Study on biodistribution and imaging of radioiodinated antisense oligonucleotides in nude mice bearing human lymphoma

The incidence of sporadic lymphoma has risen due to an increase in immunosuppressed patients, particularly those with human immunodeficiency virus (HIV) infection. Sometimes suspect lymphoma has an undetectable location and we can not get the pathological specimen. Management of lymphoma is also difficult because the persistence of a significant number of residual tumor cells after intensive treatment. These relative failures can be attributed to make us choose this study for opening a new diagnostic and therapeutic field of lymphoma from molecular level. Immunoglobulin (Ig) heavy chain framework region (FR) of V1 family have been verified to be a major determinant of malignant phenotype of V1 family B-cell lymphoma. Most of targets for tumor antisense therapy study are protooncogenes, such as c-myc, bc1-2, which are broad -spectrum tumor imaging agents. The aim of this study was to investigate the possibility of using radioiodine labeled FR antisense oligonucleotides (ASONs) as an imaging agent or antisense therapeutic radiopharmaceutical in lymphoma. A 18-mer partial phosphorothioate oligonucleotide sequence was synthesized and grafted in 5 ' with a tyramine group which was further labeled with 125I or 131I using the chloramine T method. Normal CD-1 mice were injected via a tail vein with 148 kBq of 125I-FR-ASON (2∼3 μ g). Animals were sacrificed at 1, 2, 4 and 24 h and tissue samples were studied. Liposome-mediated 3.33 MBq of 131I-FR-ASON (7 ∼ 9μ g) was injected intratumorally into tumor-bearing BALB/c mice (6 weeks after inoculation of 107 Namalwa cells) meanwhile liposome-mediated 131I labeled sense oligonucleotides served as controls. Biodistribution was monitored by sequential scintigraphy and organ radioactivity measurement 24 h after injection. The percentage of the injected dose per gram (%ID/g) of tumor and tumor/ non-tumor tissue ratios (T/NT) were calculated for each group of mice and the difference between two groups was assessed. The 5' tyramine group allowed specific and stable radiolabeling of the ASON with radioiodine. The radioactivity in the organs reached its peak at 1 h after injection, and then decreased rapidly in normal mice after intravenous administration of 125I-FR-ASON. The liver, stomach and intestine played an important role in biodistribution and radioactivity counts were low in bone, brain and blood. When 131I-FR-ASON injected intratumorally into mice xenografted with Namalwa cell line, images showed tracer accumulated in tumor. Immediately after intratumoral administration, only tumor was visible. Scintiscans performed at the end of 1 and 2 h showed elimination of the tracer from the tumor to the abdomen and at the end of 24 h the tumor was clearly seen. %ID/g of tumor and T/NT ratios for the sense group(control) were significantly lower than those of the antisense group(P<0.001). In this study it could be concluded that radiolabeled Ig FR ASON showed high specificity in V1 family B-cell lymphoma, and it should be considered further for nuclear medicine imaging application and radionuclide antisense therapy.