ImmunoPET/CT imaging of clear cell renal cell carcinoma with [18F]RCCB6: a first-in-human study.

PURPOSE: The cluster of differentiation (CD70) is a potential biomarker of clear cell renal cell carcinoma (ccRCC). This study aims to develop CD70-targeted immuno-positron emission tomography/computed tomography (immunoPET/CT) imaging tracers and explore the diagnostic value in preclinical studies and the potential value in detecting metastases in ccRCC patients. METHODS: Four novel CD70-specific single-domain antibodies (sdAbs) were produced and labelled with 18F by the aluminium fluoride restrained complexing agent (AlF-RESCA) method to develop radiotracers. The visualisation properties of the tracers were evaluated in a subcutaneous ccRCC patient-derived xenograft (PDX) model. In a registered prospective clinical trial (NCT06148220), six patients with pathologically confirmed RCC were included and underwent immunoPET/CT examination exploiting one of the developed tracers (i.e., [18F]RCCB6). RESULTS: We engineered four sdAbs (His-tagged RCCB3 and RCCB6, His-tag-free RB3 and RB6) specifically targeting recombinant human CD70 without cross-reactivity to murine CD70. ImmunoPET/CT imaging with [18F]RCCB3 and [18F]RCCB6 demonstrated a high tumour-to-background ratio in a subcutaneous ccRCC PDX model, with the latter showing better diagnostic potential supported by higher tumour uptake and lower bone accumulation. In comparison, [18F]RB6, developed by sequence optimisation, has significantly lower kidney accumulation than that of [18F]RCCB6. In a pilot translational study, [18F]RCCB6 immunoPET/CT displayed ccRCC metastases in multiple patients and demonstrated improved imaging contrast and diagnostic value than 18F-FDG PET/CT in a patient with ccRCC. CONCLUSION: The work successfully developed a series of CD70-targeted immunoPET/CT imaging tracers. Of them, [18F]RCCB6 clearly and specifically identified inoculated ccRCCs in preclinical studies. Clinical translation of [18F]RCCB6 suggests potential for identifying recurrence and/or metastasis in ccRCC patients.

ImmunoPET imaging of EpCAM in solid tumours with nanobody tracers: a preclinical study.

PURPOSE: Epithelial cell adhesion molecule (EpCAM) is a potential therapeutic target and anchoring molecule for circulating and disseminated tumour cells (CTC/DTC) in liquid biopsy. In this study, we aimed to construct EpCAM-specific immuno-positron emission tomography (immunoPET) imaging probes and assess the diagnostic abilities in preclinical cancer models. METHODS: By engineering six single-domain antibodies (e.g., EPCD1 - 6) targeting EpCAM of different binding properties and labelling with 68Ga (T1/2 = 1.1 h) and 18F (T1/2 = 110 min), we developed a series of EpCAM-targeted immunoPET imaging probes. The probes' pharmacokinetics and diagnostic accuracies were investigated in cell-derived human colorectal (LS174T) and esophageal cancer (OE19) tumour models. RESULTS: Based on in vitro binding affinities and in vivo pharmacokinetics of the first three tracers ([68Ga]Ga-NOTA-EPCD1, [68Ga]Ga-NOTA-EPCD2, and [68Ga]Ga-NOTA-EPCD3), we selected [68Ga]Ga-NOTA-EPCD3 for tumour imaging which showed an average tumour uptake of 2.06 ± 0.124%ID/g (n = 3) in LS174T cell-derived tumour model. Development and characterisation of [18F]AIF-RESCA-EPCD3 showed comparable tumour uptake of 1.73 ± 0.0471%ID/g (n = 3) in the same tumour model. Further validation of [68Ga]Ga-NOTA-EPCD3 in OE19 cell-derived tumour model showed an average tumour uptake of 4.27 ± 1.16%ID/g and liver uptake of 13.5 ± 1.30%ID/g (n = 3). Near-infrared fluorescence imaging with Cy7-EPCD3 confirmed the in vivo pharmacokinetics and relatively high liver accumulation. We further synthesized another three 18F-labeled nanobody tracers ([18F]AIF-RESCA-EPCD4, [18F]AIF-RESCA-EPCD5, and [18F]AIF-RESCA-EPCD6) and found that [18F]AIF-RESCA-EPCD6 had the best pharmacokinetics with low background. [18F]AIF-RESCA-EPCD6 showed explicit uptake in the subcutaneously inoculated OE19 tumour model with an average uptake of 4.70 ± 0.26%ID/g (n = 3). In comparison, the corresponding tumour uptake (0.17 ± 0.25%ID/g, n = 3) in the EPCD6 blocking group was substantially lower (P < 0.001), indicating the targeting specificity of the tracer. CONCLUSIONS: We developed a series of 68Ga/18F-labeled nanobody tracers targeting human EpCAM. ImmunoPET imaging with [18F]AIF-RESCA-EPCD6 may facilitate better use of EpCAM-targeted therapeutics by noninvasively displaying the target's expression dynamics.

ImmunoPET imaging of Trop2 expression in solid tumors with nanobody tracers.

PURPOSE: The high expression of the transmembrane glycoprotein trophoblast cell-surface antigen 2 (Trop2) was strongly associated with the progression of solid tumors, including pancreatic and gastric cancers. Our study aimed to construct Trop2-specific immuno-positron emission tomography (immunoPET) probes and assess the diagnostic abilities in preclinical pancreatic and gastric cancer models. METHODS: The expression of Trop2 in pancreatic cancer was determined by single-cell sequencing and immunohistochemistry on tissue microarray (TMA). Flow cytometry was used to screen the expression of Trop2 in pancreatic cancer cell lines. Two nanobodies (i.e., RTD98 and RTD01) targeting Trop2 were developed and labeled with gallium-68 (68Ga, T1/2 = 1.1 h) to construct immunoPET imaging probes. The agents were researched in cell-derived pancreatic and patient-derived gastric cancer models expressing varying Trop2. RESULTS: Single-cell sequencing results showed high expression of Trop2 in pancreatic ductal cells as well as acinar cells and immunohistochemical staining of TMA from pancreatic cancers showed significantly higher expression of Trop2 in cancerous than in paracancerous tissues. ImmunoPET utilizing [68Ga]Ga-NOTA-RTD98 could clearly delineate subcutaneous tumors, both in cell-derived pancreatic cancer models and patient-derived gastric cancer models, superior to imaging using [18F]-FDG or a non-specific probe [68Ga]Ga-NOTA-RTD161. Another probe with improved pharmacokinetics targeting Trop2, [68Ga]Ga-NOTA-RTD01, was further prepared and showed advantageous diagnostic capabilities in preclinical pancreatic cancer models. CONCLUSION: In the work, we reported two nanobody tracers targeting human Trop2 which may facilitate better use of Trop2-targeted therapeutics by noninvasively displaying expression dynamics of the target.

Site-Specific Modification of Single Domain Antibodies by Enzyme-Immobilized Magnetic Beads.

Nanobodies as imaging agents and drug conjugates have shown great potential for cancer diagnostics and therapeutics. However, site-specific modification of a nanobody with microbial transglutaminase (mTGase) encounters problems in protein separation and purification. Here, we describe a facile yet reliable strategy of immobilizing mTGase onto magnetic beads for site-specific nanobody modification. The mTGase immobilized on magnetic beads (MB-mTGase) exhibits catalytic activity nearly equivalent to that of the free mTGase, with good reusability and universality. Magnetic separation simplifies the protein purification step and reduces the loss of nanobody bioconjugates more effectively than size exclusion chromatography. Using MB-mTGase, we demonstrate site-specific conjugation of nanobodies with fluorescent dyes and polyethylene glycol molecules, enabling targeted immunofluorescence imaging and improved circulation dynamics and tumor accumulation in vivo. The combined advantages of MB-mTGase method, including high conjugation efficiency, quick purification, less protein loss, and recycling use, are promising for site-specific nanobody functionalization and biomedical applications.

ImmunoPET Imaging of CD47 with VHH-Derived Tracers in Pancreatic Cancers.

Pancreatic ductal adenocarcinoma (PDAC) is a malignant tumor with insidious onset, rapid progression, and a very poor prognosis. CD47 is a transmembrane protein associated with the development and poor prognosis of pancreatic cancer. The aim of this study was to evaluate the diagnostic value of novel immunoPET tracers targeting CD47 in preclinical pancreatic cancer models. The association of CD47 expression with pancreatic cancer was analyzed using the Gene Expression Profiling Interactive Analysis platform. Immunohistochemical analysis of tissue microarrays was performed to detect CD47 expression in PDAC. CD47 expression levels on BxPC-3 and AsPC-1 cell membranes were compared using flow cytometry. A VHH (C2)-targeting human CD47 and its albumin-binding derivative (ABDC2) were labeled with 68Ga or 89Zr, respectively. The developed tracers were evaluated by immuno-positron emission tomography (immunoPET) imaging in tumor-bearing nude and CD47-humanized mice. [68Ga]Ga-NOTA-C2 effectively detected tumor lesions in nude mice models and further showed confirmative imaging capacity in CD47-humanized PDAC models. Compared with [68Ga]Ga-NOTA-C2, [89Zr]Zr-DFO-ABDC2 had a significantly prolonged circulation time, increased tumor uptake, and reduced accumulation in the kidneys. Finally, biodistribution and histological staining confirmed the results of the immunoPET imaging studies. In this study, we validated that two novel VHH-derived molecular imaging tracers for immunoPET imaging ([68Ga]Ga-NOTA-C2 and [89Zr]Zr-DFO-ABDC2) can effectively annotate CD47 expression and diagnose PDAC in a target-specific manner. Clinical application of the imaging strategies may help select patients for CD47-targeted therapies and assess the response thereafter.

GPC3-targeted immunoPET imaging of hepatocellular carcinomas.

PURPOSE: Early detection of hepatocellular carcinoma (HCC) remains a clinical challenge. Glypican 3 (GPC3) is a proteoglycan highly specific for HCC and is a potential diagnostic and therapeutic target for HCC. This work aims to develop GPC3-targeted immuno-positron emission tomography (immunoPET) imaging strategies and to assess the diagnostic values in preclinical HCC models. METHODS: Flow cytometry was used to screen GPC3-positive HCC cell lines. The expression of GPC3 in HCCs was detected by immunohistochemistry on tissue microarray. A novel GPC3-specific single domain antibody (sdAb) was produced and labeled with gallium-68 (68Ga, T1/2 = 1.1 h) and fluorine-18 (18F, T1/2 = 1.8 h) to develop radiotracers with different half-lives. The diagnostic efficacies of the developed probes (i.e., [68Ga]Ga-NOTA-G2, [18F]F-G2, and [68Ga]Ga-NOTA-ABDG2) were interrogated in preclinical HCC models bearing varying GPC3 levels. RESULTS: GPC3 was strongly expressed on HCC cell lines and patients with poorly differentiated HCC. [68Ga]Ga-NOTA-G2 immunoPET imaging specifically delineated the subcutaneous HCC lesions, outperforming the traditional 18F-fluorodeoxyglucose PET and the nonspecific [68Ga]Ga-NOTA-NbGFP immunoPET. ImmunoPET imaging with [18F]F-G2 also efficiently diagnosed the tumors with clarity. Moreover, the fusion of G2 to an albumin-binding domain (ABD) significantly increased the tumor uptake and decreased kidney accumulation of the radiotracer when compared to [68Ga]Ga-NOTA-G2. CONCLUSIONS: In the work, we successfully developed sdAb-derived GPC3-targeted immunoPET imaging strategies and characterized the superior diagnostic accuracies in preclinical HCC models. Furthermore, we synthesized a fusion protein ABDG2 with improved targeting and pharmacokinetic properties, serving as a promising candidate for developing radioimmunotherapy agents.

PET Imaging of Lung Cancers in Precision Medicine: Current Landscape and Future Perspective.

Despite the recent advances in cancer treatment, lung cancer remains the leading cause of cancer mortality worldwide. Immunotherapies using immune checkpoint inhibitors (ICIs) achieved substantial efficacy in nonsmall cell lung cancer (NSCLC). Currently, most ICIs are still a monoclonal antibody (mAb). Using mAbs or antibody derivatives labeled with radionuclide as the tracers, immunopositron emission tomography (immunoPET) possesses multiple advantages over traditional 18F-FDG PET in imaging lung cancers. ImmunoPET presents excellent potential in detecting, diagnosing, staging, risk stratification, treatment guidance, and recurrence monitoring of lung cancers. By using radiolabeled mAbs, immunoPET can visualize the biodistribution and uptake of ICIs, providing a noninvasive modality for patient stratification and response evaluation. Some novel targets and associated tracers for immunoPET have been discovered and investigated. This Review introduces the value of immunoPET in imaging lung cancers by summarizing both preclinical and clinical evidence. We also emphasize the value of immunoPET in optimizing immunotherapy in NSCLC. Lastly, immunoPET probes developed for imaging small cell lung cancer (SCLC) will also be discussed. Although the major focus is to summarize the immunoPET tracers for lung cancers, we also highlighted several small-molecule PET tracers to give readers a balanced view of the development status.

Molecular Imaging of Renal Cell Carcinoma in Precision Medicine.

Renal cell carcinoma (RCC) is the sixth most common cancer among men and the ninth among women, and its prognosis is closely correlated with metastasis. Targeted therapy and immunotherapy are the main adjuvant treatments for advanced RCC and require early diagnosis, precise assessment, and prediction of the therapeutic responses. Current conventional imaging methods of RCC only provide structural information rather than biological processes. Noninvasive diagnostic tools are therefore needed to image RCC early and accurately at the molecular level. Nuclear medicine imaging combines the high sensitivity of radionuclides with the high resolution of structural imaging to visualize the metabolic processes and specific targets of RCC for more accurate and reliable diagnosis, staging, prognosis prediction, and response assessment. This review summarizes the most recent applications of nuclear medicine receptor imaging and metabolic imaging in RCC and highlights future development perspectives in the field.

Annotating BCMA Expression in Multiple Myelomas.

B cell maturation antigen (BCMA) is a promising theranostic target for multiple myeloma (MM). BCMA-targeted therapeutics, such as antibody-drug conjugates and chimeric antigen receptor T-cell immunotherapies, are rapidly reshaping the treatment landscape of MM. Along with the progress, a critical challenge is to noninvasively visualize the dynamic change of BCMA for a better-personalized prescription of the above-mentioned therapeutics. We aim to develop immuno-positron emission tomography (immunoPET) imaging strategies to visualize BCMA expression and realize target-specific diagnosis of MM in the work. A series of BCMA-targeting nanobodies were produced and two of them were successfully labeled with gallium-68 (68Ga). MM models were established using MM.1S cell line and NOD-Prkdcem26Cd52Il2rgem26Cd22/Nju mice. The diagnostic efficacies of the developed probes (i.e., [68Ga]Ga-NOTA-MMBC2 and [68Ga]Ga-NOTA-MMBC3) were investigated in disseminated MM models by immunoPET imaging, region of interest analysis on PET images, biodistribution study, and histopathological staining study. [68Ga]Ga-NOTA-MMBC2 and [68Ga]Ga-NOTA-MMBC3 were developed with radiochemical purities of >99%. ImmunoPET imaging with either [68Ga]Ga-NOTA-MMBC2 or [68Ga]Ga-NOTA-MMBC3 precisely visualized BCMA expression and delineated MM lesions throughout the bone marrows. Moreover, [68Ga]Ga-NOTA-MMBC3 immunoPET successfully detected remnant MM after treatment with daratumumab, a prescription medicine used to treat MM. The immunoPET imaging data correlated well with the biodistribution and immunohistochemistry staining results. The work successfully developed two state-of-the-art BCMA-targeted radiotracers for annotating BCMA expression and diagnosing MM. Translational studies interpreting the diagnostic efficacies of the immunoPET radiotracers are warranted.

Annotating CD38 Expression in Multiple Myeloma with [18F]F-Nb1053.

Noninvasive diagnosis of multiple myeloma (MM) is a clinical challenge. CD38 is an established biomarker for MM, and the development of CD38-targeted radiotracers may improve the management of MM. By taking the advantages of bioorthogonal click chemistry, a nanobody (i.e., Nb1053-LLQS) specific for CD38 was successfully labeled with 18F. The diagnostic efficacy and specificity of the developed tracer (i.e., [18F]F-Nb1053) were evaluated by immuno-positron emission tomography (immunoPET) imaging in disseminated MM.1S-bearing models. [18F]F-Nb1053 was developed with high radiochemical purity (>98%) and excellent immunoreactivity. [18F]F-Nb1053 immunoPET successfully delineated disseminated MM lesions in preclinical MM models. The uptake in the humerus, femur, and tibia was 1.42 ± 0.50%ID/g, 1.35 ± 0.53%ID/g, and 1.48 ± 0.67%ID/g (n = 6), respectively. Tumor uptake of [18F]F-Nb1053 decreased after daratumumab premedication, indicating the superior specificity of the reported probe. This work successfully developed a novel CD38-specific probe [18F]F-Nb1053 that may potentially optimize the management of MM upon clinical translation.

ImmunoPET: Concept, Design, and Applications.

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as 89Zr-Df-pertuzumab and 89Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

ImmunoPET/NIRF/Cerenkov multimodality imaging of ICAM-1 in pancreatic ductal adenocarcinoma.

PURPOSE: We dual-labeled an intercellular adhesion molecule-1 (ICAM-1) monoclonal antibody (mAb) and evaluated its effectiveness for lesion detection and surgical navigation in pancreatic ductal adenocarcinoma (PDAC) via multiple noninvasive imaging approaches, including positron emission tomography (PET), near-infrared fluorescence (NIRF), and Cerenkov luminescence imaging (CLI). METHODS: ICAM-1 expression in PDAC cell lines (BxPC-3 and AsPC-1) was assessed via flow cytometry and immunofluorescent staining. An ICAM-1 mAb labeled by IRDye 800CW and radionuclide zirconium-89 (denoted as [89Zr]Zr-DFO-ICAM-1-IR800) was synthesized. Its performance was validated via in vivo comparative PET/NIRF/CLI and biodistribution (Bio-D) studies in nude mice bearing subcutaneous BxPC-3/AsPC-1 tumors or orthotopic BxPC-3 tumor models using nonspecific IgG as an isotype control tracer. RESULTS: ICAM-1 expression was strong in the BxPC-3 and minimal in the AsPC-1 cell line. Both multimodality imaging and Bio-D data exhibited more prominent uptake of [89Zr]Zr-DFO-ICAM-1-IR800 in BxPC-3 tumors than in AsPC-1 tumors. The uptake of [89Zr]Zr-DFO-IgG-IR800 in BxPC-3 tumors was similar to that of [89Zr]Zr-DFO-ICAM-1-IR800 in AsPC-1 tumors. These results demonstrate the desirable affinity and specificity of [89Zr]Zr-DFO-ICAM-1-IR800 compared to [89Zr]Zr-DFO-IgG-IR800. Orthotopic BxPC-3 tumor foci could also be clearly delineated by [89Zr]Zr-DFO-ICAM-1-IR800. An intermodal match was achieved in the ICAM-1-targeted immunoPET/NIRF/CLI. The positive expression levels of ICAM-1 in BxPC-3 tumor tissue were further confirmed by immunohistopathology. CONCLUSION: We successfully developed a dual-labeled ICAM-1-targeted tracer for PET/NIRF/CLI of PDAC that can facilitate better diagnosis and intervention of PDAC upon clinical translation.

ImmunoPET imaging of multiple myeloma with [68Ga]Ga-NOTA-Nb1053.

PURPOSE: Multiple myeloma (MM) remains incurable and its diagnosis relies heavily on bone marrow aspiration and biopsy. CD38 is a glycoprotein highly specific for MM. Antibody therapeutics (e.g., daratumumab) targeting CD38 have shown encouraging efficacy in treating MM, either as a monotherapy agent or in combination with other regimens. However, efficient stratification of patients who might benefit from daratumumab therapy and timely monitoring of the therapeutic responses are still clinical challenges. This work aims to devise a CD38-targeted imaging strategy and assess its value in diagnosing MMs. METHODS: By labeling a CD38-specific single domain antibody (Nb1053) with 68Ga (t1/2 = 1.1 h), we developed a CD38-targeted immuno-positron emission tomography (immunoPET) imaging probe [68Ga]Ga-NOTA-Nb1053. The probe was developed with good radiochemical yield (> 50%), excellent radiochemical purity (> 99%), and immunoreactivity (> 95%). The diagnostic accuracy of the probe was thoroughly investigated in preclinical MM models. RESULTS: ImmunoPET imaging with [68Ga]Ga-NOTA-Nb1053 specifically depicted all the subcutaneous and orthotopic MM lesions, outperforming the traditional 18F-fluorodeoxyglucose PET and the nonspecific [68Ga]Ga-NOTA-NbGFP immunoPET. More importantly, daratumumab preloading significantly reduced [68Ga]Ga-NOTA-Nb1053 uptake in the disseminated bone lesions, indicating the overlapping targeting epitopes of [68Ga]Ga-NOTA-Nb1053 with that of daratumumab. Furthermore, premedication with sodium maleate or fructose significantly decreased kidney retention of [68Ga]Ga-NOTA-Nb1053 and improved the diagnostic value of the probe in lymphoma models. CONCLUSION: This work successfully developed a novel CD38-targeted immunoPET imaging approach that enabled precise visualization of CD38 and diagnosis of MMs. Upon clinical translation, [68Ga]Ga-NOTA-Nb1053 immunoPET may serve as a valuable CD38-targeted molecular imaging toolbox, facilitating early diagnosis of MM and precise assessment of the therapeutic responses.

ImmunoPET imaging of human CD8+ T cells with novel 68Ga-labeled nanobody companion diagnostic agents.

BACKGROUND: Although immunotherapy has revolutionized treatment strategies for some types of cancers, most patients failed to respond or obtain long-term benefit. Tumor-infiltrating CD8+ T lymphocytes are closely related to the treatment outcome and prognosis of patients. Therefore, noninvasive elucidation of both systemic and tumor-infiltrating CD8+ T lymphocytes is of extraordinary significance for patients during cancer immunotherapy. Herein, a panel of 68Ga-labeled Nanobodies were designed and investigated to track human CD8+ T cells in vivo through immuno-positron emission tomography (immunoPET). RESULTS: Among the screened Nanobodies, SNA006a showed the highest binding affinity and specificity to both human CD8 protein and CD8+ cells in vitro, with the equilibrium dissociation constant (KD) of 6.4 × 10-10 M and 4.6 × 10-10 M, respectively. 68Ga-NOTA-SNA006 was obtained with high radiochemical yield and purity, and stayed stable for at least 1 h both in vitro and in vivo. Biodistribution and Micro-PET/CT imaging studies revealed that all tracers specifically concentrated in the CD8+ tumors with low accumulation in CD8- tumors and normal organs except the kidneys, where the tracer was excreted and reabsorbed. Notably, the high uptake of 68Ga-NOTA-SNA006a in CD8+ tumors was rapid and persistent, which reached 24.41 ± 1.00% ID/g at 1.5 h after intravenous injection, resulting in excellent target-to-background ratios (TBRs). More specifically, the tumor-to-muscle, tumor-to-liver, and CD8+ to CD8- tumor was 28.10 ± 3.68, 5.26 ± 0.86, and 19.58 ± 2.70 at 1.5 h, respectively. Furthermore, in the humanized PBMC-NSG and HSC-NPG mouse models, 68Ga-NOTA-SNA006a accumulated in both CD8+ tumors and specific tissues such as liver, spleen and lung where human CD8 antigen was overexpressed or CD8+ T cells located during immunoPET imaging. CONCLUSIONS: 68Ga-NOTA-SNA006a, a novel Nanobody tracer targeting human CD8 antigen, was developed with high radiochemical purity and high affinity. Compared with other candidates, the long retention time, low background, excellent TBRs of 68Ga-NOTA-SNA006a make it precisely track the human CD8+ T cells in mice models, showing great potential for immunotherapy monitoring and efficacy evaluation.

Development and characterization of CD54-targeted immunoPET imaging in solid tumors.

PURPOSE: Intercellular adhesion molecule-1 (ICAM-1, CD54) is an emerging therapeutic target for a variety of solid tumors including melanoma and anaplastic thyroid cancer (ATC). This study aims to develop an ICAM-1-targeted immuno-positron emission tomography (immunoPET) imaging strategy and assess its diagnostic value in melanoma and ATC models. METHODS: Flow cytometry was used to screen ICAM-1-positive melanoma and ATC cell lines. Melanoma and ATC models were established using A375 cell line and THJ-16T cell line, respectively. An ICAM-1-specific monoclonal antibody (R6-5-D6) and a nonspecific human IgG were radiolabeled with 64Cu and the diagnostic efficacies were interrogated in tumor-bearing mouse models. Biodistribution and fluorescent imaging studies were performed to confirm the specificity of the ICAM-1-targeted imaging probes. RESULTS: ICAM-1 was strongly expressed on melanoma and advanced thyroid cancer cell lines. 64Cu-NOTA-ICAM-1 immunoPET imaging efficiently delineated A375 melanomas with a peak tumor uptake of 21.28 ± 6.56 %ID/g (n = 5), significantly higher than that of 64Cu-NOTA-IgG (10.63 ± 2.58 %ID/g, n = 3). Moreover, immunoPET imaging with 64Cu-NOTA-ICAM-1 efficiently visualized subcutaneous and orthotopic ATCs with high clarity and contrast. Fluorescent imaging with IRDye 800CW-ICAM-1 also visualized orthotopic ATCs and the tumor uptake could be blocked by the ICAM-1 parental antibody R6-5-D6, indicating the high specificity of the developed probe. Finally, blocking with the human IgG prolonged the circulation of the 64Cu-NOTA-ICAM-1 in R2G2 mice without compromising the tumor uptake. CONCLUSION: ICAM-1-targeted immunoPET imaging could characterize ICAM-1 expression in melanoma and ATC, which holds promise for optimizing ICAM-1-targeted therapies in the future.

Can pretreatment 18F-FDG PET tumor texture features predict the outcomes of osteosarcoma treated by neoadjuvant chemotherapy?

PURPOSE: To investigate whether tumor texture features derived from pretreatment with 18F-fluorodeoxyglucose positron emission tomography (FDG PET) can predict histological response or event-free survival (EFS) in patients with localized osteosarcoma of the extremities treated by neoadjuvant chemotherapy (NAC). METHODS: We retrospectively reviewed 35 patients with American Joint Committee on Cancer stage II extremity osteosarcoma treated with NAC and surgery. Primary tumor traditional parameters and texture features were measured for all 18F-FDG PET images prior to treatment. After surgery, histological responses to NAC were evaluated on the postsurgical specimens. A receiver operating characteristic curve (ROC) was constructed to evaluate the optimal predictive performance among the various indices. EFS was calculated using the Kaplan-Meier method and prognostic significance was assessed by Cox proportional hazards analysis. RESULTS: Pathologic examination revealed 16 (45.71%) good responders and 19 (54.29%) poor responders. Although both the texture features (least axis, dependence nonuniformity, run length nonuniformity, and size zone nonuniformity) and metabolic tumor volume (MTV) can predict tumor response of osteosarcoma to NAC, the traditional indicator MTV has the best performance according to ROC curve analysis (area under the curve = 0.918, p < 0.0001). In multivariate analysis, MTV (p < 0.0001), histological response (p = 0.0003), and texture feature of coarsenessNGTDM (neighboring gray tone difference matrix) (p = 0.005) were independently associated with EFS. CONCLUSIONS: Intratumoral heterogeneity of baseline 18F-FDG uptake measured by PET texture analysis can predict tumor response and EFS of patients with extremity osteosarcoma treated by NAC, but the conventional parameter MTV provides better predictive power and is a strong independent prognostic factor. KEY POINTS: • The baseline 18 F-FDG PET tumor texture features can predict tumor NAC response for patients with osteosarcoma. • Coarseness NGTDM is a new and independent prognostic factor for osteosarcoma. • MTV provides the best predictive power and is a strong independent prognostic factor for patients with osteosarcoma.

PROGRAMMED CELL DEATH-LIGAND 1 OVEREXPRESSION IN THYROID CANCER.

OBJECTIVE: Programmed cell death-ligand 1 (PD-L1) expression on tumor tissue has been associated with favorable response to anti-programmed cell death-receptor 1/PD-L1 therapy in many human cancers. Studies have reported that PD-L1 is also expressed in thyroid cancer. The objective of this paper is to introduce the potential predictive and therapeutic values of PD-L1 in thyroid cancer. METHODS: A literature search was conducted in the PubMed database using the terms "PD-L1," "B7-H1," and "thyroid cancer." PD-L1 positivity was determined by immunohistochemical assay. RESULTS: The frequency of PD-L1 positivity in different studies ranged from 6.1 to 82.5% in papillary thyroid cancer (PTC) patients and 22.2 to 81.2% in anaplastic thyroid cancer (ATC) patients. PD-L1 positivity rate was higher in ATC than in PTC within the same studies, and its expression intensity was significantly higher in tumor tissue than in the corresponding nontumor thyroid tissues. Moreover, PD-L1 expression was positively associated with the aggressiveness and recurrence of thyroid cancers and negatively associated with the differentiation status and outcomes. PD-L1 checkpoint pathway blockade may emerge as a promising therapeutic target in the treatment of thyroid cancers. CONCLUSION: PD-L1 is a potential biomarker to predict the recurrence and prognosis of thyroid cancers. It is also a novel immunotherapy target for optimizing the management landscape of radioiodine-refractory and ATCs. ABBREVIATIONS: ATC = anaplastic thyroid cancer; DTC = differentiated thyroid cancer; IHC = immunohistochemical; OS = overall survival; PD-1 = programmed cell death-receptor 1; PD-L1 = programmed cell death-ligand 1; PD-L2 = programmed cell death-ligand 2; PTC = papillary thyroid cancer; TNM = tumor-node-metastasis; Treg = regulatory T cell.

A Preliminary Study of Ankle Single Photon Emission Computed Tomography/Computed Tomography in Patients With Bony Impingement Syndrome: Association With the Visual Analogue Scale Pain Score.

Both osteoarthritis and impingement syndrome are the disorders commonly observed in sports medicine. However, failure in pain alleviation by surgical intervention introduces challenges in the diagnosis and decision-making for orthopedists. Hybrid single photon emission computed tomography/computed tomography (SPECT/CT) provides both functional and structural information of ankle pathology. The purpose of this retrospective study was to evaluate whether bone tracer uptake by ankle SPECT/CT is related to the lesion type and visual analog scale (VAS) pain score for patients with osteoarthritis and bony impingement. Fifty individuals with chronic ankle pain who underwent pretreatment ankle SPECT/CT were included in the current study. The median follow-up period was 2.5 (range 1.8 to 3.2) years. The lesion types were categorized by the positions of anatomical changes and bone tracer uptake. The VAS pain score was recorded 2 weeks before and 1.5 year after surgical intervention. Twenty-nine (58%) of 50 patients had osseous impingement. Among them, 16 (55.2%), 4 (13.8%), and 9 (31%) patients had anterior, posterior, and both types of ankle impingement, respectively. The uptake grade of bone tracer was significantly related to the lesion type of ankle impingement (p < .001). The VAS pain score was significantly correlated with bone tracer uptake before treatment (p < .001). Bone tracer uptake was related to the lesion type of impingement detected by SPECT/CT and was confirmed by surgical findings. The VAS pain score was significantly correlated with the bone tracer uptake. Preoperative ankle SPECT/CT may be helpful to clinically correlate the VAS pain score in the pre- and postsurgical periods for patients with osteoarthritis and bony impingement syndrome.

Magnetic Targeting of Nanotheranostics Enhances Cerenkov Radiation-Induced Photodynamic Therapy.

The interaction between radionuclides and nanomaterials could generate Cerenkov radiation (CR) for CR-induced photodynamic therapy (PDT) without requirement of external light excitation. However, the relatively weak CR interaction leaves clinicians uncertain about the benefits of this new type of PDT. Therefore, a novel strategy to amplify the therapeutic effect of CR-induced PDT is imminently required to overcome the disadvantages of traditional nanoparticulate PDT such as tissue penetration limitation, external light dependence, and low tumor accumulation of photosensitizers. Herein, magnetic nanoparticles (MNPs) with 89Zr radiolabeling and porphyrin molecules (TCPP) surface modification (i.e., 89Zr-MNP/TCPP) were synthesized for CR-induced PDT with magnetic targeting tumor delivery. As a novel strategy to break the depth and light dependence of traditional PDT, these 89Zr-MNP/TCPP exhibited high tumor accumulation under the presence of an external magnetic field, contributing to excellent tumor photodynamic therapeutic effect together with fluorescence, Cerenkov luminescence (CL), and Cerenkov resonance energy transfer (CRET) multimodal imaging to monitor the therapeutic process. The present study provides a major step forward in photodynamic therapy by developing an advanced phototherapy tool of magnetism-enhanced CR-induced PDT for effective targeting and treatment of tumors.

Circulating Tumor Cells Correlate with Clinicopathological Features and Outcomes in Differentiated Thyroid Cancer.

BACKGROUND/AIMS: As biomarkers, circulating tumor cells (CTCs) from solid tumors can predict metastases and prognoses, and help monitor treatment efficacy. However, conventional CellSearch methods have low sensitivity to differentiated thyroid cancer (DTC) CTCs. In this study, for the first time, we used negative enriching (NE) immunofluorescence-in situ hybridization (iFISH) of chromosome 8 to capture and identify CTCs in DTC patients; and investigated how CTCs correlate with clinicopathological factors and prognosis in DTC patients with distant metastases (DM). METHODS: In this prospective study, we enrolled 72 patients with DTC before they underwent 131I treatment, and 30 healthy controls (HC). Their CTCs were measured in 7.5 ml peripheral blood using the NE-iFISH technique. CTC was defined by the aneuploidy. RESULTS: We detected CTCs in 62 (86.1%) of the 72 subjects with DTC. The mean number of CTCs in patients with DTC with DM (DM+) was significantly higher than in the HC group (P< 0.001) and DTC patients without DM (DM-; P=0.0016). We found CTCs ≥ 5 was significantly associated with DM+ DTC (P=0.009; sensitivity: 64.3%; specificity: 83.8%); CTCs ≥ 7 was related to poor response to 131I treatment (sensitivity: 73.7 %; specificity: 69.6 %), and was also associated with worse prognosis in DM+ DTC (P< 0.001). CONCLUSION: We found CTCs ≥ 5 to be a potential predictive index for DM+ DTC; and CTCs ≥7 as a possible indicator of poor response to 131I treatment and worse prognosis in DM+ DTC.