Cisplatin interaction with phosphatidylserine bilayer studied by solid-state NMR spectroscopy

Effect of Cisplatin and Its Cationic Analogues in the Phase Behavior and Permeability of Model Lipid Bilayers

Increasing evidence suggests a critical role of lipids in both the mechanisms of toxicity and resistance of cells to platinum(II) complexes. In particular, cisplatin and other analogues were reported to interact with lipids and transiently promote lipid phase changes both in the bulk membranes and in specific membrane domains. However, these processes are complex and not fully understood. In this work, cisplatin and its cationic species formed at pH 7.4 in low chloride concentrations were tested for their ability to induce phase changes in model membranes with different lipid compositions. Fluorescent probes that partition to different lipid phases were used to report on the fluidity of the membrane, and a leakage assay was performed to evaluate the effect of cisplatin in the permeability of these vesicles. The results showed that platinum(II) complex effects on membrane fluidity depend on membrane lipid composition and properties, promoting a stronger decrease in the fluidity of membranes containing gel phase. Moreover, at high concentration, these complexes were prone to alter the permeability of lipid membranes without inducing their collapse or aggregation.

Interactions of Cationic Diruthenium Trithiolato Complexes with Phospholipid Membranes Studied by NMR Spectroscopy

To apprehend the possible mechanisms involved in the cellular uptake and the membrane interactions of cytotoxic dinuclear p-cymene trithiolato ruthenium(II) complexes, the interactions of the complexes [(η⁶-p-MeC₆H₄Prⁱ)₂Ru₂(R¹)₂(R²)]⁺ (R¹ = R² = SC₆H₄-m-Prⁱ:1; R¹ = SC₆H₄-p-OMe, R² = SC₆H₄-p-OH:2; R¹ = SCH₂C₆H₄-p-OMe, R² = SC₆H₄-p-OH:3) with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) micelles were studied using nuclear magnetic resonance (NMR) spectroscopy. ¹H NMR, nuclear Overhauser effect (NOE), diffusion ordered spectroscopy (DOSY), and T₁ and T₂ relaxation data provided information on interactions between the complexes and the model membranes and on the submolecular localization of the complexes at the membrane interface. The results suggest that (a) the interaction takes place without new covalent adduct formation, (b) the cationic diruthenium complexes interact with DOPC head groups most likely involving electrostatic interactions while remaining structurally unchanged, (c) the changes indicating interactions are more pronounced for the most lipophilic complex 1, and (d) the diruthenium complexes remain at the exterior vesicle surface and are unlikely inserted between the phospholipid chains. The complexes also interact with micellar/free DHPC and seem to induce micellization or aggregation in solutions below critical micelle concentration (CMC). Our study suggests high affinity of the Ru complexes for the membrane surface that likely plays a key role in cellular uptake and possibly also in redistribution in mitochondria.

Cisplatin-Membrane Interactions and Their Influence on Platinum Complexes Activity and Toxicity

Cisplatin and other platinum(II) analogs are widely used in clinical practice as anti-cancer drugs for a wide range of tumors. The primary mechanism by which they exert their action is through the formation of adducts with genomic DNA. However, multiple cellular targets by platinum(II) complexes have been described. In particular, the early events occurring at the plasma membrane (PM), i.e., platinum-membrane interactions seem to be involved in the uptake, cytotoxicity and cell-resistance to cisplatin. In fact, PM influences signaling events, and cisplatin-induced changes on membrane organization and fluidity were shown to activate apoptotic pathways. This review critically discusses the sequence of events caused by lipid membrane-platinum interactions, with emphasis on the mechanisms that lead to changes in the biophysical properties of the membranes (e.g., fluidity and permeability), and how these correlate with sensitivity and resistance phenotypes of cells to platinum(II) complexes.

Lipid imaging for visualizing cilastatin amelioration of cisplatin-induced nephrotoxicity

Nephrotoxicity is a major limitation to cisplatin antitumor therapies. Cilastatin, an inhibitor of renal dehydropeptidase-I, was recently proposed as a promising nephroprotector against cisplatin toxicity, preventing apoptotic cell death. In this work, cilastatin nephroprotection was further investigated in a rat model, with a focus on its effect on 76 renal lipids altered by cisplatin, including 13 new cisplatin-altered mitochondrial cardiolipin species. Lipid imaging was performed with MALDI mass spectrometry imaging (MALDI-MSI) in kidney sections from treated rats. Cilastatin was proved to significantly diminish the lipid distribution alterations caused by cisplatin, lipid levels being almost completely recovered to those of control samples. The extent of recovery of cisplatin-altered lipids by cilastatin turned out to be relevant for discriminating direct or secondary lipid alterations driven by cisplatin. Lipid peroxidation induced by cisplatin was also shown to be reduced when cilastatin was administered. Importantly, significant groups separation was achieved during multivariate analysis of cortex and outer-medullary lipids, indicating that damaged kidney can be discerned from the nephroprotected and healthy groups and classified according to lipid distribution. Therefore, we propose MALDI-MSI as a powerful potential tool offering multimolecule detection possibilities to visualize and evaluate nephrotoxicity and nephroprotection based on lipid analysis.

Cisplatin Encapsulation Generates Morphologically Different Multicompartments in the Internal Nanostructures of Nonlamellar Liquid-Crystalline Self-Assemblies

Cisplatin ( cis-diamminedichloroplatinum(II)) is among the most potent cytotoxic agents used in cancer chemotherapy. The encapsulation of cisplatin in lipid-based drug carriers has been challenging owing to its low solubility in both aqueous and lipid phases. Here, we investigated cisplatin encapsulation in nonlamellar liquid-crystalline (LC) nanodispersions formed from a ternary mixture of phytantriol (PHYT), vitamin E (Vit E), and an anionic phospholipid [either phosphatidylglycerol (DSPG) or phosphatidylserine (DPPS)]. We show an increase in cisplatin encapsulation efficiency (EE) in nanodispersions containing 1.5-4 wt % phospholipid. The EE was highest in DPPS-containing nanodispersions (53-98%) compared to DSPG-containing counterparts (25-40%) under similar experimental conditions. Through structural and morphological characterizations involving synchrotron small-angle X-ray scattering and cryogenic transmission electron microscopy, we further show that varying the phospholipid content of cisplatin-free nanodispersions triggers an internal phase transition from a neat hexagonal (H₂) phase to a biphasic phase (internal H₂ phase coexisting with the lamellar (L_α) phase). However, cisplatin encapsulation in both DPPS- and DSPG-containing nanodispersions generates the coexistence of morphologically different multicompartments in the internal nanostructures comprising vesicles as a core, enveloped by an inverted-type surface bicontinuous cubic Im3 m (primitive, Q_II^P) phase or H₂ phase. We discuss the biophysical basis of these drug-induced morphological alterations and provide insights into the potential development of inverted-type LC nanodispersions for cisplatin delivery.

Mesenchymal stem cells maintain their defining stem cell characteristics after treatment with cisplatin

Mesenchymal stem cells (MSCs) aid the regeneration of tissues damaged by treatment with cisplatin. However, the effects of this cytotoxic drug on the stem cells have been largely unknown. Here we demonstrate that human bone marrow-derived MSCs are relatively resistant to cisplatin treatment and show resistance levels comparable to these of differentiated fibroblasts. Cisplatin did not affect cellular morphology, adhesion or induction of apoptosis in MSCs. The potential for differentiation was preserved after exposure to cisplatin, and established MSC surface markers were observed to be stably expressed irrespective of cisplatin treatment. Cytoskeletal rearrangements and high expression levels of individual heat shock proteins were detected in MSCs and may be partly responsible for the observed cisplatin resistance. The cisplatin-resistant phenotype of human MSCs supports the concept of further investigating these stem cells as a potential treatment option for cisplatin-induced tissue damage.

MG53-mediated cell membrane repair protects against acute kidney injury

Injury to the renal proximal tubular epithelium (PTE) represents the underlying consequence of acute kidney injury (AKI) after exposure to various stressors, including nephrotoxins and ischemia/reperfusion (I/R). Although the kidney has the ability to repair itself after mild injury, insufficient repair of PTE cells may trigger inflammatory and fibrotic responses, leading to chronic renal failure. We report that MG53, a member of the TRIM family of proteins, participates in repair of injured PTE cells and protects against the development of AKI. We show that MG53 translocates to acute injury sites on PTE cells and forms a repair patch. Ablation of MG53 leads to defective membrane repair. MG53-deficient mice develop pronounced tubulointerstitial injury and increased susceptibility to I/R-induced AKI compared to wild-type mice. Recombinant human MG53 (rhMG53) protein can target injury sites on PTE cells to facilitate repair after I/R injury or nephrotoxin exposure. Moreover, in animal studies, intravenous delivery of rhMG53 ameliorates cisplatin-induced AKI without affecting the tumor suppressor efficacy of cisplatin. These findings identify MG53 as a vital component of reno-protection, and targeting MG53-mediated repair of PTE cells represents a potential approach to prevention and treatment of AKI.

Membrane Transition Temperature Determines Cisplatin Response

Cisplatin is a classical chemotherapeutic agent used in treating several forms of cancer including head and neck. However, cells develop resistance to the drug in some patients through a range of mechanisms, some of which are poorly understood. Using isolated plasma membrane vesicles as a model system, we present evidence suggesting that cisplatin induced resistance may be due to certain changes in the bio-physical properties of plasma membranes. Giant plasma membrane vesicles (GPMVs) isolated from cortical cytoskeleton exhibit a miscibility transition between a single liquid phase at high temperature and two distinct coexisting liquid phases at low temperature. The temperature at which this transition occurs is hypothesized to reflect the magnitude of membrane heterogeneity at physiological temperature. We find that addition of cisplatin to vesicles isolated from cisplatin-sensitive cells result in a lowering of this miscibility transition temperature, whereas in cisplatin-resistant cells such treatment does not affect the transition temperature. To explore if this is a cause or consequence of cisplatin resistance, we tested if addition of cisplatin in combination with agents that modulate GPMV transition temperatures can affect cisplatin sensitivity. We found that cells become more sensitive to cisplatin when isopropanol, an agent that lowers GPMV transition temperature, was combined with cisplatin. Conversely, cells became resistant to cisplatin when added in combination with menthol that raises GPMV transition temperatures. These data suggest that changes in plasma membrane heterogeneity augments or suppresses signaling events initiated in the plasma membranes that can determine response to cisplatin. We postulate that desired perturbations of membrane heterogeneity could provide an effective therapeutic strategy to overcome cisplatin resistance for certain patients.

A solid-state 17O NMR study of platinum-carboxylate complexes: carboplatin and oxaliplatin

We report synthesis and solid-state NMR characterization of two 17O-labeled platinum anticancer drugs: cis-diammine(1,1-cyclobutane-[17O4]dicarboxylato)platinum(II) (carboplatin) and ([17O4]oxalato)[(1R, 2R)-(−)-1,2-cyclohexanediamine)]platinum(II) (oxaliplatin). Both 17O chemical shift (CS) and quadrupolar coupling (QC) tensors were measured for the carboxylate groups in these two compounds. With the aid of plane wave DFT computations, the 17O CS and QC tensor orientations were determined in the molecular frame of reference. Significant changes in the 17O CS and QC tensors were observed for the carboxylate oxygen atom upon its coordination to Pt(II). In particular, the 17O isotropic chemical shifts for the oxygen atoms directly bonded to Pt(II) are found to be smaller (more shielded) by 200 ppm than those for the non-Pt-coordinated oxygen atoms within the same carboxylate group. Examination of the 17O CS tensor components reveals that such a large 17O coordination shift is primarily due to the shielding increase along the direction that is within the O=C–O–Pt plane and perpendicular to the O–Pt bond. This result is interpreted as due to the σ donation from the oxygen nonbonding orbital (electron lone pair) to the Pt(II) empty dyz orbital, which results in large energy gaps between σ(Pt–O) and unoccupied molecular orbitals, thus reducing the paramagnetic shielding contribution along the direction perpendicular to the O–Pt bond. We found that the 17O QC tensor of the carboxylate oxygen is also sensitive to Pt(II) coordination, and that 17O CS and QC tensors provide complementary information about the O–Pt bonding.

New mechanisms for old drugs: Insights into DNA-unrelated effects of platinum compounds and drug resistance determinants

Platinum drugs have been widely used for the treatment of several solid tumors. Although DNA has been recognized as the primary cellular target for these agents, there are unresolved issues concerning their effects and the molecular mechanisms underlying the antitumor efficacy. These cytotoxic agents interact with sub-cellular compartments other than the nucleus. Here, we review how such emerging phenomena contribute to the pharmacologic activity as well as to drug resistance phenotypes. DNA-unrelated effects of platinum drugs involve alterations at the plasma membrane and in endo-lysosomal compartments. A direct interaction with the mitochondria also appears to be implicated in drug-induced cell death. Moreover, the pioneering work of a few groups has shown that platinum drugs can act on the tumor microenvironment as well, and potentiate antitumor activity of the immune system. These poorly understood aspects of platinum drug activity sites may be harnessed to enhance their antitumor efficacy. A complete understanding of DNA-unrelated effects of platinum compounds might reveal new aspects of drug resistance allowing the implementation of the antitumor therapeutic efficacy of platinum compound-based regimens and minimization of their toxic side effects.

Enhanced photoinduced electron transfer at the surface of charged lipid bilayers

Photocatalytic systems often suffer from poor quantum yields due to fast charge recombination: The energy-wasting annihilation of the photochemically created charge-separated state. In this report, we show that the efficiency of photoinduced electron transfer from a sacrificial electron donor to positively charged methyl viologen, or to negatively charged 5,5'-dithiobis(2-nitrobenzoate), increases dramatically upon addition of charged phospholipid vesicles if the charge of the lipids is of the same sign as that of the electron acceptor. Centrifugation and UV/Vis titration experiments showed that the charged photosensitizers adsorb at the liposome surface, that is, where the photocatalytic reaction takes place. The increased photoelectron transfer efficiency in the presence of charged liposomes has been ascribed to preferential electrostatic interactions between the photosensitizer and the membrane, which prevents the formation of photosensitizer-electron-acceptor complexes that are inactive towards photoreduction. Furthermore, it is shown that the addition of liposomes results in a decrease in photoproduct inhibition, which is caused by repulsion of the reduced electron acceptor by the photocatalytic site. Thus, liposomes can be used as a support to perform efficient photocatalysis; the charged photoproducts are pushed away from the liposomes and represent "soluble electrons" that can be physically separated from the place where they were generated.

Binding of a ruthenium complex to a thioether ligand embedded in a negatively charged lipid bilayer: a two-step mechanism

The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H2O)](2+) (terpy = 2,2';6',2"-terpyridine, dcbpy = 6,6'-dichloro-2,2'-bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV-visible spectroscopy, Langmuir-Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two-step model for the coordination of the metal complex to the membrane-embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface-bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water-bilayer interface.

Cisplatin : an old drug with a newfound efficacy -- from mechanisms of action to cytotoxicity

INTRODUCTION

Cisplatin is a highly effective antineoplastic drug with an extremely current mechanism of action. Cisplatin-induced side effects are dose-dependent and limit the administration of increased dosages, thus compromising its therapeutic efficacy.

AREAS COVERED

This review aims to describe the emerging knowledge about the biochemical mechanisms that mediate cisplatin cytotoxicity and side effects. A specific section is devoted to discuss the pathogenesis of cisplatin-related toxicities and the potential measures to counteract them.

EXPERT OPINION

Although cisplatin has been used for a long time, only recently its exact mechanism of action has been better defined. The cytotoxic activity of cisplatin is largely dependent on the glycolytic metabolism of tumor cells: cisplatin redirects cancer cells to oxidative phosphorylation from the 'Warburg effect', which is considered one of the most important mechanisms of tumor cell survival. The interference of cisplatin with glucose metabolism is also a cause of its relevant toxicities. The emerging knowledge on the complex mechanisms, which mediate cisplatin cytotoxicity and side effect, may lead to a more appropriate and safe use of this drug. Further studies are warranted to define and implement its effectiveness in combination with targeted drugs able to interfere with cellular energy metabolism, such as mTOR inhibitors.

Multinuclear solid-state NMR of square-planar platinum complexes — Cisplatin and related systems

Multinuclear solid-state nuclear magnetic resonance (SSNMR) experiments have been performed on cisplatin and four related square-planar compounds. The wideband uniform rate smooth truncation – Carr–Purcell–Meiboom–Gill (WURST–CPMG) pulse sequence was utilized in NMR experiments to acquire 195Pt, 14N, and 35Cl ultra-wideline NMR spectra of high quality. Standard Hahn-echo and magic-angle spinning 195Pt NMR experiments are also performed to refine extracted chemical shielding (CS) tensor parameters. Platinum magnetic shielding (MS) tensor orientations are calculated using both plane-wave density functional theory (DFT) and standard DFT methods. The tensor orientations are shown to be highly constrained by molecular symmetry elements, but also influenced to some degree by intermolecular interactions. 14N WURST–CPMG experiments were performed on three compounds and electric field gradient (EFG) parameters (the quadrupolar coupling constant, CQ, and the asymmetry parameter, ηQ) are reported. First principles calculations of the 14N EFG tensor parameters and orientations and affirm their dependence on the local hydrogen bonding environment. 35Cl WURST–CPMG experiments on cisplatin and transplatin are reported, using two different static magnetic fields to extract EFG and CS tensor parameters, and 35Cl EFG tensor magnitudes and orientations are predicted using first principles calculations. Transverse (T2) relaxation data for all nuclei are used to investigate heteronuclear dipolar relaxation mechanisms, as well as the nature of the local hydrogen bonding environments.