title: Imaging of dihydrofolate reductase fusion gene expression in xenografts of human liver metastases of colorectal cancer in living rats.
abstract: Radionuclide imaging has been demonstrated to be feasible to monitor transgene expression in vivo. We hypothesized that a potential application of this technique is to non-invasively detect in deep tissue, such as cancer cells metastatic to the liver, a specific molecular response following systemic drug treatment. Utilizing human colon adenocarcinoma cells derived from a patient's liver lesion we first developed a nude rat xenograft model for colorectal cancer metastatic to the liver. Expression of a dihydrofolate reductase-herpes simplex virus 1 thymidine kinase fusion (DHFR-HSV1 TK) transgene in the hepatic tumors was monitored in individual animals using the tracer [(124)I]2'-fluoro-2'-deoxy-5-iodouracil-beta- d-arabinofuranoside (FIAU) and a small animal micro positron emission tomograph (microPET), while groups of rats were imaged using the tracer [(131)I]FIAU and a clinical gamma camera. Growth of the human metastatic colorectal cancer cells in the rat liver was detected using magnetic resonance imaging and confirmed by surgical inspection. Single as well as multiple lesions of different sizes and sites were observed in the liver of the animals. Next, using a subset of rats bearing hepatic tumors, which were retrovirally bulk transduced to express the DHFR-HSV1 TK transgene, we imaged the fusion protein expression in the hepatic tumor of living rats using the tracer [(124)I]FIAU and a microPET. The observed deep tissue signals were highly specific for the tumors expressing the DHFR-HSV1 TK fusion protein compared with parental untransduced tumors and other tissues as determined by gamma counting of tissue samples. A subsequent study used the tracer [(131)I]FIAU and a gamma camera to monitor two groups of transduced hepatic tumor-bearing rats. Prior to imaging, one group was treated with trimetrexate to exploit DHFR-mediated upregulation of the fusion gene product. Imaging in the living animal as well as subsequent gamma counting of tissue samples showed increased signal and tracer accumulation, respectively, as compared to the group not treated with the antifolate. It is concluded that the two examined nucleotide imaging methods are feasible techniques for monitoring of DHFR-HSV TK fusion protein expression in hepatic colorectal tumor tissue in living animals.
authors.affiliation: Molecular Pharmacology and Therapeutics Program, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
authors.forename: Philipp
authors.initials: P
authors.lastname: Mayer-Kuckuk
authors.forename: Mikhail
authors.initials: M
authors.lastname: Doubrovin
authors.forename: Niraj J
authors.initials: NJ
authors.lastname: Gusani
authors.forename: Terence
authors.initials: T
authors.lastname: Gade
authors.forename: Julius
authors.initials: J
authors.lastname: Balatoni
authors.forename: Tim
authors.initials: T
authors.lastname: Akhurst
authors.forename: Ronald
authors.initials: R
authors.lastname: Finn
authors.forename: Yuman
authors.initials: Y
authors.lastname: Fong
authors.forename: Jason A
authors.initials: JA
authors.lastname: Koutcher
authors.forename: Steven
authors.initials: S
authors.lastname: Larson
authors.forename: Ronald
authors.initials: R
authors.lastname: Blasberg
authors.forename: Juri Gelovani
authors.initials: JG
authors.lastname: Tjuvajev
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Bertino
authors.forename: Debabrata
authors.initials: D
authors.lastname: Banerjee
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified / Q000378:metabolism; D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging* / Q000235:genetics / Q000378:metabolism*; D005240:Feasibility Studies; D005493:Folic Acid Antagonists / Q000627:therapeutic use; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000378:metabolism* / Q000556:secondary; D008297:Male; D009368:Neoplasm Transplantation; D009928:Organ Specificity; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D011923:Rats, Nude; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism; D014018:Tissue Distribution; D014183:Transplantation, Heterologous; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D014915:Whole-Body Counting
chemical_list: D005493:Folic Acid Antagonists; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D001086:Arabinofuranosyluracil; C043457:fialuridine; D013762:Tetrahydrofolate Dehydrogenase; C099241:thymidine kinase, Canid herpesvirus 1; D013937:Thymidine Kinase