LOCALIZATION OF SMALL-CELL LUNG-CANCER XENOGRAFTS WITH IODINE-125-SOMATOSTATIN, INDIUM-111-SOMATOSTATIN, AND RHENIUM-188-SOMATOSTATIN ANALOGS

We examined the potential of radiolabeled somatostatin analogs, I-125- Tyr-3-octreotide (I-125-octreotide), In-111-DTPA(diethylenetriaminepen taacetatic acid)-D-Phe-1-octreotide (In-111-octreotide), and Re-188-oc treotide for targeting small-cell lung cancer (SCLC) in a mouse model, Tyr-3-octreotide was labeled with I-125 by the chloramine T method, a nd In-111-octreotide was obtained as a kit, while Re-188 was eluted fr om a W-188/Re-188 generator, and octreotide was directly labeled with Re-188 by reducing disulfide bonds. The I-125-, In-111- and Re-188-oct reotides were injected i.v. into athymic mice bearing NCI-H69 tumors, and the biodistributions were determined at 15 min, and 2, 4, 8, and 2 4 h. Tumor uptakes were 0.5 +/- 0.2, 0.3 +/- 0.1, 0.3 +/- 0.1 %ID/g, a nd tumor-to-blood ratios were 1.8, 11.9, 1.2 at 8 h for I-125-, In-111 -, and Re-188-octreotides, respectively. Accumulations of In-111-octre otide in normal tissues were lower than those of I-125- and Re-188-oct reotides. Re-188-octreotide can be used to localize SCLC lesions as ef ficiently as radioiodinated octreotide. However, In-111-octreotide was the most suitable agent to obtain high tumor-to-normal tissue contras t for localizing SCLC.