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Heterozygous germline mutations in breast cancer 1 (BRCA1) strongly predispose women to breast cancer. BRCA1 plays an important role in DNA double-strand break (DSB) repair via homologous recombination (HR), which is important for tumor suppression. Although BRCA1-deficient cells are highly sensitive to treatment with DSB-inducing agents through their HR deficiency (HRD), BRCAI-associated tumors display heterogeneous responses to platinum drugs and poly(ADP-ribose) polymerase (PARP) inhibitors in clinical trials. It is unclear whether all pathogenic BRCA1 mutations have similar effects on the response to therapy. Here, we have investigated mammary tumorigenesis and therapy sensitivity in mice carrying the [Brca1.sup.185.stop] and [Brca.sup.15382stop] alleles, which respectively mimic the 2 most common BRCA1 founder mutations, [BRCA1.sup.185delAG] and [BRCA1.sup.5382insC]. Both the [Brca1.sup.185.stop] and [Brca.sup.15382stop] mutations predisposed animals to mammary tumors, but [Brca1.sup.185.stop] tumors responded markedly worse to HRD-targeted therapy than did [Brca.sup.15382stop] tumors. Mice expressing [Brca1.sup.185stop] mutations also developed therapy resistance more rapidly than did mice expressing [Brca.sup.15382stop]. We determined that both murine [Brca1.sup.185.stop] tumors and human [BRCA1.sup.185delAC] breast cancer cells expressed a really interesting new gene domain-less (RING- less) BRCA1 protein that mediated resistance to HRD-targeted therapies. Together, these results suggest that expression of RING- less BRCA1 may serve as a marker to predict poor response to DSB-inducing therapy in human cancer patients., Introduction Breast cancer is one of the most common malignancies in women, accounting for almost 1 in 3 diagnosed cancers, and it is the second leading cause of cancer death [...]

Loss of REV7 is shown to regulate end resection of double-stranded DNA breaks in BRCA1-deficient cells, leading to PARP inhibitor resistance and restoration of homologous recombination; REV7 dictates pathway choice in BRCA1-deficient cells and during immunoglobulin class switching. MAD2L2/REV7 promotes genome integrity DNA polymerase [zeta], composed of REV3, REV7 and an associated factor, REV1, mediates a type of DNA repair involving translesion synthesis, and hence its activity is highly mutagenic. Two studies exploring the DNA damage response have converged on REV7 (also known as MAD2L2) as a factor that, by itself, can promote maintenance of genome integrity. Several protective mechanisms that prevent telomere ends being recognized as a double-strand breaks (DSBs) and triggering an inappropriate DNA damage response were known. Jacqueline Jacobs and colleagues now show that REV7/MAD2L2 suppresses homology-dependent repair at deprotected telomeres and at irradiation-induced DSBs by inhibiting resection of the 5' end. As a consequence, the ends are shunted into the non-homologous end-joining pathway. Sven Rottenberg and colleagues came to a similar conclusion by studying the development of resistance to PARP inhibitors. They found that REV7/MAD2L2 dictates pathway choice in BRCA-deficient cells and during immunoglobulin class switching. Error-free repair of DNA double-strand breaks (DSBs) is achieved by homologous recombination (HR), and BRCA1 is an important factor for this repair pathway.sup.1. In the absence of BRCA1-mediated HR, the administration of PARP inhibitors induces synthetic lethality of tumour cells of patients with breast or ovarian cancers.sup.2,3. Despite the benefit of this tailored therapy, drug resistance can occur by HR restoration.sup.4. Genetic reversion of BRCA1-inactivating mutations can be the underlying mechanism of drug resistance, but this does not explain resistance in all cases.sup.5. In particular, little is known about BRCA1-independent restoration of HR. Here we show that loss of REV7 (also known as MAD2L2) in mouse and human cell lines re-establishes CTIP-dependent end resection of DSBs in BRCA1-deficient cells, leading to HR restoration and PARP inhibitor resistance, which is reversed by ATM kinase inhibition. REV7 is recruited to DSBs in a manner dependent on the H2AX-MDC1-RNF8-RNF168-53BP1 chromatin pathway, and seems to block HR and promote end joining in addition to its regulatory role in DNA damage tolerance.sup.6. Finally, we establish that REV7 blocks DSB resection to promote non-homologous end-joining during immunoglobulin class switch recombination. Our results reveal an unexpected crucial function of REV7 downstream of 53BP1 in coordinating pathological DSB repair pathway choices in BRCA1-deficient cells., Author(s): Guotai Xu [sup.1] , J. Ross Chapman [sup.2] , Inger Brandsma [sup.3] , Jingsong Yuan [sup.4] , Martin Mistrik [sup.5] , Peter Bouwman [sup.6] , Jirina Bartkova [sup.7] , [...]

To determine the utility of the ToxTracker assay in animal alternative testing strategies, the genotoxic potential of four fragrance materials (2‐octen‐4‐one, lauric aldehyde, veratraldehyde, and p‐methoxy cinnamaldehyde) were tested in the ToxTracker assay. These materials have been previously evaluated in an in vitro as well as in vivo micronucleus assay, conducted as per OECD guidelines. In addition to these studies, reconstructed human skin micronucleus studies were conducted on all four materials. All four materials were positive in an in vitro micronucleus assay but were negative in both in vivo and 3D skin micronucleus assays. The ToxTracker assay, in combination with in silico methods to predict metabolism was used to identify mechanisms for the misleading positive outcomes observed in the in vitro micronucleus assays. The results show that the ToxTracker assay, in conjunction with in silico predictions, can provide the information needed to aid in the identification of an appropriate animal alternative follow‐up assay, for substances with positive results in the standard in vitro test battery. Thus, the ToxTracker assay is a valuable tool to identify the genotoxic potential of fragrance materials and can aid with replacing animal‐based follow‐up testing with appropriate animal alternative assay(s). [ABSTRACT FROM AUTHOR]

Whether glyphosate-based herbicides (GBHs) are more potent than glyphosate alone at activating cellular mechanisms, which drive carcinogenesis remain controversial. As GBHs are more cytotoxic than glyphosate, we reasoned they may also be more capable of activating carcinogenic pathways. We tested this hypothesis by comparing the effects of glyphosate with Roundup GBHs both in vitro and in vivo. First, glyphosate was compared with representative GBHs, namely MON 52276 (European Union), MON 76473 (United Kingdom), and MON 76207 (United States) using the mammalian stem cell-based ToxTracker system. Here, MON 52276 and MON 76473, but not glyphosate and MON 76207, activated oxidative stress and unfolded protein responses. Second, molecular profiling of liver was performed in female Sprague-Dawley rats exposed to glyphosate or MON 52276 (at 0.5, 50, and 175 mg/kg bw/day glyphosate) for 90 days. MON 52276 but not glyphosate increased hepatic steatosis and necrosis. MON 52276 and glyphosate altered the expression of genes in liver reflecting TP53 activation by DNA damage and circadian rhythm regulation. Genes most affected in liver were similarly altered in kidneys. Small RNA profiling in liver showed decreased amounts of miR-22 and miR-17 from MON 52276 ingestion. Glyphosate decreased miR-30, whereas miR-10 levels were increased. DNA methylation profiling of liver revealed 5727 and 4496 differentially methylated CpG sites between the control and glyphosate and MON 52276 exposed animals, respectively. Apurinic/apyrimidinic DNA damage formation in liver was increased with glyphosate exposure. Altogether, our results show that Roundup formulations cause more biological changes linked with carcinogenesis than glyphosate. [ABSTRACT FROM AUTHOR]