MLL-rearranged acute lymphoblastic leukaemia (ALL) represents an aggressive malignancy in infants (<1 year of age), associated with poor outcome. Current treatment intensification is not further possible, and novel therapy strategies are needed. Notably, MLL-rearranged ALL is characterised by a strongly deregulated epigenome and shows sensitivity to epigenetic perturbators. Here we demonstrate the in vivo efficacy of the histone deacetylase inhibitor panobinostat (LBH589) using xenograft mouse models of MLL-rearranged ALL. Panobinostat monotherapy showed strong anti-leukaemic effects, extending survival and reducing overall disease burden. Comprehensive molecular analyses in vitro showed that this anti-leukaemic activity involves depletion of H2B ubiquitination via suppression of the RNF20/RNF40/WAC E3 ligase complex; a pivotal pathway for MLL-rearranged leukaemic maintenance. Knockdown of WAC phenocopied loss of H2B ubiquitination and concomitant cell death induction. These combined data demonstrate that panobinostat cross-inhibits multiple epigenetic pathways, ultimately contributing to its highly efficacious targeting of MLL-rearranged ALL.,

Garrido Castro, P, van Roon, E.H.J, Pinhanços, S.S, Trentin, L. (L.), Schneider, P, Kerstjens, M.J.B, … Stam, R.W. (2018). The HDAC inhibitor panobinostat (LBH589) exerts in vivo anti-leukaemic activity against MLL-rearranged acute lymphoblastic leukaemia and involves the RNF20/RNF40/WAC-H2B ubiquitination axis. Leukemia, 32(2), 323–331. doi:10.1038/leu.2017.216