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

Modulators of cellular cholesterol homeostasis as antiproliferative and model membranes perturbing agents

Cholesterol is an important component of mammalian cell membranes affecting their fluidity and permeability. Together with sphingomyelin, cholesterol forms microdomains, called lipid rafts. They play important role in signal transduction forming platforms for interaction of signal proteins. Altered levels of cholesterol are known to be strongly associated with the development of various pathologies (e.g., cancer, atherosclerosis and cardiovascular diseases). In the present work, the group of compounds that share the property of affecting cellular homeostasis of cholesterol was studied. It contained antipsychotic and antidepressant drugs, as well as the inhibitors of cholesterol biosynthesis, simvastatin, betulin, and its derivatives. All compounds were demonstrated to be cytotoxic to colon cancer cells but not to non-cancerous cells. Moreover, the most active compounds decreased the level of free cellular cholesterol. The interaction of drugs with raft-mimicking model membranes was visualized. All compounds reduced the size of lipid domains, however, only some affected their number and shape. Membrane interactions of betulin and its novel derivatives were characterized in detail. Molecular modeling indicated that high dipole moment and significant lipophilicity were characteristic for the most potent antiproliferative agents. The importance of membrane interactions of cholesterol homeostasis-affecting compounds, especially betulin derivatives, for their anticancer potency was suggested.

Isobavachalcone as an Active Membrane Perturbing Agent and Inhibitor of ABCB1 Multidrug Transporter

Isobavachalcone (IBC) is an active substance from the medicinal plant Psoralea corylifolia. This prenylated chalcone was reported to possess antioxidative, anti-inflammatory, antibacterial, and anticancer activities. Multidrug resistance (MDR) associated with the over-expression of the transporters of vast substrate specificity such as ABCB1 (P-glycoprotein) belongs to the main causes of cancer chemotherapy failure. The cytotoxic, MDR reversing, and ABCB1-inhibiting potency of isobavachalcone was studied in two cellular models: human colorectal adenocarcinoma HT29 cell line and its resistant counterpart HT29/Dx in which doxorubicin resistance was induced by prolonged drug treatment, and the variant of MDCK cells transfected with the human gene encoding ABCB1. Because MDR modulators are frequently membrane-active substances, the interaction of isobavachalcone with model phosphatidylcholine bilayers was studied by means of differential scanning calorimetry. Molecular modeling was employed to characterize the process of membrane permeation by isobavachalcone. IBC interacted with ABCB1 transporter, being a substrate and/or competitive inhibitor of ABCB1. Moreover, IBC intercalated into model membranes, significantly affecting the parameters of their main phospholipid phase transition. It was concluded that isobavachalcone interfered both with the lipid phase of cellular membrane and with ABCB1 transporter, and for this reason, its activity in MDR cancer cells was presumptively beneficial.

8-, 9-, and 11-Aryloxy Dimeric Aporphines and Their Pharmacological Activities

Aporphines, a major group of aporphinoid alkaloids, exhibit interesting and diverse pharmacological activities. A set of dimeric aporphines with an aryloxy group at C8, C9, and C11 have been isolated from six genera and shown to elicit various biological activities such as antitumor, antimalarial, antimicrobial, antiplatelet aggregation, antifibrotic, immunosuppressive, and vasorelaxant properties. In this review, the nomenclature, chemical structures, botanical sources, pharmacological activities, and synthetic approaches of this set of dimeric alkaloids are presented.

99mTc-MIBI uptake as a marker of mitochondrial membrane potential in cancer cells and effects of MDR1 and verapamil

We investigated the relation of ^99mTc-MIBI uptake to mitochondrial membrane potential (MMP) in cancer cell lines and patient-derived tumor cells (PDCs). In T47D and HT29 cells with low MDR1 expression, FCCP dose-dependently reduced MMP and ^99mTc-MIBI accumulation in similar patterns with nearly perfect linear relationships. T47D and HT29 cells with high MDR1 expression had low ^99mTc-MIBI accumulation that was minimally affected by FCCP dose. In these cells, verapamil markedly increased ^99mTc-MIBI accumulation to magnitudes that were excessive compared to MMP increase. Decreased plasma membrane potential by verapamil and its recovery by FCCP suggested that enhanced ^99mTc-MIBI transport through modified plasma membranes contributed to the excess accumulation. Evaluation of three different colon cancer PDCs with low to modest MDR1 expression verified that FCCP significantly suppressed MMP and similarly reduced ^99mTc-MIBI accumulation. Verapamil partially recovered both MMP and ^99mTc-MIBI accumulation that was lowered by FCCP. Importantly, a high linear correlation was found (r = 0.865) between ^99mTc-MIBI accumulation and MMP in these cells. These findings indicate that low baseline ^99mTc-MIBI uptake that is markedly increased by verapamil represents cancer cells with high levels of MDR1 expression. However, in cancer cells with low or modest levels of MDR1 expression that do not markedly increase ^99mTc-MIBI uptake by verapamil, the magnitude of uptake is largely dependent on cellular MMP.

Pattern-based sensing of triple negative breast cancer cells with dual-ligand cofunctionalized gold nanoclusters

Early detection of breast cancer is a critical component in patient prognosis and establishing effective therapy regimens. Here, we developed an easily accessible yet potentially powerful sensor to detect cancer cell targets by utilizing seven dual-ligand cofunctionalized gold nanoclusters (AuNCs) as both effective cell recognition elements and signal transducers. On the basis of this AuNC multichannel sensor, we have successfully distinguished healthy, cancerous and metastatic human breast cells with excellent reproducibility and high sensitivity. Triple negative breast cancer cells (TNBCs), which exhibit low expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2, were identified. The high accuracy of the blind breast cell sample tests further validates the practical application of the sensor array. In addition, the versatility of the sensor array is further justified by identifying amongst distinct cell types, different cell concentrations and cell mixtures. Notably, the drug-resistant cancer cells can also be efficiently discriminated. Furthermore, the dual-ligand cofunctionalized AuNCs can efficiently differentiate different cells from the peripheral blood of tumor-free and tumor-bearing mice. Taken together, this fluorescent AuNCs based array provides a powerful cell analysis tool with potential applications in biomedical diagnostics.

P-glycoprotein and membrane roles in multidrug resistance

Multidrug-resistance (MDR) phenomena are a worldwide health concern. ATP-binding cassette efflux pumps as P-glycoprotein have been thoroughly studied in a frantic run to develop new efflux modulators capable to reverse MDR phenotypes. The study of efflux pumps has provided some key aspects on drug extrusion, however the answers could not be found solely on ATP-binding cassette transporters. Its counterpart – the plasma membrane – is now emerging as a critical structure able to modify drug behavior and efflux pump activity. Alterations in the membrane surrounding P-glycoprotein are now known to modulate drug efflux, with membrane-related biophysical, biochemical and mechanical aspects further increasing the complexity of an already multifaceted phenomena. This review summarizes the main knowledge comprising the plasma membrane role in MDR.

Complete plastome sequence of Thalictrum coreanum (Ranunculaceae) and transfer of the rpl32 gene to the nucleus in the ancestor of the subfamily Thalictroideae

BACKGROUND

Plastids originated from cyanobacteria and the majority of the ancestral genes were lost or functionally transferred to the nucleus after endosymbiosis. Comparative genomic investigations have shown that gene transfer from plastids to the nucleus is an ongoing evolutionary process but molecular evidence for recent functional gene transfers among seed plants have only been documented for the four genes accD, infA, rpl22, and rpl32.

RESULTS

The complete plastid genome of Thalictrum coreanum, the first from the subfamily Thalictroideae (Ranunculaceae), was sequenced and revealed the losses of two genes, infA and rpl32. The functional transfer of these two genes to the nucleus in Thalictrum was verified by examination of nuclear transcriptomes. A survey of the phylogenetic distribution of the rpl32 loss was performed using 17 species of Thalictrum and representatives of related genera in the subfamily Thalictroideae. The plastid-encoded rpl32 gene is likely nonfunctional in members of the subfamily Thalictroideae (Aquilegia, Enemion, Isopyrum, Leptopyrum, Paraquilegia, and Semiaquilegia) including 17 Thalictrum species due to the presence of indels that disrupt the reading frame. A nuclear-encoded rpl32 with high sequence identity was identified in both Thalictrum and Aquilegia. The phylogenetic distribution of this gene loss/transfer and the high level of sequence similarity in transit peptides suggest a single transfer of the plastid-encoded rpl32 to the nucleus in the ancestor of the subfamily Thalictroideae approximately 20-32 Mya.

CONCLUSIONS

The genome sequence of Thalictrum coreanum provides valuable information for improving the understanding of the evolution of plastid genomes within Ranunculaceae and across angiosperms. Thalictrum is unusual among the three sequenced Ranunculaceae plastid genomes in the loss of two genes infA and rpl32, which have been functionally transferred to the nucleus. In the case of rpl32 this represents the third documented independent transfer from the plastid to the nucleus with the other two transfers occurring in the unrelated angiosperm families Rhizophoraceae and Salicaceae. Furthermore, the transfer of rpl32 provides additional molecular evidence for the monophyly of the subfamily Thalictroideae.

Phospholipase D activation mediates cobalamin-induced downregulation of Multidrug Resistance-1 gene and increase in sensitivity to vinblastine in HepG2 cells

Failure of cancer chemotherapy due to multidrug resistance is often associated with altered Multidrug Resistance-1 gene expression. Cobalamin is the cofactor of methionine synthase, a key enzyme of the methionine cycle which synthesizes methionine, the precursor of cell S-adenosyl-methionine synthesis. We previously showed that cobalamin was able to down-regulate Multidrug Resistance-1 gene expression. Herein we report that this effect occurs through cobalamin-activation of phospholipase D activity in HepG2 cells. Cobalamin-induced down-regulation of Multidrug Resistance-1 gene expression was similar to that induced by the phospholipase D activator oleic acid and was negatively modulated by the phospholipase D inhibitor n-butanol. Cobalamin increased cell S-adenosyl-methionine content, which is the substrate for phosphatidylethanolamine-methyltransferase-dependent phosphatidylcholine production. We showed that cobalamin-induced increase in cell phosphatidylcholine production was phosphatidylethanolamine-methyltransferase-dependent. Oleic acid-dependent activation of phospholipase D was accompanied by an increased sensitivity to vinblastine of HepG2 cells while n-butanol enhanced the resistance of the cells to vinblastine. These data indicate that cobalamin mediates down-regulation of Multidrug Resistance-1 gene expression through increased S-adenosyl-methionine and phosphatidylcholine productions and phospholipase D activation. This points out phospholipase D as a potential target to down-regulate Multidrug Resistance-1 gene expression for improving chemotherapy efficacy.

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.

Synergy between verapamil and other multidrug-resistance modulators in model membranes

Various cationic lipophilic compounds can reverse the multidrug resistance of cancer cells. Possible interaction between these compounds, which are known as modulators, has been assessed by measuring leakage of Sulphan blue from anionic liposomes, induced both by verapamil alone and by verapamil in combination with diltiazem, quinine, thioridazine or clomipramine. An equation was derived to quantify the permeation doses and Hill coefficients of the drugs and mixtures between them by simultaneous fitting of the experimental data. The interaction was tested by two methods, the competition plot and the isobole method; both showed synergy between verapamil and each of diltiazem, quinine and thioridazine. The dose factor of potentiation for verapamil determined within membranes was 4.0 +/- 0.4 with diltiazem, 3.2 +/-0.4 with quinine and 2.4 +/- 0.3 with thioridazine. The results suggest that the effectiveness of reversing multidrug resistance may be increased with modulators such as verapamil and diltiazem that have a much greater effect in combination than what would be expected from their effects when considered separately.

The use of differential scanning calorimetry to study drug-membrane interactions

Differential-scanning calorimetry is a thermodynamic technique widely used for studying drug-membrane interactions. This chapter provides practical examples on this topic, highlighting the caution to be taken in analyzing thermal data as well as scientific information that can be derived by the proper use of the technique. An example is given using model bilayers containing high concentration of the anesthetic steroid alphaxalone. It is shown that the breadth of the phase transitions and the maximum of the phase-transition temperature of the bilayer depend on the equilibration conditions before acquiring the thermal scan. In addition, the quality of the thermo-gram depends on its perturbation and incorporation effects; for dissecting these effects, a complementary technique such as solid-state nuclear magnetic resonance spectroscopy is necessary. Differential-scanning calorimetry is a useful technique to study the interdigitation effect of a drug by monitoring DeltaH changes. Cholesterol, a main constituent of membrane bilayers, appears to disrupt the interdigitating effect. In general, the thermal effects of the drug incorporated into a membrane bilayer depends on the drug stereoelectronic properties.

Paclitaxel modifies the accumulation of tumor-diagnostic tracers in different ways in P-glycoprotein-positive and negative cancer cells

AIM

To study how paclitaxel treatment modifies the accumulation of tumor-diagnostic radiotracers in P-glycoprotein (P-gp) positive and negative cancer cells.

METHODS

The accumulations of different P-gp substrates, including rhodamine 123, daunorubicin and [(99m)Tc]hexakis-2-methoxybutyl isonitrile ((99m)Tc-MIBI), were measured in P-gp-positive (A2780AD) and P-gp-negative human ovarian carcinoma cells (A2780) and JY human lymphoid B cells. The uptakes of the tumor-diagnostic tracers (11)C-choline and 2-[(18)F]fluoro-2-deoxy-d-glucose ((18)FDG) were measured in the same cell lines. The P-gp expression and function were demonstrated by flow-cytometry.

RESULTS

The (18)FDG measurements revealed that the glucose metabolic rate was significantly higher (p<0.01) in the P-gp-positive A2780AD cells than in the P-gp-negative cells. Paclitaxel (1-70microM) increased the (18)FDG uptake (up to 200%) of both P-gp-positive and P-gp-negative cells, whereas it did not modulate their (11)C-choline uptake. Paclitaxel reinstated the (99m)Tc-MIBI accumulation of the A2780AD cells (to 1500% of the control) in a concentration-dependent manner, while it increased the uptake of the P-gp-negative cells to a lesser extent (to a maximum of 200% of the control).

CONCLUSION

Paclitaxel modifies the uptake of tumor-diagnostic tracers in both P-gp-dependent and independent manners. Interpretation of the multifactorial effects of paclitaxel may promote a correct in vivo diagnosis of P-gp-positive and P-gp-negative tumors.

Effects of miltefosine on membrane permeability and accumulation of [99mTc]-hexakis-2-methoxyisobutyl isonitrile, 2-[18F]fluoro-2-deoxy-d-glucose, daunorubucin and rhodamine123 in multidrug-resistant and sensitive cells

Miltefosine is a phospholipid analog that exhibits antineoplastic activity against breast cancer metastases, but its mechanism of action remains uncertain. The aim of this study was to investigate the transport mechanism for the removal of miltefosine and [99mTc]-hexakis-2-methoxyisobutyl isonitrile (99mTc-MIBI) from multidrug-resistant cells. The P-glycoprotein pump function, cell viability, and 99mTc-MIBI and 2-[18F]fluoro-2-deoxy-D-glucose (18FDG) uptakes were measured in NIH 3T3 (3T3) and NIH 3T3MDR1 G185 (3T3MDR1) mouse fibroblasts and human lymphoid B JY cells. Miltefosine treatment increased the permeability and fluidity of these tumor cells in a concentration-dependent manner. The multidrug-sensitive cells were 3-4 times more sensitive to miltefosine than the multidrug-resistant ones. The extent of 99mTc-MIBI accumulation in the P-glycoprotein-expressing cells increased in the presence of miltefosine, whereas the rhodamine123 and daunorubicin uptakes of the cells did not change significantly. In the 3T3MDR1 cells verapamil reinstated the rhodamine123 and daunorubicin accumulation, but not the 99mTc-MIBI uptake. Cyclosporin A reinstated the uptakes of 99mTc-MIBI, daunorubicin and rhodamine123 by the 3T3MDR1 cells. In a concentration-dependent manner miltefosine decreased the extents of 99mTc-MIBI, rhodamine123, daunorubicin and 18FDG accumulation in the JY and 3T3 cells. Our findings indicate a common transport mechanism for 99mTc-MIBI and miltefosine, which is distinct from that for rhodamine123 and daunorubicin in MDR cells.

Biphasic accumulation kinetics of [99mTc]-hexakis-2-methoxyisobutyl isonitrile in tumour cells and its modulation by lipophilic P-glycoprotein ligands

AIM

To study the accumulation and washout kinetics of [99mTc]-hexakis-2-methoxyisobutyl isonitrile (99mTc-MIBI) in MDR positive and MDR negative tumour cells and how this is modified by lipophilic P-glycoprotein ligands.

METHODS

The tumour cells were incubated in the presence and absence of the ligands and the uptakes of 99mTc-MIBI, rhodamine 123 and 2-[18F]fluoro-2-deoxy-D-glucose (18FDG) were measured.

RESULTS

The accumulation of 99mTc-MIBI in the tumour cells followed biphasic kinetics. Verapamil and cyclosporin A increased the membrane fluidity and significantly enhanced the 99mTc-MIBI uptake of the MDR negative cells, while the rhodamine 123 uptake was not affected. Verapamil significantly increased the uptake of rhodamine 123 and 18FDG but did not modify that of 99mTc-MIBI in the MDR positive cells. Cyclosporin A significantly increased the 18FDG uptake of the MDR positive and negative tumour cells; these effects were ouabain-sensitive. Depolarization of the cytoplasmic membrane, acidification of the extracellular medium and the administration of CCCP decreased the accumulation of 99mTc-MIBI and rhodamine 123 uptake in the tumour cells.

CONCLUSIONS

Lipophilic P-glycoprotein ligands modified the biphasic accumulation kinetics of the 99mTc-MIBI uptakes of MDR negative and positive tumour cells in different and complex ways and could therefore mask the P-glycoprotein pump-dependent changes in tracer accumulation.