Assessment of cell cytotoxicity and comet assay on HER2/neu positive cell line due to 111In Auger electrons as DNA-targeting radioimmunoconjugate

Background: Breast cancer Auger electron therapy is a growing field of study in radioimmunotherapy and oncology research. Trastuzumab is a high affinity-binding monoclonal antibody against HER2/neu, which is overexpressed in breast tumors and used in radiopharmaceutical development. Objective: In this work, the lethal effects of 111In3+, 111In-DTPA-trastuzumab, and 111In-trastuzumab coupled-nuclear localizing sequence peptide (111In-DTPA-NLS-trastuzumab) on malignant cells were studied in vitro. Methods: DTPA-NLS-trastuzumab was prepared using sulfosuccinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) conjugation with NLS peptide in the first step, followed by conjugation with diethylenetriaminepentaacetic acid (DTPA). Both DTPA-trastuzumab and DTPA-NLS-trastuzumab were labeled with 111In, followed by purification and quality control techniques. Sk-Br-3 (a HER2/neu+ cell line) was used in the cell viability assessment assay for 11In, 111In-DTPA-trastuzumab, and 111In-DTPA-NLS-trastuzumab (3.7 MBq) at 37 ºC. The cytotoxicity of the three species was studied using MTT, and comet assay was utilized by DNA damage detection. Results: A significant radiochemical purity for 111In-DTPA-NLS-trastuzumab (99.36% ± 0.30%, ITLC) at the DTPA:antibody ratio of 6.90 ± 0.34:1 was obtained. Significant cell viability difference was found for 111In-DTPA-NLS-trastuzumab compared to the other treatments at two-time points. In addition, comet assay demonstrated significant DNA damage at 144 h using 111In-DTPA-NLS-trastuzumab. Conclusion: The results of cell viability and cell death using MTT assay and comet assay, respectively, demonstrate that the NLS-peptide effectively facilitates 111In-trastuzumab transport into the HER2/neu positive cancer cell nuclei to impose the radiotherapeutic effects of Auger electrons on DNA, leading to cell death.

Au@Pt Core-Shell Nanoparticle Bioconjugates for the Therapy of HER2+ Breast Cancer and Hepatocellular Carcinoma. Model Studies on the Applicability of 193mPt and 195mPt Radionuclides in Auger Electron Therapy

193mPt and 195mPt radionuclides are therapeutically attractive Auger electron emitters with notably high Auger electron yield per decay. The present paper summarizes the first step of research on the applications of core-shell (Au@Pt) nanoparticles for electron Auger therapy of HER2+ (human epidermal growth factor receptor 2) breast cancer and hepatocellular carcinoma. Gold nanoparticles (30 nm) were synthesized covered with a platinum shell at high efficiency (>80%) and were further evaluated for in vitro studies such as binding affinity, internalization and cytotoxicity. To find the mechanism(s) responsible for platinum cytotoxicity in HepG2 cells, the platinum concentration in isolated cell nuclei and cytoplasm was determined using ICP-MS (inductively coupled plasma mass spectrometry). Lack of platinum in cell nuclei suggests that the cytotoxic effect is associated with the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Studies carried out on the SKOV-3 cell line with the use of a synthesized targeting bioconjugate (Au@Pt-PEG-trastuzumab) revealed a high affinity of this preparation to HER2+ cells, its internalization, its placement in the perinuclear area and partial intranuclear location. The specific binding for HER2 negative cells, MDA-MB-231, was negligible and Au@Pt-PEG-trastuzumab did not enter these cells. The results obtained are promising and warrant future investigation of Auger electron therapy using 193mPt and 195mPt based radiopharmaceuticals.