Vinblastine sensitivity of leukaemic lymphoblasts modulated by serum lipid

Differential Alteration of Cellular Lipids in Drug Sensitive and Resistant P388 Leukemia Cells by Clofibrate: Effects on Mitoxantrone Cytotoxicity

Earlier Investigations have Indicated a difference in the lipid profiles of drug-sensitive and drug-resistant tumor cells. This study was undertaken to evaluate the effect of alterations in the cellular lipid compositions by clofibrate (CPIB), an anti-hyperlipidemic agent, on mitoxantrone (Mtn) cytotoxicity in murine P388 leukemia cells sensitive (P388/S) and resistant (P388/Adr) to adriamycin and in human chronic myeloid leukemia (CML) cells. CPIB did not elicit any significant alterations in the lipid levels of P388/S cells, whereas in the P388/Adr cells it brought about a 14% and 49% decrease in the levels of cholesterol and triglyceride respectively. Inhibition of 3H-thymidine incorporation was utilized as a measure of cellular cytotoxicity. CPIB caused a dose dependent inhibition of DNA and RNA biosynthesis in P388/S, P388/Adr and CML cells. The combination of CPIB and Mtn induced a greater cytotoxicity in P388/Adr cells as compared to P388/S cells, as shown by enhanced inhibition of 3H-thymidine incorporation in P388/Adr cells. Similar results were observed when 3H-uridine was used as a measure of cellular cytotoxicity. These observations were further confirmed in fresh CML cell samples, in which the combination of CPIB with Mtn induced an irreversible and synergistic Inhibition of DNA biosynthesis. Results warrant extensive studies on CPIB as a clinical modulator to enhance the antiproliferative activity of Mtn.

1H NMR visible lipids are induced by phosphonium salts and 5-fluorouracil in human breast cancer cells

Cationic lipophilic phosphonium salts (CLPS) selectively accumulate in the mitochondria of neoplastic cells and inhibit mitochondrial function. The effects of the CLPS p-(triphenylphosphoniummethyl) benzaldehyde chloride (drug A), and [4-(hydrazinocarboxy)-1-butyl] tris-(4-dimethylaminophenyl) phosphonium chloride (drug B), on human breast cells of differing biological properties were assessed using growth inhibition assays and 1H NMR. Drug A and, to a lesser extent, drug B demonstrated selective growth inhibition of the highly tumorigenic DU4475 breast carcinoma cell line compared to the transformed HBL-100 human breast cell line. However, in contrast to previous studies using other cell lines, no synergistic activity was found when the drugs were used in combination. 1H NMR demonstrated significant increases in mobile lipid acyl chain resonances in both cell lines treated with cytotoxic doses (IC50, 48 h) of the drugs used either alone or in combination. Two-dimensional NMR revealed accompanying decreases in phosphocholine/Lys levels in HBL-100 cells treated with A, B, or a 1:1 combination A+B at the IC50, and in DU4475 cells treated with drug A (IC50). This was accompanied by significant increases in cho/Lys ratios with IC50 A or combination A+B treatment. Similar spectra were observed in cells treated with 5-fluorouracil but not methotrexate, indicating that mobile lipid accumulation is a general but not universal response to cytotoxic insult.

Modulation of MR-visible mobile lipid levels by cell culture conditions and correlations with chemotactic response

A transformed murine fibroblast cell line has been used to assess which criteria govern the appearance of a lipid pool that is mobile on the MR time scale. A high-resolution proton MR signal arising from neutral lipids, including triglyceride and cholesteryl esters, has previously been associated with membrane events in stimulated, transformed and malignant cells. We report that the attenuation of cellular proliferation by confluence or low pH caused significant increases in MR-visible lipid and that the lipid signal could be amplified at high density by the removal of serum. A significant decrease in chemotactic response accompanied the culture of cells at high density, but chemotactic response was not generally linked to alteration of the lipid signal. The appearance of the signal was also not correlated with the proportion of cells in any phase of the cell cycle. Significant changes in the MR-visible pools of the lipid metabolites choline, phosphocholine and glycerophosphocholine were measured under the culture conditions employed with 2D MRS and suggest that MR-visible lipid may arise from the catabolism of phospholipids.

Interaction of multidrug-resistant Chinese hamster ovary cells with the peptide ionophore gramicidin D

A major form of multidrug resistance results from the overexpression of P-glycoprotein, a 170 kDa membrane protein. Multidrug resistant (MDR) Chinese hamster ovary (CHO) cells and mdrl transfectants displayed cross-resistance to the channel-forming peptide ionophore gramicidin D, which was reversed by various chemosensitizers, thus directly implicating P-glycoprotein as the mediator of resistance. However, gramicidin D was not able to inhibit [3H]azidopine photolabelling of P-glycoprotein. MDR cells were not resistant to other pore-forming ionophores, but showed a modest level of cross-resistance to the mobile ionophore valinomycin. There was no difference in 125I-gramicidin D uptake by resistant and sensitive cells. Resistant cells showed lower 86Rb+ uptake, relative to the drug-sensitive parent. Addition of GmD increased both the rate and the level of 86Rb+ uptake in sensitive cells, but had no effect on MDR cells. MDR cells also showed much lower rates of gramicidin D-dependent 86Rb+ efflux than sensitive cells, and this was greatly increased by verapamil. These results suggest that P-glycoprotein interferes with the formation of ion-conducting gramicidin D channels. In contrast, valinomycin had the same effect on gramicidin D-dependent cation efflux in MDR and sensitive cells. Gramicidin D is thus unique among the ionophores is being a substrate for P-glycoprotein, which appears to greatly reduce the formation of active dimeric channels in the plasma membrane of MDR cells.

Esterified cholesterol and triglyceride are present in plasma membranes of Chinese hamster ovary cells

The chemical composition of highly purified plasma membrane preparations from a series of malignant Chinese hamster ovary (CHO) cell lines were undertaken to ascertain if neutral lipid, including cholesteryl ester and triacylglycerol, were present. Triacylglycerols (33-41 nmol/mg total lipid) and cholesteryl ester (226-271 nmol/mg) were measured in the plasma membranes and differences in the chemical composition of these membranes recorded. The most significant difference was a gradual decrease in the level of free cholesterol from wild type (312 +/- 7 nmol/mg total plasma membrane lipid), Pod RII-6 (268 +/- 64 nmol/mg total plasma membrane lipid), Col R-22 (243 +/- 39 nmol/mg total plasma membrane lipid) to EOT (204 +/- 20 nmol/mg total plasma membrane lipid), with a concomitant increase in the degree of saturation of the cholesteryl ester fatty acids, particularly palmitic acid. No statistically significant differences were apparent in the chemical composition of the whole cells in this series. The one-dimensional (1D) 1H-NMR spectra of the four malignant cell lines showed a gradation in intensity of lipid resonances, in the order of wild type, Pod RII-6, Col R-22 and EOT, with EOT having the strongest lipid spectrum. Interestingly, the increase in acyl-chain signal intensities in the 1H-NMR spectra of this series of CHO cells and emergence of signals from cholesterol and/or cholesteryl ester, coincide with alterations in the amount of free cholesterol and the degree of saturation of the fatty-acyl chain of the esterified cholesterol in the plasma membranes. It is our hypothesis that, together, cholesteryl ester and triacylglycerol form domains in the plasma membrane and that when the cholesteryl ester has a largely saturated fatty acid content, the lipids are in isotropic liquid phase and hence visible by NMR.