Inhibition of promyelocytic leukemia (PML)/retinoic acid receptor-alpha and PML expression in acute promyelocytic leukemia cells by anti-PML peptide nucleic acid

The fusion protein promyelocytic leukemia (PML)/retinoic acid receptor (RAR )alpha is tightly linked to the pathogenesis of acute promyelocytic leukemi a (APL); hence, it represents a tumor-associated, transformation-related mo lecule. In this study, three anti-PML adamantyl-conjugated peptide nucleic acid (PNA) oligomers previously described as in vitro inhibitors of PML/RAR alpha translation were combined and used to block PML/RAR alpha synthesis in NB4 cells. Cationic liposomes were used to achieve sufficient delivery o f PNAs into the cells. Upon treatment of cells with the liposome/PNA mixtur e, enhanced cellular uptake of PNA (approximately 5-fold compared with cont rol) was obtained, Concomitantly, a substantial reduction (> 90%) of the ex pression of PML/RAR alpha was observed when all of the three PNAs were used together. This resulted in a dramatic effect on the number and viability o f NB4 cells in culture after 48 h of treatment. This phenomenon was precede d by induction of apoptosis that could be observed 24 h after treatment. No sign of granulocytic differentiation was observed after treatment. These e ffects were also noted on other leukemic cell lines that express PML but no t the fusion transcript. These results show that it is possible to deliver PNA into hematopoietic cells and obtain specific gene inhibition, and they suggest that a growth inhibitory effect on acute promyelocytic leukemia cel ls fan be obtained through the block of PML/RAR alpha and PML expression.