Interactions between ellipticine and some derivatives and phospholipids in model membranes

Lipid model membranes for drug interaction study

The present work shows a structural study on the process of incorporation of a hydrophobic drug, Ellipticine (ELPT), into lipid model membranes for drug targeting purpose. The ELPT is an alkaloid that showed an anti-proliferation activity against several types of tumor cells and against the HIV1 virus. We used the zwitterionic lipid dipalmitoyl phosphatidylcholine (DPPC) and four different anionic lipids: cardiolipin (CL), dipalmitoyl phosphatidic acid (DPPA), dipalmitoyl phosphatidylglycerol (DPPG) and dipalmitoyl phosphatidylserine (DPPS), both spread on a Langmuir monolayer and deposited on a solid substrate to mimic a model membrane and study the interaction with the drug ELPT. X-ray reflectivity results pointed toward an increase in drug loading efficiency up to 13.5% mol/mol of ELPT into mixed systems DPPC/CL. This increase in loading efficiency was also accompanied by a slight distortion in the stacking of the bilayers less evidenced after optimization of the molar ratio between the co-lipids. Grazing incidence X-ray diffraction measurements revealed an in-plane lattice distortion due to the presence of hydrocarbon chain backbone ordering in pure systems of DPPC doped with ELPT. The same was not observed in mixed membranes with DPPC/CL and DPPC/DPPA.

Adsorption of the cationic antitumoral drug celiptium to phosphatidylglycerol in membrane model systems. Effect on membrane electrical properties

The binding of the cationic antitumoral drug Celiptium to the anionic phospholipid phosphatidylglycerol was studied by measuring surface potentials and surface pressures in monolayers, and by determination of electrophoretic mobility on liposomes. Surface potential and zeta potential data were interpreted in terms of the Gouy-Chapman-Stern theory of the diffuse electrical double layer. A unique drug-to-lipid adsorption constant KaD, could not be calculated. KaD was observed to increase rapidly from 10(4) M-1 to 10(6) M-1 with an increase in drug concentration from 5 x 10(-7) M to 7 x 10(-6) M. This was accompanied by a marked decrease (in absolute value) in the corresponding electrophoretic mobilities which, from negative at low drug concentrations, became positive at drug concentrations of 10(-5) M and above. This indicates that the drug-to-lipid binding cannot be accounted for by a simple Langmuir adsorption isotherm, but corresponds to a more complex process, probably of a cooperative nature. Comparison of delta V and zeta potential data shows that adsorption of Celiptium to phosphatidylglycerol not only lowers the electrical surface potential, psi 0 (in absolute value) but also markedly reduces the polarization potential, delta Vp. These observations suggest that Celiptium destabilizes the electrical properties of cell plasma membranes.

A comparative model membrane study on structural effects of membrane-active positively charged anti-tumor drugs

The interaction of a number of positively charged anti-tumor drugs with cardiolipin-containing model membranes has been investigated using 31P nuclear magnetic resonance (31P-NMR), differential scanning calorimetry (DSC) and monolayer techniques. It appeared that the ellipticines used (i.e., celiptium and 2-N-methylellipticinium), and also ethidium bromide, completely blocked Ca2+-induced HII phase formation in pure cardiolipin liposomes at molar ratios of drug-to-lipid of approx. 1:1. For the anthracyclines adriamycin and 4'-epi-adriamycin, a similar effect was observed, but now a 2:1 ratio was required. 31P-NMR experiments on dioleoylphosphatidylethanolamine/cardiolipin mixed liposomes indicated that the two anthracyclines, but not the other three drugs, were capable of inducing macroscopic phase separation into domains enriched in drug-cardiolipin complexes and domains enriched in the zwitterionic phospholipid species. DSC experiments on dipalmitoylphosphatidylcholine/cardiolipin mixtures led, with the exception of 2-N-methylellipticinium, to the same conclusion. Measurements of surface pressure and surface potential of cardiolipin monolayers at the air/water interface as well as conformational analysis of the various drug-cardiolipin recombinants showed that the ellipticines are deeply embedded in the acyl chain region of the bilayer, while the anthracyclines and ethidium bromide are preferentially localized in the interface. All drugs share an important electrostatic interaction with the negatively charged phosphates of cardiolipin.

Renal toxicity of the antitumor drug N2-methyl-9-hydroxyellipticinium acetate in the Wistar rat

Celiptium (N2-methyl-9-hydroxy-ellipticinium) is an antitumoral agent used to treat bone metastases from breast carcinomas. This new drug appeared to be of great interest because of the absence of hepato- or myelotoxicity. Three different investigators recently mentioned cases of celiptium-induced renal failure. We therefore undertook a study of renal function and morphology in female Wistar rats. Two single i.v. doses (10 or 20 mg/kg) were administered and animals were sacrificed 4, 8, 15, 28 and 60 days after injection. One group of rats received multiple doses, 5 mg/kg/week for 8 weeks. No mortality was observed. With the 10 mg/kg single dose creatinine clearance (Ccr) and urinary enzymes did not change, and tubular lesions were rare. With the 20 mg/kg single dose CCr decreased on day 4 and returned to normal on day 28. Urinary enzyme excretion (AAP, NAG, gamma GT) increased. Renal lesions were diffuse with tubular necrosis, luminal dilation and later (day 28) interstitial cellular infiltration. These lesions persisted on day 60 and appeared to be irreversible. Ultrastructural studies showed numerous large fat droplets in proximal tubular cells. Glycerol concentrations in renal cortex homogenates were increased while phospholipids are slightly decreased. With 5 mg/kg every week (multiple doses) Ccr decreased and tubular lesions similar to the observed with the 20 mg/kg single dose were seen. Thus celiptium induced dose-dependent nephrotoxicity in rats with prolonged tubular alterations.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between the uptake and cytotoxicity of celiptium in wild type and resistant mutants of the bacterium Streptococcus pneumoniae

Celiptium, a cationic and amphiphilic drug currently employed in cancer chemotherapy, was found to be accumulated against its concentration gradient by the bacterium Streptococcus pneumoniae. Accumulation was reduced in Celiptium resistant amiA mutants which were also observed to have reduced electric transmembrane potentials delta psi. This suggested a relationship between Celiptium toxicity and accumulation in S. pneumoniae, and indicated a delta psi - driven uptake in a manner reminiscent of that observed for other lipophilic cations such as tetraphenylphosphonium.

Inhibition of tumor cell growth in vitro and in vivo by 2-methyl 9-hydroxyellipticinium entrapped within phospholipid vesicles

Encapsulation in liposomes of the antitumoral drug 2-methyl 9-hydroxyellipticinium and the consequences of its cytotoxicity in vitro on L1210 leukemia cells and on its antitumoral activity in vivo on leukemic mice inoculated with L1210 cells are described. Provided the drugs is dissolved in the buffer below its critical micelle concentration (10(-4) M), it can be encapsulated in lipid vesicles with a very good yield in the form of a very stable combination with the lipids. The in vitro experiments show that 2-CH3 9-OH-ellipticinium is less cytotoxic against L1210 cells when entrapped than when free in solution. The in vivo experiments on tumor-bearing mice show that encapsulation of the drug reduces its toxicity. Encapsulation maintains the antitumoral activity of the drug or increases it if the leukemia is delayed (10(4) cells injected per mouse instead of 10(5) cells per mouse).

Studies on the fluorescence labeling of human red blood cell membrane ghosts with 4'-(9-acridinylamino)methanesulfon-m-anisidide

4'-(9-Acridinylamino)methanesulfon-m-anisidide (mAMSA) interacts with red cell membranes, resulting in the formation of fluorescent protein adducts. The mAMSA-membrane protein adducts exhibited an emission fluorescence maximum at 445 nm, with two shoulders at approximately 425 and 470 nm. The major labeled proteins were identified as spectrins 1 and 2 and bands 3, 4.1, 4.2 and 5. The fluorescence intensity increased with increasing mAMSA concentrations (0.03 to 1.5 mM), time (15-120 min), and temperature of the reaction. Results from sodium dodecyl sulfate gel electrophoresis show that mAMSA caused no detectable change in the molecular weight of membrane proteins. This indicates that mAMSA is a monofunctional, noncrosslinking agent. Other acridine analogs, 9-aminoacridine and acridine, did not fluorescently label membrane proteins, suggesting that the presence of the acridine nucleus is not sufficient for labeling. Addition of 2-mercaptoethanol to the mAMSA-membrane reaction mixtures reversed the fluorescence labeling. Furthermore, pretreatment of membrane proteins with N-ethylmaleimide or iodoacetamide prevented the formation of fluorescent mAMSA-membrane protein adducts. These data suggest that mAMSA interacts with sulfhydryl groups of the membrane proteins. When the membrane sulfhydryl groups were assayed by labeling with N-[ethyl-2-3H]ethylmaleimide, it was shown that the accessible membrane sulfhydryl groups were reduced after the mAMSA treatment. The above results suggest that mAMSA covalently binds to the sulfhydryl groups in the red cell membrane, with the production of fluorescent mAMSA-protein adducts.

Ellipticine derivatives interact with muscarinic receptors

Ellipticine derivatives or analogues, tetracyclic alkaloids used in human cancer treatment, have been evaluated with regard to their interaction with several neurotransmitter receptors, in order to explain or to predict the side effects which occur in man. These drugs were recently found to be reversible non-competitive inhibitors of cholinesterases. In this study, we have shown that ellipticines are also potent muscarinic antagonists, only 100-fold less active than atropine in inhibiting 50% of the specific binding of (3H) quinuclidinyl benzilate on rat brain preparation of muscarinic receptors. That the interaction with muscarinic receptors is quite unique has been demonstrated by the lack of interaction with three other neurotransmitter receptors. Tertiary amines show relatively less blockade of muscarinic receptors, while substituted ammonium ions are better inhibitors of the QNB binding. The possible mechanisms of in vivo action of these alkaloids is discussed.

Ellipticine derivatives interacting with model membranes. Influence of quaternarization of nitrogen-2

Four compounds of the ellipticine family were examined in their interaction with liposomes and with an isolated bacterial membrane. The physicochemical methods used detected only minor differences between the properties of the amphiphilic drugs (ellipticine and 2-methyl-ellipticinium) and the two dipolar drugs (9-hydroxy-ellipticine and 2-methyl 9-hydroxy-ellipticinium). The amphiphilic drugs were able to become associated to anionic liposomes in a 20-30% excess of charge neutralization, and seem to penetrate deeper into the lipid layer than the two dipolar drugs. It was also shown that ellipticine penetrates deeper into liposomes membrane than into natural membrane used. In contrast with what can be postulated from the literature dealing with the behaviour of quaternarized drugs, it seems that ellipticine and its quaternarized analogues present fast diffusion through multilayered vesicles. On the whole, the membrane effects of the ellipticines studied here are not different for quaternarized drugs and for drugs not permanently charged, but are influenced by the existence on the molecules of a second polar function.

Ellipticine-induced alteration of model and natural membranes

The modification of certain membrane properties by ellipticine derivatives was examined. The amphiphilic 9-methoxyellipticine was the most efficient in disorganizing membrane structure and in inducing leaks of liposomes, haemolysis of intact human erythrocytes. This drug and the dipolar 9-amino- and 9-hydroxyellipticine were equally efficient in decreasing the surface charge of membranes and in inhibiting the respiration of an isolated bacterial membrane.

Localization of ellipticine derivatives interacting with membranes. A fluorescence-quenching study

The interaction with membranes of three anti-cancer drugs of the ellipticine family was studied by fluorescence quenching of membrane probes. The fluorescence of three probes, located at different levels in membranes, was quenched by addition of two types of ellipticine derivatives, one amphiphilic drug (9-methoxyellipticine) and two dipolar molecules (9-aminoellipticine and 9-hydroxyellipticine). By comparing the quenching curves obtained, the following can be proposed. a) 9-Methoxyellipticine can penetrate deeper in the lipid layers than 9-aminoellipticine and 9-hydroxyellipticine can. b) The three drugs are able to penetrate at least between the first methylene groups of the acyl chains of lipids in liposomes. c) In an isolated bacterial membrane, only 9-methoxyellipticine can be located in the region of the first methylene groups of lipids, the two dipolar drugs being adsorbed on the membrane surface. It was also shown that cholesterol hindered the penetration of 9-methoxyellipticine in the bilayer of liposomes.

Interactions of ellipticine with model or natural membranes. A spectrophotometric study

Ellipticine is the type of a group of substances used against human cancer. It was shown that ellipticine and 9-methoxyellipticine strongly interact with monolayers of negatively charged phospholipids. In the present paper it is shown by spectrophotometric methods that ellipticine interacts with suspensions of a model membrane with a 1/1 charge neutralization, and with a natural membrane, both negatively charged. At a physiological pH, ellipticine undergoes protonation in the presence of these membranes. Its apparent pK is increased by 1, and its spectral behaviour, when the pH is changed, indicates that the drug is in a less polar environment, suggesting that hydrophobic bonds link the drug and the lipids. The existence of such bonds is suggested by the fact that the drug is not significantly released from anionic membranes when the pH is increased to 10, at which value ellipticine is not ionized. The consequences of these ionic and hydrophobic interactions are briefly discussed.