Synthesis and biologic study of IV-14, a new ribonucleoside radiotracer for tumor visualization.
Uridine-cytidine kinase (UCK) 2, an enzyme normally expressed in human placenta and testis and highly overexpressed in many neoplasias of blood and solid tissues, catalyzes monophosphorylation of pyrimidine ribonucleosides with efficiency 15- to 20-fold higher than that of ubiquitously expressed isozyme UCK1. In this paper, we report the synthesis of 3'-(E)-(2-iodovinyl)uridine (IV-14) and its preclinical evaluation as a new radiotracer derived from a UCK2-selective antitumor agent, 3'-(ethynyl)uridine.


METHODS
Radioiodinated IV-14 was prepared from the respective stannyl precursor. (131)I-IV-14 was studied in cellular uptake assays and tested for stability in serum as well as for stability to thymidine phosphorylase, liver-, and mucosa-specific murine uridine phosphorylases. UCK1 and UCK2 expression levels in different tumor cell lines were determined by Western blot. Cellular distribution of (131)I-IV-14 was determined in HL60 cells. Biodistribution studies and gamma-camera scintigraphy were performed on an HL60-xenografted severe combined immunodeficiency (SCID) mouse model.


RESULTS
(131)I-IV-14 demonstrated excellent stability in serum. It was stable to human thymidine phosphorylase and to liver- and mucosa-specific murine uridine phosphorylases. Cellular uptake after 24 h of incubation with (131)I-IV-14 was 4.27 +/- 0.21, 3.66 +/- 0.13, 2.69 +/- 0.07, 2.24 +/- 0.18, and 3.26 +/- 0.18 percentage injected dose per 5 x 10(5) Mia-PaCa-2, CX-1, HL60, Capan-1, and Panc-1 cells, respectively. Uptake and retention of IV-14 were regulated by 2 factors: UCK2 expression level and intracellular transport mediated partially via human equilibrating nucleoside transporter 1. A biodistribution study of (131)I-IV-14 in an HL60-xenografted SCID mouse model showed that at 4 h after injection the greatest amount of retained radioactivity was in tumor. The tissue-to-tumor ratio 4 h after injection was 1.0 +/- 0.24 for tumor, 0.40 +/- 0.18 for spleen, 0.25 +/- 0.12 for colon, 0.14 +/- 0.07 for small intestine, and less than 0.1 for other sites. Scintigraphy with (123)I-IV-14 4 h after injection showed the tumor well. In addition, high accumulation of radioiodide in the stomach content was observed and was presumably due to metabolic degradation of IV-14.


CONCLUSIONS
IV-14 is a UCK2-specific marker, allowing for in vivo addressing of tumors with high RNA synthesis independent of proliferation rate.
Zlatopolskiy
Boris D
BD
Klinik für Nuklearmedizin, Universität Ulm, Ulm, Germany.
Morgenroth
Agnieszka
A
Kunkel
Falk H-G
FH
Urusova
Elizaveta A
EA
Dinger
Cornelia
C
Kull
Thomas
T
Lepping
Christian
C
Reske
Sven N
SN
D000818:Animals; D001692:Biological Transport; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D005260:Female; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D007457:Iodine Radioisotopes / Q000737:chemistry; D008297:Male; D051379:Mice; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D011849:Radioactive Tracers; D011854:Radiochemistry; D011877:Radionuclide Imaging; D013939:Thymidine Phosphorylase / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution; D014529:Uridine / Q000031:analogs & derivatives* / Q000097:blood / Q000138:chemical synthesis* / Q000378:metabolism; D014541:Uridine Kinase / Q000378:metabolism; D014543:Uridine Phosphorylase / Q000378:metabolism; D014753:Vinyl Compounds / Q000097:blood / Q000138:chemical synthesis* / Q000378:metabolism
C545187:3'-(2-iodovinyl)uridine; D007457:Iodine Radioisotopes; D011849:Radioactive Tracers; D014753:Vinyl Compounds; D014543:Uridine Phosphorylase; D013939:Thymidine Phosphorylase; D014541:Uridine Kinase; D014529:Uridine