Mitochondrial targeting of radioprotectants using peptidyl conjugates

Abstract

Ionizing radiation activates a mitochondrial nitric oxide synthase, leading to inhibition of the respiratory chain, generation of excess superoxide, peroxynitrite production and nitrosative damage. We have measured the radioprotective effects of a nitric oxide synthase antagonist (AMT) versus a free radical scavenger (4-amino-TEMPO) using electrochemical detection of nitric oxide and peroxynitrite. To enhance their efficacy, we have conjugated these compounds to peptides and peptide isosteres--derived from the antibiotic gramicidin S--that target the mitochondria. The targeting ability of these peptidyl conjugates was measured using quantitative mass spectrometry.

Fig. 1

Unconjugated (a) and conjugated (c) 4-amino-TEMPO (XJB-5-125), at 100 μM and spectra for mitochondria incubated with unconjugated (b) and conjugated (d) 4-amino-TEMPO.

Fig. 2

Capsaicin evoked NO production and formation of ONO₂⁻ simultaneously measured by microsensors in (a) non-irradiated cells, and irradiated cells treated with (b) unconjugated 4-amino-TEMPO (100 μM), (c) high-dose conjugated 4-amino-TEMPO (XJB-5-125; 100 μM) and (d) conjugated-AMT (XJB-5-127; 10 μM).

Fig. 3

Chemical structures of compounds (a) XJB-5-234, (b) XJB-5-133, (c) XJB-5-241 and (d) XJB-5-127.