¹²⁵I-radiolabeled morpholine-containing arginine-glycine-aspartate (RGD) ligand of αvβ₃ integrin as a molecular imaging probe for angiogenesis

Biomedical applications of radioiodinated peptides

The overexpression of peptide receptors in certain tumors as compared to endogeneous expression levels represents the molecular basis for the design of peptide-based tools for targeted nuclear imaging and therapy. Receptor targeting with radiolabelled peptides became a very important imaging and/or therapeutic approach in nuclear medicine and oncology. A great variety of peptides has been radiolabelled with clinical relevant radionuclides, such as radiometals and radiohalogens. However, to the best of our knowledge concise and updated reviews providing information about the biomedical application of radioiodinated peptides are still missing. This review outlines the synthetic efforts in the preparation of radioiodinated peptides highlighting the importance of radioiodine in nuclear medicine, giving an overview of the most relevant radioiodination strategies that have been employed and describes relevant examples of their use in the biomedical field.

Diversity-Oriented Synthesis and Chemoinformatic Analysis of the Molecular Diversity of sp3-Rich Morpholine Peptidomimetics

Diversity-Oriented Synthesis (DOS) consists of generating structurally diverse compounds from a complexity-generating reaction followed by cyclization steps and appendage diversity. DOS has gathered interest to systematically explore the chemical space by generating high-quality small-molecule collections as probes to investigate biological pathways. The generation of heterocycles using amino acid and sugar derivatives as building blocks is a powerful approach to access chemical and geometrical diversity thanks to the high number of stereocenters and the polyfunctionality of such compounds. Our efforts in this field are focused on the generation of diversity-oriented molecules of peptidomimetic nature as a tool addressing protein-protein interactions, taking advantage of amino acid- and sugar-derived polyfunctional building blocks to be applied in couple-pair synthetic approaches. In this paper, the combination of diversity-oriented synthesis and chemoinformatics analysis of chemical space and molecular diversity of heterocyclic peptidomimetics are reported, with particular interest toward carbohydrate- and amino acid-derived morpholine scaffolds with a higher fraction of sp3 carbon atoms. Also, the chemoinformatic analysis of chemical space and molecular diversity of 186 morpholine peptidomimetics is outlined.

Stereodivergent synthesis of 5-aminopipecolic acids and application in the preparation of a cyclic RGD peptidomimetic as a nanomolar αVβ3 integrin ligand

A stereodivergent preparation of trans and cis-5-aminopipecolic acids (5-APAs) was developed to obtain constrained amino acids useful for peptidomimetics.

Small activating RNA upregulates NIS expression: promising potential for hepatocellular carcinoma endoradiotherapy

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Currently, the clinical strategies available for the treatment of HCC remain insufficient for the poor prognosis. Sodium/iodide symporter (NIS)-based radioiodine therapy is proposed as a promising therapeutic strategy for the treatment of HCC. However, it is difficult for HCC cells to trap iodine for the lower expression of NIS. Small activating RNA (saRNA) is a newly identified small double-stranded RNA (dsRNA) that can induce endogenous gene expression by targeting promoter sequences. Here, we designed an saRNA (saRNA-482) that targeted the NIS promoter sequences. In the cultured HepG2 cells and Hep3B cells, the expressions of NIS were upregulated after transfection of saRNA-482. In addition, the uptake of ¹²⁵I increased in the cultured HepG2 and Hep3B cells transfected with saRNA-482. Furthermore, the cell viabilities were significantly inhibited in the saRNA-482-transfected HepG2 and Hep3B cells after ¹³¹I treatment. Meanwhile, the apoptosis of saRNA-482-transfected HepG2 and Hep3B cells significantly increased after ¹³¹I treatment. The results suggest that RNA activation-mediated upregulation of NIS may have an endoradiotherapeutic potential in the treatment of HCC.

Carbohydrates in diversity-oriented synthesis: challenges and opportunities

Carbohydrates are attractive building blocks for diversity-oriented synthesis due to their stereochemical diversity and high density of polar functional groups.

Melanoma cell therapy: Endothelial progenitor cells as shuttle of the MMP12 uPAR-degrading enzyme

The receptor for the urokinase-type plasminogen activator (uPAR) accounts for many features of cancer progression, and is therefore considered a target for anti-tumoral therapy. Only full length uPAR mediates tumor progression. Matrix-metallo-proteinase-12 (MMP12)-dependent uPAR cleavage results into the loss of invasion properties and angiogenesis. MMP12 can be employed in the field of “targeted therapies” as a biological drug to be delivered directly in patient's tumor mass. Endothelial Progenitor Cells (EPCs) are selectively recruited within the tumor and could be used as cellular vehicles for delivering anti-cancer molecules. The aim of our study is to inhibit cancer progression by engeneering ECFCs, a subset of EPC, with a lentivirus encoding the anti-tumor uPAR-degrading enzyme MMP12. Ex vivo manipulated ECFCs lost the capacity to perform capillary morphogenesis and acquired the anti-tumor and anti-angiogenetic activity. In vivo MMP12-engineered ECFCs cleaved uPAR within the tumor mass and strongly inhibited tumor growth, tumor angiogenesis and development of lung metastasis.

The possibility to exploit tumor homing and activity of autologous MMP12-engineered ECFCs represents a novel way to combat melanoma by a “personalized therapy”, without rejection risk.

The i.v. injection of radiolabelled MMP12-ECFCs can thus provide a new theranostic approach to control melanoma progression and metastasis.

Synthesis and preclinical evaluation of a novel, selective 111In-labelled aminoproline-RGD-peptide for non-invasive melanoma tumor imaging

An ¹¹¹In-labelled Amp-based RGD-DOTA conjugate was synthesized and evaluated in preclinical models of human melanoma as a novel integrin-targeted SPECT imaging tracer.

Cyclic RGD Peptides Incorporating Cycloalkanes: Synthesis and Evaluation as PET Radiotracers for Tumor Imaging

Two new bicyclic arginine-glycine-aspartic acid (RGD) peptides, c(RGD-ACP-K) (1a) and c(RGD-ACH-K) (1b), incorporating the aminocyclopentane (ACP) and aminocyclohexane (ACH) carboxylic acids, respectively, were synthesized by grafting the aminocycloalkane carboxylic acids onto the tetra-peptide RGDK sequence. These peptides and their conjugates with DO3A (1,4,7,10-tetraazacyclododecane-1,4,7-trisacetic acid) (2a-b) exhibit high affinity toward U87MG glioblastoma cells. Their affinity is greater than that exhibited by c(RGDyK). Labeling these conjugates with radiometal (64)Cu resulted in high radiochemical yields (>97%) of the corresponding complexes, abbreviated as c(RGD-ACP-K)-DOTA-(64)Cu (3a) and c(RGD-ACH-K)-DOTA-(64)Cu (3b). Both 3a and 3b are stable for 24 h in human and mouse serums and show high tumor uptake, as observed by positron emission tomography (PET). Blocking experiments with 3a and 3b by preinjection of c(RGDyK) confirmed their target specificity and demonstrated their promise as PET radiotracers for imaging ανβ3-positive tumors.

Advances in imaging probes and optical microendoscopic imaging techniques for early in vivo cancer assessment

A new chapter in the history of medical diagnosis happened when the first X-ray technology was invented in the late 1800s. Since then, many non-invasive and minimally invasive imaging techniques have been invented for clinical diagnosis to research in cellular biology, drug discovery, and disease monitoring. These imaging modalities have leveraged the benefits of significant advances in computer, electronics, and information technology and, more recently, targeted molecular imaging. The development of targeted contrast agents such as fluorescent and nanoparticle probes coupled with optical imaging techniques has made it possible to selectively view specific biological events and processes in both in vivo and ex vivo systems with great sensitivity and selectivity. Thus, the combination of targeted molecular imaging probes and optical imaging techniques have become a mainstay in modern medicinal and biological research. Many promising results have demonstrated great potentials to translate to clinical applications. In this review, we describe a discussion of employing imaging probes and optical microendoscopic imaging techniques for cancer diagnosis.

Pharmacophoric modifications lead to superpotent αvβ3 integrin ligands with suppressed α5β1 activity

The selective targeting of the αvβ3 integrin subtype without affecting the structurally closely related receptor α5β1 is crucial for understanding the details of their biological and pathological functions and thus of great relevance for diagnostic and therapeutic approaches in cancer treatment. Here, we present the synthesis of highly active RGD peptidomimetics for the αvβ3 integrin with remarkable selectivity against α5β1. Incorporation of a methoxypyridine building block into a ligand scaffold and variation of different functional moieties led to αvβ3-antagonistic activities in the low nanomolar or even subnanomolar range. Furthermore, docking studies were performed to give insights into the binding modes of the novel compounds. The presented library comprises powerful ligands for specific addressing and blocking of the αvβ3 integrin subtype, thereby representing privileged tools for integrin-based personalized medicine.

RNAi-mediated gene knockdown and anti-angiogenic therapy of RCCs using a cyclic RGD-modified liposomal-siRNA system

Angiogenesis is one of crucial processes associated with tumor growth and development, and consequently a prime target for cancer therapy. Although tumor endothelial cells (TECs) play a key role in pathological angiogenesis, investigating phenotypical changes in neovessels when a gene expression in TEC is suppressed is a difficult task. Small interfering RNA (siRNA) represents a potential agent due to its ability to silence a gene of interest. We previously developed a system for in vivo siRNA delivery to cancer cells that involves a liposomal-delivery system, a MEND that contains a unique pH-sensitive cationic lipid, YSK05 (YSK-MEND). In the present study, we report on the development of a system that permits the delivery of siRNA to TECs by combining the YSK-MEND and a ligand that is specific to TECs. Cyclo(Arg-Gly-Asp-D-Phe-Lys) (cRGD) is a well-known ligand to αVβ3 integrin, which is selectively expressed at high levels in TECs. We incorporated cRGD into the YSK-MEND (RGD-MEND) to achieve an efficient gene silencing in TECs. Quantitative RT-PCR and the 5' rapid amplification of cDNA ends PCR indicated that the intravenous injection of RGD-MEND at a dose of 4.0mg/kg induced a significant RNAi-mediated gene reduction in TEC but not in endothelial cells of other organs. Finally, we evaluated the therapeutic potency of the RGD-MEND encapsulating siRNA against vascular endothelial growth factor receptor 2. A substantial delay in tumor growth was observed after three sequential RGD-MEND injections on alternate days. In conclusion, the RGD-MEND represents a new approach for the characterization of TECs and for us in anti-angiogenic therapy.

Gene therapy for advanced melanoma: selective targeting and therapeutic nucleic acids

Despite recent advances, the treatment of malignant melanoma still results in the relapse of the disease, and second line treatment mostly fails due to the occurrence of resistance. A wide range of mutations are known to prevent effective treatment with chemotherapeutic drugs. Hence, approaches with biopharmaceuticals including proteins, like antibodies or cytokines, are applied. As an alternative, regimens with therapeutically active nucleic acids offer the possibility for highly selective cancer treatment whilst avoiding unwanted and toxic side effects. This paper gives a brief introduction into the mechanism of this devastating disease, discusses the shortcoming of current therapy approaches, and pinpoints anchor points which could be harnessed for therapeutic intervention with nucleic acids. We bring the delivery of nucleic acid nanopharmaceutics into perspective as a novel antimelanoma therapeutic approach and discuss the possibilities for melanoma specific targeting. The latest reports on preclinical and already clinical application of nucleic acids in melanoma are discussed.