Galectins as new prognostic markers and potential therapeutic targets for advanced prostate cancers

Use of Glycoproteins-Prostate-Specific Membrane Antigen and Galectin-3 as Primary Tumor Markers and Therapeutic Targets in the Management of Metastatic Prostate Cancer

Simple Summary

Prostate specific membrane antigen and galectins are proteins expressed on cell surface and their expression is associated with cancer growth and spread. The goal of this research was to look at the pattern of these two glycoproteins in the human prostate cancer microenvironment. Prostate specific membrane antigen and galectins-1,3 and 8 were the most frequently detected glycoproteins in various phases of this disease. Furthermore, prostate specific membrane antigen and galectin-3 expression are good indicators of tumor aggressiveness, and their combined expression can be valuable tool for prostate cancer diagnosis and treatment in future. Together, our findings reveal a tightly regulated “Prostate specific membrane antigen-galectin-pattern” that accompanies disease in prostate cancer and point to a key role for combined prostate specific membrane antigen and galectin-3 inhibitors in prostate cancer treatment along with standard chemotherapy.

Abstract

Galectins and prostate specific membrane antigen (PSMA) are glycoproteins that are functionally implicated in prostate cancer (CaP). We undertook this study to analyze the “PSMA-galectin pattern” of the human CaP microenvironment with the overarching goal of selecting novel-molecular targets for prognostic and therapeutic purposes. We examined CaP cells and biopsy samples representing different stages of the disease and found that PSMA, Gal-1, Gal-3, and Gal-8 are the most abundantly expressed glycoproteins. In contrast, other galectins such as Gal-2, 4–7, 9–13, were uniformly expressed at lower levels across all cell lines. However, biopsy samples showed markedly higher expression of PSMA, Gal-1 and Gal-3. Independently PSA and Gleason score at diagnosis correlated with the expression of PSMA, Gal-3. Additionally, the combined index of PSMA and Gal-3 expression positively correlated with Gleason score and was a better predictor of tumor aggressiveness. Together, our results recognize a tightly regulated “PSMA-galectin- pattern” that accompanies disease in CaP and highlight a major role for the combined PSMA and Gal-3 inhibitors along with standard chemotherapy for prostate cancer treatment. Inhibitor combination studies show enzalutamide (ENZ), 2-phosphonomethyl pentanedioic acid (2-PMPA), and GB1107 as highly cytotoxic for LNCaP and LNCaP-KD cells, while Docetaxel (DOC) + GB1107 show greater efficacy in PC-3 cells. Overall, 2-PMPA and GB1107 demonstrate synergistic cytotoxic effects with ENZ and DOC in various CaP cell lines.

Galactose specific lectins from prostate tissue with different pathologies: biochemical and cellular studies

BACKGROUND

Galectins-galactose-specific lectins are involved in various types of cell activities, including apoptosis, cell cycle regulation, inflammation and cell transformation. Galectins are implicated in prostate malignat transformation. It is not known yet if prostate glands with different grade of pathologies are expressing different galectins and if these galectins express different effects on the cell viability.

METHODS

Cytosolic galactose-spesific lectin fractions from prostate tissue with different diagnosis were purified by affinity chromatography and analyzed by electrophoresis in polyacrylamide gel electrophoresis with sodium dodecyl sulphate. The lectin effects in a source-dependent maner were studied on cell viability on peripheral lymphocytes by MTT reduction method and on apoptosis by flow cytometry method.

RESULTS

Affinity purified galactose-specific lectins fractions from normal and pathological tissue samples are characterized with different protein composition and they express different effects on cell viability and apoptosis.

CONCLUSION

The effects of cytosolic galactose-specific lectins depend on the source of lectin fraction (glandular tissue disease). We suppose that the released cytosolic galectins from prostatic high grade intraepithelial neoplasia and adenocarcinoma tissue could suppress the immune status of the host patients.

Galectins as Checkpoints of the Immune System in Cancers, Their Clinical Relevance, and Implication in Clinical Trials

Galectins are small proteins with pleiotropic functions, which depend on both their lectin (glycan recognition) and non-lectin (recognition of other biomolecules besides glycans) interactions. Currently, 15 members of this family have been described in mammals, each with its structural and ligand recognition particularities. The galectin/ligand interaction translates into a plethora of biological functions that are particular for each cell/tissue type. In this sense, the cells of the immune system are highly sensitive to the action of these small and essential proteins. While galectins play central roles in tumor progression, they are also excellent negative regulators (checkpoints) of the immune cell functions, participating in the creation of a microenvironment that promotes tumor escape. This review aims to give an updated view on how galectins control the tumor’s immune attack depending on the tumor microenvironment, because determining which galectins are essential and the role they play will help to develop future clinical trials and benefit patients with incurable cancer.

A Peptide Targeting Inflammatory CNS Lesions in the EAE Rat Model of Multiple Sclerosis

Multiple sclerosis is characterized by inflammatory lesions dispersed throughout the central nervous system (CNS) leading to severe neurological handicap. Demyelination, axonal damage, and blood brain barrier alterations are hallmarks of this pathology, whose precise processes are not fully understood. In the experimental autoimmune encephalomyelitis (EAE) rat model that mimics many features of human multiple sclerosis, the phage display strategy was applied to select peptide ligands targeting inflammatory sites in CNS. Due to the large diversity of sequences after phage display selection, a bioinformatics procedure called "PepTeam" designed to identify peptides mimicking naturally occurring proteins was used, with the goal to predict peptides that were not background noise. We identified a circular peptide CLSTASNSC called "Ph48" as an efficient binder of inflammatory regions of EAE CNS sections including small inflammatory lesions of both white and gray matter. Tested on human brain endothelial cells hCMEC/D3, Ph48 was able to bind efficiently when these cells were activated with IL1β to mimic inflammatory conditions. The peptide is therefore a candidate for further analyses of the molecular alterations in inflammatory lesions.

Overexpression of the galectin-3 during tumor progression in prostate cancer and its clinical implications

Management of prostate cancer, especially advanced prostate cancer, remains clinically challenging and requires the identification of new biomarkers and therapeutic targets that can be exploited to improve patient outcome. Galectin-3 (gal-3) is a carbohydrate-binding protein involved in cancer progression and metastasis, including prostate tissues. Gal-3 function is regulated by proteolytic cleavage and the cleaved gal-3 is implicated in tumor progression. This study is the first to determine gal-3 expressions with two monoclonal anti-gal-3 antibodies in prostate tissues to distinguish expression patterns between intact and cleaved gal-3 and analyze their clinical relevance. Our results showed gal-3 cleavage occurred in prostate cancer but not normal prostate. Gal-3 presented in tumor tissues was mainly the cleaved form that can be detected by the anti-gal-3 antibody targeting C terminal. The cleaved gal-3, but not the intact gal-3, was increased in prostate cancer compared to normal prostate tissues and positively associated with malignance, tumor progression and metastasis. In addition, the expression of cleaved gal-3 was closely related to PSA level, indicating a PSA-mediated degradation of intact gal-3 in prostate cancer. In summary, our findings suggested the cleaved gal-3 could be a valuable diagnostic biomarker and a therapeutic target for the treatment of prostate cancer, especially advanced metastatic prostate cancer.

Intracellular galectin-7 expression in cancer cells results from an autocrine transcriptional mechanism and endocytosis of extracellular galectin-7

The β-galactoside binding protein galectin-7 (gal-7) is constitutively expressed at abnormally high levels in the outside milieu and intracellular compartments of many types of epithelial cancer cells, most notably in aggressive forms of ovarian and breast cancer. It is thus of utmost importance to understand how gal-7 traffics between both intracellular and extracellular compartments to develop novel drugs that target the protumorigenic functions of galectin-7. In the present work, we report that extracellular gal-7 plays a central role in controlling intracellular gal-7 in cells. It does so via two distinct yet complementary mechanisms: firstly by increasing the transcriptional activation of lgals7 gene transcription, and secondly via re-entry into the cells. Increased mRNA levels were dose- and time-dependent and occur in all cell lines tested, including ovarian and breast cancer cell lines. Addition of recombinant gal-7 to MDA-MB-231 transfected with a luciferase reporter vector containing response elements of the lgals7 promoter indicated that increased mRNA level of lgals7 occurs via de novo gene transcription. Re-entry of extracellular gal-7 inside cells was rapid, and reached cytosolic and mitochondrial compartments. Taken together, these findings reveal the existence of a positive self-amplification pathway that regulates intracellular gal-7 expression in breast and ovarian cancer cells.

Tissue and plasma levels of galectins in patients with high grade serous ovarian carcinoma as new predictive biomarkers

Galectins are moving closer to center stage in detecting glycosylation aberration in cancer cells. Here, we have investigated the expression of galectins in ovarian cancer (OC) and examined their potential as biomarkers in tissues and blood plasma samples of high grade serous ovarian carcinoma (HGSC) patients. In tissues, we found that increased protein expression of stromal gal-1 and epithelial gal-8/9 was associated with a poor response to treatment of HGSC patients. Gal-8/9 were both independent predictors of chemoresistance and overall survival (OS), respectively. This galectin signature increased the predictive value of the cancer antigen 125 (CA125) on 5-year disease-free survival (DFS), post-chemotherapy treatment and 5-year OS. In CA125^LOW patients, epithelial gal-9 was associated with a lower 5-year OS while stromal gal-1 and epithelial gal-8 were both associated with a lower 5-year DFS. Such negative predictive value of gal-8 and gal-9 was also found using plasma samples. In both cases, high plasma levels of gal-8 and gal-9 was associated with a lower OS and DFS. Overall, these data suggest that galectins may be promising biomarkers to identify subgroups of HGSC patients with poorer prognosis. Our study also contributes to better define the heterogeneity of the disease.

Towards molecular mechanisms regulating the expression of galectins in cancer cells under microenvironmental stress conditions

Galectins, a family of soluble β-galactoside-binding proteins, serve as mediators of fundamental biological processes, such as cell growth, differentiation, adhesion, migration, survival, and death. The purpose of this review is to summarize the current knowledge regarding the ways in which the expression of individual galectins differs in normal and transformed human cells exposed to various stimuli mimicking physiological and pathological microenvironmental stress conditions. A conceptual point is being made and grounded that the modulation of galectin expression profiles is a key aspect of cellular stress responses. Moreover, this modulation might be precisely regulated at transcriptional and post-transcriptional levels in the context of non-overlapping transcription factors and miRNAs specific to galectins.

G3-C12 Peptide Reverses Galectin-3 from Foe to Friend for Active Targeting Cancer Treatment

Galectin-3 is overexpressed by numerous carcinomas and is a potential target for active tumor treatments. On the other hand, galectin-3 also plays a key role in cancer progression and prevents cells from undergoing apoptosis, thereby offsetting the benefits of active targeting drugs. However, the relative contribution of the protective antiapoptotic effects of galectin-3 and the proapoptotic effects of galectin-3-targeted therapies has remained yet unrevealed. Here, we show that a galectin-3-binding peptide G3-C12 could reverse galectin-3 from foe to friend for active targeting delivery system. Results showed G3-C12 modified N-(2-hydroxypropyl)methacrylamide copolymer doxorubicin conjugates (G3-C12-HPMA-Dox) could internalize into galectin-3 overexpressed PC-3 cells via a highly specific ligand-receptor pathway (2.2 times higher cellular internalization than HPMA-Dox). The internalized Dox stimulated the translocation of galectin-3 to the mitochondria to prevent from apoptosis. In turn, this caused G3-C12-HPMA-Dox to concentrate into the mitochondria after binding to galectin-3 intracellularly. Initially, mitochondrial galectin-3 weakened Dox-induced mitochondrial damage; however, as time progressed, G3-C12 active-mediation allowed increasing amounts of Dox to be delivered to the mitochondria, which eventually induced higher level of apoptosis than nontargeted copolymers. In addition, G3-C12 downregulates galectin-3 expression, 0.43 times lower than control cells, which could possibly be responsible for the suppressed cell migration. Thus, G3-C12 peptide exerts sequential targeting to both cell membrane and mitochondria via regulating galectin-3, and eventually reverses and overcomes the protective effects of galectin-3; therefore, it could be a promising agent for the treatment of galectin-3-overexpressing cancers.

Small interfering RNA-induced silencing of galectin-3 inhibits the malignant phenotypes of osteosarcoma in vitro

Osteosarcoma (OS) is the most common malignant tumor of bone. It has recently been demonstrated that galectin-3, a multifunctional β-galactoside-binding, is significantly upregulated in OS tissues, and is correlated with its progression and metastasis. However, the detailed role of galectin‑3 in the regulation of cellular biological processes in OS cells has remained to be elucidated. The present study reported that the mRNA and protein levels of galectin‑3 were significantly increased in OS tissues compared to those in their matched normal adjacent tissues. Furthermore, galectin‑3 was upregulated in three OS cell lines, Saos‑2, MG63 and U2OS, when compared with that in the human osteoblast cell line hFOB1.19. Knockdown of galectin‑3 by galectin‑3‑specific small interfering RNA markedly inhibited OS‑cell proliferation and induced cell apoptosis. Furthermore, silencing of galectin‑3 expression significantly inhibited OS cell migration and invasion, accompanied with a marked decrease in the protein expression of matrix metalloproteinase 2 and ‑9. Mechanistic investigation suggested that the mitogen‑activated protein kinase kinase/extracellular signal‑regulated protein kinase signaling pathway may be involved in the galectin‑3‑mediated OS cell invasion. In conclusion, the present study was the first to report that silencing of galectin‑3 inhibited the malignant phenotypes of osteosarcoma in vitro. Therefore, galectin-3 may serve as a potential therapeutic target for OS.

Microfluidic blood cell sorting: now and beyond

Blood plays an important role in homeostatic regulation with each of its cellular components having important therapeutic and diagnostic uses. Therefore, separation and sorting of blood cells hasa been of a great interest to clinicians and researchers. However, while conventional methods of processing blood have been successful in generating relatively pure fractions, they are time consuming, labor intensive, and are not optimal for processing small volume blood samples. In recent years, microfluidics has garnered great interest from clinicians and researchers as a powerful technology for separating blood into different cell fractions. As microfluidics involves fluid manipulation at the microscale level, it has the potential for achieving high-resolution separation and sorting of blood cells down to a single-cell level, with an added benefit of integrating physical and biological methods for blood cell separation and analysis on the same single chip platform. This paper will first review the conventional methods of processing and sorting blood cells, followed by a discussion on how microfluidics is emerging as an efficient tool to rapidly change the field of blood cell sorting for blood-based therapeutic and diagnostic applications.

Inhibitors of Galectins and Implications for Structure-Based Design of Galectin-Specific Therapeutics

Galectins are a family of galactoside-specific lectins that are involved in a myriad of metabolic and disease processes. Due to roles in cancer and inflammatory and heart diseases, galectins are attractive targets for drug development. Over the last two decades, various strategies have been used to inhibit galectins, including polysaccharide-based therapeutics, multivalent display of saccharides, peptides, peptidomimetics, and saccharide-modifications. Primarily due to galectin carbohydrate binding sites having high sequence identities, the design and development of selective inhibitors targeting particular galectins, thereby addressing specific disease states, is challenging. Furthermore, the use of different inhibition assays by research groups has hindered systematic assessment of the relative selectivity and affinity of inhibitors. This review summarises the status of current inhibitors, strategies, and novel scaffolds that exploit subtle differences in galectin structures that, in conjunction with increasing available data on multiple galectins, is enabling the feasible design of effective and specific inhibitors of galectins.