99mTc-Hynic-TOC imaging in the diagnostic of neuroendocrine tumors

An Update on DOTA-Peptides PET Imaging and Potential Advancements of Radioligand Therapy in Intracranial Meningiomas

Meningiomas arise from the meningeal layers covering the central nervous system structures. Although most are benign, meningiomas can still cause neurological morbidity due to the mass effect and compression of the surrounding parenchyma. The prognosis also depends on several factors such as growth pattern or location. Morphological imaging approaches, such as MRI and CT, that emphasize intracranial calcifications, vascular patterns, or invasion of major vessels act as the basis of the diagnosis; PET/CT imaging is a valuable diagnostic tool for assessing somatostatin receptor activity in tumors. It enables the visualization and quantification of somatostatin receptor expression, providing insights into tumor biology, receptor status, and potential therapeutic targets. Aside from radiosurgery and neurosurgical intervention, peptide receptor radionuclide therapy (PRRT) has also shown promising results. Somatostatin receptors 1 and 2 are nearly universally expressed in meningioma tissue. This characteristic is increasingly exploited to identify patients eligible for adjuvant therapy using DOTA-conjugated somatostatin receptor-targeting peptides PET. In the treatment of relapsed/refractory meningiomas, PRRT is increasingly considered a safe and effective therapeutic option. It is often supported by artificial intelligence strategies for dose optimization and side-effect monitoring. The objective of this study is to evaluate the safety and benefits of these strategies based on the latest findings.

Real world experience with [99mTc]Tc-HYNIC-iPSMA SPECT prostate cancer detection: interim results from the global NOBLE registry

PURPOSE

[99mTc]Tc-HYNIC-iPSMA is a novel technetium-99m-labelled small molecule inhibitor of the prostate-specific membrane antigen (PSMA) for detecting prostate cancer (PC). The objective of this registry was to collect and evaluate [99mTc]Tc-HYNIC-iPSMA patient data and images to establish the safety and tolerability, and clinical utility of this agent in imaging at different stages of PC.

METHODS

Patients 18 to 80 years old with primary staging and metastatic PC were eligible. Patients unable to perform prescribed examinations, undergo a [99mTc]Tc-HYNIC-iPSMA planar and SPECT or SPECT/CT (when available), or sign a patient informed consent form were excluded from the registry. All eligible patients underwent a screening and baseline visit before imaging with [99mTc]Tc-HYNIC-iPSMA. The primary safety endpoint was assessed by collecting and grading all treatment-related adverse events using the Common Terminology Criteria for Adverse Events. Patients were followed until disease progression, death, serious or intolerable adverse events, registry termination by the sponsor, patient withdrawal, or lost to follow-up. Analysis was planned for when data was available from 40 enrolled patients.

RESULTS

40 patients enrolled in 6 countries and received [99mTc]Tc-HYNIC-iPSMA tracer administration followed by planar and SPECT imaging. Of the 40 patients included, investigators reported a change in management due to the [99mTc]Tc-HYNIC-iPSMA imaging in 17/40 of patients (42.5%). No adverse events were reported.

CONCLUSIONS

[99mTc]Tc-HYNIC-iPSMA is a promising option to identify PSMA-positive prostate cancer on SPECT and could improve patient access to PSMA imaging worldwide.

[99mTc]Tc-labeled HYNIC conjugated chlorambucil as a tumor targeting Agent: Synthesis, characterization and ex-vivo evaluation

Chlorambucil is an alkylating drug that finds application towards chemotherapy of different types of cancers. In order to explore the possibility of utilization of this drug as an imaging agent for early diagnosis of solid tumors, attempt was made to synthesize a 99mTc complex of chlorambucil and evaluate its potential in tumor bearing small animal model. HYNIC-chlorambucil was synthesized by conjugation of HYNIC with chlorambucil via an ethylenediamine linker. All the intermediates and final product were purified and characterized by standard spectroscopic techniques viz. FT-IR, 1H/13C-NMR as well as by mass spectrometry. HYNIC-chlorambucil conjugate was radiolabeled with [99mTc]Tc and found to be formed with > 95 % radiochemical purity via RP-HPLC studies. The partition coefficient (Log10Po/w) of the synthesized complex was found to be -0.78 ± 0.25 which indicated the moderate hydrophilic nature for the complex. Biological behaviour of [99mTc]Tc-HYNIC-chlorambucil, studied in fibrosarcoma bearing Swiss mice, revealed a tumor uptake of about 4.16 ± 1.52 %IA/g at 30 min post-administration, which declined to 1.91 ± 0.13 % IA/g and 1.42 ± 0.14 %IA/g at 1 h and 2 h post-administration, respectively. A comparison of different [99mTc]Tc-chlorambucil derivatives (reported in the contemporary literature) formulated using different methodologies revealed that tumor uptake and pharmacokinetics exhibited by these agents strongly depend on the lipophilicity/hydrophilicity of such agents, which in turn is dependent on the bifunctional chelators used for formulating the radiolabeled chlorambucils.

99mTc-labeled FAPI compounds for cancer and inflammation: from radiochemistry to the first clinical applications

BACKGROUND

In recent years, fibroblast activating protein (FAP), a biomarker overexpressed by cancer-associated fibroblasts, has emerged as one of the most promising biomarkers in oncology. Similarly, FAP overexpression has been detected in various fibroblast-mediated inflammatory conditions such as liver cirrhosis and idiopathic pulmonary fibrosis. Along this trajectory, FAP-targeted positron emission tomography (PET), utilizing FAP inhibitors (FAPi) labeled with positron emitters, has gained traction as a powerful imaging approach in both cancer and inflammation. However, PET represents a high-cost technology, and its widespread adoption is still limited compared to the availability of gamma cameras. To address this issue, several efforts have been made to explore the potential of [99mTc]Tc-FAPi tracers as molecular probes for imaging with gamma cameras and single photon emission computed tomography (SPECT).

MAIN BODY

Several approaches have been investigated for labeling FAPi-based compounds with 99mTc. Specifically, the mono-oxo, tricarbonyl, isonitrile, and HYNIC strategies have been applied to produce [99mTc]Tc-FAPi tracers, which have been tested in vitro and in animal models. Overall, these labeling approaches have demonstrated high efficiency and strong binding. The resulting [99mTc]Tc-FAPi tracers have shown high specificity for FAP-positive cells and xenografts in both in vitro and animal model studies, respectively. However, the majority of [99mTc]Tc-FAPi tracers have exhibited variable levels of lipophilicity, leading to preferential excretion through the hepatobiliary route and undesirable binding to lipoproteins. Consequently, efforts have been made to synthesize more hydrophilic FAPi-based compounds to improve pharmacokinetic properties and achieve a more favorable biodistribution, particularly in the abdominal region. SPECT imaging with [99mTc]Tc-FAPi has yielded promising results in patients with gastrointestinal tumors, demonstrating comparable or superior diagnostic performance compared to other imaging modalities. Similarly, encouraging outcomes have been observed in subjects with gliomas, lung cancer, breast cancer, and cervical cancer. Beyond oncological applications, [99mTc]Tc-FAPi-based imaging has been successfully employed in myocardial and idiopathic pulmonary fibrosis.

CONCLUSIONS

This overview focuses on the various radiochemical strategies for obtaining [99mTc]Tc-FAPi tracers, highlighting the main challenges encountered and possible solutions when applying each distinct approach. Additionally, it covers the preclinical and initial clinical applications of [99mTc]Tc-FAPi in cancer and inflammation.

Imaging-guided targeted radionuclide tumor therapy: From concept to clinical translation

Since the first introduction of sodium iodide I-131 for use with thyroid patients almost 80 years ago, more than 50 radiopharmaceuticals have reached the markets for a wide range of diseases, especially cancers. The nuclear medicine paradigm also shifts from solely molecular imaging or radionuclide therapy to imaging-guided radionuclide therapy, which is deemed a vital component of precision cancer therapy and an emerging medical modality for personalized medicine. The imaging-guided radionuclide therapy highlights the systematic integration of targeted nuclear diagnostics and radionuclide therapeutics. Regarding this, nuclear imaging serves to "visualize" the lesions and guide the therapeutic strategy, followed by administration of a precise patient specific dose of radiotherapeutics for treatment according to the absorbed dose to different organs and tumors calculated by dosimetry tools, and finally repeated imaging to predict the prognosis. This strategy leads to significantly enhanced therapeutic efficacy, improved patient outcomes, and manageable adverse events. In this review, we provide an overview of imaging-guided targeted radionuclide therapy for different tumors such as advanced prostate cancer and neuroendocrine tumors, with a focus on development of new radioligands and their preclinical and clinical results, and further discuss about challenges and future perspectives.

Preparation, quality control, biological evaluation, and human absorbed dose estimation of 188Re-HYNIC-TOC

In this study, concerning the advantages of rhenium-188 over other therapeutic radionuclides, such as its stock availability from 188W/188Re generator and radiolabeled peptide therapy in the treatment of patients with widespread disease, preparation and quality control of 188Re-HYNIC-TOC were studied. Optimized conditions for radiolabeling of HYNIC-TOC with 188Re were assessed by several experiments. 188Re-HYNIC-TOC was prepared with radiochemical purity >97%. The radiolabelled compound showed high stability both in PBS buffer and in human serum even after 24 h. Biodistribution of the complex in male Wistar rats was examined up to 24 h after intravenous injection and indicated fast blood clearance and significant accumulation in the kidney. The radiation absorbed dose assessment resource (RADAR) method was used to estimate the equivalent and effective absorbed dose of human organs. Kidney received the absorbed dose of 0.72 mSv/MBq, the highest estimated amount, after injection of the complex. The results showed fast preparation, easy quality control, and relatively similar biodistribution of 188Re-HYNIC-TOC to other peptides. This complex can be considered as an agent for the treatment of patients with medium-sized tumors expressing somatostatin receptors. However, more biological studies are still needed.

Somatostatin and Its Receptor System in Colorectal Cancer

Somatostatin (SST)/somatotropin release-inhibiting factor (SRIF) is a well-known neuropeptide, widely distributed in the central and peripheral nervous systems, that regulates the endocrine system and affects neurotransmission via interaction with five SST receptors (SST1-5). In the gastrointestinal tract, the main SST-producing cells include intestinal enteroendocrine cells (EECs) restricted to the mucosa, and neurons of the submucosal and myenteric plexuses. The action of the SRIF system is based on the inhibition of endocrine and exocrine secretion, as well as the proliferative responses of target cells. The SST1–5 share common signaling pathways, and are not only widely expressed on normal tissues, but also frequently overexpressed by several tumors, particularly neuroendocrine neoplasms (NENs). Furthermore, the SRIF system represents the only peptide/G protein-coupled receptor (GPCR) system with multiple approved clinical applications for the diagnosis and treatment of several NENs. The role of the SRIF system in the histogenesis of colorectal cancer (CRC) subtypes (e.g., adenocarcinoma and signet ring-cell carcinoma), as well as diagnosis and prognosis of mixed adenoneuroendocrine carcinoma (MANEC) and pure adenocarcinoma, is poorly understood. Moreover, the impact of the SRIF system signaling on CRC cell proliferation and its potential role in the progression of this cancer remains unknown. Therefore, this review summarizes the recent collective knowledge and understanding of the clinical significance of the SRIF system signaling in CRC, aiming to evaluate the potential role of its components in CRC histogenesis, diagnosis, and potential therapy.

Review on 99mTc radiopharmaceuticals with emphasis on new advancements

Rapid imaging acquisition, high spatial resolution and sensitivity, powered by advancements in solid-state detector technology, are significantly changing the perspective of single photon emission tomography (SPECT). In particular, this evolutionary step is fueling a rediscovery of technetium-99m, a still unique radionuclide within the nuclear medicine scenario because of its ideal nuclear properties and easy preparation of its radiopharmaceuticals that does not require a costly infrastructure and complex procedures. Scope of this review is to show that the arsenal of technetium-99m radiopharmaceuticals is already equipped with imaging agents that may complement and integrate the role played by analogous tracers developed for positron emission tomography (PET). These include, in particular, somatostatin (SST) and prostate-specific membrane antigen (PSMA) receptor targeting agents, and a number of peptide-derived radiopharmaceuticals. Additionally, these recent technological developments, combined with new myocardial perfusion tracers having more favorable biodistribution and pharmacokinetic properties as compared to current commercial agents, may also reinvigorate the prevailing position still hold by technetium-99m radiopharmaceuticals in nuclear cardiology.

Radiopharmaceuticals for Breast Cancer and Neuroendocrine Tumors: Two Examples of How Tissue Characterization May Influence the Choice of Therapy

Molecular medicine has gained clinical relevance for the detection and staging of oncological diseases, to guide therapy decision making and for therapy follow-up due to the availability of new highly sensitive hybrid imaging camera systems and the development of new tailored radiopharmaceuticals that target specific molecules. The knowledge of the expression of different receptors on the primary tumor and on metastases is important for both therapeutic and prognostic purposes and several approaches are available aiming to achieve personalized medicine in different oncological diseases. In this review, we describe the use of specific radiopharmaceuticals to image and predict therapy response in breast cancer and neuroendocrine tumors since they represent a paradigmatic example of the importance of tumoral characterization of hormonal receptors in order to plan a tailored treatment. The most attractive radiopharmaceuticals for breast cancer are 16α-[¹⁸F]-fluoro-17β-estradiol for PET assessment of the estrogen expression, radiolabeled monoclonal antibody trastuzumab to image the human epidermal growth factor receptor 2, but also the imaging of androgen receptors with [¹⁸F]-fluorodihydrotestosterone.

A Picture of Modern Tc-99m Radiopharmaceuticals: Production, Chemistry, and Applications in Molecular Imaging

Even today, techentium-99m represents the radionuclide of choice for diagnostic radio-imaging applications. Its peculiar physical and chemical properties make it particularly suitable for medical imaging. By the use of molecular probes and perfusion radiotracers, it provides rapid and non-invasive evaluation of the function, physiology, and/or pathology of organs. The versatile chemistry of technetium-99m, due to its multi-oxidation states, and, consequently, the ability to produce a variety of complexes with particular desired characteristics, are the major advantages of this medical radionuclide. The advances in technetium coordination chemistry over the last 20 years, in combination with recent advances in detector technologies and reconstruction algorithms, make SPECT’s spatial resolution comparable to that of PET, allowing 99mTc radiopharmaceuticals to have an important role in nuclear medicine and to be particularly suitable for molecular imaging. In this review the most efficient chemical methods, based on the modern concept of the 99mTc-metal fragment approach, applied to the development of technetium-99m radiopharmaceuticals for molecular imaging, are described. A specific paragraph is dedicated to the development of new 99mTc-based radiopharmaceuticals for prostate cancer.