Abstract 3878: A model to assess clonal evolution of metastatic colorectal cancer during chemotherapy utilizing patient derived xenografts
Authors: Grossman Julie G. , Strand Matthew , Dang Ha , White Brian , Fleming Timothy , Goedegebuure Peter , Lockhart Albert , Lim Kian , Ley Timothy , Wilson Richard , Mardis Elaine , Maher Christopher , Fields Ryan 
Published: August 2015

Abstract
Introduction
Chemotherapy (FOLFOX) with or without surgical resection is the primary treatment for metastatic colorectal cancer (mCRC). However, intrinsic and acquired resistance to chemotherapy poses a major obstacle. The lack of predictors of response to treatment and of understanding of mechanisms of resistance leads to ineffective chemotherapy and, hence, unnecessary morbidities. Patient-derived xenografts (PDXs) represent a model system to evaluate the effectiveness of treatment regimens utilizing human tumors in the context of “precision medicine.” We have developed a heterotopic PDX model of mCRC that emulates acquired chemoresistance.
Methods
Tumor samples from treatment naïve or chemo-treated mCRC patients were implanted subcutaneously into immunodeficient mice. At an optimal volume, the tumor was either divided into pieces and implanted subcutaneously or processed into a single cell suspension and implanted into mice. Mice were classified into either 5-fluorouracil, leucovorin, plus oxaliplatin (FOLFOX) (n = 10) or vehicle (n = 5) groups. FOLFOX was dosed weekly at the maximum tolerated dosage. Mice were sacrificed when tumors reached 20mm diameter, at which time a single cell suspension was created for implantation into the next generation. Tumors were passaged using this method until FOLFOX resistance was attained. DNA and RNA were isolated from all samples for genetic analysis.
Results
Liver metastasis from six patients, including chemo-treated (n = 3) and chemo-naïve (n = 3), were consecutively used to generate PDX lines. PDX tumor growth from one of the patients exhibited no difference between treatment and control. Within the remaining treatment cohorts, chemo-treated PDX tumors overall grew significantly slower than matching untreated PDX tumors at the first passage (p&lt;0.05) regardless of whether the tumor originated from single cell suspension or pieces. However, PDX tumors from the first patient entered into the study showed chemo-resistance at passage 3. Further, innate resistance was seen in some PDXs from the same patient displaying rapid growth at initiation of chemotherapy treatment. Utilizing tumor tissue obtained from this model, we are currently assessing the genetic and epigenetic mechanism(s) responsible for resistance.
Conclusion
We have developed a PDX model that recapitulates acquired chemoresistance in mCRC, which allows for the genomic characterization of FOLFOX resistant liver metastasis. We are currently defining the clonal architecture of chemotherapy resistant and responsive PDXs with the goal of identifying predictors of response and resistance. The ability to treat a patient and their personalized “model” in real time represents an ideal tool to test response to treatment and further investigate treatment resistance.
Citation Format: Julie G. Grossman, Matthew Strand, Ha Dang, Brian White, Timothy Fleming, Peter Goedegebuure, Albert Lockhart, Kian Lim, Timothy Ley, Richard Wilson, Elaine Mardis, Christopher Maher, Ryan Fields. A model to assess clonal evolution of metastatic colorectal cancer during chemotherapy utilizing patient derived xenografts. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3878. doi:10.1158/1538-7445.AM2015-3878