Development of a Retinal-Based Probe for the Profiling of Retinaldehyde Dehydrogenases in Cancer Cells

Retinaldehyde dehydrogenases belong to a superfamily
of enzymes
that regulate cell differentiation and are responsible for detoxification
of anticancer drugs. Chemical tools and methods are of great utility
to visualize and quantify aldehyde dehydrogenase (ALDH) activity in
health and disease. Here, we present the discovery of a first-in-class
chemical probe based on retinal, the endogenous substrate of retinal
ALDHs. We unveil the utility of this probe in quantitating ALDH isozyme
activity in a panel of cancer cells via both fluorescence and chemical
proteomic approaches. We demonstrate that our probe is superior to
the widely used ALDEFLUOR assay to explain the ability of breast cancer
(stem) cells to produce all-trans retinoic acid.
Furthermore, our probe revealed the cellular selectivity profile of
an advanced ALDH1A1 inhibitor, thereby prompting us to investigate
the nature of its cytotoxicity. Our results showcase the application
of substrate-based probes in interrogating pathologically relevant
enzyme activities. They also highlight the general power of chemical
proteomics in driving the discovery of new biological insights and
its utility to guide drug discovery efforts.