Surface-modified liposomes in gamma- and MR-imaging

An Underestimated Factor: The Extent of Cross-Reactions Modifying APIs in Surface-Modified Liposomal Preparations Caused by Comprised Activated Lipids

Despite the nowadays available plentitude of strategies to selectively introduce functional surface modification of liposomes, in preclinical research this process is still primarily performed after liposomal preparation utilizing comprised activated phospholipids with functionalized head groups. However, because these activated lipids are present during the liposomal preparation process, they can cross-react with incorporated drugs, especially the particularly often utilized active esters and maleimide groups. Macromolecular drugs, being composed of amino acids, are particularly prone to such cross-reactions due to their often multiple reactive functionalities such as amino and disulfide groups. To demonstrate this impact on the formulation in liposomal surface modification, we assessed the extent of cross-reaction during the liposomal preparation of two activated phospholipids with typically used head group functionalized phospholipids, with the two peptide drugs vancomycin and insulin comprising disulfide and amino functionalities. Both drugs revealed a considerable fraction of covalent modification (estimated 2 to 12%) generated during the liposome preparation process with comprised activated lipids. Modification of the active pharmaceutical ingredients (APIs) was determined by high-resolution mass spectrometric analysis. These findings clearly demonstrate the non-negligibility of potential cross reactions using the post preparation liposomal surface modification strategy in preclinical research.

Stimuli-Responsive Nano-Architecture Drug-Delivery Systems to Solid Tumor Micromilieu: Past, Present, and Future Perspectives

The microenvironment characteristics of solid tumors, renowned as barriers that harshly impeded many drug-delivery approaches, were precisely studied, investigated, categorized, divided, and subdivided into a complex diverse of barriers. These categories were further studied with a particular perspective, which makes all barriers found in solid-tumor micromilieu turn into different types of stimuli, and were considered triggers that can increase and hasten drug-release targeting efficacy. This review gathers data concerning the nature of solid-tumor micromilieu. Past research focused on the treatment of such tumors, the recent efforts employed for engineering smart nanoarchitectures with the utilization of the specified stimuli categories, the possibility of combining more than one stimuli for much-greater targeting enhancement, examples of the approved nanoarchitectures that already translated clinically as well as the obstacles faced by the use of these nanostructures, and, finally, an overview of the possible future implementations of smart-chemical engineering for the design of more-efficient drug delivery and theranostic systems and for making nanosystems with a much-higher level of specificity and penetrability features.

Bio-inspired nano tools for neuroscience

Research and treatment in the nervous system is challenged by many physiological barriers posing a major hurdle for neurologists. The CNS is protected by a formidable blood brain barrier (BBB) which limits surgical, therapeutic and diagnostic interventions. The hostile environment created by reactive astrocytes in the CNS along with the limited regeneration capacity of the PNS makes functional recovery after tissue damage difficult and inefficient. Nanomaterials have the unique ability to interface with neural tissue in the nano-scale and are capable of influencing the function of a single neuron. The ability of nanoparticles to transcend the BBB through surface modifications has been exploited in various neuro-imaging techniques and for targeted drug delivery. The tunable topography of nanofibers provides accurate spatio-temporal guidance to regenerating axons. This review is an attempt to comprehend the progress in understanding the obstacles posed by the complex physiology of the nervous system and the innovations in design and fabrication of advanced nanomaterials drawing inspiration from natural phenomenon. We also discuss the development of nanomaterials for use in Neuro-diagnostics, Neuro-therapy and the fabrication of advanced nano-devices for use in opto-electronic and ultrasensitive electrophysiological applications. The energy efficient and parallel computing ability of the human brain has inspired the design of advanced nanotechnology based computational systems. However, extensive use of nanomaterials in neuroscience also raises serious toxicity issues as well as ethical concerns regarding nano implants in the brain. In conclusion we summarize these challenges and provide an insight into the huge potential of nanotechnology platforms in neuroscience.

Nanocarriers for the treatment of glioblastoma multiforme: Current state-of-the-art

Glioblastoma multiforme, a grade IV glioma, is the most frequently occurring and invasive primary tumor of the central nervous system, which causes about 4% of cancer-associated-deaths, making it one of the most fatal cancers. With present treatments, using state-of-the-art technologies, the median survival is about 14 months and 2 year survival rate is merely 3-5%. Hence, novel therapeutic approaches are urgently necessary. However, most drug molecules are not able to cross the blood-brain barrier, which is one of the major difficulties in glioblastoma treatment. This review describes the features of blood-brain barrier, and its anatomical changes with different stages of tumor growth. Moreover, various strategies to improve brain drug delivery i.e. tight junction opening, chemical modification of the drug, efflux transporter inhibition, convection-enhanced delivery, craniotomy-based drug delivery and drug delivery nanosystems are discussed. Nanocarriers are one of the highly potential drug transport systems that have gained huge research focus over the last few decades for site specific drug delivery, including drug delivery to the brain. Properly designed nanocolloids are capable to cross the blood-brain barrier and specifically deliver the drug in the brain tumor tissue. They can carry both hydrophilic and hydrophobic drugs, protect them from degradation, release the drug for sustained period, significantly improve the plasma circulation half-life and reduce toxic effects. Among various nanocarriers, liposomes, polymeric nanoparticles and lipid nanocapsules are the most widely studied, and are discussed in this review. For each type of nanocarrier, a general discussion describing their composition, characteristics, types and various uses is followed by their specific application to glioblastoma treatment. Moreover, some of the main challenges regarding toxicity and standardized evaluation techniques are narrated in brief.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery

The use of nanoparticulate pharmaceutical drug delivery systems (NDDSs) to enhance the in vivo effectiveness of drugs is now well established. The development of multifunctional and stimulus-sensitive NDDSs is an active area of current research. Such NDDSs can have long circulation times, target the site of the disease and enhance the intracellular delivery of a drug. This type of NDDS can also respond to local stimuli that are characteristic of the pathological site by, for example, releasing an entrapped drug or shedding a protective coating, thus facilitating the interaction between drug-loaded nanocarriers and target cells or tissues. In addition, imaging contrast moieties can be attached to these carriers to track their real-time biodistribution and accumulation in target cells or tissues. Here, I highlight recent developments with multifunctional and stimuli-sensitive NDDSs and their therapeutic potential for diseases including cancer, cardiovascular diseases and infectious diseases.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery

The use of nanoparticulate pharmaceutical drug delivery systems (NDDSs) to enhance the in vivo effectiveness of drugs is now well established. The development of multifunctional and stimulus-sensitive NDDSs is an active area of current research. Such NDDSs can have long circulation times, target the site of the disease and enhance the intracellular delivery of a drug. This type of NDDS can also respond to local stimuli that are characteristic of the pathological site by, for example, releasing an entrapped drug or shedding a protective coating, thus facilitating the interaction between drug-loaded nanocarriers and target cells or tissues. In addition, imaging contrast moieties can be attached to these carriers to track their real-time biodistribution and accumulation in target cells or tissues. Here, I highlight recent developments with multifunctional and stimuli-sensitive NDDSs and their therapeutic potential for diseases including cancer, cardiovascular diseases and infectious diseases.

Multimodal liposomes for SPECT/MR imaging as a tool for in situ relaxivity measurements

One of the major challenges of MR imaging is the quantification of local concentrations of contrast agents. Cellular uptake strongly influences different parameters such as the water exchange rate and the pool of water protons, and results in alteration of the contrast agent's relaxivity, therefore making it difficult to determine contrast agent concentrations based on the MR signal only. Here, we propose a multimodal radiolabeled paramagnetic liposomal contrast agent that allows simultaneous imaging with SPECT and MRI. As SPECT-based quantification allows determination of the gadolinium concentration, the MRI signal can be deconvoluted to get an understanding of the cellular location of the contrast agent. The cell experiments indicated a reduction of the relaxivity from 2.7 ± 0.1 m m(-1)  s(-1) to a net relaxivity of 1.7 ± 0.3 m m(-1)  s(-1) upon cellular uptake for RGD targeted liposomes by means of the contrast agent concentration as determined by SPECT. This is not observed for nontargeted liposomes that serve as controls. We show that receptor targeted liposomes in comparison to nontargeted liposomes are taken up into cells faster and into subcellular structures of different sizes. We suggest that the presented multimodal contrast agent provides a functional readout of its response to the biological environment and is furthermore applicable in in vivo measurements. As this approach can be extended to several MRI-based contrast mechanisms, we foresee a broader use of multimodal SPECT/MRI nanoparticles to serve as in vivo sensors in biological or medical research.

Magnetoliposomes as multimodal contrast agents for molecular imaging and cancer nanotheragnostics

In the emerging field of molecular and cellular imaging, flexible strategies to synthesize multimodal contrast agents with targeting ligands are required. Liposomes have the ability to combine with a large variety of nanomaterials, including superparamagnetic iron oxide nanoparticles, to form magnetoliposomes (MLs). MLs can be used as highly efficient MRI contrast agents. Owing to their high flexibility, MLs can be associated with other imaging modality probes to be used as multimodal contrast agents. By using a thermosensitive lipid bilayer in the ML structure, these biocompatible systems offer many possibilities for targeting and delivering therapeutic agents for ‘theragnostics’, a coincident therapy and diagnosis strategy. This article deals with the fast-growing field of MLs as biomedical diagnostic tools. Different kinds of MLs, their preparation methods, as well as their surface modification with different imaging probes, are discussed. ML applications as multimodal contrast agents and in theragnostics are reviewed. Some important issues for the biomedical uses of magnetic liposomes, such as toxicity, are summarized.

Multi-functional liposomes having temperature-triggered release and magnetic resonance imaging for tumor-specific chemotherapy

For development of tumor-specific chemotherapy, we designed liposomes with temperature-triggered drug release and magnetic resonance imaging (MRI) functions. We prepared multi-functional liposomes by incorporating thermosensitive poly(2-ethoxy(ethoxyethyl)vinyl ether) chains with a lower critical solution temperatures around 40 °C and polyamidoamine G3 dendron-based lipids having Gd(3+) chelate residues into pegylated liposomes. These stable doxorubicin (DOX)-loaded liposomes retained DOX in their interior below physiological temperature but released DOX immediately at temperatures greater than 40 °C. They exhibited excellent ability to shorten the longitudinal proton relaxation time. When administered intravenously into colon 26 tumor-bearing mice, accumulated liposomes in tumors increased with time, reaching a constant level 8 h after administration by following T(1)-weighted MRI signal intensity in tumors. Liposome size affected the liposome accumulation efficiency in tumors: liposomes of about 100 nm diameter were accumulated more efficiently than those with about 50 nm diameter. Tumor size also affected accumulation: more efficient accumulation occurred in larger tumors. Tumor growth was strongly suppressed when liposomes loaded with DOX were administered intravenously into tumor-bearing mice and the tumor was heated mildly at 44 °C for 10 min at 8 h after administration. Multi-functional liposomes having temperature-triggered drug release and MRI functions might engender personalized chemotherapy, providing efficient patient-optimized chemotherapy.

Hybrid nanomaterials for biomedical applications

Hybrid nanomaterials, composed of both inorganic and organic components, have recently been examined as promising platforms for imaging and therapeutic applications. This unique class of nanomaterials can not only retain beneficial features of both the inorganic and organic components, but also provides the ability to systematically tune the properties of the hybrid material through the combination of functional components. This feature article will summarize recent advances in the design and synthesis of hybrid nanomaterials and their applications in biological and biomedical areas. The hybrid nanomaterials to be discussed fall into two main categories, silica based materials and nanoscale metal-organic frameworks. Their applications as imaging contrast agents and nanotherapeutics will be highlighted.

Current trends in liposome research

Among the several drug delivery systems, liposomes--phospholipid nanosized vesicles with a bilayered membrane structure--have drawn a lot of interest as advanced and versatile pharmaceutical carriers for both low and high molecular weight pharmaceuticals. At present, liposomal formulations span multiple areas, from clinical application of the liposomal drugs to the development of various multifunctional liposomal systems to be used in therapy and diagnostics. This chapter provides a brief overview of various liposomal products currently under development at experimental and preclinical level.

Multifunctional and stimuli-sensitive pharmaceutical nanocarriers

Currently used pharmaceutical nanocarriers, such as liposomes, micelles, and polymeric nanoparticles, demonstrate a broad variety of useful properties, such as longevity in the body; specific targeting to certain disease sites; enhanced intracellular penetration; contrast properties allowing for direct carrier visualization in vivo; stimuli-sensitivity, and others. Some of those pharmaceutical carriers have already made their way into clinic, while others are still under preclinical development. In certain cases, the pharmaceutical nanocarriers combine several of the listed properties. Long-circulating immunoliposomes capable of prolonged residence in the blood and specific target recognition represent one of the examples of this kind. The engineering of multifunctional pharmaceutical nanocarriers combining several useful properties in one particle can significantly enhance the efficacy of many therapeutic and diagnostic protocols. This paper considers the current status and possible future directions in the emerging area of multifunctional nanocarriers with primary attention on the combination of such properties as longevity, targetability, intracellular penetration, contrast loading, and stimuli-sensitivity.

Relaxivities of paramagnetic liposomes: on the importance of the chain type and the length of the amphiphilic complex

Nuclear magnetic relaxation dispersion (NMRD) profiles of unilamellar DPPC liposomes incorporating Gd-DTPA-bisamides with alkyl chains of 12 to 18 C atoms in their external and internal layers were recorded in order to study the influence that the chain length and structure of Gd-bisamides incorporated in the liposomal membrane have on their proton relaxivity. The NMRD profiles recorded at 310 K show that the relaxivity reaches a minimum value when the carbon chain lengths of the phospholipid and of the Gd complex match and is at a maximum in the presence of a carbon-carbon double bond. For these DPPC paramagnetic liposomes, the longer the aliphatic chains of the complex, the larger will be its immobilization in the membrane. In addition, the presence of an unsaturated carbon-carbon bond in the alkyl chain of the Gd complex induces an increase of its mobility and of its water exchange rate with, as a result, a much greater efficiency as an MRI contrast agent.

Nanotechnology: a focus on nanoparticles as a drug delivery system

This review will provide an in-depth discussion on the previous development of nanoparticle-based drug delivery systems (DDS) and discuss original research data that includes the therapeutic enhancement of antiretroviral therapy. The use of nanoparticle DDS will allow practitioners to use drugs to target specific areas of the body. In the treatment of malignancies, the use of nanoparticles as a DDS is making measurable treatment impact. Medical imaging will also utilize DDS to illuminate tumors, the brain, or other cellular functions in the body. The utility of nanoparticle DDS to improve human health is potentially enormous.

Targeted pharmaceutical nanocarriers for cancer therapy and imaging

The use of various pharmaceutical nanocarriers has become one of the most important areas of nanomedicine. Ideally, such carriers should be specifically delivered (targeted) to the pathological area to provide the maximum therapeutic efficacy. Among the many potential targets for such nanocarriers, tumors have been most often investigated. This review attempts to summarize currently available information regarding targeted pharmaceutical nanocarriers for cancer therapy and imaging. Certain issues related to some popular pharmaceutical nanocarriers, such as liposomes and polymeric micelles, are addressed, as are different ways to target tumors via specific ligands and via the stimuli sensitivity of the carriers. The importance of intracellular targeting of drug- and DNA-loaded pharmaceutical nanocarriers is specifically discussed, including intracellular delivery with cell-penetrating peptides.

Generation of superparamagnetic liposomes revealed as highly efficient MRI contrast agents for in vivo imaging

Maghemite (gamma-Fe2O3) nanocrystals stable at neutral pH and in isotonic aqueous media were synthesized and encapsulated within large unilamellar vesicles of egg phosphatidylcholine (EPC) and distearoyl-SN-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG(2000), 5 mol %), formed by film hydration coupled with sequential extrusion. The nonentrapped particles were removed by flash gel exclusion chromatography. The magnetic-fluid-loaded liposomes (MFLs) were homogeneous in size (195 +/- 33 hydrodynamic diameters from quasi-elastic light scattering). Iron loading was varied from 35 up to 167 Fe(III)/lipid mol %. Physical and superparamagnetic characteristics of the iron oxide particles were preserved after liposome encapsulation as shown by cryogenic transmission electron microscopy and magnetization curve recording. In biological media, MFLs were highly stable and avoided ferrofluid flocculation while being nontoxic toward the J774 macrophage cell line. Moreover, steric stabilization ensured by PEG-surface-grafting significantly reduced liposome association with the macrophages. The ratios of the transversal (r2) and longitudinal (r1) magnetic resonance (MR) relaxivities of water protons in MFL dispersions (6 < r2/r1 < 18) ranked them among the best T2 contrast agents, the higher iron loading the better the T2 contrast enhancement. Magnetophoresis demonstrated the possible guidance of MFLs by applying a magnetic field gradient. Mouse MR imaging assessed MFLs efficiency as contrast agents in vivo: MR angiography performed 24 h after intravenous injection of the contrast agent provided the first direct evidence of the stealthiness of PEG-ylated magnetic-fluid-loaded liposomes.

Recent advances with liposomes as pharmaceutical carriers

Liposomes - microscopic phospholipid bubbles with a bilayered membrane structure - have received a lot of attention during the past 30 years as pharmaceutical carriers of great potential. More recently, many new developments have been seen in the area of liposomal drugs - from clinically approved products to new experimental applications, with gene delivery and cancer therapy still being the principal areas of interest. For further successful development of this field, promising trends must be identified and exploited, albeit with a clear understanding of the limitations of these approaches.