Long-term Multimodal Recording Reveals Epigenetic Adaptation Routes in Dormant Breast Cancer Cells.

Patients with estrogen receptor-positive breast cancer receive adjuvant endocrine therapies (ET) that delay relapse by targeting clinically undetectable micrometastatic deposits. Yet, up to 50% of patients relapse even decades after surgery through unknown mechanisms likely involving dormancy. To investigate genetic and transcriptional changes underlying tumor awakening, we analyzed late relapse patients and longitudinally profiled a rare cohort treated with long-term neoadjuvant ETs until progression. Next, we developed an in vitro evolutionary study to record the adaptive strategies of individual lineages in unperturbed parallel experiments. Our data demonstrate that ETs induce nongenetic cell state transitions into dormancy in a stochastic subset of cells via epigenetic reprogramming. Single lineages with divergent phenotypes awaken unpredictably in the absence of recurrent genetic alterations. Targeting the dormant epigenome shows promising activity against adapting cancer cells. Overall, this study uncovers the contribution of epigenetic adaptation to the evolution of resistance to ETs. SIGNIFICANCE: This study advances the understanding of therapy-induced dormancy with potential clinical implications for breast cancer. Estrogen receptor-positive breast cancer cells adapt to endocrine treatment by entering a dormant state characterized by strong heterochromatinization with no recurrent genetic changes. Targeting the epigenetic rewiring impairs the adaptation of cancer cells to ETs. See related commentary by Llinas-Bertran et al., p. 704. This article is featured in Selected Articles from This Issue, p. 695.

Activation of endogenous retroviruses and induction of viral mimicry by MEK1/2 inhibition in pancreatic cancer.

While pancreatic ductal adenocarcinomas (PDACs) are addicted to KRAS-activating mutations, inhibitors of downstream KRAS effectors, such as the MEK1/2 kinase inhibitor trametinib, are devoid of therapeutic effects. However, the extensive rewiring of regulatory circuits driven by the attenuation of the KRAS pathway may induce vulnerabilities of therapeutic relevance. An in-depth molecular analysis of the transcriptional and epigenomic alterations occurring in PDAC cells in the initial hours after MEK1/2 inhibition by trametinib unveiled the induction of endogenous retroviruses (ERVs) escaping epigenetic silencing, leading to the production of double-stranded RNAs and the increased expression of interferon (IFN) genes. We tracked ERV activation to the early induction of the transcription factor ELF3, which extensively bound and activated nonsilenced retroelements and synergized with IRF1 (interferon regulatory factor 1) in the activation of IFNs and IFN-stimulated genes. Trametinib-induced viral mimicry in PDAC may be exploited in the rational design of combination therapies in immuno-oncology.

Mass Spectrometry-Based Profiling of Histone Post-Translational Modifications in Uveal Melanoma Tissues, Human Melanocytes, and Uveal Melanoma Cell Lines - A Pilot Study.

Purpose: Epigenetic alterations in uveal melanoma (UM) are still neither well characterized, nor understood. In this pilot study, we sought to provide a deeper insight into the possible role of epigenetic alterations in the pathogenesis of UM and their potential prognostic relevance. To this aim, we comprehensively profiled histone post-translational modifications (PTMs), which represent epigenetic features regulating chromatin accessibility and gene transcription, in UM formalin-fixed paraffin-embedded (FFPE) tissues, control tissues, UM cell lines, and healthy melanocytes. Methods: FFPE tissues of UM (n = 24), normal choroid (n = 4), human UM cell lines (n = 7), skin melanocytes (n = 6), and uveal melanocytes (n = 2) were analyzed through a quantitative liquid chromatography-mass spectrometry (LC-MS) approach. Results: Hierarchical clustering showed a clear separation with several histone PTMs that changed significantly in a tumor compared to normal samples, in both tissues and cell lines. In addition, several acetylations and H4K20me1 showed lower levels in BAP1 mutant tumors. Some of these changes were also observed when we compared GNA11 mutant tumors with GNAQ tumors. The epigenetic profiling of cell lines revealed that the UM cell lines MP65 and UPMM1 have a histone PTM pattern closer to the primary tissues than the other cell lines analyzed. Conclusions: Our results suggest the existence of different histone PTM patterns that may be important for diagnosis and prognosis in UM. However, further analyses are needed to confirm these findings in a larger cohort. The epigenetic characterization of a panel of UM cell lines suggested which cellular models are more suitable for epigenetic investigations.

A comprehensive characterisation of phaeochromocytoma and paraganglioma tumours through histone protein profiling, DNA methylation and transcriptomic analysis genome wide.

BACKGROUND: Phaeochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumours. Pathogenic variants have been identified in more than 15 susceptibility genes; associated tumours are grouped into three Clusters, reinforced by their transcriptional profiles. Cluster 1A PPGLs have pathogenic variants affecting enzymes of the tricarboxylic acid cycle, including succinate dehydrogenase. Within inherited PPGLs, these are the most common. PPGL tumours are known to undergo epigenetic reprograming, and here, we report on global histone post-translational modifications and DNA methylation levels, alongside clinical phenotypes. RESULTS: Out of the 25 histone post-translational modifications examined, Cluster 1A PPGLs were distinguished from other tumours by a decrease in hyper-acetylated peptides and an increase in H3K4me2. DNA methylation was compared between tumours from individuals who developed metastatic disease versus those that did not. The majority of differentially methylated sites identified tended to be completely methylated or unmethylated in non-metastatic tumours, with low inter-sample variance. Metastatic tumours by contrast consistently had an intermediate DNA methylation state, including the ephrin receptor EPHA4 and its ligand EFNA3. Gene expression analyses performed to identify genes involved in metastatic tumour behaviour pin-pointed a number of genes previously described as mis-regulated in Cluster 1A tumours, as well as highlighting the tumour suppressor RGS22 and the pituitary tumour-transforming gene PTTG1. CONCLUSIONS: Combined transcriptomic and DNA methylation analyses revealed aberrant pathways, including ones that could be implicated in metastatic phenotypes and, for the first time, we report a decrease in hyper-acetylated histone marks in Cluster 1 PPGLs.

Multi-omics integrative modelling for stereotactic body radiotherapy in early-stage non-small cell lung cancer: clinical trial protocol of the MONDRIAN study.

BACKGROUND: Currently, main treatment strategies for early-stage non-small cell lung cancer (ES-NSCLC) disease are surgery or stereotactic body radiation therapy (SBRT), with successful local control rates for both approaches. However, regional and distant failure remain critical in SBRT, and it is paramount to identify predictive factors of response to identify high-risk patients who may benefit from more aggressive approaches. The main endpoint of the MONDRIAN trial is to identify multi-omic biomarkers of SBRT response integrating information from the individual fields of radiomics, genomics and proteomics. METHODS: MONDRIAN is a prospective observational explorative cohort clinical study, with a data-driven, bottom-up approach. It is expected to enroll 100 ES-NSCLC SBRT candidates treated at an Italian tertiary cancer center with well-recognized expertise in SBRT and thoracic surgery. To identify predictors specific to SBRT, MONDRIAN will include data from 200 patients treated with surgery, in a 1:2 ratio, with comparable clinical characteristics. The project will have an overall expected duration of 60 months, and will be structured into five main tasks: (i) Clinical Study; (ii) Imaging/ Radiomic Study, (iii) Gene Expression Study, (iv) Proteomic Study, (v) Integrative Model Building. DISCUSSION: Thanks to its multi-disciplinary nature, MONDRIAN is expected to provide the opportunity to characterize ES-NSCLC from a multi-omic perspective, with a Radiation Oncology-oriented focus. Other than contributing to a mechanistic understanding of the disease, the study will assist the identification of high-risk patients in a largely unexplored clinical setting. Ultimately, this would orient further clinical research efforts on the combination of SBRT and systemic treatments, such as immunotherapy, with the perspective of improving oncological outcomes in this subset of patients. TRIAL REGISTRATION: The study was prospectively registered at clinicaltrials.gov (NCT05974475).

Proteomics contributions to epigenetic drug discovery.

The combined activity of epigenetic features, which include histone post-translational modifications, DNA methylation, and nucleosome positioning, regulates gene expression independently from changes in the DNA sequence, defining how the shared genetic information of an organism is used to generate different cell phenotypes. Alterations in epigenetic processes have been linked with a multitude of diseases, including cancer, fueling interest in the discovery of drugs targeting the proteins responsible for writing, erasing, or reading histone and DNA modifications. Mass spectrometry (MS)-based proteomics has emerged as a versatile tool that can assist drug discovery pipelines from target validation, through target deconvolution, to monitoring drug efficacy in vivo. Here, we provide an overview of the contributions of MS-based proteomics to epigenetic drug discovery, describing the main approaches that can be used to support different drug discovery pipelines and highlighting how they contributed to the development and characterization of epigenetic drugs.

Serum proteomics profiling identifies a preliminary signature for the diagnosis of early-stage lung cancer.

PURPOSE: Lung cancer is the most common cause of death from cancer worldwide, largely due to late diagnosis. Thus, there is an urgent need to develop new approaches to improve the detection of early-stage lung cancer, which would greatly improve patient survival. EXPERIMENTAL DESIGN: The quantitative protein expression profiles of microvesicles isolated from the sera from 46 lung cancer patients and 41 high-risk non-cancer subjects were obtained using a mass spectrometry method based on a peptide library matching approach. RESULTS: We identified 33 differentially expressed proteins that allow discriminating the two groups. We also built a machine learning model based on serum protein expression profiles that can correctly classify the majority of lung cancer cases and that highlighted a decrease in the levels of Arysulfatase A (ARSA) as the most discriminating factor found in tumors. CONCLUSIONS AND CLINICAL RELEVANCE: Our study identified a preliminary, non-invasive protein signature able to discriminate with high specificity and selectivity early-stage lung cancer patients from high-risk healthy subjects. These results provide the basis for future validation studies for the development of a non-invasive diagnostic tool for lung cancer.

A truncated and catalytically inactive isoform of KDM5B histone demethylase accumulates in breast cancer cells and regulates H3K4 tri-methylation and gene expression.

KDM5B histone demethylase is overexpressed in many cancers and plays an ambivalent role in oncogenesis, depending on the specific context. This ambivalence could be explained by the expression of KDM5B protein isoforms with diverse functional roles, which could be present at different levels in various cancer cell lines. We show here that one of these isoforms, namely KDM5B-NTT, accumulates in breast cancer cell lines due to remarkable protein stability relative to the canonical PLU-1 isoform, which shows a much faster turnover. This isoform is the truncated and catalytically inactive product of an mRNA with a transcription start site downstream of the PLU-1 isoform, and the consequent usage of an alternative ATG for translation initiation. It also differs from the PLU-1 transcript in the inclusion of an additional exon (exon-6), previously attributed to other putative isoforms. Overexpression of this isoform in MCF7 cells leads to an increase in bulk H3K4 methylation and induces derepression of a gene cluster, including the tumor suppressor Cav1 and several genes involved in the interferon-alpha and -gamma response. We discuss the relevance of this finding considering the hypothesis that KDM5B may possess regulatory roles independent of its catalytic activity.

Small molecule-induced epigenomic reprogramming of APL blasts leading to antiviral-like response and c-MYC downregulation.

Acute promyelocytic leukemia (APL) is an aggressive subtype of acute myeloid leukemia (AML) in which the PML/RARα fusion protein exerts oncogenic activities by recruiting repressive complexes to the promoter of specific target genes. Other epigenetic perturbations, as alterations of histone H3 lysine 9 trimethylation (H3K9me3), have been frequently found in AMLs and are associated with leukemogenesis and leukemia progression. Here, we characterized the epigenomic effects of maltonis, a novel maltol-derived molecule, in APL cells. We demonstrate that maltonis treatments induce a profound remodulation of the histone code, reducing global H3K9me3 signal and modulating other histone post-translational modifications. Transcriptomic and epigenomic analyses revealed that maltonis exposure induces changes of genes expression associated with a genomic redistribution of histone H3 lysine 4 trimethylation (H3K4me3) and lysine 27 acetylation (H3K27ac). Upregulation of interferon alpha and gamma response and downregulation of c-MYC target genes, in function of c-MYC reduced expression (monitored in all the hematopoietic neoplasms tested), represent the most significant modulated pathways. These data demonstrate the ability of maltonis to epigenetically reprogram the gene expression profile of APL cells, inducing an intriguing antiviral-like response, concomitantly with the downregulation of c-MYC-related pathways, thus making it an attractive candidate for antileukemic therapy.

Investigating pathological epigenetic aberrations by epi-proteomics.

Epigenetics includes a complex set of processes that alter gene activity without modifying the DNA sequence, which ultimately determines how the genetic information common to all the cells of an organism is used to generate different cell types. Dysregulation in the deposition and maintenance of epigenetic features, which include histone posttranslational modifications (PTMs) and histone variants, can result in the inappropriate expression or silencing of genes, often leading to diseased states, including cancer. The investigation of histone PTMs and variants in the context of clinical samples has highlighted their importance as biomarkers for patient stratification and as key players in aberrant epigenetic mechanisms potentially targetable for therapy. Mass spectrometry (MS) has emerged as the most powerful and versatile tool for the comprehensive, unbiased and quantitative analysis of histone proteoforms. In recent years, these approaches-which we refer to as "epi-proteomics"-have demonstrated their usefulness for the investigation of epigenetic mechanisms in pathological conditions, offering a number of advantages compared with the antibody-based methods traditionally used to profile clinical samples. In this review article, we will provide a critical overview of the MS-based approaches that can be employed to study histone PTMs and variants in clinical samples, with a strong focus on the latest advances in this area, such as the analysis of uncommon modifications and the integration of epi-proteomics data into multi-OMICs approaches, as well as the challenges to be addressed to fully exploit the potential of this novel field of research.

Mass spectrometry-based characterization of histones in clinical samples: applications, progress, and challenges.

In the last 15 years, increasing evidence linking epigenetics to various aspects of cancer biology has prompted the investigation of histone post-translational modifications (PTMs) and histone variants in the context of clinical samples. The studies performed so far demonstrated the potential of this type of investigations for the discovery of both potential epigenetic biomarkers for patient stratification and novel epigenetic mechanisms potentially targetable for cancer therapy. Although traditionally the analysis of histones in clinical samples was performed through antibody-based methods, mass spectrometry (MS) has emerged as a more powerful tool for the unbiased, comprehensive, and quantitative investigation of histone PTMs and variants. MS has been extensively used for the analysis of epigenetic marks in cell lines and animal tissue and, thanks to recent technological advances, is now ready to be applied also to clinical samples. In this review, we will provide an overview on the quantitative MS-based analysis of histones, their PTMs and their variants in cancer clinical samples, highlighting current achievements and future perspectives for this novel field of research. Among the different MS-based approaches currently available for histone PTM profiling, we will focus on the 'bottom-up' strategy, namely the analysis of short proteolytic peptides, as it has been already successfully employed for the analysis of clinical samples.

LSD1-directed therapy affects glioblastoma tumorigenicity by deregulating the protective ATF4-dependent integrated stress response.

Glioblastoma (GBM) is a fatal tumor whose aggressiveness, heterogeneity, poor blood-brain barrier penetration, and resistance to therapy highlight the need for new targets and clinical treatments. A step toward clinical translation includes the eradication of GBM tumor-initiating cells (TICs), responsible for GBM heterogeneity and relapse. By using patient-derived TICs and xenograft orthotopic models, we demonstrated that the selective lysine-specific histone demethylase 1 inhibitor DDP_38003 (LSD1i) is able to penetrate the brain parenchyma in vivo in preclinical models, is well tolerated, and exerts antitumor activity in molecularly different GBMs. LSD1 genetic targeting further strengthens the role of LSD1 in GBM TIC maintenance. GBM TIC plasticity supports their adaptation and survival under a plethora of environmental stresses, including nutrient deficiency and proteostasis perturbation. By mimicking these stresses in vitro, we found that LSD1 inhibition hampers the induction of the activating transcription factor 4 (ATF4), the master regulator of the integrated stress response (ISR). The resulting aberrant ISR sensitizes GBM TICs to stress-induced cell death, hampering tumor aggressiveness. Functionally, LSD1i interferes with LSD1 scaffolding function and prevents its interaction with CREBBP, a critical ATF4 activator. By disrupting the interaction between CREBBP and LSD1-ATF4 axis, LSD1 inhibition prevents GBM TICs from overcoming stress and sustaining GBM progression. The effectiveness of the LSD1 inhibition in preclinical models shown here places a strong rationale toward its clinical translation for GBM treatment.

Spatial epi-proteomics enabled by histone post-translational modification analysis from low-abundance clinical samples.

BACKGROUND: Increasing evidence linking epigenetic mechanisms and different diseases, including cancer, has prompted in the last 15 years the investigation of histone post-translational modifications (PTMs) in clinical samples. Methods allowing the isolation of histones from patient samples followed by the accurate and comprehensive quantification of their PTMs by mass spectrometry (MS) have been developed. However, the applicability of these methods is limited by the requirement for substantial amounts of material. RESULTS: To address this issue, in this study we streamlined the protein extraction procedure from low-amount clinical samples and tested and implemented different in-gel digestion strategies, obtaining a protocol that allows the MS-based analysis of the most common histone PTMs from laser microdissected tissue areas containing as low as 1000 cells, an amount approximately 500 times lower than what is required by available methods. We then applied this protocol to breast cancer patient laser microdissected tissues in two proof-of-concept experiments, identifying differences in histone marks in heterogeneous regions selected by either morphological evaluation or MALDI MS imaging. CONCLUSIONS: These results demonstrate that analyzing histone PTMs from very small tissue areas and detecting differences from adjacent tumor regions is technically feasible. Our method opens the way for spatial epi-proteomics, namely the investigation of epigenetic features in the context of tissue and tumor heterogeneity, which will be instrumental for the identification of novel epigenetic biomarkers and aberrant epigenetic mechanisms.

Anticancer innovative therapy congress: Highlights from the 10th anniversary edition.

During the Tenth Edition of the Annual Congress on "Anticancer Innovative Therapy" [Milan, 23/24 January 2020], experts in the fields of immuno-oncology, epigenetics, tumor cell signaling, and cancer metabolism shared their latest knowledge on the roles of i] epigenetics, and in particular, chromatin modifiers, ii] cancer metabolism, iii] cancer stem cells [CSCs], iv] tumor cell signaling, and iv] the immune system. The novel therapeutic approaches presented included epigenetic drugs, cell cycle inhibitors combined with ICB, antibiotics and other off-label drugs, small-molecules active against CSCs, liposome-delivered miRNAs, tumor-specific CAR-T cells, and T-cell-based immunotherapy. Moreover, important evidence on possible mechanisms of resistance to these innovative therapies were also discussed, in particular with respect to resistance to ICB. Overall, this conference provided scientists and clinicians with a broad overview of future challenges and hopes to improve cancer treatment reasonably in the medium-short term.

Label-Free Mass Spectrometry-Based Quantification of Linker Histone H1 Variants in Clinical Samples.

Epigenetic aberrations have been recognized as important contributors to cancer onset and development, and increasing evidence suggests that linker histone H1 variants may serve as biomarkers useful for patient stratification, as well as play an important role as drivers in cancer. Although traditionally histone H1 levels have been studied using antibody-based methods and RNA expression, these approaches suffer from limitations. Mass spectrometry (MS)-based proteomics represents the ideal tool to accurately quantify relative changes in protein abundance within complex samples. In this study, we used a label-free quantification approach to simultaneously analyze all somatic histone H1 variants in clinical samples and verified its applicability to laser micro-dissected tissue areas containing as low as 1000 cells. We then applied it to breast cancer patient samples, identifying differences in linker histone variants patters in primary triple-negative breast tumors with and without relapse after chemotherapy. This study highlights how label-free quantitation by MS is a valuable option to accurately quantitate histone H1 levels in different types of clinical samples, including very low-abundance patient tissues.

Clinical Application of Mass Spectrometry-Based Proteomics in Lung Cancer Early Diagnosis.

The current knowledge on proteomic biomarker analysis for the early diagnosis of lung cancer is summarized, underlining the diversity among the results and the current interest in translating research results into clinical practice. A MEDLINE/PubMed literature search to retrieve all the papers published in the last 10 years is performed. Proteomics studies on lung cancer have gathered evidence on the potential role of biomarkers in early diagnosis. Although promising, none of them have proved to be sufficiently reliable to achieve validation. Future research should evolve toward a multipanel analysis of proteins, considering the possibility that individual biomarkers might not be specific enough to diagnose lung cancer, but could be related to oncological conditions.

Enrichment of histones from patient samples for mass spectrometry-based analysis of post-translational modifications.

Aberrations in histone post-translational modifications (PTMs) have been implicated with the development of numerous pathologies, including cancer. Therefore, profiling histone PTMs in patient samples could provide information useful for the identification of epigenetic biomarkers, as well as for the discovery of potential novel targets. While antibody-based methods have been traditionally employed to analyze histone PTM in clinical samples, mass spectrometry (MS) can provide a more comprehensive, unbiased and quantitative view on histones and their PTMs. To combine the power of MS-based methods and the potential offered by histone PTM profiling of clinical samples, we have recently developed a series of methods for the extraction and enrichment of histones from different types of patient samples, including formalin-fixed paraffin-embedded tissues, fresh- and optimal cutting temperature-frozen tissues, and primary cells. Here, we provide a detailed description of these protocols, together with indications on the expected results and the most suitable workflow to be used downstream of each procedure.

hSWATH: Unlocking SWATH's Full Potential for an Untargeted Histone Perspective.

Mass spectrometry (MS) has become the technique of choice for large-scale analysis of histone post-translational modifications (hPTMs) and their combinatorial patterns, especially in untargeted settings where novel discovery-driven hypotheses are being generated. However, MS-based histone analysis requires a distinct sample preparation, acquisition, and data analysis workflow when compared to traditional MS-based approaches. To this end, sequential window acquisition of all theoretical fragment ion spectra (SWATH) has great potential, as it allows for untargeted accurate identification and quantification of hPTMs. Here, we present a complete SWATH workflow specifically adapted for the untargeted study of histones (hSWATH). We assess its validity on a technical dataset of time-lapse deacetylation of a commercial histone extract using HDAC1, which contains a ground truth, i.e., acetylated substrate peptides reduce in intensity. We successfully apply this workflow in a biological setting and subsequently investigate the differential response to HDAC inhibition in different breast cancer cell lines.

Profiling of Epigenetic Features in Clinical Samples Reveals Novel Widespread Changes in Cancer.

Aberrations in histone post-translational modifications (PTMs), as well as in the histone modifying enzymes (HMEs) that catalyze their deposition and removal, have been reported in many tumors and many epigenetic inhibitors are currently under investigation for cancer treatment. Therefore, profiling epigenetic features in cancer could have important implications for the discovery of both biomarkers for patient stratification and novel epigenetic targets. In this study, we employed mass spectrometry-based approaches to comprehensively profile histone H3 PTMs in a panel of normal and tumoral tissues for different cancer types, identifying various changes, some of which appear to be a consequence of the increased proliferation rate of tumors, while others are cell-cycle independent. Histone PTM changes found in tumors partially correlate with alterations of the gene expression profiles of HMEs obtained from publicly available data and are generally lost in culture conditions. Through this analysis, we identified tumor- and subtype-specific histone PTM changes, but also widespread changes in the levels of histone H3 K9me3 and K14ac marks. In particular, H3K14ac showed a cell-cycle independent decrease in all the seven tumor/tumor subtype models tested and could represent a novel epigenetic hallmark of cancer. .

Alternative digestion approaches improve histone modification mapping by mass spectrometry in clinical samples.

PURPOSE: Profiling histone posttranslational modifications (PTMs) in clinical samples holds great potential for the identification of epigenetic biomarkers and the discovery of novel epigenetic targets. MS-based approaches to analyze histone PTMs in clinical samples usually rely on SDS-PAGE separation following histone enrichment in order to eliminate detergents and further isolate histones. However, this limits the digestions options and hence the modification coverage. EXPERIMENTAL DESIGN AND RESULTS: The aim of this study is the implementation of a procedure involving acetone protein precipitation followed by histone enrichment through a C18 StageTip column to obtain histone preparations suitable for various in-solution digestion protocols. Among them, the Arg-C digestion, which allows profiling histone H4 modifications, and the Prop-PIC method, which improves the detection of short and hydrophilic peptides, are tested. This approach is validated on different types of samples, including formalin-fixed paraffin-embedded pathology tissues, and employed to profile histone H4 modifications in cancer samples and normal tissues, identifying previously reported differences, as well as novel ones. CONCLUSIONS AND CLINICAL RELEVANCE: This protocol widens the number of applications available in the toolbox of clinical epigenomics, allowing the investigation of a larger spectrum of histone marks in patient samples.