Pancreatic cancer: BRCA mutation and personalized treatment

The highly heterozygous nature of pancreatic cancer is partially responsible for its therapeutic ineffectiveness and resistance. Therefore, the ability to identify subgroups of pancreatic cancer with unique biological characteristics and treatment response is urgently needed. In addition to breast and ovarian cancer, pancreatic cancer is the third most common cancer type that is related to the early onset (BRCA) gene mutation in breast cancer. Mounting evidence has demonstrated that BRCA1/2-mutant breast and ovarian cancers are highly sensitive to DNA damage-related treatment, including poly(ADP-ribose) polymerase inhibitors (PARPi) and platinum-based agents. Preliminary evidence also showed promising results for DNA damage-related treatment in BRCA1/2-mutant pancreatic cancer. Importantly, several prospective clinical trials of PARPi-based regimens are underway for BRCA1/2-mutated pancreatic cancer. Pancreatic cancer with a BRCA1/2 mutation is a small subgroup with a promising therapeutic strategy.     

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.     

AKT1/BRCA1 in the control of homologous recombination and genetic stability: the missing link between hereditary and sporadic breast cancers

Endogenous replicative stress could be one trigger leading to tumor initiation: indeed, activation of the DNA damage response (DDR), considered the result of replicative stress, is observed in pre-cancerous cells; moreover, in hereditary breast cancers, almost all of the genes affected relate to the DDR. The most frequently mutated gene in hereditary breast cancers, BRCA1, is essential for homologous recombination (HR), a fundamental process for maintaining genome stability that permits the reactivation of blocked replication forks . Recent studies have established links between DDR and the oncogenic kinase AKT1, which is upregulated in about 50% of sporadic breast cancers. More specifically, the activation of AKT1 shows a deficient phenotype in BRCA1 and HR, revealing molecular similarities between hereditary and sporadic breast cancers. However, these results reveal a paradox regarding the physiological role of AKT1: in non-tumor cells, AKT1 promotes cellular proliferation, but consequently endangers genome integrity during replication if HR is inhibited. Since HR could itself lead to genetic instability, we propose that, under physiological conditions, moderate activation of AKT1 does not inhibit but prevents an excess of HR. The regulation of AKT1 would represent a fine transitory system for controlling HR and maintaining genomic integrity.     

Distinct functions of BRCA1 and BRCA2 in double-strand break repair

Individuals carrying BRCA mutations are predisposed to breast cancer. The BRCA1 and BRCA2 proteins are required for homologous recombination and DNA break repair, leading to the suggestion that they act in concert. However, direct evidence of a stable BRCA1/BRCA2 complex has not been demonstrated. Rather, the two proteins have been found as constituents of discrete, but perhaps nonexclusive complexes that are critical for repair. We discuss the interaction of BRCA1 with the BACH1 and BARD1 proteins, and suggest that the pleiotropic nature of mutations in BRCA1 may be associated with defects in protein--protein interactions. In contrast, the role of BRCA2 in DNA repair may be more defined by its direct interaction with the RAD51 recombinase.     

A Pan-Canadian Consensus Statement on First-Line PARP Inhibitor Maintenance for Advanced,High-Grade Serous and Endometrioid Tubal,Ovarian, and Primary Peritoneal Cancers

The majority of patients with advanced, high-grade epithelial-tubo ovarian cancer (EOC) respond well to initial treatment with platinum-based chemotherapy; however, up to 80% of patients will experience a recurrence. Poly(ADP-ribose) Polymerase (PARP) inhibitors have been established as a standard of care maintenance therapy to prolong remission and prevent relapse following a response to first-line platinum-chemotherapy. Olaparib and niraparib are the PARP inhibitors currently approved for use in the first-line maintenance setting in Canada. Selection of maintenance therapy requires consideration of patient and tumour factors, presence of germline and somatic mutations, expected drug toxicity profile, and treatment access. This paper discusses the current clinical evidence for first-line PARP inhibitor maintenance therapy in patients with advanced, high-grade EOC and presents consensus statements and a treatment algorithm to aid Canadian oncologists on the selection and use of PARP inhibitors within the Canadian EOC treatment landscape.     

EZH2 Inhibition Sensitizes CARM1-High,Homologous Recombination Proficient Ovarian Cancers to PARP Inhibition

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NUSAP1 influences the DNA damage response by controlling BRCA1 protein levels

NUSAP1 has been reported to function in mitotic spindle assembly, chromosome segregation, and regulation of cytokinesis. In this study, we find that NUSAP1 has hitherto unknown functions in the key BRCA1-regulated pathways of double strand DNA break repair and centrosome duplication. Both these pathways are important for maintenance of genomic stability, and any defects in these pathways can cause tumorigenesis. Depletion of NUSAP1 from cells led to the suppression of double strand DNA break repair via the homologous recombination and single-strand annealing pathways. The presence of NUSAP1 was also found to be important for the control of centrosome numbers. We have found evidence that NUSAP1 plays a role in these processes through regulation of BRCA1 protein levels, and BRCA1 overexpression from a plasmid mitigates the defective phenotypes seen upon NUSAP1 depletion. We found that after NUSAP1 depletion there is a decrease in BRCA1 recruitment to ionizing radiation-induced foci. Results from this study reveal a novel association between BRCA1 and NUSAP1 and suggests a mechanism whereby NUSAP1 is involved in carcinogenesis.     

Heat-induced BRCA2 degradation in human tumours provides rationale for hyperthermia-PARP-inhibitor combination therapies

Purpose: Hyperthermia (40–44?°C) effectively sensitises tumours to radiotherapy by locally altering tumour biology. One of the effects of heat at the cellular level is inhibition of DNA repair by homologous recombination via degradation of the BRCA2-protein. This suggests that hyperthermia can expand the group of patients that benefit from PARP-inhibitors, a drug exploiting homologous recombination deficiency. Here, we explore whether the molecular mechanisms that cause heat-mediated degradation of BRCA2 are conserved in cell lines from various origins and, most importantly, whether, BRCA2 protein levels can be attenuated by heat in freshly biopted human tumours.

Experimental design: Cells from four established cell lines and from freshly biopsied material of cervical (15), head- and neck (9) or bladder tumours (27) were heated to 42?°C for 60?min ex vivo. In vivo hyperthermia was studied by taking two biopsies of the same breast or cervical tumour: one before and one after treatment. BRCA2 protein levels were measured by immunoblotting.

Results: We found decreased BRCA2-levels after hyperthermia in all established cell lines and in 91% of all tumours treated ex vivo. For tumours treated with hyperthermia in vivo, technical issues and intra-tumour heterogeneity prevented obtaining interpretable results.

Conclusions: This study demonstrates that heat-mediated degradation of BRCA2 occurs in tumour material directly derived from patients. Although BRCA2-degradation may not be a practical biomarker for heat deposition in situ, it does suggest that application of hyperthermia could be an effective method to expand the patient group that could benefit from PARP-inhibitors.     

The underlying mechanism for the PARP and BRCA synthetic lethality: clearing up the misunderstandings

Poly (ADP-ribose) polymerase (PARP) inhibitors effectively kill tumours defective in the BRCA1 or BRCA2 genes through the concept of synthetic lethality. It is suggested that PARP inhibitors cause an increase in DNA single-strand breaks (SSBs), which are converted during replication to irreparable toxic DNA double-strand breaks (DSBs) in BRCA1/2 defective cells. There are a number of recent reports challenging this model. Here, alternative models that are not mutually exclusive are presented to explain the synthetic lethality between BRCA1/2 and PARP inhibitors. One such model proposes that PARP inhibition causes PARP-1 to be trapped onto DNA repair intermediates, especially during base excision repair. This may in turn cause obstruction to replication forks, which require BRCA-dependent homologous recombination to be resolved. In another model, PARP is directly involved in catalysing replication repair in a distinct pathway from homologous recombination. Experimental evidence supporting these novel models to explain the PARP-BRCA synthetic lethality are discussed.     

Prospective evaluation of the tolerability and efficacy of niraparib dosing based on baseline body weight and platelet count: Results from the PRIMA/ENGOT-OV26/GOG-3012 trial

Background

The PRIMA/ENGOT-OV26/GOG-3012 (NCT02655016) trial was amended to prospectively evaluate the safety and efficacy of an individualized starting dose (ISD) regimen of niraparib for first-line maintenance therapy in patients with newly diagnosed advanced ovarian cancer.

Methods

In the phase 3 PRIMA trial, patients with newly diagnosed advanced ovarian cancer with a complete/partial response to first-line platinum-based chemotherapy (N = 733) were initially treated with a fixed starting dose (FSD) regimen of 300 mg once daily. Subsequently, the protocol was amended so newly enrolled patients received an ISD: 200 mg once daily in patients with baseline body weight < 77 kg or baseline platelet count < 150,000/µL, and 300 mg once daily in all other patients. Efficacy and safety outcomes were assessed by starting dose.

Results

Overall, 475 (64.8%) patients were assigned to an FSD (niraparib, n = 317; placebo, n = 158) and 258 (35.2%) were assigned to an ISD (niraparib, n = 170; placebo, n = 88). Efficacy in patients who received FSD or ISD was similar for the overall (FSD hazard ratio [HR], 0.59 [95% CI, 0.46–0.76] vs. ISD HR, 0.69 [95% CI, 0.48–0.98]) and the homologous recombination–deficient (FSD HR, 0.44 [95% CI, 0.30–0.64] vs. ISD HR, 0.39 [95% CI, 0.22–0.72]) populations. In patients with low body weight/platelet count, rates of grades ≥3 and 4 hematologic treatment-emergent adverse events, dose interruptions, and dose reductions were lower for those who received ISD than for those who received FSD.

Conclusions

In PRIMA, similar dose intensity, similar efficacy, and improved safety were observed with the ISD compared with the FSD regimen.     

Autoimmune response to PARP and BRCA1/BRCA2 in cancer

Purpose

To determine the role of autoantibodies to PARP1 and BRCA1/BRCA2 which were involved in the synthetic lethal interaction in cancer.

Methods

Enzyme-Linked Immunosorbent Assay (ELISA) was used to detect autoantibodies to PARP1 and BRCA1/BRCA2 in 618 serum samples including 131 from breast cancer, 94 from lung cancer, 34 from ovarian cancer, 107 from prostate cancer, 76 from liver cancer, 41 from pancreatic cancer and 135 from normal individuals. The positive sera with ELISA were confirmed by Western blot. Immunohistochemistry was used to examine the expression of PARP1 and BRCA1/BRCA2 in breast cancer.

Results

Autoantibody frequency to PARP1, BRCA1, and BRCA2 in cancer varied from 0% to 50%. When the sera from cancer patients were tested for the presence of autoantibodies to PARP1 and BRCA1/BRCA2, the autoantibody responses slightly decreased and the positive autoantibody reactions varied from 0% to 50.0%. This was significantly higher autoantibody responses to PARP1 and BRCA1/BRCA2 (especially to PARP1 and BRCA1) in ovarian cancer and breast cancer compared to normal control sera (P < 0.001 and P < 0.01). Immunohistochemistry indicated that Pathology Grade at diagnosis to PARP1 expression in breast cancer was different (P < 0.05).

Conclusions

Different cancers have different profiles of autoantibodies. The autoantibodies to proteins involving the synthetic lethal interactions would be novel serological biomarker in some selective cancers.     

Modulation of BRCA1 mediated DNA damage repair by deregulated ER-α signaling in breast cancers

Abstract: BRCA1 mutation carriers have a greater risk of developing cancers in hormone-responsive tissues like breasts and ovaries. However, this tissue-specific incidence of BRCA1 related cancers remains elusive. The majority of the BRCA1 mutated breast cancers exhibit typical histopathological features of high-grade tumors, with basal epithelial phenotype, classified as triple-negative molecular subtype and have a higher percentage of DNA damage and chromosomal abnormality. Though there are many studies relating BRCA1 with ER-α (Estrogen receptor-α), it has not been reported whether E2 (Estrogen) -ER-α signaling can modulate the DNA repair activities of BRCA1. The present study analyzes whether deregulation of ER-α signaling, arising as a result of E2/ER-α deficiency, could impact the BRCA1 dependent DDR (DNA Damage Response) pathways, predominantly those of DNA-DSB (Double Strand break) repair and oxidative damage response. We demonstrate that E2/E2-stimulated ER-α can augment BRCA1 mediated high fidelity repairs like HRR (Homologous Recombination Repair) and BER (Base Excision Repair) in breast cancer cells. Conversely, a condition of ER-α deficiency itself or any interruption in ligand-dependent ER-α transactivation resulted in delayed DNA damage repair, leading to persistent activation of γH2AX and retention of unrepaired DNA lesions, thereby triggering tumor progression. ER-α deficiency not only limited the HRR in cells but also facilitated the DSB repair through error prone pathways like NHEJ (Non Homologous End Joining). ER-α deficiency associated persistence of DNA lesions and reduced expression of DDR proteins were validated in human mammary tumors.     

Improved survival for BRCA2-associated serous ovarian cancer compared with both BRCA-negative and BRCA1-associated serous ovarian cancer

BACKGROUND:

Multiple observational studies have suggested that breast cancer gene (BRCA)‐associated ovarian cancers have improved survival compared with BRCA‐negative ovarian cancers. However, most of those studies combined BRCA1 and BRCA2 patients or evaluated only BRCA1 patients. The objective of the current study was to examine whether BRCA1‐associated and BRCA2‐associated ovarian cancers were associated with different outcomes.

METHODS:

This was a single‐institution, retrospective analysis of patients who had a new diagnosis of histologically confirmed stage III or IV serous ovarian, fallopian tube, or primary peritoneal cancer between January 1, 1996 and February 1, 2011 and who underwent BRCA mutation testing on 1 of 2 institutional review board‐approved follow‐up studies. Patients who had been tested for BRCA mutations beyond 24 months of diagnosis were excluded from analysis to minimize selection bias from including patients who were referred for genetic testing because of long survival.

RESULTS:

Data from 190 patients (143 BRCA‐negative patients, 30 BRCA1‐positive patients, and 17 BRCA2‐positive patients) were analyzed. During the study period, 73 deaths were observed (60 BRCA‐negative patients, 10 BRCA1‐positive patients, 3 BRCA2‐positive patients). The median follow‐up for the remaining 117 survivors was 2.5 years. At 3 years, 69.4%, 90.7%, and 100% of BRCA‐negative patients, BRCA1‐positive patients, and BRCA2‐positive patients were alive, respectively. On univariate analysis, age, BRCA2 mutations, debulking status, and type of first‐line therapy (intravenous or intraperitoneal) were significant predictors of overall survival. On multivariate analysis, BRCA2 mutations (hazard ratio, 0.20; 95% confidence interval, 0.06‐0.65; P = .007), but not BRCA1 mutations (hazard ratio, 0.70; 95% confidence interval, 0.36‐1.38; P = .31), predicted for improved overall survival compared with BRCA‐negative patients. When carriers of BRCA2 mutations were directly compared with carriers of BRCA1 mutations, BRCA2 mutations appeared to confer improved overall survival (hazard ratio, 0.29; 95% confidence interval, 0.08‐1.05; P = .060), although this finding did not reach significance.

CONCLUSIONS:

The current data suggests that BRCA2 mutations confer an overall survival advantage compared with either being BRCA‐negative or having a BRCA1 mutation in high‐grade serous ovarian cancer. This finding may have important implications for clinical trial design. Cancer 2012. © 2011 American Cancer Society.     

Therapeutic potential of PARP inhibitors for metastatic breast cancer

Increasing understanding of the cellular aberrations inherent to cancer cells has allowed the development of therapies to target biological pathways, an important step towards individualization of breast cancer therapy. The clinical development of poly(ADP-ribose) polymerase (PARP) inhibitors, with their novel and selective mechanism of action, are an example of this strategy. PARP plays a key role in DNA repair mechanisms, particularly the base excision repair pathway. Initially developed as inhibitors able to enhance the cytotoxicity of radiation and certain DNA-damaging agents, they have more recently been shown to have single-agent activity in certain tumors. Inhibition of PARP in a DNA repair-defective tumor can lead to gross genomic instability and cell death by exploiting the paradigm of synthetic lethality. Several studies have evaluated the role of PARP inhibitors for treatment of breast cancer, particularly in the context of BRCA-mutated and triple-negative breast cancers. In addition, inhibition of PARPs repair functions for chemotherapy-induced DNA lesions has been shown to potentiate the effect of some chemotherapy regimens. This article discusses the current understanding of PARP inhibition as a treatment for metastatic breast cancer, evidence from clinical trials and addresses its future implications.     

New opportunities in chemosensitization and radiosensitization: modulating the DNA-damage response

Many current cancer treatments, including certain classes of chemotherapeutics and radiation, induce cytotoxicity by damaging DNA. However, many cancers are resistant to these therapies, which represents a significant challenge in the clinic. Thus, modulating DNA-damage responses to selectively enhance the sensitivity of cancer cells to these therapies is highly desirable. When DNA damage is detected, DNA checkpoint mechanisms are activated to halt cells at various phases of the cell cycle. Simultaneously, DNA-damage sensors transduce signals to activate DNA-repair mechanisms via de novo expression or post-translational modification of enzymes required for DNA repair. p53 is the major player in a checkpoint that arrests cells at the G₁/S boundary, while checkpoint kinase (Chk)1 is critical for the G₂/M checkpoint and also the S checkpoint that prevents cell cycle progression after replication defects (intra-S-phase checkpoint) or S/M uncoupling (S/M checkpoint). Poly(ADP-ribose) polymerase is involved in sensing DNA single-strand breaks and inducing DNA repair via poly(ADP-ribosyl)ating various DNA-binding and DNA-repair proteins. In this review, strategies for implementing small-molecule inhibitors of poly(ADP-ribose) polymerase and Chk1, which are emerging as potential adjuncts to current therapies, are discussed.