Targeting of hyperactivated mTOR signaling in high-risk acute lymphoblastic leukemia in a pre-clinical model.

Despite increasingly successful treatment of pediatric ALL, up to 20% of patients encounter relapse. By current biomarkers, the majority of relapse patients is initially not identified indicating the need for prognostic and therapeutic targets reflecting leukemia biology. We previously described that rapid engraftment of patient ALL cells transplanted onto NOD/SCID mice (short time to leukemia, TTLshort) is indicative of early patient relapse. Gene expression profiling identified genes coding for molecules involved in mTOR signaling to be associated with TTLshort/early relapse leukemia. Here, we now functionally address mTOR signaling activity in primograft ALL samples and evaluate mTOR pathway inhibition as novel treatment strategy for highrisk ALL ex vivo and in vivo. By analysis of S6-phosphorylation downstream of mTOR, increased mTOR activation was found in TTLshort/high-risk ALL, which was effectively abrogated by mTOR inhibitors resulting in decreased leukemia proliferation and g...