The modulation of thermal properties of vinblastine by cholesterol in membrane bilayers

A Review on Mechanistic Insight of Plant Derived Anticancer Bioactive Phytocompounds and Their Structure Activity Relationship

Cancer is a disorder that rigorously affects the human population worldwide. There is a steady demand for new remedies to both treat and prevent this life-threatening sickness due to toxicities, drug resistance and therapeutic failures in current conventional therapies. Researchers around the world are drawing their attention towards compounds of natural origin. For decades, human beings have been using the flora of the world as a source of cancer chemotherapeutic agents. Currently, clinically approved anticancer compounds are vincristine, vinblastine, taxanes, and podophyllotoxin, all of which come from natural sources. With the triumph of these compounds that have been developed into staple drug products for most cancer therapies, new technologies are now appearing to search for novel biomolecules with anticancer activities. Ellipticine, camptothecin, combretastatin, curcumin, homoharringtonine and others are plant derived bioactive phytocompounds with potential anticancer properties. Researchers have improved the field further through the use of advanced analytical chemistry and computational tools of analysis. The investigation of new strategies for administration such as nanotechnology may enable the development of the phytocompounds as drug products. These technologies have enhanced the anticancer potential of plant-derived drugs with the aim of site-directed drug delivery, enhanced bioavailability, and reduced toxicity. This review discusses mechanistic insights into anticancer compounds of natural origins and their structural activity relationships that make them targets for anticancer treatments.

Development of Natural Bioactive Alkaloids: Anticancer perspective

Cancer is a frightful disease that still poses a 'nightmare' worldwide, causing millions of casualties annually due to one of the human race's most significant healthcare challenges that requires a pragmatic treatment strategy. However, plants and plant-derived products revolutionize the field as they are quick, cleaner, eco-friendly, low-cost, effective, and less toxic than conventional treatment methods. Plants are repositories for new chemical entities and have a promising cancer research path, supplying 60% of the anticancer agents currently used. Alkaloids are important chemical compounds that serve as a rich reservoir for drug discovery and development. However, some alkaloids derived from natural herbs display anti-proliferation and antimetastatic activity on different forms of cancer, both in vitro and in vivo. Alkaloids have also been widely formulated as anticancer medications, such as camptothecin and vinblastine. Still, more research and clinical trials are required before final recommendations can be made on specific alkaloids. This review focuses on the naturally-derived bioactive alkaloids with prospective anticancer properties based on the information in the literature.

Thermodynamics and kinetics of joint action of antiviral agent tilorone and DMSO on model lipid membranes

Individual and joint action of two water-soluble drugs, DMSO and tilorone, on model l-α-dipalmitoylphosphatidylcholine (DPPC) membranes were studied in equilibrium and kinetic regimes by differential scanning calorimetry (DSC). For equilibrium experiments, the drugs were introduced during preparation of the model membrane. In kinetic studies, one of the drugs was added to the DPPC membrane already containing the other drug, and the effects of drug-membrane interactions were monitored in real-time regime. It was found that tilorone and DMSO had opposite effects on the membrane melting temperature, which were non-additive under joint introduction of these drugs. Analysis of kinetics of DSC profiles under drugs introduction allowed us to discriminate two processes in drug-membrane interactions with different characteristic times, i.e., drug sorption onto the membrane (minutes) and drug diffusion through stacks of lipid bilayers (hours). It was established that 0.1 mol% DMSO effectively enhanced membrane penetration for tilorone with the rate of tilorone diffusion being dependent upon the scheme of drugs administration. A model was proposed describing how sorption of a dopant onto lipid membrane could affect the membrane permeability for other dopants. Conditions were determined for enhancement of membrane permeability, as it was observed for DPPC/DMSO/tilorone system.

Optimization and Characterization of Thymoquinone-Loaded Liposomes with Enhanced Topical Anti-inflammatory Activity

Thymoquinone, the major constituent of Nigella sativa oil has been found to have a promising topical anti-inflammatory activity; however, exaggerated heat and photo-sensitivity and lipophilicity prevent the best use of this promising product. The present work aimed to formulate an ideal thymoquinone liposomal system for topical delivery. Different liposomal systems were developed using thin film hydration method by applying different cholesterol molar concentrations, different total lipid molar concentrations, and different drug-to-lipid ratios. Morphological characterization of the prepared formulae was performed using polarized light, scanning electron microscope, and transmission electron microscope. The optimized formula (F12) was selected on the basis of enhanced permeation through the skin and was incorporated into chitosan gel for topical application. The gel formulation was clear with suitable skin permeation and exhibited acceptable rheological properties. Using carrageenan-induced paw edema in rats, the developed chitosan gel (F12) showed significant superior in vivo anti-inflammatory activity over the chitosan gel of the TQ (p < 0.05) and comparable effect to the marketed indomethacin gel. As a conclusion, results revealed the potential of formulating thymoquinone as liposomal formulation in enhancing the anti-inflammatory effect compared to the TQ solution.

Vinca alkaloids and analogues as anti-cancer agents: Looking back, peering ahead

Cancer still represents a "nightmare" worldwide, causing annually millions of victims. Several antiproliferative molecules are currently used as drugs market and offer a pharmaceutical opportunity for attenuating and treating tumor manifestations. In this context, natural sources have a relevant role, since they provide the 60% of currently-used anticancer agents. Among the numerous natural products, acting via different mechanisms of action, microtubule-targeting agents (MTAs) have a high therapeutic potential, since they disrupt the abnormal cancer cell growth, interfering with the continuous mitotic division. Vinca alkaloids (VAs) are the earliest developed MTAs and approved for clinical use (Vincristine, Vinblastine, Vinorelbine, Vindesine, and Vinflunine) as agents in the treatment of hematological and lymphatic neoplasms. Here, we review the state-of-art of VAs, discussing their mechanism of action and pharmacokinetic properties and highlighting their therapeutic relevance and toxicological profile. Additionally, we briefly disclosed the technological approaches faced so far to ameliorate the pharmacological properties, as well as to avoid the drug resistance. Lastly, we introduced the recent advances in the discovery of new derivatives.

Drug delivery systems and combination therapy by using vinca alkaloids

Developing new methods for chemotherapy drug delivery has become a topic of great concern. Vinca alkaloids are among the most widely used chemotherapy reagents for tumor therapy; however, their side effects are particularly problematic for many medical doctors. To reduce the toxicity and enhance the therapeutic efficiency of vinca alkaloids, many researchers have developed strategies such as using liposome-entrapped drugs, chemical- or peptide-modified drugs, polymeric packaging drugs, and chemotherapy drug combinations. This review mainly focuses on the development of a vinca alkaloid drug delivery system and the combination therapy. Five vinca alkaloids (eg, vincristine, vinblastine, vinorelbine, vindesine, and vinflunine) are reviewed.

Application of Nanotechnology in Drug Delivery and Targeting

Lipidic nanoparticulate self-assembled structures are effective carriers for drug delivery. This chapter describes the most famous nanotechnological drug delivery systems that are already used in clinical practice and clinical evaluation or in academic research. Liposomes are nanocolloidal lyotropic liquid crystals that are able to deliver bioactive molecules. Their membrane biophysics and thermodynamic properties reflect to the creation of metastable phases that affect their functionality and physicochemical behavior. Thermo- and pH-responsive liposomes are innovative nanotechnological platforms for drug delivery and targeting. Polymeric micelles and polymersomes are nanostructures that are promising drug carriers, while dendrimeric structures are considered as real nanoparticulate systems that are used in drug delivery and as nonviral vectors as well as in prevention of serious infections leading to diseases. Vaccines based on nanoparticles such as liposomes are an emerging technology and liposomes seem to meet the requirement criteria of adjuvanicity.

Tetra- and Penta-Cyclic Triterpenes Interaction with Lipid Bilayer Membrane: A Structural Comparative Study

The effect of tetracyclic (cortisol, prednisolone, and 9-fluorocortisol acetate) and pentacyclic (uvaol and erythrodiol) triterpenes (TTPs) on the fluidity of dipalmitoyl phosphatidyl choline (DPPC) liposome membrane was investigated by differential scanning calorimetry, Raman spectroscopy, and fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). Liposomes were prepared in the absence and presence of TTPs at molar ratios DPPC:TTP 100:1, 100:2.5, and 100:10. All the studied TTPs abolished the pre-transition and modified the intensity of the Raman peak at 715 cm(-1) proving the interaction of TTP molecules with the choline head group of phospholipids. An increase in the Raman height intensity ratios of the peaks I 2935/2880, I 2844/2880, and I 1090/1130, giving information about the ratio disorder/order of the alkyl chains, and a decrease of the main transition temperature demonstrated the interaction of TTPs with the alkyl chains. The tetracyclic TTPs produced broadening of the phase transition profile. Besides, a scarcely splitting of the main transition peak was obtained with prednisolone and 9-fluorocortisol acetate. The results of fluorescence depolarization of DPH showed that the studied molecules fluidized the liposomal membrane at 25, 41, and 50 °C. Pentacyclic TTPs, being more hydrophobic than tetracyclic ones, demonstrated higher fluidizing effect than tetracyclic TTPs in the liquid crystalline phase suggesting a deeper incorporation in the lipid bilayer. The presence of a free polar head group at the ring D seems to control the TTP incorporation in the bilayer and consequently its effect on the membrane fluidity.

Morphological and physicochemical characterization of liposomes loading cucurbitacin E, an anti-proliferative natural tetracyclic triterpene

Cucurbitacin E (Cuc E), an oxygenated triterpene molecule, has demonstrated anti-proliferative effect on various cancer cells. Here, we examined the effect of Cuc E on the membrane morphology and properties using differential scanning calorimetry, transmission electron microscopy and atomic force microscopy techniques. Dipalmitoylphosphatidylcholine vesicles were prepared by the thin film hydration method in the absence and presence of Cuc E at molar ratios 100:12 and 100:20. The loading efficiency of Cuc E was found to be higher than 98% upon HPLC analysis. The thermodynamic parameters suggest that Cuc E does not penetrate into the bilayers and interacts with the polar/apolar interface of the lipid membranes. Blank and Cuc E loaded liposomes prepared from a mixture of DPPC/DPPE/DPPG/Cho were imaged by TEM and AFM. Images obtained by TEM revealed unilamellar liposomes for blank and Cuc E loaded liposomes. AFM images showed that the size and the height of Cuc E loaded liposomes were respectively smaller and higher than blank ones. Results suggest that Cuc E produces modifications in the lipid membrane structures.

Development of a CP 31P NMR broadline simulation methodology for studying the interactions of antihypertensive AT1 antagonist losartan with phospholipid bilayers

A cross-polarization (CP) (31)P NMR broadline simulation methodology was developed for studying the effects of drugs in phospholipids bilayers. Based on seven-parameter fittings, this methodology provided information concerning the conformational changes and dynamics effects of losartan in the polar region of the dipalmitoylphosphatidylcholine bilayers. The test molecule for this study was losartan, an antihypertensive drug known to exert its effect on AT(1) transmembrane receptors. The results were complemented and compared with those of differential scanning calorimetry, solid-state (13)C NMR spectroscopy, Raman spectroscopy, and electron spin resonance. More specifically, these physical chemical methodologies indicated that the amphipathic losartan molecule interacts with the hydrophilic-head zone of the lipid bilayers. The CP (31)P NMR broadline simulations showed that the lipid molecules in the bilayers containing losartan displayed greater collective tilt compared to the tilt displayed by the load-free bilayers, indicating improved packing. The Raman results displayed a decrease in the trans/gauche ratio and increased intermolecular interactions of the acyl chains in the liquid crystalline phase. Additional evidence, suggesting that losartan possibly anchors in the realm of the headgroup, was derived from upfield shift of the average chemical shift sigma(iso) of the (31)P signal in the presence of losartan and from shift of the observed peak at 715 cm(-1) attributed to C-N stretching in the Raman spectra.

Interaction of articaine hydrochloride with prokaryotic membrane lipids

OBJECTIVE

Local anesthetics are the most commonly used drugs in dentistry, with a wide range of effects, including antimicrobial activity. High antimicrobial effects have recently been reported on oral microbes from articaine hydrochloride, revealed by the minimum inhibitory concentration and minimal bactericidal concentration. Additionally, articaine has recently been used as an alkaline component in endodontic materials with a proposed antibacterial activity. However, the detailed mechanisms of action have not been discussed.

MATERIAL AND METHODS

We determined the Langmuir surface pressure/molecular area isotherms of prokaryotic lipid monolayers, as well as the phospholipid phase transitions, by employing differential scanning calorimetry on unilamellar prokaryotic liposomes (bilayers).

RESULTS

Articaine hydrochloride was found to interact with the prokaryotic membrane lipids in both monolayers and bilayers. An increase of the phospholipid molecular area of acidic glycerophospholipids as well as a decrease in phase transition temperature and enthalpy were found with increasing articaine hydrochloride concentration. The thermodynamic changes by adding articaine hydrochloride to prokaryotic membrane lipids are potentially related to the effects observed from antimicrobial peptides resulting from membrane insertion, aggregate composition, pore formation, and lysis.

CONCLUSION

Interaction of articaine hydrochloride with prokaryotic membrane lipids is indicated. Hence, further research is necessary to gain insight into where these compounds exert their effects at the molecular level.

Differential Scanning Calorimetry (DSC): a tool to study the thermal behavior of lipid bilayers and liposomal stability

Thermodynamical techniques are applied for determining the thermal stress of medicinal compounds of the excipients as well as their interactions during the formulation process. The physicochemical properties and the stability of the medicinal products could be measured as a function of temperature or time using thermal analysis. Differential Scanning Calorimetry (DSC) is a suitable thermal analysis technique for determining the purity, the polymorphic forms and the melting point of a sample in the Pharmaceutical Industry. It is also considered as a tool to study the thermal behavior of lipid bilayers and of lipidic drug delivery systems, like liposomes by measuring thermodynamic parameters (i.e. DeltaH and Tm), which affect the stability of the liposomal suspension under given storage conditions.

Supramolecular organization of S12363-liposomes prepared with two different remote loading processes

The S12363 anticancer drug was encapsulated into liposomes in an attempt to increase its therapeutic index. Loading of S12363 was achieved using two different processes based on the formation of either a pH gradient or an ammonium gradient between the acidic inner liposomal compartment and the basic outer phase. High encapsulation yields (>90%) were obtained using both processes for sphingomyelin/cholesterol/cholesterol-PEG vesicles. Spectrofluorimetry measurements have shown that liposomes were characterized by an internal pH around 4 for both loading processes. This internal pH was stable over a period of at least 20 days. Differential scanning calorimetry coupled with time-resolved synchrotron X-ray diffraction was used to study the drug/carrier supramolecular organization. In ammonium sulfate, S12363 was inserted into the bilayer in the vicinity of the polar headgroup. In citrate buffer, S12363 was mainly adsorbed at the water-lipid interface. The drug partitioning into the membrane was inhomogeneous and led to the formation of drug-rich and drug-poor domains. This effect was enhanced in the presence of cholesterol, especially in ammonium sulfate. To conclude, for both processes, the encapsulated drug was found inside the liposome aqueous core but strongly interacting with the membrane.

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.

The role of the anticancer drug vinorelbine in lipid bilayers using differential scanning calorimetry and molecular modeling

Differential scanning calorimetry (DSC) has been employed to investigate the thermal changes caused by the anticancer alkaloid drug vinorelbine in dipalmytoylphosphatidylcholine (DPPC) bilayers. The total enthalpy change was increased by the presence of the drug molecule, indicating a partial interdigitation of the lipid alkyl chains. The presence of cholesterol in DPPC bilayers including vinorelbine induced an obstruction of the interdigitation, since cholesterol interrupts the upraise of enthalpy change. Vinorelbine's interdigitation ability and stabilizing properties with the active site of the receptor have been compared with those of similar in structure amphipathic and bulky alkaloid vinblastine. The obtained results may in part explain their similar mechanism of action but different bioactivity.

Interaction of phloretin and 6-ketocholestanol with DPPC-liposomes as phospholipid model membranes

Phloretin and 6-ketocholestanol are penetration enhancers for percutaneous delivery of certain topically applied drugs. In the present study some physicochemical experiments have been performed to elucidate the mechanism of action of phloretin and 6-ketocholestanol. The penetration enhancing effect of phloretin and 6-ketocholestanol is believed to be due to their increase of the fluidity of the intercellular lipid bilayers of the stratum corneum. Phospholipid vesicles were chosen as a simple model to represent these bilayers. The effect of phloretin and 6-ketocholestanol on phase transition temperature and enthalpy was studied using differential scanning calorimetry. Beside of that the size of liposomes was monitored when the amount of penetration enhancer in the liposome preparation was changed. Addition of increasing amounts of phloretin and 6-ketocholestanol to the bilayer resulted in lowering of phase transition temperatures and increasing the enthalpy. Additionally the size of the liposomes was increased when penetration enhancer was added. The results suggest that phloretin as well as 6-ketocholestanol would interact with stratum corneum lipids in a similar manner, both reduce the diffusional resistance of the stratum corneum to drugs with balanced hydrophilic-lipophilic characteristics.

A comparative study of the effects of cholesterol and sclareol, a bioactive labdane type diterpene, on phospholipid bilayers

Sclareol (labd-14-ene-8,13-diol) is a highly water-insoluble molecule that belongs to the labdane type diterpenes and is characterized as a biologically active molecule, due to its cytotoxic and cytostatic effects against human leukemic cell lines. A superimposition study between sclareol and cholesterol, based on their corresponding hydrophobic and polar molecular segments calculated from their lipophilic profiles, revealed their spatial similarities. This structural similarity between the two molecules prompted us to compare their effects on the structure and stability of phospholipid dipalmitoylphosphatidylcholine (DPPC) membranes. Differential scanning calorimetry (DSC) was applied to compare the thermal changes caused by either cholesterol or sclareol when are incorporated in DPPC bilayers. The results showed that sclareol is incorporated into phospholipid model membranes and mimics the thermal effects of cholesterol especially at concentrations up to X(sclareol)=9.1 mol%. These effects can be summarized as the abolition of pre-transition, lowering of the main phase transition and reduction of the enthalpy change (DeltaH) of the gel to liquid-crystalline phase transition of DPPC bilayers. At concentrations X> or =16.7 mol%, sclareol and cholesterol caused different heterogeneity in lipid bilayers or a reversible transition from a vesicular suspension to an extended peak bilayer network. This different fluidization, exerted by the two molecules at high concentration, may be related to their different stability and the z-average mean diameter of the liposomes they form. Small unilamellar vesicles, prepared by the thin film hydration method showed that DPPC bilayers containing a high concentration of sclareol in equimolar ratio sclareol:cholesterol were unstable, in contrast to the ones containing only cholesterol.

Synthesis, liposomal formulation and thermal effects on phospholipid bilayers of leuprolide

A novel liposomal formulation was developed for the encapsulation of the oligopeptide leuprolide (GlpHisTrpSerTyr-D-LeuLeuArgProNHEt), a potent analogue of gonadotropin releasing hormone used in the treatment of advanced prostate cancer, endometriosis and precocious puberty. Leuprolide was synthesized using solid phase methodology on a {3-[(ethyl-Fmoc-amino)-methyl]-1-indol-1-yl}-acetyl AM resin and Fmoc/tBu chemistry. The new liposomal formulation, called 'liposomes in liposomes' is composed of egg phosphatidylcholine:dipalmitoylphosphatidylglycerol in a molar ratio of 98.91:1.09 (internal liposomes) and egg phosphatidylcholine:dipalmitoylphosphatidylglycerol:cholesterol in a molar ratio of 68.71:0.76:30.53 (external liposomes). It offers high encapsulation efficiency (73.8% for leuprolide); it can provide new delivery characteristics and it may have possible advantages in future applications regarding the encapsulation and delivery of bioactive peptides to target tissues. Furthermore, the physicochemical characteristics (size distribution and zeta-potential) of the liposomal formulations and the thermal effects on leuprolide in model lipidic bilayers composed of dipalmitoylphosphatidylcholine were studied using differential scanning calorimetry. Finally, the dynamic effects of leuprolide in an egg phosphatidylcholine/cholesterol system were examined using solid state 13C MAS NMR spectroscopy.