Knockdown of NRMT enhances sensitivity of retinoblastoma cells to cisplatin through upregulation of the CENPA/Myc/Bcl2 axis

Chemotherapy resistance of tumor cells causes failure in anti-tumor therapies. Recently, N-terminal regulator of chromatin condensation 1 methyltransferase (NRMT) is abnormally expressed in different cancers. Hence, we speculate that NRMT may pay a crucial role in the development of chemosensitivity in retinoblastoma. We characterized the upregulation of NRMT in the developed cisplatin (CDDP)-resistant retinoblastoma cell line relative to parental cells. Loss-of-function experiments demonstrated that NRMT silencing enhanced chemosensitivity of retinoblastoma cells to CDDP. Next, NRMT was identified to enrich histone-H3 lysine 4 trimethylation in the promoter of centromere protein A (CENPA) by chromatin immunoprecipitation assay. Rescue experiments suggested that CENPA reduced chemosensitivity by increasing the viability and proliferation and reducing apoptosis of CDDP-resistant retinoblastoma cells, which was reversed by NRMT. Subsequently, CENPA was witnessed to induce the transcription of Myc and to elevate the expression of B cell lymphoma-2. At last, in vivo experiments confirmed the promotive effect of NRMT knockdown on chemosensitivity of retinoblastoma cells to CDDP in tumor-bearing mice. Taken together, NRMT is an inhibitor of chemosensitivity in retinoblastoma. Those findings shed new light on NRMT-targeted therapies for retinoblastoma.

Anticancer Activity of New Na(I) Complex on Retinoblastoma Cells via Inhibiting PI3K/AKT/mTOR Pathway

Here, through applying 2,6-bis(4′-carboxyl-phenyl)pyridine (H2L), a rigid ligand featuring both carboxylic acid and pyridine groups, a new coordination polymer containing Na(I) has been generated with the reaction between H2L ligand and NaNO3 in a water and DMF mixed solvent, and its chemical composition is [Na2L]n. Furthermore, the antiproliferative activity of Na(I) complex against the HXO-Rb44 retinoblastoma cells was detected with CCK-8 assay. Hoechst staining along with Annexin V-FITC/PI revealed that Na(I) complex induces the HXO-Rb44 retinoblastoma cells apoptosis. Flow cytometry analysis of reactive oxygen species (ROS) showed that Na(I) complex significantly increases the level of intracellular ROS. Importantly, western blot analysis revealed that Na(I) complex might induce apoptosis through inactivation of PI3K/AKT/mTOR pathway.

Poly ADP Ribose Polymerase Inhibitor Olaparib Targeting Microhomology End Joining in Retinoblastoma Protein Defective Cancer: Analysis of the Retinoblastoma Cell-Killing Effects by Olaparib after Inducing Double-Strand Breaks

Retinoblastoma is the most common intraocular cancer in childhood. Loss of function in both copies of the RB1 gene is the causal mutation of retinoblastoma. Current treatment for retinoblastoma includes the use of chemotherapeutic agents, such as the DNA damaging agent etoposide, which is a topoisomerase II poison that mainly generates DNA double-strand breaks (DSBs) and genome instability. Unfaithful repairing of DSBs could lead to secondary cancers and serious side effects. Previously, we found that RB knocked-down mammalian cells depend on a highly mutagenic pathway, the micro-homology mediated end joining (MMEJ) pathway, to repair DSBs. Poly ADP ribose polymerase 1 (PARP1) is a major protein in promoting the MMEJ pathway. In this study, we explored the effects of olaparib, a PARP inhibitor, in killing retinoblastoma cells. Retinoblastoma cell line Y79 and primary retinoblastoma cells expressed the cone-rod homeobox protein (CRX), a photoreceptor-specific marker. No detectable RB expression was found in these cells. The co-treatment of olaparib and etoposide led to enhanced cell death in both the Y79 cells and the primary retinoblastoma cells. Our results demonstrated the killing effects in retinoblastoma cells by PARP inhibitor olaparib after inducing DNA double-strand breaks. The use of olaparib in combination with etoposide could improve the cell-killing effects. Thus, lower dosages of etoposide can be used to treat retinoblastoma, which would potentially lead to a lower level of DSBs and a relatively more stable genome.