Dual targeting PET tracer [68Ga]Ga-FAPI-RGD in patients with lung neoplasms: a pilot exploratory study

Development of a Radiogallium-Labeled Heterodivalent Imaging Probe Targeting Negative Charges and Integrin on the Surface of Cancer Cell Membranes

Radiopharmaceuticals targeting tumor-specific environments are powerful tools for cancer diagnosis and treatment. We previously demonstrated the considerable high tumor uptake of the cationic amphiphilic peptide, 67Ga-NOTA-KV6, in vivo. However, because this radioligand shows a relatively rapid clearance from the tumor over time, further structural optimization is necessary. In this study, to enhance tumor accumulation and retention, we synthesized and evaluated a heterobivalent radiogallium-labeled radiotracer, [67Ga]Ga-DOTA-KV6-Mal-c(RGDyK) ([67Ga]6a), fusing the KV6 peptide targeting negatively charged sites on the cancer cell membrane and cyclic RGD peptide targeting integrin αvβ3 on the cancer cell membrane. Cellular uptake study revealed high accumulation of [67Ga]6a in integrin αvβ3-expressing U-87MG cancer cells, but uptake was significantly inhibited in the presence of an excess of the cyclic RGD peptide, c(RGDyK) (1). Peptide 6a exhibited integrin αvβ3-binding affinity comparable to those of RGD peptides 1 and DOTA-Mal-c(RGDyK) (8). In vivo biodistribution studies of U-87MG tumor-bearing mice revealed that [67Ga]6a exhibited better accumulation and retention in tumor tissues than [67Ga]Ga-DOTA-KV6-Mal-Et ([67Ga]6b; without the RGD peptide motif) and [67Ga]Ga-DOTA-Mal-c(RGDyK) ([67Ga]9; without the KV6 peptide motif). Single-photon emission computed tomography analysis also revealed high signals of [67Ga]6a in tumor tissues, which were significantly blocked in the presence of excess peptide 1. Although reducing radiotracer accumulation in nontumor tissues, such as the kidneys, remains a challenge, our developed approach exhibits potential to enhance the selectivity and retention of radiopharmaceuticals in tumor tissues.

Preparation and evaluation of a novel albumin-binding heterodimer therapeutic radiopharmaceutical with remarkable tumor accumulation and retention

The intricate heterogeneity exhibited across diverse tumor types and the inconsistent expression levels of a specific receptor within tumors make it difficult for single-targeting radiotracers to meet clinical needs. The combination of "dual-targeting" and "albumin-binding" strategies can overcome it and effectively improve tumor uptake and retention of radiopharmaceuticals, thereby enhancing the effect of tumor theranostics. In this study, an albumin binder-conjugated heterodimeric precursor L21 targeting integrin αvβ3 and CD13 was successfully developed and labeled with 68Ga and 177Lu to evaluate therapeutic potential in BxPC-3 xenograft mice. In vitro, [68Ga]Ga-L21 and [177Lu]Lu-L21 exhibited excellent radiochemical stability in phosphate buffered saline (PBS) or fetal bovine serum (FBS) at 37 °C for 5 h. Compared to [68Ga]Ga-L00 without albumin binder, the introduction of albumin binder did not substantially alter the water solubility of [68Ga]Ga-L21, but substantially increased its affinity for serum albumin in FBS. In vivo, [68Ga]Ga-L21 showed significantly higher tumor uptake and longer tumor retention time than [68Ga]Ga-L00 (0.70 ± 0.06 standardized uptake value [SUV] vs. 0.33 ± 0.02 SUV at 3 h, P = 0.0004). [177Lu]Lu-L21 exhibited excellent tumor uptake, tumor-to-nontumor ratios and tumor retention, with tumor uptake keeping 2.79 ± 0.30 percentage of injected radioactive dose per gram of tissue (%ID/g) even at 96 h post-injection. Biodistribution results of [177Lu]Lu-L21 were consistent with SPECT imaging, demonstrating that [177Lu]Lu-L21 is a promising radiopharmaceutical for tumor radionuclide therapy.

Comparison of [68Ga]Ga-Fibroblast Activation Protein Inhibitor-04 and [18F]FDG PET Imaging for Solitary Fibrous Tumor and Preliminary Application of FAP-Targeted Radiopharmaceutical Therapy

Solitary fibrous tumor (SFT) is a rare sarcoma of mesenchymal origin. Although generally benign, SFTs carry the risk of recurrence and metastasis, with limited effective treatment options. The aims of this study are to compare the performance of fibroblast activation protein inhibitor (FAPI), [68Ga]Ga-DOTA-FAPI-04 (denoted as [68Ga]Ga-FAPI-04), and conventional [18F]FDG PET/CT in patients with recurrent or metastatic SFTs head to head and to preliminarily explore the value of FAP-targeted radiopharmaceutical therapy with 177Lu for SFT patients. Methods: Thirty-one participants (21 men, 44 ± 13 y) with suspected recurrent or metastatic SFTs underwent both [18F]FDG and [68Ga]Ga-FAPI-04 PET/CT within 1 wk. The positive-lesion rates of the 2 PET/CT scans in the different organs involved and the uptake values (SUVmax) were compared. Four patients with high [68Ga]Ga-FAPI-04 uptake received single-cycle therapy of 2.22 GBq of a [177Lu]Lu-labeled, FAP-targeted radiopharmaceutical, [177Lu]Lu-Evans blue-FAPI, and were followed up for 4 mo. Results: In 522 local recurrences and distant metastases in the 31 patients, [68Ga]Ga-FAPI-04 PET detected significantly more lesions than did [18F]FDG (87.0% vs. 45.4%, P < 0.001). In terms of lesion uptake values, [68Ga]Ga-FAPI-04 PET showed a mean SUVmax higher than that of [18F]FDG in most recurrence or metastatic organs (bone, lung, central nervous system, pancreas, and pleura, P < 0.001; kidney and abdominopelvic cavity, P = 0.001; muscle and pericardium, P < 0.05). Four patients tolerated [177Lu]Lu-Evans blue-FAPI well. The total-body absorbed dose and the effective dose were 4.02E-01 ± 3.54E-02 Gy and 4.01E+02 ± 4.18E+01 mSv, respectively. Subsequent follow-up with [68Ga]Ga-FAPI-04 PET showed that these patients were in stable condition. Conclusion: [68Ga]Ga-FAPI-04 may be a promising PET agent for the assessment of SFTs. Given the lack of effective treatments for advanced SFTs, high FAP expression in this type of tumor is expected to become a potential treatment target.

Exploring currently available fibroblast activation protein targeting molecules in adrenocortical carcinoma: Navigating theranostic pathways

INTRODUCTION

Cancer-associated fibroblasts (CAFs) expressing fibroblast activation protein (FAP) in the adrenocortical carcinoma (ACC) microenvironment may be used as potential therapeutic targets. This study investigated the diagnostic potential of four FAPi derivatives i.e. DOTA-FAPi-46 (FAPi46), DOTA.SA.FAPi (SA.FAPi), DATA5m.SA.FAPi (DATA.FAPi) and DATA5m.C4.FAPi (C4.FAPi) and compared with standard-of-care 18F-FDG (FDG) in ACC.

METHODS

Thirty histopathological proven cases of localized or metastatic ACC were recruited for both FDG and FAPi PET (number of patients (n) = 5 for SA.FAPi, n = 5 for DATA.FAPi, n = 5 for C4.FAPi and n = 15 for FAPi46). For biodistribution, standardized uptake values (SUV's) were computed by delineating region-of-interest on various body organs. For comparative analysis in disease identification, lesion tracer uptake was quantified using standardized uptake values corrected for lean body mass (SUL), tumor-to-background ratio (TBR), total lesion glycolysis (TLG for FDG) and total lesion FAP expression (TLF for FAPi).

RESULTS

In overall analysis, both FAPi and FDG PET exhibited comparable mean SULpeak [FAPi 4.3 (8.0-1.7) vs FDG 3.9 (8.1-2.5), p-0.271], mean SULavg [2.2 (4.3-1.2) vs 2.2 (3.4-1.3), p-0.897] and mean TBR [1.8 (3.2-1.2) vs 1.9 (2.7-1.2), p-0.696]. In volumetric analysis, comparable mean TLF and mean TLG was noted for the cohort [9.3 (53.7-4.5) vs 11.8 (33.0-4.3), p-0.107]. Sub-categorical analysis demonstrated complete concordant findings for both radiotracers in detection of all primary lesions, nodal lesions and distant metastases in lung and peritoneum with discordant findings in liver (22%) and skeletal lesions (33%). For lesion detection, DATA.FAPi and FAPi46 showed 100% concordance with FDG scan findings in metastatic disease. SA.FAPi exhibited 33% discordance by detecting an additional skeletal lesion, while C4.FAPi had 10% discordance, missing one liver lesion identified by FDG. Three 68 Ga-FAP derivatives (SA.FAPi, DATA.FAPi, and C4.FAPi) exhibited similar biodistribution, with uptake in the salivary glands, thyroid, liver, pancreas, muscles, and kidneys, and variable uptake in the lacrimal glands, extra-ocular muscles, oral mucosa, and uterus. In contrast, FAPi46 physiological expression was noted in salivary glands and muscles, with no uptake in other organs. Pancreatic uptake was highest for SA.FAPi (SUVmean 11.8), DATA.FAPi (12.1), and C4.FAPi (10.8), while FAPi46 had the lowest (1.7). Conversely, FAPi46 exhibited the highest muscle uptake (SUVmean 4.3) compared to SA.FAPi (1.7), DATA.FAPi (1.4), and C4.FAPi (1.0).

CONCLUSION

All the existing FAP inhibitor molecules were comparable to FDG PET for mapping disease spread and appeared as potential theranostic targets for the management of ACC.

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

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

Phase I study of [68Ga]Ga-HX01 for targeting integrin αvβ3 and CD13 in healthy and malignancy subjects

PURPOSE

Noninvasive angiogenesis visualization is essential for evaluating tumor proliferation, progression, invasion, and metastasis. This study aimed to translate the heterodimeric PET tracer [68Ga]Ga-HX01, which targets integrin αvβ3 and CD13 in neovascularization, into phase I clinical study.

METHODS

This study enrolled 12 healthy volunteers (phase Ia) and 10 patients with malignant tumors (phase Ib). The subjects in phase Ia were divided into low-dose (0.05 mCi/kg) and high-dose (0.1 mCi/kg) groups. For phase Ia subjects, PET/CT images, blood and urine samples were collected to analyze the biodistribution, pharmacokinetics, radiation dosimetry, and safety of [68Ga]Ga-HX01. For phase Ib patients, PET/MR scans were performed at 30 ± 5 and 60 ± 5 min after injection. The safety and preliminary diagnostic value of [68Ga]Ga-HX01 were assessed.

RESULTS

In phase Ia study, [68Ga]Ga-HX01 was distributed and metabolized similarly in two dosage groups as the highest accumulations in kidneys and urine. It possessed quick renal excretion and blood clearance with an elimination half-life (T1/2) of 28.92 ± 3.97 min. The total effective dose was 2.14 × 10- 2 mSv/MBq. In phase Ib study, [68Ga]Ga-HX01 clearly detected the lesions per patient, and found a total of 59 lesions with varying uptake levels. For safety evaluation, no serious adverse events were observed during the examination.

CONCLUSION

[68Ga]Ga-HX01 has proved to be a translational radiopharmaceutical with reliable security, favorable pharmacokinetics, and the ability to visualize tumors. The preliminary results in malignancy patients warrant further investigation of [68Ga]Ga-HX01 in monitoring antiangiogenic therapy of patients with malignancies.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT06416774. Registered 11 May, 2024.

Current status and future prospects of molecular imaging in targeting the tumor immune microenvironment

Molecular imaging technologies have significantly transformed cancer research and clinical practice, offering valuable tools for visualizing and understanding the complex tumor immune microenvironment. These technologies allow for the non-invasive examination of key components within the tumor immune microenvironment, including immune cells, cytokines, and stromal cells, providing crucial insights into tumor biology and treatment responses. This paper reviews the latest advancements in molecular imaging, with a focus on its applications in assessing interactions within the tumor immune microenvironment. Additionally, the challenges faced by molecular imaging technologies are discussed, such as the need for highly sensitive and specific imaging agents, issues with data integration, and difficulties in clinical translation. The future outlook emphasizes the potential of molecular imaging to enhance personalized cancer treatment through the integration of artificial intelligence and the development of novel imaging probes. Addressing these challenges is essential to fully realizing the potential of molecular imaging in improving cancer diagnosis, treatment, and patient outcomes.

[68Ga]Ga-LNC1007 versus 2-[18F]FDG in the evaluation of patients with metastatic differentiated thyroid cancer: a head-to-head comparative study

PURPOSE

This head-to-head comparison study aimed to compare the performance of [68Ga]Ga-FAPI-RGD (LNC1007) and 2-[18F]FDG PET/CT in the evaluation of patients with metastatic differentiated thyroid cancer (mDTC).

METHODS

Ten unexplained hyperthyroglobulinemia (UHTg) patients and 20 patients with definite metastatic lesions of thyroid cancer (DmDTC) were enrolled in the study. All patients underwent both [68Ga]Ga-LNC1007 and 2-[18F]FDG PET/CT within 1 week. The final diagnosis was based on histopathological results and a comprehensive evaluation of laboratory tests and multimodal imaging characteristics.

RESULTS

In patients with UHTg, [68Ga]Ga-LNC1007 PET/CT detected more metastatic lymph nodes (LNs) (17 vs. 15, P = 0.317) and lung lesions (2 vs. 0) than 2-[18F]FDG. In patients with DmDTC, [68Ga]Ga-LNC1007 PET/CT also detected more true positive lesions than 2-[18F]FDG (Total: 133 vs. 103, LN: 20 vs. 15, lung: 18 vs. 10, bone: 87 vs.73). [68Ga]Ga-LNC1007 PET/CT demonstrated significantly higher SUVmax (Total: 6.30 vs. 3.84, LN: 8.28 vs. 4.82, Lung: 3.31 vs. 1.49, Bone: 5.73 vs. 3.87, all P < 0.05) and TBR (Total: 6.92 vs. 4.93, LN: 6.48 vs. 4.16, Lung: 5.16 vs. 2.57, Bone: 7.22 vs. 5.41, all P < 0.05) in true positive lesions compared to 2-[18F]FDG. Specifically, the sensitivity of [68Ga]Ga-LNC1007 PET/CT was higher than that of 2-[18F]FDG in detecting lung and bone metastases (94.7% vs. 52.6% and 100% vs. 83.9%, all P < 0.05). [68Ga]Ga-LNC1007 PET/CT exhibited better specificity and accuracy in diagnosing LNs (96.9% vs. 66.7% and 96.3% vs. 68.5%, all P < 0.05). However, the specificity of [68Ga]Ga-LNC1007 for bone metastasis was inferior to 2-[18F]FDG (15.4% vs. 88.5%, P < 0.05).

CONCLUSION

Compared with 2-[18F]FDG, [68Ga]Ga-LNC1007 PET/CT could detect more metastatic lesions, with higher SUVmax and TBR, in patients with mDTC. [68Ga]Ga-LNC1007 had better accuracy in the diagnosis of LN and lung metastasis. Trial registration ClinicalTrials.gov NCT05515783. Registered 01 May 2022. URL of registry https://classic.

CLINICALTRIALS

gov/ct2/show/NCT05515783.

Comparative Study of [18F]AlF-LNC1007, [18F]FDG, and [18F]AlF-NOTA-FAPI-04 PET/CT in Breast Cancer Diagnosis: A Methodological Exploration and Analytical Insight

Objective: To compare the diagnostic value of [18F]AlF-LNC1007, [18F]FDG, and [18F]AlF-NOTA-FAPI-04 PET/CT in breast cancer. Methods: 33 patients with highly suspected or already diagnosed but untreated breast cancer were enrolled in the study and underwent [18F]AlF-LNC1007 (30 patients), [18F]FDG (22 patients), and [18F]AlF-NOTA-FAPI-04 (8 patients) PET/CT. Quantitative measurements included the SUVmax and tumor-to-background ratio (TBR) for all lesions and background tissues. The Chi-square test was used for intergroup diagnostic efficacy, and the Wilcoxon test was used for intergroup SUVmax or TBR. Diagnostic efficacy for lymph node metastasis was evaluated using receiver operating characteristic (ROC) analysis. Results: Compared to [18F]FDG, [18F]AlF-LNC1007 had a higher positive predictive value (100% vs 91%, P = 0.0004) in lymph node metastases (42 vs 46) and higher sensitivity (100 vs 76%, P = 0.0003) in bone metastases (33 vs 25) but lower sensitivity (93 vs 100%, P = 0.001) in liver metastases. Apart from liver metastases, [18F]AlF-LNC1007 PET/CT had higher SUVmax in primary tumor and other metastases, with no statistical difference in TBR. Compared to [18F]AlF-NOTA-FAPI-04 PET/CT, [18F]AlF-LNC1007 had less false-positive and a higher positive predictive value in bone metastases (99 vs 95%, P = 0.0003) but had lower SUVmax(P < 0.01) in all primary and metastases lesions. The TBR difference between [18F]AlF-LNC1007 and [18F]AlF-NOTA-FAPI-04 was statistically significant only in bone metastases (5.97 vs 5.02, P = 0.001). The comparison of lymph node detection efficacy between [18F]AlF-LNC1007 and [18F]FDG PET/CT showed significant differences in SUVmax cutoff values for diagnosing lymph node metastases (2.62 vs 3.90), sensitivity (95.2% vs 66.67), and specificity (100% vs 85.00) (all P < 0.001). Conclusion: [18F]AlF-LNC1007 demonstrated superior efficacy compared to [18F]FDG and [18F]AlF-NOTA-FAPI-04 and higher uptake than [18F]FDG in primary tumor, lymph node and bone metastases, and higher TBR than [18F]AlF-NOTA-FAPI-04, especially in bone metastases. [18F]AlF-LNC1007 also showed high specificity in differentiating inflammatory and metastatic lymph nodes.

Integrin Targeting and Beyond: Enhancing Cancer Treatment with Dual-Targeting RGD (Arginine-Glycine-Aspartate) Strategies

Integrins, an important superfamily of cell adhesion receptors, play an essential role in cancer progression, metastasis, and angiogenesis, establishing them as prime targets for both diagnostic and therapeutic applications. Despite their significant potential, integrin-targeted therapies have faced substantial challenges in clinical trials, including variable efficacy and unmet high expectations. Nevertheless, the consistent expression of integrins on tumor and stromal cells underscores their ongoing relevance and potential. Traditional RGD-based imaging and therapeutic agents have faced limitations, such as inconsistent target expression and rapid systemic clearance, which have reduced their effectiveness. To overcome these challenges, recent research has focused on advancing RGD-based strategies and exploring innovative solutions. This review offers a thorough analysis of the latest developments in the RGD-integrin field, with a particular focus on addressing previous limitations. It delves into new dual-targeting approaches and cutting-edge RGD-based agents designed to improve both tumor diagnosis and therapeutic outcomes. By examining these advancements, this review illuminates new pathways for enhancing the specificity and efficacy of integrin-targeted therapies, paving the way for more effective cancer diagnosis and treatment strategies.

Dual targeting heterodimer PET tracer [18F]AlF‑FAPI‑RGD in patients with rheumatoid arthritis: a pilot exploratory study

Purpose: Fibroblast-like synoviocytes and angiogenesis play crucial roles in the advancement of rheumatoid arthritis (RA). This prospective study aimed to assess the efficacy of [18F]AlF-FAPI-RGD, a dual-targeting heterodimer tracer that focuses on fibroblast activation protein (FAP) and integrin αvβ3, through PET/CT imaging for evaluating disease activity and response to treatment in RA. Methods: Twenty-eight participants with active RA (12 males and 16 females; mean age, 55 ± 9 years) underwent clinical evaluation of disease activity and [18F]AlF-FAPI-RGD PET/CT imaging at enrollment. Subsequently, after a 3-month period, a follow-up scan and clinical assessments were conducted on these participants. Imaging parameters such as PET-positive joint count (PJC), PET-positive articular index (PAI), average SUVmax (aSUVmax), and highest SUVmax (hSUVmax) in affected joints were compared with clinical and laboratory findings, as well as traditional imaging modalities. Results: [18F]AlF-FAPI-RGD PET/CT imaging produced high-quality images, revealing notable tracer uptake in the synovium of affected joints. [18F]AlF-FAPI-RGD demonstrated a higher positivity rate in detecting affected joints compared to the tender or swollen joint counts during clinical assessment (82.4% [342 of 415] vs 68.4% [284 of 415], respectively). Additionally, this imaging method successfully identified lung lesions with atypical respiratory symptoms in participants with RA. Following treatment, PJC, PAI, aSUVmax, and hSUVmax values significantly decreased in responders (P < 0.001), while no significant changes were observed in non-responders (P > 0.05). Furthermore, a notable association was found between the percentage change in certain PET parameters and modifications in specific clinical parameters. Conclusion: [18F]AlF-FAPI-RGD PET/CT represents a promising tool for the objective assessment of disease activity and treatment response in patients with RA. Furthermore, it may offer a novel imaging method for the early detection of subclinical RA and interstitial lung disease present with atypical respiratory symptoms.

Development and evaluation of albumin binder-conjugated heterodimeric radiopharmaceuticals targeting integrin αvβ3 and CD13 for cancer therapy

PURPOSE

The advancement of heterodimeric tracers, renowned for their high sensitivity, marks a significant trend in the development of radiotracers for cancer diagnosis. Our prior work on [68Ga]Ga-HX01, a heterodimeric tracer targeting CD13 and integrin αvβ3, led to its approval for phase I clinical trials by the China National Medical Production Administration (NMPA). However, its fast clearance and limited tumor retention pose challenges for broader clinical application in cancer treatment. This study aims to develop a new radiopharmaceutical with increased tumor uptake and prolonged retention, rendering it a potential therapeutic candidate.

METHODS

New albumin binder-conjugated compounds were synthesized based on the structure of HX01. In vitro and in vivo evaluation of these new compounds were performed after labelling with 68Ga. Small-animal PET/CT imaging were conducted at different time points at 0.5-6 h post injection (p.i.) using BxPC-3 xenograft mice models. The one with the best imaging performance was further radiolabeled with 177Lu for small-animal SPECT/CT and ex vivo biodistribution investigation.

RESULTS

We have synthesized novel albumin binder-conjugated compounds, building upon the structure of HX01. When radiolabeled with 68Ga, all compounds demonstrated improved pharmacokinetics (PK). Small-animal PET/CT studies revealed that these new albumin binder-conjugated compounds, particularly [68Ga]Ga-L6, exhibited significantly enhanced tumor accumulation and retention compared with [68Ga]Ga-L0 without an albumin binder. [68Ga]Ga-L6 outperformed [68Ga]Ga-L7, a compound developed using a previously reported albumin binder. Furthermore, [177Lu]Lu-L6 demonstrated rapid clearance from normal tissues, high tumor uptake, and prolonged retention in small-animal SPECT/CT and biodistribution studies, positioning it as an ideal candidate for radiotherapeutic applications.

CONCLUSION

A new integrin αvβ3 and CD13 targeting compound was screened out. This compound bears a novel albumin binder and exhibits increased tumor uptake and prolonged tumor retention in BxPC-3 tumors and low background in normal organs, making it a perfect candidate for radiotherapy when radiolabeled with 177Lu.

Targeted Radionuclide Therapy in Glioblastoma

Despite the development of various novel therapies, glioblastoma (GBM) remains a devastating disease, with a median survival of less than 15 months. Recently, targeted radionuclide therapy has shown significant progress in treating solid tumors, with the approval of Lutathera for neuroendocrine tumors and Pluvicto for prostate cancer by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). This achievement has shed light on the potential of targeted radionuclide therapy for other solid tumors, including GBM. This review presents the current status of targeted radionuclide therapy in GBM, highlighting the commonly used therapeutic radionuclides emitting alpha, beta particles, and Auger electrons that could induce potent molecular and cellular damage to treat GBM. We then explore a range of targeting vectors, including small molecules, peptides, and antibodies, which selectively target antigen-expressing tumor cells with minimal or no binding to healthy tissues. Considering that radiopharmaceuticals for GBM are often administered locoregionally to bypass the blood-brain barrier (BBB), we review prominent delivery methods such as convection-enhanced delivery, local implantation, and stereotactic injections. Finally, we address the challenges of this therapeutic approach for GBM and propose potential solutions.

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.

68Ga-DOTA.SA.FAPi as a Versatile Diagnostic Probe for Various Epithelial Malignancies: A Head-to-Head Comparison with 18F-FDG

RATIONALE AND OBJECTIVES

Fibroblast Activation Protein (FAP) expressing cancer-associated fibroblasts has been a major breakthrough causing a paradigm shift in targeted theranostics focusing on the tumor microenvironment. In this study, a squaric acid derivative DOTA.SA.FAPi (SA.FAPi) has been evaluated as a potential diagnostic probe in diverse epithelial cancers and compared to the standard-of-care 18F-FDG.

METHODS

25 patients enrolled in this prospective study underwent 18F-FDG and 68Ga-SA.FAPi PET scans on two different days. For biodistribution, standardized uptake values (SUV) were computed by delineating region-of-interest on various body organs. For comparative analysis in disease identification, lesion tracer uptake was quantified using SUVs corrected for lean body mass (SUL), SUVmax, tumor-to-background ratio (TBR) with liver and blood pool as the reference, total lesion glycolysis (TLG for 18F-FDG) and total lesion FAP expression (TLF for 68Ga-SA.FAPi).

RESULTS

25 patients (mean age: 58 ± 8 years) with four types of cancers including hepatocellular carcinoma (HCC, 56% of cohort), gall bladder carcinoma (GB Ca, 12%), adrenocortical carcinoma (ACC, 16%), and breast carcinoma (breast Ca, 16%) were prospectively evaluated. Physiological tracer uptake of 68Ga-SA.FAPi was noted in the salivary glands, thyroid, liver, pancreas, muscles and kidneys with variable uptake in the lacrimal glands, extra-ocular muscles, oral mucosa and uterus. Lesion-based comparative analysis between both the radiotracers demonstrated complete concordant findings in detection of all primary lesions and distant metastases in liver, bones, adrenals and peritoneum whereas discordant findings were noted in lung nodules (20%) and lymph nodes (13%). In overall analysis, 68Ga-SA.FAPi exhibited significantly higher SUVmax (10.3 vs 8.8, p-0.019), SULpeak (6.8 vs 4.9, p-0.000) and SULavg (5.4 vs 4.1, p-0.019) in comparison to 18F-FDG whereas TBR was comparable for both the tracers [TBRLiver: median 1.9 (IQR: 2.6-1.4) vs 1.8 (2.6-1.1), p-0.275; TBRBloodpool: 2.1 (3.7-1.4) vs 2.0 (2.7-1.4), p-0.207]. In subcategorical analysis, 68Ga-SA.FAPi demonstrated higher SUVmax, SULpeak and SULavg values for primary disease (SUVmax: 14.8 (18.7-9.7) vs (12.9-6.6), p-0.087; SULpeak: 8.2 (11.2-6.8) vs 6.3 (8.5-4.4), p-0.037; SULavg: 6.9 ± 2.5 vs 5.1 ± 2.2, p-0.023] and distant metastases (8.8 vs 7.2, p-0.038); 6.3 (8.8-4.4) vs 3.6 (4.4-2.0), p-0.000; 5.4 vs 3.5, p-0.000] whereas comparable values were noted for both the tracers in nodal metastases [9 (13.5-4.1) vs 8 (12.7-4.7), p-0.726; 4.5 (6.2-1.8) vs 4.3 (5.7-2.2), p-0.727; 4.1 ± 2.3 vs 3.7 ± 1.8, p-0.129]. In primary disease, highest 68Ga-SA.FAPi avidity was noted in ACC followed by GB Ca and HCC. In distant metastases, gall bladder, lung and skeletal lesions demonstrated higher 68Ga-SA.FAPi avidity. Moreover, 68Ga-SA.FAPi identified five additional lung lesions which were missed by 18F-FDG in one case of ACC.

CONCLUSION

68Ga-SA.FAPi emerged as an effective, versatile diagnostic probe for imaging various epithelial malignancies similar to 18F-FDG.

Synthesis, preclinical, and initial clinical evaluation of integrin αVβ3 and gastrin-releasing peptide receptor (GRPR) dual-targeting radiotracer [68Ga]Ga-RGD-RM26-03

Integrin receptor αvβ3 and gastrin-releasing peptide receptor (GRPR) expression of tumors could be detected using PET imaging with radiolabeled Arg-Gly-Asp (RGD) and the antagonistic bombesin analog RM26, respectively. The purpose of this study was to investigate the dual receptor-targeting property of the heterodimer RGD-RM26-03 (denoted as LNC1015), demonstrate the tumor diagnostic value of [68Ga]Ga-LNC1015 in preclinical experiments, and evaluate its preliminary clinical feasibility.

METHODS

LNC1015 was designed and synthesized by linking cyclic RGD and the RM26 peptide. Preclinical pharmacokinetics were detected in a PC3 xenograft model using microPET and biodistribution studies. The clinical feasibility of [68Ga]Ga-LNC1015 PET/CT was performed in patients with breast cancer, and the results were compared with those of 18F-fluorodeoxyglucose (FDG).

RESULTS

[68Ga]Ga-LNC1015 had good stability in saline for at least 2 h, and favorable binding affinity and specificity were demonstrated in vitro and in vivo. The tumor uptake and retention of [68Ga]Ga-LNC1015 during PET imaging were improved compared with its monomeric counterparts [68Ga]Ga-RGD and [68Ga]Ga-RM26 at all the time points examined. In our initial clinical studies, the tumor uptake and tumor-to-background ratio (TBR) of primary and metastatic lesions in [68Ga]Ga-LNC1015 PET/CT were significantly higher than those in [18F]FDG PET/CT, resulting in high lesion detection rate and tumor delineation.

CONCLUSION

The dual targeting radiotracer [68Ga]Ga-LNC1015 showed significantly improved tumor uptake and retention, as well as lower liver uptake than [68Ga]Ga-RGD and [68Ga]Ga-RM26 monomer. The first-in-human study showed high TBRs in patients, suggesting favorable pharmacokinetics and high clinical feasibility for PET/CT imaging of cancer.

Rational Design and Pharmacomodulation of 18F-Labeled Biotin/FAPI-Conjugated Heterodimers

Due to the complex heterogeneity in different cancer types, the heterodimeric strategy has been intensively practiced to improve the effectiveness of tumor diagnostics. In this study, we developed a series of novel 18F-labeled biotin/FAPI-conjugated heterobivalent radioligands ([18F]AlF-NSFB, [18F]AlF-NSFBP2, and [18F]AlF-NSFBP4), synergistically targeting both fibroblast activation protein (FAP) and biotin receptor (BR), to enhance specific tumor uptake and retention. The in vitro and in vivo biological properties of these dual-targeting tracers were evaluated, with a particular focus on positron emission tomography imaging in A549 and HT1080-FAP tumor-bearing mice. Notably, in comparison to the corresponding FAP-targeted monomer [18F]AlF-NSF, biotin/FAPI-conjugated heterodimers exhibited a high uptake in tumor and prolong retention. In conclusion, as a proof-of-concept study, the findings validated the superiority of biotin/FAPI-conjugated heterodimers and the positive influence of biotin and linker on pharmacokinetics of radioligands. Within them, the bispecific [18F]AlF-NSFBP4 holds significant promise as a candidate for further clinical translational studies.

A comparison of [18F]AlF- and 68Ga-labeled dual targeting heterodimer FAPI-RGD in malignant tumor: preclinical evaluation and pilot clinical PET/CT imaging

Due to the heterogeneity of tumors, strategies to improve the effectiveness of dual-targeting tracers in tumor diagnostics have been intensively practiced. In this study, the radiolabeled [18F]AlF-NOTA-FAPI-RGD (denoted as [18F]AlF-LNC1007), a dual-targeting heterodimer tracer targeting both fibroblast activation protein (FAP) and integrin αvβ3 to enhance specific tumor uptake and retention, was synthesized and evaluated. The tracer was compared with [68Ga]Ga-LNC1007 in preclinical and clinical settings.

METHODS

The preparation of [18F]AlF- and 68Ga-labeled FAPI-RGD was carried out with an optimized protocol. The stability was tested in PBS and fetal bovine serum (FBS). Cellular uptake and in vivo distribution of the two products were compared and carried out on the U87MG cell line and its xenograft model. The safety and dosimetry of [18F]AlF-LNC1007 PET/CT scan were evaluated in six patients with malignant tumors.

RESULTS

Two radiolabeling protocols of [18F]AlF-/[68Ga]Ga-LNC1007 were developed and optimized to give a high yield of tracers with good stability. In vivo microPET images showed that the two tracers exhibited comparable pharmacokinetic characteristics, with high tumor uptake and prolonged tumor retention. In vivo distribution data showed that the target-to-non-target ratios of [18F]AlF-LNC1007 were similar to[68Ga]Ga-LNC1007. A total of six patients underwent [18F]AlF-LNC1007 PET/CT evaluation while two had head-to-head [18F]FDG PET/CT scans. The total body effective dose was 9.94E-03 mSv/MBq. The biodistribution curve showed optimal normal organ uptake with high tumor uptake and long retention of up to 3h p.i., and notably, the tumor-to-background ratio increased over time.

CONCLUSION

We successfully prepared an [18F]AlF-LNC1007 dual-targeting PET probe with comparable performances as [68Ga]Ga-LNC1007. With prolonged tumor retention and tumor specificity, it produced good imaging quality in preclinical and clinical translational studies, indicating that [18F]AlF-LNC1007 is a promising non-invasive tracer for detecting tumors expressing FAP and/or integrin avβ3, with the prospect of clinical implementation.

Recent Pre-Clinical Advancements in Nuclear Medicine: Pioneering the Path to a Limitless Future

The theranostic approach in oncology holds significant importance in personalized medicine and stands as an exciting field of molecular medicine. Significant achievements have been made in this field in recent decades, particularly in treating neuroendocrine tumors using 177-Lu-radiolabeled somatostatin analogs and, more recently, in addressing prostate cancer through prostate-specific-membrane-antigen targeted radionuclide therapy. The promising clinical results obtained in these indications paved the way for the further development of this approach. With the continuous discovery of new molecular players in tumorigenesis, the development of novel radiopharmaceuticals, and the potential combination of theranostics agents with immunotherapy, nuclear medicine is poised for significant advancements. The strategy of theranostics in oncology can be categorized into (1) repurposing nuclear medicine agents for other indications, (2) improving existing radiopharmaceuticals, and (3) developing new theranostics agents for tumor-specific antigens. In this review, we provide an overview of theranostic development and shed light on its potential integration into combined treatment strategies.