Targeted therapy for cancer using PARP inhibitors

Poly (ADP-ribose) Polymerase (PARP) has a well-established role in DNA repair processes, and small molecule inhibitors of PARP have been developed as chemotherapy sensitisers for the treatment of cancer. The subsequent demonstration that PARP inhibition is selective for BRCA1 or BRCA2 deficiency suggests that PARP inhibitors may be particularly useful for the treatment of cancer with BRCA mutations. This would represent one of the first clinically implemented examples of a synthetic lethal approach for cancer treatment. However, there are still unanswered questions surrounding PARP inhibitors, namely the levels of specificity and potency that are required to elicit BRCA selectivity. The recent identification of mechanisms of cellular resistance to PARP inhibitors may provide indications as to how these drugs may be best used in the clinic.     

靶向DNA损伤反应途径:PARP抑制剂抗肿瘤治疗研究进展

细胞在长期进化过程中形成的复杂的DNA损伤反应防御机制是维护基因组稳定性的重要途径,DNA损伤反应通路缺陷可导致包括肿瘤在内的多种疾病的发生。DNA损伤反应通路是一个复杂的信号通路,包括DNA损伤修复、凋亡、细胞周期调控等,DNA损伤反应通路已经成为新的抗肿瘤药物靶点。目前,已经开发多种DNA损伤反应通路相关的抑制剂,特别是对BRCA1和BRCA2基因突变的肿瘤,利用协同致死现象而开发的聚腺苷二磷酸核糖聚合酶抑制剂广泛应用于肿瘤个体化治疗。该文重点对DNA损伤反应通路抑制剂中的聚腺苷二磷酸核糖聚合酶抑制剂的作用分子机制、临床治疗、耐药性以及面临的挑战进行综述。     

对《ASCO指南中有关PARP抑制剂治疗卵巢癌的临床推荐意见》的点评

根据ASCO指南,解读多聚（ADP-核糖）聚合酶抑制剂（PARPi）在上皮性卵巢癌、输卵管癌或原发性腹膜癌中的应用。ASCO指南建议基于既往已发表文献的循证证据、美国食品药品监督管理局的相关审批文件以及相关证据缺乏时的专家共识,最终纳入17项符合标准的临床研究。本指南适用于PARPis初治患者,对PARPis的再次使用、初诊和复发性卵巢癌的二线或以上维持治疗,以及PARPis联合治疗等几个方面提出治疗建议,并提供推荐级别及证据强度。指南对于特定不良事件的管理也提出了建议,并就患者与临床医生的沟通方法和问题,以及研究的局限性和未来的研究方向进行了说明。     

Potential clinical applications of poly(ADP-ribose) polymerase (PARP) inhibitors.

Poly(ADP-ribose) polymerases (PARPs) are defined as cell signaling enzymes that catalyze the transfer of ADP-ribose units from NAD(+)to a number of acceptor proteins. PARP-1, the best characterized member of the PARP family, that presently includes six members, is an abundant nuclear enzyme implicated in cellular responses to DNA injury provoked by genotoxic stress (oxygen radicals, ionizing radiations and monofunctional alkylating agents). Due to its involvement either in DNA repair or in cell death, PARP-1 is regarded as a double-edged regulator of cellular functions. In fact, when the DNA damage is moderate, PARP-1 participates in the DNA repair process. Conversely, in the case of massive DNA injury, elevated PARP-1 activation leads to rapid NAD(+)/ATP consumption and cell death by necrosis. Excessive PARP-1 activity has been implicated in the pathogenesis of numerous clinical conditions such as stroke, myocardial infarction, shock, diabetes and neurodegenerative disorders. PARP-1 could therefore be considered as a potential target for the development of pharmacological strategies to enhance the antitumor efficacy of radio- and chemotherapy or to treat a number of clinical conditions characterized by oxidative or NO-induced stress and consequent PARP-1 activation. Moreover, the discovery of novel functions for the multiple members of the PARP family might lead in the future to additional clinical indications for PARP inhibitors.     

聚腺苷二磷酸-核糖聚合酶抑制剂在胰腺癌中的研究进展

胰腺癌是一种高度恶性的肿瘤,聚腺苷二磷酸-核糖聚合酶(PARP)抑制剂(PARPI)是首类基于合成致死概念开发合成的抗肿瘤药物,并被临床批准用于卵巢癌和乳腺癌的治疗。由于特定的DNA修复缺陷,研究发现具有BRCA1/2种系突变的肿瘤对PARPI敏感,但具体的作用机制仍不十分清楚。目前针对胰腺癌的多项临床试验已经开展,Ⅲ期POLO研究表明Olaparib在种系BRCA1/2突变患者和铂类诱导化疗后转移性胰腺癌患者中作为维持治疗有效且耐受性良好。联合治疗的相关临床研究表明添加PARPI的益处很可能来自维持治疗阶段。总的来说,PARPI在胰腺癌治疗领域有广阔的前景。     

Targeted therapy for brain tumours: role of PARP inhibitors

The prognosis of malignant glioma and metastatic brain tumours is still extremely poor, despite recent advances in therapeutic strategies with molecular-targeted agents. Poly(ADP-ribose) polymerase (PARP) inhibitors are a promising, novel class of anticancer drugs to be used either as single agents or in combination with chemotherapy and radiotherapy. PARP-1 and PARP-2 are the only PARP proteins that bind to DNA single strand breaks (SSBs), facilitating the repair process by the base excision repair. For this reason, PARPs have been extensively investigated as targets of novel drugs that may be used to enhance the antitumour activity of SSBs inducing agents, such as the methylating compound temozolomide, which is the drug of choice for glioblastoma, or ionizing radiations. Moreover, PARP inhibitors exert cytotoxic effects in monotherapy in BRCA mutated tumours, which are defective in the homologous recombination (HR) repair. Finally, recent studies have shown that inhibition of PARP function might also induce anti-angiogenic effects which might contribute to impair tumour growth. Many clinical trials with PARP inhibitors are ongoing for the treatment of a variety of advanced solid tumours, including primary or secondary brain tumours. This review discusses the implications of targeting PARP on the design of new treatment regimens.     

Advances in PARP inhibitors for the treatment of breast cancer

Introduction: Poly(ADP-Ribose) polymerases (PARPs) are one of the important components of base excision repair pathway for single strand DNA breaks. Currently accepted hypothesis for the mechanism of action for PARP inhibitors in tumors with homologous recombination deficiency is synthetic lethality, as the simultaneous blockage of both pathways prevents the tumor cells from repairing DNA damage. Other proposed mechanisms include PARP trapping, defective BRCA1 and POLQ recruitment to sites of DNA repair. Breast cancer subgroups with germline BRCA mutations or non-mutational functional defects in BRCA proteins exemplify potential targets for PARP inhibitors.

Areas covered: Promising results have been achieved with PARP inhibitors in BRCA associated cancers, particularly in ovarian and breast cancer. Olaparib is the only PARP inhibitor approved by FDA in the treatment of patients with germline BRCA mutated advanced ovarian cancer pretreated with ≥3 prior lines of chemotherapy. In this article, we reviewed the current status of PARP inhibitors, completed and ongoing trials, safety and resistance issues in patients with breast cancer.

Expert opinion: PARP inhibitors show promise in cancers with BRCA mutation and in the treatment of sporadic cancers with defective homologous recombination. Predictors of response, strategies to overcome resistance, combination with other chemotherapies and targeted agents, optimum dose and schedule of administration should be investigated in future trials.     

Biological therapy of breast cancer: recent clinical applications

Advances have been made in breast cancer therapy, in both the adjuvant and metastatic settings. For example, in the adjuvant setting, genomic studies of breast cancer tissues have identified women with estrogen receptor-positive tumors who might not require chemotherapy, leading to the development of a diagnostic tool. There have also been significant developments with anticancer agents that target tumor cell surface receptors, such as HER2/neu, and those involved in angiogenesis and kinase-dependent pathways. New areas of research focus on the concept of breast cancer stem cells as well as the prognostic importance of bone marrow micrometastases in early-stage breast cancer. This review summarizes these advances in breast cancer clinical research.     

Development of PARP inhibitors in oncology

Poly (ADP-ribose) polymerase (PARP) plays a key role in DNA repair mechanisms by detecting and initiating repair after DNA strand breaks. Inhibition of PARP in DNA repair-defective tumors (like those with BRCA1 or BRCA2 mutations) can lead to gross genomic instability and cell death. Likewise, combining PARP inhibition with cytotoxic agents such as chemotherapy or radiation therapy is synergistic in many preclinical models. Several drugs designed to inhibit PARP are currently in clinical development, many following a development path different from that of typical anticancer agents. In this review we will focus on the early clinical data from PARP inhibitors that are entering clinical trials, the potential tumors they might target, their combination with other drugs and the different biomarkers that are being explored. Concepts such as ‘BRCAness’, synthetic lethality, Phase 0 trials and pharmacodynamic markers will be discussed in the context of the development of PARP inhibitors.     

聚腺苷二磷酸核糖聚合酶抑制剂在神经保护方面的研究进展

作者对聚腺苷二磷酸核糖聚合酶[poly（ADP—ribose）polymerase，PARP]的结构亚型和生物学功能做了简要介绍。归纳了近几年PARP抑制剂在神经保护方面的研究成果。并从结构分类的角度探讨了部分具有应用前景的化合物的构效关系。     

PARP inhibitors: mechanism of action and their potential role in the prevention and treatment of cancer

The use of poly(ADP-ribose) polymerase (PARP) inhibitors provided proof-of-concept for a synthetic lethal anti-cancer strategy as a result of their efficacy and favourable toxicity profile in BRCA1/2 mutation carriers. Efforts are underway to identify a broader group of patients with genomic susceptibility that may benefit from these agents. In an endeavour to enhance anti-tumour effects, PARP inhibitors have been combined with traditional cytotoxic therapy and radiotherapy; however, optimization of dosing schedules for these combination regimens remains key to maximizing benefit whilst mitigating the potential for increased toxicity. With ongoing clinical experience of PARP inhibition, mechanisms of resistance to these therapies are being elucidated and specific challenges to long-term administration of these drugs will need to be addressed. Development of robust predictive biomarkers of response for optimal patient selection and rational combination strategies must be pursued if the full potential of these agents is to be realized.     

Investigational cell cycle inhibitors in clinical trials for bladder cancer

Background: In asthma, inhaled corticosteroids are not always able to maintain an optimal therapeutic control despite being used at high doses; other anti-inflammatory therapies are needed. Several such therapies, including daclizumab, are currently under evaluation. Objective: To discuss the results of study on daclizumab in asthma patients. Methods: Analysis of efficacy and safety data from a randomised placebo-controlled study performed in patients with moderate to severe asthma and suboptimal control under high doses of inhaled corticosteroids. Conclusions: Daclizumab demonstrated significant efficacy and its further clinical evaluation in asthma is supported by these results.     

The safety of antiangiogenic agents and PARP inhibitors in platinum-sensitive recurrent ovarian cancer

Introduction: Recurrence is a common event in endothelial ovarian cancer (EOC) patients, and the choice of the most appropriate treatment is driven by the platinum-free interval, molecular characteristics of the disease such as BRCA mutational status, previous treatments and toxicity.

Areas covered: This review focuses on the main hematologic and non-hematologic toxicities correlated with the use of licensed antiangiogenic agents and PARP inhibitors in recurrent platinum-sensitive EOC, providing recommendations for their management.

Expert opinion: The clinical research over the next years will be focused on a more precise characterization of molecular pathways underlying tumorigenesis of the five ovarian tumors, to improve the decision-making process in these rare diseases. For this purpose, new study designs and international collaborations will become mandatory. Immunotherapy, antiangiogenic agents and PARP inhibitors will be combined to build a treatment strategy algorithm which will allow patients to receive all the available treatment option, in the more appropriate sequence.     

Angiogenesis inhibitors in cancer therapy

The formation of new blood vessels is essential for tumor growth and progression. Angiogenesis inhibitors have been demonstrated to block tumor growth and/or metastasis. Although initial clinical data have been disappointing, new strategies to increase the efficacy of these drugs have ensured their ongoing clinical development. This review highlights the broad spectrum of angiogenesis inhibitors under investigation in both preclinical and clinical studies. From 'natural' inhibitors to thalidomide analogs, the number of compounds in development is extensive. Elucidating the mechanisms of action will enable their use in conjunction with existing/other novel therapies, thereby maximizing the potential efficacy of angiogenesis inhibitors to fulfill their promise in patients with cancer.     

VEGF inhibitors in cancer therapy

Vascular endothelial growth factor (VEGF)-mediated angiogenesis is thought to play a critical role in tumor growth and metastasis. Consequently, anti-VEGF therapies are being actively investigated as potential anti-cancer treatments, either as alternatives or adjuncts to conventional chemo or radiation therapy. Among the techniques used to block the VEGF pathway are: 1) neutralizing monoclonal antibodies against VEGF or its receptor, 2) small molecule tyrosine kinase inhibitors of VEGF receptors, 3) soluble VEGF receptors which act as decoy receptors for VEGF, and 4) ribozymes which specifically target VEGF mRNA. Recent evidence from phase III clinical trials led to the approval of bevacizumab, an anti-VEGF monoclonal antibody, by the FDA as first line therapy in metastatic colorectal carcinoma in combination with other chemotherapeutic agents. However, may challenges still remain, and the role of anti-VEGF therapy in the treatment of other solid tumors remains to be elucidated. The aim of this article is to review the progress of clinical investigations involving VEGF inhibitors in the treatment of different types of solid tumors.