Integrative molecular analyses define correlates of high B7-H3 expression in metastatic castrate-resistant prostate cancer

Isolation of Plasma Extracellular Vesicles for High-Depth Analysis of Proteomic Biomarkers in Metastatic Castration-Resistant Prostate Cancer Patients

Introduction: Prostate cancer treatment has been revolutionized by targeted therapies, including PARP inhibitors, checkpoint immunotherapies, and PSMA-targeted radiotherapies. Despite such advancements, accurate patient stratification remains a challenge, with current methods relying on genomic markers, tissue staining, and imaging. Extracellular vesicle (EV)-derived proteins offer a novel non-invasive alternative for biomarker discovery, holding promise for improving treatment precision. However, the characterization of plasma-derived EVs in prostate cancer patients remains largely unexplored. Methods: We conducted proteomic analyses on EVs isolated from plasma in 27 metastatic castration-resistant prostate cancer (mCRPC) patients. EVs were purified using ultracentrifugation and analyzed via mass spectrometry. Proteomic data were correlated with clinical markers such as serum prostate-specific antigen (PSA) and bone lesion counts. Statistical significance was assessed using Mann-Whitney t-tests and Spearman correlation. Results: The median age of patients was 74 (range: 44-94) years. At the time of blood collection, the median PSA level was 70 (range: 0.5-1000) ng/mL. All patients had bone metastasis. A total of 5213 proteins were detected, including EV-related proteins (CD9, CD81, CD63, FLOT1, TSG101) and cancer-related proteins (PSMA, B7-H3, PD-L1). Proteomic profiling of plasma EVs revealed a significant correlation between specific EV-derived proteins and clinical prognostic markers. B7-H3, LAT1, and SLC29A1 showed a strong association with serum PSA levels and number of bone lesions, indicating potential for these proteins to serve as biomarkers of disease burden and therapy response. Conclusions: Our findings demonstrate the potential of EV-based proteomics for identifying biomarkers in mCRPC patients. Proteins such as B7-H3 and LAT1 could guide precision oncology approaches, improving patient stratification. Future research incorporating outcomes data and EV subpopulation analysis is needed to establish clinical relevance.

Current uses and resistance mechanisms of enzalutamide in prostate cancer treatment

INTRODUCTION

Prostate cancer continues to be a major cause of morbidity and mortality for men worldwide. Enzalutamide, a second-generation non-steroidal antiandrogen that blocks androgen receptor (AR) transcriptional activity, is a treatment for biochemically recurrent, metastatic, castration-sensitive, and castration-resistant tumors. Unfortunately, most patients ultimately develop resistance to enzalutamide, making long-term treatment with this agent challenging.

AREAS COVERED

We performed a literature search of PubMed without date restrictions to investigate the literature surrounding enzalutamide and discuss the current uses of enzalutamide, proposed mechanisms driving resistance, and summarize current efforts to mitigate this resistance.

EXPERT OPINION

Enzalutamide is an effective prostate cancer therapy that is currently used in biochemically recurrent and metastatic disease and for both castration-sensitive and castration-resistant tumors. Unfortunately, resistance to enzalutamide occurs in each of these scenarios. In the clinical setting, enzalutamide-resistant tumors are either AR-driven or AR-indifferent. AR-dependent resistance mechanisms include genomic or epigenomic events that result in enhanced AR signaling. Tumors that do not require AR signaling instead may depend on alternative oncogenic pathways. There are numerous strategies to mitigate enzalutamide resistance, including concurrent use of PARP inhibitors or immune therapies. Additional work is required to uncover novel approaches to treat patients in the enzalutamide-resistant setting.

Androgen production, uptake, and conversion (APUC) genes define prostate cancer patients with distinct clinical outcomes

BACKGROUNDProstate cancer (PC) is driven by aberrant signaling of the androgen receptor (AR) or its ligands, and androgen deprivation therapies (ADTs) are a cornerstone of treatment. ADT responsiveness may be associated with germline changes in genes that regulate androgen production, uptake, and conversion (APUC).METHODSWe analyzed whole-exome sequencing (WES) and whole-transcriptome sequencing (WTS) data from prostate tissues (SU2C/PCF, TCGA, GETx). We also interrogated the Caris Precision Oncology Alliance (POA) DNA (592-gene/whole exome) and RNA (whole transcriptome) next-generation sequencing databases. Algorithm for Linking Activity Networks (ALAN) was used to quantify all pairwise gene-to-gene associations. Real-world overall survival was determined from insurance claims data using Kaplan-Meier estimates.RESULTSSix APUC genes (HSD3B1, HSD3B2, CYP3A43, CYP11A1, CYP11B1, CYP17A1) exhibited coalescent gene behavior in a cohort of metastatic tumors (n = 208). In the Caris POA dataset, the 6 APUC genes (APUC-6) exhibited robust clustering in primary prostate (n = 4,490) and metastatic (n = 2,593) biopsies. Surprisingly, tumors with elevated APUC-6 expression had statically lower expression of AR, AR-V7, and AR signaling scores, suggesting ligand-driven disease biology. APUC-6 genes instead associated with the expression of alternative steroid hormone receptors, ESR1/2 and PGR. We used RNA expression of AR or APUC-6 genes to define 2 subgroups of tumors with differential association with hallmark pathways and cell surface targets.CONCLUSIONSThe APUC-6-high/AR-low tumors represented a subgroup of patients with good clinical outcomes, in contrast with the AR-high or neuroendocrine PCs. Altogether, measuring the aggregate expression of APUC-6 genes in current genomic tests identifies PCs that are ligand (rather than AR) driven and require distinct therapeutic strategies.FUNDINGNCI/NIH 1R37CA288972-01, NCI Cancer Center Support P30 CA077598, DOD W81XWH-22-2-0025, R01 CA249279.

CD276 Promotes an Inhibitory Tumor Microenvironment in Hepatocellular Carcinoma and is Associated with Poor Prognosis

Background

CD276 is an emerging immune checkpoint molecule that has been implicated in various cancers. However, its specific role in hepatocellular carcinoma (HCC) remains unclear. This study examined the impact of CD276 on patient prognosis and the tumor microenvironment (TME).

Methods

The Cancer Genome Atlas (TCGA) database was utilized to evaluate CD276 expression in HCC and the association between CD276 and immune indicators was also analyzed. The signaling pathways correlated with CD276 expression were identified by gene set enrichment analysis (GSEA). Different algorithms were used to assess immune cell infiltration. The effect of CD276 knockdown on HCC cell phenotypes and its relationship with macrophage polarization was examined using the cell counting kit 8 (CCK-8) assay and co-culture system.

Results

CD276 was upregulated in HCC and associated with unfavorable clinical outcomes. Hgh CD276 expression was associated with enrichment of the G2/M checkpoint, E2F targets, and mitotic spindles. CD276 expression was correlated with the infiltration of immune cells, including high level of tumor-associated macrophages and low levels of CD8+ T cells. Knockdown of CD276 decreased HCC cell proliferation and increased apoptosis. CD276 silencing in HCC cells and co-culture with THP-1-derived macrophages had a regulatory effect on macrophage polarization and macrophage-mediated cell proliferation and migration.

Conclusion

CD276 expression in HCC is associated with unfavorable clinical outcomes and may contribute to the development of an immunosuppressive microenvironment. Specifically, CD276 was associated with alterations in immune cell infiltration, immune marker expression, and macrophage polarization during HCC progression, suggesting its potential as a prognostic indicator and promising target for immunotherapeutic intervention in HCC.

B7-H3: a robust target for immunotherapy in prostate cancer

B7-H3, an immune checkpoint glycoprotein, facilitates immune evasion and the promotion of tumors and is highly expressed on the surface of prostate cancer (PCa) cells, which makes it a feasible and robust candidate for immunotherapies against advanced prostate cancer. Here, we summarize and discuss recent findings on the suitability of targeting B7-H3 in PCa treatment.

Pan-Cancer Interrogation of B7-H3 (CD276) as an Actionable Therapeutic Target Across Human Malignancies

B7-H3 (CD276) is a transmembrane glycoprotein of the B7 immune checkpoint superfamily that has emerged as a promising therapeutic target. To better understand the applicability of B7-H3-directed therapies, we analyzed 156,791 samples comprising 50 cancer types to interrogate the clinical, genomic, transcriptomic, and immunologic correlates of B7-H3 mRNA expression. DNA (592-gene/whole-exome) and RNA (whole-transcriptome) sequencing was performed from samples submitted to Caris Life Sciences. B7-H3 high versus low expression was based on top and bottom quartiles for each cancer type. Patients' overall survival was determined from insurance claims data. Pathway analysis was performed using gene set enrichment analyses. Immune cell fractions were inferred using quanTIseq. B7-H3 is expressed across several human malignancies including prostate, pancreatic, ovarian, and lung cancers. High B7-H3 expression is associated with differences in overall survival, possibly indicating a prognostic role of B7-H3 for some cancers. When examining molecular features across all cancer types, we did not identify recurrent associations between B7-H3 expression and genetic alterations in TP53, RB1, and KRAS. However, we find consistent enrichment of epithelial-to-mesenchymal transition, Wnt, TGFβ, and Notch signaling pathways. In addition, tumors with high B7-H3 expression are associated with greater proportions of M1 macrophages, but lower fractions of CD8+ T cells. We have begun to define the genomic, transcriptomic, clinical, and immunologic features associated with B7-H3 expression in 50 cancer types. We report novel clinical and molecular features of B7-H3-high tumors which may inform how current B7-H3 therapeutics should be deployed and prioritized.

SIGNIFICANCE

B7-H3-targeting therapeutics have shown promising results in initial clinical trials. In this pan-cancer analysis of B7-H3 mRNA expression, we found that B7-H3 exhibits robust expression in many common cancer types. These results may inform further development of B7-H3-targeting therapeutics and may guide clinical decisions for patients with limited treatment options.

The Current Therapeutic Landscape for Metastatic Prostate Cancer

In 2024, there will be an estimated 1,466,718 cases of prostate cancer (PC) diagnosed globally, of which 299,010 cases are estimated to be from the US. The typical clinical approach for PC involves routine screening, diagnosis, and standard lines of treatment. However, not all patients respond to therapy and are subsequently diagnosed with treatment emergent neuroendocrine prostate cancer (NEPC). There are currently no approved treatments for this form of aggressive PC. In this review, a compilation of the clinical trials regimen to treat late-stage NEPC using novel targets and/or a combination approach is presented. The novel targets assessed include DLL3, EZH2, B7-H3, Aurora-kinase-A (AURKA), receptor tyrosine kinases, PD-L1, and PD-1. Among these, the trials administering drugs Alisertib or Cabozantinib, which target AURKA or receptor tyrosine kinases, respectively, appear to have promising results. The least effective trials appear to be ones that target the immune checkpoint pathways PD-1/PD-L1. Many promising clinical trials are currently in progress. Consequently, the landscape of successful treatment regimens for NEPC is extremely limited. These trial results and the literature on the topic emphasize the need for new preventative measures, diagnostics, disease specific biomarkers, and a thorough clinical understanding of NEPC.

Pembrolizumab for metastatic castration-resistant prostate cancer: trials and tribulations

INTRODUCTION

Immunotherapies have revolutionized the management of various malignancies but have only recently been evaluated systematically in prostate cancer. Pembrolizumab, a programmed-death 1 (PD-1) blocking antibody, has been utilized in a small subset of prostate cancer patients with mismatch repair deficiency/microsatellite instability, but has now been assessed in broader populations of metastatic prostate cancer patients.

AREAS COVERED

The results of four pembrolizumab-based phase III clinical trials for metastatic castration-resistant prostate cancer (mCRPC) and metastatic hormone-sensitive prostate cancer (mHSPC) patients, including KEYNOTE-641, KEYNOTE-921, KEYNOTE-991, and KEYLYNK-010 are summarized. Programmed death-ligand 1 (PD-L1) expression, the efficacy of pembrolizumab in prostate cancer patients with certain molecular defects, and emerging pembrolizumab-based therapeutic combinations are also reviewed.

EXPERT OPINION

Pembrolizumab has not benefitted unselected metastatic prostate cancer patients when combined with chemotherapy, next-generation hormonal agents (NHA), or poly(ADP-ribose) polymerase inhibitors (PARPi). PD-L1 positivity does not predict the response to pembrolizumab in this disease. A small number of responding patients can likely be explained by rare genetic and molecular defects, and more innovative combination strategies are needed to improve outcomes in prostate cancer patients who are not sensitive to pembrolizumab. Emphasis should be placed on developing additional or alternative immuno-oncology approaches beyond classical immune checkpoint inhibition.

Mitogen-Activated Protein Kinase and Nuclear Hormone Receptor Crosstalk in Cancer Immunotherapy

The three major MAP-kinase (MAPK) pathways, ERK1/2, p38 and JNK/SAPK, are upstream regulators of the nuclear "hormone" receptor superfamily (NHRSF), with a prime example given by the estrogen receptor in breast cancer. These ligand-activated transcription factors exert non-genomic and genomic functions, where they are either post-translationally modified by phosphorylation or directly interact with components of the MAPK pathways, events that govern their transcriptional activity towards target genes involved in cell differentiation, proliferation, metabolism and host immunity. This molecular crosstalk takes place not only in normal epithelial or tumor cells, but also in a plethora of immune cells from the adaptive and innate immune system in the tumor-stroma tissue microenvironment. Thus, the drugability of both the MAPK and the NHRSF pathways suggests potential for intervention therapies, especially for cancer immunotherapy. This review summarizes the existing literature covering the expression and function of NHRSF subclasses in human tumors, both solid and leukemias, and their effects in combination with current clinically approved therapeutics against immune checkpoint molecules (e.g., PD1).

B7-H3 confers stemness characteristics to gastric cancer cells by promoting glutathione metabolism through AKT/pAKT/Nrf2 pathway

BACKGROUND

Cancer stem-like cells (CSCs) are a small subset of cells in tumors that exhibit self-renewal and differentiation properties. CSCs play a vital role in tumor formation, progression, relapse, and therapeutic resistance. B7-H3, an immunoregulatory protein, has many protumor functions. However, little is known about the mechanism underlying the role of B7-H3 in regulating gastric cancer (GC) stemness. Our study aimed to explore the impacts of B7-H3 on GC stemness and its underlying mechanism.

METHODS

GC stemness influenced by B7-H3 was detected both in vitro and in vivo . The expression of stemness-related markers was examined by reverse transcription quantitative polymerase chain reaction, Western blotting, and flow cytometry. Sphere formation assay was used to detect the sphere-forming ability. The underlying regulatory mechanism of B7-H3 on the stemness of GC was investigated by mass spectrometry and subsequent validation experiments. The signaling pathway (Protein kinase B [Akt]/Nuclear factor erythroid 2-related factor 2 [Nrf2] pathway) of B7-H3 on the regulation of glutathione (GSH) metabolism was examined by Western blotting assay. Multi-color immunohistochemistry (mIHC) was used to detect the expression of B7-H3, cluster of differentiation 44 (CD44), and Nrf2 on human GC tissues. Student's t -test was used to compare the difference between two groups. Pearson correlation analysis was used to analyze the relationship between two molecules. The Kaplan-Meier method was used for survival analysis.

RESULTS

B7-H3 knockdown suppressed the stemness of GC cells both in vitro and in vivo . Mass spectrometric analysis showed the downregulation of GSH metabolism in short hairpin B7-H3 GC cells, which was further confirmed by the experimental results. Meanwhile, stemness characteristics in B7-H3 overexpressing cells were suppressed after the inhibition of GSH metabolism. Furthermore, Western blotting suggested that B7-H3-induced activation of GSH metabolism occurred through the AKT/Nrf2 pathway, and inhibition of AKT signaling pathway could suppress not only GSH metabolism but also GC stemness. mIHC showed that B7-H3 was highly expressed in GC tissues and was positively correlated with the expression of CD44 and Nrf2. Importantly, GC patients with high expression of B7-H3, CD44, and Nrf2 had worse prognosis ( P = 0.02).

CONCLUSIONS

B7-H3 has a regulatory effect on GC stemness and the regulatory effect is achieved through the AKT/Nrf2/GSH pathway. Inhibiting B7-H3 expression may be a new therapeutic strategy against GC.

A role for androgen receptor variant 7 in sensitivity to therapy: Involvement of IGFBP-2 and FOXA1

Prostate cancer (PCa) is one of the leading causes of cancer-related deaths in men. Localised PCa can be treated effectively, but most patients relapse/progress to more aggressive disease. One possible mechanism underlying this progression is alternative splicing of the androgen receptor, with AR variant 7(ARV7) considered to play a major role. Using viability assays, we confirmed that ARV7-positive PCa cells were less sensitive to treatment with cabazitaxel and an anti-androgen-enzalutamide. Also, using live-holographic imaging, we showed that PCa cells with ARV7 exhibited an increased rate of cell division, proliferation, and motility, which could potentially contribute to a more aggressive phenotype. Furthermore, protein analysis demonstrated that ARV7 knock-down was associated with a decrease in insulin-like growth factor-2 (IGFBP-2) and forkhead box protein A1(FOXA1). This correlation was confirmed in-vivo using PCa tissue samples. Spearman rank correlation analysis showed significant positive associations between ARV7 and IGFBP-2 or FOXA1 in tissue from patients with PCa. This association was not present with the AR. These data suggest an interplay of FOXA1 and IGFBP-2 with ARV7-mediated acquisition of an aggressive prostate cancer phenotype.

Novel therapies for metastatic prostate cancer

INTRODUCTION

Patients with metastatic prostate cancer, especially in the castrate-resistant setting, have a poor prognosis. Many agents have been approved for metastatic prostate cancer, such as androgen receptor pathway inhibitors, taxane-based chemotherapy, radiopharmaceuticals, and immunotherapy. However, prostate cancer remains the leading cause of cancer deaths in nonsmoking men. Fortunately, many more novel agents are under investigation.

AREAS COVERED

We provide an overview of the broad group of novel therapies for metastatic prostate cancer, with an emphasis on active and recruiting clinical trials that have been recently published and/or presented at national or international meetings.

EXPERT OPINION

The future for patients with metastatic prostate cancer is promising, with further development of novel therapies such as radiopharmaceuticals. Based on a growing understanding of prostate cancer biology, novel agents are being designed to overcome resistance to approved therapies. There are many trials using novel agents either as monotherapy or in combination with already approved agents with potential to further improve outcomes for men with advanced prostate cancer.

B7-H3 immunoregulatory roles in cancer

B7 homolog 3 (B7-H3, also called CD276) is a checkpoint of B7 family that is aberrantly and consistently expressed in several human cancers, and its overexpression correlates with weak prognosis. B7-H3 is expressed on a number of cells, and it acts as a driver of immune evasion. This is mediated through hampering T cell infiltration and promoting exhaustion of CD8⁺ T cells. Increased B7-H3 activity also promotes macrophage polarity toward pro-tumor type 2 (M2) phenotype. In addition, high B7-H3 activity induces aberrant angiogenesis to promote hypoxia, a result of which is resistance to common immune checkpoint inhibitor (ICI) therapy. This is mediated through the impact of hypoxia on dampening CD8⁺ T cell recruitment into tumor area. The immunosuppressive property of B7-H3 offers insights into targeting this checkpoint as a desired approach in cancer immunotherapy. B7-H3 can be a target in blocking monoclonal antibodies (mAbs), combination therapies, chimeric antigen receptor-modified T (CAR-T) cells and bispecific antibodies.

Immune checkpoint B7-H3 is a therapeutic vulnerability in prostate cancer harboring PTEN and TP53 deficiencies

Checkpoint immunotherapy has yielded meaningful responses across many cancers but has shown modest efficacy in advanced prostate cancer. B7 homolog 3 protein (B7-H3/CD276) is an immune checkpoint molecule and has emerged as a promising therapeutic target. However, much remains to be understood regarding B7-H3's role in cancer progression, predictive biomarkers for B7-H3-targeted therapy, and combinatorial strategies. Our multi-omics analyses identified B7-H3 as one of the most abundant immune checkpoints in prostate tumors containing PTEN and TP53 genetic inactivation. Here, we sought in vivo genetic evidence for, and mechanistic understanding of, the role of B7-H3 in PTEN/TP53-deficient prostate cancer. We found that loss of PTEN and TP53 induced B7-H3 expression by activating transcriptional factor Sp1. Prostate-specific deletion of Cd276 resulted in delayed tumor progression and reversed the suppression of tumor-infiltrating T cells and NK cells in Pten/Trp53 genetically engineered mouse models. Furthermore, we tested the efficacy of the B7-H3 inhibitor in preclinical models of castration-resistant prostate cancer (CRPC). We demonstrated that enriched regulatory T cells and elevated programmed cell death ligand 1 (PD-L1) in myeloid cells hinder the therapeutic efficacy of B7-H3 inhibition in prostate tumors. Last, we showed that B7-H3 inhibition combined with blockade of PD-L1 or cytotoxic T lymphocyte-associated protein 4 (CTLA-4) achieved durable antitumor effects and had curative potential in a PTEN/TP53-deficient CRPC model. Given that B7-H3-targeted therapies have been evaluated in early clinical trials, our studies provide insights into the potential of biomarker-driven combinatorial immunotherapy targeting B7-H3 in prostate cancer, among other malignancies.

Metastatic Castration-Resistant Prostate Cancer, Immune Checkpoint Inhibitors, and Beyond

The therapeutic landscape of several genitourinary malignancies has been revolutionized by the development of immune checkpoint inhibitors (ICIs); however, the utility of immunotherapies in prostate cancer has been limited, partly due to the immunologically "cold" tumor terrain of prostate cancer. As of today, pembrolizumab is the only immune checkpoint inhibitor approved for the treatment of metastatic castration resistant prostate cancer (mCRPC) in a select group of patients with high microsatellite instability (MSI-H), deficient mismatch repair (dMMR), or high tumor mutational burden (TMB). Looking ahead, several combinatorial approaches with ICIs involving radioligands, radiotherapy, PARP inhibitors, interleukin inhibitors, and cancer vaccines are exploring a potential synergistic effect. Furthermore, B7-H3 is an alternative checkpoint that may hold promise in adding to the treatment landscape of mCRPC. This review aims to summarize previous monotherapy and combination therapy trials of ICIs as well as novel immunotherapy combination therapeutic strategies and treatment targets in mCRPC.