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The Pentose Phosphate Pathway (PPP) is one of the key metabolic pathways occurring in living cells to produce energy and maintain cellular homeostasis. Cancer cells have higher cytoplasmic utilization of glucose (glycolysis), even in the presence of oxygen; this is known as the “Warburg Effect”. However, cytoplasmic glucose utilization can also occur in cancer through the PPP. This pathway contributes to cancer cells by operating in many different ways: (i) as a defense mechanism via the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) to prevent apoptosis, (ii) as a provision for the maintenance of energy by intermediate glycolysis, (iii) by increasing genomic material to the cellular pool of nucleic acid bases, (iv) by promoting survival through increasing glycolysis, and so increasing acid production, and (v) by inducing cellular proliferation by the synthesis of nucleic acid, fatty acid, and amino acid. Each step of the PPP can be upregulated in some types of cancer but not in others. An interesting aspect of this metabolic pathway is the shared regulation of the glycolytic and PPP pathways by intracellular pH (pHi). Indeed, as with glycolysis, the optimum activity of the enzymes driving the PPP occurs at an alkaline pHi, which is compatible with the cytoplasmic pH of cancer cells. Here, we outline each step of the PPP and discuss its possible correlation with cancer.

Mitochondria evolved from free-living bacteria via endocytosis within a eukaryotic host cell millions of year ago. We hypothesized that antibiotics might damage mitochondria of human cancer cells and lead to oxidative damage of cancer cells. We examined three classes of antibiotics, azithromycin, doxycycline and ciprofloxacin in the human breast cancer cell lines MCF-7 and MDA-MB-231. The combination of antibiotics and the anti-glycolytic agent, 2-Deoxy-D-glucose (2-DG) was also tested in the cells. Cell growth was measured by MTT [3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide] assay. Mitochondrial membrane potential and reactive oxygen species were tested by fluorescent microscopy. Gene expression and DNA damage were measured by real time polymerase chain reaction (qPCR) and ELISA. All antibiotics suppressed mitochondrial membrane potential and growth of MCF-7 and MDA-MB-231 cells in a dose dependent pattern. The IC50of all three antibiotics were less than clinical patient’s maximum serum concentration (Cmax) or concentrations in tissues. The IC50 of ciprofloxacin in MCF-7 (1.25-2.5µM) and MDA-MB-231 (2.5-3.5µM) are much lower than the Cmax 7.7µM while patients take 500mg every 12 hours orally in clinical practice. The DNA oxidative damage metabolite, 8-OHdG, in the media was significantly increased after cancer cells were cultured in the media containing antibiotics for 24 hours. Three antibiotics upregulated gene expression of glycolytic enzymes including hexokinase 2(HK2), phosphofructokinase 1 (PFKM) and pyruvate kinase muscle isozyme M2 (PKM2), lactate dehydrogenase A (LDHA), and glucose transporters 1 (SLC2A1) and 3 (SLC2A3). The antibiotics increased uptake of 3[H]-2-DG of MCF-7 and MDA-MB-231. These results suggest that cancer cells increase aerobic glycolysis to produce ATP after antibiotic treatment. Thus, we combined 2-DG and antibiotics to treat the breast cancer cell lines. The antibiotics and 2-DG synergistically inhibited growth of the breast cancer cells. MDA-MB-231, a chemo-drug resistant cell line, has similar sensitivity to antibiotics and 2-DG as the MCF-7, a drug sensitive cell line. In summary, azithromycin, doxycycline and ciprofloxacin suppress the growth of breast cancer cells and augment the cytotoxicity of 2-DG to breast cancer cells. These findings suggest we can treat cancer with antibiotics similar to treating an infection. Citation Format: Xianpeng Jiang, Amanda Benoit, Toby Jiang, Robert L. Elliott. Antibiotics suppress growth of breast cancer cells and synergize cytotoxicity of 2-Deoxy-D-glucose: Treating cancer like an infection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3600.