Antitumoral Activity and Cooperates with Conventional Agents In In Vitro and In Vivo Models of Mantle Cell Lymphoma

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3918-3918
Author(s):  
Arnau Montraveta ◽  
Mercè de Frías ◽  
Clara Campàs ◽  
Elias Campo ◽  
Gael Roue ◽  
...  
Keyword(s):  
Mantle Cell Lymphoma ◽  
Cell Lines ◽  
Nucleoside Analogue ◽  
Cell Lymphoma ◽  
Primary Cultures ◽  
Antitumoral Activity ◽  
In Vivo Models ◽  
Mantle Cell

Abstract Abstract 3918 Mantle cell lymphoma (MCL) is a mature B-cell neoplasm characterized by the t(11;14)(q13:q32) that involves cyclin D1 overexpression and consequent cell cycle deregulation at the G1 phase. This entity is generally characterized by an aggressive course and a bad prognosis. Recently, a specific subtype of MCL has been described, showing best outcomes and that might be managed more conservatively than conventional MCL. These cases are characterized by non-nodal presentation, predominantly hypermutated IgVH, lack of genomic complexity, and absence of SOX11 expression. Acadesine is a nucleoside analogue initially developed as a cardioprotective agent, and which has shown a wide range of metabolic effects, including the activation of AMP-activated protein kinase (AMPK). Acadesine was shown to induce apoptosis in primary cells from several B lymphoid neoplasms and has been entered in a phase I/II clinical trial with relapsed/refractory chronic lymphocytic leukemia (CLL) patients. This clinical study has shown that acadesine plasmatic levels in the micro molar range are achievable and safe when CLL patients are treated with the drug. To evaluate the antitumoral properties of acadesine in MCL, we exposed a set of 11 MCL primary cultures and 9 MCL cell lines for up to 48h with increasing doses of the drug. Cytotoxicity and cytostatic effects were then assessed by flow cytometry detection of annexinV/propidium iodide labeling and MTT proliferation assay, respectively. In both MCL cell lines and MCL primary cultures, we observed a heterogeneous response to the drug, with no correlation to common genetic alterations such as deletion/mutation of P53, ATM or P16 genes. JVM2, Jeko-1, Rec-1 and UPN-1 were the more sensitive cell lines, with a mean lethal dose 50 (LD50) of 1.57 mM at 24 h and 0.95 mM at 48h, while 2 cell lines (HBL-2 and Granta-519) showed a primary resistance to the compound (LD50 > 50 mM). Among MCL primary cultures, acadesine showed selective cytotoxic activity against malignant B cells while sparing accompanying T cells. Of note, those cases corresponding to the indolent MCL group showed increased sensitivity to the drug at 24h of treatment, when compared to conventional MCL cases (p=0.03). We observed that acadesine efficiently activates the intrinsic apoptotic pathway in MCL cells by modulating Bcl-2 family protein levels, leading to conformational activation of Bax and Bak, mitochondrial depolarization, generation of reactive oxygen species and caspases processing. In drug combination assays, acadesine showed a synergistic effect when combined with Rituximab, being the Rituximab-acadesine combination more potent than other Rituximab-based polychemotherapies such as R-bendamustine and R-CHOP. Finally, a daily administration of 400mg/kg acadesine in mice previously inoculated with a MCL xenotransplant significantly reduced tumor burden when compared to control animals, as soon as 7 days of treatment. In summary, these results suggest that acadesine exerts significant antitumoral activity in both in vitro and in vivo model of MCL, and may represent an attractive model for the design of a new therapeutic approach for this entity, especially in patients presenting with the indolent form. Disclosures: de Frías: Advancell therapeutics: Employment. Campàs:Advancell therapeutics: Employment.

scholarly journals Na/K-ATPase signaling regulates collagen synthesis through microRNA-29b-3p in cardiac fibroblasts

2016 ◽  
Vol 48 (3) ◽  
pp. 220-229 ◽  
Author(s):  
Christopher A. Drummond ◽  
Michael C. Hill ◽  
Huilin Shi ◽  
Xiaoming Fan ◽  
Jeffrey X. Xie ◽  
...  
Keyword(s):  
Collagen Synthesis ◽  
Cardiac Fibrosis ◽  
Cardiac Tissue ◽  
Cardiac Fibroblasts ◽  
Primary Cultures ◽  
In Vivo Models ◽  
Adult Rat ◽  
Uremic Cardiomyopathy

Chronic kidney disease (CKD) is accompanied by cardiac fibrosis, hypertrophy, and dysfunction, which are commonly referred to as uremic cardiomyopathy. Our previous studies found that Na/K-ATPase ligands or 5/6th partial nephrectomy (PNx) induces cardiac fibrosis in rats and mice. The current study used in vitro and in vivo models to explore novel roles for microRNA in this mechanism of cardiac fibrosis formation. To accomplish this, we performed microRNA profiling with RT-qPCR based arrays on cardiac tissue from rats subjected to marinobufagenin (MBG) infusion or PNx. The analysis showed that a series of fibrosis-related microRNAs were dysregulated. Among the dysregulated microRNAs, microRNA (miR)-29b-3p, which directly targets mRNA of collagen, was consistently reduced in both PNx and MBG-infused animals. In vitro experiments demonstrated that treatment of primary cultures of adult rat cardiac fibroblasts with Na/K-ATPase ligands induced significant increases in the fibrosis marker, collagen protein, and mRNA expression compared with controls, whereas miR-29b-3p expression decreased >50%. Transfection of miR-29b-3p mimics into cardiac fibroblasts inhibited cardiotonic steroids-induced collagen synthesis. Moreover, a specific Na/K-ATPase signaling antagonist, pNaKtide, prevented ouabain-induced increases in collagen synthesis and decreases in miR-29b-3p expression in these cells. In conclusion, these data are the first to indicate that signaling through Na/K-ATPase regulates miRNAs and specifically, miR-29b-3p expression both in vivo and in vitro. Additionally, these data indicate that miR-29b-3p expression plays an important role in the formation of cardiac fibrosis in CKD.

scholarly journals Addition of the PARP Inhibitor, Talazoparib, to Gemtuzumab Ozogamicin Significantly Enhances Anti-Leukemic Activity in Human CD33+ Acute Myeloid Leukemia

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 1371-1371
Author(s):  
Scott M. Portwood ◽  
Marianna C Cantella ◽  
Tara L. Cronin ◽  
Eunice S. Wang
Keyword(s):  
Dna Damage ◽  
Parp Inhibitor ◽  
Single Agent ◽  
Parp Inhibitors ◽  
Gemtuzumab Ozogamicin ◽  
Nsg Mice ◽  
Dose Dependent ◽  
Advisory Role

Background CD33 (Siglec3) is a cell surface transmembrane receptor that is rapidly internalized and highly expressed on AML blasts but is absent on normal hematopoietic stem cells. Gemtuzumab ozogamicin (GO), a humanized anti-CD33 antibody conjugated to a DNA strand scission inducing agent (calicheamicin) was recently FDA approved for the treatment of newly-diagnosed or relapsed/refractory CD33-positive acute myeloid leukemia (AML). GO has been shown to exert clinical activity in leukemia patients. Poly (ADP-ribose) polymerase (PARP) inhibitors prevent the repair of single stranded DNA breaks by blocking the nicotinamide adenine dinucleotide (NAD) catalytic domain of the PARP protein and by preventing the dissociation of PARP from the DNA (PARP trapping). Talazoparib is unique among clinical PARP inhibitors in displaying 10,000-fold increased PARP trapping as compared to other agents . We hypothesized that combination therapy using GO and Talazoparib would result in synergistic anti-leukemic effects on human CD33+ AML cells due to the ability of the PARP inhibitor to enhance levels of DNA damage induced by GO therapy. Materials and Methods Human AML cell lines were characterized for CD33 expression using flow cytometry after staining with antibody-linked fluorescent QuantiBrite Beads. Cells were continuously exposed to varying doses of GO (10pM - 100mM) and PARP inhibitors (1nM - 100mM) for 96h alone and in combination. Cell viability was measured immediately following treatment using a WST colorimetric assay. Treatment-induced apoptosis (annexin/PI) and DNA damage (H2AX) were quantified by flow cytometric assays. Synergy reports were generated using Compusyn software. In vivo efficacy was assessed in NSG mice systematically engrafted with luciferase labeled human CD33+ AML cells following tail vein injection. Animals were treated with varying doses of vehicle, GO (1 and 50ug/kg 1x/week for 3 weeks), or talazoparib (0.1 and 0.33mg/kg 5 days/week) either alone or in combination. Treatment effects on leukemia burden, toxicity, and survival were determined by weekly whole animal bioluminescent imaging, total animal weights, and time to morbidity. Results Human AML cell lines (HEL, HL60) express high expression levels of CD33 molecules/cell (43,645 and 31,286 respectively) relative to negative controls. Continuous exposure to single agent GO and Talazoparib for 96h resulted in a dose dependent inhibition of human AML cell growth (HEL, HL60) . IC values for GO were 0.01 - 6.6μg/ml and for Talazoparib were 0.8-0.95μM. Combination in vitro therapy with GO (0.005 - 1μg/ml) and Talazoparib (fixed dose 100nM) resulted in synergistic anti-leukemic effects (p<0.01) significantly improving upon monotherapy. Software analyses yielded a combination Index (CI) <1 consistent with synergistic anti-leukemic effects. Combination GO and Talazoparib therapy also significantly enhanced AML cell apoptosis (p=0.0111) and levels of DNA damage (phosphorylated H2AX) (p=0.0054) over single agent activity. Evaluation of PARP trapping by western blot analysis is ongoing. In vivo administration of GO (1-50μg/kg) and Talazoparib (0.1-0.33mg/kg) in NSG mice with systemic engraftment of luciferase tagged human CD33+ AML cells was generally well tolerated with no significant weight loss or early morbidity. Single agent GO and Talazoparib therapy decreased systemic AML burden in a dose dependent manner and prolonged overall survival over vehicle treated mice (P<0.05). Concomitant GO (1μg/kg) and Talazoparib (0.33μg/kg) treatment was similarly well tolerated with no notable weight loss or toxicities. Combination GO and Talazoparib therapy significantly prolonged overall survival of leukemia xenografted mice over vehicle (p=0.0018) and single agent therapy with the same doses of GO (p=0.0018) and Talazoparib (p=0.0499), respectively). Conclusions In summary, our results demonstrate that the addition of the PARP inhibitor, Talazoparib, to the CD33 antibody drug conjugate, GO, results in potent in vitro and in vivo anti-tumor activity in human CD33+ AML preclinical models. Further studies investigating this novel combinatorial approach in AML are currently ongoing. Due to GO's FDA approval for CD33+ AML in 2018, this data strongly supports future clinical investigation using PARP inhibitors as a novel class of agents for combination therapy to significantly enhance the efficacy of ADCs. Figure 1 Disclosures Wang: Amgen: Other: Advisory role; Agios: Other: Advisory role; Stemline: Other: Advisory role, Speakers Bureau; Daiichi: Other: Advisory role; Abbvie: Other: Advisory role; Kite: Other: Advisory role; Jazz: Other: Advisory role; Astellas: Other: Advisory role, Speakers Bureau; celyad: Other: Advisory role; Pfizer: Other: Advisory role, Speakers Bureau.

scholarly journals DoE Optimization Empowers the Automated Preparation of Enantiomerically Pure [18F]Talazoparib and its In Vivo Evaluation as a PARP Radiotracer.

2021 ◽  
Author(s):  
Gregory D. Bowden ◽  
Sophie Stotz ◽  
Johannes Kinzler ◽  
Christian Geibel ◽  
Michael Laemmerhofer ◽  
...  
Keyword(s):  
Parp Inhibitor ◽  
Parp Inhibitors ◽  
Reversed Phase ◽  
In Vivo Evaluation ◽  
Enantiomerically Pure ◽  
Imaging Probes ◽  
Radiolabeled Compounds ◽  
Clinical Potential

PARP inhibitors are proven chemotherapeutics and serve as lead structures for the development of PARP-targeted in vivo imaging probes. Given the clinical potential of PARP imaging for the detection and stratification of various cancers, the development of novel PARP imaging probes with improved pharmacologi-cal profiles over established PARP imaging agents is warranted. Here, we present a novel 18F-labeled PARP radiotracer based on the clinically superior PARP inhibitor talazoparib. An automated radiosynthesis of [18F]talazoparib (RCY: 13 ± 3.4 %; n = 4; molar radioactivity 52 – 176 GBq/μmol) was achieved using a “Design of Experiments” (DoE) optimized copper-mediated radiofluorination reaction. The chiral product was isolated from the reaction mixture using 2D reversed-phase/chiral radio-HPLC (>99% ee). (8S, 9R)-[18F]Talazoparib demonstrated PARP binding in HCC1937 cells in vitro and showed an excellent tumor-to-blood ratio in xeno-graft-bearing mice (10.2 ± 1.5). Despite expected uptake into muscle, bone, and abdominal tissue, a favorable pharmacological profile in terms of excretion, blood half-life, and target engagement was observed in the pilot in vivo study. This synthesis of [18F]talazoparib exemplifies how a DoE based tracer development pipeline can enable the radiosyntheses of clinically relevant but synthetically challenging radiolabeled compounds of high interest to the imaging community.

scholarly journals In Vitro and In Vivo Models to Study Nephropathic Cystinosis

Cells ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 6
Author(s):  
Pang Yuk Cheung ◽  
Patrick T. Harrison ◽  
Alan J. Davidson ◽  
Jennifer A. Hollywood
Keyword(s):  
Cell Lines ◽  
Molecular Mechanisms ◽  
Primary Cultures ◽  
Model Systems ◽  
In Vivo Model ◽  
Nephropathic Cystinosis ◽  
In Vivo Models ◽  
Induced Pluripotent

The development over the past 50 years of a variety of cell lines and animal models has provided valuable tools to understand the pathophysiology of nephropathic cystinosis. Primary cultures from patient biopsies have been instrumental in determining the primary cause of cystine accumulation in the lysosomes. Immortalised cell lines have been established using different gene constructs and have revealed a wealth of knowledge concerning the molecular mechanisms that underlie cystinosis. More recently, the generation of induced pluripotent stem cells, kidney organoids and tubuloids have helped bridge the gap between in vitro and in vivo model systems. The development of genetically modified mice and rats have made it possible to explore the cystinotic phenotype in an in vivo setting. All of these models have helped shape our understanding of cystinosis and have led to the conclusion that cystine accumulation is not the only pathology that needs targeting in this multisystemic disease. This review provides an overview of the in vitro and in vivo models available to study cystinosis, how well they recapitulate the disease phenotype, and their limitations.

scholarly journals DRES-02. PARYLATION OF MGMT BY PARP IS REQUIRED FOR MGMT MEDIATED TEMOZOLOMIDE-INDUCED O6-METHYLGUANINE REPAIR: A NOVEL MECHANISM OF MGMT ACTION

2019 ◽  
Vol 21 (Supplement_6) ◽  
pp. vi71-vi72 ◽  
Author(s):  
Shaofang Wu ◽  
Feng Gao ◽  
Dimpy Koul ◽  
Alfred Yung
Keyword(s):  
Dna Repair ◽  
Dna Methyltransferase ◽  
Parp Inhibitor ◽  
Malignant Gliomas ◽  
Parp Inhibitors ◽  
Parp Inhibition ◽  
Protein Activity ◽  
Damaged Dna

Abstract Temozolomide (TMZ) is the standard chemotherapy for malignant gliomas (MG), and resistance to this drug is mediated by the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). Epigenetic silencing of the MGMT gene by promoter methylation in about 40% patients is associated with loss of MGMT expression that compromises DNA repair leading to favorable response to TMZ therapy. Understanding the mechanism of MGMT mediated repair and modulating MGMT activity will enhance TMZ activity in MGMT unmethylated MG. Here we report a novel mode of regulation of MGMT protein activity by Poly-ADP-ribose polymerase (PARP). We found that PAPR physically interacts with MGMT and PARylates MGMT in response to TMZ treatment. We further showed PARylation of MGMT by PAPR is required for MGMT binding to DNA and to remove O6-methylguanine adducts in damaged DNA induced by TMZ. All 4 PARP inhibitors (trapping and non-trapping) tested (Talazoparib, Pamiparib, Veliparib, Olaparib) can inhibit PARP-MGMT binding, PARylation of MGMT, binding to DNA and subsequent removal of O6 - lesions in damaged DNA. We showed combination of PARP inhibitor with TMZ potentiated TMZ cytotoxicity in both MGMT methylated and unmethylated Glioma stem cell lines, but more profoundly in unmethylated group in vitro and in vivo. PARP inhibition acted as a double-edged sword in MGMT unmethylated MG: blocking BER/SSBR pathway to repair TMZ induced N7-MetG and O3-MetA, and more importantly, suppressing PARP-mediated PARylation of MGMT and thus silencing MGMT activity to repair O6-MetG, resulting in augmented cytotoxicity. This is the first study to show that PARylation of MGMT by PARP is required for repairing TMZ-induced O6-methylguanine adducts, and inhibition of MGMT PARylation abolishes MGMT function and renders sensitization to TMZ treatment. This finding provides a rationale for combining TMZ/CCNU and PARP inhibitors in MGMT unmethylated MG patients to enhance the benefit of adjuvant chemotherapy.

scholarly journals DNA methyltransferase inhibitors induce a BRCAness phenotype that sensitizes NSCLC to PARP inhibitor and ionizing radiation

2019 ◽  
Vol 116 (45) ◽  
pp. 22609-22618 ◽  
Author(s):  
Rachel Abbotts ◽  
Michael J. Topper ◽  
Christopher Biondi ◽  
Daniel Fontaine ◽  
Reena Goswami ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Dna Methyltransferase ◽  
Parp Inhibitor ◽  
Nonsmall Cell Lung Cancer ◽  
Parp Inhibitors ◽  
End Joining ◽  
Brca Mutations ◽  
Dna Methyltransferase Inhibitors

A minority of cancers have breast cancer gene (BRCA) mutations that confer sensitivity to poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis), but the role for PARPis in BRCA-proficient cancers is not well established. This suggests the need for novel combination therapies to expand the use of these drugs. Recent reports that low doses of DNA methyltransferase inhibitors (DNMTis) plus PARPis enhance PARPi efficacy in BRCA-proficient AML subtypes, breast, and ovarian cancer open up the possibility that this strategy may apply to other sporadic cancers. We identify a key mechanistic aspect of this combination therapy in nonsmall cell lung cancer (NSCLC): that the DNMTi component creates a BRCAness phenotype through downregulating expression of key homologous recombination and nonhomologous end-joining (NHEJ) genes. Importantly, from a translational perspective, the above changes in DNA repair processes allow our combinatorial PARPi and DNMTi therapy to robustly sensitize NSCLC cells to ionizing radiation in vitro and in vivo. Our combinatorial approach introduces a biomarker strategy and a potential therapy paradigm for treating BRCA-proficient cancers like NSCLC.

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