Profiling of retinaldehyde dehydrogenases in cancer cells

Retinaldehyde dehydrogenases convert retinal into all-trans retinoic acid (ATRA), thereby regulating cell differentiation and cancer stem cell proliferation. Chemical tools and methods are valuable commodities to study aldehyde dehydrogenase (ALDH) activity in human cells. Here, we describe the design, synthesis and application of LEI-945, a first-in-class activity-based probe modeled on retinal that reports on individual ALDHs in cancer cells. Comparative chemical proteomics with LEI-945 explained the ability of various breast cancer cell lines to produce ATRA via retinaldehyde dehydrogenases isozymes, whereas the ALDEFLUORTM assay could not. Competitive chemical proteomics using LEI-945 revealed that the ALDH inhibitor NCT-505 inhibited both ALDH1A1 and ALDH1A3 in MDA-MB-468 breast cancer cells inducing a cell cycle arrest in the G1 phase as well as cell death through necrosis. Our results show that LEI-945 holds promise to guide the discovery of ALDH-based therapeutics