Resistance of t(17;19)-acute lymphoblastic leukemia cell lines to multiagents in induction therapy.

t(17;19)(q21-q22;p13), responsible for TCF3-HLF fusion, is a rare translocation in childhood B-cell precursor acute lymphoblastic leukemia(BCP-ALL). t(1;19)(q23;p13), producing TCF3-PBX1 fusion, is a common translocation in childhood BCP-ALL. Prognosis of t(17;19)-ALL is extremely poor, while that of t(1;19)-ALL has recently improved dramatically in intensified chemotherapy. In this study, TCF3-HLF mRNA was detectable at a high level during induction therapy in a newly diagnosed t(17;19)-ALL case, while TCF3-PBX1 mRNA was undetectable at the end of induction therapy in most newly diagnosed t(1;19)-ALL cases. Using 4 t(17;19)-ALL and 16 t(1;19)-ALL cell lines, drug response profiling was analyzed. t(17;19)-ALL cell lines were found to be significantly more resistant to vincristine (VCR), daunorubicin (DNR), and prednisolone (Pred) than t(1;19)-ALL cell lines. Sensitivities to three (Pred, VCR, and l-asparaginase [l-Asp]), four (Pred, VCR, l-Asp, and DNR) and five (Pred, VCR, l-Asp, DNR, and cyclophosphamide) agents, widely used in induction therapy, were significantly poorer for t(17;19)-ALL cell lines than for t(1;19)-ALL cell lines. Consistent with poor responses to VCR and DNR, gene and protein expression levels of P-glycoprotein (P-gp) were higher in t(17;19)-ALL cell lines than in t(1;19)-ALL cell lines. Inhibitors for P-gp sensitized P-gp-positive t(17;19)-ALL cell lines to VCR and DNR. Knockout of P-gp by CRISPRCas9 overcame resistance to VCR and DNR in the P-gp-positive t(17;19)-ALL cell line. A combination of cyclosporine A with DNR prolonged survival of NSG mice inoculated with P-gp-positive t(17;19)-ALL cell line. These findings indicate involvement of P-gp in resistance to VCR and DNR in Pgp positive t(17;19)-ALL cell lines. In all four t(17;19)-ALL cell lines, RAS pathway mutation was detected. Furthermore, among 16 t(1;19)-ALL cell lines, multiagent resistance was usually observed in the cell lines with RAS pathway mutation in comparison to those without it, suggesting at least a partial involvement of RAS pathway mutation in multiagent resistance of t(17;19)-ALL.