537MO First-in-human study of JNJ-64619178, a protein arginine methyltransferase 5 (PRMT5) inhibitor, in patients with advanced cancers

Repression of PRMT activities sensitize homologous recombination-proficient ovarian and breast cancer cells to PARP inhibitor treatment

An "induced PARP inhibitor (PARPi) sensitivity by epigenetic modulation" strategy is being evaluated in the clinic to sensitize homologous recombination (HR)-proficient tumors to PARPi treatments. To expand its clinical applications and identify more efficient combinations, we performed a drug screen by combining PARPi with 74 well-characterized epigenetic modulators that target five major classes of epigenetic enzymes. Both type I PRMT inhibitor and PRMT5 inhibitor exhibit high combination and clinical priority scores in our screen. PRMT inhibition significantly enhances PARPi treatment-induced DNA damage in HR-proficient ovarian and breast cancer cells. Mechanistically, PRMTs maintain the expression of genes associated with DNA damage repair and BRCAness and regulate intrinsic innate immune pathways in cancer cells. Analyzing large-scale genomic and functional profiles from TCGA and DepMap further confirms that PRMT1, PRMT4, and PRMT5 are potential therapeutic targets in oncology. Finally, PRMT1 and PRMT5 inhibition act synergistically to enhance PARPi sensitivity. Our studies provide a strong rationale for the clinical application of a combination of PRMT and PARP inhibitors in patients with HR-proficient ovarian or breast cancer.

A phase I study to evaluate the safety, pharmacokinetics, and pharmacodynamics of PF-06939999 (PRMT5 inhibitor) in patients with selected advanced or metastatic tumors with high incidence of splicing factor gene mutations

BACKGROUND

Protein arginine methyltransferase 5 (PRMT5) methylates multiple substrates dysregulated in cancer, including spliceosome machinery components. PF-06939999 is a selective small-molecule PRMT5 inhibitor.

PATIENTS AND METHODS

This phase I dose-escalation and -expansion trial (NCT03854227) enrolled patients with selected solid tumors. PF-06939999 was administered orally once or twice a day (q.d./b.i.d.) in 28-day cycles. The objectives were to evaluate PF-06939999 safety and tolerability to identify maximum tolerated dose (MTD) and recommended part 2 dose (RP2D), and assess pharmacokinetics (PK), pharmacodynamics [changes in plasma symmetric dimethylarginine (SDMA) levels], and antitumor activities.

RESULTS

In part 1 dose escalation, 28 patients received PF-06939999 (0.5 mg q.d. to 6 mg b.i.d.). Four of 24 (17%) patients reported dose-limiting toxicities: thrombocytopenia (n = 2, 6 mg b.i.d.), anemia (n = 1, 8 mg q.d.), and neutropenia (n = 1, 6 mg q.d.). PF-06939999 exposure increased with dose. Steady-state PK was achieved by day 15. Plasma SDMA was reduced at steady state (58%-88%). Modulation of plasma SDMA was dose dependent. No MTD was determined. In part 2 dose expansion, 26 patients received PF-06939999 6 mg q.d. (RP2D). Overall (part 1 + part 2), the most common grade ≥3 treatment-related adverse events included anemia (28%), thrombocytopenia/platelet count decreased (22%), fatigue (6%), and neutropenia (4%). Three patients (6.8%) had confirmed partial response (head and neck squamous cell carcinoma, n = 1; non-small-cell lung cancer, n = 2), and 19 (43.2%) had stable disease. No predictive biomarkers were identified.

CONCLUSIONS

PF-06939999 demonstrated a tolerable safety profile and objective clinical responses in a subset of patients, suggesting that PRMT5 is an interesting cancer target with clinical validation. However, no predictive biomarker was identified. The role of PRMT5 in cancer biology is complex and requires further preclinical, mechanistic investigation to identify predictive biomarkers for patient selection.

PRT543, a protein arginine methyltransferase 5 inhibitor, in patients with advanced adenoid cystic carcinoma: An open-label, phase I dose-expansion study

OBJECTIVES

Currently, no systemic treatments are approved for patients with recurrent and/or metastatic (R/M) adenoid cystic carcinoma (ACC). PRT543, a protein arginine methyltransferase 5 inhibitor that downregulates NOTCH1 and MYB signalling in tumours, is a potential candidate for R/M ACC treatment. We report the safety, tolerability and preliminary efficacy of PRT543 in a dose-expansion cohort of patients with R/M ACC.

MATERIALS AND METHODS

This phase I multicentre, open-label, sequential-cohort, dose-escalation and dose-expansion study (NCT03886831) enrolled patients with advanced solid tumours and select haematologic malignancies. Dose-escalation study design and results were reported previously. In the dose expansion, patients with R/M ACC received recommended phase II doses of 35 or 45 mg PRT543 orally on days 1-5 of each week. Primary objectives were to establish the safety and tolerability of PRT543. Secondary objectives included efficacy.

RESULTS

Between February 2019 and May 2022, 56 patients with ACC were enrolled across 23 US sites and received either 35 mg (n = 28) or 45 mg (n = 28) of PRT543. Overall, 23% of patients experienced a grade 3 treatment-related adverse event, most commonly anaemia (16%) and thrombocytopaenia (9%). No grade 4/5 treatment-emergent adverse events were reported. Median progression-free survival was 5.9 months (95% CI: 3.8-8.3). The clinical benefit rate was 57% (95% CI: 43-70). Overall response rate (per Response Evaluation Criteria in Solid Tumours v1.1) was 2%, with 70% of patients having stable disease.

CONCLUSION

In this analysis, PRT543 was tolerable, and the observed efficacy was limited in patients with R/M ACC.

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.

Antitumor Effects of PRMT5 Inhibition in Sarcomas

Patients with advanced soft-tissue sarcomas (STS) have few therapeutic options. Protein arginine methyltransferase 5 (PRMT5), an anticancer target, has been extensively investigated in recent years in epithelial tumors. To date, no data related to the biological role of PRMT5 inhibition and its potential effect as a treatment in STS have been reported.To investigate the therapeutic potential of PRMT5 targeting in STS, we first evaluated the prognostic value of PRMT5 expression in two different cohorts of patients with STS. We then used the potent and selective GSK3326595 (GSK595) compound to investigate the antitumor effect of the pharmacologic inhibition of PRMT5 in vitro via MTT, apoptosis, cell cycle, clonogenicity, and proliferation assays. In vivo studies were performed with two animal models to evaluate the effects of GSK595 on tumor growth. The mechanisms of action were investigated by RNA sequencing, metabolic pathway analysis, Western blotting, and glucose uptake/lactate production assays.High PRMT5 gene expression levels were significantly associated with worsened metastasis-free survival of patients with STS. GSK595 decreased the global symmetric dimethylarginine level, the proliferation rate and clonogenicity of STS cell lines in vitro and tumor growth in vivo. Moreover, PRMT5 inhibition regulated aerobic glycolysis through downregulation of key enzymes of glycolysis as well as glucose uptake and lactate production.The current study demonstrated that PRMT5 regulates STS cell metabolism and thus represents a potential therapeutic target for STS. Additional studies in diverse sarcoma subtypes will be essential to confirm and expand upon these findings.

SIGNIFICANCE

STSs have limited therapeutic options. We show here the poor prognostic value of high PRMT5 expression in STS. Moreover, we demonstrate that the pharmacologic inhibition of PRMT5 has significant antitumor activity through the downregulation of glycolysis. Our findings support the clinical investigation of PRMT5 inhibition in STSs.

RNA splicing alterations in lung cancer pathogenesis and therapy

RNA splicing alterations are widespread and play critical roles in cancer pathogenesis and therapy. Lung cancer is highly heterogeneous and causes the most cancer-related deaths worldwide. Large-scale multi-omics studies have not only characterized the mutational landscapes but also discovered a plethora of transcriptional and post-transcriptional changes in lung cancer. Such resources have greatly facilitated the development of new diagnostic markers and therapeutic options over the past two decades. Intriguingly, altered RNA splicing has emerged as an important molecular feature and therapeutic target of lung cancer. In this review, we provide a brief overview of splicing dysregulation in lung cancer and summarize the recent progress on key splicing events and splicing factors that contribute to lung cancer pathogenesis. Moreover, we describe the general strategies targeting splicing alterations in lung cancer and highlight the potential of combining splicing modulation with currently approved therapies to combat this deadly disease. This review provides new mechanistic and therapeutic insights into splicing dysregulation in cancer.

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

BACKGROUND

GSK3368715, a first-in-class, reversible inhibitor of type I protein methyltransferases (PRMTs) demonstrated anticancer activity in preclinical studies. This Phase 1 study (NCT03666988) evaluated safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of GSK3368715 in adults with advanced-stage solid tumors.

METHODS

In part 1, escalating doses of oral once-daily GSK3368715 (50, 100, and 200 mg) were evaluated. Enrollment was paused at 200 mg following a higher-than-expected incidence of thromboembolic events (TEEs) among the first 19 participants, resuming under a protocol amendment starting at 100 mg. Part 2 (to evaluate preliminary efficacy) was not initiated.

RESULTS

Dose-limiting toxicities were reported in 3/12 (25%) patients at 200 mg. Nine of 31 (29%) patients across dose groups experienced 12 TEEs (8 grade 3 events and 1 grade 5 pulmonary embolism). Best response achieved was stable disease, occurring in 9/31 (29%) patients. Following single and repeat dosing, GSK3368715 maximum plasma concentration was reached within 1 h post dosing. Target engagement was observed in the blood, but was modest and variable in tumor biopsies at 100 mg.

CONCLUSION

Based on higher-than-expected incidence of TEEs, limited target engagement at lower doses, and lack of observed clinical efficacy, a risk/benefit analysis led to early study termination.

TRIAL REGISTRATION NUMBER

NCT03666988.

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.

Comparative Study of Adenosine Analogs as Inhibitors of Protein Arginine Methyltransferases and a Clostridioides difficile-Specific DNA Adenine Methyltransferase

S-Adenosyl-l-methionine (SAM) analogs are adaptable tools for studying and therapeutically inhibiting SAM-dependent methyltransferases (MTases). Some MTases play significant roles in host-pathogen interactions, one of which is Clostridioides difficile-specific DNA adenine MTase (CamA). CamA is needed for efficient sporulation and alters persistence in the colon. To discover potent and selective CamA inhibitors, we explored modifications of the solvent-exposed edge of the SAM adenosine moiety. Starting from the two parental compounds (6e and 7), we designed an adenosine analog (11a) carrying a 3-phenylpropyl moiety at the adenine N6-amino group, and a 3-(cyclohexylmethyl guanidine)-ethyl moiety at the sulfur atom off the ribose ring. Compound 11a (IC50 = 0.15 μM) is 10× and 5× more potent against CamA than 6e and 7, respectively. The structure of the CamA-DNA-inhibitor complex revealed that 11a adopts a U-shaped conformation, with the two branches folded toward each other, and the aliphatic and aromatic rings at the two ends interacting with one another. 11a occupies the entire hydrophobic surface (apparently unique to CamA) next to the adenosine binding site. Our work presents a hybrid knowledge-based and fragment-based approach to generating CamA inhibitors that would be chemical agents to examine the mechanism(s) of action and therapeutic potentials of CamA in C. difficile infection.

Clinical advances in epigenetic therapies for lymphoma

BACKGROUND

Advances in understanding of cancer biology, genomics, epigenomics, and immunology have resulted in development of several therapeutic options that expand cancer care beyond traditional chemotherapy or radiotherapy, including individualized treatment strategies, novel treatments based on monotherapies or combination therapy to reduce toxicities, and implementation of strategies for overcoming resistance to anticancer therapy.

RESULTS

This review covers the latest applications of epigenetic therapies for treatment of B cell, T cell, and Hodgkin lymphomas, highlighting key clinical trial results with monotherapies and combination therapies from the main classes of epigenetic therapies, including inhibitors of DNA methyltransferases, protein arginine methyltransferases, enhancer of zeste homolog 2, histone deacetylases, and the bromodomain and extraterminal domain.

CONCLUSION

Epigenetic therapies are emerging as an attractive add-on to traditional chemotherapy and immunotherapy regimens. New classes of epigenetic therapies promise low toxicity and may work synergistically with other cancer treatments to overcome drug resistance mechanisms.

Approaches to the Management of Metastatic Adenoid Cystic Carcinoma

High rates of recurrence and distant metastasis are a foremost challenge in the management of adenoid cystic carcinoma (ACC), occurring in approximately 40% of all ACC patients. Despite the morbidity and mortality resulting from recurrent/metastatic (R/M) disease, there are no FDA-approved systemic agents for these patients. In this review, we summarize pertinent ACC pathophysiology and its implications for different systemic treatment regimens in R/M ACC. We review the evidence for the most widely used systemic agents - cytotoxic chemotherapy and tyrosine kinase inhibitors (TKIs) targeting VEGFR - in addition to immune checkpoint inhibitors and non-TKI biologic agents. Exciting emerging targets for R/M ACC, including inhibitors of Notch signaling, stemness, PRMT5, and Axl, are also discussed. Lastly, we review local therapies for small-volume lung disease in patients with oligometastatic ACC, specifically pulmonary metastasectomy and stereotactic body radiation therapy (SBRT). Future development of targeted molecular agents which exploit the underlying biology of this disease may yield novel therapeutic options to improve clinical outcomes in patients with R/M ACC.

Protein Arginine Methyltransferase 5 (PRMT5) Inhibitors in Oncology Clinical Trials: A review

Protein arginine methyltransferase 5 (PRMT5) inhibitors are a new class of antineoplastic agents showing promising preliminary clinical efficacy. Targeting an enzyme involved in a wide array of cellular and transcriptional pro-oncogenic processes, this class offers multifaceted tumor-suppressive effects. Partial response has been seen in adenoid cystic carcinoma from both GSK3326595 and JNJ-64619178, with four cases of stable disease seen with PRT543. Highly significant is a durable complete response in isocitrate dehydrogenase 1-mutated glioblastoma multiforme with PRT811. Both alone and in combination with existing chemotherapies and immunotherapies, this class shows promising preliminary data, particularly in cancers with splicing mutations and DNA damage repair deficiencies. Further studies are warranted, and there are clinical trials to come whose data will be telling of the efficacy of PRMT5 inhibitors in both hematologic and solid malignancies. The aim of this study is to compile available results of PRMT5 inhibitors in oncology clinical trials.

PRMT5: An Emerging Target for Pancreatic Adenocarcinoma

Simple Summary

The burden of pancreatic ductal adenocarcinoma (PDAC) increases with rising incidence, yet 5-year overall survival remains poor at 17%. Routine comprehensive genomic profiling of PDAC only finds 2.5% of patients who may benefit and receive matched targeted therapy. Protein arginine methyltransferase 5 (PRMT5) as an anti-cancer target has gained significant interest in recent years and high levels of PRMT5 protein are associated with worse survival outcomes across multiple cancer types. Inhibition of PRMT5 in pre-clinical models can lead to cancer growth inhibition. However, PRMT5 is involved in multiple cellular processes, thus determining its mechanism of action is challenging. While past reviews on PRMT5 have focused on its role in diverse cellular processes and past research studies have focused mainly on haematological malignancies and glioblastoma, this review provides an overview of the possible biological mechanisms of action of PRMT5 inhibition and its potential as a treatment in pancreatic cancer.

Abstract

The overall survival of pancreatic ductal adenocarcinoma (PDAC) remains poor and its incidence is rising. Targetable mutations in PDAC are rare, thus novel therapeutic approaches are needed. Protein arginine methyltransferase 5 (PRMT5) overexpression is associated with worse survival and inhibition of PRMT5 results in decreased cancer growth across multiple cancers, including PDAC. Emerging evidence also suggests that altered RNA processing is a driver in PDAC tumorigenesis and creates a partial dependency on this process. PRMT5 inhibition induces altered splicing and this vulnerability can be exploited as a novel therapeutic approach. Three possible biological pathways underpinning the action of PRMT5 inhibitors are discussed; c-Myc regulation appears central to its action in the PDAC setting. Whilst homozygous MTAP deletion and symmetrical dimethylation levels are associated with increased sensitivity to PRMT5 inhibition, neither measure robustly predicts its growth inhibitory response. The immunomodulatory effect of PRMT5 inhibitors on the tumour microenvironment will also be discussed, based on emerging evidence that PDAC stroma has a significant bearing on disease behaviour and response to therapy. Lastly, with the above caveats in mind, current knowledge gaps and the implications and rationales for PRMT5 inhibitor development in PDAC will be explored.

Repurposing epigenetic inhibitors to target the Clostridioides difficile-specific DNA adenine methyltransferase and sporulation regulator CamA

Epigenetically targeted therapeutic development, particularly for SAM-dependent methylations of DNA, mRNA and histones has been proceeding rapidly for cancer treatments over the past few years. However, this approach has barely begun to be exploited for developing new antibiotics, despite an overwhelming global need to counter antimicrobial resistance. Here, we explore whether SAM analogues, some of which are in (pre)clinical studies as inhibitors of human epigenetic enzymes, can also inhibit Clostridioides difficile-specific DNA adenine methyltransferase (CamA), a sporulation regulator present in all C. difficile genomes sequenced to date, but found in almost no other bacteria. We found that SGC0946 (an inhibitor of DOT1L), JNJ-64619178 (an inhibitor of PRMT5) and SGC8158 (an inhibitor of PRMT7) inhibit CamA enzymatic activity in vitro at low micromolar concentrations. Structural investigation of the ternary complexes of CamA-DNA in the presence of SGC0946 or SGC8158 revealed conformational rearrangements of the N-terminal arm, with no apparent disturbance of the active site. This N-terminal arm and its modulation of exchanges between SAM (the methyl donor) and SAH (the reaction product) during catalysis of methyl transfer are, to date, unique to CamA. Our work presents a substantial first step in generating potent and selective inhibitors of CamA that would serve in the near term as chemical probes to investigate the cellular mechanism(s) of CamA in controlling spore formation and colonization, and eventually as therapeutic antivirulence agents useful in treating C. difficile infection.

Chemogenomics for drug discovery: clinical molecules from open access chemical probes

In recent years chemical probes have proved valuable tools for the validation of disease-modifying targets, facilitating investigation of target function, safety, and translation. Whilst probes and drugs often differ in their properties, there is a belief that chemical probes are useful for translational studies and can accelerate the drug discovery process by providing a starting point for small molecule drugs. This review seeks to describe clinical candidates that have been inspired by, or derived from, chemical probes, and the process behind their development. By focusing primarily on examples of probes developed by the Structural Genomics Consortium, we examine a variety of epigenetic modulators along with other classes of probe.