Oxystress inducing antitumor therapeutics via tumor-targeted delivery of PEG-conjugated D-amino acid oxidase

Reactive oxygen species-upregulating nanomedicines towards enhanced cancer therapy

Reactive oxygen species (ROS) play a crucial role in physiological and pathological processes, emerging as a therapeutic target in cancer. Owing to the high concentration of ROS in solid tumor tissues, ROS-based treatments, such as photodynamic therapy and chemodynamic therapy, and ROS-responsive drug delivery systems have been widely explored to powerfully and specifically suppress tumors. However, their anticancer efficacy is still hampered by the heterogeneous ROS levels, and thus comprehensively upregulating the ROS levels in tumor tissues can ensure an enhanced therapeutic effect, which can further sensitize and/or synergize with other therapies to inhibit tumor growth and metastasis. Herein, we review the recently emerging drug delivery strategies and technologies for increasing the H₂O₂, ˙OH, ¹O₂, and ˙O₂^- concentrations in cancer cells, including the efficient delivery of natural enzymes, nanozymes, small molecular biological molecules, and nanoscale Fenton-reagents and semiconductors and neutralization of intracellular antioxidant substances and localized input of mechanical and electromagnetic waves (such as ultrasound, near infrared light, microwaves, and X-rays). The applications of these ROS-upregulating nanosystems in enhancing and synergizing cancer therapies including chemotherapy, chemodynamic therapy, phototherapy, and immunotherapy are surveyed. In addition, we discuss the challenges of ROS-upregulating systems and the prospects for future studies.

Reactive oxygen species-responsive nanoplatforms for nucleic acid-based gene therapy of cancer and inflammatory diseases

Nucleic acid-based gene therapy has recently made important progress toward clinical implementation, and holds tremendous promise for the treatment of some life-threatening diseases, such as cancer and inflammation. However, the on-demand delivery of nucleic acid therapeutics in target cells remains highly challenging. The development of delivery systems responsive to specific pathological cues of diseases is expected to offer promising alternatives for overcoming this problem. Among them, the reactive oxygen species (ROS)-responsive delivery systems, which in response to elevated ROS in cancer cells or activated inflammatory cells, can deliver nucleic acid therapeutics on-demand via ROS-induced structural and assembly behavior changes, constitute a promising approach for cancer and anti-inflammation therapies. In this short review, we briefly introduce the ROS-responsive chemical structures, ROS-induced release mechanisms and some representative examples to highlight the current progress in constructing ROS-responsive delivery systems. We aim to provide new insights into the rational design of on-demand gene delivery vectors.

The 35th Anniversary of the Discovery of EPR Effect: A New Wave of Nanomedicines for Tumor-Targeted Drug Delivery-Personal Remarks and Future Prospects

This Special Issue on the enhanced permeability and retention (EPR) effect commemorates the 35th anniversary of its discovery, the original 1986 Matsumura and Maeda finding being published in Cancer Research as a new concept in cancer chemotherapy. My review here describes the history and heterogeneity of the EPR effect, which involves defective tumor blood vessels and blood flow. We reported that restoring obstructed tumor blood flow overcomes impaired drug delivery, leading to improved EPR effects. I also discuss gaps between small animal cancers used in experimental models and large clinical cancers in humans, which usually involve heterogeneous EPR effects, vascular abnormalities in multiple necrotic foci, and tumor emboli. Here, I emphasize arterial infusion of oily formulations of nanodrugs into tumor-feeding arteries, which is the most tumor-selective drug delivery method, with tumor/blood ratios of 100-fold. This method is literally the most personalized medicine because arterial infusions differ for each patient, and drug doses infused depend on tumor size and anatomy in each patient. Future developments in EPR effect-based treatment will range from chemotherapy to photodynamic therapy, boron neutron capture therapy, and therapies for free radical diseases. This review focuses on our own work, which stimulated numerous scientists to perform research in nanotechnology and drug delivery systems, thereby spawning a new cancer treatment era.

Construction of Enzyme Nanoreactors to Enable Tumor Microenvironment Modulation and Enhanced Cancer Treatment

Enzymes play pivotal roles in regulating and maintaining the normal functions of all living systems, and some of them are extensively employed for diagnosis and treatment of diverse diseases. More recently, several kinds of enzymes with unique catalytic activities have been found to be promising options to directly suppress tumor growth and/or augment the therapeutic efficacy of other treatments by modulating the hostile tumor microenvironment (TME), which is reported to negatively impair the therapeutic efficacy of different cancer treatments. In this review, first a summary is presented on the chemical approaches utilized for the construction of distinct enzyme nanoreactors with well-retained catalytic performance and reduced immunogenicity. Then, the utilization of such enzyme nanoreactors in attenuating tumor hypoxia, modulating extracellular matrix, and amplifying tumor oxidative stress is discussed in depth. Afterward, some perspectives are presented on the future development of such enzyme nanoreactors in TME modulation and enhanced cancer treatment.

Importance of studying primitive neuroectodermal tumors and extraosseous Ewings sarcoma of the vagina and vulva

Primitive neuroectodermal tumor (PNT) and Ewing's sarcoma are rare, round-cell tumors, characterized by the presence of the t(11; 22)(q24; q12) chromosomal translocation. A review of the literature revealed only 38 previously reported cases of vulvar PNT and Ewing's sarcoma and 15 vaginal PNT and Ewing's sarcoma. Although rare, these types of tumors should be taken into consideration when making a differential diagnosis for vulvar or vaginal tumors. The currently available data is limited, and therefore, case reports are essential for improving knowledge and management of these types of extremely rare tumors. However, further molecular and histopathological studies are essential for an improved understanding of these conditions and for an early, correct diagnosis. Although the gathered and presented data from the present review are limited, the literature demonstrates that the outcome of these types of cancer are more favorable compared with outcomes observed for carcinomas in more typical locations.

Recent Advances and Challenges in Controlling the Spatiotemporal Release of Combinatorial Anticancer Drugs from Nanoparticles

To overcome cancer, various chemotherapeutic studies are in progress; among these, studies on nano-formulated combinatorial drugs (NFCDs) are being actively pursued. NFCDs function via a fusion technology that includes a drug delivery system using nanoparticles as a carrier and a combinatorial drug therapy using two or more drugs. It not only includes the advantages of these two technologies, such as ensuring stability of drugs, selectively transporting drugs to cancer cells, and synergistic effects of two or more drugs, but also has the additional benefit of enabling the spatiotemporal and controlled release of drugs. This spatial and temporal drug release from NFCDs depends on the application of nanotechnology and the composition of the combination drug. In this review, recent advances and challenges in the control of spatiotemporal drug release from NFCDs are provided. To this end, the types of combinatorial drug release for various NFCDs are classified in terms of time and space, and the detailed programming techniques used for this are described. In addition, the advantages of the time and space differences in drug release in terms of anticancer efficacy are introduced in depth.

Identification of Hub Genes Associated With Hepatocellular Carcinoma Using Robust Rank Aggregation Combined With Weighted Gene Co-expression Network Analysis

Background

Bioinformatics provides a valuable tool to explore the molecular mechanisms underlying pathogenesis of hepatocellular carcinoma (HCC). To improve prognosis of patients, identification of robust biomarkers associated with the pathogenic pathways of HCC remains an urgent research priority.

Methods

We employed the Robust Rank Aggregation method to integrate nine qualified HCC datasets from the Gene Expression Omnibus. A robust set of differentially expressed genes (DEGs) between tumor and normal tissue samples were screened. Weighted gene co-expression network analysis was applied to cluster DEGs and the key modules related to clinical traits identified. Based on network topology analysis, novel risk genes derived from key modules were mined and biological verification performed. The potential functions of these risk genes were further explored with the aid of miRNA–mRNA regulatory networks. Finally, the prognostic ability of these genes was assessed by constructing a clinical prediction model.

Results

Two key modules showed significant association with clinical traits. In combination with protein–protein interaction analysis, 29 hub genes were identified. Among these genes, 19 from one module showed a pattern of upregulation in HCC and were associated with the tumor node metastasis stage, and 10 from the other module displayed the opposite trend. Survival analyses indicated that all these genes were significantly related to patient prognosis. Based on the miRNA-mRNA regulatory network, 29 genes strongly linked to tumor activity were identified. Notably, five of the novel risk genes, ABAT, DAO, PCK2, SLC27A2, and HAO1, have rarely been reported in previous studies. Gene set enrichment analysis for each gene revealed regulatory roles in proliferation and prognosis of HCC. Least absolute shrinkage and selection operator regression analysis further validated DAO, PCK2, and HAO1 as prognostic factors in an external HCC dataset.

Conclusion

Analysis of multiple datasets combined with global network information presents a successful approach to uncover the complex biological mechanisms of HCC. More importantly, this novel integrated strategy facilitates identification of risk hub genes as candidate biomarkers for HCC, which could effectively guide clinical treatments.

Cooperation of endogenous and exogenous reactive oxygen species induced by zinc peroxide nanoparticles to enhance oxidative stress-based cancer therapy

Reactive oxygen species (ROS)-generating anticancer agents can act through two different mechanisms: (i) elevation of endogenous ROS production in mitochondria, or (ii) formation/delivery of exogenous ROS within cells. However, there is a lack of research on the development of ROS-generating nanosystems that combine endogenous and exogenous ROS to enhance oxidative stress-mediated cancer cell death. Methods: A ROS-generating agent based on polymer-modified zinc peroxide nanoparticles (ZnO2 NPs) was presented, which simultaneously delivered exogenous H2O2 and Zn2+ capable of amplifying endogenous ROS production for synergistic cancer therapy. Results: After internalization into tumor cells, ZnO2 NPs underwent decomposition in response to mild acidic pH, resulting in controlled release of H2O2 and Zn2+. Intriguingly, Zn2+ could increase the production of mitochondrial O2·- and H2O2 by inhibiting the electron transport chain, and thus exerted anticancer effect in a synergistic manner with the exogenously released H2O2 to promote cancer cell killing. Furthermore, ZnO2 NPs were doped with manganese via cation exchange, making them an activatable magnetic resonance imaging contrast agent. Conclusion: This study establishes a ZnO2-based theranostic nanoplatform which achieves enhanced oxidative damage to cancer cells by a two-pronged approach of combining endogenous and exogenous ROS.

Block copolymer prodrugs: Synthesis, self-assembly, and applications for cancer therapy

Block copolymer prodrugs (BCPs) have emerged as one of the most promising anticancer drug delivery strategies, which can self-assemble into nanoparticles with optimal physicochemical properties including sizes, morphologies, surface properties, and integration of multifunction for improved in vivo applications. Moreover, the utility of stimuli-responsive linkages to conjugate drugs onto the polymer backbones can achieve efficient and targeting drug release. Several BCP micellar delivery systems have been pushed ahead into the clinical trials, which showed great promising potentials for cancer therapy. In recent years, various novel and more efficient BCP systems have been developed for better in vivo performance. In this focus article, we focus on the recent advances of BCPs including the synthesis, self-assembly, and applications for cancer therapy. The synthetic methods are first introduced, and the self-assembly of BCPs for in vivo anticancer applications is discussed along the line of varying endogenous stimuli-responsive linkages including amide or ester bonds, pH, reduction, and oxidation-responsive linkages. Finally, conclusions along with the brief future perspectives are presented. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Tailored Design of an ROS-Responsive Drug Release Platform for Enhanced Tumor Therapy via "Sequential Induced Activation Processes"

The reactive oxygen species (ROS)-responsive intelligent drug delivery system has developed rapidly in recent years. However, because of the low concentration of ROS in most types of tumor cells, it is not possible to rapidly and effectively stimulate the drug delivery system to release the active drug. Here, we introduced "sequential induced activation processes" for efficient tumor therapy by designing a new ROS-responsive drug release platform. β-Lapachone, a positively charged nitrogen mustard (NM) prodrug, and two diblock molecules (mPEG-AcMH and PAsp-AcMH) are self-assembled to form prodrug primary micelles, which are further aggregated into nanoparticles that facilitate drug codelivery. When administered by intravenous injection, the nanoparticles reach the tumor site and enter the tumor cells by endocytosis. The β-lapachone released in the tumor cells induces a large amount of H₂O₂, and the ROS-responsive NM prodrug is activated to form activated NM, quinone methide, and boric acid under the induction of H₂O₂. The activated NM leads to tumor cell apoptosis.

Chemiluminescence-initiated and in situ-enhanced photoisomerization for tissue-depth-independent photo-controlled drug release

Tissue-penetration-depth-independent self-luminescence is highly expected to perform photoisomerization-related bioapplications in vivo to overcome the limitation of shallow tissue-penetration from external photoexcitation. However, it remains extremely challenging because of lacking a target-specific high-intensity self-luminescence to precisely and effectively drive the photoisomerization. Here, we first report a target-specific tissue-depth-independent photoisomerization in vivo by developing a target-specific initiated and in situ-enhanced chemiluminescence (one of self-luminescence) strategy that overcomes the limitation of lacking target-specific high-intensity self-luminescence. Considering that photoisomerization shows boundless glamour in drug-controlled release for disease-specific chemotherapy, we demonstrated applicability of our strategy to apply it in tumor-specific self-luminescence-controlled drug chemotherapy. Specifically, a chemiluminescence substrate and chemiluminescence fluorophore (antitumor drug, CPT) were co-encapsulated in host-guest carriers composed of cyclodextrin and the photoisomerization molecule azobenzene. Tumor-specific H2O2-induced chemiluminescence preliminarily isomerizes azobenzene, triggering the partial dissociation of host-guest carriers and CPT release. Particularly, the initially released CPT again functions as a chemiluminescence enhancer to achieve in situ enhanced chemiluminescence, assuring target-specific enhanced isomerization and CPT release. With high tumor-inhibition-rate (73%) and no obvious therapy-side-effect in vivo indicates the good efficiency and target-specificity of our chemiluminescence-driven photoisomerization. Although we only demonstrated one example of a photoisomerization-related bioapplication, namely photoisomerization-controlled drug chemotherapy, our work provides guidelines to design various target-specific tissue-depth-independent photoisomerization for bioapplications.

Integrated Nanoparticles To Synergistically Elevate Tumor Oxidative Stress and Suppress Antioxidative Capability for Amplified Oxidation Therapy

The improved antioxidant system of cancer cells renders them well-adaptive to the intrinsic oxidative stress in tumor tissues. On the other hand, cancer cells are more sensitive to elevated tumor oxidative stress as compared with normal cells due to their deficient reactive oxygen species-eliminating systems. Oxidation therapy of cancers refers to the strategy of killing cancer cells through selectively increasing the oxidative stress in tumor tissues. In this article, to amplify the oxidation therapy, we develop integrated nanoparticles with the properties to elevate tumor oxidative stress and concurrently suppress the antioxidative capability of cancer cells. The amphiphilic block copolymer micelles of poly(ethylene glycol)-b-poly[2-((((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)oxy)carbonyl)oxy)ethyl methacrylate] (PEG-b-PBEMA) are integrated with palmitoyl ascorbate (PA) to form hybrid micelles (PA-Micelle). PA molecules at pharmacologic concentrations serve as a prooxidant to upregulate the hydrogen peroxide (H₂O₂) level in tumor sites and the PBEMA segment exhibits H₂O₂-triggered release of quinone methide for glutathione depletion to suppress the antioxidative capability of cancer cells, which synergistically and selectively kill cancer cells for tumor growth suppression. Given the significantly low side toxicity against normal tissues, this novel integrated nanoparticle design represents a novel class of nanomedicine systems for high-efficiency oxidation therapy with the potentials to be translated to clinical applications.

How much H(2)O(2) is produced by recombinant D-amino acid oxidase in mammalian cells?

Yeast D-amino acid oxidase (DAO) can serve as a genetically encoded producer of reactive oxygen species (ROS) in redox signaling studies. However, dynamics of hydrogen peroxide production and its sensitivity to externally added D-alanine (D-Ala) in cells have not been determined. Here we show that DAO, fused to a genetically encoded H2O2 indicator HyPer, can be used for controlled production of ROS in living eukaryotic cells. We found a clear heterogeneity in ROS production dynamics between individual cells. Moreover, different cell lines demonstrated distinct sensitivity to added D-Ala. Finally, by comparing signals generated by the HyPer-DAO fusion protein versus coexpressed HyPer and DAO proteins, we show that the fusion system is more sensitive to hydrogen peroxide production. Our results show the utility of the HyPer-DAO genetically encoded system for redox signaling studies and suggest that H2O2 produced by DAO in the cytoplasm acts locally in close proximity to the enzyme.

PEGylated D-amino acid oxidase restores bactericidal activity of neutrophils in chronic granulomatous disease via hypochlorite

Chronic granulomatous disease (CGD) causes impaired hydrogen peroxide (H(2)O(2)) generation. Consequently, neutrophils in patients with CGD fail to kill infecting pathogens. We expected that supplementation with H(2)O(2) would effectively restore the bactericidal function of neutrophils in CGD. Here, we used polyethylene glycol-conjugated D-amino acid oxidase (PEG-DAO) as an H(2)O(2) source. The enzyme DAO generates H(2)O(2) by using D-amino acid and oxygen as substrates. PEG-DAO plus D-amino acid indeed exerted bacteriostatic activity against Staphylococcus aureus via H(2)O(2) in vitro. Furthermore, use of PEG-DAO plus D-amino acids, which increased the amount of intracellular H(2)O(2), restored bactericidal activity of neutrophils treated with diphenylene iodonium, in which nicotinamide adenine dinucleotide phosphate (NADPH) oxidase was defective. This restoration of bactericidal activity was mediated by myeloperoxidase, with concomitant production of H(2)O(2) by PEG-DAO plus D-Ala. We also confirmed that PEG-DAO treatment restored bactericidal activity of congenitally defective neutrophils from patients with CGD. These results indicate that PEG-DAO can supply additional H(2)O(2) for defective NADPH oxidase of neutrophils from patients with CGD, and thus neutrophils regain bactericidal activity.

HSP32 (HO-1) inhibitor, copoly(styrene-maleic acid)-zinc protoporphyrin IX, a water-soluble micelle as anticancer agent: In vitro and in vivo anticancer effect

We reported previously the antitumor effect of heme oxygenase-1 (HO-1) inhibition by zinc protoporphyrin IX (ZnPP). ZnPP per se is poorly water soluble and thus cannot be used as anticancer chemotherapeutic. Subsequently, we developed water-soluble micelles of ZnPP using styrene-maleic acid copolymer (SMA), which encapsulated ZnPP (SMA-ZnPP). In this report, the in vitro and in vivo therapeutic effects of SMA-ZnPP are described. In vitro experiments using 11 cultured tumor cell lines and six normal cell lines revealed a remarkable cytotoxicity of SMA-ZnPP against various tumor cells; average IC(50) is about 11.1 μM, whereas the IC(50) to various normal cells is significantly higher, that is, more than 50 μM. In the pharmacokinetic study, we found that SMA-ZnPP predominantly accumulated in the liver tissue after i.v. injection, suggesting its applicability for liver cancer. As expected, a remarkable antitumor effect was achieved in the VX-2 tumor model in the liver of rabbit that is known as one the most difficult tumor models to cure. Antitumor effect was also observed in murine tumor xenograft, that is, B16 melanoma and Meth A fibrosarcoma. Meanwhile, no apparent side effects were found even at the dose of ∼7 times higher concentration of therapeutics dose. These findings suggest a potential of SMA-ZnPP as a tool for anticancer therapy toward clinical development, whereas further investigations are warranted.

Protective role of D-amino acid oxidase against Staphylococcus aureus infection

D-Amino acid oxidase (DAO) is a hydrogen peroxide-generating enzyme that uses a D-amino acid as a substrate. We hypothesized that DAO may protect against bacterial infection, because hydrogen peroxide is one of the most important molecules in the antibacterial defense systems in mammals. We show here that DAO suppressed the growth of Staphylococcus aureus in a manner that depended on the concentration of DAO and D-amino acid in vitro. Addition of catalase abolished the bacteriostatic activity of DAO. Although DAO plus D-Ala showed less bactericidal activity, addition of myeloperoxidase (MPO) greatly enhanced the bactericidal activity of DAO. Furthermore, DAO was able to utilize bacterial lysate, which contains D-Ala derived from peptidoglycan; this could produce hydrogen peroxide with, in the presence of myeloperoxidase, formation of hypochlorous acid. This concerted reaction of DAO and MPO led to the bactericidal action. In vivo experiments showed that DAO(-/-) (mutant) mice were more susceptible to S. aureus infection than were DAO(+/+) (wild-type) mice. These results suggest that DAO, together with myeloperoxidase, may play an important role in antibacterial systems in mammals.

Oxidative stress and therapeutic opportunities: focus on the Ewing's sarcoma family of tumors

Reactive oxygen species (ROS) are highly reactive by-products of energy production that can have detrimental as well as beneficial effects. Unchecked, high levels of ROS result in an imbalance of cellular redox state and oxidative stress. High levels of ROS have been detected in most cancers, where they promote tumor development and progression. Many anticancer agents work by further increasing cellular levels of ROS, to overcome the antioxidant detoxification capacity of the cancer cell and induce cell death. However, adaptation of the level of cellular antioxidants can lead to drug resistance. The challenge for the design of effective cancer therapeutics exploiting oxidative stress is to tip the cellular redox balance to induce ROS-dependent cell death but without increasing the antioxidant activity of the cancer cell or inducing toxicity in normal cells.

Chemical genetics analysis of an aniline mustard anticancer agent reveals complex I of the electron transport chain as a target

The antitumor agent 11β (CAS 865070-37-7), consisting of a DNA-damaging aniline mustard linked to an androgen receptor (AR) ligand, is known to form covalent DNA adducts and to induce apoptosis potently in AR-positive prostate cancer cells in vitro; it also strongly prevents growth of LNCaP xenografts in mice. The present study describes the unexpectedly strong activity of 11β against the AR-negative HeLa cells, both in cell culture and tumor xenografts, and uncovers a new mechanism of action that likely explains this activity. Cellular fractionation experiments indicated that mitochondria are the major intracellular sink for 11β; flow cytometry studies showed that 11β exposure rapidly induced oxidative stress, mitochondria being an important source of reactive oxygen species (ROS). Additionally, 11β inhibited oxygen consumption both in intact HeLa cells and in isolated mitochondria. Specifically, 11β blocked uncoupled oxygen consumption when mitochondria were incubated with complex I substrates, but it had no effect on oxygen consumption driven by substrates acting downstream of complex I in the mitochondrial electron transport chain. Moreover, 11β enhanced ROS generation in isolated mitochondria, suggesting that complex I inhibition is responsible for ROS production. At the cellular level, the presence of antioxidants (N-acetylcysteine or vitamin E) significantly reduced the toxicity of 11β, implicating ROS production as an important contributor to cytotoxicity. Collectively, our findings establish complex I inhibition and ROS generation as a new mechanism of action for 11β, which supplements conventional DNA adduct formation to promote cancer cell death.

Polymeric carriers: preclinical safety and the regulatory implications for design and development of polymer therapeutics

Since the early 1990s polymer-protein conjugates (included PEGylated enzymes and cytokines), polymeric drugs and polymeric sequestrants have been entering the market as innovative polymer-based therapeutics. Initially these products were most frequently developed as novel anticancer agents; indeed they can be considered first generation "nanomedicines". More recently, a much broader range of life-threatening and debilitating diseases (e.g. viral infections, arthritis, multiple sclerosis and hormone abnormalities) have been targeted via intravenous (i.v.), subcutaneous (s.c.) or oral routes of administration. Given the increasing novelty of polymeric materials proposed for development as second-generation polymer therapeutics (with increasing complexity of conjugate composition), and the growing debate as to the safety of nanomedicines per se, the need for evolution of an appropriate regulatory framework is at the forefront of the scientific discussion. The adequacy of the current tests and models used to define safety are also constantly being reviewed. Here we describe the current status and future challenges in relation to these issues.

Optimization of D-amino acid oxidase for low substrate concentrations--towards a cancer enzyme therapy

D-amino acid oxidase (DAAO) has recently become of interest as a biocatalyst for industrial applications and for therapeutic treatments. It has been used in gene-directed enzyme prodrug therapies, in which its production of H2O2 in tumor cells can be regulated by administration of substrate. This approach is limited by the locally low O2 concentration and the high K(m) for this substrate. Using the directed evolution approach, one DAAO mutant was identified that has increased activity at low O2 and D-Ala concentrations and a 10-fold lower K(m) for O2. We report on the mechanism of this DAAO variant and on its cytotoxicity towards various mammalian cancer cell lines. The higher activity observed at low O2 and D-Ala concentrations results from a combination of modifications of specific kinetic steps, each being of small magnitude. These results highlight the potential in vivo applicability of this evolved mutant DAAO for tumor therapy.

Contact activation of kallikrein-kinin system by superparamagnetic iron oxide nanoparticles in vitro and in vivo

Previously we reported that plasma kallikrein and high molecular weight kininogen attach to the surface of dextran-coated superparamagnetic iron oxide nanoparticles (SPION) through the incompletely covered iron oxide core (Simberg et al., Biomaterials, 2009). Here we show that SPION also activate kallikrein-kinin system in vitro and in vivo. The serine protease activity of kallikrein was stably associated with SPION and could be detected on the nanoparticles even after extensive washing steps. The enzymatic activity was not detectable in kininogen-deficient and Factor XII-deficient plasma. The enzymatic activation could be blocked by precoating SPION with histidine-rich Domain 5 (D5) of kininogen. Importantly, the kallikrein activity was detectable in plasma of SPION-injected, but not of D5/SPION-injected mice. Tumor-targeted SPION when injected into kininogen-deficient and control mice, produced high levels of vascular clotting in tumors, suggesting that kallikrein activation is not responsible for the nanoparticle-induced thrombosis. These data could help in understanding the toxicity of nanomaterials and could be used in designing nanoparticles with controlled enzymatic activity.

D-amino acid oxidase: physiological role and applications

D-Amino acids play a key role in regulation of many processes in living cells. FAD-dependent D-amino acid oxidase (DAAO) is one of the most important enzymes responsible for maintenance proper level of D-amino acids. The most interesting and important data for regulation of the nervous system, hormone secretion, and other processes by D-amino acids as well as development of different diseases under changed DAAO activity are presented. The mechanism of regulation is complex and multi-parametric because the same enzyme simultaneously influences the level of different D-amino acids, which can result in opposing effects. Use of DAAO for diagnostic and therapeutic purposes is also considered.

Therapeutic strategies by modulating oxygen stress in cancer and inflammation

Oxygen is the essential molecule for all aerobic organisms, and plays predominant role in ATP generation, namely, oxidative phosphorylation. During this process, reactive oxygen species (ROS) including superoxide anion (O(2)(-)) and hydrogen peroxide (H(2)O(2)) are produced as by-products, while it seems indispensable for signal transduction pathways that regulate cell growth and reduction-oxidation (redox) status. However, during times of environmental stress ROS levels may increase dramatically, resulting in significant damage to cell structure and functions. This cumulated situation of ROS is known as oxidative stress, which may, however, be utilized for eradicating cancer cells. It is well known that oxidative stress, namely over-production of ROS, involves in the initiation and progression of many diseases and disorders, including cardiovascular diseases, inflammation, ischemia-reperfusion (I/R) injury, viral pathogenesis, drug-induced tissue injury, hypertension, formation of drug resistant mutant, etc. Thus, it is reasonable to counter balance of ROS and to treat such ROS-related diseases by inhibiting ROS production. Such therapeutic strategies are described in this article, that includes polymeric superoxide dismutase (SOD) (e.g., pyran copolymer-SOD), xanthine oxidase (XO) inhibitor as we developed water soluble form of 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP), heme oxygenase-1 (HO-1) inducers (e.g., hemin and its polymeric form), and other antioxidants or radical scavengers (e.g., canolol). On the contrary, because of its highly cytotoxic nature, ROS can also be used to kill cancer cells if one can modulate its generation selectively in cancer. To achieve this goal, a unique therapeutic strategy was developed named as "oxidation therapy", by delivering cytotoxic ROS directly to the solid tumor, or alternatively inhibiting the antioxidative enzyme system, such as HO-1 in tumor. This anticancer strategy was examined by use of O(2)(-) or H(2)O(2)-generating enzymes (i.e., XO and d-amino acid oxidase [DAO] respectively), and by discovering the inhibitor of HO-1 (i.e., zinc protoporphyrin [ZnPP] and its polymeric derivatives). Further for the objective of tumor targeting and thus reducing side effects, polymer conjugates or micellar drugs were prepared by use of poly(ethylene glycol) (PEG) or styrene maleic acid copolymer (SMA), which utilize EPR (enhanced permeability and retention) effect for tumor-selective delivery. These macromolecular drugs further showed superior pharmacokinetics including much longer in vivo half-life, particularly tumor targeted accumulation, and thus remarkable antitumor effects. The present review concerns primarily our own works, in the direction of "Controlling oxidative stress: Therapeutic and delivery strategy" of this volume.