Highly efficient cellular uptake of c-myb antisense oligonucleotides through specifically designed polymeric nanospheres

c-myb antisense oligonucleotides (AS ODNs) were reversibly immobilized to a novel polymeric core shell nanosphere and their cellular uptake and inhibi tory effect on HL60 leukemia cell proliferation studied. The nanosphere sur face was so designed as to directly bind ODNs via ionic interactions and re versibly release them inside the cells. Compared with the cellular uptake o f free oligonucleotide, the use of AS ODN (immobilized to the nanospheres) produced a 50-fold increase in the intracellular concentration. Specificall y, a single dose of 320 nM of AS ODN immobilized to the nanospheres was cap able of inhibiting HL60 cell proliferation with the same degree of efficien cy obtained using a 50-fold higher dose of free AS ODN, Flow cytometric exp eriments with fluoresceinated ODNs showed a temperature-dependent uptake, w hich was detectable as early as 2 h after the beginning of treatment. The i nhibitory effect on cell proliferation was maintained for up to 8 days of c ulture. Moreover, the level of c-Myb protein decreased by 24% after 2 days and by 60% after 4 days of treatment, thus indicating a continuous and sust ained release of non-degraded AS ODN from the nanospheres inside the cells.