Cancer stem cells (CSCs) are progenitor cells that contribute to treatment-resistant phenotypes during relapse. CSCs exist in specific tissue microenvironments that cell cultures and more complex models cannot mimic. Therefore, the development of new approaches that can detect CSCs and report on specific properties (e.g., stem cell plasticity) in their native environment will have profound implications for studying CSC biology. Thus, the goal of this study was to develop a probe that can sense CSC states in vivo. To accomplish this goal, we turned our attention to aldehyde dehydrogenase 1A1 (ALDH1A1), which is associated with stemness and is upregulated in CSCs from a wide variety of cancer types. We developed AlDeSense, a turn-on fluorescent probe equipped with a benzaldehyde moiety that acts as a substrate for ALDH1A1. AlDeSense exhibits a 20-fold fluorescent enhancement when treated with ALDH1A1 and does not turn over with a panel of other closely related ALDH isoforms. We also developed a matching non-responsive control reagent called Ctrl-AlDeSense to account for background or non-specific fluorescence. We demonstrated that AlDeSense and Ctrl-AlDeSense in tandem can be used for confocal fluorescence imaging of cells with CSC characteristics in several different cancer types. We then tested AlDeSense in two different animal models. The first was a melanoma metastasis model, where one cohort of mice was intravenously injected with melanoma cells enriched in CSCs (e-CSCs), while a second control group was injected with wild type melanoma cells (non-CSCs). Metastases in lungs formed from e-CSCs showed a significantly higher signal from AlDeSense compared to controls. Secondly, we tested the ability of AlDeSense to image CSCs in vivo. Mice were subcutaneously injected with e-CSCs on the right flank and non-CSCs on the left flank. Once tumors had developed, the mice were injected with AlDeSense. Using a whole-body fluorescence imager, we observed that AlDeSense injected mice showed a significant enhancement in signal only in e-CSC tumors. Prior to this study, it was unknown whether CSCs would maintain stemness properties such as high ALDH1A1 activity after introduction into a living system. Our imaging experiments demonstrate that ALDH1A1 activity persists up to several weeks in CSCs after they are introduced into a living animal, implicating that a niche must be established that supports this population of cells.

Surveillance of cancer stem cell plasticity using an isoform-selective fluorescent probe for aldehyde dehydrogenase 1A1

2019 Spring National Meeting

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