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Theranostics 2021; 11(11):5077-5091. doi:10.7150/thno.54936 This issue Cite

Research Paper

Characterization of drug-induced human mitochondrial ADP/ATP carrier inhibition

Stephany Jaiquel Baron¹, Martin S. King¹, Edmund R.S. Kunji^1✉, Tom J.J. Schirris^1,2✉

1. Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge Biomedical Campus, Keith Peters Building, Hills Road, Cambridge, CB2 0XY, United Kingdom.
2. Department of Pharmacology and Toxicology, Radboud Institute for Molecular Life Sciences, Radboud Center for Mitochondrial Medicine, Radboud University Medical Center, Nijmegen, The Netherlands.

✉ Corresponding authors: Prof. Dr. Edmund R.S. Kunji, MRC Mitochondrial Biology Unit, University of Cambridge, Keith Peters Building, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0XY, United Kingdom; Phone: +44 12 232 52 850; Fax: +44 12 232 52 875; Email: ekcam.ac.uk; Dr. T.J.J. Schirris, ERT, Department of Pharmacology and Toxicology, Radboud University Medical Center, PO Box 9101, 6500 HB Nijmegen, The Netherlands; Phone: +31 61 517 63 47; E-mail: Tom.Schirrisnl More

Abstract

An increasing number of commonly prescribed drugs are known to interfere with mitochondrial function, causing cellular toxicity, but the underlying mechanisms are largely unknown. Although often not considered, mitochondrial transport proteins form a significant class of potential mitochondrial off-targets. So far, most drug interactions have been reported for the mitochondrial ADP/ATP carrier (AAC), which exchanges cytosolic ADP for mitochondrial ATP. Here, we show inhibition of cellular respiratory capacity by only a subset of the 18 published AAC inhibitors, which questions whether all compound do indeed inhibit such a central metabolic process. This could be explained by the lack of a simple, direct model system to evaluate and compare drug-induced AAC inhibition.

Methods: For its development, we have expressed and purified human AAC1 (hAAC1) and applied two approaches. In the first, thermostability shift assays were carried out to investigate the binding of these compounds to human AAC1. In the second, the effect of these compounds on transport was assessed in proteoliposomes with reconstituted human AAC1, enabling characterization of their inhibition kinetics.

Results: Of the proposed inhibitors, chebulinic acid, CD-437 and suramin are the most potent with IC₅₀-values in the low micromolar range, whereas another six are effective at a concentration of 100 μM. Remarkably, half of all previously published AAC inhibitors do not show significant inhibition in our assays, indicating that they are false positives. Finally, we show that inhibitor strength correlates with a negatively charged surface area of the inhibitor, matching the positively charged surface of the substrate binding site.

Conclusion: Consequently, we have provided a straightforward model system to investigate AAC inhibition and have gained new insights into the chemical compound features important for inhibition. Better evaluation methods of drug-induced inhibition of mitochondrial transport proteins will contribute to the development of drugs with an enhanced safety profile.

Keywords: drug-induced mitochondrial dysfunction, mitochondrial transport proteins, adenine nucleotide translocase, thermostability shift, transport inhibition kinetics.

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