Future of Theranostics: An Outlook on Precision Oncology in Nuclear Medicine

Large-scale synthesis of non-ionic bismuth chelate for computed tomography imaging in vivo

High atomic number elements-based X-ray computed tomography (CT) contrast agents offer a promising solution to address the inherent deficiencies of FDA-approved iodine contrast agents. However, they face substantial challenges in balancing imaging performance, safety, and large-scale production for clinical translation. Herein, inspired by the history of clinical gadolinium- and iodine-based contrast agents, we report a large-scale approach for synthesizing non-ionic bismuth (Bi) chelate for high-performance CT imaging in vivo. Bi-HPDO3A can be easily obtained from low-cost precursor within 4 steps at 6 g-scale. The non-ionic macrocyclic structure endows it with low osmolality, low viscosity, high stability, good renal clearable capability and biocompatibility. Additionally, Bi-HPDO3A realizes superior imaging performance across various in vivo applications, including gastrointestinal imaging, renal imaging, and computed tomography angiography (CTA). Especially, Bi-HPDO3A exhibits superior spectral imaging capability owing to the high K-edge of element Bi, achieving metal artifact-free CTA in vivo. The proposed Bi-HPDO3A that balances overall performance can serve as a high-performance CT contrast agent with potential for clinical translation.

FAPI radiopharmaceuticals in nuclear oncology and theranostics of solid tumours: are we nearer to surrounding the hallmarks of cancer?

[18F]FDG PET/CT is the most widely used PET radiopharmaceutical in oncology, but it is not exempt of diagnostic limitations. FAPI have emerged as a great tool in the management of several different solid tumours in which [18F]FDG is not able to provide enough information. The aim of this work was to evaluate the available evidence on diagnostic and therapeutic applications of PET/CT with FAPI radiopharmaceuticals. We underwent a non-systematic review focusing in the utility of FAPI radiopharmaceuticals in PET/CT diagnosis and in the treatment of several malignancies. FAPI radiopharmaceuticals present characteristics that can potentially overcome some known diagnostic limitations of [18F]FDG. FAPI radiopharmaceuticals present a high target-to-background ratio (TBR) in many solid tumours such as oesophageal cancer, gastric cancer, pancreatic cancer, hepatic cancer, colorectal cancer, breast cancer, ovarian, cervical cancer, and head and neck cancer. Available evidence suggests the high TBR improves sensitivity and specificity compared to [18F]FDG, especially for the detection of lymphadenopathies and peritoneal metastases, and may improve patient management and radiation treatment planning. Moreover, it is important to underline the potential theranostic application of FAPI radiopharmaceuticals.

Physiological Uptake of 68Ga-FAPI-04 in Female Reproductive System

PURPOSE

Since the avid uptake of 68Ga-labeled fibroblast activation protein inhibitor (68Ga-FAPI-04) observed in female reproductive organs, our objectives were to investigate the physiological uptake characteristics and provide preliminary reference ranges for clinical use.

PROCEDURES

We reviewed the findings of female patients who underwent 68Ga-FAPI-04 PET/CT at our institution between April 2022 and June 2023. The standard uptake value (SUV) of reproductive organs and menstrual information were collected. All patients were categorized into reproductive period group, perimenopause group, and postmenopause group. We analysed the uptake levels among the three groups, and their association with age and menstrual cycle.

RESULTS

A total of 109 patients were included in this study. Higher ovarian SUVs were detected in reproductive patients (SUVright: 2.75 ± 0.84, IQR: 1.39-5.26; SUVleft: 2.72, IQR: 2.34-3.20; p = 0.315) than in postmenopausal patients (SUVright: 2.27, IQR: 2.01-2.75; SUVleft: 2.38 ± 0.55, IQR: 1.35-3.60; p = 0.767), as well as uterine 68Ga-FAPI-04 accumulations. The SUVs of uterine fundus and corpus were approximately three times higher than that of the cervix. In reproductive period group, higher SUVs were observed in bilateral ovaries around the ovulatory phase to the early luteal phase, and higher uterine SUVs were noted in the menstrual and proliferative phases. The SUVs in all reproductive organs (except the ovaries) showed significant negative correlations with age in all patients (all p < 0.01).

CONCLUSIONS

68Ga-FAPI-04 SUVs in reproductive organs are higher in premenopausal patients than in postmenopausal patients. The 68Ga-FAPI-04 accumulation in reproductive organs might be associated with menstrual cycle. Including more patients from different menstrual phases could contribute to investigating the uptake characteristics and their underlying mechanisms.

Neovascular prostate specific membrane antigen (PSMA) expression in bone and soft tissue sarcoma: a systematic analysis

Bone and soft tissue sarcomas are a highly heterogeneous group of rare cancers of mesenchymal origin. Treatment options other than surgery have limited efficacy due to low response rates with some exceptions. Radioligand therapy targeting prostate-specific membrane antigen (PSMA) may provide a novel treatment option, as it was recently suggested that soft tissue sarcomas express PSMA in the neovasculature, and on PET/CT imaging, multiple sarcomas have shown intense PSMA-tracer accumulation. Moreover, in prostate cancer patients, incidental PSMA uptake was seen in hemangiomas. In addition to confirming previous results in soft tissue sarcoma, the current study aims to systematically explore the expression of PSMA in bone tumors and in vascular tumors. Immunohistochemistry for PSMA was performed on a total of 706 tumors. High PSMA expression in the neovasculature was seen in 29% of the soft tissue sarcomas and 33% of the bone sarcomas. Malignant tumors showed a higher frequency of PSMA expression (score 2) as compared to benign tumors, with a high frequency in rhabdomyosarcoma (2 of 2, 100%), mesenchymal chondrosarcoma (14 of 20, 70%), undifferentiated sarcoma of bone (4 of 6, 67%) and of soft tissue (13 of 20, 65%), and osteosarcoma (46 of 81, 57%). In addition, giant cell tumor of bone displayed a high PSMA labelling in 67% of the cases. In contrast, high PSMA expression was seen in only 0-40% of the non-neoplastic vessels in vascular tumors, while 8% of them expressed PSMA in the tumor cells. Thus, with variable frequency among the different subtypes, a subset of bone and soft tissue tumors, both malignant and intermediate behavior, express PSMA and these patients may benefit from PSMA-targeting PET/CT scans or PSMA targeted radioligand therapy.

Fibroblast Activation Protein Inhibitor (FAPI)-Based Theranostics

Fibroblast activation protein (FAP) is a serine protease selectively expressed in cancer-associated fibroblasts (CAFs), fibrotic tissues, and areas of active tissue remodeling, making it an attractive target for diagnostic imaging across a spectrum of disease. FAP inhibitors (FAPIs) labeled with PET tracers have rapidly advanced as a novel imaging modality with broad clinical applications that offers several advantages, including rapid tumor accumulation, low background uptake, and high tumor-to-background ratios. In oncology, FAPI PET has demonstrated excellent performance in visualizing a wide range of malignancies, including those with low glycolytic activity, such as pancreatic cancer, cholangiocarcinoma, and certain sarcomas. Its high sensitivity and specificity for the stromal component enables improved tumor delineation, staging, and response assessment. Additionally, the potential to guide theranostic approaches, where the same tracer can be labeled with therapeutic radionuclides, positions FAPI as a key player in precision oncology. Beyond oncology, FAPI PET has shown promise in imaging conditions characterized by fibrotic and inflammatory processes. In the cardiovascular field, FAPI PET imaging is being investigated for its ability to detect myocardial fibrosis and active cardiac remodeling, crucial in conditions like heart failure, post-myocardial infarction remodeling, and hypertrophic cardiomyopathy. This review highlights the expanding clinical applications of FAPI-based PET imaging across oncology, inflammation, and cardiovascular disease. While the current data are promising, further large-scale studies and multicenter trials are essential to validate these findings and establish standardized protocols. The versatility and broad applicability of FAPI PET underscore its potential as a transformative tool in precision medicine.

Study of predictive factors for response to 177LU-PSMA in patients with metastatic castration-resistant prostate cancer

Introduction

Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive disease with a poor prognosis and few therapeutic options. In recent years, 177Lu-PSMA, a novel radioligand therapy, has shown promising results in patients who have failed conventional therapies. However, around 30% of patients do not respond adequately to this treatment. In this retrospective cohort study, we examined clinical, biological, and 68Ga-PSMA PET/CT-derived factors associated with poor treatment response.

Materials and methods

We conducted a retrospective cohort study including 63 patients treated at ICO Angers for progressive mCRPC following Novel Hormonal Agents and taxane-based chemotherapy. The primary endpoint was early treatment discontinuation, defined as stopping therapy at or before the 4th cycle. Secondary endpoints included PSA response and overall survival.

Results

A total of 63 patients were included in the study. Factors associated with early treatment discontinuation included a BMI < 25 kg/m2, PSA doubling time < 2 months, hemoglobin levels <10 g/dL, albumin levels <35 g/L, lactate dehydrogenase (LDH) levels >250 IU/L and alkaline phosphatase (ALP) levels >125 IU/L. On 68Ga-PSMA PET/CT imaging, low SULmax, high Total Tumor Volume, and a low PSG score were also linked to early treatment discontinuation.

Conclusion

This study identified several clinical, biological, and 68Ga-PSMA PET/CT-derived factors associated with early treatment discontinuation. Patients with poor overall health, aggressive or extensive disease, or low PSMA expression are at higher risk of treatment failure.

Assessment of radiation knowledge among medical personnel in nuclear emergency preparedness: a cross-sectional study

Background

Radiation literacy, encompassing the understanding of basic principles, applications, risks, and protective measures related to ionizing radiation, is critical for medical personnel working in jobs that involve the use of radioactive materials or medical imaging. In the context of nuclear emergency preparedness, the level of radiation knowledge among healthcare professionals-such as doctors, nurses, and radiographers-directly influences the effectiveness and safety of emergency responses. This study aims to address this gap by evaluating the radiation knowledge of medical personnel and identifying areas for improvement in profession-specific training programs.

Methods

A cross-sectional study was conducted using a convenience sampling method. The study included 723 participants attending a medical emergency response exercise and clinical management workshop on radiation injury in Suzhou, China, in November 2023. Data were collected through a structured questionnaire, descriptive statistics and chi-square tests were performed to analyze participants' radiation knowledge and identify variations across different professional groups.

Results

The majority of participants were female (64.73%), married (75.10%), and held an undergraduate degree (69.99%). Nurses (40.11%) and clinical doctors (30.29%) constituted the largest professional groups. Significant disparities in radiation knowledge were observed among healthcare workers. Nurses and management personnel demonstrated a stronger grasp of fundamental radiation concepts, such as radioactive nuclides and absorbed doses, compared to clinical doctors. For instance, 85.52% of nursing personnel and 72.34% of management personnel accurately identified the half-life of iodine-131, while only 49.32% of clinical doctors showed comparable knowledge. Furthermore, substantial differences in radiation emergency response capabilities were noted across professions. These findings emphasize the necessity for tailored, profession-specific training programs in radiation protection and emergency preparedness.

Conclusion

The study reveals a generally insufficient understanding of basic radiation concepts and emergency response principles among medical personnel. Significant variations in radiation knowledge were observed across different professional groups, highlighting the need for specialized training modules. These modules should focus on fundamental radiation concepts, radiation exposure effects, and emergency response protocols, with content customized to address the unique needs of each professional group. By implementing such targeted training, the overall effectiveness and safety of nuclear emergency responses can be significantly enhanced.

Sharpening the Blade of Precision Theranostics

While theranostics is a new term for long-standing principles in nuclear medicine, recent advances have facilitated more personalized healthcare and precision medicine. Despite the widespread enthusiasm for theranostics and well established and standardized procedures, there are a number of opportunities to enhance practice and sharpen the blade of precision theranostics. A clear understanding of the requisites of an authentic theranostic pair reveals limitations in current approaches. Indeed, standardized dosing regimes based on activity dose as opposed to absorbed dose highlight the potential enhancements to outcomes and precision medicine that predictive dosimetry could bring. Such advances increase the demand for closer matching of biological and chemical properties of theranostic pairs. In turn, the need for more authentic or true theranostic pairs is revealed. While theranostics has provided a revolutionary toolkit for cancer management, advances in instrumentation, radiochemistry or clinical domains requires similar advances in the remaining domains. This discussion explores key considerations for an evolving theranostics landscape, recognising current best practice may fall short of precision medicine over coming years.

Intravenous administration of 90Y-labeled polyoxazoline combined with tumor heating potently inhibits tumor growth in mice

The basic requirements for the development of radiopharmaceuticals for radionuclide therapy of tumors include marked tumor-specific accumulation and long-term intratumoral retention. We have previously reported an indium-111 (111In)-labeled thermoresponsive polymer (polyoxazoline (POZ)) that is soluble at body temperature with rapid clearance from normal tissues but self-aggregates in the tumor upon tumor heating treatment. POZ accumulated in the tumor via self-aggregation under hyperthermic conditions and was retained after stopping heat exposure. In this study, we investigated the cellular uptake of 111In-labeled POZ and the antitumor effects of radionuclide therapy using yttrium-90 (90Y)-labeled POZ in combination with tumor heating. A POZ derivative with a lower critical solution temperature (LCST) of 38 °C was efficiently taken up by Colon-26 tumor cells at temperatures above the LCST via phagocytosis. In the therapeutic study using 90Y-labeled POZ, a marked dose-dependent therapeutic effect of radioactivity was observed in the groups treated with 90Y-POZ combined with tumor heating with no obvious systemic side effects. These results demonstrated that thermoresponsive 90Y-labeled POZ showed a potent therapeutic effect in combination with tumor heating, suggesting the usefulness for radionuclide therapy of tumors.

360° CZT-SPECT/CT cameras: 99mTc- and 177Lu-phantom-based evaluation under clinical conditions

PURPOSE

For the first time, three currently available 360° CZT-SPECT/CT cameras were compared under clinical conditions using phantom-based measurements.

METHODS

A 99mTc- and a 177Lu-customized NEMA IEC body phantom were imaged with three different cameras, StarGuide (GE Healthcare), VERITON-CT versions 200 (V200) and 400 (V400) (Spectrum Dynamics Medical) under the same clinical conditions. Energy resolution and volumetric sensitivity were evaluated from energy spectra. Vendors provided the best reconstruction parameters dedicated to visualization and/or quantification, based on their respective software developments. For both 99mTc- and 177Lu-phantoms, noise level, quantification accuracy, and recovery coefficient (RC) were performed with 3DSlicer. Image quality metrics from an approach called "task-based" were computed with iQMetrix-CT on 99mTc visual reconstructions to assess, through spatial frequencies, noise texture in the background (NPS) and contrast restitution of a hot insert (TTF). Spatial resolution indices were calculated from frequencies corresponding to TTF10% and TTF50%.

RESULTS

Despite the higher sensitivity of VERITON cameras and the enhanced energy resolution of the V400 (3.2% at 140 keV, 5.2% at 113 keV, and 3.6% at 208 keV), StarGuide presents comparable image quality. This highlights the need to differentiate sensitivity from count quality, which is influenced by hardware design (collimator, detector block) and conditions image quality as well as the reconstruction process (algorithms, scatter correction, noise regulation). For 99mTc imaging, the quantitative image optimization approach based on RCmean for StarGuide versus RCmax for V200 and V400 systems (RCmean/RCmax: 0.9/1.8; 0.5/0.9; 0.5/0.9 respectively-Ø37 mm). SRTB10/50 showed nearly equivalent spatial resolution performances across the different reconstructed images. For 177Lu imaging, the 113 keV imaging of the V200 and V400 systems demonstrated strong performances in both image quality and quantification, while StarGuide and V400 systems offer even better potential due to their ability to exploit signals from both the 113 and 208 keV peaks. 177Lu quantification was optimized according to RCmax for all cameras and reconstructions (1.07 ± 0.09-Ø37 mm).

CONCLUSIONS

The three cameras have equivalent potential for 99mTc imaging, while StarGuide and V400 have demonstrated higher potential for 177Lu. Dedicated visual or quantitative reconstructions offer better specific performances compared to the unified visual/quantitative reconstruction. The task-based approach appears to be promising for in-depth comparison of images in the context of system characterization/comparison and protocol optimization.

Double agents in immunotherapy: Unmasking the role of antibody drug conjugates in immune checkpoint targeting

Antibody-drug conjugates (ADCs) have high specificity with lesser off-target effects, thus providing improved efficacy over traditional chemotherapies. A total of 14 ADCs have been approved for use against cancer by the US Food and Drug Administration (FDA), with more than 100 ADCs currently in clinical trials. Of particular interest ADCs targeting immune antigens PD-L1, B7-H3, B7-H4 and integrins. Specifically, we describe ADCs in development along with the gene and protein expression of these immune checkpoints across a wide range of cancer types let url = window.clickTag || window.clickTag1 || window.clickTag2 || window.clickTag3 || window.clickTag4 || window.bsClickTAG || window.bsClickTAG1 || window.bsClickTAG2 || window.url || ''; if(typeof url == 'string'){ document.body.dataset['perxceptAdRedirectUrl'] = url;}.

Technical note: Quantifying radionuclide residues in hospital wastewater: A case study on [131I]I and [177mLu]Lu/[177Lu]Lu

BACKGROUND

Historically, [131I]I has been a common isotope in radionuclide therapy, with [177Lu]Lu-labelled radiopharmaceuticals now seeing a surge in use. These can include no-carrier-added or carrier-added [177Lu]Lu with slight impurities of [177mLu]Lu with a significantly longer half-life than [131I]I. Wastewater from therapy wards can contain a mixture of these radioisotopes. In some countries, national regulations require wastewater to be stored in dedicated systems before it is discharged into the public sewage system. To fulfill legal requirements, the nuclide specific activity concentration must be verified.

PURPOSE

We evaluate a method for determining the activity concentration of [177mLu]Lu /[177Lu]Lu at equilibrium and [131I]I in pure and mixed samples in order to prove that the determined values are reliably below the limits for release.

METHODS

We analysed the emitted energy spectrum of 1 L samples with a wastewater counter using an energy window-based approach by evaluating measurements from two different time points. Based on the law of decay and the time and energy-dependent measured values, equation systems were set up to calculate the count rates for [131I]I and [177mLu]Lu, which were converted into activity concentration using calibration factors.

RESULTS

There is strong linear correlation between the nominal and determined activity concentrations (correlation coefficients R = 0.99; coefficient of determinations R2 = 0.99). We underestimate the actual activity concentration by a median of -1.4% for [177mLu]Lu and overestimate the activity concentration for [131I]I by a median of 7.1%.

CONCLUSION

We show that an undercut of the clearance levels for material release is measurable. We analyse and determine activity concentrations of mixed samples consisting of [131I]I and [177mLu]Lu/[177Lu]Lu in equilibrium. The method is simple to implement using a conventional wastewater counter, however with a slightly increased effort, as two samples and measurements are required. The methodology can be adapted for the analysis of other nuclide mixtures.

Navigating the landscape of theranostics in nuclear medicine: current practice and future prospects

Theranostics refers to the combination of diagnostic biomarkers with therapeutic agents that share a specific target expressed by diseased cells and tissues. Nuclear medicine is an exciting component explored for its applicability in theranostic concepts in clinical and research investigations. Nuclear theranostics is based on the employment of radioactive compounds delivering ionizing radiation to diagnose and manage certain diseases employing binding with specifically expressed targets. In the realm of personalized medicine, nuclear theranostics stands as a beacon of potential, potentially revolutionizing disease management. Studies exploring the theranostic profile of radioactive compounds have been presented in this review along with a detailed explanation of radioactive compounds and their theranostic applicability in several diseases. It furnishes insights into their applicability across diverse diseases, elucidating the intricate interplay between these compounds and disease pathologies. Light is shed on the important milestones of nuclear theranostics beginning with radioiodine therapy in thyroid carcinomas, MIBG labelled with iodine in neuroblastoma, and several others. Our perspectives have been put forth regarding the most important theranostic agents along with emerging trends and prospects.

A FAPα-activated MRI nanoprobe for precise grading diagnosis of clinical liver fibrosis

Molecular imaging holds the potential for noninvasive and accurate grading of liver fibrosis. It is limited by the lack of biomarkers that strongly correlate with liver fibrosis grade. Here, we discover the grading potential of fibroblast activation protein alpha (FAPα) for liver fibrosis through transcriptional analysis and biological assays on clinical liver samples. The protein and mRNA expression of FAPα are linearly correlated with fibrosis grade (R2 = 0.89 and 0.91, respectively). A FAPα-responsive MRI molecular nanoprobe is prepared for quantitatively grading liver fibrosis. The nanoprobe is composed of superparamagnetic amorphous iron nanoparticles (AFeNPs) and paramagnetic gadoteric acid (Gd-DOTA) connected by FAPα-responsive peptide chains (ASGPAGPA). As liver fibrosis worsens, the increased FAPα cut off more ASGPAGPA, restoring a higher T1-MRI signal of Gd-DOTA. Otherwise, the signal remains quenched due to the distance-dependent magnetic resonance tuning (MRET) effect between AFeNPs and Gd-DOTA. The nanoprobe identifies F1, F2, F3, and F4 fibrosis, with area under the curve of 99.8%, 66.7%, 70.4%, and 96.3% in patients' samples, respectively. This strategy exhibits potential in utilizing molecular imaging for the early detection and grading of liver fibrosis in the clinic.

Synthesis and preclinical evaluation of 68Ga-labeled PSMA tracers with improved pharmacological properties

Prostate cancer (PCa) is one of the most common tumors in men, with the overexpression of prostate-specific membrane. In this study, we developed four new 68Ga-labeled PSMA-targeting tracers by introducing quinoline, phenylalanine and decanoic acid groups to enhance their lipophilicity, strategically limiting their metabolic pathway through the urinary system. Four radiotracers were synthesized with radiochemical purity >95 %, and exhibited high stability in vivo and in vitro. The inhibition constants (Ki) of SDTWS01-04 to PSMA were in the nanomolar range (<10 nM). Micro PET/CT imaging and biodistribution analysis revealed that 68Ga-SDTWS01 enabled clear tumor visualization in PET images at 1.5 h post-injection, with excellent pharmacokinetic properties. Notably, the kidney uptake of 68Ga-SDTWS01 significantly reduced, with higher tumor-to-kidney ratio (0.36 ± 0.02), tumor-to-muscle ratio (24.31 ± 2.10), compared with 68Ga-PSMA-11 (T/K: 0.15 ± 0.01; T/M: 14.97 ± 1.40), suggesting that 68Ga-SDTWS01 is a promising radiotracer for the diagnosis of PCa. Moreover, SDTWS01 with a chelator DOTA could also label 177Lu and 225Ac, which could be used for the treatment of PCa.

On Demand Bioorthogonal Switching of an Antibody-Conjugated SPECT Probe to a Cytotoxic Payload: from Imaging to Therapy

Antibody-drug conjugates (ADCs) for the treatment of cancer aim to achieve selective delivery of a cytotoxic payload to tumor cells while sparing normal tissue. In vivo, multiple tumor-dependent and -independent processes act on ADCs and their released payloads to impact tumor-versus-normal delivery, often resulting in a poor therapeutic window. An ADC with a labeled payload would make synchronous correlations between distribution and tissue-specific pharmacological effects possible, empowering preclinical and clinical efforts to improve tumor-selective delivery; however, few methods to label small molecules without destroying their pharmacological activity exist. Herein, we present a bioorthogonal switch approach that allows a radiolabel attached to an ADC payload to be removed tracelessly at will. We exemplify this approach with a potent DNA-damaging agent, the pyrrolobenzodiazepine (PBD) dimer, delivered as an antibody conjugate targeted to lung tumor cells. The radiometal chelating group, DOTA, was attached via a novel trans-cyclooctene (TCO)-caged self-immolative para-aminobenzyl (PAB) linker to the PBD, stably attenuating payload activity and allowing tracking of biodistribution in tumor-bearing mice via SPECT-CT imaging (live) or gamma counting (post-mortem). Following TCO-PAB-DOTA reaction with tetrazines optimized for extra- and intracellular reactivity, the label was removed to reveal the unmodified PBD dimer capable of inducing potent tumor cell killing in vitro and in mouse xenografts. The switchable antibody radio-drug conjugate (ArDC) we describe integrates, but decouples, the two functions of a theranostic given that it can serve as a diagnostic for payload delivery in the labeled state, but can be switched on demand to a therapeutic agent (an ADC).

Guiding principles on the education and practice of theranostics

PURPOSE

The recent development and approval of new diagnostic imaging and therapy approaches in the field of theranostics have revolutionised nuclear medicine practice. To ensure the provision of these new imaging and therapy approaches in a safe and high-quality manner, training of nuclear medicine physicians and qualified specialists is paramount. This is required for trainees who are learning theranostics practice, and for ensuring minimum standards for knowledge and competency in existing practising specialists.

METHODS

To address the need for a training curriculum in theranostics that would be utilised at a global level, a Consultancy Meeting was held at the IAEA in May 2023, with participation by experts in radiopharmaceutical therapy and theranostics including representatives of major international organisations relevant to theranostics practice.

RESULTS

Through extensive discussions and review of existing curriculum and guidelines, a harmonised training program for theranostics was developed, which aims to ensure safe and high quality theranostics practice in all countries.

CONCLUSION

The guiding principles for theranostics training outlined in this paper have immediate relevance for the safe and effective practice of theranostics.

[68Ga]PSMA-11 for positron emission tomography (PET) imaging of prostate-specific membrane antigen (PSMA)-positive lesions in men with prostate cancer

INTRODUCTION

Theranostics targeting prostate-specific membrane antigen (PSMA) represent a new targeted approach for prostate cancer care that combines diagnostic and therapeutic radiopharmaceuticals to diagnose and treat the disease. Positron emission tomography (PET) is the imaging method of choice and several diagnostic radiopharmaceuticals for quantifying PSMA have received FDA approval and are in clinical use. [68Ga]Ga-PSMA-11 is one such imaging agent and the focus of this article. One beta-emitting radioligand therapy ([177Lu]Lu-PSMA-617) has also received FDA approval for prostate cancer treatment, and several other alpha- and beta-emitting radioligand therapies are in clinical trials.

AREAS COVERED

Theranostics targeting PSMA in men with prostate cancer are discussed with a focus on use of [68Ga]Ga-PSMA-11 for imaging PSMA-positive lesions in men with prostate cancer. The review covers [68Ga]Ga-PSMA-11 manufacture, current regulatory status, comparison of [68Ga]Ga-PSMA-11 to other imaging techniques, clinical updates, and emerging applications of artificial intelligence for [68Ga]Ga-PSMA-11 PET.

EXPERT OPINION

[68Ga]Ga-PSMA-11 is used in conjunction with a PET/CT scan to image PSMA positive lesions in men with prostate cancer. It is manufactured by chelating precursor with68Ga, either from a generator or cyclotron, and has regulatory approval around the world. It is widely used clinically in conjunction with radioligand therapies like [177Lu]Lu-PSMA-617.

Radiotheranostics Global Market and Future Developments

Radiotheranostics, a combination of diagnostic and therapeutic approaches, was first utilized in cancer management using radiopharmaceuticals to both image and selectively treat specific cancer subtypes nearly a century ago. Radiotheranostic strategies rooted in nuclear medicine have revolutionized the treatment landscape for individuals diagnosed with prostate cancer and neuroendocrine tumors in the past 10 years. In specific contexts, these approaches have emerged as the prevailing standard, yielding numerous positive results. The field of radiotheranostics shows great potential for future clinical applications. This article aims to examine the key factors that will contribute to the success of radiotheranostics in the future, as well as the current challenges and potential strategies to overcome them, with insight into the global radiotheranostic market.

TGF-β signaling: critical nexus of fibrogenesis and cancer

The transforming growth factor-beta (TGF-β) signaling pathway is a vital regulator of cell proliferation, differentiation, apoptosis, and extracellular matrix production. It functions through canonical SMAD-mediated processes and noncanonical pathways involving MAPK cascades, PI3K/AKT, Rho-like GTPases, and NF-κB signaling. This intricate signaling system is finely tuned by interactions between canonical and noncanonical pathways and plays key roles in both physiologic and pathologic conditions including tissue homeostasis, fibrosis, and cancer progression. TGF-β signaling is known to have paradoxical actions. Under normal physiologic conditions, TGF-β signaling promotes cell quiescence and apoptosis, acting as a tumor suppressor. In contrast, in pathological states such as inflammation and cancer, it triggers processes that facilitate cancer progression and tissue remodeling, thus promoting tumor development and fibrosis. Here, we detail the role that TGF-β plays in cancer and fibrosis and highlight the potential for future theranostics targeting this pathway.

[Validation of Quantitative Accuracy and Variability in 177Lu Imaging Using Monte Carlo Simulation]

PURPOSE

To predict side effects and optimize injection doses in the dosimetry of 177Lu imaging, highly accurate quantitative SPECT images are required. Monte Carlo simulations were performed to verify the accuracy and variability of quantitative values for 177Lu imaging under various imaging conditions.

METHODS

SPECT data of NEMA body phantom were assumed to simulate intrahepatic tumors 6 h after administration of 7.4 GBq of 177Lu-Dotatate. SPECT data were acquired using the SIMIND program with different combinations of collimators and energy windows. For variability evaluation, 30 SPECT images with Poisson noise were generated for each acquisition time. The relative error was evaluated for accuracy evaluation, and the coefficient of variation was estimated for variability evaluation.

RESULTS

The accuracy of BG quantification was less than 10% relative error. The accuracy of hot sphere quantification was highest with the combination of MEGP and an energy window of 208 keV±10%. However, the accuracy of hot sphere quantification decreased significantly with decreasing hot sphere diameter. Variability varied with imaging conditions and improved with longer acquisition time.

CONCLUSION

Monte Carlo simulations revealed the accuracy and variability of quantitative values for each SPECT imaging condition for 177Lu imaging.

Aptamers: Promising Reagents in Biomedicine Application

Nucleic acid aptamers, often termed "chemical antibodies," are short, single-stranded DNA or RNA molecules, which are selected by SELEX. In addition to their high specificity and affinity comparable to traditional antibodies, aptamers have numerous unique advantages such as wider identification of targets, none or low batch-to-batch variations, versatile chemical modifications, rapid mass production, and lack of immunogenicity. These characteristics make aptamers a promising recognition probe for scientific research or even clinical application. Aptamer-functionalized nanomaterials are now emerged as a promising drug delivery system for various diseases with decreased side-effects and improved efficacy. In this review, the technological strategies for generating high-affinity and biostable aptamers are introduced. Moreover, the development of aptamers for their application in biomedicine including aptamer-based biosensors, aptamer-drug conjugates and aptamer functionalized nanomaterials is comprehensively summarized.

Brain metastasis: An insight into novel molecular targets for theranostic approaches

Brain metastases (BrM) are common malignant lesions in the central nervous system, and pose a significant threat in advanced-stage malignancies due to delayed diagnosis and limited therapeutic options. Their distinct genomic profiles underscore the need for molecular profiling to tailor effective treatments. Recent advances in cancer biology have uncovered molecular drivers underlying tumor initiation, progression, and metastasis. This, coupled with the advances in molecular imaging technology and radiotracer synthesis, has paved the way for the development of innovative radiopharmaceuticals with enhanced specificity and affinity for BrM specific targets. Despite the challenges posed by the blood-brain barrier to effective drug delivery, several radiolabeled compounds have shown promise in detecting and targeting BrM. This manuscript provides an overview of the recent advances in molecular biomarkers used in nuclear imaging and targeted radionuclide therapy in both clinical and preclinical settings. Additionally, it explores potential theranostic applications addressing the unique challenges posed by BrM.

Synthesis, Screening, and Evaluation of Theranostic Molecular CPCR4-Based Probe Targeting CXCR4

Chemokines and chemokine receptors are indispensable to play a key role in the development of malignant tumors. As one of the most widely expressed chemokine receptors, chemokine (C-X-C motif) receptor 4 (CXCR4) has been a popular research focus. In most tumors, CXCR4 expression is significantly upregulated. Moreover, integrated nuclide diagnosis and therapy targeting CXCR4 show great potential. [68Ga]Ga-pentixafor, a radioligand targeting CXCR4, exhibits a strong affinity for CXCR4 both in vivo and in vitro. However, [177Lu]Lu-pentixather, the therapeutic companion of [68Ga]Ga-pentixafor, requires significant refinement to mitigate its pronounced hepatic biodistribution. The objective of this study was to synthesize theranostic molecular tracers with superior CXCR4 targeting functions. The Daudi cell line, which highly expressed CXCR4, and the MM.1S cell line, which weakly expressed CXCR4, were used in this study. Based on the pharmacophore cyclo (-d-Tyr-n-me-d-Orn-l-Arg-L-2-NAL-Gly-) (CPCR4) of pentixafor, six tracers were synthesized: [124I]I-1 ([124I]I-CPCR4), [99mTc]Tc-2 ([99mTc]Tc-HYNIC-CPCR4), [124I]I-3 ([124I]I-pentixafor), [18F]AlF-4 ([18F]AlF-NETA-CPCR4), [99mTc]Tc-5 ([99mTc]Tc-MAG3-CPCR4) and [124I]I-6 ([124I]I-pentixafor-Ga) and their radiochemical purities were all higher than 95%. After positron emission tomography (PET)/single-photon emission computed tomography (SPECT) imaging, the [124I]I-6 group exhibited the best target-nontarget ratio. At the same time, comparing the [68Ga]Ga-pentixafor group with the [124I]I-6 group, we found that the [124I]I-6 group had a better target-nontarget ratio and lower uptake in nontarget organs. Therefore, compound 6 was selected for therapeutic radionuclide (131I) labeling, and the tumor-bearing animal models were treated with [131I]I-6. The volume of the tumor site was significantly reduced in the treatment group compared with the control group, and no significant side effects were found. [124I]I-6 and [131I]I-6 showed excellent affinity for targeting CXCR4, and they showed great potential for the integrated diagnosis and treatment of tumors with high CXCR4 expression.

A proof-of-concept study on bioorthogonal-based pretargeting and signal amplify radiotheranostic strategy

BACKGROUND

Radiotheranostics differs from the vast majority of other cancer therapies in its capacity for simultaneous imaging and therapy, and it is becoming more widely implemented. A balance between diagnostic and treatment requirements is essential for achieving effective radiotheranostics. Herein, we propose a proof-of-concept strategy aiming to address the profound differences in the specific requirements of the diagnosis and treatment of radiotheranostics.

RESULTS

To validate the concept, we designed an s-tetrazine (Tz) conjugated prostate-specific membrane antigen (PSMA) ligand (DOTA-PSMA-Tz) for 68Ga or 177Lu radiolabeling and tumor radiotheranostics, a trans-cyclooctene (TCO) modified Pd@Au nanoplates (Pd@Au-PEG-TCO) for signal amplification, respectively. We then demonstrated this radiotheranostic strategy in the tumor-bearing mice with the following three-step procedures: (1) i.v. injection of the [68Ga]Ga-PSMA-Tz for diagnosis; (2) i.v. injection of the signal amplification module Pd@Au-PEG-TCO; (3) i.v. injection of the [177Lu]Lu-PSMA-Tz for therapy. Firstly, this strategy was demonstrated in 22Rv1 tumor-bearing mice via positron emission tomography (PET) imaging with [68Ga]Ga-PSMA-Tz. We observed significantly higher tumor uptake (11.5 ± 0.8%ID/g) with the injection of Pd@Au-PEG-TCO than with the injection [68Ga]Ga-PSMA-Tz alone (5.5 ± 0.9%ID/g). Furthermore, we validated this strategy through biodistribution studies of [177Lu]Lu-PSMA-Tz, with the injection of the signal amplification module, approximately five-fold higher tumor uptake of [177Lu]Lu-PSMA-Tz (24.33 ± 2.53% ID/g) was obtained when compared to [177Lu]Lu-PSMA-Tz alone (5.19 ± 0.26%ID/g) at 48 h post-injection.

CONCLUSION

In summary, the proposed strategy has the potential to expand the toolbox of pretargeted radiotherapy in the field of theranostics.

Nuclear Medicine and Molecular Imaging Applications in Gynecologic Malignancies: A Comprehensive Review

Gynecologic malignancies, consisting of endometrial, cervical, ovarian, vulvar, and vaginal cancers, pose significant diagnostic and management challenges due to their complex anatomic location and potential for rapid progression. These tumors cause substantial morbidity and mortality, often because of their delayed diagnosis and treatment. An estimated 19% of newly diagnosed cancers among women are gynecologic in origin. In recent years, there has been growing evidence supporting the integration of nuclear medicine imaging modalities in the diagnostic work-up and management of gynecologic cancers. The sensitivity of fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) combined with the anatomical specificity of computed tomography (CT) and magnetic resonance imaging (MRI) allows for the hybrid evaluation of metabolic activity and structural abnormalities that has become an indispensable tool in oncologic imaging. Lymphoscintigraphy, using technetium 99m (99mTc) based radiotracers along with single photon emission computed tomography/ computed tomography (SPECT/CT), holds a vital role in the identification of sentinel lymph nodes to minimize the surgical morbidity from extensive lymph node dissections. While not yet standard for gynecologic malignancies, promising therapeutic nuclear medicine agents serve as specialized treatment options for patients with advanced or recurrent disease. This article aims to provide a comprehensive review on the nuclear medicine applications in gynecologic malignancies through the following objectives: 1) To describe the role of nuclear medicine in the initial staging, lymph node mapping, response assessment, and recurrence/surveillance imaging of common gynecologic cancers, 2) To review the limitations of 18F-FDG PET/CT and promising applications of 18F-FDG PET/MRI in gynecologic malignancy, 3) To underscore the promising theragnostic applications of nuclear medicine, 4) To highlight the current role of nuclear medicine imaging in gynecologic cancers as per the National Comprehensive Cancer Network (NCCN), European Society of Surgical Oncology (ESGO), and European Society of Medical Oncology (ESMO) guidelines.

Preclinical Evaluation and a Pilot Clinical Positron Emission Tomography Imaging Study of [68Ga]Ga-FAPI-FUSCC-II

Fibroblast activation protein (FAP), a type II integral membrane serine protease, is a promising target for tumor diagnosis and therapy. OncoFAP has been recently discovered for PET imaging procedures for various solid malignancies. In this study, we presented the development of manual radiolabeling procedures for the preparation of OncoFAP-based radiopharmaceuticals for cancer imaging. A novel series of [68Ga/177Lu]Ga/Lu-FAPI-FUSCC-I/II were produced with high radiochemical yields. [68Ga]Ga-FAPI-FUSCC-I/II and [177Lu]Lu-FAPI-FUSCC-I/II were stable in phosphate-buffered saline, fetal bovine serum, and human serum for at least 3 h. In vitro cellular uptake and blocking experiments implied that they had specificity to FAP. Additionally, the low nanomolar IC50 values of FAPI-FUSCC-II indicated that it had a high target affinity to FAP. The in vivo biodistribution and blocking study in mice bearing HT-1080-FAP tumors showed that both exhibited specific tumor uptake. [68Ga]Ga-FAPI-FUSCC-II showed a higher tumor uptake and a higher tumor/nontarget ratio than [68Ga]Ga-FAPI-FUSCC-I and [68Ga]Ga-FAPI-04. The results of ex vivo biodistribution were in accordance with the biodistribution results. Clinical [68Ga]Ga-FAPI-FUSCC-II-PET/CT imaging further demonstrated its favorable biodistribution and kinetics with elevated and reliable uptake by primary tumors (maximum standardized uptake value (SUVmax), 12.17 ± 6.67) and distant metastases (SUVmax, 9.24 ± 4.28). In summary, [68Ga]Ga-FAPI-FUSCC-II displayed increased tumor uptake and retention compared to [68Ga]Ga-FAPI-04, giving it potential as a promising tracer for the diagnostic imaging of malignant tumors with positive FAP expression.

Challenges and opportunities in rare cancer research in China

Cancer is one of the major public health challenges in China. Rare cancers collectively account for a considerable proportion of all malignancies. The lack of awareness of rare cancers among healthcare professionals and the general public, the typically complex and delayed diagnosis, and limited access to clinical trials are key challenges. Recent years have witnessed an increase in funding for research related to rare cancers in China. In this review, we provide a comprehensive overview of rare cancers and summarize the status of research on rare cancers in China and overseas, including the trends of funding and publications. We also highlight the challenges and perspectives regarding rare cancers in China.

From Molecular Biology to Novel Immunotherapies and Nanomedicine in Uveal Melanoma

Molecular biology studies of uveal melanoma have resulted in the development of novel immunotherapy approaches including tebentafusp-a T cell-redirecting bispecific fusion protein. More biomarkers are currently being studied. As a result, combined immunotherapy is being developed as well as immunotherapy with bifunctional checkpoint inhibitory T cell engagers and natural killer cells. Current trials cover tumor-infiltrating lymphocytes (TIL), vaccination with IKKb-matured dendritic cells, or autologous dendritic cells loaded with autologous tumor RNA. Another potential approach to treat UM could be based on T cell receptor engineering rather than antibody modification. Immune-mobilizing monoclonal T cell receptors (TCR) against cancer, called ImmTAC TM molecules, represent such an approach. Moreover, nanomedicine, especially miRNA approaches, are promising for future trials. Finally, theranostic radiopharmaceuticals enabling diagnosis and therapy with the same molecule bring hope to this research.

Comparison of Nuclear Medicine Therapeutics Targeting PSMA among Alpha-Emitting Nuclides

Currently, targeted alpha therapy (TAT) is a new therapy involving the administration of a therapeutic drug that combines a substance of α-emitting nuclides that kill cancer cells and a drug that selectively accumulates in cancer cells. It is known to be effective against cancers that are difficult to treat with existing methods, such as cancer cells that are widely spread throughout the whole body, and there are high expectations for its early clinical implementation. The nuclides for TAT, including 149Tb, 211At, 212/213Bi, 212Pb (for 212Bi), 223Ra, 225Ac, 226/227Th, and 230U, are known. However, some nuclides encounter problems with labeling methods and lack sufficient preclinical and clinical data. We labeled the compounds targeting prostate specific membrane antigen (PSMA) with 211At and 225Ac. PSMA is a molecule that has attracted attention as a theranostic target for prostate cancer, and several targeted radioligands have already shown therapeutic effects in patients. The results showed that 211At, which has a much shorter half-life, is no less cytotoxic than 225Ac. In 211At labeling, our group has also developed an original method (Shirakami Reaction). We have succeeded in obtaining a highly purified labeled product in a short timeframe using this method.

Production and purification of 43Sc and 47Sc from enriched [46Ti]TiO2 and [50Ti]TiO2 targets

The radioscandium isotopes, 43Sc and 47Sc, compose a promising elementally matched theranostic pair that can be used for the development of imaging and therapeutic radiopharmaceuticals with identical structures. This study aimed to investigate the production of high radionuclidic purity 43Sc from enriched [46Ti]TiO2 targets and 47Sc from enriched [50Ti]TiO2 targets and establish a target recycling technique. Enriched [46Ti]TiO2 targets were irradiated with 18 MeV protons, and enriched [50Ti]TiO2 targets were bombarded with 24 MeV protons. 43Sc and 47Sc were purified using ion chromatography attaining recovery yields of 91.7 ± 7.4% and 89.9 ± 3.9%, respectively. The average radionuclidic purity for 43Sc was 98.8 ± 0.3% and for 47Sc 91.5 ± 0.6%, while the average recovery of enriched titanium target material was 96 ± 4.0%. The highest apparent molar activity for [43Sc]Sc-DOTA was 23.2 GBq/µmol and 3.39 GBq/µmol for [47Sc]Sc-DOTA. This work demonstrates the feasibility of using enriched recycled [46Ti]TiO2 and [50Ti]TiO2 targets to produce high purity 43Sc and 47Sc as an elementally matched theranostic isotope pair.

Distribution of prostate specific membrane antigen (PSMA) on PET-MRI in patients with and without ovarian cancer

OBJECTIVES

Ovarian cancer is the most lethal cancer and future research needs to focus on the early detection and exploration of new therapeutic agents. The objectives of this proof-of-concept study are to assess the feasibility of PSMA 18F-DCFPyl PET/MR imaging for detecting ovarian cancer and to evaluate the PSMA distribution in patients with and without ovarian cancer.

METHODS

This prospective pilot proof-of-concept study in patients with and without ovarian cancers occurred between October 2017 and January 2020. Patients were recruited from gynecologic oncology or hereditary ovarian cancer clinics, and underwent surgical removal of the uterus and ovaries for gynecologic indications. PSMA 18F-DCFPyl PET/MRI was obtained prior to standard of care surgery.

RESULTS

Fourteen patients were scanned: four patients with normal ovaries, six patients with benign ovarian lesions, and four patients with malignant ovarian lesions. Tracer uptake in normal ovaries (SUVmax = 2.8 ± 0.4) was greater than blood pool (SUVmax = 1.8 ± 0.5, p < 0.0001). Tracer uptake in benign ovarian lesions (2.2 ± 1.0) did not differ significantly from blood pool (p = 0.331). Tracer uptake in ovarian cancer (SUVmax = 7.8 ± 3.8) was greater than blood pool (p < 0.0001), normal ovaries (p = 0.0014), and benign ovarian lesions (p = 0.005).

CONCLUSION

PET/MR imaging detected PSMA uptake in ovarian cancer, with little to no uptake in benign ovarian findings. These results are encouraging and further studies in a larger patient cohort would be useful to help determine the extent and heterogeneity of PSMA uptake in ovarian cancer patients.

Theranostic Nuclear Medicine with Gallium-68, Lutetium-177, Copper-64/67, Actinium-225, and Lead-212/203 Radionuclides

Molecular changes in malignant tissue can lead to an increase in the expression levels of various proteins or receptors that can be used to target the disease. In oncology, diagnostic imaging and radiotherapy of tumors is possible by attaching an appropriate radionuclide to molecules that selectively bind to these target proteins. The term "theranostics" describes the use of a diagnostic tool to predict the efficacy of a therapeutic option. Molecules radiolabeled with γ-emitting or β+-emitting radionuclides can be used for diagnostic imaging using single photon emission computed tomography or positron emission tomography. Radionuclide therapy of disease sites is possible with either α-, β-, or Auger-emitting radionuclides that induce irreversible damage to DNA. This Focus Review centers on the chemistry of theranostic approaches using metal radionuclides for imaging and therapy. The use of tracers that contain β+-emitting gallium-68 and β-emitting lutetium-177 will be discussed in the context of agents in clinical use for the diagnostic imaging and therapy of neuroendocrine tumors and prostate cancer. A particular emphasis is then placed on the chemistry involved in the development of theranostic approaches that use copper-64 for imaging and copper-67 for therapy with functionalized sarcophagine cage amine ligands. Targeted therapy with radionuclides that emit α particles has potential to be of particular use in late-stage disease where there are limited options, and the role of actinium-225 and lead-212 in this area is also discussed. Finally, we highlight the challenges that impede further adoption of radiotheranostic concepts while highlighting exciting opportunities and prospects.

Accelerator-Based Production of Scandium Radioisotopes for Applications in Prostate Cancer: Toward Building a Pipeline for Rapid Development of Novel Theranostics

In the field of nuclear medicine, the β+ -emitting 43Sc and β- -emitting 47Sc are promising candidates in cancer diagnosis and targeted radionuclide therapy (TRT) due to their favorable decay schema and shared pharmacokinetics as a true theranostic pair. Additionally, scandium is a group-3 transition metal (like 177Lu) and exhibits affinity for DOTA-based chelators, which have been studied in depth, making the barrier to implementation lower for 43/47Sc than for other proposed true theranostics. Before 43/47Sc can see widespread pre-clinical evaluation, however, an accessible production methodology must be established and each isotope's radiolabeling and animal imaging capabilities studied with a widely utilized tracer. As such, a simple means of converting an 18 MeV biomedical cyclotron to support solid targets and produce 43Sc via the 42Ca(d,n)43Sc reaction has been devised, exhibiting reasonable yields. The NatTi(γ,p)47Sc reaction is also investigated along with the successful implementation of chemical separation and purification methods for 43/47Sc. The conjugation of 43/47Sc with PSMA-617 at specific activities of up to 8.94 MBq/nmol and the subsequent imaging of LNCaP-ENZaR tumor xenografts in mouse models with both 43/47Sc-PSMA-617 are also presented.

Radionuclide-based theranostics - a promising strategy for lung cancer

PURPOSE

This review aims to provide a comprehensive overview of the latest literature on personalized lung cancer management using different ligands and radionuclide-based tumor-targeting agents.

BACKGROUND

Lung cancer is the leading cause of cancer-related deaths worldwide. Due to the heterogeneity of lung cancer, advances in precision medicine may enhance the disease management landscape. More recently, theranostics using the same molecule labeled with two different radionuclides for imaging and treatment has emerged as a promising strategy for systemic cancer management. In radionuclide-based theranostics, the target, ligand, and radionuclide should all be carefully considered to achieve an accurate diagnosis and optimal therapeutic effects for lung cancer.

METHODS

We summarize the latest radiotracers and radioligand therapeutic agents used in diagnosing and treating lung cancer. In addition, we discuss the potential clinical applications and limitations associated with target-dependent radiotracers as well as therapeutic radionuclides. Finally, we provide our views on the perspectives for future development in this field.

CONCLUSIONS

Radionuclide-based theranostics show great potential in tailored medical care. We expect that this review can provide an understanding of the latest advances in radionuclide therapy for lung cancer and promote the application of radioligand theranostics in personalized medicine.

Organotrifluoroborate enhances tumor targeting of fibroblast activation protein inhibitors for targeted radionuclide therapy

PURPOSE

Fibroblast activation protein (FAP) is a pan-cancer target and now the state-of-the-art to develop radiopharmaceuticals. FAP inhibitors have been of great success in developing imaging tracers. Yet, the overly rapid clearance cannot match with the long half-lives of regular therapeutic radionuclides. Though strategies that aim to elongate the circulation of FAPIs are being developed, here we describe an innovation that uses α-emitters of short half-lives (e.g., 213Bi) to pair the rapid pharmacokinetics of FAPIs.

METHODS

An organotrifluoroborate linker is engineered to FAPIs to give two advantages: (1) selectively increases tumor uptake and retention; (2) facile 18F-radiolabeling for positron emission tomography to guide radiotherapy with α-emitters, which can hardly be traced in general.

RESULTS

The organotrifluoroborate linker helps to improve the internalization in cancer cells, resulting in notably higher tumor uptake while the background is clean. In FAP-expressed tumor-bearing mice, this FAPI labeled with 213Bi, a short half-life α-emitter, exhibits almost complete suppression to tumor growth while the side effect is negligible. Additional data shows that this strategy is generally applicable to guide other α-emitters, such as 212Bi, 212Pb, and 149Tb.

CONCLUSION

The organotrifluoroborate linker may be of importance to optimize FAP-targeted radiopharmaceuticals, and the short half-lived α-emitters may be of choice for the rapid-cleared small molecule-based radiopharmaceuticals.

The Future of Radioactive Medicine

The discovery of X rays in the late 19th century heralded the beginning of a new age in medicine, and the advent of channeling the power of radiation to diagnose and treat human disease. Radiation has been leveraged in medicine in a multitude of ways and is a critical element of cancer care including screening, diagnosis, surveillance, and interventional treatments. Modern radiotherapy techniques include a multitude of methodologies utilizing both externally and internally delivered radiation from a variety of approaches. This review provides a comprehensive overview of contemporary radiotherapy methodologies, the field of radiopharmaceuticals and theranostics, effects of low dose radiation and highlights the phenomena of fear of exposure to radiation and its impact in modern medicine.

A machine learning-based model for a dose point kernel calculation

PURPOSE

Absorbed dose calculation by kernel convolution requires the prior determination of dose point kernels (DPK). This study reports on the design, implementation, and test of a multi-target regressor approach to generate the DPKs for monoenergetic sources and a model to obtain DPKs for beta emitters.

METHODS

DPK for monoenergetic electron sources were calculated using the FLUKA Monte Carlo (MC) code for many materials of clinical interest and initial energies ranging from 10 to 3000 keV. Regressor Chains (RC) with three different coefficients regularization/shrinkage models were used as base regressors. Electron monoenergetic scaled DPKs (sDPKs) were used to assess the corresponding sDPKs for beta emitters typically used in nuclear medicine, which were compared against reference published data. Finally, the beta emitters sDPK were applied to a patient-specific case calculating the Voxel Dose Kernel (VDK) for a hepatic radioembolization treatment with [Formula: see text]Y.

RESULTS

The three trained machine learning models demonstrated a promising capacity to predict the sDPK for both monoenergetic emissions and beta emitters of clinical interest attaining differences lower than [Formula: see text] in the mean average percentage error (MAPE) as compared with previous studies. Furthermore, differences lower than [Formula: see text] were obtained for the absorbed dose in patient-specific dosimetry comparing against full stochastic MC calculations.

CONCLUSION

An ML model was developed to assess dosimetry calculations in nuclear medicine. The implemented approach has shown the capacity to accurately predict the sDPK for monoenergetic beta sources in a wide range of energy in different materials. The ML model to calculate the sDPK for beta-emitting radionuclides allowed to obtain VDK useful to achieve reliable patient-specific absorbed dose distributions required short computation times.

The Application of Radiolabeled Targeted Molecular Probes for the Diagnosis and Treatment of Prostate Cancer

Radiopharmaceuticals targeting prostate-specific membrane antigens (PSMA) are essential for the diagnosis, evaluation, and treatment of prostate cancer (PCa), particularly metastatic castration-resistant PCa, for which conventional treatment is ineffective. These molecular probes include [⁶⁸Ga]PSMA, [¹⁸F]PSMA, [Al¹⁸F]PSMA, [^99mTc]PSMA, and [⁸⁹Zr]PSMA, which are widely used for diagnosis, and [¹⁷⁷Lu]PSMA and [²²⁵Ac]PSMA, which are used for treatment. There are also new types of radiopharmaceuticals. Due to the differentiation and heterogeneity of tumor cells, a subtype of PCa with an extremely poor prognosis, referred to as neuroendocrine prostate cancer (NEPC), has emerged, and its diagnosis and treatment present great challenges. To improve the detection rate of NEPC and prolong patient survival, many researchers have investigated the use of relevant radiopharmaceuticals as targeted molecular probes for the detection and treatment of NEPC lesions, including DOTA-TOC and DOTA-TATE for somatostatin receptors, 4A06 for CUB domain-containing protein 1, and FDG. This review focused on the specific molecular targets and various radionuclides that have been developed for PCa in recent years, including those mentioned above and several others, and aimed to provide valuable up-to-date information and research ideas for future studies.

Next generation radiotheranostics promoting precision medicine

Radiotheranostics is a field of rapid growth with some approved treatments including 131I for thyroid cancer, 223Ra for osseous metastases, 177Lu-DOTATATE for neuroendocrine tumors, and 177Lu-PSMA (prostate-specific membrane antigen) for prostate cancer, and several more under investigation. In this review, we will cover the fundamentals of radiotheranostics, the key clinical studies that have led to current success, future developments with new targets, radionuclides and platforms, challenges with logistics and reimbursement and, lastly, forthcoming considerations regarding dosimetry, identifying the right line of therapy, artificial intelligence and more.

A cycle-consistent adversarial network for brain PET partial volume correction without prior anatomical information

PURPOSE

Partial volume effect (PVE) is a consequence of the limited spatial resolution of PET scanners. PVE can cause the intensity values of a particular voxel to be underestimated or overestimated due to the effect of surrounding tracer uptake. We propose a novel partial volume correction (PVC) technique to overcome the adverse effects of PVE on PET images.

METHODS

Two hundred and twelve clinical brain PET scans, including 50 18F-Fluorodeoxyglucose (18F-FDG), 50 18F-Flortaucipir, 36 18F-Flutemetamol, and 76 18F-FluoroDOPA, and their corresponding T1-weighted MR images were enrolled in this study. The Iterative Yang technique was used for PVC as a reference or surrogate of the ground truth for evaluation. A cycle-consistent adversarial network (CycleGAN) was trained to directly map non-PVC PET images to PVC PET images. Quantitative analysis using various metrics, including structural similarity index (SSIM), root mean squared error (RMSE), and peak signal-to-noise ratio (PSNR), was performed. Furthermore, voxel-wise and region-wise-based correlations of activity concentration between the predicted and reference images were evaluated through joint histogram and Bland and Altman analysis. In addition, radiomic analysis was performed by calculating 20 radiomic features within 83 brain regions. Finally, a voxel-wise two-sample t-test was used to compare the predicted PVC PET images with reference PVC images for each radiotracer.

RESULTS

The Bland and Altman analysis showed the largest and smallest variance for 18F-FDG (95% CI: - 0.29, + 0.33 SUV, mean = 0.02 SUV) and 18F-Flutemetamol (95% CI: - 0.26, + 0.24 SUV, mean =  - 0.01 SUV), respectively. The PSNR was lowest (29.64 ± 1.13 dB) for 18F-FDG and highest (36.01 ± 3.26 dB) for 18F-Flutemetamol. The smallest and largest SSIM were achieved for 18F-FDG (0.93 ± 0.01) and 18F-Flutemetamol (0.97 ± 0.01), respectively. The average relative error for the kurtosis radiomic feature was 3.32%, 9.39%, 4.17%, and 4.55%, while it was 4.74%, 8.80%, 7.27%, and 6.81% for NGLDM_contrast feature for 18F-Flutemetamol, 18F-FluoroDOPA, 18F-FDG, and 18F-Flortaucipir, respectively.

CONCLUSION

An end-to-end CycleGAN PVC method was developed and evaluated. Our model generates PVC images from the original non-PVC PET images without requiring additional anatomical information, such as MRI or CT. Our model eliminates the need for accurate registration or segmentation or PET scanner system response characterization. In addition, no assumptions regarding anatomical structure size, homogeneity, boundary, or background level are required.

Advances in PET imaging of cancer

Molecular imaging has experienced enormous advancements in the areas of imaging technology, imaging probe and contrast development, and data quality, as well as machine learning-based data analysis. Positron emission tomography (PET) and its combination with computed tomography (CT) or magnetic resonance imaging (MRI) as a multimodality PET-CT or PET-MRI system offer a wealth of molecular, functional and morphological data with a single patient scan. Despite the recent technical advances and the availability of dozens of disease-specific contrast and imaging probes, only a few parameters, such as tumour size or the mean tracer uptake, are used for the evaluation of images in clinical practice. Multiparametric in vivo imaging data not only are highly quantitative but also can provide invaluable information about pathophysiology, receptor expression, metabolism, or morphological and functional features of tumours, such as pH, oxygenation or tissue density, as well as pharmacodynamic properties of drugs, to measure drug response with a contrast agent. It can further quantitatively map and spatially resolve the intertumoural and intratumoural heterogeneity, providing insights into tumour vulnerabilities for target-specific therapeutic interventions. Failure to exploit and integrate the full potential of such powerful imaging data may lead to a lost opportunity in which patients do not receive the best possible care. With the desire to implement personalized medicine in the cancer clinic, the full comprehensive diagnostic power of multiplexed imaging should be utilized.

Molecular Design of 68Ga- and 89Zr-Labeled Anticalin Radioligands for PET-Imaging of PSMA-Positive Tumors

Anticalin proteins directed against the prostate-specific membrane antigen (PSMA), optionally having tailored plasma half-life using PASylation technology, show promise as radioligands for PET-imaging of xenograft tumors in mice. To investigate their suitability, the short-circulating unmodified Anticalin was labeled with ⁶⁸Ga (τ_1/2 = 68 min), using the NODAGA chelator, whereas the half-life extended PASylated Anticalin was labeled with ⁸⁹Zr (τ_1/2 = 78 h), using either the linear chelator deferoxamine (Dfo) or a cyclic derivative, fusarinine C (FsC). Different PSMA targeting Anticalin versions (optionally carrying the PASylation sequence) were produced carrying a single exposed N- or C-terminal Cys residue and site-specifically conjugated with the different radiochelators via maleimide chemistry. These protein conjugates were labeled with radioisotopes having distinct physical half-lives and, subsequently, applied for PET-imaging of subcutaneous LNCaP xenograft tumors in CB17 SCID mice. Uptake of the protein tracers into tumor versus healthy tissues was assessed by segmentation of PET data as well as biodistribution analyses. PET-imaging with both the ⁶⁸Ga-labeled plain Anticalin and the ⁸⁹Zr-labeled PASylated Anticalin allowed clear delineation of the xenograft tumor. The radioligand A3A5.1-PAS(200)-FsC·⁸⁹Zr, having an extended plasma half-life, led to a higher tumor uptake 24 h p.i. compared to the ⁶⁸Ga·NODAGA-Anticalin imaged 60 min p.i. (2.5% ID/g vs 1.2% ID/g). Pronounced demetallation was observed for the ⁸⁹Zr·Dfo-labeled PASylated Anticalin, which was ∼50% lower in the case of the cyclic radiochelator FsC (p < 0.0001). Adjusting the plasma half-life of Anticalin radioligands using PASylation technology is a viable approach to increase radioisotope accumulation within the tumor. Furthermore, ⁸⁹Zr-ImmunoPET-imaging using the FsC radiochelator is superior to that using Dfo. Our strategy for the half-life adjustment of a tumor-targeting Anticalin to match the physical half-life of the applied radioisotope illustrates the potential of small binding proteins as an alternative to antibodies for PET-imaging.

[Breakeven Analysis for Imaging Devices: Basic Introduction with Presentation of a User-Friendly Tool for in-clinic Calculation Using PET/CT as an Example]

BACKGROUND

Imaging devices such as PET/CT are becoming increasingly important in view of the growing range of innovative nuclear medicine diagnostic procedures. Since the procurement and commissioning as well as the ongoing operation of imaging devices leads to comparatively high costs, it is of great interest for clinics and practices to know the number of scans from which the (planned) device operation leads to a profit. In the following, we will introduce the breakeven point analysis and present a calculation tool that users in nuclear medicine clinics and practices can use in everyday operations using PET/CT as an example.

METHODS

In the breakeven point analysis, the intersection point is determined from which the organisation- or device-specific revenues exceed the total costs incurred for personnel, material resources, etc. For this purpose, the fixed and variable (planned) cost components for the procurement and operation of the device must be prepared on the cost side and the respective device-related (planned) revenue structure on the revenue side.

RESULTS

The authors present the break-even analysis method with the data processing required for this using the example of the planned procurement or ongoing operation of a PET/CT. In addition, a calculation tool was developed, that interested users can use to prepare a device-specific break-even analysis. For this purpose, various cost and revenue data are discussed, which have to be compiled and processed within the clinic and entered into prepared spreadsheets.

CONCLUSION

The breakeven point analysis can be used to determine the profit/loss (point) for the (planned) operation of imaging devices such as PET/CT. Users from imaging clinics/practices and administration can adapt the calculation tool presented to their specific facility and thus use it as a basic document for both the planned procurement and the ongoing operational control of imaging devices in everyday clinical practice.

Imaging biomarkers for clinical applications in neuro-oncology: current status and future perspectives

Biomarker discovery and development are popular for detecting the subtle diseases. However, biomarkers are needed to be validated and approved, and even fewer are ever used clinically. Imaging biomarkers have a crucial role in the treatment of cancer patients because they provide objective information on tumor biology, the tumor's habitat, and the tumor's signature in the environment. Tumor changes in response to an intervention complement molecular and genomic translational diagnosis as well as quantitative information. Neuro-oncology has become more prominent in diagnostics and targeted therapies. The classification of tumors has been actively updated, and drug discovery, and delivery in nanoimmunotherapies are advancing in the field of target therapy research. It is important that biomarkers and diagnostic implements be developed and used to assess the prognosis or late effects of long-term survivors. An improved realization of cancer biology has transformed its management with an increasing emphasis on a personalized approach in precision medicine. In the first part, we discuss the biomarker categories in relation to the courses of a disease and specific clinical contexts, including that patients and specimens should both directly reflect the target population and intended use. In the second part, we present the CT perfusion approach that provides quantitative and qualitative data that has been successfully applied to the clinical diagnosis, treatment and application. Furthermore, the novel and promising multiparametric MR imageing approach will provide deeper insights regarding the tumor microenvironment in the immune response. Additionally, we briefly remark new tactics based on MRI and PET for converging on imaging biomarkers combined with applications of bioinformatics in artificial intelligence. In the third part, we briefly address new approaches based on theranostics in precision medicine. These sophisticated techniques merge achievable standardizations into an applicatory apparatus for primarily a diagnostic implementation and tracking radioactive drugs to identify and to deliver therapies in an individualized medicine paradigm. In this article, we describe the critical principles for imaging biomarker characterization and discuss the current status of CT, MRI and PET in finiding imaging biomarkers of early disease.

Cancer-Associated Fibroblast: Role in Prostate Cancer Progression to Metastatic Disease and Therapeutic Resistance

Prostate cancer (PCa) is one of the most common cancers in European males. Although therapeutic approaches have changed in recent years, and several new drugs have been approved by the Food and Drug Administration (FDA), androgen deprivation therapy (ADT) remains the standard of care. Currently, PCa represents a clinical and economic burden due to the development of resistance to ADT, paving the way to cancer progression, metastasis, and to long-term side effects induced by ADT and radio-chemotherapeutic regimens. In light of this, a growing number of studies are focusing on the tumor microenvironment (TME) because of its role in supporting tumor growth. Cancer-associated fibroblasts (CAFs) have a central function in the TME because they communicate with prostate cancer cells, altering their metabolism and sensitivity to drugs; hence, targeted therapy against the TME, and, in particular, CAFs, could represent an alternative therapeutic approach to defeat therapy resistance in PCa. In this review, we focus on different CAF origins, subsets, and functions to highlight their potential in future therapeutic strategies for prostate cancer.