Background

Rearrangements involving the mixed lineage leukaemia (MLL) gene can be found in around 10% of human leukaemias and are associated with particularly poor prognosis in childhood ALL and treatment-related secondary leukaemias. These diseases are likely propagated by a deregulated self renewing pool of leukaemia stem cells (LSCs). Characterisation and targeting of the LSC pool represents a key novel strategy for the treatment of AML. It is also becoming increasingly clear that epigenetic regulation of gene expression at the chromatin level is critical for self renewal, proliferation and differentiation decisions in normal stem cells.

Method

A recent study (Somervaille et al., 2009) identified a set of genes associated with self renewal in a murine model of human MLL translocation AML. A key chromatin regulatory gene, Cbx5, is critically involved in LSC self renewal. This finding led to the current study which aims to identify other chromatin regulatory genes important for LSC self renewal. Aof2 (Lsd1) expression correlates significantly with LSC frequency in a murine model of MLL-derived AML whilst genetic knockdown of the gene, confirmed by both real time PCR and western blotting, induces myeloid-lineage differentiation. Differentiation was determined by both colony forming ability in semi-solid medium and morphological analyses.

Results

Tranylcypromine (TCP), a known inhibitor of Aof2 function, similarly induces myeloid differentiation in both murine and human MLL-derived AML cells, as well as increasing differentiation in primary AML patient samples as determined using flow cytometric analyses of mature myeloid markers. Currently, in vivo murine models of AML are being utilised to determine the effect of Aof2 genetic knockdown or enzymatic inhibition on both initiation and maintenance of disease.

Conclusion

An advantage of targeting genes involved in regulating chromatin is that whilst the underlying mutations are genetic and therefore irreversible, the downstream effects they induce are epigenetic and thus may be pharmalogically reversible