99mTc-N2S2-Tat (49-57)-bombesin internalized in nuclei of prostate and breast cancer cells

BACKGROUND: The gastrin-releasing peptide receptor (GRP-r) is overexpressed in prostate and breast cancers. technetium-99m-bombesin (Tc-BN) has been reported as a radiopharmaceutical with specific cell GRP-r binding. The HIV Tat (49-57)-derived peptide has been used to deliver a large variety of molecules to cell nuclei. A new hybrid radiopharmaceutical of type Tc-N2S2-Tat(49-57)-Lys-BN (Tc-Tat-BN) internalized in cancer cell nuclei could act as an effective system of targeted radiotherapy using Auger and internal conversion electron emissions near DNA. AIM: The aim of this study was to assess the in-vitro nucleus internalization kinetics of Tc-Tat-BN in GRP r-positive cancer cells and to evaluate the subcellular-level radiation-absorbed dose associated with the observed effect on cancer cell DNA proliferation. METHODS: Tc-Tat-BN in-vitro internalization kinetics were evaluated in human prostate cancer PC-3 cells and breast carcinoma cell lines MCF7 and MDA-MB231. Nuclei from cells were isolated using a nuclear extraction kit. Total disintegration in each subcellular compartment was calculated by the integration of experimental time-activity kinetic curves. Nucleus internalization was corroborated by confocal microscopy images using immunofluorescently labelled Tat-BN. The PENELOPE code was used to simulate and calculate the absorbed dose by the contribution of Auger and internal conversion electrons in the cytoplasm and nucleus using geometric models built from immunofluorescent cell images. A cell proliferation kit was used to evaluate DNA concentration after cancer cell incubation with Tc-Tat-BN. RESULTS: The results showed that 59.7, 61.2 and 41.5% of total disintegration per unit of Tc-Tat-BN activity (1 Bq) bound to the cell occurred in the nucleus of PC-3, MCF7 and MDA-MB231, respectively. The Tc-Tat-BN absorbed doses delivered to nuclei were 0.142 mGy/decay (PC-3), 0.434 mGy/decay (MCF7) and 0.276 mGy/decay (MDA-MB231). Tc-Tat-BN produced a significant decrease in PC-3 (52.98%), MCF7 (45.71%) and MDA-MB231 (35.80%) cellular proliferation with respect to untreated cells. CONCLUSION: The hybrid radiopharmaceutical could be potentially useful as a therapeutic agent for prostate and breast cancers.