Comparison of [99mTc]3PRGD2 Imaging and [18F]FDG PET/CT in Breast Cancer and Expression of Integrin αvβ3 in Breast Cancer Vascular Endothelial Cells

The Relationship of Metabolic Activity and αvβ3 Receptor Expression in Aggressive Breast Cancer Subtypes Tumors: A Preliminary Report

BACKGROUND/AIM

Angiogenesis imaging has been a valuable complement to metabolic imaging with 2-deoxy-2-[18F]fluoroglucose (FDG). In our longitudinal study, we investigated the tumour heterogeneity and the relationship between FDG and [68Ga]Ga-NODAGA-c(RGDfK)2 (RGD) accumulation in breast cancer xenografts.

MATERIALS AND METHODS

Two groups of cell lines, a fast-growing (4T1) and a slow-growing cell line (MDA-MB-HER2+), were inoculated into SCID mice. RGD and FDG scans were performed in all mice on separate days at four time points. Assessment of tumour uptake based on positron emission tomography/magnetic resonance imaging images was performed using tumour/muscle ratios with the Muscle-Spacing Correction Method to minimize the partial volume effect of the urinary bladder.

RESULTS

In the 4T1 group, both radiopharmaceuticals visualized the highly heterogeneous structure of the tumours and showed correlations with tumour growth. Relative linear correlations between FDG and RGD tumour/muscle ratios were observed in all tumours, evident in both high and low-activity areas of 4T1 tumours. When comparing the two groups of different cell lines, SUV ratios in the 4T1 group were higher, especially with [18F]F-FDG. Our findings highlight the correlations between FDG and RGD, particularly in aggressive breast cancer.

CONCLUSION

This preliminary study supports the combined use of FDG and RGD PET imaging to better characterize tumor heterogeneity and aggressiveness in breast cancer. The observed correlation between FDG and RGD uptake offers insights into the metabolic and vascular behavior of different cancer subtypes, highlighting distinct patterns in 4T1 and MDA-MB-HER2+ lines. This dual-tracer approach shows promise for tailoring therapies based on tumor subtype, though further studies with larger samples are needed to validate these initial findings.

Potential Probes for Targeted Intraoperative Fluorescence Imaging in Gastric Cancer

Gastric cancer (GC) is a malignant tumor of the gastrointestinal tract associated with high mortality rates and accounting for approximately 1 million new cases diagnosed annually. Surgery, particularly radical gastrectomy, remains the primary treatment; however, there are currently no specific approaches to better distinguish malignant from healthy tissue or to differentiate between metastatic and non-metastatic lymph nodes. As a result, surgeons have to remove all lymph nodes indiscriminately, increasing intraoperative risks for patients and prolonging hospital stay. Near-infrared fluorescence imaging with indocyanine green (ICG) can provide real-time visualization of the surgical field using both conventional laparoscopy and robotic mini-invasive precision surgery platforms. However, its application shows some limits, as ICG is a non-targeted contrast agent. Several studies are now investigating the potential efficacy of fluorescent targeted agents that could selectively bind to the tumor tissue, offering a valuable tool for metastatic mapping during robotic gastrectomy. This review aims to summarize the key fluorescent agents that have been developed to recognize GC markers, as well as those targeting the tumor microenvironment (TME) and metabolic features. These agents hold great potential as valuable tools for enhancing precision surgery in robotic gastrectomy procedures improving the clinical recovery of GC patients.

Evaluation of targeting αVβ3 in breast cancers using RGD peptide-based agents

Patients with HER2-positive and triple negative breast cancer (TNBC) are associated with increased risk to develop metastatic disease including reoccurring disease that is resistant to standard and targeted therapies. The αVβ3 has been implicated in BC including metastatic disease. The aims of this study were to investigate the potential of αVβ3-targeted peptides to deliver radioactive payloads to BC tumors expressing αVβ3 on the tumor cells or limited to the tumors' neovascular. Additionally, we aimed to assess the pharmacokinetic profile of the targeted α-particle therapy (TAT) agent [225Ac]Ac-DOTA-cRGDfK dimer peptide and the in vivo generated decay daughters. The expression of αVβ3 in a HER2-positive and a TNBC cell line were evaluated using western blot analysis. The pharmacokinetics of [111In]In-DOTA-cRGDfK dimer, a surrogate for the TAT-agent, was evaluated in subcutaneous mouse tumor models. The pharmacokinetic of the TAT-agent [225Ac]Ac-DOTA-cRGDfK dimer and its decay daughters were evaluated in healthy mice. Selective uptake of [111In]In-DOTA-cRGDfK dimer was shown in subcutaneous tumor models using αVβ3-positive tumor cells as well as αVβ3-negative tumor cells where the expression is limited to the neovasculature. Pharmacokinetic studies demonstrated rapid accumulation in the tumors with clearance from non-target organs. Dosimetric analysis of [225Ac]Ac-DOTA-cRGDfK dimer showed the highest radiation absorbed dose to the kidneys, which included the contributions from the free in vivo generated decay daughters. This study shows the potential of delivering radioactive payloads to BC tumors that have αVβ3 expression on the tumor cells as well as limited expression to the neovascular of the tumor. Furthermore, this work determines the radiation absorbed doses to normal organs/tissues and identified key organs that act as suppliers and receivers of the actinium-225 free in vivo generated α-particle-emitting decay daughters.

99mTc-3PRGD2 SPECT/CT Imaging for Diagnosing Lymph Node Metastasis of Primary Malignant Lung Tumors

OBJECTIVE

To evaluate 99mtechnetium-three polyethylene glycol spacers-arginine-glycine-aspartic acid (99mTc-3PRGD2) single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging for diagnosing lymph node metastasis of primary malignant lung neoplasms.

MATERIALS AND METHODS

We prospectively enrolled 26 patients with primary malignant lung tumors who underwent 99mTc-3PRGD2 SPECT/CT and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT imaging. Both imaging methods were analyzed in qualitative (visual dichotomous and 5-point grades for lymph nodes and lung tumors, respectively) and semi-quantitative (maximum tissue-to-background radioactive count) manners for the lymph nodes and lung tumors. The performance of the differentiation of lymph nodes with and without metastasis was determined at the per-lymph node station and per-patient levels using histopathological results as the reference standard.

RESULTS

Total 42 stations had metastatic lymph nodes and 136 stations had benign lymph nodes. The differences between metastatic and benign lymph nodes in the visual qualitative and semiquantitative analyses of 99mTc-3PRGD2 SPECT/CT and 18F-FDG PET/CT were statistically significant (all P < 0.001). The area under the receiver operating characteristic curve (AUC) in the semi-quantitative analysis of 99mTc-3PRGD2 SPECT/CT was 0.908 (95% confidence interval [CI], 0.851-0.966), and the sensitivity, specificity, positive predictive value, and negative predictive value were 0.86 (36/42), 0.88 (120/136), 0.69 (36/52), and 0.95 (120/126), respectively. Among the 26 patients (including two patients each with two lung tumors), 15 had pathologically confirmed lymph node metastasis. The difference between primary lung lesions in patients with and without lymph node metastasis was statistically significant only in the semi-quantitative analysis of 99mTc-3PRGD2 SPECT/CT (P = 0.007), with an AUC of 0.807 (95% CI, 0.641-0.974).

CONCLUSION

99mTc-3PRGD2 SPECT/CT imaging may notably perform in the direct diagnosis of lymph node metastasis of primary malignant lung tumors and indirectly predict the presence of lymph node metastasis through uptake in the primary lesions.

Advances in Radionuclides and Radiolabelled Peptides for Cancer Therapeutics

Radiopharmaceutical therapy, which can detect and treat tumours simultaneously, was introduced more than 80 years ago, and it has changed medical strategies with respect to cancer. Many radioactive radionuclides have been developed, and functional, molecularly modified radiolabelled peptides have been used to produce biomolecules and therapeutics that are vastly utilised in the field of radio medicine. Since the 1990s, they have smoothly transitioned into clinical application, and as of today, a wide variety of radiolabelled radionuclide derivatives have been examined and evaluated in various studies. Advanced technologies, such as conjugation of functional peptides or incorporation of radionuclides into chelating ligands, have been developed for advanced radiopharmaceutical cancer therapy. New radiolabelled conjugates for targeted radiotherapy have been designed to deliver radiation directly to cancer cells with improved specificity and minimal damage to the surrounding normal tissue. The development of new theragnostic radionuclides, which can be used for both imaging and therapy purposes, allows for more precise targeting and monitoring of the treatment response. The increased use of peptide receptor radionuclide therapy (PRRT) is also important in the targeting of specific receptors which are overexpressed in cancer cells. In this review, we provide insights into the development of radionuclides and functional radiolabelled peptides, give a brief background, and describe their transition into clinical application.

Advances in Clinical Oncology Research on 99mTc-3PRGD2 SPECT Imaging

The integrin alpha(α)v beta(β)3 receptor is ubiquitous in malignant tumors and has a certain level of specificity for tumors. Technetium-99m hydrazinonicotinamide-dimeric cyclic arginyl-glycyl-aspartic acid peptide with three polyethylene glycol spacers (99mTc-3PRGD2) can bind specifically to the integrin αvβ3 receptor with high selectivity and strong affinity. Thus, it can specifically mark tumors and regions with angiogenesis for tumor detection and be used in single-photon emission computed tomography (SPECT) imaging. This modality has good application value for diagnosing and treating tumor lesions, such as those in the lung, breast, esophagus, head, and neck. This review provides an overview of the current clinical research progress of 99mTc-3PRGD2 SPECT imaging for tumor lesions, including for the diagnosis and differential diagnosis of tumors in different body parts, evaluation of related metastases, and evaluation of efficacy. In addition, the future clinical application prospects and possibilities of 99mTc-3PRGD2 SPECT imaging are further discussed.

Radiopharmaceuticals for PET and SPECT Imaging: A Literature Review over the Last Decade

Positron emission tomography (PET) uses radioactive tracers and enables the functional imaging of several metabolic processes, blood flow measurements, regional chemical composition, and/or chemical absorption. Depending on the targeted processes within the living organism, different tracers are used for various medical conditions, such as cancer, particular brain pathologies, cardiac events, and bone lesions, where the most commonly used tracers are radiolabeled with 18F (e.g., [18F]-FDG and NA [18F]). Oxygen-15 isotope is mostly involved in blood flow measurements, whereas a wide array of 11C-based compounds have also been developed for neuronal disorders according to the affected neuroreceptors, prostate cancer, and lung carcinomas. In contrast, the single-photon emission computed tomography (SPECT) technique uses gamma-emitting radioisotopes and can be used to diagnose strokes, seizures, bone illnesses, and infections by gauging the blood flow and radio distribution within tissues and organs. The radioisotopes typically used in SPECT imaging are iodine-123, technetium-99m, xenon-133, thallium-201, and indium-111. This systematic review article aims to clarify and disseminate the available scientific literature focused on PET/SPECT radiotracers and to provide an overview of the conducted research within the past decade, with an additional focus on the novel radiopharmaceuticals developed for medical imaging.

Clinical Evaluation of Nuclear Imaging Agents in Breast Cancer

Precision medicine is the customization of therapy for specific groups of patients using genetic or molecular profiling. Noninvasive imaging is one strategy for molecular profiling and is the focus of this review. The combination of imaging and therapy for precision medicine gave rise to the field of theranostics. In breast cancer, the detection and quantification of therapeutic targets can help assess their heterogeneity, especially in metastatic disease, and may help guide clinical decisions for targeted treatments. Positron emission tomography (PET) or single-photon emission tomography (SPECT) imaging has the potential to play an important role in the molecular profiling of therapeutic targets in vivo for the selection of patients who are likely to respond to corresponding targeted therapy. In this review, we discuss the state-of-the-art nuclear imaging agents in clinical research for breast cancer. We reviewed 17 clinical studies on PET or SPECT agents that target 10 different receptors in breast cancer. We also discuss the limitations of the study designs and of the imaging agents in these studies. Finally, we offer our perspective on which imaging agents have the highest potential to be used in clinical practice in the future.

The association of 18F-fluorodeoxyglucose PET/computed tomography parameters with tissue gastrin-releasing peptide receptor and integrin αvβ3 receptor levels in patients with breast cancer

OBJECTIVE

Gastrin-releasing peptide receptor (GRPR) and integrin αvβ3 receptors are significantly associated with primary breast cancer, neovascular endothelial, and metastatic tumor cells. We aimed to evaluate GRPR and integrin αvβ3 receptor staining, F-FDG uptake patterns and possible prognostic factors in breast cancer.

METHODS

Ninety lesions of 87 subjects diagnosed with breast cancer were included in this prospective study. The sections were stained with GRPR and integrin αvβ3. Subjects were divided into four molecular subgroups: luminal A, luminal B, triple negative and HER2. PET/CT imaging was performed on all subjects. The groups were compared in terms of GRPR and integrin αvβ3 staining properties, possible prognostic factors and mean SUVmax values.

RESULTS

Increased F-FDG uptake was significantly associated with estrogen receptor and progesterone receptor negativity. Molecular subtypes were significantly associated with mean integrin scores (P = 0.030), while histopathological subtypes were significantly associated with mean GRPR scores (P = 0.029). Increased integrin αvβ3 expression is significantly associated with ER and PR negativity. Additionally, GRPR score was significantly correlated with estrogen receptor and progesterone receptor expression scores and a negative statistically significant correlation was detected between integrin and progesterone receptor scores. Mean primary lesion SUVmax had a statistically significant positive correlation with integrin αvβ3 score.

CONCLUSION

GRPR and integrin αvβ3 expression results are complementary to F-FDG PET/CT findings, and are also significantly correlated with hormone receptors associated with aggressive subtypes. These results may pave the way for GRPR and integrin αvβ3 targeted imaging with Ga-labeled molecules and systemic radionuclide treatment with Lu-labeled compounds.

An Integrin Alpha 6-Targeted Radiotracer with Improved Receptor Binding Affinity and Tumor Uptake

In this study, we reported a ^99mTc-labeled integrin α₆-targeted peptide as the molecular imaging probe for tumor imaging by single-photon emission computed tomography (SPECT). We found that replacing Cys-Cys cyclized RWY peptide (sequence: cCRWYDENAC) with lactam-bridged cyclic cKiE peptide (sequence: cKRWYDENAisoE) did not sacrifice the integrin α₆-binding affinity and specificity of cKiE radiotracer. To further improve the radiotracer's tumor targeting capability, the dimerized cKiE peptide (termed cKiE2) was designed, and the corresponding radiotracer ^99mTc-cKiE2 was evaluated for tumor uptake and in vivo pharmacokinetics properties in tumor models. We found that cKiE2 showed higher binding affinity to integrin α₆ than did monomeric RWY or cKiE peptide. The biodistribution results showed that the tumor uptake of ^99mTc-cKiE2 was twice higher than that of ^99mTc-RWY (3.20 ± 0.12 vs 1.26 ± 0.06 %ID/g, P < 0.001) at 0.5 h postinjection. The tumor to nontargeting tissue ratios were also enhanced in most normal organs. Specificity of ^99mTc-cKiE2 for integrin α₆ was demonstrated by competitive blocking of tumor uptake with excess cold peptide (3.20 ± 0.24 to 1.38 ± 0.23 %ID/g, P < 0.001). The integrin α₆-positive tumors were clearly visualized by ^99mTc-cKiE2/SPECT with low background except with a relatively high kidney uptake. The tumor uptake of ^99mTc-cKiE2 correlates well with the tumor integrin α₆ expression levels in a linear fashion (R² = 0.9623). We also compared ^99mTc-cKiE2 with an integrin α_vβ₃-targeted radiotracer ^99mTc-3PRGD₂ in the orthotopic hepatocellular carcinoma tumor models. We found that the orthotopic tumor was clearly visualized with ^99mTc-cKiE2. ^99mTc-3PRGD₂ imaging did not show tumor contours in situ as clearly as ^99mTc-cKiE2. The tumor-to-liver ratios of ^99mTc-cKiE2 and ^99mTc-3PRGD₂ were 2.20 ± 0.17 and 0.85 ± 0.20. In conclusion, ^99mTc-cKiE2 is an improved SPECT radiotracer for imaging integrin α₆-positive tumors and has great potential for further clinical application.

Recent Advances in Nuclear Imaging of Receptor Expression to Guide Targeted Therapies in Breast Cancer

Breast cancer remains the most frequent cancer in women with different patterns of disease progression and response to treatments. The identification of specific biomarkers for different breast cancer subtypes has allowed the development of novel targeting agents for imaging and therapy. To date, patient management depends on immunohistochemistry analysis of receptor status on bioptic samples. This approach is too invasive, and in some cases, not entirely representative of the disease. Nuclear imaging using receptor tracers may provide whole-body information and detect any changes of receptor expression during disease progression. Therefore, imaging is useful to guide clinicians to select the best treatments for each patient and to evaluate early response thus reducing unnecessary therapies. In this review, we focused on the development of novel tracers that are ongoing in preclinical and/or clinical studies as promising tools to lead treatment decisions for breast cancer management.