A Metastatic Colon Cancer Model Using Non-operative Trans-Anal Rectal Injection

(^) denotes superscript

Background: This study was conducted to develop a non-invasive orthotopic model for metastasis of colon and rectal cancer using a trans-anal approach that is non-operative, reproducible, and easy to perform. Currently, the most accurate orthotopic representation of metastatic human colon cancer is a cecal injection. The trans-anal model allows for further examination of systemic immune responses, tumor take, and onset of metastasis without prior surgical intervention.

Methods: Sixty (60) Balb/c mice were anesthetized and received gentle anal dilation using blunt tipped forceps at the anal opening. Using a 29 gauge syringe, murine colon cancer parental CT26 (CT26) or luciferase labeled CT26 (CT26-luc) cells were injected submucosally into the distal, posterior rectum (CT26 N=30 and CT26-luc N=30) at various concentrations: 2.5×10(^4), 1×10(^5), or 1×10(^6) in a volume of 50µL. All mice were injected using 100 x magnification. Tumor growth and metastatic development was monitored in CT26-luc (N=3) and grossly in CT26 (N=1) at 5 day intervals for 50 days. CT26-luc mice were anesthetized and injected with 150 µg/kg luciferin, then imaged with x-ray (15 second exposure) followed by luminescence (6 minute exposure) using the Kodak Molecular Imaging software. All remaining mice were sacrificed at post-injection day 50. The rectum, rectal wall, and liver were photographed, measured, processed for histology, and reviewed by a pathologist.

Results: The optimal concentration for metastasis and survival of mice was 2.5×10(^4) cells. Higher concentrations of CT26 or CT26-luc cells yielded higher mortality and did not result in metastasis. The overall success of tumor growth using the trans-anal rectal injection was 65%. Histology revealed that all tumors were poorly differentiated adenocarcinoma. Two mice (33%) from the 2.5×10(^4) CT26-luc group developed metastatic colonic adenocarcinoma to the liver at post-injection day 50. Luminescence monitoring of metastasis added no additional value.

Conclusion: Trans-anal rectal injection of colon cancer cells offers a non-operative orthotopic murine model for colon cancer that may lead to the development of metastasis. By using an orthotopic model that does not require abdominal surgery for implantation, more aspects of metastatic colon cancer can be evaluated without the influence of a previous abdominal incision. These results warrant more investigation into the metastatic capabilities of this model.

Session: Podium Presentation

Program Number: S050

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