The ERK1/2 (RAS, RAF, MEK, ERK) and PI3K (PI3K, AKT, mTOR, PTEN) pathways are the chief signaling pathways for cellular proliferation, survival, and differentiation. Overactivation and hyperphosphorylation of the ERK1/2 & PI3K pathways is frequently observed in cancer and is associated with poor patient prognosis. While it is well known that genetic alterations lead to the dysregulation of the ERK1/2 & PI3K pathways, increasing evidence showcase that epigenetic alterations also play a major role in the regulation of the ERK1/2 & PI3K pathways. Protein Arginine Methyltransferase 5 (PRMT5) is a posttranslational modifier for multiple cellular processes, which is currently being tested as a therapeutic target for cancer. PRMT5 has been shown to be overexpressed in many types of cancers, as well as negatively correlated with patient survival. Numerous studies are indicating that as a posttranslational modifier, PRMT5 is extensively involved in regulating the ERK1/2 & PI3K pathways. In addition, a large number of in vitro and in vivo studies are demonstrating that PRMT5 inhibition, as well as PRMT5 and ERK1/2 & PI3K combination therapies, show significant therapeutic effects in many cancer types. In this review, we explore the vast interactions that PRMT5 has with the ERK1/2 & PI3K pathways, and we make the case for further testing of PRMT5 inhibition, as well as PRMT5 and ERK1/2 & PI3K combination therapies, for the treatment of cancer.

Nearly 45% of colorectal cancer (CRC) patients harbor a mutation in their KRAS gene for which, despite many years of research, there are still no targeted therapies available. Protein Arginine Methyltransferase 5 (PRMT5) is a transcription regulator for multiple cellular processes that is currently being tested as a potential target in several cancer types. PRMT5 has been previously shown to be overexpressed in approximately 75% of CRC patient tumor samples, as well as negatively correlated with CRC patient survival. Here, we provide evidence that PRMT5 can act as a surrogate target for mutated KRAS in CRC. Our findings show that PRMT5 expression is upregulated, as well as positively correlated with KRAS expression, in CRC patient datasets. Moreover, our results reveal that PRMT5 is further overexpressed in KRAS mutant CRC cells when compared to KRAS wild type (WT) CRC cells at both the transcriptional and translational levels. Additionally, our data demonstrate that this further overexpression of PRMT5 in the KRAS mutant CRC cells affects an even greater degree of growth inhibition, apoptosis, and cell cycle arrest, following treatment with PRMT5 inhibitor, when compared to the KRAS WT CRC cells. Our research therefore suggests for the first time that PRMT5 and KRAS may crosstalk, and thus, PRMT5 can potentially be used as a surrogate target for mutated KRAS in CRC.

Protein arginine methyltransferases (PRMTs) are a class of enzymes that mediate critical post-translational modifications through arginine methylation as epigenetic regulators. PRMTs have been shown to have a vast array of regulatory effects including in gene expression, signal transduction, and cellular proliferation. Dysregulation of PRMT activity has been seen in the progression of various cancers, including breast, lung, and colorectal cancer. Moreover, PRMT overexpression has been shown to correlate with poor patient prognosis. This review aims to explore the roles of the individual PRMTs in cancer and aims to highlight the latest and newest developments of PRMT inhibitors as emerging therapeutic strategies. Numerous preclinical and clinical studies have identified several novel compounds that effectively target PRMT activity and have shown significant therapeutic results. As such, this review aims to not only highlight the current research findings, but to also emphasize the significant need for future research on PRMTs as novel therapeutic targets in cancer.

The ERK1/2 and PI3K signaling pathways play important roles in cellular proliferation, survival, differentiation, and metabolism. In cancer, these pathways are frequently dysregulated and overactivated, resulting in poor patient prognosis and resistance to treatment. These pathways are activated by receptor tyrosine kinases and send downstream signals to effectors such as RAS, RAF, MEK, AKT, and mTOR. In this review, we highlight the key components of the ERK1/2 and PI3K pathways, the roles they play in tumor progression, and the development of inhibitors and combination therapies designed to enhance therapeutic outcomes and address treatment resistance. Our review demonstrates the need and promise for future research and clinical trials for inhibitors and combination therapies for the ERK1/2 and PI3K pathways in cancer.

Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide with KRAS mutations present in nearly 45% of cases. Compared to KRAS wild-type (WT) CRC, KRAS-mutant CRC is associated with poorer prognosis and fewer effective treatment options. Protein Arginine Methyltransferase 5 (PRMT5), an epigenetic regulator involved in diverse cellular processes, is currently under investigation as a therapeutic target in multiple cancer types. Our previous work demonstrated that PRMT5 inhibition produces stronger therapeutic effects in KRAS-mutant CRC cells than in KRAS WT cells, suggesting potential crosstalk between PRMT5 and KRAS. In this study, we aimed to identify key downstream proteins that may mediate this interaction. Through a literature review, protein–protein interaction analysis (STRING database), gene expression analysis (GEPIA database), and correlation analysis (GEPIA database), we identified MYC, E2F1, and EIF4E as critical candidates. These proteins are shown to interact with both PRMT5 and KRAS in STRING, are overexpressed in CRC tumor samples, and show positive gene expression correlations with PRMT5 and KRAS in patient data. These findings are significant, as they provide new insights into the PRMT5–KRAS crosstalk and suggest potential targets for novel and combination therapies in KRAS-mutant CRC. Further research and biological experiments are needed to verify and outline the exact molecular processes behind MYC, E2F1, and EIF4E’s interactions with both PRMT5 and KRAS.

Introduction Protein Arginine Methyl Transferase 5 (PRMT5) is a transcription regulator for multiple cellular processes. It is being tested as a potential target/biomarker in several cancer types. Herein we analyzed the therapeutic efficacy of PRMT5 in KRAS mutated and wildtype (WT) colorectal cancer (CRC) cells. This cohort of patients (40-45%) have a worse prognosis when treated with monoclonal antibodies that have added significant therapeutic benefit for KRAS wild type CRC. Currently, there is no specific FDA approved alternate therapy guidelines for this subgroup of patients. Methodology Four CRC cell lines [HCT116 and SW620 (KRAS Mutant); and HKE3, LIM 2405 (KRAS Wildtype)] were analyzed for basal level PRMT5 expression by western blot and qPCR analysis. Next, cells were treated with PRMT5 inhibitor (EPZ015666) at 1µM and 10µM concentration for 72 hours and High-Throughput Presto Blue HS Cell Viability Assay was performed in a 96 well plate reading emission at 595 nm. Cell viability was confirmed by flow cytometry with Via Count reagent. Finally, Annexin V/7AAD Apoptosis assay and propidium Iodide cell cycle analysis were performed. Results Conclusion PRMT5 expression is significantly upregulated in KRAS mutated CRC cells when compared to KRAS WT CRC cells. While PRMT5 inhibitor treatment showed efficacy in both wildtype and mutant cells, cell cycle arrest and apoptosis are significantly upregulated for the KRAS mutant cells. In addition, significant reduction in cell viability was observed in KRAS mutant cells. PRMT5 functions by symmetrical di-methylation of several proteins including the histones. The mechanism of crosstalk between KRAS mutation and PRMT5 methylation will provide valuable insight into the disease characteristics of KRAS mutated CRC. Further analysis is in progress to delineate the molecular mechanism. Citation Format: David Shifteh, Tzuriel Sapir, Sanjay Goel, Radhashree Maitra. Protein arginine methyltransferase 5 as a therapeutic target for KRAS mutated colorectal cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2916.