Abstract B12: The effects of Irinophore C™ on the microenvironment and vasculature of a primary orthotopic model of colorectal cancer.

Introduction: Colorectal cancer is a common cancer that accounts for ∼10% of cancer cell deaths in North America. There are numerous in vivo xenograft models for colorectal cancer available, but in general, these are derived from immortalized cell lines and fail to capture the complexities and heterogeneity of tumors seen in the clinic. Our group has developed a series of orthotopic, primary tumors from samples of human colorectal cancer tissue obtained during surgical resection that maintain the characteristics of the original sample. The effects of Irinophore C™, (a liposomal formulation of irinotecan that is more efficacious and less toxic than the parent drug) on the microenvironment and vascular function of these primary colorectal tumors were examined in the present study. Materials and Methods: Primary tumor tissues, obtained from colorectal cancer patients, were validated by a reference pathologist and implanted subcutaneously in SCID mice. Small pieces of subcutaneous tumors that grew successfully were then passaged orthotopically on the ascending colon of new mice. When these tumors reached ∼200mm 3 , groups of mice were treated with vehicle control (0.9% saline), irinotecan (50mg/kg), or Irinophore C™ (25mg/kg) once a week for 6 weeks. Separate groups of tumors were harvested on days 3 and 42 after treatment started. Immunofluorescence staining was performed on tumor cryosections followed by computerized image analysis to determine levels of cell proliferation, apoptosis, hypoxia, and vessel density. Results: 4 of 14 samples were successfully propagated orthotopically and were characterized by a reference pathologist. The tumors maintain their original morphology, and one is a highly mucinous adenocarcinoma whereas the others are typical colorectal adenocarcinomas. Treatment with irinotecan and Irinophore C™ reduced tumor volumes by 54% and 92%, respectively, compared to the vehicle control. No toxic effects were seen with Irinophore C™. Immunostaining data showed that the distance between blood vessels remained the same for Irinotecan when compared to control, but increased with Irinophore C™ treatment (+30%; P Conclusion: An orthotopic model of colorectal cancer was successfully developed using patient tumor materials that retained the morphology of the primary tumor. Irinophore C™ was more effective in controlling tumor growth than irinotecan despite being delivered at a lower dose. In addition, treatment with Irinophore C™ appeared to improve overall vascular function in the tumor. Based on these data, it is clear that Irinophore C™ has different mechanisms of action and is more efficacious than irinotecan against primary models of colorectal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B12.