Cellular and karyotypic characterization of two doxorubicin resistant cell lines isolated from the same parental human leukemia cell line

Separate mechanisms underlying the multidrug resistant (MDR) phenotype were identified in 2 independent approaches to select tumour cells resistant to low concentrations of doxorubicin (Dox) from the sensitive T cell leukemia cell line CCRF-CEM. The CEM/A7 cell line was selected at an initial concentration of 0.005 microgram/ml of Dox and maintained at 0.07 microgram/ml. In contrast, the CEM/A5 line was selected using an initial concentration of 0.01 microgram/ml and maintained in Dox at a concentration of 0.05 microgram/ml. P-glycoprotein expression was demonstrated in the CEM/A7 line but not the CEM/A5 line. Amplification of the mdrI gene was not observed in the CEM/A7 cell line. Both cell lines showed cross-resistance to a number of structurally unrelated cytotoxic drugs including anthracyclines and etoposide (VP-16), although only the CEM/A7 line was cross resistant to Vinca alkaloids. Immunoblots of total cell lysates of the CEM/A5 line have revealed almost undetectable levels of topoisomerase II alpha and beta in this line. Cytogenetic analyses of both lines revealed numerous karyotypic abnormalities which were present in the parental cell line as well as both resistant cell lines. The CEM/A7 line also demonstrated a duplication of part of the long arm of chromosome 7 which included the region containing the mdrI gene, a finding not seen in the parental or CEM/A5 line. CEM/A5, however, demonstrated an abnormality of chromosome 7, outside the region of the mdrI gene, and it also contained a deletion of the short arm of chromosome 2. Abnormalities in this latter region of genome have been associated with non-P-glycoprotein-mediated MDR.

Circumvention of tamoxifen resistance by the pure anti-estrogen ICI 182,780

Both primary and acquired resistance to the growth-inhibitory effects of anti-estrogens (e.g., tamoxifen) limits the clinical usefulness of these drugs in the treatment of breast cancer. The new, steroidal anti-estrogen ICI 182,780 was tested for its ability to inhibit the proliferation of a tamoxifen-resistant variant of the parental MCF-7 human breast-cancer cell line. Two cell lines cloned from the MCF-7 line were used for these experiments: a tamoxifen-sensitive line, MCF 5-21, and a tamoxifen-resistant line, MCF 5-23. Compared with tamoxifen, ICI 182,780 appeared to be 150 and 1540 times more effective in inhibiting cell growth in the 5-21 and 5-23 sub-lines respectively. ICI 182,780 completely circumvented tamoxifen resistance at a concentration of (5 to 10) x 10(-9) M in this model. Based on IC50 concentrations, the 5-23 line was 22-fold more resistant to tamoxifen than the 5-21 line, but only 2-fold more resistant to ICI 182,780, reducing relative resistance by 10-fold in the resistant line. There were no differences in ER parameters between the 2 lines. ER numbers/cell were: 40500 and 34800 and the KD 0.48 and 0.15 x 10(-9) M in the 5-21 and 5-23 cells respectively. In the 5-23 cells, the concentrations of ICI 182,780 and tamoxifen resulting in a 50% inhibition of 3H-estradiol binding were 2.3 x 10(-8) M and 1 x 10(-6) M, respectively (cf. estradiol 0.89 x 10(-9) M). Thus, one potential mechanism for the increased effectiveness of ICI 182,780 may relate to the increased affinity of this drug for the estrogen receptor as compared with tamoxifen.

Circumvention of doxorubicin resistance in multi-drug resistant human leukaemia and lung cancer cells by the pure antioestrogen ICI 164384

ICI 164384, a new steroidal antioestrogen, entirely devoid of oestrogenic activity, modulates doxorubicin resistance in vitro. At non-cytotoxic concentrations, ICI 164384 potentiated the cytotoxicity of doxorubicin in a dose-dependent manner in both the classical multi-drug resistant (MDR) human leukaemia cell lines CEM/VLB 100 and CEM/VLB 1000 and the human small cell lung cancer cell line H69 LX4. ICI 164384 had no effect on the two respective parental cell lines, CEM/CCRF and H69 P. None of these cell lines expressed the oestrogen receptor. In comparative studies at concentrations ranging from 1.25 to 10 mumols/l, ICI 164384 was significantly more effective (1.2-6-fold) than tamoxifen in reducing the IC50 of doxorubicin in the CEM/VLB 100 line. In resistant cells, ICI 164384 increased 3H-daunomycin accumulation in a dose-dependent manner and was significantly more effective than tamoxifen at concentrations ranging from 2.5 to 10 mumol/l. ICI 164384 reduced the efflux of daunomycin from resistant cells more effectively than tamoxifen. These studies suggest that ICI 164384 is an effective modulator of MDR.

Skeletal muscle metabolism: effect of age, obesity, thyroid and nutritional status

To investigate the potential role of skeletal muscle metabolism in the determination of whole body energy balance, the rate of oxygen consumption was measured in soleus muscles isolated from mice of differing age, sex, strain (thin and obese), thyroid and nutritional status. As expected, T3-induced hyperthyroidism resulted in an increase in the intrinsic rate of energy utilization by the muscles; qualitatively similar changes were noted in both younger animals and mice induced to increase their energy intake by sucrose-overfeeding. In contrast, soleus muscle oxygen consumption was significantly reduced in genetically obese NZO mice. Parallel changes in the activity of the Na-K pump were observed in all groups of animals, with a good correlation (r greater than 0.6, P less than 0.01) noted between these two independently measured aspects of muscle metabolism. The results suggest that the intrinsic metabolic rate of the skeletal muscle mass plays an important role in the control of overall energy balance, with changes in this rate being potentially partly responsible for the altered energetic efficiency of genetic obesity and adaptive thermogenesis models. In addition, measurement of the activity of the Na-K-pump may provide a convenient marker for such observed changes in energy utilization.

The effects of diet differing in fat, carbohydrate, and fiber on carbohydrate and lipid metabolism in type II diabetes

This study was designed to determine the effects of varying the proportions of carbohydrate, fiber, and fat on metabolic control in Type II diabetes. Ten men, aged 50 to 69 years, with Type II diabetes participated. Four isocaloric diets were consumed for 2 weeks each, with a break of 6 to 14 weeks between diets to ensure no carryover effects. Two of the diets were high in carbohydrate (63% to 65% energy) and low in fat (10% to 12% energy) but differed in their fiber contents (20 vs. 45 gm/day). The other two diets were low in carbohydrate (23% to 27% energy) with either a low or a high fat content (15% vs. 55% energy) and a high or normal protein content (62% vs. 18% energy). The composition of the subjects' usual diets in the week before each of the experimental diets did not vary significantly: carbohydrate 47% to 50% energy, protein 22% to 25% energy, fat 27% to 31% energy, and fiber 24 to 25 gm/day. A 75-gm oral glucose tolerance test and a 12-hour metabolic profile in response to 3 meals typical of the particular diet were conducted before and at the conclusion of each 2-week dietary period. The most significant improvements in metabolic control (as assessed by the effects of the diets on fasting glucose and on lipids, and on the glucose and insulin responses to oral glucose and the mixed meals) were obtained with the high-fiber, high-carbohydrate, low-fat diet and with the low-carbohydrate, high-protein, low-fat diet. Metabolic control was not significantly affected by the low-fiber, high-carbohydrate, low-fat diet, but it deteriorated significantly on the low-carbohydrate, high-fat diet. The results of this study confirmed the importance of high fiber and low fat in improving metabolic control in Type II diabetes. In conclusion, if high-carbohydrate, low-fat diets are to be recommended to patients with diabetes, it is essential that the type of carbohydrate recommended be unrefined and high in fiber.

Mouse soleus muscle Na-K pump activity: direct correlation with in vitro and in vivo oxygen consumption

To evaluate the contribution of active sodium-potassium transport to energy utilization, measurements of sodium-potassium pump activity in isolated soleus muscles of normal mice were carried out and related to measurements of oxygen consumption by the tissue. A highly significant positive correlation (r = 0.89, p less than 0.001) was found between these two parameters. In addition, both the in vitro oxygen consumption and Na-K pump activity of the muscles were found to correlate with whole body oxygen utilization by the experimental animals. The results support a role for the sodium-potassium pump in the determination of energy turnover.

Parathyroid hormone stimulation of the Na+/K+ pump in rat clonal osteosarcoma cells

A clonal line of osteoblastic cells from a rat osteogenic sarcoma (UMR 106-06), known to possess parathyroid hormone (PTH)-responsive adenylate cyclase, has been shown to increase its rate of K+ uptake mediated by a Na+/K+ pump after exposure to the hormone. The increase in pump activity was not associated with significant changes in K+ efflux or Na+ influx and would therefore be expected to alter intracellular levels of both Na+ and K+. The maximal (75%) increase in pump activity was noted at a PTH concentration of 100 micrograms/l and half-maximal stimulation at 1.9 micrograms/l. The effect appeared to be independent of the adenylate cyclase system, since a synthetic peptide antagonist of PTH activation of adenylate cyclase failed to prevent stimulation of the Na+/K+ pump. Similarly, prostaglandin E2, an alternative agonist of adenylate cyclase in these cells, had no effect on the Na+/K+ pump. This novel action of PTH on monovalent cation transport in osteoblast-like cells should provide a clearer insight into the mechanisms of hormone-induced bone resorption.

Fallibility of postal questionnaire follow-up for detection of hypothyroidism after iodine-131 therapy

Four hundred and twelve patients who received radioactive iodine for thyrotoxicosis were followed up for periods from one to three years by postal questionnaire. Hypothyroidism was detected in only three instances, and, despite intensive efforts to trace subjects, 41% of them were lost to follow-up because of either failure to participate or change of address over three years. It is apparent that a postal questionnaire is an unsatisfactory method for following up a Melbourne inner-suburban population over a prolonged period.

Reduced activity of the red-cell sodium-potassium pump in human obesity

Looking for evidence of reduced energy use in the cells of obese persons, we measured the numbers of sodium-potassium-pump units in erythrocytes from a group of 21 obese human subjects and found them to be reduced by 22 per cent as compared with those of nonobese controls (P <0.001). The cation-transport activity of the pump, as measured by 86rubidium uptake by the cells, we also reduced in parallel with decrease in pump units. An increased concentration of sodium in the red cells of obese subjectes was also found (9.6 +/- 0.7 vs. 7.1 +/- 0.6 mmol per liter of cells; P<0.01). This finding demonstrates independently the physiologic importance of reduced numbers of sodium-pump units and reduced pump activity as measured by ouabain binding and rubidium transport, respectively. The magnitude of the reduction in the number of pump units was found to be negatively correlated with the percentage of ideal body weight (r = 0.56, P<0.001); this observation suggests a possible role of abnormalities of the sodium pump in the pathophysiology of obesity.

The effects of trypsin and phospholipase C on insulin binding and action in the isolated adipocyte

The effect of alterations to the insulin receptor on the insulin sensitivity of isolated adipocytes was studied. Receptor changes were induced by treatment of adipocytes with either phospholipase C or trypsin. After enzyme treatment, binding of insulin to insulin receptors and insulin-mediated glucose metabolism were examined. Exposure of adipocytes to phospholipase C (2 units/ml) significantly increased insulin binding to the cells, but destroyed the ability of the cells to oxidize glucose. After treatment with trypsin (500 micrograms/ml) for 5 min, insulin binding to the adipocytes was significantly increased. This was shown to be due to an increase in insulin-receptor affinity. Metabolic studies showed that trypsin treatment led to an increase in basal glucose transport but markedly decreased the response to insulin at all concentrations tested. Adipocytes treated with trypsin showed no significant difference in basal glucose oxidation rates when compared with controls, but were less sensitive to insulin at low insulin concentrations, and showed a decreased maximum response at high insulin concentrations. In conclusion, these findings indicate a dissociation between induced changes in binding of insulin to insulin receptors and subsequent hormone action. The importance of post-receptor events in the biological action of insulin is highlighted.