Molecular Imaging of Aminopeptidase N in Cancer and Angiogenesis

Glutathione‑degrading enzymes in the complex landscape of tumors (Review)

Glutathione (GSH)‑degrading enzymes are essential for starting the first stages of GSH degradation. These enzymes include extracellular γ‑glutamyl transpeptidase (GGT) and intracellular GSH‑specific γ‑glutamylcyclotransferase 1 (ChaC1) and 2. These enzymes are essential for cellular activities, such as immune response, differentiation, proliferation, homeostasis regulation and programmed cell death. Tumor tissue frequently exhibits abnormal expression of GSH‑degrading enzymes, which has a key impact on the development and spread of malignancies. The present review summarizes gene and protein structure, catalytic activity and regulation of GSH‑degrading enzymes, their vital roles in tumor development (including regulation of oxidative and endoplasmic reticulum stress, control of programmed cell death, promotion of inflammation and tumorigenesis and modulation of drug resistance in tumor cells) and potential role as diagnostic biomarkers and therapeutic targets.

Biomarkers and Proteomics in Sarcomeric Hypertrophic Cardiomyopathy in the Young-FGF-21 Highly Associated with Overt Disease

Background: Any difference in biomarkers between genotype-positive individuals with overt hypertrophic cardiomyopathy (HCM), and genotype-positive but phenotype-negative individuals (G+P-) in HCM-associated pathways might shed light on pathophysiological mechanisms. We studied this in young HCM patients. Methods: 29 HCM patients, 17 G+P--individuals, and age- and sex-matched controls were prospectively included. We analyzed 184 cardiovascular disease-associated proteins by two proximity extension assays, categorized into biological pathways, and analyzed with multivariate logistic regression analysis. Significant proteins were dichotomized into groups above/below median concentration in control group. Results: Dichotomized values of significant proteins showed high odds ratio (OR) in overt HCMphenotype for Fibroblast growth factor-21 (FGF-21) 10 (p = 0.001), P-selectin glycoprotein ligand-1 (PSGL-1) OR 8.6 (p = 0.005), and Galectin-9 (Gal-9) OR 5.91 (p = 0.004). For G+P-, however, angiopoietin-1 receptor (TIE2) was notably raised, OR 65.5 (p = 0.004), whereas metalloproteinase inhibitor 4 (TIMP4) involved in proteolysis, in contrast, had reduced OR 0.06 (p = 0.013). Conclusions: This study is one of the first in young HCM patients and G+P- individuals. We found significantly increased OR for HCM in FGF-21 involved in RAS-MAPK pathway, associated with cardiomyocyte hypertrophy. Upregulation of FGF-21 indicates involvement of the RAS-MAPK pathway in HCM regardless of genetic background, which is a novel finding.

Aminopeptidase N-Responsive Conjugates with Tunable Charge-Reversal Properties for Highly Efficient Tumor Accumulation and Penetration

Tumor enzyme-responsive charge-reversal carriers can induce efficient transcytosis and lead to efficient tumor infiltration and potent anticancer efficacy. However, the correlations of molecular structure with charge-reversal property, tumor penetration, and drug delivery efficiency are unknown. Herein, aminopeptidase N (APN)-responsive conjugates were synthesized to investigate these correlations. We found that the monomeric unit structure and the polymer chain structure determined the enzymatic hydrolysis and charge-reversal rates, and accordingly, the transcytosis and tumor accumulation and penetration of the APN-responsive conjugates. The conjugate with moderate APN responsiveness balanced the in vitro transcytosis and in vivo overall drug delivery process and achieved the best tumor delivery efficiency, giving potent antitumor efficacy. This work provides new insight into the design of tumor enzyme-responsive charge-reversal nanomedicines for efficient cancer drug delivery.

Hyperpolarized (1-13C)Alaninamide Is a Multifunctional In Vivo Sensor of Aminopeptidase N Activity, pH, and CO2

Spin hyperpolarization enables real-time metabolic imaging of carbon-13-labeled substrates. While hyperpolarized l-(1-¹³C)alaninamide is a probe of the cell-surface tumor marker aminopeptidase-N (APN, CD13), its activity in vivo has not been described. Scanning the kidneys of rats infused with hyperpolarized alaninamide shows both conversion to [1-¹³C]alanine and several additional spectral peaks with distinct temporal dynamics. The (1-¹³C)alaninamide chemical shift is pH-sensitive, with a pK_a of 7.9 at 37 °C, and the peaks correspond to at least three different compartments of pH 7.46 ± 0.02 (1), 7.21 ± 0.02 (2), and 6.58 ± 0.05 (3). An additional peak was assigned to the carboxyamino adduct formed by reaction with dissolved CO₂. Spectroscopic imaging showed nonuniform distribution, with the low-pH signal more concentrated in the inner medulla. Treatment with the diuretic acetazolamide resulted in significant pH shifts in compartment 1 to 7.38 ± 0.03 (p = 0.0057) and compartment 3 to 6.80 ± 0.05 (p = 0.0019). While the pH of compartment 1 correlates with blood pH, the pH of compartment 3 did not correspond to the pH of urine. In vitro experiments show that alaninamide readily enters blood cells and can detect intracellular pH. While carbamate formation depends on pH and pCO₂, the carbamate-to-alaninamide ratio did not correlate with either arterial blood pH or pCO₂, suggesting that it may reflect variations in tissue pH and pCO₂. This study demonstrates the feasibility of using hyperpolarized sensors to simultaneously image enzyme activity, pCO₂, and pH in vivo.

Discovery of Novel Tetrahydro-β-carboline Containing Aminopeptidase N Inhibitors as Cancer Chemosensitizers

Aminopeptidase N (APN, CD13) is closely associated with the development and progression of cancer. Previous studies suggested APN as a biomarker for cancer stem cells. APN inhibitors have been intensively evaluated as chemosensitizers for cancer treatments. In the present study, tetrahydro-β-carboline scaffold was introduced to the structure of APN inhibitors. The synthesized compounds showed potent enzyme inhibitory activities compared with Bestatin, an approved APN inhibitor, in cell-based enzymatic assay. In combination with chemotherapeutic drugs, representative APN inhibitor molecules D12, D14 and D16 significantly improved the antiproliferative potency of anticancer drugs in the in vitro tests. Further mechanistic studies revealed that the anticancer effects of these drug combinations are correlated with decreased APN expression, increased ROS level, and induction of cell apoptosis. The spheroid-formation assay and colony-formation assay results showed effectiveness of Paclitaxel-APN inhibitor combination against breast cancer stem cell growth. The combined drug treatment led to reduced mRNA expression of OCT-4, SOX-2 and Nanog in the cancer stem cells tested, suggesting the reduced stemness of the cells. In the in vivo study, the selected APN inhibitors, especially D12, exhibited improved anticancer activity in combination with Paclitaxel compared with Bestatin. Collectively, potent APN inhibitors were discovered, which could be used as lead compounds for tumor chemo-sensitization and cancer stem cell-based therapies.

Enzyme-activated Prodrugs and Their Release Mechanisms for Treatment of Cancer

Enzyme-activated prodrugs have received a lot of attention in recent years. These prodrugs have low toxicity to cells before they are activated, and when they interact with specific enzymes, they...

Enhancement of Tryptic Peptide Signals from Tissue Sections Using MALDI IMS Postionization (MALDI-2)

Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) allows for highly multiplexed, unlabeled mapping of analytes from tissue sections. However, further work is needed to improve the sensitivity and depth of coverage for protein and peptide IMS. We demonstrate signal enhancement of proteolytic peptides from thin tissue sections of human kidney by conventional MALDI (MALDI-1) augmented using a second ionizing laser (termed MALDI-2). Proteins were digested in situ using trypsin prior to IMS analysis. For tentative identification of peptides and proteins, a tissue homogenate from the same organ used for IMS was analyzed by LC-MS/MS, and data are available via ProteomeXchange with identifier PXD023877. These identified proteins were then digested in silico to generate a database of theoretical peptides to then match to MALDI IMS data sets. Peptides were tentatively identified by matching the MALDI peak list to the database peptide list based on mass accuracy (5 ppm mass error). This resulted in 1337 ± 96 (n = 3) peptides and 2076 ± 362 (n = 3) unique peptides matched to IMS peaks from MALDI-1 and MALDI-2, respectively. Protein identifications requiring two or more peptides per protein resulted in 276 ± 20 proteins with MALDI-1 and 401 ± 60 with MALDI-2. These results demonstrate that MALDI-2 provides enhanced sensitivity for the spatial mapping of tryptic peptides and significantly increases the number of proteins identified in IMS experiments.

Bio-vehicles of cytotoxic drugs for delivery to tumor specific targets for cancer precision therapy

Abnormal structural and molecular changes in malignant tissues were thoroughly investigated and utilized to target tumor cells, hence rescuing normal healthy tissues and lowering the unwanted side effects as non-specific cytotoxicity. Various ligands for cancer cell specific markers have been uncovered and inspected for directional delivery of the anti-cancer drug to the tumor site, in addition to diagnostic applications. Over the past few decades research related to the ligand targeted therapy (LTT) increased tremendously aiming to treat various pathologies, mainly cancers with well exclusive markers. Malignant tumors are known to induce elevated levels of a variety of proteins and peptides known as cancer "markers" as certain antigens (e.g., Prostate specific membrane antigen "PSMA", carcinoembryonic antigen "CEA"), receptors (folate receptor, somatostatin receptor), integrins (Integrin αvβ3) and cluster of differentiation molecules (CD13). The choice of an appropriate marker to be targeted and the design of effective ligand-drug conjugate all has to be carefully selected to generate the required therapeutic effect. Moreover, since some tumors express aberrantly high levels of more than one marker, some approaches investigated targeting cancer cells with more than one ligand (dual or multi targeting). We aim in this review to report an update on the cancer-specific receptors and the vehicles to deliver cytotoxic drugs, including recent advancements on nano delivery systems and their implementation in targeted cancer therapy. We will discuss the advantages and limitations facing this approach and possible solutions to mitigate these obstacles. To achieve the said aim a literature search in electronic data bases (PubMed and others) using keywords "Cancer specific receptors, cancer specific antibody, tumor specific peptide carriers, cancer overexpressed proteins, gold nanotechnology and gold nanoparticles in cancer treatment" was carried out.

Effect of non-competitive inhibitors of aminopeptidase N on viability of human and murine tumor cells

Cancer is the second leading cause of death worldwide. Peptidases participate in tumor development and growth. Mammalian neutral aminopeptidase (APN, EC 3.4.11.2, M1 family) catalyzes the cleavage of neutral and basic amino acids from the N-terminus of substrates. APN expression is dysregulated in several types of cancer, being a target for the development of new anticancer agents. Recently, we identified three new non-competitive inhibitors of soluble porcine APN (pAPN) by virtual screening (BTB11079, JFD00064, BTB07018, from Maybridge). In the present contribution we assayed their effect on the activity of APN in a microsomal preparation of porcine kidney cortex, a model of the physicochemical environment of the enzyme. These classical inhibitors had an IC50 value of 3–5 µM. Additionally, using a kinetic approach and a specific substrate, we quantified APN activity on the cell surface of human and murine lung, colon, prostate, and skin tumor cells. APN inhibitors reduced tumor cells viability, more efficiently in the higher APN activity tumor cell lines, but not in non-tumoral cells. BTB11079, JFD00064, BTB07018 effects on cell viability were stronger than that of bestatin, a positive control. Thus, these non-competitive APN inhibitors may be useful tools for cancer treatment.

Native Chemical Ligation-Based Fluorescent Probes for Cysteine and Aminopeptidase N Using meso-thioester-BODIPY

meso-Carboxyl-BODIPY responds to small electronic changes resulting from acyl substitution reactions with a marked change in fluorescence. Herein, the minute changes that accompany the thioester to amide conversion encountered in native chemical ligation (NCL) are exploited in the construction of fluorescent "turn-on" probes. Two fluorogenic probes, 1 a and 4, derived from a meso-thioester-BODIPY scaffold, were designed for the selective detection of cysteine (1 a) and aminopeptidase N (4), respectively. The aromatic (1 a) and aliphatic (4) thioesters of meso-carboxyl-BODIPY are nonfluorescent. However, specific analyte-induced conversion to the meso-amide derivative caused significant spectral changes and a dramatic fluorescence enhancement. Probe 1 a exhibited a large fluorescence "turn-on" response with high selectivity toward cysteine via a tandem NCL reaction. Probe 4 was successfully applied to the monitoring and imaging of endogenous aminopeptidase N in live cancer cells.

Structural Engineering of Fluorescent Self-Threaded Peptide Probes for Targeted Cell Imaging†

Squaraine figure-eight (SF8) molecules are a new class of deep-red fluorescent probes that are well suited for fluorescence cell microscopy due to their very high fluorescence brightness and excellent stability. Three homologous SF8 probes, with peptidyl loops that differ by very minor changes in the peptide sequence, were synthesized and assessed for probe uptake by cancer cells. One of probes included the RGD motif that is recognized by many classes of integrin receptors that reside on the surface of the cancer cells, and it permeated the cells by receptor-mediated endocytosis. In contrast, cell microscopy showed that there was negligible cell uptake of the two homologous SF8 probes indicating differences in probe targeting capability. The synthetic method allows for easy alteration of the peptide sequence; thus, it is straightforward to develop new classes of peptidyl SF8 probes with loop sequences that target other cancer biomarkers.

In silico design of novel aptamers utilizing a hybrid method of machine learning and genetic algorithm

Aptamers can be regarded as efficient substitutes for monoclonal antibodies in many diagnostic and therapeutic applications. Due to the tedious and prohibitive nature of SELEX (systematic evolution of ligands by exponential enrichment), the in silico methods have been developed to improve the enrichment processes rate. However, the majority of these methods did not show any effort in designing novel aptamers. Moreover, some target proteins may have not any binding RNA candidates in nature and a reductive mechanism is needed to generate novel aptamer pools among enormous possible combinations of nucleotide acids to be examined in vitro. We have applied a genetic algorithm (GA) with an embedded binding predictor fitness function to in silico design of RNA aptamers. As a case study of this research, all steps were accomplished to generate an aptamer pool against aminopeptidase N (CD13) biomarker. First, the model was developed based on sequential and structural features of known RNA-protein complexes. Then, utilizing RNA sequences involved in complexes with positive prediction results, as the first-generation, novel aptamers were designed and top-ranked sequences were selected. A 76-mer aptamer was identified with the highest fitness value with a 3 to 6 time higher score than parent oligonucleotides. The reliability of obtained sequences was confirmed utilizing docking and molecular dynamic simulation. The proposed method provides an important simplified contribution to the oligonucleotide-aptamer design process. Also, it can be an underlying ground to design novel aptamers against a wide range of biomarkers.

Chlorin e6 embedded in phospholipid nanoparticles equipped with specific peptides: Interaction with tumor cells with different aminopeptidase N expression

A promising direction in Biopharmaceuticals is the development of specific peptide-based systems to improve drug delivery. This approach may increase tumor specificity and drug penetration into the target cell. Similar systems have been designed for several antitumor drugs. However, for photodynamic therapy drugs, such studies are not yet enough. Previously, we have developed a method of inclusion of chlorin e6 (Ce6), a photosensitizer used in photodynamic therapy, in phospholipid nanoparticles with a diameter of up to 30 nm, and reported an increase in its effectiveness in the experiments in vivo. In this work, we propose to modify a previously developed delivery system for Ce6 by the addition of cell-penetrating (R7) and/or targeting NGR peptides. The interaction of the compositions developed with HepG2 and MCF-7 tumor cells is shown. The expression of CD13 protein with affinity to NGR on the surface of these cells has been studied using flow cytometry. The expression of this protein on the HepG2 cells and its absence on MCF-7 was demonstrated. After incubation of tumor cells with the resulting Ce6 compositions, we evaluated the cellular accumulation, photoinduced, and dark cytotoxicity of the drugs. After irradiation, the highest level of cytotoxicity was observed when R7 peptide was added to the system, either alone or in combination with NGR. In addition to R7, the NGR-motif peptide increased the internalization of Ce6 in HepG2 cells without affecting its photodynamic activity. In this work we also discuss possible mechanisms of action of the cell-penetrating peptide when attached to phospholipid nanoparticles.

The prostate-specific membrane antigen (PSMA)-targeted radiotracer 18F-DCFPyL detects tumor neovasculature in metastatic, advanced, radioiodine-refractory, differentiated thyroid cancer

Prostate-specific membrane antigen (PSMA; also termed glutamate carboxypeptidase II (GCP II)) is abundantly expressed in prostate cancer. It has been shown recently that PSMA is expressed in neovasculature of differentiated thyroid cancer. In this study, we show that ¹⁸F-DCFPyl might detect neovasculature in advanced, metastatic differentiated thyroid cancer (DTC). We first stained the preserved lymph node samples of three patients with DTC who had undergone total thyroidectomy and neck dissection for cervical lymph node metastatic disease to identify PSMA expression, with the PSMA antibody (DAKO Monoclonal). Then, we performed ¹⁸F-DCFPyl imaging in two other advanced DTC patients with elevated serum thyroglobulin (Tg), indicative of residual disease. We compared the findings with contemporaneous FDG PET/CT scan, conventional Imaging (CT,MRI) and whole-body scan performed with I¹²³/I¹³¹. All the three lymph node samples stained positive for PSMA expression in the neovasculature. In the first imaged patient, ¹⁸F-DCFPyl detected activity within the retropharyngeal CT contrast-enhancing lymph node. Compared to FDG PET/CT, the ¹⁸F-DCFPyl scan showed a greater SUV (3.1 vs 1.8). In the second imaged patient, ¹⁸F-DCFPyl showed intense uptake in the L3 vertebra (not seen on the post treatment ¹³¹I scan or the ¹⁸F-FDG PET/CT). MRI of the lumbar spine confirmed the presence of sclerotic-lytic lesion at the location, consistent with metastatic disease. Our exploratory study is proof of principle, that the prostate cancer imaging agent ¹⁸F-DCFPyl may prove useful for the localization of metastases, in patients with metastatic RAI-refractory DTC by detecting neoangiogenesis within the tumor.

In vivo assessment of aminopeptidase N (APN/CD13) specificity of different 68Ga-labelled NGR derivatives using PET/MRI imaging

Aminopeptidase N (APN/CD13) plays an important role in neoangiogenic process in malignancies. Our previous studies have already shown that ⁶⁸Ga-labelled NOTA conjugated asparagine-glycine-arginine peptide (c[KNGRE]-NH₂) specifically bind to APN/CD13 expressing tumors. The aim of this study was to evaluate and compare the APN/CD13 specificity of newly synthesized ⁶⁸Ga-labelled NGR derivatives in vivo by PET/MRI imaging using hepatocellular carcinoma (He/De) and mesoblastic nephroma (Ne/De) tumor models. PET/MRI and ex vivo biodistribution studies were performed 11 ± 1 days after subcutaneous injection of tumor cells and 90 min after intravenous injection of ⁶⁸Ga-NOTA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR) (MG1) or ⁶⁸Ga-NODAGA-c(NGR) (MG2). The APN/CD13 selectivity was confirmed by blocking experiments and the APN/CD13 expression was verified by immunohistochemistry. ⁶⁸Ga-labelled c(NGR) derivatives were produced with high specific activity and radiochemical purity. In control animals, low radiotracer accumulation was found in abdominal and thoracic organs. Using tumor-bearing animals we found that the ⁶⁸Ga-NOTA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR), and ⁶⁸Ga-NODAGA-c(NGR) (MG1) derivatives showed higher uptake in He/De and Ne/De tumors, than that of the accumulation of ⁶⁸Ga-NODAGA-c(NGR) (MG2). APN/CD13 is a very promising target in PET imaging, however, the selection of the appropriate ⁶⁸Ga-labelled NGR-based radiopharmaceutical is critical for the precise detection of tumor neo-angiogenesis and for monitoring the efficacy of anticancer therapy.

Aminopeptidases in Cardiovascular and Renal Function. Role as Predictive Renal Injury Biomarkers

Aminopeptidases (APs) are metalloenzymes that hydrolyze peptides and polypeptides by scission of the N-terminus amino acid and that also participate in the intracellular final digestion of proteins. APs play an important role in protein maturation, signal transduction, and cell-cycle control, among other processes. These enzymes are especially relevant in the control of cardiovascular and renal functions. APs participate in the regulation of the systemic and local renin-angiotensin system and also modulate the activity of neuropeptides, kinins, immunomodulatory peptides, and cytokines, even contributing to cholesterol uptake and angiogenesis. This review focuses on the role of four key APs, aspartyl-, alanyl-, glutamyl-, and leucyl-cystinyl-aminopeptidases, in the control of blood pressure (BP) and renal function and on their association with different cardiovascular and renal diseases. In this context, the effects of AP inhibitors are analyzed as therapeutic tools for BP control and renal diseases. Their role as urinary biomarkers of renal injury is also explored. The enzymatic activities of urinary APs, which act as hydrolyzing peptides on the luminal surface of the renal tubule, have emerged as early predictive renal injury biomarkers in both acute and chronic renal nephropathies, including those induced by nephrotoxic agents, obesity, hypertension, or diabetes. Hence, the analysis of urinary AP appears to be a promising diagnostic and prognostic approach to renal disease in both research and clinical settings.

Targeting aggressive osteosarcoma with a peptidase-enhanced cytotoxic melphalan flufenamide

Background:

Low survival rates in metastatic high-grade osteosarcoma (HGOS) have remained stagnant for the last three decades. This study aims to investigate the role of aminopeptidase N (ANPEP) in HGOS progression and its targeting with a novel lipophilic peptidase-enhanced cytotoxic compound melphalan flufenamide (melflufen) in HGOS.

Methods:

Meta-analysis of publicly available gene expression datasets was performed to determine the impact of ANPEP gene expression on metastasis-free survival of HGOS patients. The efficacy of standard-of-care anti-neoplastic drugs and a lipophilic peptidase-enhanced cytotoxic conjugate melflufen was investigated in patient-derived HGOS ex vivo models and cell lines. The kinetics of apoptosis and necrosis induced by melflufen and doxorubicin were compared. Anti-neoplastic effects of melflufen were investigated in vivo.

Results:

Elevated ANPEP expression in diagnostic biopsies of HGOS patients was found to significantly reduce metastasis-free survival. In drug sensitivity assays, melflufen has shown an anti-proliferative effect in HGOS ex vivo samples and cell lines, including those resistant to methotrexate, etoposide, doxorubicin, and PARP inhibitors. Further, HGOS cells treated with melflufen displayed a rapid induction of apoptosis and this sensitivity correlated with high expression of ANPEP. In combination treatments, melflufen demonstrated synergy with doxorubicin in killing HGOS cells. Finally, Melflufen displayed anti-tumor growth and anti-metastatic effects in vivo.

Conclusion:

This study may pave the way for use of melflufen as an adjuvant to doxorubicin in improving the therapeutic efficacy for the treatment of metastatic HGOS.

Carbonic anhydrase IV inhibits cell proliferation in gastric cancer by regulating the cell cycle

Carbonic anhydrase IV (CA4) is silenced in colorectal cancer. However, the effect of CA4 on the development of gastric cancer (GC) is poorly understood. The present study aimed to determine the role of CA4 in GC tumorigenesis and its underlying molecular mechanism. The levels of CA4 in GC cells and tissues were evaluated by reverse transcription-quantitative PCR and immunohistochemistry. CA4 expression was suppressed in GC cells and tissues compared with adjacent healthy tissues and normal human gastric epithelial cells, respectively. This reduced expression was significantly associated with tumor size, invasion and differentiation. Analyses with a real-time cell analyzer and clonogenic assays were conducted to validate the impact of CA4 on GC cell lines (AGS and HGC-27) and normal human gastric epithelial cell line (GES-1) proliferation. The effects of CA4 on the cell cycle in GC cells were determined by flow cytometry. The levels of CA4 and cell cycle-associated proteins were confirmed by western blotting. CA4 overexpression inhibited GC cell proliferation and reduced colony-forming ability, arrested the cell cycle in the G2/M phase, inhibited cyclin B1 and cyclin-dependent kinase 2 expression and induced p21 expression. These results indicate that CA4 may serve an important role in GC tumorigenesis by inhibiting cellular proliferation via regulating the expression of cell cycle-associated proteins. CA4 may serve as a diagnostic biomarker and a potential therapeutic target in GC.

Prevention of tumor risk associated with the reprogramming of human pluripotent stem cells

Human pluripotent embryonic stem cells have two special features: self-renewal and pluripotency. It is important to understand the properties of pluripotent stem cells and reprogrammed stem cells. One of the major problems is the risk of reprogrammed stem cells developing into tumors. To understand the process of differentiation through which stem cells develop into cancer cells, investigators have attempted to identify the key factors that generate tumors in humans. The most effective method for the prevention of tumorigenesis is the exclusion of cancer cells during cell reprogramming. The risk of cancer formation is dependent on mutations of oncogenes and tumor suppressor genes during the conversion of stem cells to cancer cells and on the environmental effects of pluripotent stem cells. Dissecting the processes of epigenetic regulation and chromatin regulation may be helpful for achieving correct cell reprogramming without inducing tumor formation and for developing new drugs for cancer treatment. This review focuses on the risk of tumor formation by human pluripotent stem cells, and on the possible treatment options if it occurs. Potential new techniques that target epigenetic processes and chromatin regulation provide opportunities for human cancer modeling and clinical applications of regenerative medicine.

Solid phase synthesis in the development of magnetic resonance imaging probes

We review the use of the solid phase synthesis methodology for the preparation of diverse and potent MRI probes.

Phosphonic Acid Analogues of Phenylglycine as Inhibitors of Aminopeptidases: Comparison of Porcine Aminopeptidase N, Bovine Leucine Aminopeptidase, Tomato Acidic Leucine Aminopeptidase and Aminopeptidase from Barley Seeds

The inhibitory activity of 14 racemic phosphonic acid analogs of phenylglycine, substituted in aromatic rings, towards porcine aminopeptidase N (pAPN) and barley seed aminopeptidase was determined experimentally. The obtained patterns of the inhibitory activity against the two enzymes were similar. The obtained data served as a basis for studying the binding modes of these inhibitors by pAPN using molecular modeling. It was found that their aminophosphonate fragments were bound in a highly uniform manner and that the difference in their affinities most likely resulted from the mode of substitution of their phenyl rings. The obtained binding modes towards pAPN were compared, with these predicted for bovine lens leucine aminopeptidase (blLAP) and tomato acidic leucine aminopeptidase (tLAPA). The performed studies indicated that the binding manner of the phenylglycine analogs to biLAP and tLAPA are significantly similar and differ slightly from that predicted for pAPN.

Altered Serum Oxytocinase and Enkephalin-Degrading Aminopeptidase Activities in Patients With Fibromyalgia

Objectives:

Fibromyalgia (FM) is a chronic pain condition of unclear etiology. We have analyzed, for the first time, the activity of a broad spectrum of aminopeptidases (APs) in patients with FM and controls to investigate whether they are involved in the pathophysiology of this syndrome.

Method:

In this case–control study, we fluorometrically measured specific AP activities in serum samples of 75 patients with FM and 29 healthy controls. The predictive value of AP activities in FM was determined by receiver operating characteristic (ROC) analysis.

Results:

Oxytocinase activity was higher in patients with FM than in controls ( p < .001). A subgroup of patients with FM ( n = 18; 24%) showed low levels of enkephalin-degrading aminopeptidase (EDA) activity when compared with the healthy controls ( p < .001) and with the rest of FM patients ( p < .001). There were no significant differences in the activity levels of aminopeptidase A, aminopeptidase B, aspartyl aminopeptidase, insulin-regulated aminopeptidase, pyroglutamyl aminopeptidase, or aminopeptidase N between FM patients and controls. According to ROC analysis, oxytocinase activity may be a good marker for differentiating individuals with FM from healthy subjects.

Conclusions:

Our findings show that serum oxytocinase activity is increased in patients with FM, which could alter the metabolism of peptides with analgesic effects such as oxytocin and enkephalins. The determination of serum oxytocinase activity may aid in FM diagnosis. Additionally, we have identified a subpopulation of FM patients with abnormally low serum EDA activity.

Photosensitizer Chlorin e6 Internalization into Tumor Cells in Phospholipid Nanoparticles Conjugated with Peptide Containing the NGR Sequence

The possibility of increased internalization of the photosensitizer chlorin e6 in tumor cells was investigatedusing soy phosphatidylcholine nanoparticles 20-30 nm with or without attached peptide containing Asn-Gly-Arg (NGR) motif was studied. This amino acid sequence exhibits affinity to aminopeptidase N (CD13), wich is overexpressed in a number of tumor cells and vessels. Nanoparticles with chlorin e6 were prepared with added of distearoylphosphatidylcholine (DSPE) conjugated through PEG with a hexapeptide containing the NGR sequence, and then were incubated with tumor cells НерG2 and MCF-7. Chlorin e6 accumulation in СD13-negative cells (MCF-7) did not depend on the presence of peptide NGR in nanoparticles. However, for НерG2 cells a twofold increase of chlorine e6 internalization was observed as compared with the same particles without NGR. Differences in the response of these two cell lines, differed in expression of aminopeptidase N (APN), suggest the possibility of this protein using for targeted delivery. The prospectivity of usage of phospholipids nanoparticles conjugated with targeting peptide for photodynamic therapy is discussed, taking into account possible variation of APN expression, inherent for many solid tumors.