Abstract 1182: Patient derived xenograft (PDX) of human melanoma to predict clinical responses
Authors: Krepler Clemens , Sproesser Katrin , Brafford Patricia , Xiao Min , Beqiri Marilda , Xu Wei , Nathanson Katherine , Wargo Jennifer , Flaherty Keith , Morton Donald L. , Hoon Dave S. , Ryan Randall , Guarino Michael , Petrelli Nicholas J. , Elder David , Xu Xiawei , Karakousis Giorgos , Schuchter Lynn , Herlyn Meenhard 
Published: May 2015

Abstract
The approval of three drugs targeting the MAPK pathway has led to new standard therapies for melanoma with BRAFV600E mutations. The excitement about these therapeutic successes is somewhat dampened by the relapse of most if not all treated patients due to the development of acquired (secondary) resistance. Early clinical trial results indicate that combining BRAF and MEK inhibitors can improve survival and delay the onset of resistance. Currently, there is a lack of good translational models to study resistance pathways found in patients. We have developed a patient-derived xenograft (PDX) bank for assessing patients' responses to therapies.
Human melanoma tissues were obtained following surgery, and small pieces were implanted subcutaneously with Matrigel® into NSG mice. This technique was advantageous over injecting single tumor cells. It also allows prior dissociation and freezing for extended time periods prior to injection. The xenografts maintained a histological architecture similar to the respective patients' lesions. NSG mice injected with tumor fragments and single cells allow a high rate of tumor growth of approximately 90%, even if few malignant cells from fine needle aspirates are injected. When injecting decreasing numbers of tumor cells after removal of endothelial cells, hematopoietic cells and red blood cells (but not fibroblasts), in 5 out of 7 cases single malignant cells induced tumors. Our current tumor bank contains 125 samples linked to patients' clinical data and characterized for mutational status and spontaneous metastasis rates (25%). DNA fingerprinting was matched to normal blood DNA if available to assure identity of the samples. The samples had a similar distribution pattern of genetic abnormalities to those in patients, thus allowing their use for mutation-specific therapy strategies. As an example, a PDX from a patient with intrinsic resistance to vemurafenib was grown to compare tumor growth on a 200 ppm BRAF inhibitor (PLX4720) diet, 200 ppm PLX4720 + 7 ppm MEK inhibitor (PD0325901) combination diet, or control diet for 21 days. As in the original patient, the BRAF inhibitor alone did not inhibit tumor growth, while the combination of BRAF and MEK inhibition showed significant tumor growth inhibition demonstrating that a PDX can predict clinical outcome.
Citation Format: Clemens Krepler, Katrin Sproesser, Patricia Brafford, Min Xiao, Marilda Beqiri, Wei Xu, Katherine Nathanson, Jennifer Wargo, Keith Flaherty, Donald L. Morton, Dave S. Hoon, Randall Ryan, Michael Guarino, Nicholas J. Petrelli, David Elder, Xiawei Xu, Giorgos Karakousis, Lynn Schuchter, Meenhard Herlyn. Patient derived xenograft (PDX) of human melanoma to predict clinical responses. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1182. doi:10.1158/1538-7445.AM2014-1182