Six Transmembrane Epithelial Antigen Of The Prostate 1 Research Articles

Abstract 6725: NTX-470, a novel multispecific T cell engager expressed from mRNA targets PSMA and STEAP1 prostate cancer antigens to generate enhanced functional activity

Abstract Prostate cancer is the most common cancer in American men and the second leading cause of cancer death in men in western countries. Most metastatic patients develop castration resistant prostate cancer, which despite advances in immunotherapy, is limited in treatment options and represents a critical unmet need. Bi-specific T cell engagers (TCEs) targeting prostate cancer antigens represent a modality that has demonstrated preliminary clinical activity. Clinically validated antigens that are highly expressed in prostate cancers include Prostate-Specific Membrane Antigen (PSMA) and Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1). TCEs targeting either PSMA or STEAP1 individually have shown promising clinical activity, but challenges with durability and toxicity have been reported, potentially attributable to antigen escape, target-independent T cell activation (bystander activation) and specificity issues. Contrary to its name, PSMA expression is not exclusive to prostate cells and can be found in several other tissues and/or conditions, including normal nonprostatic epithelial cells, inflammation/infection, nonprostatic neoplastic cells and nonprostatic tumor-associated neovasculature. The widespread expression of PSMA may limit the therapeutic window of PSMA-specific TCEs and drive immunotoxicity by increased on-target, off-tumor binding. To address these issues, Nutcracker Therapeutics (NTX) has developed novel and highly complex multispecific TCE molecules that target both PSMA and STEAP1, which can be expressed using NTX’s proprietary mRNA therapeutics platform. A wide library of molecules was designed with attenuated PSMA and CD3 binding to mitigate on-target, off-tumor binding and target-independent T cell activation. Molecules were screened and selected based on their propensity to cause bystander T cell activation and the strength of PSMA binding. We identified a small number of molecules that are capable of engaging CD3 T cells but display minimal activity in the absence of STEAP1 or PSMA expressing target cells, including molecules that retain low bystander activity and attenuated PSMA binding yet maintain robust target cell killing. These molecules include NTX-470, which targets both STEAP1 and PSMA on tumor cells with minimal bystander activity. Citation Format: Chris Rae, Sudha Adusumilli, Srinivasa Bandi, Shruti Lal, Pragyesh Dhungel, Kimmy Ferry, Shima Gholizadeh, Anushtha Sharma, Adrienne Sallets, Weiqun Liu, Evan McCartney-Melstad, Pei-Ken Hsu, Ray Low, Colin McKinlay, Meredith Leong, David Y. Oh, Lawrence Fong, Guna Kannan, Samuel Deutsch, Ole Haabeth. NTX-470, a novel multispecific T cell engager expressed from mRNA targets PSMA and STEAP1 prostate cancer antigens to generate enhanced functional activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6725.

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.

Inhibition of STEAP1 ameliorates inflammation and ferroptosis of acute lung injury caused by sepsis in LPS-induced human pulmonary microvascular endothelial cells.

Ferroptosis plays an important part in Acute lung injury (ALI) caused by sepsis. The six-transmembrane epithelial antigen of the prostate 1 (STEAP1) has potential effects on iron metabolism and inflammation but reports on its function in ferroptosis and sepsis-caused ALI are lacking. Here we explored the role of STEAP1 in sepsis-caused ALI and the possible mechanisms. Lipopolysaccharide (LPS) was added to human pulmonary microvascular endothelial cells (HPMECs) to form the sepsis-caused ALI model in vitro. The Cecal ligation and puncture (CLP) experiment was performed on C57/B6J mice to form the sepsis-caused ALI model in vivo. The effect of STEAP1 on inflammation was investigated by PCR, ELISA, and Western blot for the inflammatory factors and adhesion molecular. The reactive oxygen species (ROS) levels were detected by immunofluorescence. The effect of STEAP1 on ferroptosis was investigated by detecting malondialdehyde (MDA) levels, glutathione (GSH) levels, Fe2+ levels, cell viability, and mitochondrial morphology. Our findings suggested that STEAP1 expression was increased in the sepsis-induced ALI models. Inhibition of STEAP1 decreased the inflammatory response and ROS production as well as MDA levels but increased the levels of Nrf2 and GSH. Meanwhile, inhibition of STEAP1 improved cell viability and restored mitochondrial morphology. Western Blot results showed that inhibition of STEAP1 could affect the SLC7A11/GPX4 axis. Inhibition of STEAP1 may be valuable for pulmonary endothelial protection in lung injury caused by sepsis.

Targeting advanced prostate cancer with STEAP1 chimeric antigen receptor T cell and tumor-localized IL-12 immunotherapy

Six transmembrane epithelial antigen of the prostate 1 (STEAP1) is a cell surface antigen for therapeutic targeting in prostate cancer. Here, we report broad expression of STEAP1 relative to prostate-specific membrane antigen (PSMA) in lethal metastatic prostate cancers and the development of a STEAP1-directed chimeric antigen receptor (CAR) T cell therapy. STEAP1 CAR T cells demonstrate reactivity in low antigen density, antitumor activity across metastatic prostate cancer models, and safety in a human STEAP1 knock-in mouse model. STEAP1 antigen escape is a recurrent mechanism of treatment resistance and is associated with diminished tumor antigen processing and presentation. The application of tumor-localized interleukin-12 (IL-12) therapy in the form of a collagen binding domain (CBD)-IL-12 fusion protein combined with STEAP1 CAR T cell therapy enhances antitumor efficacy by remodeling the immunologically cold tumor microenvironment of prostate cancer and combating STEAP1 antigen escape through the engagement of host immunity and epitope spreading.

STEAP1 Knockdown Decreases the Sensitivity of Prostate Cancer Cells to Paclitaxel, Docetaxel and Cabazitaxel.

The Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) protein has been indicated as an overexpressed oncoprotein in prostate cancer (PCa), associated with tumor progression and aggressiveness. Taxane-based antineoplastic drugs such as paclitaxel, docetaxel, or cabazitaxel, have been investigated in PCa treatment, namely for the development of combined therapies with the improvement of therapeutic effectiveness. This study aimed to evaluate the expression of STEAP1 in response to taxane-based drugs and assess whether the sensitivity of PCa cells to treatment with paclitaxel, docetaxel, or cabazitaxel may change when the STEAP1 gene is silenced. Thus, wild-type and STEAP1 knockdown LNCaP and C4-2B cells were exposed to paclitaxel, docetaxel or cabazitaxel, and STEAP1 expression, cell viability, and survival pathways were evaluated. The results obtained showed that STEAP1 knockdown or taxane-based drugs treatment significantly reduced the viability and survival of PCa cells. Relatively to the expression of proliferation markers and apoptosis regulators, LNCaP cells showed a reduced proliferation, whereas apoptosis was increased. However, the effect of paclitaxel, docetaxel, or cabazitaxel treatment was reversed when combined with STEAP1 knockdown. Besides, these chemotherapeutic drugs may stimulate the cell growth of PCa cells knocked down for STEAP1. In conclusion, this study demonstrated that STEAP1 expression levels might influence the response of PCa cells to chemotherapeutics drugs, indicating that the use of paclitaxel, docetaxel, or cabazitaxel may lead to harmful effects in PCa cells with decreased expression of STEAP1.

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.

Bioinformatic analysis and machine learning to identify the diagnostic biomarkers and immune infiltration in adenomyosis.

Background: Adenomyosis is a hormone-dependent benign gynecological disease characterized by the invasion of the endometrium into the myometrium. Women with adenomyosis can suffer from abnormal uterine bleeding, severe pelvic pain, and subfertility or infertility, which can interfere with their quality of life. However, effective diagnostic biomarkers for adenomyosis are currently lacking. The aim of this study is to explore the mechanism of adenomyosis by identifying biomarkers and potential therapeutic targets for adenomyosis and analyzing their correlation with immune infiltration in adenomyosis. Methods: Two datasets, GSE78851 and GSE68870, were downloaded and merged for differential expression analysis and functional enrichment analysis using R software. Weighted gene co-expression network analysis (WGCNA), the least absolute shrinkage and selection operator (LASSO), and support vector machine-recursive feature elimination (SVE-RFE) were combined to explore candidate genes. Quantitative reverse transcriptase PCR (qRT-PCR) was conducted to verify the biomarkers and receiver operating characteristic curve analysis was used to assess the diagnostic value of each biomarker. Single-sample Gene Set Enrichment Analysis (ssGSEA) and CIBERSORT were used to explore immune cell infiltration in adenomyosis and the correlation between diagnostic biomarkers and immune cells. Results: A total of 318 genes were differentially expressed. Through the analysis of differentially expressed genes and WGCNA, we obtained 189 adenomyosis-related genes. After utilizing the LASSO and SVM-RFE algorithms, four hub genes, namely, six-transmembrane epithelial antigen of the prostate-1 (STEAP1), translocase of outer mitochondrial membrane 20 (TOMM20), glycosyltransferase eight domain-containing 2 (GLT8D2), and NME/NM23 family member 5 (NME5) expressed in nucleoside-diphosphate kinase, were identified and verified by qRT-PCR. Immune infiltration analysis indicated that T helper 17 cells, CD56dim natural killer cells, monocytes, and memory B-cell may be associated with the occurrence of adenomyosis. There were significant correlations between the diagnostic biomarkers and immune cells. Conclusion: STEAP1, TOMM20, GLT8D2, and NME5 were identified as potential biomarkers and therapeutic targets for adenomyosis. Immune infiltration may contribute to the onset and progression of adenomyosis.

Bispecific PSMA antibodies and CAR-T in metastatic castration-resistant prostate cancer.

Prostate cancer is the most common cancer among men and the second leading cause of cancer-related deaths in men in the United States. The treatment paradigm for prostate cancer has evolved with the emergence of a variety of novel therapies which have improved survival; however, treatment-related toxicities are abundant and durable responses remain rare. Immune checkpoint inhibitors have shown modest activity in a small subset of patients with prostate cancer and have not had an impact on most men with advanced disease. The discovery of prostate-specific membrane antigen (PSMA) and the understanding of its specificity to prostate cancer has identified it as an ideal tumor-associated antigen and has revived the enthusiasm for immunotherapeutics in prostate cancer. T-cell immunotherapy in the form of bispecific T-cell engagers (BiTEs) and chimeric antigen receptor (CAR) T-cell therapy have shown exceptional success in treating various hematologic malignancies, and are now being tested in patients with prostate cancer with drug design centered on various target ligands including not just PSMA, but others as well including six-transmembrane epithelial antigen of the prostate 1 (STEAP1) and prostate stem cell antigen (PSCA). This summative review will focus on the data surrounding PSMA-targeting T-cell therapies. Early clinical studies with both classes of T-cell redirecting therapies have demonstrated antitumor activity; however, there are multiple challenges with this class of agents, including dose-limiting toxicity, 'on-target, off-tumor' immune-related toxicity, and difficulty in maintaining sustained immune responses within a complex and overtly immunosuppressive tumor microenvironment. Reflecting on experiences from recent trials has been key toward understanding mechanisms of immune escape and limitations in developing these drugs in prostate cancer. Newer generation BiTE and CAR T-cell constructs, either alone or as part of combination therapy, are currently under investigation with modifications in drug design to overcome these barriers. Ongoing innovation in drug development will likely foster successful implementation of T-cell immunotherapy bringing transformational change to the treatment of prostate cancer.

A chromatographic network for the purification of detergent-solubilized six-transmembrane epithelial antigen of the prostate 1 from Komagataella pastoris mini-bioreactor lysates

The Six-Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) is an integral membrane protein involved in cellular communications, in the stimulation of cell proliferation by increasing Reactive Oxygen Species levels, and in the transmembrane-electron transport and reduction of extracellular metal-ion complexes. The STEAP1 is particularly over-expressed in prostate cancer, in contrast with non-tumoral tissues and vital organs, contributing to tumor progression and aggressiveness. However, the current understanding of STEAP1 lacks experimental data on the respective molecular mechanisms, structural determinants, and chemical modifications. This scenario highlights the relevance of exploring the biosynthesis of STEAP1 and its purification for further bio-interaction and structural characterization studies. In this work, recombinant hexahistidine-tagged human STEAP1 (rhSTEAP1-His6) was expressed in Komagataella pastoris (K. pastoris) mini-bioreactor methanol-induced cultures and successfully solubilized with Nonidet P-40 (NP-40) and n-Decyl-β-D-Maltopyranoside (DM) detergents. The fraction capacity of Phenyl-, Butyl-, and Octyl-Sepharose hydrophobic matrices were evaluated by manipulating the ionic strength of binding and elution steps. Alternatively, immobilized metal affinity chromatography packed with nickel or cobalt were also studied in the isolation of rhSTEAP1-His6 from lysate extracts. Overall, the Phenyl-Sepharose and Nickel-based resins provided the desired selectivity for rhSTEAP1-His6 capture from NP-40 and DM detergent-solubilized K. pastoris extracts, respectively. After a polishing step using the anion-exchanger Q-Sepharose, a highly pure, fully solubilized, and immunoreactive 35 kDa rhSTEAP1-His6 fraction was obtained. Altogether, the established reproducible strategy for the purification of rhSTEAP1-His6 paves the way to gather additional insights on structural, thermal, and environmental stability characterization significantly contributing for the elucidation of the functional role and oncogenic behavior of the STEAP1 in prostate cancer microenvironment.

Abstract B013: STEAP1 facilitates iron transport in ewing sarcoma to support mitochondrial activity

Abstract Ewing sarcoma (EwS) is a highly aggressive bone-associated tumor of children and young adults with strong propensity to progress and dismal outcome for patients with advanced stages of the disease. EwS is defined by a pathognomonic recurrent potent transcription factor, in 85-90% of cases EWSR1-FLI1. One of the previously described transcriptional targets of EWSR1-FLI1 is six-transmembrane epithelial antigen of the prostate 1 (STEAP1). STEAP1 is a member of the STEAP membrane-bound protein family involved in reduction of iron and copper which is a crucial step for metal transport and overexpressed in various malignancies. However, a precise functional role of STEAP1 in cancers including EwS remains elusive. EwS cell lines with knockout (KO) or knockdown (KD) of STEAP1 were created to perform functional studies for elucidating the functions of STEAP1 in EwS, including transient metal measurements. Additionally, the measurement of functional mitochondrial activity was performed by an extracellular flux analyzer. The activity of the mitochondrial electron transport chain complexes was measured by blue native PAGE. We showed that STEAP1 functions as a metalloreductase and STEAP1 KO cells have lower intracellular iron levels. Furthermore, we discovered that STEAP1 KO cells have significantly lower levels of the mitochondrial labile iron pool. Consequently, EwS cells with STEAP1 KO demonstrated impaired mitochondrial respiration and increased glycolysis rates. Additionally, the functional activity of iron-sulfur containing proteins and the the assembly of subunits of the mitochondrial electron transport chain complexes were decreased. This study is the first to demonstrate in vitro involvement of STEAP1 in transitional metal homeostasis and mitochondrial activity. These discoveries unveil alternative therapeutic strategies for EwS patients such as using compounds that promote an iron-dependent form of cell death, ferroptosis, or drugs that decrease metabolic adaptability. Citation Format: Taras Shyp, Rouhollah Mousavizadeh, Gian Luca Negri, Hai-Feng Zhang, Michael Lizardo, Poul Sorensen. STEAP1 facilitates iron transport in ewing sarcoma to support mitochondrial activity [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B013.

Broiler responses to copper levels and sources: growth, tissue mineral content, antioxidant status and mRNA expression of genes involved in lipid and protein metabolism

BackgroundFive hundred 8-d old male broilers Cobb500 were randomly allotted into 10 treatments in factorial arrangement with 5 Cu levels (0, 4, 8, 12, and 16 mg/kg), and 2 sources (Cu proteinate, CuPro and Cu sulphate, CuSO4.5H2O) for a 10-d-experiment.ResultsFeed conversion ratio (FCR) was better (P < 0.05) in CuPro fed chicks compared with CuSO4.5H2O group. Average daily feed intake (ADFI) decreased linearly (P < 0.05) as dietary Cu increased. A quadratic response (P < 0.05) to Cu levels was found for FCR, being optimized at 9.87 and 8.84 mg Cu/kg in CuPro and CuSO4.5H2O diets, respectively. Copper supplementation linearly increased liver Cu content (P < 0.05) and tended to linearly increase (P = 0.07) phosphorus (P) and copper in tibia. Manganese and zinc were higher (P < 0.05) in tibia of CuPro fed birds. Broilers fed CuPro exhibited lower liver iron (P < 0.05) content, lower activities of Cu, Zn superoxide dismutase (CuZnSOD) in breast muscle and liver, and glutathione peroxidase in liver. Glutathione peroxidase reduced linearly (P < 0.05) with CuPro levels and increased linearly (P < 0.05) with CuSO4.5H2O levels and were lower (P < 0.05) in all CuPro levels in breast muscle. Breast muscle malondialdehyde concentration tended to be higher (P = 0.08) in broilers fed CuSO4.5H2O. Copper levels linearly increased (P < 0.05) metallothionein (MT) and malate dehydrogenase (MDH) expression in liver, and six-transmembrane epithelial antigen of the prostate-1 (STEAP-1) in the intestine. Copper elicited a quadratic response (P < 0.050) in AKT-1 and mammalian target of rapamycin (mTOR) in breast muscle, CuZnSOD in liver and antioxidant 1 copper chaperone (ATOX 1) in intestine. Broilers fed CuPro exhibited higher mRNA expression of mTOR in muscle breast and lower CuZnSOD in liver and ATOX 1 in intestine. Interaction (P < 0.05) between levels and sources was found in mRNA expression for GSK-3β, MT, and CuZnSOD in breast muscle, FAS and LPL in liver and MT and CTR1 in intestine.ConclusionsCuPro showed beneficial effects on feed conversion and bone mineralization. Organic and inorganic Cu requirements are 9.87 and 8.84 mg Cu/kg, respectively.

The Prognostic Value and Immunological Role of STEAP1 in Pan-Cancer: A Result of Data-Based Analysis.

Purpose This study is aimed at systematically analyzing the expression, function, and prognostic value of six transmembrane epithelial antigen of the prostate 1 (STEAP1) in various cancers. Methods The expressions of STEAP1 between normal and tumor tissues were analyzed using TCGA and GTEx. Clinicopathologic data was collected from GEPIA and TCGA. Prognostic analysis was conducted by Cox proportional hazard regression and Kaplan-Meier survival. DNA methylation, mutation features, and molecular subtypes of cancers were also investigated. The top-100 coexpressed genes with STEAP1 were involved in functional enrichment analysis. ESTIMATE algorithm was used to analyze the correlation between STEAP1 and immunity value. The relationships of STEAP1 and biomarkers including tumor mutational burden (TMB), microsatellite instability (MSI), and stemness score as well as chemosensitivity were also illustrated. Results Among 33 cancers, STEAP1 was overexpressed in 19 cancers such as cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), colon adenocarcinoma, and lymphoid neoplasm diffuse large B cell lymphoma while was downregulated in 5 cancers such as adrenocortical carcinoma, breast invasive carcinoma (BRCA), and kidney chromophobe renal cell carcinoma. STEAP1 has significant prognostic relationships in multiple cancers. 15 cancers exhibited differences of DNA methylation including bladder urothelial carcinoma, BRCA, and CESC. STEAP1 expression was positively correlated to immune molecules especially in thyroid carcinoma and negatively especially in uveal melanoma. STEAP1 was associated with TMB and MSI in certain cancers. In addition, STEAP1 was connected with increased chemosensitivity of drugs such as trametinib and pimasertib. Conclusions STEAP1 was an underlying target for prognostic prediction in different cancer types and a potential biomarker of TMB, MSI, tumor microenvironment, and chemosensitivity.

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.

Six-transmembrane epithelial antigen of the prostate 1 accelerates cell proliferation by targeting c-Myc in liver cancer cells.

Six-transmembrane epithelial antigen of the prostate 1 (STEAP1) has emerged as an ideal target in cancer therapeutics. However, the functions of STEAP1 in liver cancer remain unexplored. The current study aimed to characterize the biological roles of STEAP1 in liver cancer. STEAP1 expression was upregulated in tumor tissues, and high STEAP1 expression was associated with poor clinical outcomes in patients with liver cancer, according to several publicly available datasets. STEAP1 silencing using small interfering RNA inhibited cell proliferation and was accompanied by G1 arrest induced by the suppression of cyclin D1 and the promotion of p27. STEAP1 silencing suppressed c-Myc expression, which was identified as a component in STEAP1 signal transduction by mining publicly available datasets and was then confirmed by PCR array. In conclusion, the knockdown of STEAP1 in liver cancer cell lines led to inhibition of cell proliferation involving G1 arrest by suppressing c-Myc. The present study provides a preclinical concept for STEAP1 as a druggable target in liver cancer.

Identification of a New Transcriptional Co-Regulator of STEAP1 in Ewing's Sarcoma.

Ewing’s sarcoma (ES) is caused by a chromosomal translocation leading to the formation of the fused EWSFLI1 gene, which codes for an aberrant transcription factor EWSFLI1. The transcriptional targets of EWSFLI1 have been viewed as promising and novel drug targets in the treatment of ES. One such target is six transmembrane epithelial antigen of the prostate 1 (STEAP1), a transmembrane protein that is upregulated by EWSFLI1 in ES. STEAP1 is a hallmark of tumor invasiveness and an indicator of tumor responsiveness to therapy. EWSFLI1 binds to the STEAP1 promoter region, but the mechanism of action by which it upregulates STEAP1 expression in ES is not entirely understood. Upon analysis of the STEAP1 promoter, we predicted two binding sites for NKX2.2, another crucial transcription factor involved in ES pathogenesis. We confirmed the interaction of NKX2.2 with the STEAP1 promoter using chromatin immunoprecipitation (ChIP) analysis. We used single-molecule RNA imaging, biochemical, and genetic studies to identify the novel role of NKX2.2 in regulating STEAP1 expression in ES. Our results show that NKX2.2 is a co-regulator of STEAP1 expression and functions by interacting with the STEAP1 promoter at sites proximal to the reported EWSFLI1 sites. The co-operative interaction of NKX2.2 with EWSFLI1 in regulating STEAP1 holds potential as a new target for therapeutic interventions for ES.

Phase I study of AMG 509, a STEAP1 x CD3 T-cell recruiting XmAb 2+1 immune therapy, in patients with metastatic castration-resistant prostate cancer (mCRPC).

TPS183 Background: Six transmembrane epithelial antigen of the prostate 1 (STEAP1) is a cell surface antigen that is highly expressed in prostate cancer. AMG 509 is a potent bispecific XmAb 2+1 immune therapy designed to direct T effector cells to STEAP1-expressing cells. AMG 509 contains two identical humanized anti-STEAP1 Fab domains that bind STEAP1-expressing cells, an anti-CD3 scFv domain that binds T cells, and an Fc domain, engineered to lack effector function, that extends serum half-life. In preclinical studies, AMG 509 induced potent and specific T-cell-mediated lysis of STEAP1-expressing cancer models. Methods: This open-label, phase 1, first-in-human study will evaluate the safety, tolerability, pharmacokinetics (PK), and efficacy of AMG 509 in patients with relapsed/refractory mCRPC. The dose exploration phase (n=40) will estimate the maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D) using a Bayesian logistic regression model. The dose expansion phase (n=30) will confirm safety, PK, and pharmacodynamics at the MTD or RP2D and collect further safety, efficacy, and biomarker data. Efficacy will be assessed by prostate-specific antigen response, circulating tumor cell response, and objective tumor response per RECIST 1.1 with Prostate Cancer Working Group 3 modifications. Key inclusion criteria: men ≥18 years with histologically/cytologically confirmed mCRPC who are refractory to novel hormonal therapy (e.g., abiraterone and/or enzalutamide) and have failed 1–2 taxane regimens or are medically unsuitable for or have refused taxanes; ongoing castration with total serum testosterone ≤50 ng/dL; evidence of progressive disease; ECOG performance status 0–1; life expectancy ≥3 months; and adequate hematologic, renal, hepatic, and cardiac function. In the dose exploration phase, novel antiandrogen therapy must have been given in the metastatic setting. Key exclusion criteria: pure small cell or neuroendocrine carcinoma of the prostate; untreated CNS metastases or leptomeningeal disease; any anticancer therapy or immunotherapy, radiation therapy, or major surgery &lt;4 weeks from first dose; history of or current autoimmune disease or any disease requiring immunosuppressive therapy (≤10 mg/d prednisone permitted); prior STEAP1-targeted therapy; infection requiring IV antimicrobials &lt;7 days from first dose. The study opened in January 2020 and is recruiting patients. ClinicalTrials.gov: NCT04221542. 2020 American Society of Clinical Oncology, Inc. Reused with permission. This abstract was accepted and previously presented at the 2020 ASCO Annual Meeting. All rights reserved. Clinical trial information: NCT04221542.

Clinical significance of STEAP1 extracellular vesicles in prostate cancer

BackgroundExtracellular 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.MethodsSTEAP1 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).ResultsEvaluation 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.ConclusionsSTEAP1 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.

Abstract DDT02-03: AMG 509: A novel, humanized, half-Life extended, bispecific STEAP1 × CD3 T cell recruiting XmAb® 2+1 antibody

Abstract AMG509, a novel STEAP1 x CD3 T cell-recruiting XmAb® 2+1 bispecific immune therapy for the treatment of prostate cancer and Ewing sarcoma. Metastatic castration resistant prostate cancer (mCRPC) and Ewing sarcoma (EWS) are both diseases with unmet medical needs. Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) is a cell surface antigen that is induced by androgens and highly expressed in prostate cancer. STEAP1 is also highly expressed in EWS, and it is a target of the EWS/FLI1 fusion, the primary oncogenic driver in this pediatric malignancy. AMG 509 is a novel, half-life extended, cynomolgus monkey cross-reactive, STEAP1 x CD3 T cell-recruiting XmAb® 2+1 bispecific antibody designed to treat STEAP1-expressing cancers. AMG 509 contains two identical humanized anti-STEAP1 Fab domains that bind STEAP1-expressing cells, an anti-CD3 scFv domain that binds T cells, and an Fc domain engineered to lack effector function and extend serum half-life. We found that membranous STEAP1 expression, as measured by IHC, was absent from most normal tissues (FDA normal organ tissue array, n = 72) except the prostate epithelium and a subset of lung macrophages. In contrast, we found membranous STEAP1 expression by IHC in 80% of primary prostate cancer tumors (n = 80) and moderate to high expression in 83% of metastatic prostate cancer lesions (n = 181) and 77% of bone metastases (n = 31). In addition, we found STEAP1 expression by IHC in all EWS cell lines (n=13) and xenograft models tested (n=12). AMG 509 bound to recombinant human and cynomolgus monkey CD3ϵ with a KD of 27.6 nM and 25.8 nM, respectively, and to 293T cells transfected with human or cynomolgus monkey STEAP1 with an EC50 of 3.8 nM and 3.1 nM, respectively. AMG 509 triggered potent T cell-redirected lysis of STEAP1-positive cancer cells, with a median EC50 of 18.9 pM across 17 different STEAP1-expressing prostate, EWS, gastric, and melanoma cancer cell lines. AMG 509 was 50-fold more potent in inducing the redirected lysis of C4-2B prostate cancer cells in vitro than an XmAb® molecule with a single anti-STEAP1 Fab domain. AMG 509 was also specific, as it showed no activity against C4-2B cancer cells engineered to lack STEAP1 expression. AMG 509 exhibited hallmarks of T-cell engagement in vitro, including T-cell proliferation and cytokine release. It also induced robust in vivo anti-tumor activity in prostate cancer and EWS xenograft models, with concomitant CD8+ T-cell activation and expansion in tumors. Data from a nonclinical safety study conducted in the cynomolgus monkey suggest that AMG 509 can be administered safely at doses that are predicted to be clinically active. AMG 509 is a potent and specific first-in-class T cell-recruiting antibody for the treatment of STEAP1-positive malignancies. We are currently evaluating the safety, tolerability, pharmacokinetics, and efficacy of AMG 509 in a phase 1, first-in-human study in patients with mCRPC (NCT04221542). Citation Format: Olivier Nolan-Stevaux. AMG 509: A novel, humanized, half-Life extended, bispecific STEAP1 × CD3 T cell recruiting XmAb® 2+1 antibody [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr DDT02-03.

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.