Jennifer Munkley

Immunotherapies have shown limited efficacy in prostate cancer, largely due to its immunosuppressive tumour microenvironment. Hypersialylation contributes to immune evasion by engaging sialic acid-binding immunoglobulin-like lectins (Siglecs) on immune cells, forming glyco-immune checkpoints. Although this pathway represents a promising therapeutic target, the distribution of Siglec ligands across diverse prostate cancer phenotypes remains poorly understood. Here, we utilised high-affinity engineered sialoglycan-binding reagents (HYDRA) to perform immunohistochemical profiling of Siglec-7/9 ligands across a panel of 40 LuCaP patient-derived xenograft (PDX) models. Ligand expression was evaluated in relation to AR status and neuroendocrine phenotype. To determine the impact of androgen deprivation on the tumour glycome, ligand expression was compared between matched PDX lines grown in intact and castrated mice. Our findings reveal widespread but heterogeneous expression of Siglec-7/9 ligands across the LuCaP cohort. Expression levels were comparable between AR-positive adenocarcinoma models and AR-negative neuroendocrine variants, demonstrating that this glyco-immune checkpoint is maintained across distinct prostate cancer lineages. Under castration conditions, glycan remodelling occurred in a model-dependent manner. To evaluate these therapeutic dynamics in human disease, individual trajectory analysis of paired clinical specimens from the Movember GAP1-UTMA cohort was performed, revealing patient-specific responses that phenocopy the model-dependent glycan remodelling observed across the LuCaP lines. These findings support the sialoglycan-Siglec axis as a lineage-independent target and suggest that strategies aimed at disrupting Siglec-mediated immune suppression may be most effective when combined with androgen deprivation therapy to enhance anti-tumour immunity.

Prostate cancer is a leading cause of cancer-related mortality in men, and effective treatment options are limited for advanced and metastatic disease. The sialoglycan immune checkpoint Siglec-15 has emerged as a key mediator of tumour-associated immune suppression in several malignancies; however, its expression and functional role in prostate cancer remain poorly defined. Here, using dual immunofluorescence and immunohistochemistry, we demonstrate that Siglec-15 is expressed by prostate tumour epithelial cells, immunosuppressive macrophage phenotypes, and bone-resorbing osteoclasts within the tumour microenvironment. Mechanistically, we show that direct Siglec-15 receptor crosslinking, either by antibodies or tumour cell-derived conditioned medium, promotes monocyte-to-macrophage differentiation, generating macrophages with immunosuppressive and pathogenic phenotypes. Using therapeutic antibodies, we show that Siglec-15 blockade suppresses supernatant-induced monocyte to macrophage differentiation, allowing for the recovery of CD8⁺ T-cell activation. Furthermore, we reveal that macrophage colony-stimulating factor (M-CSF) driven monocyte-derived macrophage differentiation is partially dependent on Siglec-15 signalling, with Siglec-15 blockade enhancing CD8⁺ T-cell responses. In addition, anti-Siglec-15 treatment suppressed osteoclast differentiation, highlighting a dual role for Siglec-15 in prostate cancer immune suppression and bone remodelling. Consistent with these in vitro findings, therapeutic Siglec-15 blockade significantly reduced subcutaneous tumour growth in a CD8⁺ T-cell-dependent manner and prolonged survival in a mouse model of prostate cancer metastasis. Together, these findings identify Siglec-15 as a central regulator of the prostate cancer glyco-immune axis, linking tumour-associated macrophage immune suppression with osteoclast-mediated bone remodelling, providing a compelling rationale for the clinical development of Siglec-15-targeted therapies for patients with advanced disease.

Background: Prostate cancer is a leading cause of male cancer-related deaths over the age of 50. New treatment options are urgently needed, especially for prostate tumours that have spread to bone. Targeting aberrant sialylation holds substantial potential for the development of new therapeutics but is relatively unexplored in the context of prostate cancer. Methods: Here, using high-affinity Siglec-based sialoglycan-binding reagents (HYDRA) for immunohistochemistry, we quantify tumour sialoglycans in tissues representing the full clinical heterogeneity of prostate cancer. Using immunofluorescence, we profile Siglec receptors in prostate tumours, and using syngeneic mouse models, we evaluate an engineered dual-action sialidase (E-612) as a treatment for prostate cancer bone metastasis. Results: We find that sialoglycans that can engage Siglec-3 (CD33), Siglec-7 and Siglec-9 are upregulated in bone metastatic prostate cancer and show that sialoglycan ligands for Siglec-7 and -9 correlate with poorer patient prognosis. Furthermore, we reveal Siglec receptors and Siglec ligands are co-expressed by immune cells in prostate-derived tumours growing in bone. Indicating the Siglec-sialoglycan axis is clinically actionable in prostate cancer, we show systemic therapy with E-612 can suppress the growth of tumours, increase immune cell infiltration and prolong survival times of mice with bone metastasis. Conclusions: Our findings identify a novel mechanism involving Siglec-engaging sialoglycans in driving the growth of prostate cancer bone metastasis and demonstrate that targeting this axis using an engineered sialidase can impede lethal prostate cancer progression.

Prostate cancer is a common cancer in males and there is an urgent unmet clinical need to identify new therapies for advanced disease. Aberrant glycosylation is a hallmark of prostate cancer and plays a functional role in disease progression. The sialyl‐Tn antigen (sTn) has been widely studied in cancer, yet its involvement in prostate cancer remains relatively unexplored. Here, we utilise a novel anti‐sTn antibody (L2A5) to comprehensively monitor sTn expression levels in clinical prostate cancer tissues encompassing normal, benign, primary, metastatic castration‐resistant prostate cancer (CRPC), and in patient‐derived xenograft (PDX) tissues. We show that while sTn is detected at low or negligible levels in normal prostate tissues, it is expressed in 44% of prostate tumours, and prostate cancer patients with high sTn levels have significantly poorer survival times. Analysis of metastatic therapy‐resistant prostate‐derived tumours growing in the liver and bone shows sTn is expressed in 37.5% of cases. Furthermore, sTn is expressed in nearly half of the PDX models tested and was found to be broadly androgen‐regulated. These findings identify sTn as a potential prognostic biomarker and therapeutic target in prostate cancer and lay the groundwork for the development of sTn‐targeted precision therapies for advanced disease.

Prostate cancer is a common cancer in males and there is an urgent unmet clinical need to improve early diagnosis and identify new treatments for advanced disease. Despite huge progress in understanding changes to the genome and proteome in prostate cancer, there is a relative delay in revealing the full aspects of the prostate cancer glycome and glycoproteome. Glycobiology has been fundamental in recent discoveries in the medical field, including translational cancer research. Glycans functionally contribute to the cancer hallmarks and serve as important diagnostic biomarkers and targets for therapeutic intervention. Changes to glycans are common in prostate cancer and include increased branching of complex N- glycans, changes in sialylation, increased fucosylation, altered PSA glycosylation and the expression of truncated O- glycans. This review discusses the role of glycans in fundamental mechanisms controlling prostate cancer growth, metastasis and immune evasion. Emphasis is placed on discoveries made during the last decade, including new insights provided by N- glycan imaging mass spectrometry (IMS) profiling of prostate cancer tissues, new discoveries into the role of aberrant glycosylation in prostate tumour biology, as well as recent studies investigating glycans, glycosyltransferase enzymes and glycan binding proteins as therapeutic targets.

Prostate cancer is a common cancer in males and there is an urgent unmet clinical need to identify new therapies for advanced disease. Aberrant glycosylation is common in prostate cancer and plays a functional role in disease progression. The sialyl-Tn antigen (sTn) has been widely studied in cancer, yet its involvement in prostate cancer remains relatively unexplored. Here, we utilise a novel anti-sTn antibody (L2A5) to comprehensively monitor sTn expression levels in clinical prostate cancer tissues encompassing normal, benign, primary, metastatic castrate-resistant prostate cancer (CRPC), and patient-derived xenografts (PDXs). We show that while sTn is detected at low or negligible levels in normal prostate tissues, it is expressed in 44% of prostate tumours, and prostate cancer patients with high sTn levels have significantly poorer survival times. Analysis of metastatic therapy resistant prostate-derived tumours growing in liver and bone, shows sTn is expressed in 37.5% of cases. Furthermore, we show sTn is expressed in nearly half of PDXs tested, supporting the use of PDX models as tools for testing anti-sTn therapeutic strategies. These findings identify sTn as potential prognostic biomarker and therapeutic target in prostate cancer and lay the groundwork for the development of sTn-targeted precision therapies for advanced disease.

Prostate cancer is a leading cause of male cancer-related deaths over the age of 50. New treatment options for prostate cancer are urgently needed, especially for tumours that have spread to bone. Aberrant sialylation holds substantial potential for the discovery of new therapeutic targets but has remained relatively unexplored in the context of prostate cancer, primarily due to the lack of reliable reagents for detecting tumour sialoglycans in clinical tissue. Here, we address this knowledge gap using high-affinity Siglec-based sialoglycan-binding reagents (HYDRAs) to quantify tumour sialoglycans in tissues representing the full clinical heterogeneity of prostate tumours. Using HYDRA immunohistochemistry, we show that sialoglycans that can engage Siglec-3, -7, and -9 are upregulated in primary prostate cancer tissue and sialoglycan ligands for Siglec-7 correlate with prostate cancer bone metastasis and poorer patient prognosis. Analysis of prostate-derived tumours growing in bone reveals Siglec receptors are expressed by immune cells in the bone metastatic tumour microenvironment, suggesting that this axis may play a role in immune cell functions in bone metastatic prostate cancer. Indicating this is clinically actionable, an engineered bisialidase (E-612) can effectively strip Siglec ligands from prostate cancer cells and prolong survival times of mice with bone metastasis. Our findings identify a novel mechanism involving Siglec-engaging sialoglycans in driving the growth of prostate cancer bone metastasis and demonstrate how this axis can be targeted to impede lethal prostate cancer progression.

Background: An unmet clinical need requires the discovery of new treatments for men facing advanced prostate cancer. Aberrant glycosylation is a universal feature of cancer cells and plays a key role in tumour growth, immune evasion and metastasis. Alterations in tumour glycosylation are closely associated with prostate cancer progression, making glycans promising therapeutic targets. Fucosyltransferase 8 (FUT8) drives core fucosylation by adding α1,6‐fucose to the innermost GlcNAc residue on N‐glycans. While FUT8 is recognised as a crucial factor in cancer progression, its role in prostate cancer remains poorly understood.Methods & Results: Here, we demonstrate using multiple independent clinical cohorts that FUT8 is upregulated in high grade and metastatic prostate tumours, and in the blood of prostate cancer patients with aggressive disease. Using novel tools, including PhosL lectin immunofluorescence and N‐glycan MALDI mass spectrometry imaging (MALDI‐MSI), we find FUT8 underpins the biosynthesis of malignant core fucosylated N‐glycans in prostate cancer cells and using both in vitro and in vivo models, we find FUT8 promotes prostate tumour growth, cell motility and invasion. Mechanistically we show FUT8 regulates the expression of genes and signalling pathways linked to prostate cancer progression. Furthermore, we find that fucosylation inhibitors can inhibit the activity of FUT8 in prostate cancer to suppress the growth of prostate tumours.Conclusions: Our study cements FUT8‐mediated core fucosylation as an important driver of prostate cancer progression and suggests targeting FUT8 activity for prostate cancer therapy as an exciting area to explore.

Prostate cancer is a lethal solid malignancy and a leading cause of cancer-related deaths in males worldwide. Treatments, including radical prostatectomy, radiotherapy, and hormone therapy, are available and have improved patient survival; however, recurrence remains a huge clinical challenge. Enzalutamide is a second-generation androgen receptor antagonist that is used to treat castrate-resistant prostate cancer. Among patients who initially respond to enzalutamide, virtually all acquire secondary resistance, and an improved understanding of the mechanisms involved is urgently needed. Aberrant glycosylation, and, in particular, alterations to sialylated glycans, have been reported as mediators of therapy resistance in cancer, but a link between tumour-associated glycans and resistance to therapy in prostate cancer has not yet been investigated. Here, using cell line models, we show that prostate cancer cells with acquired resistance to enzalutamide therapy have an upregulation of the sialyltransferase ST6 beta-galactoside alpha-2,6-sialyltransferase 1 (ST6GAL1) and increased levels of α2,6-sialylated N-glycans. Furthermore, using the sialyltransferase inhibitor P-SiaFNEtoc, we discover that acquired resistance to enzalutamide can be partially reversed by combining enzalutamide therapy with sialic acid blockade. Our findings identify a potential role for ST6GAL1-mediated aberrant sialylation in acquired resistance to enzalutamide therapy for prostate cancer and suggest that sialic acid blockade in combination with enzalutamide may represent a novel therapeutic approach in patients with advanced disease. Our study also highlights the potential to bridge the fields of cancer biology and glycobiology to develop novel combination therapies for prostate cancer.