In vivo modeling and detection of the ovarian cancer vascular marker TEM1

A19 Background: Ovarian cancer is one of the most deadly women cancers in the US. Despite advances in cancer research, efficient method and therapy are lacking for specifically detecting and eradicating ovarian cancer. Genome-wide expression profiling and histological staining studies revealed TEM1 as a gene overexpressed specifically in tumor vasculature. Moreover, TEM1 has been implicated in promoting cell adhesion, invasion, and metastasis. Given the fact that ovarian cancer usually metastasizes widely throughout the peritoneum and responds to vascular-targeted therapy, we reasoned that TEM1 can be a tumor vascular marker with potential diagnostic and therapeutic efficacy towards ovarian cancer. Purpose: To evaluate TEM1 as a tumor vascular marker and therapeutic target for ovarian cancer in mouse tumor vascular model. Specific aims: 1) to characterize TEM1 expression in normal human tissues and ovarian cancer specimens, 2) to establish a murine tumor vasculature model expressing human TEM1 3) to develop imaging strategy specifically against TEM1 in vivo Methods: Real-time PCR and immunohistochemistry are used to characterize human TEM1 expression in normal and ovarian cancer samples. Murine endothelial cell lines were transduced with human TEM1 cDNA in conjunction with luciferase (hTEM1/fLuc) or control tracer vector alone (fLuc) to establish human TEM1 expressing endothelial cell lines. These endothelial cells were then injected alone or in combination with tumor cells ID8 on the flanks of immunodeficient mice. Endothelial cell survival was monitored by bioluminescent imaging twice a week. To visualize hTEM1 expressing endothelial cells in vivo , 124-I radiolabeled hTEM1-specific antibody was injected venously and PET images were acquired eighteen hours after injection. Results: 1) High TEM1 mRNA level correlates with decreased survival in two independent cohorts. 2) Positive TEM1 staining was observed in all 52 ovarian cancer specimens studied, while no positive staining was seen in control staining. 3) The expression of hTEM1 in hTEM1/fLuc cells was confirmed by q-PCR, western and FACS analysis. hTEM1/fLuc and fLuc cells can be detected in nude mice 5 weeks after injection. 4) When co-injected with tumor cells, hTEM1/fLuc cells greatly increased the vascular density of the tumors compared to fLuc cells. 5) PET imaging studies demonstrated that hTEM1-expressing tumors have significantly more 124-I uptake in comparison of control tumors within the same animal The radioactivity in TEM1 expressing tumor lasted as long as 6 days after the antibody injection. Conclusions: Our data strongly suggest that TEM1 is a rational diagnostic and therapeutic target for ovarian cancer. The experimental model described here allows quantitative and specific monitoring of endothelial cell in vivo by bioluminescence and PET imaging, respectively. This vascular model can serve as an unprecedented platform for not only studying the function of tumor vascular markers , but also testing new diagnostics and therapeutic agents against tumor vasculature in vivo . Further studies will evaluate TEM1 as early detection marker and prognostic factor in ovarian cancer patients.