The diterpenoid ester ingenol mebutate (IngMeb) is the active ingredient in the 
topical drug Picato, a first-in-class treatment for the precancerous skin 
condition actinic keratosis. IngMeb is proposed to exert its therapeutic effects 
through a dual mode of action involving (i) induction of cell death that is 
associated with mitochondrial dysfunction followed by (ii) stimulation of a 
local inflammatory response, at least partially driven by protein kinase C (PKC) 
activation. Although this therapeutic model has been well characterized, the 
complete set of molecular targets responsible for mediating IngMeb activity 
remains ill-defined. Here, we have synthesized a photoreactive, clickable 
analogue of IngMeb and used this probe in quantitative proteomic experiments to 
map several protein targets of IngMeb in human cancer cell lines and primary 
human keratinocytes. Prominent among these targets was the mitochondrial 
carnitine-acylcarnitine translocase SLC25A20, which we show is inhibited in 
cells by IngMeb and the more stable analogue ingenol disoxate (IngDsx), but not 
by the canonical PKC agonist 12-O-tetradecanoylphorbol-13-acetate (TPA). 
SLC25A20 blockade by IngMeb and IngDsx leads to a buildup of cellular 
acylcarnitines and blockade of fatty acid oxidation (FAO), pointing to a 
possible mechanism for IngMeb-mediated perturbations in mitochondrial function.