U87 cells were incubated 24 h in complete media in presence of NRs at a final concentration of 100 µg/mL. Then, cells were washed three times with a solution of DPBS containing 1% of BSA to remove most of the unbound NRs. Cells were treated with a solution of trypsin 1x in DPBS for 10 min at 37 °C. Suspended cells were washed twice with cold DPBS by centrifugation (5 min, 1300 rpm) before being fixed with PFA at 4 % in DPBS for 15 min at room temperature. PFA was removed by washing 3 times with DPBS by centrifugation (5 min, 1300 rpm). Large aggregates and eventual fibers were removed by filtrating cells over 100 µm pluriStrainer (pluriSelect) and free NRs detached from cells surfaces during trypsin treatment were removed using 1 µm pluriStrainer (pluriSelect). Before use, strainers were conditioned with DPBS with 1 % BSA. Isolated cells were concentrated by centrifugation (15 min, 1300 rpm) and splited in two equal samples. One