Tumor-selective delivery of macromolecular drugs via the EPR effect: background and future prospects

Overcoming nucleoside analog chemoresistance of pancreatic cancer: a therapeutic challenge

Clinical refractoriness to nucleoside analogs (e.g., gemcitabine, capecitabine) is a major scientific problem and is one of the main reasons underlying the extremely poor prognostic state of pancreatic cancer. The drugs' effects are suboptimal partly due to cellular mechanisms limiting their transport, activation, and overall efficacy. Nonetheless, novel therapeutic approaches are presently under study to circumvent nucleoside analog resistance in pancreatic cancer. With these new approaches come additional challenges to be addressed. This review describes the determinants of chemoresistance in the gemcitabine cytotoxicity pathways, provides an overview of investigational approaches for overcoming chemoresistance, and discusses new challenges presented. Understanding the future directions of the field may assist in the successful development of novel treatment strategies for enhancing chemotherapeutic efficacy in pancreatic cancer.

Kaempferol nanoparticles achieve strong and selective inhibition of ovarian cancer cell viability

Ovarian cancer is one of the leading causes of cancer death for women throughout the Western world. Kaempferol, a natural flavonoid, has shown promise in the chemoprevention of ovarian cancer. A common concern about using dietary supplements for chemoprevention is their bioavailability. Nanoparticles have shown promise in increasing the bioavailability of some chemicals. Here we developed five different types of nanoparticles incorporating kaempferol and tested their efficacy in the inhibition of viability of cancerous and normal ovarian cells. We found that positively charged nanoparticle formulations did not lead to a significant reduction in cancer cell viability, whereas nonionic polymeric nanoparticles resulted in enhanced reduction of cancer cell viability. Among the nonionic polymeric nanoparticles, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) nanoparticles incorporating kaempferol led to significant reduction in cell viability of both cancerous and normal cells. Poly(DL-lactic acid-co-glycolic acid) (PLGA) nanoparticles incorporating kaempferol resulted in enhanced reduction of cancer cell viability together with no significant reduction in cell viability of normal cells compared with kaempferol alone. Therefore, both PEO-PPO-PEO and PLGA nanoparticle formulations were effective in reducing cancer cell viability, while PLGA nanoparticles incorporating kaempferol had selective toxicity against cancer cells and normal cells. A PLGA nanoparticle formulation could be advantageous in the prevention and treatment of ovarian cancers. On the other hand, PEO-PPO-PEO nanoparticles incorporating kaempferol were more effective inhibitors of cancer cells, but they also significantly reduced the viability of normal cells. PEO-PPO-PEO nanoparticles incorporating kaempferol may be suitable as a cancer-targeting strategy, which could limit the effects of the nanoparticles on normal cells while retaining their potency against cancer cells. We have identified two nanoparticle formulations incorporating kaempferol that may lead to breakthroughs in cancer treatment. Both PEO-PPO-PEO and PLGA nanoparticle formulations had superior effects compared with kaempferol alone in reducing cancer cell viability.

Chemotherapy targeting by DNA capture in viral protein particles

AIM

This study tests the hypothesis that DNA intercalation and electrophilic interactions can be exploited to noncovalently assemble doxorubicin in a viral protein nanoparticle designed to target and penetrate tumor cells through ligand-directed delivery. We further test whether this new paradigm of doxorubicin targeting shows therapeutic efficacy and safety in vitro and in vivo.

MATERIALS & METHODS

We tested serum stability, tumor targeting and therapeutic efficacy in vitro and in vivo using biochemical, microscopy and cytotoxicity assays.

RESULTS

Self-assembly formed approximately 10-nm diameter serum-stable nanoparticles that can target and ablate HER2+ tumors at >10× lower dose compared with untargeted doxorubicin, while sparing the heart after intravenous delivery. The targeted nanoparticle tested here allows doxorubicin potency to remain unaltered during assembly, transport and release into target cells,while avoiding peripheral tissue damage and enabling lower, and thus safer, drug dose for tumor killing.

CONCLUSION

This nanoparticle may be an improved alternative to chemical conjugates and signal-blocking antibodies for tumor-targeted treatment.

Glucocorticoid-loaded core-cross-linked polymeric micelles with tailorable release kinetics for targeted therapy of rheumatoid arthritis

Polymerizable and hydrolytically cleavable dexamethasone (DEX, red dot in picture) derivatives were covalently entrapped in core-cross-linked polymeric micelles that were prepared from a thermosensitive block copolymer (yellow and gray building block). By varying the oxidation degree of the thioether in the drug linker, the release rate of DEX could be controlled. The DEX-loaded micelles were used for efficient treatment of inflammatory arthritis in two animal models.

A dicarboxylic fatty acid derivative of paclitaxel for albumin-assisted drug delivery

Paclitaxel (PTX) is a potent chemotherapy for many cancers but it suffers from very poor solubility. Consequently, the TAXOL formulation uses copious amounts of the surfactant Cremophor EL to solubilize the drug for injection, resulting in severe hypersensitivity and neutropenia. In contrast to Cremophor EL, presented is a way to solubilize PTX by conjugation of a dicarboxylic fatty acid for specific binding to the ubiquitous protein, serum albumin. The conjugation chemistry was simplified to a single step using the activated anhydride form of 3-pentadecylglutaric (PDG) acid, which is reactive to a variety of nucleophiles. The PDG derivative is less cytotoxic than the parent compound and was found to slowly hydrolyze to PTX (≈ 5% over 72 h) in serum, tumor cytosol, and tumor tissue homogenate. When injected intravenously to tumor-bearing mice, [(3) H]-PTX in the TAXOL formulation was cleared rapidly with a half-life of 7 h. In the case of the PDG derivative of PTX, the drug is quickly distributed and approximately 20% of the injected dose remained in the vasculature experiencing a 23 h half-life. These improvements from modifying PTX with the PDG fatty acid present the opportunity for PDG to become a generic modification for the improvement of many therapeutics.

Surface charge-switching polymeric nanoparticles for bacterial cell wall-targeted delivery of antibiotics

Bacteria have shown a remarkable ability to overcome drug therapy if there is a failure to achieve sustained bactericidal concentration or if there is a reduction in activity in situ. The latter can be caused by localized acidity, a phenomenon that can occur as a result of the combined actions of bacterial metabolism and the host immune response. Nanoparticles (NP) have shown promise in treating bacterial infections, but a significant challenge has been to develop antibacterial NPs that may be suitable for systemic administration. Herein we develop drug-encapsulated, pH-responsive, surface charge-switching poly(D,L-lactic-co-glycolic acid)-b-poly(L-histidine)-b-poly(ethylene glycol) (PLGA-PLH-PEG) nanoparticles for treating bacterial infections. These NP drug carriers are designed to shield nontarget interactions at pH 7.4 but bind avidly to bacteria in acidity, delivering drugs and mitigating in part the loss of drug activity with declining pH. The mechanism involves pH-sensitive NP surface charge switching, which is achieved by selective protonation of the imidazole groups of PLH at low pH. NP binding studies demonstrate pH-sensitive NP binding to bacteria with a 3.5 ± 0.2- to 5.8 ± 0.1-fold increase in binding to bacteria at pH 6.0 compared to 7.4. Further, PLGA-PLH-PEG-encapsulated vancomycin demonstrates reduced loss of efficacy at low pH, with an increase in minimum inhibitory concentration of 1.3-fold as compared to 2.0-fold and 2.3-fold for free and PLGA-PEG-encapsulated vancomycin, respectively. The PLGA-PLH-PEG NPs described herein are a first step toward developing systemically administered drug carriers that can target and potentially treat Gram-positive, Gram-negative, or polymicrobial infections associated with acidity.

Analysis of immediate stress mechanisms upon injection of polymeric micelles and related colloidal drug carriers: implications on drug targeting

Polymeric micelles are ideal carriers for solubilization and targeting applications using hydrophobic drugs. Stability of colloidal aggregates upon injection into the bloodstream is mandatory to maintain the drugs' targeting potential and to influence pharmacokinetics. In this review we analyzed and discussed the most relevant stress mechanisms that polymeric micelles and related colloidal carriers encounter upon injection, including (1) dilution, (2) interactions with blood components, and (3) immunological responses of the body. In detail we analyzed the opsonin-dysopsonin hypothesis that points at a connection between a particles' protein-corona and its tissue accumulation by the enhanced permeability and retention (EPR) effect. In the established theory, size is seen as a necessary condition to reach nanoparticle accumulation in disease modified tissue. There is, however, mounting evidence of other sufficient conditions (e.g., particle charge, receptor recognition of proteins adsorbed onto particle surfaces) triggering nanoparticle extravasation by active mechanisms. In conclusion, the analyzed stress mechanisms are directly responsible for in vivo success or failure of the site-specific delivery with colloidal carrier systems.

Hyperthermia-triggered drug delivery from temperature-sensitive liposomes using MRI-guided high intensity focused ultrasound

In the continuous search for cancer therapies with a higher therapeutic window, localized temperature-induced drug delivery may offer a minimal invasive treatment option. Here, a chemotherapeutic drug is encapsulated into a temperature-sensitive liposome (TSL) that is released at elevated temperatures, for example, when passing through a locally heated tumor. Consequently, high drug levels in the tumor tissue can be achieved, while reducing drug exposure to healthy tissue. Although the concept of temperature-triggered drug delivery was suggested more than thirty years ago, several chemical and technological challenges had to be addressed to advance this approach towards clinical translation. In particular, non-invasive focal heating of tissue in a controlled fashion remained a challenge. For the latter, high intensity focused ultrasound (HIFU) allows non-invasive heating to establish hyperthermia (40-45 °C) of tumor tissue over time. Magnetic resonance imaging (MRI) plays a pivotal role in this procedure thanks to its superb spatial resolution for soft tissue as well as the possibility to acquire 3D temperature information. Consequently, MRI systems emerged with an HIFU ultrasound transducer embedded in the patient bed (MR-HIFU), where the MRI is utilized for treatment planning, and to provide spatial and temperature feedback to the HIFU. For tumor treatment, the lesion is heated to 42 °C using HIFU. At this temperature, the drug-loaded TSLs release their payload in a quantitative fashion. The concept of temperature-triggered drug delivery has been extended to MR image-guided drug delivery by the co-encapsulation of a paramagnetic MRI contrast agent in the lumen of TSLs. This review will give an overview of recent developments in temperature-induced drug delivery using HIFU under MRI guidance.

Nanovector delivery of siRNA for cancer therapy

RNA interference holds the promise to knock down expression of every cancer gene. Both academic laboratories and pharmaceutical companies have committed heavily on manpower and financial resources to develop small interfering RNA (siRNA) cancer therapeutics over the last decade. Although significant advances have been made in the design of siRNA therapeutics and mechanism of action on cancer cell killing, there are still many hurdles to overcome including effective delivery of therapeutics in vivo. Nanotechnology has had an important role in the development of delivery vectors so far. This article summarizes current nanovectors for siRNA delivery, discusses technical challenges in overcoming biological barriers, and introduces the multistage vector system for tumor-specific delivery.

Nanoprobes for hybrid SPECT/MR molecular imaging

Hybrid imaging techniques provide enhanced visualization of biological targets by synergistically combining multiple imaging modalities, thereby providing information on specific aspects of structure and function, which is difficult to obtain by a single imaging modality. Advances in the field of hybrid imaging have resulted in the recent approval of PET/magnetic resonance (MR) imaging by the US FDA for clinical use in the USA and Europe. Single-photon emission computed tomography (SPECT)/MR imaging is another evolving hybrid imaging modality with distinct advantages. Recently reported progress in the development of a SPECT/MR imaging hybrid scanner provides a cue towards the need for multimodal SPECT/MR imaging nanoprobes to take full advantage of a scanner’s simultaneous imaging capability. In this review, we present some of the latest developments in the domain of SPECT/MR hybrid imaging, particularly focusing on multimodal nanoprobes.

Macromolecular therapeutics in cancer treatment: the EPR effect and beyond

In this review, I have discussed various issues of the cancer drug targeting primarily related to the EPR (enhanced permeability and retention) effect, which utilized nanomedicine or macromolecular drugs. The content goes back to the development of the first polymer-protein conjugate anticancer agent SMANCS and development of the arterial infusion in Lipiodol formulation into the tumor feeding artery (hepatic artery for hepatoma). The brief account on the EPR effect and its definition, factors involved, heterogeneity, and various methods of augmentation of the EPR effect, which showed remarkably improved clinical outcomes are also discussed. Various obstacles involved in drug developments and commercialization are also discussed through my personal experience and recollections.

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

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

Preclinical evaluation of injectable sirolimus formulated with polymeric nanoparticle for cancer therapy

Nanoparticles are useful delivery vehicles for promising drug candidates that face obstacles for clinical applicability. Sirolimus, an inhibitor of mammalian target of rapamycin has gained attention for targeted anticancer therapy, but its clinical application has been limited by its poor solubility. This study was designed to enhance the feasibility of sirolimus for human cancer treatment. Polymeric nanoparticle (PNP)–sirolimus was developed as an injectable formulation and has been characterized by transmission electron microscopy and dynamic light scattering. Pharmacokinetic analysis revealed that PNP–sirolimus has prolonged circulation in the blood. In addition, PNP–sirolimus preserved the in vitro killing effect of free sirolimus against cancer cells, and intravenous administration displayed its potent in vivo anticancer efficacy in xenograft tumor mice. In addition, PNP–sirolimus enhanced the radiotherapeutic efficacy of sirolimus both in vitro and in vivo. Clinical application of PNP–sirolimus is a promising strategy for human cancer treatment.

Ultrasound sonication with microbubbles disrupts blood vessels and enhances tumor treatments of anticancer nanodrug

Ultrasound (US) sonication with microbubbles (MBs) has the potential to disrupt blood vessels and enhance the delivery of drugs into the sonicated tissues. In this study, mouse ear tumors were employed to investigate the therapeutic effects of US, MBs, and pegylated liposomal doxorubicin (PLD) on tumors. Tumors started to receive treatments when they grew up to about 15 mm(3) (early stage) with injection of PLD 10 mg/kg, or up to 50 mm(3) (medium stage) with PLD 6 (or 4) mg/kg. Experiments included the control, PLD alone, PLD + MBs + US, US alone, and MBs + US groups. The procedure for the PLD + MBs + US group was that PLD was injected first, MB (SonoVue) injection followed, and then US was immediately sonicated on the tumor. The results showed that: (1) US sonication with MBs was always able to produce a further hindrance to tumor growth for both early and medium-stage tumors; (2) for the medium-stage tumors, 6 mg/kg PLD alone was able to inhibit their growth, while it did not work for 4 mg/kg PLD alone; (3) with the application of MBs + US, 4 mg/kg PLD was able to inhibit the growth of medium-stage tumors; (4) for early stage tumors after the first treatment with a high dose of PLD alone (10 mg/kg), the tumor size still increased for several days and then decreased (a biphasic pattern); (5) MBs + US alone was able to hinder the growth of early stage tumors, but unable to hinder that of medium stage tumors. The results of histological examinations and blood perfusion measurements indicated that the application of MBs + US disrupts the tumor blood vessels and enhances the delivery of PLD into tumors to significantly inhibit tumor growth.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Temporal control over cellular targeting through hybridization of folate-targeted dendrimers and PEG-PLA nanoparticles

Polymeric nanoparticles (NPs) and dendrimers are two major classes of nanomaterials that have demonstrated great potential for targeted drug delivery. However, their targeting efficacy has not yet met clinical needs, largely because of a lack of control over their targeting kinetics, which often results in rapid clearance and off-target drug delivery. To address this issue, we have designed a novel hybrid NP (nanohybrid) platform that allows targeting kinetics to be effectively controlled through hybridization of targeted dendrimers with polymeric NPs. Folate (FA)-targeted generation 4 poly(amidoamine) dendrimers were encapsulated into poly(ethylene glycol)-b-poly(D,L-lactide) (PEG-PLA) NPs using a double emulsion method, forming nanohybrids with a uniform size (~100 nm in diameter) at high encapsulation efficiencies (69-85%). Targeted dendrimers encapsulated within the NPs selectively interacted with FA receptor (FR)-overexpressing KB cells upon release in a temporally controlled manner. The targeting kinetics of the nanohybrids were modulated using three different molecular weights (MW) of the PLA block (23, 30, and 45 kDa). The release rates of the dendrimers from the nanohybrids were inversely proportional to the MW of the PLA block, which dictated their binding and internalization kinetics with KB cells. Our results provide evidence that selective cellular interactions can be kinetically controlled by the nanohybrid design, which can potentially enhance targeting efficacy of nanocarriers.

Antitumor efficacy following the intracellular and interstitial release of liposomal doxorubicin

pH-triggered lipid-membranes designed from biophysical principles are evaluated in the form of targeted liposomal doxorubicin with the aim to ultimately better control the growth of vascularized tumors. We compare the antitumor efficacy of anti-HER2/neu pH-triggered lipid vesicles encapsulating doxorubicin to the anti-HER2/neu form of an FDA approved liposomal doxorubicin of DSPC/cholesterol-based vesicles. The HER2/neu receptor is chosen due to its abundance in human breast cancers and its connection to low prognosis. On a subcutaneous murine BT474 xenograft model, superior control of tumor growth is demonstrated by targeted pH-triggered vesicles relative to targeted DSPC/cholesterol-based vesicles (35% vs. 19% decrease in tumor volume after 32 days upon initiation of treatment). Superior tumor control is also confirmed on SKBR3 subcutaneous xenografts of lower HER2/neu expression. The non-targeted form of pH-triggered vesicles encapsulating doxorubicin results also in better tumor control relative to the non-targeted DSPC/cholesterol-based vesicles (34% vs. 41% increase in tumor volume). Studies in BT474 multicellular spheroids suggest that the observed efficacy could be attributed to release of doxorubicin directly into the acidic tumor interstitium from pH-triggered vesicles extravasated into the tumor but not internalized by cancer cells. pH-triggered liposome carriers engineered from gel-phase bilayers that reversibly phase-separate with lowering pH, form transiently defective interfacial boundaries resulting in fast release of encapsulated doxorubicin. Our studies show that pH-triggered liposomes release encapsulated doxorubicin intracellularly and intratumorally, and may improve tumor control at the same or even lower administered doses relative to FDA approved liposomal chemotherapy.

Polymeric conjugates for drug delivery

The field of polymer therapeutics has evolved over the past decade and has resulted in the development of polymer-drug conjugates with a wide variety of architectures and chemical properties. Whereas traditional non-degradable polymeric carriers such as poly(ethylene glycol) (PEG) and N-(2-hydroxypropyl methacrylamide) (HPMA) copolymers have been translated to use in the clinic, functionalized polymer-drug conjugates are increasingly being utilized to obtain biodegradable, stimuli-sensitive, and targeted systems in an attempt to further enhance localized drug delivery and ease of elimination. In addition, the study of conjugates bearing both therapeutic and diagnostic agents has resulted in multifunctional carriers with the potential to both "see and treat" patients. In this paper, the rational design of polymer-drug conjugates will be discussed followed by a review of different classes of conjugates currently under investigation. The design and chemistry used for the synthesis of various conjugates will be presented with additional comments on their potential applications and current developmental status.

Effects of nanoparticle surface-coupled peptides, functional endgroups, and charge on intracellular distribution and functionality of human primary reticuloendothelial cells

The medical use of nanoparticles (NPs) has to consider their interactions with the cells of the reticuloendothelial system. In this study the authors used gold nanorods coated by PEG chains bearing peptides or charged functional groups to study their influence on the uptake, subcellular distribution, and activation of human primary reticuloendothelial cells: monocytes, macrophages (MΦ), immature and mature dendritic cells (DC), and endothelial cells (EC). We found that beside MΦ and immature DC also EC internalize large quantities of NPs and observed an increased uptake of positively charged particles. Most notably, NPs accumulated in the MHC II compartment in mature DC that is involved in antigen processing. Furthermore, surface-coupled peptide sequences RGD and GLF altered the activation profile of DC, and modulated cytokine release in both DC and MΦ in a cell specific manner. These data suggest that the charge of NPs mainly influences their uptake, whereas conjugated peptides alter cell functions.

FROM THE CLINICAL EDITOR

In this paper the interactions between RES cells and nanoparticles is investigated, concluding that in the case of gold nanorods charge determines uptake characteristics, whereas conjugated peptides determine their function.

Nanomedicine and veterinary science: the reality and the practicality

Nanomedicine is a rapidly expanding field with a promising future that is already permeating veterinary science. This review summarises the current applications for nanoparticles in human medicine and explores their potential applicability for veterinary use. The principles underlying the use of nanoparticles in drug delivery, imaging and as vaccine adjuvants are explored along with the unique issues surrounding nanoparticle toxicity and regulatory approval. A brief overview of the properties of different nanoparticle systems including, liposomes, micelles, emulsions and inorganic nanoparticles, is provided, along with a description of their current and potential future applications in veterinary medicine.

Blood clearance and biodistribution of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization

The physiological properties of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization were investigated in terms of the circulation lifetime in the blood and distribution in tissues. Hydrophilic polymers consisting mainly of poly(poly(ethylene glycol) methyl ether methacrylate) were grafted onto silica particles by surface-initiated atom transfer radical polymerization that was mediated by a copper complex to produce hairy hybrid particles. A series of hybrid particles was synthesized by varying the diameter of the silica core and the chain length of the polymer brush to examine the relationship between their physicochemical and physiological properties. The hybrid particles were injected intravenously into mice to investigate systematically their blood clearance and body distribution. It was revealed that the structural features of the hybrid particles significantly affected their in vivo pharmacokinetics. Some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half life of ∼20 h. When such hybrid particles were injected intravenously into a tumor-bearing mouse, they preferentially accumulated in tumor tissue. The tumor-targeted delivery was optically visualized using hybrid particles grafted with fluorescence-labeled polymer brushes.

In vivo cancer imaging by poly(ethylene glycol)-b-poly(ɛ-caprolactone) micelles containing a near-infrared probe

Noninvasive near-infrared (NIR) fluorescence imaging is a promising technique for the intraoperative assessment of solid tumor removal. We incorporated a lipophilic NIR probe, 1,1'-dioctadecyltetramethyl indotricarbocyanine iodide (DiR), in poly(ethylene glycol)-b-poly(ɛ-caprolactone) (PEG-b-PCL) micelles, resulting in DiR solubilization in water, occupying nanoscopic PEG-b-PCL micelles. DiR in a self-quenched or nonquenched state showed different kinetics of release from PEG-b-PCL micelles in vitro; however, both obtained high tumor delineation (tumor-to-muscle ratio of 30-43 from collected organs). These results suggest that PEG-b-PCL micelles with DiR are a promising nanosized imaging agent that will provide a basis for enhanced surgical guidance via NIR visualization of tumors.

FROM THE CLINICAL EDITOR

In this paper, noninvasive near-infrared fluorescence imaging coupled with specific lipophilic probes is discussed as a promising technique for intraoperative assessment of solid tumor removal, leading to optimized outcomes for in toto removal of tumors.

Two-order targeted brain tumor imaging by using an optical/paramagnetic nanoprobe across the blood brain barrier

Surgical resection is a mainstay of brain tumor treatments. However, the completed excision of malignant brain tumor is challenged by its infiltrative nature. Contrast enhanced magnetic resonance imaging is widely used for defining brain tumor in clinic. However its ability in tumor visualization is hindered by the transient circulation lifetime, nontargeting specificity, and poor blood brain barrier (BBB) permeability of the commercially available MR contrast agents. In this work, we developed a two-order targeted nanoprobe in which MR/optical imaging reporters, tumor vasculature targeted cyclic [RGDyK] peptides, and BBB-permeable Angiopep-2 peptides are labeled on the PAMAM-G5 dendrimer. This nanoprobe is supposed to first target the α(V)β(3) integrin on tumor vasculatures. Increased local concentration of nanoprobe facilitates the association between BBB-permeable peptides and the low-density lipoprotein receptor-related protein (LRP) receptors on the vascular endothelial cells, which further accelerates BBB transverse of the nanoprobe via LRP receptor-mediated endocytosis. The nanoprobes that have penetrated the BBB secondly target the brain tumor because both α(V)β(3) integrin and LRP receptor are highly expressed on the tumor cells. In vivo imaging studies demonstrated that this nanoprobe not only efficiently crossed intact BBB in normal mice, but also precisely delineated the boundary of the orthotropic U87MG human glioblastoma xenograft with high target to background signal ratio. Overall, this two-order targeted nanoprobe holds the promise to noninvasively visualize brain tumors with uncompromised BBB and provides the possibility for real-time optical-image-guided brain tumor resection during surgery.

Polymeric micelles drug delivery system in oncology

Polymeric micelles (PM) system, as an efficient drug carrier, has received growing scientific attention in recent years owing to its solubilization, selective targeting, P-glycoprotein inhibition and altered drug internalization route and subcellular localization properties. Seven PM formulations of anti-tumor drugs being evaluated in clinical trials are reviewed in this paper, in terms of formulation study, in vitro cytotoxicity, in vivo pharmacokinetics, anti-tumor efficacy and safety as well as clinical trials, to shed new light on the discovery of novel PM formulations. In these seven PM formulations, PM system was employed to overcome the issues of low water solubility, high toxicity and (or) multidrug resistance accompanied with the conventional formulation, which greatly hampered their clinical application. Those promising preclinical and clinical results combined with rapid advancement and intense multidisciplinary collaboration enable the extension of the PM system to traditional Chinese medicine, imaging agents, gene and combination agent deliveries as well as some other administration routes, which facilitate the clinical translation of the PM drug delivery system.

The Øie-Tozer model of drug distribution and its suitability for drugs with different pharmacokinetic behavior

INTRODUCTION

Drug distribution is a major pharmacokinetic process that affects the time course of drug concentrations in tissues, biological fluids and the resulting pharmacological activities. Drug distribution may follow different pathways and patterns, and is governed by the drug's physicochemical properties and the body's physiology. The classical Øie-Tozer model is frequently used for predicting volume of drug distribution and for pharmacokinetic calculations.

AREAS COVERED

In this review, the suitability of the Øie-Tozer model for drugs that exhibit different distribution patterns is critically analyzed and illustrated. The method used is a pharmacokinetic modeling and simulation approach. It is demonstrated that the major limitation of the Øie-Tozer model stems from its focus on the total drug concentrations and not on the active (unbound) concentrations. Moreover, the Øie-Tozer model may be inappropriate for drugs with nonlinear or complex pharmacokinetic behavior, such as biopharmaceuticals, drug conjugates or for drugs incorporated into drug delivery systems. Distribution mechanisms and alternative distribution models for these drugs are discussed.

EXPERT OPINION

The Øie-Tozer model can serve for predicting unbound volume of drug distribution for 'classical' small molecular mass drugs with linear pharmacokinetics. However, more detailed mechanism-based distribution models should be used in preclinical and clinical settings for drugs that exhibit more complex pharmacokinetic behavior.

Action and reaction: the biological response to siRNA and its delivery vehicles

RNA interference (RNAi)-based therapeutics have significant potential for the treatment of human disease. Safe and effective delivery of RNA to target tissues remains a major barrier to realizing its clinical potential. Several factors can affect the in vivo performance of short interfering RNA (siRNA) delivery formulations, including siRNA sequence, structure, chemical modification, and delivery formulation. This review provides an introduction to the principles underlying the pharmacokinetics and pharmacodynamics of systemically administered siRNA and its delivery formulations, including the factors that lead to its degradation, clearance, and tissue uptake, as well as its potential for immunogenicity, toxicity, and off-target effects within the body.

Carbon monoxide, generated by heme oxygenase-1, mediates the enhanced permeability and retention effect in solid tumors

The enhanced permeability and retention (EPR) effect is a unique pathophysiological phenomenon of solid tumors that sees biocompatible macromolecules (>40 kDa) accumulate selectively in the tumor. Various factors have been implicated in this effect. Herein, we report that heme oxygenase-1 (HO-1; also known as heat shock protein 32) significantly increases vascular permeability and thus macromolecular drug accumulation in tumors. Intradermal injection of recombinant HO-1 in mice, followed by i.v. administration of a macromolecular Evans blue-albumin complex, resulted in dose-dependent extravasation of Evans blue-albumin at the HO-1 injection site. Almost no extravasation was detected when inactivated HO-1 or a carbon monoxide (CO) scavenger was injected instead. Because HO-1 generates CO, these data imply that CO plays a key role in vascular leakage. This is supported by results obtained after intratumoral administration of a CO-releasing agent (tricarbonyldichlororuthenium(II) dimer) in the same experimental setting, specifically dose-dependent increases in vascular permeability plus augmented tumor blood flow. In addition, induction of HO-1 in tumors by the water-soluble macromolecular HO-1 inducer pegylated hemin significantly increased tumor blood flow and Evans blue-albumin accumulation in tumors. These findings suggest that HO-1 and/or CO are important mediators of the EPR effect. Thus, anticancer chemotherapy using macromolecular drugs may be improved by combination with an HO-1 inducer, such as pegylated hemin, via an enhanced EPR effect.

How to improve exposure of tumor cells to drugs: promoter drugs increase tumor uptake and penetration of effector drugs

Solid tumors are characterized by an abnormal architecture and composition that limit the uptake and distribution of antitumor drugs. Over the last two decades, drugs have been identified that improve the tumor uptake and distribution of drugs that have direct antitumor effects. We propose to refer to these drugs as promoter drugs, and as effector drugs to drugs that have direct antitumor effects. Some promoter drugs have received regulatory approval, while others are in active clinical development. This review gives an overview of promoter drugs, by classifying them according to their mechanism of action: promoter drugs that modulate tumor blood flow, modify the barrier function of tumor vessels, induce tumor cell killing, and overcome stromal barriers. Eventually, we discuss those that we feel are the main conclusions to be drawn from promoter drug research that has been performed so far, and suggest areas of future investigation to improve the efficacy of promoter drugs in cancer therapy.

Vascular permeability in cancer and infection as related to macromolecular drug delivery, with emphasis on the EPR effect for tumor-selective drug targeting

Tumor and inflammation have many common features. One hallmark of both is enhanced vascular permeability, which is mediated by various factors including bradykinin, nitric oxide (NO), peroxynitrite, prostaglandins etc. A unique characteristic of tumors, however, is defective vascular anatomy. The enhanced vascular permeability in tumors is also distinctive in that extravasated macromolecules are not readily cleared. We utilized the enhanced permeability and retention (EPR) effect of tumors for tumor selective delivery of macromolecular drugs. Consequently, such drugs, nanoparticles or lipid particles, when injected intravenously, selectively accumulate in tumor tissues and remain there for long periods. The EPR effect of tumor tissue is frequently inhomogeneous and the heterogeneity of the EPR effect may reduce the tumor delivery of macromolecular drugs. Therefore, we developed methods to augment the EPR effect without inducing adverse effects for instance raising the systemic blood pressure by infusing angiotensin II during arterial injection of SMANCS/Lipiodol. This method was validated in clinical setting. Further, benefits of utilization of NO-releasing agent such as nitroglycerin or angiotensin-converting enzyme (ACE) inhibitors were demonstrated. The EPR effect is thus now widely accepted as the most basic mechanism for tumor-selective targeting of macromolecular drugs, or so-called nanomedicine.

Drug targeting systems for inflammatory disease: one for all, all for one

In various systemic disorders, structural changes in the microenvironment of diseased tissues enable both passive and active targeting of therapeutic agents to these tissues. This has led to a number of targeting approaches that enhance the accumulation of drugs in the target tissues, making drug targeting an attractive strategy for the treatment of various diseases. Remarkably, the strategic principles that form the basis of drug targeting are often employed for tumor targeting, while chronic inflammatory diseases appear to draw much less attention. To provide the reader with a general overview of the current status of drug targeting to inflammatory diseases, the passive and active targeting strategies that have been used for the treatment of rheumatoid arthritis (RA) and multiple sclerosis (MS) are discussed. The last part of this review addresses the dualism of platform technology-oriented ("one for all") and disease-oriented drug targeting research ("all for one"), both of which are key elements of effective drug targeting research.

Cationic albumin nanoparticles for enhanced drug delivery to treat breast cancer: preparation and in vitro assessment

Most anticancer drugs are greatly limited by the serious side effects that they cause. Doxorubicin (DOX) is an antineoplastic agent, commonly used against breast cancer. However, it may lead to irreversible cardiotoxicity, which could even result in congestive heart failure. In order to avoid these harmful side effects to the patients and to improve the therapeutic efficacy of doxorubicin, we developed DOX-loaded polyethylenimine- (PEI-) enhanced human serum albumin (HSA) nanoparticles. The formed nanoparticles were ~137 nm in size with a surface zeta potential of ~+15 mV, prepared using 20 μg of PEI added per mg of HSA. Cytotoxicity was not observed with empty PEI-enhanced HSA nanoparticles, formed with low-molecular weight (25 kDa) PEI, indicating biocompatibility and safety of the nanoparticle formulation. Under optimized transfection conditions, approximately 80% of cells were transfected with HSA nanoparticles containing tetramethylrhodamine-conjugated bovine serum albumin. Conclusively, PEI-enhanced HSA nanoparticles show potential for developing into an effective carrier for anticancer drugs.

Cancer nanotechnology: emerging role of gold nanoconjugates

Over the last few decades, the study of nanotechnology has grown exponentially. Nanotechnology bridges science, engineering and technology; it continues to expand in definition as well as practice. One sub-set of nanotechnology is bionanotechnology, this will be the focus of this review. Currently, bionanotechnology is being studied and exploited for utility within medicinal imaging, diagnosis and therapy in regard to cancer. Cancer is a world-wide health problem and the implication rate as well as the death rate increase year to year. However promising work is being done with gold nanoparticles for detection, diagnosis and targeted drug delivery therapy. Gold nanoparticles can be synthesized in various shapes and sizes, which directly correlates to the color; they can also be manipulated to carry various antibody, protein, plasmid, DNA or small molecule drug. Herein we summarize some of the very influential research being done in the field of Cancer Nanotechnology with an emphasis on gold nanoparticles.

Tumor accumulation of NIR fluorescent PEG-PLA nanoparticles: impact of particle size and human xenograft tumor model

Cancer therapies are often terminated due to serious side effects of the drugs. The cause is the nonspecific distribution of chemotherapeutic agents to both cancerous and normal cells. Therefore, drug carriers which deliver their toxic cargo specific to cancer cells are needed. Size is one key parameter for the nanoparticle accumulation in tumor tissues. In the present study the influence of the size of biodegradable nanoparticles was investigated in detail, combining in vivo and ex vivo analysis with comprehensive particle size characterizations. Polyethylene glycol-polyesters poly(lactide) block polymers were synthesized and used for the production of three defined, stable, and nontoxic near-infrared (NIR) dye-loaded nanoparticle batches. Size analysis based on asymmetrical field flow field fractionation coupled with multiangle laser light scattering and photon correlation spectroscopy (PCS) revealed narrow size distribution and permitted accurate size evaluations. Furthermore, this study demonstrates the constraints of particle size data only obtained by PCS. By the multispectral analysis of the Maestro in vivo imaging system the in vivo fate of the nanoparticles next to their accumulation in special red fluorescent DsRed2 expressing HT29 xenografts could be followed. This simultaneous imaging in addition to confocal microscopy studies revealed information about the accumulation characteristics of nanoparticles inside the tumor tissues. This knowledge was further combined with extended size-dependent fluorescence imaging studies at two different xenograft tumor types, the HT29 (colorectal carcinoma) and the A2780 (ovarian carcinoma) cell lines. The combination of two different size measurement methods allowed the characterization of the dependence of nanoparticle accumulation in the tumor on even rather small differences in the nanoparticle size. While two nanoparticle batches (111 and 141 nm in diameter) accumulated efficiently in the human xenograft tumor tissue, the slightly bigger nanoparticles (diameter 166 nm) were rapidly eliminated by the liver.

Reprint of "Nanobody--shell functionalized thermosensitive core-crosslinked polymeric micelles for active drug targeting"

The aim of this study was to develop poly(ethylene glycol)-b-poly[N-(2-hydroxypropyl) methacrylamide-lactate] (mPEG-b-p(HPMAm-Lac(n))) core-crosslinked thermosensitive biodegradable polymeric micelles suitable for active tumor targeting, by coupling the anti-EGFR (epidermal growth factor receptor) EGa1 nanobody to their surface. To this end, PEG was functionalized with N-succinimidyl 3-(2-pyridyldithio)-propionate (SPDP) to yield a PDP-PEG-b-p(HPMAm-Lac(n)) block copolymer. Micelles composed of 80% mPEG-b-p(HPMAm-Lac(n)) and 20% PDP-PEG-b-p(HPMAm-Lac(n)) were prepared and lysozyme (as a model protein) was modified with N-succinimidyl-S-acetylthioacetate, deprotected with hydroxylamine hydrochloride and subsequently coupled to the micellar surface. The micellar conjugates were characterized using SDS-PAGE and gel permeation chromatography (GPC). Using the knowledge obtained with lysozyme conjugation, the EGa1 nanobody was coupled to mPEG/PDP-PEG micelles and the conjugation was successful as demonstrated by western blot and dot blot analysis. Rhodamine labeled EGa1-micelles showed substantially higher binding as well as uptake by EGFR over-expressing cancer cells (A431 and UM-SCC-14C) than untargeted rhodamine labeled micelles. Interestingly, no binding of the nanobody micelles was observed to EGFR negative cells (3T3) as well as to14C cells in the presence of an excess of free nanobody. This demonstrates that the binding of the nanobody micelles is indeed by interaction with the EGF receptor. In conclusion, EGa1 decorated (mPEG/PDP-PEG)-b-(pHPMAm-Lac(n)) polymeric micelles are highly promising systems for active drug targeting.

PEGylated dendrimer-entrapped gold nanoparticles for in vivo blood pool and tumor imaging by computed tomography

We report the synthesis and characterization of dendrimer-entrapped gold nanoparticles (Au DENPs) modified by polyethylene glycol (PEG) with enhanced biocompatibility for computed tomography (CT) imaging applications. In this study, amine-terminated poly(amidoamine) dendrimers of generation 5 (G5.NH(2)) modified by PEG monomethyl ether (G5.NH(2)-mPEG(20)) were used as templates to synthesize Au DENPs, followed by acetylation of the remaining dendrimer terminal amines to generate PEGylated Au DENPs. The partial PEGylation modification of dendrimer terminal amines allows high loading of Au within the dendrimer interior, and consequently by simply varying the Au salt/dendrimer molar ratio, the size of the PEGylated Au DENPs can be controlled at a range of 2-4 nm with a narrow size distribution. The formed PEGylated Au DENPs are water-dispersible, stable in a pH range of 5-8 and a temperature range of 0-50 °C, and non-cytotoxic at a concentration as high as 100 μm. X-ray absorption coefficient measurements show that the attenuation intensity of the PEGylated Au DENPs is much higher than that of Omnipaque with iodine concentration similar to Au. With the sufficiently long half-decay time demonstrated by pharmacokinetics studies, the PEGylated Au DENPs enabled not only X-ray CT blood pool imaging of mice and rats after intravenous injection of the particles, but also effective CT imaging of a xenograft tumor model in nude mice. These findings suggest that the designed PEGylated Au DENPs can be used as a promising contrast agent with enhanced biocompatibility for CT imaging of various biological systems, especially in cancer diagnosis.