Project description:Despite considerable improvements in the treatment of B-cell precursor acute lymphoblastic leukemia (BCP-ALL), relapse is still associated with poor prognosis. We previously found that the risk for early relapse can be predicted by the rapid engraftment of patient-derived blasts transplanted into NOD/SCID mice. In search for the cellular and molecular profile associated with this phenotype, we investigated the expression of microRNAs (miRNAs) in different engraftment phenotypes and patient outcomes. We found miR-497~195 high expression in patient-derived xenograft samples with slow engraftment, derived from patients with favorable outcome. In contrast, epigenetic repression and low expression of these miRNAs was observed in rapidly engrafting samples, which were associated with early relapse. Overexpression of miR-497~195 in patient-derived cells suppressed in vivo engraftment of leukemia cells and considerably prolonged recipient survival by inhibition of regulators of cell cycle progression. As key factors for the entry in S phase were downregulated upon miR-497~195 overexpression, we identified CDK4/CCND3 mediated control of G1/S transition as a principal mechanism for miR-497~195 mediated suppression of leukemia progression in BCP-ALL. Thus, the association of the miR-497~195 cluster expression with outcome in BCP-ALL, and the importance of these miRNAs in counteracting the development of ALL in vivo indicate the relevance of the involved pathways as potential targets for therapeutic intervention.