PRMT5 inhibition drives potent anti-MCL activity in vitro. (A) Eight MCL cell lines were treated with increasing doses of the PRMT5 inhibitor PRT-382 for 9 days. Cell viability was measured by annexin-V/propidium iodide (PI) staining and flow cytometry. (B-C) Jeko-1, Z-138, and Granta-519 were treated for 6 days with increasing doses of PRT-382. The viable cell count was measured with count beads by gating on annexin-V/PI–negative cells. (D-E) CCMCL1, Jeko-1, and Z-138 were treated with PRT-382 for 3 days at the indicated doses. Protein lysates were obtained and immunoblotted for H4R3me2s, SDMA, and ADMA. β-Actin was used as a loading control. Protein expression densitometry values normalized to β-actin and relative to dimethyl sulfoxide (DMSO) control. Dots represent individual replicate experiments. (F) CCMCL1, Jeko-1, Granta-519, and Z-138 were treated with PRT-382 at day 9 IC50 values. Protein lysates were collected at the indicated time points and immunoblotted for total SDMA with β-actin, α-tubulin, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) used as loading controls. Protein expression densitometry values for total SDMA normalized to loading control and relative to the no treatment time point 0 in lane 1. (G) Primary patient samples were cocultured with a CD40-ligand overexpressing murine fibroblast cell line and stimulated with cytokines. Cells were treated with PRT-382 for 6 days and viability and growth was measured by near-IR live/dead stain and gating on human CD19⁺/CD5⁺ MCL with flow cytometry. (H) Primary patient sample 1972 was treated with PRT-382 for 2 days at the indicated doses. Protein lysates were immunoblotted for total SDMA with β-actin used as a loading control.