Aminopeptidase N regulated by zinc in human prostate participates in tumor cell invasion

Elements in trace amount with a significant role in human physiology: a tumor pathophysiological and diagnostic aspects

Cancer has a devastating impact globally regardless of gender, age, and community, which continues its severity to the population due to the lack of efficient strategy for the cancer diagnosis and treatment. According to the World Health Organisation report, one out of six people dies due to this deadly cancer and we need effective strategies to regulate it. In this context, trace element has a very hidden and unexplored role and require more attention from investigators. The variation in concentration of trace elements was observed during comparative studies on a cancer patient and a healthy person making them an effective target for cancer regulation. The percentage of trace elements present in the human body depends on environmental exposure, food habits, and habitats and could be instrumental in the early diagnosis of cancer. In this review, we have conducted inclusive analytics on trace elements associated with the various types of cancers and explored the several methods involved in their analysis. Further, intricacies in the correlation of trace elements with prominent cancers like prostate cancer, breast cancer, and leukaemia are represented in this review. This comprehensive information on trace elements proposes their role during cancer and as biomarkers in cancer diagnosis.

Combining Molecular Subtypes with Multivariable Clinical Models Has the Potential to Improve Prediction of Treatment Outcomes in Prostate Cancer at Diagnosis

Clinical management of prostate cancer is challenging because of its highly variable natural history and so there is a need for improved predictors of outcome in non-metastatic men at the time of diagnosis. In this study we calculated the model score from the leading clinical multivariable model, PREDICT prostate, and the poor prognosis DESNT molecular subtype, in a combined expression and clinical dataset that were taken from malignant tissue at prostatectomy (n = 359). Both PREDICT score (p < 0.0001, IQR HR = 1.59) and DESNT score (p < 0.0001, IQR HR = 2.08) were significant predictors for time to biochemical recurrence. A joint model combining the continuous PREDICT and DESNT score (p < 0.0001, IQR HR = 1.53 and 1.79, respectively) produced a significantly improved predictor than either model alone (p < 0.001). An increased probability of mortality after diagnosis, as estimated by PREDICT, was characterised by upregulation of cell-cycle related pathways and the downregulation of metabolism and cholesterol biosynthesis. The DESNT molecular subtype has distinct biological characteristics to those associated with the PREDICT model. We conclude that the inclusion of biological information alongside current clinical prognostic tools has the potential to improve the ability to choose the optimal treatment pathway for a patient.

Metal complexes of benzimidazole-derived as potential anti-cancer agents: synthesis, characterization, combined experimental and computational studies

In this study, a series of 14 Cu (II), Zn (II), Ni (II) and Ag (I) complexes containing bis-benzimidazole derivatives were successfully designed and synthesized from 2-(1H-benzimidazole-2-yl)-phenol derivatives and corresponding metal salt solutions. The compound structures were identified by FT-IR, ¹H-NMR, powder X-ray diffraction and ESI-MS analyses, and the presence of the metal in the complexes was confirmed by ultraviolet-visible spectroscopy and ICP optical emission spectrometry. Electronic structure calculations were also carried out to describe the detailed structures in addition to the electronic absorption spectra of the ligands. The cytotoxic activity of the complexes was evaluated against three human cancer cell lines: lung (A549), breast (MDA-MB-231) and prostate (PC3) cancer cells. All complexes inhibited anti-proliferative cancer cells better than free ligands, especially Zn (II) and Ag (I) complexes, which are most sensitive to MDA-MB-231 cells. In addition, showing the growth inhibition of three cancer cell lines with IC₅₀ < 10.4 µM, complexes C₁ , C₃ and C₁₄ could be considered potential multi-targeted anti-cancer agents.

A facile turn-on chemiluminescence probe for sensitive imaging on aminopeptidase N activity

Aminopeptidase N, as a target for drug discovery, shows remarkable relationship with many diseases, especially liver injury and cancer. Herein, we explored a chemiluminescence (CL) probe for sensing APN by tethering APN-specific substrate group to the ortho-acrylated phenoxy-dioxetane scaffold. In this manner, two CL probes (APN-CL and BAPN-CL) were designed with non-capped leucine and butoxy-carbonyl capped leucine as the protecting group to preserve the chemiexcitation energy. The uncovered leucine was demonstrated to be essential for detection of APN activity by comparing the CL intensity of two CL probes. Probe APN-CL was turned on upon APN cleavage, resulting in a high chemiluminescent emission, while the chemiexcitation energy of probe BAPN-CL was still restrained even with the high-level APN. The result was elucidated by molecular docking simulation in further. Probe APN-CL exhibited fast response and high sensitivity with a detection limit of 0.068 U/L, and an excellent specificity for the discrimination of APN from biological ions, small molecules and other proteases commonly found in living system. By virtue of good stability and cell viability, probe APN-CL imaged abnormal level of APN in tumor cells and tumor-bearing mice. Moreover, this probe APN-CL could be easily used to evaluate APN inhibitors and APN level in plasma samples from 20 patients. Overall, as a facile and cost-effective probe, APN-CL will be a promising alternative in the early diagnosis of pathologies and cost-effective screening on inhibitors.

Design, Synthesis, and Biological Evaluation of APN and AKT Dual-Target Inhibitors

Herein a novel series of APN and AKT dual inhibitors were derived from the clinical AKT inhibitor AZD5363. It was demonstrated that most compounds exhibited remarkable APN inhibitory activities with the most potent compound 8b (IC₅₀ = 0.05 ± 0.01 μM) being over 70-fold more potent than the approved APN inhibitor bestatin (IC₅₀ = 3.64 ± 0.56 μM). The moderate AKT inhibitory potencies of target compounds were also confirmed, with 5f and 5h possessing AKT1 IC₅₀ values of 0.12 and 0.27 μM, respectively. More importantly, the APN IC₅₀ values of 5f and 5h were 0.96 and 0.21 μM, respectively, indicating their balanced APN and AKT dual inhibition. HUVEC tube formation assays confirmed the superior APN inhibitory activities of 5f and 5h relative to bestatin at the cellular level. Western blot analysis demonstrated that 5h could effectively inhibit the phosphorylation of GSK3β, the intracellular substrate of AKT.

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.

Transcriptional landscape of PTEN loss in primary prostate cancer

BACKGROUND

PTEN is the most frequently lost tumor suppressor in primary prostate cancer (PCa) and its loss is associated with aggressive disease. However, the transcriptional changes associated with PTEN loss in PCa have not been described in detail. In this study, we highlight the transcriptional changes associated with PTEN loss in PCa.

METHODS

Using a meta-analysis approach, we leveraged two large PCa cohorts with experimentally validated PTEN and ERG status by Immunohistochemistry (IHC), to derive a transcriptomic signature of PTEN loss, while also accounting for potential confounders due to ERG rearrangements. This signature was expanded to lncRNAs using the TCGA quantifications from the FC-R2 expression atlas.

RESULTS

The signatures indicate a strong activation of both innate and adaptive immune systems upon PTEN loss, as well as an expected activation of cell-cycle genes. Moreover, we made use of our recently developed FC-R2 expression atlas to expand this signature to include many non-coding RNAs recently annotated by the FANTOM consortium. Highlighting potential novel lncRNAs associated with PTEN loss and PCa progression.

CONCLUSION

We created a PCa specific signature of the transcriptional landscape of PTEN loss that comprises both the coding and an extensive non-coding counterpart, highlighting potential new players in PCa progression. We also show that contrary to what is observed in other cancers, PTEN loss in PCa leads to increased activation of the immune system. These findings can help the development of new biomarkers and help guide therapy choices.

Review on the recent progress in the development of fluorescent probes targeting enzymes

Enzymes are very important for biological processes in a living being, performing similar or multiple tasks in and out of cells, tissues and other organisms at a particular location. The abnormal activity of particular enzyme usually caused serious diseases such as Alzheimer's disease, Parkinson's disease, cancers, diabetes, cardiovascular diseases, arthritis etc. Hence, nondestructive and real-time visualization for certain enzyme is very important for understanding the biological issues, as well as the drug administration and drug metabolism. Fluorescent cellular probe-based enzyme detectionin vitroandin vivohas become broad interest for human disease diagnostics and therapeutics. This review highlights the recent findings and designs of highly sensitive and selective fluorescent cellular probes targeting enzymes for quantitative analysis and bioimaging.

SLC39A8/Zinc Suppresses the Progression of Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most frequent and lethal subtype, which has high risk of metastasis or recurrence, accounting for 75–83% of renal cell carcinoma (RCC). Zrt‐ and Irt‐like proteins (ZIP) family members (SLC39A1-14) function to pass zinc into the cytoplasm for many critical biological processes when cellular zinc is depleted. However, the functional analysis of individual ZIP family genes in ccRCC is not clarified. This study aimed to investigate whether ZIP family genes are related to the clinicopathological features and survival of ccRCC patients, and to identify the function of key gene of ZIP family in ccRCC in vitro. Through bioinformatics analysis of tumor databases, SLC39A8 was identified as a key gene of ZIP family in ccRCC, which could be used as an effective indicator for diagnosing ccRCC and judging its prognosis. With the progression of tumor, the expression of SLC39A8 decreased progressively. The prognosis of patients with low expression of SLC39A8 is significantly worse. Furthermore, we found that overexpression of SLC39A8 or treatment with low concentration of zinc chloride could effectively inhibit the proliferation, migration and invasion of ccRCC cells. Moreover, the inhibition effect of SLC39A8 overexpression could be enhanced by low concentration zinc supplement. Therefore, this study provides a novel understanding for the role of SLC39A8/zinc in the regulation of ccRCC progression. These findings provide a new direction and target for progressive ccRCC drug development and combination therapy strategies.

Zinc is an important inter-kingdom signal between the host and microbe

Zinc (Zn) is an essential trace element in living organisms and plays a vital role in the regulation of both microbial virulence and host immune responses. A growing number of studies have shown that zinc deficiency or the internal Zn concentration does not meet the needs of animals and microbes, leading to an imbalance in zinc homeostasis and intracellular signalling pathway dysregulation. Competition for zinc ions (Zn²⁺) between microbes and the host exists in the use of Zn²⁺ to maintain cell structure and physiological functions. It also affects the interplay between microbial virulence factors and their specific receptors in the host. This review will focus on the role of Zn in the crosstalk between the host and microbe, especially for changes in microbial pathogenesis and nociceptive neuron-immune interactions, as it may lead to new ways to prevent or treat microbial infections.

A Structure-Activity Relationship Study of Novel Hydroxamic Acid Inhibitors around the S1 Subsite of Human Aminopeptidase N

Aminopeptidase N (APN/CD13) is a zinc-dependent ubiquitous transmembrane ectoenzyme that is widely present in different types of cells. APN is one of the most extensively studied metalloaminopeptidases as an anti-cancer target due to its significant role in the regulation of metastasis and angiogenesis. Previously, we identified a potent and selective APN inhibitor, N-(2-(Hydroxyamino)-2-oxo-1-(3',4',5'-trifluoro-[1,1'-biphenyl]-4-yl)ethyl)-4-(methylsulfonamido)benzamide (3). Herein, we report the further modifications performed to explore SAR around the S1 subsite of APN and to improve the physicochemical properties. A series of hydroxamic acid analogues were synthesised, and the pharmacological activities were evaluated in vitro. N-(1-(3'-Fluoro-[1,1'-biphenyl]-4-yl)-2-(hydroxyamino)-2-oxoethyl)-4-(methylsulfonamido)benzamide (6 f) was found to display an extremely potent inhibitory activity in the sub-nanomolar range.

CD13 Induces Autophagy to Promote Hepatocellular Carcinoma Cell Chemoresistance Through the P38/Hsp27/CREB/ATG7 Pathway

The chemoresistance of hepatocellular carcinoma (HCC) is a serious problem that directly hinders the effect of chemotherapeutic agents. We previously reported that Aminopeptidase N (CD13) inhibition can enhance the cytotoxic efficacy of chemotherapy agents. In the present study, we use liver cancer cells to explore the molecular mechanism accounting for the relationship between CD13 and chemoresistance. We demonstrate that CD13 overexpression activates the P38/heat shock protein 27/cAMP response element-binding protein (CREB) signaling pathway to limit the efficacy of cytotoxic agents. Moreover, blockade of P38 or CREB sensitizes HCC cells to 5-fluorouracil. Then we reveal that CREB binds to the autophagy related 7 (ATG7) promoter to induce autophagy and promote HCC cell chemoresistance. CD13 inhibition also downregulates the expression of ATG7, autophagy, and tumor cell growth in vivo. Overall, the combination a CD13 inhibitor and chemotherapeutic agents may be a potential strategy for overcoming drug resistance in HCC. SIGNIFICANCE STATEMENT: Our study demonstrates that Aminopeptidase N (CD13) promotes hepatocellular carcinoma (HCC) cell chemoresistance via the P38/heat shock protein 27/cAMP response element-binding protein (CREB) pathway. CREB regulates autophagy related 7 transcription and expression to induce autophagy. Our results collectively suggest that CD13 may serve as a potential target for overcoming HCC resistance.

Growth Modulatory Role of Zinc in Prostate Cancer and Application to Cancer Therapeutics

Zinc is a group IIB heavy metal. It is an important regulator of major cell signaling pathways in most mammalian cells, functions as an antioxidant and plays a role in maintaining genomic stability. Zinc deficiency leads to severe diseases in the brain, pancreas, liver, kidneys and reproductive organs. Zinc loss occurs during tumor development in a variety of cancers. The prostate normally contains abundant intracellular zinc and zinc loss is a hallmark of the development of prostate cancer development. The underlying mechanism of this loss is not clearly understood. The knowledge that excess zinc prevents the growth of prostate cancers suggests that zinc-mediated therapeutics could be an effective approach for cancer prevention and treatment, although challenges remain. This review summarizes the specific roles of zinc in several cancer types focusing on prostate cancer. The relationship between prostate cancer and the dysregulation of zinc homeostasis is examined in detail in an effort to understand the role of zinc in prostate cancer.

Advances of Zinc Signaling Studies in Prostate Cancer

Prostate cancer (PCa) is one of the most common cancers and the second leading cause of cancer-related death among men worldwide. Despite progresses in early diagnosis and therapeutic strategies, prognosis for patients with advanced PCa remains poor. Noteworthily, a unique feature of healthy prostate is its highest level of zinc content among all soft tissues in the human body, which dramatically decreases during prostate tumorigenesis. To date, several reviews have suggested antitumor activities of zinc and its potential as a therapeutic strategy of PCa. However, an overview about the role of zinc and its signaling in PCa is needed. Here, we review literature related to the content, biological function, compounds and clinical application of zinc in PCa. We first summarize zinc content in prostate tissue and sera of PCa patients with their clinical relevance. We then elaborate biological functions of zinc signaling in PCa on three main aspects, including cell proliferation, death and tumor metastasis. Finally, we discuss clinical applications of zinc-containing compounds and proteins involved in PCa signaling pathways. Based on currently available studies, we conclude that zinc plays a tumor suppressive role and can serve as a biomarker in PCa diagnosis and therapies.

MicroRNA-125a attenuates the chemoresistance against ubenimex in non-small cell lung carcinoma via targeting the aminopeptidase N signaling pathway

BACKGROUND

Since several long noncoding RNAs (lncRNAs) have been implicated in the development of chemoresistance in non-small cell lung carcinoma (NSCLC), the aim of this study was to investigate whether antisense noncoding RNA in the INK4 locus (ANRIL) was associated with the chemoresistance of NSCLC.

METHOD

Real-time polymerase chain reaction was performed to identify potential lncRNAs involved in the chemoresistance of NSCLC, while in-silicon analyses and luciferase assays were carried out to explore the regulatory relationship among ANRIL, miR-125a, and aminopeptidase N (APN).

RESULTS

Ubenimex resistant cells were associated with a high expression of ANRIL, which directly binds to miR-125a. MiR-125a directly targeted APN expression. In addition, miR-125a and ANRIL small interfering RNA inhibited the expression of APN but promoted the expression of beclin-1 and LC3, whereas ANRIL, by competing with miR-125a, promoted cell proliferation and inhibited cell apoptosis.

CONCLUSION

The data of this study suggested that, by targeting ANRIL and the APN signaling pathway, miR-125a inhibited the proliferation of NSCLC cells and promoted their apoptosis, thus attenuating the chemoresistance of NSCLC against Ubenimex.

SIX4 acts as a master regulator of oncogenes that promotes tumorigenesis in non-small-cell lung cancer cells

A number of homeobox genes are implicated in the malignancy of various cancers. Here, we investigated the role of the homeobox gene SIX4 in non-small-cell lung cancer (NSCLC). The sine oculis homeobox (SIX4) gene was found to be highly expressed at both mRNA and protein levels in NSCLC tumor tissues as compared with matching normal counterparts. In this study, the SIX4 gene of two human NSCLC cell lines (A549 and PC9) was overexpressed or silenced using the lentiviral system. We evaluated the malignancy-associated phenotype of transfected cells, which demonstrated that exogenous expression of the SIX4 gene greatly enhanced the proliferation, migration, and invasion of NSCLC cells. The opposite was true in the SIX4-silenced cells. Transcriptomic profiling analysis revealed that the SIX4 gene modulated the expression of hundreds of downstream target genes in a cell context-dependent manner. Most notably, the SIX4 gene controls the expression of crucial genes with evidently oncogenic function. We conclude that SIX4 plays an oncogenic role and may be potentially utilized as a diagnostic and therapeutic marker for NSCLC.

Serum APN/CD13 as a novel diagnostic and prognostic biomarker of pancreatic cancer

Aminopeptidase N, also known as CD13, has been reported to be overexpressed in several cancers and may contribute to tumor metastasis and angiogenesis. The aim of this study was to evaluate whether serum APN/CD13 could be a potential biomarker for the diagnosis and prognosis of pancreatic cancer (PC). Serum APN/CD13 and carbohydrate antigen 19-9 (CA19-9) levels were measured from 382 participants, which comprised of 204 participants with PC, 48 participants with benign pancreatic tumors (BPT), 43 participants with chronic pancreatitis (CP) and 87 healthy controls (HC). We used receiver operating characteristic (ROC) analysis to calculate diagnostic accuracy. The association of serum APN/CD13 levels with the clinicopathological characteristics of PC patients and their survival was investigated. Serum APN/CD13 levels were substantially higher in PC patients than in controls. ROC analysis revealed that APN/CD13 was significantly better than CA19-9 in differentiating patients with PC from controls. Similar results were noted for early-stage PC. Moreover, the combined use of APN/CD13 and CA19-9 data improved the diagnostic accuracy for PC vs. controls, compared with either test alone. High serum APN/CD13 levels were associated with tumor size, lymph nodes, and metastasis (TNM) stage. Multivariate and ROC curve analyses revealed that high serum APN/CD13 level is an independent factor for predicting mortality and overall survival (OS). Moreover, Kaplan–Meier analysis demonstrated an inverse correlation between increased serum APN/CD13 level and OS. Our study established that serum APN/CD13 may be a novel diagnostic and prognostic biomarker for PC.

Preparation and comparative evaluation of 99m Tc-HYNIC-cNGR and 99m Tc-HYNIC-PEG2 -cNGR as tumor-targeting molecular imaging probes

The tripeptide sequence asparagine-glycine-arginine (NGR) specifically recognizes aminopeptidase N (APN or CD13) receptors highly expressed on tumor cells and vasculature. Thus, NGR peptides can precisely deliver therapeutic and diagnostic compounds to CD13 expressing cancer sites. In this regard, 2 NGR peptide ligands, HYNIC-c(NGR) and HYNIC-PEG₂ -c(NGR), were synthesized, radiolabeled with ^99m Tc, and evaluated in CD13-positive human fibrosarcoma HT-1080 tumor xenografts. The radiotracers, ^99m Tc-HYNIC-c(NGR) and ^99m Tc-HYNIC-PEG₂ -c(NGR), could be prepared in approximately 95% radiochemical purity and exhibited excellent in vitro and in vivo stability. The radiotracers were hydrophilic in nature with log P values being -2.33 ± 0.05 and -2.61 ± 0.08. The uptake of 2 radiotracers ^99m Tc-HYNIC-c(NGR) and ^99m Tc-HYNIC-PEG₂ -c(NGR) was similar in nude mice bearing human fibrosarcoma HT-1080 tumor xenografts, which was significantly reduced (P < .05) during blocking studies. The 2 radiotracers being hydrophilic cleared rapidly from blood, liver, and intestine and were excreted through renal pathway. The pharmacokinetics of ^99m Tc-labeled HYNIC peptide could not be modulated through introduction of PEG₂ unit, thus posing a challenge for studies with other linkers towards enhanced tumor uptake and retention.

177Lu-labeled cyclic Asn-Gly-Arg peptide tagged carbon nanospheres as tumor targeting radio-nanoprobes

This study explores the potential of ¹⁷⁷Lu-labeled carbon nanospheres as radio-nanoprobes for molecular imaging and therapy. The carboxyl functionalized surface of carbon nanospheres (CNS) was conjugated with [Gly-Gly-Gly-c(Asn-Gly-Arg)], G3-cNGR peptide through amide bond for targeting tumor vasculature and with [2-(4-Aminobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid], p-NH₂-Bz-DOTA for chelation with ¹⁷⁷Lu. The nanosphere-peptide conjugate, DOTA-CNS-cNGR, was characterized by dynamic light scattering and zeta potential measurements, IR and UV experiments and did not show any in vitro cytotoxicity. The pharmacokinetics and biodistribution of ¹⁷⁷Lu-labeled nanosphere-peptide conjugate, ¹⁷⁷Lu-DOTA-CNS-cNGR was compared with ¹⁷⁷Lu-DOTA-CNS (without the peptide) as well as with ¹⁷⁷Lu-DOTA-cNGR (without carbon nanospheres). The radiolabeled nanosphere-peptide conjugate exhibited higher tumor accumulation than nanosphere-free radiolabeled peptide. The accumulation of the two radiolabeled probes in the tumor reduced to half during blocking studies with unlabeled G3-cNGR peptide. ¹⁷⁷Lu-DOTA-CNS exhibited higher tumor uptake than ¹⁷⁷Lu-DOTA-CNS-cNGR but rapid clearance of the latter nanoprobe from non-target organs resulted in significantly higher (p < 0.05) tumor-to-blood and tumor-to-muscle ratios at 24 and 48 h p.i. It is evident from this study that carbon nanospheres conjugated to specific vectors shall form an important part of targeted radionanomedicine in future.

Ubenimex, an APN inhibitor, could serve as an anti‑tumor drug in RT112 and 5637 cells by operating in an Akt‑associated manner

Bladder cancer, a common urinary tract tumor, has high mortality and recurrence rates associated with metastasis. Aminopeptidase N (APN) expression and metastasis have been indicated to be associated with one another. Ubenimex may function as an APN inhibitor to inhibit the degradation of the extracellular matrix during tumorigenesis. Furthermore, APN has been widely used as an adjuvant therapy for the treatment of tumors; however, little information is available regarding the impact of ubenimex on patients. Autophagy is suggested to be important in the transformation and progression of cancer. Additionally, apoptosis, which leads to the rapid demolition of cellular organelles and structures, has also been suggested as an important factor. Thus, the present study investigated the role of ubenimex in inhibiting migration and invasion by downregulating APN expression levels to induce autophagic cell death and apoptosis in bladder cancer cells. RT112 and 5637 cell lines were treated with varying doses of ubenimex. Cell viability was measured by CCK8 colorimetry and flow cytometry. Using fluorescence microscopy, autophagic cell death was assessed using acridine orange/ethidium bromide staining. Furthermore, apoptotic cell death was assessed using flow cytometry and Trypan blue staining was used to evaluate the cell death rate. Protein expression was determined by western blot analysis. Matrigel invasion assays were exploited to assess the invasion capabilities of 5637 cells. Wound-healing migration assays and Matrigel migration assays were exploited to assess the migratory abilities of 5637 cells. Treatment with ubenimex was accompanied by decreased Akt expression, indicating that ubenimex may have similar functions to Akt inhibitors. Results also indicated that ubenimex inhibited cell migration and invasion in bladder cancer cells. Furthermore, ubenimex also induced autophagic cell death and apoptosis, which suggested that mixed programmed cell death occurred in ubenimex-treated bladder cancer cells. The results from the present study suggest that ubenimex may be a potential adjuvant therapy for the treatment of bladder cancer.

Comparative evaluation of 68 Ga-labeled NODAGA, DOTAGA, and HBED-CC-conjugated cNGR peptide chelates as tumor-targeted molecular imaging probes

The biological behavior of ⁶⁸ Ga-based radiopharmaceuticals can be significantly affected by the chelators' attributes (size, charge, lipophilicity). Thus, this study aimed at examining the influence of three different chelators, DOTAGA, NODAGA, and HBED-CC on the distribution pattern of ⁶⁸ Ga-labeled NGR peptides targeting CD13 receptors. ⁶⁸ Ga-DOTAGA-c(NGR), ⁶⁸ Ga-NODAGA-c(NGR), and ⁶⁸ Ga-HBED-CC-c(NGR) were observed to be hydrophilic with respective log p values being -3.5 ± 0.2, -3.3 ± 0.08, and -2.8 ± 0.14. The three radiotracers exhibited nearly similar uptake in human fibrosarcoma HT-1080 tumor cells with 86%, 63%, and 33% reduction during blocking studies with unlabeled cNGR peptide for ⁶⁸ Ga-DOTAGA-c(NGR), ⁶⁸ Ga-NODAGA-c(NGR), and ⁶⁸ Ga-HBED-CC-c(NGR), respectively, indicating higher receptor specificity of the first two radiotracers. The neutral radiotracer ⁶⁸ Ga-NODAGA-c(NGR) demonstrated better target-to-non-target ratios during in vivo studies compared to its negatively charged counterparts, ⁶⁸ Ga-DOTAGA-c(NGR) and ⁶⁸ Ga-HBED-CC-c(NGR). The three radiotracers had similar HT-1080 tumor uptake and being hydrophilic exhibited renal excretion with minimal uptake in non-target organs. Significant reduction (p < .005) in HT-1080 tumor uptake of the radiotracers was observed during blocking studies. It may be inferred from these studies that the three radiotracers are promising probes for in vivo imaging of CD13 receptor expressing cancer sites; however, ⁶⁸ Ga-NODAGA-c(NGR) is a better candidate.

Autophagy flux inhibition, G2/M cell cycle arrest and apoptosis induction by ubenimex in glioma cell lines

This study aimed to investigate whether ubenimex could work as an anti-tumor drug alone in glioma cells and figure out the underlying potential mechanisms. Ubenimex is widely used as an adjunct therapy in multiple solid cancers. However, it is rarely used to treat glioblastoma. The function of ubenimex in enhancing JQ1 treatment sensitivity of glioma cells by blocking autophagic degradation of HEXIM1 was previously studied. However, the detailed mechanism of autophagy regulation by ubenimex remains unclear. The U87 and U251 cell lines were treated with different doses of ubenimex. Cell viability was measured by using the WST-8 assay. Cell death was assessed using trypan blue staining and flow cytometry. The migration and invasive ability of glioma cells were examined by transwell migration/invasion assay. LC3-GFP-RFP was used to measure autophagic flux. Protein expression was assessed by Western blot analysis. Autophagosomes were evaluated using the transmission electron microscopy. Moreover, cell cycle arrest (PI Staining) was measured by flow cytometry. Results revealed that ubenimex inhibited cell proliferation as well as migration/invasion in glioma cells. Besides, ubenimex increased glioma cell death via autophagic flux inhibition. Meanwhile, ubenimex induced G2/M phase arrest and apoptosis, and this effect was accompanied by the decreased levels of p-Akt, indicating the role of ubenimex in the regulation of glioma cell proliferation and metastasis. To sum up, this study concluded that ubenimex could work as an anti-tumor drug alone in the glioma cells via inhibiting autophagic flux and inducing G2/M arrest as well as apoptosis.

68Ga-Chelation and comparative evaluation of N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid (HBED-CC) conjugated NGR and RGD peptides as tumor targeted molecular imaging probes

Peptides containing RGD and NGR motifs display high affinity towards tumor vasculature molecular markers, integrin α_vβ₃ and CD13 receptors, respectively. In the present study, RGD and NGR peptides were conjugated with the novel acyclic chelator N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid (HBED-CC) for radiolabeling with ⁶⁸Ga. The radiotracers [⁶⁸Ga-HBED-CC-c(NGR)] and [⁶⁸Ga-HBED-CC-c(RGD)] were quite hydrophilic with respective log P values being -2.8 ± 0.14 and -2.1 ± 0.17. ⁶⁸Ga-HBED-CC-c(RGD) displayed a significantly higher (p < 0.05) uptake in murine melanoma B16F10 tumors as compared to ⁶⁸Ga-HBED-CC-c(NGR) indicating its higher specificity towards integrin α_vβ₃-positive tumors. The two radiotracers showed similar uptake in CD13-positive human fibrosarcoma HT-1080 tumor xenografts (∼1.5 ± 0.2% ID g^-1). The tumor uptake of the two radiotracers was significantly reduced (p < 0.05) in both animal models during blocking studies. The tumor-to-blood ratio was observed to be ∼2-2.5 for the two radiotracers, whereas the tumor-to-muscle ratio was significantly higher (p < 0.005) for ⁶⁸Ga-HBED-CC-c(RGD) in the two animal models. The two radiotracers ⁶⁸Ga-HBED-CC-c(NGR) and ⁶⁸Ga-HBED-CC-c(RGD) exhibited renal excretion with rapid clearance from blood and other non-target organs. Thus, ⁶⁸Ga-chelated HBED-CC conjugated NGR and RGD peptides expressed features conducive towards development as tumor targeted molecular imaging probes. This study further opens avenues for the successful conjugation of different peptides with the acyclic chelator HBED-CC and expansion of ⁶⁸Ga-based radiopharmaceuticals.

Ubenimex enhances the radiosensitivity of renal cell carcinoma cells by inducing autophagic cell death

Renal cell carcinoma (RCC) is resistant to standard radiotherapy. Ubenimex, an aminopeptidase N inhibitor, is widely used as an adjunct therapy after surgery to enhance the function of immunocompetent cells and confer antitumor effects. Our previous study demonstrated that ubenimex induces autophagic cell death in RCC cells. Recently, the molecular mechanism of autophagy induction has been associated with radiosensitivity in RCC cells. In the present study, the ability of ubenimex to enhance RCC cell sensitivity to radiation via the induction of autophagic cell death was determined, and the mechanism of action of this effect was investigated. The 786-O and OS-RC-2 human RCC cell lines were treated with 0.5 mg/ml ubenimex and different doses of irradiation (IR). The cell viability was measured using a colony-formation assay and flow cytometry. Acridine orange (AO)-ethidium bromide (EB) staining was assessed by fluorescence microscopy as an indicator of autophagic cell death. Protein expression was assessed by western blotting. Autophagosomes were evaluated using transmission electron microscopy. RCC cells were used to evaluate the sensitivity to radiation using clonogenic survival and lactate dehydrogenase assays. Furthermore, these parameters were also tested at physiological oxygen levels. The AO-EB staining and flow cytometry of the OS-RC-2 cells indicated that the combined treatment significantly enhanced autophagic cell death compared with ubenimex or IR alone. Therefore, treatment with ubenimex did not significantly alter cell cycle progression but increased cell death when combined with radiation. An Akt agonist could significantly weaken this effect, indicating that ubenimex may act as an Akt inhibitor. Furthermore, the western blot analysis indicated that the combined treatment inhibited the Akt signaling pathway compared with ubenimex treatment or IR alone. Ubenimex may enhance RCC cell sensitivity to radiation by inducing cell autophagy. This induction changes the role of autophagy from protective to lethal in vitro, and this switch is associated with the inhibition of the Akt signaling pathway.

A CD13 inhibitor, ubenimex, synergistically enhances the effects of anticancer drugs in hepatocellular carcinoma

Cancer stem cells (CSCs) were reported to be involved in resistance to chemo/radiation therapy. We previously reported that CD13 was both a marker of CSCs and a candidate therapeutic target in HCC. In the present study, we explored the antitumor effect of a combined therapy, where ubenimex, a CD13 inhibitor, was combined with conventional anticancer drugs, fluorouracil (5-FU), cisplatin (CDDP), doxorubicin (DXR) and sorafenib (SOR), and we elucidated the mechanism of these combination therapies. We evaluated changes in the expression of CD13 before and after treatment with anticancer drugs and with or without ubenimex in the human HCC cell lines HuH7 and PLC/PRF/5. The interactions between the anticancer drugs and ubenimex were determined with isobologram analyses. We analyzed cell cycle, apoptosis, and intracellular reactive oxygen species (ROS) levels to explore the mechanisms of the combination therapies. In both cell lines, the expression of CD13 increased after a 72-h exposure to each anticancer drug alone (P<0.05), and the expression of CD13 decreased with ubenimex administration (P<0.05). Isobologram analyses indicated that ubenimex had synergistic effects with 5-FU, CDDP and DXR, and an additive effect with SOR. Cell cycle analyses showed that ubenimex decreased the proportion of cells in G0/G1. Ubenimex enhanced the effects of 5-FU, CDDP and DXR by increasing apoptosis and intracellular ROS levels. In combination therapies, ubenimex synergistically enhanced the antitumor effects of 5-FU, CDDP and DXR on cell cycle regulation and apoptosis induction in HCC cell lines. The effects of ubenimex were due to increased intracellular ROS levels.

Ubenimex inhibits cell proliferation, migration and invasion by inhibiting the expression of APN and inducing autophagic cell death in prostate cancer cells

Prostate cancer is the second most frequently diagnosed cancer in males worldwide and is commonly associated with metastasis. Moreover, in prostate cancer, aminopeptidase N (APN) expression is closely correlated with metastasis. Ubenimex, an APN inhibitor, is widely used as an adjunct therapy for cancer, enhancing the function of immunocompetent cells and conferring antitumor effects. However, due to the low expression of APN, it is rarely used to treat prostate cancer. Recently, the induction of autophagy as a molecular mechanism has been strongly connected with tumor cell death. Thus, we investigated whether ubenimex could inhibit cell proliferation, migration and invasion by downregulating APN expression to induce autophagic cell death in prostate cancer cells. The LNCaP and PC-3 cell lines were treated with different doses of ubenimex. Cell viability was measured using growth curve analysis and WST-8 proliferation assay. Autophagic cell death was assessed using fluorescence microscopy and acridine orange/ethidium bromide (AO/EB) staining. Protein expression was assessed by immunofluorescence and western blot analyses. Autophagosomes were evaluated using transmission electron microscopy. Wound-healing migration assays were performed to determine the migratory ability of the PC-3 cells. In addition, nude mice were used in the present study to examine PC-3 cell proliferation in vivo. The results revealed that APN expression differed between the metastatic and non-metastatic prostate cancer cells. In addition, ubenimex inhibited APN expression in the prostate cancer cells. Ubenimex increased prostate cancer cell death, as determined using the lactate dehydrogenase (LDH) cytotoxicity assay. This effect was accompanied by increased levels of LC3B. Furthermore, ubenimex inhibited PC-3 cell proliferation in vivo and in vitro. Ubenimex inhibited the cell migration and invasion in prostate cancer cells by downregulating APN expression. Finally, ubenimex induced autophagic cell death in both metastatic and non-metastatic prostate cancer cells. Based on these results, ubenimex appears to be an excellent adjunctive therapy for the treatment of prostate cancer.

Ubenimex inhibits cell proliferation, migration and invasion in renal cell carcinoma: the effect is autophagy-associated

Ubenimex is a low-molecular-weight dipeptide with the ability to inhibit aminopeptidase N (APN) activity, enhance the function of immunocompetent cells and confer antitumor effects. We sought to characterize the effects of ubenimex on renal cell carcinoma (RCC). The 786-O and OS-RC-2 human RCC cell lines were positive for APN expression and ubenimex decreased APN activity without affecting the expression. Ubenimex suppressed the proliferation of both cell lines in a concentration‑dependent manner, as assessed by curve growth analysis and WST-8 proliferation assay. Wound healing and Matrigel invasion assays demonstrated that the migration and invasion of the RCC cells were also markedly suppressed by ubenimex. Furthermore, ubenimex increased the mortality of both RCC cell lines as determined by the LDH cytotoxicity assay. This affect was accompanied by increased levels of LC3B with no apparent effect on Caspase3; and we observed that autophagy increased significantly after ubenimex treatment in both RCC cell lines by electron microscopy. Moreover, rapamycin enhanced the cytotoxic effect of ubenimex, while 3-methyladenine reversed the effect, indicating that ubenimex cytotoxicity occured through an autophagy-related mechanism. To further assess the potential applicability of ubenimex in the treatment of RCC, we performed immunohistochemistry using tissue microarrays representing 76 RCC patients that underwent radical nephrectomy. The results showed that APN was expressed in most, but not all of the RCC tissues and that the expression was reduced in RCC as compared to the normal kidney tissues, suggesting a potential role for APN in RCC development. Collectively, these results indicated that ubenimex inhibits proliferation, migration and invasion of RCC cells. Ubenimex may induce autophagy, which may be associated with its effect on the growth arrest and the cell death of RCC cells.

Evaluation of (99m)Tc-probestin SPECT as a novel technique for noninvasive imaging of kidney aminopeptidase N expression

Aminopeptidase N (APN; CD13; EC 3.4.11.2) is a zinc-dependent membrane-bound exopeptidase that catalyzes the removal of N-terminal amino acids from peptides. APN is known to be highly expressed on renal cortical proximal tubules. APN expression levels are markedly decreased under the influence of nephrotoxins and in the tumor regions of renal cancers. Thus, molecular imaging of kidney APN expression could provide pathophysiological information about kidneys noninvasively. Probestin is a potent APN inhibitor and binds to APN. Abdominal SPECT imaging was conducted at 1 h postinjection of (99m)Tc-probestin in a group of 12 UPII-SV40T transgenic and wild-type mice. UPII-SV40T mice spontaneously develop urothelial carcinoma in situ and invasive transitional cell carcinoma (TCC) that invade kidneys. Histopathology and immunohistochemistry analysis were used to confirm the presence of tumor and to evaluate APN expression in kidney. Radioactivity in normal tissue regions of renal cortex was clearly visible in SPECT images, whereas tumor regions of renal cortex displayed significantly lower or no radioactivity uptake. Histopathological analysis of kidney sections showed normal morphology for both renal pelvic and cortical regions in wild-type mice and abnormal morphology in some transgenic mice. Proliferating cell nuclear antigen staining confirmed the presence of tumor in those abnormal regions. Immunohistochemical analysis of kidney sections using anti-CD13 antibody showed significantly lower APN expression in tumor regions compared to normal regions. Results obtained in this study demonstrate the potential use of (99m)Tc-probestin SPECT as a novel technique for noninvasive imaging of kidney APN expression.

[Effect of bisphosphonates on anticancer activity in prostate cancer cells]

Bisphosphonates are widely used to treat for osteoporosis and have recently been suggested to be effective in preventing tumor metastasis to the bone. One of the mechanisms underlying metastasis inhibition by bisphosphonates has been explained on the basis of the direct effects of these drugs on cancer cells in the bone microenvironment. Here we have focused on the effect of bisphosphonates on anticancer activity in prostate cancer cells because these cancer cells frequently metastasize to the bone. We found that nitrogen-containing bisphosphonates induced apoptosis and inhibited invasion in prostate cancer PC-3 cells. Bisphosphonate pretreatment was found to enhance cell death induced by anticancer drugs. The expression of the apoptosis- or invasion- related factors, bcl-2, protein kinase C (PKC), aminopeptidase-N (AP-N), and urokinase-type plasminogen activator (uPA) decreased on treatment with nitrogen-containing bisphosphonates. The molecular mechanisms underlying the decrease in bcl-2, AP-N, and uPA expression involved suppression of protein prenylation through inhibition of the mevalonate pathway. These findings have implications with respect to understanding the mechanisms underlying the suppressive effect of bisphosphonates on bone metastasis of prostate cancer.

Positioning of aminopeptidase inhibitors in next generation cancer therapy

Aminopeptidases represent a class of (zinc) metalloenzymes that catalyze the cleavage of amino acids nearby the N-terminus of polypeptides, resulting in hydrolysis of peptide bonds. Aminopeptidases operate downstream of the ubiquitin-proteasome pathway and are implicated in the final step of intracellular protein degradation either by trimming proteasome-generated peptides for antigen presentation or full hydrolysis into free amino acids for recycling in renewed protein synthesis. This review focuses on the function and subcellular location of five key aminopeptidases (aminopeptidase N, leucine aminopeptidase, puromycin-sensitive aminopeptidase, leukotriene A4 hydrolase and endoplasmic reticulum aminopeptidase 1/2) and their association with different diseases, in particular cancer and their current position as target for therapeutic intervention by aminopeptidase inhibitors. Historically, bestatin was the first prototypical aminopeptidase inhibitor that entered the clinic 35 years ago and is still used for the treatment of lung cancer. More recently, new generation aminopeptidase inhibitors became available, including the aminopeptidase inhibitor prodrug tosedostat, which is currently tested in phase II clinical trials for acute myeloid leukemia. Beyond bestatin and tosedostat, medicinal chemistry has emerged with additional series of potential aminopeptidases inhibitors which are still in an early phase of (pre)clinical investigations. The expanded knowledge of the unique mechanism of action of aminopeptidases has revived interest in aminopeptidase inhibitors for drug combination regimens in anti-cancer treatment. In this context, this review will discuss relevant features and mechanisms of action of aminopeptidases and will also elaborate on factors contributing to aminopeptidase inhibitor efficacy and/or loss of efficacy due to drug resistance-related phenomena. Together, a growing body of data point to aminopeptidase inhibitors as attractive tools for combination chemotherapy, hence their implementation may be a step forward in a new era of personalized treatment of cancer patients.

68Ga-DOTA-NGR as a novel molecular probe for APN-positive tumor imaging using MicroPET

Aminopeptidase N (APN) is selectively expressed on many tumors and the endothelium of tumor neovasculature, and may serve as a promising target for cancer diagnosis and therapy. Asparagine-glycine-arginine (NGR) peptides have been shown to bind specifically to the APN receptor and have served as vehicles for the delivery of various therapeutic drugs in previous studies. The purpose of this study was to synthesize and evaluate the efficacy of a (68)Ga-labeled NGR peptide as a new molecular probe that binds to APN.

METHODS

NGR peptide was conjugated with 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) and labeled with (68)Ga at 95°C for 10 min. In vitro uptake and binding analysis was performed with A549 and MDA-MB231 cells. Biodistribution of (68)Ga-DOTA-NGR was determined in normal mice by dissection method. (68)Ga-DOTA-NGR PET was performed in A549 and MDA-MB231 xenografts, and included dynamic and static imaging. APN expression in tumors and new vasculatures was analyzed by immunohistochemistry.

RESULTS

The radiochemical purity of (68)Ga-DOTA-NGR was 98.0% ± 1.4% with a specific activity of about 17.49 MBq/nmol. The uptake of (68)Ga-DOTA-NGR in A549 cells increased with longer incubation times, and could be blocked by cold DOTA-NGR, while no specific uptake was found in MDA-MB231 cells. In vivo biodistribution studies showed that (68)Ga-DOTA-NGR was mainly excreted from the kidney, and rapidly cleared from blood and nonspecific organs. MicroPET imaging showed that high focal accumulation had occurred in the tumor site at 1 h post-injection (pi) in A549 tumor xenografts. A significant reduction of tumor uptake was observed following coinjection with a blocking dose of DOTA-NGR, whereas only mild uptake was found in MDA-MB231 tumor xenografts. Tumor uptake, measured as the tumor/lung ratio, increased with time peaking at 12.58 ± 1.26 at 1.5 h pi. Immunohistochemical staining confirmed that APN was overexpressed on A549 cells and neovasculature.

CONCLUSIONS

(68)Ga-DOTA-NGR was easily synthesized and showed favorable biodistribution and kinetics. (68)Ga-DOTA-NGR could also specifically bind to the APN receptor in vitro and in vivo, and might be a potential molecular probe for the noninvasive detection of APN-positive tumors and neovasculature.

In vitro and in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass

In order to enhance the corrosion resistance of the Ca65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass because of the unique properties of high-entropy alloys. Our results showed that the mechanical properties and corrosion behavior were enhanced. The in vitro tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass did not show any obvious degradation after 4 weeks of implantation, and they can promote osteogenesis and new bone formation after 2 weeks of implantation. The improved mechanical properties and corrosion behavior can be attributed to the different chemical composition as well as the formation of a unique high-entropy atomic structure with a maximum degree of disorder.

Evaluation of 99mTc-probestin for imaging APN expressing tumors by SPECT

Aminopeptidase N (APN) is known to play important roles in tumor angiogenesis, tumor cell invasion, and metastasis. Thus, APN is an attractive biomarker for imaging tumor angiogenesis. Here we report results obtained from biodistribution and single photon emission computed tomography (SPECT) imaging studies of a technetium-99m labeled probestin (a potent APN inhibitor) conjugate containing a tripeptide, Asp-DAP-Cys (DAP=2,3-diaminopropionic acid), chelator and a 8-amino-3,6-dioxaoctanoic acid (PEG2) linker conducted in nude mice xenografted with HT-1080 human fibrosarcoma tumors (APN-positive tumors). These results collectively demonstrate that (99m)Tc-probestin uptake by tumors and other APN expressing tissues in vivo is specific and validate the use of probestin as a vector for targeting APN in vivo.

Suppression of metallothionein 3 gene expression by androgen in LNCaP prostate cancer cells

Androgen deprivation therapy is the standard treatment for prostate cancer. However, tumors often progress towards a more aggressive phenotype despite treatment. Prostate tissue has a high zinc concentration, which may correlate with prostate cancer progression. Therefore, we investigated the effect of dihydrotestosterone (DHT) on the gene expression of metallothioneins (MTs) and zinc transporters in prostate cancer with quantitative real-time polymerase chain reaction (PCR). The MT3 gene expression in LNCaP cells was suppressed by DHT in a dose-dependent manner. However, it increased in a culture medium containing androgen-deficient charcoal-stripped fetal bovine serum (FBS). Bicalutamide, an androgen receptor antagonist, increased the gene expression of MT3 and partially reversed the suppression of MT3 gene expression induced by DHT. In PC-3 cells lacking androgen receptors, DHT and bicalutamide exerted no effect on MT3 gene expression. The reporter gene assay with a luciferase reporter plasmid containing the 5'-flanking region of MT3 demonstrated a decrease in luciferase activity caused by DHT that was reversed by bicalutamide. These results suggest that MT3 gene expression is downregulated by androgen.

Solid phase synthesis and biological evaluation of probestin as an angiogenesis inhibitor

Probestin is a potent aminopeptidase N (APN) inhibitor originally isolated from the bacterial culture broth. Here, we report probestin synthesis by solid phase peptide synthesis (SPPS) method and evaluated its activity to inhibit angiogenesis using a chicken embryo chorioallantoic membrane (CAM) assay and a CAM tumor xenograft model. Results from these studies demonstrate that probestin inhibits the angiogenic activity and tumor growth.

Design and synthesis of small-molecule fluorescent photoprobes targeted to aminopeptdase N (APN/CD13) for optical imaging of angiogenesis

We report here the synthesis of a nonpeptide, small-molecule fluorescent imaging agent with high affinity to aminopeptidase N (APN/CD13), a key player in a variety of pathophysiological angiogenic processes. On the basis of a recently described lead structure, we synthesized three putative precursor compounds by introducing polyethylene glycol (PEG) spacers comprising amino groups for dye labeling. Different attachment sites resulted in substantial differences in target affinity, cell toxicity, and target imaging performance. In comparison to bestatin, a natural inhibitor of many aminopeptidases, two of our compounds (22, 23) exhibit comparable inhibition potency, while a third (21) does not show any inhibiting effect. Cell binding assays with APN-positive BT-549 and APN-negative BT-20 cells and the final fluorescent probes Cy 5.5-21 and Cy 5.5-23 confirm these findings. The favorable characteristics of Cy 5.5-23 will now be proven in in vivo experiments with murine models of high APN expression and may serve as a tool to better understand APN pathophysiology.

Identification of APN/CD13 as the target antigen of FU3, a human monoclonal antibody that recognizes malignant fibrous histiocytoma

Malignant fibrous histiocytoma (MFH), a high-grade, undifferentiated sarcoma, is highly aggressive, resistant to radiochemotherapy and associated with poor prognosis. There are no specific immunohistochemical markers for its diagnosis. The MFH cell line SFT7913 served as and immunogen for the generation of the FU3 monoclonal antibody in our laboratory. FU3 reacted strongly with MFH cells and with perivascular mesenchymal cells. In this study, we demonstrated that the antigen recognized by FU3 was identical to aminopeptidase N (APN/CD13) using FU3 immunoaffinity chromatography and N-terminal amino acid sequencing. Frequent (80%) and high-grade (>50% of cells) expression of APN/CD13 was observed in MFH, although low-grade expression was seen in some other sarcomas. Moreover, small interfering RNA (siRNA) that specifically targets APN/CD13 significantly suppressed MFH cell invasion in vitro. The newly developed monoclonal antibody FU3 specifically recognizes CD13 on MFH cells. Decreased expression of CD13, mediated by siRNA-mediated knockdown, attenuated the invasive capacity of MFH cells. Thus, results indicate that APN/CD13 could be an important diagnostic biomarker and therapeutic target for MFH.

Zinc and zinc transporters in prostate carcinogenesis

The healthy human prostate accumulates the highest level of zinc of any soft tissue in the body. This unique property is retained in BPH, but is lost in prostatic malignancy, which implicates changes in zinc and its transporters in carcinogenesis. Indeed, zinc concentrations diminish early in the course of prostate carcinogenesis, preceding histopathological changes, and continue to decline during progression toward castration-resistant disease. Numerous studies suggest that increased zinc intake might protect against progression of prostatic malignancy. In spite of increased dietary intake, zinc accumulation might be limited by the diminished expression of zinc uptake transporters, resulting in decreased intratumoural zinc levels. This finding can explain the conflicting results of various epidemiological studies evaluating the role of zinc supplementation on primary and secondary prostate cancer prevention. Overall, more research into the mechanisms of zinc homeostasis are needed to fully understand its impact on prostate carcinogenesis. Only then can the potential of zinc and zinc transport proteins be harnessed in the diagnosis and treatment of men with prostate cancer.

Prognostic significance of aberrantly silenced ANPEP expression in prostate cancer

Background:

Novel biomarkers for prostate cancer (PC) are urgently needed. This study investigates the expression, epigenetic regulation, and prognostic potential of ANPEP in PC.

Methods:

Aminopeptidase N (APN; encoded by ANPEP) expression was analysed by immunohistochemistry using tissue microarrays representing 267 radical prostatectomy (RP) and 111 conservatively treated (CT) PC patients. Clinical end points were recurrence-free survival (RFS) and cancer-specific survival (CSS), respectively. The ANPEP promoter methylation levels were determined by bisulphite sequencing or MethyLight analysis in 278 nonmalignant and PC tissue samples, and in cell lines.

Results:

The APN expression was significantly downregulated in PC compared with nonmalignant prostate tissue samples. Aberrant promoter hypermethylation was frequently observed in PC tissue samples, and 5-aza-2′-deoxycytidine induced ANPEP expression in three hypermethylated prostate cell lines, suggesting epigenetic silencing. Negative APN immunoreactivity was significantly associated with short RFS and short CSS in the RP and CT cohort, respectively, independently of routine clinicopathological predictors. Combining APN with a known angiogenesis marker (vascular endothelial growth factor or microvessel density) improved risk prediction significantly in both cohorts.

Conclusion:

Our results suggest negative APN immunoreactivity as a new independent adverse prognostic factor for patients with clinically localised PC and, furthermore, that epigenetic mechanisms are involved in silencing of ANPEP in PC.

Cellular mechanisms of zinc dysregulation: a perspective on zinc homeostasis as an etiological factor in the development and progression of breast cancer

Worldwide, breast cancer is the most commonly diagnosed cancer among women and is the leading cause of female cancer deaths. Zinc (Zn) functions as an antioxidant and plays a role in maintaining genomic stability. Zn deficiency results in oxidative DNA damage and increased cancer risk. Studies suggest an inverse association between dietary and plasma Zn levels and the risk for developing breast cancer. In contrast, breast tumor biopsies display significantly higher Zn levels compared with normal tissue. Zn accumulation in tumor tissue also correlates with increased levels of Zn importing proteins. Further, aberrant expression of Zn transporters in tumors correlates with malignancy, suggesting that altered metal homeostasis in the breast could contribute to malignant transformation and the severity of cancer. However, studies have yet to link dysregulated Zn transport and abnormal Zn-dependent functions in breast cancer development. Herein, we summarize studies that address the multi-modal role of Zn dyshomeostasis in breast cancer with respect to the role of Zn in modulating oxidative stress, DNA damage response/repair pathways and cell proliferation/apoptosis, and the relationship to aberrant regulation of Zn transporters. We also compare Zn dysregulation in breast tissue to that of prostate, pancreatic and ovarian cancer where possible.

Synthesis and biodistribution studies of technetium-99m-labeled aminopeptidase N inhibitor conjugates

Probestin is a potent aminopeptidase N (APN) inhibitor. Four probestin conjugates containing a tripeptide chelator (N(3)S) and a PEG(2) linker were synthesized and radiolabeled with Tc-99m. The number of -COOH groups on the chelator was altered to increase the excretion of the radiotracer from blood stream via the renal-urinary pathway and to decrease its hepatobiliary uptake. Biodistribution of the radiolabeled conjugates was evaluated in healthy CF-1™ mice at 1h post-injection. The results revealed that the Tc-99m labeled probestin conjugate preferentially (>85% injected dose) excreted via the renal route when an aspartic acid residue was added to the linker (conjugate 4). These results suggest that the pharmacokinetic properties of probestin-based APN-targeted agents could be optimized by adding an appropriate amino acid residue in between the linker and the payload.

The immunological contribution of NF-κB within the tumor microenvironment: a potential protective role of zinc as an anti-tumor agent

Over decades, cancer treatment has been mainly focused on targeting cancer cells and not much attention to host tumor microenvironment. Recent advances suggest that the tumor microenvironment requires in-depth investigation for understanding the interactions between tumor cell biology and immunobiology in order to optimize therapeutic approaches. Tumor microenvironment consists of cancer cells and tumor associated reactive fibroblasts, infiltrating non-cancer cells, secreted soluble factors or molecules, and non-cellular support materials. Tumor associated host immune cells such as Th(1), Th(2), Th17, regulatory cells, dendritic cells, macrophages, and myeloid-derived suppressor cells are major components of the tumor microenvironment. Accumulating evidence suggests that these tumor associated immune cells may play important roles in cancer development and progression. However, the exact functions of these cells in the tumor microenvironment are poorly understood. In the tumor microenvironment, NF-κB plays an important role in cancer development and progression because this is a major transcription factor which regulates immune functions within the tumor microenvironment. In this review, we will focus our discussion on the immunological contribution of NF-κB in tumor associated host immune cells within the tumor microenvironment. We will also discuss the potential protective role of zinc, a well-known immune response mediator, in the regulation of these immune cells and cancer cells in the tumor microenvironment especially because zinc could be useful for conditioning the tumor microenvironment toward innovative cancer therapy.

Synthesis and evaluation of novel Tc-99m labeled probestin conjugates for imaging APN/CD13 expression in vivo

The enzyme aminopeptidase N (APN, also known as CD13) is known to play an important role in tumor proliferation, attachment, angiogenesis, and tumor invasion. In this study, we hypothesized that a radiolabeled high affinity APN inhibitor could be potentially useful for imaging APN expression in vivo. Here, we report synthesis, radiolabeling, and biological evaluation of new probestin conjugates containing a tripeptide, N,N-dimethylglycyl-l-lysinyl-l-cysteinylamide (N(3)S), chelator. New probestin conjugates were synthesized by solid-phase peptide synthesis method, purified by reversed-phase HPLC, and characterized by electrospray mass spectrometry. The conjugates were complexed with Re(V) and (99m)Tc(V) by transmetalation using corresponding Re(V) or (99m)Tc(V) gluconate synthon. The mass spectral analyses of ReO-N(3)S-Probestin conjugates were consistent with the formation of neutral Re(V)O-N(3)S complexes. Initial biological activity of ReO-N(3)S-Probestin conjugates determined by performing an in vitro APN enzyme assay using intact HT-1080 cells demonstrated higher inhibition of APN enzyme activity than bestatin. In vivo biodistribution and whole body planar imaging studies of (99m)TcO-N(3)S-PEG(2)-Probestin performed in nude mice xenografted with human fibrosarcoma tumors derived from HT-1080 cells demonstrated a tumor uptake value of 2.88 ± 0.64%ID/g with tumor-to-blood and tumor-to-muscle ratios of 4.8 and 5.3, respectively, at 1 h postinjection (p.i.). Tumors were clearly visible in whole body planar image obtained at 1 h p.i., but not when the APN was competitively blocked with a coinjection of excess nonradioactive ReO-N(3)S-PEG(2)-Probestin conjugate. These results demonstrate the feasibility of using high affinity APN inhibitor conjugates as targeting vectors for in vivo targeting of APN.

Identification of markers of prostate cancer progression using candidate gene expression

BACKGROUND

Metastatic prostate cancer (PCa) has no curative treatment options. Some forms of PCa are indolent and slow growing, while others metastasise quickly and may prove fatal within a very short time. The basis of this variable prognosis is poorly understood, despite considerable research. The aim of this study was to identify markers associated with the progression of PCa.

METHODS

Artificial neuronal network analysis combined with data from literature and previous work produced a panel of putative PCa progression markers, which were used in a transcriptomic analysis of 29 radical prostatectomy samples and correlated with clinical outcome.

RESULTS

Statistical analysis yielded seven putative markers of PCa progression, ANPEP, ABL1, PSCA, EFNA1, HSPB1, INMT and TRIP13. Two data transformation methods were utilised with only markers that were significant in both selected for further analysis. ANPEP and EFNA1 were significantly correlated with Gleason score. Models of progression co-utilising markers ANPEP and ABL1 or ANPEP and PSCA had the ability to correctly predict indolent or aggressive disease, based on Gleason score, in 89.7% and 86.2% of cases, respectively. Another model of TRIP13 expression in combination with preoperative PSA level and Gleason score was able to correctly predict recurrence in 85.7% of cases.

CONCLUSION

This proof of principle study demonstrates a novel association of carcinogenic and tumourigenic gene expression with PCa stage and prognosis.