Soluble CD44 v5 and v6 in serum of patients with breast cancer. Correlation with expression of CD44 v5 and v6 variants in primary tumors and location of distant metastasis

Label-free fiber-optic spherical tip biosensor to enable picomolar-level detection of CD44 protein

Increased level of CD44 protein in serum is observed in several cancers and is associated with tumor burden and metastasis. Current clinically used detection methods of this protein are time-consuming and use labeled reagents for analysis. Therefore exploring new label-free and fast methods for its quantification including its detection in situ is of importance. This study reports the first optical fiber biosensor for CD44 protein detection, based on a spherical fiber optic tip device. The sensor is easily fabricated from an inexpensive material (single-mode fiber widely used in telecommunication) in a fast and robust manner through a CO2 laser splicer. The fabricated sensor responded to refractive index change with a sensitivity of 95.76 dB/RIU. The spherical tip was further functionalized with anti-CD44 antibodies to develop a biosensor and each step of functionalization was verified by an atomic force microscope. The biosensor detected a target of interest with an achieved limit of detection of 17 pM with only minor signal change to two control proteins. Most importantly, concentrations tested in this work are very broad and are within the clinically relevant concentration range. Moreover, the configuration of the proposed biosensor allows its potential incorporation into an in situ system for quantitative detection of this biomarker in a clinical setting.

Metastatic heterogeneity of breast cancer: Molecular mechanism and potential therapeutic targets

Breast cancer is one of the most common malignancies among women throughout the world and is the major cause of most cancer-related deaths. Several explanations account for the high rate of mortality of breast cancer, and metastasis to vital organs is identified as the principal cause. Over the past few years, intensive efforts have demonstrated that breast cancer exhibits metastatic heterogeneity with distinct metastatic precedence to various organs, giving rise to differences in prognoses and responses to therapy in breast cancer patients. Bone, lung, liver, and brain are generally accepted as the primary target sites of breast cancer metastasis. However, the underlying molecular mechanism of metastatic heterogeneity of breast cancer remains to be further elucidated. Recently, the advent of novel genomic and pathologic approaches as well as technological breakthroughs in imaging analysis and animal modelling have yielded an unprecedented change in our understanding of the heterogeneity of breast cancer metastasis and provided novel insight for establishing more effective therapeutics. This review summarizes recent molecular mechanisms and emerging concepts on the metastatic heterogeneity of breast cancer and discusses the potential of identifying specific molecules against tumor cells or tumor microenvironments to thwart the development of metastatic disease and improve the prognosis of breast cancer patients.

Evaluating the Efficiency of Hyaluronic Acid for Tumor Targeting via CD44

The development of delivery systems capable of tumor targeting represents a promising strategy to overcome issues related to nonspecific effects of conventional anticancer therapies. Currently, one of the most investigated agents for cancer targeting is hyaluronic acid (HA), since its receptor, CD44, is overexpressed in many cancers. However, most of the studies on CD44/HA interaction have been so far performed in cell-free or genetically modified systems, thus leaving some uncertainty regarding which cell-related factors influence HA binding and internalization (collectively called "uptake") into CD44-expressing cells. To address this, the expression of CD44 (both standard and variants, designated CD44s and CD44v, respectively) was evaluated in human dermal fibroblasts (HDFs) and a large panel of cancer cell lines, including breast, prostate, head and neck, pancreatic, ovarian, colorectal, thyroid, and endometrial cancers. Results showed that CD44 isoform profiles and expression levels vary across the cancer cell lines and HDF and are not consistent within the cell origin. Using composite information of CD44 expression, HA binding, and internalization, we found that the expression of CD44v can negatively influence the uptake of HA, and, instead, when cells primarily expressed CD44s, a positive correlation was observed between expression and uptake. In other words, CD44shigh cells bound and internalized more HA compared to CD44slow cells. Moreover, CD44shigh HDFs were less efficient in uptaking HA compared to CD44shigh cancer cells. The experiments described here are the first step toward understanding the interplay between CD44 expression, its functionality, and the underlying mechanism(s) for HA uptake. The results show that factors other than the amount of CD44 receptor can play a role in the interaction with HA, and this represents an important advance with respect to the design of HA-based carriers and the selection of tumors to treat according to their CD44 expression profile.

Mechanisms involved in breast cancer liver metastasis

Liver metastasis is a frequent occurrence in patients with breast cancer; however, the available treatments are limited and ineffective. While liver-specific homing of breast cancer cells is an important feature of metastasis, the formation of liver metastases is not random. Indeed, breast cancer cell factors contribute to the liver microenvironment. Major breakthroughs have been achieved recently in understanding breast cancer liver metastasis (BCLM). The process of liver metastasis consists of multiple steps and involves various factors from breast cancer cells and the liver microenvironment. A further understanding of the roles of breast cancer cells and the liver microenvironment is crucial to guide future work in clinical treatments. In this review we discuss the contribution of breast cancer cells and the liver microenvironment to liver metastasis, with the aim to improve therapeutic efficacy for patients with BCLM.

Cationic conjugated polymer/fluoresceinamine-hyaluronan complex for sensitive fluorescence detection of CD44 and tumor-targeted cell imaging

Simple, rapid, and sensitive detection of CD44 is of paramount importance since it plays pivotal roles in tumor initiation, growth and metastasis. Herein, we describe a novel method for sensitive, visual and facile fluorescence detection of CD44 and CD44-mediated cancer cell imaging, using a probe based on cationic conjugated polymer (CCP)-PFEP and fluoresceinamine-hyaluronan (FA-HA). HA is an anionic natural glycosaminoglycan that can specifically bind to the overexpressed CD44 on various kinds of cancer cells. PFEP and FA-HA formed a complex through electronic interactions, resulting in a highly efficient fluorescence resonance energy transfer (FRET) from PFEP to FA-HA; moreover, the efficiencies of FRET correlated with the concentrations of CD44 because the specific binding of HA-CD44 would separate FA-HA away from PFEP. This method did not require laborious and expensive dual-labeling or protein-labeling needed in previously reported detection methods of CD44. Just mix the sample and test solution containing the PFEP/FA-HA complex, and the results allowed naked-eye detection by observing fluorescent color of solutions with the assistance of a UV lamp. Most importantly, the use of a conjugated polymer with excellent amplification property as well as the specific binding of HA-CD44 endowed this method with high sensitivity and specificity, making it applicable for reliable quantitative detection of CD44. Furthermore, the PFEP/FA-HA complex formed nanoparticles in aqueous solution, and the nanoparticles can be selectively taken up by MCF-7 cells (cancer cell) through the HA-CD44 interaction, thereby giving rise to a dual-color tumor-targeted imaging probe with good photostability. The development of this fluorescent probe showed promising potential to make a reliable and routine method available for early diagnosis of cancer.

Serum CD44 levels and overall survival in patients with HER2-positive breast cancer

CD44 is an adhesion molecule involved in tumor cell invasion and metastasis. The function of CD44 in breast cancer is not understood completely, or is its role as a predictive or prognostic factor. In this study, we tested for the hypothesis that the concentration of soluble CD44 (sCD44) in serum is correlated with clinicopathological factors, especially HER2, and survival in patients with breast cancer. We retrospectively identified 110 patients with breast cancer who had been treated at The University of Texas MD Anderson Cancer Center (MDACC) from September 2001 to May 2004. Sera were collected before definitive surgery in patients with stage I or II breast cancer, before initiation of neoadjuvant chemotherapy (if indicated) for patients with stage I-III breast cancer, and before initiation of systemic therapy in patients with stage IV breast cancer. sCD44 levels were determined using an enzyme-linked immunosorbent assay. The median age at diagnosis was 51 years (range, 28.6-87.1 years). sCD44 concentration was correlated with tumor stage (P = 0.0308). sCD44 serum concentration did not predict pathological response in patients treated with neoadjuvant chemotherapy. Among patients with distant metastases, sCD44 levels were significantly higher in patients with liver involvement than in patients with metastases at other sites. The overall survival rate did not differ between patients with high sCD44 concentration and patients with low sCD44 concentration. However, sCD44 concentration was a significant predictor of overall survival for patients with HER2-positive breast cancer, while no difference in overall survival rates was observed in patients with HER2-negative breast cancer. To the best of our knowledge, this is the first study to show an association between circulating sCD44 levels and survival in HER2-positive breast cancer patients. Our results suggest a role for sCD44 as a prognostic marker. Furthermore, sCD44 level may offer a new clinical therapeutic target in HER2-positive breast cancer.

Increased soluble CD44 concentrations are associated with larger tumor size and lymph node metastasis in breast cancer patients

PURPOSE

CD44 is a cell surface glycoprotein involved in cell-cell and cell-substrate interactions, which may be shed or released into circulation by proteolytic enzymatic mechanisms. Alternative splicing of CD44 and aberrant levels of soluble CD44 variants in the serum of cancer patients have been correlated to tumor progression and metastasis in different tumors including breast cancer. In this study we evaluated the clinical value of CD44 serum levels (sCD44) in patients with primary breast cancer.

METHODS

Concentrations of soluble isoforms sCD44std, sCD44v5 and sCD44v6 were determined with a sensitive ELISA and normalized against the total protein concentration (TP). Pre-operative serum samples from 82 patients and 67 age-matched healthy blood donors were analyzed. The results were correlated to clinico-pathological parameters (tumor size, grading, lymph node metastasis, etc.).

RESULTS

In sera of breast cancer patients, we detected elevated concentrations of sCD44v6 (P = 0.0001) and total protein TP (P = 0.0001) in comparison to healthy controls, whereas overall sCD44 (sCD44std) and sCD44v5 did not differ. Patients with sCD44v6-concentrations above the 75%-percentile showed an increased T stage (2.9 cm vs. 1.8 cm) as well as a higher risk for lymph node metastasis (55% vs. 35%). In breast cancer patients with lymph node metastasis the median value of sCD44v6 was significantly higher (P = 0.025) in comparison to patients without lymph node metastasis and healthy controls.

CONCLUSIONS

Our data suggest an upregulated expression of alternatively spliced soluble CD44 isoforms in breast cancer patients. The specific alterations of certain CD44 isoform concentrations (especially sCD44v6) may reflect disturbances of the nuclear splicing machinery in tumor cells. The clinical significance of our findings are underlined by the positive correlation of elevated sCD44v6 concentrations and lymph node metastases (r (s) = 0.25).

Soluble CD44 secretion contributes to the acquisition of aggressive tumor phenotype in human colon cancer cells

CD44, a widely distributed cell surface glycoprotein and a receptor for hyaluronan (HA), has been implicated in facilitating tumor growth and metastasis, antiapoptosis and directional motility of cancer cells. In order to investigate the role of soluble CD44 (CD44(sol)) in colon cancer cell growth, SW620, a human colon cancer cell line deficient in CD44 expression was stably transfected with human CD44 cDNA containing exons 1-5, 15 and 16 of the human CD44. Western blot analyses demonstrated the presence of 78 kDa soluble CD44 protein in the culture supernatant of stably transfected cell lines (CD44(sol) clones) and were not detected in the empty vector control line (clone m). The CD44(sol) transfected cells showed higher cell proliferation and clonal growth in vitro, confirmed by MTT and clonogenic assays respectively, when compared to the control cells. Cell adhesion to hyaluronan was significantly lower with CD44(sol) cells compared to the control cells. Western blot analyses were negative for cleaved PARP in lysates from CD44(sol) cells, suggesting resistance to apoptosis. These findings indicate that the secretion of soluble CD44 contributes to colon cancer growth in vitro, possibly as a decoy receptor.

Evaluation of soluble adhesion molecules CD44 (CD44st, CD44v5, CD44v6), ICAM-1, and VCAM-1 as tumor markers in head and neck cancer

PURPOSE

Standard CD44 (CD44st), CD44 variant 5 (CD44v5), and CD44 variant 6 (CD44v6), intercellular adhesion molecule 1(ICAM-1), and vascular cell adhesion molecule 1(VCAM-1) are expressed in human malignant cells and tissues. Their mechanism remains unclear but has been reported to be associated with the progression and metastasis of malignancies.

MATERIALS AND METHODS

In this study, we investigated any correlations between the soluble adhesion molecule CD44 (st, v5, and v6), ICAM-1, and VCAM-1 and the clinicopathologic variables (eg, age, sex, histological grading, tumor size, lymph node status, distant metastasis, and TNM staging) and evaluated the difference between the pretreatment level in the patients with head and neck cancer and that in the control group. Furthermore, we examined the difference between the pretreatment serum levels and the after-treatment serum levels in the group with head and neck cancer. The pretreatment and after-treatment serum levels of soluble CD44st, CD44v5, CD44v6, ICAM-1, and VCAM-1 were measured in 81 patients with head and neck cancer and in 20 healthy volunteers as controls.

RESULTS

There were no significant differences between the serum levels of sCD44st, sCD44v5, sCD44v6, sICAM-1, and sVCAM-1 and the clinicopathologic variables in cancer patients. However, the higher serum level of sCD44v6 was significantly associated with distant metastasis (P = .02). Especially, we found that the pretreatment serum levels of sCD44st, sCD44v5, and sCD44v6 were markedly associated with TNM staging (CD44st P = .0017, CD44v5 P = .0005, CD44v6 P = .0046). Furthermore, the median serum levels of sCD44st, sCD44v5, sCD44v6, sICAM-1, and sVCAM-1 before treatment of head and neck cancer were significantly higher than those of the control group (CD44st P = .0067, CD44v5 P = .0048, CD44v6 P = .0007, ICAM-1 P = .0089, VCAM-1 P = .0178). The median serum level of sCD44st after treatment in the group of patients was significantly lower than that of pretreatment (CD44st P = .0001). And, both the median serum levels of sCD44v5 and sCD44v6 after treatment were also lower than those of pretreatment (CD44v5 P = .0004, CD44v6 P = .0025).

CONCLUSIONS

The possible roles of soluble adhesion molecules in the prognosis of head and neck carcinoma deserve further elucidation and evaluation with long-term patient follow-up.

The prognostic significance of CD44s and CD44v6 expression in stage two breast carcinoma: an immunohistochemical study

AIMS

Expression of the v6 variant isoform of CD44 has been causally associated with the development of metastases. This study, using immunohistochemical techniques, examined the prognostic significance of CD44s and CD44v6 expression.

METHODS

A cohort of 109 women presenting with stage 2 breast cancer, with a minimum follow-up of 5 years, were assessed.

RESULTS

Eighty percent of patients demonstrated CD44v6 expression on immunohistochemical studies. CD44v6 expression in tissue sections was found to be independent of age, tumour size, grade, and lymph-node status. No significant association was demonstrated between CD44v6 expression and either disease-free or overall survival. Similar findings were observed for CD44s.

CONCLUSIONS

CD44s and CD44v6 do not appear to be useful as prognostic indicators in early breast cancer. The increased expression of variant CD44 isoforms seen in breast neoplasia may merely be a marker for loss of control of alternative splicing within tumour tissue.

Soluble CD44 inhibits melanoma tumor growth by blocking cell surface CD44 binding to hyaluronic acid

Proteolytic cleavage of the extracellular domain of CD44 from the surface of cells has been observed recently in different cell types. In cell culture supernatants of human melanoma cell lines a 70 kDa soluble CD44 protein (solCD44) was detected at concentrations of 250-300 ng/ml. Protease inhibitor studies revealed that serine proteases and metalloproteases are involved in the cleavage of CD44 from the surface of melanoma cells. To analyse a possible function of soluble CD44 a human malignant melanoma cell line was stably transfected with cDNAs encoding either wild type soluble CD44s or mutated forms with defective HA binding properties (CD44sR41A and CD44sR150A/R154A). Soluble CD44s almost completely inhibited hyaluronic acid binding by melanoma cells, whereas soluble CD44 mutated in the HA binding domain had no effect. When cultivated on hyaluronic acid, melanoma cell proliferation was induced by 30% for both the parental and the control transfected cells. This increase in proliferation was blocked completely in solCD44s-secreting transfectants, whereas solCD44sR41A and solCD44sR150A/R154A-secreting cells again showed hyaluronic acid-induced cell proliferation. These cell lines were subcutaneously injected into MF1 nu/nu mice to compare their growth as tumors in vivo. Compared to tumors derived from parental and control transfected cells, we observed a dramatic reduction of primary tumor growth with solCD44s expressing MM cells. Transfectants expressing solCD44s mutated in the HA binding domain in contrast developed fast-growing primary tumors. These results provide strong evidence that direct solCD44 interactions with hyaluronic acid interfere competitively with processes induced by hyaluronic acid binding to surface CD44. Autocrine, or drug-induced secretion of solCD44 by human melanoma cells may thus exert potent antitumoral effects in vivo.

Differential expression of CD44 isoforms during liver regeneration in rats

BACKGROUND

CD44 is a transmembrane glycoprotein known to bind hyaluronic acid (HA). This molecule is a multifunctional cell surface glycoprotein involved in lymphocyte homing and activation, tumor growth and metastasis. We have investigated the qualitative modification of CD44 in the regenerating liver as a model for studying cellular proliferation in vivo. Molecules involved in cell adhesion and the extracellular matrix (ECM), which influence differentiation, growth, cell-cell interactions and cellular polarity, play an important role in the liver regeneration. We studied the modulation of CD44 gene expression and its post-transcriptional modifications, analyzing the expression of different isoforms containing exon v6 in the regenerating liver, in sham operated liver and in the hepatoma cells H-35.

METHODS

The expression of CD44 and CD44v6 were analyzed in RNA extracted from regenerating liver at different times after partial hepatectomy (PH), and H-35 hepatoma cells by Northern blot, RT-PCR and Southern blot, and in protein extracts from regenerating liver by Western blot. H-35 hepatoma cells were assayed with the antibody cross-linked technique with CD44 antibodies.

RESULTS

The standard CD44 form is expressed in regenerating liver and its levels were not modified following PH. However, our analysis revealed CD44 isoforms containing v6 in the first hours after PH as well as in the H-35 hepatoma cell line. H-35 cells treated with cross-linked anti-CD44 antibodies or HA show an increased rate of incorporation of [3H]thymidine (30 and 25%, respectively) with respect to the control.

CONCLUSION

These findings suggest that CD44 may play a role in the proliferation of residual hepatocytes following PH.

Expression of CD44 variant exons in acute myeloid leukemia is more common and more complex than that observed in normal blood, bone marrow or CD34+ cells

CD44 is an adhesion molecule that is expressed on hematopoietic cells and has been implicated in the interactions between bone marrow stromal layers and hematopoietic progenitors. The expression of variant forms of CD44, particularly forms containing exon v6, have been associated with poor prognosis in a number of hematological malignancies. The expression of CD44 variants on normal bone marrow (BM), peripheral blood (PBMC) and CD34+ hematopoietic progenitors was compared with those expressed on blasts from 30 patients with acute myeloid leukemia (AML). Normal BM, PBMC and CD34+ progenitor cells were negative for all variants tested by flow cytometry. In contrast exon v3 was expressed on 13%, v4 on 67%, v5 on 19%, v6 on 7% and v7 on 65% of AML cases. RT-PCR and Southern blotting revealed the expression of exons v3, v6, v8, v9 and v10 in normal bone marrow and peripheral blood mononuclear cells and the expression of exons v3, v6, v8 and v10 in CD34+ progenitors. A more complex pattern of variant exon expression was observed in leukemic samples in comparison to normal hematopoietic cells. Sixty-two percent of AML cases expressed exon v3 and 70% exon v6. Exons v4 and v5 were not detected while exons v7, v8, v9 and v10 were detected in 21, 83, 71 and 92% of cases, respectively. In summary, our data demonstrate a striking increase in the complexity of CD44 variant expression in cells from patients with AML, along with surface expression of some variant CD44 proteins. Further analysis will be directed at how these alter the interaction of leukemic blasts with the bone marrow microenvironment and their diagnostic, prognostic and therapeutic potential.

Human mast cells express the hyaluronic-acid-binding isoform of CD44 and adhere to hyaluronic acid

CD44 is expressed in various isoforms on multiple cell lineages including those of hematopoietic origin and is believed in part to mediate cell adhesion to hyaluronic acid. Elevated levels of soluble CD44 (sCD44) have been identified in the serum of some patients with specific neoplasms. We thus sought to determine whether human mast cells express functional CD44 and whether sCD44 might be associated with systemic mast cell disease. Using a standard assay, CD34(+)-derived cultured human mast cells were first demonstrated to adhere to hyaluronic-acid-coated surfaces. Human mast cells were then found by flow cytometry to express CD44S, but not the v5, v6, v7, and v8 isoforms, and to shed CD44S following activation induced by PMA or aggregation of FcvarepsilonRI. However, CD44S was not found to be consistently elevated in serum obtained from patients with mastocytosis or individuals experiencing anaphylaxis. Thus, human cultured mast cells express and shed CD44S, which appears to mediate the attachment of these cells to hyaluronic acid.

Cytosol concentrations of CD44 isoforms in breast cancer tissue

The role of the adhesion molecule CD44 in the natural history of breast cancer is controversial. We investigated the CD44 isoform CD44v5 and CD44v6 concentrations in the cytosol of 90 breast cancer specimens, 9 fibroadenomas and 22 normal breast tissue specimens by means of ELISA. CD44v5 and CD44v6 cytosol concentrations were statistically significantly higher in breast cancer compared with fibroadenoma and normal breast tissue (Mann-Whitney U-test, p = 0.009 and p < 0.001, respectively). When CD44 isoforms were correlated with lymph node involvement, histological grading, histological type, tumor stage and age at diagnosis, we found no statistically significant correlation with any of the investigated clinico-pathological parameters. In univariate and multivariate analyses, CD44v5 and CD44v6 were of no prognostic relevance regarding disease-free survival in breast cancer patients (log-rank test, p = 0.16 and p = 0.08, respectively). Our results indicate that CD44 isoforms are increased in samples from tumors relative to normal tissue. Our data show that CD44v5 and CD44v6 isoform expression, although up-regulated by malignant transformation, is not required to acquire a metastatic phenotype in breast cancer. Furthermore, our data support the assumption that cytosolic CD44 isoforms are of no prognostic relevance for disease-free survival of breast cancer patients.