Abstract A07: Speedy mouse models to study melanomagenesis
Authors: Bok Ilah , Karreth Florian A. 
Published: May 2018

Abstract
Melanoma accounts for only about 1% of the skin cancer, but contributes to a vast majority of skin cancer deaths. Despite extensive progress in treating melanoma with immunotherapy and small-molecule inhibitors, melanoma patients still suffer from tumor recurrence, mainly due to inherent or acquired resistance to these treatments. A better understanding of the detailed molecular mechanisms that contribute to melanoma formation and resistance may provide novel avenues for the development of improved treatment strategies. Genetically engineered mouse models (GEMMs) closely recapitulate the genetics and etiology of human malignancies and have significantly contributed to our understanding of the mechanisms underlying melanoma initiation and progression. However, the generation and characterization of GEMMs is often challenging due to their time-consuming, laborious, and expensive nature. To overcome some of these limitations, we sought to develop a melanoma mouse-modeling platform, which allows for accelerated speed, increased throughput, and lower cost of in vivo melanoma studies compared to conventional mouse models. To this end, we established several embryonic stem cell (ESC) lines harboring multiple alleles to aide in creating versatile melanoma mouse models. These alleles include Cre-inducible endogenous BrafV600E or NrasQ61R alleles for melanoma initiation, conditional PTEN knockout alleles for melanoma progression, the melanocyte-specific, tamoxifen-inducible Tyr-CreERt2 allele, a Cags-LSL-rtTA3 allele to activate Tet-inducible expression cassettes, and the collagen homing cassette (CHC) for the efficient delivery of such expression cassettes via recombination-mediated cassette exchange (RMCE). We demonstrated that our newly derived ESCs can be targeted with various constructs via RMCE with extremely high efficiency, thus significantly reducing the number of clones one has to screen for successful targeting. Moreover, we confirmed pluripotency of our ESC lines by Oct4 and Nanog staining, and by demonstrating their ability to generate chimeras via blastocyst injection and completely ESC-derived mice via tetraploid complementation. Topical application of 4-hydroxytamoxifen (4-OHT) on chimeras carrying the BrafV600E and PTENFlox alleles resulted in the development of nevi and melanomas within a few weeks. Importantly, our melanoma ESC-GEMM approach is compatible with novel genetic tools including inducible shRNA and CRISPR, thus providing a versatile and modular platform for the study of gene function in melanomagenesis. Thus, we have established a speedy mouse-modeling platform that will stimulate and accelerate in vivo melanoma research, and will provide a useful resource to investigate the pathobiology of melanomagenesis and to develop and preclinically test novel treatments.
Citation Format: Ilah Bok, Florian A. Karreth. Speedy mouse models to study melanomagenesis [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A07.