S-Nitrosated Human Serum Albumin Dimer is not only a Novel Anti-Tumor Drug but also a Potentiator for Anti-Tumor Drugs with Augmented EPR Effects

Emerging nanotechnological approaches to regulating tumor vasculature for cancer therapy

Abnormal angiogenesis stands for one of the most striking manifestations of malignant tumor. The pathologically and structurally abnormal tumor vasculature facilitates a hostile tumor microenvironment, providing an ideal refuge exclusively for cancer cells. The emergence of vascular regulation drugs has introduced a distinctive class of therapeutics capable of influencing nutrition supply and drug delivery efficacy without the need to penetrate a series of physical barriers to reach tumor cells. Nanomedicines have been further developed for more precise regulation of tumor vasculature with the capacity of co-delivering multiple active pharmaceutical ingredients, which overall reduces the systemic toxicity and boosts the therapeutic efficacy of free drugs. Additionally, precise structure design enables the integration of specific functional motifs, such as surface-targeting ligands, droppable shells, degradable framework, or stimuli-responsive components into nanomedicines, which can improve tissue-specific accumulation, enhance tissue penetration, and realize the controlled and stimulus-triggered release of the loaded cargo. This review describes the morphological and functional characteristics of tumor blood vessels and summarizes the pivotal molecular targets commonly used in nanomedicine design, and then highlights the recent cutting-edge advancements utilizing nanotechnologies for precise regulation of tumor vasculature. Finally, the challenges and future directions of this field are discussed.

Smart Multistage "Trojan Horse"-Inspired Bovine Serum Albumin-Coated Liposomes for Enhancing Tumor Penetration and Antitumor Efficacy

Poor antitumor drug penetration into tumor tissues is a global challenge in clinical cancer treatment. Here, we reported a smart multistage "Trojan Horse"-inspired bovine serum albumin (BSA)-coated liposome (HBM), including the mimics of capsid and secondary BSA-coated polymeric nanoparticles (NPs) for enhancing tumor penetration and antitumor efficacy. These drug-loaded polymeric NPs possess a capsid-like component, a well-distributed nanostructure (size: 190.1 ± 4.98 nm, PDI: 0.259), and an excellent drug loading content (15.85 ± 1.36%). Meaningfully, after the smart multistage BSA-coated liposome targeted the tumor tissue, the mimics of capsid were "taken off" under the condition of tumor-specific enzymes, releasing "Heart" BSA-modified secondary NPs to increase the ability to penetrate tumor cells for enhancing antitumor efficacy. As expected, the HBM efficiently achieves high drug penetration into PAN02 tumor cells. Moreover, compared to free DOX and HM (HBM without BSA) NPs, DOX/HBM NPs exhibited the strongest tumor penetration and the highest cytotoxicity against PAN02 tumor cells both in vitro (IC50 = 0.141 μg/mL) and in vivo. This smart multistage "Trojan Horse"-inspired BSA-coated liposome should provide a new hathpace for further development of polymeric NPs in clinical treatment.

Spectroscopy, Structure, Biomacromolecular Interactions, and Antiproliferation Activity of a Fe(II) Complex With DPA-Bpy as Pentadentate Ligand

An Fe(II) complex with DPA-Bpy (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,20-bipyridine-6 -methanamine) as the ligand was synthesized and characterized to mimic bleomycin. The binding constants (K_b) of the complex with calf thymus DNA and human serum albumin (HSA) were quantitatively evaluated using fluorescence spectroscopy, with K_b as 5.53×10⁵ and 2.40×10⁴ M⁻¹, respectively; the number of the average binding site (n) is close to 1. The thermodynamic analyses suggested that the electrostatic interactions exist between the complex and DNA, and the hydrogen bonding and Van der Waals force exist for the complex and HSA. The Fe complex exhibits cleavage ability toward pBR322 DNA, and the crystal structure of the HSA Fe complex adduct at 2.4 Å resolution clearly shows that His288 serves as the axial ligand of the Fe center complexed with a pentadentate DPA-Bpy ligand. Furthermore, the cytotoxicity of the complex was evaluated against HeLa cells. Both the Fe complex and HSA Fe complex adduct show obvious effect on cell proliferation with an IC₅₀ of 1.18 and 0.82 μM, respectively; they induced cell apoptosis and arrested cell cycles at S phase. This study provides insight into the plausible mechanism underlying their metabolism and pharmacological activity.

Strategies to improve the EPR effect: A mechanistic perspective and clinical translation

Many efforts have been made to achieve targeted delivery of anticancer drugs to enhance their efficacy and to reduce their adverse effects. These efforts include the development of nanomedicines as they can selectively penetrate through tumor blood vessels through the enhanced permeability and retention (EPR) effect. The EPR effect was first proposed by Maeda and co-workers in 1986, and since then various types of nanoparticles have been developed to take advantage of the phenomenon with regards to drug delivery. However, the EPR effect has been found to be highly variable and thus unreliable due to the complex tumor microenvironment. Various physical and pharmacological strategies have been explored to overcome this challenge. Here, we review key advances and emerging concepts of such EPR-enhancing strategies. Furthermore, we analyze 723 clinical trials of nanoparticles with EPR enhancers and discuss their clinical translation.

Feasibility of using a 99mTc-hydroxamamide complex containing an albumin binder moiety for in vivo albumin labeling-based tumor imaging

Human serum albumin (HSA), which is distributed throughout the blood, is used as a carrier for transporting drugs to tumors based on the enhanced permeability and retention (EPR) effect. To develop an agent for the in vivo radiolabeling of endogenous albumin, we designed and synthesized novel hydroxamamide (Ham)-based technetium-99m (^99mTc) complexes, which contained a monovalent or bivalent 4-(4-iodophenyl)butyric acid (IA) derivative as an albumin binder (ALB) moiety ([^99mTc]AB2 and [^99mTc]ALB2, respectively), and evaluated their utility for in vivo tumor imaging. In an in vitro HSA-binding assay, [^99mTc]AB2 and [^99mTc]ALB2 showed greater binding to HSA than [^99mTc]BHam, a ^99mTc-Ham complex without an ALB moiety. In an in vivo biodistribution assay, [^99mTc]ALB2 showed marked blood and tumor retention (25.13 and 4.61% injected dose (ID)/g, respectively, at 1 h postinjection), suggesting that the EPR effect had been induced. However, [^99mTc]AB2 showed no marked blood or tumor retention (4.16 and 0.75% ID/g, respectively, at 1 h postinjection), probably because the affinity of the monovalent IA derivative for albumin was insufficient to induce the EPR effect. These findings indicated that the multivalent interactions of [^99mTc]ALB2 had enhanced its affinity for albumin. ^99mTc-complexes containing multivalent ALB moieties may be useful for tumor imaging.

Acid-responsive HPMA copolymer-bradykinin conjugate enhances tumor-targeted delivery of nanomedicine

Obstructed blood flow and erratic blood supply in the tumor region attenuate the distribution and accumulation of nanomedicines in the tumor. Therefore, improvement of these conditions is crucial for efficient drug delivery. In this study, we designed and synthesized a novel N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymer conjugate of BK, which possessed adequate systemic stability and tumor-selective action required to improve the accumulation of nanomedicines in the tumor. Levulinoyl-BK (Lev-BK) was conjugated to an HPMA-based polymer via an acid-cleavable hydrazone bond (P-BK). An acid-responsive release of Lev-BK from P-BK was observed, and P-BK alone after intradermal application showed below 10% of the BK activity, thus proving a reduction in the vascular permeability activity of BK when attached to the polymer carrier. P-BK pre-treatment improved blood flow in the tumor tissue by 1.4-1.7-fold, which was maintained for more than 4 h. In addition, P-BK pre-treatment increased the tumor accumulation of pegylated liposomal doxorubicin (PLD) by approximately 3-fold. Furthermore, P-BK pre-treatment led to superior antitumor activity of PLD and significantly improved the survival of tumor-bearing mice. The release of BK from P-BK in the acidic milieu of the tumor was a prerequisite for P-BK to exert its effect, as the vascular permeability enhancing activity of P-BK was negligible. Collectively, P-BK pre-treatment improved intratumoral blood flow and augmented tumor accumulation of nanomedicine, thereby resulting in a significant suppression of tumor growth. Therefore, these findings demonstrate that P-BK is a potential concomitant drug for improving the tumor delivery of nanomedicines.

The Therapeutic Effect of Human Serum Albumin Dimer-Doxorubicin Complex against Human Pancreatic Tumors

Human serum albumin (HSA) is a versatile drug carrier with active tumor targeting capacity for an antitumor drug delivery system. Nanoparticle albumin-bound (nab)-technology, such as nab-paclitaxel (Abraxane^®), has attracted significant interest in drug delivery research. Recently, we demonstrated that HSA dimer (HSA-d) possesses a higher tumor distribution than HSA monomer (HSA-m). Therefore, HSA-d is more suitable as a drug carrier for antitumor therapy and can improve nab technology. This study investigated the efficacy of HSA-d-doxorubicin (HSA-d-DOX) as next-generation nab technology for tumor treatment. DOX conjugated to HSA-d via a tunable pH-sensitive linker for the controlled release of DOX. Lyophilization did not affect the particle size of HSA-d-DOX or the release of DOX. HSA-d-DOX showed significantly higher cytotoxicity than HSA-m-DOX in vitro. In the SUIzo Tumor-2 (SUIT2) human pancreatic tumor subcutaneous inoculation model, HSA-d-DOX could significantly inhibit tumor growth without causing serious side effects, as compared to the HSA binding DOX prodrug, which utilized endogenous HSA as a nano-drug delivery system (DDS) carrier. These results indicate that HSA-d could function as a natural solubilizer of insoluble drugs and an active targeting carrier in intractable tumors with low vascular permeability, such as pancreatic tumors. In conclusion, HSA-d can be an effective drug carrier for the antitumor drug delivery system against human pancreatic tumors.

Structural and Photodynamic Studies on Nitrosylruthenium-Complexed Serum Albumin as a Delivery System for Controlled Nitric Oxide Release

How to deliver nitric oxide (NO) to a physiological target and control its release quantitatively is a key issue for biomedical applications. Here, a water-soluble nitrosylruthenium complex, [(CH₃)₄N][RuCl₃(5cqn)(NO)] (H5cqn = 5-chloro-8-quinoline), was synthesized, and its structure was confirmed with ¹H NMR and X-ray crystal diffraction. Photoinduced NO release was investigated with time-resolved Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The binding constant of the [RuCl₃(5cqn)(NO)]^- complex with human serum albumin (HSA) was determined by fluorescence spectroscopy, and the binding mode was identified by X-ray crystallography of the HSA and Ru-NO complex adduct. The crystal structure reveals that two molecules of the Ru-NO complex are located in the subdomain IB, which is one of the major drug binding regions of HSA. The chemical structures of the Ru complexes were [RuCl₃(5cqn)(NO)]^- and [RuCl₃(Glycerin)NO]^-, in which the electron densities for all ligands to Ru are unambiguously identified. EPR spin-trapping data showed that photoirradiation triggered NO radical generation from the HSA complex adduct. Moreover, the near-infrared image of exogenous NO from the nitrosylruthenium complex in living cells was observed using a NO-selective fluorescent probe. This study provides a strategy to design an appropriate delivery system to transport NO and metallodrugs in vivo for potential applications.

Reduction-Responsive and Multidrug Deliverable Albumin Nanoparticles: An Antitumor Drug to Abraxane against Human Pancreatic Tumor-Bearing Mice

Many macromolecular antitumor drugs were developed based on the enhanced permeability and retention (EPR) effect, for example, albumin-bound paclitaxel nanoparticles (nab-PTX and Abraxane) and pegylated liposomal doxorubicin (Doxil). However, these EPR effect-based therapeutic systems are less effective in malignant tumors with low vascular permeability, such as pancreatic tumors. Because the EPR effect depends on nanoparticles' size, we first determined nanoparticles' size associated with a high tumor-targeting rate in a human pancreatic tumor xenograft model with low vascular permeability. Abraxane appears to behave as an albumin monomer (7 nm) in the blood circulation following intravenous injection. The in vitro and in vivo tumor-targeted delivery and antitumor activity of PTX-loaded albumin nanoparticles were significantly improved by optimizing the mean nanoparticle diameter to 30 nm. Furthermore, nitric oxide was added to 30 nm PTX-loaded albumin nanoparticles to examine the feasibility of albumin nanoparticles as a platform for multiple drug delivery. Their antitumor effect was evaluated in an orthotopic transplantation mouse model of a human pancreatic tumor. The nitric oxide PTX-loaded 30 nm albumin nanoparticle treatment on model mice achieved a significantly higher survival rate than Abraxane treatment. These findings suggest that 30 nm albumin nanoparticles have a high therapeutic effect as a useful platform for multiple drugs against human pancreatic tumors.

Synthesis and In Vitro Assessment of pH-Sensitive Human Serum Albumin Conjugates of Pirarubicin

In a previous study, we reported on the development of a synthetic polymer conjugate of pirarubicin (THP) that was formed via an acid-labile hydrazone bond between the polymer and the THP. However, the synthetic polymer itself was non-biodegradable, which could lead to unexpected adverse effects. Human serum albumin (HSA), which has a high biocompatibility and good biodegradability, is also a potent carrier for delivering antitumor drugs. The objective of this study was to develop pH-sensitive HSA conjugates of THP (HSA-THP), and investigate the release of THP and the cytotoxicity under acidic conditions in vitro for further clinical development. HSA-THP was synthesized by conjugating maleimide hydrazone derivatives of THP with poly-thiolated HSA using 2-iminothiolane, via a thiol-maleimide coupling reaction. We synthesized two types of HSA-THP that contained different amounts of THP (HSA-THP2 and HSA-THP4). Free THP was released from both of the HSA conjugates more rapidly at an acidic pH, and the rates of release for HSA-THP2 and HSA-THP4 were similar. Moreover, both HSA-THPs exhibited a higher cytotoxicity at acidic pH than at neutral pH, which is consistent with the effective liberation of free THP under acidic conditions. These findings suggest that these types of HSA-THPs are promising candidates for further development.

Pharmaceutical Technology Innovation Strategy Based on the Function of Blood Transport Proteins as DDS Carriers for the Treatment of Intractable Disorders and Cancer

Blood transport proteins are biogenic molecules with unique and interesting inherent characteristics that make up living organisms. As the utilization of their inherent characteristics can be a groundbreaking strategy to resolve and improve several clinical problems, attempts have been made to develop pharmaceutical and biomedical preparations based on blood transport proteins for the treatment and diagnosis of disorders. Among various blood transport proteins, we focus on the immense potential of hemoglobin and albumin to serve as carriers of biomedical gases (oxygen and carbon monoxide) and anticancer agents (low-molecular compounds and antisense oligodeoxynucleotides), respectively, for the development of innovative drug delivery systems (DDS) to treat intractable disorders and solid cancers. In this review, I introduce the pharmaceutical technology, strategies, and application of DDS carriers that have been designed on the basis of the structure and function of hemoglobin and albumin. In addition, the prospect of using hemoglobin and albumin as materials for DDS carriers is discussed.

Modification of nitric oxide donors onto a monoclonal antibody boosts accumulation in solid tumors

Although monoclonal antibodies (mAbs) have revolutionized cancer treatment, their accumulation in solid tumors is limited and requires improvement to enhance therapeutic efficacy. Here we developed a strategy to modify mAb with a donor of nitric oxide (NO) because NO functions to vasodilate as well as to enhance the permeability of vascular endothelium, which will contribute to enhancing the tumor accumulation of mAb. We selected S-nitrosothiol as a NO donor and established the procedure to modify S-nitrosothiol group on mAb under ambient conditions. The modified mAb (Ab-SNO) thus obtained released NO in a preferable speed and maintained its original properties such as binding affinity to a target antigen and efficacy to induce antibody-dependent cellular cytotoxicity. We demonstrated that Ab-SNO enhanced the tumor accumulation of co-administered proteins such as antibody and serum albumin.

LCRF-0006, a small molecule mimetic of the N-cadherin antagonist peptide ADH-1, synergistically increases multiple myeloma response to bortezomib

N-cadherin is a homophilic cell-cell adhesion molecule that plays a critical role in maintaining vascular stability and modulating endothelial barrier permeability. Pre-clinical studies have shown that the N-cadherin antagonist peptide, ADH-1, increases the permeability of tumor-associated vasculature thereby increasing anti-cancer drug delivery to tumors and enhancing tumor response. Small molecule library screens have identified a novel compound, LCRF-0006, that is a mimetic of the classical cadherin His-Ala-Val sequence-containing region of ADH-1. Here, we evaluated the vascular permeability-enhancing and anti-cancer properties of LCRF-0006 using in vitro vascular disruption and cell apoptosis assays, and a well-established pre-clinical model (C57BL/KaLwRij/5TGM1) of the hematological cancer multiple myeloma (MM). We found that LCRF-0006 disrupted endothelial cell junctions in a rapid, transient and reversible manner, and increased vascular permeability in vitro and at sites of MM tumor in vivo. Notably, LCRF-0006 synergistically increased the in vivo anti-MM tumor response to low-dose bortezomib, a frontline anti-MM agent, leading to regression of disease in 100% of mice. Moreover, LCRF-0006 and bortezomib synergistically induced 5TGM1 MM tumor cell apoptosis in vitro. Our findings demonstrate the potential clinical utility of LCRF-0006 to significantly increase bortezomib effectiveness and enhance the depth of tumor response in patients with MM.

[Delivery of Anticancer Drugs Using a Supramolecular Complex to Cancer Tissues Having High Interstitial Fluid Pressure]

Pancreatic cancer is the fourth-leading cause of death from cancer in Japan, after lung, colorectal, and stomach cancers and has the lowest survival among these tumors, because of not only no symptoms, no screening tool and no biomarkers but also high rates of recurrence and metastasis. In addition, pancreatic cancer has excessive stroma which serves as a severe biological barrier for anticancer drug delivery and successful treatment. Therefore, there are many challenges for drug delivery systems for the treatment of pancreatic cancer. Recently, we developed self-assembly PEGylation retaining activity (SPRA) technology, which comprises a reversible pegylated protein complex without loss of bioactivity. SPRA technology is based on a host-guest interaction between PEGylated β-cyclodextrin and adamantane-appended protein. In this review, first pancreatic cancer is introduced, second, principle drug delivery systems for the treatment of pancreatic cancer are described, and third the concept of SPRA technology as well as examples of SPRA proteins, especially focusing on the potential of SPRA-bromelain for treatment of pancreatic cancer, are introduced.

The application of nitric oxide delivery in nanoparticle-based tumor targeting drug delivery and treatment

Nitric oxide (NO) shows great role in tumor biology. Recent years, more and more researches utilized NO donor in tumor targeting drug delivery and treatment. In this review, we summarized the NO donors by their endogenous and exogenous stimuli. Then the application of NO donors, which was the main aim of the review, was discussed in detailed according to their functions, including inducing tumor cell apoptosis, reversing tumor multidrug resistance, inhibiting tumor metastasis and improving drug delivery.

Rapid and continuous accumulation of nitric oxide-releasing liposomes in tumors to augment the enhanced permeability and retention (EPR) effect

The modulation of blood flow to tumors is a prominent strategy for improving the tumor accumulation of nanomedicines, resulting from the enhanced permeability and retention (EPR) effect. We previously reported a promising EPR enhancer-a nitric oxide (NO) donor-containing liposome (NO-LP)-which showed enhanced accumulation in tumor tissue. Herein, we study NO-LP in greater detail to clarify its practical use as an EPR enhancer. NO-LP was found to have advantages as a NO donor, including the ability to maintain NO donation over long periods of time, and a constant rate of NO-release irrespective of the environmental pH. NO-LP showed rapid accumulation in tumor tissue after injection (1 h), and then accumulation was continuously enhanced until 48 h. Enhanced NO-LP accumulation was observed specifically in tumor, while the accumulation in other organs remained relatively unchanged. The results obtained show the promising features of NO-LP as an EPR enhancer.

A switchable NO-releasing nanomedicine for enhanced cancer therapy and inhibition of metastasis

Clinical chemotherapy for cancer is limited by the physiological barrier of tumors, resulting in low drug delivery to tumors, poor efficacy of drugs and inability to block tumor metastasis. Here we developed an intelligent switchable nitric oxide (NO)-releasing nanoparticle, IPH-NO, which loads a photosensitizer (IR780) and the chemotherapy drug paclitaxel (PTX) into NO donor-S-nitrosated human serum albumin (HSA-NO). NO exhibits two effects based on its concentration: enhancement of chemotherapy by increasing the enhanced permeability and retention (EPR) effect at low concentrations and direct killing of cancer cells at high concentrations. IPH-NO can slowly release NO in the presence of glutathione to boost tumor vascular permeability and improve drug accumulation. Near-infrared light irradiation was utilized to induce a quick release of NO that can directly kill cancer cells at high concentrations. This combination of phototherapy and NO gas therapy activated by NIR together with chemotherapy showed significant effects in tumor inhibition. Furthermore, IPH-NO blocked tumor metastasis by inhibiting epithelial mesenchymal transition. PH-NO provides a novel strategy to control NO release at tumor site for drug accumulation and combination therapies, consequently potentiating the anticancer efficacy and inhibiting tumor metastasis.

Microfluidic Device for Screening for Target Cell-Specific Binding Molecules by Using Adherent Cells

This paper proposes a microfluidic device for screening molecules such as aptamers, antibodies, proteins, etc. for target cell-specific binding molecules. The discovery of cancer cell-specific binding molecules was the goal of this study. Its functions include filtering non-target cell-binding molecules, trapping molecules on the surface of target cells, washing away unbound molecules, and collecting target cell-specific binding molecules from target cells. These functions were effectively implemented by using our previously developed micro pillar arrays for cell homogeneous dispersion and pneumatic microvalves for tall microchannels. The device was also equipped with serially connected filter chambers in which non-target cells were cultured to reduce the molecules binding to non-target cells as much as possible. We evaluated the performance of the device using cancer cell lines (N87 cells as target cells and HeLa cells as non-target cells) and two fluorescent dye-labeled antibodies: Anti-human epidermal growth factor receptor 2 (anti-HER2) antibody that binds to target cells and anti-integrin antibody that binds to non-target cells. The results showed that the device could reduce anti-integrin antibodies to the detection limit of fluorescent measurement and collect anti-HER2 antibodies from the target cells.

Controlled Delivery of Nitric Oxide for Cancer Therapy

Nitric oxide (NO) is a short-lived, endogenously produced, signaling molecule which plays multiple roles in mammalian physiology. Underproduction of NO is associated with several pathological processes; hence a broad range of NO donors have emerged as potential therapeutics for cardiovascular and respiratory disorders, wound healing, the immune response to infection, and cancer. However, short half-lives, chemical reactivity, rapid systemic clearance, and cytotoxicity have hindered the clinical development of most low molecular weight NO donors. Hence, for controlled NO delivery, there has been extensive effort to design novel NO-releasing biomaterials for tumor targeting. This review covers the effects of NO in cancer biology, NO releasing moieties which can be used for NO delivery, and current advances in the design of NO releasing biomaterials focusing on their applications for tumor therapy.

Enhancing the Accumulation of Polymer Micelles by Selectively Dilating Tumor Blood Vessels with NO for Highly Effective Cancer Treatment

The accumulation of nanoparticles in tumors by the enhanced permeability and retention (EPR) effect is effective and well known. However, how to maximize accumulation is still a bottleneck in the development of nanomedicine. Herein, a tumor vascular-targeted hybrid polymeric micelle, which has a great capacity to selectively augment the EPR effect of nanoparticles by dilating tumor blood vessels via the activity of nitric oxide (NO), is presented. Under neutral conditions, the micelle is stable, with a long blood circulation half-life due to the carboxylated poly(ethylene glycol) (PEG) layer; in mildly acidic tumor tissues, the micelle can selectively target the tumor blood vessels by the exposed cyclic Arg-Gly-Asp peptide (cRGD) peptides, which is realized with a pH-dependent hydrolysis of the monomethoxy PEG layer. Simultaneously, exposed copper ions catalyze the decomposition of endogenous NO donors, which generates NO in situ, leading to vasodilation and increased tumor vascular permeability. As a result, the accumulation of nanoparticles is significantly enhanced, and a high accumulation of doxorubicin in tumors is achieved at 48 h after injection. This high dose of therapeutic agent produces a large inhibition of tumor growth (94%) in cancer treatment, and shows no general toxicity, with 100% of the mice surviving the treatment regimen.

Recombinant Human Serum Albumin Containing 3 Copies of Domain I, Has Significant in Vitro Antioxidative Capacity Compared to the Wild-Type

Human serum albumin (HSA), the most abundant protein in serum, functions as carrier of drugs and contributes to maintaining serum colloid osmotic pressure. We report herein on the preparation of a genetic recombinant HSA, in which domains II and III were changed to domain I (triple domain I; TDI). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results indicated that the purity of the TDI was equivalent to that of the wild type (WT). Both far- and near-UV circular dichroism (CD) spectra of the TDI showed that its structural characteristics were similar to the WT. Ligand binding capacity was examined by an ultrafiltration method using 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and ketoprofen as markers for site I and site II, respectively. The binding capacity of TDI for both ligands was lower than that for the wild type. TDI significantly suppressed the oxidation of dihydrorhodamine 123 (DRD) by H₂O₂ compared to the WT. Our current results suggest that TDI has great potential for further development as HSA a product having antioxidative functions.

Strategies for Preparing Albumin-based Nanoparticles for Multifunctional Bioimaging and Drug Delivery

Biosafety is the primary concern in clinical translation of nanomedicine. As an intrinsic ingredient of human blood without immunogenicity and encouraged by its successful clinical application in Abraxane, albumin has been regarded as a promising material to produce nanoparticles for bioimaging and drug delivery. The strategies for synthesizing albumin-based nanoparticles could be generally categorized into five classes: template, nanocarrier, scaffold, stabilizer and albumin-polymer conjugate. This review introduces approaches utilizing albumin in the preparation of nanoparticles and thereby provides scientists with knowledge of goal-driven design on albumin-based nanomedicine.

Polymer donors of nitric oxide improve the treatment of experimental solid tumours with nanosized polymer therapeutics

Polymer carriers based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers with incorporated organic nitrates as nitric oxide (NO) donors were designed with the aim to localise NO generation in solid tumours, thus highly increasing the enhanced permeability and retention (EPR) effect. The NO donors were coupled to the polymer carrier either through a stable bond or through a hydrolytically degradable, pH sensitive, bond. In vivo, the co-administration of the polymer NO donor and HPMA copolymer-bound cytotoxic drug (doxorubicin; Dox) resulted in an improvement in the treatment of murine EL4 T-cell lymphoma. The polymer NO donors neither potentiated the in vitro toxicity of the cytotoxic drug nor exerted any effect on in vivo model without the EPR effect, such as BCL1 leukaemia. Thus, an increase in passive accumulation of the nanomedicine carrying cytotoxic drug via NO-enhanced EPR effect was the operative mechanism of action. The most significant improvement in the therapy was observed in a combination treatment with such a polymer conjugate of Dox, which is characterised by increased circulation in the blood and efficient accumulation in solid tumours. Notably, the combination treatment enabled the development of an anti-tumour immune response, which was previously demonstrated as an important feature of HPMA-based polymer cytotoxic drugs.

Improved anticancer effects of albumin-bound paclitaxel nanoparticle via augmentation of EPR effect and albumin-protein interactions using S-nitrosated human serum albumin dimer

In the latest trend of anticancer chemotherapy research, there were many macromolecular anticancer drugs developed based on enhanced permeability and retention (EPR) effect, such as albumin bound paclitaxel nanoparticle (nab- PTX, also called Abraxane^®). However, cancers with low vascular permeability posed a challenge for these EPR based therapeutic systems. Augmenting the intrinsic EPR effect with an intrinsic vascular modulator such as nitric oxide (NO) could be a promising strategy. S-nitrosated human serum albumin dimer (SNO-HSA Dimer) shown promising activity previously was evaluated for the synergistic effect when used as a pretreatment agent in nab-PTX therapy against various tumor models. In the high vascular permeability C26 murine colon cancer subcutaneous inoculation model, SNO-HSA Dimer enhanced tumor selectivity of nab-PTX, and attenuated myelosuppression. SNO-HSA Dimer also augmented the tumor growth inhibition of nab-PTX in low vascular permeability B16 murine melanoma subcutaneous inoculation model. Furthermore, nab-PTX therapy combined with SNO-HSA Dimer showed higher antitumor activity and improved survival rate of SUIT2 human pancreatic cancer orthotopic model. In conclusion, SNO-HSA Dimer could enhance the therapeutic effect of nab-PTX even in low vascular permeability or intractable pancreatic cancers. The possible underlying mechanisms of action of SNO-HSA Dimer were discussed.

Encapsulation of a nitric oxide donor into a liposome to boost the enhanced permeation and retention (EPR) effect

We propose a method to improve the enhanced permeability and retention (EPR) effect of nanomedicines based on tumor-specific vasodilation using a nitric oxide (NO) donor-containing liposome. NONOate, a typical NO donor, was incorporated into a PEGylated liposome to retard the protonation-induced release of NO from NONOate by the protecting lipid bilayer membrane. The NONOate-containing liposome (NONOate-LP) showed similar blood retention to an empty PEGylated liposome but almost twice the amount accumulated within the tumor. This improvement in the EPR effect is thought to have been caused by specific vasodilation in the tumor tissue by NO released from the NONOate-LP accumulated in the tumor. The improved EPR effect by NONOate-LP will be useful for the accumulation of co-administered nanomedicines.

Non-internalizing antibody-drug conjugates display potent anti-cancer activity upon proteolytic release of monomethyl auristatin E in the subendothelial extracellular matrix

Antibody-drug conjugates (ADCs) represent a promising class of biopharmaceuticals with the potential to localize at the tumor site and improve the therapeutic index of cytotoxic drugs. While it is generally believed that ADCs need to be internalized into tumor cells in order to display optimal therapeutic activity, it has recently been shown that non-internalizing antibodies can efficiently liberate disulfide-linked drugs at the extracellular tumor site, leading to potent anti-cancer activity in preclinical animal models. Here, we show that engineered variants of the F16 antibody, specific to a splice isoform of tenascin-C, selectively localize to the subendothelial tumor extracellular matrix in three mouse models of human cancer (U87, A431, MDA-MB-231). A site-specific coupling of F16 in IgG format with a monomethyl auristatin E (MMAE) derivative, featuring a valine-citrulline dipeptide linker equipped with a self-immolative spacer, yielded an ADC product, which cured tumor-bearing mice at a dose of 7 mg/Kg. The observation of an efficient extracellular proteolytic cleavage of the valine-citrulline linker was surprising, as it has generally been assumed that this peptidic structure would be selectively cleaved by cathepsin B in intracellular compartments. The products described in this article may be useful for the treatment of human malignancies, as their cognate antigen is strongly expressed in the majority of human solid tumors, lymphomas and aggressive leukemias, while being virtually undetectable in most normal adult tissues.

Preparation and characterization of DOX loaded keratin nanoparticles for pH/GSH dual responsive release

Smart drug carriers are the current need of the hour in controlled drug delivery applications. In this work, pH and redox dual responsive keratin based drug-loaded nanoparticles (KDNPs) were fabricated through two-step strategies. Keratin nanoparticles were first prepared by desolvation method and chemical crosslinking, followed by electrostatic adsorbing doxorubicin (DOX) to afford drug loaded keratin nanoparticles (KDNPs). The size, size distribution, and morphology of the KDNPs were characterized with dynamic light scattering (DLS) and Scan electronic microscope (SEM). Drug delivery profiles showed that KDNPs exhibited pH and glutathione (GSH) dual-responsive characters. Under tumor tissue/cell microenvironments (more acidic and high GSH level), KDNPs tended to accumulate at the tumor region through a potential enhanced permeability and retention (EPR) effect and perform surface negative-to-positive charge conversion. Hemolysis assay indicated that KDNPs had good blood compatibility. Cellular uptake assay demonstrated that KDNPs could be internalized by A 549 cells through endocytosis. Intriguingly, KDNPs were capable of promoting nitric oxide (NO) release from endogenous donor of S-nitrosoglutathione in the presence of GSH. All of these results demonstrated that keratin based drug carriers had potential for drug/NO delivery and cancer therapy in clinical medicine.

[Human Serum Albumin as Carrier in Drug Delivery Systems]

  Recently, human serum albumin (HSA) has emerged as a versatile carrier for therapeutic agents against diabetes, cancer, and infectious diseases. Market-approved products include fatty acid derivatives of human insulin for diabetes and the paclitaxel-HSA nanoparticle for various cancers such as metastatic breast cancer and advanced pancreatic cancer. In this review, we focus on the next-generation approach including HSA-binding bioactive gas such as nitric oxide (NO) for treating ischemic/reperfusion injury, cancer, and bacterial infection. To date, pharmacologically active compounds that release NO within the body, such as organic nitrates, have been used as therapeutic agents, but their efficacy is significantly limited by unwanted side effects. Therefore, novel NO donors with better pharmacological and pharmacokinetic properties are highly desirable. The S-nitrosothiol fraction in plasma is largely composed of endogenous S-nitrosated HSA (SNO-HSA), which is why we are investigating whether this albumin form can be therapeutically useful. Recently, we have developed SNO-HSA analogues such as SNO-HSA with many conjugated SNO groups (poly-SNO-HSA) prepared using chemical modification. Unexpectedly, we found striking inverse effects between poly-SNO-HSA and SNO-HSA. Despite the fact that SNO-HSA inhibits apoptosis, poly-SNO-HSA possesses very strong pro-apoptotic effects against tumor cells. Furthermore, poly-SNO-HSA can reduce or even completely eliminate the multidrug resistance often developed by cancer cells. In this review, we put forward the possibility that poly-SNO-HSA can be used as a safe, effective multifunctional antitumor agent.

Poly-S-nitrosated human albumin enhances the antitumor and antimetastasis effect of bevacizumab, partly by inhibiting autophagy through the generation of nitric oxide

Autophagy is one of the major causes of drug resistance. For example, the angiogenesis inhibitor bevacizumab shows only transient and short-term therapeutic effects, whereas long-term therapeutic benefits are rarely observed, probably due to hypoxia-induced autophagy. Nitric oxide (NO) is an important molecule with multiple functions, and it has recently been reported to function as a regulator of autophagy. Therefore, a reasonable therapeutic strategy for overcoming drug resistance by NO would involve it being directly delivered to the tumor. Here, we investigated the inhibitory effect of NO on autophagy by using a macromolecular NO donor S-nitrosated human serum albumin (SNO-HSA) with a high degree of NO loading and tumor targeting potential. In colon 26 (C26) cells, SNO-HSA significantly suppressed hypoxia-induced autophagy by inhibiting the phosphorylation of JNK1 and the expression of its downstream molecule Beclin1. The effect of SNO-HSA was also confirmed in vivo by combining it with Bev. In C26-bearing mice, significant suppression of tumor growth as well as lung metastasis was achieved in the combination group compared to the SNO-HSA or bevacizumab alone group. Similar to the in vitro experiments, the immunostaining of tumor tissues clearly showed that SNO-HSA inhibited the autophagy of tumor cells induced by bevacizumab treatment. In addition to other known antitumor effects of SNO-HSA, that is, the induction of apoptosis and the inhibition of multidrug efflux pumps, these data may open alternate strategies for cancer chemotherapy by taking advantage of the ability of SNO-HSA to suppress autophagy-mediated drug resistance and enhance the efficacy of chemotherapy.

Cross-linked human serum albumin dimer has the potential for use as a plasma-retaining agent for the fatty acid-conjugated antidiabetic drugs

Objectives

The half-life of fatty acid-conjugated antidiabetic drugs are prolonged through binding to albumin, but this may not occur in diabetic patients with nephropathy complicated with hypoalbuminemia. We previously showed that human serum albumin (HSA) dimerized at the protein's Cys34 by 1,6-bis(maleimido)hexane has longer half-life than the monomer under high permeability conditions. The aim of this study was to investigate the superior ability of this HSA dimer as a plasma-retaining agent for fatty acid conjugated antidiabetic drugs.

Methods

The diabetic nephropathy rat model was prepared by administering a single injection of streptozotocin (STZ) intravenously, and the pharmacokinetic properties of HSA monomer and dimer were evaluated. Site-specific fluorescent probe displacement experiments were performed using warfarin and dansylsarcosine as site I and site II specific fluorescent probes, respectively.

Key findings

The half-life of the HSA dimer in STZ-induced diabetic nephropathy model rats was 1.5 times longer than the HSA monomer. The fluorescent probe displacement experiment results for HSA monomer and dimer were similar, where fatty acid-conjugated antidiabetic drugs displaced dansylsarcosine but not warfarin in a concentration-dependent manner.

Conclusions

The HSA dimer shows potential for use as a plasma-retaining agent for antidiabetic drugs due to its favourable pharmacokinetic properties.

Development of human serum albumin conjugated with near-infrared dye for photoacoustic tumor imaging

Photoacoustic (PA) imaging has emerged as a noninvasive diagnostic method which detects ultrasonic waves thermoelastically induced by optical absorbers irradiated with laser. For tumor diagnosis, PA contrast agent has been proposed to enhance the PA effect for detecting tumors sensitively. Here, we prepared a human serum albumin (HSA) conjugated with indocyanine green (ICG) as a PA contrast agent allowing enhanced permeability and retention effect for sensitive tumor imaging. The feasibility of PA imaging with HSA-ICG to detect allografted tumors was evaluated in tumor-bearing mice. In vivo fluorescence imaging and radiolabeled biodistribution study showed that the biodistribution dramatically changed as the number of ICG bound to HSA increased, and the maximum accumulation of ICG was achieved when around three ICG molecules were loaded on an HSA. In vivo PA imaging demonstrated a tumor-selective and dose-dependent increase of PA signal intensity in mice injected with HSA-ICG (R2 = 0.88, 387% increase for HSA-ICG, 104 nmol ICG). In conclusion, HSA-ICG clearly visualized the allografted tumors with high tumor-to-background ratios having high quantitative and spatial resolution for the sensitive PA imaging of tumors. HSA-ICG could be useful as a favorable contrast agent for PA tumor imaging for the management of cancer.

Nitric oxide modulators: an emerging class of medicinal agents

Nitric oxide, a unique messenger in biological system, is ubiquitously present virtually in all tissues revealing its versatile nature of being involved in diverse physiological functions such as vascular tone, inhibition of platelet aggregation, cell adhesion, neurotransmission and enzyme and immune regulation. The tremendous advancements made in the past few decades in this area suggests that the nitric oxide modulation either by its exogenous release through nitric oxide donors or inhibition of its synthesis by nitric oxide synthase inhibitors in physiological milieu may provide newer clinical strategies for the treatment of some diseases. In this review, an attempt is made to document and understand the biological chemistry of different classes of nitric oxide modulators that would prove to be a fruitful area in the years to come.

Redox properties of serum albumin

BACKGROUND

Oxidative damage results in protein modification, and is observed in numerous diseases. Human serum albumin (HSA), the most abundant circulating protein in the plasma, exerts important antioxidant activities against oxidative damage.

SCOPE OF REVIEW

The present review focuses on the characterization of chemical changes in HSA that are induced by oxidative damage, their relevance to human pathology and the most recent advances in clinical applications.

MAJOR CONCLUSIONS

The antioxidant properties of HSA are largely dependent on Cys34 and its contribution to the maintenance of intravascular homeostasis, including protecting the vascular endothelium under disease conditions related to oxidative stress. Recent studies also evaluated the susceptibility of other important amino acid residues to free radicals. The findings suggest that a redox change in HSA is related to the oxidation of several amino acid residues by different oxidants. Further, Cys34 adducts, such as S-nitrosylated and S-guanylated forms also play an important role in clinical applications. On the other hand, the ratio of the oxidized form to the normal form of albumin (HMA/HNA), which is a function of the redox states of Cys34, could serve as a useful marker for evaluating systemic redox states, which would be useful for the evaluation of disease progression and therapeutic efficacy.

GENERAL SIGNIFICANCE

This review provides new insights into our current understanding of the mechanism of HSA oxidation, based on in vitro and in vivo studies. This article is part of a Special Issue entitled Serum Albumin.

Superoxide dismutase as a novel macromolecular nitric oxide carrier: preparation and characterization

Nitric oxide (NO) is an important molecule that exerts multiple functions in biological systems. Because of the short-lived nature of NO, S-nitrosothiols (RSNOs) are believed to act as stable NO carriers. Recently, sulfhydryl (SH) containing macromolecules have been shown to be promising NO carriers. In the present study, we aimed to synthesize and characterize a potential NO carrier based on bovine Cu,Zn-superoxide dismutase (bSOD). To prepare S-nitrosated bSOD, the protein was incubated with S-nitrosoglutathione (GSNO) under varied experimental conditions. The results show that significant S-nitrosation of bSOD occurred only at high temperature (50 °C) for prolonged incubation time (>2 h). S-nitrosation efficiency increased with reaction time and reached a plateau at ~4 h. The maximum amount of NO loaded was determined to be about 0.6 mol SNO/mol protein (~30% loading efficiency). The enzymatic activity of bSOD, however, decreased with reaction time. Our data further indicate that NO functionality can only be measured in the presence of extremely high concentrations of Hg²⁺ or when the protein was denatured by guanidine. Moreover, mildly acidic pH was shown to favor S-nitrosation of bSOD. A model based on unfolding and refolding of bSOD during preparation was proposed to possibly explain our observation.

Elucidation of the therapeutic enhancer mechanism of poly-S-nitrosated human serum albumin against multidrug-resistant tumor in animal models

Human serum albumin (HSA) is the most abundant circulating protein and its S-nitrosated form serves as a reservoir of nitric oxide (NO). Previously, we prepared poly-S-nitrosated HSA (Poly-SNO-HSA) by incubation with Traut's Reagent and isopentyl nitrite and evaluated its potential as a novel anticancer agent through apoptosis involving the caspase-3 pathway. Recently, NO donors such as nitroglycerin were reported to revert the resistance to anticancer agents. Therefore, now we have evaluated the effect of the above type of Poly-SNO-HSA on the resistance to doxorubicin (dx) in human myelogenous leukemic cells (K562 cells). P-gp expression and dx accumulation in K562 and dx-resistant K562 cells (K562/dx cells) were quantified using Western blot and FACS analysis, respectively. Compared with parent K562 cells, higher expression of P-gp and lower accumulation of dx were shown in K562/dx cells. Poly-SNO-HSA caused increased dx accumulation in K562/dx cells by decreasing the expressions of P-gp and HIF-1α. Other experiments with the guanylate cyclase inhibitor ODQ and 8-Br-cGMP revealed that also a cGMP signaling pathway is involved in the Poly-SNO-HSA induced increase in dx accumulation. Furthermore, in vivo studies showed that co-treatment with Poly-SNO-HSA enhanced the anticancer effect of dx in K562/dx cells-bearing mice. Thus, in addition to its proapoptotic effect Poly-SNO-HSA can in an efficient manner revert drug resistance both in vitro and in vivo, and two pathways for this effect have been identified.

Pharmaceutical aspects of the recombinant human serum albumin dimer: structural characteristics, biological properties, and medical applications

Human serum albumin is the most abundant protein in the blood. It is clinically used in the treatment of severe hypoalbuminemia and as a plasma expander. The use of albumins as a carrier for drugs is currently being developed, and some are now in the preclinical and clinical trial stages. The main technologies for utilizing an albumin as a drug carrier are protein fusion, polymerization and surface modification, and so on. Among these technologies, albumin dimerization has wide clinical applications as a plasma expander as well as a drug carrier. Despite the fact that many reports have appeared on drugs using an albumin dimer as a carrier, our knowledge of the characteristics of the albumin dimer itself is incomplete. In this review, we summarize the structural characteristics of recombinant albumin dimers produced by two methods, namely, chemical linkage with 1,6-bis(maleimido)hexane and genetically linked with an amino acid linker, and the physicochemical characteristics and biological properties of these preparations. Finally, the potential for pharmaceutical applications of albumin dimers in clinical situations is discussed.