The limited efficacy of immune checkpoint inhibitor treatment in triple-negative breast cancer (TNBC) patients is attributed to sparse or unresponsive tumor-infiltrating lymphocytes, but the ...mechanisms that lead to a therapy resistant tumor immune microenvironment are incompletely known. Here we show a strong correlation between MYC expression and loss of immune signatures in human TNBC. In mouse models of TNBC proficient or deficient of breast cancer type 1 susceptibility gene (BRCA1), MYC overexpression dramatically decreases lymphocyte infiltration in tumors, along with immune signature remodelling. MYC-mediated suppression of inflammatory signalling induced by BRCA1/2 inactivation is confirmed in human TNBC cell lines. Moreover, MYC overexpression prevents the recruitment and activation of lymphocytes in both human and mouse TNBC co-culture models. Chromatin-immunoprecipitation-sequencing reveals that MYC, together with its co-repressor MIZ1, directly binds promoters of multiple interferon-signalling genes, resulting in their downregulation. MYC overexpression thus counters tumor growth inhibition by a Stimulator of Interferon Genes (STING) agonist via suppressing induction of interferon signalling. Together, our data reveal that MYC suppresses innate immunity and facilitates tumor immune escape, explaining the poor immunogenicity of MYC-overexpressing TNBCs.
The high frequency of homologous recombination deficiency (HRD) is the main rationale of testing platinum-based chemotherapy in triple-negative breast cancer (TNBC), however, the existing methods to ...identify HRD are controversial and there is a medical need for predictive biomarkers. We assess the in vivo response to platinum agents in 55 patient-derived xenografts (PDX) of TNBC to identify determinants of response. The HRD status, determined from whole genome sequencing, is highly predictive of platinum response. BRCA1 promoter methylation is not associated with response, in part due to residual BRCA1 gene expression and homologous recombination proficiency in different tumours showing mono-allelic methylation. Finally, in 2 cisplatin sensitive tumours we identify mutations in XRCC3 and ORC1 genes that are functionally validated in vitro. In conclusion, our results demonstrate that the genomic HRD is predictive of platinum response in a large cohort of TNBC PDX and identify alterations in XRCC3 and ORC1 genes driving cisplatin response.
BRCA1-mutated breast cancer is primarily driven by DNA copy-number alterations (CNAs) containing large numbers of candidate driver genes. Validation of these candidates requires novel approaches for ...high-throughput in vivo perturbation of gene function. Here we develop genetically engineered mouse models (GEMMs) of BRCA1-deficient breast cancer that permit rapid introduction of putative drivers by either retargeting of GEMM-derived embryonic stem cells, lentivirus-mediated somatic overexpression or in situ CRISPR/Cas9-mediated gene disruption. We use these approaches to validate Myc, Met, Pten and Rb1 as bona fide drivers in BRCA1-associated mammary tumorigenesis. Iterative mouse modeling and comparative oncogenomics analysis show that MYC-overexpression strongly reshapes the CNA landscape of BRCA1-deficient mammary tumors and identify MCL1 as a collaborating driver in these tumors. Moreover, MCL1 inhibition potentiates the in vivo efficacy of PARP inhibition (PARPi), underscoring the therapeutic potential of this combination for treatment of BRCA1-mutated cancer patients with poor response to PARPi monotherapy.
Glucocorticoid receptor (GR) is a transcription factor that plays a crucial role in cancer biology. In this study, we utilized an in silico‐designed GR activity signature to demonstrate that GR ...relates to the proliferative capacity of numerous primary cancer types. In breast cancer, the GR activity status determines luminal subtype identity and has implications for patient outcomes. We reveal that GR engages with estrogen receptor (ER), leading to redistribution of ER on the chromatin. Notably, GR activation leads to upregulation of the ZBTB16 gene, encoding for a transcriptional repressor, which controls growth in ER‐positive breast cancer and associates with prognosis in luminal A patients. In relation to ZBTB16's repressive nature, GR activation leads to epigenetic remodeling and loss of histone acetylation at sites proximal to cancer‐driving genes. Based on these findings, epigenetic inhibitors reduce viability of ER‐positive breast cancer cells that display absence of GR activity. Our findings provide insights into how GR controls ER‐positive breast cancer growth and may have implications for patients' prognostication and provide novel therapeutic candidates for breast cancer treatment.
Synopsis
Activity of the Glucocorticoid Receptor across various cancer types is inversely related to proliferative signatures. In breast cancer, heightened Glucocorticoid Receptor (GR) activity correlates with improved patient outcomes and is linked to the regulation of the tumor suppressor ZBTB16.
GR activity correlates negatively with proliferative capacity across various cancer types.
In breast cancer, a distinct link is observed between GR activity status and luminal subtype identity, influencing patient outcomes.
Hormone‐regulated gene ZBTB16, is pivotal in controlling the growth of ER‐positive breast cancer.
Significant epigenetic changes accompanied GR activation, including diminished histone acetylation near cancer‐driving genes.
The insights gained suggest potential novel therapeutic candidates and advanced patient prognostication methods in breast cancer treatment.
Activity of the glucocorticoid receptor across various cancer types is inversely related to proliferative signatures. In breast cancer, heightened glucocorticoid receptor (GR) activity correlates with improved patient outcomes and is linked to the regulation of the tumor suppressor ZBTB16.
Hormone receptor-positive (HR
+
) breast cancer (BC) is the most common type of breast cancer among women worldwide, accounting for 70–80% of all invasive cases. Patients with HR
+
BC are commonly ...treated with endocrine therapy, but intrinsic or acquired resistance is a frequent problem, making HR
+
BC a focal point of intense research. Despite this, the malignancy still lacks adequate in vitro and in vivo models for the study of its initiation and progression as well as response and resistance to endocrine therapy. No mouse models that fully mimic the human disease are available, however rat mammary tumor models pose a promising alternative to overcome this limitation. Compared to mice, rats are more similar to humans in terms of mammary gland architecture, ductal origin of neoplastic lesions and hormone dependency status. Moreover, rats can develop spontaneous or induced mammary tumors that resemble human HR
+
BC. To date, six different types of rat models of HR
+
BC have been established. These include the spontaneous, carcinogen-induced, transplantation, hormone-induced, radiation-induced and genetically engineered rat mammary tumor models. Each model has distinct advantages, disadvantages and utility for studying HR
+
BC. This review provides a comprehensive overview of all published models to date.
Selective elimination of BRCA1-deficient cells by inhibitors of poly(ADP-ribose) polymerase (PARP) is a prime example of the concept of synthetic lethality in cancer therapy. This interaction is ...counteracted by the restoration of BRCA1-independent homologous recombination through loss of factors such as 53BP1, RIF1, and REV7/MAD2L2, which inhibit end resection of DNA double-strand breaks (DSBs). To identify additional factors involved in this process, we performed CRISPR/SpCas9-based loss-of-function screens and selected for factors that confer PARP inhibitor (PARPi) resistance in BRCA1-deficient cells. Loss of members of the CTC1-STN1-TEN1 (CST) complex were found to cause PARPi resistance in BRCA1-deficient cells in vitro and in vivo. We show that CTC1 depletion results in the restoration of end resection and that the CST complex may act downstream of 53BP1/RIF1. These data suggest that, in addition to its role in protecting telomeres, the CST complex also contributes to protecting DSBs from end resection.
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•PARP inhibitor resistance screens independently identify loss of CTC1 as major hit•The CST complex promotes PARP inhibitor sensitivity in BRCA1-deficient cells•Depletion of CTC1 restores end resection in BRCA1-deficient cells•CTC1 facilitates double-strand break repair via canonical non-homologous end joining
Using CRISPR/SpCas9-based loss-of-function screens, Barazas et al. show that loss of the CTC1-STN1-TEN1 (CST) complex promotes PARP inhibitor resistance in BRCA1-deficient cells. Mechanistically, the CST complex maintains double-strand break end stability in addition to its role in protecting telomeric ends.
Genetically engineered mouse models (GEMMs) of cancer have proven to be of great value for basic and translational research. Although CRISPR‐based gene disruption offers a fast‐track approach for ...perturbing gene function and circumvents certain limitations of standard GEMM development, it does not provide a flexible platform for recapitulating clinically relevant missense mutations in vivo. To this end, we generated knock‐in mice with Cre‐conditional expression of a cytidine base editor and tested their utility for precise somatic engineering of missense mutations in key cancer drivers. Upon intraductal delivery of sgRNA‐encoding vectors, we could install point mutations with high efficiency in one or multiple endogenous genes in situ and assess the effect of defined allelic variants on mammary tumorigenesis. While the system also produces bystander insertions and deletions that can stochastically be selected for when targeting a tumor suppressor gene, we could effectively recapitulate oncogenic nonsense mutations. We successfully applied this system in a model of triple‐negative breast cancer, providing the proof of concept for extending this flexible somatic base editing platform to other tissues and tumor types.
Synopsis
Most human cancers, including breast cancer, are predominantly characterized by missense mutations in driver genes. This study describes a genetically engineered mouse model, in which conditional expression of the BE3 cytidine base editor in the adult mammary gland permits installation of missense or nonsense mutations at one or multiple genomic loci.
Introduction of point mutations in endogeneous genes by CRISPR‐Cas9‐mediated base editing allows for assessment of their contribution to mammary tumor formation.
Rapid somatic engineering of allelic series of oncogenic missense mutations determines the relative effect size of each genetic perturbation.
Biallelic inactivation of endogenous tumor suppressor genes by base editing, although bystander indels are also observed.
Simultaneous base editing at multiple genomic loci using arrayed sgRNA vectors.
A new knock‐in mouse model allows for Cre‐mediated conditional expression of the BE3 cytidine base editor and in vivo analysis of somatic missense mutations.
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