Conjugates of anticancer agents and polymers: advantages of macromolecular therapeutics in vivo

Albumin-based delivery systems: Recent advances, challenges, and opportunities

Albumin and albumin-based biomaterials have been explored for various applications, including therapeutic delivery, as therapeutic agents, as components of tissue adhesives, and in tissue engineering applications. Albumin has been approved as a nanoparticle containing paclitaxel (Abraxane®), as an albumin-binding peptide (Victoza®), and as a glutaraldehyde-crosslinked tissue adhesive (BioGlue®). Albumin is also approved as a supportive therapy for various conditions, including hypoalbuminemia, sepsis, and acute respiratory distress syndrome (ARDS). However, no other new albumin-based systems in a hydrogel format have been used in the clinic. A review of publicly available clinical trials indicates that no new albumin drug delivery formats are currently in the clinical development pipeline. Although albumin has shown promise as a carrier of therapeutics for various diseases, including diabetes, cancers, and infectious diseases, its potential for treating blood-borne diseases such as HIV and leukemia has not been translated. This review offers a perspective on the use of albumin-based drug delivery systems for a broader range of disease applications, considering the protein properties and a review of the currently approved albumin-based technologies. This review supports ongoing efforts to advance biomedical research and clinical interventions through albumin-based delivery systems.

End-Group Dye-Labeled Poly(hemiacetal ester) Block Copolymers: Enhancing Hydrolytic Stability and Loading Capacity for Micellar (Immuno-)Drug Delivery

Polymers with hemiacetal esters integrated in their backbone provide beneficial degradation profiles for (immuno-) drug delivery. However, their fast hydrolysis and low drug loading capacity have limited their applications so far. Therefore, this study focuses on the stability and loading capacity of hemiacetal ester polymers. The hydrophobicity of the micellar core has a tremendous effect on the hemiacetal ester stability. For that purpose, we introduce a new monomer with a phenyl moiety for stabilizing the micellar core and improving drug loading. The carrier functionality can further be expanded by post-polymerization modifications via activated ester groups at the polymer chain end. This allows for covalent dye labeling, which provides substantial insights into the polymers' in vitro performance. Flow cytometric analyses on RAW dual macrophages revealed intact micelles exhibiting significantly higher cellular uptake compared to degraded species, thus, highlighting the potential of end group functionalized poly(hemiacetal ester)s for (immuno)drug delivery purposes.

Improving the Photodynamic Activity of Water-Soluble Porphyrin-Polysaccharide Complexes by Folic Acid Modification

Studies have shown that folate receptors are highly expressed in various cancer cells. Here, we synthesized folic acid-conjugated pullulan (FAPL) as a solubilizing agent to improve the photodynamic activity of porphyrin derivative-polysaccharide complexes. The porphyrin derivative-FAPL complex exhibited long-term stability in an aqueous solution, attributed to the folic acid modification. Furthermore, in vitro and in vivo experiments highlighted the enhanced photodynamic activity of the porphyrin derivative-FAPL complex toward 4T1 breast-cancer cells, compared with the activities of the porphyrin derivative-pullulan complex and Photofrin. This enhanced activity is attributed to the improvement of intracellular uptake by the folate receptor.

Photoacoustic Imaging Using Polysaccharide-Porphyrin Complexes by Photoirradiation at Long Wavelengths

Photoacoustic (PA) imaging is a novel biological imaging technique with superior depth resolution compared to fluorescence imaging. The efficacy of PA imaging depends on contrast agents that possess considerable absorbance at longer wavelengths, coupled with high permeability in biological tissue and minimal fluorescence, achieved through mitigating aggregation-caused quenching (ACQ) that attenuates PA intensity. Despite the successful transfer of porphyrin 2 featuring amino moieties from polysaccharides to liposomes, most of 2 incorporated within λ-carrageenan (CGN-2 complex) remained in CGN under acidic lysosomal conditions (pH 5.0). Consequently, the CGN-2 complex exhibited a strong PA signal under 680 nm photoirradiation in Colon26 cells owing to the ACQ of 2. Moreover, the PA intensity of the CGN-2 complex was further enhanced under 780 nm photoirradiation owing to the increased absorbance at 780 nm facilitated by the redshift of the Q-band at pH 5.0.

Steric stabilization of bioactive nanoparticles using elastin-like polypeptides

Elastin-like polypeptides (ELP) are versatile, thermo-responsive polymers that can be conjugated to virtually any therapeutic cargo. Derived from short amino-acid sequences and abundant in humans, certain ELPs display low immunogenicity. Substrates for endogenous proteases, ELPs are biodegradable and thus, are candidate biomaterials. Peptides and proteins can be directly coupled with ELPs through genetic engineering, while other polymers and small molecules can be appended through covalent bioconjugation or non-covalent complexation. ELPs that phase separate at physiological temperatures can form the core of nano assemblies; however, ELPs that remain soluble can sterically stabilize the corona of a variety of nanoparticles. Nanoparticles with ELPs at their corona promote colloids with favorable pharmacokinetic (PK) properties that enables therapeutic efficacy with intermittent administration. This review highlights a comprehensive spectrum of ELP fusions shown to stabilize the solubility, and sometimes bioactivity, of their cargo - with a focus on biophysical properties that underlie their therapeutic effects.

Impact of the polymer backbone chemistry on interactions of amino-acid-derived zwitterionic polymers with cells

Zwitterionic polymers are known to interact with cells and have been shown to reveal cancer cell specificity. In this work, the importance of the chemistry of the polymer backbone for the cellular specificity of amino-acid-derived polyzwitterions is demonstrated. A series of glutamic acid (Glu)-based vinyl monomers (i.e., an acrylate, a methacrylate, an acrylamide, and a methacrylamide) were prepared and used for reversible addition-fragmentation chain-transfer (RAFT) polymerisation, yielding defined polymers with narrow size distribution (Р< 1.3). All Glu-functionalised, zwitterionic polymers revealed high cytocompatibility; however, differences in cellular association and specificity were observed. In particular, the methacrylamide-derived polymers showed high association with both, breast cancer cells and non-cancerous dendritic cells and, consequently, lack specificity. In contrast, high specificity to only breast cancer cells was observed for polyacrylates, -methacrylates, and -acrylamides. Detailed analysis of the polymers revealed differences in hydrophobicity, zeta potential, and potential side chain hydrolysis, which are impacted by the polymer backbone and might be responsible for the altered the cell association of these polymers. It is shown that a slightly negative net charge is preferred over a neutral charge to retain cell specificity. This was also confirmed by association experiments in the presence of competitive amino acid transporter substrates. The affinity of slightly negatively charged Glu-derived polymers to the xCT Glu/cystine cell membrane antiporter was found to be higher than that of neutrally charged polymers. Our results emphasise the importance of the polymer backbone for the design of cell-specific polymers. This study further highlights the potential to tailor amino-acid-derived zwitterionic materials beyond their side chain functionality.

Zwitterionic Amino Acid Polymer-Grafted Core-Crosslinked Particle toward Tumor Delivery

Zwitterionic amino acid polymers (ZAPs) exhibit biocompatibility and recognition capability for amino acid transporters (AATs) overexpressed on cancer cells. They are potential cancer-targeting ligands in nanoparticle-based nanomedicines utilized in cancer chemotherapy. Here, a poly(glutamine methacrylate) (pGlnMA)-grafted core-crosslinked particle (pGlnMA-CCP) is prepared through the formation of nanoemulsions stabilized using amphiphilic block copolymers comprising pGlnMA as the hydrophilic block. The chain conformation of the grafted polymer and the particle structure of pGlnMA-CCP are precisely elucidated by dynamic light scattering, X-ray scattering, and transmission electron microscopy. pGlnMA-CCP demonstrates active cellular uptake and deep penetration behaviors for cancer cells and spheroids, respectively, via an AAT-mediated mechanism. The in vivo pharmacokinetics of pGlnMA-CCP is practically comparable to those of a CCP covered with poly(polyethylene glycol methacrylate) (pPEGMA), which inhibits protein adsorption and prolongs blood retention, implying that the biocompatible properties of pGlnMA are similar to those of pPEGMA. Furthermore, pGlnMA-CCP accumulates in cancer tissues at a higher level than that of pPEGMA systems. The results demonstrate that the properties of cancer targetability, tumor permeability, efficient tumor accumulation, and biocompatibility can be obtained by grafting pGlnMA onto nanoparticles, suggesting a high potential of pGlnMA as a ligand for cancer-targeting nanomedicines.

Poly(methacrylate citric acid) as a Dual Functional Carrier for Tumor Therapy

Owing to its pH-sensitive property and chelating Cu²⁺ effect, poly(methacrylate citric acid) (PCA) can be utilized as a dual functional nanocarrier to construct a nanodelivery system. Negatively charged carboxyl groups can interact with positively charged antineoplastic drugs through electrostatic interaction to form stable drug nanoparticles (NPs). Through drug experimental screening, doxorubicin (DOX) was selected as the model drug, PCA/DOX NPs with a diameter of 84 nm were prepared, and the drug-loading content was 68.3%. PCA/DOX NPs maintained good stability and a sustained release profile. Cell experiments presented that PCA/DOX NPs could inhibit effectively the growth of 4T1 cells; the IC₅₀ value was decreased by approximately 15-fold after incubation for 72 h. The cytotoxicity toward H9C2 was decreased significantly. Moreover, based on its ability to efficiently adsorb copper ions, PCA showed good vascular growth inhibition effect in vitro. Furthermore, animal experiments showed that PCA/DOX NPs presented stronger anticancer effects than DOX; the tumor inhibition rate was increased by 1.5-fold. Myocardial toxicity experiments also confirmed that PCA reduced the cardiotoxicity of DOX. In summary, PCA/DOX NPs show good antitumor efficacy and low toxicity, and have good potential for clinical application.

Circulation Time-Optimized Albumin Nanoplatform for Quantitative Visualization of Lung Metastasis via Targeting of Macrophages

The development of molecular imaging probes to identify key cellular changes within lung metastases may lead to noninvasive detection of metastatic lesions in the lung. In this study, we constructed a macrophage-targeted clickable albumin nanoplatform (CAN) decorated with mannose as the targeting ligand using a click reaction to maintain the intrinsic properties of albumin in vivo. We also modified the number of mannose molecules on the CAN and found that mannosylated serum albumin (MSA) harboring six molecules of mannose displayed favorable pharmacokinetics that allowed high-contrast imaging of the lung, rendering it suitable for in vivo visualization of lung metastases. Due to the optimized control of functionalization and surface modification, MSA enhanced blood circulation time and active/passive targeting abilities and was specifically incorporated by mannose receptor (CD206)-expressing macrophages in the metastatic lung. Moreover, extensive in vivo imaging studies using single-photon emission computed tomography (SPECT)/CT and positron emission tomography (PET) revealed that blood circulation of time-optimized MSA can be used to discern metastatic lesions, with a strong correlation between its signal and metastatic burden in the lung.

Cyclodextrin-induced release of drug-entrapping liposomes associated with the solation of liposome gels

In this work, we demonstrate that liposome gels in which liposomes are connected by polyethylene glycol terminated by cholesterol groups at both ends can store hydrophilic and hydrophobic drugs in the gel interiors, inner aqueous phases, and lipid membranes. The addition of cyclodextrins (CDxs) as extrinsic stimuli led to the release of drug-entrapping liposomes due to the interactions between CDxs and cholesteryl groups and/or the alkyl chains of lipids. The addition of aqueous solutions of β-CDx, dimethyl-β-CDx, trimethyl-β-CDx, and γ-CDx (final concentration: 7.5 mM) induced the solation of liposome gels and the release of liposomes accompanying the solation. Furthermore, the addition of β-CDx led to the partial release of hydrophilic drugs encapsulated in the liposomes, although the drug release was scarcely observed in other CDxs. In particular, the addition of trimethyl-β-CDx, which has low cytotoxicity, accelerated solation, and cationic liposomes released from the gels were effectively taken up by murine colon cancer (Colon26) cells. Thus, we propose that liposomes released from liposome gels can function as drug carriers.

The solation of liposome gels owing to the addition of trimethyl-β-cyclodextrin (TMe-β-CDx) and the uptake of cationic liposomes released from liposome gels by Colon26 cells are demonstrated.

Zwitterionic Amino Acid-Derived Polyacrylates as Smart Materials Exhibiting Cellular Specificity and Therapeutic Activity

The synthesis of new amino acid-containing, cell-specific, therapeutically active polymers is presented. Amino acids served as starting material for the preparation of tailored polymers with different amino acids in the side chain. The reversible addition-fragmentation chain-transfer (RAFT) polymerization of acrylate monomers yielded polymers of narrow size distribution (Đ ≤ 1.3). In particular, glutamate (Glu)-functionalized, zwitterionic polymers revealed a high degree of cytocompatibility and cellular specificity, i.e., showing association to different cancer cell lines, but not with nontumor fibroblasts. Energy-dependent uptake mechanisms were confirmed by means of temperature-dependent cellular uptake experiments as well as localization of the polymers in cellular lysosomes determined by confocal laser scanning microscopy (CLSM). The amino acid receptor antagonist O-benzyl-l-serine (BzlSer) was chosen as an active ingredient for the design of therapeutic copolymers. RAFT copolymerization of Glu acrylate and BzlSer acrylate resulted in tailored macromolecules with distinct monomer ratios. The targeted, cytotoxic activity of copolymers was demonstrated by means of multiday in vitro cell viability assays. To this end, polymers with 25 mol % BzlSer content showed cytotoxicity against cancer cells, while leaving fibroblasts unaffected over a period of 3 days. Our results emphasize the importance of biologically derived materials to be included in synthetic polymers and the potential of zwitterionic, amino acid-derived materials for cellular targeting. Furthermore, it highlights that the fine balance between cellular specificity and unspecific cytotoxicity can be tailored by monomer ratios within a copolymer.

Effect of meso Positioned Substituents on the Stability and Photodynamic Activity of Lipid-Membrane-Incorporated Porphyrin Derivatives

Here, we prepared aqueous solutions of lipid-membrane incorporated tetraarylporphyrins and tetrapyridylporphyrin (LMIPors) by the injection method using dimethyl sulfoxide. The porphyrins with proton-donor groups at the meso position afforded stable aqueous solutions of LMIPors. However, although tetrakis(carboxyphenyl)porphyrin was scarcely incorporated in lipid membranes, it was soluble in water. Among these LMIPors, the photodynamic activity of tetrakis(hydroxyphenyl)porphyrin was higher than that of tetrakis(aminophenyl)porphyrin. This was attributed to the self-aggregation of a part of tetrakis(aminophenyl)porphyrin in the liposomes, which induced self-quenching and the consequent decrease of its photodynamic activity.

Phytochemical-loaded liposomes for anticancer therapy: an updated review

The major obstacles observed in current chemotherapy are severe adverse effects, narrow therapeutic indexes and multidrug resistance. Anticancer phytochemicals are extracted and purified from natural plants, providing alternative therapeutic approaches with recognized biomedical benefits. However, poor bioavailability, high dose requirements and non-specific targeting have made those molecules less effective. To tackle those issues, liposomal nanovesicles for phytochemical delivery are taken into consideration for improving the therapeutic effectiveness by increasing transportation across cell barriers and conferring attractive cancer-specific targeting capabilities. In the present review, the liposomal approaches of anticancer phytochemicals are discussed, and recent advances in these formulations applied to cancer phytotherapy are further reviewed by an informed approach.

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.

The double-edged sword effect of macrophage targeting delivery system in different macrophage subsets related diseases

Background

Monocyte/macrophage-targeting delivery systems (MTDSs) have been focused upon as an emerging routine for delivering drugs to treat various macrophage-related diseases. However, the ability of MTDSs to distinguish different macrophage-related diseases and their impact on macrophage function and disease progression have not been systematically revealed, which is important for actively targeted therapeutic or diagnostic strategies.

Results

Herein, we used dextran-modified polystyrene nanoparticles (DEX-PS) to demonstrate that modification of nanoparticles by dextran can specifically enhance their recognition by M2 macrophages in vitro, but it is obstructed by monocytes in peripheral blood according to in vivo assays. DEX-PS not only targeted and became distributed in tumors, an M2 macrophage-related disease, but was also highly distributed in an M1 macrophage-related disease, namely acute peritonitis. Thus, DEX-PS acts as a double-edged sword in these two different diseases by reeducating macrophages to a pro-inflammatory phenotype.

Conclusions

Our results suggest that MTDSs, even those designed based on differential expression of receptors on specific macrophage subtypes, lack the ability to distinguish different macrophage subtype-related diseases in vivo. In addition to the potential impact of these carrier materials on macrophage function, studies of MTDSs should pay greater attention to the distribution of nanoparticles in non-target macrophage-infiltrated disease sites and their impact on disease processes.

Hydroxyethylcellulose as a methotrexate carrier in anticancer therapy

Clinical and experimental cancer therapy is multifaceted; one such facet is the use of drug carriers. Drug carriers are various nano- and macromolecules, e.g., oligosaccharides, proteins, and liposomes. The present study aimed to verify the suitability of cellulose as a carrier for methotrexate (MTX). Hydroxyethylcellulose, with a molecular weight of 90 kDa and soluble in water, was used. Methotrexate was linked to cellulose by methyl ester bonds. A conjugate containing on average 9.5 molecules of MTX per molecule of cellulose was developed. Gel filtration HPLC analysis showed that the conjugate contained approximately 2% free drug. Dynamic light scattering analysis showed an increase in the polydispersity of the conjugate. The degradation of the conjugate in phosphate buffer and plasma followed first-order kinetics. The conjugate showed the lowest stability (half-life 154 h) in plasma. The conjugate showed 10-fold lower cytotoxicity to the 4 T1 mammary tumour cell line than the free drug. In the in vivo experiment to treat orthotopically implanted mammary tumours, the conjugate and the free drug, both applied intravenously, showed maximum inhibition of tumour growth of 48.4% and 11.2%, respectively. In conclusion, cellulose, which is a non-biodegradable chain glucose polymer, can be successfully used as a drug carrier, which opens up new research perspectives.

HPMA-based polymeric conjugates in anticancer therapeutics

Polymer therapeutics has gained prominence due to an attractive structural polymer chemistry and its applications in diseases therapy. In this review, we discussed the development and capabilities of N-(2-hydroxypropyl) methacrylamide (HPMA) and HPMA-drug conjugates in cancer therapy. The design, architecture, and structural properties of HPMA make it a versatile system for the synthesis of polymeric conjugations for biomedical applications. Research suggests that HPMA could be a possible alternative for polymers such polyethylene glycol (PEG) in biomedical applications. Although numerous clinical trials of HPMA-drug conjugates are ongoing, yet no product has been successfully brought to the market. Thus, further research is required to develop HPMA-drug conjugates as successful cancer therapeutics.

Hyaluronic Acid-Based Activatable Nanomaterials for Stimuli-Responsive Imaging and Therapeutics: Beyond CD44-Mediated Drug Delivery

There is a rapidly increasing interest in developing stimuli-responsive nanomaterials for treating a variety of diseases. By enabling the activation of function locally at the sites of interest, it is possible to increase therapeutic efficacy significantly while simultaneously reducing adverse side effects. While there are many sophisticated nanomaterials available, they are often highly complex and not easily transferrable to industrial scales and clinical settings. However, nanomaterials based on hyaluronic acid offer a compelling strategy for reducing their complexity while retaining several desirable benefits such as active targeting and stimuli-responsive degradation. Herein, the basic properties of hyaluronic acid, its binding partners, and natural routes for degradation by hyaluronidases-hyaluronic-acid-degrading enzymes-and oxidative stresses are discussed. Recent advances in designing hyaluronic acid-based, actively targeted, hyaluronidase- or reactive-oxygen-species-responsive nanomaterials for both diagnostic imaging and therapeutic delivery, which go beyond merely the classical targeting of CD44, are summarized.

Tailored therapeutics based on 1,2,3-1H-triazoles: a mini review

Contemporary drug discovery approaches rely on library synthesis coupled with combinatorial methods and high-throughput screening to identify leads. However, due to the multitude of components involved, a majority of optimization techniques face persistent challenges related to the efficiency of synthetic processes and the purity of compound libraries. These methods have recently found an upgradation as fragment-based approaches for target-guided synthesis of lead molecules with active involvement of their biological target. The click chemistry approach serves as a promising tool for tailoring the therapeutically relevant biomolecules of interest, improving their bioavailability and bioactivity and redirecting them as efficacious drugs. 1,2,3-1H-Triazole nucleus, being a planar and biologically acceptable scaffold, plays a crucial role in the design of biomolecular mimetics and tailor-made molecules with therapeutic relevance. This versatile scaffold also forms an integral part of the current fragment-based approaches for drug design, kinetic target guided synthesis and bioorthogonal methodologies.

Hyaluronic Acid-Coated Nanomedicine for Targeted Cancer Therapy

Hyaluronic acid (HA) has been widely investigated in cancer therapy due to its excellent characteristics. HA, which is a linear anionic polymer, has biocompatibility, biodegradability, non-immunogenicity, non-inflammatory, and non-toxicity properties. Various HA nanomedicines (i.e., micelles, nanogels, and nanoparticles) can be prepared easily using assembly and modification of its functional groups such as carboxy, hydroxy and N-acetyl groups. Nanometer-sized HA nanomedicines can selectively deliver drugs or other molecules into tumor sites via their enhanced permeability and retention (EPR) effect. In addition, HA can interact with overexpressed receptors in cancer cells such as cluster determinant 44 (CD44) and receptor for HA-mediated motility (RHAMM) and be degraded by a family of enzymes called hyaluronidase (HAdase) to release drugs or molecules. By interaction with receptors or degradation by enzymes inside cancer cells, HA nanomedicines allow enhanced targeting cancer therapy. In this article, recent studies about HA nanomedicines in drug delivery systems, photothermal therapy, photodynamic therapy, diagnostics (because of the high biocompatibility), colloidal stability, and cancer targeting are reviewed for strategies using micelles, nanogels, and inorganic nanoparticles.

Conjugate of Doxorubicin to Albumin-Binding Peptide Outperforms Aldoxorubicin

Short circulation time and off-target toxicity are the main challenges faced by small-molecule chemotherapeutics. To overcome these shortcomings, an albumin-binding peptide conjugate of chemotherapeutics is developed that binds specifically to endogenous albumin and harnesses its favorable pharmacokinetics and pharmacodynamics for drug delivery to tumors. A protein-G-derived albumin-binding domain (ABD) is conjugated with doxorubicin (Dox) via a pH-sensitive linker. One to two Dox molecules are conjugated to ABD without loss of aqueous solubility. The albumin-binding ABD-Dox conjugate exhibits nanomolar affinity for human and mouse albumin, and upon administration in mice, shows a plasma half-life of 29.4 h, which is close to that of mouse albumin. Additionally, 2 h after administration, ABD-Dox exhibits an approximately 4-fold higher concentration in the tumor than free Dox. Free Dox clears quickly from the tumor, while ABD-Dox maintains a steady concentration in the tumor for at least 72 h, so that its relative accumulation at 72 h is ≈120-fold greater than that of free Dox. The improved pharmacokinetics and biodistribution of ABD-Dox result in enhanced therapeutic efficacy in syngeneic C26 colon carcinoma and MIA PaCa-2 pancreatic tumor xenografts, compared with free Dox and aldoxorubicin, an albumin-reactive Dox prodrug currently in clinical development.

Redox Nano-Architectures: Perspectives and Implications in Diagnosis and Treatment of Human Diseases

SIGNIFICANCE

Efficient targeted therapy with minimal side-effects is the need of the hour. Locally altered redox state is observed in several human ailments, such as inflammation, sepsis, and cancer. This has been taken advantage of in designing redox-responsive nanodrug carriers. Redox-responsive nanosystems open a door to a multitude of possibilities for the control of diseases over other drug delivery systems. Recent Advances: The first-generation nanotherapy relies on novel properties of nanomaterials to shield the drug and deliver it to the diseased tissue or organ. The second generation is based on targeting the drug or diagnostic material to the diseased cell-specific receptors, or to a particular organ to improve the efficacy of the drug. The third and the latest generation of nanocarriers, the stimuli-responsive nanocarriers exploit the disease condition or environment to specifically deliver the drug or diagnostic probe for the best diagnosis and treatment. Several different kinds of stimuli such as temperature, magnetic field, pH, and altered redox state-responsive nanosystems have educed immense promise in the field of nanomedicine and therapy.

CRITICAL ISSUES

We describe the evolution of nanomaterial since its inception with an emphasis on stimuli-responsive nanocarriers, especially redox-sensitive nanocarriers. Importantly, we discuss the future perspectives of redox-responsive nanocarriers and their implications.

FUTURE DIRECTIONS

Redox-responsive nanocarriers achieve a near-to-zero premature release of the drug, thus avoiding off-site toxicity associated with the free drug. This bears great potential for the development of more effective drug delivery with better pharmacokinetics and pharmacodynamics.

Photodynamic Activity of Fullerene Derivatives Solubilized in Water by Natural-Product-Based Solubilizing Agents

Water-soluble fullerenes prepared by using solubilizing agents based on natural products are promising photosensitizers for photodynamic therapy. Cyclodextrin, β-1,3-glucan, lysozyme, and liposomes can stably solubilize not only C₆₀ and C₇₀ , but also some C₆₀ derivatives in water. To improve the solubilities of fullerenes, specific methods have been developed for each solubilizing agent. Water-soluble C₆₀ and C₇₀ exhibit photoinduced cytotoxicity under near-ultraviolet irradiation, but not at wavelengths over 600 nm, which are the appropriate wavelengths for photodynamic therapy. However, dyad complexes of solubilized C₆₀ derivatives combined with light-harvesting antenna molecules improve the photoinduced cytotoxicities at wavelengths over 600 nm. Furthermore, controlling the fullerene and antenna molecule positions within the solubilizing agents affects the performance of the photosensitizer.

The antioxidant, aged garlic extract, exerts cytotoxic effects on wild-type and multidrug-resistant human cancer cells by altering mitochondrial permeability

Aged garlic extract (AGE) has been shown to possess therapeutic properties in cancer; however its mechanisms of action are unclear. In this study, we demonstrate by MTT assay that AGE exerts an anti-proliferative effect on a panel of both sensitive and multidrug-resistant (MDR) human cancer cell lines and enhances the effects of hyperthermia (42˚C) on M14 melanoma cells. The evaluation of the mitochondrial activity in whole cancer cells treated with AGE, performed by cytofluorimetric analysis in the presence of the lipophilic cationic fluorochrome JC-1, revealed the occurrence of dose-dependent mitochondrial membrane depolarization. Membrane potential was measured by the TPP+ selective electrode. In order to shed light on its mechanisms of action, the effects of AGE on isolated rat liver mitochondria were also examined. In this regard, AGE induced a mitochondrial membrane hyperpolarization of approximately 15 mV through a mechanism that was similar to that observed with the ionophores, nigericin or salinomycin, by activating an exchange between endogenous K+ with exogenous H+. The prolonged incubation of the mitochondria with AGE induced depolarization and matrix swelling, indicative of mitochondrial permeability transition induction that, however, occurs through a different mechanism from the well-known one. In particular, the transition pore opening induced by AGE was due to the rearrangement of the mitochondrial membranes following the increased activity of the K+/H+ exchanger. On the whole, the findings of this study indicate that AGE exerts cytotoxic effects on cancer cells by altering mitochondrial permeability. In particular, AGE in the mitochondria activates K+/H+ exchanger, causes oxidative stress and induces mitochondrial permeability transition (MPT).

From Conventional to Stealth Liposomes a new Frontier in Cancer Chemotherapy

Many attempts have been made to achieve good selectivity to targeted tumor cells by preparing specialized carrier agents that are therapeutically profitable for anticancer therapy. Among these, liposomes are the most studied colloidal particles thus far applied in medicine and in particular in antitumor therapy. Although they were first described in the 1960s, only at the beginning of 1990s did the first therapeutic liposomes appear on the market. The first-generation liposomes (conventional liposomes) comprised a liposome-containing amphotericin B, Ambisome (Nexstar, Boulder, CO, USA), used as an antifungal drug, and Myocet (Elan Pharma Int, Princeton, NJ, USA), a doxorubicin-containing liposome, used in clinical trials to treat metastatic breast cancer. The second-generation liposomes (“pure lipid approach”) were long-circulating liposomes, such as Daunoxome, a daunorubicin-containing liposome approved in the US and Europe to treat AIDS-related Kaposi's sarcoma. The third-generation liposomes were surface-modified liposomes with gangliosides or sialic acid, which can evade the immune system responsible for removing liposomes from circulation. The fourth-generation liposomes, pegylated liposomal doxorubicin, were called “stealth liposomes” because of their ability to evade interception by the immune system, in the same way as the stealth bomber was able to evade radar. Actually, the only stealth liposome on the market is Caelyx/Doxil (Schering-Plough, Madison NJ, USA), used to cure AIDS-related Kaposi's sarcoma, resistant ovarian cancer and metastatic breast cancer. Pegylated liposomal doxorubicin is characterized by a very long-circulation half-life, favorable pharmacokinetic behavior and specific accumulation in tumor tissues. These features account for the much lower toxicity shown by Caelyx in comparison to free doxorubicin, in terms of cardiotoxicity, vesicant effects, nausea, vomiting and alopecia. Pegylated liposomal doxorubicin also appeared to be less myelotoxic than doxorubicin. Typical forms of toxicity associated to it are acute infusion reaction, mucositis and palmar plantar erythrodysesthesia, which occur especially at high doses or short dosing intervals. Active and cell targeted liposomes can be obtained by attaching some antigen-directed monoclonal antibodies (Moab or Moab fragments) or small proteins and molecules (folate, epidermal growth factor, transferrin) to the distal end of polyethylene glycol in pegylated liposomal doxorubicin. The most promising therapeutic application of liposomes is as non-viral vector agents in gene therapy, characterized by the use of cationic phospholipids complexed with the negatively charged DNA plasmid. The use of liposome formulations in local-regional anticancer therapy is also discussed. Finally, pegylated liposomal doxorubicin containing radionuclides are used in clinical trials as tumor-imaging agents or in positron emission tomography.

Poly(N-(2-Hydroxypropyl) Methacrylamide)-Valproic Acid Conjugates as Block Copolymer Nanocarriers

We report nanoassemblies based on block copolymers of N-(2-hydroxypropyl) methacrylamide (HPMA) in which drug cleavage enhances the biological compatibility of the original polymer carrier by regeneration of HPMA units. Drug release via ester hydrolysis suggests this approach offers potential for stimuli-responsive drug delivery under acidic conditions.

Mesoporous silica nanoparticles (MSNs)-based organic/inorganic hybrid nanocarriers loading 5-Fluorouracil for the treatment of colon cancer with improved anticancer efficacy

Novel methods to improve the anticancer performance of 5-fluorouracil (5-FU) is quite necessary for clinical medicines. In the present work, we fabricated a novel type of mesoporous silica nanoparticles (MSNs)-based inorganic/organic hybrid nanoparticles covalently attached with poly(oligo(ethylene glycol) monomethyl ether methacrylate) (POEGMA) for improved stabilization and targeting peptide (RGD) for targeted delivery with the aim of improving the anticancer performance of 5-FU. Atom transfer radical polymerization (ATRP) initiator functionalized MSN (MSN-Br) was synthesized at first, which was followed by surface-initiated ATRP of water soluble OEGMA and carboxyl-containing monomer (2-succinyloxyethyl methacrylate, SEMA). Functionalization of RGD onto the hydrophilic P(OEGMA-co-SEMA) chains afforded the final hybrid nanoparticle, MSN-P(OEGMA-co-RGD). 5-FU can be effectively loaded into the meso-pores of MSN-P(OEGMA-co-RGD) (5-FU@MSN-RGD) with drug content ∼7.5wt%. And the dynamic diameter (D_h) and zeta potential (ζ) of 5-FU@MSN-RGD were determined to be 199.3±5.4nm and -8.7±0.5mV, respectively. It was demonstrated that MSN-P(OEGMA-co-RGD) exhibited improved internalization into colon cancer cells and enhanced accumulation in tumor tissues. In addition, compared with free 5-FU, 5-FU@MSN-RGD showed enhanced anticancer efficacy both in vitro and in vivo, implying promising clinical applications.

Nanomedicine for prostate cancer using nanoemulsion: A review

Prostate cancer (PCa) is a worldwide issue, with burgeoning rise in prevalence, morbidity and mortality. Targeted drug delivery, a long sort solution in this regard using controlled release (CR) - nanocarriers, is still a challenge. There is an emerging criticism that, the challenges are due to less appreciation for the biological barriers and lack of corresponding newer technologies. Over the years, more understanding about the biological barriers has come with the progress in characterization techniques. Correspondingly, there is a change in opinion about approaches in clinical trial that; focus of the end point need to be shifted towards disease stabilization for these explorative technologies. Currently, there is a requirement to overcome these newly identified challenges to develop newer affordable therapeutics. The ongoing clinical protocol for therapy using CR-nanocarriers is intravenous injection followed by local targeting to cancer site. This is the most accepted protocol and new CR-nanocarriers are being developed to suit this protocol. In this review, recent progress in treatment of PCa using CR-nanocarriers is analyzed with respect to newly identified biological barriers and design challenges. Possibilities of exploring nanoemulsion (NE) platform for targeted drug delivery to PCa are examined. Repurposing of drugs and combination therapy using NE platform targeted to PCa can be explored for design and development of affordable nanomedicine. In 20yrs. from now there expected to be numerous affordable nanomedicine technologies available in market exploring these lines.

Color-Convertible, Unimolecular, Micelle-Based, Activatable Fluorescent Probe for Tumor-Specific Detection and Imaging In Vitro and In Vivo

Recent years have witnessed significant progress in molecular probes for cancer diagnosis. However, the conventional molecular probes are designed to be "always-on" by attachment of tumor-targeting ligands, which limits their abilities to diagnose tumors universally due to the variations of targeting efficiency and complex environment in different cancers. Here, it is proposed that a color-convertible, activatable probe is responding to a universal tumor microenvironment for tumor-specific diagnosis without targeting ligands. Based on the significant hallmark of up-regulated hydrogen peroxide (H₂ O₂ ) in various tumors, a novel unimolecular micelle constructed by boronate coupling of a hydrophobic hyperbranched poly(fluorene-co-2,1,3-benzothiadiazole) core and many hydrophilic poly(ethylene glycol) arms is built as an H₂ O₂ -activatable fluorescent nanoprobe to delineate tumors from normal tissues through an aggregation-enhanced fluorescence resonance energy transfer strategy. This color-convertible, activatable nanoprobe is obviously blue-fluorescent in various normal cells, but becomes highly green-emissive in various cancer cells. After intravenous injection to tumor-bearing mice, green fluorescent signals are only detected in tumor tissue. These observations are further confirmed by direct in vivo and ex vivo tumor imaging and immunofluorescence analysis. Such a facile and simple methodology without targeting ligands for tumor-specific detection and imaging is worthwhile to further development.

Preclinical evaluation of taxane-binding peptide-modified polymeric micelles loaded with docetaxel in an orthotopic breast cancer mouse model

We developed a novel taxane-binding peptide (TBP) modified, biodegradable polymeric micelle that overcomes limitations of drug loading and poor serum stability typically seen with particle delivery, leading to enhanced pharmacokinetics and tumor distribution of docetaxel (DTX). The use of the taxane-binding peptide to increase docetaxel loading is particularly compelling as it takes advantage of a known intracellular binding mechanism in a new way. Docetaxel is a potent chemotherapeutic with a therapeutic index often limited by the toxicity of the excipients that are necessary to enhance its solubility for intravenous delivery. Our polymeric micelle has terminal furan groups that enable facile antibody Fab conjugation by Diels-Alder chemistry for targeted delivery. Compared to the conventional ethanolic polysorbate 80 formulation (Free DTX), our nanoparticle (NP DTX) formulation exhibited a two-fold increase in exposure and tumor accumulation. Notably, the reduced toxicity of the NP DTX formulation increased the therapeutic index and allowed for higher dosing regimens, with a maximum tolerated dose (MTD) 1.6-fold higher than that of the Free DTX formulation, which is significant and similar to enhancements observed in clinical products for docetaxel and other drugs. These improved properties led to enhanced mouse survival in an orthotopic model of breast cancer; however, the targeted formulation of Fab-NP DTX did not further improve efficacy. Together, these results clearly demonstrate the benefits of the TBP-modified polymeric micelles as promising carriers for docetaxel.

Biocompatible and fluorescent superparamagnetic iron oxide nanoparticles with superior magnetic properties coated with charged polysaccharide derivatives

Syntheses and characterizations of biocompatible superparamagnetic iron oxide nanoparticles with embedded curcumin and coated with ultrathin layer of hyaluronic acid-curcumin (HA-Cur) conjugate have been reported. Zeta potential measurements confirmed effective coating of native iron oxide nanoparticles stabilized by cationic derivative of chitosan (SPION-CCh) with the synthesized HA-Cur conjugate. Both SPIONs with embedded curcumin and the ones coated with HA-Cur (SPION-CCh/HA-Cur) revealed desired magnetic characteristics while fluorescent properties were much better for the coated nanoparticles. SPION-CCh/HA-Cur nanoparticles were shown to be very promising candidates for T₂ MRI contrast agents as they can easily penetrate cell membrane and their relaxivity is exceptionally high (ca. 470mM^-1s^-1). They may be also tracked using confocal fluorescence microscopy due to the presence of fluorescent curcumin in the coating. In vitro studies indicated that the obtained SPIONs-CCh/HA-Cur were non-toxic for EA.hy926 endothelial cells.

Efficacy Interactions of PEG-DOX-N-acetyl Glucosamine Prodrug Conjugate for Anticancer Therapy

Present investigation is exploring structure-biocompatibility interaction of tumour targeted polyethylene glycol (PEG) based drug conjugate of doxorubicin using N-acetyl glucosamine as targeting ligand. The synthesized polymer drug conjugate was evaluated for particle size, zeta potential, molecular weight, haemolysis activity, cytotoxicity, protein binding and in vitro receptor (lectin) binding study. The particle size of synthesized conjugate was observed to be around 30 nm with polydispersability index of 0.213 indicating mono-disperse particles. Fluorescence quenching assay addressed relatively lower binding interactions of polymer drug conjugate to bovine serum albumin in comparison with free doxorubicin which may be governed to the hydrophilicity of polyethylene glycol and N-acetyl glucosamine. The cell compatibility and haemolysis study showed that PEG drug conjugate was nontoxic and biocompatible, which recommends the suitability of polymer drug conjugates for delivering biological active agents systemically. In vitro ligand-lectin receptor binding assays of synthesized targeted polymer conjugate suggest the possibility of promising interaction of N-acetyl glucosamine in vivo. Thus, the study indicated the suitability of N-acetyl glucosamine anchored targeted polymer drug conjugate in delivering bio-therapeutics for specifically targeting to tumour tissues.

Use of New Aminosugar Derivatives as Comonomers for the Synthesis of Glycosylated Poly(Amido-Amines)

New sugar functionalized poly(amido-amines) (PAA) polymers were synthesized. The PAA made by the addition polymerization of 2-methylpiperazine-2,2-bisacrylamidoacetic acid (ISA) was chosen for its potential applications in the biomedical field and the sugar monomers were obtained by chemical and enzymatic synthetic strategies. Specifically, the 2-aminoethyl fi-D-galactopyranosyl monomer was directly obtained by enzymatic catalysis, while the 2-aminoethyl amide and the 3-aminopropyl amide of lactobionic acid were obtained by ning-opening reactions of the corresponding lactone. The presence of sugar moieties in the polymer chains was confirmed by FT-IR, 'H NMR, 13C NMR analysis and calorimetric assay. The sugar content of polymer derivatives is sufficient for targeting purpose, making these compounds potential soluble drug carriers.

Enzymatic Degradation of Poly(ethylene glycol) Modified Dextrans

Poly(ethylene glycol) (PEG), with molecular weight 2,000 and 5,100, were conjugated to dextran (T40) with three different degrees of substi tution. The biodegradation of the six PEG-dextran conjugates was evaluated, using dextranase, isolated rat cecum cell free extracts (CFE), and rat liver lysosomal enzymes. All the substrates were degraded by dextranase; however, the rate of the degradation decreased with an increase in the degree of modification as well as in the molecular weight of PEG. When incubated with CFE, these conjugates were degraded with reduced rates, but a similar trend was observed, indicating the presence of an endo-acting dextranase in the rat cecum contents. The modified dextrans, however, resisted degradation by lyso somal enzymes in vitro during 36 h incubation at 37°C. The degradation of modified dextrans was evaluated by gel permeation chromatography (GPC). For the degradation of dextran conjugates by dextranase, two additional methods were also employed, i.e., static light scattering (SLS), and dynamic light scat tering (DLS). The results, as compared to those published on the modification of dextrans with low molecular weight reagents, demonstrated the PEGs' unique effects on the interaction of modified substrates with proteins. It ap pears that PEG conjugation reduced the enzymatic degradability of dextran conjugates not only due to the modification of dextran structure and the sterical hindrance to the formation of the enzyme-substrate complex, but also by the participation of PEG chains in the repulsion of enzyme molecules.

Succinoylated Poly[N-(2- Hydroxyethyl)-L-Glutamine] Derivatives for Drug Delivery

A series of succinoylated poly[N-(2-)- L-glutamine] (PHEG) derivatives was synthesized by reacting PHEG with succinic anhydride in the presence of N,N-dimethylaminopyridine as a catalyst. The size of the derivatives were measured by dynamic light scattering in buffers (pH 5.5 and 7.4, respectively) the lysosomal and physiological pH. The degradability of the succinoylated polymers toward cathepsin B was followed by gel permeation chromatography. It was demonstrated that an increase of modification results in decreased biodegradability. Conjugation of mitomycin C (MMC) with a succinoylated PHEG derivative through a collagenase-sensitive Pro-Leu-Gly-Pro- Leu spacer resulted in a water-soluble MMC conjugate. This conjugate was shown to be hydrolytically stable in buffers of lysosomal and physiological pH and able to release MMC in the presence of the bacterial collagenase clostridium histolyticum.

Dendritic Poly-[N-(2-Hydroxyethyl)-L-Glutamine] as Potential Drug Carrier

Dendritic poly-[ N-(2-hydroxyethyl)-L-glutamine] (PHEG) with different molecular weights were synthesized by aminolysis of dendritic poly-(γ-benzyl-L-glutamate) (PBG), which was obtained by polymerization of the corresponding N-carboxyanhydride (NCA) with poly(amido amine) (PAMAM, starburst®) of the fourth generation as initiator. Dynamic light scattering (DLS) was used to determine the size of the polymeric carriers and to compare the dendritic polymer to the linear analogue. The body distribution and blood clearance of 125 I-radiolabelled linear and dendritic PHEG with similar molecular weight were investigated in female BALB/c mice.

Biodistribution and Antitumor Activity Induced by Carboxymethylcellulose Conjugates

New polymers with antitumor activity were synthesized by conjugating ethyl p-aminobenzoate (benzocaine) and N-hydroxy-2,3-dihydroxybenzamide (Didox) onto carboxymethylcellulose (CMC) and oxidized CMC. The biological tests ( in vitro and in vivo) for these CMC derivatives exhibited prolonged half-life in serum, accumulation in the solid tumors, and inhibition of the tumor growth. The latter effect was attributed to the permeability and retention (EPR) effect.

Antitumoral Activity Induced by Alkylating Agents Conjugated to Poly(maleic anhydride-alt-vinyl acetate)

New polyanionic polymer conjugates with antitumoral activity are synthesized by chemically binding mustard type alkylating derivatives of di-(β-chloroethyl)-amine and tri-(β-chloroethyl)-amine, respectively, onto poly(maleic anhydride-alt-vinyl acetate). The structures of the compounds are verified by FTIR, 1H NMR, and elemental analysis. The antitumoral activity of these polymeric drugs is evaluated in vivo using carcinosarcoma Walker 256 solid tumors in Wister rats. The conjugates exhibit antitumor regression (ATR) values between 25 and 44% depending on comonomers' structure. In addition, an accumulation in the solid tumors (enhanced permeability and retention (EPR) effect) by these compounds is observed. These compounds also cause small organotropic effects, such as increases in the liver, spleen, and kidney weight.

Influence of Molecular Weight on the Biological Effects of Benzocaine Modified Maleic Anhydride Copolymer

A new series of polyanionic polymers with antitumor activity were synthesized by conjugating ethyl 4-aminobenzoate onto a series of maleic anhydride (MA) copolymers of vinyl acetate, methyl methacrylate, and styrene. The molecular weight of these copolymers ranged from 18 103 to 2 105. The in vivo and in vitro biological tests showed that the maleic anhydride synthesized copolymers exhibit prolonged half-life in serum, accumulate in K562 erythroleukemia solid tumors, and inhibit tumor growth. The antitumor activity appears to be increased by the enhanced permeability and retention (EPR) effect which is related to the macromolecular size of the antitumor agent.