TGFB1-driven mesenchymal stem cell-mediated NIS gene transfer

Abstract

Based on their excellent tumor-homing capacity, genetically engineered mesenchymal stem cells (MSCs) are under investigation as tumor-selective gene delivery vehicles. Transgenic expression of the sodium iodide symporter (NIS) in genetically engineered MSCs allows noninvasive tracking of MSC homing by imaging of functional NIS expression as well as therapeutic application of 131I. The use of tumor stroma-activated promoters can improve tumor-specific MSC-mediated transgene delivery. The essential role of transforming growth factor B1 (TGFB1) and the SMAD downstream target in the signaling between tumor and the surrounding stroma makes the biology of this pathway a potential option to better control NIS expression within the tumor milieu. Bone marrow-derived MSCs were stably transfected with a NIS-expressing plasmid driven by a synthetic SMAD-responsive promoter (SMAD-NIS-MSCs). Radioiodide uptake assays revealed a 4.9-fold increase in NIS-mediated perchlorate-sensitive iodide uptake in SMAD-NIS-MSCs after TGFB1 stimulation compared to unstimulated cells demonstrating the successful establishment of MSCs, which induce NIS expression in response to activation of TGFB1 signaling using a SMAD-responsive promoter. 123I-scintigraphy revealed significant tumor-specific radioiodide accumulation and thus NIS expression after systemic application of SMAD-NIS-MSCs into mice harboring subcutaneous tumors derived from the human hepatocellular carcinoma (HCC) cell line HuH7, which express TGFB1. 131I therapy in SMAD-NIS-MSCs-treated mice demonstrated a significant delay in tumor growth and prolonged survival. Making use of the tumoral TGFB1 signaling network in the context of MSC-mediated NIS gene delivery is a promising approach to foster tumor stroma-selectivity of NIS transgene expression and tailor NIS-based gene therapy to TGFB1-rich tumor environments.

Thyroid Hormone Effects on Mesenchymal Stem Cell Biology in the Tumour Microenvironment

“…Further, we engineered MSCs to express the sodium iodide symporter (NIS) reporter gene under the control of a synthetic hypoxia-responsive promoter. NIS is a transmembrane protein that transports iodide, thus allowing quantification and analysis of biodistribution of functional NIS expression by measurement of radioiodide uptake in vitro and in vivo, as well as application of therapeutic radionuclides [18,19,[34][35][36][37][38][39][40]. Stimulation of MSCs transfected with the hypoxia-responsive reporter construct with tumour cell-conditioned medium and cobalt chloride leads to an increase in NISmediated radioiodide uptake activity under T4 and, to a lower extent, T3 stimulation [26,38].…”

“…On a different note, modulation of MSC recruitment and engraftment is of central clinical importance in the context of MSCbased gene delivery in cancer therapy. Based on their natural tropism for solid tumours and metastases, MSCs have been exploited by several groups, including our own, to act as "Trojan horses" that can deliver therapeutic payloads deep into the tumour environment [16,18,19,[35][36][37][38][39][40][53][54][55]. Conditioning of MSCs with thyroid hormones may effectively enhance the potency of gene delivery by MSCs.…”

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

“…We have previously shown that the use of tissue or signalspecific gene promoters, whose activation is linked to tumorderived signals, allows a more selective and focused activation of MSC-based transgenes such as NIS and can thereby improve the specificity of tumor treatment (14)(15)(16)25). The cytokine TGFB plays important and diverse roles in the biology of tumor growth and has been shown to be expressed by most solid tumors (28).…”

“…On the basis of this biology, the potential efficacy of a synthetic TGFB1-inducible SMAD-responsive promoter was recently evaluated in engineered MSCs as a means to control and focus NIS transgene expression (SMAD-NIS-MSCs) within tumors. We reported that the systemic application of SMAD-NIS-MSCs to mice harboring a subcutaneous human HCC derived from the TGFB1-expressing HuH7 cell line resulted in a significant delay in tumor growth and prolonged survival of animals upon treatment with radioiodine (25). This proof-of-principle of using a TGFB1inducible SMAD-responsive promoter as a tumor signalresponsive promoter in NIS gene-based therapy, together with the findings from our previous study demonstrating an enhanced recruitment of MSCs in response to EBRT tumor pretreatment with the identification of increased TGFB1 following EBRT treatment, suggested that EBRT may not only enhance the migratory behavior of MSCs but may also act to amplify promoter activation in SMAD-NIS-MSCs due to increased TGFB1 expression in irradiated tumors (25,26).…”

“…We reported that the systemic application of SMAD-NIS-MSCs to mice harboring a subcutaneous human HCC derived from the TGFB1-expressing HuH7 cell line resulted in a significant delay in tumor growth and prolonged survival of animals upon treatment with radioiodine (25). This proof-of-principle of using a TGFB1inducible SMAD-responsive promoter as a tumor signalresponsive promoter in NIS gene-based therapy, together with the findings from our previous study demonstrating an enhanced recruitment of MSCs in response to EBRT tumor pretreatment with the identification of increased TGFB1 following EBRT treatment, suggested that EBRT may not only enhance the migratory behavior of MSCs but may also act to amplify promoter activation in SMAD-NIS-MSCs due to increased TGFB1 expression in irradiated tumors (25,26). In this regard, we and others have previously speculated that gene promoters that are directly or indirectly responsive to radiation-induced signals could potentially allow an amplification of therapy transgene expression when used in the setting of NIS-mediated radioiodine therapy.…”