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

Abstract

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 high-risk 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 growth. In a preclinical setting treating individual patient-derived ALL in vivo, mTOR inhibition alone, and even more pronounced together with conventional remission induction therapy, significantly delayed post-treatment leukemia reoccurrence in TTLshort/high-risk ALL.Thus, the TTLshort phenotype is functionally characterized by hyperactivated mTOR signaling and can effectively be targeted ex vivo and in vivo providing a novel therapeutic strategy for high-risk ALL.

Intrinsic and chemo-sensitizing activity of SMAC-mimetics on high-risk childhood acute lymphoblastic leukemia

“…Cells were mycoplasma-negative, and authenticated by single-tandem-repeat profiling and kept under standard conditions. 39 All four cell lines are of a BCP immunophenotype (BCP-ALL), REH and UoCB6 were derived from ETV6 / RUNX1 − -rearranged, RS4;11 from MLL / AF4 -rearranged leukemias. 40 Analysis of the cell lines for TP53 mutations by denaturing high-performance liquid chromatography followed by Sanger sequencing of exons 4–10 41 identified TP53 mutations in the cell lines REH and RS4;11 while UoCB6 and Nalm-6 were found to be TP53 wild type.…”

“…Primograft leukemias were established transplanting patient ALL cells onto female, 6-week-old NOD/SCID mice (NOD/LtSz-scid/scid, Charles River, Germany) as previously described. 7 , 8 , 39 Patient samples were obtained after informed consent of patients and/or their legal guardians in accordance with the institution's ethical review board, and all animal experiments were approved by the appropriate authority (Regierungspräsidium Tübingen, TVA-Nr. 1147).…”

Tight regulation of FOXO1 is essential for maintenance of B-cell precursor acute lymphoblastic leukemia

“…Cell death was analyzed (according to forward-scattered/side-scattered light [FSC/SSC] criteria) by flow cytometry. For in vivo analyses, recipients were transplanted with primograft samples, and upon leukemia manifestation ($5% huCD19 1 cells in peripheral blood as detected by flow cytometry), 22,23 randomly grouped receiving either AS1842856 or dimethyl sulfoxide (DMSO). After treatment, animals were either euthanized estimating leukemia loads in spleen, bone marrow, or central nervous system or further followed up until reoccurrence of leukemia.…”

Leukemia reconstitution in vivo is driven by cells in early cell cycle and low metabolic state

“…“Time To Leukemia short” (TTL short ) and “Time To Leukemia long” (TTL long ), reflecting early and late engraft ment of primary cells in a BCP-huALL model. 14 These two phenotypes were strongly associated with patients’ outcome and the TTL short /high-risk phenotype involved increased activation of the mammalian target or rapamycin (mTOR) pathway 14 , 15 and deficient apoptosis signaling. 16 …”