Real time RT/PCR expression of cassini in pro-B ALL cells treated with therapeutic drugs in the presence of direct stromal support. (A) Schematic representing the nature of a co-culture system in which ALL cells and stromal cells are in direct contact with one another. Due to partial infiltration of ALL cells underneath the stromal layer, only ALL cells in the supernatant were harvested for RNA isolation and gene expression purposes. (B) Viability of murine 8093 ALL cells over the course of drug treatment in the presence of MEFs. (C) Real time RT/PCR analysis of cassini expression in 8093 ALL cells at indicated time points during drug treatment (n = 3). **p < 0.01 d1-d10 compared to 0 hr. (D) 8093 cells treated with ASA, nilotinib or nilotinib + ASA (n = 2). ASA + nilotinib on d2, d8 and d12 versus nilotinib on d2, d8 and d12 *p < 0.05, **p < 0.01 and *p < 0.05, respectively. (E, F) Expression of CASSINI in human ALL cells in direct co-culture with irradiated OP9 stromal cells (n = 1 each) and treated with (E) 2.5 nM vincristine over the course of 20 days, with US7 cells harvested at indicated time points, day 9 and day 20 or (F) TXL2R cells cultured for 24 days without nilotinib (control), or cultured for 14 days without nilotinib, then treated with 500 nM nilotinib for 10 days. Values are represented as mean ± SD of duplicate real-time RT/PCR. ***p < 0.001 US7 d20 vincristine compared to DMSO; p = 0.06 (ns) TXLR control compared to TXLR2 d10 nilotinib.