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

Deficiency of betaine-homocysteine methyltransferase activates glucose-6-phosphate dehydrogenase (G6PD) by decreasing arginine methylation of G6PD in hepatocellular carcinogenesis

Betaine-homocysteine methyltransferase (BHMT) regulates protein methylation and is correlated with tumorigenesis; however, the effects and regulation of BHMT in hepatocarcinogenesis remain largely unexplored. Here, we determined the clinical significance of BHMT in the occurrence and progression of hepatocellular carcinoma (HCC) using tissue samples from 198 patients. BHMT was to be frequently found (86.6%) expressed at relatively low levels in HCC tissues and was positively correlated with the overall survival of patients with HCC. Bhmt overexpression effectively suppressed several malignant phenotypes in hepatoma cells in vitro and in vivo, whereas complete knockout of Bhmt (Bhmt-/-) produced the opposite effect. We combined proteomics, metabolomics, and molecular biological strategies and detected that Bhmt-/- promoted hepatocarcinogenesis and tumor progression by enhancing the activity of glucose-6-phosphate dehydrogenase (G6PD) and PPP metabolism in DEN-induced HCC mouse and subcutaneous tumor-bearing models. In contrast, restoration of Bhmt with an AAV8-Bhmt injection or pharmacological inhibition of G6PD attenuated hepatocarcinogenesis. Additionally, coimmunoprecipitation identified monomethylated modifications of the G6PD, and BHMT regulated the methylation of G6PD. Protein sequence analysis, generation and application of specific antibodies, and site-directed mutagenesis indicated G6PD methylation at the arginine residue 246. Furthermore, we established bidirectionally regulated BHMT cellular models combined with methylation-deficient G6PD mutants to demonstrate that BHMT potentiated arginine methylation of G6PD, thereby inhibiting G6PD activity, which in turn suppressed hepatocarcinogenesis. Taken together, this study reveals a new methylation-regulatory mechanism in hepatocarcinogenesis owing to BHMT deficiency, suggesting a potential therapeutic strategy for HCC treatment.

New therapy for pancreatic cancer based on extracellular vesicles

Pancreatic Ductal Adenocarcinoma (PDAC), is the most common aggressive cancer of the pancreas. The standard care of PDAC includes tumor resection and chemotherapy, but the lack of early diagnosis and the limited response to the treatment worsens the patient's condition. In order to improve the efficiency of chemotherapy, we look for more efficient systems of drug delivery. We isolated and fully characterized small Extracellular Vesicles (EVs) from the RWP-1 cell line. Our study indicates that the direct incubation method was the most efficient loading protocol and that a minimum total amount of drug triggers an effect on tumor cells. Therefore, we loaded the small EVs with two chemotherapeutic drugs (Temozolomide and EPZ015666) by direct incubation method and the amount of drug loaded was measured by high-performance liquid chromatography (HPLC). Finally, we tested their antiproliferative effect on different cancer cell lines. Moreover, the system is highly dependent on the drug structure and therefore RWP-1 small EVs^TMZ were more efficient than RWP-1 small EVs^EPZ015666. RWP-1 derived small EVs represent a promising drug delivery tool that can be further investigated in preclinical studies and its combination with PRMT5 inhibitor can be potentially developed in clinical trials for the treatment of PDAC.

Glioblastoma-Derived Small Extracellular Vesicles: Nanoparticles for Glioma Treatment

Glioblastoma (GBM), characterized by fast growth and invasion into adjacent tissue, is the most aggressive cancer of brain origin. Current protocols, which include cytotoxic chemotherapeutic agents, effectively treat localized disease; however, these aggressive therapies present side effects due to the high doses administered. Therefore, more efficient ways of drug delivery have been studied to reduce the therapeutic exposure of the patients. We have isolated and fully characterized small extracellular vesicles (EVs) from seven patient-derived GBM cell lines. After loading them with two different drugs, Temozolomide (TMZ) and EPZ015666, we observed a reduction in the total amount of drugs needed to trigger an effect on tumor cells. Moreover, we observed that GBM-derived small EVs, although with lower target specificity, can induce an effect on pancreatic cancer cell death. These results suggest that GBM-derived small EVs represent a promising drug delivery tool for further preclinical studies and potentially for the clinical development of GBM treatments.

PRMT5 is a therapeutic target in choroidal neovascularization

Ocular neovascular diseases including neovascular age-related macular degeneration (nvAMD) are widespread causes of blindness. Patients' non-responsiveness to currently used biologics that target vascular endothelial growth factor (VEGF) poses an unmet need for novel therapies. Here, we identify protein arginine methyltransferase 5 (PRMT5) as a novel therapeutic target for nvAMD. PRMT5 is a well-known epigenetic enzyme. We previously showed that PRMT5 methylates and activates a proangiogenic and proinflammatory transcription factor, the nuclear factor kappa B (NF-κB), which has a master role in tumor progression, notably in pancreatic ductal adenocarcinoma and colorectal cancer. We identified a potent and specific small molecule inhibitor of PRMT5, PR5-LL-CM01, that dampens the methylation and activation of NF-κB. Here for the first time, we assessed the antiangiogenic activity of PR5-LL-CM01 in ocular cells. Immunostaining of human nvAMD sections revealed that PRMT5 is highly expressed in the retinal pigment epithelium (RPE)/choroid where neovascularization occurs, while mouse eyes with laser induced choroidal neovascularization (L-CNV) showed PRMT5 is overexpressed in the retinal ganglion cell layer and in the RPE/choroid. Importantly, inhibition of PRMT5 by PR5-LL-CM01 or shRNA knockdown of PRMT5 in human retinal endothelial cells (HRECs) and induced pluripotent stem cell (iPSC)-derived choroidal endothelial cells (iCEC2) reduced NF-κB activity and the expression of its target genes, such as tumor necrosis factor α (TNF-α) and VEGF-A. In addition to inhibiting angiogenic properties of proliferation and tube formation, PR5-LL-CM01 blocked cell cycle progression at G1/S-phase in a dose-dependent manner in these cells. Thus, we provide the first evidence that inhibition of PRMT5 impedes angiogenesis in ocular endothelial cells, suggesting PRMT5 as a potential therapeutic target to ameliorate ocular neovascularization.

A Review of the Regulatory Mechanisms of N-Myc on Cell Cycle

Neuroblastoma has obvious heterogeneity. It is one of the few undifferentiated malignant tumors that can spontaneously degenerate into completely benign tumors. However, for its high-risk type, even with various intensive treatment options, the prognosis is still unsatisfactory. At the same time, a large number of research data show that the abnormal amplification and high-level expression of the MYCN gene are positively correlated with the malignant progression, poor prognosis, and mortality of neuroblastoma. In this context, this article explores the role of the N-Myc, MYCN gene expression product on its target genes related to the cell cycle and reveals its regulatory network in promoting tumor proliferation and malignant progression. We hope it can provide ideas and direction for the research and development of drugs targeting N-Myc and its downstream target genes.

PRMT5 promotes retinoblastoma development

Epigenetic mechanism, including DNA methylation and histone modifications, contributes to alterations in the expression patterns of genes regulating malignant phenotype of cancer cells. However, the epigenetic modulation of vascular endothelial growth factor-A (VEGFA) in retinoblastoma (RB) has not been clearly established. We aimed to examine the epigenetic regulation of VEGFA by protein arginine methyltransferase 5 (PRMT5) in RB. Using the GEO database, we identified VEGFA as a pathogenic gene in RB. Silencing of VEGFA in SO-RB50 and Y79 cells inhibited cell proliferation, angiogenesis, and migration, promoted apoptosis, and suppressed tumor growth in mice. Mechanistically, PRMT5 promoted H3K4me3 modification of the VEGFA promoter, thereby activating VEGFA expression. VEGFA could regulate the expression of MMP1, MMP2, and MMP9. Further silencing of VEGFA in RB cells overexpressing PRMT5 constrained the expression of MMP1, MMP2 and MMP9, and suppressed the growth of tumors in mice. In conclusion, this study clarifies that the depletion of PRMT5 reduces H3K4me3-mediated VEGFA transcription and retards the carcinogenesis of RB by suppressing the expression of MMPs.

Endothelial PRMT5 plays a crucial role in angiogenesis after acute ischemic injury

Arginine methylation mediated by protein arginine methyltransferases (PRMTs) has been shown to be an important posttranslational mechanism involved in various biological processes. Herein, we sought to investigate whether PRMT5, a major type II enzyme, is involved in pathological angiogenesis and, if so, to elucidate the molecular mechanism involved. Our results show that PRMT5 expression is significantly upregulated in ischemic tissues and hypoxic endothelial cells (ECs). Endothelial-specific Prmt5-KO mice were generated to define the role of PRMT5 in hindlimb ischemia-induced angiogenesis. We found that these mice exhibited impaired recovery of blood perfusion and motor function of the lower limbs, an impairment that was accompanied by decreased vascular density and increased necrosis as compared with their WT littermates. Furthermore, both pharmacological and genetic inhibition of PRMT5 significantly attenuated EC proliferation, migration, tube formation, and aortic ring sprouting. Mechanistically, we showed that inhibition of PRMT5 markedly attenuated hypoxia-induced factor 1-α (HIF-1α) protein stability and vascular endothelial growth factor-induced (VEGF-induced) signaling pathways in ECs. Our results provide compelling evidence demonstrating a crucial role of PRMT5 in hypoxia-induced angiogenesis and suggest that inhibition of PRMT5 may provide novel therapeutic strategies for the treatment of abnormal angiogenesis-related diseases, such as cancer and diabetic retinopathy.

LncRNA HOTAIR facilitates proliferation and represses apoptosis of retinoblastoma cells through the miR-20b-5p/RRM2/PI3K/AKT axis

Purpose

Retinoblastoma (RB) represents an adolescent eye malignancy. Long non-coding RNA (LncRNA) HOTAIR shows aberrant expression in many malignancies. This research investigated the mechanism of HOTAIR in RB.

Methods

Normal retinal cell lines (ARPE-19 and RPE-1) and RB cell lines (ORB50, Y79, HXO-RB44, and WERI-RB) were selected for detection of HOTAIR expression by qRT-PCR. sh-HOTAIR was delivered into Y79 and HXO-RB44 cells. Cell-cycle distribution, proliferation, and apoptosis were detected by CCK-8 assay and flow cytometry. Binding relationships among HOTAIR, miR-20b-5p, and RRM2 were confirmed using dual-luciferase assay. Roles of miR-20b-5p and RRM2 in RB cell-cycle distribution, proliferation, and apoptosis were ascertained by functional rescue experiments. Murine model of xenograft tumor was established, followed by detection of tumor growth and counting of Ki67-positive cells. Expressions of proliferation- and apoptosis-associated proteins and PI3K/AKT pathway-related proteins were determined by Western blot.

Results

HOTAIR was elevated in RB cells relative to that in normal retinal cells and showed relatively high expression in Y79 and HXO-RB44 cells. sh-HOTAIR induced RB cell-cycle arrest, restrained proliferation, and strengthened apoptosis. HOTAIR functioned as the ceRNA of miR-20b-5p and targeted RRM2. RB cells had poorly-expressed miR-20b-5p and highly-expressed RRM2. miR-20b-5p downregulation or RRM2 overexpression facilitated RB cell-cycle and proliferation, suppressed apoptosis, and reversed the protective effect of sh-HOTAIR on RB. sh-HOTAIR reduced tumor growth and Ki67-positive cells in vivo and inactivated PI3K/AKT pathway.

Conclusion

LncRNA HOTAIR upregulated RRM2 by competitively binding to miR-20b-5p and activated PI3K/AKT pathway, thereby facilitating proliferation and repressing apoptosis of RB cells.

SP2509, a Selective Inhibitor of LSD1, Suppresses Retinoblastoma Growth by Downregulating β-catenin Signaling

Purpose

To study the role of lysine-specific demethylase 1 (LSD1) in retinoblastoma (RB) growth and to determine whether the LSD1 inhibitor SP2509 can inhibit RB progression.

Methods

We detected the levels of LSD1 in 12 RB tissue samples, two RB cell lines (Y79 and Weri-RB1), and a retinal pigment epithelium cell line (ARPE-19). Overexpression or knockdown of LSD1 was performed to examine the role of LSD1 in RB cancer cell survival. In vitro and in vivo experiments were conducted to detect the antitumor effect of SP2509, and the antitumor mechanism of SP2509 was examined by RNA sequencing and Western blot.

Results

LSD1 is overexpressed in RB tissues and cells and increases RB cancer cell viability and colony formation ability. The LSD1 inhibitor SP2509 inhibits RB cell proliferation in vitro and in vivo. Treatment with SP2509 increases the levels of dimethylated histone 3 lysine 4 (H3K4me2) and inhibits the expression of β-catenin signaling pathway–related proteins in RB cells.

Conclusions

We demonstrated that LSD1 is overexpressed in RB cells and promotes RB cell survival. The LSD1 inhibitor SP2509 exerted strong growth inhibition in vitro and in vivo, which was at least partially mediated by suppression of the β-catenin pathway.