Development of DNA-based radiopharmaceuticals carrying Auger-electron emitters for antigene radiotherapy

Purpose: Antigene radiotherapy (AR) is based on targeting localized radioda mage to specific sites in the genome by using sequence-specific tripler-for ming oligonucleotides (TFO) to carry Auger-electron-emitters (A-Ettr) such as Iodine-125 (I-125) to the target gene sequence. The radiodecay of an A-E ttr produces a cascade of low-energy electrons and creates a highly positiv ely-charged daughter atom; delivered by a TFO, it should produce double-str and breaks (dsb) localized to the specific DNA target sequence. The result should be a "knock-out" of the targeted gene, Methods and Materials: As a model, we used the MDR1 gene amplified nearly 1 00 times in the human KB-V1 carcinoma cen line, Chemically modified TFO com plementary to the polypurine/polypyrimidine region of the MDR1 gene were sy nthesized and radiolabeled with I-125-dCTP by the primer extension method. Purified plasmid and genomic DNA and extracted nuclei were treated with I-1 25-TFO and analyzed for sequence specific cleavage by electrophoresis in ag arose gel and Southern hybridization. Results: We created I-125-TFO that could effectively recognize, bind, and c leave the target sequence in plasmid and genomic DNA, We showed that these I-125-TFO in nanomolar concentrations were able to cleave the target MDR1 g ene sequence in a natural environment, i.e., within the eucaryotic nucleus, Conclusion: I-125-TFO can effectively introduce sequence-specific dsb to a target within the MDR1 gene, both in purified DNA and inside intact nuclei. Chemically modified TFO conjugated with nuclear localization signal appear to be a promising delivery vehicle for future in vivo trials of AR. (C) 20 01 Elsevier Science Inc.