Emergence of a High-Plasticity Cell State during Lung Cancer Evolution

Tumor evolution from a single cell into a malignant, heterogeneous tissue remains poorly understood. Here, we profile single-cell transcriptomes of genetically engineered mouse lung tumors at seven stages, from pre-neoplastic hyperplasia to adenocarcinoma. The diversity of transcriptional states increases over time and is reproducible across tumors and mice. Cancer cells progressively adopt alternate lineage identities, computationally predicted to be mediated through a common transitional, high-plasticity cell state (HPCS). Accordingly, HPCS cells prospectively isolated from mouse tumors and human patient-derived xenografts display high capacity for differentiation and proliferation. The HPCS program is associated with poor survival across human cancers and demonstrates chemoresistance in mice. Our study reveals a central principle underpinning intra-tumoral heterogeneity and motivates therapeutic targeting of the HPCS.

Abstract A24: Using single-cell RNA-seq approaches to decipher heterogeneity in autochthonous mouse models of small cell lung cancer

Small cell lung cancer (SCLC) is one of the most aggressive cancer types, and patients in clinic usually (>60% cases) present with metastasis. Current therapies for SCLC have not changed from 1980, and they include a combination therapy of cisplatin and etoposide. Most patients relapse after initial response, and the 5-year survival for extensive stage SCLC is 2%. One possible explanation for the failure of conventional and targeted therapies in cancers is the cellular heterogeneity that exists within tumors. Thus, understanding phenotypic heterogeneity at the single-cell level can be leveraged to predict mechanisms of resistance, which enables the design of effective combination therapies. In this project, we used as a model system an autochthonous mouse model of human SCLC, in which we deleted p53, RB, and p130. We collected multiple primary tumors, circulating tumor cells (CTC), and lymph node (proximal site) and liver (distant site) metastases from the same mouse, and across different mice. These samples were collected at the stage that should correspond to the limited/extensive stage of human SCLC, which is most commonly seen in clinic. Then we used single-cell RNA-seq (sc-RNAseq) methods to define and understand transcriptional heterogeneity in these samples. Furthermore, we aimed to understand the evolutionary relationships between primary tumors, CTCs, lymph node and liver metastases using different computational approaches such as diffusion maps. Further defining and functionally annotating transcriptional heterogeneity will help us better understand the disease, and find the new Achilles heel for targeting.

Note: This abstract was not presented at the conference.

Citation Format: Nemanja Despot Marjanovic, Sheng Rong Ng, Aviv Regev, Tyler Jacks. Using single-cell RNA-seq approaches to decipher heterogeneity in autochthonous mouse models of small cell lung cancer [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr A24.

Anatomically and Functionally Distinct Lung Mesenchymal Populations Marked by Lgr5 and Lgr6

The diversity of mesenchymal cell types in the lung that influence epithelial homeostasis and regeneration is poorly defined. We used genetic lineage tracing, single-cell RNA sequencing, and organoid culture approaches to show that Lgr5 and Lgr6, well-known markers of stem cells in epithelial tissues, are markers of mesenchymal cells in the adult lung. Lgr6⁺ cells comprise a subpopulation of smooth muscle cells surrounding airway epithelia and promote airway differentiation of epithelial progenitors via Wnt-Fgf10 cooperation. Genetic ablation of Lgr6⁺ cells impairs airway injury repair in vivo. Distinct Lgr5⁺ cells are located in alveolar compartments and are sufficient to promote alveolar differentiation of epithelial progenitors through Wnt activation. Modulating Wnt activity altered differentiation outcomes specified by mesenchymal cells. This identification of region- and lineage-specific crosstalk between epithelium and their neighboring mesenchymal partners provides new understanding of how different cell types are maintained in the adult lung.

•

Lgr5 and Lgr6 mark mesenchymal cells in adult lungs

•

Single-cell transcriptome analysis defines mesenchymal heterogeneity

•

Distinct mesenchymal niches drive airway and alveolar differentiation

•

Wnt activity affects epithelial differentiation specified by mesenchymal cells