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

Circulating and Imaging Biomarkers of Radium-223 Response in Metastatic Castration-Resistant Prostate Cancer

PURPOSE

Radium-223 improves overall survival (OS) and reduces skeletal events in patients with bone metastatic castration-resistant prostate cancer (CRPC), but relevant biomarkers are lacking. We evaluated automated bone scan index (aBSI) and circulating tumor cell (CTC) analyses as potential biomarkers of prognosis and activity.

PATIENTS AND METHODS

Patients with bone metastatic CRPC were enrolled on a prospective single-arm study of standard radium-223. 99mTc-MDP bone scan images at baseline, 2 months, and 6 months were quantitated using aBSI. CTCs at baseline, 1 month, and 2 months were enumerated and assessed for RNA expression of prostate cancer-specific genes using microfluidic enrichment followed by droplet digital polymerase chain reaction.

RESULTS

The median OS was 21.3 months in 22 patients. Lower baseline aBSI and minimal change in aBSI (<+0.7) from baseline to 2 months were each associated with better OS (P = .00341 and P = .0139, respectively). The higher baseline CTC count of ≥5 CTC/7.5 mL was associated with worse OS (median, 10.1 v 32.9 months; P = .00568). CTCs declined at 2 months in four of 15 patients with detectable baseline CTCs. Among individual genes in CTCs, baseline expression of the splice variant AR-V7 was significantly associated with worse OS (hazard ratio, 5.20 [95% CI, 1.657 to 16.31]; P = .00195). Baseline detectable AR-V7, higher aBSI, and CTC count ≥5 CTC/7.5 mL continued to have a significant independent negative impact on OS after controlling for prostate-specific antigen or alkaline phosphatase.

CONCLUSION

Quantitative bone scan assessment with aBSI and CTC analyses are prognostic markers in patients treated with radium-223. AR-V7 expression in CTCs is a particularly promising prognostic biomarker and warrants validation in larger cohorts.

STEAP4 modulates cell proliferation and oxidative stress in benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a quite common chronic disease plagued elderly men and its etiology remains unclear. It was reported that the six-transmembrane epithelial antigen of prostate 4 (STEAP4) could modulate cell proliferation/apoptosis ratio and oxidative stress in cancers. Our current study aimed to explore the expression, biological function, and underlying mechanism of STEAP4 in BPH progress. Human prostate tissues and cell lines were utilized. qRT-PCR and immunofluorescence staining were employed. STEAP4 knockdown (STEAP4-KD) or STEAP4 overexpression (STEAP4-OE) cell models were established. Cell proliferation, cell cycle, apoptosis, and reactive oxygen species (ROS) were determined by cell counting kit-8 (CCK-8) assay and flow cytometry. Apoptosis-related proteins and antioxidant enzymes were identified by Western Blot. In addition, the epithelial-mesenchymal transition (EMT) process and fibrosis biomarker (collagen I and α-SMA) were analyzed. It was indicated that STEAP4 was mainly located in the prostate epithelium and upregulated in BPH tissues. STEAP4 deficiency induced apoptosis and inhibited cell survival, but had no effect on the cell cycle, fibrosis, and EMT process. In addition, ROS changes were observed in the STEAP4-KD model. Consistently, overproduction of STEAP4 suppressed apoptosis and promoted cell proliferation, as well as facilitated ROS production. We further examined AKT / mTOR, p38MAPK / p-p38MAPK, and WNT/ β-Catenin signaling pathway and demonstrated that STEAP4 regulated the proliferation and apoptosis of prostate cells through AKT / mTOR signaling, rather than p38MAPK / p-p38MAPK and WNT/ β-Catenin pathways. Furthermore, activating AKT / mTOR signaling with SC79 significantly reversed apoptosis triggered by STEAP4 deficiency, whereas suppressing AKT / mTOR signaling with MK2206 reduced the increase of cell viability triggered by STEAP4 overproduction. Our original data demonstrated that STEAP4 is crucial in the onset and progression of prostate hyperplasia and may become a new target for the treatment of BPH.

Molecular characterization of STEAP3 in lung squamous cell carcinoma: Regulating EGFR to affect cell proliferation and ferroptosis

Six-transmembrane epithelial antigen of the prostate 3 (STEAP3) has been reported to play a regulatory role in various types of cancers. However, its involvement in lung squamous cell carcinoma (LUSC) remains understudied. Here, we aimed to explore the biological functions and underlying mechanisms of STEAP3 in LUSC. Intersection genes associated with LUSC and ferroptosis were analyzed using the Venn method, STRING, GEPIA and UALCAN databases. The expression of STEAP3 was detected by qPCR and western blotting assay. Cell proliferation and viability were determined using the cell counting kit-8 assay and EDU staining. Oxidative stress and lipid peroxidation were measured by corresponding kits and DCFH-DA staining. Ferroptosis was evaluated by Phen Green SK and Western blot assay. The correlation between STEAP3 and EGFR was predicted by the TIMER and starBase database. Co-immunoprecipitation was conducted to verify the binding of STEAP3 and EGFR. The data demonstrated a significant upregulation of STEAP3 expression in LUSC cell lines. Silencing of STEAP3 suppressed H2170 cell viability and proliferation while promoting oxidative stress and lipid peroxidation through increased levels of MDA and ROS, as well as inhibited SOD activity. In addition, knockdown of STEAP3 induced ferroptosis through the regulation of ferroptosis-related proteins. Moreover, the binding between STEAP3 and EGFR was predicted and confirmed in LUSC. EGFR overexpression reversed the effects of STEAP3 silencing on H2170 cell viability, proliferation, oxidative stress, and ferroptosis. To summarize, the inhibition of STEAP3/EGFR may serve as a promising therapeutic target for LUSC treatment, as it can suppress LUSC proliferation and promote lipid peroxidation and ferroptosis.

Antitumor activity of AZD0754, a dnTGFβRII-armored, STEAP2-targeted CAR-T cell therapy, in prostate cancer

Prostate cancer is generally considered an immunologically "cold" tumor type that is insensitive to immunotherapy. Targeting surface antigens on tumors through cellular therapy can induce a potent antitumor immune response to "heat up" the tumor microenvironment. However, many antigens expressed on prostate tumor cells are also found on normal tissues, potentially causing on-target, off-tumor toxicities and a suboptimal therapeutic index. Our studies revealed that six-transmembrane epithelial antigen of prostate-2 (STEAP2) was a prevalent prostate cancer antigen that displayed high, homogeneous cell surface expression across all stages of disease with limited distal normal tissue expression, making it ideal for therapeutic targeting. A multifaceted lead generation approach enabled development of an armored STEAP2 chimeric antigen receptor T cell (CAR-T) therapeutic candidate, AZD0754. This CAR-T product was armored with a dominant-negative TGF-β type II receptor, bolstering its activity in the TGF-β-rich immunosuppressive environment of prostate cancer. AZD0754 demonstrated potent and specific cytotoxicity against antigen-expressing cells in vitro despite TGF-β-rich conditions. Further, AZD0754 enforced robust, dose-dependent in vivo efficacy in STEAP2-expressing cancer cell line-derived and patient-derived xenograft mouse models, and exhibited encouraging preclinical safety. Together, these data underscore the therapeutic tractability of STEAP2 in prostate cancer as well as build confidence in the specificity, potency, and tolerability of this potentially first-in-class CAR-T therapy.

Targeting STEAP1 as an anticancer strategy

Although the six-transmembrane epithelial antigen of prostate 1 (STEAP1) was first identified in advanced prostate cancer, its overexpression is recognized in multiple types of cancer and associated with a poor prognosis. STEAP1 is now drawing attention as a promising therapeutic target because of its tumor specificity and membrane-bound localization. The clinical efficacy of an antibody-drug conjugate targeting STEAP1 in metastatic, castration-resistant, prostate cancer was demonstrated in a phase 1 trial. Furthermore, growing evidence suggests that STEAP1 is an attractive target for immunotherapies such as chimeric antigen receptor-T cell therapy. In this review, we summarize the oncogenic functions of STEAP1 by cancer type. This review also provides new insights into the development of new anticancer strategies targeting STEAP1.

Immune responses of six-transmembrane epithelial antigen of the prostate 4 functions as a novel biomarker in gastric cancer

BACKGROUND

Immune cells play an important role in regulating the behavior of tumor cells. According to emerging evidence, six-transmembrane epithelial antigen of the prostate 4 (STEAP4) performs a crucial part in tumor microenvironmental immune response and tumorigenesis, and serves as the potential target for cellular and antibody immunotherapy. However, the immunotherapeutic role of STEAP4 in gastric cancer (GC) remains unclear.

AIM

To investigate the expression of STEAP4 in GC and its relationship with immune infiltrating cells, and explore the potential value of STEAP4 as an immune prognostic indicator in GC.

METHODS

The expression level of STEAP4 was characterized by immunohistochemistry in tumors and adjacent non-cancerous samples in 96 GC patients. Tumor Immune Estimation Resource was used to study the correlation between STEAP4 and tumor immune infiltration level and immune infiltration gene signature. R package was used to analyze the relationship between STEAP4 expression and immune and stromal scores in GC (GSE62254) by the ESTIMATE algorithm, and Kaplan-Meier Plotter and Gene Expression Profiling Interactive Analysis were applied to analyze the effect of STEAP4 on clinical prognosis.

RESULTS

Immunohistochemistry analysis showed that STEAP4 expression was higher in GC tissues than in adjacent tissues, and STEAP4 expression was positively correlated with the clinical stage of GC. In GC, the expression of STEAP4 was positively correlated with the infiltration levels of B cells, CD4+ T cells, macrophages, neutrophils, and dendritic cells. The expression level of STEAP4 was strongly correlated with most of the immune markers. In addition, STEAP4 expression was inversely correlated with tumor purity, but correlated with stromal score (r = 0.43, P < 0.001), immune score (r = 0.29, P < 0.001) and estimate score (r = 0.39, P < 0.001). Moreover, stromal, immune, and estimate scores were higher in the STEAP4 high expression group, whereas tumor purity was higher in the STEAP4 Low expression group. The relationship between STEAP4 expression and prognosis of patients with GC was further investigated, and the results showed that high STEAP4 expression was associated with poor overall survival and disease-free survival. In addition, Kaplan-Meier Plotter showed that high expression of STEAP4 was significantly correlated with poor survival of patients with GC.

CONCLUSION

The current findings suggest an oncogenic role for STEAP4 in GC, with significantly high levels being associated with poor prognosis. Investigation of the GC tumor microenvironment suggests the potential function of STEAP4 is connected with the infiltration of diverse immune cells, which may contribute to the regulation of the tumor microenvironment. In conclusion, STEAP4 may serve as a potential therapeutic target for GC to improve the immune infiltration, as well as serve as a prognostic biomarker for judging the prognosis and immune infiltration status of GC.

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.

Relevant Membrane Transport Proteins as Possible Gatekeepers for Effective Pharmacological Ascorbate Treatment in Cancer

Despite the increasing number of newly diagnosed malignancies worldwide, therapeutic options for some tumor diseases are unfortunately still limited. Interestingly, preclinical but also some clinical data suggest that the administration of pharmacological ascorbate seems to respond well, especially in some aggressively growing tumor entities. The membrane transport and channel proteins are highly relevant for the use of pharmacological ascorbate in cancer therapy and are involved in the transfer of active substances such as ascorbate, hydrogen peroxide, and iron that predominantly must enter malignant cells to induce antiproliferative effects and especially ferroptosis. In this review, the relevant conveying proteins from cellular surfaces are presented as an integral part of the efficacy of pharmacological ascorbate, considering the already known genetic and functional features in tumor tissues. Accordingly, candidates for diagnostic markers and therapeutic targets are mentioned.

Bispecific T-Cell Engagers Therapies in Solid Tumors: Focusing on Prostate Cancer

Over the past decade, immunotherapy has demonstrated an impressive improvement in treatment outcomes for multiple cancers. Following the landmark approvals for use of immune checkpoint inhibitors, new challenges emerged in various clinical settings. Not all tumor types harbor immunogenic characteristics capable of triggering responses. Similarly, many tumors' immune microenvironment allows them to become evasive, leading to resistance and, thus, limiting the durability of responses. To overcome this limitation, new T-cell redirecting strategies such as bispecific T-cell engager (BiTE) have become attractive and promising immunotherapies. Our review provides a comprehensive perspective of the current evidence of BiTE therapies in solid tumors. Considering that immunotherapy has shown modest results in advanced prostate cancer to date, we review the biologic rationale and promising results of BiTE therapy in this clinical setting and discuss potential tumor-associated antigens that may be integrated into BiTE construct designs. Our review also aims to evaluate the advances of BiTE therapies in prostate cancer, illustrate the major obstacles and underlying limitations, and discuss directions for future research.

Six-Transmembrane Epithelial Antigen of Prostate 4: An Indicator of Prognosis and Tumor Immunity in Hepatocellular Carcinoma

Purpose

The six-transmembrane epithelial antigen of prostate 4 (STEAP4) has been linked to tumor progression via its involvement in inflammatory responses, oxidative stress, and metabolism. However, STEAP4 has rarely been studied in hepatocellular carcinoma (HCC). We explored STEAP4 expression associated with tumor prognosis to understand its role in tumor biology in HCC.

Patients and Methods

STEAP4 mRNA and protein expressions were primarily analyzed using bioinformatics tools based on The Cancer Genome Atlas database to understand the expression pattern, molecular mechanism, prognostic impact, and association with immune cell infiltration. We further investigated the association between STEAP4 protein expression and clinicopathological parameters and their predictive value in HCC patients using immunohistochemical staining of tissue microarrays.

Results

The expression of STEAP4 mRNA and protein in HCC tissues was significantly lower than in normal liver tissues. Reduced expression of STEAP4 was linked to advanced HCC stages, poor recurrence-free survival (RFS), and overall survival. Furthermore, reduced STEAP4 expression was a significant predictor of worse RFS in univariate and multivariate analyses in the immunohistochemical cohort. GO, KEGG, and GSEA analyses revealed that STEAP4 is related to numerous biological processes and pathways, including drug metabolism, DNA replication, RNA metabolism, and immune response. In terms of the immune system, the decreased level of STEAP4 was correlated with the immunosuppressive microenvironment.

Conclusion

Our data indicated that reduced STEAP4 expression was significantly associated with tumor aggressiveness and poor prognosis, possibly because of its link to various biological processes and induction of HCC immune evasion. Therefore, STEAP4 expression may serve as a potential prognostic biomarker for cancer progression and immunity, as well as a therapeutic target in HCC.

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.

Comprehensive Landscape of STEAP Family Members Expression in Human Cancers: Unraveling the Potential Usefulness in Clinical Practice Using Integrated Bioinformatics Analysis

The human Six-Transmembrane Epithelial Antigen of the Prostate (STEAP) family comprises STEAP1-4. Several studies have pointed out STEAP proteins as putative biomarkers, as well as therapeutic targets in several types of human cancers, particularly in prostate cancer. However, the relationships and significance of the expression pattern of STEAP1-4 in cancer cases are barely known. Herein, the Oncomine database and cBioPortal platform were selected to predict the differential expression levels of STEAP members and clinical prognosis. The most common expression pattern observed was the combination of the over- and underexpression of distinct STEAP genes, but cervical and gastric cancer and lymphoma showed overexpression of all STEAP genes. It was also found that STEAP genes’ expression levels were already deregulated in benign lesions. Regarding the prognostic value, it was found that STEAP1 (prostate), STEAP2 (brain and central nervous system), STEAP3 (kidney, leukemia and testicular) and STEAP4 (bladder, cervical, gastric) overexpression correlate with lower patient survival rate. However, in prostate cancer, overexpression of the STEAP4 gene was correlated with a higher survival rate. Overall, this study first showed that the expression levels of STEAP genes are highly variable in human cancers, which may be related to different patients’ outcomes.

Predictors and Real-World Use of Prostate-Specific Radioligand Therapy: PSMA and Beyond

PSMA is a transmembrane protein that is markedly overexpressed in prostate cancer, making it an excellent target for imaging and treating patients with prostate cancer. Several small molecule inhibitors and antibodies of PSMA have been radiolabeled for use as therapeutic agents and are currently under clinical investigation. PSMA-based radionuclide therapy is a promising therapeutic option for men with metastatic prostate cancer. The phase II TheraP study demonstrated superior efficacy, lower side effects, and improved patient-reported outcomes compared with cabazitaxel. The phase III VISION study demonstrated that radionuclide therapy with β-emitter ¹⁷⁷Lu-PSMA-617 can prolong survival and improve quality of life when offered in addition to standard-of-care therapy in men with PSMA-positive metastatic castration-resistant prostate cancer whose disease had progressed with conventional treatments. Nevertheless, up to 30% of patients have inherent resistance to PSMA-based radionuclide therapy, and acquired resistance is inevitable. Hence, strategies to increase the efficacy of PSMA-based radionuclide therapy have been under clinical investigation. These include better patient selection; increased radiation damage delivery via dosimetry-based administered dose or use of α-emitters instead of β-emitters; or using combinatorial approaches to overcome radioresistance mechanisms (innate or acquired), such as with novel hormonal agents, PARP inhibitors, or immunotherapy.

Novel Redirected T-Cell Immunotherapies for Advanced Prostate Cancer

Immunotherapy has failed to achieve durable remissions in advanced prostate cancer patients. More potent T-cell-redirecting strategies may be needed to overcome the immunologically exclusive and suppressive tumor microenvironment. Clinical trials are underway, seeking to define the optimal target for T-cell redirection, such as PSMA, PSCA, or STEAP-1, as well as the optimal strategy, with CAR or bispecific antibodies. As results continue to emerge from these trials, understanding differential toxicity and efficacy of these therapies based on their targets and functional modifications will be key to advancing these promising therapies toward clinical practice. This review provides a unique depth and breadth of perspective regarding the diverse immunotherapy strategies currently under clinical investigation for men with advanced prostate cancer.

Long-term first-in-man Phase I/II study of an adjuvant dendritic cell vaccine in patients with high-risk prostate cancer after radical prostatectomy

BACKGROUND

Patients with high-risk prostate cancer (PC) can experience biochemical relapse (BCR), despite surgery, and develop noncurative disease. The present study aimed to reduce the risk of BCR with a personalized dendritic cell (DC) vaccine, given as adjuvant therapy, after robot-assisted laparoscopic prostatectomy (RALP).

METHODS

Twelve weeks after RALP, 20 patients with high-risk PC and undetectable PSA received DC vaccinations for 3 years or until BCR. The primary endpoint was the time to BCR. The immune response was assessed 7 weeks after surgery (baseline) and at one-time point during the vaccination period.

RESULTS

Among 20 patients, 11 were BCR-free over a median of 96 months (range: 84-99). The median time from the end of vaccinations to the last follow-up was 57 months (range: 45-60). Nine patients developed BCR, either during (n = 4) or after (n = 5) the vaccination period. Among five patients diagnosed with intraductal carcinoma, three experienced early BCR during the vaccination period. All patients that developed BCR remained in stable disease within a median of 99 months (range: 74-99). The baseline immune response was significantly associated with the immune response during the vaccination period (p = 0.015). For patients diagnosed with extraprostatic extension (EPE), time to BCR was longer in vaccine responders than in non-responders (p = 0.09). Among 12 patients with the International Society of Urological Pathology (ISUP) grade 5 PC, five achieved remission after 84 months, and all mounted immune responses.

CONCLUSION

Patients diagnosed with EPE and ISUP grade 5 PC were at particularly high risk of developing postsurgical BCR. In this subgroup, the vaccine response was related to a reduced BCR incidence. The vaccine was safe, without side effects. This adjuvant first-in-man Phase I/II DC vaccine study showed promising results. DC vaccines after curative surgery should be investigated further in a larger cohort of patients with high-risk PC.

The Role of Iron in Cancer Progression

Iron is an essential trace element for the human body, and its deficiency or excess can induce a variety of biological processes. Plenty of evidences have shown that iron metabolism is closely related to the occurrence and development of tumors. In addition, iron plays an important role in cell death, which is very important for the development of potential strategies for tumor treatment. Here, we reviewed the latest research about iron metabolism disorders in various types of tumors, the functions and properties of iron in ferroptosis and ferritinophagy, and new opportunities for iron-based on treatment methods for tumors, providing more information regarding the prevention and treatment of tumors.

STEAP4 knockdown inhibits the proliferation of prostate cancer cells by activating the cGMP-PKG pathway under lipopolysaccharide-induced inflammatory microenvironment

Six-transmembrane epithelial antigen of prostate 4 (STEAP4) is involved in the development of human cancers. However, the role of STEAP4 in prostate cancer remains largely unknown. The purpose of this research is to explore the role and action mechanism of STEAP4 in prostate cancer development under lipopolysaccharide (LPS)-induced inflammatory microenvironment. STEAP4 expression was analyzed by Gene Expression Profiling Interactive Analysis (GEPIA), UALCAN and Cancer Cell Line Encyclopedia (CCLE), and its prognostic value was analyzed by LinkedOmics. STEAP4-correlated genes were analyzed by LinkedOmics and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. STEAP4 level was detected by Western blotting or qRT-PCR. Proliferation was investigated by CCK-8 and EdU staining. Inflammatory cytokine levels were detected by ELISA. The cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) pathway was detected by ELISA and Western blotting. STEAP4 level was increased in prostate cancer tissues, and high expression of STEAP4 was associated with the poor overall survival. LPS promoted cell viability and STEAP4 expression. STEAP4 knockdown attenuated LPS-induced inflammation in prostate cancer cells. STEAP4 downregulation mitigated LPS-induced tumorigenesis by decreasing cell proliferation. STEAP4 silencing reversed LPS-induced inactivation of the cGMP-PKG pathway. Inhibition of the cGMP-PKG pathway using inhibitor KT5823 relieved STEAP4 silencing-mediated suppression of cell proliferation and inflammation in LPS-stimulated cells. In conclusion, STEAP4 silencing inhibits LPS-induced proliferation of prostate cancer cells by activating the cGMP-PKG pathway.

Predictive potential of STEAP family for survival, immune microenvironment and therapy response in glioma

Glioma is the most commonly diagnosed primary tumor of central nervous system. Previous studies found that the six-transmembrane epithelial antigen of prostate (STEAP) family can regulate the biological behaviors of several cancers. However, the role of STEAP family in glioma remains unclear. Here, we systematically evaluated the relationship between STEAP family and prognosis of glioma patients in multiple cohorts. The analysis showed that dysregulation of STEAP family may affect cancer-immunity cycle, immune infiltration and phenotypes resulting in an immunosuppressive microenvironment in glioma. To accurately predict the prognosis of glioma patients, gene-based risk models were established based on the expression of STEAP1, 2 and 3. Multivariate and univariate Cox analyses demonstrated that the risk models could independently predict the prognosis of glioma. Finally, chemotherapy and immune therapy responses for high- and low-risk patients were predicted. In conclusion, this study systematically analyzed the role of STEAP family in glioma and established a model for predicting therapy response in patients with glioma.

Clinical significance of STEAP1 extracellular vesicles in prostate cancer

BACKGROUND

Extracellular vesicles (EVs) are cell-derived lipid bilayer enclosed structures shed from the plasma membrane by all cell types. Evidence of EV presence in biological fluids has led to considerable efforts focused on identifying their cargo and determining their utility as a non-invasive diagnostic platform for cancer. In this study, we identify circulating STEAP1 (six-transmembrane epithelial antigen of the prostate 1)-positive EVs in the plasma of healthy males and prostate cancer patients and evaluate its diagnostic and prognostic significance.

METHODS

STEAP1 was identified on EVs in prostate cancer patient plasma. EVs were validated using electron microscopy, Western blot, nanoparticle tracking analysis, and nanoscale flow cytometry. STEAP1-positive EVs were quantified for 121 males with prostate cancer and 55 healthy age-matched control males. An evaluation of STEAP1 in prostate cancer tissue was also performed using established prostate cancer cohort data (TCGA, MSKCC, and SU2C/PCF Dream Team).

RESULTS

Evaluation of STEAP1-positive EVs by nanoscale flow cytometry identified a significant increase in prostate cancer patient plasma compared to healthy males. However, no association was found between total STEAP1 EV levels and disease recurrence or overall survival. Cohort data from prostate cancer tissue also found STEAP1 to be elevated in prostate cancer while no significant association with recurrence or overall survival was identified.

CONCLUSIONS

STEAP1 is known to be enriched on the cells of the prostate with potential clinical significance in prostate cancer. Our results identify and quantitate STEAP1-positive EVs in plasma and provide rationale for a STEAP1 EV-based liquid biopsy as a diagnostic strategy in prostate cancer.

Fusion Protein Vaccine Based on Ag85B and STEAP1 Induces a Protective Immune Response against Prostate Cancer

(1) Background: There are currently limited treatments for castration-resistant prostate cancer. Immunotherapy involving Sipuleucel-T has increasingly drawn attention for prostate cancer management. BCG plays a vital role in treating bladder cancer, mainly by inducing immune activation, but is rarely used for prostate cancer. (2) Methods: The TCGA database, PCR, and Western blotting were used to analyze the expression of STEAP1 in mouse and human tissues. Then, we constructed a fusion protein vaccine with Mycobacterium tuberculosis Ag85B and three repeated octapeptide epitopes of a six-transmembrane epithelial antigen of the prostate 1 (STEAP1_186-193), Ag85B-3×STEAP1_186-193. The uptake of the fusion protein vaccine by DCs was evaluated by confocal microscopy, and DC markers were detected using flow cytometry after incubation with the fusion protein. The immune response against prostate cancer was evaluated by the LDH assay and xenografts in vitro and in vivo. Then, the tumor microenvironment was determined using IHC and ELISA. In addition, the epitope was mutated using CRISPR-Cas9 to illustrate that the fusion protein elicited immunization against STEAP1. (3) Results: The TCGA database analysis, PCR, and Western blotting showed that STEAP1 was highly expressed in human and murine prostate cancer. After the uptake of the purified fusion protein vaccine by DCs, CD11c, CD80, CD86, and MHC II were upregulated and triggered a cytotoxic T lymphocyte (CTL) response against TRAMP-C1 and RM1 cells in vitro. Furthermore, the fusion protein vaccine inhibited tumor growth and improved the tumor microenvironment in vivo, with more CD3⁺ cells and fewer FOXP3⁺ cells in the tumor. Serum IFN-γ and IL-2 were significantly higher than in the control group, while IL-4 expression was lower, indicating that the fusion protein vaccine activated Th1 immunity. The immune response against prostate cancer was greatly suppressed when the antigen targets were knocked out using CRISPR-Cas9. (4) Conclusion: In summary, our results provide the first evidence that a vaccine based on a fusion protein consisting of Ag85B and a prostate cancer octapeptide epitope with complete Freund’s adjuvant (CFA), triggers a robust immune response and inhibits tumor growth in murine prostate cancer.

Prostate Cancer Biomarkers: From diagnosis to prognosis and precision-guided therapeutics

Prostate cancer (PCa) is one of the most commonly diagnosed malignancies and among the leading causes of cancer-related death worldwide. It is a highly heterogeneous disease, ranging from remarkably slow progression or inertia to highly aggressive and fatal disease. As therapeutic decision-making, clinical trial design and outcome highly depend on the appropriate stratification of patients to risk groups, it is imperative to differentiate between benign versus more aggressive states. The incorporation of clinically valuable prognostic and predictive biomarkers is also potentially amenable in this process, in the timely prevention of metastatic disease and in the decision for therapy selection. This review summarizes the progress that has so far been made in the identification of the genomic events that can be used for the classification, prediction and prognostication of PCa, and as major targets for clinical intervention. We include an extensive list of emerging biomarkers for which there is enough preclinical evidence to suggest that they may constitute crucial targets for achieving significant advances in the management of the disease. Finally, we highlight the main challenges that are associated with the identification of clinically significant PCa biomarkers and recommend possible ways to overcome such limitations.

Discovery and Pharmacological Evaluation of STEAP4 as a Novel Target for HER2 Overexpressing Breast Cancer

Breast cancer (BC) is a highly heterogeneous disease encompassing multiple subtypes with different molecular and histopathological features, disease prognosis, and therapeutic responses. Among these, the Triple Negative BC form (TNBC) is an aggressive subtype with poor prognosis and therapeutic outcome. With respect to HER2 overexpressing BC, although advanced targeted therapies have improved the survival of patients, disease relapse and metastasis remains a challenge for therapeutic efficacy. In this study the aim was to identify key membrane-associated proteins which are overexpressed in these aggressive BC subtypes and can serve as potential biomarkers or drug targets. We leveraged on the development of a membrane enrichment protocol in combination with the global profiling GeLC-MS/MS technique, and compared the proteomic profiles of a HER2 overexpressing (HCC-1954) and a TNBC (MDA-MB-231) cell line with that of a benign control breast cell line (MCF-10A). An average of 2300 proteins were identified from each cell line, of which approximately 600 were membrane-associated proteins. Our global proteomic methodology in tandem with invigoration by Western blot and Immunofluorescence analysis, readily detected several previously-established BC receptors like HER2 and EPHA2, but importantly STEAP4 and CD97 emerged as novel potential candidate markers. This is the first time that the mitochondrial iron reductase STEAP4 protein up-regulation is linked to BC (HER2+ subtype), while for CD97, its role in BC has been previously described, but never before by a global proteomic technology in TNBC. STEAP4 was selected for further detailed evaluation by the employment of Immunohistochemical analysis of BC xenografts and clinical tissue microarray studies. Results showed that STEAP4 expression was evident only in malignant breast tissues whereas all the benign breast cases had no detectable levels. A functional role of STEAP4 intervention was established in HER2 overexpressing BC by pharmacological studies, where blockage of the STEAP4 pathway with an iron chelator (Deferiprone) in combination with the HER2 inhibitor Lapatinib led to a significant reduction in cell growth in vitro. Furthermore, siRNA mediated knockdown of STEAP4 also suppressed cell proliferation and enhanced the inhibition of Lapatinib in HER2 overexpressing BC, confirming its potential oncogenic role in BC. In conclusion, STEAP4 may represent a novel BC related biomarker and a potential pharmacological target for the treatment of HER2 overexpressing BC.

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.

Recurrence-Associated Multi-RNA Signature to Predict Disease-Free Survival for Ovarian Cancer Patients

Ovarian cancer (OvCa) is an intractable gynecological malignancy due to the high recurrence rate. Several molecular biomarkers have been previously screened for early identifying patients with a high recurrence risk and poor prognosis. However, all the known studies focused on a single type of RNAs, not integrating various types. This study was to construct a new multi-RNA-based model to predict the recurrence and prognosis for OvCa patients by using the messenger RNA (mRNA, including long noncoding RNA (lncRNA)) and microRNA (miRNA) sequencing data of The Cancer Genome Atlas database. After univariate Cox regression and least absolute shrinkage and selection operator analyses, a multi-RNA-based signature (2 miRNAs: hsa-miR-508, hsa-miR-506; 1 lncRNA: TM4SF1-AS1; 11 mRNAs: MAGI3, SLAMF7, GLI2, PDK1, ARID3A, PLEKHG4B, TNFAIP8L3, C1QTNF3, NDUFAF1, CH25H, TMEM129) was generated and used to establish a risk score model. The high- and low-risk patients classified by the median risk score exhibited significantly different recurrence risks (89% versus 61%, p < 0.001) and survival time (the area under the receiver operating characteristic curve (AUC) = 0.901 for 5-year disease-free survival (DFS)). This risk model was independent of other clinical features and superior to pathologic staging for DFS prediction (AUC, 0.906 versus 0.524; C-index, 0.633 versus 0.510). Furthermore, some new interaction axes were revealed to explain the possible functions of these RNAs (competing endogenous RNA: TM4SF1-AS1-miR-186-STEAP2, LINC00536-miR-508-STEAP2, LINC00475-miR-506-TMEM129; coexpression: LINC00598-PLEKHG4B). In conclusion, this multi-RNA-based risk model may be clinically useful to stratify OvCa patients with different recurrence risks and survival outcomes and included RNAs may be potential therapeutic targets.

The Tumor Suppressive Roles and Prognostic Values of STEAP Family Members in Breast Cancer

OBJECTIVE

To investigate the expression patterns and prognostic values of STEAP family members in the occurrence and development of breast cancer.

MATERIALS AND METHODS

The Human Protein Atlas was used to analyze the expression level of STEAPs in human normal tissues and malignant tumors. ONCOMINE datasets were analyzed for the comparison of the STEAPs levels between malignant cancers and corresponding normal tissues. Kaplan-Meier plotter was used to analyze the prognostic value of STEAPs in breast cancer patients.

RESULTS

STEAPs were widely distributed in human normal tissues with diverse levels. Normally, it is predicted that STEAP1 and STEAP2 were involved in the mineral absorption process, while STEAP3 participated in the TP53 signaling pathway and iron apoptosis. The results from ONCOMINE showed downregulation of STEAP1, STEAP2, and STEAP4 in breast cancers. Survival analysis revealed that breast cancer patients with high levels of STEAP1, STEAP2, and STEAP4 had a good prognosis, while those with low expression had high overall mortality.

CONCLUSION

STEAP1, STEAP2, and STEAP4 are predicted to be the potential prognostic biomarkers for breast cancer patients, providing novel therapeutic strategies for them.