In renal cell carcinoma (RCC), the presence of higher gangliosides correlates with systematic metastasis. Disialosyl globopentaosylceramide (DSGb5) was identified previously as one of the major gangliosides from RCC tissues. Siglec-7 (sialic acid-binding Ig-like lectin-7), expressed on natural killer (NK) cells as an inhibitory receptor, has a striking preference for internally branched α2,6-linked disialic gangliosides such as DSGb5. To clarify the functional role of DSGb5 in RCC metastases, we have investigated whether DSGb5 expressed on RCC cells can modulate NK cell cytotoxicity in a Siglec-7-dependent manner. The binding activity of RCC cells to Siglec-7-Fc fusion protein was specifically inhibited by anti-DSGb5 monoclonal antibody and transfection of siRNA for ST6GalNAcVI (synthetase of DSGb5). These observations showed that Siglec-7-Fc fusion protein specifically bound to DSGb5 expressed on RCC cells. In contrast, the sialic acid-binding site of Siglec-7 on NK cells was masked by cis interactions with endogenous sialoconjugates at the cell surface, but it could be unmasked by sialidase treatment of the NK cells. Following sialidase treatment of NK cells, NK cell cytotoxicity against RCC cells with high DSGb5 expression was significantly decreased relative to cells with low DSGb5 expression. These findings indicate that such NK cell cytotoxicity against RCC cells could be inhibited by the interaction between Siglec-7 on effecter cells and DSGb5 on target cells. The results of the present study suggest that DSGb5 expressed on RCC cells can downregulate NK cell cytotoxicity in a DSGb5-Siglec-7-dependent manner and that RCC cells with DSGb5 create favorable circumstance for their own survival and metastases.

Stage-specific embryonic antigen-4 (SSEA-4), a specific marker for pluripotent stem cells, plays an important role in the malignant behavior of several cancers. Here, SSEA-4 expression was evaluated by immunohistochemistry using monoclonal antibody RM1 specific to SSEA-4 in 181 and 117 prostate cancer (PC) specimens obtained by biopsy and radical prostatectomy (RP), respectively. The relationships between SSEA-4 expression in cancer cells or the presence of SSEA-4-positive tumor-infiltrating immune cells (TICs) and clinicopathological parameters were analyzed. SSEA-4 expression in cancer cells was significantly associated with Gleason score, local progression, and lymph node and distant metastasis. In RP specimens, high SSEA-4 expression in cancer cells and the presence of SSEA-4-positive TICs were significant predictors of pT3, i.e., invasion and worse biochemical recurrence (BCR) after RP, respectively, in univariate analysis. In contrast, combination of high SSEA-4 expression in cancer cells and the presence of SSEA-4-positive TICs was an independent predictor for pT3 and BCR in multivariate analysis. Biologically this combination was also independently associated with suppression of apoptosis. Thus, the co-expression of SSEA-4 in cancer cells and TICs may have crucial roles in the malignant aggressiveness and prognosis of PC. Invasive potential and suppression of apoptosis may be linked to SSEA-4 expression.

In our previous study, monoclonal antibody RM2, established toward the glycosyl epitope, reflected grade of malignancy of prostate cancer cells whereas RM2 reactivity to benign glands was negative or weak. RM2 reactivity was also detected in stroma, suggesting the glycoprotein RM2 recognizes could be released into the bloodstream. Then, we explored RM2 reactivity to sera of early prostate cancer. We compared RM2 reactivity to sera between 62 patients with early prostate cancer and 43 subjects with benign prostatic disease, and examined RM2 reactivity before and after radical prostatectomy in 15 patients by Western blotting. We also examined RM2 reactivity to sera of the other urogenital cancers. RM2 reactivity was significantly enhanced on a serum glycoprotein with molecular mass ∼40 kDa, hereby termed GPX, in the patients with early prostate cancer when compared with those with benign prostatic disease (p < 0.0001). Setting an appropriate cutoff level, RM2 reactivity to GPX for detection of prostate cancer had sensitivity of 87% and specificity of 84%, respectively. Furthermore, the level of RM2 reactivity significantly decreased after radical prostatectomy (p 5 0.006). However, increased RM2 reactivity to GPX was also observed in the other urogenital cancers. The proteomics approach identified GPX as haptoglobin-b chain and RM2 showed preferential reactivity toward haptoglobin-b chain derived from prostate cancer when compared with polyclonal anti-haptoglobin antibody. Haptoglobin-b chain defined by RM2 is a novel serum marker that may be useful for detection of early prostate cancer when coupled with prostate-specific antigen because it is not specific to prostate cancer.

5F3 expression reflects the clinical and pathological features of prostate cancer and is correlated with the outcomes following RP. Further studies are necessary to clarify the functional roles of DSGb5 and establish a novel biomarker for prostate cancer.

INTRODUCTION AND OBJECTIVE: PSA has been utilized for more than 25 years. Despite the success that this marker has had in changing the course of the disease, its lack of specificity has limited its utility in the early detection of prostate cancer. It is apparent that more specific markers are required. We have previously identified a prostate cancer biomarker, Early Prostate Cancer Antigen (EPCA), that at the tissue level is capable of differentiating between patients with prostate cancer and those without the disease. Utilizing anti-EPCA antibodies, an ELISA was developed which is able to detect the protein in the serum of men with prostate cancer. In these studies we evaluated the sensitivity and specificity of this marker both alone and in combination with PSA for the detection of men with prostate cancer.METHODS: A serum-based ELISA assay was developed to detect EPCA and used to screen serum sample sets. Serum was collected from the following patient groups: men with no evidence of prostate cancer, multiple biopsy proven men with no evidence of prostate cancer with PSA>2.5, prostate cancer-organ confined, prostate cancer-non-organ confined and benign prostatic hyperplasia (BPH). The plates were incubated overnight and incubated with blocking solution, anti-EPCA antibody followed by HRP-Iinked goat anti-rabbit lgG. An initial training set was used to set up the cutoff that was applied prospectively in the study samples.RESULTS: Serum EPCA levels are capable of separating patients with prostate cancer from those without prostate cancer. The EPCA assay has a sensitivity of approximately 80% and a specificity of approximately 84%. Combining the EPCA assay with the results of the PSA assay increased the ability of determining between those who do and those who do not have prostate cancer. As individual assays EPCA had an overall error rate of 23.4% and PSA has an error rate of 25.1 %, but when the predicting value of both assays was combined the overall error rate fell to 4.6%.CONCLUSIONS: Serum EPCA is a highly specific assay for prostate cancer. Serum EPCA and PSA levels are synergistic and together provide for a highly accurate means for the detection of men with the disease.