Enhanced albumin uptake by rat tumors

Albumin-conjugated flumethasone for targeting and normalization of pancreatic stellate cells

The tumor microenvironment (TME) plays a critical role in the poor clinical outlook for pancreatic ductal adenocarcinoma (PDAC). Activated pancreatic stellate cells (PSC) drive the complex interactions within the TME, resulting in a microenvironment that is resistant to chemotherapy and tolerant to the immune system, thereby promoting tumor growth. Effective deactivation of PSC is vital in treating pancreatic cancer. However, previous studies have only focused on limited changes in PSC phenotype without comprehensively analysing their overall function. Our transcriptome analysis identified agents capable of modulating multiple biological functions of PSC, including fibrosis, extracellular matrix generation, and the secretion of cytokines and immune factors. Through this comprehensive assessment, we discovered that flumethasone (Flu) effectively deactivates PSC. This glucocorticoid analogue remodels the tumor microenvironment by regulating the secretomes of PSC and their interaction with tumor cells. Additionally, our research revealed that activated PSC exhibited heightened albumin endocytosis. As a result, we propose that albumin conjugation could serve as an effective targeted drug delivery approach for PSC. Our findings also demonstrate that albumin-conjugated Flu maintained reprogramming capabilities in stromal cells, and enhanced the efficacy of chemotherapy in orthotopic mouse models of PDAC and KrasG12D/+; LSL-Trp53R172H/+; Pdx-1-Cre (KPC) pancreatic tumor allograft mouse model. Our investigation into the mechanism of PSC deactivation by flumethasone has revealed its potential for clinical cancer treatment through its effects on the tumor microenvironment. Furthermore, the conjugation of flumethasone to albumin enhances its safety and targeted delivery, offering a promising approach for PSC-targeted drug application in pancreatic cancer treatment.

Design, optimization, and evaluation of methotrexate loaded and albumin coated polymeric nanoparticles

Methotrexate is a potent anticancer drug whose strong efflux is facilitated by the brain's efflux transporter. As an efflux transporter blocker, albumin increased the drug's concentration in the brain. Methotrexate-loaded nanoparticles were produced by evaporating the emulsification fluid. Improvements and analyses were made to the following aspects of the generated nanoparticles: size, polydispersity, zeta potential, entrapment efficiency, percentage yield, scanning electron microscopy, in vitro drug release studies, and sterilization. The particle size was determined to be in the nano range, and homogeneity of particle size was suggested by a low polydispersity index result. Particle diameters of 168 nm were observed in the F5 preparation, and zeta potential values of -1.5 mV suggested that the preparation produced adequate repulsive interactions between the nanoparticles. Albumin and dopamine HCl were employed to coat the methotrexate-loaded nanoparticles to guarantee that the brain received an adequate amount of them. The homogeneity of albumin coated nanoparticles was demonstrated by the low% PDI values of 0.129 and 0.122 for albumin coated nanoparticles (MNPs-Alb) and polymerized dopamine HCl and albumin coated nanoparticles (MNPs-PMD-Alb), respectively. After 48 h of incubation, the cell viability measured at the same drug concentration (5 mg) decreased for the F5, albumin coated nanoparticles, polymerized dopamine HCl coated nanoparticles, and polymerized dopamine HCl and albumin coated nanoparticles, respectively. Our primary findings demonstrate that the albumin nanoparticles containing methotrexate are designed to deliver the drug gradually. With minimal cytotoxicity, the intended preparation might give the brain an appropriate dosage of methotrexate.

Cathepsin B Processing Is Required for the In Vivo Efficacy of Albumin-Drug Conjugates

Targeted drug delivery approaches that selectively and preferentially deliver therapeutic agents to specific tissues are of great interest for safer and more effective pharmaceutical treatments. We investigated whether cathepsin B cleavage of a valine-citrulline [VC(S)]-containing linker is required for the release of monomethyl auristatin E (MMAE) from albumin-drug conjugates. In this study, we used an engineered version of human serum albumin, Veltis High Binder II (HBII), which has enhanced binding to the neonatal Fc (fragment crystallizable) receptor (FcRn) to improve drug release upon binding and FcRn-mediated recycling. The linker-payload was conjugated to cysteine 34 of albumin using a carbonylacrylic (caa) reagent which produced homogeneous and plasma stable conjugates that retained FcRn binding. Two caa-linker-MMAE reagents were synthesized─one with a cleavable [VC(S)] linker and one with a noncleavable [VC(R)] linker─to question whether protease-mediated cleavage is needed for MMAE release. Our findings demonstrate that cathepsin B is required to achieve efficient and selective antitumor activity. The conjugates equipped with the cleavable [VC(S)] linker had potent antitumor activity in vivo facilitated by the release of free MMAE upon FcRn binding and internalization. In addition to the pronounced antitumor activity of the albumin conjugates in vivo, we also demonstrated their preferable tumor biodistribution and biocompatibility with no associated toxicity or side effects. These results suggest that the use of engineered albumins with high FcRn binding combined with protease cleavable linkers is an efficient strategy to target delivery of drugs to solid tumors.

Structural optimization of siRNA conjugates for albumin binding achieves effective MCL1-directed cancer therapy

The high potential of siRNAs to silence oncogenic drivers remains largely untapped due to the challenges of tumor cell delivery. Here, divalent lipid-conjugated siRNAs are optimized for in situ binding to albumin to improve pharmacokinetics and tumor delivery. Systematic variation of the siRNA conjugate structure reveals that the location of the linker branching site dictates tendency toward albumin association versus self-assembly, while the lipid hydrophobicity and reversibility of albumin binding also contribute to siRNA intracellular delivery. The lead structure increases tumor siRNA accumulation 12-fold in orthotopic triple negative breast cancer (TNBC) tumors over the parent siRNA. This structure achieves approximately 80% silencing of the anti-apoptotic oncogene MCL1 and yields better survival outcomes in three TNBC models than an MCL-1 small molecule inhibitor. These studies provide new structure-function insights on siRNA-lipid conjugate structures that are intravenously injected, associate in situ with serum albumin, and improve pharmacokinetics and tumor treatment efficacy.

Recent Advancements and Strategies for Overcoming the Blood-Brain Barrier Using Albumin-Based Drug Delivery Systems to Treat Brain Cancer, with a Focus on Glioblastoma

Glioblastoma multiforme (GBM) is a highly aggressive malignant tumor, and the most prevalent primary malignant tumor affecting the brain and central nervous system. Recent research indicates that the genetic profile of GBM makes it resistant to drugs and radiation. However, the main obstacle in treating GBM is transporting drugs through the blood-brain barrier (BBB). Albumin is a versatile biomaterial for the synthesis of nanoparticles. The efficiency of albumin-based delivery systems is determined by their ability to improve tumor targeting and accumulation. In this review, we will discuss the prevalence of human glioblastoma and the currently adopted treatment, as well as the structure and some essential functions of the BBB, to transport drugs through this barrier. We will also mention some aspects related to the blood-tumor brain barrier (BTBB) that lead to poor treatment efficacy. The properties and structure of serum albumin were highlighted, such as its role in targeting brain tumors, as well as the progress made until now regarding the techniques for obtaining albumin nanoparticles and their functionalization, in order to overcome the BBB and treat cancer, especially human glioblastoma. The albumin drug delivery nanosystems mentioned in this paper have improved properties and can overcome the BBB to target brain tumors.

Gold Complexes in Anticancer Therapy: From New Design Principles to Particle-Based Delivery Systems

The discovery of the medicinal properties of gold complexes has fuelled the design and synthesis of new anticancer metallodrugs, which have received special attention due to their unique modes of action. Current research in the development of gold compounds with therapeutic properties is predominantly focused on the molecular design of drug leads with superior pharmacological activities, e.g., by introducing targeting features. Moreover, intensive research aims at improving the physicochemical properties of gold compounds, such as chemical stability and solubility in the physiological environment. In this regard, the encapsulation of gold compounds in nanocarriers or their chemical grafting onto targeted delivery vectors could lead to new nanomedicines that eventually reach clinical applications. Herein, we provide an overview of the state-of-the-art progress of gold anticancer compounds, andmore importantly we thoroughly revise the development of nanoparticle-based delivery systems for gold chemotherapeutics.

Structural Optimization of siRNA Conjugates for Albumin Binding Achieves Effective MCL1-Targeted Cancer Therapy

The high potential for therapeutic application of siRNAs to silence traditionally undruggable oncogenic drivers remains largely untapped due to the challenges of tumor cell delivery. Here, siRNAs were optimized for in situ binding to albumin through C18 lipid modifications to improve pharmacokinetics and tumor delivery. Systematic variation of siRNA conjugates revealed a lead structure with divalent C18 lipids each linked through three repeats of hexaethylene glycol connected by phosphorothioate bonds. Importantly, we discovered that locating the branch site of the divalent lipid structure proximally (adjacent to the RNA) rather than at a more distal site (after the linker segment) promotes association with albumin, while minimizing self-assembly and lipoprotein association. Comparison to higher albumin affinity (diacid) lipid variants and siRNA directly conjugated to albumin underscored the importance of conjugate hydrophobicity and reversibility of albumin binding for siRNA delivery and bioactivity in tumors. The lead conjugate increased tumor siRNA accumulation 12-fold in orthotopic mouse models of triple negative breast cancer over the parent siRNA. When applied for silencing of the anti-apoptotic oncogene MCL-1, this structure achieved approximately 80% MCL1 silencing in orthotopic breast tumors. Furthermore, application of the lead conjugate structure to target MCL1 yielded better survival outcomes in three independent, orthotopic, triple negative breast cancer models than an MCL1 small molecule inhibitor. These studies provide new structure-function insights on optimally leveraging siRNA-lipid conjugate structures that associate in situ with plasma albumin for molecular-targeted cancer therapy.

Octyl syringate is preferentially cytotoxic to cancer cells via lysosomal membrane permeabilization and autophagic flux inhibition

The autophagy-mediated lysosomal pathway plays an important role in conferring stress tolerance to tumor cells during cellular stress such as increased metabolic demands. Thus, targeted disruption of this function and inducing lysosomal cell death have been proved to be a useful cancer therapeutic approach. In this study, we reported that octyl syringate (OS), a novel phenolic derivate, was preferentially cytotoxic to various cancer cells but was significantly less cytotoxic to non-transformed cells. Treatment with OS resulted in non-apoptotic cell death in a caspase-independent manner. Notably, OS not only enhanced accumulation of autophagic substrates, including lapidated LC3 and sequestosome-1, but also inhibited their degradation via an autophagic flux. In addition, OS destabilized the lysosomal function, followed by the intracellular accumulation of the non-digestive autophagic substrates such as bovine serum albumin and stress granules. Furthermore, OS triggered the release of lysosomal enzymes into the cytoplasm that contributed to OS-induced non-apoptotic cell death. Finally, we demonstrated that OS was well tolerated and reduced tumor growth in mouse xenograft models. Taken together, our study identifies OS as a novel anticancer agent that induces lysosomal destabilization and subsequently inhibits autophagic flux and further supports development of OS as a lysosome-targeting compound in cancer therapy. • Octyl syringate, a phenolic derivate, is preferentially cytotoxic to various cancer cells. • Octyl syringate destabilizes the lysosomal function. • Octyl syringate blocks the autophagic flux. • Octyl syringate is a potential candidate compound for cancer therapy.

Harnessing molecular recognition for localized drug delivery

A grand challenge in drug delivery is providing the right dose, at the right anatomic location, for the right duration of time to maximize therapeutic efficacy while minimizing off-target toxicity and other deleterious side-effects. Two general modalities are receiving broad attention for localized drug delivery. In the first, referred to as "targeted accumulation", drugs or drug carriers are engineered to have targeting moieties that promote their accumulation at a specific tissue site from circulation. In the second, referred to as "local anchoring", drugs or drug carriers are inserted directly into the tissue site of interest where they persist for a specified duration of time. This review surveys recent advances in harnessing molecular recognition between proteins, peptides, nucleic acids, lipids, and carbohydrates to mediate targeted accumulation and local anchoring of drugs and drug carriers.

Interaction of Lipoplex with Albumin Enhances Gene Expression in Hepatitis Mice

Understanding the in vivo fate of lipoplex, which is composed of cationic liposomes and DNA, is an important issue toward gene therapy. In disease conditions, the fate of lipoplex might change compared with the normal condition. Here, we examined the contribution of interaction with serum components to in vivo transfection using lipoplex in hepatitis mice. Prior to administration, lipoplex was incubated with serum or albumin. In the liver, the interaction with albumin enhanced gene expression in hepatitis mice, while in the lung, the interaction with serum or albumin enhanced it. In normal mice, the interaction with albumin did not enhance hepatic and pulmonary gene expression. Furthermore, hepatic and pulmonary gene expression levels of albumin-interacted lipoplex were correlated with serum transaminases in hepatitis mice. The albumin interaction increased the hepatic accumulation of lipoplex and serum tumor necrosis factor-α level. We suggest that the interaction with albumin enhanced the inflammation level after the administration of lipoplex in hepatitis mice. Consequently, the enhancement of the inflammation level might enhance the gene expression level. Information obtained in the current study will be valuable toward future clinical application of the lipoplex.

Development of a Novel Imaging Agent for Determining Albumin Uptake in Solid Tumors

Purpose

The purpose of this study was to investigate the albumin-binding compound ¹¹¹In-C4-DTPA as an imaging agent for the detection of endogenous albumin accumulation in tumors.

Methods

¹¹¹In-C4-DTPA was injected in healthy nude mice for pharmacokinetic and biodistribution studies (10 min, 1, 6, 24, and 48 h, n = 4) and subsequently in tumor-bearing mice for single-photon emission computed tomography/X-ray-computed tomography (SPECT/CT) imaging studies. Four different human tumor xenograft models (LXFL529, OVXF899, MAXFTN401, and CXF2081) were implanted subcutaneously unilaterally or bilaterally (n = 4-8). After intravenous administration of ¹¹¹In-C4-DTPA, SPECT/CT images were collected over 72 h at 4-6 time points. Additionally, gamma counting was performed for the blood, plasma, lungs, heart, liver, spleen, kidneys, muscle, and tumors at 72 h post-injection.

Results

¹¹¹In-C4-DTPA bound rapidly to circulating albumin upon injection, and the radiolabeled albumin conjugate thus formed was stable in murine and human serum. SPECT/CT images demonstrated a time-dependent uptake with a maximum of 2.7-3.8% ID/cm³ in the tumors at approximately 24 h post-injection and mean tumor/muscle ratios in the range of 3.2-6.2 between 24 and 72 h post-injection. The kidneys and bladder were the predominant elimination organs. Gamma counting at 72 h post-injection showed 1.3-2.5% ID/g in the tumors and mean tumor/muscle ratios in the range of 4.9-9.4.

Conclusion

¹¹¹In-C4-DTPA bound rapidly to circulating albumin upon injection and showed time-dependent uptake in the tumors demonstrating a potential for clinical application as a companion imaging diagnostic for albumin-binding anticancer drugs.

The nanoparticle-facilitated autophagy inhibition of cancer stem cells for improved chemotherapeutic effects on glioblastomas

Paclitaxel (PTX) and chloroquine (CQ) loaded bovine serum albumin (BSA) nanoparticles can achieve efficient glioma therapyviaautophagy inhibition.

Synthesis and Biological Evaluation of Homogeneous Thiol-Linked NHC*-Au-Albumin and -Trastuzumab Bioconjugates

Targeted delivery of potent cytotoxic drugs to cancer cells minimizes systemic toxicity and several side effects. NHC*-Au-Cl has already been proven to be a potent anticancer agent. In this study, we explore a strategy based on chemoselective cysteine conjugation of NHC*-Au-Cl to albumin and trastuzumab (Thiomab LC-V205C) to potentiate drug-ligand ratio, pharmacokinetics, as well as drug efficacy and safety. This strategy is a step forward towards the use of gold-based anticancer agents as targeted therapies.

Roles of Albumin-Binding Proteins in Cancer Progression and Biomimetic Targeted Drug Delivery

Nutrient transporters have attracted significant attention for their promising application in biomimetic delivery. Due to the active consumption of nutrients, cancer cells generally overexpress nutrient transporters to meet their increased need for energy and materials. For example, albumin-binding proteins (ABPs) are highly overexpressed in malignant cells, stromal cells, and tumor vessel endothelial cells responsible for albumin uptake. ABP (e.g., SPARC) is a promising target for tumor-specific drug delivery, and albumin has been widely used as a biomimetic delivery carrier. Apart from the transportation function, ABPs are closely associated with neoplasia, invasion, and metastasis. Herein, a summary of the roles of ABP in cancer progression and the application of albumin-based biomimetic tumor-targeted delivery through the ABP pathway is presented.

Learning from nature: the role of albumin in drug delivery

Graphical Abstract

[Formula: see text]

Curcumin/sunitinib co-loaded BSA-stabilized SPIOs for synergistic combination therapy for breast cancer

Curcumin/sunitinib co-loaded BSA-SPIOs exhibited unparalleled properties in both in vivo MR imaging and tumor therapy as a promising theranostic material.

Catabolism of (64)Cu and Cy5.5-labeled human serum albumin in a tumor xenograft model

Human serum albumin (HSA), the most abundant protein in blood plasma, has been used as a drug carrier for the last few decades. Residualizingly radiolabeled serum albumin has been reported to be avidly taken up by tumors of sarcoma-bearing mice and to most likely undergo lysosomal degradation. In this study, we prepared (64)Cu-1,4,7,10-tetraazacyclododecane-N,N',N″,N'″-tetraacetic acid (DOTA) and Cy5.5-conjugated HSA (dual probe), and evaluated its tumor uptake and catabolism. Two dual probes were prepared using different DOTA conjugation sites of HSA (one via Lys residues and the other via the Cys residue). (64)Cu-DOTA-Lys-HSA-Cy5.5 (dual probe-Lys) exhibited higher uptake by RR1022 sarcoma cells in vitro than (64)Cu-DOTA-Cys-HSA-Cy5.5 (dual probe-Cys). In RR1022 tumor-bearing mice, the two dual probes showed a similar level of tumor uptake, but uptake of dual probe-Lys was reduced in the liver and spleen compared to dual probe-Cys, probably because of the presence of a higher number of DOTA molecules in the former. At 24 and 48 h after injection, dual probe-Lys was intact or partially degraded in blood, liver, kidney, and tumor samples, but (64)Cu-DOTA-Lys was observed in the urine using radioactivity detection. Similarly, Cy5.5-Lys was observed in the urine using fluorescence detection. These results indicate that dual probe-Lys may be useful for predicting the catabolic fate of drug-HSA conjugates.

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.

Co-opting biology to deliver drugs

The goal of drug delivery is to improve the safety and therapeutic efficacy of drugs. This review focuses on delivery platforms that are either derived from endogenous pathways, long-circulating biomolecules and cells or that piggyback onto long-circulating biomolecules and cells. The first class of such platforms is protein-based delivery systems--albumin, transferrin, and fusion to the Fc domain of antibodies--that have a long-circulation half-life and are designed to transport different molecules. The second class is lipid-based delivery systems-lipoproteins and exosomes-that are naturally occurring circulating lipid particles. The third class is cell-based delivery systems--erythrocytes, macrophages, and platelets--that have evolved, for reasons central to their function, to exhibit a long life-time in the body. The last class is small molecule-based delivery systems that include folic acid. This article reviews the biology of these systems, their application in drug delivery, and the promises and limitations of these endogenous systems for drug delivery.

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.

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.

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.

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.

Synthesis, pharmacoscintigraphic evaluation and antitumor efficacy of methotrexate-loaded, folate-conjugated, stealth albumin nanoparticles

Aim: The present study aims to develop a multifunctional nanoformulation based on technetium-99m labeled, folate conjugated, methotrexate-loaded human serum albumin nanoparticles (HSA NPs) and explore their potential in cancer theragnostics. Materials & Methods: Methotrexate-loaded HSA NPs were synthesized by a reverse microemulsion technique, followed by chemical crosslinking with glutaraldehyde. These NPs were conjugated with folic acid (FA) through a hydrophilic polyethylene glycol spacer to render them long-circulatory and augment their tumor-specific localization. The therapeutic conjugate was further radiolabeled with a γ-emitter technetium-99m for real-time monitoring of its blood clearance kinetics and biodistribution through the measurement of blood/organ-associated radioactivity and scintigraphic imaging. Results & Conclusion: In vitro cell-uptake and cytotoxicity studies corroborated that FA conjugation enabled these NPs to specifically target and kill folate-receptor overexpressing cancer cells via S phase arrest. Blood clearance kinetics and biodistribution studies clearly indicated that circulation time, as well as tumor-specific localization of methotrexate-loaded HSA nanocarriers, could be significantly augmented upon polyethylene glycolylation and conjugation of FA. Finally, we demonstrated that these targeted HSA NPs inhibited tumor growth more effectively, as compared with the nontargeted controls.

Original submitted: 16/11/2010; Revised submitted: 21/02/2011

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.

A novel D-glyceraldehyde-3-phosphate binding protein, a truncated albumin, with D-glyceraldehyde-3-phosphate dehydrogenase inhibitory property

We have purified a novel protein from mice muscle, which through N-terminal amino acid sequencing was identified as a truncated form of mouse albumin. The protein was found to be a monomer of approximately 64 kDa and located in the cytosol. The purified protein strongly crossreacted with commercial albumin antibody. Presence of this protein was observed in different mouse organs. Further biochemical studies as well as CD spectroscopy indicated that the protein binds D-glyceraldehyde-3-phosphate limiting the availability of the substrate to the enzyme D-glyceraldehyde-3-phosphate dehydrogenase, thereby inhibiting its catalytic activity. The implication of this protein in the control of glycolysis has been discussed.

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.

The role of extracellular factors in human metastatic chordoma cell growth in vitro

STUDY DESIGN

Human metastatic chordoma cells were isolated, and initial in vitro characterization was performed. Biochemical and physiologic changes were observed in response to pH, oxygen, and glucose.

OBJECTIVE

The extracellular microenvironment directly affects metastatic chordoma cell phenotype in vitro.

SUMMARY OF BACKGROUND DATA

Chordomas are primary bone tumors that usually occur in the spine or skull. Chordomas arise from embryonic notochordal remnants along the axial skeleton, most commonly the sacrum, followed by the base of the skull and the mobile spine. Due to a high degree of resistance to radiation and chemotherapy, chordomas eventually cause death by direct growth or by metastasizing to other organs.

METHODS

Extracellular pH, oxygen, and glucose levels in the culture medium were controlled, and cell response was assessed using MTT staining, SDS-PAGE, Western blotting, tandem mass spectrometry, TUNEL, immunofluorescence, and flow cytometry.

RESULTS

In this study, we present a new chordoma cell line established from metastatic tissue and novel data characterizing some aspects of chordoma cell phenotype in different conditions in vitro. Chordoma biologic markers were expressed in the new cell line. Alkaline pH dramatically increased intracellular protein tyrosine phosphorylation, metabolic activity, and albumin accumulation in the cells, while acidic pH caused apoptosis.

CONCLUSION

The level of proliferation, apoptosis, and tyrosine phosphorylation, as well as the overall protein expression profile, strongly depended on extracellular media pH and oxygen/glucose levels. Chordoma's preferred extracellular microenvironment in vitro was rather alkaline, with an optimum at pH 8.5, and apoptotic changes were induced at acidic pH. We found that bovine serum albumin was accumulated by chordoma cells from the incubation media, and this accumulation depended on extracellular pH, with the highest accumulation at alkaline pH.

Imaging tumors with an albumin-binding Fab, a novel tumor-targeting agent

Association with albumin as a means to improve biodistribution and tumor deposition of a Fab was investigated using AB.Fab4D5, a bifunctional molecule derived from trastuzumab (HERCEPTIN) capable of binding albumin and tumor antigen HER2 (erbB2) simultaneously. AB.Fab4D5 was compared with trastuzumab and a trastuzumab-derived Fab (Fab4D5) for the ability to target tumors overexpressing HER2 in mouse mammary tumor virus/HER2 allograft models. Biodistribution was monitored using intravital microscopy, histology, and integrated single-photon emission computed tomography/computed tomography analysis. Fab4D5 tumor deposition was characterized by rapid but transient appearance in tumor at 2 h with little retention, followed by rapid accumulation in kidney by 6 h. Trastuzumab was slow to accumulate in tumors and slow to clear from normal tissues, although significant tumor deposition was achieved by 24 h. In contrast, AB.Fab4D5 was observed at 2 h in tumor and its presence was sustained beyond 24 h similar to trastuzumab. Intravital microscopy revealed that at peak tumor accumulation, tumor cell staining by AB.Fab4D5 was more uniform than for Fab4D5 or trastuzumab. Similar tumor deposition was achieved for both AB.Fab4D5 and trastuzumab at 48 h (35.9 +/- 1.8% and 38.2 +/- 3.1% injected dose/g); however, AB.Fab4D5 targeted tumors more rapidly and quickly cleared from blood, leading to a lower overall normal tissue exposure. Importantly, unlike Fab4D5, AB.Fab4D5 did not accumulate in kidney, suggesting that association with albumin leads to an altered route of clearance and metabolism. Rapid targeting, excellent tumor deposition and retention, coupled with high tumor to blood ratios may make AB.Fab an exceptional molecule for imaging and cancer therapy.

Phase II study of MTX-HSA in combination with Cisplatin as first line treatment in patients with advanced or metastatic transitional cell carcinoma

PURPOSE

To assess the efficacy, tolerability and safety of MTX-HSA (methotrexate (MTX) covalently linked to human serum albumin (HSA)) combined with cisplatin as first line therapy for advanced bladder cancer.

METHODS

Patients (pat) were treated with a loading dose of 110 mg/m(2) of MTX-HSA followed by a weekly dose of 40 mg/m(2) starting on day 8. Cisplatin was given on day 2 of each 28 day cycle at a dose of 75 mg/m(2).

RESULTS

Tumor response evaluation was possible in 7 patients. Complete response (CR) and partial response (PR) was observed in 1 patient each (overall response rate: 29%). Key toxicities included CTC Grade (G) 3/4 stomatitis in 6 patients, vomiting G3 in 1 patient, fatigue G3 in 1 patient and thrombocytopenia G3 in 3 patients.

CONCLUSION

The combination of MTX-HSA with cisplatin is feasible and shows antitumor activity against urothelial carcinomas combined with an acceptable toxicity profile.

Polymer Therapeutics: Concepts and Applications

Polymer therapeutics encompass polymer-protein conjugates, drug-polymer conjugates, and supramolecular drug-delivery systems. Numerous polymer-protein conjugates with improved stability and pharmacokinetic properties have been developed, for example, by anchoring enzymes or biologically relevant proteins to polyethylene glycol components (PEGylation). Several polymer-protein conjugates have received market approval, for example the PEGylated form of adenosine deaminase. Coupling low-molecular-weight anticancer drugs to high-molecular-weight polymers through a cleavable linker is an effective method for improving the therapeutic index of clinically established agents, and the first candidates have been evaluated in clinical trials, including, N-(2-hydroxypropyl)methacrylamide conjugates of doxorubicin, camptothecin, paclitaxel, and platinum(II) complexes. Another class of polymer therapeutics are drug-delivery systems based on well-defined multivalent and dendritic polymers. These include polyanionic polymers for the inhibition of virus attachment, polycationic complexes with DNA or RNA (polyplexes), and dendritic core-shell architectures for the encapsulation of drugs. In this Review an overview of polymer therapeutics is presented with a focus on concepts and examples that characterize the salient features of the drug-delivery systems.

Albumin-based drug delivery as novel therapeutic approach for rheumatoid arthritis

We reported recently that albumin is a suitable drug carrier for targeted delivery of methotrexate (MTX) to tumors. Due to pathophysiological conditions in neoplastic tissue, high amounts of albumin accumulate in tumors and are metabolized by malignant cells. MTX, covalently coupled to human serum albumin (MTX-HSA) for cancer treatment, is currently being evaluated in phase II clinical trials. Because synovium of patients with rheumatoid arthritis (RA) shares various features observed also in tumors, albumin-based drug targeting of inflamed joints might be an attractive therapeutic approach. Therefore, the pharmacokinetics of albumin and MTX in a mouse model of arthritis was examined. Additionally, uptake of albumin by synovial fibroblasts of RA patients and the efficacy of MTX and MTX-HSA in arthritic mice were studied. The results show that when compared with MTX, significantly higher amounts of albumin accumulate in inflamed paws, and significantly lower amounts of albumin are found in the liver and the kidneys. The protein is metabolized by human synovial fibroblasts in vitro and in vivo. MTX-HSA was significantly more effective in suppression of the onset of arthritis in mice than was MTX. In conclusion, albumin appears to be a suitable drug carrier in RA, most likely due to effects on synovial fibroblasts, which might increase therapeutic efficacy and reduce side effects of MTX.

Efficacy and tolerability of an aminopterin-albumin conjugate in tumor-bearing rats

The antifolate aminopterin (AMPT) was developed before methotrexate (MTX), but was not clinically established or generally used due its increased toxicity compared to MTX. Recently, we reported on the increased metabolism of albumin conjugates such as methotrexate-albumin (MTX-SA) in malignant tumors and the feasibility of using albumin as a carrier for drug targeting. Consequently, AMPT was covalently bound to serum albumin (AMPT-SA) at a 1:1 molar ratio. Biodistribution, tolerability and efficacy of this novel conjugate were studied in Walker-256 (W-256) carcinoma-bearing rats. As compared to native albumin, the same biodistribution and plasma clearance were found for AMPT-SA, which achieved 20.1% tumor uptake (estimated uptake per g tumor 6.4%) within 24 h after i.v. administration in rats. In a randomized study, AMPT-SA, repeatedly i.v. injected, was compared with low-molecular-weight AMPT. Depending on the molar concentration, the maximum tolerated dose (MTD) of AMPT covalently bound to SA was twice that of unbound AMPT (three repeated injections of 1.0 mg AMPT-SA/kg body weight versus three repeated injections of 0.5 mg AMPT/kg body weight; p=0.0006). Efficacy was studied at the level of the MTD and MTD/2, and demonstrated that AMPT-SA was significantly more active. At the MTD/2 in W-256 carcinoma-bearing rats, AMPT-SA achieved a 100% volume reduction and an optimal volume reduction during treatment/control (T/C) of 8.3% compared to a 53% volume reduction of AMPT and a T/C of 16.5% (p=0.032). Tumor relapses were reduced and occurred later in the AMPT-SA group (two tumor recurrences for AMPT-SA versus seven for AMPT; p=0.05). In this comparative study, the AMPT-SA conjugate showed high antitumor activity in vivo and a favorable toxicity compared to low-molecular-weight AMPT. These effects are attributed to the albumin carrier which seems to be an effective tool for selective tumor drug targeting.

In vitro and in vivo efficacy of acid-sensitive transferrin and albumin doxorubicin conjugates in a human xenograft panel and in the MDA-MB-435 mamma carcinoma model

Acid-sensitive transferrin and albumin conjugates with doxorubicin have recently been developed with the aim of circumventing the systemic toxicity and improving the therapeutic efficacy of this anticancer agent. The in vitro activity of two acid-sensitive transferrin and albumin doxorubicin conjugates and free doxorubicin was evaluated in twelve human tumour xenografts using a clonogenic assay. The inhibitory effects and the activity profile of the conjugates was, in general, comparable to that of doxorubicin (mean IC(70) -value for doxorubicin approximately 0.1 microM and 0.1 - 0.4 microM for the conjugates). Subsequently, the efficacy of an acid-sensitive transferrin and albumin doxorubicin conjugate, which both incorporated a phenylacetyl hydrazone bond as a predetermined breaking point, was evaluated in the xenograft mamma carcinoma model MDA-MB-435 in comparison to free doxorubicin (dose, i.v.: 2 x 4, 8 and 12 mg/kg). The conjugates showed significantly reduced toxicity (reduced lethality and body weight loss) with a concomitantly stable or slightly improved antitumour activity compared to free doxorubicin. At the dose of 12 mg/kg mortality was unacceptably high in the doxorubicin treated group ( approximately 80%); in contrast, no mortality was observed with the conjugate treated animals with body weight loss < 10 %. In a further experiment, therapy with the acid-sensitive doxorubicin albumin conjugate at 3 x 12 mg/kg in the MDA-MB-435 model resulted in a significantly improved antitumour activity over free doxorubicin at its optimal dose of 2 x 8 mg/kg. In conclusion, acid-sensitive transferrin and albumin doxorubicin conjugates can be administered at higher doses than free doxorubicin in nude mice models with a concomitant improvement in antitumour activity. Interestingly, there is no pronounced difference between identically constructed transferrin and albumin doxorubicin conjugates with regard to in vitro or in vivo efficacy.

Antitumor activity of methotrexate-albumin conjugates in rats bearing a Walker-256 carcinoma

We have recently reported that albumin accumulates in solid tumors and serves there as a source of nitrogen and energy. Methotrexate-albumin conjugates [MTX(I)-RSA] derivatized at a molar ratio of 1:1 differ favorably from original MTX in terms of plasma presence and tumor uptake. The purpose of this study was to evaluate the therapeutic efficacy of these novel conjugates in a comparative study with low m.w. MTX is Sprague-Dawley rats bearing a Walker-256 carcinoma. The maximum tolerated dose (MTD) for MTX and MTX(I)-RSA was determined (2 mg/kg based on MTX injected on days 1, 3 and 8). The tumor-bearing rats received injections of either the MTD or MTD/2 of MTX, MTX-albumin or mixtures containing the MTD/2 or MTD/4 of both MTX and MTX-albumin. No toxic side effects were observed. Cure rate and tumor growth retardation were slightly better for the conjugate compared with MTX alone in the MTD group (16 complete remissions vs. 14 of 20 rats). The best results were achieved for the combination treatment with MTX and MTX-albumin, with complete remission in all 20 rats. In conclusion, MTX-albumin conjugates show therapeutic activity in vivo without toxic side effects. Additive effects were observed for a combination of MTX-albumin and MTX. These effects might be caused by the much longer tumor exposition time of the conjugate in conjunction with a different route of uptake (pinocytosis for MTX-albumin vs. folate receptors for MTX).