Environmental-mediated vincristine drug resistance of human precursor B-acute lymphoblastic leukemia (pre-B ALL)

First-line treatment for pre-B acute lymphoblastic leukemia (pre-B ALL) typically encompasses a period of so-called induction therapy in which the patient is treated for 28 days with chemotherapy to induce a remission. A bone marrow sample is subsequently taken to determine the number of remaining leukemia cells, which are called minimal residual disease (MDR). MRD is a key prognostic factor, with higher MRD levels predicting worse outcome for patients. Induction therapy usually is able to drastically reduce the number of leukemic cells but chemoresistance, as first detected by higher MRD levels, remains a major clinical problem. MRD persists not only by leukemia cell-intrinsic mechanisms such as clonal selection and genetic changes, but also through protective interactions of the leukemia cells with the surrounding supporting stroma. This mechanism of drug resistance has been named environment-mediated drug resistance (EMDR) and is a general route through which MRD cells, regardless of underlying genetics of the leukemia cells, can persist after chemotherapy. The EMDR component contributing to the persistence of MRD leukemia cells can be studied in tissue culture models by treating leukemia cells with a non-lethal drug dose in the presence of stromal cell protection. Here we analysed the transcriptome of a PDX-derived human pre-B ALL cell line co-cultured with OP9 stromal cells as they developed drug insensitivity against the chemotherapeutic drug vincristine. Overall design: ICN13 PDX/patient-derived pre-B ALL cells were grown in co-culture with mitotically inactivated OP9 bone marrow stromal cells. Cells cultured with 2 nM vincristine or 4 nM were collected from triplicate wells for RNA isolation at day 18 and d30, respectively, along with controls cultured for the same period of time but without drug. At the time of cell harvest, total cell counts were increasing in the vincristine-treated samples and their viability (% of \Trypan-blue excluding cells/total cell number) was >70%.