B-NHL cells display acute sensitivity to apilimod in vitro. (A) Sensitivity of 48 human B-NHL lines to apilimod, with sensitivity defined as an IC₅₀ < 200 nM in a 5-day Cell-Titer Glo assay. The number of cell lines screened is indicated in parentheses. (B) Box-and-whiskers plot of average IC₅₀ values (geometric mean) in human B-NHL (N = 48) and normal human cell lines (N = 12) treated with apilimod for 5 days. Each cell line was tested a minimum of 2 independent times. P < .0001 by the unpaired 2-tailed Student t test. (C) Representative viability curves of lymphoma cell lines in 5-day Cell-Titer Glo assays. (D) Viability of WSU-DLCL2 lymphoma cells after the induction of either control or PIKFYVE shRNA with doxycycline for 5 days. Values normalized to uninduced cells. (E) A PIKFYVE mutation that induces a N1939K amino acid change in the kinase domain confers apilimod resistance. Ten-point dose response of WSU-DLCL2 analysis of overexpression clones (CTRL [GFP], PIKfyve WT, and N1939K) to 3-day treatment with apilimod. Data are represented as mean ± standard deviation (SD). ABC, activated B cell; CTRL, control; GCB, germinal center B cell; GFP, green fluorescent protein; WT, wild type.