Redox and structural determinants of mitochondrial complex III inhibition by triphenylphosphonium-conjugated atovaquone analogs
Abstract
Growing evidence indicates that cancer cell mitochondria remain functional and represent attractive therapeutic targets. Mitochondria-targeted drug delivery commonly uses triphenylphosphonium (TPP + )-conjugated compounds, which preferentially accumulate in cancer cell mitochondria because of their highly negative membrane potential. Many TPP + -conjugated agents inhibit mitochondrial electron transport chain complexes I and II, suppressing mitochondrial respiration and cancer cell proliferation. Recent studies suggest that electronwithdrawing substituents, such as trifluoromethyl groups, on the TPP + phenyl rings alter electron density around the phosphorus center, enhancing mitochondrial uncoupling activity and antiproliferative effects. To determine how TPP + electronic substituents influence redox properties, mitochondrial complex III interactions, and biological activity, we used mitochondria-targeted atovaquone (Mito-ATO) as a model system.
Atovaquone (ATO), a hydroxy-1,4-naphthoquinone and the only FDA-approved mitochondrial complex III inhibitor, is currently undergoing clinical evaluation for cancer therapy. We synthesized a series of mitochondriatargeted ATO derivatives (MitoR-ATOs) containing electron-donating or electron-withdrawing substituents on the TPP + moiety. Their effects on enzymatic superoxide generation were assessed by EPR spin trapping, mitochondrial oxygen consumption by Seahorse XF96 analysis, complex III Qi-site binding by computational modeling, and cancer cell proliferation using IncuCyte live-cell imaging. Unexpectedly, several MitoR-ATO derivatives emerged as potent complex III inhibitors through enhanced binding at the Qi site.
Structure-activity relationship analysis revealed that the intrinsic redox properties of TPP + -conjugated MitoR-ATO analogs alone do not predict biological activity. Instead, accurate prediction of the therapeutic efficacy of mitochondria-targeted complex III inhibitors requires integrating redox properties with computational analyses of ligand-protein interactions at the mitochondrial complex III Qi site.
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BibTeX
@article{resende2026redox,
title = {{Redox and structural determinants of mitochondrial complex III inhibition by triphenylphosphonium-conjugated atovaquone analogs}},
author = {Bruna Rafaela Pereira Resende and Gang Cheng and Gabriel Canard and Didier Siri and Vanessa Leone and Micael Hardy and Balaraman Kalyanaraman},
journal = {Redox Biology},
year = {2026},
month = sep,
doi = {10.1016/j.redox.2026.104370},
url = {https://hal.science/hal-05769164v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Redox and structural determinants of mitochondrial complex III inhibition by triphenylphosphonium-conjugated atovaquone analogs
AU - Bruna Rafaela Pereira Resende
AU - Gang Cheng
AU - Gabriel Canard
AU - Didier Siri
AU - Vanessa Leone
AU - Micael Hardy
AU - Balaraman Kalyanaraman
PY - 2026
DA - 2026/09/29
JO - Redox Biology
DO - 10.1016/j.redox.2026.104370
UR - https://hal.science/hal-05769164v1
AB - Growing evidence indicates that cancer cell mitochondria remain functional and represent attractive therapeutic targets. Mitochondria-targeted drug delivery commonly uses triphenylphosphonium (TPP + )-conjugated compounds, which preferentially accumulate in cancer cell mitochondria because of their highly negative membrane potential. Many TPP + -conjugated agents inhibit mitochondrial electron transport chain complexes I and II, suppressing mitochondrial respiration and cancer cell proliferation. Recent studies suggest that electronwithdrawing substituents, such as trifluoromethyl groups, on the TPP + phenyl rings alter electron density around the phosphorus center, enhancing mitochondrial uncoupling activity and antiproliferative effects. To determine how TPP + electronic substituents influence redox properties, mitochondrial complex III interactions, and biological activity, we used mitochondria-targeted atovaquone (Mito-ATO) as a model system. Atovaquone (ATO), a hydroxy-1,4-naphthoquinone and the only FDA-approved mitochondrial complex III inhibitor, is currently undergoing clinical evaluation for cancer therapy. We synthesized a series of mitochondriatargeted ATO derivatives (MitoR-ATOs) containing electron-donating or electron-withdrawing substituents on the TPP + moiety. Their effects on enzymatic superoxide generation were assessed by EPR spin trapping, mitochondrial oxygen consumption by Seahorse XF96 analysis, complex III Qi-site binding by computational modeling, and cancer cell proliferation using IncuCyte live-cell imaging. Unexpectedly, several MitoR-ATO derivatives emerged as potent complex III inhibitors through enhanced binding at the Qi site. Structure-activity relationship analysis revealed that the intrinsic redox properties of TPP + -conjugated MitoR-ATO analogs alone do not predict biological activity. Instead, accurate prediction of the therapeutic efficacy of mitochondria-targeted complex III inhibitors requires integrating redox properties with computational analyses of ligand-protein interactions at the mitochondrial complex III Qi site.
SN - 2213-2317
ER -