Relativistic effects in elastic scattering of electrons in TEM.

Transmission electron microscopy typically works with highly accelerated thus relativistic electrons. Consequently the scattering process is described within a relativistic formalism. In the following, we will examine three different relativistic formalisms for elastic electron scattering: Dirac, Klein-Gordon and approximated Klein-Gordon, the standard approach. This corresponds to a different consideration of spin effects and a different coupling to electromagnetic potentials. A detailed comparison is conducted by means of explicit numerical calculations. For this purpose two different formalisms have been applied to the approaches above: a numerical integration with predefined boundary conditions and the multislice algorithm, a standard procedure for such simulations. The results show a negligibly small difference between the different relativistic equations in the vicinity of electromagnetic potentials, prevailing in the electron microscope. The differences between the two numeric approaches are found to be small for small-angle scattering but eventually grow large for large-angle scattering, recorded for instance in high-angle annular dark field.

The statistics of the thermal motion of the atoms during imaging process in transmission electron microscopy and related techniques.

The concern of this work is the influence of the thermal motion of the atoms on electron scattering simulations, used for quantitative interpretation of results in high-resolution electron microscopy. We distinguish between the influence of inelastic phonon excitation and the effect of a moving lattice on images generated by elastically scattered electrons. It is shown that, analog to aberrations, the impact of a moving lattice differs substantially with respect to different imaging conditions and cannot be described by the Debye-Waller damping applicable in XRD. We derive a new formalism, based on the frozen lattice and multislice approach, to incorporate the statistics of the thermal motion into elastic TEM imaging simulations, taking into account different imaging conditions. The averaging over different atom positions is generally performed within a density matrix framework, which can be linearized in the special case of off-axis electron holography. All findings are supported by explicit numerical simulations: molecular dynamics simulations are performed to get a realistic thermal motion and the electron scattering simulations are performed within the new multislice algorithm.

Identification and evaluation of a new tumor cell-binding peptide, FROP-1.

UNLABELLED: Peptides are useful tools for the targeted delivery of radionuclides or chemotherapeutic drugs to their site of action within an organism. Given that the peptide receptor is overexpressed at the tumor, therapeutically active doses can be delivered to the tumor with reduced side effects. Because currently known peptides are restricted to a small number of tumors, new molecules and their corresponding receptors have to be identified to enlarge the spectrum of malignancies that can be diagnosed or treated using tumor-targeting peptides. METHODS: A 12-amino-acid peptide phage display system was applied to identify a new peptide binding to follicular thyroid carcinoma cells. The properties of the radiolabeled peptide were assessed in binding, competition, and internalization experiments in a variety of tumor cell lines including FRO82-2 and MCF-7 cells, and the pharmacokinetic behavior of the radiolabeled peptide was evaluated in tumor-bearing mice. Peptide stability was studied in human serum. RESULTS: After 5 selection rounds, the new peptide, FROP-1 (EDYELMDLLAYL), was identified. It showed binding to follicular thyroid carcinoma as well as anaplastic thyroid carcinoma, mammary carcinoma, cervix carcinoma, prostate carcinoma, and cell lines derived from head and neck tumors, and low affinity could be observed to control cells such as human umbilical vein endothelial cells or immortalized keratinocytes. In MCF7 cells, 78% and 86% of the bound activity was internalized after 10 and 60 min of incubation, respectively. Stability experiments in human serum showed the appearance of a degradation product after 15 min. Tumor uptake of the radioactive labeled peptide increased for 45 min in nude mouse models, reaching an accumulation level of approximately 3.6 percentage injected dose (%ID)/g for FRO82-2 tumors or approximately 3.8 %ID/g for MCF-7 tumors. CONCLUSION: The target of FROP-1 is most likely a molecule found generally in tumors, making this peptide highly attractive for diagnostic or therapeutic applications. However, modifications are needed to increase stability and affinity.

Bispecific antibody pretargeting of tumor neovasculature for improved systemic radiotherapy of solid tumors.

PURPOSE: Extra domain B (ED-B) fibronectin is a specific tumor matrix marker for targeting angiogenesis in solid tumors. In this study, the radiotherapeutic potential of the directly radioiodinated divalent anti-ED-B antibody fragment, L19 small immunoprotein (L19-SIP; 75,000 Da), was compared with a pretargeting approach using the bispecific antibody AP39xm679 (bsMAb; 75,000 Da). EXPERIMENTAL DESIGN: The bsMAb was prepared by coupling an anti-ED-B single-chain Fv (AP39) to the Fab' of the murine antibody m679, which binds to the small peptidic hapten histamine-succinyl-glycine (HSG). As an effector molecule for the pretargeting approach, the 111In-labeled HSG-DOTA complex was injected 25 or 41 hours after the bsMAb. The kinetics of both the iodinated bsMAb and the pretargeted 111In-labeled HSG hapten were investigated in mice bearing human glioblastoma xenografts (U251) and compared with the kinetics and tumor accumulation of radioiodinated L19-SIP. 111In and 125I were used as surrogate marker for the therapeutic radioisotopes 90Y/177Lu and 131I, respectively. RESULTS: Tumor uptake of the pretargeted 111In-labeled peptide was significantly higher than 125I-L19-SIP over 7 days. At the calculated maximally tolerated dose for each agent (with the kidney being the dose-limiting organ for pretargeting and the bone marrow for direct targeting), a mouse tumor dose of 146 Gy could be given by pretargeting versus 45 Gy delivered by the direct approach. CONCLUSIONS: These data suggest that pretargeting of ED-B with AP39xm679 and subsequent injection of the 90Y-hapten-peptide would improve the therapeutic efficacy in solid tumors by >3-fold compared with directly radiolabeled 131I-L19-SIP.

Radioimmunotherapy of solid tumors by targeting extra domain B fibronectin: identification of the best-suited radioimmunoconjugate.

PURPOSE: The expression of extra domain B (ED-B) fibronectin is always associated with angiogenic processes and can be exclusively observed in tissues undergoing growth and/or extensive remodeling. Due to this selective expression, ED-B fibronectin is an interesting target for radioimmunotherapy of malignant diseases. The aim of this study was to identify the most appropriate ED-B-targeting radioimmunoconjugate for the therapy of solid tumors. EXPERIMENTAL DESIGN: Three ED-B fibronectin-binding human antibody formats of L19 were investigated: dimeric single-chain Fv (approximately 50 kDa), "small immunoprotein" (SIP, approximately 80 kDa), and immunoglobulin G1 (IgG1, approximately 150 kDa). These L19 derivatives were either labeled with I-125 or with In-111 (using MX-diethylenetriaminepentaacetic acid, MX-DTPA). Pharmacokinetics and tumor accumulation of the radiolabeled immunoconjugates were investigated in F9 (murine teratocarcinoma) tumor-bearing mice. Subsequently, dosimetry for the corresponding therapeutic isotopes I-13-1 and Y-90 was done. After testing the myelotoxicity of I-131-L19-SIP and I-131-L19-IgG1 in non-tumor-bearing mice, the therapeutic efficacy of these iodinated antibody formats was finally investigated in F9 tumor-bearing mice. RESULTS: The most favorable therapeutic index was found for I-131-L19-SIP followed by I-131-L19-IgG1. The therapeutic index of all In-111-labeled derivatives was significantly inferior. Considering the bone marrow as the dose-limiting organ, it was calculated that activities of 74 MBq I-131-L19-SIP and 25 MBq I-131-L19-IgG1 could be injected per mouse without causing severe myelotoxicity. The best therapeutic efficacy was observed using I-131-L19-SIP, resulting in significant tumor growth delay and prolonged survival after a single injection. CONCLUSION: Compared with other L19-based radioimmunoconjugates, I-131-L19-SIP is characterized by superior antitumor efficacy and toxicity profile in the F9 teratocarcinoma animal model. These results indicate that ED-B fibronectin-targeted radioimmunotherapy using I-131-L19-SIP has potential to be applied to treatment of solid cancers.