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, a high affinity-binding monoclonal antibody against HER2/neu is which is over-expressed in breast tumors, is used in radiopharmaceutical development. OBJECTIVES: 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 111In, 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 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 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.

The effect of 111In radionuclide distance and auger electron energy on direct induction of DNA double-strand breaks: a Monte Carlo study using Geant4 toolkit.

PURPOSE: In this study, the effect of 111In position and Auger electron energy on direct induction of DSBs was investigated. MATERIALS AND METHODS: The Geant4-DNA simulation toolkit was applied using a simple B-DNA form extracted from PDBlib library. First, the simulation was performed for electrons with energies of 111In and equal emission probabilities to find the most effective electron energies. Then, 111In Auger electrons' actual spectrum was considered and their contribution in DSB induction analysed. RESULTS: The results showed that the most effective electron energy is 183 eV, but due to the higher emission probability of 350 eV electrons, most of the DSBs were induced by the latter electrons. Also, it was observed that most of the DSBs are induced by electrons emitted within 4 nm of the central axis of the DNA and were mainly due to breaks with <4 base pairs distance in opposing strands. Whilst, when 111In atoms are very close to the DNA, 1.3 DSBs have been obtained per decay of 111In atoms. CONCLUSIONS: The results show that the most effective Auger electrons are the 350 eV electrons from 111In atoms with <4 nm distance from the central axis of the DNA which induce ∼1.3 DSBs per decay when bound to the DNA. This value seems reasonable when compared with the reported experimental data.

Preclinical evaluation of [¹¹¹ In]-DOTA-trastuzumab for clinical trials.

CONTEXT: Herceptin and its fragments have been radiolabeled and used in the imaging of human epidermal growth factor receptor 2 (HER2)/neu-positive tumors and development of diagnostic kits is of great importance in radiopharmacy. AIMS: In this study, ¹¹¹ In-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-trastuzumab (¹¹¹ In-DOTA-trastuzumab) was successively prepared and evaluated for ultimate use in the HER2 antigen imaging in oncology. SETTINGS AND DESIGN: The conjugate was prepared, labeled and evaluated using in vitro (radioimmunoassay [RIA], enzyme-linked immunosorbent assay (ELISA), stability, binding, internalization)/in vivo (bio-distribution, single-photon emission computed tomography [SPECT]) experiments. MATERIALS AND METHODS: ¹¹¹ In-DOTA-trastuzumab was prepared followed by determination of radiochemical purity (RCP), integrity of protein, immunoreactivity of radiolabeled antibody with HER2/neu antigen (by SkBr3 cell line binding and RIA methods) were determined followed by stability tests, internalization studies and the tissue bio-distribution determination in wild-type rats as well as SPECT imaging in SkBr3-bearing mice. STATISTICAL ANALYSIS USED: All values were expressed as mean ± standard deviation (mean ± SD) and the data were compared using Student's t-test. Statistical significance was defined as P < 0.05. RESULTS: ¹¹¹ In-DOTA-trastuzumab was prepared (RCP >95 ± 0.5%, S.A. 5.3 µCi/µg) with the average number of chelators per antibody of 6:1 showing significant immune-reactivity retention using ELISA. In vitro stability was >90% in phosphate buffered saline and 80 ± 0.5% in serum over 48 h. Cell binding was significant (>0.79). In vitro internalization reached up to %12-13 in 10 h. Significant tumor uptake was observed. CONCLUSIONS: In vitro and in vivo/SPECT imaging in SkBr3-bearing mice demonstrated that ¹¹¹ In-DOTA-trastuzumab is a potential compound for molecular imaging of SPECT for diagnosis and follow-up of HER2 expression in oncology.

Production and tumour uptake of [64Cu]Pyruvaldehyde-bis (N4-methylthiosemicarbazone) for PET and/or therapeutic purposes.

BACKGROUND: Copper-64 (T(1/2)=12.7 degrees h) is an important radionuclide used both in PET imaging and therapy. [(64)Cu]-pyruvaldehyde- bis(N(4)-methylthiosemicarbazone) ([64Cu]-PTSM) has already been used in the detection of cerebral and myocardial blood flow. In this study, a simple production method and tumor accumulation of [(64)Cu]-PTSM in fibrosarcoma-bearing mice were reported. MATERIAL AND METHODS: Cu-64 was produced via the 68Zn(p, alpha n)(64)Cu nuclear reaction. [(64)Cu]-PTSM was prepared using in-house made PTSM ligand and [(64)Cu]cuprous acetate and injected to fibrosarcoma-bearing mice. RESULTS: Copper-64 was prepared in chloride form ( approximately 200 mCi, > 95% chemical yield at 180 degrees microA for 1.1 h irradiation, radionuclidic purity > 96%, copper-67 as impurity). The solution of (64)Cu- PTSM was prepared in > 80% radiochemical yield and more than 98% radiochemical purity. A significant tumor uptake was observed 2 hours post injection in tumor-bearing mice (tumor/muscle: 9, tumor/blood: 6). CONCLUSION: [(64)Cu]-PTSM was prepared on a radiopharmaceutical scale using readily available zinc-68, with high quality and was shown to possess application in the therapy and/or imaging of fibrosarcoma.