Investigation of the Effect of Detonation Nanodiamonds and their Conjugates with Doxorubicin and Dioxadet on the Mitochondrial Membrane

Targeted drug delivery is aimed at preventing drugs’ nonspecific distribution in different tissues. One of efficient ways for drug’s targeted delivery is using denonation nanodiamonds. These nanoparticles are an advantageous material for nanomedicine due to their low cost, biocompatibility, hardness and chemical stability. Majority of blood plasma proteins and blood cell surfaces are charged negatively. Therefore biocompatibility and long circulation lifetimes of carboxylated nanodiamonds can be partially attributed to their negative surface charge. The presence of different functional groups on nanodiamond surfaces enables their functionalization with a variety of therapeutic agents, including antitumour drugs. One of them is dioxadet, a derivative of symmetric triazine. It is becoming evident that mitochondria play crucial role in metastasis and chemoresistance of tumors, which makes them a very promising target for anticancer therapy. In particular, proton translocating F1Fo-ATPase/ATP synthase can be one of these targets. This enzyme is responsible for making the majority of ATP in the cell by oxidative phosphorylation. More than 300 natural and synthesized compounds are currently known to interact with or inhibit F1Fo, but a comparative study of their effects on energy metabolism has only recently started. In this work we estimated effects of the cytostatic drugs doxorubicin, dioxadet and their DND conjugates on the activity of F1Fo ATPase as well as on the membrane potential. Two model systems were employed: 1) E. coli F1Fo-ATPase reconstituted into phosphatidylcholine liposomes; 2) Pancreatic carcinoma cell line PANC1. It was found that the nanodiamonds and conjugates exhibited the same uncoupling effect, partially dissipating the proton gradient across the membrane of proteoliposomes containing F1Fo-ATPase. In addition, the nanodiamonds inhibited ATPase activity. In an experiment on the effect on the mitochondrial membrane potential (PANC 1 cell line), conjugates of nanodiamonds with doxorubicin demonstrated a more pronounced effect compared to doxorubicin, which may be due to a combination of the uncoupling effect of nanodiamonds and doxorubicin-dependent generation of reactive oxygen species. The data reported in this paper shed light on effect of the carboxylated nanodiamonds on the cellular bioenergetics. These findings are crucial for further development of nanodiamond-based targeted drug delivery systems, in particular decreasing their toxicity by selecting optimal strategies of nanodiamond synthesis as well as drug immobilization on their surfaces. The use of artificial models of natural membranes, along with cell cultures, is necessary for a deeper and more accurate understanding of the mechanism of action of cytostatics.