Phase 1 study of GSK3368715, a type I PRMT inhibitor, in patients with advanced solid tumors

Discovery of a first-in-class protein arginine methyltransferase 1 (PRMT1) degrader for nonenzymatic functions studies

Among the type I Protein Arginine Methyltransferases (PRMTs), PRMT1 plays a predominant part in catalyzing asymmetric dimethylation of arginine residues on histone or nonhistone substrates. PRMT1 level is abnormally elevated in numerous cancer cell types and inflammation diseases. Compared to the enzymatic functions of PRMT1, its nonenzymatic functions are shortly investigated in diseases. Previous study has confirmed that the stability of orphan receptor TR3, a binding partner of PRMT1, is closely regulated by PRMT1, but the effect is independent of PRMT1's methyltransferase activity, but depends on the physical binding of PRMT1. To date, multiple inhibitors targeting methyltransferase enzymatic activity of PRMT1 are developed, but all of them lack selectivity for PRMT1. Among them, only GSK3368715 advanced to clinical trials but was discontinued in phase I due to inadequate efficacy and thrombosis toxicity. Currently, small molecule degraders are gaining significant attention due to their advantages in efficacy and selectivity in therapeutic applications. Presumably, a potent and selective PRMT1 degrader could serve as a valuable alternative in the treatment of PRMT1-driven diseases and act as an instrumental tool in uncovering additional nonenzymatic functions of PRMT1. To date, however, the development of a PRMT1 degrader remains a challenge, with no such agents reported. In this study, we present the design, synthesis and characterization of CM112 (compound 12), a first-in-class PRMT1 degrader, designed by tethering adamantane to MS023, a type I PRMTs pan inhibitor, via a 5-PEG linker. CM112 demonstrates a concentration- and time-dependent ability to induce PRMT1 degradation in various solid cancer cell lines. Additionally, CM112 shows high selectivity for PRMT1 degradation, without causing degradation of other type I PRMTs (PRMT3/4/6), although it retains potent inhibitory effects on their enzymatic activity. Pharmacokinetics studies indicated that CM112 possesses favorable bioavailability in mice. Notably, as anticipated, CM112 could target PRMT1's nonenzymatic function by downregulating the stability of the orphan receptor TR3, an effect not observed with the PRMT1 inhibitor MS023, that is in consistence with the previous findings. Taken together, CM112 represents a valuable tool for elucidating the unknown, methyltransferase-independent roles of PRMT1 in disease progression and pave the way for developing more potent and drug like PRMT1 degraders in future.

Alternative splicing: A key regulator in T cell response and cancer immunotherapy

Alternative splicing (AS), a key post-transcriptional regulatory mechanism, is frequently dysregulated in cancer, driving both tumor progression and immune modulation. Aberrant AS influences antigen presentation, T cell activation, immune checkpoint regulation, and cytokine signaling, contributing to immune evasion but also presenting unique therapeutic vulnerabilities. Targeting AS has emerged as a promising strategy in cancer immunotherapy. Splicing-derived neoantigens have been identified as potent inducers of CD8⁺ T cell responses, offering potential for personalized treatment. AS modulators such as PRMT5 inhibitor GSK3326595 enhance immunotherapy efficacy by upregulating MHC class II expression and promoting T cell infiltration, while RBM39 inhibitor indisulam induces tumor-specific neoantigens. Furthermore, combining AS-targeting drugs with immune checkpoint inhibitors (ICIs) has demonstrated synergistic effects, improved response rates and overcoming resistance in preclinical models. Despite these advances, challenges remain in optimizing drug specificity and minimizing toxicity. Future efforts should focus on refining AS-targeting therapies, identifying predictive biomarkers, and integrating these approaches into clinical applications. This review highlights the therapeutic potential of AS modulation in cancer immunotherapy and its implications for advancing precision oncology.

PRMT1-mediated modification of H4R3me2a promotes liver cancer progression by enhancing the transcriptional activity of SOX18

BACKGROUND

HCC is one of the most prevalent and deadliest malignancies worldwide, with a poor prognosis. Altered histone modifications have been shown to play a significant role in HCC. However, the biological roles and clinical relevance of specific histone modifications, such as the asymmetric dimethylation on arginine 3 of histone H4 (H4R3me2a), remain poorly understood in HCC.

METHODS

In this study, immunohistochemical staining was performed to assess histone H4R3me2a modification in 32 pairs of HCC tissues and corresponding adjacent nontumor liver tissues. Cellular-level experiments and subcutaneous xenograft models in nude mice were used to investigate the effects of silencing protein arginine methyltransferase 1 (PRMT1) with shRNA or pharmacologically blocking PRMT1 activity on HCC cell proliferation, migration, and invasion. RNA-seq analysis combined with Chip-qPCR validation was employed to explore the regulatory mechanism of PRMT1 on SOX18 expression. The downstream target of SOX18 was identified using the JASPAR database and a dual-luciferase reporter system.

RESULTS

The level of histone H4R3me2a modification was significantly elevated in HCC tissues and closely associated with poor prognosis in patients with HCC. Silencing PRMT1 or pharmacologically inhibiting its activity effectively suppressed the proliferation, migration, and invasion of HCC cells. Mechanistically, PRMT1 was found to regulate SOX18 expression by modulating histone H4R3me2a modification in the SOX18 promoter region. LOXL1 was identified as a downstream target of the transcription factor SOX18.

CONCLUSIONS

This study revealed the clinical relevance of histone H4R3me2a modification in HCC and demonstrated that PRMT1 promotes malignant behavior in HCC cells by modulating H4R3me2a modification in the SOX18 promoter region. The findings elucidate the role and molecular mechanism of PRMT1-mediated histone H4R3me2a modification in HCC progression and highlight the potential clinical applications of PRMT1 inhibitors. These results may provide new insights into the treatment of HCC.

Small-Molecule Modulators Targeting Coactivator-Associated Arginine Methyltransferase 1 (CARM1) as Therapeutic Agents for Cancer Treatment: Current Medicinal Chemistry Insights and Emerging Opportunities

Overexpression of coactivator associated arginine methyltransferase 1 (CARM1) is associated with various diseases including cancer. Therefore, CARM1 has emerged as an attractive therapeutic target and a drug response biomarker for anticancer drug discovery. However, the development of conventional CARM1 inhibitors has been hampered by their limited clinical efficacy, acquired resistance, and inability to inhibit nonenzymatic functions of CARM1. To overcome these challenges, new strategies such as isoform-selective inhibitors, dual-acting inhibitors, targeted protein degradation technology (e.g., PROTACs), and even activators, are essential to enhance the anticancer activity of CARM1 modulators. In this perspective, we first summarize the structure and biofunctions of CARM1 and its association with cancer. Next, we focus on the recent advances in CARM1 modulators, including isoform-selective CARM1 inhibitors, dual-target inhibitors, PROTAC degraders, and activators, from the perspectives of rational design, pharmacodynamics, pharmacokinetics, and clinical status. Finally, we discuss the challenges and future directions for CARM1-based drug discovery.

Biomedical effects of protein arginine methyltransferase inhibitors

Protein arginine methyltransferases (PRMTs) are enzymes that catalyze the methylation of arginine residues in eukaryotic proteins, playing critical roles in modulating diverse cellular processes. The importance of PRMTs in the incidence and progression of a wide range of diseases, particularly cancers, such as breast, liver, lung, colorectal cancer, lymphoma, leukemia, and acute myeloid leukemia is increasingly recognized. This underscores the critical need for the development of effective PRMT inhibitors as therapeutic intervention. The field of PRMT inhibitors is in the rapidly growing phase and it is necessary to conduct a summative review of how the so-far developed inhibitors impact PRMT functions and cellular physiology. Our review aims to summarize molecular action mechanisms of these PRMT inhibitors and particularly elaborate their triggered biomedical effects. We describe the cellular phenotype consequences of select PRMT inhibitors across various disease models, thereby providing an understanding of the pharmacological mechanisms underpinning PRMT inhibition. The promising effects of PRMT5 inhibitors in targeted therapy of methylthioadenosine phosphorylase-deleted cancers are particularly highlighted. At last, we provide a perspective on the challenges and further opportunities of developing and applying novel PRMT inhibitors for clinical advancement.

TRIM21-mediated PRMT1 degradation attenuates colorectal cancer malignant progression

Tripartite motif-containing 21 (TRIM21) plays a crucial role in antiviral responses and autoimmune diseases. While the impact of TRIM21 on cancer has been studied in various tumors, its role in colorectal cancer (CRC) remains unclear. In this study, we found that TRIM21 expression is reduced in primary CRC tissues. Low levels of TRIM21 in CRC are associated with unfavorable clinicopathological characteristics and shorter survival. Furthermore, we demonstrate that TRIM21 suppresses the proliferation, tumorigenesis, migration, and metastasis of CRC cells by promoting the ubiquitination-mediated degradation of PRMT1. These findings suggest that TRIM21 holds potential as a valuable predictive biomarker for assessing the prognosis of CRC patients.

Targeting RNA splicing modulation: new perspectives for anticancer strategy?

The excision of introns from pre-mRNA is a crucial process in the expression of the majority of genes. Alternative splicing allows a single gene to generate diverse mRNA and protein products. Aberrant RNA splicing is recognized as a molecular characteristic present in almost all types of tumors. Therefore, identifying cancer-specific subtypes from aberrant processing offers new opportunities for therapeutic development. Numerous splicing modulators, each utilizing different mechanisms, have been developed as promising anticancer therapies, some of which are in clinical trials. In this review, we summarize the splice-altered signatures of cancer cell transcriptomes and the contributions of splicing aberrations to tumorigenesis and progression. Especially, we discuss current and emerging RNA splicing-targeted strategies for cancer therapy, including pharmacological approaches and splice-switching antisense oligonucleotides (ASOs). Finally, we address the challenges and opportunities in translating these findings into clinical practice.

Protein Arginine Methyltransferase 1: A Multi-Purpose Player in the Development of Cancer and Metabolic Disease

Protein arginine methyltransferase 1 (PRMT1) is the main PRMT family member involved in the formation of monomethylarginine and asymmetric dimethylarginine on its protein substrates. Many protein substrates of PRMT1 are key mediators of cell proliferation and oncogenesis. As such, the function of PRMT1 has been most prominently investigated in the context of cancer development. However, recent in vitro and in vivo studies have highlighted that PRMT1 may also promote metabolic disorders. With the current review, we aim to present an in-depth overview of how PRMT1 influences epigenetic modulation, transcriptional regulation, DNA damage repair, and signal transduction in cancer. Furthermore, we summarize the current knowledge regarding the role of PRMT1 in metabolic reprogramming, lipid metabolism, and glucose metabolism and describe the association of PRMT1 with numerous metabolic pathologies such as obesity, liver disease, and type 2 diabetes. It has become apparent that inhibiting the function of PRMT1 will likely serve as the most beneficial therapeutic approach, since several PRMT1 inhibitors have already been shown to exert positive effects on both cancer and metabolic disease in preclinical settings. However, pharmacological PRMT1 inhibition has not yet been shown to be therapeutically effective in clinical studies.

Targeting PRMT1 Reduces Cancer Persistence and Tumor Relapse in EGFR- and KRAS-Mutant Lung Cancer

SIGNIFICANCE

Eliminating "persisters" before relapse is crucial for achieving durable treatment efficacy. This study provides a rationale for developing PRMT1-selective inhibitors to target cancer persisters and achieve more durable outcomes in oncogene-targeting therapies.

The role of PRMT1 in cellular regulation and disease: Insights into biochemical functions and emerging inhibitors for cancer therapy

Protein Arginine Methyltransferase 1 (PRMT1), a primary protein arginine methyltransferase, plays a pivotal role in cellular regulation, influencing processes such as gene expression, signal transduction, and cell differentiation. Dysregulation of PRMT1 has been linked to the development of various cancers, establishing it as a key target for therapeutic intervention. This review synthesizes the biochemical characteristics, structural domains, and functional mechanisms of PRMT1, focusing on its involvement in tumorigenesis. Additionally, the development and efficacy of emerging PRMT1 inhibitors as potential cancer therapies are examined. By employing molecular modeling and insights from existing literature, this review posits that targeting PRMT1's methyltransferase activity could disrupt cancer progression, providing valuable insights for future drug development.

Fuel for thought: targeting metabolism in lung cancer

For over a century, we have appreciated that the biochemical processes through which micro- and macronutrients are anabolized and catabolized-collectively referred to as "cellular metabolism"-are reprogrammed in malignancies. Cancer cells in lung tumors rewire pathways of nutrient acquisition and metabolism to meet the bioenergetic demands for unchecked proliferation. Advances in precision medicine have ushered in routine genotyping of patient lung tumors, enabling a deeper understanding of the contribution of altered metabolism to tumor biology and patient outcomes. This paradigm shift in thoracic oncology has spawned a new enthusiasm for dissecting oncogenotype-specific metabolic phenotypes and creates opportunity for selective targeting of essential tumor metabolic pathways. In this review, we discuss metabolic states across histologic and molecular subtypes of lung cancers and the additional changes in tumor metabolic pathways that occur during acquired therapeutic resistance. We summarize the clinical investigation of metabolism-specific therapies, addressing successes and limitations to guide the evaluation of these novel strategies in the clinic. Beyond changes in tumor metabolism, we also highlight how non-cellular autonomous processes merit particular consideration when manipulating metabolic processes systemically, such as efforts to disentangle how lung tumor cells influence immunometabolism. As the future of metabolic therapeutics hinges on use of models that faithfully recapitulate metabolic rewiring in lung cancer, we also discuss best practices for harmonizing workflows to capture patient specimens for translational metabolic analyses.

Overview of the PRMT6 modulators in cancer treatment: Current progress and emerged opportunity

Protein Arginine Methyltransferase 6 (PRMT6) is a Type I PRMT enzyme that plays a role in the epigenetic regulation of gene expression by methylating histone and non-histone proteins. It is also involved in various cellular processes, including alternative splicing, DNA repair, and cell signaling. Furthermore, PRMT6 exerts multiple effects on cellular processes such as growth, migration, invasion, apoptosis, and drug resistance in various cancers, positioning it as a promising target for anti-tumor therapeutics. In this review, we initially provide an overview of the structure and biological functions of PRMT6, along with its association with cancer. Subsequently, we focus on recent progress in the design and development of modulators targeting PRMT6. This includes a comprehensive review of PRMT6 inhibitors (isoform-selective and non-selective), dual-target inhibitors based on PRMT6, PRMT6 covalent inhibitors, and PRMT6-targeting hydrophobic tagging (HyT) degraders, from the perspectives of rational design, pharmacodynamics, pharmacokinetics, and the clinical status of these modulators. Finally, we also provided the challenges and prospective directions for PRMT6 targeting drug discovery in cancer therapy.

Overview of PRMT1 modulators: Inhibitors and degraders

Protein arginine methyltransferase 1 (PRMT1) is pivotal in executing normal cellular functions through its catalytic action on the methylation of arginine side chains on protein substrates. Emerging research has revealed a correlation between the dysregulation of PRMT1 expression and the initiation and progression of tumors, significantly influence on patient prognostication, attributed to the essential role played by PRMT1 in a number of biological processes, including transcriptional regulation, signal transduction or DNA repair. Therefore, PRMT1 emerged as a promising therapeutic target for anticancer drug discovery in the past decade. In this review, we first summarize the structure and biological functions of PRMT1 and its association with cancer. Next, we focus on the recent advances in the design and development of PRMT1 modulators, including isoform-selective PRMT1 inhibitors, pan type I PRMT inhibitors, PRMT1-based dual-target inhibitors, and PRMT1-targeting PROTAC degraders, from the perspectives of rational design, pharmacodynamics, pharmacokinetics, and clinical status. Finally, we discuss the challenges and future directions for PRMT1-based drug discovery for cancer therapy.

Therapeutic strategies targeting aberrant RNA splicing in myeloid malignancies

In recent years, large-scale sequencing efforts have identified targetable driver mutations in haematopoietic stem cells. These efforts have led to the development and approval of nine novel agents for relapsed or refractory acute myelogenous leukaemia (R/R AML). However, despite an expansion in targeted therapies, achieving a durable remission in AML and high-risk myelodysplastic syndrome (HR-MDS) remains a significant challenge, and there is an urgent need for new effective treatments. Modulation of aberrant RNA splicing has emerged as a novel therapeutic approach in myeloid diseases. Aberrant splicing drives dysregulated gene expression that promotes tumourigenesis through increased proliferation and metastatic potential, immune evasion, decreased apoptosis, and chemotherapy resistance. Mutations in spliceosomal components have been identified in numerous cancer subtypes, with mutations in RNA binding proteins SF3B1, SRSF2, U2AF1, and ZRSR2 occurring frequently in AML and in up to 60% of patients with MDS, as well as in chronic myelomonocytic leukaemia and in 10% of patients with chronic lymphocytic leukaemia. In this review, we explore therapeutic strategies targeting aberrant splicing and the potential of these approaches to drive clinical responses.

Epigenetics-targeted drugs: current paradigms and future challenges

Epigenetics governs a chromatin state regulatory system through five key mechanisms: DNA modification, histone modification, RNA modification, chromatin remodeling, and non-coding RNA regulation. These mechanisms and their associated enzymes convey genetic information independently of DNA base sequences, playing essential roles in organismal development and homeostasis. Conversely, disruptions in epigenetic landscapes critically influence the pathogenesis of various human diseases. This understanding has laid a robust theoretical groundwork for developing drugs that target epigenetics-modifying enzymes in pathological conditions. Over the past two decades, a growing array of small molecule drugs targeting epigenetic enzymes such as DNA methyltransferase, histone deacetylase, isocitrate dehydrogenase, and enhancer of zeste homolog 2, have been thoroughly investigated and implemented as therapeutic options, particularly in oncology. Additionally, numerous epigenetics-targeted drugs are undergoing clinical trials, offering promising prospects for clinical benefits. This review delineates the roles of epigenetics in physiological and pathological contexts and underscores pioneering studies on the discovery and clinical implementation of epigenetics-targeted drugs. These include inhibitors, agonists, degraders, and multitarget agents, aiming to identify practical challenges and promising avenues for future research. Ultimately, this review aims to deepen the understanding of epigenetics-oriented therapeutic strategies and their further application in clinical settings.

A chemical screen identifies PRMT5 as a therapeutic vulnerability for paclitaxel-resistant triple-negative breast cancer

Paclitaxel-resistant triple negative breast cancer (TNBC) remains one of the most challenging breast cancers to treat. Here, using an epigenetic chemical probe screen, we uncover an acquired vulnerability of paclitaxel-resistant TNBC cells to protein arginine methyltransferases (PRMTs) inhibition. Analysis of cell lines and in-house clinical samples demonstrates that resistant cells evade paclitaxel killing through stabilizing mitotic chromatin assembly. Genetic or pharmacologic inhibition of PRMT5 alters RNA splicing, particularly intron retention of aurora kinases B (AURKB), leading to a decrease in protein expression, and finally results in selective mitosis catastrophe in paclitaxel-resistant cells. In addition, type I PRMT inhibition synergies with PRMT5 inhibition in suppressing tumor growth of drug-resistant cells through augmenting perturbation of AURKB-mediated mitotic signaling pathway. These findings are fully recapitulated in a patient-derived xenograft (PDX) model generated from a paclitaxel-resistant TNBC patient, providing the rationale for targeting PRMTs in paclitaxel-resistant TNBC.

Aberrant pre-mRNA processing in cancer

Dysregulation of the flow of information from genomic DNA to RNA to protein occurs within all cancer types. In this review, we described the current state of understanding of how RNA processing is dysregulated in cancer with a focus on mutations in the RNA splicing factor machinery that are highly prevalent in hematologic malignancies. We discuss the downstream effects of these mutations highlighting both individual genes as well as common pathways that they perturb. We highlight examples of how alterations in RNA processing have been harnessed for therapeutic intent as well as to promote the selective toxicity of cancer cells.

MTAP as an emerging biomarker in thoracic malignancies

S-methyl-5'-thioadenosine phosphorylase (MTAP) deficiency is an emerging biomarker in non-small cell lung cancer (NSCLC) and beyond. The MTAP gene is located in the chromosomal region 9p21.3, which shows one of the most common homozygous deletions across all human cancers (9p21 loss). Loss of 9p21 is found in the majority of pleural mesotheliomas, where it serves as an established diagnostic marker. Until recently, fluorescence in situ hybridization (FISH) was the gold standard for the detection of 9p21 losses, but loss of MTAP expression by immunohistochemistry (IHC) gains increasing importance as an easy to apply and cost-effective diagnostic surrogate marker. Besides, MTAP loss, which has been reported in 13% of NSCLC, is becoming an emerging predictive biomarker in two different scenarios in NSCLC and other cancer types: 1) MTAP loss seems to negatively predict the response to immune checkpoint inhibitor (ICI) treatment via silencing of the tumor microenvironment, and 2) MTAP loss serves as a predictive biomarker for novel targeted treatment strategies. MTAP deficiency leads to an impaired function of the protein arginine methyltransferase 5 (PRMT5) due to its partial inhibition by MTAP's accumulating substrate methylthioadenosine (MTA). This process leaves MTAP deficient tumor cells heavily dependent on the remaining function of PRMT5, making it a perfect target for synthetic lethality. Indeed, MTA-cooperative PRMT5-inhibitors are now tested in several clinical trials with promising early results in solid malignancies. With its emergence as a predictive biomarker, the implementation of MTAP IHC into diagnostic routine for NSCLC and other tumors is likely to take place soon. In this review article, we summarize the current literature on the role of MTAP in thoracic tumors and evaluate different testing methods, including IHC, FISH and next generation sequencing.

Methylarginine targeting chimeras for lysosomal degradation of intracellular proteins

A paradigm shift in drug development is the discovery of small molecules that harness the ubiquitin-proteasomal pathway to eliminate pathogenic proteins. Here we provide a modality for targeted protein degradation in lysosomes. We exploit an endogenous lysosomal pathway whereby protein arginine methyltransferases (PRMTs) initiate substrate degradation via arginine methylation. We developed a heterobifunctional small molecule, methylarginine targeting chimera (MrTAC), that recruits PRMT1 to a target protein for induced degradation in lysosomes. MrTAC compounds degraded substrates across cell lines, timescales and doses. MrTAC degradation required target protein methylation for subsequent lysosomal delivery via microautophagy. A library of MrTAC molecules exemplified the generality of MrTAC to degrade known targets and neo-substrates-glycogen synthase kinase 3β, MYC, bromodomain-containing protein 4 and histone deacetylase 6. MrTAC selectively degraded target proteins and drove biological loss-of-function phenotypes in survival, transcription and proliferation. Collectively, MrTAC demonstrates the utility of endogenous lysosomal proteolysis in the generation of a new class of small molecule degraders.

Structure, Function, and Activity of Small Molecule and Peptide Inhibitors of Protein Arginine Methyltransferase 1

Protein arginine N-methyltransferases (PRMT) are a family of S-adenosyl-l-methionine (SAM)-dependent enzymes that transfer methyl-groups to the ω-N of arginyl residues in proteins. PRMTs are involved in regulating gene expression, RNA splicing, and other activities. PRMT1 is responsible for most cellular arginine methylation, and its dysregulation is involved in many cancers. Accordingly, many groups have targeted PRMT1 using small molecules and peptide inhibitors. In this Perspective, we discuss the structure and function of selected peptide and small molecule inhibitors of PRMT1. We examine inhibitors that target the substrate arginyl peptide, SAM, or both binding sites, and the type of inhibition that results. Small molecules, and peptides that are bisubstrate, and/or PRMT transition state mimic inhibitors as well as inhibitors that alkylate PRMTs will be discussed. We define a structure-activity relationship for the aromatic/heteroaromatic N-methylethylenediamine inhibitors of PRMT1 and review current progress of PRMT1 inhibitors in clinical trials.

A Chemoenzymatic Method Enables Global Enrichment and Characterization of Protein Arginine Methylation

Arginine methylation is one of the most important post-translational modifications involved in the regulation of numerous biological processes. To better understand the biological significance of arginine methylation, enrichment methods need to be developed to analyze the methylated proteome at large-scale. Unfortunately, the prevailing enrichment method based on immunoaffinity purification can only enrich a subset of them due to the lack of pan-specific antibodies. Therefore, it is crucial to develop a stable and efficient antibody-free approach for the global analysis of arginine methylation. In this study, we developed a chemoenzymatic method for the simultaneous identification of mono- and dimethylated arginine. Totally, we identified 1006 arginine methylation events in Jurkat T cells, corresponding to 645 dimethylated sites and 361 monomethylated sites. We further applied the developed approach to global identification of the substrate proteins regulated by type I protein arginine methyltransferases (PRMTs) and identified 49 substrate proteins of type I PRMTs, which will facilitate a better understanding of PRMTs-regulated biological processes. Given the robust performance of this method, it would have broad application in methylproteomics analysis.

Towards the Targeted Protein Degradation of PRMT1

Targeting the protein arginine methyltransferase 1 (PRMT1) has emerged as a promising therapeutic strategy in cancer treatment. The phase 1 clinical trial for GSK3368715, the first PRMT1 inhibitor to enter the clinic, was terminated early due to a lack of clinical efficacy, extensive treatment-emergent effects, and dose-limiting toxicities. The incidence of the latter two events may be associated with inhibition-driven pharmacology as a high and sustained concentration of inhibitor is required for therapeutic effect. The degradation of PRMT1 using a proteolysis targeting chimera (PROTAC) may be superior to inhibition as proceeds via event-driven pharmacology where a PROTAC acts catalytically at a low dose. PROTACs containing the same pharmacophore as GSK3368715, combined with a motif that recruits the VHL or CRBN E3-ligase, were synthesised. Suitable cell permeability and target engagement were shown for selected candidates by the detection of downstream effects of PRMT1 inhibition and by a NanoBRET assay for E3-ligase binding, however the candidates did not induce PRMT1 degradation. This paper is the first reported investigation of PRMT1 for targeted protein degradation and provides hypotheses and insights to assist the design of PROTACs for PRMT1 and other novel target proteins.

Methylation modification of non-histone proteins in breast cancer: an emerging targeted therapeutic strategy

Breast cancer is a major public health concern worldwide, being the most commonly diagnosed cancer among women and a leading cause of cancer-related deaths. Recent studies have highlighted the significance of non-histone methylation in breast cancer, which modulates the activity, interaction, localization, and stability of target proteins. This regulation affects critical processes such as oncogenesis, tumor growth, proliferation, invasion, migration, and immune responses. This review delves into the enzymes responsible for non-histone methylation, such as protein arginine methyltransferases (PRMTs), lysine methyltransferases (KMTs), and demethylases, and explores their roles in breast cancer. By elucidating the molecular mechanisms and functional consequences of non-histone methylation, this review aims to provide insights into novel therapeutic strategies targeting these pathways. The therapeutic potential of targeting non-histone methylation to overcome drug resistance and enhance treatment efficacy in breast cancer is also discussed, highlighting promising avenues for future research and clinical applications.

Role of PRMT1 and PRMT5 in Breast Cancer

Breast cancer is the most common cancer diagnosed in women worldwide. Early-stage breast cancer is curable in ~70-80% of patients, while advanced metastatic breast cancer is considered incurable with current therapies. Breast cancer is a highly heterogeneous disease categorized into three main subtypes based on key markers orientating specific treatment strategies for each subtype. The complexity of breast carcinogenesis is often associated with epigenetic modification regulating different signaling pathways, involved in breast tumor initiation and progression, particularly by the methylation of arginine residues. Protein arginine methyltransferases (PRMT1-9) have emerged, through their ability to methylate histones and non-histone substrates, as essential regulators of cancers. Here, we present an updated overview of the mechanisms by which PRMT1 and PRMT5, two major members of the PRMT family, control important signaling pathways impacting breast tumorigenesis, highlighting them as putative therapeutic targets.

The Interplay of Acetylation and Ubiquitination Controls PRMT1 Homeostasis

PRMT1 plays many important roles in both normal and disease biology, thus understanding it's regulation is crucial. Herein, we report the role of p300-mediated acetylation at K228 in triggering PRMT1 degradation through FBXL17-mediated ubiquitination. Utilizing mass-spectrometry, cellular biochemistry, and genetic code-expansion technologies, we elucidate a crucial mechanism independent of PRMT1 transcript levels. These results underscore the significance of acetylation in governing protein stability and expand our understanding of PRMT1 homeostasis. By detailing the molecular interplay between acetylation and ubiquitination involved in PRMT1 degradation, this work contributes to broader efforts in deciphering post-translational mechanisms that influence protein homeostasis.

CRISPR/Cas9 screenings unearth protein arginine methyltransferase 7 as a novel essential gene in prostate cancer metastasis

Due to the limited effectiveness of current treatments, the survival rate of patients with metastatic castration-resistant prostate cancer (mCRPC) is significantly reduced. Consequently, it is imperative to identify novel therapeutic targets for managing these patients. Since the invasive ability of cells is crucial for establishing and maintaining metastasis, the aim of this study was to identify the essential regulators of invasive abilities of mCRPC cells by conducting two independent high-throughput CRISPR/Cas9 screenings. Furthermore, some of the top hits were validated using siRNA technology, with protein arginine methyltransferase 7 (PRMT7) emerging as the most promising candidate. We demonstrated that its inhibition or depletion via genetic or pharmacological approaches significantly reduces invasive, migratory and proliferative abilities of mCRPC cells in vitro. Moreover, we confirmed that PRMT7 ablation reduces cell dissemination in chicken chorioallantoic membrane and mouse xenograft assays. Molecularly, PRMT7 reprograms the expression of several adhesion molecules by methylating various transcription factors, such as FoxK1, resulting in the loss of adhesion from the primary tumor and increased motility of mCRPC cells. Furthermore, PRMT7 higher expression correlates with tumor aggressivity and poor overall survival in prostate cancer patients. Thus, this study demonstrates that PRMT7 is a potential therapeutic target and potential biomarker for mPCa.

Protein Arginine Methyltransferases in Pancreatic Ductal Adenocarcinoma: New Molecular Targets for Therapy

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignant disease with a low 5-year overall survival rate. It is the third-leading cause of cancer-related deaths in the United States. The lack of robust therapeutics, absence of effective biomarkers for early detection, and aggressive nature of the tumor contribute to the high mortality rate of PDAC. Notably, the outcomes of recent immunotherapy and targeted therapy against PDAC remain unsatisfactory, indicating the need for novel therapeutic strategies. One of the newly described molecular features of PDAC is the altered expression of protein arginine methyltransferases (PRMTs). PRMTs are a group of enzymes known to methylate arginine residues in both histone and non-histone proteins, thereby mediating cellular homeostasis in biological systems. Some of the PRMT enzymes are known to be overexpressed in PDAC that promotes tumor progression and chemo-resistance via regulating gene transcription, cellular metabolic processes, RNA metabolism, and epithelial mesenchymal transition (EMT). Small-molecule inhibitors of PRMTs are currently under clinical trials and can potentially become a new generation of anti-cancer drugs. This review aims to provide an overview of the current understanding of PRMTs in PDAC, focusing on their pathological roles and their potential as new therapeutic targets.

Androgen receptor cofactors: A potential role in understanding prostate cancer

Prostate cancer (PCa) is witnessing a concerning rise in incidence annually, with the androgen receptor (AR) emerging as a pivotal contributor to its growth and progression. Mounting evidence underscores the AR's ability to recruit cofactors, influencing downstream gene transcription and thereby fueling the proliferation and metastasis of PCa cells. Although, clinical strategies involving AR antagonists provide some relief, managing castration resistant prostate cancer (CRPC) remains a formidable challenge. Thus, the need of the hour lies in unearthing new drugs or therapeutic targets to effectively combat PCa. This review encapsulates the pivotal roles played by coactivators and corepressors of AR, notably androgen receptor-associated protein (ARA) and steroid receptor Coactivators (SRC) in PCa. Our data unveils how these cofactors intricately modulate histone modifications, cell cycling, SUMOylation, and apoptosis through their interactions with AR. Among the array of cofactors scrutinised, such as ARA70β, ARA24, ARA160, ARA55, ARA54, PIAS1, PIAS3, SRC1, SRC2, SRC3, PCAF, p300/CBP, MED1, and CARM1, several exhibit upregulation in PCa. Conversely, other cofactors like ARA70α, PIASy, and NCoR/SMRT demonstrate downregulation. This duality underscores the complexity of AR cofactor dynamics in PCa. Based on our findings, we propose that manipulating cofactor regulation to modulate AR function holds promise as a novel therapeutic avenue against advanced PCa. This paradigm shift offers renewed hope in the quest for effective treatments in the face of CRPC's formidable challenges.

Targeting type I PRMTs as promising targets for the treatment of pulmonary disorders: Asthma, COPD, lung cancer, PF, and PH

Pulmonary disorders, including asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), pulmonary hypertension (PH), and lung cancer, seriously impair the quality of lives of patients. A deeper understanding of the occurrence and development of the above diseases may inspire new strategies to remedy the scarcity of treatments. Type I protein arginine methyltransferases (PRMTs) can affect processes of inflammation, airway remodeling, fibroblast proliferation, mitochondrial mass, and epithelial dysfunction through substrate methylation and non-enzymatic activity, thus affecting the occurrence and development of asthma, COPD, lung cancer, PF, and PH. As potential therapeutic targets, inhibitors of type I PRMTs are developed, moreover, representative compounds such as GSK3368715 and MS023 have also been used for early research. Here, we collated structures of type I PRMTs inhibitors and compared their activity. Finally, we highlighted the physiological and pathological associations of type I PRMTs with asthma, COPD, lung cancer, PF, and PH. The developing of type I PRMTs modulators will be beneficial for the treatment of these diseases.

PRMT1 acts as a suppressor of MHC-I and anti-tumor immunity

Cancer immunotherapies have demonstrated remarkable success; however, the majority of patients do not respond or develop resistance. Here, we conduct epigenetic gene-targeted CRISPR-Cas9 screens to identify epigenomic factors that limit CD8+ T cell-mediated anti-tumor immunity. We identify that PRMT1 suppresses interferon gamma (Ifnγ)-induced MHC-I expression, thus dampening CD8+ T cell-mediated killing. Indeed, PRMT1 knockout or pharmacological targeting of type I PRMT with the clinical inhibitor GSK3368715 enhances Ifnγ-induced MHC-I expression through elevated STAT1 expression and activation, while re-introduction of PRMT1 in PRMT1-deficient cells reverses this effect. Importantly, loss of PRMT1 enhances the efficacy of anti-PD-1 immunotherapy, and The Cancer Genome Atlas analysis reveals that PRMT1 expression in human melanoma is inversely correlated with expression of human leukocyte antigen molecules, infiltration of CD8+ T cells, and overall survival. Taken together, we identify PRMT1 as a negative regulator of anti-tumor immunity, unveiling clinical type I PRMT inhibitors as immunotherapeutic agents or as adjuncts to existing immunotherapies.

PRMT1 in human neoplasm: cancer biology and potential therapeutic target

Protein arginine methyltransferase 1 (PRMT1), the predominant type I protein arginine methyltransferase, plays a crucial role in normal biological functions by catalyzing the methylation of arginine side chains, specifically monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), within proteins. Recent investigations have unveiled an association between dysregulated PRMT1 expression and the initiation and progression of tumors, significantly impacting patient prognosis, attributed to PRMT1's involvement in regulating various facets of tumor cell biology, including DNA damage repair, transcriptional and translational regulation, as well as signal transduction. In this review, we present an overview of recent advancements in PRMT1 research across different tumor types, with a specific focus on its contributions to tumor cell proliferation, metastasis, invasion, and drug resistance. Additionally, we expound on the dynamic functions of PRMT1 during distinct stages of cancer progression, elucidating its unique regulatory mechanisms within the same signaling pathway and distinguishing between its promotive and inhibitory effects. Importantly, we sought to provide a comprehensive summary and analysis of recent research progress on PRMT1 in tumors, contributing to a deeper understanding of its role in tumorigenesis, development, and potential treatment strategies.

Promising role of protein arginine methyltransferases in overcoming anti-cancer drug resistance

Drug resistance remains a major challenge in cancer treatment, necessitating the development of novel strategies to overcome it. Protein arginine methyltransferases (PRMTs) are enzymes responsible for epigenetic arginine methylation, which regulates various biological and pathological processes, as a result, they are attractive therapeutic targets for overcoming anti-cancer drug resistance. The ongoing development of small molecules targeting PRMTs has resulted in the generation of chemical probes for modulating most PRMTs and facilitated clinical treatment for the most advanced oncology targets, including PRMT1 and PRMT5. In this review, we summarize various mechanisms underlying protein arginine methylation and the roles of specific PRMTs in driving cancer drug resistance. Furthermore, we highlight the potential clinical implications of PRMT inhibitors in decreasing cancer drug resistance. PRMTs promote the formation and maintenance of drug-tolerant cells via several mechanisms, including altered drug efflux transporters, autophagy, DNA damage repair, cancer stem cell-related function, epithelial-mesenchymal transition, and disordered tumor microenvironment. Multiple preclinical and ongoing clinical trials have demonstrated that PRMT inhibitors, particularly PRMT5 inhibitors, can sensitize cancer cells to various anti-cancer drugs, including chemotherapeutic, targeted therapeutic, and immunotherapeutic agents. Combining PRMT inhibitors with existing anti-cancer strategies will be a promising approach for overcoming anti-cancer drug resistance. Furthermore, enhanced knowledge of the complex functions of arginine methylation and PRMTs in drug resistance will guide the future development of PRMT inhibitors and may help identify new clinical indications.

Recent Advances in Drug Discovery for Triple-Negative Breast Cancer Treatment

Triple-negative breast cancer (TNBC) is one of the most heterogeneous and aggressive breast cancer subtypes with a high risk of death on recurrence. To date, TNBC is very difficult to treat due to the lack of an effective targeted therapy. However, recent advances in the molecular characterization of TNBC are encouraging the development of novel drugs and therapeutic combinations for its therapeutic management. In the present review, we will provide an overview of the currently available standard therapies and new emerging therapeutic strategies against TNBC, highlighting the promises that newly developed small molecules, repositioned drugs, and combination therapies have of improving treatment efficacy against these tumors.

Epigenetic targeting to enhance acute myeloid leukemia-directed immunotherapy

AML is a malignant disease of hematopoietic progenitor cells with unsatisfactory treatment outcome, especially in patients that are ineligible for intensive chemotherapy. Immunotherapy, comprising checkpoint inhibition, T-cell engaging antibody constructs, and cellular therapies, has dramatically improved the outcome of patients with solid tumors and lymphatic neoplasms. In AML, these approaches have been far less successful. Discussed reasons are the relatively low mutational burden of AML blasts and the difficulty in defining AML-specific antigens not expressed on hematopoietic progenitor cells. On the other hand, epigenetic dysregulation is an essential driver of leukemogenesis, and non-selective hypomethylating agents (HMAs) are the current backbone of non-intensive treatment. The first clinical trials that evaluated whether HMAs may improve immune checkpoint inhibitors' efficacy showed modest efficacy except for the anti-CD47 antibody that was substantially more efficient against AML when combined with azacitidine. Combining bispecific antibodies or cellular treatments with HMAs is subject to ongoing clinical investigation, and efficacy data are awaited shortly. More selective second-generation inhibitors targeting specific chromatin regulators have demonstrated promising preclinical activity against AML and are currently evaluated in clinical trials. These drugs that commonly cause leukemia cell differentiation potentially sensitize AML to immune-based treatments by co-regulating immune checkpoints, providing a pro-inflammatory environment, and inducing (neo)-antigen expression. Combining selective targeted epigenetic drugs with (cellular) immunotherapy is, therefore, a promising approach to avoid unintended effects and augment efficacy. Future studies will provide detailed information on how these compounds influence specific immune functions that may enable translation into clinical assessment.