Multifunctional targeted therapy system based on (99m) Tc/(177) Lu-labeled gold nanoparticles-Tat(49-57)-Lys(3) -bombesin internalized in nuclei of prostate cancer cells.

Radiolabeled gold nanoparticles may function simultaneously as radiotherapy and thermal ablation systems. The gastrin-releasing peptide receptor (GRP-r) is overexpressed in prostate cancer, and Lys(3) -bombesin is a peptide that binds with high affinity to the GRP-r. HIV Tat(49-57) is a cell-penetrating peptide that reaches the DNA. In cancer cells, (177) Lu shows efficient crossfire effect, whereas (99m) Tc that is internalized in the cancer cell nuclei acts as an effective system of targeted radiotherapy because of the biological Auger effect. The aim of this research was to evaluate the in vitro potential of (99m) Tc-labeled and (177) Lu-labeled gold nanoparticles conjugated to Tat(49-57)-Lys(3) -bombesin peptides ((99m) Tc/(177) Lu-AuNP-Tat-BN) as a plasmonic photothermal therapy and targeted radiotherapy system in PC3 prostate cancer cells. Peptides were conjugated to AuNPs (5 nm) by spontaneous reaction with the thiol group of cysteine (Cys). The effect on PC3 cell viability after laser heating of the AuNP-Tat-BN incubated with the cancer cells was conducted using an Nd:YAG laser pulsed for 5 ns at 532 nm (0.65 W/cm(2) ). For the (99m) Tc/(177) Lu-AuNP-Tat-BN to be obtained, the (177) Lu-DOTA-Gly-Gly-Cys and (99m) Tc-HYNIC-octreotide radiopeptides were first prepared and added simultaneously to a solution of AuNP-Tat-BN. (99m) Tc/(177) Lu-AuNP-Tat-BN (20 Bq/cell) was incubated with PC3 cells, and the effect on the cell proliferation was evaluated after 3 days. Fluorescence images of (99m) Tc/(177) Lu-AuNP-Tat-BN internalized in nuclei of PC3 were also obtained. After laser irradiation, the presence of AuNP-Tat-BN caused a significant increase in the temperature of the medium (46.4 vs 39.5 °C of that without AuNP) resulting in a significant decrease in PC3 cell viability down to 1.3%. After treatment with (99m) Tc/(177) Lu-AuNP-Tat-BN, the PC3 cell proliferation was inhibited. The nanosystem exhibited properties suitable for plasmonic photothermal therapy and targeted radiotherapy in the treatment of prostate cancer.