Radiotheranostics in oncology: current challenges and emerging opportunities

Effect of Linker Entities on Pharmacokinetics of 111In-Labeled Prostate-Specific Membrane Antigen-Targeting Ligands with an Albumin Binder

In the field of radiopharmaceutical development targeting cancer, an albumin binder (ALB) is commonly used to improve accumulation of radioligands in tumors because it has high binding affinity for albumin and extends the circulation time of radioligands. The further development of ALB-containing radioligands is also expected to regulate their pharmacokinetics. In this study, we newly designed and synthesized [111In]In-PNT-DA1 derivatives, prostate-specific membrane antigen (PSMA)-targeting radioligands including a functional linker (d-glutamic acid or 4-(aminomethyl)benzoic acid), and evaluated the relationships among the structure, albumin-binding affinity, and pharmacokinetics. These derivatives showed a different binding affinity for albumin by the introduction of a linker. Biodistribution studies revealed that the introduction of a linker affects the pharmacokinetics of each derivative. The biodistribution studies also suggested that moderate albumin-binding affinity enhances the tumor/kidney ratio of the derivative. SPECT imaging using [111In]In-PNT-DA3 with the highest tumor/kidney ratio among [111In]In-PNT-DA1 derivatives led to clear visualization of a PSMA-positive LNCaP tumor. The results suggest that the appropriate introduction of linker entities may be necessary to improve the pharmacokinetics of PSMA-targeting radioligands.

CdTe XG-Cam: A new high-resolution x-ray and gamma-ray camera for studies of the pharmacokinetics of radiopharmaceuticals in small animals

BACKGROUND

The recent emergence of targeted radionuclide therapy has increased the demand for imagers capable of visualizing pharmacokinetics in developing radiopharmaceuticals in the preclinical phase. Some radionuclides emit hard x-rays and gamma-rays below 100 keV, in which energy range the performance of conventional NaI scintillators is poor. Multipinhole collimators are also used for small animal imaging with a good spatial resolution but have a limited field of view (FOV).

PURPOSE

In this study, a new imager with high sensitivity over a wide FOV in the low-energy band ( < $<$ 100 keV) was developed for the pharmacokinetic study.

METHODS

We developed an x-ray and gamma-ray camera for high-resolution spectroscopy, named "CdTe XG-Cam," equipped with a cadmium telluride semiconductor detector and a parallel-hole collimator using a metal 3D printer. To evaluate the camera-system performance, phantom measurements with single and dual nuclides (99 m Tc $^{\rm 99m}{\rm Tc}$ ,111 In $^{111}{\rm In}$ , and125 I ) $^{125}{\rm I)}$ were performed. The performance for in vivo imaging was evaluated using tumor-bearing mice to which a nuclide (99 m Tc $^{\rm 99m}{\rm Tc}$ or125 I ) $^{125}{\rm I)}$  administered.

RESULTS

We simultaneously obtained information on111 In $^{111}{\rm In}$ and125 I $^{125}{\rm I}$ , which emit emission lines in the low-energy band with peak energies close to each other (23-26 keV for111 In $^{111}{\rm In}$ and 27-31 keV for125 I ) $^{125}{\rm I)}$ , and applied an analytical method based on spectral model fitting to determine the individual radioactivities accurately. In the small animal imaging, the distributions of the nuclide in tumors were accurately quantified and time-activity curves in tumors are obtained.

CONCLUSIONS

The demonstrated capability of our system to perform in vivo imaging suggests that the camera can be used for applications of pharmacokinetics research.

Engineered Antibodies as Cancer Radiotheranostics

Radiotheranostics is a rapidly growing approach in personalized medicine, merging diagnostic imaging and targeted radiotherapy to allow for the precise detection and treatment of diseases, notably cancer. Radiolabeled antibodies have become indispensable tools in the field of cancer theranostics due to their high specificity and affinity for cancer-associated antigens, which allows for accurate targeting with minimal impact on surrounding healthy tissues, enhancing therapeutic efficacy while reducing side effects, immune-modulating ability, and versatility and flexibility in engineering and conjugation. However, there are inherent limitations in using antibodies as a platform for radiopharmaceuticals due to their natural activities within the immune system, large size preventing effective tumor penetration, and relatively long half-life with concerns for prolonged radioactivity exposure. Antibody engineering can solve these challenges while preserving the many advantages of the immunoglobulin framework. In this review, the goal is to give a general overview of antibody engineering and design for tumor radiotheranostics. Particularly, the four ways that antibody engineering is applied to enhance radioimmunoconjugates: pharmacokinetics optimization, site-specific bioconjugation, modulation of Fc interactions, and bispecific construct creation are discussed. The radionuclide choices for designed antibody radionuclide conjugates and conjugation techniques and future directions for antibody radionuclide conjugate innovation and advancement are also discussed.

Design of a Fibroblast Activation Protein-Targeted Radiopharmaceutical Therapy with High Tumor-to-Healthy-Tissue Ratios

Because of upregulated expression on cancer-associated fibroblasts, fibroblast activation protein (FAP) has emerged as an attractive biomarker for the imaging and therapy of solid tumors. Although many FAP ligands have already been developed for radiopharmaceutical therapies (RPTs), most suffer from inadequate tumor uptake, insufficient tumor residence times, or off-target accumulation in healthy tissues, suggesting a need for further improvements. Methods: A new FAP-targeted RPT with a novel ligand (FAP8-PEG3-IP-DOTA) was designed by combining the desirable features of several previous ligand-targeted RPTs. Uptake and retention of [111In]In or [177Lu]Lu-FAP8-PEG3-IP-DOTA were assessed in KB, HT29, MDA-MB-231, and 4T1 murine tumor models by radioimaging or ex vivo biodistribution analyses. Radiotherapeutic potencies and gross toxicities were also investigated by monitoring tumor growth, body weight, and tissue damage in tumor-bearing mice. Results: FAP8-PEG3-IP-DOTA exhibited high affinity (half-maximal inhibitory concentration, 1.6 nM) and good selectivity for FAP relative to its closest homologs, prolyl oligopeptidase (half-maximal inhibitory concentration, ∼14.0 nM) and dipeptidyl peptidase-IV (half-maximal inhibitory concentration, ∼860 nM). SPECT/CT scans exhibited high retention in 2 different solid tumor models and minimal uptake in healthy tissues. Quantitative biodistribution analyses revealed tumor-to-healthy-tissue ratios of more than 5 times for all major organs, and live animal studies demonstrated 65%-93% suppression of tumor growth in all 4 models tested, with minimal or no evidence of systemic toxicity. Conclusion: We conclude that [177Lu]Lu-FAP8-PEG3-IP-DOTA constitutes a promising and safe RPT candidate for FAPα-targeted radionuclide therapy of solid tumors.

A first-in-class dual-chelator theranostic agent designed for use with imaging-therapy radiometal pairs of different elements

A covalent adduct of DFOB and DOTA separated by a l-lysine residue (DFOB-l-Lys-N 6-DOTA) exhibited remarkable regioselective metal binding, with {1H}-13C NMR spectral shifts supporting Zr(iv) coordinating to the DFOB unit, and Lu(iii) coordinating to the DOTA unit. This first-in-class, dual-chelator theranostic design could enable the use of imaging-therapy radiometal pairs of different elements, such as 89Zr for positron emission tomography (PET) imaging and 177Lu for low-energy β--particle radiation therapy. DFOB-l-Lys-N 6-DOTA was elaborated with an amine-terminated polyethylene glycol extender unit (PEG4) to give DFOB-N 2-(PEG4)-l-Lys-N 6-DOTA (compound D2) to enable installation of a phenyl-isothiocyanate group (Ph-NCS) for subsequent monoclonal antibody (mAb) conjugation (mAb = HuJ591). D2-mAb was radiolabeled with 89Zr or 177Lu to produce [89Zr]Zr-D2-mAb or [177Lu]Lu-D2-mAb, respectively, and in vivo PET/CT imaging and in vivo/ex vivo biodistribution properties measured with the matched controls [89Zr]Zr-DFOB-mAb or [177Lu]Lu-DOTA-mAb in a murine LNCaP prostate tumour xenograft model. The 89Zr-immuno-PET imaging function of [89Zr]Zr-D2-mAb and [89Zr]Zr-DFOB-mAb showed no significant difference in tumour accumulation at 48 or 120 h post injection. [89Zr]Zr-D2-mAb and [177Lu]Lu-D2-mAb showed similar ex vivo biodistribution properties at 120 h post-injection. Tumour uptake of [177Lu]Lu-D2-mAb shown by SPECT/CT imaging at 48 h and 120 h post-injection supported the therapeutic function of D2, which was corroborated by similar therapeutic efficacy between [177Lu]Lu-D2-mAb and [177Lu]Lu-DOTA-mAb, both showing a sustained reduction in tumour volume (>80% over 65 d) compared to vehicle. The work identifies D2 as a trifunctional chelator that could expand capabilities in mixed-element radiometal theranostics to improve dosimetry and the clinical outcomes of molecularly targeted radiation.

Prospective comparison of 68Ga-DOTA-ibandronate and bone scans for detecting bone metastases in breast cancer

Introduction

68Ga labeled DOTA-Ibandronate (68Ga-DOTA-IBA) positron emission tomography/computed tomography (PET/CT), is a novel bone-targeting imaging tracer and promising diagnostic method for bone metastases detection. Therefore, this study aimed to compare 68Ga-DOTA-IBA PET/CT to the 99mTc-MDP whole-body bone scan (WBBS) for detecting bone metastases in breast cancer (BC).

Materials and methods

In this prospective study, 45 women with BC underwent imaging via 68Ga-DOTA-IBA PET/CT and 99mTc-MDP WBBS. Clinical and demographic information as well as BC imaging features were recorded. The two methods were compared in terms of their detection rate for bone metastases and the number of lesions.

Results

The 45 women were aged 53.5 ± 11.0 years. The bone metastases detection rate with 68Ga-DOTA-IBA PET/CT was 100% (45/45) and with 99mTc-MDP WBBS was 95.6% (43/45). A total of 546 bone metastases lesions were detected. The lesion detection rate using 68Ga-DOTA-IBA PET/CT was 100% (546/546) and using 99mTc-MDP WBBS was 67.8% (370/546). More lesions were found at each site via 68Ga-DOTA-IBA than via 99mTc-MDP WBBS.

Conclusions

68Ga-DOTA-IBA PET/CT is a more sensitive method than 99mTc-MDP WBBS for assessing bone metastases in BC and may therefore represent a useful imaging technique for bone metastases, while offering a visual basis for 177Lu-DOTA-IBA diagnosis and therapy response assessments for BC. Further validation using a broader study cohort is warranted to confirm these findings.

Clinical trial registration

https://www.chictr.org.cn/showproj.html?proj=170163, identifier ChiCTR2200064487.

PYTA: a universal chelator for advancing the theranostic palette of nuclear medicine

To clinically advance the growing arsenal of radiometals available to image and treat cancer, chelators with versatile binding properties are needed. Herein, we evaluated the ability of the py2[18]dieneN6 macrocycle PYTA to interchangeably bind and stabilize 225Ac3+, [177Lu]Lu3+, [111In]In3+ and [44Sc]Sc3+, a chemically diverse set of radionuclides that can be used complementarily for targeted alpha therapy, beta therapy, single-photon emission computed tomography (SPECT) imaging, and positron emission tomography (PET) imaging, respectively. Through NMR spectroscopy and X-ray diffraction, we show that PYTA possesses an unusual degree of flexibility for a macrocyclic chelator, undergoing dramatic conformational changes that enable it to optimally satisfy the disparate coordination properties of each metal ion. Subsequent radiolabeling studies revealed that PYTA quantitatively binds all 4 radiometals at room temperature in just minutes at pH 6. Furthermore, these complexes were found to be stable in human serum over 2 half-lives. These results surpass those obtained for 2 state-of-the-art chelators for nuclear medicine, DOTA and macropa. The stability of 225Ac-PYTA and [44Sc]Sc-PYTA, the complexes having the most disparity with respect to metal-ion size, was further probed in mice. The resulting PET images (44Sc) and ex vivo biodistribution profiles (44Sc and 225Ac) of the PYTA complexes differed dramatically from those of unchelated [44Sc]Sc3+ and 225Ac3+. These differences provide evidence that PYTA retains this size-divergent pair of radionuclides in vivo. Collectively, these studies establish PYTA as a new workhorse chelator for nuclear medicine and warrant its further investigation in targeted constructs.

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).

Locally unlocks prodrugs by radiopharmaceutical in tumor for cancer therapy

Chemotherapy is the first-line treatment for cancer, but its systemic toxicity can be severe. Tumor-selective prodrug activation offers promising opportunities to reduce systemic toxicity. Here, we present a strategy for activating prodrugs using radiopharmaceuticals. This strategy enables the targeted release of chemotherapeutic agents due to the high tumor-targeting capability of radiopharmaceuticals. [18F]FDG (2-[18F]-fluoro-2-deoxy-D-glucose), one of the most widely used radiopharmaceuticals in clinics, can trigger Pt(IV) complex for controlled release of axial ligands in tumors, it might be mediated by hydrated electrons generated by water radiolysis resulting from the decay of radionuclide 18F. Its application offers the controlled release of fluorogenic probes and prodrugs in living cells and tumor-bearing mice. Of note, an OxaliPt(IV) linker is designed to construct an [18F]FDG-activated antibody-drug conjugate (Pt-ADC). Sequential injection of Pt-ADC and [18F]FDG efficiently releases the toxin in the tumor and remarkably suppresses the tumor growth. Radiotherapy is booming as a perturbing tool for prodrug activation, and we find that [18F]FDG is capable of deprotecting various radiotherapy-removable protecting groups (RPGs). Our results suggest that tumor-selective radiopharmaceutical may function as a trigger, for developing innovative prodrug activation strategies with enhanced tumor selectivity.

Evaluation of a novel 177Lu-labelled therapeutic Affibody molecule with a deimmunized ABD domain and improved biodistribution profile

PURPOSE

Fusion of Affibody molecules with an albumin-binding domain (ABD) provides targeting agents, which are suitable for radionuclide therapy. To facilitate clinical translation, the low immunogenic potential of such constructs with targeting properties conserved is required.

METHODS

The HER2-targeting Affibody molecule ZHER2:2891 was fused with a deimmunized ABD variant and DOTA was conjugated to a unique C-terminal cysteine. The novel construct, PEP49989, was labelled with 177Lu. Affinity, specificity, and in vivo targeting properties of [177Lu]Lu-PEP49989 were characterised. Experimental therapy in mice with human HER2-expressing xenografts was evaluated.

RESULTS

The maximum molar activity of 52 GBq/µmol [177Lu]Lu-PEP49989 was obtained. [177Lu]Lu-PEP49989 bound specifically to HER2-expressing cells in vitro and in vivo. The HER2 binding affinity of [177Lu]Lu-PEP49989 was similar to the affinity of [177Lu]Lu-ABY-027 containing the parental ABD035 variant. The renal uptake of [177Lu]Lu-PEP49989 was 1.4-fold higher, but hepatic and splenic uptake was 1.7-2-fold lower than the uptake of [177Lu]Lu-ABY-027. The median survival of xenograft-bearing mice treated with 21 MBq [177Lu]Lu-PEP49989 (> 90 days) was significantly longer than the survival of mice treated with vehicle (38 days) or trastuzumab (45 days). Treatment using a combination of [177Lu]Lu-PEP49989 and trastuzumab increased the number of complete tumour remissions. The renal and hepatic toxicity was minimal to mild.

CONCLUSION

In preclinical studies, [177Lu]Lu-PEP49989 demonstrated favourable biodistribution and a strong antitumour effect, which was further enhanced by co-treatment with trastuzumab.

Biospecific Chemistry for Covalent Linking of Biomacromolecules

Interactions among biomacromolecules, predominantly noncovalent, underpin biological processes. However, recent advancements in biospecific chemistry have enabled the creation of specific covalent bonds between biomolecules, both in vitro and in vivo. This Review traces the evolution of biospecific chemistry in proteins, emphasizing the role of genetically encoded latent bioreactive amino acids. These amino acids react selectively with adjacent natural groups through proximity-enabled bioreactivity, enabling targeted covalent linkages. We explore various latent bioreactive amino acids designed to target different protein residues, ribonucleic acids, and carbohydrates. We then discuss how these novel covalent linkages can drive challenging protein properties and capture transient protein-protein and protein-RNA interactions in vivo. Additionally, we examine the application of covalent peptides as potential therapeutic agents and site-specific conjugates for native antibodies, highlighting their capacity to form stable linkages with target molecules. A significant focus is placed on proximity-enabled reactive therapeutics (PERx), a pioneering technology in covalent protein therapeutics. We detail its wide-ranging applications in immunotherapy, viral neutralization, and targeted radionuclide therapy. Finally, we present a perspective on the existing challenges within biospecific chemistry and discuss the potential avenues for future exploration and advancement in this rapidly evolving field.

Engineering focusing on cancer

While cancer research and care have benefited from revolutionary advances in the ability to manipulate and study living systems, the field is limited by a lack of synergy to leverage the power of engineering approaches. Cancer engineering is an emerging subfield of biomedical engineering that unifies engineering and cancer biology to better understand, diagnose, and treat cancer. We highlight cancer engineering's unique challenges, the importance of creating dedicated centers and departments that enable translational collaboration, and educational approaches to arm a new generation of scientists with engineering expertise and a fundamental understanding of cancer biology to transform clinical cancer care.

Dotatate PET/CT and 225Ac-Dotatate Therapy for Somatostatin Receptor-expressing Metastatic Breast Cancer

Background Somatostatin receptors, and specifically somatostatin receptor type 2 (SSTR2), have primarily been associated with neuroendocrine tumors and have revolutionized the imaging and therapy of patients with these tumors. SSTR2 is expressed on other tumors at lower prevalence. Purpose To evaluate the potential of SSTR2-targeted imaging and therapy in patients with breast cancer. Materials and Methods In a preclinical experiment, SSTR2 expression was assessed in tissue microarrays of breast cancer samples using H-score analysis. H-scores higher than 50 (0-300 scale) were considered positive. Then, a prospective phase 2 clinical trial of SSTR2-targeted tetraazacyclododecane tetraacetic acid octreotate (Dotatate) PET/CT was performed in participants with biopsy-proven estrogen receptor (ER)-positive breast cancer from January to August 2023. A positive Dotatate PET/CT scan was defined as tumors with a Krenning score of 3 (avidity greater than liver) or 4 (avidity greater than spleen). The proportion of positive scans and the 95% CI were calculated. One participant with metastatic ER-positive breast cancer and a Krenning 4 Dotatate PET/CT result underwent treatment with SSTR2-targeted actinium 225 (225Ac) Dotatate. Results Preclinical microarrays demonstrated that 63 of 123 ER-positive breast cancer tissue samples (51% [95% CI: 42, 60]) but only 22 of 121 ER-negative breast cancer tissue samples (18% [95% CI: 12, 26]) were enriched for SSTR2 (P < .001). Thirty female participants (mean age, 66 years ± 15) with metastatic ER-positive breast cancer were accrued to the phase 2 SSTR2-targeted imaging trial and underwent Dotatate PET/CT. Dotatate PET/CT demonstrated that nine of 30 participants (30% [95% CI: 15, 49]) had tumors with Krenning scores of 3 or 4, indicating strong SSTR2 expression. SSTR2-targeted therapy with alpha-emitting 225Ac-Dotatate resulted in a near complete response in a heavily pretreated participant with metastatic ER-positive breast cancer and a Krenning 4 Dotatate PET result. Conclusion Molecular imaging targeting SSTR2 and radioligand therapy with SSTR2-targeted 225Ac-Dotatate enables a new therapeutic option for patients with metastatic breast cancer. Clinical trial registration no. NCT05880394 © RSNA, 2024 See also the editorial by Lin and Choyke in this issue.

Preparation and Evaluation of a Novel 99mTc-Labeled Niraparib Isonitrile Complex as a Potential PARP-1 Imaging Agent

Poly ADP-ribose polymerase (PARP) plays an important role in the DNA repair process and has become an attractive target for cancer therapy in recent years. Given that niraparib has good clinical efficacy as a PARP inhibitor, this study aimed to develop radiolabeled niraparib derivatives for tumor imaging to detect PARP expression and improve the accuracy of stratified patient therapy. The niraparib isonitrile derivative (CNPN) was designed, synthesized, and radiolabeled to obtain the [99mTc]Tc-CNPN complex with high radiochemical purity (>95%). It was lipophilic and stable in vitro. In HeLa cell experiments, the uptake of [99mTc]Tc-CNPN was effectively inhibited by the ligand CNPN, indicating the binding affinity for PARP. According to the biodistribution studies of HeLa tumor-bearing mice, [99mTc]Tc-CNPN has moderate tumor uptake and can be effectively inhibited, demonstrating its specificity for targeting PARP. The SPECT imaging results showed that [99mTc]Tc-CNPN had tumor uptake at 2 h postinjection. All of the results of this study indicated that [99mTc]Tc-CNPN is a promising tumor imaging agent that targets PARP.

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.

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.

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Covalent targeted radioligands potentiate radionuclide therapy

Targeted radionuclide therapy, in which radiopharmaceuticals deliver potent radionuclides to tumours for localized irradiation, has addressed unmet clinical needs and improved outcomes for patients with cancer1-4. A therapeutic radiopharmaceutical must achieve both sustainable tumour targeting and fast clearance from healthy tissue, which remains a major challenge5,6. A targeted ligation strategy that selectively fixes the radiopharmaceutical to the target protein in the tumour would be an ideal solution. Here we installed a sulfur (VI) fluoride exchange (SuFEx) chemistry-based linker on radiopharmaceuticals to prevent excessively fast tumour clearance. When the engineered radiopharmaceutical binds to the tumour-specific protein, the system undergoes a binding-to-ligation transition and readily conjugates to the tyrosine residues through the 'click' SuFEx reaction. The application of this strategy to a fibroblast activation protein (FAP) inhibitor (FAPI) triggered more than 80% covalent binding to the protein and almost no dissociation for six days. In mice, SuFEx-engineered FAPI showed 257% greater tumour uptake than did the original FAPI, and increased tumour retention by 13-fold. The uptake in healthy tissues was rapidly cleared. In a pilot imaging study, this strategy identified more tumour lesions in patients with cancer than did other methods. SuFEx-engineered FAPI also successfully achieved targeted β- and α-radionuclide therapy, causing nearly complete tumour regression in mice. Another SuFEx-engineered radioligand that targets prostate-specific membrane antigen (PSMA) also showed enhanced therapeutic efficacy. Considering the broad scope of proteins that can potentially be ligated to SuFEx warheads, it might be possible to adapt this strategy to other cancer targets.

Trends in nuclear medicine and the radiopharmaceutical sciences in oncology: workforce challenges and training in the age of theranostics

Although the promise of radionuclides for the diagnosis and treatment of disease was recognised soon after the discovery of radioactivity in the late 19th century, the systematic use of radionuclides in medicine only gradually increased over the subsequent hundred years. The past two decades, however, has seen a remarkable surge in the clinical application of diagnostic and therapeutic radiopharmaceuticals, particularly in oncology. This development is an exciting time for the use of theranostics in oncology, but the rapid growth of this area of nuclear medicine has created challenges as well. In particular, the infrastructure for the manufacturing and distribution of radiopharmaceuticals remains in development, and regulatory bodies are still optimising guidelines for this new class of drug. One issue of paramount importance for achieving equitable access to theranostics is building a sufficiently trained workforce in high-income, middle-income, and low-income countries. Here, we discuss the key challenges and opportunities that face the field as it seeks to build its workforce for the 21st century.

Recent advances and impending challenges for the radiopharmaceutical sciences in oncology

This paper is the first of a Series on theranostics that summarises the current landscape of the radiopharmaceutical sciences as they pertain to oncology. In this Series paper, we describe exciting developments in radiochemistry and the production of radionuclides, the development and translation of theranostics, and the application of artificial intelligence to our field. These developments are catalysing growth in the use of radiopharmaceuticals to the benefit of patients worldwide. We also highlight some of the key issues to be addressed in the coming years to realise the full potential of radiopharmaceuticals to treat cancer.

Effectiveness of [67Cu]Cu-trastuzumab as a theranostic against HER2-positive breast cancer

PURPOSE

To evaluate the imaging and therapeutic properties (theranostic) of 67Cu-labeled anti-human epidermal growth factor receptor II (HER2) monoclonal antibody trastuzumab against HER2-positive breast cancer (BC).

METHODS

We conjugated trastuzumab with p-SCN-Bn-NOTA, 3p-C-NETA-NCS, or p-SCN-Bn-DOTA, and radiolabeled with [67Cu]CuCl2. Immunoconjugate internalization was evaluated in BT-474, JIMT-1 and MCF-7 BC cells. In vitro stability was studied in human serum (HS) and Phosphate Buffered Saline (PBS). Flow cytometry, radioligand binding and immunoreactive fraction assays were carried out. ImmunoSPECT imaging of [67Cu]Cu-NOTA-trastuzumab was done in mice bearing BT-474, JIMT-1 and MCF-7 xenografts. Pharmacokinetic was studied in healthy Balb/c mice while dosimetry was done in both healthy Balb/c and in athymic nude mice bearing JIMT-1 xenograft. The therapeutic effectiveness of [67Cu]Cu-NOTA-trastuzumab was evaluated in mice bearing BT-474 and JIMT-1 xenografts after a single intravenous (i.v.) injection of ~ 16.8 MBq.

RESULTS

Pure immunoconjugates and radioimmunoconjugates (> 95%) were obtained. Internalization was HER2 density-dependent with highest internalization observed with NOTA-trastuzumab. After 5 days, in vitro stabilities were 97 ± 1.7%, 31 ± 6.2%, and 28 ± 4% in HS, and 79 ± 3.5%, 94 ± 1.2%, and 86 ± 2.3% in PBS for [67Cu]Cu-NOTA-trastuzumab, [67Cu]Cu-3p-C-NETA-trastuzumab and [67Cu]Cu-DOTA-trastuzumab, respectively. [67Cu]Cu-NOTA-trastuzumab was chosen for further evaluation. BT-474 flow cytometry showed low KD, 8.2 ± 0.2 nM for trastuzumab vs 26.5 ± 1.6 nM for NOTA-trastuzumab. There were 2.9 NOTA molecules per trastuzumab molecule. Radioligand binding assay showed a low KD of 2.1 ± 0.4 nM and immunoreactive fraction of 69.3 ± 0.9. Highest uptake of [67Cu]Cu-NOTA-trastuzumab was observed in JIMT-1 (33.9 ± 5.5% IA/g) and BT-474 (33.1 ± 10.6% IA/g) xenograft at 120 h post injection (p.i.). Effectiveness of the radioimmunoconjugate was also expressed as percent tumor growth inhibition (%TGI). [67Cu]Cu-NOTA-trastuzumab was more effective than trastuzumab against BT-474 xenografts (78% vs 54% TGI after 28 days), and JIMT-1 xenografts (90% vs 23% TGI after 19 days). Mean survival of [67Cu]Cu-NOTA-trastuzumab, trastuzumab and saline treated groups were > 90, 77 and 72 days for BT-474 xenografts, while that of JIMT-1 were 78, 24, and 20 days, respectively.

CONCLUSION

[67Cu]Cu-NOTA-trastuzumab is a promising theranostic agent against HER2-positive BC.

Can current preclinical strategies for radiopharmaceutical development meet the needs of targeted alpha therapy?

Preclinical studies are essential for effectively evaluating TAT radiopharmaceuticals. Given the current suboptimal supply chain of these radionuclides, animal studies must be refined to produce the most translatable TAT agents with the greatest clinical potential. Vector design is pivotal, emphasizing harmonious physical and biological characteristics among the vector, target, and radionuclide. The scarcity of alpha-emitting radionuclides remains a significant consideration. Actinium-225 and lead-212 appear as the most readily available radionuclides at this stage. Available animal models for researchers encompass xenografts, allografts, and PDX (patient-derived xenograft) models. Emerging strategies for imaging alpha-emitters are also briefly explored. Ultimately, preclinical research must address two critical aspects: (1) offering valuable insights into balancing safety and efficacy, and (2) providing guidance on the optimal dosing of the TAT agent.

A T-Cell Inspired Sonoporation System Enhances Low-Dose X-Ray-Mediated Pyroptosis and Radioimmunotherapy Efficacy by Restoring Gasdermin-E Expression

Genome editing has the potential to improve the unsatisfactory therapeutic effect of antitumor immunotherapy. However, the cell plasma membrane prevents the entry of almost all free genome-manipulation agents. Therefore, a system can be spatiotemporally controlled and can instantly open the cellular membrane to allow the entry of genome-editing agents into target cells is needed. Here, inspired by the ability of T cells to deliver cytotoxins to cancer cells by perforation, an ultrasound (US)-controlled perforation system (UPS) is established to enhance the delivery of free genome-manipulating agents. The UPS can perforate the tumor cell membrane while maintaining cell viability via a controllable lipid peroxidation reaction. In vitro, transmembrane-incapable plasmids can enter cells and perform genome editing with the assistance of UPS, achieving an efficiency of up to 90%. In vivo, the UPS is biodegradable, nonimmunogenic, and tumor-targeting, enabling the puncturing of tumor cells under US. With the application of UPS-assisted genome editing, gasdermin-E expression in 4T1 tumor-bearing mice is successfully restored, which leads to pyroptosis-mediated antitumor immunotherapy via low-dose X-ray irradiation. This study provides new insights for designing a sonoporation system for genome editing. Moreover, the results demonstrate that restoring gasdermin expression by genome editing significantly improves the efficacy of radioimmunotherapy.

Production and regulatory issues for theranostics

Theranostics has become a major area of innovation and progress in cancer care over the last decade. In view of the introduction of approved therapeutics in neuroendocrine tumours and prostate cancer in the last 10 years, the ability to provide access to these treatments has emerged as a key factor in ensuring global benefits from this cancer therapy approach. In this Series paper we explore the issues that affect access to and availability of theranostic radiopharmaceuticals, including supply and regulatory issues that might affect the availability of theranostic treatments for patients with cancer.

Theranostic digital twins: Concept, framework and roadmap towards personalized radiopharmaceutical therapies

Radiopharmaceutical therapy (RPT) is a rapidly developing field of nuclear medicine, with several RPTs already well established in the treatment of several different types of cancers. However, the current approaches to RPTs often follow a somewhat inflexible "one size fits all" paradigm, where patients are administered the same amount of radioactivity per cycle regardless of their individual characteristics and features. This approach fails to consider inter-patient variations in radiopharmacokinetics, radiation biology, and immunological factors, which can significantly impact treatment outcomes. To address this limitation, we propose the development of theranostic digital twins (TDTs) to personalize RPTs based on actual patient data. Our proposed roadmap outlines the steps needed to create and refine TDTs that can optimize radiation dose to tumors while minimizing toxicity to organs at risk. The TDT models incorporate physiologically-based radiopharmacokinetic (PBRPK) models, which are additionally linked to a radiobiological optimizer and an immunological modulator, taking into account factors that influence RPT response. By using TDT models, we envisage the ability to perform virtual clinical trials, selecting therapies towards improved treatment outcomes while minimizing risks associated with secondary effects. This framework could empower practitioners to ultimately develop tailored RPT solutions for subgroups and individual patients, thus improving the precision, accuracy, and efficacy of treatments while minimizing risks to patients. By incorporating TDT models into RPTs, we can pave the way for a new era of precision medicine in cancer treatment.

Affibody PET Imaging of HER2-Expressing Cancers as a Key to Guide HER2-Targeted Therapy

Human epidermal growth factor receptor 2 (HER2) is a major prognostic and predictive marker overexpressed in 15-20% of breast cancers. The diagnostic reference standard for selecting patients for HER2-targeted therapy is based on the analysis of tumor biopsies. Previously patients were defined as HER2-positive or -negative; however, with the approval of novel treatment options, specifically the antibody-drug conjugate trastuzumab deruxtecan, many breast cancer patients with tumors expressing low levels of HER2 have become eligible for HER2-targeted therapy. Such patients will need to be reliably identified by suitable diagnostic methods. Biopsy-based diagnostics are invasive, and repeat biopsies are not always feasible. They cannot visualize the heterogeneity of HER2 expression, leading to a substantial number of misdiagnosed patients. An alternative and highly accurate diagnostic method is molecular imaging with radiotracers. In the case of HER2, various studies demonstrate the clinical utility and feasibility of such approaches. Radiotracers based on Affibody® molecules, small, engineered affinity proteins with a size of ~6.5 kDa, are clinically validated molecules with favorable characteristics for imaging. In this article, we summarize the HER2-targeted therapeutic landscape, describe our experience with imaging diagnostics for HER2, and review the currently available clinical data on HER2-Affibody-based molecular imaging as a novel diagnostic tool in breast cancer and beyond.

Recent Advances in Radiotracers Targeting Novel Cancer-Specific Biomarkers in China: A Brief Overview

Radiopharmaceuticals play a critical role in nuclear medicine, providing novel tools for specifically delivering radioisotopes for the diagnosis and treatment of cancers. As the starting point for developing radiopharmaceuticals, cancer-specific biomarkers are important and receive worldwide attention. This field in China is currently experiencing a rapid expansion, with multiple radiotracers targeting novel targets being developed and translated into clinical studies. This review provides a brief overview of the exploration of novel imaging targets, preclinical evaluation of their targeting ligands, and translational research in China from 2020 to 2023, for detecting cancer, guiding targeted therapy, and visualizing the immune microenvironment. We believe that China will play an even more important role in the development of nuclear medicine in the world in the future.

Advances in Radioligand Theranostics in Oncology

Theranostics with radioligands (radiotheranostics) has played a pivotal role in oncology. Radiotheranostics explores the molecular targets expressed on tumor cells to target them for imaging and therapy. In this way, radiotheranostics entails non-invasive demonstration of the in vivo expression of a molecular target of interest through imaging followed by the administration of therapeutic radioligand targeting the tumor-expressed molecular target. Therefore, radiotheranostics ensures that only patients with a high likelihood of response are treated with a particular radiotheranostic agent, ensuring the delivery of personalized care to cancer patients. Within the last decades, a couple of radiotheranostics agents, including Lutetium-177 DOTATATE (177Lu-DOTATATE) and Lutetium-177 prostate-specific membrane antigen (177Lu-PSMA), were shown to prolong the survival of cancer patients compared to the current standard of care leading to the regulatory approval of these agents for routine use in oncology care. This recent string of successful approvals has broadened the interest in the development of different radiotheranostic agents and their investigation for clinical translation. In this work, we present an updated appraisal of the literature, reviewing the recent advances in the use of established radiotheranostic agents such as radioiodine for differentiated thyroid carcinoma and Iodine-131-labeled meta-iodobenzylguanidine therapy of tumors of the sympathoadrenal axis as well as the recently approved 177Lu-DOTATATE and 177Lu-PSMA for differentiated neuroendocrine tumors and advanced prostate cancer, respectively. We also discuss the radiotheranostic agents that have been comprehensively characterized in preclinical studies and have shown some clinical evidence supporting their safety and efficacy, especially those targeting fibroblast activation protein (FAP) and chemokine receptor 4 (CXCR4) and those still being investigated in preclinical studies such as those targeting poly (ADP-ribose) polymerase (PARP) and epidermal growth factor receptor 2.

Radiopharmaceuticals for Cancer Diagnosis and Therapy: New Targets, New Therapies-Alpha-Emitters, Novel Targets

ABSTRACT

Radiopharmaceutical therapy has emerged as a promising approach for the treatment of various cancers. The exploration of novel targets such as tumor-specific antigens, overexpressed receptors, and intracellular biomolecules using antibodies, peptides, or small molecules has expanded the scope of radiopharmaceutical therapy, enabling precise and effective cancer treatment for an increasing number of tumor types. Alpha emitters, characterized by their high linear energy transfer and short path length, offer unique advantages in targeted therapy due to their potent cytotoxicity against cancer cells while sparing healthy tissues. This article reviews recent advancements in identifying novel targets for radiopharmaceutical therapy and applications in utilizing α-emitters for targeted treatment.

Recent advances in the development of 225Ac- and 211At-labeled radioligands for radiotheranostics

Radiotheranostics utilizes a set of radioligands incorporating diagnostic or therapeutic radionuclides to achieve both diagnosis and therapy. Imaging probes using diagnostic radionuclides have been used for systemic cancer imaging. Integration of therapeutic radionuclides into the imaging probes serves as potent agents for radionuclide therapy. Among them, targeted alpha therapy (TAT) is a promising next-generation cancer therapy. The α-particles emitted by the radioligands used in TAT result in a high linear energy transfer over a short range, inducing substantial damage to nearby cells surrounding the binding site. Therefore, the key to successful cancer treatment with minimal side effects by TAT depends on the selective delivery of radioligands to their targets. Recently, TAT agents targeting biomolecules highly expressed in various cancer cells, such as sodium/iodide symporter, norepinephrine transporter, somatostatin receptor, αvβ3 integrin, prostate-specific membrane antigen, fibroblast-activation protein, and human epidermal growth factor receptor 2 have been developed and have made remarkable progress toward clinical application. In this review, we focus on two radionuclides, 225Ac and 211At, which are expected to have a wide range of applications in TAT. We also introduce recent fundamental and clinical studies of radiopharmaceuticals labeled with these radionuclides.

Orthotopic and metastatic tumour models in preclinical cancer research

Mouse models of disease play a pivotal role at all stages of cancer drug development. Cell-line derived subcutaneous tumour models are predominant in early drug discovery, but there is growing recognition of the importance of the more complex orthotopic and metastatic tumour models for understanding both target biology in the correct tissue context, and the impact of the tumour microenvironment and the immune system in responses to treatment. The aim of this review is to highlight the value that orthotopic and metastatic models bring to the study of tumour biology and drug development while pointing out those models that are most likely to be encountered in the literature. Important developments in orthotopic models, such as the increasing use of early passage patient material (PDXs, organoids) and humanised mouse models are discussed, as these approaches have the potential to increase the predictive value of preclinical studies, and ultimately improve the success rate of anticancer drugs in clinical trials.

Novel CDK19-Targeted Radiotracers: A Potential Design Strategy to Improve the Pharmacokinetics and Tumor Uptake

Cyclin-dependent kinase 19 (CDK19) is overexpressed in prostate cancer, making it an attractive target for both imaging and therapy. Since little is known about the optimized approach for radioligands of nuclear proteins, linker optimization strategies were used to improve pharmacokinetics and tumor absorption, including the adjustment of the length, flexibility/rigidity, and hydrophilicity/lipophilicity of linkers. Molecular docking was conducted for virtual screening and followed by IC50 determination. Both BALB/c mice and P-16 xenografts were used for tissue distribution and PET/CT imaging. The ligand 68Ga-10c demonstrated high absorption in tumor 5 min after injection and sustains long-term imaging within 3 h. Furthermore, 68Ga-10c exhibited slow clearance within the tumor and was predominantly metabolized in both the liver and kidneys, showing the potential to alleviate metabolic pressure and enhance tissue safety. Therefore, the linker optimization strategy is well suited for CDK19 and provides a reference for the radioactive ligands of other nuclear targets.

GRPR-Antagonists Carrying DOTAGA-Chelator via Positively Charged Linkers: Perspectives for Prostate Cancer Theranostics

Gastrin-releasing peptide receptor (GRPR)-antagonists have served as motifs in the development of theranostic radioligands for prostate cancer. Our efforts have been focused on the development of radiolabeled RM26 (H-DPhe6-Gln7-Trp8-Ala9-Val10-Gly11-His12-Sta13-Leu14-NH2) analogs, such as [111In]In-DOTAGA-PEG2-RM26. We recently showed that its Gly11/Sar11-substituted version, [111In]In-AU-RM26-M1, resisted degradation by neprilysin (NEP) while in circulation and achieved higher tumor uptake in mice. We herein introduce the following three new AU-RM26-M1 mimics labeled with In-111, with basic residues in the linker: (i) AU-RM26-M2 (PEG2-Pip), (ii) AU-RM26-M3 (PEG2-Arg), and (iii) AU-RM26-M4 (Arg-Arg-Pip). These analogs were compared in PC-3 cells and animal models vs. AU-RM26-M1 (reference). The new analogs showed high affinity and specificity for the GRPR, exhibiting an uptake and distribution pattern in PC-3 cells typical for a radiolabeled GRPR-antagonist. They showed high stability in peripheral mice blood, except for [111In]In-AU-RM26-M3. AU-RM26-M4 achieved the highest tumor uptake and promising background clearance, followed by [111In]In-RM26-M2, showing lower background levels. These findings were confirmed for [111In]In-AU-RM26-M2 and [111In]In-AU-RM26-M4 by micro-SPECT/CT at 4 and 24 h post-injection. Hence, the type of positively charged residues in the linker of AU-RM26-M1 mimics strongly influenced biological behavior. The analogs with Pip next to DPhe6 demonstrated the best overall characteristics and warrant further investigation.

Interrogating the Theranostic Capacity of a MUC16-Targeted Antibody for Ovarian Cancer

Aberrantly expressed glycans on mucins such as mucin-16 (MUC16) are implicated in the biology that promotes ovarian cancer (OC) malignancy. Here, we investigated the theranostic potential of a humanized antibody, huAR9.6, targeting fully glycosylated and hypoglycosylated MUC16 isoforms. Methods: In vitro and in vivo targeting of the diagnostic radiotracer [89Zr]Zr-DFO-huAR9.6 was investigated via binding experiments, immuno-PET imaging, and biodistribution studies on OC mouse models. Ovarian xenografts were used to determine the safety and efficacy of the therapeutic version, [177Lu]Lu-CHX-A″-DTPA-huAR9.6. Results: In vivo uptake of [89Zr]Zr-DFO-huAR9.6 supported in vitro-determined expression levels: high uptake in OVCAR3 and OVCAR4 tumors, low uptake in OVCAR5 tumors, and no uptake in OVCAR8 tumors. Accordingly, [177Lu]Lu-CHX-A″-DTPA-huAR9.6 displayed strong antitumor effects in the OVCAR3 model and improved overall survival in the OVCAR3 and OVCAR5 models in comparison to the saline control. Hematologic toxicity was transient in both models. Conclusion: PET imaging of OC xenografts showed that [89Zr]Zr-DFO-huAR9.6 delineated MUC16 expression levels, which correlated with in vitro results. Additionally, we showed that [177Lu]Lu-CHX-A″-DTPA-huAR9.6 displayed strong antitumor effects in highly MUC16-expressing tumors. These findings demonstrate great potential for 89Zr- and 177Lu-labeled huAR9.6 as theranostic tools for the diagnosis and treatment of OC.

Theranostics - a sure cure for cancer after 100 years?

Cancer has remained a formidable challenge in medicine and has claimed an enormous number of lives worldwide. Theranostics, combining diagnostic methods with personalized therapeutic approaches, shows huge potential to advance the battle against cancer. This review aims to provide an overview of theranostics in oncology: exploring its history, current advances, challenges, and prospects. We present the fundamental evolution of theranostics from radiotherapeutics, cellular therapeutics, and nanotherapeutics, showcasing critical milestones in the last decade. From the early concept of targeted drug delivery to the emergence of personalized medicine, theranostics has benefited from advances in imaging technologies, molecular biology, and nanomedicine. Furthermore, we emphasize pertinent illustrations showcasing that revolutionary strategies in cancer management enhance diagnostic accuracy and provide targeted therapies customized for individual patients, thereby facilitating the implementation of personalized medicine. Finally, we describe future perspectives on current challenges, emerging topics, and advances in the field.

Selenium promotes immunogenic radiotherapy against cervical cancer metastasis through evoking P53 activation

Radiotherapy is still the recommended treatment for cervical cancer. However, radioresistance and radiation-induced side effects remain one of the biggest clinical problems. Selenium (Se) has been confirmed to exhibit radiation-enhancing effects for cancer treatment. However, Se species dominate the biological activities and which form of Se possesses better radiosensitizing properties and radiation safety remains elusive. Here, different Se species (the valence state of Se ranged from - 2, 0, +4 to + 6) synergy screen was carried out to identify the potential radiosensitizing effects and radiation safety of Se against cervical cancer. We found that the therapeutic effects varied with the changes in the Se valence state. Sodium selenite (+4) displayed strong cancer-killing effects but also possessed severe cytotoxicity. Sodium selenate (+6) neither enhanced the killing effects of X-ray nor possessed anticancer activity by its alone treatment. Although nano-selenium (0), especially Let-SeNPs, has better radiosensitizing activity, the - 2 organic Se, such as selenadiazole derivative SeD (-2) exhibited more potent anticancer effects and possessed a higher safe index. Overall, the selected Se drugs were able to synergize with X-ray to inhibit cell growth, clone formation, and cell migration by triggering G2/M phase arrest and apoptosis, and SeD (-2) was found to exhibit more potent enhancing capacity. Further mechanism studies showed that SeD mediated p53 pathway activation by inducing DNA damage through promoting ROS production. Additionally, SeD combined with X-ray therapy can induce an anti-tumor immune response in vivo. More importantly, SeD combined with X-ray significantly inhibited the liver metastasis of tumor cells and alleviated the side effects caused by radiation therapy in tumor-bearing mice. Taken together, this study demonstrates the radiosensitization and radiation safety effects of different Se species, which may shed light on the application of such Se-containing drugs serving as side effects-reducing agents for cervical cancer radiation treatment.

Advancements in the development of radiopharmaceuticals for nuclear medicine applications in the treatment of bone metastases

Bone metastases are a painful and complex condition that overwhelmingly impacts the prognosis and quality of life of cancer patients. Over the years, nuclear medicine has made remarkable progress in the diagnosis and management of bone metastases. This review aims to provide a comprehensive overview of the recent advancements in nuclear medicine for the diagnosis and management of bone metastases. Furthermore, the review explores the role of targeted radiopharmaceuticals in nuclear medicine for bone metastases, focusing on radiolabeled molecules that are designed to selectively target biomarkers associated with bone metastases, including osteocytes, osteoblasts, and metastatic cells. The applications of radionuclide-based therapies, such as strontium-89 (Sr-89) and radium-223 (Ra-223), are also discussed. This review also highlights the potential of theranostic approaches for bone metastases, enabling personalized treatment strategies based on individual patient characteristics. Importantly, the clinical applications and outcomes of nuclear medicine in osseous metastatic disease are discussed. This includes the assessment of treatment response, predictive and prognostic value of imaging biomarkers, and the impact of nuclear medicine on patient management and outcomes. The review identifies current challenges and future perspectives on the role of nuclear medicine in treating bone metastases. It addresses limitations in imaging resolution, radiotracer availability, radiation safety, and the need for standardized protocols. The review concludes by emphasizing the need for further research and advancements in imaging technology, radiopharmaceutical development, and integration of nuclear medicine with other treatment modalities. In summary, advancements in nuclear medicine have significantly improved the diagnosis and management of osseous metastatic disease and future developements in the integration of innovative imaging modalities, targeted radiopharmaceuticals, radionuclide production, theranostic approaches, and advanced image analysis techniques hold great promise in improving patient outcomes and enhancing personalized care for individuals with bone metastases.

DNA-Targeted Complexes of Tc and Re for Biomedical Applications

Due to their favorable chemical features, Re and Tc complexes have been widely used for the development of new therapeutic agents and imaging probes to solve problems of biomedical relevance. This review provides an update of the most relevant research efforts towards the development of novel cancer theranostic agents using Re and Tc-based compounds interacting with specific DNA structures. This includes a variety of homometallic complexes, namely those containing M(CO)3 (M=Re, Tc) moieties, that exhibit different modes of interaction with DNA, such as covalent binding, intercalation, groove binding or G-quadruplex DNA binding. Additionally, heterometallic complexes, designed to potentiate synergistic effects of different metal centers to improve DNA-targeting, cytotoxicity and fluorescence properties, are also reviewed. Particular attention is also given to 99m Tc- and 188 Re-labeled oligonucleotides that have been widely explored to develop imaging and therapeutic radiopharmaceuticals through the in vivo hybridization with a specific complementary DNA or RNA target sequence to provide useful molecular tools in precision medicine for cancer diagnosis and treatment. Finally, the need for further improvement of DNA-targeted Re and Tc-based compounds as potential therapeutic and diagnostic agents is highlighted, and future directions are discussed.

Metals in Cancer Research: Beyond Platinum Metallodrugs

The discovery of the medicinal properties of platinum complexes has fueled the design and synthesis of new anticancer metallodrugs endowed with unique modes of action (MoA). Among the various families of experimental antiproliferative agents, organometallics have emerged as ideal platforms to control the compounds' reactivity and stability in a physiological environment. This is advantageous to efficiently deliver novel prodrug activation strategies, as well as to design metallodrugs acting only via noncovalent interactions with their pharmacological targets. Noteworthy, another justification for the advance of organometallic compounds for therapy stems from their ability to catalyze bioorthogonal reactions in cancer cells. When not yet ideal as drug leads, such compounds can be used as selective chemical tools that benefit from the advantages of catalytic amplification to either label the target of interest (e.g., proteins) or boost the output of biochemical signals. Examples of metallodrugs for the so-called "catalysis in cells" are considered in this Outlook together with other organometallic drug candidates. The selected case studies are discussed in the frame of more general challenges in the field of medicinal inorganic chemistry.

Design of Novel 18F-Labeled Amino Acid Tracers Using Sulfur 18F-Fluoride Exchange Click Chemistry

[18F]Gln-OSO2F, [18F]Arg-OSO2F, and [18F]FSY-OSO2F were designed by introducing sulfonyl 18F-fluoride onto glutamine, arginine, and tyrosine, respectively. [18F]FSY-OSO2F can be prepared directly by sulfur 18F-fluoride exchange, while [18F]Gln-OSO2F and [18F]Arg-OSO2F require a two-step labeling method. Those tracers retain their typical transport characteristics for unmodified amino acids. Both PET imaging and biodistribution confirmed that [18F]FSY-OSO2F visualized MCF-7 and 22Rv1 subcutaneous tumors with high contrast, and its tumor-to-muscle ratio was better than that of [18F]FET. However, [18F]Gln-OSO2F and [18F]Arg-OSO2F poorly image MCF-7 subcutaneous tumors, possibly due to differences in the types and amounts of transporters expressed in tumors. All three tracers can visualize the U87MG glioma. According to our biological evaluation, none of the tracers evaluated in this study exhibited obvious defluorination, and subtle structural changes led to different imaging characteristics, indicating that the application of sulfur 18F-fluoride exchange click chemistry in the design of radioactive sulfonyl fluoride amino acids is feasible and offers significant advantages.

Bis(Disulfide)-Bridged Somatostatin-14 Analogs and Their [111In]In-Radioligands: Synthesis and Preclinical Profile

The overexpression of one or more somatostatin receptors (SST1-5R) in human tumors has provided an opportunity for diagnosis and therapy with somatostatin-like radionuclide carriers. The application of "pansomatostatin" analogs is expected to broaden the clinical indications and upgrade the diagnostic/therapeutic efficacy of currently applied SST2R-prefering radioligands. In pursuit of this goal, we now introduce two bicyclic somatostatin-14 (SS14) analogs, AT5S (DOTA-Ala1-Gly2-c[Cys3-Lys4-Asn5-c[Cys6-Phe7-DTrp8-Lys9-Thr10-Cys11]-Thr12-Ser13-Cys14]) and AT6S (DOTA-Ala1-Gly2-c[Cys3-Lys4-c[Cys5-Phe6-Phe7-DTrp8-Lys9-Thr10-Phe11-Cys12]-Ser13-Cys14]), suitable for labeling with trivalent radiometals and designed to sustain in vivo degradation. Both AT5S and AT6S and the respective [111In]In-AT5S and [111In]In-AT6S were evaluated in a series of in vitro assays, while radioligand stability and biodistribution were studied in mice. The 8/12-mer bicyclic AT6S showed expanded affinity for all SST1-5R and agonistic properties at the SST2R, whereas AT5S lost all affinity to SST1-5R. Both [111In]In-AT5S and [111In]In-AT6S remained stable in the peripheral blood of mice, while [111In]In-AT6S displayed low, but specific uptake in AR4-2J tumors and higher uptake in HEK293-SST3R tumors in mice. In summary, high radioligand stability was acquired by the two disulfide bridges introduced into the SS14 motif, but only the 8/12-mer ring AT6S retained a pansomatostatin profile. In consequence, [111In]In-AT6S targeted SST2R-/SST3R-positive xenografts in mice. These results call for further research on pansomatostatin-like radioligands for cancer theranostics.

Establishing a robust radioligand therapy program: A practical approach for North American centers

Radioligand therapy (RLT) is a targeted approach to treating cancer that has been shown to be safe and effective in a variety of disease states, including gastroenteropancreatic neuroendocrine tumors, lymphoma, and most recently, advanced prostate cancer. In the United States, patient access to this therapy is currently variable. Implementation of new RLT programs and expansion of existing programs are needed to broaden patient access to and standardize the delivery of RLT, especially as new therapies are introduced into clinical practice. Drawing from experience in establishing RLT programs in different settings, we have developed practical recommendations for building and implementing a robust RLT program. In this review, we present our recommendations for minimal requirements and optimal requirements, as well as system considerations, and special issues associated with implementing an RLT program in North American centers.

Position paper to facilitate patient access to radiopharmaceuticals: considerations for a suitable pharmaceutical regulatory framework

BACKGROUND

Nuclear medicine has made enormous progress in the past decades. However, there are still significant inequalities in patient access among different countries, which could be mitigated by improving access to and availability of radiopharmaceuticals.

MAIN BODY

This paper summarises major considerations for a suitable pharmaceutical regulatory framework to facilitate patient access to radiopharmaceuticals. These include the distinct characteristics of radiopharmaceuticals which require dedicated regulations, considering the impact of the variable complexity of radiopharmaceutical preparation, personnel requirements, manufacturing practices and quality assurance, regulatory authority interfaces, communication and training, as well as marketing authorisation procedures to ensure availability of radiopharmaceuticals. Finally, domestic and regional supply to ensure patient access via alternative regulatory pathways, including in-house production of radiopharmaceuticals, is described, and an outlook on regulatory challenges faced by new developments, such as the use of alpha emitters, is provided.

CONCLUSIONS

All these considerations are an outcome of a dedicated Technical Meeting organised by the IAEA in 2023 and represent the views and opinions of experts in the field, not those of any regulatory authorities.

PSMA PET/MR is a New Imaging Option for Identifying Glioma Recurrence and Predicting Prognosis

BACKGROUND

Glioma is characterized by a high recurrence rate, while the results of the traditional imaging methods (including magnetic resonance imaging, MRI) to distinguish recurrence from treatment-related changes (TRCs) are poor. Prostate-specific membrane antigen (PSMA) (US10815200B2, Deutsches Krebsforschungszentrum, German Cancer Research Center) is a type II transmembrane glycoprotein overexpressed in glioma vascular endothelium, and it is a promising target for imaging and therapy.

OBJECTIVE

The study aimed to assess the performance of PSMA positron emission tomography/ magnetic resonance (PET/MR) for diagnosing recurrence and predicting prognosis in glioma patients.

MATERIALS AND METHODS

Patients suspected of glioma recurrence who underwent 18F-PSMA-1007 PET/MR were prospectively enrolled. Eight metabolic parameters and fifteen texture features of the lesion were extracted from PSMA PET/MR. The ability of PSMA PET/MR to diagnose glioma recurrence was investigated and compared with conventional MRI. The diagnostic agreement was assessed using Cohen κ scores and the predictive parameters of PSMA PET/MR were obtained. Kaplan-Meier method and Cox proportional hazard model were used to analyze recurrence- free survival (RFS) and overall survival (OS). Finally, the expression of PSMA was analyzed by immunohistochemistry (IHC).

RESULTS

Nineteen patients with a mean age of 48.11±15.72 were assessed. The maximum tumorto- parotid ratio (TPRmax) and texture features extracted from PET and T1-weighted contrast enhancement (T1-CE) MR showed differences between recurrence and TRCs (all p <0.05). PSMA PET/MR and conventional MRI exhibited comparable power in diagnosing recurrence with specificity and PPV of 100%. The interobserver concordance was fair between the two modalities (κ = 0.542, p = 0.072). The optimal cutoffs of metabolic parameters, including standardized uptake value (SUV, SUVmax, SUVmean, and SUVpeak) and TPRmax for predicting recurrence were 3.35, 1.73, 1.99, and 0.17 respectively, with the area under the curve (AUC) ranging from 0.767 to 0.817 (all p <0.05). In grade 4 glioblastoma (GBM) patients, SUVmax, SUVmean, SUVpeak, TBRmax, TBRmean, and TPRmax showed improved performance of AUC (0.833-0.867, p <0.05). Patients with SUVmax, SUVmean, or SUVpeak more than the cutoff value had significantly shorter RFS (all p <0.05). In addition, patients with SUVmean, SUVpeak, or TPRmax more than the cutoff value had significantly shorter OS (all p <0.05). PSMA expression of glioma vascular endothelium was observed in ten (10/11, 90.9%) patients with moderate-to-high levels in all GBM cases (n = 6/6, 100%).

CONCLUSION

This primitive study shows multiparameter PSMA PET/MR to be useful in identifying glioma (especially GBM) recurrence by providing excellent tumor background comparison, tumor heterogeneity, recurrence prediction and prognosis information, although it did not improve the diagnostic performance compared to conventional MRI. Further and larger studies are required to define its potential clinical application in this setting.

Synthesis and Preclinical Evaluation of PSMA-Targeted 111In-Radioconjugates Containing a Mitochondria-Tropic Triphenylphosphonium Carrier

Nuclear DNA is the canonical target for biological damage induced by Auger electrons (AE) in the context of targeted radionuclide therapy (TRT) of cancer, but other subcellular components might also be relevant for this purpose, such as the energized mitochondria of tumor cells. Having this in mind, we have synthesized novel DOTA-based chelators carrying a prostate-specific membrane antigen (PSMA) inhibitor and a triphenyl phosphonium (TPP) group that were used to obtain dual-targeted 111In-radioconjugates ([111In]In-TPP-DOTAGA-PSMA and [111In]In-TPP-DOTAGA-G3-PSMA), aiming to promote a selective uptake of an AE-emitter radiometal (111In) by PSMA+ prostate cancer (PCa) cells and an enhanced accumulation in the mitochondria. These dual-targeted 111In-radiocomplexes are highly stable under physiological conditions and in cell culture media. The complexes showed relatively similar binding affinities toward the PSMA compared to the reference tracer [111In]In-PSMA-617, in line with their high cellular uptake and internalization in PSMA+ PCa cells. The complexes compromised cell survival in a dose-dependent manner and in the case of [111In]In-TPP-DOTAGA-G3-PSMA to a higher extent than observed for the single-targeted congener [111In]In-PSMA-617. μSPECT imaging studies in PSMA+ PCa xenografts showed that the TPP pharmacophore did not interfere with the excellent in vivo tumor uptake of the "golden standard" [111In]In-PSMA-617, although it led to a higher kidney retention. Such kidney retention does not necessarily compromise their usefulness as radiotherapeutics due to the short tissue range of the Auger/conversion electrons emitted by 111In. Overall, our results provide valuable insights into the potential use of mitochondrial targeting by PSMA-based radiocomplexes for efficient use of AE-emitting radionuclides in TRT, giving impetus to extend the studies to other AE-emitting trivalent radiometals (e.g., 161Tb or 165Er) and to further optimize the designed dual-targeting constructs.

[Radiotheranostics Based on Chemical Control of Radioactivity Pharmacokinetics]

Recently, radiotheranostics, which systematically combines diagnosis by nuclear medicine imaging and treatment by internal radiotherapy, constitutes a new modality in cancer treatment, with some clinical reports showing marked effects on cancer. We have been developing multifunctional chelates containing a target recognition unit, a radiation release unit, and a radioactivity pharmacokinetics control unit in the same molecule to develop efficient agents for cancer radiotheranostics based on chemical control of radioactivity pharmacokinetics. Using these compounds, we have achieved improved cancer accumulation and reduced renal accumulation in tumor-bearing mice, and have developed novel hybrid radiotheranostic agents that can be applied to simultaneously perform target-specific molecular imaging using γ-ray emitting radionuclides and internal radiotherapy using α-particle-emitting radionuclides. For example, 111In/225Ac-labeled PSMA-DA1, which targets prostate-specific membrane antigen (PSMA) for radiotheranostics, achieved clear in vivo imaging of PSMA in tumor-bearing mice and showed marked tumor growth inhibition. In addition to PSMA, this platform for radiotheranostics has also shown efficacy against various cancer target molecules, including carbonic anhydrase IX (CA-IX), which is highly expressed in hypoxic regions of cancer, and glucagon-like peptide-1 receptor (GLP-1R), which is highly expressed in insulinomas. This review presents these recent results of our studies on radiotheranostics for cancer.

In situ theranostic platform combining highly localized magnetic fluid hyperthermia, magnetic particle imaging, and thermometry in 3D

Theranostic platforms, combining diagnostic and therapeutic approaches within one system, have garnered interest in augmenting invasive surgical, chemical, and ionizing interventions. Magnetic particle imaging (MPI) offers a quite recent alternative to established radiation-based diagnostic modalities with its versatile tracer material (superparamagnetic iron oxide nanoparticles, SPION). It also offers a bimodal theranostic framework that can combine tomographic imaging with therapeutic techniques using the very same SPION. Methods: We show the interleaved combination of MPI-based imaging, therapy (highly localized magnetic fluid hyperthermia (MFH)) and therapy safety control (MPI-based thermometry) within one theranostic platform in all three spatial dimensions using a commercial MPI system and a custom-made heating insert. The heating characteristics as well as theranostic applications of the platform were demonstrated by various phantom experiments using commercial SPION. Results: We have shown the feasibility of an MPI-MFH-based theranostic platform by demonstrating high spatial control of the therapeutic target, adequate MPI-based thermometry, and successful in situ interleaved MPI-MFH application. Conclusions: MPI-MFH-based theranostic platforms serve as valuable tools that enable the synergistic integration of diagnostic and therapeutic approaches. The transition into in vivo studies will be essential to further validate their potential, and it holds promising prospects for future advancements.

How to design a theranostic trial?

The field of nuclear theranostic clinical trials is continuously expanding as an increasing number of novel agents and treatment combinations are explored for treating advanced and metastatic cancers. Moving from 'bench-to-bedside' is oftentimes a complex and lengthy process. The objective of this overview is to explore the basic elements involved in designing clinical trials with a special focus on theranostics in nuclear medicine. The 'bench-to-bedside' journey involves translating basic scientific research into patient-effective treatments. Preclinical studies, a crucial initial step, are a complex process encompassing in vitro experiments, in vivo studies, and animal models to explore hypotheses in humans. Clinical trials follow, with predefined phases assessing safety, effectiveness, and comparisons to existing treatments. This process demands investments in data management, statistics, good clinical practice (GCP) accreditations, and collaborative efforts for funding and sustainable pricing. Theranostics, merging diagnostics and personalized treatment, is at the forefront. Continuous efforts to enhance existing agents involve reducing adverse effects, exploring new indications, and incorporating advanced imaging modalities. Radionuclide therapy, unique with non-uniform distribution and complex radiobiology, plays a distinct role. This article explores trends and challenges in each clinical trial phase in light of the emerging field of theranostics in nuclear medicine, emphasizing meticulous trial design, dosimetry optimization, and the necessity of collaborative stakeholder efforts for successful implementation.

Development and Utility of an Imaging System for Internal Dosimetry of Astatine-211 in Mice

In targeted radionuclide therapy, determining the absorbed dose of the ligand distributed to the whole body is vital due to its direct influence on therapeutic and adverse effects. However, many targeted alpha therapy drugs present challenges for in vivo quantitative imaging. To address this issue, we developed a planar imaging system equipped with a cadmium telluride semiconductor detector that offers high energy resolution. This system also comprised a 3D-printed tungsten collimator optimized for high sensitivity to astatine-211, an alpha-emitting radionuclide, and adequate spatial resolution for mouse imaging. The imager revealed a spectrum with a distinct peak for X-rays from astatine-211 owing to the high energy resolution, clearly distinguishing these X-rays from the fluorescent X-rays of tungsten. High collimator efficiency (4.5 × 10-4) was achieved, with the maintenance of the spatial resolution required for discerning mouse tissues. Using this system, the activity of astatine-211 in thyroid cancer tumors with and without the expression of the sodium iodide symporter (K1-NIS/K1, respectively) was evaluated through in vivo imaging. The K1-NIS tumors had significantly higher astatine-211 activity (sign test, p = 0.031, n = 6) and significantly decreased post-treatment tumor volume (Student's t-test, p = 0.005, n = 6). The concurrent examination of intratumor drug distribution and treatment outcome could be performed with the same mice.