NDUFS3 knockout cancer cells and molecular docking reveal specificity and mode of action of anti-cancer respiratory complex I inhibitors

Inhibition of respiratory complex I (CI) is becoming a promising anti-cancerstrategy, encouraging the design and the use of inhibitors, whose mechanismof action, efficacy and specificity remain elusive. As CI is a central player ofcellular bioenergetics, a finely tuned dosing of targeting drugs is requiredto avoid side effects. We compared the specificity and mode of action of CIinhibitors metformin, BAY 87-2243 and EVP 4593 using cancer cell modelsdevoid of CI. Here we show that both BAY 87-2243 and EVP 4593 were selec-tive, while the antiproliferative effects of metformin were considerablyindependent from CI inhibition. Molecular docking predictions indicatedthat the high efficiency of BAY 87-2243 and EVP 4593 may derive from thetight network of bonds in the quinone binding pocket, although in differentsites. Most of the amino acids involved in such interactions are conservedacross species and only rarely found mutated in human. Our data make acase for caution when referring to metformin as a CI-targeting compound,and highlight the need for dosage optimization and careful evaluation ofmolecular interactions between inhibitors and the holoenzyme.