Integrin αvβ6 Positron Emission Tomography Imaging in Lung Cancer Patients Treated With Pulmonary Radiation Therapy

Early, non-invasive detection of radiation-induced lung injury using PET/CT by targeting CXCR4

PURPOSE

Radiation-induced lung injury (RILI) is a severe side effect of radiotherapy (RT) for thoracic malignancies and we currently lack established methods for the early detection of RILI. In this study, we synthesized a new tracer, [18F]AlF-NOTA-QHY-04, targeting C-X-C-chemokine-receptor-type-4 (CXCR4) and investigated its feasibility to detect RILI.

METHODS

An RILI rat model was constructed and scanned with [18F]AlF-NOTA-QHY-04 PET/CT and [18F]FDG PET/CT periodically after RT. Dynamic, blocking, autoradiography, and histopathological studies were performed on the day of peak uptake. Fourteen patients with radiation pneumonia, developed during or after thoracic RT, were subjected to PET scan using [18F]AlF-NOTA-QHY-04.

RESULTS

The yield of [18F]AlF-NOTA-QHY-04 was 28.5-43.2%, and the specific activity was 27-33 GBq/μmol. [18F]AlF-NOTA-QHY-04 was mainly excreted through the kidney. Significant increased [18F]AlF-NOTA-QHY-04 uptake in the irradiated lung compared with that in the normal lung in the RILI model was observed on day 6 post-RT and peaked on day 14 post-RT, whereas no apparent uptake of [18F]FDG was shown on days 7 and 15 post-RT. MicroCT imaging did not show pneumonia until 42 days post-RT. Significant intense [18F]AlF-NOTA-QHY-04 uptake was confirmed by autoradiography. Immunofluorescence staining demonstrated expression of CXCR4 was significantly increased in the irradiated lung tissue, which correlated with results obtained from hematoxylin-eosin and Masson's trichrome staining. In 14 patients with radiation pneumonia, maximum standardized uptake values (SUVmax) were significantly higher in the irradiated lung compared with those in the normal lung. SUVmax of patients with grade 2 RILI was significantly higher than that of patients with grade 1 RILI.

CONCLUSION

This study indicated that [18F]AlF-NOTA-QHY-04 PET/CT imaging can detect RILI non-invasively and earlier than [18F]FDG PET/CT in a rat model. Clinical studies verified its feasibility, suggesting the clinical potential of [18F]AlF-NOTA-QHY-04 as a PET/CT tracer for early monitoring of RILI.

Acidity-induced ITGB6 promote migration and invasion of lung cancer cells by epithelial-mesenchymal transition and focal adhesion

Non-small cell lung cancer (NSCLC) is a prevalent tumor and acidic tumor microenvironment provides an energy source driving tumor progression. We previously demonstrated significantly upregulated Integrin β6 (ITGB6) in NSCLC cells. This study was designed to investigate the role of ITGB6 in NSCLC metastasis and explore the potential mechanisms. The expression of ITGB6 was evaluated in patients with NSCLC. Migration and invasion assays were utilized to investigate the role of ITGB6, and ChIP-qPCR and dual-luciferase reporter experiments preliminarily analyzed the relationship between ETS proto-oncogene 1 (ETS1) and ITGB6. Bioinformatics analysis and rescue models were performed to explore the underlying mechanisms. The results demonstrated that ITGB6 was upregulated in NSCLC patients and the difference was even more pronounced in patients with poor prognosis. Functionally, acidity-induced ITGB6 promoted migration and invasion of NSCLC cells in vitro, and epithelial-mesenchymal transition (EMT) and focal adhesion were the important mechanisms responsible for ITGB6-involved metastasis. Mechanistically, we revealed ETS1 enriched in the ITGB6 promoter region and promoted transcription to triggered the activation of subsequent signaling pathways. Moreover, ChIP-qPCR and dual-luciferase reporter experiments demonstrated that ETS1 played an important role in directly mediating ITGB6 expression. Furthermore, we found ITGB6 was responsible for the acidic microenvironment-mediated migration and invasion processes in NSCLC by performing rescue experiments with ITGB6 knockdown. Our findings indicated acidic microenvironment directly induced ETS1 to regulate the expression of ITGB6, and then the highly expressed ITGB6 further mediate EMT and activates the downstream focal adhesion pathways, eventually promotes the invasion and migration in NSCLC progression and metastasis.

Structural analysis of peptide binding to integrins for cancer detection and treatment

Integrins are cell receptors involved in several metabolic pathways often associated with cell proliferation. Some of these integrins are downregulated during human physical development, but when these integrins are overexpressed in adult humans, they can be associated with several diseases, such as cancer. Molecules that specifically bind to these integrins are useful for cancer detection, diagnosis, and treatment. This review focuses on the structures of integrin-peptidic ligand complexes to dissect how the binding occurs and the molecular basis of the specificity and affinity of these peptidic ligands. Understanding these interactions at the molecular level is fundamental to be able to design new peptides that are more specific and more sensitive to a particular integrin. The integrin complexes covered in this review are α5β1, αIIbβ3, αvβ3, αvβ6, and αvβ8, because the molecular structures of the complex have been experimentally determined and their presence on tumor cancer cells are associated with a poor prognosis, making them targets for cancer detection and treatment.

Early Prediction of Radiation-Induced Pulmonary Fibrosis Using Gastrin-Releasing Peptide Receptor-Targeted PET Imaging

Early diagnosis of radiation-induced pulmonary fibrosis (RIPF) in lung cancer patients after radiation therapy is important. A gastrin-releasing peptide receptor (GRPR) mediates the inflammation and fibrosis after irradiation in mice lungs. Previously, our group synthesized a GRPR-targeted positron emission tomography (PET) imaging probe, [⁶⁴Cu]Cu-NODAGA-galacto-bombesin (BBN), an analogue peptide of GRP. In this study, we evaluated the usefulness of [⁶⁴Cu]Cu-NODAGA-galacto-BBN for the early prediction of RIPF. We prepared RIPF mice and acquired PET/CT images of [¹⁸F]F-FDG and [⁶⁴Cu]Cu-NODAGA-galacto-BBN at 0, 2, 5, and 11 weeks after irradiation (n = 3-10). We confirmed that [⁶⁴Cu]Cu-NODAGA-galacto-BBN targets GRPR in irradiated RAW 264.7 cells. In addition, we examined whether [⁶⁴Cu]Cu-NODAGA-galacto-BBN monitors the therapeutic efficacy in RIPF mice (n = 4). As a result, the lung uptake ratio (irradiated-to-normal) of [⁶⁴Cu]Cu-NODAGA-galacto-BBN was the highest at 2 weeks, followed by its decrease at 5 and 11 weeks after irradiation, which matched with the expression of GRPR and was more accurately predicted than [¹⁸F]F-FDG. These uptake results were also confirmed by the cell uptake assay. Furthermore, [⁶⁴Cu]Cu-NODAGA-galacto-BBN could monitor the therapeutic efficacy of pirfenidone in RIPF mice. We conclude that [⁶⁴Cu]Cu-NODAGA-galacto-BBN is a novel PET imaging probe for the early prediction of RIPF-targeting GRPR expressed during the inflammatory response.

Delivery of Theranostic Nanoparticles to Various Cancers by Means of Integrin-Binding Peptides

Active targeting of tumors is believed to be the key to efficient cancer therapy and accurate, early-stage diagnostics. Active targeting implies minimized off-targeting and associated cytotoxicity towards healthy tissue. One way to acquire active targeting is to employ conjugates of therapeutic agents with ligands known to bind receptors overexpressed onto cancer cells. The integrin receptor family has been studied as a target for cancer treatment for almost fifty years. However, systematic knowledge on their effects on cancer cells, is yet lacking, especially when utilized as an active targeting ligand for particulate formulations. Decoration with various integrin-targeting peptides has been reported to increase nanoparticle accumulation in tumors ≥ 3-fold when compared to passively targeted delivery. In recent years, many newly discovered or rationally designed integrin-binding peptides with excellent specificity towards a single integrin receptor have emerged. Here, we show a comprehensive analysis of previously unreviewed integrin-binding peptides, provide diverse modification routes for nanoparticle conjugation, and showcase the most notable examples of their use for tumor and metastases visualization and eradication to date, as well as possibilities for combined cancer therapies for a synergetic effect. This review aims to highlight the latest advancements in integrin-binding peptide development and is directed to aid transition to the development of novel nanoparticle-based theranostic agents for cancer therapy.

Integrin Alpha v Beta 6 (αvβ6) and Its Implications in Cancer Treatment

Integrins are necessary for cell adhesion, migration, and positioning. Essential for inducing signalling events for cell survival, proliferation, and differentiation, they also trigger a variety of signal transduction pathways involved in mediating invasion, metastasis, and squamous-cell carcinoma. Several recent studies have demonstrated that the up- and down-regulation of the expression of αv and other integrins can be a potent marker of malignant diseases and patient prognosis. This review focuses on an arginine-glycine-aspartic acid (RGD)-dependent integrin αVβ6, its biology, and its role in healthy humans. We examine the implications of αVβ6 in cancer progression and the promotion of epithelial-mesenchymal transition (EMT) by contributing to the activation of transforming growth factor beta TGF-β. Although αvβ6 is crucial for proper function in healthy people, it has also been validated as a target for cancer treatment. This review briefly considers aspects of targeting αVβ6 in the clinic via different therapeutic modalities.

New PET Tracers: Current Knowledge and Perspectives in Lung Cancer

PET/CT with the tracer 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) has improved diagnostic imaging in cancer and is routinely used for diagnosing, staging and treatment planning in lung cancer patients. However, pitfalls of [¹⁸F]FDG-PET/CT limit the use in specific settings. Additionally, lung cancer is still the leading cause of cancer associated death and has high risk of recurrence after curative treatment. These circumstances have led to the continuous search for more sensitive and specific PET tracers to optimize lung cancer diagnosis, staging, treatment planning and evaluation. The objective of this review is to present and discuss current knowledge and perspectives of new PET tracers for use in lung cancer. A literature search was performed on PubMed and clinicaltrials.gov, limited to the past decade, excluding case reports, preclinical studies and studies on established tracers such as [¹⁸F]FDG and DOTATE. The most relevant papers from the search were evaluated. Several tracers have been developed targeting specific tumor characteristics and hallmarks of cancer. A small number of tracers have been studied extensively and evaluated head-to-head with [¹⁸F]FDG-PET/CT, whereas others need further investigation and validation in larger clinical trials. At this moment, none of the tracers can replace [¹⁸F]FDG-PET/CT. However, they might serve as supplementary imaging methods to provide more knowledge about biological tumor characteristics and visualize intra- and inter-tumoral heterogeneity.

Integrin αvβ6 as a Target for Tumor-Specific Imaging of Vulvar Squamous Cell Carcinoma and Adjacent Premalignant Lesions

Surgical removal of vulvar squamous cell carcinoma (VSCC) is associated with significant morbidity and high recurrence rates. This is at least partially related to the limited visual ability to distinguish (pre)malignant from normal vulvar tissue. Illumination of neoplastic tissue based on fluorescent tracers, known as fluorescence-guided surgery (FGS), could help resect involved tissue and decrease ancillary mutilation. To evaluate potential targets for FGS in VSCC, immunohistochemistry was performed on paraffin-embedded premalignant (high grade squamous intraepithelial lesion and differentiated vulvar intraepithelial neoplasia) and VSCC (human papillomavirus (HPV)-dependent and -independent) tissue sections with healthy vulvar skin as controls. Sections were stained for integrin αvβ6, CAIX, CD44v6, EGFR, EpCAM, FRα, MRP1, MUC1 and uPAR. The expression of each marker was quantified using digital image analysis. H-scores were calculated and percentages positive cells, expression pattern, and biomarker localization were assessed. In addition, tumor-to-background ratios were established, which were highest for (pre)malignant vulvar tissues stained for integrin αvβ6. In conclusion, integrin αvβ6 allowed for the most robust discrimination of VSCCs and adjacent premalignant lesions compared to surrounding healthy tissue in immunohistochemically stained tissue sections. The use of an αvβ6 targeted near-infrared fluorescent probe for FGS of vulvar (pre)malignancies should be evaluated in future studies.

Harnessing the power of foot-and-mouth-disease virus for targeting integrin alpha-v beta-6 for the therapy of cancer

Introduction: The integrin αvβ6 is a promising therapeutic target due to its limited expression in healthy tissue and significant overexpression in cancer and fibrosis. The peptide A20FMDV2, derived from the foot and mouth disease virus, is highly selective for αvβ6, and can be used therapeutically to target αvβ6 expressing cells.Areas covered: In this review, the authors discuss the logic that led to the discovery of A20FMDV2, the importance of its stereochemistry in receptor-binding, and the strategies employed to use it as a molecular-specific drug delivery system. These strategies include creating A20FMDV2-drug conjugates, genetically modifying oncolytic viruses to express A20FMDV2 and thus redirect their tropism to predominantly αvβ6 expressing cells, creation of A20FMDV2 expressing CAR T-cells, and modifying antibody tropism by inserting A20FMDV2 into the CDR3 loop.Expert opinion: αvβ6 is one of the most promising therapeutic targets in cancer and fibrosis discovered in the last few decades. The potential use of A20FMDV2 as a molecular-specific αvβ6-targeting agent is extremely promising, particularly when considering the success of the peptide and its variants in clinical imaging.

Optimized serum stability and specificity of an αvβ6 integrin-binding peptide for tumor targeting

The integrin αvβ6 is an antigen expressed at low levels in healthy tissue but upregulated during tumorigenesis, which makes it a promising target for cancer imaging and therapy. A20FMDV2 is a 20-mer peptide derived from the foot-and-mouth disease virus that exhibits nanomolar and selective affinity for αvβ6 versus other integrins. Despite this selectivity, A20FMDV2 has had limited success in imaging and treating αvβ6+ tumors in vivo because of its poor serum stability. Here, we explore the cyclization and modification of the A20FMDV2 peptide to improve its serum stability without sacrificing its affinity and specificity for αvβ6. Using cysteine amino acid substitutions and cyclization by perfluoroarylation with decafluorobiphenyl, we synthesized six cyclized A20FMDV2 variants and discovered that two retained binding to αvβ6 with modestly improved serum stability. Further d-amino acid substitutions and C-terminal sequence optimization outside the cyclized region greatly prolonged peptide serum stability without reducing binding affinity. While the cyclized A20FMDV2 variants exhibited increased nonspecific integrin binding compared with the original peptide, additional modifications with the non-natural amino acids citrulline, hydroxyproline, and d-alanine were found to restore binding specificity, with some modifications leading to greater αvβ6 integrin selectivity than the original A20FMDV2 peptide. The peptide modifications detailed herein greatly improve the potential of utilizing A20FMDV2 to target αvβ6 in vivo, expanding opportunities for cancer targeting and therapy.

Expression of Integrin β6 and HAX-1 Correlates with Aggressive Features and Poor Prognosis in Esophageal Squamous Cell Carcinoma

Purpose

The development of esophageal squamous cell carcinoma (ESCC) is a complicated process in which cell adhesion and motility, mediated by integrins, are involved through connecting the cytoskeleton to extracellular matrix. Different mechanisms via which integrin β6 participates in cancer invasion and metastasis have been described by numerous studies; however, the expression and clinical significance of integrin β6 in ESCC remain unknown.

Methods

To investigate the differential expression of integrin β6 in ESCC, qPCR and immunohistochemistry assays were performed in 10 paired human samples. A total of 137 ESCC samples were further enrolled to evaluate the expression levels of integrin β6 and its endocytic trafficking regulator HS1-associated protein X-1 (HAX-1), followed by the evaluation of their correlation with clinicopathological parameters. The overall survival was analyzed using the Kaplan–Meier method, with significant variables further evaluated by multivariate Cox regression analyses.

Results

The expression of integrin β6 was markedly increased in ESCC compared with matched adjacent normal tissues. Among the ESCC samples, positive expression of integrin β6 was observed in 41.6% tumors, which was associated with histological differentiation, lymph node metastasis and TNM stage. High expression of HAX-1 was detected in 47.4% tumors, and there was a positive relationship between the expression levels of integrin β6 and HAX-1. Furthermore, the expression of integrin β6 and HAX-1 were independent unfavorable indicators for prognosis. Patients with positive integrin β6 and high HAX-1 expression demonstrated worst outcomes.

Conclusion

The present findings suggested the predictive value of integrin β6 and HAX-1 as independent indicators of poor prognosis for patients with ESCC, both of which may contribute to the tumor proliferation and metastasis, leading to ESCC progression. Therefore, combined targeting of integrin β6 and HAX-1 may provide a potential novel approach for the treatment of ESCC.