Evaluation of Chelator-to-Antibody Ratio on Development of 89Zr-iPET Tracer for Imaging of PD-L1 Expression on Tumor.

89Zr-iPET has been widely used for preclinical and clinical immunotherapy studies to predict patient stratification or evaluate therapeutic efficacy. In this study, we prepared and evaluated 89Zr-DFO-anti-PD-L1-mAb tracers with varying chelator-to-antibody ratios (CARs), including 89Zr-DFO-anti-PD-L1-mAb_3X (tracer_3X), 89Zr-DFO-anti-PD-L1-mAb_10X (tracer_10X), and 89Zr-DFO-anti-PD-L1-mAb_20X (tracer_20X). The DFO-anti-PD-L1-mAb conjugates with varying CARs were prepared using a random conjugation method and then subjected to quality control. The conjugates were radiolabeled with 89Zr and evaluated in a PD-L1-expressing CT26 tumor-bearing mouse model. Next, iPET imaging, biodistribution, pharmacokinetics, and ex vivo pathological and immunohistochemical examinations were conducted. LC-MS analysis revealed that DFO-anti-PD-L1-mAb conjugates were prepared with CARs ranging from 0.4 to 2.0. Radiochemical purity for all tracer groups was >99% after purification. The specific activity levels of tracer_3X, tracer_10X, and tracer_20X were 2.2 ± 0.6, 8.2 ± 0.6, and 10.5 ± 1.6 µCi/µg, respectively. 89Zr-iPET imaging showed evident tumor uptake in all tracer groups and reached the maximum uptake value at 24 h postinjection (p.i.). Biodistribution data at 168 h p.i. revealed that the tumor-to-liver, tumor-to-muscle, and tumor-to-blood uptake ratios for tracer_3X, tracer_10X, and tracer_20X were 0.46 ± 0.14, 0.58 ± 0.33, and 1.54 ± 0.51; 4.7 ± 1.3, 7.1 ± 3.9, and 14.7 ± 1.1; and 13.1 ± 5.8, 19.4 ± 13.8, and 41.3 ± 10.6, respectively. Significant differences were observed between tracer_3X and tracer_20X in the aforementioned uptake ratios at 168 h p.i. The mean residence time and elimination half-life for tracer_3X, tracer_10X, and tracer_20X were 25.4 ± 4.9, 24.2 ± 6.1, and 25.8 ± 3.3 h and 11.8 ± 0.5, 11.1 ± 0.7, and 11.7 ± 0.6 h, respectively. No statistical differences were found between-tracer in the aforementioned pharmacokinetic parameters. In conclusion, 89Zr-DFO-anti-PD-L1-mAb tracers with a CAR of 1.4-2.0 may be better at imaging PD-L1 expression in tumors than are traditional low-CAR 89Zr-iPET tracers.

Automated identification of single and clustered chromosomes for metaphase image analysis.

Background: Chromosome analysis is laborious and time-consuming. Automated methods can significantly increase the efficiency of chromosome analysis. For the automated analysis of chromosome images, single and clustered chromosomes must be identified. Herein, we propose a feature-based method for distinguishing between single chromosomes and clustered chromosome. Method: The proposed method comprises three main steps. In the first step, chromosome objects are segmented from metaphase chromosome images in advance. In the second step, seven features are extracted from each segmented object, i.e., the normalized area, area/boundary ratio, side branch index, exhaustive thresholding index, normalized minimum width, minimum concave angle, and maximum boundary shift. Finally, the segmented objects are classified as a single chromosome or chromosome cluster using a combination of the seven features. Results: In total, 43,391 segmented objects, including 39,892 single chromosomes and 3,499 chromosome clusters, are used to evaluate the proposed method. The results show that the proposed method achieves an accuracy of 98.92% by combining the seven features using support vector machine. Conclusions: The proposed method is highly effective in distinguishing between single and clustered chromosomes and can be used as a preprocessing procedure for automated chromosome image analysis.

Intercomparison of conventional and QuickScan dicentric scoring for the validation of individual biodosimetry analysis in Taiwan.

PURPOSE: The dicentric chromosome assay (DCA), the gold standard for radiation biodosimetry, evaluates an individual absorbed radiation dose by the analysis of DNA damage in human lymphocytes. The conventional (C-DCA) and QuickScan (QS-DCA) scoring methods are sensitive for estimating radiation dose. The Biodosimetry Laboratory at Institute of Nuclear Energy Research (INER), Taiwan, participated in intercomparison exercises conducted by Health Canada (HC) in 2014, 2015 and 2018 to validate the laboratory's accuracy and performance. MATERIAL AND METHODS: Blood samples for the conventional dose response curve for Taiwan were irradiated with 0, 0.25, 0.5, 1, 2, 3, 4 and 5 Gy. Ten blind blood samples were provided by HC. Either or both of two methods of conventional (C) or QuickScan (QS) scoring could be chosen for the HC's intercomparison. For C-DCA triage scoring, only cells with 46 centromeres were counted and each scorer recorded the number of dicentrics in the first 50 metaphases or stopped scoring when 30 dicentrics were reached. Scorers also recorded how much time it took to analyze 10, 20, and 50 cells. Subsequently, the data were entered into the Dose Estimate software (DoseEstimate_v5.1) and dose estimates were calculated. With QS-DCA scoring, a minimum of 50 metaphase cells (or 30 dicentrics) were scored in apparently complete metaphases without verification of exactly 46 centromeres. RESULTS: For the blinded blood samples irradiated at HC and shipped to INER, the mean absolute deviation (MAD) derived after scoring 50 cells for C-DCA and QS-DCA was <0.5 Gy for all three intercomparisons, meeting the criteria for acceptance. CONCLUSION: The results indicated that the Biodosimetry Laboratory at INER can provide reliable dose estimates in the case of a large-scale radiation accident.