Circulating tumor cells (CTCs) are indicative of disease burden in metastatic colorectal cancer (mCRC) and high counts are believed to adversely affect outcome. However there has been a lack of suitable mouse models to study CTCs in mCRC. Here we report the development of an orthotopic model of mCRC in athymic nude mice from which we have successfully isolated and enumerated CTCs using the FDA-approved Veridex Cellsearch technology (Table 1). So far we have injected 5 mice with a million cells each of the human CRC cell line DLD-1 within the layers of the cecal wall for tumor xenografts to grow. 200 microL of blood has been collected every 2 weeks, till the endpoint of 16 weeks or a humane endpoint, from the medial saphenous vein of the mouse for CTC detection. In our protocol, human leucocyte filters are used as a RBC source. The blood is centrifuged at 800 G for 10 minutes in a CellSave tube, the serum removed and replaced by an equal volume of PBS. Mouse blood is transferred to this tube after collection. Efforts are on to show CTCs from mice injected with tumor cells labeled with a suitable cellular dye like Cellvue. At the endpoint, after humanely euthanizing a mouse, the cecum and organs are analyzed for possible secondary spread (liver, lungs, mesenteric lymph nodes) following resection and preservation. H/E staining is performed for evidence of primary or metastatic tumor tissue. Positive tissue samples are further analysed using immunostaining for stem cell markers and prognostic markers CD133, CD26, ALDH1, Mcl-1, EFGR, Ki67. We are analyzing isolated CTCs for expression of these markers and note the extent of concordance. The mouse model should help to understand the role of CTCs in evaluating metastasis as well as to validate the use of CTCs as tools for “liquid biopsy” of tumors. Table 1. CTC counts in the mice at different time points from injection of cells. Mouse 4 is the negative control mouse of the cohort which received injection of normal saline instead of cancer cell suspension. * denotes clotted sample.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2393. doi:1538-7445.AM2012-2393