Design strategies to improve soluble macromolecular delivery constructs

Gemcitabine-Doxorubicin Combination Polymer-Drug Conjugate Prepared by SPAAC Click Chemistry: In Vitro Characterization

Combination chemotherapy is preferred for the treatment of ovarian cancer (OC). Systemic toxicity, however, frequently limits the effectiveness of treatment. Polymer-drug conjugates (PDCs) containing synergistic combinations of chemotherapeutic drugs can be used to enhance therapeutic efficacy. We earlier reported the use of a strain-promoted [3 + 2] azide-alkyne cycloaddition (SPAAC)-mediated polymerization method for the preparation of single-drug PDCs. In this report, the polymerization method was used to prepare gemcitabine-doxorubicin combination PDC. The PDC had a high molecular weight (Mw 1360 kDa) and high drug loading (36.6% weight gemcitabine; 7.0% weight doxorubicin). It demonstrated cathepsin B-catalyzed drug release at pH 5.0 and good hydrolytic stability at pH 7.4. The combination index analysis of free gemcitabine and free doxorubicin showed a concentration-dependent synergism (combination index < 1) in OVCAR-3 OC cells. Compared to individual gemcitabine PDC (the concentration that inhibited 50% growth (IC50) > 50 µg/mL) and doxorubicin PDC (IC50 = 1.79 µg/mL), the combination PDC (IC50 = 0.99 µg/mL) showed greater cytotoxicity against OVCAR-3 cells and was less cytotoxic than the equivalent free drug combination (IC50 = 0.11 µg/mL). The gemcitabine-doxorubicin combination PDC is promising for targeted combination chemotherapy of OC.

Nanoencapsulation as a Promising Platform for the Delivery of the Morin-Cu(II) Complex: Antibacterial and Anticancer Potential

Nanoencapsulation has emerged as a promising approach for the effective delivery of poorly aqueous soluble compounds. The current study focuses on the preparation of human serum albumin (HSA)-based nanoparticles (NPs) and poly lactic-co-glycolic acid (PLGA)-based nanoparticles for effective delivery of the morin-Cu(II) complex. The NPs were analyzed based on different parameters such as particle size, surface charge, morphology, encapsulation efficiency, and in vitro release properties. The average particle sizes were found to be 214 ± 6 nm for Mor-Cu-HSA-NPs and 185 ± 7.5 nm for Mor-Cu-PLGA-NPs. The release of the morin-Cu(II) complex from both the NPs (Mor-Cu-HSA-NPs and Mor-Cu-PLGA-NPs) followed a biphasic behavior, which comprises an early burst release followed by a sustained and controlled release. The resulting NPs also exhibit free radical scavenging activity confirmed by a standard antioxidant assay. The antibacterial activities of the NPs were investigated using a disk diffusion technique, and it was observed that both the NPs showed better antibacterial activity than morin and the morin-Cu(II) complex. The anticancer activities of the prepared NPs were examined on MDA-MB-468 breast cancer cell lines using a cytotoxicity assay, and the mode of cell death was visualized using fluorescence microscopy. Our results revealed that NPs kill the cancer cells with greater efficiency than free morin and the morin-Cu(II) complex. Thus, both HSA-based NPs and PLGA-based NPs can act as promising delivery systems for the morin-Cu(II) complex and can be utilized for further biomedical applications.

Responsive polyprodrug for anticancer nanocarriers

Nanocarriers responsive to glutathione (GSH), a molecule overexpressed in cancer cells, are extensively investigated for the delivery of Pt-based chemotherapeutics for cancer treatment.

Exhausting tumor associated macrophages with sialic acid-polyethyleneimine-cholesterol modified liposomal doxorubicin for enhancing sarcoma chemotherapy

To overstep the dilemma of chemical drug degradation within powerful lysosomes of tumor associated macrophages (TAMs), a sialic acid-polyethylenimine-cholesterol (SA-PEI-CH) modified liposomal doxorubicin (DOX-SPCL) was designed with both TAMs targeting and smart lysosomal trafficking. The modified liposome DOX-SPCL performed particle size as 103.2 ± 3.1 nm and zeta potential as -4.5 ± 0.9 mV with encapsulation efficiency as 95.8 ± 0.5%. In in vitro cell experiments, compared with conventional liposomal doxorubicin (DOX-CL) and PEGylated liposomal doxorubicin (DOX-PL), DOX-SPCL showed a selective binding on TAMs and a mere lysosomal concentration. In pharmacokinetic study, DOX-SPCL effectively impeded/delayed the disposition of mononuclear phagocyte system (MPS) with a value of AUC_0-t as 796.03 ± 66.93 mg L^-1 h. In S180 sarcomas bearing mice, DOX-SPCL showed the greatest tumor inhibition rate (92.7% ± 3.6%) compared with DOX-CL (46.4% ± 2.0%) or DOX-PL (58.8% ± 7.6%). The <0.5% positive region of TAMs in tumor section indicated a super TAMs exhaustion for DOX-SPCL treatment. Conclusively, DOX-SPCL was supposed as a safe and effective liposomal preparation for clinical sarcoma treatment via TAMs targeting/deletion delivery strategy.

Investigation of pH-responsive block glycopolymers with different structures for the delivery of doxorubicin

To understand the influence of the construction of pH-responsive glycopolymer carriers on loading and release behaviors of the drug, three types of block glycopolymers with similar compositions but different constructions, PEG-b-P(DEA-co-GAMA), PEG-b-PDEA-b-PGAMA and PEG-b-PGAMA-b-PDEA, were successfully synthesized via atom transfer radical polymerization (ATRP) method. The compositions and structures of the three glycopolymers were characterized using 1H NMR (nuclear magnetic resonance) and GPC (gel permeation chromatography), while the morphology and size of aggregates from pH-sensitive block glycopolymers were measured using TEM (transmission electron microscopy) and DLS (dynamic light scattering). The results indicated that the micelles prepared from PEG-b-PGAMA-b-PDEA had a more compact shell structure. The drug-loaded micelles were prepared using the diafiltration method at pH 10, and the loading content and loading efficiency were analyzed using a UV-visible spectrophotometer. DOX-loaded micelles formed by PEG-b-PGAMA-b-PDEA with the more compact shell construction showed the highest loading content and loading efficiency (12.0 wt% and 58.0%) compared with the other two micelles. Moreover, the DOX release tests of these micelles were carried out under two PBS conditions (pH 7.4 and pH 5.5), and the DOX release amount in a certain time was analyzed using a UV-visible spectrophotometer. The results showed that the more compact shell construction of the three layered micelle obstructed the diffusion of a proton into the PDEA core at pH 5.5 and delayed the drug from releasing under both conditions. Moreover the two-layered micelle with a PDEA and PGAMA mixed core showed a relatively high release amount owing to the porous core permitting unimpeded releasing at pH 7.4 and promoted the protonation of PDEA at pH 5.5. Insights gained from this study show that the structure of block copolymers, leading to different constructions of micelles, could adjust the drug loading and release behavior to certain extent, thus it may contribute to improving the design of desirable drug delivery systems.

Antitumor activity of a molecularly imprinted nanopreparation of 5-flurouracil against Ehrlich's carcinoma solid tumors grown in mice: Comparison to free 5-flurouracil

Recently, nanotechnology has received great attention in war against cancer. The present study investigated the antitumor efficacy of molecularly imprinted nanopreparation of 5-fluorouracil (nano-5-FU) against Ehrlich ascites carcinoma (EAC) solid tumors grown in mice. Tumor cells were transplanted into female albino mice. Mice were allocated into 5 groups; Group 1: control EAC bearing mice. Groups 2&3: EAC-bearing mice treated orally with 5-FU (5 and 10 mg/kg) twice weekly. Groups 4&5: EAC bearing mice treated with nano-5-FU (5 and 10 mg/kg) twice weekly. Treatment with nano-5-FU showed higher antitumor effect compared to free 5-FU as indicated by enhanced apoptosis and reduction in tumor weight. Additionally, lower number of mitotic figures and greater area for necrosis were observed in the tumor specimens alongside with a decline in the number of intratumoral proliferating nuclei in comparison to free 5-FU. Furthermore, the results showed a significant down-regulation in tumoral expression of caspase-3 and vascular endothelial growth factor. Together, these results further support the potential of using nanotechnology to enhance anticancer efficacy of 5-FU.

Affibody molecules for molecular imaging and targeted drug delivery in the management of breast cancer

Breast cancer is one of the leading reasons for the morbidity and mortality of cancer related death globally. The modern therapies are basically the combination of the breast-preserving surgeries or ablation with or without node biopsy or destroying the carcinoma cells adjuvant with chemotherapy, radiotherapy, hormonal or biological therapies depending upon the nature of the receptor of the cancerous cells, nature of the lymph node, as well as the tendency of the recurrence. For decade's carcinoma management suffered by the limitation of imagining, targeting and penetrability problem associated with management and cure of this deadly disease leads to unwanted chemo-toxicity and side effects. Alike other antibody mimetics, affibodies are designed with the combinatorial protein engineering approaches which are small and robust protein scaffolds retaining the favorable folding and stability. Affibody is one of the significantly important tools for imaging and diagnosis of the affinity specific over expressed proteins in the breast cancer management. The review summarizes the various affibody strategies uses in the management of breast cancer.

ROS-Responsive Polyprodrug Nanoparticles for Triggered Drug Delivery and Effective Cancer Therapy

The application of nanoparticles (NPs) to drug delivery has led to the development of novel nanotherapeutics for the treatment of various diseases including cancer. However, clinical use of NP-mediated drug delivery has not always translated into improved survival of cancer patients, in part due to the suboptimal properties of NP platforms, such as premature drug leakage during preparation, storage, or blood circulation, lack of active targeting to tumor tissue and cells, and poor tissue penetration. Herein, an innovative reactive oxygen species (ROS)-responsive polyprodrug is reported that can self-assemble into stable NPs with high drug loading. This new NP platform is composed of the following key components: (i) polyprodrug inner core that can respond to ROS for triggered release of intact therapeutic molecules, (ii) polyethylene glycol (PEG) outer shell to prolong blood circulation; and (iii) surface-encoded internalizing RGD (iRGD) to enhance tumor targeting and tissue penetration. These targeted ROS-responsive polyprodrug NPs show significant inhibition of tumor cell growth both in vitro and in vivo.

Trileucine residues in a ligand-CPP-based siRNA delivery platform improve endosomal escape of siRNA

siRNA entrapment within endosomes is a significant problem encountered with siRNA delivery platforms that co-opt receptor-mediated entry pathways. Attachment of a cell-penetrating peptide (CPP), such as nona-arginine (9R) to a cell receptor-binding ligand like the Rabies virus glycoprotein, RVG, allows effective siRNA delivery to the cytoplasm by non-endocytic pathways, but a significant amount of siRNA complexes also enters the cell by ligand-induced receptor endocytosis and remain localized in endosomes. Here, we report that the incorporation of trileucine (3 Leu) residues as an endo-osmolytic moiety in the peptide improves endosomal escape and intracellular delivery of siRNA. The trileucine motif did not affect early non-endosomal mechanism of cytoplasmic siRNA delivery but enhanced target gene silencing by >20% only beyond 24 h of transfection when siRNA delivery is mostly through the endocytic route and siRNA trapped in the endosomes at later stages were subject to release into cytoplasm. The mechanism may involve endosomal membrane disruption as trileucine residues lysed RBCs selectively under endosomal pH conditions. Interestingly <3 Leu or >3 Leu residues were not as effective, suggesting that 3 Leu residues are useful for enhancing cytoplasmic delivery of siRNA routed through endosomes.

Targeted nanoparticles from xyloglucan–doxorubicin conjugate loaded with doxorubicin against drug resistance

The novel targeted Xyloglucan–doxorubicin nanoparticle drug delivery systems (DOX nano-DDSs) exhibited improved cellular uptake, increased accumulation in tumor, higher cytotoxicity against drug resistant tumor cells and reduced side effects.

Redox-Responsive Self-Assembled Chain-Shattering Polymeric Therapeutics

We report the design and development of redox-responsive chain-shattering polymeric therapeutics (CSPTs). CSPTs were synthesized by condensation polymerization and further modified with poly(ethylene glycol) (PEG) via "Click" reaction. Size-controlled CSPT nanoparticles (NPs) were formed through nanoprecipitation with high drug loading (up to 18%); the particle size increased in a concentration dependent manner. Drug release from particles was well controlled over 48 h upon redox triggering. The anticancer efficacy of the CSPT NPs was validated both in vitro and in vivo.

Self-organized nanoparticle drug delivery systems from a folate-targeted dextran–doxorubicin conjugate loaded with doxorubicin against multidrug resistance

DOX nano-DDSs with the function of both targeting tumors and controlling drug release were prepared which exhibited larger drug releases, higher cytotoxicity against HepG2/DOX cells, improved cellular uptake and decreased side toxicities.

Human immunodeficiency virus-1 (HIV-1)-mediated apoptosis: new therapeutic targets

HIV has posed a significant challenge due to the ability of the virus to both impair and evade the host’s immune system. One of the most important mechanisms it has employed to do so is the modulation of the host’s native apoptotic pathways and mechanisms. Viral proteins alter normal apoptotic signaling resulting in increased viral load and the formation of viral reservoirs which ultimately increase infectivity. Both the host’s pro- and anti-apoptotic responses are regulated by the interactions of viral proteins with cell surface receptors or apoptotic pathway components. This dynamic has led to the development of therapies aimed at altering the ability of the virus to modulate apoptotic pathways. These therapies are aimed at preventing or inhibiting viral infection, or treating viral associated pathologies. These drugs target both the viral proteins and the apoptotic pathways of the host. This review will examine the cell types targeted by HIV, the surface receptors exploited by the virus and the mechanisms whereby HIV encoded proteins influence the apoptotic pathways. The viral manipulation of the hosts’ cell type to evade the immune system, establish viral reservoirs and enhance viral proliferation will be reviewed. The pathologies associated with the ability of HIV to alter apoptotic signaling and the drugs and therapies currently under development that target the ability of apoptotic signaling within HIV infection will also be discussed.

A cell-based pharmacokinetics assay for evaluating tubulin-binding drugs

Increasing evidence reveals that traditional pharmacokinetics parameters based on plasma drug concentrations are insufficient to reliably demonstrate accurate pharmacological effects of drugs in target organs or cells in vivo. This underscores the increasing need to improve the types and qualities of cellular pharmacokinetic information for drug preclinical screening and clinical efficacy assessments. Here we report a whole cell-based method to assess drugs that disturb microtubule dynamics to better understand different formulation-mediated intracellular drug release profiles. As proof of concept for this approach, we compared the well-known taxane class of anti-microtubule drugs based on paclitaxel (PTX), including clinically familiar albumin nanoparticle-based Abraxane™, and a polymer nanoparticle-based degradable paclitaxel carrier, poly(L-glutamic acid)-paclitaxel conjugate (PGA-PTX, also known as CT-2103) versus control PTX. This in vitro cell-based evaluation of PTX efficacy includes determining the cellular kinetics of tubulin polymerization, relative populations of cells under G2 mitotic arrest, cell proliferation and total cell viability. For these taxane tubulin-binding compounds, the kinetics of cell microtubule stabilization directly correlate with G2 arrest and cell proliferation, reflecting the kinetics and amounts of intracellular PTX release. Each individual cell-based dose-response experiment correlates with published, key therapeutic parameters and taken together, provide a comprehensive understanding of drug intracellular pharmacokinetics at both cellular and molecular levels. This whole cell-based evaluating method is convenient, quantitative and cost-effective for evaluating new formulations designed to optimize cellular pharmacokinetics for drugs perturbing tubulin polymerization as well as assisting in explaining drug mechanisms of action at cellular levels.

Synthesis and evaluation of degradable polyurea block copolymers as siRNA delivery agents

Chain extension by diisocyanate condensation provides a versatile and convenient means for preparing block copolymers. We have utilized this chemistry to prepare reducible multiblock polycations for siRNA delivery. This approach, an alternative to oxidative coupling, was suitable for preparing multiblock polycations with defined molecular weight and architecture. The polymer, PEG-b-multi-(polyhexylurea-co-oligo-L-lysine)-b-PEG, was capable of electrostatically condensing siRNA to form nano-sized polyplexes across a broad compositional range. We demonstrated that the polyplexes enter the cells via endocytosis and interact with the endosome membrane leading to destabilization and hence endosome escape. Another feature of these polymers is their multiple intra-chain disulfide linkages. This enables weakening of the polyplex via chain scission within the cytosol's reductive environment. In addition to the controlled preparation of the polymer, the polyplexes were capable of delivering siRNA in vitro to silence greater than 50% green fluorescent protein expression with negligible toxicity.

177Lu-labeled HPMA copolymers utilizing cathepsin B and S cleavable linkers: synthesis, characterization and preliminary in vivo investigation in a pancreatic cancer model

INTRODUCTION

A major barrier to the advancement of therapeutic nanomedicines has been the non-target toxicity caused by the accumulation of the drug delivery systems in organs associated with the reticuloendothelial system, particularly the liver and spleen. Herein, we report the development of peptide based metabolically active linkers (MALs) that are enzymatically cleaved by cysteine cathepsin B and S, two proteases highly expressed in the liver and spleen. The overall goal of this approach is to utilize the MALs to lower the non-target retention and toxicity of radiolabeled drug delivery systems, thus resulting in higher diagnostic and radiotherapeutic efficacy.

METHODS

In this study three MALs (MAL0, MAL1 and MAL2) were investigated. MAL1 and MAL2 are composed of known substrates of cathepsin B and S, respectively, while MAL0 is a non-cleavable control. Both MAL1 and MAL2 were shown to undergo enzymatic cleavage with the appropriate cathepsin protease. Subsequent to conjugation to the HPMA copolymer and radiolabeling with (177)Lu, the peptide-polymer conjugates were renamed (177)Lu-metabolically active copolymers ((177)Lu-MACs) with the corresponding designations: (177)Lu-MAC0, (177)Lu-MAC1 and (177)Lu-MAC2.

RESULTS

In vivo evaluation of the (177)Lu-MACs was performed in an HPAC human pancreatic cancer xenograft mouse model. (177)Lu-MAC1 and (177)Lu-MAC2 demonstrated 3.1 and 2.1 fold lower liver retention, respectively, compared to control ((177)Lu-MAC0) at 72h post-injection. With regard to spleen retention, (177)Lu-MAC1 and (177)Lu-MAC2 each exhibited a nearly fourfold lower retention, relative to control, at the 72h time point. However, the tumor accumulation of the (177)Lu-MAC0 was two to three times greater than (177)Lu-MAC1 and (177)Lu-MAC2 at the same time point. The MAL approach demonstrated the capability of substantially reducing the non-target retention of the (177)Lu-labeled HPMA copolymers.

CONCLUSIONS

While further studies are needed to optimize the pharmacokinetics of the (177)Lu-MACs design, the ability of the MAL to significantly decrease non-target retention establishes the potential this avenue of research may have for the improvement of diagnostic and radiotherapeutic drug delivery systems.

Chain-shattering polymeric therapeutics with on-demand drug-release capability

Design of smart polymeric therapeutics

We designed and synthesized trigger-responsive chain-shattering polymeric therapeutics (CSPTs) via condensation polymerization of a UV-or hydrogen peroxide-responsive domain and a bisfunctional drug as co-monomers. CSPTs have precisely controlled molecular composition and unique chain-shattering type of drug release mechanism. Drug release kinetics can be precisely controlled by means of the trigger treatment. Chemotherapeutic-containing CSPTs showed trigger-responsive in vitro and in vivo antitumor efficacy.

Integration of biosensors and drug delivery technologies for early detection and chronic management of illness

Recent advances in biosensor design and sensing efficacy need to be amalgamated with research in responsive drug delivery systems for building superior health or illness regimes and ensuring good patient compliance. A variety of illnesses require continuous monitoring in order to have efficient illness intervention. Physicochemical changes in the body can signify the occurrence of an illness before it manifests. Even with the usage of sensors that allow diagnosis and prognosis of the illness, medical intervention still has its downfalls. Late detection of illness can reduce the efficacy of therapeutics. Furthermore, the conventional modes of treatment can cause side-effects such as tissue damage (chemotherapy and rhabdomyolysis) and induce other forms of illness (hepatotoxicity). The use of drug delivery systems enables the lowering of side-effects with subsequent improvement in patient compliance. Chronic illnesses require continuous monitoring and medical intervention for efficient treatment to be achieved. Therefore, designing a responsive system that will reciprocate to the physicochemical changes may offer superior therapeutic activity. In this respect, integration of biosensors and drug delivery is a proficient approach and requires designing an implantable system that has a closed loop system. This offers regulation of the changes by means of releasing a therapeutic agent whenever illness biomarkers prevail. Proper selection of biomarkers is vital as this is key for diagnosis and a stimulation factor for responsive drug delivery. By detecting an illness before it manifests by means of biomarkers levels, therapeutic dosing would relate to the severity of such changes. In this review various biosensors and drug delivery systems are discussed in order to assess the challenges and future perspectives of integrating biosensors and drug delivery systems for detection and management of chronic illness.

RNA therapeutics targeting osteoclast-mediated excessive bone resorption

RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing technique developed with dramatically increasing utility for both scientific and therapeutic purposes. Short interfering RNA (siRNA) is currently exploited to regulate protein expression relevant to many therapeutic applications, and commonly used as a tool for elucidating disease-associated genes. Osteoporosis and their associated osteoporotic fragility fractures in both men and women are rapidly becoming a global healthcare crisis as average life expectancy increases worldwide. New therapeutics are needed for this increasing patient population. This review describes the diversity of molecular targets suitable for RNAi-based gene knock down in osteoclasts to control osteoclast-mediated excessive bone resorption. We identify strategies for developing targeted siRNA delivery and efficient gene silencing, and describe opportunities and challenges of introducing siRNA as a therapeutic approach to hard and connective tissue disorders.

Polymer nanoassemblies for cancer treatment and imaging

Amphiphilic polymers represented by block copolymers self-assemble into well-defined nanostructures capable of incorporating therapeutics. Polymer nanoassemblies currently developed for cancer treatment and imaging are reviewed in this article. Particular attention is paid to three representative polymer nanoassemblies: polymer micelles, polymer micellar aggregates and polymer vesicles. Rationales, design and performance of these polymer nanoassemblies are addressed, focusing on increasing the solubility and chemical stability of drugs. Also discussed are polymer nanoassembly formation, the distribution of polymer materials in the human body and applications of polymer nanoassemblies for combined therapy and imaging of cancer. Updates on tumor-targeting approaches, based on preclinical and clinical results are provided, as well as solutions for current issues that drug-delivery systems have, such as in vivo stability, tissue penetration and therapeutic efficacy. These are discussed to provide insights on the future development of more effective polymer nanoassemblies for the delivery of therapeutics in the body.

Biomimetic Design of Protein Nanomaterials for Hydrophobic Molecular Transport

Biomaterials such as self-assembling biological complexes have demonstrated a variety of applications in materials science and nanotechnology. The functionality of protein-based materials, however, is often limited by the absence or locations of specific chemical conjugation sites. In this investigation, we developed a new strategy for loading organic molecules into the hollow cavity of a protein nanoparticle that relies only on non-covalent interactions, and we demonstrated its applicability in drug delivery. Based on a biomimetic model that incorporates multiple phenylalanines to create a generalized binding site, we retained and delivered the antitumor compound doxorubicin by redesigning a caged protein scaffold. Through an iterative combination of structural modeling and protein engineering, we obtained new variants of the E2 subunit of pyruvate dehydrogenase with varying levels of drug-carrying capabilities. We found that an increasing number of introduced phenylalanines within the scaffold cavity generally resulted in greater drug loading capacities. Drug loading levels could be achieved that were greater than conventional nanoparticle delivery systems. These protein nanoparticles containing doxorubicin were taken up by breast cancer cells and induced significant cell death. Our novel approach demonstrates a universal strategy to design de novo hydrophobic binding domains within protein-based scaffolds for molecular encapsulation and transport, and it broadens the ability to attach guest molecules to this class of materials.

Self-assembling, protein-based intracellular bacterial organelles: emerging vehicles for encapsulating, targeting and delivering therapeutical cargoes

Many bacterial species contain intracellular nano- and micro-compartments consisting of self-assembling proteins that form protein-only shells. These structures are built up by combinations of a reduced number of repeated elements, from 60 repeated copies of one unique structural element self-assembled in encapsulins of 24 nm to 10,000-20,000 copies of a few protein species assembled in a organelle of around 100-150 nm in cross-section. However, this apparent simplicity does not correspond to the structural and functional sophistication of some of these organelles. They package, by not yet definitely solved mechanisms, one or more enzymes involved in specific metabolic pathways, confining such reactions and sequestering or increasing the inner concentration of unstable, toxics or volatile intermediate metabolites. From a biotechnological point of view, we can use the self assembling properties of these particles for directing shell assembling and enzyme packaging, mimicking nature to design new applications in biotechnology. Upon appropriate engineering of the building blocks, they could act as a new family of self-assembled, protein-based vehicles in Nanomedicine to encapsulate, target and deliver therapeutic cargoes to specific cell types and/or tissues. This would provide a new, intriguing platform of microbial origin for drug delivery.

Synthetic polymers as drug-delivery vehicles in medicine

Cancerous diseases present a formidable health problem worldwide. While the chemotherapy of cancer, in conjunction with other treatment modalities, has reached a significant level of maturity, efficacious use of such agents is still restricted by numerous pharmacological deficiencies, such as poor water solubility, short serum circulation lifetimes, and low bioavailability resulting from lack of affinity to cancer tissue and inadequate mechanisms of cell entry. More critically still, most drugs suffer from toxic side effects and a risk of drug resistance. The class of platinum anticancer drugs, although outstandingly potent, is particularly notorious in that respect. Among the countless methods developed in recent years in an effort to overcome these deficiencies, the technology of polymer-drug conjugation stands out as a particularly advanced treatment modality. The strategy involves the bioreversible binding, conjugating, of a medicinal agent to a water-soluble macromolecular carrier. Following pharmacokinetic pathways distinctly different from those of the common, nonpolymeric drugs, the conjugate so obtained will act as a prodrug providing safe transport of the bioactive agent to and into the affected, that is, cancerous cell for its ultimate cell-killing activity. The present treatise will acquaint us with the pharmacological fundamentals of this drug delivery approach, applied here specifically to the metalorganic platinum-type drug systems and the organometallic ferrocene drug model. We will see just how this technology leads to conjugates distinctly superior in antiproliferative activity to cisplatin, a clinically used antitumor agent used here as a standard. Polymer-drug conjugation involving metal-based and other medicinal agents has unquestionably matured to a practical tool to the pharmaceutical scientist, and all indications point to an illustrious career for this nascent drug delivery approach in the fight against cancer and other human maladies.

The effects of substituent grafting on the interaction of pH-responsive polymers with phospholipid monolayers

pH-responsive amphiphilic polymers with suitable graftings have demonstrated highly efficient cell membrane activity and hence are promising applicants for drug-delivery. Grafting the hydrophobic amino acid l-phenylalanine and the hydrophilic methoxy poly(ethylene glycol) amine onto the pendant carboxylic acid moieties of a linear polyamide, poly(l-lysine isophthalamide), can effectively modify the amphiphilicity and conformation of the amphiphilic polymers. Here, the interactions of these polymers with phospholipid monolayers adsorbed on mercury (Hg) electrodes have been studied. AC voltammetry (ACV), rapid cyclic voltammetry (RCV), and electrochemical impedance spectroscopy (EIS) have been applied to monitor phospholipid monolayer associations with different polymer concentrations under different pH values. The polymers interact reversibly with the monolayer shown by altering the monolayer capacitance and inhibiting the phospholipid reorientation in electric field. Polymer grafting enhances the pH-mediated conformational change of the polymers which in turn increases their phospholipid monolayer activity. The most significant monolayer interactions have been observed with the polymer grafted with hydrophobic l-phenylalanine. A low level of PEGylation of the backbone also increases the monolayer activity. The polymer/DOPC interactions have been represented with an impedance model, which takes account of the interaction giving rise to an increase in monolayer capacitance and inhomogeneity and a Debye type dielectric relaxation. The extent of penetration of the polymers into the monolayer is inversely related to the electrical resistance they give rise to during the Debye relaxation. The cell membrane activities of these amphiphilic polymers have been successfully mirrored in this supported DOPC monolayer system, isolating the key parameters for biomembrane activities and giving insight into the mechanism of the interactions. The conclusions from this study provide strategic directions in material design catering to different requirements in biomedical applications.

The role of counterions in the membrane-disruptive properties of pH-sensitive lysine-based surfactants

Surfactants are among the most versatile and widely used excipients in pharmaceuticals. This versatility, together with their pH-responsive membrane-disruptive activity and low toxicity, could also enable their potential application in drug delivery systems. Five anionic lysine-based surfactants which differ in the nature of their counterion were studied. Their capacity to disrupt the cell membrane was examined under a range of pH values, concentrations and incubation times, using a standard hemolysis assay as a model for endosomal membranes. The surfactants showed pH-sensitive hemolytic activity and improved kinetics at the endosomal pH range. Low concentrations resulted in negligible hemolysis at physiological pH and high membrane lytic activity at pH 5.4, which is in the range characteristic of late endosomes. With increasing concentration, the surfactants showed an enhanced capacity to lyse cell membranes, and also caused significant membrane disruption at physiological pH. This observation indicates that, at high concentrations, surfactant behavior is independent of pH. The mechanism of surfactant-mediated membrane destabilization was addressed, and scanning electron microscopy studies were also performed to evaluate the effects of the compounds on erythrocyte morphology as a function of pH. The in vitro cytotoxicity of the surfactants was assessed by MTT and NRU assays with the 3T3 cell line. The influence of different types of counterion on hemolytic activity and the potential applications of these surfactants in drug delivery are discussed. The possibility of using pH-sensitive surfactants for endosome disruption could hold great promise for intracellular drug delivery systems in future therapeutic applications.

Polymer-based therapeutics: nanoassemblies and nanoparticles for management of atherosclerosis

Coronary arterial disease, one of the leading causes of adult mortality, is triggered by atherosclerosis. A disease with complex etiology, atherosclerosis results from the progressive long-term combination of atherogenesis, the accumulation of modified lipoproteins within blood vessel walls, along with vascular and systemic inflammatory processes. The management of atherosclerosis is challenged by the localized flare-up of several multipronged signaling interactions between activated monocytes, atherogenic macrophages and inflamed or dysfunctional endothelial cells. A new generation of approaches is now emerging founded on multifocal, targeted therapies that seek to reverse or ameliorate the atheroinflammatory cascade within the vascular intima. This article reviews the various classes and primary examples of bioactive configurations of nanoscale assemblies. Of specific interest are polymer-based or polymer-lipid micellar assemblies designed as multimodal receptor-targeted blockers or drug carriers whose activity can be tuned by variations in polymer hydrophobicity, charge, and architecture. Also reviewed are emerging reports on multifunctional nanoassemblies and nanoparticles for improved circulation and enhanced targeting to atheroinflammatory lesions and atherosclerotic plaques.

Protein nanocapsules containing doxorubicin as a pH-responsive delivery system

The E2 component of pyruvate dehydrogenase is engineered to form a caged, hollow dodecahedral protein assembly, and the feasibility of this scaffold to be used as a drug delivery system is examined by introducing cysteines to the internal cavity (D381C). The fluorescent dye Alexa Fluor 532 (AF532M) and the antitumor drug doxorubicin are coupled to this internal cavity through maleimides on the guest molecules. The viruslike particle's structure and stability remain intact after binding of the molecules within the interior of the nanocapsule. The pH-dependent hydrolysis of a hydrazone linkage to doxorubicin allows 90% drug release from the D381C scaffold within 72 h at pH 5.0. Fluorescence microscopy of MDA-MB-231 breast cancer cells indicates significant uptake of the D381C scaffold incorporating AF532M and doxorubicin, and suggests internalization of the nanoparticles through endocytosis. It is observed that the protein scaffold does not induce cell death, but doxorubicin encapsulated in D381C is indeed cytotoxic, yielding an IC(50) of 1.3 ± 0.3 μM. While the majority of particulate-based drug delivery strategies encapsulates drugs within polymeric nanoparticles, these results show the potential for using macromolecular protein assemblies. This approach yields a promising new opportunity for designing highly defined nanomaterials for therapeutic delivery.

Concentration-dependent toxicity of iron oxide nanoparticles mediated by increased oxidative stress

Iron oxide nanoparticles with unique magnetic properties have a high potential for use in several biomedical, bioengineering and in vivo applications, including tissue repair, magnetic resonance imaging, immunoassay, drug delivery, detoxification of biologic fluids, cell sorting, and hyperthermia. Although various surface modifications are being done for making these nonbiodegradable nanoparticles more biocompatible, their toxic potential is still a major concern. The current in vitro study of the interaction of superparamagnetic iron oxide nanoparticles of mean diameter 30 nm coated with Tween 80 and murine macrophage (J774) cells was undertaken to evaluate the dose- and time-dependent toxic potential, as well as investigate the role of oxidative stress in the toxicity. A 15–30 nm size range of spherical nanoparticles were characterized by transmission electron microscopy and zeta sizer. MTT assay showed >95% viability of cells in lower concentrations (25–200 μg/mL) and up to three hours of exposure, whereas at higher concentrations (300–500 μg/mL) and prolonged (six hours) exposure viability reduced to 55%–65%. Necrosis-apoptosis assay by propidium iodide and Hoechst-33342 staining revealed loss of the majority of the cells by apoptosis. H₂DCFDDA assay to quantify generation of intracellular reactive oxygen species (ROS) indicated that exposure to a higher concentration of nanoparticles resulted in enhanced ROS generation, leading to cell injury and death. The cell membrane injury induced by nanoparticles studied using the lactate dehydrogenase assay, showed both concentration- and time-dependent damage. Thus, this study concluded that use of a low optimum concentration of superparamagnetic iron oxide nanoparticles is important for avoidance of oxidative stress-induced cell injury and death.

The pharmacokinetics of cell-penetrating peptides

Cell-penetrating peptides (CPPs) are able to penetrate the cell membrane carrying cargoes such as peptides, proteins, oligonucleotides, siRNAs, radioisotopes, liposomes, and nanoparticles. Consequently, many delivery approaches have been developed to use CPPs as tools for drug delivery. However, until now a systematic analysis of their in vivo properties including potential tumor binding specificity for drug targeting purposes has not been conducted. Ten of the most commonly applied CPPs were obtained by solid phase peptide synthesis and labeled with (111)In or (68)Ga. Uptake studies were conducted using a panel of six tumor cell lines of different origin. The stability of the peptides was examined in human serum. Biodistribution experiments were conducted in nude mice bearing human prostate carcinoma. Finally, positron emission tomography (PET) measurements were performed in male Wistar rats. The in vitro uptake studies revealed high cellular uptake values, but no specificity toward any of the cell lines. The biodistribution in PC-3 tumor-bearing nude mice showed a high transient accumulation in well-perfused organs and a rapid clearance from the blood. All of the CPPs revealed a relatively low accumulation rate in the brain. The highest uptake values were observed in the liver (with a maximal uptake of 51 %ID/g observed for oligoarginine (R(9))) and the kidneys (with a maximal uptake of 94 %ID/g observed for NLS). The uptake values in the PC-3 tumor were low at all time points, indicating a lack of tumor specific accumulation for all peptides studied. A micro-PET imaging study with (68)Ga-labeled penetratin, Tat and transportan(10) (TP(10)) confirmed the organ distribution data. These data reveal that CPPs do not show evidence for application in tumor targeting purposes in vivo. However, CPPs readily penetrate into most organs and show rapid clearance from the circulation. The high uptake rates observed in vitro and the relatively low specificity in vivo imply that CPPs would be better suited for topical application in combination with cargoes which show passive targeting and dominate the pharmacokinetic behavior. In conclusion, CPPs are suitable as drug carriers for in vivo application provided that their pharmacokinetic properties are also considered in design of CPP drug delivery systems.

Micellar nanocarriers assembled from doxorubicin-conjugated amphiphilic macromolecules (DOX-AM)

Amphiphilic macromolecules (AMs) have unique branched hydrophobic domains attached to linear PEG chains. AMs self-assemble in aqueous solution to form micelles that are hydrolytically stable in physiological conditions (37 degrees C, pH 7.4) over 4 weeks. Evidence of AM biodegradability was demonstrated by complete AM degradation after 6 d in the presence of lipase. Doxorubicin (DOX) was chemically conjugated to AMs via a hydrazone linker to form DOX-AM conjugates that self-assembled into micelles in aqueous solution. The conjugates were compared with DOX-loaded AM micelles (i.e., physically loaded DOX) on DOX content, micellar sizes and in vitro cytotoxicity. Physically encapsulated DOX loading was higher (12 wt.-%) than chemically bound DOX (6 wt.-%), and micellar sizes of DOX-loaded AMs (approximately 16 nm) were smaller than DOX-AMs (approximately 30 nm). In vitro DOX release from DOX-AM conjugates was faster at pH 5.0 (100%) compared to pH 7.4 (78%) after 48 h, 37 degrees C. Compared to free DOX and physically encapsulated DOX, chemically bound DOX had significantly higher cytotoxicity at 10(-7) M DOX dose against human hepatocellular carcinoma cells after 72 h. Overall, DOX-AM micelles showed promising characteristics as stable, biodegradable DOX nanocarriers.

pH-triggered disassembly in a caged protein complex

Self-assembling protein cage structures have many potential applications in nanotechnology, one of which is therapeutic delivery. For intracellular targeting, pH-controlled disassembly of virus-like particles and release of their molecular cargo is particularly strategic. We investigated the potential of using histidines for introducing pH-dependent disassembly in the E2 subunit of pyruvate dehydrogenase. Two subunit interfaces likely to disrupt stability, an intratrimer interface (the N-terminus) and an intertrimer interface (methionine-425), were redesigned. Our results show that changing the identity of the putative anchor site 425 to histidine does not decrease stability. In contrast, engineering non-native pH-dependent behavior and modulating the transition pH at which disassembly occurs can be accomplished by mutagenesis of the N-terminus and by ionic strength changes. The observed pH-triggered disassembly is due to electrostatic repulsions generated by histidine protonation. These results suggest that altering the degree of electrostatic repulsion at subunit interfaces could be a generally applicable strategy for designing pH-triggered assembly in protein macromolecular structures.

Photochemical internalization: a new tool for gene and oligonucleotide delivery

Photochemical internalization (PCI) is a novel technology for release of endocytosed macromolecules into the cytosol. The technology is based on the use of photosensitizers located in endocytic vesicles. Upon activation by light such photosensitizers induce a release of macromolecules from their compartmentalization in endocytic vesicles. PCI has been shown to increase the biological activity of a large variety of macromolecules and other molecules that do not readily penetrate the plasma membrane, including type I ribosome-inactivating proteins, immunotoxins, plasmids, adenovirus, various oligonucleotides, dendrimer-based delivery of chemotherapeutica and unconjugated chemotherapeutica such as bleomycin and doxorubicin. This review will present the basis for the PCI concept and the most recent significant developments.

Effect of L-leucine graft content on aqueous solution behavior and membrane-lytic activity of a pH-responsive pseudopeptide

A series of pH-responsive polymers have been synthesized by grafting L-leucine onto the pendant carboxylic acid groups of the linear pseudopeptide, poly(L-lysine iso-phthalamide). The effect of the degree of grafting on aqueous solution properties, cell membrane-disruptive activity, and in vitro cytotoxicity was examined by UV-visible and fluorescence spectroscopy, hemolysis, alamar blue staining, and propidium iodide fluorescence assays. Modification of poly(L-lysine iso-phthalamide) with < or =23.6 mol % L-leucine caused a marginal effect on the pH-mediated hydrophobic association and hemolytic activity. Increasing the degree of grafting from 31.9 to 61.2 mol % resulted in polymers with progressively enhanced hydrophobic association and cell membrane disruption, thus confirming that the pH responsiveness and the extent of hydrophobic association and membrane disruption of the polymers can be modulated by varying the degree of grafting with hydrophobic amino acids. The pH responses were demonstrated to be concentration-dependent. At certain degrees of leucine grafting, the polymers were nonmembrane-lytic at physiological pH but mediated considerable membrane lysis at endosomal pH values (5.0-6.8), a feature critical for potential drug delivery applications.

Lactose mediated liver-targeting effect observed by ex vivo imaging technology

Two kinds of micelles containing Rhodamine B were prepared by a solvent evaporation method. One (Lac-f-micelles: lactose-free micelles) was from a Rhodamine-containing copolymer, poly(ethylene glycol)-b-poly(l-lactide-co-2,2-dihydroxylmethyl-propylene carbonate/Rhodamine) [PEG(5000)-b-P(LA(4000)-co-DHP(600)/Rhodamine)], and the other (Lac+micelles lactose-containing micelles) was from a mixture of the targeting copolymer lactose-poly(ethylene glycol)-poly (l-Lactide) [Lac-PEG(4600)-PLA(4500)] and the Rhodamine-containing copolymer PEG(5000)-b-P(LA(4000)-co-DHP(600)/Rhodamine). ESEM and DLS measurements showed that the two kinds of micelles have similar size (in the range of 60-100 nm) and size distribution. Cellular uptake studies in vitro revealed that the Lac+micelles showed stronger endocytosis ability than Lac-f-micelles in SMMC7221 human liver cancer cells, but the Lac+micelles were rarely internalized by Vero cells. The micelle solutions were administrated into mice via tail intravenous injection. Then, five visceral organs were isolated from the mice at specified time intervals and relative fluorescent intensities of the ex vivo organs and their homogenates were examined by CRI Maestro 500FL in vivo imaging system. The results showed that the Lac+micelles showed more remarkable liver-targeting effect than the Lac-f-micelles. And the liver-targeting effect could be established in ca. 12 h after tail i.v. injection.

E. coli expression of a soluble, active single-chain antibody variable fragment containing a nuclear localization signal

Single-chain antibody variable fragment (scFv) proteins consist of an antibody heavy chain variable sequence joined via a flexible linker to a light chain variable sequence. Prior work has shown that ScFv 18-2 binds the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and sensitizes cancer cells to radiation following nuclear microinjection. A potential clinical delivery strategy is based on modification of the scFv so that it can be taken up into cells and imported to the nucleus. This will require development of an expression system for a nuclear localization signal (NLS)-tagged scFv derivative. We found, however, that addition of the highly basic NLS severely compromised expression in the host-vector system used for the parental scFv. After testing a variety of host strains, fusion partners, and NLS sequences and placements, successful expression was obtained with a construct containing a stabilizing N-terminal maltose binding protein tag and a single, optimized, C-terminal NLS moiety. Amylose affinity-purified ScFv 18-2 NLS protein was stable to storage at 4 degrees C in the presence of glycerol or trehalose, bound selectively to an epitope peptide, and was cleavable at an engineered Factor Xa protease site. Following lipid-mediated uptake into cultured cells, NLS-tagged ScFv 18-2, unlike the parental ScFv 18-2, localized predominantly in the cell nucleus.

Comparison of photodynamic efficacy of tetraarylporphyrin pegylated or encapsulated in liposomes: in vitro studies

Two photosensitizing systems: (1) tetrakis(4-hydroxyphenyl)porphyrin (p-THPP) encapsulated in sterically stabilized liposomes (SSL) and (2) p-THPP functionalized by covalent attachment of poly(ethylene glycol) (p-THPP-PEG(2000)) were studied in vitro. The dark and photo cytotoxicity of these systems were evaluated on two cell lines: HCT 116, a human colorectal carcinoma cell line, and DU 145, a prostate cancer cell line and compared with these determined for free p-THPP. It was demonstrated that both encapsulation in liposomes as well as attachment of PEG chain result in pronounced reduction of the dark cytotoxicity of the parent porphyrin. The liposomal formulation showed higher than p-THPP-PEG(2000) photocytotoxicity towards both cell lines used in the studies.