Noninvasive and real-time monitoring of the therapeutic response of tumors in vivo with an optimized hTERT promoter.
BACKGROUND
Telomerase is commonly recognized as an effective anticancer target. The human telomerase reverse transcriptase (hTERT), the rate-limiting component of telomerase, is expressed in most malignant tumors, but it is not found in most normal somatic cells. Here, we report a real-time and noninvasive method to monitor tumor response to a lentivirus-based hTERT-conditional suicidal gene therapy.


METHODS
In this study, we constructed a lentivirus system in which an optimized hTERT promoter was used to drive the expression of the cytosine deaminase (CD) gene, one of the suicide genes, and a green fluorescent protein (GFP) reporter gene (pLenti-CD/GFP). The lentivirus was used to infect telomerase-positive or telomerase-negative cell lines. In vitro and in vivo experiments were conducted to analyze the dynamic processes of exogenous gene expression noninvasively in cell culture and living animals in real time via optical imaging.


RESULTS
The lentivirus was able to express the CD gene and GFP in telomerase-positive tumor cells and significantly decrease cell proliferation after the use of prodrug 5-flucytosine. However, it could not express GFP and CD in telomerase-negative cell lines, nor could it induce any suicidal effect in those cells. The in vivo study showed that telomerase-positive tumors can be visualized after intratumor injection of the lentivirus in tumor-bearing nude mice via an optical imaging system. Significant tumor growth suppression was observed in telomerase-positive tumors.


CONCLUSIONS
Collectively, this technology provides a valuable, noninvasive method to evaluate the real-time therapeutic response of tumors in vivo.
Institute of Gastroenterology, Southwest Hospital, Third Military Medical University, Chongqing, People's Republic of China.
Song-Tao
ST
Yu
Chuan
C
Li
Mu-Han
MH
Lü
Guang-Ping
GP
Liang
Ning
N
Li
Xu-Dong
XD
Tang
Yu-Yun
YY
Wu
Chun-Meng
CM
Shi
Ling
L
Chen
Chang-Zhu
CZ
Li
Ya-Ling
YL
Cao
Dian-Chun
DC
Fang
Shi-Ming
SM
Yang
D000818:Animals; D045744:Cell Line, Tumor; D003199:Computer Systems; D043525:Cytosine Deaminase / Q000235:genetics / Q000378:metabolism*; D016903:Drug Monitoring / Q000379:methods*; D005437:Flucytosine; D017930:Genes, Reporter; D041722:Genes, Transgenic, Suicide; D015316:Genetic Therapy / Q000379:methods*; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D016086:Lentivirus / Q000235:genetics; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000235:genetics / Q000628:therapy*; D011401:Promoter Regions, Genetic; D019098:Telomerase / Q000235:genetics*; D016896:Treatment Outcome; D023041:Xenograft Model Antitumor Assays
D049452:Green Fluorescent Proteins; D005437:Flucytosine; C509186:TERT protein, human; D019098:Telomerase; D043525:Cytosine Deaminase