a, Chemical probes developed for study. b, Cell viability profile of compound 1 against a panel of 92 cancer cell lines, derived via CellTiter Glo (CTG) read-out after 72h of compound treatment in 11-point dose-response from 30 µM to 0.1 nM final concentration. Crossing Point was defined as the concentration at which the fitted curve of compound 1 for a given cell line achieved 50% of the positive control compound MG132. Amax was defined as the maximal inhibition observed with compound 1 for a given cell line over the range of tested concentrations. Cancer cell lines are color-coded by tumor primary site for bone (red, 7 cell lines), hematopoietic and lymphoid (blue, 39 cell lines), or other (grey, 46 cell lines). See Supplementary Table 1 for list of all 92 lines tested detailing primary site, lineage and compound sensitivity.