Loss of 53BP1 partially restores the HR defect of Brca1-deleted mouse embryonic stem cells and reverts their hypersensitivity to DNA-damaging agents (159, 160). (3, 4). Platinum analogues have been used to treat ovarian cancer since the late 1970s when clinical trials demonstrated that cisplatin was capable of achieving almost double the overall response rates and the number of complete responses compared with non-platinum agents (5, 6). Since then, platinum agents (initially cisplatin, then carboplatin which is better tolerated but equally effective (7)) have constituted the backbone of chemotherapy used in EOC and have defined the comparison arms for the majority of the clinical trials conducted in this disease. However, despite important advancements in the efficacy of platinum chemotherapy achieved by incorporation of taxanes (8) in the 1990s and by administration of chemotherapy via the intraperitoneal (IP) route (9) in early 2000, the plateau of the survival curve has not changed appreciably (3, 8, 10C12), suggesting that alternative approaches are urgently needed. Platinum analogs induce intrastrand and interstrand cross-links (ICLs) between purine bases of the DNA. ICLs are extremely deleterious lesions that covalently tether both duplex DNA strands and pose formidable blocks to DNA repair (13). Repair of ICLs is dependent on both Fanconi Anemia (FA) and BRCA proteins, which act in a common DNA repair pathway (also referred to as the Fanconi Anemia/BRCA pathway) that involves homologous recombination (HR) (14, 15) (Figure 1). The striking platinum sensitivity of EOC tumors is thought to be related to an underlying defect in HR-mediated DNA repair, particularly in those with high grade serous histology (approximately 70% of all EOCs). In this regard, a plethora of genetic studies, and most recently The Cancer Genome Atlas (TCGA) project, have consistently shown that high grade serous ovarian cancers (HGSOCs) are characterized by frequent genetic and epigenetic alterations of HR pathway genes, most commonly BRCA1 and BRCA2 genes (16, 17). Defective HR is an important therapeutic target in EOC, as exemplified by the central role of platinum agents in the management of this disease as well as the advent Pamidronate Disodium of poly-ADP ribose polymerase inhibitors (PARPis), a novel class of anticancer agents which exhibit synthetic lethal effects when applied to cells with defective HR (18C21). In this review, we discuss the molecular alterations and clinical phenotype of HR deficient EOCs, describe current and emerging approaches for targeting HR deficient ovarian cancers, and present the difficulties associated with these methods focusing on development and overcoming drug resistance. Open in a separate window Number 1 Cooperation of the Fanconi Anemia (FA) and BRCA1/2 proteins inside a common ICL restoration pathwayStalling of replication forks on DNA ICLs induces lesion acknowledgement from the FANCMCFAAP24CMHF1/2 complex and subsequent recruitment of the FA core complex, which in turn recruits the mono-ubiquitinated FANCD2-FANCI to the ICL region. FANCM also initiates checkpoint response, which phosphorylates multiple FA proteins. Ubiquitinated FANCD2 functions as a landing pad for recruiting several nucleases to coordinate nucleolytic incisions. Unhooking the DNA leaves the cross-linked nucleotides tethered to the complementary strand, which are bypassed by TLS polymerases. DNA incisions develop a DSB, which is definitely then repaired by HR. Downstream FA proteins such as BRCA1, BRCA2, and PALB2 promote RAD51-dependent strand invasion and resolution of recombinant intermediates. HR PATHWAY ALTERATIONS IN EOC Approximately 50% of HGSOCs show genetic or epigenetic alterations in the FA/BRCA pathway (Number 2) (16). Although these alterations are most commonly experienced in high grade serous histology, nonserous histologies including obvious cell, endometrioid and carcinosarcomas have also been shown to harbor such alterations (22). Germline BRCA1 and BRCA2 mutations are the most common alterations, and are present in 14C15% of all EOCs (23, 24) and as high as 22.6%.Increased in P-glycoprotein Pamidronate Disodium (PGP)Cmediated efflux, notably through ABCB1 upregulation (via fusion with SLC25A40) reduces intracellular PARPi concentrations inducing resistance. 1970s when medical trials shown that cisplatin was capable of achieving almost double the overall response rates and the number of total responses compared with non-platinum providers (5, 6). Since then, platinum providers (in the beginning cisplatin, then carboplatin which is better tolerated but equally effective (7)) have constituted the backbone of chemotherapy used in EOC and have defined the comparison arms for the majority of the medical trials conducted with this disease. However, despite important developments in the effectiveness of platinum chemotherapy achieved by incorporation of taxanes (8) in the 1990s and by administration of chemotherapy via the intraperitoneal (IP) route (9) in early 2000, the plateau of the survival curve has not changed appreciably (3, 8, 10C12), suggesting that alternative methods are urgently needed. Platinum analogs induce intrastrand and interstrand cross-links (ICLs) between purine bases of the DNA. ICLs are extremely deleterious lesions that covalently tether both duplex DNA strands and present formidable blocks to DNA restoration (13). Restoration of ICLs is dependent on both Fanconi Anemia (FA) and BRCA proteins, which take action inside a common DNA restoration pathway (also referred to as the Fanconi Anemia/BRCA pathway) that involves homologous recombination (HR) (14, 15) (Number 1). The impressive platinum level of sensitivity of EOC tumors is definitely thought to be related to an underlying defect in HR-mediated DNA restoration, particularly in those with high grade serous histology (approximately 70% of all EOCs). In this regard, a plethora of genetic studies, and most recently The Malignancy Genome Atlas (TCGA) project, have consistently demonstrated that high grade serous ovarian cancers (HGSOCs) are characterized by frequent genetic and epigenetic alterations of HR pathway genes, most commonly BRCA1 and BRCA2 genes (16, 17). Defective HR is an important therapeutic target in EOC, as exemplified from the central part of platinum providers in the management of this disease as well as the arrival of poly-ADP ribose polymerase inhibitors (PARPis), a novel class of anticancer providers which exhibit synthetic lethal effects when applied to cells with defective HR (18C21). With this review, we discuss the molecular alterations and medical phenotype of HR deficient EOCs, describe current and growing methods for focusing on HR deficient ovarian cancers, and present the difficulties associated with these methods focusing on development and overcoming drug resistance. Open in a separate window Number 1 Cooperation of the Fanconi Anemia (FA) and BRCA1/2 proteins inside a common ICL restoration pathwayStalling of replication forks on DNA ICLs induces lesion acknowledgement from the FANCMCFAAP24CMHF1/2 complex and subsequent recruitment of the FA core complex, which in turn recruits the mono-ubiquitinated FANCD2-FANCI to the ICL region. FANCM also initiates checkpoint response, which phosphorylates multiple FA proteins. Ubiquitinated FANCD2 functions as a landing pad for recruiting several nucleases to coordinate nucleolytic incisions. Unhooking the DNA leaves the cross-linked nucleotides tethered to the complementary strand, which are bypassed by TLS polymerases. DNA incisions develop a DSB, which is definitely then repaired by HR. Downstream FA proteins such as BRCA1, BRCA2, and PALB2 promote RAD51-dependent strand invasion and resolution of recombinant intermediates. HR PATHWAY ALTERATIONS IN EOC Approximately 50% of HGSOCs show genetic or epigenetic alterations in the FA/BRCA pathway (Number 2) (16). Although these alterations are most commonly encountered in high grade serous histology, nonserous histologies including obvious cell, endometrioid and carcinosarcomas have also been shown to harbor such alterations (22). Germline BRCA1 and BRCA2 mutations are the most common alterations, and are present in 14C15% of all EOCs (23, 24) and as high as 22.6% of HGSOCs (16, 23, 24) while somatic BRCA1 and BRCA2 mutations have been recognized in 6C7% of high grade serous EOCs (16, 25). Although in the TCGA dataset there was a similar incidence of germline and somatic BRCA1 and BRCA2 mutations, BRCA1 mutations are more commonly observed (60% of all BRCA mutations) in additional datasets (23, 24). Importantly, Pamidronate Disodium 81% of BRCA1 and 72% of BRCA2 mutations are accompanied by heterozygous loss (26) indicating that both alleles are inactivated, as expected by Knudsons two-hit hypothesis. The majority of germline and somatic BRCA1/2 mutations are frameshift insertions or deletions, while.The standard of care management of EOC consists of primary surgical cytoreduction followed by platinum-based chemotherapy (3, 4). EOC individuals are diagnosed with advanced disease which is definitely curable only inside a minority of the cases resulting in a moderate 5-year overall survival rate of 20C30% (2, 3). The standard of care management of EOC consists of primary medical cytoreduction followed by platinum-based chemotherapy (3, 4). Platinum analogues have been used to treat ovarian cancer since the late 1970s when medical trials shown that cisplatin was capable of achieving almost double the overall response rates and the number of total responses compared with non-platinum providers (5, 6). Since then, platinum providers (in the beginning cisplatin, then carboplatin which is better tolerated but equally effective (7)) have constituted the backbone of chemotherapy used in EOC and have defined the comparison arms for the majority of the medical trials conducted with this disease. However, despite important developments in the effectiveness of platinum chemotherapy achieved by incorporation of taxanes (8) in the 1990s and by administration of chemotherapy via the intraperitoneal (IP) route (9) in early 2000, the plateau of the survival curve has not changed appreciably (3, 8, 10C12), suggesting that alternative methods are urgently needed. Platinum analogs induce intrastrand and interstrand cross-links (ICLs) between purine bases of the DNA. ICLs are extremely deleterious lesions that covalently tether both duplex DNA strands and present formidable blocks to DNA restoration (13). Restoration of ICLs is dependent on both Fanconi Anemia (FA) and BRCA proteins, which take action inside a common DNA restoration pathway (also referred to as the Fanconi Anemia/BRCA pathway) that involves homologous recombination (HR) (14, 15) (Number 1). The impressive platinum level of sensitivity of EOC tumors is definitely thought to be related to an underlying defect in HR-mediated DNA restoration, particularly in those with high grade serous histology (approximately 70% of all EOCs). In this regard, a plethora of genetic studies, and most recently The Malignancy Genome Atlas (TCGA) project, have consistently demonstrated that high grade serous ovarian cancers (HGSOCs) are characterized by frequent genetic and epigenetic alterations of HR pathway genes, most commonly BRCA1 and BRCA2 genes (16, 17). Defective HR is an important therapeutic target in EOC, as exemplified from the central part of platinum providers in the management of this disease as well as the arrival of poly-ADP ribose polymerase inhibitors (PARPis), a novel class of anticancer providers which exhibit synthetic lethal effects when applied to cells with defective HR (18C21). With this review, we discuss the molecular alterations and medical phenotype of HR deficient EOCs, describe current and growing methods for focusing on HR deficient ovarian cancers, and present the difficulties associated with these methods focusing on development and overcoming drug resistance. Open in a separate window Number 1 Cooperation of the Fanconi Anemia (FA) and BRCA1/2 proteins inside a common ICL restoration pathwayStalling of replication forks on DNA ICLs induces lesion acknowledgement from the FANCMCFAAP24CMHF1/2 complex and subsequent recruitment of the FA core complex, which in turn recruits the mono-ubiquitinated FANCD2-FANCI to the ICL region. FANCM also initiates checkpoint response, which phosphorylates multiple FA proteins. Ubiquitinated FANCD2 functions as a landing pad for recruiting several nucleases to coordinate nucleolytic incisions. Unhooking the DNA leaves the cross-linked nucleotides tethered to the complementary strand, which are bypassed TNN by TLS polymerases. Pamidronate Disodium DNA incisions develop a DSB, which is definitely then repaired by HR. Downstream FA Pamidronate Disodium proteins such as BRCA1, BRCA2, and PALB2 promote RAD51-dependent strand invasion and resolution of recombinant intermediates. HR PATHWAY ALTERATIONS IN EOC Approximately 50% of HGSOCs show genetic or epigenetic alterations in the FA/BRCA pathway (Number 2) (16). Although these alterations are most commonly encountered in high grade serous histology, nonserous histologies including obvious cell, endometrioid and carcinosarcomas have also been shown to harbor such alterations (22). Germline BRCA1 and BRCA2 mutations are the most common alterations, and are present in 14C15% of all EOCs (23, 24) and as high as 22.6% of HGSOCs (16, 23, 24) while somatic BRCA1 and BRCA2 mutations have been recognized in 6C7% of high grade serous EOCs (16, 25). Although in the TCGA dataset there was a similar incidence of germline and somatic BRCA1 and BRCA2 mutations, BRCA1 mutations are more commonly observed (60% of all BRCA mutations) in other datasets (23, 24). Importantly, 81% of BRCA1 and 72% of BRCA2 mutations are accompanied by heterozygous loss (26) indicating that both alleles are inactivated, as predicted by Knudsons two-hit hypothesis. The majority of germline and somatic BRCA1/2 mutations are frameshift insertions or deletions, while missense mutations are rare; mutations have been identified in all functional domains of BRCA1 (RING, coiled coil and BRCT domains) and BRCA2 (BRC, DNA binding, oligonucleotide-binding folds,.Repair of ICLs is dependent on both Fanconi Anemia (FA) and BRCA proteins, which act in a common DNA repair pathway (also referred to as the Fanconi Anemia/BRCA pathway) that involves homologous recombination (HR) (14, 15) (Physique 1). (2, 3). The standard of care management of EOC consists of primary surgical cytoreduction followed by platinum-based chemotherapy (3, 4). Platinum analogues have been used to treat ovarian cancer since the late 1970s when clinical trials exhibited that cisplatin was capable of achieving almost double the overall response rates and the number of total responses compared with non-platinum brokers (5, 6). Since then, platinum brokers (in the beginning cisplatin, then carboplatin which is better tolerated but equally effective (7)) have constituted the backbone of chemotherapy used in EOC and have defined the comparison arms for the majority of the clinical trials conducted in this disease. However, despite important developments in the efficacy of platinum chemotherapy achieved by incorporation of taxanes (8) in the 1990s and by administration of chemotherapy via the intraperitoneal (IP) route (9) in early 2000, the plateau of the survival curve has not changed appreciably (3, 8, 10C12), suggesting that alternative methods are urgently needed. Platinum analogs induce intrastrand and interstrand cross-links (ICLs) between purine bases of the DNA. ICLs are extremely deleterious lesions that covalently tether both duplex DNA strands and present formidable blocks to DNA repair (13). Repair of ICLs is dependent on both Fanconi Anemia (FA) and BRCA proteins, which take action in a common DNA repair pathway (also referred to as the Fanconi Anemia/BRCA pathway) that involves homologous recombination (HR) (14, 15) (Physique 1). The striking platinum sensitivity of EOC tumors is usually thought to be related to an underlying defect in HR-mediated DNA repair, particularly in those with high grade serous histology (approximately 70% of all EOCs). In this regard, a plethora of genetic studies, and most recently The Malignancy Genome Atlas (TCGA) project, have consistently shown that high grade serous ovarian cancers (HGSOCs) are characterized by frequent genetic and epigenetic alterations of HR pathway genes, most commonly BRCA1 and BRCA2 genes (16, 17). Defective HR is an important therapeutic target in EOC, as exemplified by the central role of platinum brokers in the management of this disease as well as the introduction of poly-ADP ribose polymerase inhibitors (PARPis), a novel class of anticancer brokers which exhibit synthetic lethal effects when applied to cells with defective HR (18C21). In this review, we discuss the molecular alterations and clinical phenotype of HR deficient EOCs, describe current and emerging methods for targeting HR deficient ovarian cancers, and present the difficulties associated with these methods focusing on development and overcoming drug resistance. Open in a separate window Physique 1 Cooperation of the Fanconi Anemia (FA) and BRCA1/2 proteins in a common ICL repair pathwayStalling of replication forks on DNA ICLs induces lesion acknowledgement by the FANCMCFAAP24CMHF1/2 complex and subsequent recruitment of the FA core complex, which in turn recruits the mono-ubiquitinated FANCD2-FANCI to the ICL region. FANCM also initiates checkpoint response, which phosphorylates multiple FA proteins. Ubiquitinated FANCD2 acts as a landing pad for recruiting several nucleases to coordinate nucleolytic incisions. Unhooking the DNA leaves the cross-linked nucleotides tethered to the complementary strand, which are bypassed by TLS polymerases. DNA incisions produce a DSB, which is usually then repaired by HR. Downstream FA proteins such as BRCA1, BRCA2, and PALB2 promote RAD51-dependent strand invasion and resolution of recombinant intermediates. HR PATHWAY ALTERATIONS IN EOC Around 50% of HGSOCs show hereditary or epigenetic modifications in the FA/BRCA pathway (Shape 2) (16). Although these modifications are mostly encountered in high quality serous histology, nonserous histologies including very clear cell, endometrioid and carcinosarcomas are also proven to harbor such modifications (22). Germline BRCA1 and BRCA2 mutations will be the most common modifications, and are within 14C15% of most EOCs (23, 24) so that as high as 22.6% of HGSOCs (16, 23, 24) while somatic BRCA1 and BRCA2 mutations have already been determined in 6C7% of high quality serous EOCs (16, 25). Although in the TCGA dataset there is a similar occurrence of germline and somatic BRCA1 and BRCA2 mutations, BRCA1 mutations commonly are more.
Loss of 53BP1 partially restores the HR defect of Brca1-deleted mouse embryonic stem cells and reverts their hypersensitivity to DNA-damaging agents (159, 160)