Peptide-based imaging agents for cancer detection

EDB-FN-targeted probes for near infrared fluorescent imaging and positron emission tomography imaging of breast cancer in mice

The extra domain B splice variant of fibronectin (EDB-FN), which is overexpressed in several cancers, is an approved diagnostic and therapeutic target of cancers. The aim of this study was to evaluate the EDB-FN-targeting peptide EDBp as a noninvasive imaging modality for molecular imaging of breast cancer in mice. Western blot, flow cytometry and immunofluorescence were used to assess the expression level of EDB-FN and its binding to EDRp in MCF7, SKBR3, 4T1, EMT6, MDA-MB-231 and MDA-MB-453 cells. Establishment MDA-MB-231-luc cells-based subcutaneous tumor model mice or pulmonary metastasis model mice. The EDRp molecular probes to perform fluorescent probes for near-infrared fluorescence (NIRF)·and PET imaging of model mice. Our results demonstrate that EDBp-Cy5 had a strong binding ability to the MDA-MB-231 cells and exhibited specific tumor accumulation in MDA-MB-231 subcutaneous and pulmonary metastasis model mice. Importantly, the EDBp peptide-based radiotracer [18F]-AlF-NOTA-EDBp provided excellent diagnostic value for positron emission tomography (PET) imaging of breast cancer, especially in subcutaneous model mice. The uptake of [18F]-AlF-NOTA-EDBp in subcutaneous tumors (6.53 ± 0.89%, ID/g) was unexpectedly higher than that in the kidney (4.96 ± 0.20, %ID/g). The high tumor uptake of these probes in mice suggests their potential for application in imaging of EDB-FN-positive breast cancer for disease staging of regional and distant metastases.

Novel Gd-DTPA-peptide for targeted breast tumor magnetic resonance imaging

The prevalence of breast cancer underscores the imperative for early diagnosis in guiding treatment decisions. This study introduces a novel contrast agent, Gd-DTPA-VGB3, derived from the peptide VGB3 targeting vascular endothelial growth factor receptor-1 (VEGFR1) and VEGFR2, to enhance the contrast of conventional drug Magnevist in breast tumor MRI. The MRI contrast agent was synthesized on rink amide resin via Fmoc strategy, incorporating amino acids, and coupling to diethylenetriaminepentaacetic acid (DTPA). Gadolinium (Gd)-DTPA-VGB3 displayed specific binding to VEGFR1/2 in a displacement binding assay. Gd-DTPA-VGB3 exhibited minimal cytotoxicity to normal MCF-10 cells while inhibiting 4T1 mammary carcinoma cell proliferation. Compared to Magnevist, Gd-DTPA-VGB3 demonstrated a 2.8-fold increase in contrast-to-noise ratio (CNR) (355 vs. 125). Gd-DTPA-VGB3 exhibited enhanced accumulation in 4T1 tumor-bearing mice, resulting in significant signal intensity improvement. The findings highlight Gd-DTPA-VGB3's specific binding to VEGFRs, substantiating its potential as a candidate for enhancing MRI contrast in breast cancer diagnostics.

Assessing Krenning's score on 68 Ga-DOTATATE PET-CT and miPSMA score on 68 Ga-PSMA-11 PET-CT in TENIS: a comparison with FDG PET/CT and examining the feasibility of targeted radionuclide therapy

OBJECTIVES

The objective of this study was to assess receptor expression in metastatic differentiated thyroid carcinoma patients with progressive elevated thyroglobulin and negative iodine scintigraphy, we used 68 Ga-DOTATATE [Gallium-68 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-octreotate (DOTATATE)] (Krenning's score) and 68 Ga-PSMA-11 (Gallium-68 prostate-specific membrane antigen-11) PET-computed tomography (CT) [molecular imaging prostate-specific membrane antigen (miPSMA) score]. Patients with Krenning's score 3 and above and miPSMA score 2 and above were considered to determine the incidence of patients, who would qualify for treatment with 177 Lu-DOTATATE/PSMA [Lutetium-177 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-octreotate (DOTATATE)/prostate-specific membrane antigen]-based therapy. In addition, we compared 68 Ga-DOTATATE and 68 Ga-PSMA-11 PET-CT with 2-deoxy-2-[F-18]fluoroglucose ( 18 F-FDG) PET-CT (using maximum standardized uptake value).

MATERIALS AND METHODS

A total of 74 patients with histopathologically proven metastatic differentiated thyroid carcinoma with thyroglobulin elevation and negative iodine scintigraphy syndrome were studied retrospectively. They all had 18 F-FDG, 68 Ga-DOTATATE, and 68 Ga-PSMA-11 PET-CT scans available for undertaking this analysis. The lesions detected by 68 Ga-DOTATATE and 68 Ga-PSMA-11 were evaluated using Krenning's and miPSMA scores. In addition, quantitative comparisons of maximum standardized uptake values for 68 Ga-DOTATATE and 68 Ga-PSMA-11, as well as with 18 F-FDG, were conducted.

RESULTS

Patient-wise analysis revealed positivity rates of 40.5% for 68 Ga-DOTATATE, 41.89% for 68 Ga-PSMA-11, and 75.67% for 18 F-FDG. Among the 74 patients, 14 (18.91%) were deemed eligible for 177 Lu-DOTATATE/PSMA-617 therapy based on Krenning's score of 3 and above both/either miPSMA score of 2 and above on 68 Ga-DOTATATE or 68 Ga-PSMA-11 PET-CT. Within this subgroup, seven out of 74 patients (9.45%) were eligible for 177 Lu-DOTATATE therapy, and nine out of 74 patients (12.16%) were eligible for 177 Lu-PSMA-targeted therapy. Four patients were eligible for both therapies.

CONCLUSION

Among thyroglobulin elevation and negative iodine scintigraphy patient's subgroup, 9.45% could qualify for 177 Lu-DOTATATE and 12.16% for 177 Lu-PSMA-617. Four were eligible for both therapies. Given the lack of effective therapies, this subset of patients warrants consideration for radionuclide therapy exploration.

Development of New CD38 Targeted Peptides for Cancer Imaging

PURPOSE

Multiple myeloma (MM) affects over 35,000 patients each year in the US. There remains a need for versatile Positron Emission Tomography (PET) tracers for the detection, accurate staging, and monitoring of treatment response of MM that have optimal specificity and translational attributes. CD38 is uniformly overexpressed in MM and thus represents an ideal target to develop CD38-targeted small molecule PET radiopharmaceuticals to address these challenges.

PROCEDURES

Using phage display peptide libraries and pioneering algorithms, we identified novel CD38 specific peptides. Imaging bioconjugates were synthesized using solid phase peptide chemistry, and systematically analyzed in vitro and in vivo in relevant MM systems.

RESULTS

The CD38-targeted bioconjugates were radiolabeled with copper-64 (64Cu) with100% radiochemical purity and an average specific activity of 3.3 - 6.6 MBq/nmol. The analog NODAGA-PEG4-SL022-GGS (SL022: Thr-His-Tyr-Pro-Ile-Val-Ile) had a Kd of 7.55 ± 0.291 nM and was chosen as the lead candidate. 64Cu-NODAGA-PEG4-SL022-GGS demonstrated high binding affinity to CD38 expressing human myeloma MM.1S-CBR-GFP-WT cells, which was blocked by the non-radiolabeled version of the peptide analog and anti-CD38 clinical antibodies, daratumumab and isatuximab, by 58%, 73%, and 78%, respectively. The CD38 positive MM.1S-CBR-GFP-WT cells had > 68% enhanced cellular binding when compared to MM.1S-CBR-GFP-KO cells devoid of CD38. Furthermore, our new CD38-targeted radiopharmaceutical allowed visualization of tumors located in marrow rich bones, remaining there for up to 4 h. Clearance from non-target organs occurred within 60 min. Quantitative PET data from a murine disseminated tumor model showed significantly higher accumulation in the bones of tumor-bearing animals compared to tumor-naïve animals (SUVmax 2.06 ± 0.4 versus 1.24 ± 0.4, P = 0.02). Independently, tumor uptake of the target compound was significantly higher (P = 0.003) compared to the scrambled peptide, 64Cu-NODAGA-PEG4-SL041-GGS (SL041: Thr-Tyr-His-Ile-Pro-Ile-Val). The subcutaneous MM model demonstrated significantly higher accumulation in tumors compared to muscle at 1 and 4 h after tracer administration (SUVmax 0.8 ± 0.2 and 0.14 ± 0.04, P = 0.04 at 1 h; SUVmax 0.89 ± 0.01 and 0.09 ± 0.01, P = 0.0002 at 4 h).

CONCLUSIONS

The novel CD38-targeted, radiolabeled bioconjugates were specific and allowed visualization of MM, providing a starting point for the clinical translation of such tracers for the detection of MM.

Homodimeric peptide radiotracer [68Ga]Ga-NOTA-(TMVP1)2 for VEGFR-3 imaging of cervical cancer patients

PURPOSE

Vascular endothelial growth factor receptor 3 (VEGFR-3) plays a critical role in tumor lymphangiogenesis and metastasis, holding promise as a promising therapeutic target for solid tumors. TMVP1 (LARGR) is a 5-amino acid peptide previously identified in our laboratory from bacterial peptide display system that specifically targets VEGFR-3. Radiolabeled TMVP1 can be used for non-invasive imaging of VEGFR-3 expressing tumors. Homodimeric peptides have better targeting ability than monomeric peptides, and it is worth exploring whether homodimers of TMVP1 ((TMVP1)2) can achieve better imaging effects. This study aimed to explore the peptide properties and tumor assessment value of [68Ga]Ga-labeled (TMVP1)2.

METHODS

In this study, we developed a TMVP1 homodimer that was conjugated with 1,4,7-triazacyclononane-N, N', N″-triacetic acid (NOTA) via tetraethyleneglycol (PEG4) and triglyicine (Gly3) spacer, and labeled with 68Ga, to construct [68Ga]Ga-NOTA-(TMVP1)2. Binding of VEGFR-3 by TMVP1 and (TMVP1)2, respectively, was modeled by molecular docking. The affinity of [68Ga]Ga-NOTA-(TMVP1)2 for VEGFR-3 and its ability to bind to cells were evaluated. MicroPET imaging and biodistribution studies of [68Ga]Ga-NOTA-(TMVP1)2 were performed in subcutaneous C33A cervical cancer xenografts. Five healthy volunteers and eight patients with cervical cancer underwent whole-body PET/CT acquisition 30-45 min after intravenous injection of [68Ga]Ga-NOTA-(TMVP1)2.

RESULTS

Both molecular docking and cellular experiments showed that homodimeric TMVP1 had a higher affinity for VEGFR-3 than monomeric TMVP1. [68Ga]Ga-NOTA-(TMVP1)2 was excreted mainly through the renal route and partly through the liver route. In mice bearing C33A xenografts, [68Ga]Ga-NOTA-(TMVP1)2 specifically localized in the tumor (2.32 ± 0.10% ID/g). Pretreatment of C33A xenograft mice with the unlabeled peptide NOTA-(TMVP1)2 reduced the enrichment of [68Ga]Ga-NOTA-(TMVP1)2 in tumors (0.58 ± 0.01% ID/g). [68Ga]Ga-NOTA-(TMVP1)2 proved to be safe in all healthy volunteers and recruited patients, with no side effects or allergies noted. In cervical cancer patients, a majority of the [18F]-FDG identified lesions (18/22, 81.8%) showed moderate to high signal intensity on [68Ga]Ga-NOTA-(TMVP1)2. SUVmax and SUVmean were 2.32 ± 0.77 and 1.61 ± 0.48, respectively. With normal muscle (gluteus maximus) as background, tumor-to-background ratios were 3.49 ± 1.32 and 3.95 ± 1.64 based on SUVmax and SUVmean, respectively.

CONCLUSION

The favorable characterizations of [68Ga]Ga-NOTA-(TMVP1)2 such as convenient synthesis, high specific activity, and high tumor uptake enable the evaluation of VEGFR-3 in cervical cancer patients and warrant further clinical studies.

TRIAL REGISTRATION

ChiCTR-DOD-17012458. Registered August 23, 2017 (retrospectively registered).

Structural Defect-Enabled Magnetic Neutrality Nanoprobes for Ultra-High-Field Magnetic Resonance Imaging of Isolated Tumor Cells in Vivo

The identification of metastasis "seeds," isolated tumor cells (ITCs), is of paramount importance for the prognosis and tailored treatment of metastatic diseases. The conventional approach to clinical ITCs diagnosis through invasive biopsies is encumbered by the inherent risks of overdiagnosis and overtreatment. This underscores the pressing need for noninvasive ITCs detection methods that provide histopathological-level insights. Recent advancements in ultra-high-field (UHF) magnetic resonance imaging (MRI) have ignited hope for the revelation of minute lesions, including the elusive ITCs. Nevertheless, currently available MRI contrast agents are susceptible to magnetization-induced strong T2-decaying effects under UHF conditions, which compromises T1 MRI capability and further impedes the precise imaging of small lesions. Herein, this study reports a structural defect-enabled magnetic neutrality nanoprobe (MNN) distinguished by its paramagnetic properties featuring an exceptionally low magnetic susceptibility through atomic modulation, rendering it almost nonmagnetic. This unique characteristic effectively mitigates T2-decaying effect while concurrently enhancing UHF T1 contrast. Under 9 T MRI, the MNN demonstrates an unprecedentedly low r2/r1 value (≈1.06), enabling noninvasive visualization of ITCs with an exceptional detection threshold of ≈0.16 mm. These high-performance MNNs unveil the domain of hitherto undetectable minute lesions, representing a significant advancement in UHF-MRI for diagnostic purposes and fostering comprehensive metastasis research.

Biological Activity of Natural and Synthetic Peptides as Anticancer Agents

Cancer is one of the leading causes of morbidity and death worldwide, making it a serious global health concern. Chemotherapy, radiotherapy, and surgical treatment are the most used conventional therapeutic approaches, although they show several side effects that limit their effectiveness. For these reasons, the discovery of new effective alternative therapies still represents an enormous challenge for the treatment of tumour diseases. Recently, anticancer peptides (ACPs) have gained attention for cancer diagnosis and treatment. ACPs are small bioactive molecules which selectively induce cancer cell death through a variety of mechanisms such as apoptosis, membrane disruption, DNA damage, immunomodulation, as well as inhibition of angiogenesis, cell survival, and proliferation pathways. ACPs can also be employed for the targeted delivery of drugs into cancer cells. With over 1000 clinical trials using ACPs, their potential for application in cancer therapy seems promising. Peptides can also be utilized in conjunction with imaging agents and molecular imaging methods, such as MRI, PET, CT, and NIR, improving the detection and the classification of cancer, and monitoring the treatment response. In this review we will provide an overview of the biological activity of some natural and synthetic peptides for the treatment of the most common and malignant tumours affecting people around the world.

Preclinical evaluation of 68 Ga-labeled peptide CK2 for PET imaging of NRP-1 expression in vivo

PURPOSE

Neuropilin-1 (NRP-1) is a multifunctional protein involved in a variety of biological processes such as angiogenesis, tumorigenesis and immunomodulation. It was usually overexpressed in many cancer cell lines and correlated with poor prognosis of breast cancer. Positron emission tomography (PET) is an advanced imaging technique for detecting the function and metabolism of tumor-associated molecules in real time, dynamically, quantitatively and noninvasively. To improve the level of early diagnosis and evaluate the prognosis of breast cancer, an NRP-1 targeting peptide-based tracer [68 Ga]Ga-NOTA-PEG4-CK2 was designed to sensitively and specifically detect the NRP-1 expression in vivo via PET imaging.

METHODS

In silico modeling and microscale thermophoresis (MST) assay were carried out to design the NRP-1 targeting peptide NOTA-PEG4-CK2, and it was further radiolabeled with 68 Ga to prepare the tracer [68 Ga]Ga-NOTA-PEG4-CK2. The radiochemical yield (RCY), radiochemical purity (RCP), molar activity (Am), lipid-water partition coefficient (Log P) and stability of [68 Ga]Ga-NOTA-PEG4-CK2 were assessed. The targeting specificity of the tracer for NRP-1 was investigated by in vitro cellular uptake assay and in vivo PET imaging as well as blocking studies. The sensitivity of the tracer in monitoring the dynamic changes of NRP-1 expression induced by chemical drug was also investigated in vitro and in vivo. Ex vivo biodistribution, autoradiography, western blot, and immunofluorescence staining were also performed to study the specificity of [68 Ga]Ga-NOTA-PEG4-CK2 for NRP-1.

RESULTS

[68 Ga]Ga-NOTA-PEG4-CK2 was designed and synthesized with high RCY (> 98%), high stability (RCP > 95%) and high affinity to NRP-1 (KD = 25.39 ± 1.65 nM). In vitro cellular uptake assay showed that the tracer [68 Ga]Ga-NOTA-PEG4-CK2 can specifically bind to NRP-1 positive cancer cells MDA-MB-231 (1.04 ± 0.04% at 2 h) rather than NRP-1 negative cancer cells NCI-H1299 (0.43 ± 0.05%). In vivo PET imaging showed the maximum tumor uptake of [68 Ga]Ga-NOTA-PEG4-CK2 in MDA-MB-231 xenografts (4.16 ± 0.67%ID/mL) was significantly higher than that in NCI-H1299 xenografts (1.03 ± 0.19%ID/mL) at 10 min post injection, and the former exhibited higher tumor-to-muscle uptake ratio (5.22 ± 0.18) than the latter (1.07 ± 0.27) at 60 min post injection. MDA-MB-231 xenografts pretreated with nonradioactive precursor NOTA-PEG4-CK2 showed little tumor uptake of [68 Ga]Ga-NOTA-PEG4-CK2 (1.67 ± 0.38%ID/mL at 10 min post injection). Both cellular uptake assay and PET imaging revealed that NRP-1 expression in breast cancer MDA-MB-231 could be effectively suppressed by SB-203580 treatment and can be sensitively detected by [68 Ga]Ga-NOTA-PEG4-CK2. Ex vivo analysis also proved the high specificity and sensitivity of [68 Ga]Ga-NOTA-PEG4-CK2 for NRP-1 expression in MDA-MB-231 xenografts.

CONCLUSION

A promising NRP-1 targeting PET tracer [68 Ga]Ga-NOTA-PEG4-CK2 was successfully prepared. It showed remarkable specificity and sensitivity in monitoring the dynamic changes of NRP-1 expression. Hence, it could provide valuable information for early diagnosis of NRP-1 relevant cancers and evaluating the prognosis of cancer patients.

Synthesis and preclinical evaluation of a novel probe [18F]AlF-NOTA-IPB-GPC3P for PET imaging of GPC3 positive tumor

Glypican-3 (GPC3) is markedly overexpressed in hepatocellular carcinoma (HCC) and not expressed in normal liver tissues. In this study, a novel peptide PET imaging agent ([18F]AlF-NOTA-IPB-GPC3P) was developed to target GPC3 expressed in tumors. The overall radiochemical yield of [18F]AlF-NOTA-IPB-GPC3P was 10-15 %, and its lipophilicity, expressed as the logD value at a pH of 7.4, was -1.18 ± 0.06 (n = 3). Compared to the previously reported tracer [18F]AlF-GP2633, [18F]AlF-NOTA-IPB-GPC3P exhibited higher cellular uptake (15.13 vs 5.96) and internalized rate (80.63 % vs 35.93 %) in Huh7 cells at 120 min. Micro-PET/CT and biodistribution studies further demonstrated that [18F]AlF-NOTA-IPB-GPC3P exhibited significantly increased tumor uptake and prolonged tumor residence in Huh7 tumors compared to [18F]AlF-GP2633 (4.66 ± 0.22 % ID/g vs 0.72 ± 0.09 % ID/g at 60 min, p < 0.001; 5.05 ± 0.23 % ID/g vs 0.35 ± 0.08 % ID/g at 120 min, p < 0.001, respectively). Furthermore, the tumor-to-organ ratios of [18F]AlF-NOTA-IPB-GPC3P surpassed those of [18F]AlF-GP2633. Our results support the utilization of [18F]AlF-NOTA-IPB-GPC3P as a PET imaging agent targeting the GPC3 receptor for tumor detection.

68Ga labeled EphA2-targeted cyclic peptide: a novel positron imaging tracer for triple-negative breast cancer?

The absence of better biomarkers currently limits early diagnosis and treatment of triple-negative breast cancer (TNBC). Our previously published study reported that the cyclic-peptide SD01 exhibited specific binding to EphA2 (Ephrin type-A receptor 2) on TNBC. To develop a novel PET imaging agent, we prepared gallium-68 (68Ga) labeled-DOTA-SD01 and evaluated its specificity and effectiveness through micro PET/CT imaging in a TNBC-bearing mouse model. SD01 and a control linear peptide YSA were conjugated to DOTA and subsequently labeled with 68Ga, obtaining 68Ga-DOTA-SD01 and 68Ga-DOTA-YSA. Both showed high radiochemical purity, stability, good hydrophilicity, and high binding affinity to 4T1 cells. Micro PET/CT imaging showed high radioactivity accumulation in tumors; SUVmean (mean standardized uptake value) of tumors in the group of 68Ga-DOTA-SD01 was 3.34 ± 0.25 and 2.65 ± 0.32 in the group of 68Ga-DOTA-YSA; T/NT ratios (target to non-target, SUVmean ratios of tumor to muscle) were 3.12 ± 0.06 and 2.77 ± 0.11 at 30 min, respectively (p < 0.05). The biodistribution study showed that tumor uptake % ID per g (percentage of injected dose per gram of tissue) in the group of 68Ga-DOTA-SD01 was 2.73 ± 0.34, and 1.77 ± 0.38 in the group of 68Ga-DOTA-YSA; T/NT ratios (radioactivity of tumor to muscle) were 3.55 ± 0.12 and 3.05 ± 0.10 for both groups at 30 min, respectively (p < 0.05). All these suggest that 68Ga-DOTA-SD01 may act as a better novel PET imaging agent for EphA2 positive tumors, such as TNBC.

Facile Peptide Macrocyclization and Multifunctionalization via Cyclen Installation

Cyclen-peptide bioconjugates are usually prepared in multiple steps that require individual preparation and purification of the cyclic peptide and hydrophilic cyclen derivatives. An efficient strategy is discovered for peptide cyclization and functionalization toward lanthanide probe via three components intermolecular crosslinking on solid-phase peptide synthesis with high conversion yield. Multifunctionality can be conferred by introducing different modular parts or/and metal ions on the cyclen-embedded cyclopeptide. As a proof-of-concept, a luminescent Eu3+ complex and a Gd3+-based contrasting agent for in vitro optical imaging and in vivo magnetic resonance imaging, respectively, are demonstrated through utilizing this preparation of cyclen-embedded cyclic arginylglycylaspartic acid (RGD) peptide.

Strategies to address key challenges of metallacycle/metallacage-based supramolecular coordination complexes in biomedical applications

Owing to their capacity for dynamically linking two or more functional molecules, supramolecular coordination complexes (SCCs), exemplified by two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages, have gained increasing significance in biomedical applications. However, their inherent hydrophobicity and self-assembly driven by heavy metal ions present common challenges in their applications. These challenges can be overcome by enhancing the aqueous solubility and in vivo circulation stability of SCCs, alongside minimizing their side effects during treatment. Addressing these challenges is crucial for advancing the fundamental research of SCCs and their subsequent clinical translation. In this review, drawing on extensive contemporary research, we offer a thorough and systematic analysis of the strategies employed by SCCs to surmount these prevalent yet pivotal obstacles. Additionally, we explore further potential challenges and prospects for the broader application of SCCs in the biomedical field.

Ligand-Mediated Magnetism-Conversion Nanoprobes for Activatable Ultra-High Field Magnetic Resonance Imaging

Ultra-high field (UHF) magnetic resonance imaging (MRI) has emerged as a focal point of interest in the field of cancer diagnosis. Despite the ability of current paramagnetic or superparamagnetic smart MRI contrast agents to selectively enhance tumor signals in low-field MRI, their effectiveness at UHF remains inadequate due to inherent magnetism. Here, we report a ligand-mediated magnetism-conversion nanoprobe (MCNP) composed of 3-mercaptopropionic acid ligand-coated silver-gadolinium bimetallic nanoparticles. The MCNP exhibits a pH-dependent magnetism conversion from ferromagnetism to diamagnetism, facilitating tunable nanomagnetism for pH-activatable UHF MRI. Under neutral pH, the thiolate (-S- ) ligands lead to short τ'm and increased magnetization of the MCNPs. Conversely, in the acidic tumor microenvironment, the thiolate ligands are protonated and transform into thiol (-SH) ligands, resulting in prolonged τ'm and decreased magnetization of the MCNP, thereby enhancing longitudinal relaxivity (r1) values at UHF MRI. Notably, under a 9 T MRI field, the pH-sensitive changes in Ag-S binding affinity of the MCNP lead to a remarkable (>10-fold) r1 increase in an acidic medium (pH 5.0). In vivo studies demonstrate the capability of MCNPs to amplify MRI signal of hepatic tumors, suggesting their potential as a next-generation UHF-tailored smart MRI contrast agent.

Peptide Therapeutics: Unveiling the Potential against Cancer-A Journey through 1989

The United States Food and Drug Administration (FDA) has approved a plethora of peptide-based drugs as effective drugs in cancer therapy. Peptides possess high specificity, permeability, target engagement, and a tolerable safety profile. They exhibit selective binding with cell surface receptors and proteins, functioning as agonists or antagonists. They also serve as imaging agents for diagnostic applications or can serve a dual-purpose as both diagnostic and therapeutic (theragnostic) agents. Therefore, they have been exploited in various forms, including linkers, peptide conjugates, and payloads. In this review, the FDA-approved prostate-specific membrane antigen (PSMA) peptide antagonists, peptide receptor radionuclide therapy (PRRT), somatostatin analogs, antibody-drug conjugates (ADCs), gonadotropin-releasing hormone (GnRH) analogs, and other peptide-based anticancer drugs are analyzed in terms of their chemical structures and properties, therapeutic targets and mechanisms of action, development journey, administration routes, and side effects.

Advances in MRI: Peptide and peptidomimetic-based contrast agents

Magnetic resonance imaging (MRI) is a common medical imaging technique that provides three-dimensional body images. MRI contrast agents improve image contrast by raising the rate of water proton relaxation in specific tissues. Peptides and peptidomimetics act as scaffolds for MRI imaging agents because of their increased size and offer the possibility to engine a higher hydration value within the design. The design of a new Gd-based contrast agent must take into account high stability constants to avoid free Gd(III), with the subsequent nephrotoxicity, and high relaxivity values. This review analyzes various synthetic approaches, reports studies of relaxometric parameters, and focuses on the description and application of Gd(III)-chelates based on peptide and peptidomimetic scaffolds. In addition, the X-ray molecular structures of three DOTA complexes will be reported to emphasize the necessity of using the X-ray diffraction analysis to identify the coordination sphere of the metals and the mechanism of action of the compounds.

Precision peptide theranostics: developing N- to C-terminus optimized theranostics targeting cholecystokinin-2 receptor

Peptides are ideal for theranostic development as they afford rapid target accumulation, fast clearance from background tissue, and exhibit good tissue penetration. Previously, we developed a novel series of peptides that presented discreet folding propensity leading to an optimal candidate [68Ga]Ga-DOTA-GA1 ([D-Glu]6-Ala-Tyr-NMeGly-Trp-NMeNle-Asp-Nal-NH2) with 50 pM binding affinity against cholecystokinin-2 receptors (CCK2R). However, we were confronted with challenges of unfavorably high renal uptake. Methods: A structure activity relationship study was undertaken of the lead theranostic candidate. Prudent structural modifications were made to the peptide scaffold to evaluate the contributions of specific N-terminal residues to the overall biological activity. Optimal candidates were then evaluated in nude mice bearing transfected A431-CCK2 tumors, and their biodistribution was quantitated ex vivo. Results: We identified and confirmed that D-Glu3 to D-Ala3 substitution produced 2 optimal candidates, [68Ga]Ga-DOTA-GA12 and [68Ga]Ga-DOTA-GA13. These radiopeptides presented with high target/background ratios, enhanced tumor retention, excellent metabolic stability in plasma and mice organ homogenates, and a 4-fold reduction in renal uptake, significantly outperforming their non-alanine counterparts. Conclusions: Our study identified novel radiopharmaceutical candidates that target the CCK2R. Their high tumor uptake and reduced renal accumulation warrant clinical translation.

Deciphering the Synthetic and Refolding Strategy of a Cysteine-Rich Domain in the Tumor Necrosis Factor Receptor (TNF-R) for Racemic Crystallography Analysis and d-Peptide Ligand Discovery

Many cell-surface receptors are promising targets for chemical synthesis because of their critical roles in disease development. This synthetic approach enables investigations by racemic protein crystallography and ligand discovery by mirror-image methodologies. However, due to their complex nature, the chemical synthesis of a receptor can be a significant challenge. Here, we describe the chemical synthesis and folding of a central, cysteine-rich domain of the cell-surface receptor tumor necrosis factor 1 which is integral to binding of the cytokine TNF-α, namely, TNFR-1 CRD2. Racemic protein crystallography at 1.4 Å confirmed that the native binding conformation was preserved, and TNFR-1 CRD2 maintained its capacity to bind to TNF-α (KD ≈ 7 nM). Encouraged by this discovery, we carried out mirror-image phage display using the enantiomeric receptor mimic and identified a d-peptide ligand for TNFR-1 CRD2 (KD = 1 μM). This work demonstrated that cysteine-rich domains, including the central domains, can be chemically synthesized and used as mimics for investigations.

Peptide-Drug Conjugates: Design, Chemistry, and Drug Delivery System as a Novel Cancer Theranostic

The emergence of peptide-drug conjugates (PDCs) that utilize target-oriented peptide moieties as carriers of cytotoxic payloads, interconnected with various cleavable/noncleavable linkers, resulted in the key-foundation of the new era of targeted therapeutics. They are capable of retaining the integrity of conjugates in the blood circulatory system as well as releasing the drugs at the tumor microenvironment. Other valuable advantages are specificity and selectivity toward targeted-receptors, higher penetration ability, and drug-loading capacity, making them a suitable candidate to play their vital role as promising carrier agents. In this review, we summarized the types of cell-targeting (CTPs) and cell-penetrating peptides (CPPs) that have broad applications in the advancement of targeted drug-delivery systems (DDS). Moreover, the techniques to overcome the limitations of peptide-chemistry for their extensive implementation to construct the PDCs. Besides this, the diversified breakthrough of linker chemistry, and ample knowledge of various cytotoxic payloads used in PDCs in recent years, as well as the mechanism of action of PDCs was critically discussed. The principal aim is to provide scattered and diversified knowledge in one place and to help researchers understand the pinching knots in the science of PDC development, also their progression toward a bright future for PDCs as novel theranostics in clinical practice.

Targeting the Oxytocin Receptor for Breast Cancer Management: A Niche for Peptide Tracers

Breast cancer is a leading cause of death in women, and its management highly depends on early disease diagnosis and monitoring. This remains challenging due to breast cancer's heterogeneity and a scarcity of specific biomarkers that could predict responses to therapy and enable personalized treatment. This Perspective describes the diagnostic landscape for breast cancer management, molecular strategies targeting receptors overexpressed in tumors, the theranostic potential of the oxytocin receptor (OTR) as an emerging breast cancer target, and the development of OTR-specific optical and nuclear tracers to study, visualize, and treat tumors. A special focus is on the chemistry and pharmacology underpinning OTR tracer development, preclinical in vitro and in vivo studies, challenges, and future directions. The use of peptide-based tracers targeting upregulated receptors in cancer is a highly promising strategy complementing current diagnostics and therapies and providing new opportunities to improve cancer management and patient survival.

The role of clinical imaging in oncology drug development: progress and new challenges

In 2008, the role of clinical imaging in oncology drug development was reviewed. The review outlined where imaging was being applied and considered the diverse demands across the phases of drug development. A limited set of imaging techniques was being used, largely based on structural measures of disease evaluated using established response criteria such as response evaluation criteria in solid tumours. Beyond structure, functional tissue imaging such as dynamic contrast-enhanced MRI and metabolic measures using [18F]flourodeoxyglucose positron emission tomography were being increasingly incorporated. Specific challenges related to the implementation of imaging were outlined including standardisation of scanning across study centres and consistency of analysis and reporting. More than a decade on the needs of modern drug development are reviewed, how imaging has evolved to support new drug development demands, the potential to translate state-of-the-art methods into routine tools and what is needed to enable the effective use of this broadening clinical trial toolset. In this review, we challenge the clinical and scientific imaging community to help refine existing clinical trial methods and innovate to deliver the next generation of techniques. Strong industry-academic partnerships and pre-competitive opportunities to co-ordinate efforts will ensure imaging technologies maintain a crucial role delivering innovative medicines to treat cancer.

Preclinical Research Highlighting Contemporary Targeting Mechanisms of Radiolabelled Compounds for PET Based Infection Imaging

It is important to constantly monitor developments in the preclinical imaging arena of infection. Firstly, novel radiopharmaceuticals with the correct characteristics must be identified to funnel into the clinic. Secondly, it must be evaluated if enough innovative research is being done and adequate resources are geared towards the development of radiopharmaceuticals that could feed into the Nuclear Medicine Clinic in the near future. It is proposed that the ideal infection imaging agent will involve PET combined with CT but more ideally MRI. The radiopharmaceuticals currently presented in preclinical literature have a wide selection of vectors and targets. Ionic formulations of PET-radionuclides such 64CuCl2 and 68GaCl2 are evaluated for bacterial infection imaging. Many small molecule based radiopharmaceuticals are being investigated with the most prominent targets being cell wall synthesis, maltodextrin transport (such as [18F]F-maltotriose), siderophores (bacterial and fungal infections), the folate synthesis pathway (such as [18F]F-PABA) and protein synthesis (radiolabelled puromycin). Mycobacterial specific antibiotics, antifungals and antiviral agents are also under investigation as infection imaging agents. Peptide based radiopharmaceuticals are developed for bacterial, fungal and viral infections. The radiopharmaceutical development could even react quickly enough on a pandemic to develop a SARS-CoV-2 imaging agent in a timely fashion ([64Cu]Cu-NOTA-EK1). New immuno-PET agents for the imaging of viruses have recently been published, specifically for HIV persistence but also for SARS-CoV2. A very promising antifungal immuno-PET agent (hJ5F) is also considered. Future technologies could include the application of aptamers and bacteriophages and even going as far as the design of theranostic infection. Another possibility would be the application of nanobodies for immuno-PET applications. Standardization and optimization of the preclinical evaluation of radiopharmaceuticals could enhance clinical translation and reduce time spent in pursuing less than optimal candidates.

Peptide-Based Agents for Cancer Treatment: Current Applications and Future Directions

Peptide-based strategies have received an enormous amount of attention because of their specificity and applicability. Their specificity and tumor-targeting ability are applied to diagnosis and treatment for cancer patients. In this review, we will summarize recent advancements and future perspectives on peptide-based strategies for cancer treatment. The literature search was conducted to identify relevant articles for peptide-based strategies for cancer treatment. It was performed using PubMed for articles in English until June 2023. Information on clinical trials was also obtained from ClinicalTrial.gov. Given that peptide-based strategies have several advantages such as targeted delivery to the diseased area, personalized designs, relatively small sizes, and simple production process, bioactive peptides having anti-cancer activities (anti-cancer peptides or ACPs) have been tested in pre-clinical settings and clinical trials. The capability of peptides for tumor targeting is essentially useful for peptide-drug conjugates (PDCs), diagnosis, and image-guided surgery. Immunomodulation with peptide vaccines has been extensively tested in clinical trials. Despite such advantages, FDA-approved peptide agents for solid cancer are still limited. This review will provide a detailed overview of current approaches, design strategies, routes of administration, and new technological advancements. We will highlight the success and limitations of peptide-based therapies for cancer treatment.

Discovery of Ghrelin(1-8) Analogues with Improved Stability and Functional Activity for PET Imaging

The highest affinity ghrelin-based analogue for fluorine-18 positron emission tomography, [Inp1,Dpr3(6-FN),1Nal4,Thr8]ghrelin(1-8) amide (1), has remarkable subnanomolar receptor affinity (IC50 = 0.11 nM) toward the growth hormone secretagogue receptor 1a (GHSR). However, initial in vivo PET imaging and biodistribution of [18F]1 in mice demonstrated an unfavorable pharmacokinetic profile with rapid clearance and accumulation in liver and intestinal tissue, prompting concerns about the metabolic stability of this probe. The aims of the present study were to examine the proteolytic stability of ghrelin analogue 1 in the presence of blood and liver enzymes, structurally modify the peptide to improve stability without impeding the strong binding affinity, and measure the presently unknown functional activity of ghrelin(1-8) analogues. The in vitro stability and metabolite formation of 1 in human serum and liver S9 fraction revealed a metabolic soft spot between amino acids Leu5 and Ser6 in the peptide sequence. A focused library of ghrelin(1-8) analogues was synthesized and evaluated in a structure-activity-stability relationship study to further understand the structural importance of the residues at these positions in the context of stability and receptor affinity. The critical nature of l-stereochemistry at position 5 was identified and substitution of Ser6 with l-2,3-diaminopropionic acid led to a novel ligand with substantially improved in vitro stability while maintaining subnanomolar GHSR affinity. Despite the highly modified nature of these analogues compared to human ghrelin, ghrelin(1-8) analogues were found to recruit all G protein subtypes (Gαq/11/13/i1/oB) known to associate with GHSR as well as β-arrestins with low micromolar to nanomolar potencies. The study of these analogues demonstrates the ability to balance desirable ligand properties, including affinity, stability, and potency to produce well-rounded candidate molecules for further in vivo evaluation.

In Vivo Staging the Progression of Colitis and Associated Cancer by Concurrent Microimaging of Key Biomarkers

Currently colorectal cancer (CRC) staging (colitis, adenoma, and carcinoma) mainly relies on ex vivo pathologic analysis requiring an invasive surgical process with limited sample collection and increased metastatic risk. Thus, in vivo noninvasive pathological diagnosis is extremely demanded. By verifying the samples of clinical patients and CRC mouse models, it was found that vascular endothelial growth factor receptor 2 (VEGFR2) was barely expressed in the colitis stage and only appeared in adenoma and carcinoma stages with obvious elevation, while prostaglandin E receptor 4 (PTGER4) could be observed from colitis to adenoma and carcinoma stages with a gradient increase of expression. VEGFR2 and PTGER4 were further chosen as key biomarkers for molecular pathological diagnosis in vivo and corresponding molecular probes were constructed. The feasibility of in vivo noninvasive CRC staging by concurrent microimaging of dual biomarkers using confocal laser endoscopy (CLE) was verified in CRC mouse models and further confirmed by ex vivo pathological analysis. In vivo CLE imaging exhibited the correlation of severe colonic crypt structural alteration with a higher biomarker expression in adenoma and carcinoma stages. This strategy shows promise in benefiting patients undergoing CRC progression with in-time, noninvasive, and precise pathological staging, thus providing valuable guidance for selecting therapeutic strategies.

Asymmetric rotaxanes as dual-modality supramolecular imaging agents for targeting cancer biomarkers

Dual-modality imaging agents featuring both a radioactive complex for positron emission tomography (PET) and a fluorophore for optical fluorescence imaging (OFI) are crucial tools for reinforcing clinical diagnosis and intraoperative surgeries. We report the synthesis and characterisation of bimodal mechanically interlocked rotaxane-based imaging agents, constructed via the cucurbit[6]uril CB[6]-mediated alkyne-azide 'click' reaction. Two synthetic routes involving four- or six-component reactions are developed to access asymmetric rotaxanes. Furthermore, by using this rapid and versatile approach, a peptide-based rotaxane targeted toward the clinical prostate cancer biomarker, prostate-specific membrane antigen (PSMA), and bearing a ⁶⁸Ga-radiometal ion complex for positron emission tomography and fluorescein as an optically active imaging agent, was synthesised. The chemical and radiochemical stability, and the cellular uptake profile of the radiolabelled and fluorescent rotaxane was evaluated in vitro where the experimental data demonstrate the viability of using an asymmetric rotaxane platform to produce dual-modality imaging agents that specifically target prostate cancer cells.

Mucins as contrast agent targets for fluorescence-guided surgery of pancreatic cancer

Pancreatic cancer is difficult to resect due to its unique challenges, often leading to incomplete tumor resections. Fluorescence-guided surgery (FGS), also known as intraoperative molecular imaging and optical surgical navigation, is an intraoperative tool that can aid surgeons in complete tumor resection through an increased ability to detect the tumor. To target the tumor, FGS contrast agents rely on biomarkers aberrantly expressed in malignant tissue compared to normal tissue. These biomarkers allow clinicians to identify the tumor and its stage before surgical resection and provide a contrast agent target for intraoperative imaging. Mucins, a family of glycoproteins, are upregulated in malignant tissue compared to normal tissue. Therefore, these proteins may serve as biomarkers for surgical resection. Intraoperative imaging of mucin expression in pancreatic cancer can potentially increase the number of complete resections. While some mucins have been studied for FGS, the potential ability to function as a biomarker target extends to the entire mucin family. Therefore, mucins are attractive proteins to investigate more broadly as FGS biomarkers. This review summarizes the biomarker traits of mucins and their potential use in FGS for pancreatic cancer.

A Chemical Strategy for the Preparation of Multimodified Peptide Imaging Probes

Multimodality probes appear of great interest for innovative imaging applications in disease diagnosis. Herein, we present a chemical strategy enabling site-specific double-modification and cyclization of a peptide probe exploiting native chemical ligation (NCL) and thiol-maleimide addition. The synthetic strategy is straightforward and of general applicability for the development of double-labeled peptide multimodality probes.

A Systematic Investigation into the Influence of Net Charge on the Biological Distribution of Radiometalated Peptides Using [68Ga]Ga-DOTA-TATE Derivatives

Recently, several radiometalated peptides have been approved for clinical imaging and/or therapy (theranostics) of several types of cancer; nonetheless, the primary challenge that most of these peptides confront is significant renal uptake and retention, which is often dose limiting and can cause nephrotoxicity. In response to this, numerous methods have been employed to reduce the uptake of radiometalated peptides in the kidneys, and among these is adding a linker to modulate polarity and/or charge. To better understand the influence of net charge on the biodistribution of radiometalated peptides, we selected the clinically popular construct DOTA-TATE (NETSPOT/LUTATHERA) as a model system. We synthesized derivatives using manual solid-phase peptide synthesis methods including mechanical and ultrasonic agitation to effectively yield the gold standard DOTA-TATE and a series of derivatives with different net charges (+2, +1, 0, -1, -2). Dynamic PET imaging from 0 to 90 min in healthy female mice (CD1) revealed high accumulation and retention of activity in the kidneys for the net-neutral (0) charged [⁶⁸Ga]Ga-DOTA-TATE and even higher for positively charged derivatives, whereas negatively charged derivatives exhibited low accumulation and fast renal excretion. Ex vivo biodistribution at 2 h post injection demonstrated a significant retention of [⁶⁸Ga]Ga-DOTA-TATE (∼74 %ID/g) in the kidneys, which increased as the net positive charge per molecule increased to +1 and +2 (∼272 %ID/g and ∼333 %ID/g, respectively), but the -1 and -2 net charged molecules exhibited lower renal uptake (∼15 %ID/g and 16 %ID/g, respectively). Interestingly, the net -2 charged [⁶⁸Ga]Ga-DOTA-(Glu)₂-PEG₄-TATE was stable in blood serum but had much higher healthy organ uptake (lungs, liver, spleen) than the net -1 compound, suggesting instability in vivo. Although the [⁶⁸Ga]Ga-DOTA-PEG₄-TATE derivative with a net charge of 0 also showed a decrease in kidney uptake, it also showed instability in blood serum and in vivo. Despite the superior pharmacokinetics of the net -1 charged [⁶⁸Ga]Ga-DOTA-Glu-PEG₄-TATE in healthy mice with respect to kidney uptake and overall profile, dynamic PET images and ex vivo biodistribution in male mice (NSG) bearing AR42J (SSTR2 overexpressing) subcutaneous tumor xenografts showed significantly diminished tumor uptake when compared to the gold standard [⁶⁸Ga]Ga-DOTA-TATE. Taken together, these findings indicate unambiguously that kidney uptake and retention are significantly influenced by the net charge of peptide-based radiotracers. In addition, it was illustrated that the negatively charged peptides had substantially decreased kidney uptake, but in this instantiation the tumor uptake was also impaired.

Non-invasive molecular imaging for precision diagnosis of metastatic lymph nodes: opportunities from preclinical to clinical applications

Lymph node metastasis is an indicator of the invasiveness and aggressiveness of cancer. It is a vital prognostic factor in clinical staging of the disease and therapeutic decision-making. Patients with positive metastatic lymph nodes are likely to develop recurrent disease, distant metastasis, and succumb to death in the coming few years. Lymph node dissection and histological analysis are needed to detect whether regional lymph nodes have been infiltrated by cancer cells and determine the likely outcome of treatment and the patient's chances of survival. However, these procedures are invasive, and tissue biopsies are prone to sampling error. In recent years, advanced molecular imaging with novel imaging probes has provided new technologies that are contributing to comprehensive management of cancer, including non-invasive investigation of lymphatic drainage from tumors, identifying metastatic lymph nodes, and guiding surgeons to operate efficiently in patients with complex lesions. In this review, first, we outline the current status of different molecular imaging modalities applied for lymph node metastasis management. Second, we summarize the multi-functional imaging probes applied with the different imaging modalities as well as applications of cancer lymph node metastasis from preclinical studies to clinical translations. Third, we describe the limitations that must be considered in the field of molecular imaging for improved detection of lymph node metastasis. Finally, we propose future directions for molecular imaging technology that will allow more personalized treatment plans for patients with lymph node metastasis.

Molecular and functional imaging in cancer-targeted therapy: current applications and future directions

Targeted anticancer drugs block cancer cell growth by interfering with specific signaling pathways vital to carcinogenesis and tumor growth rather than harming all rapidly dividing cells as in cytotoxic chemotherapy. The Response Evaluation Criteria in Solid Tumor (RECIST) system has been used to assess tumor response to therapy via changes in the size of target lesions as measured by calipers, conventional anatomically based imaging modalities such as computed tomography (CT), and magnetic resonance imaging (MRI), and other imaging methods. However, RECIST is sometimes inaccurate in assessing the efficacy of targeted therapy drugs because of the poor correlation between tumor size and treatment-induced tumor necrosis or shrinkage. This approach might also result in delayed identification of response when the therapy does confer a reduction in tumor size. Innovative molecular imaging techniques have rapidly gained importance in the dawning era of targeted therapy as they can visualize, characterize, and quantify biological processes at the cellular, subcellular, or even molecular level rather than at the anatomical level. This review summarizes different targeted cell signaling pathways, various molecular imaging techniques, and developed probes. Moreover, the application of molecular imaging for evaluating treatment response and related clinical outcome is also systematically outlined. In the future, more attention should be paid to promoting the clinical translation of molecular imaging in evaluating the sensitivity to targeted therapy with biocompatible probes. In particular, multimodal imaging technologies incorporating advanced artificial intelligence should be developed to comprehensively and accurately assess cancer-targeted therapy, in addition to RECIST-based methods.

Nanostructured multifunctional stimuli-responsive glycopolypeptide-based copolymers for biomedical applications

Inspired by natural resources, such as peptides and carbohydrates, glycopolypeptide biopolymer has recently emerged as a new form of biopolymer being recruited in various biomedical applications. Glycopolypeptides with well-defined secondary structures and pendant glycosides on the polypeptide backbone have sparked lots of research interest and they have an innate ability to self-assemble in diverse structures. The nanostructures of glycopolypeptides have also opened up new perspectives in biomedical applications due to their stable three-dimensional structures, high drug loading efficiency, excellent biocompatibility, and biodegradability. Although the development of glycopolypeptide-based nanocarriers is well-studied, their clinical translation is still limited. The present review highlights the preparation and characterization strategies related to glycopolypeptides-based copolymers, followed by a comprehensive discussion on their biomedical applications with a specific focus on drug delivery by various stimuli-responsive (e.g., pH, redox, conduction, and sugar) nanostructures, as well as their beneficial usage in diagnosis and regenerative medicine.

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.

A Dimeric FAP-Targeting Small-Molecule Radioconjugate with High and Prolonged Tumor Uptake

Imaging procedures based on small-molecule radioconjugates targeting fibroblast activation protein (FAP) have recently emerged as a powerful tool for the diagnosis of a wide variety of tumors. However, the therapeutic potential of radiolabeled FAP-targeting agents is limited by their short residence time in neoplastic lesions. In this work, we present the development and in vivo characterization of BiOncoFAP, a new dimeric FAP-binding motif with an extended tumor residence time and favorable tumor-to-organ ratio. Methods: The binding properties of BiOncoFAP and its monovalent OncoFAP analog were assayed against recombinant human FAP. Preclinical experiments with ¹⁷⁷Lu-OncoFAP-DOTAGA (¹⁷⁷Lu-OncoFAP) and ¹⁷⁷Lu-BiOncoFAP-DOTAGA (¹⁷⁷Lu-BiOncoFAP) were performed on mice bearing FAP-positive HT-1080 tumors. Results: OncoFAP and BiOncoFAP displayed comparable subnanomolar dissociation constants toward recombinant human FAP in solution, but the bivalent BiOncoFAP bound more avidly to the target immobilized on solid supports. In a comparative biodistribution study, ¹⁷⁷Lu-BiOncoFAP exhibited a more stable and prolonged tumor uptake than ¹⁷⁷Lu-OncoFAP (∼20 vs. ∼4 percentage injected dose/g, respectively, at 24 h after injection). Notably, ¹⁷⁷Lu-BiOncoFAP showed favorable tumor-to-organ ratios with low kidney uptake. Both ¹⁷⁷Lu-OncoFAP and ¹⁷⁷Lu-BiOncoFAP displayed potent antitumor efficacy when administered at therapeutic doses to tumor-bearing mice. Conclusion: ¹⁷⁷Lu-BiOncoFAP is a promising candidate for radioligand therapy of cancer, with favorable in vivo tumor-to-organ ratios, a long tumor residence time, and potent anticancer efficacy.

Targeting caveolae to pump bispecific antibody to TGF-β into diseased lungs enables ultra-low dose therapeutic efficacy

The long-sought-after "magic bullet" in systemic therapy remains unrealized for disease targets existing inside most tissues, theoretically because vascular endothelium impedes passive tissue entry and full target engagement. We engineered the first "dual precision" bispecific antibody with one arm pair to precisely bind to lung endothelium and drive active delivery and the other to precisely block TGF-β effector function inside lung tissue. Targeting caveolae for transendothelial pumping proved essential for delivering most of the injected intravenous dose precisely into lungs within one hour and for enhancing therapeutic potency by >1000-fold in a rat pneumonitis model. Ultra-low doses (μg/kg) inhibited inflammatory cell infiltration, edema, lung tissue damage, disease biomarker expression and TGF-β signaling. The prodigious benefit of active vs passive transvascular delivery of a precision therapeutic unveils a new promising drug design, delivery and therapy paradigm ripe for expansion and clinical testing.

Cell-Penetrating Peptides (CPPs) as Therapeutic and Diagnostic Agents for Cancer

Cell-Penetrating Peptides (CPPs) are short peptides consisting of <30 amino acids. Their ability to translocate through the cell membrane while carrying large cargo biomolecules has been the topic of pre-clinical and clinical trials. The ability to deliver cargo complexes through membranes yields potential for therapeutics and diagnostics for diseases such as cancer. Upon cellular entry, some CPPs have the ability to target specific organelles. CPP-based intracellular targeting strategies hold tremendous potential as they can improve efficacy and reduce toxicities and side effects. Further, recent clinical trials show a significant potential for future CPP-based cancer treatment. In this review, we summarize recent advances in CPPs based on systematic searches in PubMed, Embase, Web of Science, and Scopus databases until 30 September 2022. We highlight targeted delivery and explore the potential uses for CPPs as diagnostics, drug delivery, and intrinsic anti-cancer agents.

Preparation, In Vitro Affinity, and In Vivo Biodistribution of Receptor-Specific 68Ga-Labeled Peptides Targeting Vascular Endothelial Growth Factor Receptors

As angiogenesis plays a key role in tumor growth and metastasis, the angiogenic process has attracted scientific interest as a target for diagnostic and therapeutic agents. Factors influencing angiogenesis include the vascular endothelial growth factor (VEGF) family and the two associated receptor types (VEGFR-1 and VEGFR-2). VEGFR-1/-2 detection and quantification in cancer lesions are essential for tumor process management. As a result of the advantageous pharmacokinetics and image contrast, peptides radiolabeled with PET emitters have become interesting tools for the visualization of VEGFR-1/-2-positive tumors. In this study, we prepared ⁶⁸Ga-labeled peptides containing 15 (peptide 1) and 23 (peptide 2) amino acids as new PET tracers for tumor angiogenic process imaging.

METHODS

The peptides were conjugated with NODAGA-tris(t-Bu ester) and subsequently radiolabeled with [⁶⁸Ga]Ga-chloride. The prepared [⁶⁸Ga]Ga-NODAGA-peptide 1 and [⁶⁸Ga]Ga-NODAGA-peptide 2 were tested for radiochemical purity and saline/plasma stability. Consequently, the binding affinity toward VEGFRs was assessed in vitro on human glioblastoma and kidney carcinoma cells. The found peptide receptor affinity was compared with the calculated values in the PROtein binDIng enerGY prediction (PRODIGY) server. Finally, the biodistribution study was performed on BALB/c female mice to reveal the basic pharmacokinetic behavior of radiopeptides.

RESULTS

The in vitro affinity testing of [⁶⁸Ga]Ga-NODAGA-peptides 1 and 2 showed retained receptor binding as characterized by equilibrium dissociation constant (K_D) values in the range of 0.5-1.2 μM and inhibitory concentration 50% (IC₅₀) values in the range of 3.0-5.6 μM. Better binding properties of peptide 2 to VEGFR-1/-2 were found in the PRODIGY server. The biodistribution study on mice showed remarkable accumulation of both peptides in the kidneys and urinary bladder with a short half-life after intravenous application. The in vitro plasma stability of [⁶⁸Ga]Ga-NODAGA-peptide 2 was superior to that of [⁶⁸Ga]Ga-NODAGA-peptide 1.

CONCLUSIONS

The obtained results demonstrated a high radiolabeling yield with no need for purification and preserved binding potency of ⁶⁸Ga-labeled peptides 1 and 2 toward VEGFRs in cancer cells. The peptide-receptor protein interaction assessed in protein-peptide docking determined the strongest interaction of peptide 2 with domain 2 of VEGFR-2 in addition to a more acceptable plasma stability (t_1/2 = 120 min) than that for peptide 1. We found both radiolabeled peptides very potent in their receptor binding, which makes them suitable imaging agents. The rapid transition of the radiopeptides into the urinary tract indicates suitable pharmacokinetic characteristics.

Imaging ligands targeting glypican-3 receptor expression in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality. Early detection of HCC is important since potentially curative therapies exist in the initial stages of HCC; no curative therapies exist for late-stage HCC. However, the initial detection of HCC remains challenging due to the lack of symptoms during the early stage of the disease. Other methods of screening and detecting HCC, including blood serum tests and conventional imaging methods, remain inadequate due to genetic differences between patients and the high background activity of liver tissues. Thus, there is a need for an accurate imaging agent for the diagnosis, staging, and prognosis of HCC. Glypican-3 (GPC3) is an oncofetal receptor responsible for regulating cell division, growth, and survival. GPC3 is a clinically relevant biomarker for imaging and therapeutics, as its expression is HCC tumor-specific and absent from normal and other pathological liver tissues. The development of novel GPC3-targeting imaging agents has encompassed three classes of biomolecules: peptides, antibodies, and aptamers. These biomolecules serve as constructs for diagnostic imaging (demonstrating potential as positron emission tomography [PET], single-photon emission tomography [SPECT], and optical imaging agents) and HCC treatment delivery. More than 20 unique ligands have been identified in the literature as showing specificity for the GPC3 receptor. Although several ligands are currently under clinical investigation as therapies for HCC, clinical translation of GPC3-targeting ligands as imaging agents is lacking. This review highlights the current landscape of ligands targeting GPC3 and describes their promising possibilities as imaging agents for HCC.

Application of molecular imaging in immune checkpoints therapy: From response assessment to prognosis prediction

Recently, immune checkpoint therapy (ICT) represented by programmed cell death1 (PD-1) and its major ligands, programmed death ligand 1 (PD-L1), has achieved significant success. Detection of PD-L1 by immunohistochemistry (IHC) is a classic method to guide the treatment of ICT patients. However, PD-L1 expression in the tumor microenvironment is highly complex. Thus, PD-L1 IHC is inadequate to fully understand the relevance of PD-L1 levels in the whole body and their dynamics to improve therapeutic outcomes. Intriguingly, numerous studies have revealed that molecular imaging technologies could potentially meet this need. Therefore, the purpose of this narrative review is to summarize the preclinical and clinical application of ICT guided by molecular imaging technology, and to explore the future opportunities and practical difficulties of these innovations.

Development of Radiotracers for Imaging of the PD-1/PD-L1 Axis

Immune checkpoint inhibitor (ICI) therapy has emerged as a major treatment option for a variety of cancers. Among the immune checkpoints addressed, the programmed death receptor 1 (PD-1) and its ligand PD-L1 are the key targets for an ICI. PD-L1 has especially been proven to be a reproducible biomarker allowing for therapy decisions and monitoring therapy success. However, the expression of PD-L1 is not only heterogeneous among and within tumor lesions, but the expression is very dynamic and changes over time. Immunohistochemistry, which is the standard diagnostic tool, can only inadequately address these challenges. On the other hand, molecular imaging techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) provide the advantage of a whole-body scan and therefore fully address the issue of the heterogeneous expression of checkpoints over time. Here, we provide an overview of existing PET, SPECT, and optical imaging (OI) (radio)tracers for the imaging of the upregulation levels of PD-1 and PD-L1. We summarize the preclinical and clinical data of the different molecule classes of radiotracers and discuss their respective advantages and disadvantages. At the end, we show possible future directions for developing new radiotracers for the imaging of PD-1/PD-L1 status in cancer patients.

The role of cell-penetrating peptides in potential anti-cancer therapy

Due to the complex physiological structure, microenvironment and multiple physiological barriers, traditional anti-cancer drugs are severely restricted from reaching the tumour site. Cell-penetrating peptides (CPPs) are typically made up of 5-30 amino acids, and can be utilised as molecular transporters to facilitate the passage of therapeutic drugs across physiological barriers. Up to now, CPPs have widely been used in many anti-cancer treatment strategies, serving as an excellent potential choice for oncology treatment. However, their drawbacks, such as the lack of cell specificity, short duration of action, poor stability in vivo, compatibility problems (i.e. immunogenicity), poor therapeutic efficacy and formation of unwanted metabolites, have limited their further application in cancer treatment. The cellular uptake mechanisms of CPPs involve mainly endocytosis and direct penetration, but still remain highly controversial in academia. The CPPs-based drug delivery strategy could be improved by clever design or chemical modifications to develop the next-generation CPPs with enhanced cell penetration capability, stability and selectivity. In addition, some recent advances in targeted cell penetration that involve CPPs provide some new ideas to optimise CPPs.

Nontoxic Tumor-Targeting Optical Agents for Intraoperative Breast Tumor Imaging

Precise identification of the tumor margins during breast-conserving surgery (BCS) remains a challenge given the lack of visual discrepancy between malignant and surrounding normal tissues. Therefore, we developed a fluorescent imaging agent, ICG-p28, for intraoperative imaging guidance to better aid surgeons in achieving negative margins in BCS. Here, we determined the pharmacokinetics (PK), biodistribution, and preclinical toxicity of ICG-p28. The PK and biodistribution of ICG-p28 indicated rapid tissue uptake and localization at tumor lesions. There were no dose-related effect and no significant toxicity in any of the breast cancer and normal cell lines tested. Furthermore, ICG-p28 was evaluated in clinically relevant settings with transgenic mice that spontaneously developed invasive mammary tumors. Intraoperative imaging with ICG-p28 showed a significant reduction in the tumor recurrence rate. This simple, nontoxic, and cost-effective method can offer a new approach that enables surgeons to intraoperatively identify tumor margins and potentially improves overall outcomes by reducing recurrence rates.

SPECT Imaging of Acute Disc Herniation by Targeting Integrin α5β1 in Rat Models

Objective

Traditional morphological imaging of intervertebral disc herniation (IVDH) is challenging in early disease diagnosis. Aiming at the early diagnosis of IVD by non-invasive molecular imaging targeting of integrin α5β1, we performed novel imaging in rats with acute IVDH for the first time.

Methods

Animal models were prepared by conducting an established needle puncture procedure through the normal intervertebral disc (IVD). The disc-injured rats underwent SPECT/CT imaging of the ^99mTc-3PisoDGR2 peptide at 1 day to 2 months postinjury. The expression change of integrin α5β1 was determined by anti-integrin α5 and anti-integrin α5β1 immunohistochemistry (IHC). Magnetic resonance imaging (MRI) was performed for comparison during disease progression. The morphological changes of the disc were determined by safranin-O staining.

Results

Rats with acute IVDH showed gradually increased disc uptake of ^99mTc-3PisoDGR2 from 1 to 7 days posttreatment, which was a significantly higher level than that of the normal disks in degenerative diseases. IHC results showed the expression of integrin α5β1 on the surface of annulus fibrosus (AF) cells and nucleus pulposus (NP) cells, which agreed with the uptake data. MRI showed a progressively decreased T2 density and MRI index throughout the investigation. Hematoxylin and eosin (HE) staining and safranin-O staining revealed a disorganized structure of the IVD as well as loss of proteoglycans after puncture.

Conclusions

The present study demonstrated a good correlation between integrin α5β1 expression and acute disc herniation. The SPECT/CT imaging of ^99mTc-3PisoDGR2 targeting integrin α5β1 may diagnose IVDH in an acute phase for early disease management.

[99mTc]Tc-Labeled Plectin-Targeting Peptide as a Novel SPECT Probe for Tumor Imaging

Certain receptors are often overexpressed during tumor occurrence and development and closely correlate with carcinogenesis. Owing to its overexpression on the cell membrane and cytoplasm of various tumors, plectin, which is involved in tumor proliferation, migration, and invasion, has been viewed as a promising target for cancer imaging. Hence, plectin-targeting agents have great potential as imaging probes for tumor diagnosis. In this study, we developed a [99mTc]Tc-labeled plectin-targeted peptide (PTP) as a novel single-photon emission computed tomography (SPECT) probe for tumor imaging and investigated its pharmacokinetics, biodistribution, and targeting ability in several types of tumor-bearing mouse models. The PTP had good biocompatibility and targeting ability to tumor cells in vitro and could be readily labeled with [99mTc]Tc after modification with the bifunctional chelator 6-hydrazino nicotinamide (HYNIC). Furthermore, the prepared [99mTc]Tc-labeled PTP ([99mTc]Tc-HYNIC-PTP) showed high radiochemical purity and excellent stability in vitro. In addition, favorable biodistribution, fast blood clearance, and clear accumulation of [99mTc]Tc-HYNIC-PTP in several types of tumors were observed, with a good correlation between tumor uptake and plectin expression levels. These results indicate the potential of [99mTc]Tc-HYNIC-PTP as a novel SPECT probe for tumor imaging.

Homomultimer strategy for improvement of radiolabeled peptides and antibody fragments in tumor targeting

A homomultimeric radioligand is composed of multiple identical ligands connected to the linker and radionuclide to detect a variety of overexpressed receptors on cancer cells. Multimer strategy holds great potential for introducing new radiotracers based on peptide and monoclonal antibody (mAb) derivatives in molecular imaging and therapy. It offers a reliable procedure for the preparation of biological-based targeting with diverse affinities and pharmacokinetics. In this context, we provide a useful summary and interpretation of the main results by a comprehensive look at multimeric radiopharmaceuticals in nuclear oncology. Therefore, there will be explanations for the strategy mechanisms and the main variables affecting the biodistribution results. The discussion is followed by highlights of recent work in the targeting of various types of receptors. The consequences are expressed based on comparing some parameters between monomer and multimer counterparts in each relevant section.

Electrochemical Sensing of the Peptide Drug Exendin-4 Using a Versatile Nucleic Acid Nanostructure

Although endogenous peptides and peptide-based therapeutics are both highly relevant to human health, there are few approaches for sensitive biosensing of this class of molecules with minimized workflow. In this work, we have further expanded on the generalizability of our recently developed DNA nanostructure architecture by applying it to electrochemical (EC) peptide quantification. While DNA-small molecule conjugates were used in a prior work to make sensors for small molecule and protein analytes, here DNA-peptide conjugates were incorporated into the nanostructure at the electrode surfaces, and antibody displacement permitted rapid peptide sensing. Interestingly, multivalent DNA-peptide conjugates were found to be detrimental to the assay readout, yet these effects could be minimized by solution-phase bioconjugation. The final biosensor was validated for quantifying exendin-4 (4.2 kDa)─a human glucagon-like peptide-1 receptor agonist important in diabetes therapy─for the first time using EC methods with minimal workflow. The sensor was functional in 98% human serum, and the low nanomolar assay range lies between the injected dose concentration and the therapeutic range, boding well for future applications in therapeutic drug monitoring.

Complexation of specific residues by carboxylatopillar[6]arene for improving the zymolytic stability of arginine-containing peptides

A general strategy for improving the zymolytic stability against proteases is reported. Carboxylatopillar[6]arene (CP6A) could effectively bind arginine and arginine-containing peptides, thereby improving the stability of angiotensin peptides in the presence of trypsin by the complexation of the side chain of the arginine residue.

Novel Synovial Targeting Peptide-Sinomenine Conjugates as a Potential Strategy for the Treatment of Rheumatoid Arthritis

Sinomenine (SIN) is an effective anti-inflammatory agent, but its therapeutic efficacy is limited by its short half-life and the high dosage required. Tissue-specific strategies have the potential to overcome these limitations. The synovial homing peptide (CKSTHDRLC) was identified to have high synovial endothelium targeting affinity. In this work, two peptide-drug conjugates (PDCs), conjugate (L) and conjugate (C), were synthesized, in which SIN was covalently connected to the linear and cyclic synovial homing peptide, respectively, via a 6-aminocaproic acid linker. An evaluation of biostability showed that conjugate (C) was more stable in mouse serum and inflammatory joint homogenate than conjugate (L). The two conjugates gradually released free SIN. Interestingly, conjugate (L) self-cyclized via a disulfide bridge in a biological environment, which significantly impacted its biostability. It had an almost equipotent half-life in serum but faster degradation in the inflammatory joint than conjugate (C). Therefore, conjugate (C) exhibited better therapeutic efficacy and tissue targeting. All the results indicated that PDCs particularly in its cyclic form might be more efficient for targeted deliver and represent a potential strategy for the treatment of rheumatoid arthritis.

Therapeutic peptides: current applications and future directions

Peptide drug development has made great progress in the last decade thanks to new production, modification, and analytic technologies. Peptides have been produced and modified using both chemical and biological methods, together with novel design and delivery strategies, which have helped to overcome the inherent drawbacks of peptides and have allowed the continued advancement of this field. A wide variety of natural and modified peptides have been obtained and studied, covering multiple therapeutic areas. This review summarizes the efforts and achievements in peptide drug discovery, production, and modification, and their current applications. We also discuss the value and challenges associated with future developments in therapeutic peptides.