Rhodamine 123 inhibits import of rat liver mitochondrial transhydrogenase

Mechanism of inhibition of FaDu hypopharyngeal carcinoma cell growth by tetraphenylphosphonium chloride

Cationic phosphonium salts are interesting because they inhibit the proliferation of carcinoma cells more than untransformed epithelial cells in vitro. This differential anti-proliferative effect has been used to identify phosphonium salts and other lipophilic cations that later demonstrated effects in animals. Using 6 carcinoma-derived and 2 untransformed epithelial cell lines, tetraphenylphosphonium chloride (TPP) and other cationic aryl phosphonium salts (CAPS) demonstrated a growth inhibition pattern similar to that of cation rhodamine 123, suggesting that CAPS may inhibit mitochondrial function. We tested this hypothesis for the effect of phosphonium salt TPP on FaDu human hypopharyngeal carcinoma cells. TPP inhibited the proliferation of FaDu carcinoma cells at submicromolar concentrations. Uptake of 3H-TPP by FaDu cells was partially inhibited in medium containing high K+ and fully inhibited by valinomycin in this medium, indicating that TPP accumulates preferentially in mitochondria, and to a lesser extent in the cytoplasm. FaDu cells exposed to TPP exhibited damage to mitochondrial inner membranes, reduced ATP/ADP ratios, decreased oxygen uptake rates and decreased mitochondrial membrane potentials. The treated cells secreted lactate more rapidly than untreated controls and exhibited hypersensitivity to 2-deoxyglucose, an inhibitor of glycolysis. TPP's antimitochondrial effects apparently enhance cytoplasmic glycolysis. In conclusion, TPP inhibits FaDu carcinoma cell growth by inhibiting mitochondrial respiration and ATP synthesis. Cationic phosphonium salts that inhibit carcinoma cell growth through antimitochondrial effects might be used to treat solid tumors without the risk of secondary tumors associated with agents affecting nuclear DNA.

Inhibitory effects of two structurally related carbocyanine laser dyes on the activity of bovine heart mitochondrial and Paracoccus denitrificans NADH-ubiquinone reductase. Evidence for a rotenone-type mechanism

Two cationic, lipophilic laser dyes, 1,1',3,3,3',3'-hexamethylindodicarbocyanine iodide (HIDC) and 1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide (HITC), inhibit bovine heart mitochondrial and Paracoccus denitrificans NADH oxidase activities. The mitochondrial I50 values were 0.5 microM (HIDC) and 1.2 microM (HITC), and the P. denitrificans I50 values 1.2 microM (HIDC) and 1.5 microM (HITC). Neither succinate nor cytochrome oxidase (EC 1.9.3.1) activities were inhibited significantly by either compound, localizing the site of inhibition to the segment of each electron transport chain between NADH and ubiquinone. With submitochrondrial particles (SMP), NADH-dependent reduction of menadione, duroquinone and coenzyme Q1 was inhibited markedly (HIDC was the more potent inhibitor). Using purified complex I, only NADH-dependent reduction of duroquinone and coenzyme Q1 was inhibited markedly (HIDC was the more potent inhibitor) and reduction of menadione was inhibited slightly. With P. denitrificans membrane vesicles, NADH-dependent reduction of menadione, juglone, and coenzyme Q1 was inhibited slightly and duroquinone reduction was inhibited markedly. Membrane-dependent interactions appear to be involved, since the compounds were more inhibitory with membrane preparations than with complex I. The mechanism of inhibition (except for the HIDC effect on coenzyme Q1 reduction with P. denitrificans) appeared to be through the interaction of dye with the rotenone site on NADH-ubiquinone reductase (EC 1.6.99.3), since rotenone-insensitive preparations of complex I and P. denitrificans membrane vesicles were also insensitive to HIDC and HITC inhibition.

Identification by flow cytometry of two distinct rhodamine-123-stained mitochondrial populations in rat liver

Isolated rat liver mitochondria were split into three fractions of increasing density when applied to a Percoll gradient. NADH-ubiquinone oxidoreductase, succinate dehydrogenase and cytochrome-c oxidase but not F1-ATPase activities increased with density as well as respiratory rate in state 3 and the respiratory control index. Flow cytometry of mitochondrial density fractions stained with rhodamine-123 revealed the occurrence in each density fraction of two distinct mitochondrial populations with different fluorescence intensity. The high fluorescence population was minor and its proportion decreased with density. The extent of high fluorescence population staining depended on the deenergized state of the mitochondria suggesting that this population represents an immature form of the mitochondria which may develop into a fully functional organelle by the incorporation of structural and/or functional proteins.

Comparative developmental toxicity of cationic and neutral rhodamines in mice

Rhodamines 123 and 6G (Rh 123 and Rh 6G) are cationic fluorescent dyes that inhibit oxidative phosphorylation following their selective accumulation within mitochondria. Neutral rhodamines (e.g., Rh 116 and Rh B) do not share these properties. To determine if cationic and neutral rhodamines differ in their effect on mammalian development, pregnant CD-1 mice were injected i.p. with Rh 123, Rh B, or Rh 116 at doses of 15 mg/kg/day. The rhodamines were given alone or in combination with 500 mg/kg/day 2-deoxy-D-glucose (2-DOG), an inhibitor of glycolysis, daily on gestation days 7-10 (copulation plug = day 1). Additional pregnant mice were similarly treated with Rh 6G at a dose of 0.5 mg/kg/day. Controls were given saline equimolar to the dose of 2-DOG. Treatment with Rh 6G, alone or in combination with 2-DOG, significantly increased the incidences of prenatal mortality (17% and 35%, respectively) when compared with the control incidence (6%). Treatment with Rh 123 or Rh 6G, alone or with 2-DOG, inhibited fetal growth. Treatment with the neutral rhodamines had little effect on prenatal survival or growth. Exposure to Rh 6G, with or without 2-DOG, was associated with high incidences of gross malformations (41% and 61%, respectively). Rh 116 or Rh B, with or without 2-DOG, and Rh 123 alone were not associated with statistically significant teratogenic effects, but results of the latter treatment were suggestive of such an effect (9.1% grossly malformed fetuses vs. 0% for controls). The incidences of skeletal malformations were significantly increased in the test groups given Rh 6G + 2-DOG, Rh 123 + 2-DOG, or Rh 6G alone.(ABSTRACT TRUNCATED AT 250 WORDS)