Abstract 1389: Development and characterization of a natural model of triple negative breast micrometastasis.
Authors: Ihnat Michael A. , Bailey-Downs Lora C. , Thorpe Jessica E. , Disch Bryan C. , Bastian Anja , Farasyn Taleah C. , Hauser Paul J. , Hurst Robert E. 
Published: August 2014

Abstract
Physiologically relevant animal models of micrometastasis are lacking; yet micrometastasis activation leading to macrometastasis and/or recurrent tumors is a major cause of cancer mortality and treatment resistance. Tumor cell implantation metastasis models typically use large numbers of tumor cells and immune compromised rodents together with removal of primary tumors to maximize the number, size and speed of macrometastases. Genetic and chemical/physical tumorigenesis models are often inconveniently slow and do not provide consistent metastasis. In order to develop a platform for investigating the biology of micrometastasis and for drug development to target micrometastases, we developed a model to study this phenomenon in vivo. The 4T1 triple negative syngeneic breast cancer model was chosen without resection of the primary tumor. A cell titration from 100,000 to 500 4T1-GFP tagged cells was first completed, with cells implanted into fat pad 3 of immune proficient 8 wk female BALB/c mice. Implantation of 15,000-100,000 cells resulted in 90-100% primary tumor take by 7 days; a small number (less than 15) micrometastases into the lungs by 2 wk; 70-90% of the animals having macrometastases (as evidenced by a distinct blood supply using tetrarhodamine labeled dextran) by 4 wk; and with most animals becoming moribund by 5 wk. Implantation of 7,500 cells resulted in &gt;90% tumor take by 10 days; in 30-250 micrometastases in the lung (with many animals having 5-10 brain micrometastases) 2 wk post-implantation; with the first small macrometastases present at 4 wk; with most (80%) animals having macrometastases at 5 wk and animals becoming moribund by 6 wk post-implantation. With animals seeded with 500-1500 cells, the time of micrometastasis to macrometastasis conversion and animal survival could be prolonged, though primary tumor take was less (40-60%) than with 7,500 cells. Finally, this model using 7,500 cells was used to test the efficacy of a first-line chemotherapeutic agent for breast cancer, docetaxel, given at its maximal tolerated dose (MTD; 30 mg/kg weekly). Although primary tumor growth could be significantly reduced by docetaxel (P&lt;0.01; two way ANOVA/repeated measures post-test), the number of micro and macrometastases at the experiment end was not significantly affected by docetaxel treatment and animal weight, a measure of systemic toxicity, was significantly reduced in the docetaxel group (P&lt;0.01, unpaired two-tailed students’ t-test).
Citation Format: Michael A. Ihnat, Lora C. Bailey-Downs, Jessica E. Thorpe, Bryan C. Disch, Anja Bastian, Taleah C. Farasyn, Paul J. Hauser, Robert E. Hurst. Development and characterization of a natural model of triple negative breast micrometastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1389. doi:10.1158/1538-7445.AM2013-1389