Initial Experience with 68Ga-FAP-2286 PET Imaging in Patients with Urothelial Cancer

Emerging Paradigms in Genitourinary Cancers: Integrating Molecular Imaging, Hypoxia-Inducible Factor-Targeted Therapies, and Antibody-Drug Conjugates in Renal Cell and Urothelial Carcinomas

Novel approaches in molecular imaging and targeted therapeutics are transforming the management of renal cell carcinoma (RCC) and urothelial carcinoma (UC). This review focuses on three key areas of innovation: molecular imaging, hypoxia-inducible factor-2α (HIF-2α) inhibition, and antibody-drug conjugates (ADCs). In molecular imaging, prostate-specific membrane antigen positron emission tomography/computed tomography has shown promise in RCC, while novel tracers targeting carbonic anhydrase IX and nectin-4 are emerging for RCC and UC, respectively. These approaches may enable better characterization of disease and treatment response monitoring. HIF-2α inhibition represents a breakthrough in targeting the fundamental pathobiology of clear cell RCC, with belzutifan demonstrating significant clinical benefit in both von Hippel-Lindau disease and sporadic RCC. Next-generation HIF-2α inhibitors, including casdatifan, show promising early clinical results with distinct pharmacologic properties. ADCs have become a cornerstone of UC treatment, with enfortumab vedotin plus pembrolizumab now approved as first-line therapy. Multiple human epidermal growth factor receptor 2 (HER2)-directed ADCs have shown efficacy in HER2-expressing UC, including trastuzumab deruxtecan, which recently received tumor-agnostic approval. While ADC development in RCC faces unique challenges, novel approaches including immunostimulatory payloads and bispecific antibodies are being explored. The integration of these advances in molecular imaging and therapeutics offers opportunities for more personalized treatment approaches in RCC and UC.

68Ga-FAPI and 18F-FAPI PET/CT for detection of nodal metastases prior radical cystectomy in high-risk urothelial carcinoma patients

INTRODUCTION

To determine the best therapeutic strategy for muscle-invasive bladder cancer (BC), the accuracy of lymph node staging is of paramount importance. However, diagnostic performance of conventional computed tomography in BC prior to radical cystectomy (RC) remains unsatisfactory. There is an increased interest in evaluating 18F-FAPI PET/CT for hybrid imaging due to their logistical advantages compared to [68Ga]Ga-based FAPI tracers in clinical routine. Recently, the potential diagnostic value of [68Ga]Ga-FAPI- 46 PET/CT was demonstrated in BC. Thus, we aimed to examine the diagnostic performance of [18F]F-FAPI- 74 and [68Ga]Ga-FAPI- 46 PET/CT for preoperative evaluation of locoregional lymph node metastases.

METHODS

Fifty-one patients underwent FAPI PET/CT with either [68Ga]Ga-FAPI- 46 (n = 23) or [18F]F-FAPI- 74 (n = 28) prior to RC and PLND. SUVmax, SUVmean and the ratio between the SUVmax of lymph nodes and the SUVmean of the background (SUVmax_lymph node/SUVmean_background) were assessed. Additionally, short axis diameter (SAD) for a representative lymph node were documented in each lymph node region (n = 123) and compared to histopathological findings. Each scan was interpreted visually and quantitatively. ROC-analyses were performed to determine cut-off values with highest diagnostic accuracy.

RESULTS

20/123 (16.3%) lymph node regions showed UC lymph node metastases. Histopathologically positive lymph nodes were associated with a significantly higher FAPI uptake compared to negative lymph nodes regarding SUVmax, SUVmean values and SUVmax_lymph node/SUVmean_background ratios. Visual analysis based on FAPI uptake showed a sensitivity and specificity, PPV and NPV of 63.6%, 95.8%, 77.7%, and 92.0% for [68Ga]Ga-FAPI- 46 and 55.5%, 98.1%, 83.3%, and 93.1% for [18F]F-FAPI- 74, respectively. ROC analysis revealed an optimal cut-off for SUVmax, SUVmean and SUVmax_lymph node/SUVmean_background of 1.35, 1.20 and 5.95 for [68Ga]Ga-FAPI- 46 and 1.55, 1.25 and 4.15 for [18F]F-FAPI- 74 to discriminate between histopathologically proven lymph node metastases and non-malignant lymph nodes resulting for example using SUVmax in a sensitivity and specificity, PPV and NPV of 81.8%, 89.5%, 64.2%, 95.5% for [68Ga]Ga-FAPI- 46 and 100%, 81.8%, 47.3%, 100% for [18F]F-FAPI- 74, respectively. CT visual analysis of locoregional lymph nodes showed a sensitivity, specificity, PPV and NPV of 30.0%, 97.0%, 66.6% and 87.7%, respectively. ROC analysis regarding SAD revealed a cutoff at 0.8 cm with a sensitivity, specificity, PPV and NPV of 75.0%, 84.4%, 48.3%, 94.5%, respectively.

CONCLUSION

Overall, FAPI PET imaging shows a significantly higher sensitivity than CT analysis for detection of locoregional lymph node metastases in UC. [18F]F-FAPI- 74 demonstrates a comparable diagnostic performance compared to [68Ga]Ga-FAPI- 46. Of note, the quantitative analysis with a pre-defined SUVmax as well as SUVmean values, and SUVmax_lymph node/SUVmean_background ratio-based cut-offs provided a higher sensitivity compared to visual assessment.

A Look to the Future: Potential Theranostic Applications in Head and Neck Tumors

Theranostics, the practice of using a diagnostic radiopharmaceutical to guide radiotherapy with a chemically identical (or nearly identical) therapeutic radiopharmaceutical, is an exciting new field under development within the auspices of nuclear medicine. We aim to provide a narrative review of the areas of theranostics use and development which are occurring specifically in the head and neck, with attention to the therapeutic use of existing diagnostically used radiotracers such as agents that target prostate-specific membrane antigen (PSMA) and somatostatin receptors (e.g., DOTATATE derivatives), as well as developing classes of radiotracers such as those targeting fibrinogen-activating protein (FAP) and carbonic anhydrase IX (CAIX), as well as new meta-iodo-benzylguanidine (MIBG) derivatives. Most of those agents are still at the preclinical or early clinical stages of development, but as this is an emerging field, we aim to both outline current progress and suggest future directions.

Nuclear Medicine and Molecular Imaging in Urothelial Cancer: Current Status and Future Directions

Background: The role of molecular imaging in urothelial cancer is less defined than other cancers, and its utility remains controversial due to limitations such as high urinary tracer excretion, complicating primary tumour assessment in the bladder and upper urinary tract. This review explores the current landscape of PET imaging in the clinical management of urothelial cancer, with a special emphasis on potential future advancements including emerging novel non-18F FDG PET agents, PET radiopharmaceuticals, and PET-MRI applications. Methods: We conducted a comprehensive literature search in the PubMed database, using keywords such as "PET", "PET-CT", "PET-MRI", "FDG PET", "Urothelial Cancer", and "Theranostics". Studies were screened for relevance, focusing on imaging modalities and advances in PET tracers for urothelial carcinoma. Non-English language, off-topic papers, and case reports were excluded, resulting in 80 articles being selected for discussion. Results: 18F FDG PET-CT has demonstrated superior sensitivity over conventional imaging, such as contrast-enhanced CT and MRI, for detecting lymph node metastasis and distant disease. Despite these advantages, FDG PET-CT is limited for T-staging of primary urothelial tumours due to high urinary excretion of the tracer. Emerging evidence supports the role of PETC-CT in assessing response to neoadjuvant chemotherapy and in identifying recurrence, with a high diagnostic accuracy reported in several studies. Novel PET tracers, such as 68Ga-labelled FAPI, have shown promising results in targeting cancer-associated fibroblasts, providing higher tumour-to-background ratios and detecting lesions missed by traditional imaging. Antibody-based PET tracers, like those targeting Nectin-4, CAIX, and uPAR, are under investigation for their diagnostic and theranostic potential, and initial studies indicate that these agents may offer advantages over conventional imaging and FDG PET. Conclusions: Molecular imaging is a rapidly evolving field in urothelial cancer, offering improved diagnostic and prognostic capabilities. While 18F FDG PET-CT has shown utility in staging, further prospective research is needed to establish and refine standardised protocols and validate new tracers. Advances in theranostics and precision imaging may revolutionise urothelial cancer management, enhancing the ability to tailor treatments and improve patient outcomes.

Is There a Role for FAPI PET in Urological Cancers?

This work aims to investigate the utility of positron emission tomography/computed tomography (PET/CT) with fibroblast activation protein inhibitors (FAPI) in urological neoplasms, including prostate cancer, urothelial carcinoma, and renal cell carcinoma. Although the available data are very preliminary, FAPI PET showed potential for detecting primary prostate cancer with low prostate-specific membrane antigen expression, while prostate-specific membrane antigen PET/CT outperformed FAPI PET/CT in detecting biochemical recurrence. In urothelial carcinoma, FAPI PET/CT demonstrated increased detection rates compared with deoxy-2-[18F]fluoro-D-glucose PET/CT, in particular in small lymph node metastases, whose identification is still an unmet clinical need. Limited data are available for renal cell carcinoma. In conclusion, FAPI PET emerges as a promising imaging modality for urological neoplasms, in particular bladder cancer. Further research is warranted to establish its role in guiding therapeutic decisions and as a potential novel theranostic agent.

The cutting edge: Promising oncology radiotracers in clinical development

Molecular imaging moves forward with the development of new imaging agents, and among these are new radiotracers for nuclear medicine applications, particularly positron emission tomography (PET). A number of new targets are becoming accessible for use in oncologic applications. In this review, major new radiotracers in clinical development are discussed. Prominent among these is the family of fibroblast-activation protein-targeted agents that interact with the tumor microenvironment and may show superiority to 2-deoxy-2-[18F]fluoro-d-glucose in a subset of different tumor histologies. Additionally, carbonic anhydrase IX (CAIX) inhibitors are directed at clear cell renal cell carcinoma, which has long lacked an effective PET imaging agent. Those CAIX agents may also have utility in hypoxic tumors. Pentixafor, which binds to a transmembrane receptor, may similarly allow for visualization by PET of low-grade lymphomas, as well as being a second agent for multiple myeloma that opens theranostic possibilities. There are new adrenergic agents aimed at providing a PET-visible replacement to the single-photon-emitting radiotracer meta-[123I]iodobenzylguanidine (MIBG). Finally, in response to a major development in oncologic chemotherapy, there are new radiotracers targeted at assessing the suitability or use of immunotherapeutic agents. All of these and the existing evidence for their utility are discussed.

Comparison of 68Ga-FAP-2286 and 18F-FDG PET/CT in the diagnosis of advanced lung cancer

Purpose

The 68Ga/177Lu-FAP-2286 is a newly developed tumor imaging agent that shows potential for visualizing and treating tumor stroma. The objective of this research was to evaluate the effectiveness of 68Ga-FAP-2286 PET/CT and 18F-FDG PET/CT in diagnosing advanced lung cancer.

Methods

In this prospective study, patients with lung cancer who underwent 68Ga-FAP-2286 and 18F-FDG PET/CT examinations between September 2022 and June 2023 were analyzed. Lesion uptake was converted to SUVmax. A paired T-test was used to compare the SUVmax, and the number of positive lesions detected by the two methods was recorded.

Results

In total, 31 participants (median age: 56 years) were assessed. The uptake of 68Ga-FAP-2286 was significantly higher than that of 18F-FDG in primary lesions (9.90 ± 5.61 vs. 6.09 ± 2.84, respectively, P < 0.001), lymph nodes (7.95 ± 2.75 vs. 5.55 ± 1.59, respectively, P=0.01), and bone metastases (7.74 ± 3.72 vs. 5.66 ± 3.55, respectively, P=0.04). Furthermore, the detection sensitivity of lymph nodes using 68Ga-FAP-2286 PET/CT was superior to that with 18F-FDG PET/CT [100% (137/137) vs. 78.8% (108/137), respectively], as well as for bone metastases [100% (384/384) vs. 68.5% (263/384), respectively]. However, the detection sensitivity for primary tumors using both modalities was comparable [100% (13/13) for both].

Conclusion

Compared to 18F-FDG PET/CT, 68Ga-FAP-2286 PET/CT demonstrated better lesion detection capabilities for lung cancer, particularly in lymph nodes and bone metastases, providing compelling imaging evidence for the efficacy of 177Lu-FAP-2286 treatment.

Radiomolecular Theranostics With Fibroblast-Activation-Protein Inhibitors and Peptides

The advancement of theranostics, which combines therapeutic and diagnostic capabilities in oncology, has significantly impacted cancer management. This review explores fibroblast activation protein (FAP) expression in the tumor microenvironment (TME) and its association with various malignancies, highlighting its potential as a theranostic marker for PET/CT imaging using FAP-targeted tracers and for FAP-targeted radiopharmaceutical therapy. We examine the development and clinical applications of FAP inhibitors (FAPIs) and peptides, providing insights into their diagnostic accuracy, initial therapeutic efficacy, and clinical impact across diverse cancer types, as well as the synthesis of novel FAP-targeted ligands. This review aims to showcase the promising outcomes and challenges in integrating FAP-targeted approaches into cancer management.

Diagnostic and Therapeutic Application of Fibroblast Activation Protein Inhibitors in Oncologic and Nononcologic Diseases

ABSTRACT

Fibroblast activation protein inhibitor positron emission tomography (PET) has gained interest for its ability to demonstrate uptake in a diverse range of tumors. Its molecular target, fibroblast activation protein, is expressed in cancer-associated fibroblasts, a major cell type in tumor microenvironment that surrounds various types of cancers. Although existing literature on FAPI PET is largely from single-center studies and case reports, initial findings show promise for some cancer types demonstrating improved imaging when compared with the widely used 18F-fludeoxyglucose PET for oncologic imaging. As we expand our knowledge of the utility of FAPI PET, accurate understanding of noncancerous uptake seen on FAPI PET is crucial for accurate evaluation. In this review, we summarize potential diagnostic and therapeutic applications of radiolabeled FAP inhibitors in oncological and nononcological disease processes.

Recent Progress in Peptide-Based Molecular Probes for Disease Bioimaging

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