Theranostics: Leveraging Molecular Imaging and Therapy to Impact Patient Management and Secure the Future of Nuclear Medicine

A systematic review on the current status of PSMA-targeted imaging and radioligand therapy

Prostate specific membrane antigen (PSMA) has been the subject of several studies in recent decades as a promising molecular target for prostate cancer (PCa), in fact it is considered an excellent molecular target for both PCa imaging (both for staging and follow-up), by means of PET/CT and for radioligand therapy. Its interesting molecular features have enabled the development of a new diagnostic and therapeutic approach for PCa, called "theranostics." Considering the abundance of PSMA-based probes that have appeared so far in the literature, the present work focuses the attention on radiopharmaceuticals with increasing clinical application, highlighting advantages and disadvantages in terms of different metabolization and excretion processes, pharmacokinetic, binding affinity and variable internalization rate, tumor-to-background ratio, residence times and toxicity profile.

NECTIN-4 targeted theranostics for urothelial cancer: getting ready for primetime?

Locally advanced and metastatic urothelial carcinoma (UC) presents a bleak prognosis, with limited treatment options. NECTIN-4, an overexpressed protein in UC, has become a target for therapy. Enfortumab vedotin (EV) gained Food and Drug Administration approval for advanced UC treatment, but patient selection based on NECTIN-4 expression remains challenging. In the study under evaluation, Duan et al. introduced a novel PET/CT imaging approach using 68Ga-N188, a molecular probe, to visualize NECTIN-4 expression in UC. Their study encompassed preclinical evaluations and translational assessments in both healthy individuals and UC patients. Results demonstrated the potential of 68Ga-N188 in identifying NECTIN-4 expression in UC lesions. Additionally, the study utilized long axial field-of-view (LAFOV) PET/CT, enhancing sensitivity and enabling dynamic studies for improved radiopharmaceutical evaluation. In summary, the study from Duan and colleagues introduces a promising molecular imaging technique that could aid in patient selection for EV therapy and the development of targeted drugs for UC. It also highlights the potential of LAFOV PET/CT in enhancing imaging precision and expanding future therapeutic possibilities for UC.

[18F]-FDHT PET for the Imaging of Androgen Receptor in Prostate and Breast Cancer: A Systematic Review

The aim of this systematic review is to provide a comprehensive overview of the role of fluoro-5α-dihydrotestosterone ([18F]-FDHT) for the in vivo imaging of androgen receptors (AR) through positron emission tomography (PET) in metastatic breast (mBC) and metastatic castration-resistant prostate cancer (mCRPC). Relevant studies published from 2013 up to May 2023 were selected by searching Scopus, PubMed and Web of Science. The selected imaging studies were analyzed using a modified version of the critical Appraisal Skills Programme (CASP). Eleven studies encompassing 321 patients were selected. Seven of the eleven selected papers included 266 subjects (82.2%) affected by mCRPC, while four encompassed 55 (17.2%) patients affected by mBC. [18F]-FDHT PET showed a satisfying test/retest reproducibility, and when compared to a histochemical analysis, it provided encouraging results for in vivo AR quantification both in mCRPC and mBC. [18F]-FDHT PET had a prognostic relevance in mCRPC patients submitted to AR-targeted therapy, while a clear association between [18F]-FDHT uptake and the bicalutamide response was not observed in women affected by AR-positive mBC. Further studies are needed to better define the role of [18F]-FDHT PET, alone or in combination with other tracers (i.e., [18F]-FDG/[18F]-FES), for patients' selection and monitoring during AR-targeted therapy, especially in the case of mBC.

Radionuclide-based theranostics - a promising strategy for lung cancer

PURPOSE

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

BACKGROUND

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

METHODS

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

CONCLUSIONS

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

PSMA-GCK01: A Generator-Based 99mTc/188Re Theranostic Ligand for the Prostate-Specific Membrane Antigen

Prostate-specific membrane antigen (PSMA) theranostics have been introduced with 68Ga and 177Lu, the most used radionuclides. However, 188Re is a well-known generator-based therapeutic nuclide that completes a theranostic tandem with 99mTc and may offer an interesting alternative to the currently used radionuclides. In the present work, we aimed at the development of a PSMA-targeted 99mTc/188Re theranostic tandem. Methods: The ligand HYNIC-iPSMA was chosen as the lead structure. Its HYNIC chelator has limitations for 188Re labeling and was replaced by mercaptoacetyltriserine to obtain PSMA-GCK01, a precursor for stable 99mTc and 188Re labeling. 99mTc-PSMA-GCK01 was used for in vitro evaluation of the ligand and comparison with 99mTc-EDDA/HYNIC-iPSMA. Planar imaging using 99mTc-PSMA-GCK01 and organ biodistribution with 188Re-PSMA-GCK01 were performed using LNCaP tumor-bearing mice. Finally, the theranostic tandem was applied for imaging and therapy in 3 prostate cancer patients in compassionate care. Results: Efficient radiolabeling of PSMA-GCK01 with both radionuclides was demonstrated. Cell-based assays with 99mTc-PSMA-GCK01 versus 99mTc-EDDA/HYNIC-iPSMA revealed comparable uptake characteristics. Planar imaging and organ distribution revealed good tumor uptake of both 99mTc-PSMA-GCK01 and 188Re-PSMA-GCK01 at 1 and 3 h after injection, with low uptake in nontarget organs. In patients, similar distribution patterns were observed for 99mTc-PSMA-GCK01 and 188Re-PSMA-GCK01 and in comparison with 177Lu-PSMA-617. Conclusion: The ligand PSMA-GCK01 labels stably with 99mTc and 188Re, both generator-based radionuclides, and thus provides access to on-demand labeling at reasonable costs. Preclinical evaluation of the compounds revealed favorable characteristics of the PSMA-targeted theranostic tandem. This result was confirmed by successful translation into first-in-humans application.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Head-to-Head Comparison between FDG and 11C-Methionine in Multiple Myeloma: A Systematic Review

The aim of this systematic review is to provide a comprehensive overview of the existing literature, comparing ¹⁸F-fluorodeoxyglucose (FDG) and ¹¹C-methionine (MET) for the imaging of multiple myeloma (MM) with positron emission computed tomography (PET/CT). Relevant studies published from 2013 up to March 2023 were selected by searching Scopus, PubMed, and Web of Science. Selected imaging studies were analyzed using a modified version of the critical Appraisal Skills Programme (CASP). Ten studies encompassing 335 patients were selected. On a patient-based analysis, MET sensitivity ranged between 75.6% and 100%, resulting higher than that measured for FDG (0-100%). MET outperformed FDG for the detection of focal lesions, diffuse bone marrow involvement and mixed patterns. PET-derived parameters resulted higher for MET than for FDG, with a strong correlation with clinical variables (e.g., monoclonal component and beta-2-microglobulin levels, bone marrow infiltration, etc.), although FDG maintained a prognostic impact on outcome prediction. When compared to other tracers or imaging modalities, MET showed stronger correlation and inter-observer agreement than FDG. Although biased by the small cohorts and requiring confirmation through multicenter studies, preliminary findings suggest that MET-PET should be preferred to FDG for PET imaging of MM, or alternatively used as a complementary imaging modality. Some issues, such as tracer availability and the role of MET with respect to other emerging tracers (i.e., ⁶⁸Ga-pentixafor, ¹⁸F-FACBC and ¹⁸F-FET), should be the topic of further investigations.

Role of Exendin-4 Functional Imaging in Diagnosis of Insulinoma: A Systematic Review

BACKGROUND

Insulinomas are the most common neuroendocrine neoplasms of the pancreas. Diagnosis is made through patient clinical presentation with hypoglycemia symptoms and imaging, such as EUS, CT, MRI, and functional imaging. Exendin-4 PET/CT (and SPECT/CT) is a new prominent radiotracer developed to image insulinomas. The aim of the study is to evaluate whether exendin-4 imaging is a useful tool in imaging for insulinoma patients when other imaging methods do not reach them.

METHODS

MEDLINE research conducted on PubMed, Scopus, and Web of Science gathered a total of 501 papers. Studies that evaluated exendin-4 SPECT and PET in insulinoma patients were screened and assessed through QUADAS-2 for risk of bias and applicability concerns' assessment. Sensitivity, specificity, and accuracy were reported when available.

RESULTS

A total of 13 studies were deemed eligible for a QUADAS 2 review. Studies included ranged from 2009 to 2022. The most-used tracer was ⁶⁸Ga-DOTA-exendin-4 in PET and ¹¹¹In-DTPA-exendin-4 in SPECT. Exendin-4 labeled with ⁹⁹mTc was also reported. The QUADAS-2 risk of bias assessment was overall low, with some unclear reports in the reference and index domains. Only two domains were at high risk of bias because of an explicated non-blind imaging review. Applicability concerns for bias were low in all domains. Reported sensitivities ranged from 95% to 100% and specificities from 20% to 100%.

CONCLUSIONS

exendin-4 imaging is a sensitive functional imaging tracer in both SPECT and PET applications, especially in suspicion of benign insulinomas located where endoscopic ultrasound cannot reach, being more sensitive than morfostructural imaging.

Engineering a modular 44Ti/44Sc generator: eluate evaluation in preclinical models and estimation of human radiation dosimetry

BACKGROUND

⁴⁴Sc/⁴⁷Sc is an attractive theranostic pair for targeted in vivo positron emission tomographic (PET) imaging and beta-particle treatment of cancer. The ⁴⁴Ti/⁴⁴Sc generator allows daily onsite production of this diagnostic isotope, which may provide an attractive alternative for PET facilities that lack in-house irradiation capabilities. Early animal and patient studies have demonstrated the utility of ⁴⁴Sc. In our current study, we built and evaluated a novel clinical-scale ⁴⁴Ti/⁴⁴Sc generator, explored the pharmacokinetic profiles of ⁴⁴ScCl₃, [⁴⁴Sc]-citrate and [⁴⁴Sc]-NODAGA (1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid) in naïve mice, and estimated the radiation burden of ⁴⁴ScCl₃ in humans.

METHODS

⁴⁴Ti/⁴⁴Sc (101.2 MBq) in 6 M HCl solution was utilized to assemble a modular ZR resin containing generator. After assembly, ⁴⁴Sc was eluted with 0.05 M HCl for further PET imaging and biodistribution studies in female Swiss Webster mice. Based on the biodistribution data, absorbed doses of ^44/47ScCl₃ in human adults were calculated for 18 organs and tissues using the IDAC-Dose software.

RESULTS

⁴⁴Ti in 6 M HCl was loaded onto the organic resin generator with a yield of 99.97%. After loading and initial stabilization, ⁴⁴ScCl₃ was eluted with 0.05 M HCl in typical yields of 82.9 ± 5.3% (N = 16), which was normalized to the estimated generator capacity. Estimated generator capacity was computed based on elution time interval and the total amount of ⁴⁴Ti loaded on the generator. Run in forward and reverse directions, the ⁴⁴Sc/⁴⁴Ti ratio from a primary column was significantly improved from 1038 ± 440 to 3557 ± 680 (Bq/Bq) when a secondary, replaceable, ZR resin cartridge was employed at the flow outlet. In vivo imaging and ex vivo distribution studies of the reversible modular generator for ⁴⁴ScCl₃, [⁴⁴Sc]-citrate and [⁴⁴Sc]-NODAGA show that free ⁴⁴Sc remained in the circulation significantly longer than the chelated ⁴⁴Sc. The dose estimation of ⁴⁴ScCl₃ reveals that the radiation burden is 0.146 mSv/MBq for a 70 kg adult male and 0.179 mSv/MBq for a 57 kg adult female. Liver, spleen and heart wall will receive the highest absorbed dose: 0.524, 0.502, and 0.303 mGy/MBq, respectively, for the adult male.

CONCLUSIONS

A clinical-scale ⁴⁴Ti/⁴⁴Sc generator system with a modular design was developed to supply ⁴⁴ScCl₃ in 0.05 M HCl, which is suitable for further radiolabeling and in vivo use. Our data demonstrated that free ⁴⁴ScCl₃ remained in the circulation for extended periods, which resulted in approximately 10 times greater radiation burden than stably chelated ⁴⁴Sc. Stable ⁴⁴Sc/⁴⁷Sc-complexation will be more favorable for in vivo use and for clinical utility.

A Machine Learning based model for a Dose Point Kernel calculation

PURPOSE

Absorbed dose calculation by kernel convolution requires the prior determination of dose point kernels (DPK). This study shows applications of machine learning to generate the DPKs for monoenergetic sources and a model to obtain DPKs for beta emitters.

METHODS

DPK for monoenergetic electron sources were calculated using the FLUKA Monte Carlo (MC) code for many materials of clinical interest and initial energies ranging from 10 to 3000 keV. Three machine learning (ML) algorithms were trained using the MC DPKs. Electron monoenergetic scaled DPKs (sDPKs) were used to assess the corresponding sDPKs for beta emitters typically used in nuclear medicine, which were compared against reference published data. Finally, the ML sDPK approach was applied to a patient-specific case calculating the dose voxel kernels (DVK) for a hepatic radioembolization treatment with \(^{90}\)Y.

RESULTS

The three trained machine learning models demonstrated a promising capacity to predict the sDPK for both monoenergetic emissions and beta emitters of clinical interest attaining differences lower than \(10%\) in the mean average percentage error (MAPE) as compared with previous studies. Furthermore, differences lower than \(7 %\) were obtained for the absorbed dose in patient-specific dosimetry comparing against full stochastic MC calculations.

CONCLUSION

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

Predicting Microenvironment in CXCR4- and FAP-Positive Solid Tumors-A Pan-Cancer Machine Learning Workflow for Theranostic Target Structures

(1) Background: C-X-C Motif Chemokine Receptor 4 (CXCR4) and Fibroblast Activation Protein Alpha (FAP) are promising theranostic targets. However, it is unclear whether CXCR4 and FAP positivity mark distinct microenvironments, especially in solid tumors. (2) Methods: Using Random Forest (RF) analysis, we searched for entity-independent mRNA and microRNA signatures related to CXCR4 and FAP overexpression in our pan-cancer cohort from The Cancer Genome Atlas (TCGA) database-representing n = 9242 specimens from 29 tumor entities. CXCR4- and FAP-positive samples were assessed via StringDB cluster analysis, EnrichR, Metascape, and Gene Set Enrichment Analysis (GSEA). Findings were validated via correlation analyses in n = 1541 tumor samples. TIMER2.0 analyzed the association of CXCR4 / FAP expression and infiltration levels of immune-related cells. (3) Results: We identified entity-independent CXCR4 and FAP gene signatures representative for the majority of solid cancers. While CXCR4 positivity marked an immune-related microenvironment, FAP overexpression highlighted an angiogenesis-associated niche. TIMER2.0 analysis confirmed characteristic infiltration levels of CD8+ cells for CXCR4-positive tumors and endothelial cells for FAP-positive tumors. (4) Conclusions: CXCR4- and FAP-directed PET imaging could provide a non-invasive decision aid for entity-agnostic treatment of microenvironment in solid malignancies. Moreover, this machine learning workflow can easily be transferred towards other theranostic targets.

Photorealistic three-dimensional visualization of fusion datasets: cinematic rendering of PET/CT

PURPOSE

Cinematic rendering (CR) is a method of photorealistic 3D visualization of volumetric imaging data. We applied this technique to fusion PET/CT data.

METHODS

Two recent PET/CT cases were selected, one each of prostate-specific membrane antigen (PSMA)-targeted ¹⁸F-DCFPyL, and somatostatin-receptor-targeted ⁶⁸ Ga-DOTATATE. Targeted radiotracers were selected in order to provide high-contrast images for this proof-of-principle study. Cinematic rendering was performed with an enhanced algorithm that incorporated internal lighting within the PET-avid organs and lesions to allow for a distinct visual signature.

RESULTS

The use of internal lighting for PET data provided CR of fused PET/CT scans. The interpreting radiologist must make judicious use of presets and cut planes in order to ensure important findings are not missed.

CONCLUSIONS

CR of PET/CT data provides a photorealistic means of visualizing complex fusion imaging datasets. Such visualizations may aid anatomic understanding for surgical or procedural applications, may improve teaching of trainees, and may allow improved communication with patients.

Key Factors to Attract More U.S. Diagnostic Radiology Residents into the Field of Nuclear Medicine and Molecular Imaging: A National Survey

RATIONALE AND OBJECTIVES

To understand the current state of radiology residents' exposure to nuclear medicine and molecular imaging (NM/MI), determine key factors that may attract more trainees into the field, and identify differentiating aspects between those specializing in NM/MI and those who are not.

MATERIALS AND METHODS

An anonymous web-based survey was sent to contacts at all diagnostic radiology residency programs in the United States for dissemination to their residents, collecting information about trainees' NM/MI exposure during residency and factors that may attract them to NM/MI.

RESULTS

A total of 198 trainees responded to the survey, 34 of whom plan on pursuing a career in NM/MI. Most trainees reported early exposure to NM/MI during residency; most (97.4%) reported ample exposure to general NM/MI and oncologic studies. Less than 3% of trainees reported adequate exposure to therapies, neurological applications, molecular imaging/research advances, and physics. Respondents reported a need for better quality education (38.9%) and exposure to mentors (28.8%) as ways to attract trainees to NM/MI. Routinely encountered clinical pathology was the most interesting for those specializing in NM/MI (29.4%), whereas lifestyle was the most attractive aspect of NM/MI for those not pursuing a career in the field (27.4%). NM/MI-associated research was the least attractive for those specializing in NM/MI (35.3%), while job market concerns was the least attractive aspect for those not specializing in NM/MI (37.2%). Trainees planning to specialize in NM/MI reported higher satisfaction with their orientation to NM/MI during their first clinical rotation compared to those who do not plan to specialize in the field (3.03/5.00 and 2.67/5.00, respectively, p = 0.04).

CONCLUSION

This survey highlights several factors that training programs and national societies can target to improve interest in NM/MI among radiology residents. We found that optimized education initiatives, including improved orientation to the field, increased mentoring, and career opportunities are essential levers for recruiting radiology trainees into the NM/MI workforce.

Lutetium-177 Radiopharmeceutical Therapy Extravasation Lessons Learned

Lutetium-177 ( 177 Lu) dotatate has been offered at Fox Chase Cancer Center since 2017 as part of a clinical trial and then in 2018 as a commercially available cancer therapy, and we thought we were prepared for most 177 Lu issues by the fall of 2020. A single phone call identified that the Radiation Safety Department had not been prepared to address extravasations. Fortunately for the patient and Radiation Safety, the 177 Lu therapies are administered by an infusion nurse and Fox Chase Cancer Center has a robust infusion center. The expertise of our infusion center team helped to quickly identify specific mitigation efforts to employ. A team of radiation safety and diagnostic medical physicists worked together to estimate a tissue dose. Research was also started with the aim of identifying therapeutic 177 Lu extravasations as early as possible. The lessons we learned and plans for future early identification of 177 Lu dotatate extravasations are the basis of this paper.

Rechallenge With Additional Doses of 177 Lu-DOTATOC After Failure of Maintenance Therapy With Cold Somatostatin Analogs

ABSTRACT

Here, we report a case of a 52-year-old woman with a well-differentiated, metastasized neuroendocrine tumor (NET G1) of the duodenum. Initial imaging with 68 Ga-DOTATOC revealed multiple sites of disease with intense uptake. Peptide receptor radionuclide therapy (PRRT) with 177 Lu-DOTATOC induced partial remission. Treatment was then switched to cold somatostatin analog as a maintenance therapy. After 2 years of follow-up, progressive disease with multiple lesions in the skeleton was noted. Given the initial response to PRRT, a rechallenge with another 2 cycles of PRRT were given, and the patient had an excellent response to treatment, in particular in the skeleton.

ASTRO's Framework for Radiopharmaceutical Therapy Curriculum Development for Trainees

In 2017, the American Society for Radiation Oncology (ASTRO) board of directors prioritized radiopharmaceutical therapy (RPT) as a leading area for new therapeutic development, and the ASTRO RPT workgroup was created. Herein, the workgroup has developed a framework for RPT curriculum development upon which education leaders can build to integrate this modality into radiation oncology resident education. Through this effort, the workgroup aims to provide a guide to ensure robust training in an emerging therapeutic area within the context of existing radiation oncology training in radiation biology, medical physics, and clinical radiation oncology. The framework first determines the core RPT knowledge required to select patients, prescribe, safely administer, and manage related adverse events. Then, it defines the most important topics for preparing residents for clinical RPT planning and delivery. This framework is designed as a tool to supplement the current training that exists for radiation oncology residents. The final document was approved by the ASTRO board of directors in the fall of 2021.

Molecular imaging in oncology: Current impact and future directions

The authors define molecular imaging, according to the Society of Nuclear Medicine and Molecular Imaging, as the visualization, characterization, and measurement of biological processes at the molecular and cellular levels in humans and other living systems. Although practiced for many years clinically in nuclear medicine, expansion to other imaging modalities began roughly 25 years ago and has accelerated since. That acceleration derives from the continual appearance of new and highly relevant animal models of human disease, increasingly sensitive imaging devices, high-throughput methods to discover and optimize affinity agents to key cellular targets, new ways to manipulate genetic material, and expanded use of cloud computing. Greater interest by scientists in allied fields, such as chemistry, biomedical engineering, and immunology, as well as increased attention by the pharmaceutical industry, have likewise contributed to the boom in activity in recent years. Whereas researchers and clinicians have applied molecular imaging to a variety of physiologic processes and disease states, here, the authors focus on oncology, arguably where it has made its greatest impact. The main purpose of imaging in oncology is early detection to enable interception if not prevention of full-blown disease, such as the appearance of metastases. Because biochemical changes occur before changes in anatomy, molecular imaging-particularly when combined with liquid biopsy for screening purposes-promises especially early localization of disease for optimum management. Here, the authors introduce the ways and indications in which molecular imaging can be undertaken, the tools used and under development, and near-term challenges and opportunities in oncology.

A multimodal nanoparticles‐based theranostic method and system

We propose a nanoparticles‐based system for the early detection of tumors, treatment under real‐time feedback, and monitoring. The building blocks of the system comprise a few modalities that are integrated into one powerful system which can operate at the patient's bedside in an outpatient clinic setting. The method relies on the unique characteristics of superparamagnetic nanoparticles. It takes advantage of their ability to produce acoustical signals under alternating magnetic fields (AMFs) and to produce heat under these same AMFs with different parameters. It utilizes the nanoparticles' coating for specific binding. The manuscript describes the various parts of this method for localization, source separation, confined heat elevation, triggering of cell death, and monitoring the response to treatment through fluorescence signaling. The entire system continues to evolve into a minimally invasive trans‐endoscopic set‐up.

This article is categorized under:

Diagnostic Tools > In Vivo Nanodiagnostics and Imaging

Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease

177 Lu-PSMA radioligand therapy effectiveness in metastatic castration-resistant prostate cancer: An updated systematic review and meta-analysis

BACKGROUND

An updated systematic review and meta-analysis of relevant studies to evaluate the effectiveness of prostate-specific membrane antigen (PSMA)-targeted endoradiotherapy/radioligand therapy (PRLT) in castration resistant prostate cancer (CRPC).

METHODS

A systematic search was performed in July 2020 using PubMed/Medline database to update our prior systematic review. The search was limited to papers published from 2019 to June 2020. A total of 472 papers were reviewed. The studied parameters included pooled proportion of patients showing any or ≥50% prostate-specific antigen (PSA) decline after PRLT. Survival effects of PRLT were assessed based on pooled hazard ratios (HRs) of the overall survival (OS) according to any PSA as well as ≥50% PSA decline after PRLT. Response to therapy based on ≥50% PSA decrease after PRLT versus controls was evaluated using Mantel-Haenszel random effect meta-analysis. All p values < 0.05 were considered as statistically significant.

RESULTS

A total of 45 publications were added to the prior 24 studies. 69 papers with total of 4157 patients were included for meta-analysis. Meta-analysis of the two recent randomized controlled trials showed that patients treated with ¹⁷⁷ Lu-PSMA 617 had a significantly higher response to therapy compared to controls based on ≥50% PSA decrease. Meta-analysis of the HRs of OS according to any PSA decline and ≥50% PSA decline showed survival prolongation after PRLT.

CONCLUSIONS

PRLT results in higher proportion of patients responding to therapy based on ≥50% PSA decline compared to controls. Any PSA decline and ≥50% PSA decline showed survival prolongation after PRLT.

ADVANCES IN KNOWLEDGE

This is the first meta-analysis to aggregate the recent randomized controlled trials of PRLT which shows CRPC patients had a higher response to therapy after PRLT compared to controls.

EANM dosimetry committee recommendations for dosimetry of 177Lu-labelled somatostatin-receptor- and PSMA-targeting ligands

The purpose of the EANM Dosimetry Committee is to provide recommendations and guidance to scientists and clinicians on patient-specific dosimetry. Radiopharmaceuticals labelled with lutetium-177 (177Lu) are increasingly used for therapeutic applications, in particular for the treatment of metastatic neuroendocrine tumours using ligands for somatostatin receptors and prostate adenocarcinoma with small-molecule PSMA-targeting ligands. This paper provides an overview of reported dosimetry data for these therapies and summarises current knowledge about radiation-induced side effects on normal tissues and dose-effect relationships for tumours. Dosimetry methods and data are summarised for kidneys, bone marrow, salivary glands, lacrimal glands, pituitary glands, tumours, and the skin in case of radiopharmaceutical extravasation. Where applicable, taking into account the present status of the field and recent evidence in the literature, guidance is provided. The purpose of these recommendations is to encourage the practice of patient-specific dosimetry in therapy with 177Lu-labelled compounds. The proposed methods should be within the scope of centres offering therapy with 177Lu-labelled ligands for somatostatin receptors or small-molecule PSMA.

Absolute Quantification in Diagnostic SPECT/CT: The Phantom Premise

The application of absolute quantification in SPECT/CT has seen increased interest in the context of radionuclide therapies where patient-specific dosimetry is a requirement within the European Union (EU) legislation. However, the translation of this technique to diagnostic nuclear medicine outside this setting is rather slow. Clinical research has, in some examples, already shown an association between imaging metrics and clinical diagnosis, but the applications, in general, lack proper validation because of the absence of a ground truth measurement. Meanwhile, additive manufacturing or 3D printing has seen rapid improvements, increasing its uptake in medical imaging. Three-dimensional printed phantoms have already made a significant impact on quantitative imaging, a trend that is likely to increase in the future. In this review, we summarize the data of recent literature to underpin our premise that the validation of diagnostic applications in nuclear medicine using application-specific phantoms is within reach given the current state-of-the-art in additive manufacturing or 3D printing.

Dual-Modality PET-SPECT Image-Guided Pretargeting Delivery in HER2(+) Breast Cancer Models

Pretargeted drug delivery has been explored for decades as a promising approach in cancer therapy. An image-guided pretargeting strategy significantly enhances the intrinsic advantages of this approach since imaging the pretargeting step can be used for diagnostic purposes, while imaging of the drug delivery step can be utilized to evaluate drug distribution and assess therapeutic response. A trastuzumab (Tz)-based HER2 pretargeting component (Tz-TCO-[89Zr-DFO]) was developed by conjugating with trans-cyclooctene (TCO) bioorthogonal click chemistry functional groups and deferoxamine (DFO) to enable radiolabeling with a 89Zr PET tracer. The drug delivery component (HSA-DM1-Tt-[99mTc-HyNic]) was developed by conjugating human serum albumin (HSA) with mertansine (DM1), tetrazine (Tt) functional groups, and a HyNic chelator and radiolabeling with 99mTc. For ex vivo biodistribution studies, pretargeting and delivery components (without drug) were administered subsequently to mice bearing human HER2(+) breast cancer xenografts, and a high tumor uptake of Tz-TCO-[89Zr-DFO] (26.4% ID/g) and HSA-Tt-[99mTc-HyNic] (4.6% ID/g) was detected at 24 h postinjection. In vivo treatment studies were performed in the same HER2(+) breast cancer model using PET-SPECT image guidance. The increased tumor uptake of the pretargeting and drug delivery components was detected by PET-CT and SPECT-CT, respectively. The study showed a significant 92% reduction of the relative tumor volume in treated mice (RTV = 0.08 in 26 days), compared to the untreated control mice (RTV = 1.78 in 11 days) and to mice treated with only HSA-DM1-Tt-[99mTc-HyNic] (RTV = 1.88 in 16 days). Multimodality PET-SPECT image-guided and pretargeted drug delivery can be utilized to maximize efficacy, predict therapeutic response, and minimize systemic toxicity.

Synthetic Pept-Ins as a Generic Amyloid-Like Aggregation-Based Platform for In Vivo PET Imaging of Intracellular Targets

Amyloid-like aggregation of proteins is induced by short amyloidogenic sequence segments within a specific protein sequence resulting in self-assembly into β-sheets. We recently validated a technology platform in which synthetic amyloid peptides ("Pept-ins") containing a specific aggregation-prone region (APR) are used to induce specific functional knockdown of the target protein from which the APR was derived, including bacterial, viral, and mammalian cell proteins. In this work, we investigated if Pept-ins can be used as vector probes for in vivo Positron Emission Tomography (PET) imaging of intracellular targets. The radiolabeled Pept-ins [⁶⁸Ga]Ga-NODAGA-PEG₄-vascin (targeting VEGFR2) and [⁶⁸Ga]Ga-NODAGA-PEG₂-P2 (targeting E. coli) were evaluated as PET probes. The Pept-in based radiotracers were cross-validated in a murine tumor and muscle infection model, respectively, and were found to combine target specificity with favorable in vivo pharmacokinetics. When the amyloidogenicity of the interacting region of the peptide is suppressed by mutation, cellular uptake and in vivo accumulation are abolished, highlighting the importance of the specific design of synthetic Pept-ins. The ubiquity of target-specific amyloidogenic sequence segments in natural proteins, the straightforward sequence-based design of the Pept-in probes, and their spontaneous internalization by cells suggest that Pept-ins may constitute a generic platform for in vivo PET imaging of intracellular targets.

The application of theranostics in different stages of prostate cancer

Despite the remarkable achievements in treating metastatic prostate cancer over the last two decades, castrate-resistant status is still considered the lethal stage of the disease. Theranostics combines a targeting compound (ligand) with a therapeutic radioisotope (radioactive particle) injected into the blood to target the cancer cells. The most studied radioligand is ¹⁷⁷Lu-PSMA-617, which targets PSMA, a protein found in prostate cancer cells. This new approach has shown promising results in treating metastatic castration-resistant prostate cancer. Currently, many trials are using PSMA-targeting radioligands in combination with conventional therapies in advanced prostate cancer or even in the earlier stages of the disease. Other preclinical trials are exploring the possibility of using newer ligands or radioisotopes to treat prostate cancer to increase the specificity and efficacy of this treatment.

Theranostics in Oncology-Thriving, Now More than Ever

Tracing its roots back to the 1940s, theranostics in nuclear oncology has proved successful mainly due to the beneficial effects of image-guided therapeutic concepts for patients afflicted with a variety of different cancers. The majority of these treatments are not only characterized by substantial prolongation of progression-free and overall survival, but are also generally safe, rendering theranostic agents as an attractive treatment option in various clinical scenarios in oncology. In this Special Issue Novel Theranostic Agents, nine original articles from around the globe provide further evidence on the use of the theranostic concept for neuroendocrine neoplasm (NEN), prostate cancer (PC), meningioma, and neuroblastoma. The investigated diagnostic and therapeutic radiotracers target not only established structures, such as somatostatin receptor, prostate-specific membrane antigen or norepinephrine transporter, but also recently emerging targets such as the C-X-C motif chemokine receptor 4. Moreover, the presented original articles also combine the concept of theranostics with in-depth read-out techniques such as radiomics or novel reconstruction algorithms on pretherapeutic scans, e.g., for outcome prediction. Even 80 years after its initial clinical introduction, theranostics in oncology continues to thrive, now more than ever.

Quantitative PET in the 2020s: a roadmap

Positron emission tomography (PET) plays an increasingly important role in research and clinical applications, catalysed by remarkable technical advances and a growing appreciation of the need for reliable, sensitive biomarkers of human function in health and disease. Over the last 30 years, a large amount of the physics and engineering effort in PET has been motivated by the dominant clinical application during that period, oncology. This has led to important developments such as PET/CT, whole-body PET, 3D PET, accelerated statistical image reconstruction, and time-of-flight PET. Despite impressive improvements in image quality as a result of these advances, the emphasis on static, semi-quantitative 'hot spot' imaging for oncologic applications has meant that the capability of PET to quantify biologically relevant parameters based on tracer kinetics has not been fully exploited. More recent advances, such as PET/MR and total-body PET, have opened up the ability to address a vast range of new research questions, from which a future expansion of applications and radiotracers appears highly likely. Many of these new applications and tracers will, at least initially, require quantitative analyses that more fully exploit the exquisite sensitivity of PET and the tracer principle on which it is based. It is also expected that they will require more sophisticated quantitative analysis methods than those that are currently available. At the same time, artificial intelligence is revolutionizing data analysis and impacting the relationship between the statistical quality of the acquired data and the information we can extract from the data. In this roadmap, leaders of the key sub-disciplines of the field identify the challenges and opportunities to be addressed over the next ten years that will enable PET to realise its full quantitative potential, initially in research laboratories and, ultimately, in clinical practice.

Separation of no-carrier-added 71,72As from 46 MeV alpha particle irradiated gallium oxide target

No-carrier-added (NCA) 71,72As radionuclides were produced by irradiating gallium oxide target by 46 MeV α-particles. NCA 71,72As was separated from the target matrix by liquid-liquid extraction (LLX) using trioctyl amine (TOA) and tricaprylmethylammonium chloride (aliquat-336) diluted in cyclohexane. The bulk gallium was quantitatively extracted into the organic phase leaving 71,72As in the aqueous phase. Complete separation was observed at 3 M HCl + 0.1 M TOA and 2 M HCl + 0.01 M aliquat-336.

Theranostics: The Role of Quantitative Nuclear Medicine Imaging

Theranostics is a precision medicine discipline that integrates diagnostic nuclear medicine imaging with radionuclide therapy in a manner that provides both a tumor phenotype and personalized therapy to patients with cancer using radiopharmaceuticals aimed at the same target-specific biological pathway or receptor. The aim of quantitative nuclear medicine imaging is to plan the alpha or beta-emitting therapy based on an accurate 3-dimensional representation of the in-vivo distribution of radioactivity concentration within the tumor and normal organs/tissues in a noninvasive manner. In general, imaging may be either based on positron emission tomography (PET) or single photon emission computed tomography (SPECT) invariably in combination with X-ray CT (PET/CT; SPECT/CT) or, to a much lesser extent, MRI. PET and SPECT differ in terms of the radionuclides and physical processes that give rise to the emission of high energy photons, as well as the sets of technologies involved in their detection. Using a variety of standardized quantitative parameters, system calibration, patient preparation, imaging acquisition and reconstruction protocols, and image analysis protocols, an accurate quantification of the tracer distribution can be obtained, which helps prescribe the therapeutic dose for each patient.

Recent advances in theranostic polymeric nanoparticles for cancer treatment: A review

Nanotheranostics is fast-growing pharmaceutical technology for simultaneously monitoring drug release and its distribution, and to evaluate the real time therapeutic efficacy through a single nanoscale for treatment and diagnosis of deadly disease such as cancers. In recent two decades, biodegradable polymers have been discovered as important carriers to accommodate therapeutic and medical imaging agents to facilitate construction of multi-modal formulations. In this review, we summarize various multifunctional polymeric nano-sized formulations such as polymer-based super paramagnetic nanoparticles, ultrasound-triggered polymeric nanoparticles, polymeric nanoparticles bearing radionuclides, and fluorescent polymeric nano-sized formulations for purpose of theranostics. The use of such multi-modal nano-sized formulations for near future clinical trials can assist clinicians to predict therapeutic properties (for instance, depending upon the quantity of drug accumulated at the cancerous site) and observed the progress of tumor growth in patients, thus improving tailored medicines.