Peptide-based radiopharmaceuticals and cytotoxic conjugates: potential tools against cancer

Surface functionalized nanomaterial systems for targeted therapy of endocrine related tumors: a review of recent advancements

The application of multidisciplinary techniques in the management of endocrine-related cancers is crucial for harnessing the advantages of multiple disciplines and their coordinated efforts in eliminating tumors. Due to the malignant characteristics of cancer cells, they possess the capacity to develop resistance to traditional treatments such as chemotherapy and radiotherapy. Nevertheless, despite diligent endeavors to enhance the prediction of outcomes, the overall survival rate for individuals afflicted with endocrine-related malignancy remains quite miserable. Hence, it is imperative to investigate innovative therapy strategies. The latest advancements in therapeutic tactics have offered novel approaches for the therapy of various endocrine tumors. This paper examines the advancements in nano-drug delivery techniques and the utilization of nanomaterials for precise cancer cures through targeted therapy. This review provides a thorough analysis of the potential of combined drug delivery strategies in the treatment of thyroid cancer, adrenal gland tumors, and pancreatic cancer. The objective of this study is to gain a deeper understanding of current therapeutic approaches, stimulate the development of new drug DDS, and improve the effectiveness of treatment for patients with these diseases. The intracellular uptake of pharmaceuticals into cancer cells can be significantly improved through the implantation of synthetic or natural substances into nanoparticles, resulting in a substantial reduction in the development of endocrine malignancies.

Peptide Binder to Glypican-3 as a Theranostic Agent for Hepatocellular Carcinoma

Glypican-3 (GPC3) is a membrane-associated glycoprotein that is significantly upregulated in hepatocellular carcinomas (HCC) with minimal to no expression in normal tissues. The differential expression of GPC3 between tumor and normal tissues provides an opportunity for targeted radiopharmaceutical therapy to treat HCC, a leading cause of cancer-related deaths worldwide. Methods: DOTA-RYZ-GPC3 (RAYZ-8009) comprises a novel macrocyclic peptide binder to GPC3, a linker, and a chelator that can be complexed with different radioisotopes. The binding affinity was determined by surface plasma resonance and radioligand binding assays. Target-mediated cellular internalization was radiometrically measured at multiple time points. In vivo biodistribution, monotherapy, and combination treatments with 177Lu or 225Ac were performed on HCC xenografts. Results: RAYZ-8009 showed high binding affinity to GPC3 protein of human, mouse, canine, and cynomolgus monkey origins and no binding to other glypican family members. Potent cellular binding was confirmed in GPC3-positive HepG2 cells and was not affected by isotope switching. RAYZ-8009 achieved efficient internalization on binding to HepG2 cells. Biodistribution study of 177Lu-RAYZ-8009 showed sustained tumor uptake and fast renal clearance, with minimal or no uptake in other normal tissues. Tumor-specific uptake was also demonstrated in orthotopic HCC tumors, with no uptake in surrounding liver tissue. Therapeutically, significant and durable tumor regression and survival benefit were achieved with 177Lu- and 225Ac-labeled RAYZ-8009, as single agents and in combination with lenvatinib, in GPC3-positive HCC xenografts. Conclusion: Preclinical in vitro and in vivo data demonstrate the potential of RAYZ-8009 as a theranostic agent for the treatment of patients with GPC3-positive HCC.

Selection of potential targets for stratifying congenital pulmonary airway malformation patients with molecular imaging: is MUC1 the one?

Currently there is a global lack of consensus about the best treatment for asymptomatic congenital pulmonary airway malformation (CPAM) patients. The somatic KRAS mutations commonly found in adult lung cancer combined with mucinous proliferations are sometimes found in CPAM. For this risk of developing malignancy, 70% of paediatric surgeons perform a resection for asymptomatic CPAM. In order to stratify these patients into high- and low-risk groups for developing malignancy, a minimally invasive diagnostic method is needed, for example targeted molecular imaging. A prerequisite for this technique is a cell membrane bound target. The aim of this study was to review the literature to identify potential targets for molecular imaging in CPAM patients and perform a first step to validate these findings.A systematic search was conducted to identify possible targets in CPAM and adenocarcinoma in situ (AIS) patients. The most interesting targets were evaluated with immunofluorescent staining in adjacent lung tissue, KRAS+ CPAM tissue and KRAS- CPAM tissue.In 185 included studies, 143 possible targets were described, of which 20 targets were upregulated and membrane-bound. Six of them were also upregulated in lung AIS tissue (CEACAM5, E-cadherin, EGFR, ERBB2, ITGA2 and MUC1) and as such of possible interest. Validating studies showed that MUC1 is a potential interesting target.This study provides an extensive overview of all known potential targets in CPAM that might identify those patients at risk for malignancy and conducted the first step towards validation, identifying MUC1 as the most promising target.

Lutetium-177-Labeled Prostate-Specific Membrane Antigen-617 for Molecular Imaging and Targeted Radioligand Therapy of Prostate Cancer

Prostate-specific membrane antigen (PSMA) represents a promising target for PSMA-overexpressing diseases, especially prostate cancer-a common type of cancer among men worldwide. In response to the challenges in tackling prostate cancers, several promising PSMA inhibitors from a variety of molecular scaffolds (e.g., phosphorous-, thiol-, and urea-based molecules) have been developed. In addition, PSMA inhibitors bearing macrocyclic chelators have attracted interest due to their favorable pharmacokinetic properties. Recently, conjugating a small PSMA molecule inhibitor-bearing 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator, as exemplified by [177Lu]Lu-PSMA-617 could serve as a molecular imaging probe and targeted radioligand therapy (TRT) of metastatic castration resistant prostate cancer (mCRPC). Hence, studies related to mCRPC have drawn global attention. In this review, the recent development of PSMA ligand-617-labeled with 177Lu for the management of mCRPC is presented. Its molecular mechanism of action, safety, efficacy, and future direction are also described.

Mucin Glycans: A Target for Cancer Therapy

Mucin glycans are an important component of the mucus barrier and a vital defence against physical and chemical damage as well as pathogens. There are 20 mucins in the human body, which can be classified into secreted mucins and transmembrane mucins according to their distributions. The major difference between them is that secreted mucins do not have transmembrane structural domains, and the expression of each mucin is organ and cell-specific. Under physiological conditions, mucin glycans are involved in the composition of the mucus barrier and thus protect the body from infection and injury. However, abnormal expression of mucin glycans can lead to the occurrence of diseases, especially cancer, through various mechanisms. Therefore, targeting mucin glycans for the diagnosis and treatment of cancer has always been a promising research direction. Here, we first summarize the main types of glycosylation (O-GalNAc glycosylation and N-glycosylation) on mucins and the mechanisms by which abnormal mucin glycans occur. Next, how abnormal mucin glycans contribute to cancer development is described. Finally, we summarize MUC1-based antibodies, vaccines, radio-pharmaceuticals, and CAR-T therapies using the best characterized MUC1 as an example. In this section, we specifically elaborate on the recent new cancer therapy CAR-M, which may bring new hope to cancer patients.

Radioenhancement with the Combination of Docetaxel and Ultrasound Microbubbles: In Vivo Prostate Cancer

Using an in vitro prostate cancer model, we previously demonstrated the significant enhancement of radiotherapy (XRT) with the combined treatment of docetaxel (Taxotere; TXT) and ultrasound-microbubbles (USMB). Here, we extend these findings to an in vivo cancer model. Severe combined immune-deficient male mice were xenografted with the PC-3 prostate cancer cell line in the hind leg and treated with USMB, TXT, radiotherapy (XRT), and their combinations. The tumors were imaged with ultrasound pre-treatment and 24 h post-treatment, following which they were extracted for the histological analysis of the tumor-cell death (D_N; H&E) and apoptosis (D_A; TUNEL). The tumors' growths were assessed for up to ~6 weeks and analysed using the exponential Malthusian tumor-growth model. The tumors' doubling time (V_T) was characterized as growth (positive) or shrinkage (negative). The cellular death and apoptosis increased ~5-fold with the TXT + USMB + XRT (D_n = 83% and D_a = 71%) compared to the XRT alone (D_n = 16% and D_a = 14%), and by ~2-3-fold with the TXT + XRT (D_n = 50% and D_a = 38%) and USMB + XRT (D_n = 45% and D_a = 27%) compared to the XRT. The USMB enhanced the cellular bioeffects of the TXT by ~2-5-fold with the TXT + USMB (D_n = 42% and D_a = 50%), compared with the TXT alone (D_n = 19% and D_a = 9%). The USMB alone caused cell death (D_n = 17% and D_a = 10%) compared to the untreated control (D_n = 0.4% and D_a = 0%). The histological cellular bioeffects were correlated with the changes in the ultrasound RF mid-band-fit data, which were associated with the cellular morphology. The linear regression analysis displayed a positive linear correlation between the mid-band fit and the overall cell death (R² = 0.9164), as well as a positive linear correlation between the mid-band fit and the apoptosis (R² = 0.8530). These results demonstrate a correlation between the histological and spectral measurements of the tissue microstructure and that cellular morphological changes can be detected by ultrasound scattering analysis. In addition, the tumor volumes from the triple-combination treatment were significantly smaller than those from the control, XRT, USMB + XRT, and TXT + XRT, from day 2 onward. The TXT + USMB + XRT-treated tumors shrank from day 2 and at each subsequent time-point measured (V_T ~-6 days). The growth of the XRT-treated tumors was inhibited during the first 16 days, following which the tumors grew (V_T ~9 days). The TXT + XRT and USMB + XRT groups displayed an initial decrease in tumor size (day 1-14; TXT + XRT V_T ~-12 days; USMB + XRT V_T ~-33 days), followed by a growth phase (day 15-37; TXT + XRT V_T ~11 days; USMB + XRT V_T ~22 days). The triple-combination therapy induced tumor shrinkage to a greater extent than any of the other treatments. This study demonstrates the in vivo radioenhancement potential of chemotherapy combined with therapeutic ultrasound-microbubble treatment in inducing cell death and apoptosis, as well as long-term tumor shrinkage.

Generation of peptides using phage display technology for cancer diagnosis and molecular imaging

Cancer is one of the leading causes of mortality worldwide; nearly 10 million people died from it in 2020. The high mortality rate results from the lack of effective screening approaches where early detection cannot be achieved, reducing the chance of early intervention to prevent cancer development. Non-invasive and deep-tissue imaging is useful in cancer diagnosis, contributing to a visual presentation of anatomy and physiology in a rapid and safe manner. Its sensitivity and specificity can be enhanced with the application of targeting ligands with the conjugation of imaging probes. Phage display is a powerful technology to identify antibody- or peptide-based ligands with effective binding specificity against their target receptor. Tumour-targeting peptides exhibit promising results in molecular imaging, but the application is limited to animals only. Modern nanotechnology facilitates the combination of peptides with various nanoparticles due to their superior characteristics, rendering novel strategies in designing more potent imaging probes for cancer diagnosis and targeting therapy. In the end, a myriad of peptide candidates that aimed for different cancers diagnosis and imaging in various forms of research were reviewed.

Anticancer peptides mechanisms, simple and complex

Peptide therapy has started since 1920s with the advent of insulin application, and now it has emerged as a new approach in treatment of diseases including cancer. Using anti-cancer peptides (ACPs) is a promising way of cancer therapy as ACPs are continuing to be approved and arrived at major pharmaceutical markets. Traditional cancer treatments face different problems like intensive adverse effects to patient's body, cell resistance to conventional chemical drugs and in some worse cases the occurrence of cell multidrug resistance (MDR) of cancerous tissues against chemotherapy. On the other hand, there are some benefits conceived for peptides usage in treatment of diseases specifically cancer, as these compounds present favorable characteristics such as smaller size, high activity, low immunogenicity, good biocompatibility in vivo, convenient and rapid way of synthesis, amenable to sequence modification and revision and there is no limitation for the type of cargo they carry. It is possible to achieve an optimum molecular and functional structure of peptides based on previous experience and bank of peptide motif data which may result in novel peptide design. Bioactive peptides are able to form pores in cell membrane and induce necrosis or apoptosis of abnormal cells. Moreover, recent researches have focused on the tumor recognizing peptide motifs with the ability to permeate to cancerous cells with the aim of cancer treatment at earlier stages. In this strategy the most important factors for addressing cancer are choosing peptides with easy accessibility to tumor cell without cytotoxicity effect towards normal cells. The peptides must also meet acceptable pharmacokinetic requirements. In this review, the characteristics of peptides and cancer cells are discussed. The various mechanisms of peptides' action proposed against cancer cells make the next part of discussion. It will be followed by giving information on peptides application, various methods of peptide designing along with introducing various databases. Future aspects of peptides for employing in area of cancer treatment come as conclusion at the end.

The preparation, biodistribution, and human's absorbed dose evaluation of Radio-Scandium-HYNIC-TOC for somatostatin-receptor-positive neuroendocrine tumors therapy by animal study

BACKGROUND

Most of the neuroendocrine tumors (NETs) express Somatostatin receptors (SSTr), which are the main bases for the development of several radiopharmaceuticals for therapy and imaging of these types of tumors. In this study, 46 Scandium nuclide was used to label a peptide compound via hydrazinonicotinyl-Tyr3-Octreotide (HYNIC-TOC) and researched further for somatostatin-receptor NETs treatment.

METHODS AND MATERIALS

The labeling procedure was conducted at 95°C for 10 min. The compound stability was tested in the environment of human serum at 37°C. The biodistribution of compound was investigated in balb/c normal mice and mice bearing AR4-2J tumor. Absorbed Doses of Human Organs were estimated by extrapolation of the biokinetics data of compound in mice to human's organs and then the absorbed doses were estimated by application of MATLAB and MIRDOSE software.

RESULTS

Labeling yield was more than 90% with 555 MBq/mg specific activity. The radio-labeled compound expressed well consistency in human serum. The tumor uptake reached 3.831 ID/g% until 4 h post-injection and increased to 5.564%ID/g until 24 h post-injection.

CONCLUSION

The main achievement of this study was high tumor uptake of 46 Sc-HYNIC-TOC which may be therapeutically valuable for the therapy of NETs. The estimation of the absorbed dose of human from 47 Scandium-HYNIC-TOC showed low absorbed doses in critical organs and the elimination of the radiopharmaceutical was through the gastrointestinal tract.

Using GPCRs as Molecular Beacons to Target Ovarian Cancer with Nanomedicines

The five-year survival rate for women with ovarian cancer is very poor despite radical cytoreductive surgery and chemotherapy. Although most patients initially respond to platinum-based chemotherapy, the majority experience recurrence and ultimately develop chemoresistance, resulting in fatal outcomes. The current administration of cytotoxic compounds is hampered by dose-limiting severe adverse effects. There is an unmet clinical need for targeted drug delivery systems that transport chemotherapeutics selectively to tumor cells while minimizing off-target toxicity. G protein-coupled receptors (GPCRs) are the largest family of membrane receptors, and many are overexpressed in solid tumors, including ovarian cancer. This review summarizes the progress in engineered nanoparticle research for drug delivery for ovarian cancer and discusses the potential use of GPCRs as molecular entry points to deliver anti-cancer compounds into ovarian cancer cells. A newly emerging treatment paradigm could be the personalized design of nanomedicines on a case-by-case basis.

MUC1-Targeted Radiopharmaceuticals in Cancer Imaging and Therapy

Mucin 1 (MUC1) is a large, transmembrane mucin glycoprotein overexpressed in most adenocarcinomas and plays an important role in tumor progression. Regarding its cellular distribution, biochemical features, and function, tumor-related MUC1 varies from the MUC1 expressed in normal cells. Therefore, targeting MUC1 for cancer immunotherapy and imaging can exploit the difference between cancerous and normal cells. Radiopharmaceuticals have a potential use as carriers for the delivery of radionuclides to tumors for a diagnostic imaging and radiotherapy. Several radiolabeled targeting molecules like peptides, antibodies, and aptamers have been efficiently demonstrated in detecting and treating cancer by targeting MUC1. This review provides a brief overview of the current status of developments and applications of MUC1-targeted radiopharmaceuticals in cancer imaging and therapy.

Peptide-Chitosan Engineered Scaffolds for Biomedical Applications

Peptides are signaling epitopes that control many vital biological events. Increased specificity, synthetic feasibility with concomitant lack of toxicity, and immunogenicity make this emerging class of biomolecules suitable for different applications including therapeutics, diagnostics, and biomedical engineering. Further, chitosan, a naturally occurring linear polymer composed of d-glucosamine and N-acetyl-d-glucosamine units, possesses anti-microbial, muco-adhesive, and hemostatic properties along with excellent biocompatibility. As a result, chitosan finds application in drug/gene delivery, tissue engineering, and bioimaging. Despite these applications, chitosan demonstrates limited cell adhesion and lacks biosignaling. Therefore, peptide-chitosan hybrids have emerged as a new class of biomaterial with improved biosignaling properties and cell adhesion properties. As a result, recent studies encompass increased application of peptide-chitosan hybrids as composites or conjugates in drug delivery, cell therapy, and tissue engineering and as anti-microbial material. This review discusses the recent investigations involving chitosan-peptide materials and uncovers various aspects of these interesting hybrid materials for biomedical applications.

Advances in Development of Radiometal Labeled Amino Acid-Based Compounds for Cancer Imaging and Diagnostics

Radiolabeled biomolecules targeted at tumor-specific enzymes, receptors, and transporters in cancer cells represent an intensively investigated and promising class of molecular tools for the cancer diagnosis and therapy. High specificity of such biomolecules is a prerequisite for the treatment with a lower burden to normal cells and for the effective and targeted imaging and diagnosis. Undoubtedly, early detection is a key factor in efficient dealing with many severe tumor types. This review provides an overview and critical evaluation of novel approaches in the designing of target-specific probes labeled with metal radionuclides for the diagnosis of most common death-causing cancers, published mainly within the last three years. Advances are discussed such traditional peptide radiolabeling approaches, and click and nanoparticle chemistry. The progress of radiolabeled peptide based ligands as potential radiopharmaceuticals is illustrated via novel structure and application studies, showing how the molecular modifications reflect their binding selectivity to significant onco-receptors, toxicity, and, by that, practical utilization. The most impressive outputs in categories of newly developed structures, as well as imaging and diagnosis approaches, and the most intensively studied oncological diseases in this context, are emphasized in order to show future perspectives of radiometal labeled amino acid-based compounds in nuclear medicine.

Targeting GRP receptor: Design, synthesis and preliminary biological characterization of new non-peptide antagonists of bombesin

We report the rational design, synthesis, and in vitro preliminary evaluation of a new small library of non-peptide ligands of Gastrin Releasing Peptide Receptor (GRP-R), able to antagonize its natural ligand bombesin (BN) in the nanomolar range of concentration. GRP-R is a transmembrane G-protein coupled receptor promoting the stimulation of cancer cell proliferation. Being overexpressed on the surface of different human cancer cell lines, GRP-R is ideal for the selective delivery to tumor cells of both anticancer drug and diagnostic devices. What makes very challenging the design of non-peptide BN analogues is that the 3D structure of the GRP-R is not available, which is the case for many membrane-bound receptors. Thus, the design of GRP-R ligands has to be based on the structure of its natural ligands, BN and GRP. We recently mapped the BN binding epitope by NMR and here we exploited the same spectroscopy, combined with MD, to define BN conformation in proximity of biological membranes, where the interaction with GRP-R takes place. The gained structural information was used to identify a rigid C-galactosidic scaffold able to support pharmacophore groups mimicking the BN key residues' side chains in a suitable manner for binding to GRP-R. Our BN antagonists represent hit compounds for the rational design and synthesis of new ligands and modulators of GRP-R. The further optimization of the pharmacophore groups will allow to increase the biological activity. Due to their favorable chemical properties and stability, they could be employed for the active receptor-mediated targeting of GRP-R positive tumors.

A HCBP1 peptide conjugated ruthenium complex for targeted therapy of hepatoma

An HCBP1 peptide-ruthenium conjugate (Ru-β-Ala-FQHPSFI) as a potential candidate for targeted therapy of hepatoma was synthesized. Ru-β-Ala-FQHPSFI shows drastically enhanced cytotoxicity and high selectivity for hepatoma cells versus noncancer liver cells. Raman imaging shows that this peptide-based drug can be taken up well by the hepatoma cells compared with the bare ruthenium complex (Ru) and the opposite sequence peptide-ruthenium conjugate (Ru-β-Ala-IFSPHQF). This study presents a new strategy for the construction of tumor-targeting metal-based anticancer therapeutics.

Recent Advances in Peptide-Based Approaches for Cancer Treatment

BACKGROUND

Peptide-based pharmaceuticals have recently experienced a renaissance due to their ability to fill the gap between the two main classes of available drugs, small molecules and biologics. Peptides combine the high potency and selectivity typical of large proteins with some of the characteristic advantages of small molecules such as synthetic accessibility, stability and the potential of oral bioavailability.

METHODS

In the present manuscript we review the recent literature on selected peptide-based approaches for cancer treatment, emphasizing recent advances, advantages and challenges of each strategy.

RESULTS

One of the applications in which peptide-based approaches have grown rapidly is cancer therapy, with a focus on new and established targets. We describe, with selected examples, some of the novel peptide-based methods for cancer treatment that have been developed in the last few years, ranging from naturally-occurring and modified peptides to peptidedrug conjugates, peptide nanomaterials and peptide-based vaccines.

CONCLUSION

This review brings out the emerging role of peptide-based strategies in oncology research, critically analyzing the advantages and limitations of these approaches and the potential for their development as effective anti-cancer therapies.

Fluorescent RGD-based pro-apoptotic peptide conjugates as mitochondria-targeting probes for enhanced anticancer activities

We have designed 2-domain anticancer peptides with RGD-based KLAK bi-functional short motifs (linear and cyclic analogues). RGD tripeptide acts as tumor blood vessel 'homing' motif while KLAK tetrapeptide internalized in mitochondria and causes cell apoptosis. All three peptides (RGDKLAK; HM, cyclic-RGDKLAK; HMC-1, and RGD-cyclic-KLAK; HMC-2) were conjugated with fluorescein isothiocyanate isomer-I (5-FITC; F) for in-vivo and in-vitro optical imaging studies. These fluorescent-peptide (FL-peptide) analogues were analyzed to possess α_vβ₃-integrin targeting affinity, high uptake in in-vitro cell binding assays followed by in-vivo tumor xenograft mice studies. Pharmacological profile reveals that F-HMC-1 analogue exhibited selectively and specifically higher affinity for α_vβ₃-integrin than other analogues in U87MG cells in comparison with HeLa cells. The subcutaneous U87MG tumor xenograft mice models clearly visualized the uptake of F-HMC-1 in tumor tissue in contrast with normal tissues with tumor-to-normal tissue ratio (T/NT = 15.9 ± 1.1) at 2 h post-injection. These results suggested that F-HMC-1 peptide has potential diagnostic applications for targeting α_vβ₃-integrin assessed by optical imaging study in U87MG tumor xenograft mice models.

On-cell saturation transfer difference NMR study of Bombesin binding to GRP receptor

We report the NMR characterization of the molecular interaction between Gastrin Releasing Peptide Receptor (GRP-R) and its natural ligand bombesin (BN). GRP-R is a transmembrane G-protein coupled receptor promoting the stimulation of cancer cell proliferation; in addition, being overexpressed on the surface of different human cancer cell lines, it is ideal for the development of new strategies for the selective targeted delivery of anticancer drugs and diagnostic devices to tumor cells. However, the design of new GRP-R binders requires structural information on receptor interaction with its natural ligands. The experimental protocol presented herein, based on on-cell STD NMR techniques, is a powerful tool for the screening and the epitope mapping of GRP-R ligands aimed at the development of new anticancer and diagnostic tools. Notably, the study can be carried out in a physiological environment, at the surface of tumoral cells overespressing GRP-R. Moreover, to the best of our knowledge, this is the first example of an NMR experiment able to detect and investigate the structural determinants of BN/GRP-R interaction.

The Influence of Different Spacers on Biological Profile of Peptide Radiopharmaceuticals for Diagnosis and Therapy of Human Cancers

BACKGROUND

Cancer is the leading cause of death worldwide. Early detection can reduce the disadvantageous effects of diseases and the mortality in cancer. Nuclear medicine is a powerful tool that has the ability to diagnose malignancy without harming normal tissues. In recent years, radiolabeled peptides have been investigated as potent agents for cancer detection. Therefore, it is necessary to modify radiopeptides in order to achieve more effective agents.

OBJECTIVE

This review describes modifications in the structure of radioconjugates with spacers who have improved the specificity and sensitivity of the peptides that are used in oncologic diagnosis and therapy.

METHODS

To improve the biological activity, researchers have conjugated these peptide analogs to different spacers and bifunctional chelators. Many spacers of different kinds, such as hydrocarbon chain, amino acid sequence, and poly (ethyleneglycol) were introduced in order to modify the pharmacokinetic properties of these biomolecules.

RESULTS

Different spacers have been applied to develop radiolabeled peptides as potential tracers in nuclear medicine. Spacers with different charge and hydrophilicity affect the characteristics of peptide conjugate. For example, the complex with uncharged and hydrophobic spacers leads to increased liver uptake, while the composition with positively charged spacers results in high kidney retention. Therefore, the pharmacokinetics of radio complexes correlates to the structure and total charge of the conjugates.

CONCLUSION

Radio imaging technology has been successfully applied to detect a tumor in the earliest stage. For this purpose, the assessment of useful agents to diagnose the lesion is necessary. Developing peptide radiopharmaceuticals using spacers can improve in vitro and in vivo behavior of radiotracers leading to better noninvasive detection and monitoring of tumor growth.

Selective Neuropeptide Y Conjugates with Maximized Carborane Loading as Promising Boron Delivery Agents for Boron Neutron Capture Therapy

G-protein-coupled receptors like the human Y₁ receptor (hY₁R) are promising targets in cancer therapy due to their high overexpression on cancer cells and their ability to internalize together with the bound ligand. This mechanism was exploited to shuttle boron atoms into cancer cells for the application of boron neutron capture therapy (BNCT), a noninvasive approach to eliminate cancer cells. A maximized number of carboranes was introduced to the hY₁R-preferring ligand [F⁷,P³⁴]-NPY by solid phase peptide synthesis. Branched conjugates loaded with up to 80 boron atoms per peptide molecule exhibited a maintained receptor activation profile, and the selective uptake into hY₁R-expressing cells was demonstrated by internalization studies. In order to ensure appropriate solubility in aqueous solution, we proved the need for eight hydroxyl groups per carborane. Thus, we suggest the utilization of bis-deoxygalactosyl-carborane building blocks in solid phase peptide synthesis to produce selective boron delivery agents for BNCT.

Systematic Meta-Analysis Identifies Co-Expressed Kinases and GPCRs in Ovarian Cancer Tissues Revealing a Potential for Targeted Kinase Inhibitor Delivery

The use of many anticancer drugs is problematic due to severe adverse effects. While the recent clinical launch of several kinase inhibitors led to tremendous progress, these targeted agents tend to be of non-specific nature within the kinase target class. Moreover, target mediated adverse effects limit the exploitation of some very promising kinase targets, including mitotic kinases. A future strategy will be the development of nanocarrier-based systems for the active delivery of kinase inhibitors using cancer specific surface receptors. The G-protein-coupled-receptors (GPCRs) represent the largest cell surface receptor family and some members are known to be frequently overexpressed in various cancer types. In the presented study, we used ovarian cancer tissues as an example to systematically identify concurrently overexpressed GPCRs and kinases. The rationale of this approach will guide the future design of nanoparticles, which will dock to GPCRs on cancer cells via specific ligands and deliver anticancer compounds after receptor mediated internalization. In addition to this, the approach is expected to be most effective by matching the inhibitor profiles of the delivered kinase inhibitors to the observed kinase gene expression profiles. We validated the suggested strategy in a meta-analysis, revealing overexpression of selected GPCRs and kinases in individual samples of a large ovarian cancer data set. The presented data demonstrate a large untapped potential for personalized cancer therapy using high-end targeted nanopharmaceuticals with kinase inhibitors.

Enhanced tumor retention of NTSR1-targeted agents by employing a hydrophilic cysteine cathepsin inhibitor

We explored the approach of using an analog of E-64, a well-known and hydrophilic cysteine cathepsin (CC) inhibitor, as a potent cysteine cathepsin-trapping agent (CCTA) to improve the tumor retention of low-molecular-weight, receptor-targeted radiopharmaceuticals. The synthesized hydrophilic CCTA-incorporated, NTSR1-targeted agents demonstrated a substantial increase in cellular retention upon uptake into the NTRS1-positive HT-29 human colon cancer cell line. Similarly, biodistribution studies using HT-29 xenograft mice revealed a significant and substantial increase in tumor retention for the CCTA-incorporated, NTSR1-targeted agent. The intracellular trapping mechanism of the CCTA-incorporated agents by macromolecular adduct formation was confirmed using multiple in vitro and in vivo techniques. Furthermore, utilization of the more hydrophilic CCTA greatly increased the hydrophilicity of the resulting NTSR1-targeted constructs leading to substantial decreases in most non-target tissues in contrast to our previously reported dipeptidyl acyloxymethyl ketone (AOMK) constructs. This work further confirms that the CCTA trapping approach can make significant improvements in the clinical potential of NTSR1-and other receptor-targeted radiopharmaceuticals.

Tumor targeting with 99m Tc radiolabeled peptides: Clinical application and recent development

Targeting overexpressed receptors on the cancer cells with radiolabeled peptides has become very important in nuclear oncology in the recent years. Peptides are small and have easy preparation and easy radiolabeling protocol with no side-effect and toxicity. These properties made them a valuable tool for tumor targeting. Based on the successful imaging of neuroendocrine tumors with ¹¹¹ In-octreotide, other receptor-targeting peptides such as bombesin (BBN), cholecystokinin/gastrin analogues, neurotensin analogues, glucagon-like peptide-1, and RGD peptides are currently under development or undergoing clinical trials. The most frequently used radionuclides for tumor imaging are ^99m Tc and ¹¹¹ In for single-photon emission computed tomography and ⁶⁸ Ga and ¹⁸ F for positron emission tomography imaging. This review presents some of the ^99m Tc-labeled peptides, with regard to their potential for radionuclide imaging of tumors in clinical and preclinical application.

Increasing time on target: utilization of inhibitors of cysteine cathepsins to enhance the tumor retention of receptor-targeted agents

We report a strategy of utilizing irreversible cysteine cathepsin inhibitor as trapping agent to increase the tumor residence time of receptor-targeted agents. The targeted constructs incorporating these cysteine cathepsin trapping agents were able to form high molecular weight adducts with intracellular cysteine cathepsins, thus achieving superior retention in tumor tissues.

Large set data mining reveals overexpressed GPCRs in prostate and breast cancer: potential for active targeting with engineered anti-cancer nanomedicines

Over 800 G-protein-coupled receptors (GPCRs) are encoded by the human genome and many are overexpressed in tumors. GPCRs are triggered by ligand molecules outside the cell and activate internal signal transduction pathways driving cellular responses. The receptor signals are desensitized by receptor internalization and this mechanism can be exploited for the specific delivery of ligand-linked drug molecules directly into cells. Detailed expression analysis in cancer tissue can inform the design of GPCR-ligand decorated drug carriers for active tumor cell targeting. The active targeting process utilizes ligand receptor interactions leading to binding and in most cases internalization of the ligand-attached drug carrier resulting in effective targeting of cancer cells. In this report public microarray data from the Gene Expression Omnibus (GEO) repository was used to identify overexpressed GPCRs in prostate and breast cancer tissues. The analyzed data confirmed previously known cancer receptor associations and identified novel candidates for potential active targeting. Prioritization of the identified targeting receptors is also presented based on high expression levels and frequencies in cancer samples but low expression in healthy tissue. Finally, some selected examples were used in ligand docking studies to assess the feasibility for chemical conjugation to drug nanocarriers without interference of receptor binding and activation. The presented data demonstrate a large untapped potential to improve efficacy and safety of current and future anti-cancer compounds through active targeting of GPCRs on cancer cells.

Development of a peptide-based bifunctional chelator conjugated to a cytotoxic drug for the treatment of melanotic melanoma

The cytotoxic drug gemcitabine (GEM) has been conjugated to receptor-binding peptides to target melanoma tumors. A hexapeptide having a Lys-Gly-His-Lys sequence (pep-1), an octapeptide with an Arg-Gly-Asp-Lys-Gly-His-Lys sequence (pep-2), a GEM-conjugated Lys-Gly-His-Lys peptide (GEM-pep-3) and a GEM-conjugated Asp-Gly-Arg peptide (GEM-pep-4) were synthesized and characterized. In vitro uptake of fluorescently labeled GEM-pep-3 and GEM-pep-4 on B16F10 cells was investigated. Fluorescence microscopy studies demonstrated significant uptake of GEM-pep-3 in the B16F10 mouse melanoma cell line. The peptides and GEM-coupled peptides were radiolabeled with [99mTc(CO)3(H2O)3]+ and examined for in vitro cell binding in the B16F10 melanoma cell line and in vivo biodistribution and scintigraphic studies in a B16F10 melanoma tumor-bearing mice model. In vitro cellular uptake studies and biological evaluation confirmed significant deposition of GEM-pep-3 at the melanoma tumor site. The MTT assay depicted higher cytotoxic behaviour of GEM-pep-3 than free GEM. A considerable amount of cell apoptosis was also observed in B16F10 cells. Finally, the in vivo therapeutic efficacy study revealed a significant decrease in tumor growth in the GEM-pep-3-treated animal model. These studies reveal enough potentiality of GEM-pep-3 to treat melanoma and underline the need for further evaluation.

Somatostatin analogues labeled with copper radioisotopes: current status

Peptide receptor radionuclide therapy (PRRT) is a promising way to treat patients with inoperable tumors or metastatic neuroendocrine tumors. This therapeutic strategy is using radiolabeled peptides, which are capable of selective biding to receptors overexpressed in the cancer cells. One of the group of receptor-avid peptide used in the PRRT are the analogues of somatostatin (SST) connected to the complexes of radionuclides (e.g. ⁹⁰Y, ¹⁷⁷Lu or ¹¹¹In). Many studies have shown that radiopharmaceuticals based on Cu radioisotopes are promising for the diagnosis and treatment of various cancers. This mini-review focuses on recent developments and summarises the results of multiple studies addressing SST agonists and antagonists radiolabeled to Cu radioisotopes.

Peptide-based PET imaging of the tumor restricted IL13RA2 biomarker

Peptides that target cancer cell surface receptors are promising platforms to deliver diagnostic and therapeutic payloads specifically to cancer but not normal tissue. IL13RA2 is a tumor-restricted receptor found to be present in several aggressive malignancies, including in the vast majority of high-grade gliomas and malignant melanoma. This receptor has been successfully targeted for diagnostic and therapeutic purposes using modified IL-13 ligand and more recently using a specific peptide, Pep-1L. In the current work, we establish the in vitro and in vivo tumor binding properties of radiolabeled Pep-1L, designed for tumor imaging. We radiolabeled Pep-1L with Copper-64 and demonstrated specific cell uptake in the IL13RA2-over expressing G48 glioblastoma cell line having abundant IL13RA2 expression. [⁶⁴Cu]Pep-1L binding was blocked by unlabeled ligand, demonstrating specificity. To demonstrate in vivo tumor uptake, we intravenously injected into tumor-bearing mice and demonstrated that [⁶⁴Cu]Pep-1L specifically bound tumors at 24 hours, which was significantly blocked (3-fold) by pre-injecting unlabeled peptide. To further demonstrate specificity of Pep-1L towards IL13RA2 in vivo, we exploited an IL13RA2-inducible melanoma tumor model that does not express receptor at baseline but expresses abundant receptor after treatment with doxycycline. We injected [⁶⁴Cu]Pep-1L into mice bearing IL13RA2-inducible melanoma tumors and performed in vivo PET/CT and post-necropsy biodistribution studies and found that tumors that were induced to express IL13RA2 receptor by doxycycline pretreatment bound radiolabeled Pep-1L 3-4 fold greater than uninduced tumors, demonstrating receptor specificity. This work demonstrates that [⁶⁴Cu]Pep-1L selectively binds hIL13RA2-expressing tumors and validates Pep-1L as an effective platform to deliver diagnostics and therapeutics to IL13RA2-expressing cancers.

Synthesis and exploration of novel radiolabeled bombesin peptides for targeting receptor positive tumor

Increasing evidence of peptide receptor overexpression in various cancer cells, warrant the development of receptor specific radiolabeled peptides for molecular imaging and therapy in nuclear medicine. Gastrin-releasing-peptide (GRP) receptor, are overexpressed in a variety of human cancer cells. The present study report the synthesis and biological evaluation of new bombesin (BBN) analogs, HYNIC-Asp-[Phe¹³]BBN(7-13)-NH-CH₂-CH₂-CH3:BA1, HYNIC-Pro-[Tyr¹³Met¹⁴]BBN(7-14)NH₂:BA2 as prospective tumor imaging agent with compare to BBN(7-14)NH₂:BS as standard. The pharmacophores were radiolabeled in high yields with ^99mTc, characterized for their stability in serum and saline, cysteine/histidine and were found to be substantially stable. Internalization/externalization and receptor binding studies were assessed using MDA-MB-231 cells and showed high receptor binding-affinity and favourable internalization. Fluorescence studies revealed that BA1 changed the morphology of the cells and could localize in the nucleus more effectively than BA2/BS. Cell-viability studies displayed substantial antagonistic and nuclear-internalization effect of BA1. BA1 also exhibited antiproliferative effect on MDA-MB-231 cell by inducing apoptosis. In vivo behaviour of the radiopeptides was evaluated in GRP receptor positive tumor bearing mice. The ^99mTc-BA1/^99mTc-BA2 demonstrated rapid blood/urinary clearance through the renal pathway and comparatively more significant tumor uptake image and favourable tumor-to-non-target ratios provided by ^99mTc-BA1. The specificity of the in vivo uptake was confirmed by co-injection with BS. Moreover, ^99mTc-BA1 provided a much clearer tumor image in scintigraphic studies than others. Thus the combination of favourable in vitro and in vivo properties renders BA1 as more potential antagonist bombesin-peptide for targeting GRP-receptor positive tumor. These properties are encouraging to carry out further experiments for non-invasive receptor targeting potential diagnostinc and therapeutic agent for tumors.

In vitro cytotoxic and genotoxic evaluation of peptides used in nuclear medicine (DOTATATE and Ubiquicidin29-41) in CHO-K1 cells

Micronucleus (MN) assay constitutes a valuable surrogate to the chromosome aberration technique for in vitro testing of the genotoxicity of substances. As test substances, two peptidic compounds (DOTATATE and Ubiquicidin_29-41) used in nuclear medicine, were tested for in vitro cytotoxicity and genotoxicity in CHO-K1 cells. None of the compounds showed detectable cytotoxicity (0.5-7.3 ng/mL for DOTATATE and 0.3-4.5 ng/mL for UBI_29-41), genotoxicity (0.72, 7.2 and 72.0 ng/ml for DOTATATE and 0.45, 4.5 and 45.0 ng/mL for UBI_29-41) or cell cycle changes as compared to untreated controls at the concentrations tested. Statistical analysis showed good concordance between two independent analysts. The results corroborate the notion of the safety of the compounds and present improvements of the in vitro MN assay when performed in a pre-clinical trial context that increase the throughput of small-to-medium testing facilities as an alternative to high content screening systems.

Analysis of argentinated peptide complexes using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: Peptide = oxytocin, arg(8) -vasopressin, bradykinin, bombesin, somatostatin, neurotensin

RATIONALE

The increased use of silver nanoparticles (AgNPs) for various biological applications, and over-expression of various peptide receptors in different tumors/cancer cells, necessitate the need for dedicated investigations on the intrinsic binding ability of Ag with various biologically important peptides for better understanding of AgNPs-peptide interactions and for the future development of contrasting agents as well as drugs for imaging/biomedical applications.

METHODS

The [M+(Ag)n ](+) complexes are prepared and characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS).

RESULTS

Silver complexes of the peptides [M+(Ag)n ](+) , where M = oxytocin, arg(8) -vasopressin, bradykinin, bombesin, somatostatin, and neurotensin, have been investigated for their intrinsic Ag(+) -binding ability. Unusual binding of up to seven Ag(+) with these small peptides is observed. The mass spectra show n = 1-5 for bombesin and somatostatin, n = 1-6 for bradykinin and arg(8) -vasopressin, and n = 1-7 for oxytocin and neurotensin. In addition, oxytocin and arg(8) -vasopressin show the formation of dimers and their complexes [M2 +(Ag)n ](+) with n = 1-8 and n = 1-5, respectively. The possible amino acid residues responsible for Ag(+) binding in each peptide have been identified on the basis of density functional theory (DFT)-calculated binding energy values of Ag(+) towards individual amino acids.

CONCLUSIONS

Mass spectrometric evidence indicates that the peptides, viz., oxytocin, arg(8) -vasopressin, bradykinin, bombesin, somatostatin, and neurotensin, show greater affinity for Ag(+) . Hence, they may be used as carriers for AgNPs in targeted drug delivery as well as an alternative for iodinated contrasting agents in dual energy X-ray imaging techniques. Radio-labeled Ag with these peptides can also be used in radio-pharmaceuticals for diagnostic and therapeutic applications. Copyright © 2016 John Wiley & Sons, Ltd.

Preparation and evaluation of the tumor-specific antigen-derived synthetic mucin 1 peptide: A potential candidate for the targeting of breast carcinoma

PURPOSE

The goal of this study was to prepare a synthetic peptide derived from breast tumor associated antigen and to evaluate its potential as a breast cancer imaging agent.

METHODS

A mucin 1 derived peptide was synthesized by solid-phase peptide synthesis and examined for its radiochemical and metabolic stability. The tumor cell binding affinity of (99m)Tc-MUC1 peptide was investigated on MUC1-positive T47D and MCF7 breast cancer cell lines. In vivo biodistribution was studied in normal Balb/c mice and in vivo tumor targeting and imaging in MCF7 and T47D tumor-bearing nude mice.

RESULTS

The synthesized MUC1-derived peptide displayed high radiochemical and metabolic stability. In vitro tumor cell-binding on T47D and MCF7 cell lines demonstrated high affinity of (99m)Tc-MUC1 peptide towards human breast cancer cells (binding affinities in nanomolar range). Pharmacokinetic studies performed on Balb/c mice are characterized by an efficient clearance from the blood and excretion predominantly through the urinary system. In vivo tumor uptake in nude mice with MCF7 tumor xenografts was 2.77±0.63% ID/g as early as 1h p.i. whereas in nude mice with T47D human ductal breast epithelial cancer cells, the accumulation in the tumor was found to be 2.65±0.54% ID/g at 1h p.i. Also tumor lesion was detectable in γ-camera imaging. The tumor uptake values were always higher than the blood and muscle uptake, with good tumor retention and good tumor-to-blood and tumor-to-muscle ratios. A low to moderate (<5% ID/g) accumulation and retention of (99m)Tc-MUC1 was found in the major organs (i.e., lungs, stomach, liver, intestines, kidneys, etc.) in both normal and tumor-bearing mice.

CONCLUSION

This study suggests that (99m)Tc-MUC1 tumor-antigen peptide may be a potential candidate for the targeted imaging of MUC1-positive human tumors and warrants further investigation.

Apoptosis imaging studies in various animal models using radio-iodinated peptide

Apoptosis has a role in many medical disorders and treatments; hence, its non-invasive evaluation is one of the most riveting research topics. Currently annexin V is used as gold standard for imaging apoptosis. However, several drawbacks, including high background, slow body clearance, make it a suboptimum marker for apoptosis imaging. In this study, we radiolabeled the recently identified histone H1 targeting peptide (ApoPep-1) and evaluated its potential as a new apoptosis imaging agent in various animal models. ApoPep-1 (CQRPPR) was synthesized, and an extra tyrosine residue was added to its N-terminal end for radiolabeling. This peptide was radiolabeled with (124)I and (131)I and was tested for its serum stability. Surgery- and drug-induced apoptotic rat models were prepared for apoptosis evaluation, and PET imaging was performed. Doxorubicin was used for xenograft tumor treatment in mice, and the induced apoptosis was studied. Tumor metabolism and proliferation were assessed by [(18)F]FDG and [(18)F]FLT PET imaging and compared with ApoPep-1 after doxorubicin treatment. The peptide was radiolabeled at high purity, and it showed reasonably good stability in serum. Cell death was easily imaged by radiolabeled ApoPep-1 in an ischemia surgery model. And, liver apoptosis was more clearly identified by ApoPep-1 rather than [(124)I]annexin V in cycloheximide-treated models. Three doxorubicin doses inhibited tumor growth, which was evaluated by 30-40% decreases of [(18)F]FDG and [(18)F]FLT PET uptake in the tumor area. However, ApoPep-1 demonstrated more than 200% increase in tumor uptake after chemotherapy, while annexin V did not show any meaningful uptake in the tumor compared with the background. Biodistribution data were also in good agreement with the microPET imaging results. All of the experimental data clearly demonstrated high potential of the radiolabeled ApoPep-1 for in vivo apoptosis imaging.

Nestin as a marker of cancer stem cells

The crucial role of cancer stem cells (CSCs) in the pathology of malignant diseases has been extensively studied during the last decade. Nestin, a class VI intermediate filament protein, was originally detected in neural stem cells during development. Its expression has also been reported in different tissues under various pathological conditions. Specifically, nestin has been shown to be expressed in transformed cells of various human malignancies, and a correlation between its expression and the clinical course of some diseases has been proved. Furthermore, the coexpression of nestin with other stem cell markers was described as a CSC phenotype that was subsequently verified using tumorigenicity assays. The primary aim of this review is to summarize the recent findings regarding nestin expression in CSCs, its possible role in CSC phenotypes, particularly with respect to capacity for self-renewal, and its utility as a putative marker of CSCs.

Advanced targeted therapies in cancer: Drug nanocarriers, the future of chemotherapy

Cancer is the second worldwide cause of death, exceeded only by cardiovascular diseases. It is characterized by uncontrolled cell proliferation and an absence of cell death that, except for hematological cancers, generates an abnormal cell mass or tumor. This primary tumor grows thanks to new vascularization and, in time, acquires metastatic potential and spreads to other body sites, which causes metastasis and finally death. Cancer is caused by damage or mutations in the genetic material of the cells due to environmental or inherited factors. While surgery and radiotherapy are the primary treatment used for local and non-metastatic cancers, anti-cancer drugs (chemotherapy, hormone and biological therapies) are the choice currently used in metastatic cancers. Chemotherapy is based on the inhibition of the division of rapidly growing cells, which is a characteristic of the cancerous cells, but unfortunately, it also affects normal cells with fast proliferation rates, such as the hair follicles, bone marrow and gastrointestinal tract cells, generating the characteristic side effects of chemotherapy. The indiscriminate destruction of normal cells, the toxicity of conventional chemotherapeutic drugs, as well as the development of multidrug resistance, support the need to find new effective targeted treatments based on the changes in the molecular biology of the tumor cells. These novel targeted therapies, of increasing interest as evidenced by FDA-approved targeted cancer drugs in recent years, block biologic transduction pathways and/or specific cancer proteins to induce the death of cancer cells by means of apoptosis and stimulation of the immune system, or specifically deliver chemotherapeutic agents to cancer cells, minimizing the undesirable side effects. Although targeted therapies can be achieved directly by altering specific cell signaling by means of monoclonal antibodies or small molecules inhibitors, this review focuses on indirect targeted approaches that mainly deliver chemotherapeutic agents to molecular targets overexpressed on the surface of tumor cells. In particular, we offer a detailed description of different cytotoxic drug carriers, such as liposomes, carbon nanotubes, dendrimers, polymeric micelles, polymeric conjugates and polymeric nanoparticles, in passive and active targeted cancer therapy, by enhancing the permeability and retention or by the functionalization of the surface of the carriers, respectively, emphasizing those that have received FDA approval or are part of the most important clinical studies up to date. These drug carriers not only transport the chemotherapeutic agents to tumors, avoiding normal tissues and reducing toxicity in the rest of the body, but also protect cytotoxic drugs from degradation, increase the half-life, payload and solubility of cytotoxic agents and reduce renal clearance. Despite the many advantages of all the anticancer drug carriers analyzed, only a few of them have reached the FDA approval, in particular, two polymer-protein conjugates, five liposomal formulations and one polymeric nanoparticle are available in the market, in contrast to the sixteen FDA approval of monoclonal antibodies. However, there are numerous clinical trials in progress of polymer-protein and polymer-drug conjugates, liposomal formulations, including immunoliposomes, polymeric micelles and polymeric nanoparticles. Regarding carbon nanotubes or dendrimers, there are no FDA approvals or clinical trials in process up to date due to their unresolved toxicity. Moreover, we analyze in detail the more promising and advanced preclinical studies of the particular case of polymeric nanoparticles as carriers of different cytotoxic agents to active and passive tumor targeting published in the last 5 years, since they have a huge potential in cancer therapy, being one of the most widely studied nano-platforms in this field in the last years. The interest that these formulations have recently achieved is stressed by the fact that 90% of the papers based on cancer therapeutics with polymeric nanoparticles have been published in the last 6 years (PubMed search).

Drug delivery and release systems for targeted tumor therapy

Most toxic agents currently used for chemotherapy show a narrow therapeutic window, because of their inability to distinguish between healthy and cancer cells. Targeted drug delivery offers the possibility to overcome this issue by selectively addressing structures on the surface of cancer cells, therefore reducing undesired side effects. In this broad field, peptide-drug conjugates linked by intracellular cleavable structures have evolved as highly promising agents. They can specifically deliver toxophores to tumor cells by targeting distinct receptors overexpressed in cancer. In this review, we focus on these compounds and describe important factors to develop a highly efficient peptide-drug conjugate. The necessary properties of tumor-targeting peptides are described, and the different options for cleavable linkers used to connect toxic agents and peptides are discussed, and synthetic considerations for the introduction of these structures are reported. Furthermore, recent examples and current developments of peptide-drug conjugates are critically evaluated with a special focus on the applied linker structures and their future use in cancer therapy.

Fmoc Solid-Phase Peptide Synthesis

Synthetic peptides are important as drugs and in research. Currently, the method of choice for producing these compounds is solid-phase peptide synthesis. In this nonspecialist review, we describe the scope and limitations of Fmoc solid-phase peptide synthesis. Furthermore, we provide a detailed protocol for Fmoc peptide synthesis.

Effect of somatostatin in advanced gastric cancer after D2 radical gastrectomy

AIM: To study the effect of somatostatin in patients with advanced gastric cancer who received D2 lymphadenectomy and vagina vasorum dissection.

METHODS: Using a prospective, single-blind, placebo-controlled design, patients with advanced gastric cancer were randomized into a study group (n = 61) and a control group (n = 59). Patients in the study group were given somatostatin for 5-7 d starting 6 h after the operation, and patients in the control group were given normal saline. Preoperative and nonoperative complications in the perioperative period, as well as different types of postoperative drainage in the two groups were compared.

RESULTS: There was no significant difference between the study group and the control group for preoperative clinicopathological indicators. We found no significant difference between the two groups for the overall incidence of complications, but a lower percentage of peritoneal effusion was observed in the treatment group (1.6% vs 10.2%, P < 0.05). There were no significant differences between the two groups in the incidence of postoperative pancreatic dysfunction and chylous fistula. However, there were significant differences in the amylase concentration in drainage fluid, volume and duration of drainage, volume and duration of chylous fistula and peritoneal drainage, and volume and duration of gastric tube drainage. The study group did not show any increase in mean hospitalization cost and the cost reduced when the postoperative complications occurred.

CONCLUSION: Postoperative somatostatin reduces volume and duration of surgical drainage and related complications. Somatostatin may improve safety of gastric cancer surgery, reducing postoperative complications and promoting recovery.

Preclinical pharmacokinetic, biodistribution, imaging and therapeutic efficacy of (177)Lu-Labeled glycated bombesin analogue for gastrin-releasing peptide receptor-positive prostate tumor targeting

The gastrin-releasing peptide receptor (GRPR) has been shown to be overexpressed in many human tumors, including prostate, colon, gastric, breast, pancreatic, and small cell lung cancers. Because bombesin (BBS) binds to GRPR with high affinity, BBS derivatives have been labeled with various radionuclides and have been demonstrated to be successful candidates for peptide receptor radiotherapy (PRRT). The present study describes the in vitro and in vivo preclinical characteristics of (177)Lu-DOTA-Lys(glucose)-4 aminobenzoic acid-BBS7-14 ((177)Lu-DOTA-gluBBN) to prepare radiolabeled candidates for the treatment of GRPR-expressing prostate tumors.

METHODS

(177)Lu-DOTA-gluBBN was prepared as previously published [1]. Human prostate PC-3 tumor cells were used to determine the binding (Kd) retention and efflux of (177)Lu-DOTA-gluBBN. Pharmacokinetic, imaging, and radiotherapy studies were performed in PC-3 xenografted mice.

RESULTS

The Kd value of (177)Lu-DOTA-gluBBN was 0.63 nM, with a maximum binding capacity (Bmax) of 669.7 fmol/10(6) cells (4.04×10(5) GRPR/cell). During a 2-hr incubation, 90.1±0.4% of the cell-associated radio-peptide was internalized, and 56.3±7.1% of the internalized radio-peptide was externalized in vitro. High amounts of the radio-peptide were rapidly accumulated in a PC-3 tumor in vivo, and the % ID/g of the tumor was 12.42±2.15 1 hr p.i. The radio-peptide was quickly cleared from the blood, yielding tumor-to-blood ratios of 39.22±17.36 at 1 hr p.i. and 330.67±131.23 at 24hr p.i. In addition, (177)Lu-DOTA-gluBBN was clearly visualized in PC-3 tumors 1 hr p.i. and significantly inhibited the tumor growth (P<0.05). Treatment-related toxicity in the pancreas and kidneys was not observed, except for slight glomerulopathy.

CONCLUSIONS

The pharmacokinetic, imaging, and therapy studies suggest that this (177)Lu-DOTA-gluBBN has promising characteristics for application in nuclear medicine, namely, for the diagnosis and treatment of GRPR-overexpressing prostate tumors.