BRCA1/2突变和同源重组修复缺陷(HRD)检测在乳腺癌中的临床研究进展

乳腺癌已成为发病率最高的癌症。DNA修复缺陷是乳腺癌最重要的特征之一。先前的研究表明,乳腺癌易感基因1/2(breast cancer susceptibility gene 1/2,BRCA1/2)突变是预测乳腺癌同源重组修复缺陷(homologous recombination deficiency, HRD)最主要的生物标志物,能识别铂类药物和多腺苷二磷酸核糖聚合酶(poly ADP ribose polymerase, PARP)抑制剂治疗的获益人群。美国食品药品监督管理局(FDA)已批准Olaparib和Talazoparib两种PARP抑制剂,用于BRCA1/2突变的早期和晚期乳腺癌的辅助治疗。但中国尚未获批。现有研究表明,一部分非BRCA1/2突变的乳腺癌患者也具有HRD特征,可以从铂类药物或PARP抑制剂中获益。本综述总结了涉及到BRCA1/2突变、同源重组修复(homologous recombination repair, HRR)基因突变和HRD状态检测的临床研究。阐明了各种检测方法在识别乳腺癌患者HRD状态和预测疗效方面的价值,并提出应尽快开发用于中国乳腺癌HR...     

Homologous recombination deficiency and ovarian cancer

The discovery that PARP inhibitors block an essential pathway of DNA repair in cells harbouring a BRCA mutation has opened up a new therapeutic avenue for high-grade ovarian cancers. BRCA1 and BRCA2 proteins are essential for high-fidelity repair of double-strand breaks of DNA through the homologous recombination repair (HRR) pathway. Deficiency in HRR (HRD) is a target for PARP inhibitors. The first PARP inhibitor, olaparib, has now been licensed for BRCA-mutated ovarian cancers. While mutated BRCA genes are individually most commonly associated with HRD other essential HRR proteins may be mutated or functionally deficient potentially widening the therapeutic opportunities for PARP inhibitors. HRD is the first phenotypically defined predictive marker for therapy with PARP inhibitors in ovarian cancer. Several different PARP inhibitors are being trialled in ovarian cancer and this class of drugs has been shown to be a new selective therapy for high-grade ovarian cancer. Around 20% of high-grade serous ovarian cancers harbour germline or somatic BRCA mutations and testing for BRCA mutations should be incorporated into routine clinical practice. The expanded use of PARP inhibitors in HRD deficient (non-BRCA mutant) tumours using a signature of HRD in clinical practice requires validation.     

Recent advances in targeting DNA repair pathways for the treatment of ovarian cancer and their clinical relevance

Poly (ADP-ribose) polymerase (PARP) inhibitors have attracted much attention as one of the major molecular-targeted therapeutics for inhibiting DNA damage response. The PARP inhibitor, olaparib, has been clinically applied for treating certain recurrent ovarian cancer patients with BRCA1/2 mutations in Europe and the United States. It was also designated on 24 March 2017 as an orphan drug in Japan for similar clinical indications. In this review, we discuss (i) the prevalence of BRCA1/2 mutations in ovarian cancer, (ii) clinical trials of PARP inhibitors in ovarian cancer, (iii) genetic counseling for hereditary breast and ovarian cancer patients, and (iv) non-BRCA genes that may be associated with homologous recombination deficiency.     

Development of PARP inhibitors in gynecological malignancies

PARP inhibitors demonstrate synthetic lethality in tumors with BRCA1/2 mutations and other homologous recombination repair deficiencies by interfering with DNA repair and causing direct toxicity to DNA through PARP trapping. PARP inhibitors have been shown to be beneficial in the treatment of BRCA1/2-mutated ovarian cancers, which has led to a shift in the treatment paradigm of this disease. Further studies to establish the role of PARP inhibitors during earlier stages of treatment are ongoing. The use of PARP inhibitors in other cancers with homologous recombination repair deficiencies, such as breast cancer and prostate cancer, is gradually evolving as well, including their use in the neoadjuvant and adjuvant settings. PARP inhibitor combination strategies with chemotherapy, targeted agents, radiotherapy, and immunotherapy are also being explored. The role of predictive biomarkers, including molecular signatures and homologous recombination deficiency scores based on loss of heterozygosity and other structural genomic aberrations, will be crucial to improved patient stratification to enhance the clinical utility of PARP inhibitors. This may also allow the use of PARP inhibitors to be extended beyond tumors with specific homologous recombination DNA repair gene mutations in the future. An improved understanding of the mechanisms underlying PARP inhibitor resistance will also be important to enable the development of new approaches to increase efficacy. This is a field rich in opportunity, and the coming years should see a better understanding of which patients we should be treating with PARP inhibitors and where these agents should come in over the course of treatment.     

A decade of clinical development of PARP inhibitors in perspective

Genomic instability is a hallmark of cancer, and often is the result of altered DNA repair capacities in tumour cells. DNA damage repair defects are common in different cancer types; these alterations can also induce tumour-specific vulnerabilities that can be exploited therapeutically. In 2009, a first-in-man clinical trial of the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib clinically validated the synthetic lethal interaction between inhibition of PARP1, a key sensor of DNA damage, and BRCA1/BRCA2 deficiency. In this review, we summarize a decade of PARP inhibitor clinical development, a work that has resulted in the registration of several PARP inhibitors in breast (olaparib and talazoparib) and ovarian cancer (olaparib, niraparib and rucaparib, either alone or following platinum chemotherapy as maintenance therapy). Over the past 10 years, our knowledge on the mechanism of action of PARP inhibitor as well as how tumours become resistant has been extended, and we summarise this work here. We also discuss opportunities for expanding the precision medicine approach with PARP inhibitors, identifying a wider population who could benefit from this drug class. This includes developing and validating better predictive biomarkers for patient stratification, mainly based on homologous recombination defects beyond BRCA1/BRCA2 mutations, identifying DNA repair deficient tumours in other cancer types such as prostate or pancreatic cancer, or by designing combination therapies with PARP inhibitors.     

Crosstalk of DNA double‐strand break repair pathways in poly(ADP‐ribose) polymerase inhibitor treatment of breast cancer susceptibility gene 1/2‐mutated cancer

Germline mutations in breast cancer susceptibility gene 1 or 2 (BRCA1 or BRCA2) significantly increase cancer risk in hereditary breast and ovarian cancer syndrome (HBOC). Both genes function in the homologous recombination (HR) pathway of the DNA double‐strand break (DSB) repair process. Therefore, the DNA‐repair defect characteristic of cancer cells brings about a therapeutic advantage for poly(ADP‐ribose) polymerase (PARP) inhibitor‐induced synthetic lethality. PARP inhibitor‐based therapeutics initially cause cancer lethality but acquired resistance mechanisms have been found and need to be elucidated. In particular, it is essential to understand in detail the mechanism of DNA damage and repair to PARP inhibitor treatment. Further investigations have shown the roles of BRCA1/2 and its associations to other molecules in the DSB repair system. Notably, the repair pathway chosen in BRCA1‐deficient cells could be entirely different from that in BRCA2‐deficient cells after PARP inhibitor treatment. The present review describes synthetic lethality and acquired resistance mechanisms to PARP inhibitor through the DSB repair pathway and subsequent repair process. In addition, recent knowledge of resistance mechanisms is discussed. Our model should contribute to the development of novel therapeutic strategies.     

Genomic scars as biomarkers of homologous recombination deficiency and drug response in breast and ovarian cancers

Poly (ADP-ribose) polymerase (PARP) inhibitors and platinum-based chemotherapies have been found to be particularly effective in tumors that harbor deleterious germline or somatic mutations in the BRCA1 or BRCA2 genes, the products of which contribute to the conservative homologous recombination repair of DNA double-strand breaks. Nonetheless, several setbacks in clinical trial settings have highlighted some of the issues surrounding the investigation of PARP inhibitors, especially the identification of patients who stand to benefit from such drugs. One potential approach to finding this patient subpopulation is to examine the tumor DNA for evidence of a homologous recombination defect. However, although the genomes of many breast and ovarian cancers are replete with aberrations, the presence of numerous factors able to shape the genomic landscape means that only some of the observed DNA abnormalities are the outcome of a cancer cell’s inability to faithfully repair DNA double-strand breaks. Consequently, recently developed methods for comprehensively capturing the diverse ways in which homologous recombination deficiencies may arise beyond BRCA1/2 mutation have used DNA microarray and sequencing data to account for potentially confounding features in the genome. Scores capturing telomeric allelic imbalance, loss of heterozygosity (LOH) and large scale transition score, as well as the total number of coding mutations are measures that summarize the total burden of certain forms of genomic abnormality. By contrast, other studies have comprehensively catalogued different types of mutational pattern and their relative contributions to a given tumor sample. Although at least one study to explore the use of the LOH scar in a prospective clinical trial of a PARP inhibitor in ovarian cancer is under way, limitations that result in a relatively low positive predictive value for these biomarkers remain. Tumors whose genome has undergone one or more events that restore high-fidelity homologous recombination are likely to be misclassified as double-strand break repair-deficient and thereby sensitive to PARP inhibitors and DNA damaging chemotherapies as a result of prior repair deficiency and its genomic scarring. Therefore, we propose that integration of a genomic scar-based biomarker with a marker of resistance in a high genomic scarring burden context may improve the performance of any companion diagnostic for PARP inhibitors.     

BRCA1/2 mutation analysis in 41 ovarian cell lines reveals only one functionally deleterious BRCA1 mutation

Mutations in BRCA1/2 increase the risk of developing breast and ovarian cancer. Germline BRCA1/2 mutations occur in 8.6–13.7% of unselected epithelial ovarian cancers, somatic mutations are also frequent. BRCA1/2 mutated or dysfunctional cells may be sensitive to PARP inhibition by synthetic lethality. The aim of this study is to comprehensively characterise the BRCA1/2 status of a large panel of ovarian cancer cell lines available to the research community to assist in biomarker studies of novel drugs and in particular of PARP inhibitors.The BRCA1/2 genes were sequenced in 41 ovarian cell lines, mRNA expression of BRCA1/2 and gene methylation status of BRCA1 was also examined. The cytotoxicity of PARP inhibitors olaparib and veliparib was examined in 20 cell lines.The cell line SNU-251 has a deleterious BRCA1 mutation at 5564G > A, and is the only deleterious BRCA1/2 mutant in the panel. Two cell lines (UPN-251 and PEO1) had deleterious mutations as well as additional reversion mutations that restored the protein functionality. Heterozygous mutations in BRCA1/2 were relatively common, found in 14.6% of cell lines. BRCA1 was methylated in two cell lines (OVCAR8, A1847) and there was a corresponding decrease in gene expression. The BRCA1 methylated cell lines were more sensitive to PARP inhibition than wild-type cells. The SNU-251 deleterious mutant was more sensitive to PARP inhibition, but only in a long-term exposure to correct for its slow growth rate. Cell lines derived from metastatic disease are significantly more resistant to veliparib (2.0 fold p = 0.03) compared to those derived from primary tumours. Resistance to olaparib and veliparib was correlated Pearsons-R 0.5393, p = 0.0311.The incidence of BRCA1/2 deleterious mutations 1/41 cell lines derived from 33 different patients (3.0%) is much lower than the population incidence. The reversion mutations and high frequency of heterozygous mutations suggest that there is a selective pressure against BRCA1/2 in cell culture similar to the selective pressure seen in the clinic after treatment with chemotherapy. PARP inhibitors may be useful in patients with BRCA1 deleterious mutations or gene methylation.     

PARP Inhibitors in Breast Cancer: Latest Evidence

Purpose of Review

Breast cancer treatment continues to evolve as targeted therapeutic strategies are developed for the various molecular subtypes of breast cancer. The PARP inhibitors represent a novel targeted therapy for tumors with defective homologous recombination DNA repair. These agents may become standard new treatment options for patients harboring BRCA1/2 mutations and show promise in BRCA1/2 wild-type patients with triple-negative breast cancers, which are treated predominantly with traditional cytotoxic chemotherapy. This review will discuss the results of clinical trials of these agents in breast cancer as well as important ongoing and anticipated trials.

Recent Findings

Recent reports support the use of olaparib monotherapy in BRCA1/2-mutated metastatic cancer. Results of PARP inhibitor combinations with chemotherapy have been mixed. The addition of veliparib failed to improve pathological complete response rates in patients with early-stage triple-negative breast cancer treated with carboplatin (AUC6) and paclitaxel followed by doxorubicin plus cyclophosphamide in a phase 3 trial. The PARP inhibitors talazoparib and olaparib are currently being tested in the neoadjuvant and adjuvant settings but impact on survival measures will likely take years prior to reporting in these early-stage breast cancer studies.

Summary

While data from the first phase 3 trials of PARP inhibitors in breast cancers are encouraging in patients with germline deleterious BRCA1/2 mutations, continued work is needed to elucidate their utility beyond the BRCA1/2-mutated population as has been possible in ovarian cancer. Additionally, defining the ideal population and setting for combination treatment remains a challenge and has been limited by synergistic toxicities.

     

The role of poly adenosine diphosphate ribose polymerase inhibitors in breast and ovarian cancer: current status and future directions

Poly adenosine diphosphate ribose polymerase (PARP) inhibitors have demonstrated single agent activity in the treatment of patients with recurrent BRCA1-mutated and BRCA2-mutated breast and ovarian cancers. They also appear to have a potential role as maintenance therapy following chemotherapy in patients with platinum sensitive recurrent sporadic and BRCA1/2 related high-grade serous ovarian cancers. The concept of BRCAness raises the possibility that PARP inhibitors may be active in selected patients with homologous recombination (HR) DNA repair-deficient tumors, even if they do not harbor a BRCA1/2 germline mutation. Further research will be required to identify the subset of patients with sporadic cancers who may benefit from PARP inhibitor therapy. Precise details on the mechanisms of action, relative potency and anti-cancer effects of different PARP inhibitors remain to be clarified and are being investigated. PARP inhibitors are known to inhibit the base excision repair (BER) pathway but in addition, recent reports indicate that aberrant activation of the error-prone non-homologous end-joining (NHEJ) pathway occurs in HR-deficient cells and that cell death provoked by PARP inhibition is dependent on NHEJ-induced genomic instability. Characterization of the precise molecular mechanisms responsible for PARP inhibitor activity should lead to the identification of predictive biomarkers of response and help identify which patients should be treated with PARP inhibitors. This is a very active field of research and the current status and future directions are reviewed.     

PARP Inhibitors for the Treatment and Prevention of Breast Cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors, a novel class of drugs that target tumors with DNA repair defects, have received tremendous enthusiasm. Early preclinical studies identified BRCA1 and BRCA2 tumors to be highly sensitive to PARP inhibitors as a result of homologous recombination defect. Based on this premise, PARP inhibitors have been tested in early phase clinical trials as a single agent in BRCA1 or BRCA2 mutation carriers and in combination with chemotherapy in triple-negative breast cancer patients. For high-risk populations, use of PARP inhibition as a prevention agent has been postulated, but no robust preclinical or clinical studies exist yet. We review the preclinical and clinical studies in treatment of breast cancer and rationale for use of PARP inhibitors as a prevention agent for high-risk populations. Of significance, PARP inhibitors vary significantly in mechanism of action, dosing intervals, and toxicities, which are highlighted in this review.     

BRCA2-deficient CAPAN-1 cells are extremely sensitive to the inhibition of Poly (ADP-Ribose) polymerase: an issue of potency

We have previously demonstrated that deficiency of either the BRCA1 or BRCA2 breast cancer susceptibility proteins confers substantial cellular sensitivity to the inhibition of Poly(ADP-Ribose) polymerase (PARP). PARP is a key enzyme in the repair of single strand DNA damage via the Base Excision Repair pathway. We suggested that PARP inhibition produces persistent single-strand DNA breaks or gaps which degenerate into stalled replication forks and double-strand breaks, which may be repaired by homologous recombination, a process partially dependent on BRCA1 and BRCA2. It has recently been suggested that our results might be limited to certain BRCA2 mutations as the CAPAN-1 cell line, which carries a naturally occurring 6174delT mutation in one BRCA2 allele accompanied by loss of the wild-type allele, is apparently insensitive to two PARP inhibitors 3-aminobenzamide (IC50 33 microM) and NU1025 (IC50 400 nM). Here we show that CAPAN-1 cells are in fact very sensitive to the potent PARP inhibitors KU0058684 (IC50 3.2 nM) and KU0058948 (IC50 3.4 nM). In contrast, our results reveal much less sensitivity to a chemically related but much less active compound KU0051529 (IC50 730 nM) and to NU1025. These results confirm that treatment with potent PARP inhibitors remains an exciting potential therapy for cancers involving BRCA1 or BRCA2 deficiency.     

PARP inhibitors in older patients with ovarian and breast cancer: Young International Society of Geriatric Oncology review paper

Breast and ovarian cancer are common malignancies among older adults, causing significant morbidity and mortality. Although most cases of breast and ovarian cancer are sporadic, a significant proportion is caused by mutations in cancer susceptibility genes, most often breast cancer susceptibility genes (BRCA) 1 and 2. Furthermore, some breast and ovarian tumors are phenotypically similar to those with BRCA mutations, a phenomenon known as “BRCAness”. BRCA mutations and “BRCAness” lead to defects in DNA repair, which may be a target for therapeutic agents such as Poly ADP-Ribose Polymerase (PARP) inhibitors. PARP inhibitors are novel medications which lead to double-strand breaks resulting in cell death due to synthetic lethality, and which have been shown to be effective in patients with advanced breast and ovarian cancers with or without BRCA mutations. Three different PARP inhibitors (olaparib, niraparib, and rucaparib) have been approved for the treatment of ovarian cancer and one (olaparib) for breast cancer harboring BRCA mutations. Here, we review the currently available evidence regarding the use of PARP inhibitors for the treatment of patients with breast and ovarian cancer, with a particular focus on the inclusion of older adults in clinical trials of these therapies. Additionally, we provide an overview of currently ongoing studies of PARP inhibitors in breast and ovarian cancer, and include recommendations for increasing the evidence-base for using these medications among older patients.     

Secondary BRCA1 and BRCA2 alterations and acquired chemoresistance

Tumor suppressor BRCA1 and BRCA2 are frequently mutated in familial breast and ovarian cancer. More than ten percent of women with breast or ovarian cancer carry BRCA1 or BRCA2 (BRCA1/2) mutations. Cancers that arise in mutation carriers have often lost the wild-type allele through somatic alterations during tumor progression. BRCA1/2 play important roles in homologous recombination repair of DNA double-strand breaks. Because of this, BRCA1/2-deficient cancers often have a better response to DNA cross-linking agents such as platinum analogues and to poly(ADP-ribose) polymerase (PARP) inhibitors. However, over time, the majority of these BRCA1/2-deficient cancers become resistant and patients die from refractory diseases. Three recent studies demonstrated that acquired resistance to platinum analogues or PARP inhibitors in tumors carrying frame-shift BRCA1/2 mutations came from restored BRCA1/2 expression and HR function due to secondary intragenic mutations that corrected the open reading frames of mutated BRCA1/2.     

Secondary mutations of BRCA1/2 and drug resistance

Inherited mutations in the tumor suppressor genes BRCA1 and BRCA2 cause increased risk of developing various cancers, especially breast and ovarian cancers. Tumors that develop in patients with inherited BRCA1/2 mutations are generally believed to be BRCA1/2-deficient. Cancer cells with BRCA1/2 deficiency are defective in DNA repair by homologous recombination and sensitive to interstrand DNA crosslinking agents, such as cisplatin and carboplatin, and poly(ADP-ribose) polymerase inhibitors. Therefore, these agents are logical choices for the treatment for BRCA1/2-deficient tumors and have shown to be clinically effective. However, BRCA1/2-mutated tumors often develop resistance to these drugs. Restoration of BRCA1/2 functions due to secondary BRCA1/2 mutations has been recognized as a mechanism of acquired resistance to cisplatin and poly(ADP-ribose) polymerase inhibitors in BRCA1/2-mutated cancer cells. This indicates that even disease-causing inherited mutations of tumor suppressor genes can be genetically reverted in cancer cells, if the genetic reversion is advantageous for the cells' survival. In this review, we will discuss this drug resistance mechanism.     

Complementary genetic screens identify the E3 ubiquitin ligase CBLC,as a modifier of PARP inhibitor sensitivity

Based on a series of basic, preclinical and clinical studies, the Poly (ADP-ribose) Polymerase 1 (PARP1) inhibitor, olaparib, has recently been approved for use in ovarian cancer patients with BRCA1 or BRCA2 mutations. By identifying novel predictive biomarkers of tumour cell sensitivity to olaparib, it is possible that the utility of PARP inhibitors could be extended beyond this patient subgroup. Many of the known genetic determinants of PARP inhibitor response have key roles in DNA damage response (DDR) pathways. Although protein ubiquitylation is known to play an important role in regulating the DDR, the exact mechanisms by which this occurs are not fully understood. Using two parallel RNA interference-based screening approaches, we identified the E3 ubiquitin ligase, CBLC, as a candidate biomarker of response to olaparib. We validated this observation by demonstrating that silencing of CBLC causes increased sensitivity to olaparib in breast cancer cell line models and that defective homologous recombination (HR) DNA repair is the likely cause. This data provides an example of how defects in the ubiquitin machinery have the potential to influence the response of tumour cells to PARP inhibitors.     

BRCA突变乳腺癌的临床研究进展

BRCA1和BRCA2是遗传性乳腺癌的主要相关基因。随着PARP抑制剂的临床应用,BRCA突变也成为了乳腺癌的治疗靶点。在BRCA突变乳腺癌患者中,talazoparib、veliparib、奥拉帕利、尼拉帕利等PARP抑制剂已被广泛应用在新辅助治疗、辅助治疗和晚期治疗各个阶段,治疗模式有PARP抑制剂单药、联合化疗、联合免疫治疗等多种方式。本文就BRCA突变乳腺癌的临床研究进展进行综述。      

Combination treatment using DDX3 and PARP inhibitors induces synthetic lethality in BRCA1-proficient breast cancer

Triple-negative breast cancers have unfavorable outcomes due to their inherent aggressive behavior and lack of targeted therapies. Breast cancers occurring in BRCA1 mutation carriers are mostly triple-negative and harbor homologous recombination deficiency, sensitizing them to inhibition of a second DNA damage repair pathway by, e.g., PARP inhibitors. Unfortunately, resistance against PARP inhibitors in BRCA1-deficient cancers is common and sensitivity is limited in BRCA1-proficient breast cancers. RK-33, an inhibitor of the RNA helicase DDX3, was previously demonstrated to impede non-homologous end-joining repair of DNA breaks. Consequently, we evaluated DDX3 as a therapeutic target in BRCA pro- and deficient breast cancers and assessed whether DDX3 inhibition could sensitize cells to PARP inhibition. High DDX3 expression was identified by immunohistochemistry in breast cancer samples of 24% of BRCA1 (p = 0.337) and 21% of BRCA2 mutation carriers (p = 0.624), as compared to 30% of sporadic breast cancer samples. The sensitivity to the DDX3 inhibitor RK-33 was similar in BRCA1 pro- and deficient breast cancer cell lines, with IC50 values in the low micromolar range (2.8–6.6 μM). A synergistic interaction was observed for combination treatment with RK-33 and the PARP inhibitor olaparib in BRCA1-proficient breast cancer, with the mean combination index ranging from 0.59 to 0.62. Overall, we conclude that BRCA pro- and deficient breast cancers have a similar dependency upon DDX3. DDX3 inhibition by RK-33 synergizes with PARP inhibitor treatment, especially in breast cancers with a BRCA1-proficient background.     

Defective homologous recombination in human cancers

Homologous recombination (HR) is a process by which DNA double strand breaks are repaired through the alignment of homologous sequences of DNA. Interest continues to increase in HR pathway function due to the development of new therapeutic agents which selectively exploit DNA damage repair pathways. Currently the most promising of these new agents are inhibitors of poly(ADP ribose) polymerase (PARP). The response of cancers known to be deficient in HR, due to BRCA1 or 2 mutations has been demonstrated, and a wider use of PARP inhibitors in cancers with mutations of other HR pathway genes has been suggested. With ongoing clinical studies into the use of PARP inhibitors, further understanding of the HR pathway, to allow patient selection by cancer biology, is now essential. Numerous studies have investigated individual aberrations of genes involved in the HR pathway. Here we collate this evidence to give an overview of the role of the HR pathway in human cancer.