Author ORCID Identifier

https://orcid.org/0000-0001-7983-1808

Document Type

Dissertation

Date of Award

2022

Degree Name

Doctor of Philosophy (PhD)

Department

Basic Biomedical Science

First Advisor

Michael S Kareta, Randolph Faustino

Abstract

Small Cell Lung Cancer (SCLC) is a devastating disease characterized by a very low two-year survival rate and almost universal acquisition of chemoresistance. Nearly all patients have tumors driven by functional inactivation of the tumor suppressors Rb and p53, but despite the uniform origins of this tumor, not all patients are genetically or phenotypically identical. SCLC can be subtyped into four unique molecular subtypes, determined by the expression of ASCL1, NEUROD1, POU2F3, or YAP1. These subtypes are plastic, and subtype switching after chemotherapy has been documented. Without the understanding of how tumor heterogeneity arises, we cannot solve the challenge of chemoresistance in SCLC. In recent years, a powerful new tool in studying tumor heterogeneity has emerged. Genetic barcoding allows for the identification and tracking of individual tumor populations by inserting a small genetic sequence (“barcode”) into the genome of tumor cells. As the cells divide, the barcode is passed on and a high-resolution lineage map is constructed. Here, genetic barcoding is used for the first time in SCLC, combined with single-cell RNA sequencing in a genetically engineered mouse model and a xenograft model of SCLC. In the mouse model of SCLC, tumors were sequenced at early, middle, and late stages of tumor development, as well as chemoresistant tumors. While no barcodes were detected by scRNA-seq, valuable information about the process of tumor development in SCLC is observed. I identify two cellular populations (“early” and “late”) that arise during tumor development. A notable difference in the two populations is the expression of genes corresponding to members of the AP-1 network. The AP-1 network was validated to be critical for tumorigenesis in SCLC. Barcoded SCLC xenografts and chemoresistant xenografts belonging to two SCLC subtypes were generated. scRNA-seq revealed increased transcriptomic plasticity following chemotherapy treatment in SCLC-A xenografts but not SCLC-N xenografts. The Cancer Testis Antigens PAGE5 and GAGE2A were identified and validated as mediators of chemoresistance in SCLC. This work represents the first application of genetic barcoding in SCLC and identifies actionable drug targets for future development.

Subject Categories

Genetics

Keywords

Cellular Barcoding, Chemoresistance, Genomics, Lineage Tracing, SCLC, Single-Cell RNA sequencing

Number of Pages

191

Publisher

University of South Dakota

Included in

Genetics Commons

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