A robust and rapid xenograft model to assess efficacy of chemotherapeutic agents for human acute myeloid leukemia.

Relevant preclinical mouse models are crucial to screen new therapeutic agents for acute myeloid leukemia (AML). Current in vivo models based on the use of patient samples are not easy to establish and manipulate in the laboratory. Our objective was to develop robust xenograft models of human AML using well-characterized cell lines as a more accessible and faster alternative to those incorporating the use of patient-derived AML cells. Five widely used AML cell lines representing various AML subtypes were transplanted and expanded into highly immunodeficient non-obese diabetic/LtSz-severe combined immunodeficiency IL2Rγc(null) mice (for example, cell line-derived xenografts). We show here that bone marrow sublethal conditioning with busulfan or irradiation has equal efficiency for the xenotransplantation of AML cell lines. Although higher number of injected AML cells did not change tumor engraftment in bone marrow and spleen, it significantly reduced the overall survival in mice for all tested AML cell lines. On the basis of AML cell characteristics, these models also exhibited a broad range of overall mouse survival, engraftment, tissue infiltration and aggressiveness. Thus, we have established a robust, rapid and straightforward in vivo model based on engraftment behavior of AML cell lines, all vital prerequisites for testing new therapeutic agents in preclinical studies.

L-type amino-acid transporter 1 (LAT1): a therapeutic target supporting growth and survival of T-cell lymphoblastic lymphoma/T-cell acute lymphoblastic leukemia.

The altered metabolism of cancer cells is a treasure trove to discover new antitumoral strategies. The gene (SLC7A5) encoding system L amino-acid transporter 1 (LAT1) is overexpressed in murine lymphoma cells generated via T-cell deletion of the pten tumor suppressor, and also in human T-cell acute lymphoblastic leukemia (T-ALL)/lymphoma (T-LL) cells. We show here that a potent and LAT1 selective inhibitor (JPH203) decreased leukemic cell viability and proliferation, and induced transient autophagy followed by apoptosis. JPH203 could also alter the in vivo growth of luciferase-expressing-tPTEN-/- cells xenografted into nude mice. In contrast, JPH203 was nontoxic to normal murine thymocytes and human peripheral blood lymphocytes. JPH203 interfered with constitutive activation of mTORC1 and Akt, decreased expression of c-myc and triggered an unfolded protein response mediated by the C/EBP homologous protein (CHOP) transcription factor associated with cell death. A JPH203-resistant tPTEN-/-clone appeared CHOP induction deficient. We also demonstrate that targeting LAT1 may be an efficient broad spectrum adjuvant approach to treat deadly T-cell malignancies as the molecule synergized with rapamycin, dexamethasone, doxorubicin, velcade and l-asparaginase to alter leukemic cell viability.

Overexpression of wild-type or mutants forms of CEBPA alter normal human hematopoiesis.

CCAAT/enhancer-binding protein-α (C/EBPα/CEBPA) is mutated in approximately 8% of acute myeloid leukemia (AML) in both familial and sporadic AML and, with FLT3 and NPM1, has received most attention as a predictive marker of outcome in patients with normal karyotype disease. Mutations clustering to either the N- or C-terminal (N- and C-ter) portions of the protein have different consequences on the protein function. In familial cases, the N-ter form is inherited with patients exhibiting long latency period before the onset of overt disease, typically with the acquisition of a C-ter mutation. Despite the essential insights murine models provide the functional consequences of wild-type C/EBPα in human hematopoiesis and how different mutations are involved in AML development have received less attention. Our data underline the critical role of C/EBPα in human hematopoiesis and demonstrate that C/EBPα mutations (alone or in combination) are insufficient to convert normal human hematopoietic stem/progenitor cells into leukemic-initiating cells, although individually each altered normal hematopoiesis. It provides the first insight into the effects of N- and C-ter mutations acting alone and to the combined effects of N/C double mutants. Our results mimicked closely what happens in CEBPA mutated patients.

Pharmacological targeting of NF-kappaB potentiates the effect of the topoisomerase inhibitor CPT-11 on colon cancer cells.

NF-kappaB interferes with the effect of most anti-cancer drugs through induction of anti-apoptotic genes. Targeting NF-kappaB is therefore expected to potentiate conventional treatments in adjuvant strategies. Here we used a pharmacological inhibitor of the IKK2 kinase (AS602868) to block NF-kappaB activation. In human colon cancer cells, inhibition of NF-kappaB using 10 microM AS602868 induced a 30-50% growth inhibitory effect and strongly enhanced the action of SN-38, the topoisomerase I inhibitor and CPT-11 active metabolite. AS602868 also potentiated the cytotoxic effect of two other antineoplasic drugs: 5-fluorouracil and etoposide. In xenografts experiments, inhibition of NF-kappaB potentiated the antitumoural effect of CPT-11 in a dose-dependent manner. Eighty-five and 75% decreases in tumour size were observed when mice were treated with, respectively, 20 or 5 mg kg(-1) AS602868 associated with 30 mg kg(-1) CPT-11 compared to 47% with CPT-11 alone. Ex vivo tumour analyses as well as in vitro studies showed that AS602868 impaired CPT-11-induced NF-kappaB activation, and enhanced tumour cell cycle arrest and apoptosis. AS602868 also enhanced the apoptotic potential of TNFalpha on HT-29 cells. This study is the first demonstration that a pharmacological inhibitor of the IKK2 kinase can potentiate the therapeutic efficiency of antineoplasic drugs on solid tumours.

AS602868, a dual inhibitor of IKK2 and FLT3 to target AML cells.

Acute myeloid leukemia (AML) cells carry molecular defects that promote their leukemic proliferation, resistance to apoptosis and defect in differentiation. Pharmacological targeting of the nuclear factor kappaB (NF-kappaB) pathway has been shown to promote apoptosis of primary AML cells and to sensitize blasts to neoplastic drugs (Frelin, Blood 2005, 105, 804). The Fms-like tyrosine kinase 3 (FLT3), which sustains proliferation of normal hematopoietic progenitors is frequently overexpressed or mutated in AML patients. Using Ba/F3 murine pre-B cells transfected with various mutants of FLT3 (ITD, D835V, D835Y) and the MV4-11 human AML line, we show that normal or oncogenic stimulation of FLT3 led to activation of NF-kappaB. Pharmacological inhibition of either FLT3 with AG1296 or NF-kappaB with the small molecule inhibitor of IkappaB kinase-2 AS602868 reduced viability and triggered cell death. Moreover, AS602868 was also found to interfere directly with FLT3 kinase activation. AS602868 thus appears to target two different kinases that play a crucial role in the pathogenesis of AML, making it particularly attractive as a new therapeutical approach for AML.