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The "Warburg effect," also termed aerobic glycolysis, describes the increased reliance of cancer cells on glycolysis for ATP production, even in the presence of oxygen. Consequently, there is continued interest in inhibitors of glycolysis as cancer therapeutics. One example is dichloroacetate (DCA), a pyruvate mimetic that stimulates oxidative phosphorylation through inhibition of pyruvate dehydrogenase kinase. In this study, the mechanistic basis for DCA anti-cancer activity was re-evaluated in vitro using biochemical, cellular and proteomic approaches. Results demonstrated that DCA is relatively inactive (IC(50) ≥ 17 mM, 48 hr), induces apoptosis only at high concentrations (≥ 25 mM, 48 hr) and is not cancer cell selective. Subsequent 2D-PAGE proteomic analysis confirmed DCA-induced growth suppression without apoptosis induction. Furthermore, DCA depolarizes mitochondria and promotes reactive oxygen species (ROS) generation in all cell types. However, DCA was found to have selective activity against rho(0) cells [mitochondrial DNA (mtDNA) deficient] and to synergize with 2-deoxyglucose in complex IV deficient HCT116 p53(-/-) cells. DCA also synergized in vitro with cisplatin and topotecan, two antineoplastic agents known to damage mitochondrial DNA. These data suggest that in cells "hardwired" to selectively utilize glycolysis for ATP generation (e.g., through mtDNA mutations), the ability of DCA to force oxidative phosphorylation confers selective toxicity. In conclusion, although we provide a mechanism distinct from that reported previously, the ability of DCA to target cell lines with defects in the electron transport chain and to synergize with existing chemotherapeutics supports further preclinical development.

The alpha subunits of five members of the Gi family of bovine brain proteins were reconstituted with adenylate cyclase in phospholipid vesicles. Our results support both the views that much of the inhibition of the enzyme by Gi is due to the action of its liberated beta gamma subunits, and that the alpha subunits themselves interact with the enzyme. Inhibition of basal or Gs-stimulated adenylate cyclase activity is small or undetectable by alpha subunits of Go, Go* and Gi-2B. On the other hand, adenylate cyclase activity is stimulated by the alpha subunits of Gi-1 and Gi-2A. The G proteins act in the absence of added GTP when reconstituted with phospholipids of low but not high fluidity.

Treatment of all-trans-retinal with a series of 1,3-diketones using Knoevenagel conditions gave the expected condensation products. These retinylidene 1,3-diketones were characterized and their biological activities in the hamster tracheal organ culture test measured. It was found that the cyclohexane- 1,3-dione derivatives are highly active in this in vitro assay, while other 1,3-diketones are less active. Retinylidenedimedone has been chosen for further evaluation.