The targeting of solid tumors requires delivery tools that resist intracellular and extracellular inactivation, and that are taken up specifically by tumor cells. We have shown previously that the recombinant nontoxic B-subunit of Shiga toxin (STxB) can serve as a delivery tool to target digestive tumors in animal models. The aim of this study was to expand these experiments to human colorectal cancer. Tissue samples of normal colon, benign adenomas, colorectal carcinomas, and liver metastases from 111 patients were obtained for the quantification of the expression of the cellular STxB receptor, the glycosphingolipid globotriaosyl ceramide (Gb 3 or CD77). We found that compared with normal tissue, the expression of Gb 3 was strongly increased in colorectal adenocarcinomas and their metastases, but not in benign adenomas. Short-term primary cultures were prepared from samples of 43 patients, and STxB uptake was studied by immunofluorescence microscopy. Of a given tumor sample, on average, 80% of the cells could visibly bind STxB, and upon incubation at 37°C, STxB was transported to the Golgi apparatus, following the retrograde route. This STxB-specific intracellular targeting allows the molecule to avoid recycling and degradation, and STxB could consequently be detected on tumor cells even 5 days after initial uptake. In conclusion, the targeting properties of STxB could be diverted for the delivery of contrast agents to human colorectal tumors and their metastases, whose early detection and specific targeting remains one of the principal challenges in oncology. [Mol Cancer Ther 2008;7(8):2498 -508]

Pancreatic carcinoma is one of the most aggressive tumor entities, and standard chemotherapy provides only modest benefit. Therefore, specific targeting of pancreatic cancer for early diagnosis and therapeutic intervention is of great interest. We have previously shown that the cellular receptor for Shiga toxin B (STxB), the glycosphingolipid globotriaosylceramide (Gb 3 or CD77) is strongly increased in colorectal adenocarcinoma and their metastases. Here, we report an upregulation of Gb 3 in pancreatic adenocarcinoma (21 of 27 cases) as compared with matched normal tissue (n ¼ 27). The mean expression was highly significantly increased from 30 AE 16 ng Gb 3 /mg tissue in normal pancreas to 61 AE 41 ng Gb 3 /mg tissue (mean AE SD, P ¼ 0.0006), as evidenced by thin layer chromatography. Upregulation of Gb 3 levels did not depend on tumor stage or grading and showed no correlation with clinical outcome. Tumor cells and endothelial cells were identified as the source of increased Gb 3 expression by immunocytochemistry. Pancreatic cancer cell lines showed rapid intracellular uptake of STxB to the Golgi apparatus, following the retrograde pathway. The therapeutic application of STxB was tested by specific delivery of covalently coupled SN38, an active metabolite of the topoisomerase I inhibitor irinotecan. The cytotoxic effect of the STxB-SN38 compound in pancreatic cancer cell lines was increased more than 100-fold compared with irinotecan. Moreover, this effect was effectively blocked by competing incubation with nonlabeled STxB, showing the specificity of the targeting. Thus, STxB constitutes a promising new tool for specific targeting of pancreatic cancer. Mol Cancer Ther; 10(10); 1918-28. Ó2011 AACR.