Article

Secondary Somatic Mutations Restoring BRCA1/2 Predict Chemotherapy Resistance in Hereditary Ovarian Carcinomas

University of Washington Medical Center, Department of Obstetrics and Gynecology, Box 356460, Seattle, WA, USA.
Journal of Clinical Oncology (Impact Factor: 18.43). 06/2011; 29(22):3008-15. DOI: 10.1200/JCO.2010.34.2980
Source: PubMed

ABSTRACT

Secondary somatic BRCA1/2 mutations may restore BRCA1/2 protein in hereditary ovarian carcinomas. In cell lines, BRCA2 restoration mediates resistance to platinum chemotherapy and poly (ADP-ribose) polymerase (PARP) inhibitors. We assessed primary and recurrent BRCA1/2-mutated ovarian carcinomas to define the frequency of secondary mutations and correlate these changes with clinical outcomes.
Neoplastic cells were isolated with laser capture microdissection, and DNA was sequenced at the site of the known germline BRCA1/2 mutation. When secondary mutations were found that restored wild-type sequence, haplotyping was performed using single nucleotide polymorphisms in tumor and paired lymphocyte DNA to rule out retention of the wild-type allele.
There were 64 primary and 46 recurrent ovarian carcinomas assessed. Thirteen (28.3%) of 46 (95% CI, 17.3% to 42.6%) recurrent carcinomas had a secondary mutation compared with two (3.1%) of 64 (95% CI, 1.0% to 10.7%) primary carcinomas (P = .0003, Fisher's exact test). Twelve (46.2%) of 26 (95% CI, 28.7% to 64.7%) platinum-resistant recurrences had secondary mutations restoring BRCA1/2, compared with one (5.3%) of 19 (95% CI, 1.2% to 24.8%) platinum-sensitive recurrences (P = .003, Fisher's exact test). Six (66.7%) of nine (95% CI, 34.8% to 87.8%) women with prior breast carcinoma had a recurrent carcinoma with a secondary mutation, compared with six (17.1%) of 35 (95% CI, 8.2% to 32.8%) with no history of breast carcinoma (P = .007, Fisher's exact test).
Secondary somatic mutations that restore BRCA1/2 in carcinomas from women with germline BRCA1/2 mutations predict resistance to platinum chemotherapy and may also predict resistance to PARP inhibitors. These mutations were detectable only in ovarian carcinomas of women whom have had previous chemotherapy, either for ovarian or breast carcinoma.

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    • "Although BRCA1/2-deficient tumours respond better to platinum-based chemotherapy, BRCA1/2 alterations, which occur in w30% of HGSOCs, only partially explain the spectrum of platinum sensitivity in primary HGSOC [4]. Secondary re-activating BRCA1/2 mutations have been proposed to underlie platinum resistance of recurrent BRCA1/2-mutated HGSOC [5]. This was confirmed by Patch et al., who in addition to BRCA1/2 reversal mutations, observed a decrease in BRCA1 promoter methylation, as well as recurrent promoter fusion associated with overexpression of the drug efflux pump MDR1 [6]. "
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    ABSTRACT: Background: Most high-grade serous ovarian carcinoma (HGSOC) patients benefit from first-line platinum-based chemotherapy, but progressively develop resistance during subsequent lines. Re-activating BRCA1 or MDR1 mutations can underlie platinum resistance in end-stage patients. However, little is known about resistance mechanisms occurring after a single line of platinum, when patients still qualify for other treatments. Methods: In 31 patients with primary platinum-sensitive HGSOC, we profiled tumours collected during debulking surgery before and after first-line chemotherapy using whole-exome sequencing and single nucleotide polymorphism profiling. Results: Besides germline BRCA1/2 mutations, we observed frequent loss-of-heterozygosity in homologous recombination (HR) genes and mutation spectra characteristic of HR-deficiency in all tumours. At relapse, tumours differed considerably from their primary counterparts. There was, however, no evidence of events reactivating the HR pathway, also not in tumours resistant to second-line platinum. Instead, a platinum score of 13 copy number regions, among other genes including MECOM, CCNE1 and ERBB2, correlated with platinum-free interval (PFI) after first-line therapy, whereas an increase of this score in recurrent tumours predicted the change in PFI during subsequent therapy. Conclusions: Already after a single line of platinum, there is huge variability between primary and recurrent tumours, advocating that in HGSOC biopsies need to be collected at relapse to tailor treatment options to the underlying genetic profile. Nevertheless, all primary platinum-sensitive HGSOCs remained HR-deficient, irrespective of whether they became resistant to second-line platinum, further suggesting these tumours qualify for second-line Poly APD ribose polymerase (PARP) inhibitor treatment. Finally, chromosomal instability contributes to acquired resistance after a single line of platinum therapy.
    No preview · Article · Jan 2016 · European journal of cancer (Oxford, England: 1990)
    • "A secondary mutation restoring the open reading frame of BRCA1 has been reported in one of four resistant cases. Thus, restoration of BRCA1/2 mutations seems to be a rare event in primary resistance and more involved in acquired resistance than in intrinsic resistance (Norquist et al., 2011). Whether or not secondary restoration of HR function also plays a role in acquiring platinum resistance in BRCAness ovarian cancer patients remains to be elucidated. "
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    ABSTRACT: High-grade serous ovarian cancer (HGSOC) has the highest mortality rate among all gynecological cancers. Patients are generally diagnosed in an advanced stage with the majority of cases displaying platinum resistant relapses. Recent genomic interrogation of large numbers of HGSOC patient samples indicated high complexity in terms of genetic aberrations, intra- and intertumor heterogeneity and underscored their lack of targetable oncogenic mutations. Sub-classifications of HGSOC based on expression profiles, termed 'differentiated', 'immunoreactive', 'mesenchymal' and 'proliferative', were shown to have prognostic value. In addition, in almost half of all HGSOC patients, a deficiency in homologous recombination (HR) was found that potentially can be targeted using PARP inhibitors. Developing precision medicine requires advanced experimental models. In the current review, we discuss experimental HGSOC models in which resistance to platinum therapy and the use of novel therapeutics can be carefully studied. Panels of better-defined primary cell lines need to be established to capture the full spectrum of HGSOC subtypes. Further refinement of cell lines is obtained with a 3-dimensional culture model mimicking the tumor microenvironment. Alternatively, ex vivo ovarian tumor tissue slices are used. For in vivo studies, larger panels of ovarian cancer patient-derived xenografts (PDXs) are being established, encompassing all expression subtypes. Ovarian cancer PDXs grossly retain tumor heterogeneity and clinical response to platinum therapy is preserved. PDXs are currently used in drug screens and as avatars for patient response. The role of the immune system in tumor responses can be assessed using humanized PDXs and immunocompetent genetically engineered mouse models. Dynamic tracking of genetic alterations in PDXs as well as patients during treatment and after relapse is feasible by sequencing circulating cell-free tumor DNA and analyzing circulating tumor cells. We discuss how various models and methods can be combined to delineate the molecular mechanisms underlying platinum resistance and to select HGSOC patients other than BRCA1/2-mutation carriers that could potentially benefit from the synthetic lethality of PARP inhibitors. This integrated approach is a first step to improve therapy outcomes in specific subgroups of HGSOC patients.
    No preview · Article · Nov 2015
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    • "Previous selection for cisplatin-resistant clones revealed BRCA2 reversion mutations that restore HR, as in the C4-2 clone (Fig. 1A–C), as well as clones that were resistant by an unknown mechanism (Sakai et al. 2009). Thus, the screen was performed in PEO1 cells because they reflect BRCA2 mutant ovarian cancers that develop both reversion and reversion-independent mechanisms of cisplatin resistance (Norquist et al. 2011). Cells were infected with viral pools containing the pGIPZ library comprised of ;81,000 shRNAs directed against 28,000 unique targets or a nonsilencing control (NSC), selected with puromycin, cisplatin-treated, and analyzed for colony formation (see the Materials and Methods) (Fig. 1D). "
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    ABSTRACT: Hereditary cancers derive from gene defects that often compromise DNA repair. Thus, BRCA-associated cancers are sensitive to DNA-damaging agents such as cisplatin. The efficacy of cisplatin is limited, however, by the development of resistance. One cisplatin resistance mechanism is restoration of homologous recombination (HR), which can result from BRCA reversion mutations. However, in BRCA2 mutant cancers, cisplatin resistance can occur independently of restored HR by a mechanism that remains unknown. Here we performed a genome-wide shRNA screen and found that loss of the nucleosome remodeling factor CHD4 confers cisplatin resistance. Restoration of cisplatin resistance is independent of HR but correlates with restored cell cycle progression, reduced chromosomal aberrations, and enhanced DNA damage tolerance. Suggesting clinical relevance, cisplatin-resistant clones lacking genetic reversion of BRCA2 show de novo loss of CHD4 expression in vitro. Moreover, BRCA2 mutant ovarian cancers with reduced CHD4 expression significantly correlate with shorter progression-free survival and shorter overall survival. Collectively, our findings indicate that CHD4 modulates therapeutic response in BRCA2 mutant cancer cells. © 2015 Guillemette et al.; Published by Cold Spring Harbor Laboratory Press.
    Preview · Article · Mar 2015 · Genes & Development
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