The relationship of doxorubicin binding to membrane lipids with drug resistance

Rlip Depletion Suppresses Growth of Breast Cancer

RLIP76 (RAL-binding protein-1, Rlip) is a stress-protective mercapturic-acid-pathway transporter protein that also plays a key role in regulating clathrin-dependent endocytosis as a Ral effector. Targeted inhibition or depletion of Rlip causes regression of xenografts of many cancers and is capable of abrogating tumor formation in p53-null mice. This is associated with the reversion of the abnormal methylomic profile of p53-null mice to wild-type. In a query of The Cancer Genome Atlas (TCGA) databases, we found that Rlip expression was associated with poor survival and with significant differences in the frequencies of PIK3CA mutation, MYC amplification, and CDKN2A/B deletion, which were the most commonly mutated, amplified, and deleted genes, respectively, among TCGA breast cancer patients. We conducted the present study to further examine the effects of Rlip inhibition and to evaluate the in vitro and in vivo efficacy in breast cancer. Using immunogold electron microscopy, we found that plasma-membrane Rlip was accessible to cell-surface antibodies in the MCF7 (ER+) breast cancer cell line. Rlip depletion resulted in decreased survival of MCF7 and MDA-MB-231 cells and increased terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positivity and DNA laddering, indicating apoptotic cell death. Additionally, in vitro knockdown of Rlip inhibited EGF endocytosis and WNT/MAPK signaling. Xenograft studies in nude mice showed regression of breast cancer via antisense-mediated depletion of Rlip mRNA as well as by anti-Rlip antibody. Finally, knockdown of Rlip by antisense locked nucleic acid oligonucleotides increased markers for apoptotic signaling and decreased markers for proliferation, angiogenesis, and cell cycling in MCF7 and MDA-MB-231luc xenografts. Our findings validate Rlip as an attractive target in breast cancer.

Long-Circulating Amphiphilic Doxorubicin for Tumor Mitochondria-Specific Targeting

The mitochondria have emerged as a novel target for cancer chemotherapy primarily due to their central roles in energy metabolism and apoptosis regulation. Here, we report a new molecular approach to achieve high levels of tumor- and mitochondria-selective deliveries of the anticancer drug doxorubicin. This is achieved by molecular engineering, which functionalizes doxorubicin with a hydrophobic lipid tail conjugated by a solubility-promoting poly(ethylene glycol) polymer (amphiphilic doxorubicin or amph-DOX). In vivo, the amphiphile conjugated to doxorubicin exhibits a dual function: (i) it binds avidly to serum albumin and hijacks albumin's circulating and transporting pathways, resulting in prolonged circulation in blood, increased accumulation in tumor, and reduced exposure to the heart; (ii) it also redirects doxorubicin to mitochondria by altering the drug molecule's intracellular sorting and transportation routes. Efficient mitochondrial targeting with amph-DOX causes a significant increase of reactive oxygen species levels in tumor cells, resulting in markedly improved antitumor efficacy than the unmodified doxorubicin. Amphiphilic modification provides a simple strategy to simultaneously increase the efficacy and safety of doxorubicin in cancer chemotherapy.

Nuclear uptake of ultrasmall gold-doxorubicin conjugates imaged by fluorescence lifetime imaging microscopy (FLIM) and electron microscopy

Fluorescence lifetime imaging microscopy (FLIM) has been used to image free and encapsulated doxorubicin (Dox) uptake into cells, since interaction of Dox with DNA leads to a characteristic lifetime change. However, none of the reported Dox conjugates were able to enter cell nuclei. In this work, we use FLIM to show nuclear uptake of 2.7 nm mean diameter Au nanoparticles conjugated to Dox. The pattern of labelling differed substantially from what was seen with free Dox, with slower nuclear entry and stronger cytoplasmic labelling at all time points. As the cells died, the pattern of labelling changed further as intracellular structures disintegrated, consistent with association of Au-Dox to membranes. The patterns of Au distribution and intracellular structure changes were confirmed using electron microscopy, and indicate different mechanisms of cytotoxicity with stable Au-Dox conjugates compared to Dox alone. Such conjugates are promising tools for overcoming resistance in Dox-resistant cancers.

Focused ultrasound mediated drug delivery from temperature-sensitive liposomes: in-vitro characterization and validation

Nanomedicine-based delivery with non-invasive techniques is a promising approach to increase local drug concentration and to reduce systemic side effects. Focused ultrasound (FUS) has become a promising strategy for non-invasive local drug delivery by mild hyperthermia. In this study, traditional temperature-sensitive liposomes (TTSLs) encapsulating doxorubicin (DOX) were evaluated for FUS-mediated drug delivery with an in-vitro FUS setup. In-vitro studies showed quantitative release of the DOX from the lumen of the temperature-sensitive liposomes when heated to 42 °C with FUS using 1 MHz sinusoidal waves at 1.75 MPa for 10 min. No release was observed when heated at 37 °C. Moreover, we showed that DOX released from TTSLs by FUS is as efficiently internalized by glioblastoma cells as free DOX at 37 °C. In-vitro therapeutic evaluation showed that exposure of a cell monolayer to FUS-activated TTSLs induced a 60% and a 50% decrease in cell viability compared to cell medium and to TTSLs preheated at 37 °C, respectively. Using an in-vitro 3D cell culture model, the results showed that after FUS-mediated hyperthermia, preheated liposomes induced a 1.7-fold decrease in U-87 MG spheroid growth in comparison to the preheated liposomes at 37 °C. In conclusion, our results show that in-vitro FUS allows the evaluation of TTSLs and does not modify the cellular uptake of the released DOX nor its cytotoxic activity.

Drug resistance in breast cancer cells: biophysical characterization of and doxorubicin interactions with membrane lipids

Understanding the role of lipids in drug transport is critical in cancer chemotherapy to overcome drug resistance. In this study, we isolated lipids from doxorubicin-sensitive (MCF-7) and -resistant (MCF-7/ADR) breast cancer cells to characterize the biophysical properties of membrane lipids (particularly lipid packing and membrane fluidity) and to understand the role of the interaction of cell membrane lipids with drug/nanocarrier on drug uptake and efficacy. Resistant cell membrane lipids showed significantly different composition and formed more condensed, less fluid monolayers than did lipids from sensitive cells. Doxorubicin, used as a model anticancer agent, showed a strong hydrophobic interaction with resistant cell membrane lipids but significantly less interaction, as well as a different pattern of interaction (i.e., ionic), with sensitive ones. The threshold intracellular doxorubicin concentration required to produce an antiproliferative effect was similar for both sensitive and resistant cell lines, suggesting that drug transport is a major barrier in determining drug efficacy in resistant cells. In addition to the biophysical characteristics of resistant cell membrane lipids, lipid-doxorubicin interactions appear to decrease intracellular drug transport via diffusion as the drug is trapped in the lipid bilayer. The rigid nature of resistant cell membranes also seems to influence endosomal functions that inhibit drug uptake when a liposomal formulation of doxorubicin is used. In conclusion, biophysical properties of resistant cell membrane lipids significantly influence drug transport, and hence drug efficacy. A better understanding of the mechanisms of cancer drug resistance is vital to developing more effective therapeutic interventions. In this regard, biophysical interaction studies with cell membrane lipids might be helpful to improve drug transport and efficacy through drug discovery and/or drug delivery approaches by overcoming the lipid barrier in resistant cells.

Antioxidant enzyme activities and lipid peroxidation induced by eicosapentaenoic acid (EPA) in PC12 cells

Eicosapentaenoic acid (EPA) is one of the major dietary polyunsaturated fatty acids and induces apoptosis in several cancer cells. In this study, the EPA induced lipid peroxidation and response of antioxidative enzymes have been investigated in rat pheochromocytoma PC12 cells to elucidate the mechanisms of apoptosis induced by the polyunsaturated fatty acid EPA. We have analyzed superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities and glutathione (GSH) contents in PC12 cells after exposure to different concentrations of EPA. Lipid peroxidation was shown to increase in the presence of EPA as an indication of the oxidative damage. Lipid peroxidation was enhanced by EPA in a dose-dependent manner, and the loss of cell viability was partially reversed by vitamin E. In the case of antioxidant enzyme activities, SOD and GPX activities and GSH contents increased significantly at 50 micromol/L EPA and were respectively 2.41-fold (p < 0.01), 3.49-fold (p < 0.05), and 1.43-fold (p < 0.05) higher than controls. The CAT activity at 10 micromol/L had the highest value and was increased by 25.83% (p < 0.05) compared to control. The results suggest that in PC12 cells the mechanism of apoptosis induced by EPA may be partly due to lipid peroxidation.

Membrane effects of the antitumor drugs doxorubicin and thaliblastine: comparison to multidrug resistance modulators verapamil and trans-flupentixol

The interactions of the antitumor drugs doxorubicin and thaliblastine with model membranes composed of neutral (phosphatidylcholine) and negatively charged (phosphatidylserine) phospholipids were studied by differential scanning calorimetry and nuclear magnetic resonance. The membrane activities of doxorubicin and thaliblastine were compared to those of the powerful multidrug resistance (MDR) modulators trans-flupentixol and verapamil. The results point out to the potential role of the drug-membrane interactions for the effects of doxorubicin and thaliblastine in resistant tumor cells. They direct also to the artificial membranes as a suitable tool for screening of compounds with potential ability to modulate MDR.

Role of glutathione S-transferase P1, P-glycoprotein and multidrug resistance-associated protein 1 in acquired doxorubicin resistance

While P-glycoprotein (Pgp) and multidrug resistance-associated protein 1 (MRP1) are known to be important in acquired doxorubicin resistance, the role of glutathione S-transferases (GST) remains unclear. Our study assessed roles of these 3 factors in a human drug-sensitive carcinoma cell line (HEp2), a subclone made resistant by prolonged incubation in doxorubicin (HEp2A), and HEp2 cells stably transfected with human GSTP1. Drug-resistant HEp2A cells showed greater total GST activity, GSTP class enzyme expression, Pgp expression, MRP1 transcript expression, drug efflux and at least 13-fold greater resistance to doxorubicin than the parent HEp2 cell line. GSTM class enzyme expression was similar in both cell types, while GSTA class enzymes were not detected. In the resistant HEp2A cells, cytotoxicity was markedly enhanced by the Pgp/MRP inhibitor verapamil at low doxorubicin concentrations. The GST inhibitor curcumin also enhanced cytotoxicity in HEp2A cells when the Pgp/MRP efflux barrier had been reversed by verapamil or overcome by high doxorubicin concentrations. In addition, curcumin had a chemosensitising effect at low doxorubicin concentrations in HEp2 cells. Stable transfection of HEp2 cells with human GSTP1 increases doxorubicin resistance 3-fold over control cells. Our study indicates involvement of GSTP enzymes as well as efflux mechanisms in the acquired doxorubicin-resistance phenotype.

pH and drug resistance. II. Turnover of acidic vesicles and resistance to weakly basic chemotherapeutic drugs

Resistance to chemotherapeutic agents is a major cause of treatment failure in patients with cancer. The primary mechanism leading to a multidrug-resistant phenotype is assumed to be plasma-membrane localized overexpression of drug efflux transporters, such as P-glycoprotein (P-gp). However, acidic intracellular organelles can also participate in resistance to chemotherapeutic drugs. In this study, we investigated, both experimentally and theoretically, the effect of acidic vesicle turnover on drug resistance. We have developed a general model to account for multiple mechanisms of resistance to weakly basic organic cations, e.g. anthracyclines and Vinca alkaloids. The model predicts that lower cytosolic concentrations of drugs can be achieved through a combination of high endosomal turnover rates, a low endosomal pH, and an alkaline-inside pH gradient between cytosol and the extracellular fluid. Measured values for these parameters have been inserted into the model. Computations using conservative values of all parameters indicate that turnover of acidic vesicles can be an important contributor to the drug-resistant phenotype, especially if vesicles contain an active uptake system, such as H+/cation exchange. Even conservative estimates of organic cation-proton antiport activity would be sufficient to make endosomal drug extrusion a potent mechanism of resistance to weakly basic drugs. The effectiveness of such a drug export mechanism would be comparable to drug extrusion via drug pumps such as P-gp. Thus, turnover of acidic vesicles can be an important factor in chemoresistance, especially in cells that do not overexpress plasma membrane-bound drug pumps like P-glycoprotein.

Deciphering the fluorescence signature of daunomycin and doxorubicin

The fluorescence characteristics of daunomycin (DNM), doxorubicin (DXR), and other anthracycline drugs are often used to monitor localization of the drug within lipid bilayers and liposomal delivery systems and to assess interaction of the drug with DNA and other macromolecules. However, the binding of DNM and DXR to proteins and membrane systems has been observed to exhibit variable effects on the anthracycline's fluorescence. We have delineated the spectroscopic response of DXR and DNM to their surroundings in several systems, including solvents of differing dielectric constant, aqueous solutions of varying pH or fluorophore concentration, and the reverse micellar system of AOT/heptane/water with a range of doxorubicin concentrations. We have observed that the ratio of fluorescence intestinal at the two principal lambda max values shows a parabolic dependence on solvent dielectric constant, i.e. inverted solvatochromism. This behavior has been overlooked by previous investigators and, together with the appearance of a long-wavelength band near 630 nm in solvents of low dielectric strength (also previously not reported), is key to understanding the partitioning of anthracyclines in membrane systems as well as resolving the conflicting interpretation of data in the literature.

Membrane interactions of some catamphiphilic drugs and relation to their multidrug-resistance-reversing ability

The multidrug-resistance (MDR)-reversing ability of the catamphiphilic drugs could be mediated through their interaction with the membrane phospholipids. This could lead directly (through changes in membrane permeability and fluidity) and/or indirectly (through inhibition of P-glycoprotein phosphorylation via inhibition of the phosphatidylserine-dependent protein kinase C or changes in the conformation and functioning of the membrane-integrated proteins via changes in the structure organization of the surrounding membrane bilayer) to the reversal of MDR. Using differential scanning calorimetry and NMR techniques and artificial membranes composed of phosphatidylcholine or phosphatidylserines we found a significant correlation between the MDR-reversing activity of the drugs in doxorubicin-resistant human breast carcinoma MCF-7/DOX and murine leukaemia P388/DOX tumour cells (data taken from the literature) and their ability to interact with phosphatidylserines. Trans- and cis-flupentixol were found to interact most strongly with both the phospholipids, followed by trifluoperazine, chlorpromazine, triflupromazine, flunarizine, imipramine, quinacrine and lidocaine. Differences in the interaction of trans- and cis-flupentixol with the phospholipids studied are suggested to be responsible for their different MDR-reversing ability. Verapamil showed moderate membrane activity, assuming that the membrane interactions are not the only reason for its high MDR-reversing ability. Amiodarone showed very strong interactions with phosphatidylserines and is recommended for further MDR-reversal studies.

Comparative study of intracellular calcium and adenosine 3',5'-cyclic monophosphate levels in human breast carcinoma cells sensitive or resistant to Adriamycin: contribution to reversion of chemoresistance

Multidrug resistance (MDR) corresponds to the cross-over resistance of tumour cells to structurally unrelated cytotoxic chemotherapeutic drugs. One of the mechanisms causing this resistance is the enhanced expression of a transmembrane drug efflux pump P-glycoprotein (P-170). Reversal of P-glycoprotein-associated MDR has received much attention in recent years. In experimental cell lines, P-170 and the glutathione redox cycle seem to contribute to this phenomenon; P-170 may be inactivated by calcium and calmodulin antagonists and the glutathione redox cycle altered by buthionine sulphoximine (BSO). Treatment of human MCF-7 breast cancer cells with chemosensitizers (CS), such as verapamil, trifluoperazine or BSO, for 72 hr resulted in an enhanced sensitization of cells to Adriamycin, trifluoperazine being the most potent compound in the reversion of chemoresistance. In these Adriamycin sensitive or resistant cells, treated or not by the CS, the possible role of calcium and cyclic adenosine monophosphate (cAMP) in mediating the reversion of chemoresistance to Adriamycin was investigated. It was found that intracellular calcium was approximately 2-fold higher in resistant than in sensitive cells, the opposite was true for cAMP. Modifications in calcium and cAMP levels were observed in MCF-7 resistant cells after treatment with verapamil and BSO; trifluoperazine had no effect on these two parameters. These results seemed to rule out any implication of calcium and cAMP levels in the contribution of these three chemosensitizers in the mechanisms of reversion of chemoresistance to Adriamycin.

Adenosine triphosphate-dependent transport of doxorubicin, daunomycin, and vinblastine in human tissues by a mechanism distinct from the P-glycoprotein

Previous studies have demonstrated that a human glutathione conjugate transporter, designated as dinitrophenyl-S-glutathione ATPase (DNP-SG ATPase), catalyzed ATP hydrolysis in the presence of several amphiphilic compounds other than glutathione conjugates (Singhal, S. S., R. Sharma, S. Gupta, H. Ahmad, P. Zimniak, A. Radominska, R. Lester, and Y. C. Awasthi. 1991. FEBS [Fed. Eur. Biochem. Soc.] Lett. 281:255-257). We now demonstrate that DNP-SG ATPase purified from human lung and erythrocyte membranes catalyzed the hydrolysis of ATP in the presence of doxorubicin and its metabolites. Doxorubicin-stimulated ATP hydrolysis by DNP-SG ATPase was saturable with respect to doxorubicin (Km 1.2 and 2.8 microM for the lung and erythrocyte enzymes, respectively). Antibodies against DNP-SG ATPase immunoprecipitated the ATP hydrolyzing activity stimulated by doxorubicin, its metabolites, and glutathione conjugates. Inside our vesicles prepared from erythrocyte membranes took up doxorubicin, daunomycin, and vinblastine in an ATP-dependent manner. The uptake was linear with respect to time and vesicle protein, was dependent on ATP and magnesium, was inhibited by heavy metal salts or by heating the vesicles, and was sensitive to both osmolarity and orientation of the vesicles. The transport had an activation energy of 13 kcal/mol, was saturable with respect to both doxorubicin and ATP (Km values of 1.8 microM and 1.9 mM, respectively), and was competitively inhibited by glutathione conjugates as well as by a number of amphiphiles such as daunomycin or vinblastine. Transport was diminished upon coating the vesicles with antibodies against DNP-SG ATPase. Incorporation of increasing amounts of purified DNP-SG ATPase into the vesicles resulted in a linear increase in transport of doxorubicin. These studies demonstrated for the first time that a membrane protein that catalyzed the transport of anionic amphiphilic molecules such as glutathione conjugates could also mediate the transport of weakly cationic antitumor antibiotic, doxorubicin. Notably, the Km of transport was in the range of doxorubicin concentration achievable in human serum after intravenous dosing of doxorubicin.