Abstract 6944: Transcriptional programs underpinning reoccurring cancer cell states, plasticity and tumour phylogenies in clear cell kidney cancer
Authors: Lombardi Olivia , Li Ran , Browning Lisa , Jabbar Faiz , Evans Hannah , Ratcliffe Peter J. , Mole David R. 
Published: March 2024

Abstract
Intratumor heterogeneity (ITH) is a substrate for tumor evolution and confers amenability to stressors and therapies. Sources of ITH include subclonal mutations, microenvironmental factors, and plasticity whereby a cell has the ability to adopt different cell states. Clear cell kidney cancer (ccRCC) has a well-characterized genetic initiating event - VHL inactivation - resulting in activation of HIF-1 and HIF-2 transcription factors. Although VHL inactivation is consistently clonal in nature, ccRCC nonetheless exhibits extensive genetic and morphological ITH. This makes ccRCC an excellent model in which to study ITH.
We performed single cell RNA-seq on multiregional samples from kidney tumors and macroscopically normal kidney tissue. We obtained 55 samples from 16 tumors and used the 10x Genomics platform to obtain gene expression data from ~150,000 single cells, including ~80,000 cancer and normal epithelial cells.
We identified three cancer cell states, co-existing in all clear cell kidney cancer tumors analyzed and marked by different gene expression programs: 1) differentiated-like cells marked by proximal tubule cell genes characteristic of the cancer cell of origin; 2) epithelial-mesenchymal transition (EMT)-like cells and 3) injured-like cells. Differentiated markers and EMT markers were associated with good and poor prognosis, respectively, indicating that these cell subpopulations are clinically important. Notably, these cell states are also present in the normal proximal tubule although in different proportions to the tumor samples, which contain more cells in the EMT-like and injured-like states. This suggests that the core features of ITH are inherent to the cell of origin of the cancer, but that the cell state trajectories are dysregulated in the tumor. Furthermore, in tumors these states exist as a continuum, whereby transitional cells in between states appear to exist, suggesting that cancer cells are continually and dynamically transitioning between states.
Lastly, we used chromosomal copy number variation (CNV) patterns to study genetic ITH. We examined the effect of 14q loss, which is associated with ccRCC metastasis, on gene expression. We found that 14q loss is associated with downregulation of HIF-1 transcriptional activity together with a reciprocal increase in HIF-2 activity, MYC activity and oxidative phosphorylation, highlighting potential mechanisms by which 14q loss may driver ccRCC metastasis.
Citation Format: Olivia Lombardi, Ran Li, Lisa Browning, Faiz Jabbar, Hannah Evans, Peter J. Ratcliffe, David R. Mole. Transcriptional programs underpinning reoccurring cancer cell states, plasticity and tumour phylogenies in clear cell kidney cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6944.