Tumor endothelial marker 7 (TEM-7): a novel target for antiangiogenic therapy.

Antiangiogenesis has been validated as a therapeutic strategy to treat cancer, however, a need remains to identify new targets and therapies for specific diseases and to improve clinical benefit from antiangiogenic agents. Tumor endothelial marker 7 (TEM-7) was investigated as a possible target for therapeutic antiangiogenic intervention in cancer. TEM-7 expression was assessed by in situ hybridization or by immunohistochemistry (IHC) in 130 formalin-fixed paraffin-embedded (FFPE) and 410 frozen human clinical specimens of cancer plus 301 normal tissue samples. In vitro TEM-7 expression was evaluated in 4 human endothelial cell models and in 32 human cancer cell lines by RT-PCR and flow cytometry. An anti-TEM-7 antibody was tested in vitro on human SKOV3 ovarian and MDA-MB-231 breast carcinoma cells that expressed TEM-7 in antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis assays. In frozen tumor tissues, TEM-7 mRNA and protein was detected in all but one of the cancer types tested and was infrequently expressed in normal frozen tissues. In FFPE tumor tissues, TEM-7 protein was detected by IHC in colon, breast, lung, bladder, ovarian and endometrial cancers and in sarcomas. TEM-7 protein was not detected in head and neck, prostate or liver cancers. TEM-7 expression was restricted to the vasculature and was absent from tumor cells. In vitro, TEM-7 was not detected in human microvascular endothelial cells (HMVEC) or human umbilical vein endothelial cells (HUVEC) but was induced in endothelial precursor/progenitor cells (EPC) in the presence of the mitogen phorbol ester PMA. An anti-TEM-7 antibody mediated ADCC and phagocytosis in SKOV3 and MDA-MB-231 cell lines infected with an adenovirus expressing TEM-7. These data demonstrate that TEM-7 is a vascular protein associated with angiogenic states. TEM-7 is a novel and attractive target for antiangiogenic therapy.

Endosialin: a novel malignant cell therapeutic target for neuroblastoma.

Endosialin emerged recently as a potential therapeutic target for sarcoma. Since some sarcoma subtypes, such as Ewing's sarcoma, show characteristics of neuroendocrine differentiation, we wondered whether cancers with neuro-endocrine properties and/or neuroectodermal origin, such as neuroblastoma, small cell lung cancer and melanoma, may express endosialin. Endosialin protein expression was surveyed in neuroblastoma, small cell lung cancer and melanoma in human clinical specimens by immunohistochemistry (IHC) and in human cell lines by flow cytometry. Side population cells were examined to determine whether cancer stem cells can express endosialin. Endosialin-expressing neuroblastoma cell lines were implanted in immunodeficient mice and allowed to grow. The xenograft tumors were resected and tested for endosialin expression by IHC. In human clinical specimens, vascular endosialin staining was observed in neuroblastoma, small cell lung cancer and melanoma. Malignant cell staining was strongest in neuroblastoma, weak in melanoma and rare in small cell lung cancer. In human cell lines, endosialin was detected in neuroblastoma cell lines, including cancer stem cell-like side population (SP) cells, but was absent in melanoma and was both rare and weak in small cell lung cancer. Human neuroblastoma xenograft tumors were found to be positive for endosialin. Our work suggests that endosialin may be a suitable therapeutic target for neuroblastoma.

Endosialin is expressed in high grade and advanced sarcomas: evidence from clinical specimens and preclinical modeling.

We previously surveyed the expression of endosialin/ CD248/TEM-1 by immunohistochemistry in human clinical specimens of sarcomas and documented expression in tumor cells, stromal cells and vasculature. In the present study, we completed a retrospective analysis of the diagnostic reports available for these same samples in order to identify high-grade and metastatic disease. Our results show that endosialin can be detected in advanced disease. We screened human sarcoma cell lines in vitro for endosialin expression and developed preclinical human xenograft models of disseminated sarcoma. We found that 22 out of 42 human sarcoma cell lines were positive for endosialin with a positive correlation between mRNA and protein levels. When implanted in vivo, endosialin was expressed at all sites of dissemination. These data provide clinical and preclinical evidence that endosialin can be detected in advanced sarcoma. These results demonstrate for the first time that endosialin is a suitable therapeutic target for poor prognosis and advanced disease.

Endosialin protein expression and therapeutic target potential in human solid tumors: sarcoma versus carcinoma.

PURPOSE: Endosialin/CD248/tumor endothelial marker 1 is expressed in stromal cells, endothelial cells, and pericytes in various tumors; however, few studies have focused on expression in malignant cells. EXPERIMENTAL DESIGN: We studied expression of endosialin in clinical specimens, cell culture, and animal models and designed an anti-endosialin therapeutic prototype. RESULTS: Fifty human tumor cell lines and 6 normal cell types in culture were assayed by reverse transcription-PCR and/or flow cytometry for endosialin. Cell surface protein was found on 7 sarcoma lines, 1 neuroblastoma, and 4 normal cell types in culture. A fully human anti-endosialin antibody bound to human A-673 Ewing's sarcoma cells and SK-N-AS neuroblastoma cells but not HT-1080 cells. Exposure of cells to an anti-human IgG conjugated to saporin resulted in growth inhibition only of endosialin-expressing cells. Endosialin expression was assessed by immunohistochemistry in 250 clinical specimens of human cancer including 20 cancer subtypes. Endosialin is frequently found in human cancers. Endosialin expression is mainly a perivascular feature in carcinomas, with some expression in stromal cells. In sarcomas, endosialin is expressed by malignant cells, perivascular cells, and stromal cells. Development and characterization of experimental models for studying endosialin biology in sarcomas and evaluating anti-endosialin therapies is presented. CONCLUSIONS: Findings suggest that an anti-endosialin immunotoxin might be a promising therapeutic approach for endosialin-positive neoplasia, especially synovial sarcoma, fibrosarcoma, malignant fibrous histiocytoma, liposarcoma, and osteosarcoma. Thus, a diagnostic/therapeutic targeted therapeutic approach to treatment of endosialin-expressing tumors may be possible.