Radiation-Induced Amplification of TGFB1-Induced Mesenchymal Stem Cell-Mediated Sodium Iodide Symporter (NIS) Gene 131I Therapy.

The innate tumor homing potential of mesenchymal stem cells (MSCs) has been used for a targeted delivery of the theranostic sodium iodide symporter (NIS) transgene into solid tumors. We have previously shown that external beam radiotherapy (EBRT) results in the enhanced recruitment of NIS-expressing MSCs into human hepatocellular carcinoma (HuH7). In parallel, the tumor-associated cytokine TGFB1 becomes strongly upregulated in HuH7 tumors in response to EBRT. We therefore evaluated the effects of combining focused EBRT (5 Gy) with MSC-mediated systemic delivery of the theranostic NIS transgene under control of a synthetic TGFB1-inducible SMAD-responsive promoter (SMAD-NIS-MSCs) using 123I-scintigraphy followed by 131I therapy in CD1 nu/nu mice harboring subcutaneous human hepatocellular carcinoma (HuH7). Following tumor irradiation and SMAD-NIS-MSC application, tumoral iodide uptake monitored in vivo by 123I-scintigraphy was enhanced as compared with nonirradiated tumors. Combination of EBRT and SMAD-NIS-MSC-mediated 131I therapy resulted in a significantly improved delay in tumor growth and prolonged survival in therapy mice as compared with the combined therapy using CMV-NIS-MSCs or to control groups receiving EBRT or saline only, or EBRT together with SMAD-NIS-MSCs and saline applications. MSC-based NIS-mediated 131I therapy after EBRT treatment dramatically enhanced therapeutic efficacy when a TGFB1-inducible SMAD-responsive promoter was used to drive NIS expression in adoptively applied MSCs. The remarkable therapeutic effect seen is thought to be linked in large part to the enhanced TGFB1 produced in this context, which leads to a highly selective and focused amplification of MSC-based NIS expression within the tumor milieu.