Targeting PML/RARalpha transcript with DNAzymes results in reduction of proliferation and induction of apoptosis in APL cells.

DNAzymes are nucleic acid enzymes that can recognise specific RNA substrate via Watson-Crick base pairing and cleave it with multiple turnovers. We have designed and examined the effects of DNAzymes targeting the PML/RARalpha fusion gene in acute promyelocytic leukaemia (APL). The DNAzymes (DZ1 and DZ3) were designed to cleave the PML/RARalpha transcript at the GC nucleotides at the fusion point and three nucleotides upstream of that respectively. Disabled DNAzymes were synthesised and used as controls. Cell-free cleavage reactions were performed on total RNA from NB4 cell line and PML/RARalpha and RARalpha-amplified RNA fragments (aRNA). Postcleavage examination showed that DZ1 and DZ3 cleave PML/RARalpha efficiently and specifically. NB4 APL cells transfected with DZ1 or DZ3 showed a significant suppression of PML/RARalpha protein expression. These DNAzymes also inhibited the proliferation of NB4 cells, reduced the viability rate, and induced apoptosis in these cells. The disabled DNAzymes showed no effect on NB4 cells. The two DNAzymes did not produce any significant effect on K562 cells, which were used as control cells. DNAzymes are more resistant to serum than ribozymes. These data show that targeting the PML/RARalpha fusion gene with DNAzymes can induce apoptosis in APL cells and may have a role in the treatment of APL. They also show DNAzymes are promising tools for targeting specific genes in leukaemia.