Antisense oligonucleotides with antitumor activity

Antisense oligonucleotides (AONs) provide an efficient approach for developing target-selective anticancer drugs, because they can inhibit gene expression sequence specifically. To improve the therapeutic effenciency of AONs, two new types of the compounds have been developed. The first group of antisense oligodeoxynucleotides investigated contains base modified nucleotide units. Incorporation of 5-substituted pyrimidines into AONs increases cell membrane permeability (a), duplex stability (b), and nuclease resistance (c). These properties were studied using a large number of model oligonucleotides. The application of 5-(1-hexynyl)dU has been found to be the best modification. Application of MMP-9 collagenase inhibitor oligonucleotides (potential metastasis inhibitors) containing these nucleotide units instead of thymidines increased the collagenase inhibition potency by one order of magnitude compared to that of parental oligonucleotide including thymine bases. The second group of the compounds investigated represents a new type of antisense oligonucleotide synthesized by the antisense directed prodrug therapy (ADPT) conception. According to this principle, a telomerase inhibitor AON was conjugated with 5-fluoro-2'-deoxyuridine (FdU) and oligo-FdUs by phosphodiester bond at the 3'-terminus. The antitumor activities of conjugates in comparison with that of FdU were tested in HT1080 human fibrosarcoma and HT29 human colon adenocarcinoma cell lines. In HT29 cell culture the antiproliferative activity of prodrugs significantly increased with increasing length of the 3'-(FdU)n tail. The conjugate with one FdU unit was about 5 times, while the AON-(FdU)3 analogue was almost 19 times more active than FdU. Antitumor activity of the prodrug containing six FdU units was extremely high (relative efficiency = 26.6), therefore, in vivo testing of this analogue seems to be reasonable and promising. Antiproliferative activity of (FdU)n conjugated with a telomerase inhibitor increased by 5-13 times in HT1080 cells as compared to FdU administered in nucleoside form.