We thus shifted our attention to human cell lines and the corresponding toxic effects evoked by the probe molecules. MTT assays were performed in HEK-293 and PDL-hTERT cells after 3 d of co-incubation and approximate apparent IC50 values ranged from 120 to 950 µM demonstrating no acute cell toxicity with the probes and therefore enabling their use for offtarget studies in human cells (Figure ).