Glucose transporters and transport kinetics in retinoic acid-differentiated T47D human breast cancer cells.

The rates of glucose transport and of glycolysis and the expression of the glucose transporters GLUT-1 through GLUT-4 were measured in T47D human breast cancer cells that underwent differentiation by retinoic acid. Glucose transport was found to be the rate-limiting step of glycolysis in control and differentiated cells. The transporters GLUT-1, GLUT-3, and GLUT-4 were present in the cell membrane and in the cytoplasm, and GLUT-2 was present solely in the cytoplasm. Differentiation led to a reduction in GLUT-1 and to an increase in cytoplasmic GLUT-2 and GLUT-3 with no change in GLUT-4. Differentiation also caused a reduction in the maximal velocity of glucose transport by approximately 40% without affecting the Michaelis-Menten constant of glucose transport. These changes did not alter the steady-state concentration of the phosphate metabolites regulating cell energetics but increased the content of phospholipid breakdown phosphodiesters. In conclusion, differentiation of human breast cancer cells appears to be associated with decreased glycolysis by a mechanism that involves a reduction in GLUT-1 and a slowdown of glucose transport.

Kinetics of cyclocreatine and Na(+) cotransport in human breast cancer cells: mechanism of activity.

The growth-inhibitory effect of cyclocreatine (CCr) and the kinetics of CCr and Na(+) cotransport were investigated in MCF7 human breast cancer cells and its adriamycin-resistant subline with use of (31)P- and (23)Na-NMR spectroscopy. The growth-inhibitory effect in the resistant line occurred at a lower CCr concentration and was more pronounced than in the wild-type line. This correlated with an approximately 10-fold higher affinity of CCr to the transporter in the resistant line. The passive diffusion coefficient of CCr was also higher in the resistant line by three- to fourfold. The transport of CCr was accompanied by a rapid increase in intracellular Na(+). This increase was found to depend on the rate of CCr transport and varied differently with CCr concentration in the two cell lines. It is proposed that the cotransport of CCr and Na(+) followed by increased Na(+) concentration, together with the accumulation of the highly charged phosphocyclocreatine, are responsible for cell swelling and death.

Tamoxifen induced changes in MCF7 human breast cancer: in vitro and in vivo studies using nuclear magnetic resonance spectroscopy and imaging.

The effects of 17 beta-estradiol versus tamoxifen on the growth and metabolism of MCF7 human breast cancer cells, in culture and in tumors implanted in nude mice, were studied by 31P and 13C nuclear magnetic resonance spectroscopy and by proton magnetic resonance imaging. In culture, the content of the phosphate metabolites including nucleoside triphosphates (NTP), phosphomonoesters, phosphodiesters and inorganic phosphate (Pi) were not affected by tamoxifen treatment. However, in the presence of estrogen the rate of glucose consumption and lactate production via glycolysis (270 and 280 fmol/cell.h, respectively) were twice that of tamoxifen treated cells. Estrogen rescue of tamoxifen treated cells indicated that glycolysis induction occurs at the early stages of the hormonal response. The in vivo studies included recording of proton images that provided an accurate measure of tumor size and distribution of tumor cells, necrotic regions and stromal tissue. Tamoxifen caused enhanced necrosis extending from the center of the tumor during the first two days of treatment (12 h to 6 days). This was followed by growth of reparative tissue along with tumor regression. Tamoxifen also modified the content of the phosphate metabolites, increasing markedly (P less than 0.0002) the ratio of NTP to Pi from 0.41 before treatment to 1.75 9-19 days after treatment. This change was attributed to the enhanced growth of repair tissue. The results provide new information regarding the response of human breast cancer to hormonal treatment and suggest a mechanism for the induction of tumor regression by tamoxifen.

Lipid metabolism in large T47D human breast cancer spheroids: 31P- and 13C-NMR studies of choline and ethanolamine uptake.

31P- and 13C-NMR were used to determine the kinetics of choline and ethanolamine incorporation in T47D clone 11 human breast cancer cells grown as large (300 microns) spheroids. Spheroids were perfused inside the spectrometer with 1,2-13C-labeled choline or ethanolamine (0.028 mM) and the buildup of labeled phosphorylcholine (PC) or phosphorylethanolamine (PE) was monitored. To analyze the NMR kinetic data, it was assumed that each signal represents a weighted average of signal from the proliferating and non-proliferating compartments of the large spheroid. The average ATP pool size was 4 +/- 1 fmol/cell compared to 8 +/- 1 fmol/cell in small (150 microns) proliferating spheroids (P less than 0.0002). The average PC pool size at steady state was reduced to 11 +/- 6 fmol/cell compared to 22 +/- 8 (P less than 0.007). This could be correlated with an overall reduction of choline uptake in the non-proliferating spheroid fraction. The rate of the enzyme choline kinase was 0.3 fmol/(cell h) compared to 1.0 fmol/(cell h) (P less than 0.0001) for proliferating cells. The rate constant of CTP:phosphocholine cytidyltransferase (0.05 h-1) was not significantly altered, but the rate of the enzyme was reduced from 1.3 to 0.2-0.5 fmol/(cell h). The pool size of PE in medium containing serum ethanolamine (1.7 microM) was approximately the same (15 fmol/cell) in small and large spheroids. In the presence of high ethanolamine (0.028 mM) the average PE level decreased slightly (11 fmol/cell) and the rate of the enzyme ethanolamine kinase in the non-proliferating fraction was 0.7 fmol/(cell h) versus 1.0 fmol/(cell h) in the proliferating cells (P less than 0.07). The rate constant of CTP:phosphoethanolamine cytidyltransferase (0.07 h-1) was not significantly altered but the corresponding reaction rate was reduced from 1.4 to 0.2-0.8 fmol/(cell h). The kinetics of choline incorporation did not alter in the presence of 0.028 mM ethanolamine.

Lipid metabolism in T47D human breast cancer cells: 31P and 13C-NMR studies of choline and ethanolamine uptake.

31P and 13C-NMR were used to determine the kinetics of choline and ethanolamine incorporation in T47D clone 11 human breast cancer cells grown as small (150 microns) spheroids. Spheroids were perfused inside the spectrometer with 1,2-13C-labeled choline or 1,2-13C-labeled ethanolamine (0.028 mM) and the buildup of labeled phosphoryl-choline (PC) or phosphorylethanolamine (PE) was monitored. Alternatively the PC and GPC pools were prelabeled with 13C and the reduction of label was monitored. 31P spectra were recorded from which the overall energetic status as well as total pool sizes could be determined. The ATP content was 8 +/- 1 fmol/cell, and the total PC and PE pool sizes were 16 and 14 fmol/cell, respectively. PC either increased by 50% over 24 h or remained constant, while PE remained constant in medium without added ethanolamine but increased 2-fold within 30 h in medium containing ethanolamine, indicating a dependence on precursor concentration in the medium. The 31P and 13C data yielded similar kinetic results: the rate of the enzymes phosphocholine kinase and phosphoethanolamine kinase were both on the order of 1.0 fmol/cell per h, and the rate constants for CTP:phosphocholine cytidyltransferase and CTP:phosphoethanolamine kinase were 0.06 h-1 for both enzymes. The kinetics of choline incorporation did not alter in the presence of 0.028 mM ethanolamine indicating that they have non-competing pathways.

Chemotherapy-induced changes in the energetics of human breast cancer cells; 31P- and 13C-NMR studies.

The early changes in the energetics of T47D-clone 11 human breast cancer cells, following treatment with adriamycin and several other anti-cancer drugs were characterized by 31P- and 13C-NMR spectroscopy. Treatment of the cells with cytotoxic doses of either adriamycin (10(-5) M), daunomycin (10(-5) M) or actinomycin-D (2 x 10(-6) M) induced an immediate increase in the content of the nucleoside triphosphate (NTP) pool. A maximum increase of 30 to 50% was reached 6 to 8 h after treatment, and was followed by a gradual decrease, in accord with the decline in cell number due to cell death. High-performance liquid chromatography measurements indicated that the adriamycin-induced build-up of the NTP pool was mainly due to a specific increase in ATP and GTP. Treatment with cytotoxic doses of cytosine arabinofuranoside (10(-4) M) and cis-platin (10(-4) M) and with the antiestrogen tamoxifen at a dose which inhibited growth (2 x 10(-6) M) did not induce an early increase in the NTP content. Adriamycin and actinomycin-D did not alter significantly the rates of glucose consumption and lactate production via glycolysis during the first 4 to 8 h of treatment. Both drug, however, caused during this time interval a 50% inhibition in the rate of glutamate synthesis via the Krebs cycle. Complementary flow cytometry studies have indicated that within 4 h of treatment with either adriamycin or actinomycin-D there is no detectable change in cell cycle distribution. Treatment for longer time periods indicated that each drug affects the cell cycle distribution in a different manner. Thus, the early increase in NTP can not be associated with a specific cell cycle distribution. The results suggest therefore that drugs of the anthracycline and actinomycin type exert a similar specific and early metabolic induction which may affect the energy state of the cells. This induction may relate to the cytotoxic mechanism and could potentially serve as an early marker for response to treatment.

Adaptation of culture methods for NMR studies of anchorage-dependent cells.

Two methods for growing anchorage-dependent cells were adapted for nuclear magnetic resonance (NMR) measurements: growing cells on agarose polyacrolein microsphere beads and on "filters" made of nonwoven polyester fabric. Both were found to be convenient and most suitable for NMR studies in any conventional spectrometer without probe modification. These methods were employed in studies of human breast cancer T47D-A11 cells, using scanning electron microscopy and 31P NMR spectroscopy. The results show that the contents per cell of phosphorylcholine, phosphorylethanolamine, and their glycerol derivatives depend on the mode of cell assembly and decrease gradually with the increase in cell-cell interaction along the growth curve.

31P-NMR studies of phosphate transfer rates in T47D human breast cancer cells.

The concentration of phosphates and the kinetics of phosphate transfer reactions were measured in the human breast cancer cell line, T47D, using 31P-NMR spectroscopy. The cells were embedded in agarose filaments and perifused with oxygenated medium during the NMR measurements. The following phosphates were identified in spectra of perifused cells and of cell extracts: phosphorylcholine (PC), phosphorylethanolamine (PE), the glycerol derivatives of PC and PE, inorganic phosphate (Pi), phosphocreatine (PCr), nucleoside triphosphate (primarily ATP) and uridine diphosphate glucose. The rates of the transfers: PC----gamma ATP (0.2 mM/s), Pi----gamma ATP (0.2 mM/s) and the conversion beta ATP----beta ADP (1.3 mM/s) were determined from analysis of data obtained in steady-state saturation transfer and inversion recovery experiments. Data from spectrophotometric assays of the specific activity of creatine kinase (approx. 0.1 mumol/min per mg protein) and adenylate kinase (approx. 0.4 mumol/min per mg protein) suggest that the beta ATP----beta ADP rate is dominated by the latter reaction. The ratio between the rate of ATP synthesis from Pi and the rate of consumption of oxygen atoms (4 X 10(-3) mM/s) was approx. 50. This high value and preliminary measurements of the rate of lactate production from glucose, indicated that aerobic glycolysis is the main pathway of ATP synthesis.

Highly potent germination inhibitors in aqueous eluate of fruits of Bishop's weed (Ammi majus L.) and avoidance of autoinhibition.

The aqueous eluate from fruits ofAmmi majus (Bishop's weed, Umbelliferae) remarkably inhibited germination of adjacent seeds ofAnastatica hierochuntica, lettuce, or tomato but had no effect on intact fruits ofAmmi. Similar inhibition was found in dark or in light, except that seeds ofA. hierochuntica were significantly more inhibited in the dark than in the light. Xanthotoxin was isolated, identified, and found to account for about a sixth of the inhibitory activity of the eluate. After fruits ofAmmi were submerged in a large volume of water for 4 days, the fruits still exuded enough inhibitors to prevent germination ofA. hierochuntica, lettuce, or tomato. Data support also the proposal that the phytotoxins are compartmentalized between the inner and the outer fruit envelopes. The inner layer excludes inhibitors from the embryo and autotoxicity is thus avoided, whereas the outer one ensures a gradual liberation of the phytotoxic compounds. This, as well as the high reactivity of the eluate, the high densities ofAmmi fruits in nature, and their relatively limited annual germination, suggest chemical inhibition of neighboring plant species other thanAmmi. Hence, in addition to their chemical protection against predators of either lower or higher organisms, furanocoumarins in fruits ofAmmi majus may contribute to its success as a weed.