MR molecular imaging of tumors based on an optimal hTERT promoter tyrosinase expression system

Chuan Li,Chang-Jiang Hu,Bo Tang,Yu-Yun Wu,Xin Yong,Shi-Ming Yang,Gang Luo,Su-Min Wang,Song-Tao Yu

doi:10.18632/oncotarget.9888

Abstract

The early diagnosis and treatment of tumors is of vital significance to increase patient survival. Therefore, we constructed a lentiviral vector expressing tyrosinase (TYR) driven by an optimized human telomerase reverse transcriptase (hTERT) promoter or a cytomegalovirus(CMV) promoter in the hopes of performing noninvasive and real-time tumor-specific imaging. First, hTERT-TYR and CMV-TYR were constructed to infect cancer cell lines (telomerase-negative cell line: U2OS; telomerase-positive cell lines: SGC-7901, SW480 and HepG2). Subsequently, stable tyrosinase-expressing cell lines were sorted by flow cytometry out of these infected cancer cell lines. Then, the mRNA and protein levels of tyrosinase were analyzed. Thetyrosinase activity, melanin production and ferric ion adsorption were measured followed by an MR scan. Consequently the results showed that tyrosinase was only expressed in telomerase-positive tumor cells infected by hTERT-TYR, whereas tyrosinase was expressed in both telomerase-negative and telomerase-positive tumor cells infected by CMV-TYR. Finally, we performed in vivo tumor MR using a clinical 3T MR scanner and found increased signals at T1W1 from telomerase-positive cells infected by hTERT-TYR, which revealed that MR scanning could distinguish cells with hTERT -positive cells from hTERT-negative cells infected with the optimized lentivirus. The mechanism underlying this effect is that tyrosinase promotes melanin production and ferric ion adsorption only in hTERT-expressing cells. Taken together, these data show that this optimized hTERT promoter-driving tyrosinase expression system might be a useful diagnostic tool for the detection of tumors using MR imaging.

Highlights

With new developments in molecular biology and applications of molecular probes, MR molecular imaging has provided new ideas for the diagnosis of tumors [1]
We performed in vivo tumor MR using a clinical 3T MR scanner and found increased signals at T1W1 from telomerase-positive cells infected by human telomerase reverse transcriptase (hTERT)-TYR, which revealed that MR scanning could distinguish cells with hTERT -positive cells from hTERT-negative cells infected with the optimized lentivirus
To test the selective expression of hTERT-TYR, three hTERT-positive cell lines (SGC-7901, SW480 and HepG2) were infected with the lentiviral constructs, as was an hTERT negative cell line (U2OS) that served as a negative control

Summary

Introduction

With new developments in molecular biology and applications of molecular probes, MR molecular imaging has provided new ideas for the diagnosis of tumors [1]. If the TYR gene can be driven by specific promoters that are active in tumor cells but not in normal tissues or cells, it could be used as an MR readout for tumors. It has been reported that adding three Myc-binding E-box (CACGTG) motifs to the hTERT promoter improved its tumor targeting effect [12, 13]. We successfully designed and constructed an optimized hTERT promoter, which contained the core region of the hTERT promoter and three Myc-binding motifs [14]. The cytosine deaminase (CD) gene driven by the optimized hTERT promoter significantly improved the suicidal effect of the hTERT-positive tumor cells [15]. We first constructed a recombinant tyrosinase expression plasmid driven by the optimized hTERT promoter to test the signal of xenograft tumors in vivo using MR scanning

Methods

Results

Conclusion