Gerrit Storm

Drug targeting to tumors: principles, pitfalls and (pre-) clinical progress

Many different systems and strategies have been evaluated for drug targeting to tumors over the years. Routinely used systems include liposomes, polymers, micelles, nanoparticles and antibodies, and examples of strategies are passive drug targeting, active drug targeting to cancer cells, active drug targeting to endothelial cells and triggered drug delivery. Significant progress has been made in this area of research both at the preclinical and at the clinical level, and a number of (primarily passively tumor-targeted) nanomedicine formulations have been approved for clinical use. Significant progress has also been made with regard to better understanding the (patho-) physiological principles of drug targeting to tumors. This has led to the identification of several important pitfalls in tumor-targeted drug delivery, including I) overinterpretation of the EPR effect; II) poor tumor and tissue penetration of nanomedicines; III) misunderstanding of the potential usefulness of active drug targeting; IV) irrational formulation design, based on materials which are too complex and not broadly applicable; V) insufficient incorporation of nanomedicine formulations in clinically relevant combination regimens; VI) negligence of the notion that the highest medical need relates to metastasis, and not to solid tumor treatment; VII) insufficient integration of non-invasive imaging techniques and theranostics, which could be used to personalize nanomedicine-based therapeutic interventions; and VIII) lack of (efficacy analyses in) proper animal models, which are physiologically more relevant and more predictive for the clinical situation. These insights strongly suggest that besides making ever more nanomedicine formulations, future efforts should also address some of the conceptual drawbacks of drug targeting to tumors, and that strategies should be developed to overcome these shortcomings.

Adhesion molecules: a new target for immunoliposome-mediated drug delivery

The anti‐ICAM‐1 monoclonal antibody F10.2 was conjugated to liposomes to target to cells expressing the cell adhesion molecule ICAM‐1. We demonstrate that F10.2 immunoliposomes bind to human bronchial epithelial cells (BEAS‐2B) and human umbilical vein endothelial cells (HUVEC) in a specific, dose‐ and time‐dependent manner. It appears that the degree of ICAM‐1 expression is the limiting factor in the degree of immunoliposome binding to the cells. These results are a first step in the strategy for specific drug delivery to target sites characterised by increased expression of adhesion molecules.

Role of complement activation in hypersensitivity reactions to doxil and hynic PEG liposomes: experimental and clinical studies.

ABSTRACT Pegylated liposomal doxorubicin (Doxil) and 99mTc-HYNIC PEG liposomes (HPL) were reported earlier to cause hypersensitivity reactions (HSRs) in a substantial percentage of patients treated i.v. with these formulations. Here we report that (1) Doxil, HPL, pegylated phosphatidylethanolamine (PEG-PE)-containing empty liposomes matched with Doxil and HPL in size and lipid composition, and phosphatidylglycerol (PG)-containing negatively charged vesicles were potent C activators in human serum in vitro, whereas small neutral liposomes caused no C activation. (2) Doxil and other size-matched PEG-PE and/or PG-containing liposomes also caused massive cardiopulmonary distress with anaphylactoid shock in pigs via C activation, whereas equivalent neutral liposomes caused no hemodynamic changes. (3) A clinical study showed more frequent and greater C activation in patients displaying HSR than in non-reactive patients. These data suggest that liposome-induced HSRs in susceptible individuals may be due to C activation, which, in turn, is due to the presence of negatively charged PEG-PE in these vesicles.

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.

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.

Doxorubicin decomposition on storage: effect of pH, type of buffer and liposome encapsulation

Abstract An HPLC technique was used to monitor the stability of doxorubicin-HCl (DXR) in aqueous media. In this study pH (4.0 and 7.4), composition of the aqueous medium (Tris or phosphate buffer, cell culture medium), temperature (4–91 °C), DXR concentration (range 50–500 μg/ml) and liposome encapsulation of DXR were variables under investigation. The results obtained in this study indicated that pH 4 and 4 °C provide optimum shelf-life conditions. At pH 7.4 the DXR decomposition rates increased with the DXR concentration. For the 50–100 μg/ml DXR solutions energies of activation were: 58 (Tris) and 73 (phosphate) kJ/mol between 4 and 61°C. Only in one case (pH 7.4, phosphate buffer and incubation temperature 37°C) did liposome encapsulation affect the DXR decomposition kinetics.

Radiolabeled liposomes for scintigraphic imaging.

Liposomes have been investigated extensively as carriers for drugs in attempts to achieve selective deposition and/or reduced toxicity. Liposomes radiolabeled with gamma emitters such as (67)Ga, (111)In and (99m)Tc, can be used for imaging purposes. Liposomes as formulated in the past, are rapidly taken up by cells of the mononuclear phagocyte system (MPS), primarily those located in liver and spleen. The recent development of long-circulating liposomes (LCLs), yielded liposomes that oppose recognition by the MPS. The development of these LCLs with enhanced circulatory half-lives has broadened the potential of liposomes to scintigraphically visualize pathologic processes in vivo. Liposomes have been proposed for tumor imaging, infection imaging and blood pool imaging. Strategies have been developed that allow rapid, easy and efficient labeling of preformed liposomes with (111)In and (99m)Tc. There is now a vast body of preclinical evidence showing that LCLs can be used to image a wide variety of tumors as well as inflammatory lesions. The first studies in patients show that radiolabeled liposomes can image tumor and inflammatory lesions with good sensitivity and good specificity. Here, the present status of liposome-based radiopharmaceuticals for scintigraphic application is reviewed.

Intrinsically active nanobody-modified polymeric micelles for tumor-targeted combination therapy

Various different passively and actively targeted nanomedicines have been designed and evaluated over the years, in particular for the treatment of cancer. Reasoning that the potential of ligand-modified nanomedicines can be substantially improved if intrinsically active targeting moieties are used, we have here set out to assess the in vivo efficacy of nanobody-modified core-crosslinked polymeric micelles containing covalently entrapped doxorubicin. Nanobody-modified polymeric micelles were found to inhibit tumor growth even in the absence of a drug, and nanobody-modified micelles containing doxorubicin were significantly more effective than nanobody-free micelles containing doxorubicin. Based on these findings, we propose that the combination of two therapeutic strategies within one nanomedicine formulation, i.e. the intrinsic pharmacological activity of ligand-modified carrier materials with the cytostatic activity of the incorporated chemotherapeutic agents, is a highly promising approach for improving the efficacy of tumor-targeted combination therapy.

Strategies for encapsulation of small hydrophilic and amphiphilic drugs in PLGA microspheres: State-of-the-art and challenges

Poly(lactide-co-glycolide) (PLGA) microspheres are efficient delivery systems for controlled release of low molecular weight drugs as well as therapeutic macromolecules. The most common microencapsulation methods are based on emulsification procedures, in which emulsified droplets of polymer and drug solidify into microspheres when the solvent is extracted from the polymeric phase. Although high encapsulation efficiencies have been reported for hydrophobic small molecules, encapsulation of hydrophilic and/or amphiphilic small molecules is challenging due to the partitioning of drug from the polymeric phase into the external phase before solidification of the particles. This review addresses formulation-related aspects for efficient encapsulation of small hydrophilic/amphiphilic molecules into PLGA microspheres using conventional emulsification methods (e.g., oil/water, water/oil/water, solid/oil/water, water/oil/oil) and highlights novel emulsification technologies such as microfluidics, membrane emulsification and other techniques including spray drying and inkjet printing. Collectively, these novel microencapsulation technologies afford production of this type of drug loaded microspheres in a robust and well controlled manner.

Theranostic USPIO-Loaded Microbubbles for Mediating and Monitoring Blood-Brain Barrier Permeation

Efficient and safe drug delivery across the blood-brain barrier (BBB) remains to be one of the major challenges of biomedical and (nano-) pharmaceutical research. Here, we show that poly(butyl cyanoacrylate)-based microbubbles (MB), carrying ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles within their shell, can be used to mediate and monitor BBB permeation. Upon exposure to transcranial ultrasound pulses, USPIO-MB are destroyed, resulting in acoustic forces inducing vessel permeability. At the same time, USPIO are released from the MB shell, they extravasate across the permeabilized BBB and they accumulate in extravascular brain tissue, thereby providing non-invasive R2*-based magnetic resonance imaging information on the extent of BBB opening. Quantitative changes in R2* relaxometry were in good agreement with 2D and 3D microscopy results on the extravascular deposition of the macromolecular model drug FITC-dextran into the brain. Such theranostic materials and methods are considered to be useful for mediating and monitoring drug delivery across the BBB, and for enabling safe and efficient treatment of CNS disorders.