Identification of the multidrug resistance-related membrane glycoprotein as an acceptor for cyclosporine

Pretreatment with the Cyclosporin Derivative, NIM811, Improves the Function of Synaptic Mitochondria following Spinal Cord Contusion in Rats

Trauma to the spinal cord causes a cascade of secondary events, such as mitochondrial dysfunction, which disrupts cellular functions and ultimately leads to cell death. Cyclosporin A (CsA) is a potent immunosuppressant that promotes mitochondrial function by inhibiting mitochondrial permeability transition (mPT). Clinical trials examining CsA in traumatic brain injury are currently under-way, but CsA is potentially neurotoxic. NIM811 is a non-immunosuppressive CsA derivative that inhibits mPT at nanomolar concentrations and with significantly less cytotoxicity than CsA. In the present study, we investigated the effects of NIM811 treatment on mitochondrial bioenergetics and the production of reactive oxygen species following spinal cord injury (SCI) in rats. Rats were pretreated with NIM811 or vehicle, and after 15 min the rats received a "mild/moderate" spinal cord contusion. After 24 h, the spinal cords were rapidly removed and synaptosomal mitochondria were isolated. NIM811 pretreatment significantly improved mitochondrial respiratory control ratios, and the maximal electron transport capacity of complex I and II, as well as their ATP-producing capacity. Consistent with the improvements in mitochondrial function, NIM811 pretreatment significantly decreased free radical production in isolated mitochondria. These studies are the first to demonstrate the therapeutic potential of CsA derivatives in a model of SCI, and support the need for continued investigation of compounds like NIM811 as an acute treatment for human SCI.

Mitochondrial dysfunction induced by a cytotoxic adenine dinucleotide produced by ADP-ribosyl cyclases from cADPR

ADP-ribosyl cyclases were previously shown to produce three new adenine dinucleotides, P1,P2 diadenosine 5'-diphosphate (Ap2A) and two isomers thereof (P18 and P24), from cyclic ADP-ribose (cADPR) and adenine (Basile, G., Taglialatela-Scafati, O., Damonte, G., Armirotti, A., Bruzzone, S., Guida, L., Franco, L., Usai, C., Fattorusso, E., De Flora, A., and Zocchi, E. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 14509-14514). The Ap2A isomer P24, containing an unusual C1'-N3 N-glycosidic bond, is shown here to affect mitochondrial function through (i) opening of the permeability transition pore complex (and consequent proton gradient dissipation) and (ii) inhibition of Complex I of the respiratory chain. Whereas proton gradient dissipation is dependent upon the extracellular Ca(2+) influx triggered by P24, the effect on oxygen consumption is Ca(2+) independent. The proton gradient dissipation induces apoptosis in HeLa cells and thus appears to be responsible for the already described potent cytotoxic effect of P24 on several human cell types. The other products of ADP-ribosyl cyclase activity, Ap2A and cADPR, antagonize P24-induced proton gradient dissipation and cytotoxicity, suggesting that the relative concentration of P24, cADPR, and Ap2A in cyclase-positive cells may affect the balance between cell life and death.

Development and application of diazirines in biological and synthetic macromolecular systems

Many different reagents and methodologies have been utilised for the modification of synthetic and biological macromolecular systems. In addition, an area of intense research at present is the construction of hybrid biosynthetic polymers, comprised of biologically active species immobilised or complexed with synthetic polymers. One of the most useful and widely applicable techniques available for functionalisation of macromolecular systems involves indiscriminate carbene insertion processes. The highly reactive and non-specific nature of carbenes has enabled a multitude of macromolecular structures to be functionalised without the need for specialised reagents or additives. The use of diazirines as stable carbene precursors has increased dramatically over the past twenty years and these reagents are fast becoming the most popular photophors for photoaffinity labelling and biological applications in which covalent modification of macromolecular structures is the basis to understanding structure-activity relationships. This review reports the synthesis and application of a diverse range of diazirines in macromolecular systems.

Cyclosporins: structure-activity relationships for the inhibition of the human MDR1 P-glycoprotein ABC transporter

Cyclic undecapeptide cyclo-[MeBmt(1)-Abu(2)-MeGly(3)-MeLeu(4)-Val(5)-MeLeu(6)-Ala(7)-D-Ala(8)-MeLeu(9)-MeLeu(10)-MeVal(11)], the immunosuppressive and antifungal antibiotic cyclosporin A (CsA), was reported to interfere with the MDR1 P-glycoprotein (Pgp), a transmembranous adenosine 5'-triphosphate binding cassette (ABC) transporter with phospholipid flippase or "hydrophobic vacuum cleaner" properties that mediate multidrug resistance (MDR) of cancer cells. By use of photoaffinity-labeled cyclosporins and membranes from Pgp-expressing cells, it was recently shown that in vitro, Pgp molecules could bind a large cyclosporin domain involving residues 4-9 as well as the side chain of residue 1. Tumor cell MDR can also be reversed by a product more distantly related to cyclosporin with the structure [Thr(2), Leu(5), D-Hiv(8), Leu(10)]-CsA (SDZ 214-103). In a standardized assay that measures Pgp function in vivo (on intact live cells) by the Pgp-mediated efflux of the calcein-AM Pgp substrate and uses human lymphoblastoid MDR-CEM (VBL(100)) cells as highly resistant Pgp-expressing cells, SDZ 214-103 was found to be one of the most active Pgp inhibitors among naturally occurring cyclosporins, with an IC(50) of 1.6 microM in an assay where CsA gives an IC(50) of 3.4 microM. Using the in vivo assay, 60, mostly natural, cyclosporin analogues were analyzed to establish structure-activity relationships (SAR). Our SAR are compatible with the in vitro-defined Pgp binding domain model and further disclose that in vivo Pgp inhibition is favored by larger hydrophobic side chains on cyclosporin residues 1, 4, 6, and 8 and a smaller one on residue 7, although with no effect on the residue 5 side chain; moreover, larger hydrophobic side chains on other residues 2, 3, 10, and 11 (outside the in vitro-defined Pgp binding domain) also favor the eventual inhibition of Pgp function. The N-desmethylation of any of the seven N-methylated amides, as naturally occurring in numerous cyclosporins, regularly leads to a decreased Pgp inhibitory activity (Pgp-InhA), up to its abrogation if it occurs at residues 4 and 9. Nevertheless, despite unfavorable use of [Thr(2)] and [Leu(10)] residues, all [D-Hiv(8)] analogues whose lead is SDZ 214-103 show a large Pgp-InhA. The SAR for Pgp inhibition by cyclosporins are thus very complex. Because CsA and SDZ 214-103 show largely different conformations when free in solution, but remarkably similar ones when bound to the cytosolic cyclophilins, SAR for Pgp inhibition must similarly include requirements for occurrence of suitable conformers for insertion in the cell membrane, sufficient conformational plasticity for gaining access to Pgp binding sites, and an adequate conformer structure there to achieve such binding with a high enough affinity and possibly escape from sequestration on cyclophilins.

Cyclosporin A, FK506 and rapamycin produce multiple, temporally distinct, effects on memory following single-trial, passive avoidance training in the chick

Few studies have used a pharmaco-behavioural methodology to directly investigate roles for the calcium-dependent protein phosphatase calcineurin (CaN) in memory formation, due partly to the absence of specific inhibitory agents. A number of drugs with different inhibitory profiles were used to examine this issue in groups of chicks trained on a single-trial, passive-avoidance task. Bilateral intracranial administration of the immunosuppressants FK506 and cyclosporin A (CyA) led to two temporally distinct effects, distinguished by the concentration of drug required and the effective time of administration relative to training. In addition to inhibiting CaN, CyA and FK506 inhibit distinct classes of peptidyl prolyl-cis/trans-isomerases (PPIases). Other agents known to inhibit these enzymes, including the Map kinase inhibitor Rapamycin, also induced memory deficits in a complex, dose- and time-of-administration-dependent, manner. The data fail to conclusively implicate CaN in memory formation, but are consistent with proposals that a phosphatase cascade may participate in an early stage of information storage. PPIases may be required at a later stage to catalyse the folding of new or translocated proteins, the synthesis of which is required for formation of long-term memory, although other possible explanations for the data remain to be investigated.

Reversal of multidrug resistance by novel cyclosporin A analogues and the cyclopeptolide SDZ 214-103 biosynthesized in vitro

It was shown that cyclopeptolide SDZ 214-103 (10 microM) is more active in rhodamine-123 accumulation in actinomycin-D-resistant human lymphoma cells CCRF/ACTD400 than cyclosporin A (10 microM), but equipotent in the doxorubicin-resistant Friend erythroleukemia cell line F4-6/ADR. In F4-6/ADR cells, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay showed comparable cytotoxic effects of doxorubicin at various concentrations in the presence of SDZ 214-103 and cyclosporin A. For the other novel cyclosporin A analogues minor multidrug-resistance-modulating potency was demonstrated. At equipotent modulating doses of verapamil (10 microM) and cyclosporin A (10 microM) in the MTT assay regarding doxorubicin cytotoxicity, cyclosporin A was efficient in the rhodamine-123-uptake assay while verapamil was not active when identical incubation times were used.

Collateral sensitivity of multidrug resistant cells to narcotic analgesics is due to effects on the plasma membrane

It has previously been demonstrated that opiates interact directly with P-glycoprotein in drug resistant Chinese hamster ovary (CHO) cells (Callaghan, R. and Riordan, J.R. (1993) J. Biol. Chem. 268, 16059-16064). In this study we have examined the effects of several opiates on the growth of drug sensitive and resistant CHO and human MCF7 cell lines. The growth of P-glycoprotein expressing cells was inhibited by the opiates pentazocine, pethidine and naloxone to a greater extent than in drug sensitive cells. Since P-glycoprotein is localised at the plasma membrane the effects of opiates on membrane biophysical properties were investigated. The opiates caused a fluidizing effect in membranes from P-glycoprotein expressing cells and decreased the basal level of P-glycoprotein phosphorylation. In addition, they were able to increase the leakage of the membrane impermeant compound 6-carboxyfluorescein entrapped in model membrane vesicles. The ability to alter membrane biophysical properties correlated with the inhibitory effects on growth of drug resistant cells. These results suggest that the collateral sensitivity of P-glycoprotein expressing cell lines to opiates is mediated by the drugs' effects on the plasma membrane.

Interaction of tamoxifen with the multidrug resistance P-glycoprotein

Tamoxifen is an anti-oestrogen which is currently being assessed as a prophylactic for women at high risk of breast cancer. Taxoxifen has also been shown to reverse multidrug resistance in P-glycoprotein (P-gp)-expressing cells, although the mechanism of action is unknown. In this study we demonstrate that tamoxifen interacts directly with P-gp. Plasma membranes from P-gp-expressing cells bound [3H]tamoxifen in a specific and saturable fashion. A 180 kDa membrane protein in these membranes, labelled by the affinity analogue tamoxifen aziridine and azidopine, was shown to be P-gp. Tamoxifen reduced the binding of vinblastine and azidopine to P-gp, and tamoxifen increased [3H]vinblastine accumulation in P-gp-expressing cells to levels approaching those in non-P-gp-expressing cells. However, the cellular accumulation of [3H]tamoxifen itself was not influenced by the presence of P-gp. Thus, tamoxifen appears to reverse multidrug resistance by binding to P-gp and inhibiting the transport of cytotoxic drugs, but does not itself appear to be transported by the protein.

Secondary combined resistance to the multidrug-resistance-reversing activity of cyclosporin A in the cell line F4-6RADR-CsA

Multidrug-resistant tumor cells can be resensitized by combined application of the selecting cytostatic drug and a chemosensitizer, such as cyclosporin A (CsA) or a calcium channel blocker. Since clinical trials on the circumvention of multidrug resistance (MDR) with chemosensitizers report disparate results, we investigated whether tumor cells of the MDR phenotype can develop additional resistance to the cytostatic chemosensitizer combination. Thus, the Adriamycin(ADR)-selected, P-glycoprotein-positive MDR Friend leukemia cell line F4-6RADR was exposed to stepwise increased concentrations of CsA at a constant level of 0.05 microgram/ml ADR. The initial CsA concentration (plus 0.05 microgram/ml ADR) to inhibit cell growth of F4-6RADR cells by 50% (IC50) was 0.04 microgram/ml. By continuous incubation for more than 6 months, the IC50 for CsA (at constant ADR) was elevated to 3.6 micrograms/ml (90-fold), thus generating the variant F4-6RADR-CsA. The F4-6RADR-CsA cells were cross-resistant for cyclosporin H (CsH), a non-immunosuppressive derivative of CsA. As shown by immunocytochemistry as well as by the polymerase chain reaction and by Western blotting including densitometry, P-glycoprotein was preserved in the F4-6RADR-CsA variant and was expressed at a 4-fold higher level than in F4-6RADR cells. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis analysis could detect no new proteins in F4-6RADR-CsA as compared to F4-6RADR. Interestingly, resistance of F4-6RADR-CsA cells remained reversible for the calcium antagonists verapamil and dihydropyridine B859-35 (dexniguldipine-HCl), indicating that CsA and these compounds interfere with the P glycoprotein function by different pharmacodynamic mechanisms. Transport studies with [14C]ADR, performed in the presence and absence of chemosensitizers, confirmed the good correlation of P-glycoprotein function with the pattern of resistance found in proliferation assays. Cellular accumulation of [3H]cyclosporin was reduced to 71% of that of the F4-6 controls in F4-6RADR-CsA cells, but remained at the level of controls in F4-6RADR cells. Results indicate that increased amounts of the P-glycoprotein--besides other, perhaps more important mechanisms that are as yet unknown--partially mediate CsA resistance in F4-6RADR-CsA cells. We have designated this new form of resistance "secondary combined resistance" (SCR). The results suggest that at least some clinical cases of insensitivity to chemosensitizers or of relapse after reversing therapy could be explained by SCR, and that resensitizing treatment of tumor patients should be based on the consideration of several chemosensitizers of different pharmacodynamics.

A marine natural product, patellamide D, reverses multidrug resistance in a human leukemic cell line

A cyclic octapeptide (patellamide D) isolated from the marine tunicate, Lissaclinum patella, acts as a resistance-modifying agent in the multidrug resistant CEM/VLB100 human leukemic cell line. A three-day microculture tetrazolium proliferation assay was used to determine the 50% inhibitory concentration (IC50) for vinblastine, colchicine and adriamycin and calculate the degree of resistance modulation. Patellamide D at 3.3 microM was compared with 5.1 microM verapamil in modulating drug resistance in vitro. The IC50 for vinblastine was reduced from 100 ng/ml to 1.5 ng/ml in the presence of patellamide D or to 2.1 ng/ml when exposed to verapamil. Colchicine cytotoxicity was enhanced only 1.4-fold by verapamil, as compared with 2.8-fold using patellamide D (IC50 was reduced from 140 ng/ml to 100 ng/ml or 50 ng/ml). Adriamycin toxicity was reduced from IC50 > 1000 ng/ml to 110 ng/ml and 160 ng/ml when coexposed to patellamide D and verapamil, respectively. Our results indicate that patellamide D acts as a selective antagonist in multidrug resistance and stresses the importance of investigating marine-derived compounds as a potential new source for modulators of the drug-resistance phenotype.

Binding and subcellular distribution of cyclosporine in human fibroblasts

The uptake, binding, and subcellular sites of accumulation of [3H]-cyclosporine (CS) in two human gingival fibroblast strains, GN 23 and GN 54, have been examined. GN 23 responds to CS treatment with a decrease in collagenolysis, while GN 54 does not. Binding of the drug was determined using [3H]-CS concentrations ranging from 10(-5) to 10(-8) M in the absence or presence of excess unlabeled CS (1 mM). The binding of the drug to both strains was specific and reached a plateau within 10 min, remaining at that level for up to 1 h. Scatchard analysis of the specific binding of [3H]-CS to the responsive GN 23 strain revealed two dissociation constants: KD = 5 x 10(-8) M (1.2 x 10(7) sites/cell) and KD = 1.4 x 10(-6) M (2.2 x 10(8) sites/cell). GN 54, on the other hand, had only one class of low affinity binding site (KD = 0.47 x 10(-6) M [1.2 x 10(8) sites/cell]). Unlabeled CS (0.01-1 mM) inhibited the binding of [3H]-CS in a dose-dependent manner to both strains, as did the calmodulin antagonist W-7, to a lesser extent. However, W-7 inhibited CS binding much more efficiently in GN 54 than in GN 23, suggesting that calmodulin may be the predominant CS receptor in GN 54. In both strains, 70% of the drug accumulated in the crude nuclear fraction after a 1 min incubation, with very little (< or = 4%) being membrane associated, and the remainder was in the cytosol.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and partial characterization of membrane-associated cyclophilin and a related 22-kDa glycoprotein

The presence of membrane-associated proteins which stereospecifically bind cyclosporin A and react with anti-cyclophilin antibodies has been documented in rat tissues. Extraction of membranes with 6 M urea or 0.5% Chaps releases cyclosporin-binding activity that is 5-12% of that found in cytosol. Cyclosporin-A-binding proteins are present in most subcellular organelles of liver, but microsomes contain the greatest activity. These proteins can be purified by adsorption onto a cyclosporin-A affinity column and elution with cyclosporin A. Two major fractions are resolved on SDS/PAGE: an 18-kDa fraction is comprised of two isoforms that are similar if not identical to the two major cytosolic isoforms of cyclophilin. In addition, in microsomes an approximately equal quantity of a 22-kDa glycoprotein was detected. Based on partial sequencing (five peptides, 89 amino acids) this protein is similar but not identical to human cyclophilin B. This 22-kDa isoform is poorly recognized by affinity-purified anti-cyclophilin antibodies and comprises several predominant isoforms (pI approximately 9.3-9.6). Selective binding of membrane 22-kDa cyclophilin to peanut lectin suggests the oligosaccharides contain a terminal galactosyl-N-galactosamine residue.