Cationic liposomes enhance cellular/nuclear localization of 99mTc-antisense oligonucleotides in target tumor cells

Efforts are underway to apply strategies developed in connection with antisense chemotherapy to antisense imaging in nuclear medicine. One such strategy is the use of cationic liposome to enhance the cellular uptake of antisense oligonucleotides.

Using a 99mTc-labeled 18-mer uniformly phosphorothioate DNA antisense to the mRNA of the RI alpha subunit of PKA, the effects of a cationic liposome as carrier on cell uptake and efflux kinetics in tissue culture was evaluated in a RI alpha mRNA positive ACHN cell line. The sense DNA was used as control.

Cell uptake was increased 4-5 fold using the liposome carrier compared to the same dosage of naked DNA. Whether naked or liposome-bound, the antisense DNA showed slower efflux from cells compared to the control, resulting in statistically higher accumulation of the antisense compared to the control DNA and suggesting an antisense effect. The internalization and increased cellular accumulation for both antisense and control DNAs with liposomes were demonstrated by microautoradiography and by subcellular fractionation. Finally, using 99mTc-labeled 15-mer antisense DNA against the c-myc oncogene mRNA in MDA-MB-231 cells, significantly more radiolabel was found in total mRNA for the antisense compared to the sense control DNA, both with and without liposome carrier. In conclusion, in tissue culture, the use of a cationic liposome carrier greatly increased cellular uptake and target mRNA binding of 99mTc-labeled antisense DNA.