In an initial PROTAC approach for c-IAP, ME-BS was coupled to all-trans retinoic acid (ATRA), which binds cellular retinoic acid binding protein (CRABP-1 and -2), with the latter chosen due to the involvement of CRABP1/2 in Alzheimer’s disease, neuroblastoma, Wilms tumor, and head and neck squamous cell carcinoma [99]. Here, CRABP1 is linked to early-onset autosomal dominant Alzheimer disease.