Abstract B40: Minimal mutational determinants of human squamous cell carcinoma

Dozens of driver mutations and copy number changes have been implicated in human squamous cell carcinomas (SCCs), and each tumor harbors multiple putative driver mutations. However, the minimal set of mutations sufficient to transform a normal keratinocyte into squamous cell carcinoma is unknown. By analyzing TCGA data and previously published datasets, we have identified common combinations of driver mutations in SCCs. Among the most common driver events are mutations in TP53, CDKN2A, and NOTCH1. Using CRISPR editing at endogenous loci in primary human keratinocytes, we demonstrate that no single driver mutation is sufficient to transform keratinocytes, and in fact many single gene mutations appear toxic to keratinocytes. The combination of loss-of-function mutations in TP53 and CDKN2A is sufficient to immortalize both skin and oral primary human keratinocytes in 2D culture and confer a selective advantage in competition assays. Simultaneous mutation of TP53, CDKN2A, and NOTCH1 demonstrates a very similar phenotype in 2D culture as mutation of TP53 and CDKN2A alone. However, using 3D organotypic squamous epithelial cultures consisting of genome-edited keratinocytes grown on decellularized dermis impregnated with fibroblasts and grown at an air-liquid interface demonstrates that keratinocytes with TP53 and CDKN2A mutation alone are sufficient to induce dysplasia, whereas keratinocytes harboring TP53, CDKN2A, and NOTCH1 mutation exhibit an SCC-like phenotype, including invasion through the basement membrane. RNAseq analysis demonstrates that the transition to SCC by NOTCH1 loss involves a partial EMT-like program. Targeted hybrid capture sequencing of edited keratinocytes revealed no other driver mutations or copy number changes other than the experimentally induced ones, consistent with the notion that TP53, CDKN2A, and NOTCH1 mutations alone are sufficient to reprogram a normal keratinocyte into SCC. Thus, despite a high mutation burden and frequent chromosomal instability, as few as three mutational events appear to be sufficient to induce SCC. Citation Format: Vicente Planells-Palop, Angie Koo, Heydi Malave, Katharine Lee, Aaron Tward. Minimal mutational determinants of human squamous cell carcinoma [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr B40.