We recently reported the significant therapeutic efficacy of radioiodine therapy in various tumor mouse models following transcriptionally targeted sodium iodide symporter (NIS) gene transfer. These studies showed the high potential of NIS as a novel diagnostic and therapeutic gene for the treatment of extrathyroidal tumors. As a next crucial step towards clinical application of NIS-mediated radionuclide therapy we aim at systemic delivery of the NIS gene to target extrathyroidal tumors even in the metastatic stage.
In the current study, we used synthetic polymeric vectors based on pseudodendritic oligoamines with high intrinsic tumor affinity (G2-HD-OEI) to target a NIS-expressing plasmid (CMV-NIS-pcDNA3) to neuroblastoma (Neuro2A) cells.
Incubation with NIS-containing polyplexes (G2-HD-OEI/NIS) resulted in a 51-fold increase in perchlorate-sensitive iodide uptake activity in Neuro2A cells in vitro. Through 123I-scintigraphy and ex vivo gamma counting Neuro2A tumors in syngeneic A/J mice were shown to accumulate 8% to 13% ID/g 123I with a biological half-life of 13 hours, resulting in a tumor-absorbed dose of 247 mGy/MBq 131I after i.v. application of G2-HD-OEI/NIS. Nontarget organs, including liver, lung, kidneys, and spleen revealed no significant iodide uptake. Moreover, two cycles of systemic NIS gene transfer followed by 131I application (55.5 MBq) resulted in a significant delay in tumor growth associated with markedly improved survival.
In conclusion, our data clearly show the high potential of novel pseudo-endritic polymers for tumor-specific NIS gene delivery after systemic application, opening the prospect of targeted NIS-mediated radionuclide therapy of nonthyroidal tumors even in metastatic disease.