Evidence of Local Concentration of α-Particles from 211At-Labeled Antibodies in Liver Metastasis Tissue

We investigated the local concentration of α-particles from 211At-labeled trastuzumab antibodies against HER2 (human epidermal growth factor receptor type2) antigens in liver metastasis tissue of mice. Mice carrying metastatic cancer in their liver were injected with 211At-agent. After 12 hours, the liver was removed and sliced, and two tissue samples of liver tissues without lesions and one containing metastatic lesions were mounted on the CR-39 plastic nuclear track detector. Microscope images of the tissues on CR-39 were acquired. After irradiation for 31 hours, the tissues were removed from CR-39. A microscope image of α-particle tracks on CR-39 was acquired after chemical etching. The positions of each tissue sample and the emitted α-particle tracks were adjusted to the same coordinates. The positional distribution of α-particle tracks emitted from 211At was consistent within the tissue. The α-particle tracks were mainly allocated in the tumor region of the tissue. The absorbed dose in individual cells segmented by 10 µm intervals was obtained by the spectroscopic analysis of the LET (linear energy transfer) spectrum. The concentration efficiency, the track density ratio of α-particle tracks in the necrotized tissue, which was the tumor region, to the normal tissue, was found to be 6.0 ± 0.2. In the tumor region, the high LET α-particles deposited a large enough dose to cause lethal damage to the cancer cells. The total absorbed dose ranged from 1 to 7 Gy with a peak at around 2 Gy, which would correspond to 2-3 times higher biologically equivalent dose because of the high RBE of the α-particles emitted from 211At

Validating α-particle emission from 211At-labeled antibodies in single cells for cancer radioimmunotherapy using CR-39 plastic nuclear track detectors.

Recently, 211At has received increasing attention as a potential radionuclide for cancer radioimmunotherapy. It is a α-particle emitter, which is extremely effective against malignant cells. We demonstrate a method to verify the efficiency of 211At-labeled trastuzumab antibodies (211At-trastuzumab) against HER2 antigens, which has not been determined for radioimmunotherapy. A CR-39 plastic nuclear detector is used for measuring the position and the linear energy transfer (LET) of individual 211At α- particle tracks. The tracks and 211At-trastuzumab-binding cells were co-visualized by using the geometric information recorded on the CR-39. HER2-positive human gastric cancer cells (NCI-N87), labelled with 211At-trastuzumab, were dropped on the centre of the CR-39 plate. Microscope images of the cells and the corresponding α-tracks acquired by position matching were obtained. In addition, 3.5 cm × 3.5 cm macroscopic images of the whole plate were acquired. The distribution of number of α-particles emitted from single cells suggests that 80% of the 211At-trastuzumab-binding cells emitted α-particles. It also indicates that the α-particles may strike the cells several times along their path. The track-averaged LET of the α-particles is evaluated to be 131 keV/μm. These results will enable quantitative evaluation of delivered doses to target cells, and will be useful for the in vitro assessment of 211At-based radioimmunotherapeutic agents

Targeted cancer cell ablation in mice by an α-particle-emitting astatine-211-labeled antibody against major histocompatibility complex class I chain-related protein A and B

Major histocompatibility complex class I chain-related protein A and B (MICA/B) are ligands of the immune receptor, natural-killer group 2 member D. MICA/B expression is often found in several types of cancer but is restricted in normal tissues. Here, we show that an α-particle emitting astatine-211 (211At)-labeled antibody targeting MICA/B (211At-anti MICA/B Ab) efficiently ablates cancer cells in vitro and in vivo. We generated 211At-anti MICA/B Ab, an anti-MICA/B antibody conjugated with a highly cytotoxic α-particle emitting radionuclide 211At. 211At-anti MICA/B Ab binds to human osteosarcoma SaOS2 and U2OS cells that exhibit high levels of MICA/B expression and efficiently kills those cells in vitro. Biodistribution analysis using xenograft mouse models of HCT116 p53-/- positive for MICA/B expression, showed increased 211At in the xenografts for up to 22 h after injection as time proceeded. A single dose of 211At-anti MICA/B Ab (1 MBq) showed significant reduction in the tumor growth rate of HCT116 p53-/- xenografts compared to 211At-labeled mouse IgG (1 MBq) at 21 days after injection. No body weight loss and erythrocytopenia was evident in mice that received 211At-anti MICA/B. Leukocytopenia and thrombocytopenia were observed within a week after 211At-anti MICA/B injection, but counts of red blood cells and platelets were recovered to control levels at about 3-4 weeks after injection. Taken together, these data strongly demonstrate that targeted α-particle therapy using 211At-anti-MICA/B Ab emitting highly cytotoxic a-particles is a potential new therapeutic option for several types of cancer

Transcriptomic Signatures of Auger Electron Radioimmunotherapy Using Nuclear Targeting (111)In-Trastuzumab for Potential Combination Therapies.

(111)In-labeled trastuzumab modified with nuclear localizing signal (NLS) peptides ((111)In-trastuzumab-NLS) efficiently delivers an Auger electron (AE) emitter (111)In into the cell nucleus and is thus a promising radiopharmaceutical in AE radioimmunotherapy (AE-RIT) for targeted killing of HER2-positive cancer. However, further improvement of its therapeutic efficacy is required. In this study, the authors show a transcriptomic approach to identify potential targets for enhancing the cytotoxic effects of (111)In-trastuzumab-NLS. They generated two types of (111)In-trastuzumab-NLS harboring different numbers of NLS peptides, (111)In-trastuzumab-NLS-S and -L. These radioimmunoconjugates (230 and 460 kBq) showed a significant higher cytotoxicity to SKBR3 human breast cancer cells overexpressing HER2 compared to (111)In-trastuzumab. Microarray analysis revealed that NF-kB-related genes (38 genes) were significantly changed in transcription by (111)In trastuzumab-NLS-L (230 kBq) treatment. Quantitative reverse transcription polymerase chain reaction confirmed the microarray data by showing transcriptional alternation of selected NF-κB target genes in cells treated with (111)In-trastuzumab-NLS-L. Interestingly, bortezomib, a drug known as a NF-κB modulator, significantly enhanced the cytotoxicity of (111)In-trastuzumab-NLS-L in SKBR3 cells. Taken together, the transcriptome data suggest the possibility that the modulation of NF-kB signaling activity is a molecular signature of (111)In-trastuzumab-NLS and coadministration of bortezomib may be efficacious in enhancement of AE-RIT with (111)In-trastuzumab-NLS

Microscope images of cells and emitted α-tracks from those cells on aCR-39 detector.

<p>A) Cells and B) corresponding α-tracks. A dot arrow indicates that no α-tracks are observed in the corresponding cell position. The enlarged images of C) cells and D) α-tracks recognized by ellipse fitting result are inset by the colored circles.</p

Scatter plots and contour maps of cells and α-tracks positions.

<p>Scatter plots of the positions of A) cells and B) α-tracks over the entire surface of the CR-39 detector and C) their overlay, respectively. The macroscopic autoradiography as a contour map by counting the number of D) cells and E) α-tracks in binned positions (Δ<i>x</i>, Δ<i>y</i>) with 200 μm intervals.</p

LET spectrum of α-particles from single cells.

<p>LET spectrum of α-particles from single cells.</p