To further confirm this notion, we exemplarily tested inhibition of one of the S. aureus cognate targets, the topoisomerase IV, with Cipro P1 and an approx. 16-fold reduction in activity compared to the parent Ciprofloxacin (IC50 of approx. 25 µM, in line with literature values of 7-20 µM) was observed (Figure ). Although the focus of this study is on human offtargets, these results confirm the desired effects of the P1-probes in bacteria which is a promising starting point for human off-target discovery. For the same reason, also P2-probes, despite showing no antibiotic activity, were subjected to the following human cell AfBPP experiments.