HMGB3 promotes PARP inhibitor resistance through interacting with PARP1 in ovarian cancer

Poly (ADP-ribose) polymerase (PARP) inhibitor (PARPi) resistance remains a therapeutic challenge in ovarian cancer. High-mobility group box 3 (HMGB3) plays significant roles in the development of drug resistance of many cancers. However, the function of HMGB3 in PARPi resistance is poorly understood. In the current study, we clarified that HMGB3 was aberrantly overexpressed in high-grade serous ovarian carcinoma (HGSOC) tissues, and high HMGB3 levels indicated shorter overall survival and drug resistance in HGSOC. The overexpression of HMGB3 increased the insensitivity of ovarian cancer to PARPi, whereas HMGB3 knockdown reduced PARPi resistance. Mechanistically, PARP1 was identified as a novel interaction partner of HMGB3, which could be blocked using olaparib and was enhanced upon DNA damage conditions. We further showed that loss of HMGB3 induced PARP1 trapping at DNA lesions and inhibited the PARylation activity of PARP1, resulting in an increased DNA damage response and cell apoptosis. The PARPi-resistant role of HMGB3 was also verified in a xenograft mouse model. In conclusion, HMGB3 promoted PARPi resistance via interacting with PARP1, and the targeted inhibition of HMGB3 might overcome PARPi resistance in ovarian cancer therapy.Subject terms: Chemotherapy, Ovarian cancer, Ovarian cancer, Cancer therapeutic resistance     

Synergistic effect of PARP inhibitor and BRD4 inhibitor in multiple models of ovarian cancer

Ovarian cancer has the highest facility rate among gynaecological tumours. Current therapies including PARP inhibitors have a defect that ovarian tumour is easy to recurrent and become resistant to therapy. To solve this problem, we found that BRD4 inhibitor AZD5153 and PARP inhibitor olaparib had a widespread synergistic effect in multiple models with different gene backgrounds. AZD5153 sensitizes cells to olaparib and reverses the acquired resistance by down-regulating PTEN expression levels to destabilize hereditary materials. In this study, we used the following multiple ovarian cancer models PDX, PDO and 3D/2D cell lines to elucidate the co-effect of AZD5153 and olaparib in vivo and in vitro. The similar results of these models further proved that the mechanism identified was consistent with the biological process occurring in ovarian cancer patients after drug treatment. This consistency between the results of different models suggests the possibility of translating these laboratory research findings into clinical studies towards developing treatments.     

The PARP inhibitor PJ34 causes a PARP1-independent, p21 dependent mitotic arrest

Poly(ADP)-ribose polymerase (PARP) inhibitors modify the enzymatic activity of PARP1/2. When certain PARP inhibitors are used either alone or in combination with DNA damage agents they may cause a G2/M mitotic arrest and/or apoptosis in a susceptible genetic context. PARP1 interacts with the cell cycle checkpoint proteins Ataxia Telangectasia Mutated (ATM) and ATM and Rad3-related (ATR) and therefore may influence growth arrest cascades. The PARP inhibitor PJ34 causes a mitotic arrest by an unknown mechanism in certain cell lines, therefore we asked whether PJ34 conditionally activated the checkpoint pathways and which downstream targets were necessary for mitotic arrest. We found that PJ34 produced a concentration dependent G2/M mitotic arrest and differentially affected cell survival in cells with diverse genetic backgrounds. p53 was activated and phosphorylated at Serine15 followed by p21 gene activation through both p53-dependent and -independent pathways. The mitotic arrest was caffeine sensitive and UCN01 insensitive and did not absolutely require p53, ATM or Chk1, while p21 was necessary for maintaining the growth arrest. Significantly, by using stable knockdown cell lines, we found that neither PARP1 nor PARP2 was required for any of these effects produced by PJ34. These results raise questions and cautions for evaluating PARP inhibitor effectiveness, suggesting whether effects should be considered not only on PARP's diverse ADP-ribosylation independent protein interactions but also on homologous proteins that may be producing either overlapping or distinct effect.     

MND1 and PSMC3IP control PARP inhibitor sensitivity in mitotic cells

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PARP inhibitor olaparib enhances the efficacy of radiotherapy on XRCC2-deficient colorectal cancer cells

The use of PARP inhibitors in combination with radiotherapy is a promising strategy to locally enhance DNA damage in tumors. Loss of XRCC2 compromises DNA damage repairs, and induced DNA damage burdens may increase the reliance on PARP-dependent DNA repairs of cancer cells to render cell susceptibility to PARP inhibitor therapy. Here we tested the hypothesis that XRCC2 loss sensitizes colorectal cancer (CRC) to PARP inhibitor in combination with radiotherapy (RT). We show that high levels of XRCC2 or PARP1 in LARC patients were significantly associated with poor overall survival (OS). Co-expression analyses found that low levels of PARP1 and XRCC2 were associated with better OS. Our in vitro experiments indicated that olaparib+IR led to reduced clonogenic survival, more DNA damage, and longer durations of cell cycle arrest and senescence in XRCC2-deficient cells relative to wild-type cells. Furthermore, our mouse xenograft experiments indicated that RT + olaparib had greater anti-tumor effects and led to long-term remission in mice with XRCC2-deficient tumors. These findings suggest that XRCC2-deficient CRC acquires high sensitivity to PARP inhibition after IR treatment and supports the clinical development for the use of olaparib as a radiosensitizer for treatment of XRCC2-deficient CRC.Subject terms: Colorectal cancer, Prognostic markers     

TOPBP1 regulates RAD51 phosphorylation and chromatin loading and determines PARP inhibitor sensitivity

Topoisomerase IIβ-binding protein 1 (TOPBP1) participates in DNA replication and DNA damage response; however, its role in DNA repair and relevance for human cancer remain unclear. Here, through an unbiased small interfering RNA screen, we identified and validated TOPBP1 as a novel determinant whose loss sensitized human cells to olaparib, an inhibitor of poly(ADP-ribose) polymerase. We show that TOPBP1 acts in homologous recombination (HR) repair, impacts olaparib response, and exhibits aberrant patterns in subsets of human ovarian carcinomas. TOPBP1 depletion abrogated RAD51 loading to chromatin and formation of RAD51 foci, but without affecting the upstream HR steps of DNA end resection and RPA loading. Furthermore, TOPBP1 BRCT domains 7/8 are essential for RAD51 foci formation. Mechanistically, TOPBP1 physically binds PLK1 and promotes PLK1 kinase–mediated phosphorylation of RAD51 at serine 14, a modification required for RAD51 recruitment to chromatin. Overall, our results provide mechanistic insights into TOPBP1’s role in HR, with potential clinical implications for cancer treatment.     

PARP inhibitors for cancer therapy

Poly(ADP-ribose) polymerase 1 (PARP-1) is a zinc-finger DNA-binding enzyme that is activated by binding to DNA breaks. Poly(ADP-ribosyl)ation of nuclear proteins by PARP-1 converts DNA damage into intracellular signals that activate either DNA repair by the base-excision pathway or cell death. A family of 18 PARPs has been identified, but only the most abundant, PARP-1 and PARP-2, which are both nuclear enzymes, are activated by DNA damage. PARP inhibitors of ever-increasing potency have been developed in the 40 years since the discovery of PARP-1, both as tools for the investigation of PARP-1 function and as potential modulators of DNA-repair-mediated resistance to cytotoxic therapy. Owing to the high level of homology between the catalytic domains of PARP-1 and PARP-2, the inhibitors probably affect both enzymes. Convincing biochemical evidence, which has been corroborated by genetic manipulation of PARP-1 activity, shows that PARP inhibition is associated with increased sensitivity to DNA-alkylating agents, topoisomerase I poisons and ionising radiation. Novel PARP inhibitors of sufficient potency and suitable pharmacokinetic properties to allow evaluation in animal models have been shown to enhance the antitumour activity of temozolomide (a DNA-methylating agent), topoisomerase poisons and ionising radiation; indeed, the combination with temozolomide resulted in complete tumour regression in two independent studies. The combination of a PARP inhibitor and temozolomide is currently undergoing clinical evaluation for the first time.     

多聚二磷酸腺苷聚合酶1与动脉粥样硬化

心血管疾病已经成为发达国家威胁生命的主要疾病,而动脉粥样硬化是最常见的心血管疾病之一．近来研究发现,多聚二磷酸腺苷聚合酶1(PARP1)在动脉粥样硬化致病机理中起着重要的作用．PARP1为PARP家族中含量最丰富的核酶,担负着DNA缺口敏感酶的功能,具有双向作用．正常情况下,它参与DNA损伤的修复,但过量激活则消耗NAD⁺和ATP使细胞功能紊乱,最终坏死．一些疾病的细胞程序性死亡机制可能与此相关,这些疾病包括动脉粥样硬化、冠心病、糖尿病及相关的心血管功能紊乱．有趣的是,除DNA损伤激活PARP1外,最近又发现激酶、多胺、咖啡因代谢物、茶碱和四环素等也可以参与PARP1的调节,核因子(NF-κB)和细胞内Ca²⁺也参与PARP1的调节．本文总结了靶点PARP的生物功能和基本原理,动脉粥样硬化致病的可能机制以及PARP1对其调节的研究进展,将对动脉粥样硬化的研究提供有力帮助．     

Inhibition of PARP1 activity enhances chemotherapeutic efficiency in cisplatin-resistant gastric cancer cells

Cisplatin (DDP) is the first line chemotherapeutic drug for several cancers, including gastric cancer (GC). Unfortunately, the rapid development of drug resistance remains a significant challenge for the clinical application of cisplatin. There is an urgent need to develop new strategies to overcome DDP resistance for cancer treatment. In this study, four types of human GC cells have been divided into naturally sensitive or naturally resistant categories according to their responses to cisplatin. PARP1 activity (poly (ADP-ribose), PAR) was found to be greatly increased in cisplatin-resistant GC cells. PARP1 inhibitors significantly enhanced cisplatin-induced DNA damage and apoptosis in the resistant GC cells via the inhibition of PAR. Mechanistically, PARP1 inhibitors suppress DNA-PKcs stability and reduce the capability of DNA double-strand break (DSB) repair via the NHEJ pathway. This was also verified in BGC823/DDP GC cells with acquired cisplatin resistance. In conclusion, we identified that PARP1 is a useful interceptive target in cisplatin-resistant GC cells. Our data provide a promising therapeutic strategy against cisplatin resistance in GC cells that has potential translational significance.     

Re-evaluating the cost of outpatient cancer chemotherapy.

Chemotherapy for common malignant tumours has historically been considered relatively expensive. An examination of costs at the Toronto-Bayview Regional Cancer Centre and Sunnybrook Medical Centre, Toronto, suggests that this perception is not accurate. The cost of chemotherapeutic agents administered on an outpatient basis over 4 to 6 months in established drug protocols ranged from $260 to $5374 (mean $2224). The total cost of outpatient administration was estimated to be $152.53 per dose, compared with $185.39 for inpatient administration of the same protocol, a difference of 22%. The difference was predominantly due to a higher allocated per-diem charge at the medical centre. The results indicate that outpatient administration reduces the overall cost of chemotherapy.     

PARP inhibitor Olaparib increases the sensitization to radiotherapy in FaDu cells

Radioresistance causes a major problem for improvement of outcomes of patients treated with radiation. Targeting for DNA repair deficient mechanisms is a hallmark of sensitization to resistance. We tested whether Olaparib, a (poly) ADP‐ribose polymerase (PARP) inhibitor, can sensitize the radioresistant FaDu cells to radiotherapy. Radioresistant FaDu cells, called FaDu‐RR cells, were used as the radioresistant hypopharyngeal cancer models. The expression of PARP1 was detected in both FaDu and FaDu‐RR cells. The role of Olaparib in radiosensitization was analysed with several assays including clonogenic cell survival, cell proliferation and cell cycle, and radioresistant xenograft. High expression of PARP1 had a significant effect on enhancing radioresistance in FaDu‐RR cells compared with FaDu cells. After treatment of Olaparib, FaDu‐RR cells showed significantly less and smaller surviving colonies, lower proliferation ability and G2/M arrest than those in the group without treatment. Moreover, Olaparib significantly reduced growth of tumours in FaDu‐RR cell xenografts treated with ionizing radiation. Olaparib can significantly inhibit PARP1 expression and consequently has significant effects on radiosensitization in FaDu‐RR cells. These results indicate that Olaparib may help individualize treatment and improve their outcomes of hypopharyngeal cancer patients treated with radiation.     

Captured snapshots of PARP1 in the active state reveal the mechanics of PARP1 allostery

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Potent beta-cell protection in vitro by an isoquinolinone-derived PARP inhibitor.

Activation of the nuclear enzyme poly(ADP-ribose)polymerase (PARP) is a critical step in beta-cell death in response to exposure with free radicals or other DNA damaging agents. Nicotinamide, a B vitamin, exerts its beta-cell protective action primarily via its ability to block excessive PARP activity. We show here that the isoquinolinone derivative PD128763, a specific PARP inhibitor, provides protection from cell death in islet cells exposed in vitro to nitric oxide or oxygen radical generating compounds or to the beta-cell toxin streptozotocin, at concentrations 100 times less than required for nicotinamide. Furthermore, while the protective action of nicotinamide is rapidly lost after washing of islet cells, the effects of PD128763 are more long lasting. Both compounds had little capacity to rescue damaged islet cells from subsequent lysis. We conclude that the isoquinolinone derivative PD128763 is superior to nicotinamide in enhancing the resistance of beta-cells towards inflammatory attacks.