pemrametostat (GSK3326595)

Collectively, our results provide a strong rationale and mechanistic insights for the clinical development of MRTX1719-based IO combinations in MTAP-loss tumors.

The safety profile was broadly consistent with other published PRMT5 inhibitor studies. ClinicalTrials.gov: NCT03614728.

Furthermore, treatment with the PRMT5 inhibitor pemrametostat and a selective ER degrader fulvestrant synergistically inhibits growth of ER+/RB-deficient cell-derived and patient-derived xenografts. These findings highlight dual ER and PRMT5 blockade as a potential therapeutic strategy to overcome resistance to CDK4/6i in ER+/RB-deficient breast cancer.

P1, N=288, Completed, GlaxoSmithKline | Active, not recruiting --> Completed

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.

Combination MTDIA and AG-270 treatment differs from direct inhibition of PRMT5 by GSK3326595 by avoiding toxicity caused by cell death in the normal gut epithelium induced by the PRMT5 inhibitor. The combination of MTAP and MAT2a inhibitors expands this synthetic lethal approach to include MTAP cancers, especially the remaining 98% of CRCs without the MTAP genotype.

The drug combinations were performed using proliferation and colony formation assays on TNBC cell lines that were sensitive or resistant to EPZ015938, a PRMT5 inhibitor that has been evaluated in clinical trials. The chemotherapies analyzed were cisplatin, doxorubicin, camptothecin, and paclitaxel. The targeted therapies tested were erlotinib (EGFR inhibitor), neratinib (EGFR/HER2/HER4 inhibitor) and tucatinib (HER2 inhibitor)...We noticed that synergy can be obtained in TNBC cell lines that were resistant to PRMT5 inhibition alone. Altogether, our data highlight the therapeutic potential of targeting PRMT5 using combinatorial strategies for the treatment of subsets of TNBC patients.

The proliferation effects of MTA-cooperative PRMT5 inhibitors, TNG908 or TNG462, and a SAM-cooperative PRMT5 inhibitor, GSK3326595, on MTAP-deleted and MTAP-intact MPNST cell lines were determined using CellTiter-Glo (CTG) assays. The clinical stage MTA-cooperative PRMT5 inhibitors TNG908 (NCT05275478) and TNG462 (NCT05732831) are efficacious in MPNST models in vitro and in vivo and are therefore promising therapeutic agents for patients with MTAP-deleted MPNST.

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...The present 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.

These data demonstrate that inhibition of PRMT5 induced signatures of DNA damage in models of breast and ovarian cancer. Furthermore, combination with the PARP inhibitor, Niraparib, resulted in increased anti-tumor activity in vitro and in vivo. Overall, these data suggest inhibition of PRMT5 as a mechanism to broaden and enhance the clinical application of PARP inhibitors.

We validated the synergistic effects and mechanisms of combined treatment with a type I PRMT inhibitor and a PRMT5 inhibitor (JNJ-64619178, GSK3326595/EPZ015938 or an in-house PRMT5i) using cell-based assays and in vivo studies...In vitro and in vivo studies revealed that inhibitors of type I PRMT and MAT2A (AG-270) dosing combination indeed exhibited stronger anti-cancer activity than mono-treatment...In vivo, the combination of type I PRMT inhibitor with different FLT3 inhibitors (Gilteritinib, Midostaurin, or CTS2016) led to deeper antitumor responses in a variety of FLT3-ITD AML models. Taken together, these findings support the co-administration of type I PRMT inhibitor with various therapies including epigenetic reprogramming, cancer metabolism modulation, or targeted therapies for receptor tyrosine kinases, which could benefit cancer patients as a promising therapeutic strategy.

P2, N=40, Completed, Ottawa Hospital Research Institute | Not yet recruiting --> Completed | N=60 --> 40 | Trial completion date: Dec 2022 --> Aug 2022 | Trial primary completion date: Dec 2022 --> Aug 2022

Herein, a series of tetrahydroisoquinoline (THIQ) derivatives were designed and synthesized as PRMT5 inhibitors using GSK-3326595 as the lead compound...Furthermore, compound 20 possesses acceptable pharmacokinetic profiles and displays considerable in vivo antitumor efficacy in a MV-4-11 xenograft model. Taken together, compound 20 is an antitumor compound worthy of further study.

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...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.

b N=14 efficacy evaluable pop. c Confirmed responses (CR or PR) based on RECIST 1.1 (solid tumors) or Lugano (NHL) criteria.

PRMT5 inhibition reduced the expression of upstream DNA repair kinases ATM and ATR, which may in part explain our observation that EPZ015938 and the DNA-alkylating agent, melphalan, have combinatory effects. Moreover, PRMT5 was shown to be involved in splicing regulation of MMSET and SLAMF7, known genes of importance in MM disease. As such, we broaden the understanding of the exact role of PRMT5 in MM disease and further underline its use as a possible therapeutic target.

To harness the potential vulnerability presented by PRMT5i-mediated G2/M arrest, we combined PRMT5i treatment with ionizing radiation (IR) exposure to find that the combination of EPZ015938 and IR displayed a greater reduction in PDAC cell growth in vitro over individual treatments. In conclusion, we find that PRMT5 is a critical player in DNA damage via modulation of the ATM/ATR pathways, and combined PRMT5i and IR have beneficial anti-tumor effects in vitro, revealing an exciting avenue for further exploration as a potential new therapeutic strategy in PDAC.

Knockout of RB1 in MCF-7 and T47D cells increased IC 50 of abemaciclib, palbociclib, and ribociclib 10-200 fold compared to WT cells...We are currently testing the antitumor activity of fulvestrant plus GSK3326595 against RBKO xenografts as well as the requirement of arginine methyltransferase activity associated with PRMT5 for growth of ER+/ RB1 -deficient breast cancer cells. PRMT5 is essential for proliferation of ER+/ RB1 -deficient breast cancer cells. Targeting PRMT5 in combination with anti-estrogens is a novel and testable strategy to suppress E2F-regulated cell cycle progression of this CDK4/6 inhibitor-resistant breast cancer subtype.

Combination of GSK3326595 with anti-PD-1 immune checkpoint therapy (ICT) improved therapeutic efficacy in HCC. This study revealed that PRMT5 is an epigenetic executer of MYC leading to repression of the transcriptional regulation of downstream genes that promote hepatocellular carcinogenesis, highlights a mechanism-based therapeutic strategy for MYC-driven HCC via PRMT5 inhibition through synergistically suppressed proliferation and enhanced anti-tumor immunity, and finally provides an opportunity to mitigate the resistance of "immune-cold" tumor to ICT.

P2, N=60, Not yet recruiting, Ottawa Hospital Research Institute | Initiation date: Dec 2020 --> Mar 2021

P2, N=60, Not yet recruiting, Ottawa Hospital Research Institute

P1, N=412, Recruiting, GlaxoSmithKline | Trial completion date: Dec 2021 --> Apr 2025 | Trial primary completion date: Dec 2021 --> Apr 2025

Combination of pharmacological (GSK3326595) or genetic (shRNA) inhibition of PRMT5 with immune checkpoint therapy limited growth of murine melanoma tumors (B16F10 and YUMM1.7) and enhanced therapeutic efficacy, compared with the effect of either treatment alone. Overall, our findings provide a rationale to test PRMT5 inhibitors in immunotherapy-based clinical trials as a means to enhance an antitumor immune response.

Trial completion date: Dec 2022 --> Mar 2023 | Trial primary completion date: Dec 2022 --> Mar 2023

Importantly, combining palbociclib with the PRMT5 inhibitor GSK3326595 enhances the efficacy of palbociclib in treating naive and resistant models and also delays the emergence of resistance. Furthermore, we have established that palbociclib inhibition of the PRMT5-MDM4 axis is essential for robust melanoma cell sensitivity and provide preclinical evidence that coinhibition of CDK4/6 and PRMT5 is an effective and well-tolerated therapeutic strategy. Overall, our data provide a strong rationale for further investigation of novel combinations of CDK4/6 and PRMT5 inhibitors, not only in melanoma but other tumor types, including breast, pancreatic, and esophageal carcinoma.

P1, N=416, Recruiting, GlaxoSmithKline | N=317 --> 416 | Trial completion date: Oct 2020 --> Dec 2021 | Trial primary completion date: Oct 2020 --> Dec 2021