Genotoxic evaluation of [DOTA,Tyr3]octreotate labeled with 131I and 177Lu in human peripheral lymphocytes in vitro by micronucleus assay

The radiolabeled receptor-binding peptides have being used for cancer diagnosis and therapy. The octreotate, a somatostatin analogue peptide, bound to various tumors expressing sst receptors (thyroid, pancreas, prostrate, melanoma and lymphomas). The amount and the type of receptors for somatostatin influence the tissue uptake. The [DOTA, Tyr3]octreotate has been used because of its high affinity to somatostatin subtype receptors sstr2 and sstr5. The pharmacokinetic study showed that the blood clearance is rapid and only 9% of the intravenous injected activity remains in human blood after one hour. The aim of this study was to evaluate the cytogenetic effect of radiolabeled [DOTA, Tyr3]octreotate in blood cells in vitro, using the cytokinesis-block micronucleus (MN) assay. This technique allows evaluating the mutagenic effects of both endogenous and exogenous agents at chromosome level. Blood samples of healthy donors were collected in heparinized syringes and exposed to different activities of [DOTA, Tyr3]octreotate labeled with with 131I (n=3) and 177Lu (n=3), where radioactive concentration ranged from 600 to 5600 kBq/mL, corresponding to an injected activity of 3.1 to 28.9 GBq in a reference man of 70 kg weight. 131I and 177Lu are beta- and gamma-emitters. After one-hour exposition to radiopharmaceuticals at 37 deg C, the cells were washed with culture medium for removing the non internalised octreotate and cultivated for 72 hours, according to criteria adopted by the IAEA. The results showed a positive correlation between radioactive concentrations (X) and the frequency of binucleated cells with micronuclei (Y) (P<0.05). The model for the best fit of data was the linear one (Y = a + bX). The equation for [131I-DOTA, Tyr3]octreotate was Y = (1.634 ± 0.236) + (0.912 ± 0.137) 10-3 X and for [177Lu-DOTA, Tyr3]octreotate was Y = (1.715 ± 0.342) + (0.743 ± 0.135) 10-3 X. The non labeled molecule, [DOTA, Tyr3]octreotate, has no influence in the induction of cytogenetic damage. The micronucleus assay with rat pancreatic tumor cells (AR42J) that express the sstr2 receptor for somatostatin, submitted to these radiopharmaceuticals, are in course. (author)