ABSTRACT
Current regimens for induction therapy of pediatric acute lymphoblastic leukemia (ALL), or for re-induction post relapse, use a combination of vincristine (VCR), a glucocorticoid, and L-asparaginase (ASP) with or without an anthracycline. With cure rates now approximately 80%, robust pre-clinical models are necessary to prioritize active new drugs for clinical trials in relapsed/refractory patients, and the ability of these models to predict synergy/antagonism with established therapy is an essential attribute. In this study, we report optimization of an induction-type regimen by combining VCR, dexamethasone (DEX) and ASP (VXL) against ALL xenograft models established from patient biopsies in immune-deficient mice. We demonstrate that the VXL combination was synergistic in vitro against leukemia cell lines as well as in vivo against ALL xenografts. In vivo, VXL treatment caused delays in progression of individual xenografts ranging from 22 to >146 days. The median progression delay of xenografts derived from long-term surviving patients was 2-fold greater than that of xenografts derived from patients who died of their disease. Pharmacokinetic analysis revealed that systemic DEX exposure in mice increased 2-fold when administered in combination with VCR and ASP, consistent with clinical findings, which may contribute to the observed synergy between the 3 drugs. Finally, as proof-of-principle we tested the in vivo efficacy of combining VXL with either the Bcl-2/Bcl-xL/Bcl-w inhibitor, ABT-737, or arsenic trioxide to provide evidence of a robust in vivo platform to prioritize new drugs for clinical trials in children with relapsed/refractory ALL.
Subject(s)
Antineoplastic Combined Chemotherapy Protocols/pharmacokinetics , Induction Chemotherapy , Precursor Cell Lymphoblastic Leukemia-Lymphoma/drug therapy , Animals , Antineoplastic Agents/administration & dosage , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Asparaginase/administration & dosage , Biphenyl Compounds/administration & dosage , Cell Line, Tumor , Child , Dexamethasone/administration & dosage , Disease Models, Animal , Drug Synergism , Female , Humans , Male , Mice , Mice, Inbred NOD , Mice, SCID , Nitrophenols/administration & dosage , Piperazines/administration & dosage , Precursor Cell Lymphoblastic Leukemia-Lymphoma/metabolism , Precursor Cell Lymphoblastic Leukemia-Lymphoma/mortality , Sulfonamides/administration & dosage , Vincristine/administration & dosage , Xenograft Model Antitumor AssaysABSTRACT
Antiapoptotic Bcl-2 proteins are overexpressed in a number of cancers, including leukemias, and are frequently associated with resistance to conventional chemotherapeutic drugs. ABT-737, a Bcl-2 homology domain 3 mimetic (for structure, see Nature 435:677-681, 2005) inhibits the prosurvival function of Bcl-2, Bcl-X(L), and Bcl-w. We show that ABT-737 was effective as a single agent against a panel of pediatric acute lymphoblastic leukemia (ALL) xenografts, previously established, from patient biopsies, in immunodeficient mice. Although in vitro resistance of leukemia cell lines correlated with expression of the prosurvival protein Mcl-1, there was no relationship between Mcl-1 expression and in vivo xenograft response to ABT-737. However, expression of the pro-apoptotic protein Bim, and the extent of its association with Bcl-2, significantly correlated with in vivo ABT-737 sensitivity. ABT-737 potentiated the antileukemic effects of L-asparaginase, topotecan, vincristine, and etoposide against drug-resistant xenografts in vitro and in vivo. Finally, we show that the combination of L-asparaginase (by specifically down-regulating Mcl-1 protein levels), topotecan (by activating p53 via DNA damage), and ABT-737 (by inhibiting antiapoptotic Bcl-2 family members) caused profound synergistic antileukemic efficacy both in vitro and in vivo. Rational targeting of specific components of the apoptotic pathway may be a useful approach to improve the treatment of refractory or relapsed pediatric ALL. Overall, this study supports the inclusion of the clinical derivative of ABT-737, ABT-263 (for structure, see Cancer Res 68:3421-3428, 2008), into clinical trials against relapsed/refractory pediatric ALL.
Subject(s)
Antineoplastic Agents/administration & dosage , Apoptosis/drug effects , Biphenyl Compounds/administration & dosage , Drug Delivery Systems/methods , Molecular Mimicry , Nitrophenols/administration & dosage , Pharmaceutical Preparations/metabolism , Precursor Cell Lymphoblastic Leukemia-Lymphoma/drug therapy , Proto-Oncogene Proteins c-bcl-2/antagonists & inhibitors , Sulfonamides/administration & dosage , Animals , Antineoplastic Agents/chemistry , Antineoplastic Agents/metabolism , Apoptosis/physiology , Biphenyl Compounds/chemistry , Biphenyl Compounds/metabolism , Drug Synergism , HL-60 Cells , HeLa Cells , Humans , Jurkat Cells , K562 Cells , Mice , Mice, Inbred C57BL , Mice, SCID , Nitrophenols/chemistry , Nitrophenols/metabolism , Pharmaceutical Preparations/administration & dosage , Piperazines/administration & dosage , Piperazines/chemistry , Piperazines/metabolism , Precursor Cell Lymphoblastic Leukemia-Lymphoma/metabolism , Proto-Oncogene Proteins c-bcl-2/genetics , Proto-Oncogene Proteins c-bcl-2/metabolism , Sulfonamides/chemistry , Sulfonamides/metabolism , Xenograft Model Antitumor Assays/methodsABSTRACT
Defects in apoptosis signaling contribute to poor outcome in pediatric acute lymphoblastic leukemia (ALL), and overexpression of antiapoptotic Bcl-2 (Bcl-2 and Bcl-X(L)) family proteins has been observed in ALL. ABT-737 is a small-molecule BH3-mimetic that inhibits the antiapoptotic Bcl-2 family proteins. We evaluated the cytotoxicity of ABT-737 in combination with vincristine, dexamethasone, and L-asparaginase (VXL) in 7 ALL cell lines. Multilog synergistic cytotoxicity was observed in all 7 cell lines with ABT-737 plus L-asparaginase or vincristine, and in 5 of 7 cell lines with ABT-737 plus dexamethasone or VXL. In leukemia cells, but not in normal lymphocytes, ABT-737 plus L-asparaginase induced greater mitochondrial depolarization (JC-1 staining); mitochondrial cytochrome c release; activation of Bax, Bid, and caspases (immunoblotting); and eventually apoptosis (annexin V staining) than did either drug alone. In mouse xenografts derived from patients with ALL at diagnosis (ALL-7) or at relapse (ALL-19), event-free survival (EFS) was significantly enhanced with ABT-737 plus VXL relative to VXL or ABT-737 alone (P
