Targeting of histone methyltransferase DOT1L plays a dual role in chemosensitization of retinoblastoma cells and enhances the efficacy of chemotherapy

DOT1L maintains NK cell phenotype and function for optimal tumor control

Histone methyltransferases (HMTs) are crucial in gene regulation and function, yet their role in natural killer (NK) cell biology within the tumor microenvironment (TME) remains largely unknown. We demonstrate that the HMT DOT1L limits NK cell conversion to CD49a+ CD49b+ intILC1, a subset that can be observed in the TME in response to stimulation with transforming growth factor (TGF)-β and is correlated with impaired tumor control. Deleting Dot1l in NKp46-expressing cells reveals its pivotal role in maintaining NK cell phenotype and function. Loss of DOT1L skews NK cells toward intILC1s even in the absence of TGF-β. Transcriptionally, DOT1L-null NK cells closely resemble intILC1s and ILC1s, correlating with altered NK cell responses and impaired solid tumor control. These findings deepen our understanding of NK cell biology and could inform approaches to prevent NK cell conversion to intILC1s in adoptive NK cell therapies for cancer.

Deciphering metabolic heterogeneity in retinoblastoma unravels the role of monocarboxylate transporter 1 in tumor progression

BACKGROUND

Tumors exhibit metabolic heterogeneity, influencing cancer progression. However, understanding metabolic diversity in retinoblastoma (RB), the primary intraocular malignancy in children, remains limited.

METHODS

The metabolic landscape of RB was constructed based on single-cell transcriptomic sequencing from 11 RB and 5 retina samples. Various analyses were conducted, including assessing overall metabolic activity, metabolic heterogeneity, and the correlation between hypoxia and metabolic pathways. Additionally, the expression pattern of the monocarboxylate transporter (MCT) family in different cell clusters was examined. Validation assays of MCT1 expression and function in RB cell lines were performed. The therapeutic potential of targeting MCT1 was evaluated using an orthotopic xenograft model. A cohort of 47 RB patients was analyzed to evaluate the relationship between MCT1 expression and tumor invasion.

RESULTS

Distinct metabolic patterns in RB cells, notably increased glycolysis, were identified. This metabolic heterogeneity correlated closely with hypoxia. MCT1 emerged as the primary monocarboxylate transporter in RB cells. Disrupting MCT1 altered cell viability and energy metabolism. In vivo studies using the MCT1 inhibitor AZD3965 effectively suppressed RB tumor growth. Additionally, a correlation between MCT1 expression and optic nerve invasion in RB samples suggested prognostic implications.

CONCLUSIONS

This study enhances our understanding of RB metabolic characteristics at the single-cell level, highlighting the significance of MCT1 in RB pathogenesis. Targeting MCT1 holds promise as a therapeutic strategy for combating RB, with potential prognostic implications.

Therapeutic Strategies for RB1-Deficient Cancers: Intersecting Gene Regulation and Targeted Therapy

The retinoblastoma (RB) transcriptional corepressor 1 (RB1) is a critical tumor suppressor gene, governing diverse cellular processes implicated in cancer biology. Dysregulation or deletion in RB1 contributes to the development and progression of various cancers, making it a prime target for therapeutic intervention. RB1's canonical function in cell cycle control and DNA repair mechanisms underscores its significance in restraining aberrant cell growth and maintaining genomic stability. Understanding the complex interplay between RB1 and cellular pathways is beneficial to fully elucidate its tumor-suppressive role across different cancer types and for therapeutic development. As a result, investigating vulnerabilities arising from RB1 deletion-associated mechanisms offers promising avenues for targeted therapy. Recently, several findings highlighted multiple methods as a promising strategy for combating tumor growth driven by RB1 loss, offering potential clinical benefits in various cancer types. This review summarizes the multifaceted role of RB1 in cancer biology and its implications for targeted therapy.

Antitumoral Potential of the Histone Demethylase Inhibitor GSK-J4 in Retinoblastoma

Purpose

The purpose of this study was to investigate the antitumor effects of GSK-J4 on retinoblastoma, as well as its related biological functions and molecular mechanisms.

Methods

The antitumor effect of GSK-J4 on retinoblastoma was evaluated by in vitro and in vivo assays. CCK-8, EdU incorporation, and soft agar colony formation assays were performed to examine the effect of GSK-J4 on cell proliferation. Flow cytometry was used to evaluate the effect of GSK-J4 on the cell cycle and apoptosis. RNA-seq and Western blotting were conducted to explore the molecular mechanisms of GSK-J4. An orthotopic xenograft model was established to determine the effect of GSK-J4 on tumor growth.

Results

GSK-J4 significantly inhibited retinoblastoma cell proliferation both in vitro and in vivo, arrested the cell cycle at G2/M phase, and induced apoptosis. Mechanistically, GSK-J4 may suppress retinoblastoma cell growth by regulating the PI3K/AKT/NF-κB signaling pathway.

Conclusions

The antitumor effects of GSK-J4 were noticeable in retinoblastoma and were at least partially mediated by PI3K/AKT/NF-κB pathway suppression. Our study provides a novel strategy for the treatment of retinoblastoma.

Heterogeneous Expression Patterns of the Minichromosome Maintenance Complex Members in Retinoblastoma Unveil Its Clinical Significance

Purpose

To explore the expression patterns and clinical significance of minichromosome maintenance (MCM) complex members in retinoblastoma (RB).

Methods

Single-cell RNA sequencing datasets from five normal retina, six intraocular, and five extraocular RB samples were integrated to characterize the expression patterns of MCM complex members at the single-cell level. Western blot and quantitative PCR were used to detect the expression of MCM complex members in RB cell lines. Immunohistochemistry was conducted to validate the expression of MCM complex members in RB patient samples and a RB mouse model.

Results

The expression of MCM2-7 is increased in RB tissue, with MCM2/3/7 showing particularly higher levels in extraocular RB. MCM3/7 are abundantly detected in cell types associated with oncogenesis. Both mRNA and protein levels of MCM3/4/6/7 are increased in RB cell lines. Immunohistochemistry further confirmed the elevated expression of MCM3 in extraocular RB, with MCM6 being the most abundantly expressed MCM in RB.

Conclusions

The distinct MCM expression patterns across various RB cell types suggest diverse functional roles, offering valuable insights for targeted therapeutic strategies. The upregulation of MCM3, MCM4, MCM6, and MCM7 in RB, with a specific emphasis on MCM6 as a notable marker, highlights their potential significance.

Novel insights into histone lysine methyltransferases in cancer therapy: From epigenetic regulation to selective drugs

The reversible and precise temporal and spatial regulation of histone lysine methyltransferases (KMTs) is essential for epigenome homeostasis. The dysregulation of KMTs is associated with tumor initiation, metastasis, chemoresistance, invasiveness, and the immune microenvironment. Therapeutically, their promising effects are being evaluated in diversified preclinical and clinical trials, demonstrating encouraging outcomes in multiple malignancies. In this review, we have updated recent understandings of KMTs' functions and the development of their targeted inhibitors. First, we provide an updated overview of the regulatory roles of several KMT activities in oncogenesis, tumor suppression, and immune regulation. In addition, we summarize the current targeting strategies in different cancer types and multiple ongoing clinical trials of combination therapies with KMT inhibitors. In summary, we endeavor to depict the regulation of KMT-mediated epigenetic landscape and provide potential epigenetic targets in the treatment of cancers.

Targeted Epigenetic Interventions in Cancer with an Emphasis on Pediatric Malignancies

Over the past two decades, novel hallmarks of cancer have been described, including the altered epigenetic landscape of malignant diseases. In addition to the methylation and hyd-roxymethylation of DNA, numerous novel forms of histone modifications and nucleosome remodeling have been discovered, giving rise to a wide variety of targeted therapeutic interventions. DNA hypomethylating drugs, histone deacetylase inhibitors and agents targeting histone methylation machinery are of distinguished clinical significance. The major focus of this review is placed on targeted epigenetic interventions in the most common pediatric malignancies, including acute leukemias, brain and kidney tumors, neuroblastoma and soft tissue sarcomas. Upcoming novel challenges include specificity and potential undesirable side effects. Different epigenetic patterns of pediatric and adult cancers should be noted. Biological significance of epigenetic alterations highly depends on the tissue microenvironment and widespread interactions. An individualized treatment approach requires detailed genetic, epigenetic and metabolomic evaluation of cancer. Advances in molecular technologies and clinical translation may contribute to the development of novel pediatric anticancer treatment strategies, aiming for improved survival and better patient quality of life.

Emerging therapeutic targets for retinoblastoma

INTRODUCTION

Retinoblastoma (Rb) is an early childhood intraocular tumor of the retina and is managed by multimodal therapeutic approaches. Recent advanced targeted delivery of chemotherapeutic drugs to the eye has improved the possibility of globe salvage. However, enucleation is inevitable for advanced and recurrent Rb. The cumulative knowledge of identification of newer molecular biology tools, exosomal cargo, role of cancer stem cells (CSCs), and its microenvironment in the progression of the diseases warrants a relook at the traditional treatment protocol and explore the feasibility of targeted therapies.

AREAS COVERED

This review covers Rb pathobiology, novel molecular-targeted therapeutics, and strategies targeting Rb CSCs and provides an update on potential therapeutic targets such as second messengers and exosomal cargo.

EXPERT OPINION

The emergence of early diagnosis and multimodality treatment protocols have significantly improved the clinical outcome of children with advanced Rb; however, the problem of tumor recurrence has not yet been overcome. Improved understanding of the molecular pathways, identification, and characterization of CSCs opens up new targeted therapy approaches. The contemporary evidence from other fields shows promising evidence that combining conservative treatment modalities with targeting therapies specific for CSCs in clinical practice is essential for achieving high globe salvage rate in Rb patients.

An Epigenetic Role of Mitochondria in Cancer

Mitochondria are not only the main energy supplier but are also the cell metabolic center regulating multiple key metaborates that play pivotal roles in epigenetics regulation. These metabolites include acetyl-CoA, α-ketoglutarate (α-KG), S-adenosyl methionine (SAM), NAD⁺, and O-linked beta-N-acetylglucosamine (O-GlcNAc), which are the main substrates for DNA methylation and histone post-translation modifications, essential for gene transcriptional regulation and cell fate determination. Tumorigenesis is attributed to many factors, including gene mutations and tumor microenvironment. Mitochondria and epigenetics play essential roles in tumor initiation, evolution, metastasis, and recurrence. Targeting mitochondrial metabolism and epigenetics are promising therapeutic strategies for tumor treatment. In this review, we summarize the roles of mitochondria in key metabolites required for epigenetics modification and in cell fate regulation and discuss the current strategy in cancer therapies via targeting epigenetic modifiers and related enzymes in metabolic regulation. This review is an important contribution to the understanding of the current metabolic-epigenetic-tumorigenesis concept.

Genome maintenance in retinoblastoma: Implications for therapeutic vulnerabilities (Review)

Retinoblastoma (RB) is a pediatric ocular malignancy that is initiated mostly by biallelic inactivation of the RB transcriptional corepressor 1 (RB1) tumor suppressor gene in the developing retina. Unlike the prevailing prediction based on multiple studies involving RB1 gene disruption in experimental models, human RB tumors have been demonstrated to possess a relatively stable genome, characterized by a low mutation rate and a few recurrent chromosomal alterations related to somatic copy number changes. This suggests that RB may harbor heightened genome maintenance mechanisms to counteract or compensate for the risk of massive genome instability, which can potentially be driven by the early RB1 loss as a tumor-initiating event. Although the genome maintenance mechanisms might have been evolved to promote RB cell survival by preventing lethal genomic defects, emerging evidence suggests that the dependency of RB cells on these mechanisms also exposes their unique vulnerability to chemotherapy, particularly when the genome maintenance machineries are tumor cell-specific. This review summarizes the genome maintenance mechanisms identified in RB, including findings on the roles of chromatin regulators in DNA damage response/repair and protein factors involved in maintaining chromosome stability and promoting survival in RB. In addition, advantages and challenges for exploiting these therapeutic vulnerabilities in RB are discussed.

Histone Methyltransferase DOT1L as a Promising Epigenetic Target for Treatment of Solid Tumors

The histone lysine methyltransferase DOT1L (DOT1-like histone lysine methyltransferase) is responsible for the epigenetic regulation of gene expression through specific methylation of lysine79 residue of histone H3 (H3K79) in actively transcribed genes. Its normal activity is crucial for embryonic development and adult tissues functions, whereas its aberrant functioning is known to contribute to leukemogenesis. DOT1L is the only lysine methyltransferase that does not contain a SET domain, which is a feature that allowed the development of selective DOT1L inhibitors that are currently investigated in Phase I clinical trials for cancer treatment. Recently, abnormal expression of this enzyme has been associated with poor survival and increased aggressiveness of several solid tumors. In this review evidences of aberrant DOT1L expression and activity in breast, ovarian, prostate, colon, and other solid tumors, and its relationships with biological and clinical behavior of the disease and response to therapies, are summarized. Current knowledge of the structural basis of DOT1L ability to regulate cell proliferation, invasion, plasticity and stemness, cell cycle progression, cell-to-cell signaling, epithelial-to-mesenchymal transition, and chemoresistance, through cooperation with several molecular partners including noncoding RNAs, is also reviewed. Finally, available options for the treatment of therapeutically challenging solid tumors by targeting DOT1L are discussed.