Experiment of study on 99Tcm labeling MDM2 antisense oligonucleotide

Objective: The aim of the study was to investigate the possibility of using mouse double minute 2 (MDM2) mRNA antisense oligonucleotide (ASON) labeled with 99Tcm for diagnosing breast cancer. Methods: ASON and mismatch oligonucleotide(ASONM), targeted to mRNA MDM2, were synthesized and radiolabeled with 99Tcm using the bifunctional chelator hydrazino-nicotinamide (HYNIC). Labeling efficiency, radiochemical purity and the ability of the labeled ASON to hybridize to the sense oligonucleotide (SON) were analyzed. Antisense probe hybridized to respective sequence on the whole MDM2 mRNA strand after radiolabeling. MCF-7 cells were incubated with 99Tcm-HYNIC-ASON(0, 100, 500 nmol/L) and 99Tcm-HYNIC- ASONM(500 nmol/L) at various concentrations for 24 h in the presence of lipofectamine 2000. RT-PCR and Western-blotting were then carried out to assay the MDM2 mRNA and protein level. After established MCF-7 human breast cancer bearing nude mice models, biodistribution of 99Tcm-HYNIC-ASON and 99Tcm- HYNIC-ASONM was investigated and tumor images were acquired with SPECT for these animal models. Resuits: The ASON (n=5) was radiolabeled with labeling efficiency of (57.2 ± 2.98)% for the bifunctional chelator HYNIC and (56.3 ± 3.01)% for ASONM. The radiochemical purity was above 95% and the labeled ASON had the ability to hybridize to the SON. The levels of mRNA and protein were significantly different when the concentration of 99Tcm-HYNIC-ASON was different (P<0.01). The excretion of 99Tcm-HYNIC-ASON and 99Tcm-HYNIC-ASONM was mainly through liver and kidney. The ratios of tumor/blood and tumor/ muscle increased with time after injection of 99Tcm-HYNIC-ASON. At 1 h postinjection antisense probe, tumor could be visualized and also with increased uptake with time. Significantly lower tumor to muscle was observed in 99Tcm-HYNIC-ASONM than in 99Tcm-HYNIC-ASON (P<0.01). Conclusion: The 99Tcm- HYNIC-ASON could bind to the breast cancer tissue in mice model, indicating the promising of becoming a diagnostic agent in the future. (authors)