Small-molecule targeting of the mitochondrial compartment with an endogenously cleaved reversible tag.

Targeted accumulation of chemically unaltered compounds within the mitochondrial compartment has not yet been achieved. Here we describe a reversible tag that is endogenously cleaved after mitochondrial accumulation has occurred. Specifically, we have reversibly tagged alpha-lipoic acid with a triphenylphosphonium moiety that is cleaved by the physiologically contained mitochondrial aldehyde dehydrogenase (ALDH-2). This reversibly tagged compound activates the lipoic acid-sensitive pyruvate dehydrogenase complex, and this results in increased glucose oxidation. We observed a reduction in ROS accumulation after preincubation with the reversibly tagged compound, whereas untagged or irreversibly tagged compounds either had no effect on ROS formation or rather caused increased oxidative stress, respectively. Lastly, the cytotoxicity of the reversibly tagged compound is less than that of the irreversibly tagged compound. Overall, reversible tagging combines decreased tag-related cytotoxicity with increased bioactivity, and this potentially provides a novel concept in mitochondrial pharmacology.