Evaluation of 4-[18F]fluorobenzoyl-FALGEA-NH2 as a positron emission tomography tracer for epidermal growth factor receptor mutation variant III imaging in cancer

Peptide‑based therapeutic strategies for glioma: Current state and prospects

Glioma is a prevalent form of primary malignant central nervous system tumor, characterized by its cellular invasiveness, rapid growth, and the presence of the blood-brain barrier (BBB)/blood-brain tumor barrier (BBTB). Current therapeutic approaches, such as chemotherapy and radiotherapy, have shown limited efficacy in achieving significant antitumor effects. Therefore, there is an urgent demand for new treatments. Therapeutic peptides represent an innovative class of pharmaceutical agents with lower immunogenicity and toxicity. They are easily modifiable via chemical means and possess deep tissue penetration capabilities which reduce side effects and drug resistance. These unique pharmacokinetic characteristics make peptides a rapidly growing class of new therapeutics that have demonstrated significant progress in glioma treatment. This review outlines the efforts and accomplishments in peptide-based therapeutic strategies for glioma. These therapeutic peptides can be classified into four types based on their anti-tumor function: tumor-homing peptides, inhibitor/antagonist peptides targeting cell surface receptors, interference peptides, and peptide vaccines. Furthermore, we briefly summarize the results from clinical trials of therapeutic peptides in glioma, which shows that peptide-based therapeutic strategies exhibit great potential as multifunctional players in glioma therapy.

Innovative Diagnostic Peptide-Based Technologies for Cancer Diagnosis: Focus on EGFR-Targeting Peptides

Active targeting using biological ligands has emerged as a novel strategy for the targeted delivery of diagnostic agents to tumor cells. Conjugating functional targeting moieties with diagnostic probes can increase their accumulation in tumor cells and tissues, enhancing signal detection and, thus, the sensitivity of diagnosis. Due to their small size, ease of chemical synthesis and site-specific modification, high tissue penetration, low immunogenicity, rapid blood clearance, low cost, and biosafety, peptides offer several advantages over antibodies and proteins in diagnostic applications. Epidermal growth factor receptor (EGFR) is one of the most promising cancer biomarkers for actively targeting diagnostic and therapeutic agents to tumor cells due to its active involvement and overexpression in various cancers. Several peptides for EGFR-targeting have been identified in the last decades, which have been obtained by multiple means including derivation from natural proteins, phage display screening, positional scanning synthetic combinatorial library, and in silico screening. Many studies have used these peptides as a targeting moiety for diagnosing different cancers in vitro, in vivo, and in clinical trials. This review summarizes the progress of EGFR-targeting peptide-based assays in the molecular diagnosis of cancer.

Identification of a novel peptide ligand for the cancer-specific receptor mutation EGFRvIII using high-throughput sequencing of phage-selected peptides

We report here the selection and characterization of a novel peptide ligand using phage display targeted against the cancer-specific epidermal growth factor tyrosine kinase receptor mutation variant III (EGFRvIII). This receptor is expressed in several kinds of cancer: ovarian cancer, breast cancer and glioblastoma, but not in normal tissues. A 12-mer random peptide library was screened against EGFRvIII. Phage-selected peptides were sequenced in high-throughput by next generation sequencing (NGS), and their diversity was studied to identify highly abundant clones expected to bind with the highest affinities to EGFRvIII. The enriched peptides were characterized and their binding capacity towards stable cell lines expressing EGFRvIII, EGFR wild type (EGFR WT), or a low endogenous level of EGFR WT was confirmed by flow cytometry analysis. The best peptide candidate, VLGREEWSTSYW, was synthesized, and its binding specificity towards EGFRvIII was validated in vitro. Additionally, computational docking analysis suggested that the identified peptide binds selectively to EGFRvIII. The novel VLGREEWSTSYW peptide is thus a promising EGFRvIII-targeting agent for future applications in cancer diagnosis and therapy.

Recent Advances in Photo-mediated Radiofluorination

Carbon-fluorine bond formations have received a lot of attention because organofluorine compounds are widely used in pharmaceutical, agricultural, and materials science applications. In particular, the incorporation of fluorine-18, which is a commonly used radioisotope for radiopharmaceuticals for positron emission tomography (PET), a molecular imaging tool for the visualization of biochemical events, human metabolism processes, and the measurement and diagnosis of diseases in humans, plays a crucial role in clinical and preclinical studies. Several synthetic methodologies for carbon-fluorine-18 bond formation have been developed. However, conventional fluorination methods have some remaining drawbacks such as the high temperature and basic environment. Photo-induced catalysis is an emerging technique that allow chemists to achieve the synthesis of target molecular architectures under mild conditions. Moreover, several radiofluorination strategies have been developed via photocatalysis. In this review, we focused on describing recent advances in the field of light-mediated radiofluorination.

Novel Receptor Tyrosine Kinase Pathway Inhibitors for Targeted Radionuclide Therapy of Glioblastoma

Glioblastoma (GB) remains the most fatal brain tumor characterized by a high infiltration rate and treatment resistance. Overexpression and/or mutation of receptor tyrosine kinases is common in GB, which subsequently leads to the activation of many downstream pathways that have a critical impact on tumor progression and therapy resistance. Therefore, receptor tyrosine kinase inhibitors (RTKIs) have been investigated to improve the dismal prognosis of GB in an effort to evolve into a personalized targeted therapy strategy with a better treatment outcome. Numerous RTKIs have been approved in the clinic and several radiopharmaceuticals are part of (pre)clinical trials as a non-invasive method to identify patients who could benefit from RTKI. The latter opens up the scope for theranostic applications. In this review, the present status of RTKIs for the treatment, nuclear imaging and targeted radionuclide therapy of GB is presented. The focus will be on seven tyrosine kinase receptors, based on their central role in GB: EGFR, VEGFR, MET, PDGFR, FGFR, Eph receptor and IGF1R. Finally, by way of analyzing structural and physiological characteristics of the TKIs with promising clinical trial results, four small molecule RTKIs were selected based on their potential to become new therapeutic GB radiopharmaceuticals.

Magnetic Resonance Signal Amplification by Reversible Exchange of Selective PyFALGEA Oligopeptide Ligands Towards Epidermal Growth Factor Receptors

The biorelevant PyFALGEA oligopeptide ligand, which is selective towards the epidermal growth factor receptor (EGFR), has been successfully employed as a substrate in magnetic resonance signal amplification by reversible exchange (SABRE) experiments. It is demonstrated that PyFALGEA and the iridium catalyst IMes form a PyFALGEA:IMes molecular complex. The interaction between PyFALGEA:IMes and H₂ results in a ternary SABRE complex. Selective 1D EXSY experiments reveal that this complex is labile, which is an essential condition for successful hyperpolarization by SABRE. Polarization transfer from parahydrogen to PyFALGEA is observed leading to significant enhancement of the ¹ H NMR signals of PyFALGEA. Different iridium catalysts and peptides are inspected to discuss the influence of their molecular structures on the efficiency of hyperpolarization. It is observed that PyFALGEA oligopeptide hyperpolarization is more efficient when an iridium catalyst with a sterically less demanding NHC ligand system such as IMesBn is employed. Experiments with shorter analogues of PyFALGEA, that is, PyLGEA and PyEA, show that the bulky phenylalanine from the PyFALGEA oligopeptide causes steric hindrance in the SABRE complex, which hampers hyperpolarization with IMes. Finally, a single-scan ¹ H NMR SABRE experiment of PyFALGEA with IMesBn revealed a unique pattern of NMR lines in the hydride region, which can be treated as a fingerprint of this important oligopeptide.

An Electrochemical Biosensor Designed by Using Zr-Based Metal-Organic Frameworks for the Detection of Glioblastoma-Derived Exosomes with Practical Application

Glioblastoma (GBM) is one of the most fatal tumors in the brain, and its early diagnosis remains technically challenging due to the complex repertoires of oncogenic alterations and blood-brain barrier (BBB). GBM-derived specific exosomes can cross the BBB and circulate in body fluids, so they can be noninvasive biomarkers for the early diagnosis of GBM. Herein, we propose a sensitive and label-free electrochemical biosensor designed by using Zr-based metal-organic frameworks (Zr-MOFs) for the detection of GBM-derived exosomes with practical application. In the design, a peptide ligand can specifically bind with human epidermal growth factor receptor (EGFR) and EGFR variant (v) III mutation (EGFRvIII), which are overexpressed on the GBM-derived exosomes. Meanwhile, Zr-MOFs encapsulated with methylene blue can absorb on the surface of the exosomes due to the interaction between Zr⁴⁺ and the intrinsic phosphate groups outside of exosomes. Consequently, the concentration of exosomes can be directly quantified by monitoring the electroactive molecules inside MOFs, ranging from 9.5 × 10³ to 1.9 × 10⁷ particles/μL with the detection of limit of 7.83 × 10³ particles/μL. Furthermore, this proposed biosensor can distinguish GBM patients from healthy groups, demonstrating the great prospect for early clinical diagnosis.

Site-Selective, Late-Stage C-H 18 F-Fluorination on Unprotected Peptides for Positron Emission Tomography Imaging

Peptides are often ideal ligands for diagnostic molecular imaging due to their ease of synthesis and tuneable targeting properties. However, labelling unmodified peptides with ¹⁸ F for positron emission tomography (PET) imaging presents a number of challenges. Here we show the combination of photoactivated sodium decatungstate and [¹⁸ F]-N-fluorobenzenesulfonimide effects site-selective ¹⁸ F-fluorination at the branched position in leucine residues in unprotected and unaltered peptides. This streamlined process provides a means to directly convert native peptides into PET imaging agents under mild aqueous conditions, enabling rapid discovery and development of peptide-based molecular imaging tools.

In vivo evaluation of EGFRvIII mutation in primary glioblastoma patients via complex multiparametric MRI signature

Background

Epidermal growth factor receptor variant III (EGFRvIII) is a driver mutation and potential therapeutic target in glioblastoma. Non-invasive in vivo EGFRvIII determination, using clinically acquired multiparametric MRI sequences, could assist in assessing spatial heterogeneity related to EGFRvIII, currently not captured via single-specimen analyses. We hypothesize that integration of subtle, yet distinctive, quantitative imaging/radiomic patterns using machine learning may lead to non-invasively determining molecular characteristics, and particularly the EGFRvIII mutation.

Methods

We integrated diverse imaging features, including the tumor's spatial distribution pattern, via support vector machines, to construct an imaging signature of EGFRvIII. This signature was evaluated in independent discovery (n = 75) and replication (n = 54) cohorts of de novo glioblastoma, and compared with the EGFRvIII status obtained through an assay based on next-generation sequencing.

Results

The cross-validated accuracy of the EGFRvIII signature in classifying the mutation status in individual patients of the independent discovery and replication cohorts was 85.3% (specificity = 86.3%, sensitivity = 83.3%, area under the curve [AUC] = 0.85) and 87% (specificity = 90%, sensitivity = 78.6%, AUC = 0.86), respectively. The signature was consistent with EGFRvIII+ tumors having increased neovascularization and cell density, as well as a distinctive spatial pattern involving relatively more frontal and parietal regions compared with EGFRvIII- tumors.

Conclusions

An imaging signature of EGFRvIII was found, revealing a complex, yet distinct macroscopic glioblastoma phenotype. By non-invasively capturing the tumor in its entirety, the proposed methodology can assist in evaluating the tumor's spatial heterogeneity, hence overcoming common spatial sampling limitations of tissue-based analyses. This signature can preoperatively stratify patients for EGFRvIII-targeted therapies, and potentially monitor dynamic mutational changes during treatment.

EGFR/EGFRvIII Dual-Targeting Peptide-Mediated Drug Delivery for Enhanced Glioma Therapy

Tumor-homing peptides have been widely used to mediate active targeted drug delivery. l-AE is a reported targeting peptide demonstrating high binding affinity to epidermal growth factor receptor (EGFR) and mutation variant III (EGFRvIII) overexpressed on neovasculature, vasculogenic mimicry, tumor cells, and tumor stem cells. To improve its proteolytic stability, a d-peptide ligand (termed d-AE, the enantiomer of l-AE) was developed. d-AE was confirmed to bind receptors EGFR and EGFRvIII with targeting capability comparable to l-AE. In vivo biodistribution demonstrated the superiority of d-AE in prolonged circulation and enhanced intratumoral accumulation. Furthermore, stabilized peptide modification endowed micelles higher transcytosis efficiency and penetrating capability on blood-brain tumor barrier/U87 tumor spheroids coculture model. When paclitaxel (PTX) was loaded, d-AE-micelle/PTX demonstrated excellent antitumor effect in comparison to Taxol, micelle/PTX, and l-AE-micelle/PTX. These findings indicated that the multitargeted drug delivery system enabled by d-AE ligand provides a promising way for glioma therapy.

An EGFRvIII targeted dual-modal gold nanoprobe for imaging-guided brain tumor surgery

Surgery is a mainstay to treat malignant brain tumors. However, due to the infiltrative nature of these tumors, it is a great challenge for surgeons to accurately identify and excise all the tumor foci. EGFRvIII, a variant of epidermal growth factor receptor (EGFR), is found in 20% of glioblastoma cases, which is the brain tumor with the highest malignancy. In this study, we developed an EGFRvIII-targeted nanoprobe to guide glioblastoma surgery by pre-operatively defining the tumor boundary via magnetic resonance imaging (MRI) and intra-operatively guiding resection by surface-enhanced resonance Raman scattering (SERRS) imaging. In vivo MRI studies show that this nanoprobe delineates an orthotopic EGFRvIII+ U87MG glioblastoma xenograft with a higher target to background ratio than the control nanoprobe without targeting specificity. With the assistance of a handheld Raman scanner, this nanoprobe successfully guided EGFRvIII+ glioblastoma resection by tracking its characteristic SERRS signal peaks. Ex vivo Raman microscopy and histological images verified that this nanoprobe precisely demarcated the glioblastoma boundary and no residual neoplastic foci were observed in the tumor bed. This dual-modal nanoprobe not only precisely guided glioblastoma resection, but also overcame the brain shift induced false-positive signal by real-timely co-registering pre-operative and intra-operative images. This nanoprobe is promising for the improvement in diagnostic accuracy and surgical outcome of EGFRvIII+ glioblastoma.