Doxycycline, Azithromycin and Vitamin C (DAV): A potent combination therapy for targeting mitochondria and eradicating cancer stem cells (CSCs)

Abstract

Here, we devised a new strategy for eradicating cancer stem cells (CSCs), via a “synthetic-metabolic” approach, involving two FDA-approved antibiotics and a dietary vitamin supplement. This approach was designed to induce a “rho-zero-like” phenotype in cancer cells. This strategy effectively results in the synergistic eradication of CSCs, using vanishingly small quantities of two antibiotics. The 2 metabolic targets are i) the large mitochondrial ribosome and ii) the small mitochondrial ribosome. Azithromycin inhibits the large mitochondrial ribosome as an off-target side-effect. In addition, Doxycycline inhibits the small mitochondrial ribosome as an off-target side-effect. Vitamin C acts as a mild pro-oxidant, which can produce free radicals and, as a consequence, induces mitochondrial biogenesis. Remarkably, treatment with a combination of Doxycycline (1 μM), Azithromycin (1 μM) plus Vitamin C (250 μM) very potently inhibited CSC propagation by >90%, using the MCF7 ER(+) breast cancer cell line as a model system. The strong inhibitory effects of this DAV triple combination therapy on mitochondrial oxygen consumption and ATP production were directly validated using metabolic flux analysis. Therefore, the induction of mitochondrial biogenesis due to mild oxidative stress, coupled with inhibition of mitochondrial protein translation, may be a new promising therapeutic anti-cancer strategy. Consistent with these assertions, Vitamin C is known to be highly concentrated within mitochondria, by a specific transporter, namely SVCT2, in a sodium-coupled manner. Also, the concentrations of antibiotics used here represent sub-antimicrobial levels of Doxycycline and Azithromycin, thereby avoiding the potential problems associated with antibiotic resistance. Finally, we also discuss possible implications for improving health-span and life-span, as Azithromycin is an anti-aging drug that behaves as a senolytic, which selectively kills and removes senescent fibroblasts.

Combination Therapy with Vitamin C Could Eradicate Cancer Stem Cells

“…A triple combination therapy using lower doses of two clinically approved drugs-Doxycycline and Azithromycin-at a concentration of 1 µM and a dosage of Vit.C of 250 µM, showed a complete eradication of CSC propagation [20] (Figure 2). The synergistic effect of these compounds on the breast cancer cell line MCF7 were induced by the inhibition of two key targets, namely the large (39 s) and small mitochondrial ribosomes (28 s).…”

“…Although Vit.C generally acts as an antioxidant, due to its relative concentration and cellular localization, they acted as a mild pro-oxidant and stimulated free radical production leading to mitochondrial biogenesis in addition to mitochondrial oxidative stress. However, in this study no Vit.C inhibiting glycolysis via inhibiting glycolytic enzyme GAPDH was observed [20].…”

“…In addition, Ferrous (Fe3+) ion reduces to ferric (Fe 2+ ) ion and enters the CSCs as Fe 2+ and hydrogen peroxide (H2O2), thereby increasing the ROS production. Studies have shown the doxycyclin [117,120], azithromycin [20] and dodecyl tri-phenyl-phosphonium (dTPP) [121] inhibit mitochondrial activity which in turn leads to Vit.C induced cell death.…”

A guide to plasma membrane solute carrier proteins

“…The varying localization of SLC23A2 in cells may be important for helping increase the therapeutic effect of vitamin C, as its mitochondrial localization in most cancer cell lines has allowed for mitochondria to be targeted in cancer therapeutics [238]. A recent study showed that a combinatorial therapy of doxycycline, azithromycin, and vitamin C effectively eradicates cancer stem cells [239]. Similarly, a combination treatment of vitamin C and cetuximab was recently shown to be an effective treatment to limit the development of acquired resistances in colorectal cancer, slowed the growth of cancerous cells, and impaired the structure of organoids [240].…”

Pro- and Antioxidant Effects of Vitamin C in Cancer in correspondence to Its Dietary and Pharmacological Concentrations

“…It was argued that the observed effect was due to synthetic lethality induced by the combined treatment in that doxycycline targeted mitochondrial respiration and vitamin C-glycolysis. The effectiveness of the combined treatment with doxycycline and vitamin C in cancer by targeting mitochondria was confirmed in subsequent studies in which azithromycin was also applied [119].…”