For co-culture experiments with Luciferase-expressing B-ALL PDX samples, 3x104/cm2 mesenchymal stem cells (MSC) were plated in 96-well tissue culture plates and 2x104 B-ALL PDX cells were added in StemSpan Serum-Free Expansion Medium II (SFEM II, STEMCELL Technologies, Cambridge, UK).17 (link),18 (link) Cells were treated for 5 days with indicated drugs and luminescence analyzed with the Steady-Glo Luciferase Assay System (Promega, Southampton, UK), according to manufacturer’s instruction, and detected with Infinite m200 Pro microplate reader (Tecan, Reading, UK). The following reagents and inhibitors were used, S3I-201 (Cayman Chemical, MI, USA), Napabucasin (BBI608; MedChemExpress, NJ, USA), C188-9 (MedChemExpress and Adooq Biosciences, CA, USA), Nutlin-3a (Merck Life Science, Dorset, UK) and Idasanutlin (Bio-Techne, Abingdon, UK).