The repertoire of mutational signatures in human cancer

A review on trends in development and translation of omics signatures in cancer

The field of cancer genomics and transcriptomics has evolved from targeted profiling to swift sequencing of individual tumor genome and transcriptome. The steady growth in genome, epigenome, and transcriptome datasets on a genome-wide scale has significantly increased our capability in capturing signatures that represent both the intrinsic and extrinsic biological features of tumors. These biological differences can help in precise molecular subtyping of cancer, predicting tumor progression, metastatic potential, and resistance to therapeutic agents. In this review, we summarized the current development of genomic, methylomic, transcriptomic, proteomic and metabolic signatures in the field of cancer research and highlighted their potentials in clinical applications to improve diagnosis, prognosis, and treatment decision in cancer patients.

Image-based deep learning model using DNA methylation data predicts the origin of cancer of unknown primary

Cancer of unknown primary (CUP) is a rare type of metastatic cancer in which the origin of the tumor is unknown. Since the treatment strategy for patients with metastatic tumors depends on knowing the primary site, accurate identification of the origin site is important. Here, we developed an image-based deep-learning model that utilizes a vision transformer algorithm for predicting the origin of CUP. Using DNA methylation dataset of 8,233 primary tumors from The Cancer Genome Atlas (TCGA), we categorized 29 cancer types into 18 organ classes and extracted 2,312 differentially methylated CpG sites (DMCs) from non-squamous cancer group and 420 DMCs from squamous cell cancer group. Using these DMCs, we created organ-specific DNA methylation images and used them for model training and testing. Model performance was evaluated using 394 metastatic cancer samples from TCGA (TCGA-meta) and 995 samples (693 primary and 302 metastatic cancers) obtained from 20 independent external studies. We identified that the DNA methylation image reveals a distinct pattern based on the origin of cancer. Our model achieved an overall accuracy of 96.95 % in the TCGA-meta dataset. In the external validation datasets, our classifier achieved overall accuracies of 96.39 % and 94.37 % in primary and metastatic tumors, respectively. Especially, the overall accuracies for both primary and metastatic samples of non-squamous cell cancer were exceptionally high, with 96.79 % and 96.85 %, respectively.

A perylene diimide probe for NIR-II fluorescence imaging guided photothermal and type I/type II photodynamic synergistic therapy

Phototherapy has garnered significant attention in the past decade. Photothermal and photodynamic synergistic therapy combined with NIR fluorescence imaging has been one of the most attractive treatment options because of the deep tissue penetration, high selectivity and excellent therapeutic effect. Benefiting from the superb photometrics and ease of modification, perylene diimide (PDI) and its derivatives have been employed as sensing probes and therapeutic agents in the biological and biomedical research fields, and exhibiting excellent potential. Herein, we reported the development of a novel organic small-molecule phototherapeutic agent, PDI-TN. The absorption of PDI-TN extends into the NIR region, which provides feasibility for NIR phototherapy. PDI-TN overcomes the traditional Aggregation-Caused Quenching (ACQ) effect and exhibits typical characteristics of Aggregation-Induced Emission (AIE). Subsequently, PDI-TN NPs were obtained by using an amphiphilic triblock copolymer F127 to encapsulate PDI-TN. Interestingly, the PDI-TN NPs not only exhibit satisfactory photothermal effects, but also can generate O2•- and 1O2 through type I and type II pathways, respectively. Additionally, the PDI-TN NPs emit strong fluorescence in the NIR-II region, and show outstanding therapeutic potential for in vivo NIR-II fluorescence imaging. To our knowledge, PDI-TN is the first PDI derivative used for NIR-II fluorescence imaging-guided photodynamic and photothermal synergistic therapy, which suggests excellent potential for future biological/biomedical applications.

The cytidine deaminase APOBEC3C has unique sequence and genome feature preferences

APOBEC proteins are cytidine deaminases that restrict the replication of viruses and transposable elements. Several members of the APOBEC3 family, APOBEC3A, APOBEC3B, and APOBEC3H-I, can access the nucleus and cause what is thought to be indiscriminate deamination of the genome, resulting in mutagenesis and genome instability. Although APOBEC3C is also present in the nucleus, the full scope of its deamination target preferences is unknown. By expressing human APOBEC3C in a yeast model system, I have defined the APOBEC3C mutation signature, as well as the preferred genome features of APOBEC3C targets. The APOBEC3C mutation signature is distinct from those of the known cancer genome mutators APOBEC3A and APOBEC3B. APOBEC3C produces DNA strand-coordinated mutation clusters, and APOBEC3C mutations are enriched near the transcription start sites of active genes. Surprisingly, APOBEC3C lacks the bias for the lagging strand of DNA replication that is seen for APOBEC3A and APOBEC3B. The unique preferences of APOBEC3C constitute a mutation profile that will be useful in defining sites of APOBEC3C mutagenesis in human genomes.

Recent Advancements in Subcellular Proteomics: Growing Impact of Organellar Protein Niches on the Understanding of Cell Biology

The mammalian cell is a complex entity, with membrane-bound and membrane-less organelles playing vital roles in regulating cellular homeostasis. Organellar protein niches drive discrete biological processes and cell functions, thus maintaining cell equilibrium. Cellular processes such as signaling, growth, proliferation, motility, and programmed cell death require dynamic protein movements between cell compartments. Aberrant protein localization is associated with a wide range of diseases. Therefore, analyzing the subcellular proteome of the cell can provide a comprehensive overview of cellular biology. With recent advancements in mass spectrometry, imaging technology, computational tools, and deep machine learning algorithms, studies pertaining to subcellular protein localization and their dynamic distributions are gaining momentum. These studies reveal changing interaction networks because of "moonlighting proteins" and serve as a discovery tool for disease network mechanisms. Consequently, this review aims to provide a comprehensive repository for recent advancements in subcellular proteomics subcontexting methods, challenges, and future perspectives for method developers. In summary, subcellular proteomics is crucial to the understanding of the fundamental cellular mechanisms and the associated diseases.

The SMC5/6 complex prevents genotoxicity upon APOBEC3A-mediated replication stress

Mutational patterns caused by APOBEC3 cytidine deaminase activity are evident throughout human cancer genomes. In particular, the APOBEC3A family member is a potent genotoxin that causes substantial DNA damage in experimental systems and human tumors. However, the mechanisms that ensure genome stability in cells with active APOBEC3A are unknown. Through an unbiased genome-wide screen, we define the Structural Maintenance of Chromosomes 5/6 (SMC5/6) complex as essential for cell viability when APOBEC3A is active. We observe an absence of APOBEC3A mutagenesis in human tumors with SMC5/6 dysfunction, consistent with synthetic lethality. Cancer cells depleted of SMC5/6 incur substantial genome damage from APOBEC3A activity during DNA replication. Further, APOBEC3A activity results in replication tract lengthening which is dependent on PrimPol, consistent with re-initiation of DNA synthesis downstream of APOBEC3A-induced lesions. Loss of SMC5/6 abrogates elongated replication tracts and increases DNA breaks upon APOBEC3A activity. Our findings indicate that replication fork lengthening reflects a DNA damage response to APOBEC3A activity that promotes genome stability in an SMC5/6-dependent manner. Therefore, SMC5/6 presents a potential therapeutic vulnerability in tumors with active APOBEC3A.

From Detection to Cure - Emerging Roles for Urinary Tumor DNA (utDNA) in Bladder Cancer

PURPOSE OF REVIEW

This review sought to define the emerging roles of urinary tumor DNA (utDNA) for diagnosis, monitoring, and treatment of bladder cancer. Building from early landmark studies the focus is on recent studies, highlighting how utDNA could aid personalized care.

RECENT FINDINGS

Recent research underscores the potential for utDNA to be the premiere biomarker in bladder cancer due to the constant interface between urine and tumor. Many studies find utDNA to be more informative than other biomarkers in bladder cancer, especially in early stages of disease. Points of emphasis include superior sensitivity over traditional urine cytology, broad genomic and epigenetic insights, and the potential for non-invasive, real-time analysis of tumor biology. utDNA shows promise for improving all phases of bladder cancer care, paving the way for personalized treatment strategies. Building from current research, future comprehensive clinical trials will validate utDNA's clinical utility, potentially revolutionizing bladder cancer management.

Histopathological, Molecular and Clinical Profiling of Lymphoepithelioma-Like Carcinoma of the Bladder (LELC-B)

Lymphoepithelioma-like urothelial carcinoma of the urinary bladder (LELC-B) is a rare histologic subtype characterized by strong immune cell infiltrates. A better prognosis and favorable response rates to immune-checkpoint inhibitors (ICI) have been described. We aimed to characterize the molecular profiles and immune cell infiltration of LELC-B for a better understanding and its therapeutic implications. We identified eleven muscle-invasive bladder cancer cases with pure and mixed LELC-B. PD-L1 expression and mismatch-repair (MMR) proteins were evaluated using immunohistochemistry. We calculated the tumor-mutational burden (TMB) and characterized mutational profiles using whole exome DNA-sequencing data. Transcriptomic signatures were detected using the NanoString nCounter PanCancer IO360 panel. Multiplex immunofluorescence of tumor microenvironment (PD-L1, PanCK, aSMA, Vimentin, CD45, Ki67) and T-cells (CD4, CD3, PD-1, CD163, CD8, FoxP3) was used to quantify cell populations. All LELC-B cases were highly positive for PD-L1 (median TPS/TC 70%; range 20-100; median CPS 100; range 50-100), MMR-proficient and negative for Epstein-Barr virus infection. Immune cell infiltrates were characterized by high CD8+ T-cell count and high PD-1/PD-L1 expression on immune and tumor cells. LELC-B showed upregulation of signaling pathways involved in immune cell response. Most common mutations were found in chromatin remodeling genes causing epigenetic dysregulation. All LELC-B cases showed high TMB of 39 Mut/Mb (IQR 29-66). In conclusion, LELC-B is a highly immunogenic tumor, showing strong upregulation of PD1/PD-L1 and making ICI a promising treatment option.

Genomic progression for local invasion of cutaneous squamous cell carcinoma from the superficial to the deep portion

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer. While many treatments exist, our understanding of its genomic progression, especially from the epidermis to the deep dermis, remains limited. This study aims to identify genetic mutations associated with the progression of cSCC into the deep dermis, providing insights into its aggressive behavior and high-risk features. We performed high-depth whole-exome sequencing on 12 cSCC tissues, along with paired normal tissues from six patients, using microdissection techniques. The mutational analysis focused on identifying alterations enriched during cSCC progression. Gene Ontology enrichment analysis, immunohistochemical assays, and external single-cell RNA data were utilized for validation. A total of 8863 non-synonymous somatic mutations were identified in 4092 genes across the superficial and deep portions of cSCCs. Analysis of deep portion mutations revealed a significant correlation with gene ontology biological processes, particularly cell junction organization, and cell-cell adhesion. Clonal mutations in these processes were more prevalent in the deep portions, indicating their impact on the cSCC mutation landscape. Genetic evolution analysis identified 29 causal genes associated with dermal invasion in cSCC. We highlight somatic mutations in cSCC, revealing heterogeneity between superficial and deep regions. Altered genes in cell junction organization and cell-cell adhesion emerged as pivotal in dermal invasion. We identified 29 causal genes primarily in deep tumor regions. Our findings emphasize analyzing multiple tumor regions to capture varied mutational landscapes. These insights advance our understanding of cSCC progression, emphasizing genetic and cellular changes during tumor evolution.

The DNA Methyltransferase Inhibitor 5-Aza-4'-thio-2'-Deoxycytidine Induces C>G Transversions and Acute Lymphoid Leukemia Development

DNA methyltransferase inhibitors (DNMTi), most commonly cytidine analogs, are compounds that decrease 5'-cytosine methylation. DNMTi are used clinically based on the hypothesis that cytosine demethylation will lead to re-expression of tumor suppressor genes. 5-Aza-4'-thio-2'-deoxycytidine (Aza-TdCyd or ATC) is a recently described thiol-substituted DNMTi that has been shown to have anti-tumor activity in solid tumor models. In this study, we investigated the therapeutic potential of ATC in a murine transplantation model of myelodysplastic syndrome. ATC treatment led to the transformation of transplanted wild-type bone marrow nucleated cells into lymphoid leukemia, and healthy mice treated with ATC also developed lymphoid leukemia. Whole-exome sequencing revealed 1,000 acquired mutations, almost all of which were C>G transversions in a specific 5'-NCG-3' context. These mutations involved dozens of genes involved in human lymphoid leukemia, such as Notch1, Pten, Pax5, Trp53, and Nf1. Human cells treated in vitro with ATC showed 1,000 acquired C>G transversions in a similar context. Deletion of Dck, the rate-limiting enzyme for the cytidine salvage pathway, eliminated C>G transversions. Taken together, these findings demonstrate a highly penetrant mutagenic and leukemogenic phenotype associated with ATC. Significance: Treatment with a DNA methyltransferase inhibitor generates a distinct mutation signature and triggers leukemic transformation, which has important implications for the research and clinical applications of these inhibitors.

Genetic variation across and within individuals

Germline variation and somatic mutation are intricately connected and together shape human traits and disease risks. Germline variants are present from conception, but they vary between individuals and accumulate over generations. By contrast, somatic mutations accumulate throughout life in a mosaic manner within an individual due to intrinsic and extrinsic sources of mutations and selection pressures acting on cells. Recent advancements, such as improved detection methods and increased resources for association studies, have drastically expanded our ability to investigate germline and somatic genetic variation and compare underlying mutational processes. A better understanding of the similarities and differences in the types, rates and patterns of germline and somatic variants, as well as their interplay, will help elucidate the mechanisms underlying their distinct yet interlinked roles in human health and biology.

Beyond driver mutations: exploring the landscape of mutational signatures in adenocarcinomas of the bladder†

The emergence of mutational signatures in cancer research represents a paradigm shift, offering profound insights into tumor biology, therapeutic strategies, and risk assessment. A recent article published in The Journal of Pathology delves into the significance of mutational signatures, assessing their role as molecular fingerprints that illuminate the etiology of individual cancer cases. By deciphering the diverse patterns of DNA alterations, in the context of urachal and nonurachal bladder adenocarcinomas, researchers can unravel intrinsic and environmental risk factors shaping cancer development. The study highlighted a predominance of environmental risk factors in Chinese populations affected by bladder adenocarcinomas. In this context, in this commentary, we highlight some of the potential applications of molecular signatures in differential diagnosis and therapy prediction. As the field continues to evolve, a deeper understanding of mutational signatures promises to revolutionize precision oncology by offering personalized approaches informed by comprehensive mutational patterns of tumors. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Alcohol and colorectal cancer risk, subclassified by mutational signatures of DNA mismatch repair deficiency

BACKGROUND

We examined whether the association between alcohol consumption and colorectal cancer (CRC) incidence was stronger for tumors with higher contributions of defective mismatch repair (dMMR)-related tumor mutational signatures.

METHODS

We used data from 227 916 men and women who participated in the Nurses' Health Study (1980-2016), the Nurses' Health Study II (1991-2017), and the Health Professionals Follow-Up Study (1986-2016). Dietary data were collected every 4 years through validated food frequency questionnaires. Relative contributions of 2 defective mismatch repair-related tumor mutational signatures with single-based substitutions (c-dMMRa/SBS15 and c-dMMRb/SBS26) were quantified using whole-exome sequencing data in a subset of incident CRC patients. Duplication-method Cox proportional hazards regression models were used to assess the association between alcohol consumption and the risk of CRC subtypes according to different contributions of the tumor mutational signatures. All statistical tests were 2-sided.

RESULTS

We documented 825 incident CRC patients with available tumor mutational signature data over 26 to 36 years of follow-up. The association between alcohol consumption and CRC incidence was stronger for tumors with higher contributions of c-dMMRb/SBS26 (Ptrend = .02 for heterogeneity) compared with tumors with lower contributions of this tumor mutational signature. Compared with nondrinkers, drinkers who imbibed 15 g/d or more of alcohol had a high risk of c-dMMRb/SBS26-high CRC (multivariable-adjusted hazard ratio = 2.43, 95% confidence interval = 1.55 to 3.82) but not c-dMMRb/SBS26-low CRC (multivariable-adjusted hazard ratio = 0.86, 95% confidence interval = 0.57 to 1.28) or c-dMMRb/SBS26-moderate CRC (multivariable-adjusted hazard ratio = 1.14, 95% confidence interval = 0.76 to 1.71). No significant differential associations were observed for c-dMMRa/SBS15 (Ptrend = .41 for heterogeneity).

CONCLUSIONS

High alcohol consumption was associated with an increased incidence of CRC containing higher contributions of c-dMMRb/SBS26, suggesting that alcohol consumption may be involved in colorectal carcinogenesis through the DNA mismatch repair pathway.

Comprehensive investigation of the mutagenic potential of six pesticides classified by IARC as probably carcinogenic to humans

Pesticides are significant environmental pollutants, and many of them possess mutagenic potential, which is closely linked to carcinogenesis. Here we tested the mutagenicity of all six pesticides classified probably carcinogenic (Group 2A) by the International Agency of Research on Cancer: 4,4'-DDT, captafol, dieldrin, diazinon, glyphosate and malathion. Whole genome sequencing of TK6 human lymphoblastoid cell clones following 30-day exposure at subtoxic concentrations revealed a clear mutagenic effect of treatment with captafol or malathion when added at 200 nM or 100 μM initial concentrations, respectively. Each pesticide induced a specific base substitution mutational signature: captafol increased C to A mutations primarily, while malathion induced mostly C to T mutations. 4,4'-DDT, dieldrin, diazinon and glyphosate were not mutagenic. Whereas captafol induced chromosomal instability, H2A.X phosphorylation and cell cycle arrest in G2/M phase, all indicating DNA damage, malathion did not induce DNA damage markers or cell cycle alterations despite its mutagenic effect. Hypersensitivity of REV1 and XPA mutant DT40 chicken cell lines suggests that captafol induces DNA adducts that are bypassed by translesion DNA synthesis and are targets for nucleotide excision repair. The experimentally identified mutational signatures of captafol and malathion could shed light on the mechanism of action of these compounds. The signatures are potentially suitable for detecting past exposure in tumour samples, but the reanalysis of large cancer genome databases did not reveal any evidence of captafol or malathion exposure.

Pan-cancer mutational signature analysis of 111,711 targeted sequenced tumors using SATS

Tumor mutational signatures are informative for cancer diagnosis and treatment. However, targeted sequencing, commonly used in clinical settings, lacks specialized analytical tools and a dedicated catalogue of mutational signatures. Here, we introduce SATS, a scalable mutational signature analyzer for targeted sequencing data. SATS leverages tumor mutational burdens to identify and quantify signatures in individual tumors, overcoming the challenges of sparse mutations and variable gene panels. Validations across simulated data, pseudo-targeted sequencing data, and matched whole-genome and targeted sequencing samples show that SATS can accurately detect common mutational signatures and estimate their burdens. Applying SATS to 111,711 tumors from the AACR Project GENIE, we created a pan-cancer mutational signature catalogue specific to targeted sequencing. We further validated signatures in lung, breast and colorectal cancers using an additional 16,774 independent samples. This signature catalogue is a valuable resource for estimating signature burdens in individual targeted sequenced tumors, facilitating the integration of mutational signatures with clinical data.

Spatial molecular profiling of mixed invasive ductal and lobular breast cancers reveals heterogeneity in intrinsic molecular subtypes, oncogenic signatures, and mutations

Mixed invasive ductal and lobular carcinoma (MDLC) is a rare histologic subtype of breast cancer displaying both E-cadherin positive ductal and E-cadherin negative lobular morphologies within the same tumor, posing challenges with regard to anticipated clinical management. It remains unclear whether these distinct morphologies also have distinct biology and risk of recurrence. Our spatially resolved transcriptomic, genomic, and single-cell profiling revealed clinically significant differences between ductal and lobular tumor regions including distinct intrinsic subtype heterogeneity - e.g., MDLC with triple-negative breast cancer (TNBC) or basal ductal and estrogen receptor positive (ER+) luminal lobular regions, distinct enrichment of cell cycle arrest/senescence and oncogenic (ER and MYC) signatures, genetic and epigenetic CDH1 inactivation in lobular but not ductal regions, and single-cell ductal and lobular subpopulations with unique oncogenic signatures further highlighting intraregional heterogeneity. Altogether, we demonstrated that the intratumoral morphological/histological heterogeneity within MDLC is underpinned by intrinsic subtype and oncogenic heterogeneity which may result in prognostic uncertainty and therapeutic dilemma.

Pathologic complete response to KEYNOTE522 and HER2-directed therapy for synchronous TNBC and HER2+ breast cancer

Simultaneous presentation of two separate primary breast cancers of differing histology at initial diagnosis is an uncommon phenomenon; it is even rarer to find these pathologically distinct populations within the same biopsy. Here we report the case of a patient diagnosed with clearly demarcated, pathologically heterogenous triple negative breast cancer (TNBC) and HER2+ breast cancer that was treated with a hybrid chemoimmunotherapy regimen combining elements of Keynote-522 and a standard HER2-directed neoadjuvant regimen, yielding apathologic complete response by the time of surgery with no notable adverse events. Molecular analysis of the histologically distinct tumor populations confirmed molecular evidence of differential HER2 expression but also suggested clonal relatedness of the two tumor populations based upon mutational profile, with phenotypic divergence potentially resulting from copy number alterations in NF1. Overall, this case highlights a rare histologic phenomenon that was successfully treated by combining both TNBC and HER2 directed neoadjuvant therapies.

In silico analysis of DEL-1 and inflammation-related genes in lung squamous cell carcinoma

AIM

Twenty to thirty percent of non-small cell lung cancers (NSCLC) are caused by lung squamous cell carcinoma (LUSC), especially in smokers and there has been limited study previously evaluating the situation in terms of the genome and gene expression profile, which demonstrates the relationship among DEL-1, leucocyte recruitment, and pro-inflammatory cytokines in LUSC.

MATERIAL AND METHODS

In the current study, the m-RNA expression patterns and mutation profiles of our target genes, such as, pro-inflammatory cytokines, chemoattractant molecules, and DEL-1 genes, in 511 LUSC patients. To find the harmful mutations, the PolyPhen-2 and SNAP programs were employed. Not only gene expression was detected, but also survival analysis and correlation between DEL-1 and other target genes' expression levels were explored too.

RESULTS

Target genes such as, DEL-1, TNF, IL-18, IL-1, CXCL8, CXCL13, and IL-6 were found to have a total genetic anomaly carrying rate of 16.4%. Seven mutations were found, and two of those mutations have a pathogenic aspect. Deep deletion and gene amplification of the genetic anomalies were also observed. According to gene expression analysis results in the LUSC patient group; DEL-1 and IL-6 levels were significantly lower than those of the control group, whereas the CXCL13 level was found to be higher.

CONCLUSION

Findings of the current study revealed that, there is a significant role of DEL-1 in LUSC pathogenesis. Since present study is an in silico-centered study, this approach can give more insight on experimental studies. These events may support that one of the cancer improvement mechanisms depending on DEL-1 gene at the molecular level.

Genetic evolution of keratinocytes to cutaneous squamous cell carcinoma

We performed multi-omic profiling of epidermal keratinocytes, precancerous actinic keratoses, and squamous cell carcinomas to understand the molecular transitions during skin carcinogenesis. Single-cell mutational analyses showed that most keratinocytes in normal skin had lower mutation burdens than melanocytes and fibroblasts, however keratinocytes with TP53 or NOTCH1 mutations had substantially higher mutation burdens, suggesting that these mutations prime keratinocytes for transformation by increasing their mutation rate. Mutational profiling and spatial transcriptomics on squamous cell carcinomas adjacent to actinic keratoses revealed TERT promoter and CDKN2A mutations emerging in actinic keratoses, whereas additional mutations inactivating ARID2 and activating the MAPK-pathway delineated the transition to squamous cell carcinomas. Spatial variation in gene expression patterns was common in both tumor and immune cells, with high expression of checkpoint molecules at the invasive front of tumors. In conclusion, this study documents key events during the evolution of cutaneous squamous cell carcinoma.

Polymerase theta is a synthetic lethal target for killing Epstein-Barr virus lymphomas

Treatment options for Epstein-Barr virus (EBV)-cancers are limited, underscoring the need for new therapeutic approaches. We have previously shown that EBV-transformed cells and cancers lack homologous recombination (HR) repair, a prominent error-free pathway that repairs double-stranded DNA breaks; instead, EBV-transformed cells demonstrate genome-wide scars of the error-prone microhomology-mediated end joining (MMEJ) repair pathway. This suggests that EBV-cancers are vulnerable to synthetic lethal therapeutic approaches that target MMEJ repair. Indeed, we have previously found that targeting PARP, an enzyme that contributes to MMEJ, results in the death of EBV-lymphoma cells. With the emergence of clinical resistance to PARP inhibitors and the recent discovery of inhibitors of Polymerase theta (POLθ), the polymerase essential for MMEJ, we investigated the role of POLθ in EBV-lymphoma cells. We report that EBV-transformed cell lines, EBV-lymphoma cell lines, and EBV-lymphomas in AIDS patients demonstrate greater abundance of POLθ, driven by the EBV protein EBNA1, compared to EBV-uninfected primary lymphocytes and EBV-negative lymphomas from AIDS patients (a group that also abundantly expresses POLθ). We also find POLθ enriched at cellular DNA replication forks and exposure to the POLθ inhibitor Novobiocin impedes replication fork progress, impairs MMEJ-mediated repair of DNA double-stranded breaks, and kills EBV-lymphoma cells. Notably, cell killing is not due to Novobiocin-induced activation of the lytic/replicative phase of EBV. These findings support a role for POLθ not just in DNA repair but also DNA replication and as a therapeutic target in EBV-lymphomas and potentially other EBV-cancers as EBNA1 is expressed in all EBV-cancers.IMPORTANCEEpstein-Barr virus (EBV) contributes to ~2% of the global cancer burden. With a recent estimate of >200,000 deaths a year, identifying molecular vulnerabilities will be key to the management of these frequently aggressive and treatment-resistant cancers. Building on our earlier work demonstrating reliance of EBV-cancers on microhomology-mediated end-joining repair, we now report that EBV lymphomas and transformed B cell lines abundantly express the MMEJ enzyme POLθ that likely protects cellular replication forks and repairs replication-related cellular DNA breaks. Importantly also, we show that a newly identified POLθ inhibitor kills EBV-cancer cells, revealing a novel strategy to block DNA replication and repair of these aggressive cancers.

Mitochondrial DNA mosaicism in normal human somatic cells

Somatic cells accumulate genomic alterations with age; however, our understanding of mitochondrial DNA (mtDNA) mosaicism remains limited. Here we investigated the genomes of 2,096 clones derived from three cell types across 31 donors, identifying 6,451 mtDNA variants with heteroplasmy levels of ≳0.3%. While the majority of these variants were unique to individual clones, suggesting stochastic acquisition with age, 409 variants (6%) were shared across multiple embryonic lineages, indicating their origin from heteroplasmy in fertilized eggs. The mutational spectrum exhibited replication-strand bias, implicating mtDNA replication as a major mutational process. We evaluated the mtDNA mutation rate (5.0 × 10-8 per base pair) and a turnover frequency of 10-20 per year, which are fundamental components shaping the landscape of mtDNA mosaicism over a lifetime. The expansion of mtDNA-truncating mutations toward homoplasmy was substantially suppressed. Our findings provide comprehensive insights into the origins, dynamics and functional consequences of mtDNA mosaicism in human somatic cells.

Regulation, functional impact, and therapeutic targeting of APOBEC3A in cancer

Enzymes of the apolipoprotein B mRNA editing catalytic polypeptide like (APOBEC) family are cytosine deaminases that convert cytosine to uracil in DNA and RNA. Among these proteins, APOBEC3 sub-family members, APOBEC3A (A3A) and APOBEC3B (A3B), are prominent sources of mutagenesis in cancer cells. The aberrant expression of A3A and A3B in cancer cells leads to accumulation of mutations with specific single-base substitution (SBS) signatures, characterized by C→T and C→G changes, in a number of tumor types. In addition to fueling mutagenesis, A3A and A3B, particularly A3A, induce DNA replication stress, DNA damage, and chromosomal instability through their catalytic activities, triggering a range of cellular responses. Thus, A3A/B have emerged as key drivers of genome evolution during cancer development, contributing to tumorigenesis, tumor heterogeneity, and therapeutic resistance. Yet, the expression of A3A/B in cancer cells presents a cancer vulnerability that can be exploited therapeutically. In this review, we discuss the recent studies that shed light on the mechanisms regulating A3A expression and the impact of A3A in cancer. We also review recent advances in the development of A3A inhibitors and provide perspectives on the future directions of A3A research.

Genomic and immune determinants of resistance to daratumumab-based therapy in relapsed refractory multiple myeloma

Targeted immunotherapy combinations, including the anti-CD38 monoclonal antibody (MoAb) daratumumab, have shown promising results in patients with relapsed/refractory multiple myeloma (RRMM), leading to a considerable increase in progression-free survival. However, a large fraction of patients inevitably relapse. To understand this, we investigated 32 relapsed MM patients treated with daratumumab, lenalidomide, and dexamethasone (Dara-Rd; NCT03848676). We conducted an integrated analysis using whole-genome sequencing (WGS) and flow cytometry in patients with RRMM. WGS before and after treatment pinpointed genomic drivers associated with early progression, including RPL5 loss, APOBEC mutagenesis, and gain of function structural variants involving MYC and chromothripsis. Flow cytometry on 202 blood samples, collected every 3 months until progression for 31 patients, revealed distinct immune changes significantly impacting clinical outcomes. Progressing patients exhibited significant depletion of CD38-positive NK cells, persistence of T-cell exhaustion, and reduced depletion of regulatory T cells over time. These findings underscore the influence of immune composition and daratumumab-induced immune changes in promoting MM resistance. Integrating genomics and flow cytometry unveiled associations between adverse genomic features and immune patterns. Overall, this study sheds light on the intricate interplay between genomic complexity and the immune microenvironment driving resistance to Dara-Rd in patients with RRMM.

Epigenetic modulators provide a path to understanding disease and therapeutic opportunity

The discovery of epigenetic modulators (writers, erasers, readers, and remodelers) has shed light on previously underappreciated biological mechanisms that promote diseases. With these insights, novel biomarkers and innovative combination therapies can be used to address challenging and difficult to treat disease states. This review highlights key mechanisms that epigenetic writers, erasers, readers, and remodelers control, as well as their connection with disease states and recent advances in associated epigenetic therapies.

Timing of whole genome duplication is associated with tumor-specific MHC-II depletion in serous ovarian cancer

Whole genome duplication is frequently observed in cancer, and its prevalence in our prior analysis of end-stage, homologous recombination deficient high grade serous ovarian cancer (almost 80% of samples) supports the notion that whole genome duplication provides a fitness advantage under the selection pressure of therapy. Here, we therefore aim to identify potential therapeutic vulnerabilities in primary high grade serous ovarian cancer with whole genome duplication by assessing differentially expressed genes and pathways in 79 samples. We observe that MHC-II expression is lowest in tumors which have acquired whole genome duplication early in tumor evolution, and further demonstrate that reduced MHC-II expression occurs in subsets of tumor cells rather than in canonical antigen-presenting cells. Early whole genome duplication is also associated with worse patient survival outcomes. Our results suggest an association between the timing of whole genome duplication, MHC-II expression and clinical outcome in high grade serous ovarian cancer that warrants further investigation for therapeutic targeting.

Somatic CpG hypermutation is associated with mismatch repair deficiency in cancer

Somatic hypermutation in cancer has gained momentum with the increased use of tumour mutation burden as a biomarker for immune checkpoint inhibitors. Spontaneous deamination of 5-methylcytosine to thymine at CpG dinucleotides is one of the most ubiquitous endogenous mutational processes in normal and cancer cells. Here, we performed a systematic investigation of somatic CpG hypermutation at a pan-cancer level. We studied 30,191 cancer patients and 103 cancer types and developed an algorithm to identify somatic CpG hypermutation. Across cancer types, we observed the highest prevalence in paediatric leukaemia (3.5%), paediatric high-grade glioma (1.7%), and colorectal cancer (1%). We discovered germline variants and somatic mutations in the mismatch repair complex MutSα (MSH2-MSH6) as genetic drivers of somatic CpG hypermutation in cancer, which frequently converged on CpG sites and TP53 driver mutations. We further observe an association between somatic CpG hypermutation and response to immune checkpoint inhibitors. Overall, our study identified novel cancer types that display somatic CpG hypermutation, strong association with MutSα-deficiency, and potential utility in cancer immunotherapy.

Detection of human papillomavirus (HPV) in malignant melanoma

The most common type of melanoma is cutaneous melanoma (CM). The predominant mutational signature is that of ultraviolet radiation (UVR) exposure. The Cancer Genome Atlas (TCGA) molecular classification includes four major subtypes of CM based on common genetic alterations involving the following genes: BRAF, NRAS, and NF1, with a small fraction being "triple" wild-type. The two main signaling pathway abnormalities in CM are the mitogen-activated protein kinase (MAPK) pathway and the phosphoinositol-3-kinase (PI3K) pathway. Other less common types include mucosal melanomas (MM) and uveal melanoma (UM), which have a significantly different genomic landscape. Although few studies reported rare cases with HPV-positive (HPV+) melanoma, the clinicopathological and molecular characteristic of this entity has not been well-described. Among the 2084 melanoma cases queried at our institution, we identified seven patients diagnosed with HPV+ melanoma (prevalence 0.03 %), including five instances of CM and two of MM. The majority of cases were positive for HPV16 (n = 6). Most of the patients were elderly and with advanced disease (n = 6), although this finding may be attributed to the relative frequency of our institution testing advanced-stage tumors. Histologically, most cases showed high degree of pleomorphism and high mitotic count (5 or more mitoses/mm2) (n = 6). UVR signature was present in the CM, but not in the MM cases. Alterations in either MAPK and/or PI3K pathways were detected in the majority of cases (n = 6). The most common genetic abnormalities detected in this study occurred in the TERT promoter (TERTp) (n = 5), a finding that has been reported to be associated with aggressive disease. Our data shows that while HPV+ melanoma is rare, identifying this disease entity could help guide therapy given the demonstrated genomic alterations.

Selective pressures of platinum compounds shape the evolution of therapy-related myeloid neoplasms

Therapy-related myeloid neoplasms (t-MN) arise as a complication of chemo- and/or radiotherapy. Although t-MN can occur both in adult and childhood cancer survivors, the mechanisms driving therapy-related leukemogenesis likely vary across different ages. Chemotherapy is thought to induce driver mutations in children, whereas in adults pre-existing mutant clones are selected by the exposure. However, selective pressures induced by chemotherapy early in life are less well studied. Here, we use single-cell whole genome sequencing and phylogenetic inference to show that the founding cell of t-MN in children starts expanding after cessation of platinum exposure. In patients with Li-Fraumeni syndrome, characterized by a germline TP53 mutation, we find that the t-MN already expands during treatment, suggesting that platinum-induced growth inhibition is TP53-dependent. Our results demonstrate that germline aberrations can interact with treatment exposures in inducing t-MN, which is important for the development of more targeted, patient-specific treatment regimens and follow-up.

Potential Role of APOBEC3 Family Proteins in SARS-CoV-2 Replication

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has acquired multiple mutations since its emergence. Analyses of the SARS-CoV-2 genomes from infected patients exhibit a bias toward C-to-U mutations, which are suggested to be caused by the apolipoprotein B mRNA editing enzyme polypeptide-like 3 (APOBEC3, A3) cytosine deaminase proteins. However, the role of A3 enzymes in SARS-CoV-2 replication remains unclear. To address this question, we investigated the effect of A3 family proteins on SARS-CoV-2 replication in the myeloid leukemia cell line THP-1 lacking A3A to A3G genes. The Wuhan, BA.1, and BA.5 variants had comparable viral replication in parent and A3A-to-A3G-null THP-1 cells stably expressing angiotensin-converting enzyme 2 (ACE2) protein. On the other hand, the replication and infectivity of these variants were abolished in A3A-to-A3G-null THP-1-ACE2 cells in a series of passage experiments over 20 days. In contrast to previous reports, we observed no evidence of A3-induced SARS-CoV-2 mutagenesis in the passage experiments. Furthermore, our analysis of a large number of publicly available SARS-CoV-2 genomes did not reveal conclusive evidence for A3-induced mutagenesis. Our studies suggest that A3 family proteins can positively contribute to SARS-CoV-2 replication; however, this effect is deaminase-independent.

Whole genome sequencing refines stratification and therapy of patients with clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney cancer, but a comprehensive description of its genomic landscape is lacking. We report the whole genome sequencing of 778 ccRCC patients enrolled in the 100,000 Genomes Project, providing for a detailed description of the somatic mutational landscape of ccRCC. We identify candidate driver genes, which as well as emphasising the major role of epigenetic regulation in ccRCC highlight additional biological pathways extending opportunities for therapeutic interventions. Genomic characterisation identified patients with divergent clinical outcome; higher number of structural copy number alterations associated with poorer prognosis, whereas VHL mutations were independently associated with a better prognosis. The observations that higher T-cell infiltration is associated with better overall survival and that genetically predicted immune evasion is not common supports the rationale for immunotherapy. These findings should inform personalised surveillance and treatment strategies for ccRCC patients.

Detecting HRD in whole-genome and whole-exome sequenced breast and ovarian cancers

Breast and ovarian cancers harboring homologous recombination deficiency (HRD) are sensitive to PARP inhibitors and platinum chemotherapy. Conventionally, detecting HRD involves screening for defects in BRCA1, BRCA2, and other relevant genes. Recent analyses have shown that HRD cancers exhibit characteristic mutational patterns due to the activities of HRD-associated mutational signatures. At least three machine learning tools exist for detecting HRD based on mutational patterns. Here, using sequencing data from 1,043 breast and 182 ovarian cancers, we trained Homologous Recombination Proficiency Profiler (HRProfiler), a machine learning method for detecting HRD using six mutational features. HRProfiler's performance is assessed against prior approaches using additional independent datasets of 417 breast and 115 ovarian cancers, including retrospective data from a clinical trial involving patients treated with PARP inhibitors. Our results demonstrate that HRProfiler is the only tool that robustly and consistently predicts clinical response from whole-exome sequenced breast and ovarian cancers.

CanCellVar: A database for single-cell variants map in human cancer

Numerous variants, including both single-nucleotide variants (SNVs) in DNA and A>G RNA edits in mRNA as essential drivers of cellular proliferation and tumorigenesis, are commonly associated with cancer progression and growth. Thus, mining and summarizing single-cell variants will provide a refined and higher-resolution view of cancer and further contribute to precision medicine. Here, we established a database, CanCellVar, which aims to provide and visualize the comprehensive atlas of single-cell variants in tumor microenvironment. The current CanCellVar identified ∼3 million variants (∼1.4 million SNVs and ∼1.4 million A>G RNA edits) involved in 2,754,531 cells of 5 major cell types across 37 cancer types. CanCellVar provides the basic annotation information as well as cellular and molecular function properties of variants. In addition, the clinical relevance of variants can be obtained including tumor grade, treatment, metastasis, and others. Several flexible tools were also developed to aid retrieval and to analyze cell-cell interactions, gene expression, cell-development trajectories, regulation, and molecular structure affected by variants. Collectively, CanCellVar will serve as a valuable resource for investigating the functions and characteristics of single-cell variations and their roles in human tumor evolution and treatment.

Uncovering molecular features driving lung adenocarcinoma heterogeneity in patients who formerly smoked

BACKGROUND

An increasing proportion of lung adenocarcinoma (LUAD) occurs in patients even after they have stopped smoking. Here, we aimed to determine whether tobacco smoking induced changes across LUADs from patients who formerly smoked correspond to different biological and clinical factors.

METHODS

Random forest models (RFs) were trained utilizing a smoking associated signature developed from differentially expressed genes between LUAD patients who had never smoked (NS) or currently smoked (CS) from TCGA (n = 193) and BCCA (n = 69) cohorts. The RFs were subsequently applied to 299 and 131 formerly smoking patients from TCGA and MSKCC cohorts, respectively. FS were RF-classified as either CS-like or NS-like and associations with patient characteristics, biological features, and clinical outcomes were determined.

RESULTS

We elucidated a 123 gene signature that robustly classified NS and CS in both RNA-seq (AUC = 0.85) and microarray (AUC = 0.92) validation test sets. The RF classified 213 patients who had formerly smoked as CS-like and 86 as NS-like from the TCGA cohort. CS-like and NS-like status in formerly smoking patients correlated poorly with patient characteristics but had substantially different biological features including tumor mutational burden, number of mutations, mutagenic signatures and immune cell populations. NS-like formerly smoking patients had 17.5 months and 18.6 months longer overall survival than CS-like patients from the TCGA and MSKCC cohorts, respectively.

CONCLUSIONS

Patients who had formerly smoked with LUAD harbor heterogeneous tumor biology. These patients can be divided by smoking induced gene expression to inform prognosis and underlying biological characteristics for treatment selection.

Multi-scale signaling and tumor evolution in high-grade gliomas

Although genomic anomalies in glioblastoma (GBM) have been well studied for over a decade, its 5-year survival rate remains lower than 5%. We seek to expand the molecular landscape of high-grade glioma, composed of IDH-wildtype GBM and IDH-mutant grade 4 astrocytoma, by integrating proteomic, metabolomic, lipidomic, and post-translational modifications (PTMs) with genomic and transcriptomic measurements to uncover multi-scale regulatory interactions governing tumor development and evolution. Applying 14 proteogenomic and metabolomic platforms to 228 tumors (212 GBM and 16 grade 4 IDH-mutant astrocytoma), including 28 at recurrence, plus 18 normal brain samples and 14 brain metastases as comparators, reveals heterogeneous upstream alterations converging on common downstream events at the proteomic and metabolomic levels and changes in protein-protein interactions and glycosylation site occupancy at recurrence. Recurrent genetic alterations and phosphorylation events on PTPN11 map to important regulatory domains in three dimensions, suggesting a central role for PTPN11 signaling across high-grade gliomas.

Resistance mechanisms of EGFR tyrosine kinase inhibitors, in EGFR exon 20 insertion-mutant lung cancer

BACKGROUND

Mobocertinib, an EGFR exon 20 insertion (Ex20ins)-specific tyrosine kinase inhibitor has been used for treatment of advanced/metastatic EGFR Ex20ins-mutant non-small cell lung cancer (NSCLC). However, resistance mechanisms to EGFR Ex20ins-specific inhibitors and the efficacy of subsequent amivantamab treatment is unknown.

METHODS

To investigate resistance mechanisms, tissue and cfDNA samples were collected before treatment initiation and upon development of resistance from NSCLC patients with EGFR Ex20ins mutations received mobocertinib, poziotinib, and amivantamab treatments. Genetic alterations were analyzed using whole-genome and targeted sequencing, and in vitro resistant cell lines were generated for validation.

RESULTS

EGFR amplification (n = 6, including 2 broad copy number gain) and EGFR secondary mutation (n = 3) were observed at the resistance of mobocertinib. One patient had both EGFR secondary mutation and high EGFR focal amplification. In vitro models harboring EGFR alterations were constructed to validate resistance mechanisms and identify overcoming strategies to resistance. Acquired EGFR-dependent alterations were found to mediate resistance to mobocertinib in patients and in vitro models. Furthermore, two of six patients who received sequential amivantamab followed by an EGFR tyrosine kinase inhibitor had MET amplification and showed partial response.

CONCLUSIONS

Our study revealed EGFR-dependent and -independent mechanisms of mobocertinib resistance in patients with advanced EGFR Ex20ins-mutant NSCLC.

Implications of noncoding regulatory functions in the development of insulinomas

Insulinomas are rare neuroendocrine tumors arising from pancreatic β cells, characterized by aberrant proliferation and altered insulin secretion, leading to glucose homeostasis failure. With the aim of uncovering the role of noncoding regulatory regions and their aberrations in the development of these tumors, we coupled epigenetic and transcriptome profiling with whole-genome sequencing. As a result, we unraveled somatic mutations associated with changes in regulatory functions. Critically, these regions impact insulin secretion, tumor development, and epigenetic modifying genes, including polycomb complex components. Chromatin remodeling is apparent in insulinoma-selective domains shared across patients, containing a specific set of regulatory sequences dominated by the SOX17 binding motif. Moreover, many of these regions are H3K27me3 repressed in β cells, suggesting that tumoral transition involves derepression of polycomb-targeted domains. Our work provides a compendium of aberrant cis-regulatory elements affecting the function and fate of β cells in their progression to insulinomas and a framework to identify coding and noncoding driver mutations.

Targeted Next Generation Sequencing molecular profiling and its clinical application in adrenocortical cancer

OBJECTIVE

Adrenal cortical carcinoma (ACC) is a rare malignancy with a generally poor but heterogeneous prognosis, especially depending on the tumour stage at diagnosis. Identification of somatic gene alterations combined with clinical/histopathological evaluation of the tumour can help improve prognostication. We applied a simplified targeted-Next-Generation Sequencing (NGS) panel to characterise the mutational profiles of ACCs, providing potentially relevant information for better patient management.

DESIGN AND METHODS

Thirty frozen tumour specimens from a local ACC series were retrospectively analysed by a custom-NGS panel (CDKN2A, CTNNB1, DAXX, MED12, NF1, PRKAR1A, RB1, TERT, TP53, ZNRF3) to detect somatic prioritised single-nucleotide variants. This cohort was integrated with 86 patients from the ACC-TCGA series bearing point-mutations in the same genes and their combinations identified by our panel. Primary endpoints of the analysis on the total cohort (113 patients) were overall survival (OS) and progression-free survival (PFS), and hazard ratio (HR) for the different alterations grouped by the signalling pathways/combinations affected.

RESULTS

Different PFS, OS, and HR were associated to the different pathways/combinations, being NF1 + TP53 and Wnt/β-catenin + Rb/p53 combined mutations the most deleterious, with a statistical significance for progression HR which is retained only in low-(I/II) stages-NF1 + TP53 combination: HR = 2.96[1.01-8.69] and HR = 13.23[3.15-55.61], all and low stages, respectively; Wnt/β-catenin + Rb/p53 combined pathways: HR = 6.47[2.54-16.49] and HR = 16.24[3.87-68.00], all and low-stages, respectively.

CONCLUSIONS

A simplified targeted-NGS approach seems the best routinely applicable first step towards somatic genetic characterisation of ACC for prognostic assessment. This approach proved to be particularly promising in low-stage cases, suggesting the need for more stringent surveillance and personalised treatment.

The genomic landscape of breast and non-breast cancers from individuals with germline CHEK2 deficiency

CHEK2 is considered to be involved in homologous recombination repair (HRR). Individuals who have germline pathogenic variants (gPVs) in CHEK2 are at increased risk to develop breast cancer and likely other primary cancers. PARP inhibitors (PARPi) have been shown to be effective in the treatment of cancers that present with HRR deficiency-for example, caused by inactivation of BRCA1/2. However, clinical trials have shown little to no efficacy of PARPi in patients with CHEK2 gPVs. Here, we show that both breast and non-breast cancers from individuals who have biallelic gPVs in CHEK2 (germline CHEK2 deficiency) do not present with molecular profiles that fit with HRR deficiency. This finding provides a likely explanation why PARPi therapy is not successful in the treatment of CHEK2-deficient cancers.

Replication-Independent ICL Repair: From Chemotherapy to Cell Homeostasis

Interstrand crosslinks (ICLs) are a type of covalent lesion that can prevent transcription and replication by inhibiting DNA strand separation and instead trigger cell death. ICL inducing compounds are commonly used as chemotherapies due to their effectiveness in inhibiting cell proliferation. Naturally occurring crosslinking agents formed from metabolic processes can also pose a challenge to genome stability especially in slowly or non-dividing cells. Cells maintain a variety of ICL repair mechanisms to cope with this stressor within and outside the S phase of the cell cycle. Here, we discuss the mechanisms of various replication-independent ICL repair pathways and how crosslink repair efficiency is tied to aging and disease.

Liquid-liquid phase separation in diseases

Liquid-liquid phase separation (LLPS), an emerging biophysical phenomenon, can sequester molecules to implement physiological and pathological functions. LLPS implements the assembly of numerous membraneless chambers, including stress granules and P-bodies, containing RNA and protein. RNA-RNA and RNA-protein interactions play a critical role in LLPS. Scaffolding proteins, through multivalent interactions and external factors, support protein-RNA interaction networks to form condensates involved in a variety of diseases, particularly neurodegenerative diseases and cancer. Modulating LLPS phenomenon in multiple pathogenic proteins for the treatment of neurodegenerative diseases and cancer could present a promising direction, though recent advances in this area are limited. Here, we summarize in detail the complexity of LLPS in constructing signaling pathways and highlight the role of LLPS in neurodegenerative diseases and cancers. We also explore RNA modifications on LLPS to alter diseases progression because these modifications can influence LLPS of certain proteins or the formation of stress granules, and discuss the possibility of proper manipulation of LLPS process to restore cellular homeostasis or develop therapeutic drugs for the eradication of diseases. This review attempts to discuss potential therapeutic opportunities by elaborating on the connection between LLPS, RNA modification, and their roles in diseases.

Passive Smoking-Induced Mutagenesis as a Promoter of Lung Carcinogenesis

INTRODUCTION

The International Agency for Research on Cancer has classified passive smoking (PS) or secondhand smoke exposure as a group 1 carcinogen linked to lung cancer. However, in contrast to active smoking, the mutagenic properties of PS remain unclear.

METHODS

A consecutive cohort of 564 lung adenocarcinoma samples from female never-smokers, who provided detailed information about their exposure to PS during adolescence and in their thirties through a questionnaire, was prepared. Of these, all 291 cases for whom frozen tumor tissues were available were subjected to whole exome sequencing to estimate tumor mutational burden, and the top 84 cases who were exposed daily, or not, to PS during adolescence, in their thirties or in both periods, were further subjected to whole genome sequencing.

RESULTS

A modest yet statistically significant increase in tumor mutational burden was observed in the group exposed to PS compared with the group not exposed to PS (median values = 1.44 versus 1.29 per megabase, respectively; p = 0.020). Instead of inducing driver oncogene mutations, PS-induced substantial subclonal mutations exhibiting APOBEC-type signatures, including SMAD4 and ADGRG6 hotspot mutations. A polymorphic APOBEC3A/3B allele-specific to the Asian population that leads to up-regulated expression of APOBEC3A accentuated the mutational load in individuals exposed daily to PS during adolescence.

CONCLUSIONS

This study reveals that PS-induced mutagenesis can promote lung carcinogenesis. The APOBEC3A/3B polymorphism may serve as a biomarker for identifying passive nonsmoking individuals at high risk of developing lung cancer.

Deconstructing Intratumoral Heterogeneity through Multiomic and Multiscale Analysis of Serial Sections

Tumors may contain billions of cells, including distinct malignant clones and nonmalignant cell types. Clarifying the evolutionary histories, prevalence, and defining molecular features of these cells is essential for improving clinical outcomes, since intratumoral heterogeneity provides fuel for acquired resistance to targeted therapies. Here we present a statistically motivated strategy for deconstructing intratumoral heterogeneity through multiomic and multiscale analysis of serial tumor sections (MOMA). By combining deep sampling of IDH-mutant astrocytomas with integrative analysis of single-nucleotide variants, copy-number variants, and gene expression, we reconstruct and validate the phylogenies, spatial distributions, and transcriptional profiles of distinct malignant clones. By genotyping nuclei analyzed by single-nucleus RNA-seq for truncal mutations, we further show that commonly used algorithms for identifying cancer cells from single-cell transcriptomes may be inaccurate. We also demonstrate that correlating gene expression with tumor purity in bulk samples can reveal optimal markers of malignant cells and use this approach to identify a core set of genes that are consistently expressed by astrocytoma truncal clones, including AKR1C3, whose expression is associated with poor outcomes in several types of cancer. In summary, MOMA provides a robust and flexible strategy for precisely deconstructing intratumoral heterogeneity and clarifying the core molecular properties of distinct cellular populations in solid tumors.

Quantifying DNA replication speeds in single cells by scEdU-seq

In a human cell, thousands of replication forks simultaneously coordinate duplication of the entire genome. The rate at which this process occurs might depend on the epigenetic state of the genome and vary between, or even within, cell types. To accurately measure DNA replication speeds, we developed single-cell 5-ethynyl-2'-deoxyuridine sequencing to detect nascent replicated DNA. We observed that the DNA replication speed is not constant but increases during S phase of the cell cycle. Using genetic and pharmacological perturbations we were able to alter this acceleration of replication and conclude that DNA damage inflicted by the process of transcription limits the speed of replication during early S phase. In late S phase, during which less-transcribed regions replicate, replication accelerates and approaches its maximum speed.

The cytidine deaminase APOBEC3A regulates nucleolar function to promote cell growth and ribosome biogenesis

Cancer initiates as a consequence of genomic mutations and its subsequent progression relies in part on increased production of ribosomes to maintain high levels of protein synthesis for unchecked cell growth. Recently, cytidine deaminases have been uncovered as sources of mutagenesis in cancer. In an attempt to form a connection between these 2 cancer driving processes, we interrogated the cytidine deaminase family of proteins for potential roles in human ribosome biogenesis. We identified and validated APOBEC3A and APOBEC4 as novel ribosome biogenesis factors through our laboratory's established screening platform for the discovery of regulators of nucleolar function in MCF10A cells. Through siRNA depletion experiments, we highlight APOBEC3A's requirement in making ribosomes and specific role within the processing and maturation steps that form the large subunit 5.8S and 28S ribosomal (r)RNAs. We demonstrate that a subset of APOBEC3A resides within the nucleolus and associates with critical ribosome biogenesis factors. Mechanistic insight was revealed by transient overexpression of both wild-type and a catalytically dead mutated APOBEC3A, which both increase cell growth and protein synthesis. Through an innovative nuclear RNA sequencing methodology, we identify only modest predicted APOBEC3A C-to-U target sites on the pre-rRNA and pre-mRNAs. Our work reveals a potential direct role for APOBEC3A in ribosome biogenesis likely independent of its editing function. More broadly, we found an additional function of APOBEC3A in cancer pathology through its function in ribosome biogenesis, expanding its relevance as a target for cancer therapeutics.

Comprehensive genomic and transcriptomic characterization of high-grade gastro-entero-pancreatic neoplasms

BACKGROUND

High-grade gastro-entero-pancreatic neoplasms (HG GEP-NENs) can be stratified according to their morphology and Ki-67 values into three prognostic classes: neuroendocrine tumors grade 3 (NETs G3), neuroendocrine carcinomas with Ki-67 < 55% (NECs <55) and NECs with Ki-67 ≥ 55% (NECs ≥55).

METHODS

We analyzed a cohort of 49 HG GEP-NENs by targeted Next-Generation Sequencing (TrueSight Oncology 500), RNA-seq, and immunohistochemistry for p53, Rb1, SSTR-2A, and PD-L1.

RESULTS

Frequent genomic alterations affected TP53 (26%), APC (20%), KRAS and MEN1 (both 11%) genes. NET G3 were enriched in MEN1 (p = 0.02) mutations, while both NECs groups were enriched in TP53 (p = 0.001), APC (p = 0.002) and KRAS (p = 0.02) mutations and tumors with TMB ≥ 10 muts/Mb (p = 0.01). No differentially expressed (DE) gene was found between NECs <55% and NECs ≥55%, while 1129 DE genes were identified between NET G3 and NECs. A slight enrichment of CD4+ and CD8+ T cells in NECs and of cancer-associated fibroblasts and macrophages (M2-like) in NET G3. Multivariate analysis identified histologic type and Rb1 loss as independent prognostic factors for overall survival.

CONCLUSIONS

This study showed that GEP-NET G3 and GEP-NECs exhibit clear genomic and transcriptomic differences, differently from GEP-NECs <55% and GEP-NECs ≥55%, and provided molecular findings with prognostic and potentially predictive value.

The mutagenic consequences of defective DNA repair

Multiple separate repair mechanisms safeguard the genome against various types of DNA damage, and their failure can increase the rate of spontaneous mutagenesis. The malfunction of distinct repair mechanisms leads to genomic instability through different mutagenic processes. For example, defective mismatch repair causes high base substitution rates and microsatellite instability, whereas homologous recombination deficiency is characteristically associated with deletions and chromosome instability. This review presents a comprehensive collection of all mutagenic phenotypes associated with the loss of each DNA repair mechanism, drawing on data from a variety of model organisms and mutagenesis assays, and placing greatest emphasis on systematic analyses of human cancer datasets. We describe the latest theories on the mechanism of each mutagenic process, often explained by reliance on an alternative repair pathway or the error-prone replication of unrepaired, damaged DNA. Aided by the concept of mutational signatures, the genomic phenotypes can be used in cancer diagnosis to identify defective DNA repair pathways.

Clonal expansion in normal tissues

Cancer originates from a single ancestral cell that acquires a driver mutation, which confers a growth or survival advantage, followed by the acquisition of additional driver mutations by descendant cells. Recently, it has become evident that somatic cell mutations accumulate in normal tissues with aging and exposure to environmental factors, such as alcohol, smoking, and UV rays, increases the mutation rate. Clones harboring driver mutations expand with age, leading to tissue remodeling. Lineage analysis of myeloproliferative neoplasms and der(1;16)-positive breast cancer revealed that driver mutations were acquired early in our lives and that the development of cancer takes decades, unveiling the previously unknown early process of cancer development. Evidence that clonal hematopoiesis affects various diseases, including nonneoplastic diseases, highlights the potential role of the identification and functional analysis of mutated clones in unraveling unknown pathologies. In this review, we summarize the recent updates on clonal expansion in normal tissues and the natural history of cancer revealed through lineage analysis of noncancerous and cancerous tissues.

Impact of genomic and epigenomic alterations of multigene on a multicancer pedigree

BACKGROUND

Germline mutations have been identified in a small number of hereditary cancers, but the genetic predisposition for many familial cancers remains to be elucidated.

METHODS

This study identified a Chinese pedigree that presented different cancers (breast cancer, BRCA; adenocarcinoma of the esophagogastric junction, AEG; and B-cell acute lymphoblastic leukemia, B-ALL) in each of the three generations. Whole-genome sequencing and whole-exome sequencing were performed on peripheral blood or bone marrow and cancer biopsy samples. Whole-genome bisulfite sequencing was conducted on the monozygotic twin brothers, one of whom developed B-ALL.

RESULTS

According to the ACMG guidelines, bioinformatic analysis of the genome sequencing revealed 20 germline mutations, particularly mutations in the DNAH11 (c.9463G > A) and CFH (c.2314G > A) genes that were documented in the COSMIC database and validated by Sanger sequencing. Forty-one common somatic mutated genes were identified in the cancer samples, displaying the same type of single nucleotide substitution Signature 5. Meanwhile, hypomethylation of PLEK2, MRAS, and RXRA as well as hypermethylation of CpG island associated with WT1 was shown in the twin with B-ALL.

CONCLUSIONS

These findings reveal genomic alterations in a pedigree with multiple cancers. Mutations found in the DNAH11, CFH genes, and other genes predispose to malignancies in this family. Dysregulated methylation of WT1, PLEK2, MRAS, and RXRA in the twin with B-ALL increases cancer susceptibility. The similarity of the somatic genetic changes among the three cancers indicates a hereditary impact on the pedigree. These familial cancers with germline and somatic mutations, as well as epigenomic alterations, represent a common molecular basis for many multiple cancer pedigrees.