Rational Design, synthesis and biological evaluation of novel triazole derivatives as potent and selective PRMT5 inhibitors with antitumor activity

Overview of the development of protein arginine methyltransferase modulators: Achievements and future directions

Protein methylation is a post-translational modification (PTM) that organisms undergo. This process is considered a part of epigenetics research. In recent years, there has been an increasing interest in protein methylation, particularly histone methylation, as research has advanced. Methylation of histones is a dynamic process that is subject to fine control by histone methyltransferases and demethylases. In addition, many non-histone proteins also undergo methylation, and these modifications collectively regulate physiological phenomena, including RNA transcription, translation, signal transduction, DNA damage response, and cell cycle. Protein arginine methylation is a crucial aspect of protein methylation, which plays a significant role in regulating the cell cycle and repairing DNA. It is also linked to various diseases. Therefore, protein arginine methyltransferases (PRMTs) that are involved in this process have gained considerable attention as a potential therapeutic target for treating diseases. Several PRMT inhibitors are in phase I/II clinical trials. This paper aims to introduce the structure, biochemical functions, and bioactivity assays of PRMTs. Additionally, we will review the structure-function of currently popular PRMT inhibitors. Through the analysis of various data on known PRMT inhibitors, we hope to provide valuable assistance for future drug design and development.

Protein Arginine Methyltransferases as Therapeutic Targets in Hematological Malignancies

Arginine methylation is a common post-translational modification affecting protein activity and the transcription of target genes when methylation occurs on histone tails. There are nine protein arginine methyltransferases (PRMTs) in mammals, divided into subgroups depending on the methylation they form on a molecule of arginine. During the formation and maturation of the different types of blood cells, PRMTs play a central role by controlling cell differentiation at the transcriptional level. PRMT enzymatic activity is necessary for many cellular processes in hematological malignancies, such as the activation of cell cycle and proliferation, inhibition of apoptosis, DNA repair processes, RNA splicing, and transcription by methylating histone tails' arginine. Chemical tools have been developed to inhibit the activity of PRMTs and have been tested in several models of hematological malignancies, including primary samples from patients, xenografts into immunodeficient mice, mouse models, and human cell lines. They show a significant effect by reducing cell viability and increasing the overall survival of mice. PRMT5 inhibitors have a strong therapeutic potential, as phase I clinical trials in hematological malignancies that use these molecules show promising results, thus, underlining PRMT inhibitors as useful therapeutic tools for cancer treatment in the future.

Discovery of novel PRMT5 inhibitors bearing a methylpiperazinyl moiety

Background: PRMT5 is an epigenetics-related enzyme, which plays a critical role in cancer development. Hence PRMT5 inhibition has been validated as a promising therapeutic strategy. Methods & Results: We synthesized a series of methylpiperazinyl derivatives as novel PRMT5 inhibitors that were achieved by scaffold-hopping from EPZ015666 by virtual screening followed by rational drug design. Among all compounds 43g, bearing a thiourea linker, showed antitumor activity across multiple cancer cell lines and reduced the level of symmetric arginine dimethylation of SmD3 dose-dependently. Moreover, 43g selectively inhibited PRMT5 among protein arginine methyltransferase isoforms. Further proteomics analysis revealed that 43g remarkably reduced the global arginine dimethylation level in a cellular context. Conclusion: This work provides new chemical templates for future structural optimization of PRMT5-related cancer treatments.

An update on allosteric modulators as a promising strategy targeting histone methyltransferase

Histone methylation is a vital post-translational modification process in epigenetic regulation. The perturbation of histone methylation accounts for many diseases, including malignant cancers. Although achieving significant advances over past decades, orthosteric inhibitors targeting histone methyltransferases still suffer from challenges on subtype selectivity and acquired drug-resistant mutations. As an alternative, new compounds targeting the evolutionarily less conserved allosteric sites, exemplified by HKMTs and PRMTs inhibitors, offer a promising strategy to address this quandary. Herein, we highlight the allosteric sites and mechanisms in histone methyltransferases along with representative allosteric modulators, expecting to facilitate the discovery of allosteric modulators in favor of epigenetic therapy.

Acquired resistance to PRMT5 inhibition induces concomitant collateral sensitivity to paclitaxel

Epigenetic regulators play key roles in cancer and are increasingly being targeted for treatment. However, for many, little is known about mechanisms of resistance to the inhibition of these regulators. We have generated a model of resistance to inhibitors of protein arginine methyltransferase 5 (PRMT5). This study was conducted in Kras ^G12D;Tp53-null lung adenocarcinoma (LUAD) cell lines. Resistance to PRMT5 inhibitors (PRMT5i) arose rapidly, and barcoding experiments showed that this resulted from a drug-induced transcriptional state switch, not selection of a preexisting population. This resistant state is both stable and conserved across variants arising from distinct LUAD lines. Moreover, it brought with it vulnerabilities to other chemotherapeutics, especially the taxane paclitaxel. This paclitaxel sensitivity depended on the presence of stathmin 2 (STMN2), a microtubule regulator that is specifically expressed in the resistant state. Remarkably, STMN2 was also essential for resistance to PRMT5 inhibition. Thus, a single gene is required for both acquisition of resistance to PRMT5i and collateral sensitivity to paclitaxel in our LUAD cells. Accordingly, the combination of PRMT5i and paclitaxel yielded potent and synergistic killing of the murine LUAD cells. Importantly, the synergy between PRMT5i and paclitaxel also extended to human cancer cell lines. Finally, analysis of The Cancer Genome Atlas patient data showed that high STMN2 levels correlate with complete regression of tumors in response to taxane treatment. Collectively, this study reveals a recurring mechanism of PRMT5i resistance in LUAD and identifies collateral sensitivities that have potential clinical relevance.

1,2,3,4-Tetrahydroisoquinoline (THIQ) as privileged scaffold for anticancer de novo drug design

Introduction: Cancer is a dreadful disorder that is emerging as one of the leading causes of mortality across the globe. The complex tumor environment, supplemented with drawbacks of the existing drugs, has made it a global health concern. The Tetrahydroisoquinoline (THIQ) ring holds an important position in medicinal chemistry due to its wide range of pharmacological properties. Several THIQ based natural products have been previously explored for their antitumor properties, making it a vital scaffold for anticancer drug design.Areas covered: This review article addresses the potential of THIQ as anticancer agents. Various medicinal chemistry strategies employed for the design and development of THIQ analogs as inhibitors or modulators of relevant anticancer targets have been discussed in detail. Moreover, the common strategies employed for the synthesis of the core scaffold are also highlighted.Expert opinion: Evidently, THIQs have tremendous potential in anticancer drug design. Some of these analogs exhibited potent activity against various cancer molecular targets. However, there are some drawbacks, such as selectivity that need addressing. The synthetic ease for constructing the core scaffold complimented with its reactivity makes it ideal for further structure-activity relationship studies. For these reasons, THIQ is a privileged scaffold for the design and development of novel anticancer agents.

The Discovery of Two Novel Classes of 5,5-Bicyclic Nucleoside-Derived PRMT5 Inhibitors for the Treatment of Cancer

Protein arginine methyltransferase 5 (PRMT5) is a type II arginine methyltransferase that catalyzes the post-translational symmetric dimethylation of protein substrates. PRMT5 plays a critical role in regulating biological processes including transcription, cell cycle progression, RNA splicing, and DNA repair. As such, dysregulation of PRMT5 activity is implicated in the development and progression of multiple cancers and is a target of growing clinical interest. Described herein are the structure-based drug designs, robust synthetic efforts, and lead optimization strategies toward the identification of two novel 5,5-fused bicyclic nucleoside-derived classes of potent and efficacious PRMT5 inhibitors. Utilization of compound docking and strain energy calculations inspired novel designs, and the development of flexible synthetic approaches enabled access to complex chemotypes with five contiguous stereocenters. Additional efforts in balancing bioavailability, solubility, potency, and CYP3A4 inhibition led to the identification of diverse lead compounds with favorable profiles, promising in vivo activity, and low human dose projections.

Cancer Dependencies: PRMT5 and MAT2A in MTAP/p16-Deleted Cancers

Discovery of targeted therapies that selectively exploit the genetic inactivation of specific tumor suppressors remains a major challenge. This includes the prevalent deletion of the CDKN2A/ MTAP locus, which was first reported nearly 40 years ago. The more recent advent of RNA interference and functional genomic screening technologies led to the identification of hidden collateral lethalities occurring with passenger deletions of MTAP in cancer cells. In particular, small-molecule inhibition of the type II arginine methyltransferase PRMT5 and the S-adenosylmethionine-producing enzyme MAT2A each presents a precision medicine approach for the treatment of patients whose tumors have homozygous loss of MTAP. In this review, we highlight key aspects of MTAP, PRMT5, and MAT2A biology to provide a conceptual framework for developing novel therapeutic strategies in tumors with MTAP deletion and to summarize ongoing efforts to drug PRMT5 and MAT2A.

EPZ015666, a selective protein arginine methyltransferase 5 (PRMT5) inhibitor with an antitumour effect in retinoblastoma

Retinoblastoma (RB) is the most common intraocular malignant tumour in infants, and chemotherapy has been the primary therapy method in recent years. PRMT5 is an important member of the protein arginine methyltransferase family, which plays an important role in various tumours. Our study showed that PRMT5 was overexpressed in retinoblastoma and played an important role in retinoblastoma cell growth. EPZ015666 is a novel PRMT5 inhibitor, and we found that it inhibited retinoblastoma cell proliferation and led to cell cycle arrest at the G1 phase. At the same time, EPZ015666 regulated cell cycle related protein (P53, P21, P27, CDK2) expression. In brief, our study showed that PRMT5 promoted retinoblastoma growth, the PRMT5 inhibitor EPZ015666 inhibited retinoblastoma in vitro by regulating P53-P21/P27-CDK2 signaling pathways and slowed retinoblastoma growth in a xenograft model.