Plasma protein (albumin) catabolism by the tumor itself--implications for tumor metabolism and the genesis of cachexia

A polyphenylene dendrimer drug transporter with precisely positioned amphiphilic surface patches

The design and synthesis of a polyphenylene dendrimer (PPD 3) with discrete binding sites for lipophilic guest molecules and characteristic surface patterns is presented. Its semi-rigidity in combination with a precise positioning of hydrophilic and hydrophobic groups at the periphery yields a refined architecture with lipophilic binding pockets that accommodate defined numbers of biologically relevant guest molecules such as fatty acids or the drug doxorubicin. The size, architecture, and surface textures allow to even penetrate brain endothelial cells that are a major component of the extremely tight blood-brain barrier. In addition, low to no toxicity is observed in in vivo studies using zebrafish embryos. The unique PPD scaffold allows the precise placement of functional groups in a given environment and offers a universal platform for designing drug transporters that closely mimic many features of proteins.

Synthesis and therapeutic effect of styrene-maleic acid copolymer-conjugated pirarubicin

Previously, we prepared a pirarubicin (THP)-encapsulated micellar drug using styrene-maleic acid copolymer (SMA) as the drug carrier, in which active THP was non-covalently encapsulated. We have now developed covalently conjugated SMA-THP (SMA-THP conjugate) for further investigation toward clinical development, because covalently linked polymer-drug conjugates are known to be more stable in circulation than drug-encapsulated micelles. The SMA-THP conjugate also formed micelles and showed albumin binding capacity in aqueous solution, which suggested that this conjugate behaved as a macromolecule during blood circulation. Consequently, SMA-THP conjugate showed significantly prolonged circulation time compared to free THP and high tumor-targeting efficiency by the enhanced permeability and retention (EPR) effect. As a result, remarkable antitumor effect was achieved against two types of tumors in mice without apparent adverse effects. Significantly, metastatic lung tumor also showed the EPR effect, and this conjugate reduced metastatic tumor in the lung almost completely at 30 mg/kg once i.v. (less than one-fifth of the maximum tolerable dose). Although SMA-THP conjugate per se has little cytotoxicity in vitro (1/100 of free drug THP), tumor-targeted accumulation by the EPR effect ensures sufficient drug concentrations in tumor to produce an antitumor effect, whereas toxicity to normal tissues is much less. These findings suggest the potential of SMA-THP conjugate as a highly favorable candidate for anticancer nanomedicine with good stability and tumor-targeting properties in vivo.

Albumin-based micro-composite drug carriers with dual chemo-agents for targeted breast cancer treatment

Albumin-based drug-carrying micro-composite spheres were fabricated and studied to evaluate their potentials for breast cancer treatment. Magnetic nanoparticles and albumin were incorporated within poly(D l-lactide-co-glycolide) microspheres to increase accumulation of the microspheres at the target site. Two chemotherapeutics, cyclophosphamide and 5-fluorouracil, were encapsulated into the microspheres. The drug-release study revealed an initial burst of drug and then sustained release by diffusion. A Fourier transform infrared spectroscopy study confirmed the presence of all components of the drug delivery system. An in vitro study using fibroblast cells (3T3) and breast cancer cells (MDA-486) exhibited an effective cytotoxicity behavior when exposed to the drug delivery system in a dose- and time-dependent manner. The therapeutic influence of the drug delivery system was evaluated in vivo using a nude mouse breast cancer model. A continuous decrease in tumor size was observed in groups treated with microspheres containing the chemotherapeutics, whereas mice treated with direct chemotherapy without drug delivery system showed less efficacy and suggested tumor relapse after cessation of treatment. The enhanced therapeutic influence of the drug delivery system may be attributed to the increased uptake of the microspheres by malignant cells due to the presence of albumin and magnetic force. The bioavailability of chemotherapeutics at the target site was further increased due to the sustained release of the drugs by diffusion following the burst release. Continuous investigations will optimize the size of the drug delivery system and portions of the target driving-force components (magnetic nanoparticles and albumin) in the drug delivery system to maximize its therapeutic efficacy and minimize potential long-term side effects.

Influence of the binding of reduced NAMI-A to human serum albumin on the pharmacokinetics and biological activity

Chemical transformations of NAMI-A in biological environments.

SiRNA gene therapy using albumin as a carrier

RNA interference or post-transcriptional gene silencing is one of the latest, innovative, highly specific, and efficient technologies for gene therapy application in molecular oncology. It is already a well-established research tool for analyses of molecular mechanisms for various diseases including cancer as it efficiently silences the expression of genes of interest. However, for its proper therapeutic use, an efficient tumor-specific in-vivo delivery mechanism is essential. Many scientific groups and companies are involved in the development of efficient in-vivo delivery mechanisms for small interfering RNA, but are still struggling. The present article suggests utilization of albumin as a delivery module for small interfering RNA as it is an endogenous natural nanoparticle known for its binding properties to various endogenous metabolites, drugs, and metal ions.

Albumin nanocapsules containing fenretinide: pre-clinical evaluation of cytotoxic activity in experimental models of human non-small cell lung cancer

The present study deals with the preparation of albumin nanocapsules containing fenretinide and their evaluation in experimental models of human non-small cell lung cancer. These nanocapsules showed enhanced antitumor activity with respect to free fenretinide due to the solubilization effect of albumin on the hydrophobic drug, known to improve bioavailability. The high expression of caveolin-1 on the A549 cell surface further enhanced the antitumor activity of the nanoencapsulated fenretinide. Caveolin-1 favored albumin uptake and improved the efficacy of the fenretinide-loaded albumin nanocapsules, especially in 3-D cultures where the densely packed 3-D structures impaired drug diffusibility and severely reduced the activity of the free drug. The efficacy of the fenretinide albumin nanocapsules was further confirmed in tumor xenograft models of A549 by the significant delay in tumor progression observed with respect to control after intravenous administration of the novel formulation.

FROM THE CLINICAL EDITOR

This study describes the preparation of fenretinide containing albumin nanocapsules and their evaluation in experimental models of non-small cell lung cancer, showing enhanced antitumor activity compared to free fenretinide.

Albumin-based nanocomposite spheres for advanced drug delivery systems

A novel drug delivery system incorporating human serum albumin, poly(lactic-co-glycolic acid, magnetite nanoparticles, and therapeutic agent(s) was developed for potential application in the treatment of diseases such as rheumatoid arthritis and skin cancer. An oil-in-oil emulsion/solvent evaporation (O/OSE) method was modified to produce a drug delivery system with a diameter of 0.5–2 μm. The diameter was mainly controlled by adjusting the viscosity of albumin in the discontinuous phase of the O/OSE method. The drug-release study showed that the release of drug and albumin was mostly dependent on the albumin content of the drug delivery system, which is very similar to the drug occlusion-mesopore model. Cytotoxicity tests indicated that increasing the albumin content in the drug delivery system increased cell viability, possibly due to the improved biocompatibility of the system. Overall, these studies show that the proposed system could be a viable option as a drug delivery system in the treatment of many illnesses, such as rheumatoid arthritis, and skin and breast cancers.

Cellular specificity of the blood-CSF barrier for albumin transfer across the choroid plexus epithelium

To maintain the precise internal milieu of the mammalian central nervous system, well-controlled transfer of molecules from periphery into brain is required. Recently the soluble and cell-surface albumin-binding glycoprotein SPARC (secreted protein acidic and rich in cysteine) has been implicated in albumin transport into developing brain, however the exact mechanism remains unknown. We postulate that SPARC is a docking site for albumin, mediating its uptake and transfer by choroid plexus epithelial cells from blood into cerebrospinal fluid (CSF). We used in vivo physiological measurements of transfer of endogenous (mouse) and exogenous (human) albumins, in situ Proximity Ligation Assay (in situ PLA), and qRT-PCR experiments to examine the cellular mechanism mediating protein transfer across the blood–CSF interface. We report that at all developmental stages mouse albumin and SPARC gave positive signals with in situ PLAs in plasma, CSF and within individual plexus cells suggesting a possible molecular interaction. In contrast, in situ PLA experiments in brain sections from mice injected with human albumin showed positive signals for human albumin in the vascular compartment that were only rarely identifiable within choroid plexus cells and only at older ages. Concentrations of both endogenous mouse albumin and exogenous (intraperitoneally injected) human albumin were estimated in plasma and CSF and expressed as CSF/plasma concentration ratios. Human albumin was not transferred through the mouse blood–CSF barrier to the same extent as endogenous mouse albumin, confirming results from in situ PLA. During postnatal development Sparc gene expression was higher in early postnatal ages than in the adult and changed in response to altered levels of albumin in blood plasma in a differential and developmentally regulated manner. Here we propose a possible cellular route and mechanism by which albumin is transferred from blood into CSF across a sub-population of specialised choroid plexus epithelial cells.

Unraveling the mysteries of serum albumin-more than just a serum protein

Serum albumin is a multi-functional protein that is able to bind and transport numerous endogenous and exogenous compounds. The development of albumin drug carriers is gaining increasing importance in the targeted delivery of cancer therapy, particularly as a result of the market approval of the paclitaxel-loaded albumin nanoparticle, Abraxane®. Considering this, there is renewed interest in isolating and characterizing albumin-binding proteins or receptors on the plasma membrane that are responsible for albumin uptake. Initially, the cellular uptake and intracellular localization of albumin was unknown due to the large confinement of the protein within the vascular and interstitial compartment of the body. Studies have since assessed the intracellular localization of albumin in order to understand the mechanisms and pathways responsible for its uptake, distribution and catabolism in multiple tissues, and this is reviewed herein.

Simulation of monoclonal antibody pharmacokinetics in humans using a minimal physiologically based model

Compared to small chemical molecules, monoclonal antibodies and Fc-containing derivatives (mAbs) have unique pharmacokinetic behaviour characterised by relatively poor cellular permeability, minimal renal filtration, binding to FcRn, target-mediated drug disposition, and disposition via lymph. A minimal physiologically based pharmacokinetic (PBPK) model to describe the pharmacokinetics of mAbs in humans was developed. Within the model, the body is divided into three physiological compartments; plasma, a single tissue compartment and lymph. The tissue compartment is further sub-divided into vascular, endothelial and interstitial spaces. The model simultaneously describes the levels of endogenous IgG and exogenous mAbs in each compartment and sub-compartment and, in particular, considers the competition of these two species for FcRn binding in the endothelial space. A Monte-Carlo sampling approach is used to simulate the concentrations of endogenous IgG and mAb in a human population. Existing targeted-mediated drug disposition (TMDD) models are coupled with the minimal PBPK model to provide a general platform for simulating the pharmacokinetics of therapeutic antibodies using primarily pre-clinical data inputs. The feasibility of utilising pre-clinical data to parameterise the model and to simulate the pharmacokinetics of adalimumab and an anti-ALK1 antibody (PF-03446962) in a population of individuals was investigated and results were compared to published clinical data.

Improving the pharmacokinetic properties of biologics by fusion to an anti-HSA shark VNAR domain

Advances in recombinant antibody technology and protein engineering have provided the opportunity to reduce antibodies to their smallest binding domain components and have concomitantly driven the requirement for devising strategies to increase serum half-life to optimise drug exposure, thereby increasing therapeutic efficacy. In this study, we adopted an immunization route to raise picomolar affinity shark immunoglobulin new antigen receptors (IgNARs) to target human serum albumin (HSA). From our model shark species, Squalus acanthias, a phage display library encompassing the variable binding domain of IgNAR (VNAR) was constructed, screened against target, and positive clones were characterized for affinity and specificity. N-terminal and C-terminal molecular fusions of our lead hit in complex with a naïve VNAR domain were expressed, purified and exhibited the retention of high affinity binding to HSA, but also cross-selectivity to mouse, rat and monkey serum albumin both in vitro and in vivo. Furthermore, the naïve VNAR had enhanced pharmacokinetic (PK) characteristics in both N- and C-terminal orientations and when tested as a three domain construct with naïve VNAR flanking the HSA binding domain at both the N and C termini. Molecules derived from this platform technology also demonstrated the potential for clinical utility by being available via the subcutaneous route of delivery. This study thus demonstrates the first in vivo functional efficacy of a VNAR binding domain with the ability to enhance PK properties and support delivery of multifunctional therapies.

Evolution of taxanes in the treatment of metastatic breast cancer

Taxanes have become effective therapies for patients with metastatic breast cancer (MBC); however, understanding the differences among them is important. Each of the taxanes currently approved for treating MBC has a unique formulation, which translates to differences in toxicity profiles and administration considerations. In this article, the rationale for the development of the taxanes paclitaxel, docetaxel, and nab-paclitaxel is reviewed from a historical perspective. The mechanisms of action, formulations, and indications of taxanes also are discussed. The impact of their formulations on clinical practice and patient care, particularly solvent-based versus novel solvent-free formulations, will be reviewed from the nursing perspective.

Kinetics and efficiency of a methyl-carboxylated 5-Fluorouracil-bovine serum albumin adduct for targeted delivery

5-Fluorouracil (5-FU) is a clinically well-established anti-cancer drug effectively applied in chemotherapy, mainly for the treatment of breast and colorectal cancer. Substantial disadvantages are adverse effects, arising from serious damage of healthy tissues, and shortcoming pharmacokinetics due to its low molecular weight. A promising approach for improvement of such drugs is their coupling to suitable carriers. Here, a 5-FU adduct, 5-fluorouracil acetate (FUAc) is synthesized and covalently coupled to bovine serum albumin (BSA) as model carrier molecule. On average, 12 molecules FUAc are bound to one BSA. Circular dichriosm (CD)-spectra of BSA and FUAc-BSA are identical, suggesting no significant conformational differences. FUAc-BSA is tested on T-47D and MDA-MB-231 breast cancer cells. Proliferation inhibition of membrane albumin-binding protein (mABP)-expressing T-47D cells by FUAc-BSA is similar to that of 5-FU and only moderate for MDA-MB-231 cells that lack such expression. Therefore, a crucial role of mABP expression in effective cell growth inhibition by FUAc-BSA is assumed.

Fatty acids as therapeutic auxiliaries for oral and parenteral formulations

Many drugs have decreased therapeutic activity due to issues with absorption, distribution, metabolism and excretion. The co-formulation or covalent attachment of drugs with fatty acids has demonstrated some capacity to overcome these issues by improving intestinal permeability, slowing clearance and binding serum proteins for selective tissue uptake and metabolism. For orally administered drugs, albeit at low level of availability, the presence of fatty acids and triglycerides in the intestinal lumen may promote intestinal uptake of small hydrophilic molecules. Small lipophilic drugs or acylated hydrophilic drugs also show increased lymphatic uptake and enhanced passive diffusional uptake. Fatty acid conjugation of small and large proteins or peptides has exhibited protracted plasma half-lives, site-specific delivery and sustained release upon parenteral administration. These improvements are most likely due to associations with lipid-binding serum proteins, namely albumin, LDL and HDL. These molecular interactions, although not fully characterized, could provide the ability of using the endogenous carrier systems for improving therapeutic outcomes.

Development and characterization of small bispecific albumin-binding domains with high affinity for ErbB3

Affinity proteins based on small scaffolds are currently emerging as alternatives to antibodies for therapy. Similarly to antibodies, they can be engineered to have high affinity for specific proteins. A potential problem with small proteins and peptides is their short in vivo circulation time, which might limit the therapeutic efficacy. To circumvent this issue, we have engineered bispecificity into an albumin-binding domain (ABD) derived from streptococcal Protein G. The inherent albumin binding was preserved while the opposite side of the molecule was randomized for selection of high-affinity binders. Here we present novel ABD variants with the ability to bind to the epidermal growth factor receptor 3 (ErbB3). Isolated candidates were shown to have an extraordinary thermal stability and affinity for ErbB3 in the nanomolar range. Importantly, they were also shown to retain their affinity to albumin, hence demonstrating that the intended strategy to engineer bispecific single-domain proteins against a tumor-associated receptor was successful. Moreover, competition assays revealed that the new binders could block the natural ligand Neuregulin-1 from binding to ErbB3, indicating a potential anti-proliferative effect. These new binders thus represent promising candidates for further development into ErbB3-signaling inhibitors, where the albumin interaction could result in prolonged in vivo half-life.

Self-crosslinked human serum albumin nanocarriers for systemic delivery of polymerized siRNA to tumors

The safe and effective systemic delivery of siRNA is a prerequisite for the successful development of siRNA-based cancer therapeutics. For the enhanced delivery of siRNA, cationic lipids and polymers have been widely used as siRNA carriers to form electrolyte complexes with anionic siRNA. However, the considerable toxicity of strong cationic-charged molecules hampers their clinical use. In this study, we utilized human serum albumin (HSA), which is the most abundant of the plasma proteins, as a siRNA carrier for systemic tumor-targeted siRNA delivery. Both HSA and siRNA molecules were thiol-introduced to improve the binding affinity for each other. The resulting thiolated HSA (tHSA) and polymerized siRNA (psi) formed stable nanosized complexes (psi-tHSAs) by chemical crosslinking and self-crosslinking. After internalization, the psi-tHSAs showed target gene silencing activity in vitro comparable to conventional Lipofectamine™-siRNA complexes, without remarkable cytotoxicity. After intravenous injection in tumor-bearing mice, psi-tHSAs accumulated specifically at the tumor sites, leading to efficient gene silencing in the tumors in a sequential manner. The therapeutic VEGF siRNA was loaded into psi-tHSAs, which significantly inhibited tumor-related angiogenesis in PC-3 tumor xenografts and resulted in retarding the growth of PC-3 tumors. The results showed that self-crosslinked psi-tHSA nanocarriers might provide a promising approach for the systemic siRNA therapy of various human cancers.

nab-Paclitaxel mechanisms of action and delivery

Taxanes are a key chemotherapy component for several malignancies, including metastatic breast cancer (MBC), ovarian cancer, and advanced non-small cell lung cancer (NSCLC). Despite the clinical benefit achieved with solvent-based (sb) taxanes, these agents can be associated with significant and severe toxicities. Albumin-bound paclitaxel (Abraxane; nab®-Paclitaxel), a novel solvent-free taxane, has demonstrated higher response rates and improved tolerability when compared with solvent-based formulations in patients with advanced MBC and NSCLC. The technology used to create nab-paclitaxel utilizes albumin to deliver paclitaxel, resulting in an advantageous pharmacokinetic (PK) profile. This review discusses the proposed mechanism of delivery of nab-paclitaxel, including an examination into a hypothesized greater ability to leverage albumin-based transport relative to sb-paclitaxel. An advantageous PK profile and the more efficient use of albumin-based transport may contribute to the preclinical finding that nab-paclitaxel achieves a 33% higher tumor uptake relative to sb-paclitaxel. Another possible contributing factor to the tumor accumulation of nab-paclitaxel is the binding of albumin to secreted protein acidic and rich in cysteine (SPARC), although the data supporting this relationship between SPARC and nab-paclitaxel remain largely correlative at this point. Recent data also suggest that nab-paclitaxel may enhance tumor accumulation of gemcitabine in pancreatic cancer treated with both agents. Additionally, a possible mechanistic synergy between nab-paclitaxel and capecitabine has been cited as the rationale to combine the two agents for MBC treatment. Thus, nab-paclitaxel appears to interact with tumors in a number of interesting, but not fully understood, ways. Continued preclinical and clinical research across a range of tumor types is warranted to answer the questions that remain on the mechanisms of delivery and antitumor activity of nab-paclitaxel.

Macropinocytosis of protein is an amino acid supply route in Ras-transformed cells

Macropinocytosis is a highly conserved endocytic process by which extracellular fluid and its contents are internalized into cells through large, heterogeneous vesicles known as macropinosomes. Oncogenic Ras proteins have been shown to stimulate macropinocytosis but the functional contribution of this uptake mechanism to the transformed phenotype remains unknown. Here we show that Ras-transformed cells use macropinocytosis to transport extracellular protein into the cell. The internalized protein undergoes proteolytic degradation, yielding amino acids including glutamine that can enter central carbon metabolism. Accordingly, the dependence of Ras-transformed cells on free extracellular glutamine for growth can be suppressed by the macropinocytic uptake of protein. Consistent with macropinocytosis representing an important route of nutrient uptake in tumours, its pharmacological inhibition compromises the growth of Ras-transformed pancreatic tumour xenografts. These results identify macropinocytosis as a mechanism by which cancer cells support their unique metabolic needs and point to the possible exploitation of this process in the design of anticancer therapies.

Skin cancer treatment by albumin/5-Fu loaded magnetic nanocomposite spheres in a mouse model

Albumin/drug loaded magnetic nanocomposite spheres were fabricated using an oil-in-oil emulsion/solvent evaporation method, and tested on a mouse model (experimental squamous cell carcinoma) to determine the efficacy of the drug delivery system (DDS) on skin cancer. This novel DDS consists of human serum albumin, poly(lactic-co-glycolic acid) (PLGA), 5-fluorouracil (5-Fu), magnetic nanoparticles (10 nm) and fluorescent labeling molecule (diphenylhexatriene). One of the major purposes of using albumin is that it likely provides internal binding to and retention by the inflammatory tissues to reduce the amount of magnetic nanoparticles needed in the drug loaded microspheres (750–1100 nm). This study is aimed at reducing many negative side effects of conventionally used chemotherapy drugs by localizing the chemotherapy drug, controlling the release of the therapeutic agent and encouraging uptake of the DDS into cancerous cells. A group of mice treated with (1) the magnetic targeted DDS were compared to the other three groups, including, (2) DDS without a magnet, (3) 5-Fu local injection, and (4) untreated groups. The fluorescent tracer was ubiquitously identified inside the tumor tissue, and the DDS/tumor tissue boundary presented a leaky interface. The test results clearly showed that the magnetic targeted DDS exhibited significantly superior therapeutic effects in treating the skin cancer, with the increased efficacy to halt the tumor growth.

On the origin of cancer metastasis

Metastasis involves the spread of cancer cells from the primary tumor to surrounding tissues and to distant organs and is the primary cause of cancer morbidity and mortality. In order to complete the metastatic cascade, cancer cells must detach from the primary tumor, intravasate into the circulatory and lymphatic systems, evade immune attack, extravasate at distant capillary beds, and invade and proliferate in distant organs. Currently, several hypotheses have been advanced to explain the origin of cancer metastasis. These involve an epithelial mesenchymal transition, an accumulation of mutations in stem cells, a macrophage facilitation process, and a macrophage origin involving either transformation or fusion hybridization with neoplastic cells. Many of the properties of metastatic cancer cells are also seen in normal macrophages. A macrophage origin of metastasis can also explain the long-standing "seed and soil" hypothesis and the absence of metastasis in plant cancers. The view of metastasis as a macrophage metabolic disease can provide novel insight for therapeutic management.

Synthesis and characterization of near IR fluorescent albumin nanoparticles for optical detection of colon cancer

Near IR (NIR) fluorescent human serum albumin (HSA) nanoparticles hold great promise as contrast agents for tumor diagnosis. HSA nanoparticles are considered to be biocompatible, non-toxic and non-immunogenic. In addition, NIR fluorescence properties of these nanoparticles are important for in vivo tumor diagnostics, with low autofluorescence and relatively deep penetration of NIR irradiation due to low absorption of biomatrices. The present study describes the synthesis of new NIR fluorescent HSA nanoparticles, by entrapment of a NIR fluorescent dye within the HSA nanoparticles, which also significantly increases the photostability of the dye. Tumor-targeting ligands such as peanut agglutinin (PNA) and anti-carcinoembryonic antigen antibodies (anti-CEA) were covalently conjugated to the NIR fluorescent albumin nanoparticles, increasing the potential fluorescent signal in tumors with upregulated corresponding receptors. Specific colon tumor detection by the NIR fluorescent HSA nanoparticles was demonstrated in a chicken embryo model and a rat model. In future work we also plan to encapsulate cancer drugs such as doxorubicin within the NIR fluorescent HSA nanoparticles for both colon cancer imaging and therapy.

Taxanes for the treatment of metastatic breast cancer

Taxanes have remained a cornerstone of breast cancer treatment over the past three decades, improving the lives of patients with both early- and late-stage disease. The purpose of this review is to summarize the current role of taxanes, including an albumin-bound formulation that enhances delivery of paclitaxel to tumors, in the management of metastatic breast cancer (MBC). Since the introduction of Cremophor EL-paclitaxel to the clinic in the mid-1990s, a substantial amount of investigation has gone into subjects such as formulation, dose, schedule, and taxane resistance, allowing physicians greater flexibility in treating patients with MBC. This review will also examine how the shrinking pool of taxane-naive patients, a result of the expansion of taxanes into the neoadjuvant and adjuvant settings, will respond to taxane retreatment for metastatic disease. Taxane treatment seems likely to continue to play an important role in the treatment of MBC.

Heterocoagulation as a facile route to prepare stable serum albumin-nanoparticle conjugates for biomedical applications: synthetic protocols and mechanistic insights

There is increasing interest in using serum albumin, the most abundant plasma protein, as a stabilizing agent in the context of nanomedicine. Using poly(vinyl amine)-stabilized polypyrrole nanoparticles as an example, we report a facile generic route to prepare serum albumin-nanoparticle conjugates via heterocoagulation. Time-resolved dynamic light scattering (DLS), disk centrifuge photosedimentometry (DCP), and circular dichroism (CD) spectroscopy studies confirm that bovine serum albumin (BSA) adsorbs rapidly onto the cationic poly(vinyl amine)-stabilized polypyrrole nanoparticles and suggest that the initial well-defined protein coronal is subsequently cross-linked via thiol-disulfide exchange. These BSA-nanoparticle conjugates were further characterized by X-ray photoelectron spectroscopy (XPS), aqueous electrophoresis, field emission scanning electron microscopy (FE SEM), and transmission electron microscopy (TEM). They exhibit excellent long-term colloidal stability under physiological conditions without further purification, suggesting strong irreversible adsorption by the BSA. Protein adsorption appears to be co-operative and both thermodynamic and mechanistic aspects were examined via aqueous electrophoresis, DCP, and DLS studies.

Near IR fluorescent polystyrene/albumin core/shell nanoparticles for specific targeting of colonic neoplasms

Previous studies have shown that albumin has a high affinity towards tumours, and, as a result, many drug/albumin conjugates, as well as albumin nanoparticles, have been studied as antineoplastic drug carriers. Numerous studies have also shown the high affinity of cyanine dyes for albumin. This work combines the former and the latter for the preparation of NIR fluorescent and photostable nanoparticles as diagnostic biomaterials. Tumour-specific labelling by NIR fluorescent polystyrene/albumin core/shell nanoparticles is demonstrated, without the presence of additional targeting moieties, and they possess great potential for clinical applications.

Analysis on the current status of targeted drug delivery to tumors

Targeted drug delivery to tumor sites is one of the ultimate goals in drug delivery. Recent progress in nanoparticle engineering has certainly improved drug targeting, but the results are not as good as expected. This is largely due to the fact that nanoparticles, regardless of how advanced they are, find the target as a result of blood circulation, like the conventional drug delivery systems do. Currently, the nanoparticle-based drug delivery to the target tumor tissues is based on wrong assumptions that most of the nanoparticles, either PEGylated or not, reach the target by the enhanced permeation and retention (EPR) effect. Studies have shown that so-called targeting moieties, i.e., antibodies or ligands, on the nanoparticle surface do not really improve delivery to target tumors. Targeted drug delivery to tumor sites is associated with highly complex biological, mechanical, chemical and transport phenomena, of which characteristics vary spatiotemporally. Yet, most of the efforts have been focused on design and surface manipulation of the drug carrying nanoparticles with relatively little attention to other aspects. This article examines the current misunderstandings and the main difficulties in targeted drug delivery.

A dicarboxylic fatty acid derivative of paclitaxel for albumin-assisted drug delivery

Paclitaxel (PTX) is a potent chemotherapy for many cancers but it suffers from very poor solubility. Consequently, the TAXOL formulation uses copious amounts of the surfactant Cremophor EL to solubilize the drug for injection, resulting in severe hypersensitivity and neutropenia. In contrast to Cremophor EL, presented is a way to solubilize PTX by conjugation of a dicarboxylic fatty acid for specific binding to the ubiquitous protein, serum albumin. The conjugation chemistry was simplified to a single step using the activated anhydride form of 3-pentadecylglutaric (PDG) acid, which is reactive to a variety of nucleophiles. The PDG derivative is less cytotoxic than the parent compound and was found to slowly hydrolyze to PTX (≈ 5% over 72 h) in serum, tumor cytosol, and tumor tissue homogenate. When injected intravenously to tumor-bearing mice, [(3) H]-PTX in the TAXOL formulation was cleared rapidly with a half-life of 7 h. In the case of the PDG derivative of PTX, the drug is quickly distributed and approximately 20% of the injected dose remained in the vasculature experiencing a 23 h half-life. These improvements from modifying PTX with the PDG fatty acid present the opportunity for PDG to become a generic modification for the improvement of many therapeutics.

Analysis of immediate stress mechanisms upon injection of polymeric micelles and related colloidal drug carriers: implications on drug targeting

Polymeric micelles are ideal carriers for solubilization and targeting applications using hydrophobic drugs. Stability of colloidal aggregates upon injection into the bloodstream is mandatory to maintain the drugs' targeting potential and to influence pharmacokinetics. In this review we analyzed and discussed the most relevant stress mechanisms that polymeric micelles and related colloidal carriers encounter upon injection, including (1) dilution, (2) interactions with blood components, and (3) immunological responses of the body. In detail we analyzed the opsonin-dysopsonin hypothesis that points at a connection between a particles' protein-corona and its tissue accumulation by the enhanced permeability and retention (EPR) effect. In the established theory, size is seen as a necessary condition to reach nanoparticle accumulation in disease modified tissue. There is, however, mounting evidence of other sufficient conditions (e.g., particle charge, receptor recognition of proteins adsorbed onto particle surfaces) triggering nanoparticle extravasation by active mechanisms. In conclusion, the analyzed stress mechanisms are directly responsible for in vivo success or failure of the site-specific delivery with colloidal carrier systems.

Photochemically generated elemental selenium forms conjugates with serum proteins that are preferentially cytotoxic to leukemia and selected solid tumor cells

The objective of this study was to determine if and how photoproducts contribute to the antitumor effect of merocyanine-mediated PDT. A panel of barbituric, thiobarbituric and selenobarbituric acid analogues of Merocyanine 540 was photobleached, and the resulting photoproducts were characterized by absorption, fluorescence emission, mass, energy dispersive X-ray, and X-ray photoelectron spectroscopy and tested for cytotoxic activity against tumor cell lines and freshly explanted bone marrow cells. While all dyes were readily photobleached, only photoproducts of selone dyes showed cytotoxic activity. One-hour incubations with micromolar concentrations of selone-derived photoproducts were sufficient to reduce leukemia/lymphoma cells ≥10 000 fold, whereas preserving virtually all normal CD34-positive bone marrow cells. Of six multidrug-resistant tumor cell lines tested, five were as sensitive or more sensitive to photoproducts than the corresponding wild-type lines. Physicochemical characterizations of the cytotoxic activity indicated that it consisted of conjugates of subnano particles of elemental selenium and (lipo)proteins. The discovery of cytotoxic Se-protein conjugates provides a rare example of photoproducts contributing substantially to the antitumor effect of PDT and challenges the long-held view that Se in oxidation state zero is biologically inert. Agents modeled after our Se-protein conjugates may prove useful for the treatment of leukemia.

Structure-based mutagenesis reveals the albumin-binding site of the neonatal Fc receptor

Albumin is the most abundant protein in blood where it has a pivotal role as a transporter of fatty acids and drugs. Like IgG, albumin has long serum half-life, protected from degradation by pH-dependent recycling mediated by interaction with the neonatal Fc receptor, FcRn. Although the FcRn interaction with IgG is well characterized at the atomic level, its interaction with albumin is not. Here we present structure-based modelling of the FcRn–albumin complex, supported by binding analysis of site-specific mutants, providing mechanistic evidence for the presence of pH-sensitive ionic networks at the interaction interface. These networks involve conserved histidines in both FcRn and albumin domain III. Histidines also contribute to intramolecular interactions that stabilize the otherwise flexible loops at both the interacting surfaces. Molecular details of the FcRn–albumin complex may guide the development of novel albumin variants with altered serum half-life as carriers of drugs.

Albumin transport proteins circulate in the blood and are protected from degradation by interaction with the neonatal Fc receptor. Andersen et al. investigate the albumin binding site of the neonatal Fc receptor and find pH sensitive ionic networks at the binding interface.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Clinical impact of serum proteins on drug delivery

Among serum proteins albumin and transferrin have attracted the most interest as drug carriers in the past two decades. Prior to that, their potential use was overshadowed by the advent of monoclonal antibodies that was initiated by Milstein and Koehler in 1975. Meanwhile intensive pursuit of exploiting transferrin, but above all albumin as an exogenous or endogenous carrier protein for treating various diseases, primarily cancer, rheumatoid arthritis, diabetes and hepatitis has resulted in several marketed products and numerous clinical trials. While the use of transferrin has clinically been primarily restricted to immunotoxins, albumin-based drug delivery systems ranging from albumin drug nanoparticles, albumin fusion protein, prodrugs and peptide derivatives that bind covalently to albumin as well as physically binding antibody fragments and therapeutically active peptides are in advanced clinical trials or approved products. For treating diabetes, Levemir and Victoza that are myristic acid derivatives of human insulin or glucagon-like peptide 1 (GLP-1) act as long-acting peptides by binding to the fatty acid binding sites on circulating albumin to control glucose levels. Levemir from Novo Nordisk has already developed into a blockbuster since its market approval in 2004. Abraxane, an albumin paclitaxel nanoparticle as a water-soluble galenic formulation avoiding the use of cremophor/ethanol, transports paclitaxel through passive targeting as an albumin paclitaxel complex to the tumor site and is superior to conventional Taxol against metastatic breast cancer. INNO-206, an albumin-binding doxorubicin prodrug that also accumulates in solid tumors due to the enhanced permeability and retention (EPR) effect but releases the parent drug through acid cleavage, either intra- or extracellularly, is entering phase II studies against sarcoma. An expanding field is the use of albumin-binding antibody moieties which do not contain the fragment crystallizable (Fc) portion of, conventional immunoglobulin G (IgG) but are comprised of monovalent or bivalent light and/or heavy chains and incorporate an additional albumin-binding peptide or antibody domain. The most advanced antibody of this kind is ATN-103 (Ozoralizumab), a trivalent albumin-binding nanobody that neutralizes the pro-inflammatory tumor necrosis factor alpha (TNF-α) as a causative agent for exacerbating rheumatoid arthritis. ATN-103 is currently in multi-center phase II trials against this debilitating disease. In summary, because albumin as the most abundant circulating protein cannot only be used to improve the pharmacokinetic profile of therapeutically relevant peptides and the targeting moiety of antibodies but also for peptide-based targeting as well as low-molecular weight drugs to inflamed or malignant tissue, it is anticipated that R&D efforts of academia and the pharmaceutical industry in this field of drug delivery will prosper.

SPARC Expression Correlates with Tumor Response to Albumin-Bound Paclitaxel in Head and Neck Cancer Patients

SPARC up-regulation is a poor prognostic factor in head and neck cancer. It was hypothesized that because of a SPARC-albumin interaction, tumoral SPARC facilitates the accumulation of albumin in the tumor and increases the effectiveness of albumin-bound paclitaxel (nab-paclitaxel). This hypothesis was tested by correlating the response to nab-paclitaxel and SPARC tumor expression in a retrospective analysis of a 60-patient clinical study of nab-paclitaxel as monotherapy against head and neck cancer. Sixteen tumor specimens were available for analysis. There were 11 responders (CR/PR) and 5 nonresponders (SD/PD) among the 16 nab-paclitaxel-treated patients (12/16 SPARC-positive, 75%). Response to nab-paclitaxel was higher for SPARC-positive patients (10/12, 83%) than SPARC-negative patients (1/4, 25%). The SPARC-negative patients exhibited significantly lower response than the overall response rate among all 60 patients (1/4, 25% vs 45/60, 75%). Although preliminary, data are supportive of the hypothesis that SPARC overexpression may correlate with response to nab-paclitaxel. If confirmed in larger studies, treatment with nab-paclitaxel may convert a poor prognosis SPARC-positive patient population into a group with better clinical outcomes.

Albumin binding ligands and albumin conjugate uptake by cancer cells

The scope of this short review is to summarise the knowledge gleaned from the fate of drugs transported by albumin upon contact with the target cancer cell or cells in inflamed tissues. The authors expertise covers covalently bound drugs and their cellular uptake and release from albumin. This review therefore aims to deduce what will happen to drugs such as insulin detemir which is considered to bind non-covalently to albumin and may have a fate similar to fatty acids transported by albumin.

Preparation, characterization and in vivo assessment of Gd-albumin and Gd-dendrimer conjugates as intravascular contrast-enhancing agents for MRI

We report in vivo and in vitro MRI properties of six gadolinium-dendrimer and gadolinium-albumin conjugates of derivatized acyclic diethylenetriamine-N,N',N',N″, N″-pentaacetic acid (1B4M) and macrocyclic 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid (C-DOTA). The three albumin-based agents have comparable protein to chelate ratios (1:16-18) as well as molar relaxivity (8.8-10.4 mM(-1) s(-1)). The three dendrimer based agents have blood clearance half-lives ranging from 17 to 66 min while that of the three albumin-based agents are comparable to one another (40-47 min). The dynamic image obtained from use of the albumin conjugate based on the macrocycle (C-DOTA) showed a higher contrast compared to the remaining two albumin based agents. Our conclusion from all of the results is that the macrocyclic-based (DOTA) agents are more suitable than the acyclic-based (1B4M) agent for in vivo use based on their MRI properties combined with the kinetic inertness property associated with the more stable Gd(III) DOTA complex.

Magnitude of enhanced permeability and retention effect in tumors with different phenotypes: 89Zr-albumin as a model system

Targeted nanoparticle-based technologies show increasing prevalence in radiotracer design. As a consequence, quantitative contribution of nonspecific accumulation in the target tissue, mainly governed by the enhanced permeability and retention (EPR) effect, becomes highly relevant for evaluating the specificity of these new agents. This study investigated the influence of different tumor phenotypes on the EPR effect, hypothesizing that a baseline level of uptake must be exceeded to visualize high and specific uptake of a targeted macromolecular radiotracer.

METHODS

These preliminary studies use (89)Zr-labeled mouse serum albumin ((89)Zr-desferrioxamine-mAlb) as a model radiotracer to assess uptake and retention in 3 xenograft models of human prostate cancer (CWR22rv1, DU-145, and PC-3). Experiments include PET and contrast-enhanced ultrasound imaging to assess morphology, vascularization, and radiotracer uptake; temporal ex vivo biodistribution studies to quantify radiotracer uptake over time; and histologic and autoradiographic studies to evaluate the intra- and intertumoral distribution of (89)Zr-desferrioxamine-mAlb.

RESULTS

Early uptake profiles show statistically significant but overall small differences in radiotracer uptake between different tumor phenotypes. By 20 h, nonspecific radiotracer uptake was found to be independent of tumor size and phenotype, reaching at least 5.0 percentage injected dose per gram in all 3 tumor models.

CONCLUSION

These studies suggest that minimal differences in tumor uptake exist at early time points, dependent on the tumor type. However, these differences equalize over time, reaching around 5.0 percentage injected dose per gram at 20 h after injection. These data provide strong support for the introduction of mandatory experimental controls of future macromolecular or nanoparticle-based drugs, particularly regarding the development of targeted radiotracers.

Perspectives on the mesenchymal origin of metastatic cancer

Emerging evidence suggests that many metastatic cancers arise from cells of the myeloid/macrophage lineage regardless of the primary tissue of origin. A myeloid origin of metastatic cancer stands apart from origins involving clonal evolution or epithelial-mesenchymal transitions. Evidence is reviewed demonstrating that numerous human cancers express multiple properties of macrophages including phagocytosis, fusogenicity, and gene/protein expression. It is unlikely that the macrophage properties expressed in metastatic cancers arise from sporadic random mutations in epithelial cells, but rather from damage to an already existing mesenchymal cell, e.g., a myeloid/macrophage-type cell. Such cells would naturally embody the capacity to express the multiple behaviors of metastatic cells. The view of metastasis as a myeloid/macrophage disease will impact future cancer research and anti-metastatic therapies.

Serum proteins as drug carriers of anticancer agents: a review

Targeted delivery of anticancer drugs is one of the most actively pursued goals in anticancer chemotherapy. Serum proteins such as transferrin, albumin, and low-density lipoprotein (LDL) offer promise for the selective delivery of antineoplastic agents due to their accumulation in tumor tissue. Uptake of these proteins in solid tumors is mediated by a number of factors, including an increased metabolic activity of tumors, an enhanced vascular permeability of tumor blood vessels for circulating macromolecules, and a lack of a functional lymphatic drainage system in tumor tissue. At the tumor site, transferrin, low-density lipoprotein, and albumin are taken up by the tumor cell through receptor-mediated and fluid phase endocytosis, respectively. Serum protein conjugates can be designed to release the bound antitumor drug after cellular uptake of the drug conjugate. This review covers the diagnostic evidence for tumor accumulation of serum proteins and the design, development, and biological evaluation of drug conjugates with transferrin, albumin, and low-density lipoprotein.

Review of Neurosurgical Fluorescence Imaging Methodologies

Fluorescence imaging in neurosurgery has a long historical development, with several different biomarkers and biochemical agents being used, and several technological approaches. This review focuses on the different contrast agents, summarizing endogenous fluorescence, exogenously stimulated fluorescence and exogenous contrast agents, and then on tools used for imaging. It ends with a summary of key clinical trials that lead to consensus studies. The practical utility of protoporphyrin IX (PpIX) as stimulated by administration of δ-aminolevulinic acid (ALA) has had substantial pilot clinical studies and basic science research completed. Recently multi-center clinical trials using PpIx fluorescence to guide resection have shown efficacy for improved short term survival. Exogenous agents are being developed and tested pre-clinically, and hopefully hold the potential for long term survival benefit if they provide additional capabilities for resection of micro-invasive disease or certain tumor sub-types that do not produce PpIX or help delineate low grade tumors. The range of technologies used for measurement and imaging ranges widely, with most clinical trials being carried out with either point probes or modified surgical microscopes. At this point in time, optimized probe approaches are showing efficacy in clinical trials, and fully commercialized imaging systems are emerging, which will clearly help lead to adoption into neurosurgical practice.

Intraoperative fluorescence staining of malignant brain tumors using 5-aminofluorescein-labeled albumin

OBJECTIVE

The newly developed conjugate 5-aminofluorescein (AFL)-human serum albumin (HSA) was investigated in a clinical trial for fluorescence-guided surgery of malignant brain tumors to assess its efficacy and tolerability.

METHODS

AFL, covalently linked to human serum albumin at a molar ratio of 1:1, was administered intravenously 0.5 to 4 days before surgery at 0.5 or 1.0 mg/kg of body weight to 13 patients aged 38 to 71 years who were suspected of having malignant gliomas. Fluorescence guidance using a 488-nm argon laser was performed during surgery at will. The extent of tumor resection was verified by early postoperative magnetic resonance imaging. Fluorescent and nonfluorescent samples were collected for neuropathology. Blood samples for laboratory and pharmacokinetic analyses were taken over the course of 4 weeks.

RESULTS

Fluorescence staining of tumor tissue was bright in 11 patients (84%), resulting in complete resection of fluorescent tumor tissue in 9 patients (69%). In 2 patients, residual fluorescent tumor tissue was also confirmed by magnetic resonance imaging. Neither bleaching nor penetration of AFL-HSA into the surrounding brain edema or into necrotic tissue was seen. The agreement between fluorescence and histopathology in tumor samples and samples of the tumor border was 83.3%. There were no toxic side effects. The quality of fluorescence was independent of the dose administered. The optimal time for surgery is between 1 and 4 days after AFL-HSA administration.

CONCLUSION

Tumor fluorescence using AFL-HSA made fluorescence-guided brain tumor resection possible, demonstrating that albumin is a suitable carrier system for selective targeting of aminofluorescein into malignant gliomas.