The EPR effect for macromolecular drug delivery to solid tumors: Improvement of tumor uptake, lowering of systemic toxicity, and distinct tumor imaging in vivo

Spatial-temporal event adaptive characteristics of nanocarrier drug delivery in cancer therapy

In cancer therapy, drug delivery is a complex process that aims to transit the cargo to the destination with as little damage to the normal tissue as possible. In the last decade, tremendous development and research on nanomedicine have been exploring an ideal system with efficient drug transportation and release property. For this end, series of barriers need to be circumvented by nanomedicine, including systemic barriers, such as biosurface adsorption, phagocytic clearance, bloodstream washing, interstitial pressure, degradation, as well as intracellular barriers, such as cell membrane reorganization and internalization, endo/lysosomal escape, cytosolic or subcellular localization. Rather than being random, these barriers follow a specific spatial-temporal sequence. Therefore, the nanocarriers have to be endowed with characteristics that are adaptive to particular biological milieu on systemic and intracellular levels. To this end, we reviewed the correlations between the spatial-temporal sequences of drug delivery and nanocarrier characteristics in cancer therapy, as well as strategies to achieve efficient drug delivery upon both systemic and intracellular levels.

Complete regression of local cancer using temperature-sensitive liposomes combined with ultrasound-mediated hyperthermia

The development of treatment protocols that result in a complete response to chemotherapy has been hampered by free drug toxicity and the low bioavailability of nano-formulated drugs. Here, we explore the application of temperature-sensitive liposomes that have been formulated to enhance stability in circulation. We formed a pH-sensitive complex between doxorubicin (Dox) and copper (CuDox) in the core of lysolipid-containing temperature-sensitive liposomes (LTSLs). The complex remains associated at neutral pH but dissociates to free Dox in lower pH environments. The resulting CuDox-LTSLs were injected intravenously into a syngeneic murine breast cancer model (6 mg Dox/kg body weight) and intravascular release of the drug was triggered by ultrasound. The entire tumor was insonified for 5 min prior to drug administration and 20 min post drug injection. A single-dose administration of CuDox-LTSLs combined with insonation suppressed tumor growth. Moreover, after twice per week treatment over a period of 28 days, a complete response was achieved in which the NDL tumor cells and the tumor interstitium could no longer be detected. All mice treated with ultrasound combined with CuDox-LTSLs survived, and tumor was undetectable 8 months post treatment. Iron and copper-laden macrophages were observed at early time points following treatment with this temperature sensitive formulation. Systemic toxicity indicators, such as cardiac hypertrophy, leukopenia, and weight and hair loss were not detected with CuDox-LTSLs after the 28-day therapy.

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.

Challenges, expectations and limits for nanoparticles-based therapeutics in cancer: a focus on nano-albumin-bound drugs

Improving the efficacy-toxicity balance of anticancer agents remains an ongoing challenge in oncology. Beside the ever-growing development of innovative drugs addressing newly discovered molecular targets, nanotechnologies provide today a promising and exciting strategy to achieve this goal. The idea of carrying active compounds to their respective targets so as to improve their efficacy while sparing healthy tissue and reducing side-effects is not new. However, this area of research is in constant rise, and benefits from the latest advances in the field of biopharmaceutics, medicinal chemistry and nanomedicine. In addition to anthracyclines already widely present as liposomal drugs on the shelves, a variety of anticancer drugs can be now encapsulated into different chemical of structures so as to enhance their specificity toward malignant cells, mainly through improved pharmacokinetics profiles. Indeed, the recent advances in chemistry allow now a wide variety of scaffolds to be used as drug-carriers, so as optimize the delivery of cytotoxics. Even more recently, conjugated-drugs such as nanoalbumin (Nab) conjugates have emerged as a new promising alternative to improve both anticancer drugs distribution in the body and efficacy/toxicity balance eventually. This review covers the achievements and current limits of nanoparticles in oncology, with a special focus on nab-paclitaxel as a paradigmatic drug for this new generation of conjugated entities.

Intravenous magnetic nanoparticle cancer hyperthermia

Magnetic nanoparticles heated by an alternating magnetic field could be used to treat cancers, either alone or in combination with radiotherapy or chemotherapy. However, direct intratumoral injections suffer from tumor incongruence and invasiveness, typically leaving undertreated regions, which lead to cancer regrowth. Intravenous injection more faithfully loads tumors, but, so far, it has been difficult achieving the necessary concentration in tumors before systemic toxicity occurs. Here, we describe use of a magnetic nanoparticle that, with a well-tolerated intravenous dose, achieved a tumor concentration of 1.9 mg Fe/g tumor in a subcutaneous squamous cell carcinoma mouse model, with a tumor to non-tumor ratio > 16. With an applied field of 38 kA/m at 980 kHz, tumors could be heated to 60°C in 2 minutes, durably ablating them with millimeter (mm) precision, leaving surrounding tissue intact.

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.

Determination of drug release kinetics from nanoparticles: overcoming pitfalls of the dynamic dialysis method

Dynamic dialysis is one of the most common methods for the determination of release kinetics from nanoparticle drug delivery systems. Drug appearance in the "sink" receiver compartment is a consequence of release from the nanoparticles into the dialysis chamber followed by diffusion across the dialysis membrane. This dual barrier nature inherent in the method complicates data interpretation and may lead to incorrect conclusions regarding nanoparticle release half-lives. Although the need to consider the barrier properties of the dialysis membrane has long been recognized, there is insufficient quantitative appreciation for the role of the driving force for drug transport across that membrane. Reversible nanocarrier binding of the released drug reduces the driving force for drug transport across the dialysis membrane leading to a slower overall apparent release rate. This may lead to the conclusion that a given nanoparticle system will provide a sustained release in vivo when it will not. This study demonstrates these phenomena using model lipophilic drug-loaded liposomes varying in lipid composition to provide variations in bilayer permeability and membrane binding affinities. Model simulations of liposomal transport as measured by dynamic dialysis were conducted to illustrate the interplay between the liposome concentration, membrane/water partition coefficient, and the apparent release rate. Reliable determination of intrinsic liposomal bilayer permeability coefficients for lipophilic drugs by dynamic dialysis requires validation of drug release kinetics at varying nanoparticle concentration and the determination of membrane binding coefficients along with appropriate mechanism-based mathematical modeling to ensure the reliability and proper interpretation of the data.

The architecture and biological performance of drug-loaded LbL nanoparticles

Layer-by-Layer (LbL) nanoparticles are an emerging class of therapeutic carriers that afford precise control over key design parameters that facilitate improved drug and carrier pharmacokinetics, and enhanced molecular-targeting capabilities. This paper advances the development of these systems by establishing them as drug carriers, with the means to control drug release in a systemic environment and retard particle clearance from circulation, promoting improved biodistribution of the drug-containing system. Using dual-fluorescent tracking in vivo, this work establishes a robust means of screening libraries of LbL systems generated, affording simultaneous resolution over persistence and biodistribution of both the drug and carrier following systemic administration of a single particle formulation. Employing a PLGA drug-containing core as a substrate for LbL deposition, a range of coated systems were fabricated to investigate the abilities of these films to stabilize drug for delivery as well as to improve the pharmacokinetics of both the drug and carrier. Significant reductions in liver accumulation were observed for different formulations of the layered architectures within the first 30 min of systemic circulation. LbL architectures diminished liver localization of the surrogate drug, cardiogreen, by 10-25% ID/g relative to native PLGA nanoparticles and modulated carrier accumulation in the liver >50% ID/g. Further, enhanced persistence of the drug was observed with the coated systems, significantly increasing the drug half-life from 2 to 3 min for free drug and 1.87 h for the uncoated core to 4.17 h and 4.54 h for the coated systems. These systems provide an exciting, modular platform that improves the pharmacokinetic properties of the therapeutic, reduces bolus release of drug from nanoparticles, and enhances the safety and circulation half-life of the drug in vivo, proving them to be highly clinically-relevant and a promising approach for future development of molecularly-targeted and combination therapeutics.

Recent progress in nanomedicine: therapeutic, diagnostic and theranostic applications

In recent years, the use of nanomedicine formulations for therapeutic and diagnostic applications has increased exponentially. Many different systems and strategies have been developed for drug targeting to pathological sites, as well as for visualizing and quantifying important (patho-) physiological processes. In addition, ever more efforts have been undertaken to combine diagnostic and therapeutic properties within a single nanomedicine formulation. These so-called nanotheranostics are able to provide valuable information on drug delivery, drug release and drug efficacy, and they are considered to be highly useful for personalizing nanomedicine-based (chemo-) therapeutic interventions.

Exploring polymeric micelles for improved delivery of anticancer agents: recent developments in preclinical studies

As versatile drug delivery systems, polymeric micelles have demonstrated particular strength in solubilizing hydrophobic anticancer drugs while eliminating the use of toxic organic solvents and surfactants. However, the true promise of polymeric micelles as drug carriers for cancer therapy resides in their potential ability to preferentially elevate drug exposure in the tumor and achieve enhanced anticancer efficacy, which still remains to be fully exploited. Here, we review various micellar constructs that exhibit the enhanced permeation and retention effect in the tumor, the targeting ligands that potentiate the anticancer efficacy of micellar drugs, and the polyplex micelle systems suitable for the delivery of plasmid DNA and small interference RNA. Together, these preclinical studies in animal models help us further explore polymeric micelles as emerging drug carriers for targeted cancer therapy.

Clinical trials with pegylated liposomal Doxorubicin in the treatment of ovarian cancer

Among the pharmaceutical options available for treatment of ovarian cancer, increasing attention has been progressively focused on pegylated liposomal doxorubicin (PLD), whose unique formulation prolongs the persistence of the drug in the circulation and potentiates intratumor accumulation. Pegylated liposomal doxorubicin (PLD) has become a major component in the routine management of epithelial ovarian cancer. In 1999 it was first approved for platinum-refractory ovarian cancer and then received full approval for platinum-sensitive recurrent disease in 2005. PLD remains an important therapeutic tool in the management of recurrent ovarian cancer in 2012. Recent interest in PLD/carboplatin combination therapy has been the object of phase III trials in platinum-sensitive and chemonaïve ovarian cancer patients reporting response rates, progressive-free survival, and overall survival similar to other platinum-based combinations, but with a more favorable toxicity profile and convenient dosing schedule. This paper summarizes data clarifying the role of pegylated liposomal doxorubicin (PLD) in ovarian cancer, as well as researches focusing on adding novel targeted drugs to this cytotoxic agent.

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.

Targeted imaging and therapy of brain cancer using theranostic nanoparticles

The past decade has seen momentous development in brain cancer research in terms of novel imaging-assisted surgeries, molecularly targeted drug-based treatment regimens or adjuvant therapies and in our understanding of molecular footprints of initiation and progression of malignancy. However, mortality due to brain cancer has essentially remained unchanged in the last three decades. Thus, paradigm-changing diagnostic and therapeutic reagents are urgently needed. Nanotheranostic platforms are powerful tools for imaging and treatment of cancer. Multifunctionality of these nanovehicles offers a number of advantages over conventional agents. These include targeting to a diseased site thereby minimizing systemic toxicity, the ability to solubilize hydrophobic or labile drugs leading to improved pharmacokinetics and their potential to image, treat and predict therapeutic response. In this article, we will discuss the application of newer theranostic nanoparticles in targeted brain cancer imaging and treatment.