Six-transmembrane epithelial antigen of the prostate-1 plays a role for in vivo tumor growth via intercellular communication

Zinc oxide nanoparticles damage the prefrontal lobe in mouse: Behavioral impacts and key mechanisms

Zinc Oxide nanoparticles (ZnO NPs) have dualistic properties due to their advantage and toxicity. However, the impact and mechanisms of ZnO NPs on the prefrontal lobe have limited research. This study investigates the behavioral changes following exposure to ZnO NPs (34 mg/kg, 30 days), integrating multiple behaviors and bioinformatics analysis to identify critical factors and regulatory mechanisms. The essential differentially expressed genes (DEGs) were identified, including ORC1, DSP, AADAT, SLITRK6, and STEAP1. Analysis of the DEGs based on fold change reveals that ZnO NPs primarily regulate cell survival, proliferation, and apoptosis in neural cells, damaging the prefrontal lobe. Moreover, disruption of cell communication, mineral absorption, and immune pathways occurs. Gene set enrichment analysis (GSEA) further shows enrichment of behavior, neuromuscular process, signal transduction in function, synapses-related, cAMP signaling, and immune pathways. Furthermore, alternative splicing (AS) genes highlight synaptic structure/function, synaptic signal transduction, immune responses, cell proliferation, and communication.

Inflammatory response in gastrointestinal cancers: Overview of six transmembrane epithelial antigens of the prostate in pathophysiology and clinical implications

Chronic inflammation is known to increase the risk of gastrointestinal cancers (GICs), the common solid tumors worldwide. Precancerous lesions, such as chronic atrophic inflammation and ulcers, are related to inflammatory responses in vivo and likely to occur in hyperplasia and tumorigenesis. Unfortunately, due to the lack of effective therapeutic targets, the prognosis of patients with GICs is still unsatisfactory. Interestingly, it is found that six transmembrane epithelial antigens of the prostate (STEAPs), a group of metal reductases, are significantly associated with the progression of malignancies, playing a crucial role in systemic metabolic homeostasis and inflammatory responses. The structure and functions of STEAPs suggest that they are closely related to intracellular oxidative stress, responding to inflammatory reactions. Under the imbalance status of abnormal oxidative stress, STEAP members are involved in cell transformation and the development of GICs by inhibiting or activating inflammatory process. This review focuses on STEAPs in GICs along with exploring their potential molecular regulatory mechanisms, with an aim to provide a theoretical basis for diagnosis and treatment strategies for patients suffering from these types of cancers.

AMG 509 (Xaluritamig), an Anti-STEAP1 XmAb 2+1 T-cell Redirecting Immune Therapy with Avidity-Dependent Activity against Prostate Cancer

The tumor-associated antigen STEAP1 is a potential therapeutic target that is expressed in most prostate tumors and at increased levels in metastatic castration-resistant prostate cancer (mCRPC). We developed a STEAP1-targeted XmAb 2+1 T-cell engager (TCE) molecule, AMG 509 (also designated xaluritamig), that is designed to redirect T cells to kill prostate cancer cells that express STEAP1. AMG 509 mediates potent T cell-dependent cytotoxicity of prostate cancer cell lines in vitro and promotes tumor regression in xenograft and syngeneic mouse models of prostate cancer in vivo. The avidity-driven activity of AMG 509 enables selectivity for tumor cells with high STEAP1 expression compared with normal cells. AMG 509 is the first STEAP1 TCE to advance to clinical testing, and we report a case study of a patient with mCRPC who achieved an objective response on AMG 509 treatment.

SIGNIFICANCE

Immunotherapy in prostate cancer has met with limited success due to the immunosuppressive microenvironment and lack of tumor-specific targets. AMG 509 provides a targeted immunotherapy approach to engage a patient's T cells to kill STEAP1-expressing tumor cells and represents a new treatment option for mCRPC and potentially more broadly for prostate cancer. See related commentary by Hage Chehade et al., p. 20. See related article by Kelly et al., p. 76. This article is featured in Selected Articles from This Issue, p. 5.

A novel prognostic signature and therapy guidance for hepatocellular carcinoma based on STEAP family

BACKGROUND

The six-transmembrane epithelial antigen of prostate (STEAP) family members are known to be involved in various tumor-related biological processes and showed its huge potential role in tumor immunotherapy.

METHODS

Biological differences were investigated through Gene set enrichment analysis (GSEA) and tumor microenvironment analysis by CIBERSORT. Tumor mutation burden (TMB), immunotherapy response and chemotherapeutic drugs sensitivity were estimated in R.

RESULTS

We established a prognostic signature with the formula: risk score = STEAP1 × 0.3994 + STEAP4 × (- 0.7596), which had a favorable concordance with the prediction. The high-risk group were enriched in cell cycle and RNA and protein synthesis related pathways, while the low-risk group were enriched in complement and metabolic related pathways. And the risk score was significantly correlated with immune cell infiltration. Most notably, the patients in the low-risk group were characterized with increased TMB and decreased tumor immune dysfunction and exclusion (TIDE) score, indicating that these patients showed better immune checkpoint blockade response. Meanwhile, we found the patients with high-risk were more sensitive to some drugs related to cell cycle and apoptosis.

CONCLUSIONS

The novel signature based on STEAPs may be effective indicators for predicting prognosis, and provides corresponding clinical treatment recommendations for HCC patients based on this classification.

Extracellular vesicle biomarkers for prostate cancer diagnosis: A systematic review and meta-analysis

Extracellular vesicle (EV) biomarkers have promising diagnostic and screening capabilities for several cancers, and growing evidence indicates that EV biomarkers can be used as diagnostic markers for prostate cancer (CaP). However, data on the diagnostic accuracy of EV biomarkers for CaP diagnosis are conflicting. We performed a systematic review and meta-analysis, aimed to summarize the diagnostic performance of EV biomarkers for CaP. We systematically searched PubMed, Medline, and Web of Science from inception to 12 September 2022 for studies that assessed the diagnostic accuracy of EV biomarkers for CaP. We summarized the pooled sensitivity and specificity calculated using a random-effects model. We identified 19 studies involving 976 CaP patients and 676 noncancerous controls; one study conducted independent validation tests. Ten studies emphasized EV RNAs, 6 on EV proteins, and 9 on biomarker panels. MiR-141, miR-221, and PSMA were the most frequently reported RNAs and proteins for CaP diagnosis. For individual RNAs and proteins, the pooled sensitivity and specificity were 70% (95% CI: 68%-71%), 79% (95% CI: 77%-80%), 85% (95% CI: 81%-87%), and 83% (95% CI: 80%-86%), respectively. The pooled sensitivity and specificity of the EV panels were 84% (95% CI: 82%-86%) and 86% (95% CI: 84%-88%), respectively. The studies may have been somewhat limited by the EV isolation and detection techniques. EV biomarkers showed promising diagnostic capability for CaP. Addressing deficiencies in EV isolation and detection techniques has important implications for the application of these novel noninvasive biomarkers in clinical practice.

Proteomic analysis of STEAP1 knockdown in human LNCaP prostate cancer cells

Prostate cancer (PCa) continues to be one of the most common cancers in men worldwide. The six transmembrane epithelial antigen of the prostate 1 (STEAP1) protein is overexpressed in several types of human tumors, particularly in PCa. Our research group has demonstrated that STEAP1 overexpression is associated with PCa progression and aggressiveness. Therefore, understanding the cellular and molecular mechanisms triggered by STEAP1 overexpression will provide important insights to delineate new strategies for PCa treatment. In the present work, a proteomic strategy was used to characterize the intracellular signaling pathways and the molecular targets downstream of STEAP1 in PCa cells. A label-free approach was applied using an Orbitrap LC-MS/MS system to characterize the proteome of STEAP1-knockdown PCa cells. More than 6700 proteins were identified, of which a total of 526 proteins were found differentially expressed in scramble siRNA versus STEAP1 siRNA (234 proteins up-regulated and 292 proteins down-regulated). Bioinformatics analysis allowed us to explore the mechanism through which STEAP1 exerts influence on PCa, revealing that endocytosis, RNA transport, apoptosis, aminoacyl-tRNA biosynthesis, and metabolic pathways are the main biological processes where STEAP1 is involved. By immunoblotting, it was confirmed that STEAP1 silencing induced the up-regulation of cathepsin B, intersectin-1, and syntaxin 4, and the down-regulation of HRas, PIK3C2A, and DIS3. These findings suggested that blocking STEAP1 might be a suitable strategy to activate apoptosis and endocytosis, and diminish cellular metabolism and intercellular communication, leading to inhibition of PCa progression.

Development of a novel electrochemical biosensor based on plastic antibodies for detection of STEAP1 biomarker in cancer

STEAP1 is a cell surface protein of the STEAP family whose main function focuses on intercellular communication and cell growth. STEAP1 is considered a promising putative biomarker and a candidate target for prostate cancer treatment. For specific and selective detection of STEAP1, a molecularly imprinted polymers (MIP) was developed on a screen-printed electrode (C-SPE) whose surface was modified with a nanocomposite based on carbon nanotubes decorated with dendritic platinum nanoparticles (CNTs- PAH /Pt). Then, the MIPs were produced on the modified C-SPE by electropolymerization of a mixture of STEAP1 and a monomer (pyrrole-2-carboxylic acid). Then, the protein was removed from the polymeric network by enzymatic treatment with trypsin, which created the specific template cavities for further STEAP1 detection. Electrochemical techniques such as EIS and CV were used to follow the chemical modification steps of C-SPE. The analytical performance of the biosensor was evaluated by SWV in PBS buffer and in lysates of neoplastic prostate cancer cells (LNCaP) extracts. The MIP material showing a linear range from 130 pg/ml to 13 µg/ml. Overall, the biosensor exhibits essential properties such as selectivity, sensitivity and reproducibility for its application in medical and clinical research diagnosis and/or prognosis of prostate cancer.

Specific Six-Transmembrane Epithelial Antigen of the Prostate 1 Capture with Gellan Gum Microspheres: Design, Optimization and Integration

This work demonstrates the potential of calcium- and nickel-crosslinked Gellan Gum (GG) microspheres to capture the Six-Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) directly from complex Komagataella pastoris mini-bioreactor lysates in a batch method. Calcium-crosslinked microspheres were applied in an ionic exchange strategy, by manipulation of pH and ionic strength, whereas nickel-crosslinked microspheres were applied in an affinity strategy, mirroring a standard immobilized metal affinity chromatography. Both formulations presented small diameters, with appreciable crosslinker content, but calcium-crosslinked microspheres were far smoother. The most promising results were obtained for the ionic strategy, wherein calcium-crosslinked GG microspheres were able to completely bind 0.1% (v/v) DM solubilized STEAP1 in lysate samples (~7 mg/mL). The target protein was eluted in a complexed state at pH 11 with 500 mM NaCl in 10 mM Tris buffer, in a single step with minimal losses. Coupling the batch clarified sample with a co-immunoprecipitation polishing step yields a sample of monomeric STEAP1 with a high degree of purity. For the first time, we demonstrate the potential of a gellan batch method to function as a clarification and primary capture method towards STEAP1, a membrane protein, simplifying and reducing the costs of standard purification workflows.

STEAP1 regulation and its influence modulating the response of LNCaP prostate cancer cells to bicalutamide, enzalutamide and apalutamide

Anti‑androgen drugs are the standard pharmacological therapies for treatment of non‑metastatic prostate cancer (PCa). However, the response of PCa cells may depend on the anti‑androgen used and often patients become resistant to treatment. Thus, studying how the anti‑androgen drugs affect oncogenes expression and action and the identification of the best strategy for combined therapies are essential to improve the efficacy of treatments. The Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) is an oncogene associated with PCa progression and aggressiveness, although its relationship with the androgen receptor signaling remains to be elucidated. The present study aimed to evaluate the effect of anti‑androgens in regulating STEAP1 expression and investigate whether silencing STEAP1 can make PCa cells more sensitive to anti‑androgen drugs. For this purpose, wild‑type and STEAP1 knockdown LNCaP cells were exposed to bicalutamide, enzalutamide and apalutamide. Bicalutamide decreased the expression of STEAP1, but enzalutamide and apalutamide increased its expression. However, decreased cell proliferation and increased apoptosis was observed in response to all drugs. Overall, the cellular and molecular effects were similar between LNCaP wild‑type and LNCaP‑STEAP1 knockdown cells, except for c‑myc expression levels, where a cumulative effect between anti‑androgen treatment and STEAP1 knockdown was observed. The effect of STEAP1 knockdown alone or combined with anti‑androgens in c‑myc levels is required to be addressed in future studies.

STEAP1-4 (Six-Transmembrane Epithelial Antigen of the Prostate 1-4) and Their Clinical Implications for Prostate Cancer

Simple Summary

Despite recent therapeutic advances in the treatment of prostate cancer, metastatic castration-resistant prostate cancer continues to cause significant morbidity and mortality. New research into highly expressed proteins in metastatic castration-resistant prostate cancer shows that Six-Transmembrane Epithelial Antigen of the Prostate 1–4 (STEAP1–4) are significant drivers of prostate cancer aggressiveness and metastasis. STEAP1, in particular, is highly expressed on the plasma membrane of prostate cancer cells and has received significant attention as a potential therapeutic target. This review highlights what is known about STEAP1–4 and identifies knowledge gaps that require further research.

Abstract

Six-Transmembrane Epithelial Antigen of the Prostate 1–4 (STEAP1–4) compose a family of metalloproteinases involved in iron and copper homeostasis and other cellular processes. Thus far, five homologs are known: STEAP1, STEAP1B, STEAP2, STEAP3, and STEAP4. In prostate cancer, STEAP1, STEAP2, and STEAP4 are overexpressed, while STEAP3 expression is downregulated. Although the metalloreductase activities of STEAP1–4 are well documented, their other biological functions are not. Furthermore, the properties and expression levels of STEAP heterotrimers, homotrimers, heterodimers, and homodimers are not well understood. Nevertheless, studies over the last few decades have provided sufficient impetus to investigate STEAP1–4 as potential biomarkers and therapeutic targets for prostate cancer. In particular, STEAP1 is the target of many emerging immunotherapies. Herein, we give an overview of the structure, physiology, and pathophysiology of STEAP1–4 to provide context for past and current efforts to translate STEAP1–4 into the clinic.

Antibody-Drug Conjugates in Uro-Oncology

Currently available treatment options for patients with refractory metastatic prostate, bladder, or kidney cancers are limited with the prognosis remaining poor. Advances in the pathobiology of tumors has led to the discovery of cancer antigens that may be used as the target for cancer treatment. Antibody-drug conjugates (ADCs) are a relatively new concept in cancer treatment that broaden therapeutic landscape. ADCs are examples of a 'drug delivery into the tumor' system composed of an antigen-directed antibody linked to a cytotoxic drug that may release cytotoxic components after binding to the antigen located on the surface of tumor cells. The clinical properties of drugs are influenced by every component of ADCs. Regarding uro-oncology, enfortumab vedotin (EV) and sacituzumab govitecan (SG) are currently registered for patients with locally advanced or metastatic urothelial cancer following previous treatment with an immune checkpoint inhibitor (iCPI; programmed death receptor-1 [PD-1] or programmed death-ligand 1 [PD-L1]) inhibitor) and platinum-containing chemotherapy. The EV-301 trial showed that EV significantly prolonged the overall survival compared with classic chemotherapy. The TROPHY-U-01 trial conducted to evaluate SG demonstrated promising results as regards the objective response rate and duration of response. The safety and efficacy of ADCs in monotherapy and polytherapy (mainly with iCPIs) for different cancer stages and tumor types are assessed in numerous ongoing clinical trials. The aim of this review is to present new molecular biomarkers, specific mechanisms of action, and ongoing clinical trials of ADCs in genitourinary cancers. In the expert discussion, we assess the place of ADCs in uro-oncology and discuss their clinical value.

Promoter Demethylation Upregulates STEAP1 Gene Expression in Human Prostate Cancer: In Vitro and In Silico Analysis

The Six Transmembrane Epithelial Antigen of the Prostate (STEAP1) is an oncogene overexpressed in several human tumors, particularly in prostate cancer (PCa). However, the mechanisms involved in its overexpression remain unknown. It is well known that epigenetic modifications may result in abnormal gene expression patterns, contributing to tumor initiation and progression. Therefore, this study aimed to analyze the methylation pattern of the STEAP1 gene in PCa versus non-neoplastic cells. Bisulfite amplicon sequencing of the CpG island at the STEAP1 gene promoter showed a higher methylation level in non-neoplastic PNT1A prostate cells than in human PCa samples. Bioinformatic analysis of the GEO datasets also showed the STEAP1 gene promoter as being demethylated in human PCa, and a negative association with STEAP1 mRNA expression was observed. These results are supported by the treatment of non-neoplastic PNT1A cells with DNMT and HDAC inhibitors, which induced a significant increase in STEAP1 mRNA expression. In addition, the involvement of HDAC in the regulation of STEAP1 mRNA expression was corroborated by a negative association between STEAP1 mRNA expression and HDAC4,5,7 and 9 in human PCa. In conclusion, our work indicates that STEAP1 overexpression in PCa can be driven by the hypomethylation of STEAP1 gene promoter.

Enhanced Stability of Detergent-Free Human Native STEAP1 Protein from Neoplastic Prostate Cancer Cells upon an Innovative Isolation Procedure

BACKGROUND

The STEAP1 is a cell-surface antigen over-expressed in prostate cancer, which contributes to tumor progression and aggressiveness. However, the molecular mechanisms underlying STEAP1 and its structural determinants remain elusive.

METHODS

The fraction capacity of Butyl- and Octyl-Sepharose matrices on LNCaP lysates was evaluated by manipulating the ionic strength of binding and elution phases, followed by a Co-Immunoprecipitation (Co-IP) polishing. Several potential stabilizing additives were assessed, and the melting temperature (Tm) values ranked the best/worst compounds. The secondary structure of STEAP1 was identified by circular dichroism.

RESULTS

The STEAP1 was not fully captured with 1.375 M (Butyl), in contrast with interfering heterologous proteins, which were strongly retained and mostly eluted with water. This single step demonstrated higher selectivity of Butyl-Sepharose for host impurities removal from injected crude samples. Co-IP allowed recovering a purified fraction of STEAP1 and contributed to unveil potential physiologically interacting counterparts with the target. A Tm of ~55 °C was determined, confirming STEAP1 stability in the purification buffer. A predominant α-helical structure was identified, ensuring the protein's structural stability.

CONCLUSIONS

A method for successfully isolating human STEAP1 from LNCaP cells was provided, avoiding the use of detergents to achieve stability, even outside a membrane-mimicking environment.

Impact of glycerol feeding profiles on STEAP1 biosynthesis by Komagataella pastoris using a methanol-inducible promoter

Currently, the lack of reliable strategies for the diagnosis and treatment of cancer makes the identification and characterization of new therapeutic targets a pressing matter. Several studies have proposed the Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) as a promising therapeutic target for prostate cancer. Although structural and functional studies may provide deeper insights on the role of STEAP1 in cancer, such techniques require high amounts of purified protein through biotechnological processes. Based on the results presented, this work proposes the application, for the first time, of a fed-batch profile to improve STEAP1 biosynthesis in mini-bioreactor Komagataella pastoris X-33 Mut⁺ methanol-induced cultures, by evaluating three glycerol feeding profiles-constant, exponential, and gradient-during the pre-induction phase. Interestingly, different glycerol feeding profiles produced differently processed STEAP1. This platform was optimized using a combination of chemical chaperones for ensuring the structural stabilization and appropriate processing of the target protein. The supplementation of culture medium with 6 % (v/v) DMSO and 1 M proline onto a gradient glycerol/constant methanol feeding promoted increased biosynthesis levels of STEAP1 and minimized aggregation events. Deglycosylation assays with peptide N-glycosidase F showed that glycerol constant feed is associated with an N-glycosylated pattern of STEAP1. The biological activity of recombinant STEAP1 was also validated, once the protein enhanced the proliferation of LNCaP and PC3 cancer cells, in comparison with non-tumoral cell cultures. This methodology could be a crucial starting point for large-scale production of active and stable conformation of recombinant human STEAP1. Thus, it could open up new strategies to unveil the structural rearrangement of STEAP1 and to better understand the biological role of the protein in cancer onset and progression.

Immunotherapy of prostate cancer using novel synthetic DNA vaccines targeting multiple tumor antigens

Prostate cancer is a prevalent cancer in men and consists of both indolent and aggressive phenotypes. While active surveillance is recommended for the former, current treatments for the latter include surgery, radiation, chemo and hormonal therapy. It has been observed that the recurrence in the treated patients is high and results in castration resistant prostate cancer for which treatment options are limited. This scenario has prompted us to consider immunotherapy with synthetic DNA vaccines, as this approach can generate antigen-specific tumor-killing immune cells. Given the multifocal and heterogeneous nature of prostate cancer, we hypothesized that synthetic DNA vaccines targeting different prostate specific antigens are likely to induce broader and improved immunity who are at high risk as well as advanced clinical stage of prostate cancer, compared to a single antigen approach. Utilizing a bioinformatics approach, synthetic enhanced DNA vaccine (SEV) constructs were generated against STEAP1, PAP, PARM1, PSCA, PCTA and PSP94. Synthetic enhanced vaccines for prostate cancer antigens were shown to elicit antigen-specific immune responses in mice and the anti-tumor activity was evident in a prostate tumor challenge mouse model. These studies support further evaluation of the DNA tools for immunotherapy of prostate cancer and perhaps other cancers.

Iron Metabolism in the Tumor Microenvironment: Contributions of Innate Immune Cells

Cells of the innate immune system are a major component of the tumor microenvironment. They play complex and multifaceted roles in the regulation of cancer initiation, growth, metastasis and responses to therapeutics. Innate immune cells like neutrophils and macrophages are recruited to cancerous tissues by chemotactic molecules released by cancer cells and cancer-associated stromal cells. Once they reach the tumor, they can be instructed by a network of proteins, nucleic acids and metabolites to exert protumoral or antitumoral functions. Altered iron metabolism is a feature of cancer. Epidemiological studies suggest that increased presence of iron and/or iron binding proteins is associated with increased risks of cancer development. It has been shown that iron metabolism is involved in shaping the immune landscapes in inflammatory/infectious diseases and cancer-associated inflammation. In this article, we will dissect the contribution of macrophages and neutrophils to dysregulated iron metabolism in malignant cells and its impact on cancer growth and metastasis. The mechanisms involved in regulating the actions of macrophages and neutrophils will also be discussed. Moreover, we will examine the effects of iron metabolism on the phenotypes of innate immune cells. Both iron chelating and overloading agents are being explored in cancer treatment. This review highlights alternative strategies for management of iron content in cancer cells by targeting the iron donation and modulation properties of macrophages and neutrophils in the tumor microenvironment.

Regulatory Roles of Six-Transmembrane Epithelial Antigen of the Prostate Family Members in the Occurrence and Development of Malignant Tumors

The human six-transmembrane epithelial antigen of the prostate (STEAP) proteins, which include STEAP1-4 and atypical STEAP1B, contain six transmembrane domains and are located in the cell membrane. STEAPs are considered archaeal metal oxidoreductases, based on their heme groups and F420H2:NADP+ oxidoreductase (FNO)-like structures, and play an important role in cell metal metabolism. Interestingly, STEAPs not only participate in biological processes, such as molecular transport, cell cycling, immune response, and intracellular and extracellular activities, but also are closely related to the occurrence and development of several diseases, especially malignant tumors. Up to now, the expression patterns of STEAPs have been found to be diverse in different types of tumors, with controversial participation in different aspects of malignancy, such as cell proliferation, migration, invasion, apoptosis, and therapeutic resistance. It is clinically important to explore the potential roles of STEAPs as new immunotherapeutic targets for the treatment of different malignant tumors. Therefore, this review focuses on the molecular mechanism and function of STEAPs in the occurrence and development of different cancers in order to understand the role of STEAPs in cancer and provide a new theoretical basis for the treatment of diverse cancers.

Cryo-electron microscopy structure and potential enzymatic function of human six-transmembrane epithelial antigen of the prostate 1 (STEAP1)

Six-transmembrane epithelial antigen of the prostate 1 (STEAP1) is an integral membrane protein that is highly up-regulated on the cell surface of several human cancers, making it a promising therapeutic target to manage these diseases. It shares sequence homology with three enzymes (STEAP2–STEAP4) that catalyze the NADPH-dependent reduction of iron(III). However, STEAP1 lacks an intracellular NADPH-binding domain and does not exhibit cellular ferric reductase activity. Thus, both the molecular function of STEAP1 and its role in cancer progression remain elusive. Here, we present a ∼3.0-Å cryo-EM structure of trimeric human STEAP1 bound to three antigen-binding fragments (Fabs) of the clinically used antibody mAb120.545. The structure revealed that STEAP1 adopts a reductase-like conformation and interacts with the Fabs through its extracellular helices. Enzymatic assays in human cells revealed that STEAP1 promotes iron(III) reduction when fused to the intracellular NADPH-binding domain of its family member STEAP4, suggesting that STEAP1 functions as a ferric reductase in STEAP heterotrimers. Our work provides a foundation for deciphering the molecular mechanisms of STEAP1 and may be useful in the design of new therapeutic strategies to target STEAP1 in cancer.

Six-transmembrane epithelial antigen of the prostate 1 expression promotes ovarian cancer metastasis by aiding progression of epithelial-to-mesenchymal transition

Ovarian cancer is a severe malignant tumour of the female genital organs. Six-transmembrane epithelial antigen of the prostate 1 (STEAP1) expression is correlated with the occurrence and progression of multiple cancers. Here, we assessed STEAP1 expression in ovarian cancer and explored the relationship between STEAP1 and ovarian cancer progression. We used immunohistochemistry and public databases to test STEAP1 expression in normal human ovarian tissues, benign ovarian tumours, and ovarian cancer. The expression of STEAP1 and epithelial-to-mesenchymal transition (EMT)-related genes was analysed using immunocytochemistry, quantitative reverse transcription polymerase chain reaction, and western blotting in ovarian cancer cell lines. Lentivirus was used to knockdown and overexpress STEAP1. Invasion, migration, growth, clonogenicity, and apoptosis were assessed using transwell assay, growth curve, plate clone formation assay, and flow cytometry. We used a tumour xenograft to verify the relationship between STEAP1 and in vivo ovarian cancer cell growth. Matrix metalloproteinase-2 (MMP2) and matrix metalloproteinase-9 (MMP9) activities were examined using Matrix metalloproteinase zymography assay. STEAP1 was highly expressed in the human ovarian cancer tissues and a highly invasive ovarian cancer cell line. Overexpression of STEAP1 was related to poor prognosis in ovarian cancer patients. Down-regulation of STEAP1 suppressed the invasion, migration, proliferation, clonogenicity, EMT progression in human ovarian cancer cells and xenograft tumour growth in vivo, but it enhanced apoptosis. In human ovarian cancer, the STEAP1 gene is highly expressed, and its function is correlated with human ovarian cancer cell metastasis and growth. STEAP1 may be a possible target for suppressing ovarian cancer metastasis.

Estradiol-17β-Induced Changes in the Porcine Endometrial Transcriptome In Vivo

Estradiol-17β (E2) is a key hormone regulating reproductive functions in females. In pigs, E2, as the main conceptus signal, initiates processes resulting in prolonged corpus luteum function, embryo development, and implantation. During early pregnancy the endometrium undergoes morphological and physiological transitions that are tightly related to transcriptome changes. Recently, however, the importance of E2 as a primary conceptus signal in the pig has been questionable. Thus, the aim of the present study was to determine the effects of E2 on the porcine endometrial transcriptome in vivo and to compare these effects with transcriptome profiles on day 12 of pregnancy. Microarray analysis revealed differentially expressed genes (DEGs) in response to E2 with overrepresented functional terms related to secretive functions, extracellular vesicles, cell adhesion, proliferation and differentiation, tissue rearrangements, immune response, lipid metabolism, and many others. Numerous common DEGs and processes for the endometrium on day 12 of pregnancy and E2-treated endometrium were identified. In summary, the present study is the first evidence for the effect of E2 on transcriptome profiles in porcine endometrium in vivo in the period corresponding to the maternal recognition of pregnancy. The presented results provide a valuable resource for further targeted studies considering genes and pathways regulated by conceptus-derived estrogens and their role in pregnancy establishment.

STEAP2 is down-regulated in breast cancer tissue and suppresses PI3K/AKT signaling and breast cancer cell invasion in vitro and in vivo

The six-transmembrane epithelial antigen of prostate 2 (STEAP2) protein was identified in advanced prostate cancer, and is highly over-expressed in various types of cancer. This study aimed to investigate the prognostic value and the function of STEAP2 in breast cancer. STEAP2 mRNA and protein expressions in breast normal and cancer tissues, breast cancer cell lines (MCF-7, BT-549, BT-474, MDA-MB-361, HCC1937, and MDA-MB-468) and normal mammary epithelial cell lines (HBL-100 and MCF-10A) were evaluated by immunohistochemistry, real time RT-qPCR and western blotting. The expression of STEAP2 in breast cancer tissues and its value of evaluating the prognosis of breast cancer patients was validated in the Public Databases (Oncomine and Kaplan-Meier plotter database). Lentiviral vectors with STEAP2 cDNA and shRNA were constructed and used to infect breast cancer cell lines and normal mammary epithelial cell line to investigate the effects of STEAP2 up- and down- regulation on the biological behavior of breast cells. The low expression of STEAP2 was detected in breast cancer tissues, which was associated with malignant phenotype and poor prognosis of breast cancer. The public databases analyses were consistent with our findings. STEAP2 up-regulation hindered cellular proliferation, invasion and metastasis abilities by inhibiting EMT process and suppressing PI3K/AKT/mTOR signaling pathway. On the other hand, STEAP2 down-regulation could promote cell proliferation and invasion by inducing EMT and activating the PI3K/AKT/mTOR signaling pathway. Collectively, STEAP2 acted as an anti-oncogene in breast cancer development, which suggested a new research objective for the future studies.

Utilisation of the STEAP protein family in a diagnostic setting may provide a more comprehensive prognosis of prostate cancer

Prostate cancer is the second most common cancer diagnosed in men worldwide; however, few patients are affected by clinically significant disease within their lifetime. Unfortunately, the means to discriminate between patients with indolent disease and those who progress to aggressive prostate cancer is currently unavailable, resulting in over-treatment of patients. We therefore aimed to determine biomarkers of prostate cancer that can be used in the clinic to aid the diagnosis and prognosis. Immunohistochemistry analysis was carried out on prostate cancer specimens with a range of Gleason scores. Samples were stained and analysed for intensity of the Seven Transmembrane Epithelial Antigen of the Prostate (STEAP)-1, -2, -3, -4 and the Divalent Metal Transporter 1 (DMT1) proteins to determine suitable biomarkers for classification of patients likely to develop aggressive prostate cancer. Additionally, these proteins were also analysed to determine whether any would be able to predict future relapse using Kaplan Meier analysis. Data generated demonstrated that the protein expression levels of STEAP2 correlated significantly with Gleason score; furthermore, STEAP4 was a significant predictor of relapse. This data indicates that STEAP2 could be potential prognostic candidate for use in combination with the current prostate cancer detection methods and the presence of STEAP4 could be an indicator of possible relapse.

Six-transmembrane epithelial antigen of the prostate 1 is associated with tumor invasion and migration in endometrial carcinomas

Six-transmembrane epithelial antigen of the prostate 1 (STEAP1), a member of the STEAP family, is a general tumor antigen. However, no information has been available to date regarding the function of STEAP1 in the progression of endometrial carcinoma. In this study, we used in vitro and in vivo strategies to prove that STEAP1 plays an important role in the progression of endometrial carcinoma. Immunohistochemistry, immunocytochemistry, quantitative reverse transcription polymerase chain reaction (RT-qPCR), and Western blot analysis were used to detect the expression of STEAP1 in normal endometrial cells and endometrial cancer cell lines. The progression of the cell cycle, plate clone formation assay, and transwell migration and invasion assays were performed to examine the effects of STEAP1 on cell proliferation, clonogenicity, migration, and their invasive capacity. In addition, we confirmed that STEAP1 was tightly correlated with the development of tumor in vivo. The relationship between epithelial to mesenchymal transition (EMT) and STEAP1 expression was evaluated by RT-qPCR and Western blot analysis. Matrix metalloproteinase (MMP) zymography assay was used to detect the activities of MMP2 and MMP9. STEAP1 was restrictively expressed in endometrial carcinoma and downregulation of the STEAP1 gene increased proliferation and clonogenicity, as well as promoted cell migration, invasion, and the progress of EMT. STEAP1 is downregulated in endometrial carcinoma and can restrict migration and invasion of endometrial carcinoma cells. Overall, STEAP1 may be an ideal target for tumor therapy and diagnosis in the future.

Six-Transmembrane Epithelial Antigen of the Prostate-1 (STEAP-1)-Targeted Ultrasound Imaging Microbubble Improves Detection of Prostate Cancer In Vivo

PURPOSE

To investigate the feasibility of the 6-transmembrane epithelial antigen of the prostate-1 (STEAP-1)-targeted microbubbles for enhancing ultrasound imaging of prostate tumors in the nude mouse xenograft models.

METHODS

Contrast agents were established by conjugating biotinylated STEAP-1 monoclonal antibodies with streptavidin coated SonoVue microbubbles. Then, ordinary SonoVue (Bracco, Milan, Italy) microbubble and STEAP-1-targeted SonoVue microbubble were used, respectively, for contrast-enhanced sonography to detect prostate tumors in the nude mouse xenograft models. The characteristics, including peak intensity, time to peak, area under the curve, and mean transit time, were measured.

RESULTS

The biological characteristics of STEAP-1-targeted SonoVue microbubbles were stable. STEAP-1-targeted SonoVue microbubbles can successfully conjugate to prostate cancer cell lines in vitro. Enhancement of ultrasound signal intensity was determined after injection of STEAP-1-targeted SonoVue microbubble, compared with ordinary SonoVue microbubble. Higher intensities of ultrasound signals in xenograft tumor of prostate cancer were associated with increased levels of STEAP-1 expression.

CONCLUSION

Our results suggest that SonoVue microbubble carrying STEAP-1 monoclonal antibody could improve the ultrasound visualization of prostate cancer and identify the tumor more effectively in vivo. A prospective study is required to validate our finding in patients with prostate cancer.

Inhibition of mouse RM-1 prostate cancer and B16F10 melanoma by the fusion protein of HSP65 & STEAP1 186-193

The research of tumor vaccine plays a crucial role in tumor immunotherapy. This study has constructed and prepared a fusion protein vaccine of heat shock protein 65 (HSP65) and the octapeptide epitope 186-193 of the six transmembrane epithelial antigen of the prostate 1 (STEAP1 _186-193), and investigated the inhibitory effect of the fusion protein on mouse RM-1 prostate cancer and B16F10 melanoma xenografts. The fusion protein His-HSP65-STEAP1 _186-193 (HHST1), His-HSP65-2×STEAP1 _186-193 (HHST2) and His-HSP65-6×STEAP1 _186-193 (HHST6) were obtained by setting different copy number of STEAP1 _186-193 and adding His purification tag before HSP65. Firstly the inhibitory effect of fusion protein on mouse RM-1 prostate cancer xenografts has been studied, which could be the basis of the study the inhibitory effect of the best fusion protein on mouse B16F10 melanoma xenografts. All studies compared with the fusion protein His-HSP65 (HHSP65), the fusion proteins HHST1, HHST2 and HHST6 all could significantly inhibit the growth of mouse RM-1 prostate cancer xenografts. In addition, the fusion protein HHST2 was proved to be the best compared with the fusion proteins HHST1 and HHST6 (P<0.05). Apart from this, compared with the fusion protein HHSP65, the fusion protein HHST2 also significantly inhibited the growth of mouse beared B16F10 melanoma. The results above indicate that HSP65 and STEAP1 _186-193 can significantly inhibit the growth of mouse RM-1 prostate cancer and B16F10 melanoma xenografts, and the appropriate increase of copy number can effectively improve that the fusion protein has an excellent anti-tumor ability.

Knockdown of STEAP1 inhibits cell growth and induces apoptosis in LNCaP prostate cancer cells counteracting the effect of androgens

Six transmembrane epithelial antigen of the prostate 1 (STEAP1) is overexpressed in numerous types of tumors, especially in prostate cancer. STEAP1 is located in the plasma membrane of epithelial cells and may play an important role in inter- and intracellular communication. Several studies suggest STEAP1 as a potential biomarker and an immunotherapeutic target for prostate cancer. However, the role of STEAP1 in cell proliferation and apoptosis remains unclear. Therefore, the role of STEAP1 in prostate cancer cells proliferation and apoptosis was determined by inducing STEAP1 gene knockdown in LNCaP cells. In addition, the effect of DHT on the proliferation of LNCaP cells knocked down for STEAP1 gene was evaluated. Our results demonstrated that silencing the STEAP1 gene reduces LNCaP cell viability and proliferation, while inducing apoptosis. In addition, we showed that the cellular and molecular effects of STEAP1 gene knockdown may be independent of DHT treatment, and blocking STEAP1 may reveal to be an appropriate strategy to activate apoptosis in cancer cells, as well as to prevent the proliferative and anti-apoptotic effects of DHT in prostate cancer.

Immunogenicity and efficacy of the novel cancer vaccine based on simian adenovirus and MVA vectors alone and in combination with PD-1 mAb in a mouse model of prostate cancer

Prostate cancer possesses several characteristics that make it a suitable candidate for immunotherapy; however, prostate cancer vaccines to date demonstrate modest efficacy and low immunogenicity. The goal of the present pre-clinical study was to explore the immunogenic properties and protective efficacy of a novel prostate cancer immunotherapy based on the heterologous prime–boost viral-vectored vaccination platform. The simian adenovirus, ChAdOx1, and modified vaccinia Ankara virus, MVA, encoding a prostate cancer-associated antigen, the six transmembrane epithelial antigen of the prostate 1 (STEAP1), induced strong sustained antigen-specific CD8+ T-cell responses in C57BL/6 and BALB/c male mice. Unexpectedly, the high vaccine immunogenicity translated into relatively low protective efficacy in the murine transplantable and spontaneous models of prostate cancer. A combination of the vaccine with PD-1 blocking antibody significantly improved survival of the animals, with 80 % of mice remaining tumour-free. These results indicate that the ChAdOx1–MVA vaccination regime targeting STEAP1 combined with PD-1 therapy might have high therapeutic potential in the clinic.

A role for STEAP2 in prostate cancer progression

Prostate adenocarcinoma is the second most frequent cancer worldwide and is one of the leading causes of male cancer-related deaths. However, it varies greatly in its behaviour, from indolent non-progressive disease to metastatic cancers with high associated mortality. The aim of this study was to identify predictive biomarkers for patients with localised prostate tumours most likely to progress to aggressive disease, to facilitate future tailored clinical treatment and identify novel therapeutic targets. The expression of 602 genes was profiled using oligoarrays, across three prostate cancer cell lines: CA-HPV-10, LNCaP and PC3, qualitatively identifying several potential prognostic biomarkers. Of particular interest was six transmembrane epithelial antigen of the prostate (STEAP) 1 and STEAP 2 which was subsequently analysed further in prostate cancer tissue samples following optimisation of an RNA extraction method from laser captured cells isolated from formalin-fixed paraffin-embedded biopsy samples. Quantitative analysis of STEAP1 and 2 gene expression were statistically significantly associated with the metastatic cell lines DU145 and PC3 as compared to the normal prostate epithelial cell line, PNT2. This expression pattern was also mirrored at the protein level in the cells. Furthermore, STEAP2 up-regulation was observed within a small patient cohort and was associated with those that had locally advanced disease. Subsequent mechanistic studies in the PNT2 cell line demonstrated that an over-expression of STEAP2 resulted in these normal prostate cells gaining an ability to migrate and invade, suggesting that STEAP2 expression may be a crucial molecule in driving the invasive ability of prostate cancer cells.