Macromolecular therapeutics in cancer treatment: the EPR effect and beyond

Lipid nanoparticles for gene delivery

Nonviral vectors which offer a safer and versatile alternative to viral vectors have been developed to overcome problems caused by viral carriers. However, their transfection efficacy or level of expression is substantially lower than viral vectors. Among various nonviral gene vectors, lipid nanoparticles are an ideal platform for the incorporation of safety and efficacy into a single delivery system. In this chapter, we highlight current lipidic vectors that have been developed for gene therapy of tumors and other diseases. The pharmacokinetic, toxic behaviors and clinic trials of some successful lipids particles are also presented.

A tumor-targeting dextran–apoprotein conjugate integrated with enediyne chromophore shows highly potent antitumor efficacy

A novel dextran–apoprotein conjugate that could selectively stay in tumor tissues for a prolonged time was prepared. After integrating with enediyne chromophore, this conjugate showed highly potent antitumor efficacy.

Smart drug delivery systems: from fundamentals to the clinic

Smart materials can endow implantable depots, targetable nanocarriers and insertable medical devices with activation-modulated and feedback-regulated control of drug release.

Cellulose-graft-poly(l-lactic acid) nanoparticles for efficient delivery of anti-cancer drugs

BA-loaded cellulose-graft-poly(l-lactic acid) nanoparticles were fabricated by employing cellulose and poly(l-lactic acid) as materials and betulinic acid as a model drug. The nanoparticles have appropriate size and excellent antitumor activities.

Prediction of drug disposition on the basis of its chemical structure

The chemical structure of any drug determines its pharmacokinetics and pharmacodynamics. Detailed understanding of relationships between the drug chemical structure and individual disposition pathways (i.e., distribution and elimination) is required for efficient use of existing drugs and effective development of new drugs. Different approaches have been developed for this purpose, ranging from statistics-based quantitative structure-property (or structure-pharmacokinetic) relationships (QSPR) analysis to physiologically based pharmacokinetic (PBPK) models. This review critically analyzes currently available approaches for analysis and prediction of drug disposition on the basis of chemical structure. Models that can be used to predict different aspects of disposition are presented, including: (a) value of the individual pharmacokinetic parameter (e.g., clearance or volume of distribution), (b) efficiency of the specific disposition pathway (e.g., biliary drug excretion or cytochrome P450 3A4 metabolism), (c) accumulation in a specific organ or tissue (e.g., permeability of the placenta or accumulation in the brain), and (d) the whole-body disposition in the individual patients. Examples of presented pharmacological agents include "classical" low-molecular-weight compounds, biopharmaceuticals, and drugs encapsulated in specialized drug-delivery systems. The clinical efficiency of agents from all these groups can be suboptimal, because of inefficient permeability of the drug to the site of action and/or excessive accumulation in other organs and tissues. Therefore, robust and reliable approaches for chemical structure-based prediction of drug disposition are required to overcome these limitations. PBPK models are increasingly being used for prediction of drug disposition. These models can reflect the complex interplay of factors that determine drug disposition in a mechanistically correct fashion and can be combined with other approaches, for example QSPR-based prediction of drug permeability and metabolism, pharmacogenomic data and tools, pharmacokinetic-pharmacodynamic modeling approaches, etc. Moreover, the PBPK models enable detailed analysis of clinically relevant scenarios, for example the effect of the specific conditions on the time course of the analyzed drug in the individual organs and tissues, including the site of action. It is expected that further development of such combined approaches will increase their precision, enhance the effectiveness of drugs, and lead to individualized drug therapy for different patient populations (geriatric, pediatric, specific diseases, etc.).

Serum biomarkers for personalization of nanotherapeutics-based therapy in different tumor and organ microenvironments

Enhanced permeation and retention (EPR) effect, the mechanism by which nanotherapeutics accumulate in tumors, varies in patients based on differences in the tumor and organ microenvironment. Surrogate biomarkers for the EPR effect will aid in selecting patients who will accumulate higher amounts of nanotherapeutics and show better therapeutic efficacy. Our data suggest that the differences in the vascular permeability and pegylated liposomal doxorubicin (PLD) accumulation are tumor type as well as organ-specific and significantly correlated with the relative ratio of MMP-9 to TIMP-1 in the circulation, supporting development of these molecules as biomarkers for the personalization of nanoparticle-based therapy.

Improving conventional enhanced permeability and retention (EPR) effects; what is the appropriate target?

Nano-sized therapeutic agents have several advantages over low molecular weight agents such as a larger loading capacity, the ability to protect the payload until delivery, more specific targeting due to multivalency and the opportunity for controlled/sustained release. However, the delivery of nano-sized agents into cancer tissue is problematic because it mostly relies on the enhanced permeability and retention (EPR) effect that depends on the leaky nature of the tumor vasculature and the prolonged circulation of nano-sized agents, allowing slow but uneven accumulation in the tumor bed. Delivery of nano-sized agents is dependent on several factors that influence the EPR effect; 1. Regional blood flow to the tumor, 2. Permeability of the tumor vasculature, 3. Structural barriers imposed by perivascular tumor cells and extracellular matrix, 4. Intratumoral pressure. In this review, these factors will be described and methods to enhance nano-agent delivery will be reviewed.

Combination cytotoxicity of backbone degradable HPMA copolymer gemcitabine and platinum conjugates toward human ovarian carcinoma cells

Multiblock, backbone degradable HPMA copolymer-drug conjugates containing gemcitabine and DACH platinum (mP-GEM and mP-DACH Pt), respectively were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequent chain extension by click chemistry. Using combination index analysis, the cytotoxicities of the two multiblock conjugates, as single agent and in combination, were evaluated in vitro in A2780 human ovarian cancer cells, with free drugs as controls. The greatest synergistic cytotoxic effect was observed when A2780 cells were sequentially exposed to mP-GEM for 24h and mP-DACH Pt for 48h. In addition, mechanistic studies support the rationale of the synergy between mP-GEM and mP-DACH Pt: mP-GEM pretreatment was able to enhance the platinum-DNA adduct accumulation and inhibit cell proliferation to a higher extent than single mP-DACH Pt treatment. These observations are useful for the development of combination macromolecular therapeutics for ovarian cancer based on the second-generation backbone degradable HPMA copolymers.

Liposomal chemotherapeutics

Currently, six liposomal chemotherapeutics have received clinical approval and many more are in clinical trials or undergoing preclinical evaluation. Liposomes exhibit low toxicity and improve the biopharmaceutical features and therapeutic index of drugs, thereby increasing efficacy and reducing side effects. In this review we discuss the advantages of using liposomes for the delivery of chemotherapeutics. Gemcitabine and paclitaxel have been chosen as examples to illustrate how the performance of a metabolically unstable or poorly water-soluble drug can be greatly improved by liposomal incorporation. We look at the beneficial effects of liposomes in a variety of solid and blood-borne tumors, including thyroid cancer, pancreatic cancer, breast cancer and multiple myeloma.

Ligand-targeted liposome design: challenges and fundamental considerations

Nanomedicine, particularly liposomal drug delivery, has expanded considerably over the past few decades, and several liposomal drugs are already providing improved clinical outcomes. Liposomes have now progressed beyond simple, inert drug carriers and can be designed to be highly responsive in vivo, with active targeting, increased stealth, and controlled drug-release properties. Ligand-targeted liposomes (LTLs) have the potential to revolutionize the treatment of cancer. However, these highly engineered liposomes generate new problems, such as accelerated clearance from circulation, compromised targeting owing to non-specific serum protein binding, and hindered tumor penetration. This article highlights recent challenges facing LTL strategies and describes the advanced design elements used to circumvent them.

Multidrug resistance: Physiological principles and nanomedical solutions

Multidrug resistance (MDR) is a pathophysiological phenomenon employed by cancer cells which limits the prolonged and effective use of chemotherapeutic agents. MDR is primarily based on the over-expression of drug efflux pumps in the cellular membrane. Prominent examples of such efflux pumps, which belong to the ATP-binding cassette (ABC) superfamily of proteins, are Pgp (P-glycoprotein) and MRP (multidrug resistance-associated protein), nowadays officially known as ABCB1 and ABCC1. Over the years, several strategies have been evaluated to overcome MDR, based not only on the use of low-molecular-weight MDR modulators, but also on the implementation of 1-100(0) nm-sized drug delivery systems. In the present manuscript, after introducing the most important physiological principles of MDR, we summarize prototypic nanomedical strategies to overcome multidrug resistance, including the use of carrier materials with intrinsic anti-MDR properties, the use of nanomedicines to modify the mode of cellular uptake, and the co-formulation of chemotherapeutic drugs together with low- and high-molecular-weight MDR inhibitors within a single drug delivery system. While certain challenges still need to be overcome before such constructs and concepts can be widely applied in the clinic, the insights obtained and the progress made strongly suggest that nanomedicine formulations hold significant potential for improving the treatment of multidrug-resistant malignancies.

Multifunctional nanoparticles for targeted delivery of immune activating and cancer therapeutic agents

Nanoparticles (NPs) have been extensively investigated for applications in both experimental and clinical settings to improve delivery efficiency of therapeutic and diagnostic agents. Most recently, novel multifunctional nanoparticles have attracted much attention because of their ability to carry diverse functionalities to achieve effective synergistic therapeutic treatments. Multifunctional NPs have been designed to co-deliver multiple components, target the delivery of drugs by surface functionalization, and realize therapy and diagnosis simultaneously. In this review, various materials of diverse chemistries for fabricating multifunctional NPs with distinctive architectures are discussed and compared. Recent progress involving multifunctional NPs for immune activation, anticancer drug delivery, and synergistic theranostics is the focus of this review. Overall, this comprehensive review demonstrates that multifunctional NPs have distinctive properties that make them highly suitable for targeted therapeutic delivery in these areas.

Thermal potentiation of chemotherapy by magnetic nanoparticles

Clinical studies have demonstrated the effectiveness of hyperthermia as an adjuvant for chemotherapy and radiotherapy. However, significant clinical challenges have been encountered, such as a broader spectrum of toxicity, lack of patient tolerance, temperature control and significant invasiveness. Hyperthermia induced by magnetic nanoparticles in high-frequency oscillating magnetic fields, commonly termed magnetic fluid hyperthermia, is a promising form of heat delivery in which thermal energy is supplied at the nanoscale to the tumor. This review discusses the mechanisms of heat dissipation of iron oxide-based magnetic nanoparticles, current methods and challenges to deliver heat in the clinic, and the current work related to the use of magnetic nanoparticles for the thermal-chemopotentiation of therapeutic drugs.

Fluorescent organic nanocrystals and non-doped nanoparticles for biological applications

The recently developed fluorescent organic nanocrystals and non-doped nanoparticles (FONs) occupy a special position among other nanoparticle systems that are used for studying a variety of fundamental processes in the life sciences. Understanding their particular photophysical behavior allows proper design of FONs. The usual preparation methods are described. It is shown that FONs lead to original applications as biochemical sensors and biolabels for immunoassays. They also show high potentialities for bio-imaging of cell cultures, drug-delivery control, angiography and in vivo bio-imaging of solid tumors.

Rational design of multifunctional upconversion nanocrystals/polymer nanocomposites for cisplatin (IV) delivery and biomedical imaging

By combining upconversion nanoparticles with the cisplatin (IV) prodrug we have demonstrated that a stable and multifunctional drug delivery system can be designed that will both reduce the drawbacks of cisplatin and give insight in to its in vitro/in vivo imaging. The up/down-conversion fluorescence are detectable and show obvious co-localization, demonstrating that the nanoparticles are rather stable inside cells and retain the UCNPs and block copolymer.

Formulation development and evaluation of hybrid nanocarrier for cancer therapy: Taguchi orthogonal array based design

Taguchi orthogonal array design is a statistical approach that helps to overcome limitations associated with time consuming full factorial experimental design. In this study, the Taguchi orthogonal array design was applied to establish the optimum conditions for bovine serum albumin (BSA) nanocarrier (ANC) preparation. Taguchi method with L9 type of robust orthogonal array design was adopted to optimize the experimental conditions. Three key dependent factors namely, BSA concentration (% w/v), volume of BSA solution to total ethanol ratio (v : v), and concentration of diluted ethanolic aqueous solution (% v/v), were studied at three levels 3%, 4%, and 5% w/v; 1 : 0.75, 1 : 0.90, and 1 : 1.05 v/v; 40%, 70%, and 100% v/v, respectively. The ethanolic aqueous solution was used to impart less harsh condition for desolvation and attain controlled nanoparticle formation. The interaction plot studies inferred the ethanolic aqueous solution concentration to be the most influential parameter that affects the particle size of nanoformulation. This method (BSA, 4% w/v; volume of BSA solution to total ethanol ratio, 1 : 0.90 v/v; concentration of diluted ethanolic solution, 70% v/v) was able to successfully develop Gemcitabine (G) loaded modified albumin nanocarrier (M-ANC-G) of size 25.07 ± 2.81 nm (ζ = −23.03 ± 1.015 mV) as against to 78.01 ± 4.99 nm (ζ = −24.88 ± 1.37 mV) using conventional method albumin nanocarrier (C-ANC-G). Hybrid nanocarriers were generated by chitosan layering (solvent gelation technique) of respective ANC to form C-HNC-G and M-HNC-G of sizes 125.29 ± 5.62 nm (ζ = 12.01 ± 0.51 mV) and 46.28 ± 2.21 nm (ζ = 15.05 ± 0.39 mV), respectively. Zeta potential, entrapment, in vitro release, and pH-based stability studies were investigated and influence of formulation parameters are discussed. Cell-line-based cytotoxicity assay (A549 and H460 cells) and cell internalization assay (H460 cell line) were performed to assess the influence on the bioperformance of these nanoformulations.

Current trends in the use of liposomes for tumor targeting

The use of liposomes for drug delivery began early in the history of pharmaceutical nanocarriers. These nanosized, lipid bilayered vesicles have become popular as drug delivery systems owing to their efficiency, biocompatibility, nonimmunogenicity, enhanced solubility of chemotherapeutic agents and their ability to encapsulate a wide array of drugs. Passive and ligand-mediated active targeting promote tumor specificity with diminished adverse off-target effects. The current field of liposomes focuses on both clinical and diagnostic applications. Recent efforts have concentrated on the development of multifunctional liposomes that target cells and cellular organelles with a single delivery system. This review discusses the recent advances in liposome research in tumor targeting.

Smart drug delivery nanocarriers with self-assembled DNA nanostructures

Self-assembled DNA nanostructures have emerged as a type of nano-biomaterials with precise structures, versatile functions and numerous applications. One particularly promising application of these DNA nanostructures is to develop universal nanocarriers for smart and targeted drug delivery. DNA is the genetic material in nature, and inherently biocompatible. Nevertheless, cell membranes are barely permeable to naked DNA molecules, either single- or double- stranded; transport across the cell membrane is only possible with the assistance of transfection agents. Interestingly, recent studies revealed that many DNA nanostructures could readily go into cells with high cell uptake efficiency. In this Progress Report, we will review recent advances on using various DNA nanostructures, e.g., DNA nanotubes, DNA tetrahedra, and DNA origami nanorobot, as drug delivery nanocarriers, and demonstrate several examples aiming at therapeutic applications with CpG-based immunostimulatory and siRNA-based gene silencing oligonucleotides.

Cisplatin-incorporated nanoparticles of poly(acrylic acid-co-methyl methacrylate) copolymer

Background

Although cisplatin is extensively used in the clinical field, its intrinsic toxicity limits its clinical use. We investigated nanoparticle formations of poly(acrylic acid-co-methyl methacrylate) (PAA-MMA) incorporating cisplatin and their antitumor activity in vitro and in vivo.

Methods

Cisplatin-incorporated nanoparticles were prepared through the ion-complex formation between acrylic acid and cisplatin. The anticancer activity of cisplatin-incorporated nanoparticles was assessed with CT26 colorectal carcinoma cells.

Results

Cisplatin-incorporated nanoparticles have small particle sizes of less than 200 nm with spherical shapes. Drug content was increased according to the increase of the feeding amount of cisplatin and acrylic acid content in the copolymer. The higher acrylic acid content in the copolymer induced increase of particle size and decrease of zeta potential. Cisplatin-incorporated nanoparticles showed a similar growth-inhibitory effect against CT26 tumor cells in vitro. However, cisplatin-incorporated nanoparticles showed improved antitumor activity against an animal tumor xenograft model.

Conclusion

We suggest that PAA-MMA nanoparticles incorporating cisplatin are promising carriers for an antitumor drug-delivery system.

Tumor extracellular acidity-activated nanoparticles as drug delivery systems for enhanced cancer therapy

pH-responsive nanoparticles (NPs) are currently under intense development as drug delivery systems for cancer therapy. Among various pH-responsiveness, NPs that are designed to target slightly acidic extracellular pH environment (pHe) of solid tumors provide a new paradigm of tumor targeted drug delivery. Compared to conventional specific surface targeting approaches, the pHe-targeting strategy is considered to be more general due to the common occurrence of acidic microenvironment in solid tumors. This review mainly focuses on the design and applications of pHe-activated NPs, with special emphasis on pHe-activated surface charge reversal NPs, for drug and siRNA delivery to tumors. The novel development of NPs described here offers great potential for achieving better therapeutic effects in cancer treatment.

Multifunctional targeted therapy system based on (99m) Tc/(177) Lu-labeled gold nanoparticles-Tat(49-57)-Lys(3) -bombesin internalized in nuclei of prostate cancer cells

Radiolabeled gold nanoparticles may function simultaneously as radiotherapy and thermal ablation systems. The gastrin-releasing peptide receptor (GRP-r) is overexpressed in prostate cancer, and Lys(3) -bombesin is a peptide that binds with high affinity to the GRP-r. HIV Tat(49-57) is a cell-penetrating peptide that reaches the DNA. In cancer cells, (177) Lu shows efficient crossfire effect, whereas (99m) Tc that is internalized in the cancer cell nuclei acts as an effective system of targeted radiotherapy because of the biological Auger effect. The aim of this research was to evaluate the in vitro potential of (99m) Tc-labeled and (177) Lu-labeled gold nanoparticles conjugated to Tat(49-57)-Lys(3) -bombesin peptides ((99m) Tc/(177) Lu-AuNP-Tat-BN) as a plasmonic photothermal therapy and targeted radiotherapy system in PC3 prostate cancer cells. Peptides were conjugated to AuNPs (5 nm) by spontaneous reaction with the thiol group of cysteine (Cys). The effect on PC3 cell viability after laser heating of the AuNP-Tat-BN incubated with the cancer cells was conducted using an Nd:YAG laser pulsed for 5 ns at 532 nm (0.65 W/cm(2) ). For the (99m) Tc/(177) Lu-AuNP-Tat-BN to be obtained, the (177) Lu-DOTA-Gly-Gly-Cys and (99m) Tc-HYNIC-octreotide radiopeptides were first prepared and added simultaneously to a solution of AuNP-Tat-BN. (99m) Tc/(177) Lu-AuNP-Tat-BN (20 Bq/cell) was incubated with PC3 cells, and the effect on the cell proliferation was evaluated after 3 days. Fluorescence images of (99m) Tc/(177) Lu-AuNP-Tat-BN internalized in nuclei of PC3 were also obtained. After laser irradiation, the presence of AuNP-Tat-BN caused a significant increase in the temperature of the medium (46.4 vs 39.5 °C of that without AuNP) resulting in a significant decrease in PC3 cell viability down to 1.3%. After treatment with (99m) Tc/(177) Lu-AuNP-Tat-BN, the PC3 cell proliferation was inhibited. The nanosystem exhibited properties suitable for plasmonic photothermal therapy and targeted radiotherapy in the treatment of prostate cancer.

Dimeric DNA Aptamer Complexes for High-capacity-targeted Drug Delivery Using pH-sensitive Covalent Linkages

Treatment with doxorubicin (Dox) results in serious systemic toxicities that limit effectiveness for cancer treatment and cause long-term health issues for cancer patients. We identified a new DNA aptamer to prostate-specific membrane antigen (PSMA) using fixed sequences to promote Dox binding and developed dimeric aptamer complexes (DACs) for specific delivery of Dox to PSMA(+) cancer cells. DACs are stable under physiological conditions and are internalized specifically into PSMA(+) C4-2 cells with minimal uptake into PSMA-null PC3 cells. Cellular internalization of DAC was demonstrated by confocal microscopy and flow cytometry. Covalent modification of DAC with Dox (DAC-D) resulted in a complex with stoichiometry ~4:1. Dox was covalently bound in DAC-D using a reversible linker that promotes covalent attachment of Dox to genomic DNA following cell internalization. Dox was released from the DAC-D under physiological conditions with a half-life of 8 hours, sufficient for in vivo targeting. DAC-D was used to selectively deliver Dox to C4-2 cells with endosomal release and nuclear localization of Dox. DAC-D was selectively cytotoxic to C4-2 cells with similar cytotoxicity as the molar equivalent of free-Dox. In contrast, DAC-D displayed minimal cytotoxicity to PC3 cells, demonstrating the complex displays a high degree of selectivity for PSMA(+) cells. DAC-D displays specificity and stability features that may be useful for improved delivery of Dox selectively to malignant tissue in vivo.Molecular Therapy-Nucleic Acids (2013) 2, e107; doi:10.1038/mtna.2013.37; published online 16 July 2013.

The link between infection and cancer: tumor vasculature, free radicals, and drug delivery to tumors via the EPR effect

This review focuses primarily on my own research, including pathogenic mechanisms of microbial infection, vascular permeability in infection and tumors, and effects of nitric oxide (NO), superoxide anion radical (O₂⁻), and 8-nitroguanosine in the enhanced permeability and retention (EPR) effect for the tumor-selective delivery of macromolecular agents (nanomedicines). Infection-induced vascular permeability is mediated by activation of the kinin-generating protease cascade (kallikrein-kinin) triggered by exogenous microbial proteases. A similar mechanism operates in cancer tissues and in carcinomatosis of the pleural and peritoneal cavities. Infection also stimulates O₂⁻ generation via activation of xanthine oxidase while generating NO by inducing NO synthase. These chemicals function in mutation and carcinogenesis and promote inflammation, in which peroxynitrite (a product of O₂⁻ and NO) activates MMP, damages DNA and RNA, and regenerates 8-nitroguanosine and 8-oxoguanosine. We showed vascular permeability by using macromolecular drugs, which are not simply extravasated through the vascular wall into the tumor interstitium but remain there for prolonged periods. We thus discovered the EPR effect, which led to the rational development of tumor-selective delivery of polymer conjugates, micellar and liposomal drugs, and genes. Our styrene-maleic acid copolymer conjugated with neocarzinostatin was the first agent of its kind used to treat hepatoma. The EPR effect occurs not only because of defective vascular architecture but also through the generation of various vascular mediators such as kinin, NO, and vascular endothelial growth factor. Although most solid tumors, including human tumors, show the EPR effect, heterogeneity of tumor tissue may impede drug delivery. This review describes the barriers and countermeasures for improved drug delivery to tumors by using nanomedicines.

Biodegradable multiblock poly(N-2-hydroxypropyl)methacrylamide gemcitabine and paclitaxel conjugates for ovarian cancer cell combination treatment

The synthesis, characterization, and in vitro evaluation of a combination delivery of multiblock poly(N-2-hydroxypropyl)methacrylamide (HPMA), gemcitabine (GEM) and paclitaxel (PTX) conjugates is described in this study. Multiblock copolymer conjugates of a large molecular weight (Mw>200 kDa) were studied and compared to traditional, small molecular weight (Mw<45 kDa) conjugates. Stability of the conjugates in different pH was assessed, and their cytotoxicity in combination toward A2780 human ovarian cancer cells was evaluated by combination index analysis. Treatment duration (4 and 72 h) and sequence of addition were explored. In addition, an HPMA copolymer conjugate with both GEM and PTX in the side chains was evaluated in a similar manner and compared to a physical mixture of individual conjugates. Conjugates with narrow molecular weight distribution (Mw/Mn<1.1) were obtained via RAFT polymerization, and drug loadings of between 5.5 and 9.2 wt% were achieved. Conjugates demonstrated moderate stability with less than 65% release over 24h at pH 7.4, and near complete drug release in the presence of the lysosomal enzyme cathepsin B in 3h. In combination, the cytotoxic effects of a mixture of the conjugates were primarily additive. Synergistic effects were observed when A2780 human ovarian cancer cells were treated simultaneously for 4h with multiblock conjugates (CI<0.7). When both GEM and PTX were conjugated to the same copolymer backbone, moderate antagonism (CI 1.3-1.6) was observed. These results demonstrate that multiblock HPMA copolymer-GEM and -PTX conjugates, when delivered as a mixture of individual agents, are promising for the treatment of ovarian cancer.

Self-reinforced endocytoses of smart polypeptide nanogels for "on-demand" drug delivery

The pH and reduction dual-responsive polypeptide nanogels with self-reinforced endocytoses were prepared through ring-opening polymerization of l-glutamate N-carboxyanhydrides, deprotection of benzyl group and subsequent quaternization reaction between γ-2-chloroethyl-l-glutamate unit in polypeptide block and 2,2'-dithiobis(N,N-dimethylethylamine). The nanogels were revealed to exhibit smart pH and reduction dual-responsiveness, and excellent biocompatibilities, which expressed great potential as antitumor drug nanocarriers. Doxorubicin (DOX) as a model antitumor drug was loaded into nanogels through dispersion. DOX-loaded nanogels displayed a stable core-cross-linked structure under normal physiological condition (pH7.4), while rapidly releasing the payloads in the mimicking endosomal (pH5.3), tumor tissular (pH6.8) or intracellular reductive microenvironments (10.0mM glutathione). Confocal fluorescence microscopy demonstrated that DOX-loaded nanogels could deliver DOX into HepG2 cells (a human hepatoma cell line) more efficiently than the parent DOX-loaded micelle and free DOX. The enhanced cellular internalizations of DOX-loaded nanogels were more significant under tumor tissular acidic condition (pH6.8) ascribed to the quaternary ammonium groups in the cores. In addition, DOX-loaded nanogels exhibited improved in vitro and in vivo antitumor activities, and in vivo securities compared with DOX-loaded micelle and free DOX. These excellent features of the smart nanogels with quaternary ammonium groups were endowed with a bright prospect for intracellular targeting antitumor drug delivery.

Molecular Magnetic Resonance Imaging of Tumors with a PTPµ Targeted Contrast Agent

Molecular magnetic resonance imaging (MRI) of tumors improves the specificity of MRI by using targeted probes conjugated to contrast-generating metals. The limitation of this approach is in the identification of a target molecule present in sufficient concentration for visualization and the development of a labeling reagent that can penetrate tumor tissue with the fast kinetics required for use in a clinical setting. The receptor protein tyrosine phosphatase PTPµ is a transmembrane protein that is continuously proteolyzed in the tumor microenvironment to generate a high concentration of extracellular fragment that can be recognized by the SBK2 probe. We conjugated the SBK2 peptide to a gadolinium chelate [SBK2-Tris-(Gd-DOTA)3] to test whether the SBK2 probe could be developed as an MR molecular imaging probe. When intravenously injected into mice bearing flank tumors of human glioma cells, SBK2-Tris-(Gd-DOTA)3 labeled the tumors within 5 minutes with a high level of contrast for up to 2 hours post-injection. The contrast enhancement of SBK2-Tris-(Gd-DOTA)3 was significantly higher than that observed with a current MRI macrocyclic gadolinium chelate (Gadoteridol, ProHance) alone or a scrambled control. These results demonstrate that SBK2-Tris-(Gd-DOTA)3 labeling of the PTPµ extracellular fragment is a more specific MR molecular imaging probe than ProHance or a scrambled control. Consequently, the SBK2 probe may be more useful than the current gold standard reagent for MRI to identify tumors and to co-register tumor borders during surgical resection.

Gene therapy for advanced melanoma: selective targeting and therapeutic nucleic acids

Despite recent advances, the treatment of malignant melanoma still results in the relapse of the disease, and second line treatment mostly fails due to the occurrence of resistance. A wide range of mutations are known to prevent effective treatment with chemotherapeutic drugs. Hence, approaches with biopharmaceuticals including proteins, like antibodies or cytokines, are applied. As an alternative, regimens with therapeutically active nucleic acids offer the possibility for highly selective cancer treatment whilst avoiding unwanted and toxic side effects. This paper gives a brief introduction into the mechanism of this devastating disease, discusses the shortcoming of current therapy approaches, and pinpoints anchor points which could be harnessed for therapeutic intervention with nucleic acids. We bring the delivery of nucleic acid nanopharmaceutics into perspective as a novel antimelanoma therapeutic approach and discuss the possibilities for melanoma specific targeting. The latest reports on preclinical and already clinical application of nucleic acids in melanoma are discussed.

Challenges and key considerations of the enhanced permeability and retention effect for nanomedicine drug delivery in oncology

Enhanced permeability of the tumor vasculature allows macromolecules to enter the tumor interstitial space, whereas the suppressed lymphatic filtration allows them to stay there. This phenomenon, enhanced permeability and retention (EPR), has been the basis of nanotechnology platforms to deliver drugs to tumors. However, progress in developing effective drugs using this approach has been hampered by heterogeneity of EPR effect in different tumors and limited experimental data from patients on effectiveness of this mechanism as related to enhanced drug accumulation. This report summarizes the workshop discussions on key issues of the EPR effect and major gaps that need to be addressed to effectively advance nanoparticle-based drug delivery.

Towards more effective advanced drug delivery systems

This position paper discusses progress made and to be made with so-called advanced drug delivery systems, particularly but not exclusively those in the nanometre domain. The paper has resulted from discussions with a number of international experts in the field who shared their views on aspects of the subject, from the nomenclature used for such systems, the sometimes overwrought claims made in the era of nanotechnology, the complex nature of targeting delivery systems to specific destinations in vivo, the need for setting standards for the choice and characterisation of cell lines used in in vitro studies, to attention to the manufacturability, stability and analytical profiling of systems and more relevant studies on toxicology. The historical background to the development of many systems is emphasised. So too is the stochastic nature of many of the steps to successful access to and action in targets. A lacuna in the field is the lack of availability of data on a variety of carrier systems using the same models in vitro and in vivo using standard controls. The paper asserts that greater emphasis must also be paid to the effective levels of active attained in target organs, for without such crucial data it will be difficult for many experimental systems to enter the clinic. This means the use of diagnostic/imaging technologies to monitor targeted drug delivery and stratify patient groups, identifying patients with optimum chances for successful therapy. Last, but not least, the critical importance of the development of science bases for regulatory policies, scientific platforms overseeing the field and new paradigms of financing are discussed.

Markedly enhanced permeability and retention effects induced by photo-immunotherapy of tumors

A major barrier to cancer treatment is the inability to deliver sufficient concentrations of drug to the tumor without incurring systemic toxicities. Nanomaterials are appealing because they can carry a large drug payload; however, tumor delivery is limited by modest leakage and retention in most tumors. We observed that after photoimmunotherapy (PIT), which is a light-mediated treatment based on an antibody-photosensitizer conjugate, there was surprisingly high leakage of nanosized (10-200 nm) agents into the tumor bed. PIT rapidly induced death in perivascular cancer cells, leading to immediate and dramatic increases in vascular permeability, resulting in up to 24-fold greater accumulation of nanomaterials within the PIT-treated tumor compared with controls, an effect termed "super-enhanced permeability and retention". In a treatment study, PIT followed by liposome-containing daunorubicin, DaunoXome (diameter 50 nm), resulted in greater survival in tumor-bearing mice than either PIT or DaunoXome alone. Thus, PIT greatly enhances delivery of nanosized reagents and thus holds promise to improve therapeutic responses.

Micelles of zinc protoporphyrin conjugated to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer for imaging and light-induced antitumor effects in vivo

We synthesized N-(2-hydroxypropyl)methacrylamide polymer conjugated with zinc protoporphyrin (HPMA-ZnPP) and evaluated its application for tumor detection by imaging and treatment by light exposure using in mouse sarcoma model. To characterize HPMA-ZnPP micelle, we measured its micellar size, surface charge, stability, photochemical, biochemical properties and tissue distribution. In vivo anti-tumor effect and fluorescence imaging were carried out to validate the tumor selective accumulation and therapeutic effect by inducing singlet oxygen by light exposure. HPMA-ZnPP was highly water soluble and formed micelles spontaneously having hydrophobic clustered head group of ZnPP, in aqueous solution, with a hydrodynamic diameter of 82.8±41.8 nm and zeta-potential of +1.12 mV. HPMA-ZnPP had a long plasma half-life and effectively and selectively accumulated in tumors. Although HPMA-ZnPP alone had no toxicity in S-180 tumor-bearing mice, light-irradiation significantly suppressed tumor growth in vivo, similar to the cytotoxicity to HeLa cells in vitro upon endoscopic light-irradiation. HPMA-ZnPP can visualize tumors by fluorescence after i.v. injection, which suggests that this micelle may be useful for both tumor imaging and therapy. Here we describe preparation of a new fluorescence nanoprobe that is useful for simultaneous tumor imaging and treatment, and application to fluorescence endoscopy is now at visible distance.