(A) Neuro-2a cells were transduced with lentiviral vectors expressing HPRT shRNA (RRL-HPRTshRNA) or no shRNA (control construct; RRL-ctr) at different MOI, and whole cell lysates were analyzed after transduction at the indicated time points by Western blot. Lane 1: mock, untransduced; Lane 2: ctr, MOI 10; Lane 3: HPRT shRNA, MOI 10; Lane 4: mock, untransduced; Lane 5: ctr, MOI 100; Lane 6: HPRT shRNA, MOI 100; Lane 7: HPRT shRNA, MOI 400. (B) At weekly intervals, Neuro-2a cells (untransduced (mock), or transduced with RRL-ctr or RRL-HPRTshRNA at MOI 100) were incubated with 0, 3 or 6 µM 6TG for 3 days before cell viability was measured by MTS assay. Cell viability values for cells treated with 3 µM 6TG (white bars) and 6 µM 6TG (black bars) were normalized to each respective set of untreated (0 µM 6TG) cells. (*: below limit of quantitation.)