Abstract P6-12-04: An Inducible Lineage Tracing System for the Identification of Tumor-Initiating Cells

Abstract

Abstract Background: Metastasis and therapeutic resistance are a major clinical challenge, responsible for the vast majority of cancer deaths. A subpopulation of tumor cells known to have intrinsic resistance to standard therapies and contribute to metastasis function as “cancer stem”, or tumor-initiating, cells (TICs). Enriched populations of TICs are typically identified by markers such as aldehyde dehydrogenase activity, the cell surface marker combination of CD44+/CD24-, or fluorescent reporters for signaling pathways that regulate TIC function such as STAT3. Despite their utility, TIC markers and reporters have limitations. Marker expression can be unstable and there is no established method to lineage trace long-lived TICs or to follow them as they undergo cell state changes. Methods: To augment existing TIC reporters, we developed a two component TAM-inducible, Cre recombinase-dependent, STAT3 signaling-specific lentiviral LT system. The first component is a vector that labels cells with active STAT3 signaling (EGFP+), followed by a self-cleaving peptide and TAM-inducible Cre-recombinase (4M67-EGFP-P2A-CreERT2). The second component is a constitutively expressed dual-color switching Cre-dependent reporter vector (EFS-loxPdsRedloxP-mNeptune2). Addition of TAM drives color switching from dsRed to mNeptune2 via CreERT2 recombination in STAT3 signaling cells. Both lentiviral vectors were constructed using Gateway® Cloning. Sum159 cells were transduced with the LT system and reporter activity was validated both in vitro and in vivo using confocal microscopy and flow cytometry. Four LT cell populations (EGFP+/mNeptune2+, EGFP+/dsRed+, EGFP-/mNeptune2+, and EGFP-/dsRed+) were enriched using fluorescence activated cell sorting, then analyzed by single cell RNA sequencing (scRNA seq). Results: Our results confirm the STAT3 LT reporter identifies STAT3 signaling cells (EGFP+), which can be labelled (mNeptune2+) upon addition of TAM. We conducted a TAM dose response curve to identify the optimal TAM dose for complete and partial labeling of STAT3 signaling cells. scRNA seq uncovered gene expression patterns within the TIC compartment and revealed similarities and differences in gene expression between the TIC compartment and the remaining LT reporter populations. Conclusion: These data demonstrate our LT system is a powerful tool that can be applied to uncover the role of TICs in metastasis and therapeutic resistance, as well as identify genetic vulnerabilities to specifically target TICs. Citation Format: Eric P. Souto, Michael T. Lewis. An Inducible Lineage Tracing System for the Identification of Tumor-Initiating Cells [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-12-04.