Synthesis and evaluation of an 18 F-labeled derivative of F3 for targeting surface-expressed nucleolin in cancer and tumor endothelial cells

Nucleolin‑based targeting strategies in cancer treatment: Focus on cancer immunotherapy (Review)

The benefits of treating several types of cancers using immunotherapy have recently been established. The overexpression of nucleolin (NCL) in a number of types of cancer provides an attractive antigen target for the development of novel anticancer immunotherapeutic treatments. NCL is a multifunctional protein abundantly distributed in the nucleus, cytoplasm and cell membrane. It influences carcinogenesis, and the proliferation, survival and metastasis of cancer cells, leading to cancer progression. Additionally, the meta‑analysis of total and cytoplasmic NCL overexpression indicates a poor prognosis of patients with breast cancer. The AS1411 aptamers currently appear to have therapeutic action in the phase II clinical trial. The authors' research group has recently explored the anticancer function of NCL through the activation of T cells by dendritic cell‑based immunotherapy. The present review describes and discusses the mechanisms through which the multiple functions of NCL can participate in the progression of cancer. In addition, the studies that define the utility of NCL‑dependent anticancer therapies are summarized, with specific focus being paid to cancer immunotherapeutic approaches.

Quantum Dot-Based Screening Identifies F3 Peptide and Reveals Cell Surface Nucleolin as a Therapeutic Target for Rhabdomyosarcoma

Active drug delivery by tumor-targeting peptides is a promising approach to improve existing therapies for rhabdomyosarcoma (RMS), by increasing the therapeutic effect and decreasing the systemic toxicity, e.g., by drug-loaded peptide-targeted nanoparticles. Here, we tested 20 different tumor-targeting peptides for their ability to bind to two RMS cell lines, Rh30 and RD, using quantum dots Streptavidin and biotin-peptides conjugates as a model for nanoparticles. Four peptides revealed a very strong binding to RMS cells: NCAM-1-targeting NTP peptide, nucleolin-targeting F3 peptide, and two Furin-targeting peptides, TmR and shTmR. F3 peptide showed the strongest binding to all RMS cell lines tested, low binding to normal control myoblasts and fibroblasts, and efficient internalization into RMS cells demonstrated by the cytoplasmic delivery of the Saporin toxin. The expression of the nucleophosphoprotein nucleolin, the target of F3, on the surface of RMS cell lines was validated by competition with the natural ligand lactoferrin, by colocalization with the nucleolin-binding aptamer AS1411, and by the marked sensitivity of RMS cell lines to the growth inhibitory nucleolin-binding N6L pseudopeptide. Taken together, our results indicate that nucleolin-targeting by F3 peptide represents a potential therapeutic approach for RMS.

Advances in aptamer-based nuclear imaging

Aptamers are short oligonucleotides that bind to specific target molecules. They have been extensively explored in biomedical applications, including biosensing, medical imaging, and disease treatment. Their adjustable affinity for specific biomarkers stimulates more translational efforts, such as nuclear imaging of tumors in preclinical and clinical settings. In this review, we present recent advances of aptamer-based nuclear imaging and compare aptamer tracers with other biogenic probes in forms of peptides, nanobodies, monoclonal antibodies, and antibody fragments. Fundamental properties of aptamer-based radiotracers are highlighted and potential directions to improve aptamer's imaging performance are discussed. Despite many translational obstacles to overcome, we envision aptamers to be a versatile tool for cancer nuclear imaging in the near future.

Cell surface nucleolin as active bait for nanomedicine in cancer therapy: a promising option

Conventional chemotherapy used against cancer is mostly limited due to their non-targeted nature, affecting normal tissue and causing undesirable toxic effects to the affected tissue. With the aim of improving these treatments both therapeutically and in terms of their safety, numerous studies are currently being carried out using nanoparticles (NPs) as a vector combining tumor targeting and carrying therapeutic tools. In this context, it appears that nucleolin, a molecule over-expressed on the surface of tumor cells, is an interesting therapeutic target. Several ligands, antagonists of nucleolin of various origins, such as AS1411, the F3 peptide and the multivalent pseudopeptide N6L have been developed and studied as therapeutic tools against cancer. Over the last ten years or so, numerous studies have been published demonstrating that these antagonists can be used as tumor targeting agents with NPs from various origins. Focusing on nucleolin ligands, the aim of this article is to review the literature recently published or under experimentation in our research team to evaluate the efficacy and future development of these tools as anti-tumor agents.

Design, Synthesis and Binding Affinity Evaluation of Cytochrome P450 1B1 Targeted Chelators

BACKGROUND

Cytochrome P450 1B1 (CYP1B1) is specifically expressed in a variety of tumors which makes it a promise imaging target of tumor.

OBJECTIVE

We aimed to design and synthesize CYP1B1 targeted chelators for the potential application in positron emission tomography (PET) imaging of tumor.

METHODS

1,4,7-triazacyclononane-1,4-diiacetic acid (NODA) was connected to the CYP1B1 selective inhibitor we developed before through polyethylene glycol (PEG) linkers with different lengths. The inhibitory activities of chelators 6a-c against CYP1 family were evaluated by 7-ethoxyresorufin o-deethylation (EROD) assay. The manual docking between the chelators and the CYP1B1 are conducted subsequently. To determine the binding affinities of 6a-c to CYP1B1 in cells, we further performed a competition study at the cell level.

RESULTS

Among three chelators, 6a with the shortest linker showed the best inhibitory activity against CYP1B1. In the following molecular simulation study, protein-inhibitor complex of 6a showed the nearest F-heme distance which is consistent with the results of enzymatic assay. Finally, the cell based competitive assay proved the binding affinity of 6a-c to CYP1B1 enzyme.

CONCLUSION

We designed and synthesized a series of chelators which can bind to CYP1B1 enzyme in cancer cells.To our knowledge, this work is the first attempt to construct CYP1B1 targeted chelators for radiolabeling and we hope it will prompt the application of CYP1B1 imaging in tumor detection.

Ligand-Targeted Delivery of Photosensitizers for Cancer Treatment

Photodynamic therapy (PDT) is a promising cancer treatment which involves a photosensitizer (PS), light at a specific wavelength for PS activation and oxygen, which combine to elicit cell death. While the illumination required to activate a PS imparts a certain amount of selectivity to PDT treatments, poor tumor accumulation and cell internalization are still inherent properties of most intravenously administered PSs. As a result, common consequences of PDT include skin photosensitivity. To overcome the mentioned issues, PSs may be tailored to specifically target overexpressed biomarkers of tumors. This active targeting can be achieved by direct conjugation of the PS to a ligand with enhanced affinity for a target overexpressed on cancer cells and/or other cells of the tumor microenvironment. Alternatively, PSs may be incorporated into ligand-targeted nanocarriers, which may also encompass multi-functionalities, including diagnosis and therapy. In this review, we highlight the major advances in active targeting of PSs, either by means of ligand-derived bioconjugates or by exploiting ligand-targeting nanocarriers.

A recent update on the use of microbial transglutaminase for the generation of biotherapeutics

The recent scientific progresses on the use of enzyme-mediated reactions in organic, non-aqueous and aqueous media have significantly supported the growing demand of new biotechnological and/or pharmacological products. Today, a plethora of microbial enzymes, used as biocatalysts, are available. Among these, microbial transglutaminases (MTGs) are broadly used for their ability to catalyse the formation of an isopeptide bond between the γ-amide group of glutamines and the ε-amino group of lysine. Due to their promiscuity towards primary amine-containing substrates and the more stringent specificity for glutamine-containing peptide sequences, several combined approaches can be tailored for different settings, making MTGs very attractive catalysts for generating protein-protein and protein small molecule's conjugates. The present review offers a recent update on the modifications attainable by MTG-catalysed bioreactions as reported between 2014 and 2019. In particular, we present a detailed and comparative overview on the MTG-based methods for proteins and antibodies engineering, with a particular outlook on the synthesis of homogeneous antibody-drug conjugates.

Engineering a Nanostructured Nucleolin-Binding Peptide for Intracellular Drug Delivery in Triple-Negative Breast Cancer Stem Cells

Five peptide ligands of four different cell surface receptors (nucleolin, CXCR1, CMKLR1, and CD44v6) have been evaluated as targeting moieties for triple-negative human breast cancers. Among them, the peptide F3, derived from phage display, promotes the fast and efficient internalization of a genetically fused green fluorescent protein (GFP) inside MDA-MB-231 cancer stem cells in a specific receptor-dependent fashion. The further engineering of this protein into the modular construct F3-RK-GFP-H6 and the subsequent construct F3-RK-PE24-H6 resulted in self-assembling polypeptides that organize as discrete and regular nanoparticles. These materials, 15-20 nm in size, show enhanced nucleolin-dependent cell penetrability. We show that the F3-RK-PE24-H6, based on the Pseudomonas aeruginosa exotoxin A (PE24) as a core functional domain, is highly cytotoxic over target cells. The combination of F3, the cationic peptide (RK)n, and the toxin domain PE24 in such unusual presentation appears as a promising approach to cell-targeted drug carriers in breast cancers and addresses selective drug delivery in otherwise difficult-to-treat triple-negative breast cancers.

A positron emission tomography image-guidable unimolecular micelle nanoplatform for cancer theranostic applications

Unimolecular micelles based on hyperbranched polyamidoamine (PAMAM) dendrimer were synthesized as both a cargo delivery vector and an imaging agent for triple-negative breast tumors, and the chemical synthesis procedures are detailed in this study. With the chemical conjugation of a peptide (F3, against cellular nucleolin) to increase its cellular internalization, these micelles can accumulate potently and specifically in breast cancer cells (e.g., MDA-MB-231). The size and morphology of these PAMAM-based micelles have been measured by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The hydrazone bond (responsive to pH alteration) between the loaded doxorubicin (DOX, as a model drug here) and PAMAM micelles enables cargo release following pH changes. Flow cytometry and confocal fluorescence microscopy revealed that PAMAM micelles with F3 attachment (PAMAM-DOX-F3) had stronger internalization into MDA-MB-231 cells (nucleolin-positive) than PAMAM micelles without F3 conjugation (PAMAM-DOX), whereas both of them have minimal interactions with L929 fibroblasts (nucleolin-negative). The positron-emitting isotope ⁶⁴Cu was added into PAMAM micelles by chelation to track their pharmacokinetic behavior (organ distribution profile) in vivo by positron emission tomography (PET) imaging. Serial PET imaging demonstrated that the accumulation of ⁶⁴Cu-PAMAM-DOX-F3 in MDA-MB-231 tumors was fast, potent, and persistent (tumor uptake: 6.1 ± 1.2% injection dose per gram [%ID/g] at 24 h p.i.), significantly higher than that of ⁶⁴Cu-PAMAM-DOX (2.5 ± 0.4%ID/g at the same time). Their distribution profiles in other organs/tissues were quite similar, with a relatively short circulation time. In addition, ex vivo fluorescence imaging confirmed that DOX can be delivered efficiently by these PAMAM micelles to MDA-MB-231 tumors. Deducing from these data, we believe that PAMAM-based micelles can be useful for selective combinational treatment of cancer.

STATEMENT OF SIGNIFICANCE

Micelles are a very useful biomaterial for theranostic purposes, and one of the major hurdles for micelles (particularly those from self-assembling) is their relatively low stability, especially when administered in vivo. In this study, we have attempted to overcome this limitation by designing unimolecular micelles (based on the concept of "one micelle is composed of one macromolecule") from polyamidoamine (PAMAM) dendrimers, in which the drug cargos (e.g., doxorubicin) are chemically attached to PAMAM through a hydrazone bond; hence, they can be used as a tumor-selective diagnostic/therapeutic platform. These unimolecular micelles possess superior stability compared to conventional micelles and can undertake stimulus (pH)-responsive cargo release for more "targeted" cancer therapy. With the incorporation of a tumor-targeting peptide sequence (F3) and a positron-emitting isotope (copper-64), the pharmacokinetic behavior of these micelles can be readily monitored by positron emission tomography imaging technique to confirm their specificity against cancer tissues. With further optimization, this micellar platform can have a broad clinical applicability owing to its biocompatibility, selectivity, and stability.

Nucleus-targeted DNA tetrahedron as a nanocarrier of metal complexes for enhanced glioma therapy

A negatively-charged and nucleus-targeted DNA tetrahedron is rationally designed and used as a nanocarrier of positively-charged metal complexes. This tetrahedron speeds up the translocation of metal complexes into the cell nucleus, and inhibits the growth and invasion of glioma cells by triggering vascular mimicry-associated signaling pathways, thus achieving precise glioma treatment.

New perspectives of physiological and pathological functions of nucleolin (NCL)

Nucleolin (NCL) is a multifunctional protein that mainly localized in the nucleolus, it is also found in the nucleoplasm, cytoplasm and cell membrane. The three main structural domains allow the interaction of NCL with different proteins and RNA sequences. Moreover, specific post-translational modifications and its shuttling property also contribute to its multifunctionality. NCL has been demonstrated to be involved in a variety of aspects such as ribosome biogenesis, chromatin organization and stability, DNA and RNA metabolism, cytokinesis, cell proliferation, angiogenesis, apoptosis regulation, stress response and microRNA processing. NCL has been increasingly implicated in several pathological processes, especially in tumorigenesis and viral infection, which makes NCL a potential target for the development of anti-tumor and anti-viral strategies. In this review, we present an overview on the structure, localizations and various functions of NCL, and further describe how the multiple functions of NCL are correlated to its multiple cellular distributions.

Smart AS1411-aptamer conjugated pegylated PAMAM dendrimer for the superior delivery of camptothecin to colon adenocarcinoma in vitro and in vivo

In the current study camptothecin-loaded pegylated PAMAM dendrimer were synthesized and were functionalized with AS1411 anti-nucleolin aptamers for site-specific targeting against colorectal cancer cells which over expresses nucleolin receptors. The morphological properties and size dispersity of the prepared nanoparticles were evaluated using transmission electron microscope (TEM) and DLS. The drug-loading content and encapsulation efficiency were obtained 8.1% and 93.67% respectively. The in vitro release of camptothecin from the formulation was provided the sustained release of encapsulated camptothecin during 4days. Comparative in vitro cytotoxicity experiments demonstrated that the targeted camptothecin loaded-pegylated dendrimers had higher antiproliferation activity, towards nucleolin-positive HT29 and C26 colorectal cancer cells than nucleolin-negative CHO cell line. Fluorscence microscopy and flow cytometry also confirmed the enhanced cellular uptake of AS1411 targeted pegylated-dendrimer. In vivo study in C26 tumor-bearing BALB/C mice revealed that the AS1411-functionalized camptothecin loaded pegylated dendrimers improved antitumor activity and survival rate of the encapsulated camptothecin. Conjugation of AS1411 aptamer to the camptothecin loaded-pegylated dendrimer surface provides site-specific delivery of camptothecin, inhibit C26 tumor growth in vivo and significantly decrease systemic toxicity. These results suggested that the new nucleolin-targeted pegylated PAMAM dendrimer as a delivery system for camptothecin have the potential for the treatment of nucleolin-overexpressed colorectal cancer.

Synthesis and evaluation of an 18 F-labeled derivative of F3 for targeting surface-expressed nucleolin in cancer and tumor endothelial cells

The surface overexpression of nucleolin provides an anchor for the specific attachment of biomolecules to cancer and angiogenic endothelial cells. The peptide F3 is a high-affinity ligand of the nucleolin receptor (NR) that has been investigated as a carrier to deliver biologically active molecules to tumors for both therapeutic and imaging applications. A site-specific PEGylated F3 derivative was radiolabeled with [18 F]Al-F. The binding affinity and cellular distribution of the compound was assessed in tumor (H2N) and tumor endothelial (2H-11) cells. Specific uptake via the NR was demonstrated by the siRNA knockdown of nucleolin in both cell lines. The partition and the plasma stability of the compound were assessed at 37°C. The enzyme-mediated site-specific modification of F3 to give NODA-PEG-F3 (NP-F3) was achieved. Radiolabeling with [18 F]Al-F gave 18 F-NP-F3. 18 F-NP-F3 demonstrated high affinity for cancer and tumor endothelial cells. The siRNA knockdown of nucleolin resulted in a binding affinity reduction of 50% to 60%, confirming cell surface binding via the NR. NP-F3 was stable in serum for 2 h. 18 F-NP-F3 is reported as the first 18 F-labeled F3 derivative. It was obtained in a site-specific, high-yield, and efficient manner and binds to surface NR in the low nanomolar range, suggesting it has potential as a tumor and angiogenesis tracer.