[99mTc]3PRGD2 for integrin receptor imaging of esophageal cancer: a comparative study with [18F]FDG PET/CT

Clinical Translation of a Dual-Integrin αvβ3- and CD13-Targeting PET Tracer

PURPOSE

Angiogenesis is essential in the development and progression of tumors. This study aimed to investigate the clinical application of 68 Ga-labeled heterodimeric peptide ( 68 Ga-HX01) targeting integrin αvβ3 and CD13 in tumor neovascularization.

PATIENTS AND METHODS

Six healthy volunteers were recruited to study the biodistribution, pharmacokinetics, and radiation of 68 Ga-HX01. Twelve patients with various malignancies were enrolled to seek the preliminary clinical value of 68 Ga-HX01. In healthy volunteers, SUVs of each major organ on 68 Ga-HX01 PET were measured. The clinical data, lesion numbers, and uptake were recorded in patients. The integrin αvβ3 and CD13 expression of the resected tumors was checked via immunohistochemistry staining.

RESULTS

With a mean injected dose of 167.98 ± 26.32 MBq, 68 Ga-HX01 was well tolerated and safe without side effects in 6 healthy volunteers. The radiation absorbed effective dose of 68 Ga-HX01 was 1.94 × 10 -2 mSv/MBq, and the urinary bladder wall held the highest absorbed effective dose (0.15 ± 5.87 × 10 -2 mSv/MBq). In 12 patients with various malignancies, 68 Ga-HX01 PET could clearly visualize the lesions from the surrounding tissues. The SUV max values in tumors were significantly higher than those in the surrounding tissues ( P < 0.05). A positive correlation trend between tumor SUV max and semiquantitative integrin αvβ3 and CD13 expression was determined ( P < 0.05).

CONCLUSIONS

For clinical use, 68 Ga-HX01 is safe with low radiation absorbed effective dose. It also indicates the efficiency of dual integrin αvβ3 and CD13-targeting PET radiotracer in tumor diagnosis, which may assist in patient prognosis and selecting eligible patients for antiangiogenic therapy.

Potential Probes for Targeted Intraoperative Fluorescence Imaging in Gastric Cancer

Gastric cancer (GC) is a malignant tumor of the gastrointestinal tract associated with high mortality rates and accounting for approximately 1 million new cases diagnosed annually. Surgery, particularly radical gastrectomy, remains the primary treatment; however, there are currently no specific approaches to better distinguish malignant from healthy tissue or to differentiate between metastatic and non-metastatic lymph nodes. As a result, surgeons have to remove all lymph nodes indiscriminately, increasing intraoperative risks for patients and prolonging hospital stay. Near-infrared fluorescence imaging with indocyanine green (ICG) can provide real-time visualization of the surgical field using both conventional laparoscopy and robotic mini-invasive precision surgery platforms. However, its application shows some limits, as ICG is a non-targeted contrast agent. Several studies are now investigating the potential efficacy of fluorescent targeted agents that could selectively bind to the tumor tissue, offering a valuable tool for metastatic mapping during robotic gastrectomy. This review aims to summarize the key fluorescent agents that have been developed to recognize GC markers, as well as those targeting the tumor microenvironment (TME) and metabolic features. These agents hold great potential as valuable tools for enhancing precision surgery in robotic gastrectomy procedures improving the clinical recovery of GC patients.

Prospective study of 99mTc-3PRGD2 SPECT/CT diagnosing metastatic lymph nodes in esophageal squamous cell carcinoma

BACKGROUND

Lymph node (LN) metastasis is a significant prognostic factor for esophageal squamous cell carcinoma (ESCC), and there are no satisfactory methods for accurately predicting metastatic LNs. The present study aimed to assess the efficacy of 99mTc-3PRGD2 single-photon emission computed tomography (SPECT)/computed tomography (CT) for diagnosing metastatic LNs in ESCC.

METHODS

A total of 15 enrolled patients with ESCC underwent 99mTc-3PRGD2 SPECT/CT and 18F-fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET/CT) examinations preoperatively. High-definition bone carving reconstruction technology (HD-xSPECT Bone) was applied to quantitatively assess the LN's SUVmax via SPECT/CT. The two methods were compared for diagnosing metastatic LNs with pathology as the gold standard.

RESULTS

Among 15 patients, 23 metastatic lymph node stations (mLNSs) were predicted by SPECT/CT, with a mean SUVmax of 2.71 ± 1.34, of which 15 were pathologically confirmed; 32 mLNSs were predicted by PET/CT with a mean SUVmax of 4.41 ± 4.02, of which 17 were pathologically confirmed. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value of SPECT/CT for diagnosing metastatic LNs were 62.50%, 91.30%, 85.34%, 65.22%, and 90.32%, respectively, and those of PET/CT were 70.83%, 83.70%, 81.03%, 53.13%, and 91.67%, respectively. There was no significant difference in sensitivity (p = 0.061) or specificity (p = 0.058) between the two methods. The AUCSPECT/CT was 0.816 and the SUVmax threshold was 2.5.

CONCLUSION

99mTc-3PRGD2 SPECT/CT might be an effective method for diagnosing metastatic LNs in ESCC, especially in combination with HD-xSPECT Bone. The diagnostic efficiency of this method was noninferior to that of 18F-FDG PET/CT. The SUVmax threshold of 2.5 showed the highest agreement with the pathology findings.

A comparison of [18F]AlF- and 68Ga-labeled dual targeting heterodimer FAPI-RGD in malignant tumor: preclinical evaluation and pilot clinical PET/CT imaging

Due to the heterogeneity of tumors, strategies to improve the effectiveness of dual-targeting tracers in tumor diagnostics have been intensively practiced. In this study, the radiolabeled [18F]AlF-NOTA-FAPI-RGD (denoted as [18F]AlF-LNC1007), a dual-targeting heterodimer tracer targeting both fibroblast activation protein (FAP) and integrin αvβ3 to enhance specific tumor uptake and retention, was synthesized and evaluated. The tracer was compared with [68Ga]Ga-LNC1007 in preclinical and clinical settings.

METHODS

The preparation of [18F]AlF- and 68Ga-labeled FAPI-RGD was carried out with an optimized protocol. The stability was tested in PBS and fetal bovine serum (FBS). Cellular uptake and in vivo distribution of the two products were compared and carried out on the U87MG cell line and its xenograft model. The safety and dosimetry of [18F]AlF-LNC1007 PET/CT scan were evaluated in six patients with malignant tumors.

RESULTS

Two radiolabeling protocols of [18F]AlF-/[68Ga]Ga-LNC1007 were developed and optimized to give a high yield of tracers with good stability. In vivo microPET images showed that the two tracers exhibited comparable pharmacokinetic characteristics, with high tumor uptake and prolonged tumor retention. In vivo distribution data showed that the target-to-non-target ratios of [18F]AlF-LNC1007 were similar to[68Ga]Ga-LNC1007. A total of six patients underwent [18F]AlF-LNC1007 PET/CT evaluation while two had head-to-head [18F]FDG PET/CT scans. The total body effective dose was 9.94E-03 mSv/MBq. The biodistribution curve showed optimal normal organ uptake with high tumor uptake and long retention of up to 3h p.i., and notably, the tumor-to-background ratio increased over time.

CONCLUSION

We successfully prepared an [18F]AlF-LNC1007 dual-targeting PET probe with comparable performances as [68Ga]Ga-LNC1007. With prolonged tumor retention and tumor specificity, it produced good imaging quality in preclinical and clinical translational studies, indicating that [18F]AlF-LNC1007 is a promising non-invasive tracer for detecting tumors expressing FAP and/or integrin avβ3, with the prospect of clinical implementation.

Recent Progress in Peptide-Based Molecular Probes for Disease Bioimaging

Recent strides in molecular pathology have unveiled distinctive alterations at the molecular level throughout the onset and progression of diseases. Enhancing the in vivo visualization of these biomarkers is crucial for advancing disease classification, staging, and treatment strategies. Peptide-based molecular probes (PMPs) have emerged as versatile tools due to their exceptional ability to discern these molecular changes with unparalleled specificity and precision. In this Perspective, we first summarize the methodologies for crafting innovative functional peptides, emphasizing recent advancements in both peptide library technologies and computer-assisted peptide design approaches. Furthermore, we offer an overview of the latest advances in PMPs within the realm of biological imaging, showcasing their varied applications in diagnostic and therapeutic modalities. We also briefly address current challenges and potential future directions in this dynamic field.

99mTc-3PRGD2 SPECT/CT Imaging for Diagnosing Lymph Node Metastasis of Primary Malignant Lung Tumors

OBJECTIVE

To evaluate 99mtechnetium-three polyethylene glycol spacers-arginine-glycine-aspartic acid (99mTc-3PRGD2) single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging for diagnosing lymph node metastasis of primary malignant lung neoplasms.

MATERIALS AND METHODS

We prospectively enrolled 26 patients with primary malignant lung tumors who underwent 99mTc-3PRGD2 SPECT/CT and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT imaging. Both imaging methods were analyzed in qualitative (visual dichotomous and 5-point grades for lymph nodes and lung tumors, respectively) and semi-quantitative (maximum tissue-to-background radioactive count) manners for the lymph nodes and lung tumors. The performance of the differentiation of lymph nodes with and without metastasis was determined at the per-lymph node station and per-patient levels using histopathological results as the reference standard.

RESULTS

Total 42 stations had metastatic lymph nodes and 136 stations had benign lymph nodes. The differences between metastatic and benign lymph nodes in the visual qualitative and semiquantitative analyses of 99mTc-3PRGD2 SPECT/CT and 18F-FDG PET/CT were statistically significant (all P < 0.001). The area under the receiver operating characteristic curve (AUC) in the semi-quantitative analysis of 99mTc-3PRGD2 SPECT/CT was 0.908 (95% confidence interval [CI], 0.851-0.966), and the sensitivity, specificity, positive predictive value, and negative predictive value were 0.86 (36/42), 0.88 (120/136), 0.69 (36/52), and 0.95 (120/126), respectively. Among the 26 patients (including two patients each with two lung tumors), 15 had pathologically confirmed lymph node metastasis. The difference between primary lung lesions in patients with and without lymph node metastasis was statistically significant only in the semi-quantitative analysis of 99mTc-3PRGD2 SPECT/CT (P = 0.007), with an AUC of 0.807 (95% CI, 0.641-0.974).

CONCLUSION

99mTc-3PRGD2 SPECT/CT imaging may notably perform in the direct diagnosis of lymph node metastasis of primary malignant lung tumors and indirectly predict the presence of lymph node metastasis through uptake in the primary lesions.

Comparison of integrin αvβ3 expression with 68Ga-NODAGA-RGD PET/CT and glucose metabolism with 18F-FDG PET/CT in esophageal or gastroesophageal junction cancers

BACKGROUND

The primary aims of this study were to compare in patients with esophageal or esophagogastric junction cancers the potential of ⁶⁸Ga-NODAGA-RGD PET/CT with that of ¹⁸F-FDG PET/CT regarding tumoral uptake and distribution, as well as histopathologic examination.

METHODS

Ten ⁶⁸Ga-NODAGA-RGD and ten ¹⁸F-FDG PET/CT were performed in nine prospectively included participants (1 woman; aged 58 ± 8.4 y, range 40-69 y). Maximum SUV (SUV_max) and metabolic tumor volumes (MTV) were calculated. The Mann-Whitney U test and Spearman correlation analysis (ρ) were used.

RESULTS

⁶⁸Ga-NODAGA-RGD PET/CT detected positive uptake in 10 primary sites (8 for primary tumors and 2 for local relapse suspicion), 6 lymph nodes and 3 skeletal sites. ¹⁸F-FDG PET/CT detected positive uptake in the same sites but also in 16 additional lymph nodes and 1 adrenal gland. On a lesion-based analysis, SUV_max of ¹⁸F-FDG was significantly higher than those of ⁶⁸Ga-NODAGA-RGD (4.9 [3.7-11.3] vs. 3.2 [2.6-4.2] g/mL, p = 0.014). Only one participant showed a higher SUV_max in an osseous metastasis with ⁶⁸Ga-NODAGA-RGD as compared to ¹⁸F-FDG (6.6 vs. 3.9 g/mL). Correlation analysis showed positive correlation between ¹⁸F-FDG and ⁶⁸Ga-NODAGA-RGD PET parameters (ρ = 0.56, p = 0.012 for SUV_max, ρ = 0.78, p < 0.001 for lesion-to-background ratios and ρ = 0.58, p = 0.024 for MTV). We observed that ¹⁸F-FDG uptake was homogenous inside all the confirmed primary sites (n = 9). In contrast, ⁶⁸Ga-NODAGA-RGD PET showed more heterogenous uptake in 6 out of the 9 confirmed primary sites (67%), seen mostly in the periphery of the tumor in 5 out of the 9 confirmed primary sites (56%), and showed slight extensions into perilesional structures in 5 out of the 9 confirmed primary sites (56%).

CONCLUSIONS

In conclusion, ⁶⁸Ga-NODAGA-RGD has lower potential in the detection of esophageal or esophagogastric junction malignancies compared to ¹⁸F-FDG. However, the results suggest that PET imaging of integrin α_vβ₃ expression may provide complementary information and could aid in tumor diversity and delineation.

TRIAL REGISTRATION

Trial registration: NCT02666547. Registered January 28, 2016-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT02666547 .

Evaluation of integrin αvβ3-targeted imaging for predicting disease progression in patients with high-risk differentiated thyroid cancer (using 99mTc-3PRGD2)

BACKGROUND

High-risk differentiated thyroid cancer (DTC) needs effective early prediction tools to improving clinical management and prognosis. This cohort study aimed to investigate the prognostic impact of ^99mTc-PEG₄-E[PEG₄-c(RGDfK)]₂ (^99mTc-3PRGD₂) SPECT/CT in high-risk DTC patients after initial radioactive iodine (RAI) therapy.

METHODS

Thirty-three patients with high-risk DTC were prospectively recruited; all patients underwent total thyroidectomy and received ^99mTc-3PRGD₂ SPECT/CT before RAI ablation. Follow-up was done with serological and imaging studies. The correlation between ^99mTc-3PRGD₂ avidity and remission rate for initial RAI therapy was evaluated using logistic regression analysis. The prognostic value of ^99mTc-3PRGD₂ SPECT/CT was evaluated by Kaplan-Meier curve and Cox regression analysis.

RESULTS

^99mTc-3PRGD₂ avidity was significantly correlated with the efficacy of initial RAI ablation and an effective predictor for non-remission in high-risk DTC (OR = 9.36; 95% CI = 1.10-79.83; P = 0.041). ^99mTc-3PRGD₂ avidity was associated with poor prognosis in patients with high-risk DTC and an independent prognostic factor for shorter progression-free survival (PFS) (HR = 9.47; 95% CI = 1.08-83.20; P = 0.043). Survival analysis, which was performed between DTC patients with concordant (¹³¹I positive/^99mTc-3PRGD₂ positive) and discordant (¹³¹I negative/^99mTc-3PRGD₂ positive) lesions, indicated that patients with concordant lesions had significantly better PFS than those with discordant lesions (P = 0.022). Moreover, compared with repeated RAI, additional surgery or targeted therapy with multikinase inhibitors could lead to a higher rate of remission in ^99mTc-3PRGD₂-positive patients with progressive disease.

CONCLUSIONS

^99mTc-3PRGD₂ SPECT/CT is a useful modality in predicting progression of the disease after initial RAI and guiding further treatment in high-risk DTC patients.

Glycosylated phospholipid-coated upconversion nanoparticles for bioimaging of non-muscle invasive bladder cancers

Detection of non-muscle invasive bladder cancer (NMIBC) is crucial to facilitate complete tumor resection, thus improving the survival rate as well as reducing the recurrence frequency and treatment expense. Fluorescence imaging cystoscopy is an effective method for the detection of NMIBC. However, its application is limited as the commonly applied fluorescent agents such as dyes and photosensitizers usually lack specific tumor accumulation and are vulnerable to photobleaching. Furthermore, the broad emission band of conventional fluorescent agents limits their imaging and detection efficacy. To overcome these limitations, upconversion nanoparticles (UCNPs) have been selected as the fluorescent agent, due to their resistance to photobleaching, less background auto-fluorescence, and narrow emission bands. In order to achieve active tumor targeting, the UCNPs are coated with a glycosylated phospholipid layer. The glycosylated phospholipid-coated UCNPs exhibited high selective accumulation in cancer cells over normal cells and enhanced the upconversion luminescence (UCL) (at 540 nm and 660 nm) from bladder cancer cells under 980 nm laser irradiation. Glycosylated phospholipid coating that promotes uptake of UCNPs by cancer cells, and UCL emitted from UCNPs under NIR (980 nm) laser irradiation for cancer cell imaging.

Advances in Clinical Oncology Research on 99mTc-3PRGD2 SPECT Imaging

The integrin alpha(α)v beta(β)3 receptor is ubiquitous in malignant tumors and has a certain level of specificity for tumors. Technetium-99m hydrazinonicotinamide-dimeric cyclic arginyl-glycyl-aspartic acid peptide with three polyethylene glycol spacers (99mTc-3PRGD2) can bind specifically to the integrin αvβ3 receptor with high selectivity and strong affinity. Thus, it can specifically mark tumors and regions with angiogenesis for tumor detection and be used in single-photon emission computed tomography (SPECT) imaging. This modality has good application value for diagnosing and treating tumor lesions, such as those in the lung, breast, esophagus, head, and neck. This review provides an overview of the current clinical research progress of 99mTc-3PRGD2 SPECT imaging for tumor lesions, including for the diagnosis and differential diagnosis of tumors in different body parts, evaluation of related metastases, and evaluation of efficacy. In addition, the future clinical application prospects and possibilities of 99mTc-3PRGD2 SPECT imaging are further discussed.

Radiopharmaceuticals for PET and SPECT Imaging: A Literature Review over the Last Decade

Positron emission tomography (PET) uses radioactive tracers and enables the functional imaging of several metabolic processes, blood flow measurements, regional chemical composition, and/or chemical absorption. Depending on the targeted processes within the living organism, different tracers are used for various medical conditions, such as cancer, particular brain pathologies, cardiac events, and bone lesions, where the most commonly used tracers are radiolabeled with 18F (e.g., [18F]-FDG and NA [18F]). Oxygen-15 isotope is mostly involved in blood flow measurements, whereas a wide array of 11C-based compounds have also been developed for neuronal disorders according to the affected neuroreceptors, prostate cancer, and lung carcinomas. In contrast, the single-photon emission computed tomography (SPECT) technique uses gamma-emitting radioisotopes and can be used to diagnose strokes, seizures, bone illnesses, and infections by gauging the blood flow and radio distribution within tissues and organs. The radioisotopes typically used in SPECT imaging are iodine-123, technetium-99m, xenon-133, thallium-201, and indium-111. This systematic review article aims to clarify and disseminate the available scientific literature focused on PET/SPECT radiotracers and to provide an overview of the conducted research within the past decade, with an additional focus on the novel radiopharmaceuticals developed for medical imaging.

China’s radiopharmaceuticals on expressway: 2014–2021

This review provides an essential overview on the progress of rapidly-developing China’s radiopharmaceuticals in recent years (2014–2021). Our discussion reflects on efforts to develop potential, preclinical, and in-clinical radiopharmaceuticals including the following areas: (1) brain imaging agents, (2) cardiovascular imaging agents, (3) infection and inflammation imaging agents, (4) tumor radiopharmaceuticals, and (5) boron delivery agents (a class of radiopharmaceutical prodrug) for neutron capture therapy. Especially, the progress in basic research, including new radiolabeling methodology, is highlighted from a standpoint of radiopharmaceutical chemistry. Meanwhile, we briefly reflect on the recent major events related to radiopharmaceuticals along with the distribution of major R&D forces (universities, institutions, facilities, and companies), clinical study status, and national regulatory supports. We conclude with a brief commentary on remaining limitations and emerging opportunities for China’s radiopharmaceuticals.

Integrin-Mediated Tumorigenesis and Its Therapeutic Applications

Integrins, a family of adhesion molecules generally exist on the cell surface, are essential for regulating cell growth and its function. As a bi-directional signaling molecule, they mediate cell-cell and cell-extracellular matrix interaction. The recognitions of their key roles in many human pathologies, including autoimmunity, thrombosis and neoplasia, have revealed their great potential as a therapeutic target. This paper focuses on the activation of integrins, the role of integrins in tumorigenesis and progression, and advances of integrin-dependent tumor therapeutics in recent years. It is expected that understanding function and signaling transmission will fully exploit potentialities of integrin as a novel target for tumors.

Molecular Imaging of Angiogenesis in Oncology: Current Preclinical and Clinical Status

Angiogenesis is an active process, regulating new vessel growth, and is crucial for the survival and growth of tumours next to other complex factors in the tumour microenvironment. We present possible molecular imaging approaches for tumour vascularisation and vitality, focusing on radiopharmaceuticals (tracers). Molecular imaging in general has become an integrated part of cancer therapy, by bringing relevant insights on tumour angiogenic status. After a structured PubMed search, the resulting publication list was screened for oncology related publications in animals and humans, disregarding any cardiovascular findings. The tracers identified can be subdivided into direct targeting of angiogenesis (i.e., vascular endothelial growth factor, laminin, and fibronectin) and indirect targeting (i.e., glucose metabolism, hypoxia, and matrix metallo-proteases, PSMA). Presenting pre-clinical and clinical data of most tracers proposed in the literature, the indirect targeting agents are not 1:1 correlated with angiogenesis factors but do have a strong prognostic power in a clinical setting, while direct targeting agents show most potential and specificity for assessing tumour vascularisation and vitality. Within the direct agents, the combination of multiple targeting tracers into one agent (multimers) seems most promising. This review demonstrates the present clinical applicability of indirect agents, but also the need for more extensive research in the field of direct targeting of angiogenesis in oncology. Although there is currently no direct tracer that can be singled out, the RGD tracer family seems to show the highest potential therefore we expect one of them to enter the clinical routine.

Design, Synthesis and Binding Affinity Evaluation of Cytochrome P450 1B1 Targeted Chelators

BACKGROUND

Cytochrome P450 1B1 (CYP1B1) is specifically expressed in a variety of tumors which makes it a promise imaging target of tumor.

OBJECTIVE

We aimed to design and synthesize CYP1B1 targeted chelators for the potential application in positron emission tomography (PET) imaging of tumor.

METHODS

1,4,7-triazacyclononane-1,4-diiacetic acid (NODA) was connected to the CYP1B1 selective inhibitor we developed before through polyethylene glycol (PEG) linkers with different lengths. The inhibitory activities of chelators 6a-c against CYP1 family were evaluated by 7-ethoxyresorufin o-deethylation (EROD) assay. The manual docking between the chelators and the CYP1B1 are conducted subsequently. To determine the binding affinities of 6a-c to CYP1B1 in cells, we further performed a competition study at the cell level.

RESULTS

Among three chelators, 6a with the shortest linker showed the best inhibitory activity against CYP1B1. In the following molecular simulation study, protein-inhibitor complex of 6a showed the nearest F-heme distance which is consistent with the results of enzymatic assay. Finally, the cell based competitive assay proved the binding affinity of 6a-c to CYP1B1 enzyme.

CONCLUSION

We designed and synthesized a series of chelators which can bind to CYP1B1 enzyme in cancer cells.To our knowledge, this work is the first attempt to construct CYP1B1 targeted chelators for radiolabeling and we hope it will prompt the application of CYP1B1 imaging in tumor detection.

Competitive binding assays for measuring the binding affinity of thyroid-disrupting chemicals for integrin αvβ3

Some thyroid-disrupting chemicals (TDCs) affect thyroid function by activating the pathways mediated by a typical thyroid hormone (TH) membrane receptor, integrin α_vβ₃. The present study introduces improved competitive binding assays for the rapid and sensitive evaluation of the binding affinities of TDCs for integrin α_vβ_3. Based on different probes, two assays were modified: a fluorescence competitive binding assay and a radioligand competitive binding assay. The chemicals tested included the known TH, 3,3',5,5'-tetraiodo-l-thyronine (T4); a deaminated analog of T4, tetraiodothyroacetic acid (tetrac); and phthalate esters (PAEs). The relative binding potency of T4 was studied, and the concentration required to displace 50% of the ligands from their receptors (RIC50) of T4 was 4.9 × 10⁵ and 9.7 × 10⁴ nM for the fluorescence and radioligand competitive binding assays, respectively, suggesting that the radioligand competitive binding assay might be more sensitive for the evaluation of the binding affinity for integrin α_vβ₃. The three PAEs, including diethyl hexyl phthalate (DEHP), benzyl butyl phthalate (BBP) and dibutyl phthalate (DnBP), demonstrated binding affinities for integrin α_vβ₃ in the following order of potency: DnBP > DEHP > BBP tested by the radioligand competitive binding assay. A docking simulation of each of the three PAEs with integrin α_vβ₃ confirmed the calculated binding energies, which had a strong positive relationship with the log RIC20 values of the 3 PAEs (R = 0.99, p < 0.001). The present study shows that the established radioligand competitive binding assay could be used as a valuable tool for quantifying the affinity of TDCs for integrin α_vβ₃.

Bioconjugates of Chelators with Peptides and Proteins in Nuclear Medicine: Historical Importance, Current Innovations, and Future Challenges

Molecular radiopharmaceuticals based on bioconjugates of chelators with peptides and proteins have had significant clinical impact in the diagnosis and treatment of several types of cancers. In the 1990s, indium-111 and yttrium-90 labeled chelator-peptide/protein conjugates established the clinical utility of these radiopharmaceuticals for receptor-targeted γ-scintigraphy imaging and systemic radiotherapy. Second-generation bioconjugates based on peptides targeting the somatostatin II receptor and the prostate-specific membrane antigen are now widely used for management of neuroendocrine and prostate cancer, respectively. These bioconjugates are typically radiolabeled with gallium-68 for imaging of target receptor expression with positron emission tomography, and the β--emitter, lutetium-177, for targeted radiotherapy. Innovations in radioisotope technology and biomolecular therapies are likely to drive the future clinical development of radiopharmaceuticals based on radiometals. New chelator-peptide and chelator-protein bioconjugates will underpin nuclear medicine advances in molecular imaging and radiotherapy.