The Histone Deacetylase Inhibitor Panobinostat (LBH-589) Exerts Anti-Leukaemic Activity in a MLL-Rearranged ALL Xenograft Mouse Model

• Published in: Blood 2014-12, Vol.124 (21), p.3709-3709
• Main Authors: Garrido Castro, Patricia, Van Roon, Eddy HJ, Mimoso Pinhancos, Sandra S, Schneider, Pauline, Kerstjens, Mark JB, Willekes, Merel, Pieters, Rob, Stam, Ronald
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V124.21.3709.3709

BACKGROUND: Infant acute lymphoblastic leukaemia (ALL) is a rare but aggressive malignancy, mainly presenting with chromosomal rearrangements of the MLL (Mixed Lineage Leukaemia) gene locus on 11q23. The majority of these MLL rearrangements involve the translocation partners AF4, AF9 or ENL within the translocation events t(4;11)(q21;q23), t(9;11)(p22;q23) and t(11;19)(q23;p13.3), respectively. The resulting fusion genes, MLL-AF4, MLL-AF9 and MLL-ENL, code for chimeric transcription regulators acting as strong oncogenic drivers, rewriting the epigenetic landscape of the cell and profoundly altering gene expression. Consequently, these cytogenetic lesions define an ALL subtype both biologically and clinically distinct from other subtypes, strongly associated with drug resistance to first-line chemotherapeutics, high relapse rates and a dismal prognosis. Hence, novel treatment strategies which specifically target the underlying molecular pathobiology of this disease are urgently needed. AIMS: Previously, our group performed extensive patient cohort profiling on both transcript and epigenetic level in order to understand the molecular events underlying the disease, and identified histone deacetylase inhibitors (HDACi) as effective therapeutic drugs both in silico and in vitro. The aim of the current study was to elucidate potential molecular mechanisms by which the candidate HDACi Panobinostat is able to target MLL-rearranged ALL (MLLr-ALL) cells, and to confirm its efficacy in vivo using pre-clinical MLLr-ALL xenograft mouse models able to recapitulate the disease phenotype observed in humans. METHODS: Immunodeficient NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice were injected intrafemurally with a MLL-AF4+ B-ALL cell line (SEM) genetically modified to express a luciferase reporter. These mice were subsequently either treated with low-dose (1mg/kg) or high-dose (5mg/kg) Panobinostat using a continuous 5-day-on-2-day-off regimen for a period of up to 12 weeks, or they were assigned to a control group and left untreated. Disease onset and progression was monitored using in vivo bioluminescence imaging, and systemic human ALL cell infiltration was determined by multi-colour flow cytometry and histochemistry. In addition, molecular changes induced by Panobinostat exposure in MLLr-ALL and non-MLLr-ALL cell lines were assessed in vitro using immunoblotting and cell death assays. RESULTS: High-dose Panobinostat resulted in a significantly and substantially delayed MLL