PRMT5: An Emerging Target for Pancreatic Adenocarcinoma

Personalized Medicine in Pancreatic Cancer: The Promise of Biomarkers and Molecular Targeting with Dr. Michael J. Pishvaian

Pancreatic cancer, with its alarming rising incidence, is predicted to become the second deadliest type of solid tumor by 2040, highlighting the urgent need for improved diagnostic and treatment strategies. Despite medical advancements, the five-year survival rate for pancreatic cancer remains about 14%, dropping further when metastasized. This review explores the promise of biomarkers for early detection, personalized treatment, and disease monitoring. Molecular classification of pancreatic cancer into subtypes based on genetic mutations, gene expression, and protein markers guides treatment decisions, potentially improving outcomes. A plethora of clinical trials investigating different strategies are currently ongoing. Targeted therapies, among which those against CLAUDIN 18.2 and inhibitors of Claudin 18.1, have shown promise. Next-generation sequencing (NGS) has emerged as a powerful tool for the comprehensive genomic analysis of pancreatic tumors, revealing unique genetic alterations that drive cancer progression. This allows oncologists to tailor therapies to target specific molecular abnormalities. However, challenges remain, including limited awareness and uptake of biomarker-guided therapies. Continued research into the molecular mechanisms of pancreatic cancer is essential for developing more effective treatments and improving patient survival rates.

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.

MST2 methylation by PRMT5 inhibits Hippo signaling and promotes pancreatic cancer progression

The Hippo signaling axis is a tumor suppressor pathway that is activated by various extra-pathway factors to regulate cell differentiation and organ development. Recent studies have reported that autophosphorylation of the core kinase cassette stimulates activation of the Hippo signaling cascade. Here, we demonstrate that protein arginine methyltransferase 5 (PRMT5) contributes to inactivation of the Hippo signaling pathway in pancreatic cancer. We show that the Hippo pathway initiator serine/threonine kinase 3 (STK3, also known as MST2) of Hippo signaling pathway can be symmetrically di-methylated by PRMT5 at arginine-461 (R461) and arginine-467 (R467) in its SARAH domain. Methylation suppresses MST2 autophosphorylation and kinase activity by blocking its homodimerization, thereby inactivating Hippo signaling pathway in pancreatic cancer. Moreover, we also show that the specific PRMT5 inhibitor GSK3326595 re-activates the dysregulated Hippo signaling pathway and inhibits the growth of human pancreatic cancer xenografts in immunodeficient mice, thus suggesting potential clinical application of PRMT5 inhibitors in pancreatic cancer.

PRMT5 and CDK4/6 inhibition result in distinctive patterns of alternative splicing in melanoma

Drugs targeting cyclin-dependent kinases 4 and 6 (CDK4/6) are promising new treatments for melanoma and other solid malignancies. In studies on CDK4/6 inhibitor resistance, protein arginine methyltransferase 5 (PRMT5) regulation of alternative splicing was shown to be an important downstream component of the CDK4/6 pathway. However, the full effects of inhibition of CDK4/6 on splicing events in melanoma and the extent to which they are dependent on PRMT5 has not been established. We performed full-length mRNA sequencing on CHL1 and A375 melanoma cell lines treated with the CDK4/6 inhibitor palbociclib and the PRMT5 inhibitor GSK3326595 and analysed data for differential gene expression and differential pre-mRNA splicing induced by these agents. Changes in gene expression and RNA splicing were more extensive under PRMT5 inhibition than under CDK4/6 inhibition. Although PRMT5 inhibition and CDK4/6 inhibition induced common RNA splicing events and gene expression profiles, the majority of events induced by CDK4/6 inhibition were distinct. Our findings indicate CDK4/6 has the ability to regulate alternative splicing in a manner that is distinct from PRMT5 inhibition, resulting in divergent changes in gene expression under each therapy.

Targeting Arginine Methyltransferase PRMT5 for Cancer Therapy: Updated Progress and Novel Strategies

As a predominant type II protein arginine methyltransferase, PRMT5 plays critical roles in various normal cellular processes by catalyzing the mono- and symmetrical dimethylation of a wide range of histone and nonhistone substrates. Clinical studies have revealed that high expression of PRMT5 is observed in different solid tumors and hematological malignancies and is closely associated with cancer initiation and progression. Accordingly, PRMT5 is becoming a promising anticancer target and has received great attention in both the pharmaceutical industry and the academic community. In this Perspective, we comprehensively summarize recent advances in the development of first-generation PRMT5 enzymatic inhibitors and highlight novel strategies targeting PRMT5 in the past 5 years. We also discuss the challenges and opportunities of PRMT5 inhibition, with the aim of shedding light on future PRMT5 drug discovery.

Establishment and validation of a ubiquitination-related gene signature associated with prognosis in pancreatic duct adenocarcinoma

Background

Patients with pancreatic duct adenocarcinoma (PDAC) have varied prognoses that depend on numerous variables. However, additional research is required to uncover the latent impact of ubiquitination-related genes (URGs) on determining PDAC patients' prognoses.

Methods

The URGs clusters were discovered via consensus clustering, and the prognostic differentially expressed genes (DEGs) across clusters were utilized to develop a signature using a least absolute shrinkage and selection operator (LASSO) regression analysis of data from TCGA-PAAD. Verification analyses were conducted across TCGA-PAAD, GSE57495 and ICGC-PACA-AU to show the robustness of the signature. RT-qPCR was used to verify the expression of risk genes. Lastly, we formulated a nomogram to improve the clinical efficacy of our predictive tool.

Results

The URGs signature, comprised of three genes, was developed and was shown to be highly correlated with the prognoses of PAAD patients. The nomogram was established by combining the URGs signature with clinicopathological characteristics. We discovered that the URGs signature was remarkably superior than other individual predictors (age, grade, T stage, et al). Also, the immune microenvironment analysis indicated that ESTIMATEscore, ImmuneScores, and StromalScores were elevated in the low-risk group. The immune cells that infiltrated the tissues were different between the two groups, as did the expression of immune-related genes.

Conclusion

The URGs signature could act as the biomarker of prognosis and selecting appropriate therapeutic drugs for PDAC patients.

Methylthioadenosine phosphorylase deficiency in tumors: A compelling therapeutic target

The methionine salvage pathway is responsible for recycling sulfur-containing metabolites to methionine. This salvage pathway has been found to be implicated in cell apoptosis, proliferation, differentiation and inflammatory response. Methylthioadenosine phosphorylase (MTAP) catalyzes the reversible phosphorolysis of 5′-methylthioadenosine, a by-product produced from polyamine biosynthesis. The MTAP gene is located adjacent to the cyclin-dependent kinase inhibitor 2A gene and co-deletes with CDKN2A in nearly 15% of tumors. Moreover, MTAP-deleted tumor cells exhibit greater sensitivity to methionine depletion and to the inhibitors of purine synthesis. In this review, we first summarized the molecular structure and expression of MTAP in tumors. Furthermore, we discussed PRMT5 and MAT2A as a potential vulnerability for MTAP-deleted tumors. The complex and dynamic role of MTAP in diverse malignancies has also been discussed. Finally, we demonstrated the implications for the treatment of MTAP-deleted tumors.

Research progress on the relationship between the TOR signaling pathway regulator, epigenetics, and tumor development

Almost all cellular activities depend on protein folding, signaling complex assembly/disassembly, and epigenetic regulation. One of the most important regulatory mechanisms responsible for controlling these cellular processes is dynamic protein phosphorylation/dephosphorylation. Alterations in phosphorylation networks have major consequences in the form of disorders, including cancer. Many signaling cascades, including the target of rapamycin (TOR) signaling, are important participants in the cell cycle, and dysregulation in their phosphorylation/dephosphorylation status has been linked to malignancies. As a TOR signaling regulator, protein phosphatase 2A (PP2A) is responsible for most of the phosphatase activities inside the cells. On the other hand, TOR signaling pathway regulator (TIPRL) is an essential PP2A inhibitory protein. Many other physiological roles have also been suggested for TIPRL, such as modulation of TOR pathways, apoptosis, and cell proliferation. It is also reported that TIPRL was increased in various carcinomas, including non-small-cell lung carcinoma (NSCLC) and hepatocellular carcinomas (HCC). Considering the function of PP2A as a tumor suppressor and also the effect of the TIPRL/PP2A axis on apoptosis and proliferation of cancer cells, this review aims to provide a complete view of the role of TIPRL in cancer development in addition to describing TIPRL/PP2A axis and its epigenetic regulation.

PP2A and cancer epigenetics: a therapeutic opportunity waiting to happen

The epigenetic state of chromatin is altered by regulators which influence gene expression in response to environmental stimuli. While several post-translational modifications contribute to chromatin accessibility and transcriptional programs, our understanding of the role that specific phosphorylation sites play is limited. In cancer, kinases and phosphatases are commonly deregulated resulting in increased oncogenic signaling and loss of epigenetic regulation. Aberrant epigenetic states are known to promote cellular plasticity and the development of therapeutic resistance in many cancer types, highlighting the importance of these mechanisms to cancer cell phenotypes. Protein Phosphatase 2A (PP2A) is a heterotrimeric holoenzyme that targets a diverse array of cellular proteins. The composition of the PP2A complex influences its cellular targets and activity. For this reason, PP2A can be tumor suppressive or oncogenic depending on cellular context. Understanding the nuances of PP2A regulation and its effect on epigenetic alterations can lead to new therapeutic avenues that afford more specificity and contribute to the growth of personalized medicine in the oncology field. In this review, we summarize the known PP2A-regulated substrates and potential phosphorylation sites that contribute to cancer cell epigenetics and possible strategies to therapeutically leverage this phosphatase to suppress tumor growth.