Lilian E. van Vlerken

Multi-functional nanocarriers to overcome tumor drug resistance

The development of resistance to variety of chemotherapeutic agents is one of the major challenges in effective cancer treatment. Tumor cells are able to generate a multi-drug resistance (MDR) phenotype due to microenvironmental selection pressures. This review addresses the use of nanotechnology-based delivery systems to overcome MDR in solid tumors. Our own work along with evidence from the literature illustrates the development of various types of engineered nanocarriers specifically designed to enhance tumor-targeted delivery through passive and active targeting strategies. Additionally, multi-functional nanocarriers are developed to enhance drug delivery and overcome MDR by either simultaneous or sequential delivery of resistance modulators (e.g., with P-glycoprotein substrates), agents that regulate intracellular pH, agents that lower the apoptotic threshold (e.g., with ceramide), or in combination with energy delivery (e.g., sound, heat, and light) to enhance the effectiveness of anticancer agents in refractory tumors. In preclinical studies, the use of multi-functional nanocarriers has shown significant promise in enhancing cancer therapy, especially against MDR tumors.

Multi-functional polymeric nanoparticles for tumour-targeted drug delivery

The use of nanoparticles as drug delivery vehicles for anticancer therapeutics has great potential to revolutionise the future of cancer therapy. As tumour architecture causes nanoparticles to preferentially accumulate at the tumour site, their use as drug delivery vectors results in the localisation of a greater amount of the drug load at the tumour site; thus improving cancer therapy and reducing the harmful nonspecific side effects of chemotherapeutics. In addition, formulation of these nanoparticles with imaging contrast agents provides a very efficient system for cancer diagnostics. Given the exhaustive possibilities available to polymeric nanoparticle chemistry, research has quickly been directed at multi-functional nanoparticles, combining tumour targeting, tumour therapy and tumour imaging in an all-in-one system, providing a useful multi-modal approach in the battle against cancer. This review will discuss the properties of nanoparticles that allow for such multiple functionality, as well as recent scientific advances in the area of multi-functional nanoparticles for cancer therapeutics.

Modulation of intracellular ceramide using polymeric nanoparticles to overcome multidrug resistance in cancer.

Although multidrug resistance (MDR) is known to develop through a variety of molecular mechanisms within the tumor cell, many tend to converge toward the alteration of apoptotic signaling. The enzyme glucosylceramide synthase (GCS), responsible for bioactivation of the proapoptotic mediator ceramide to a nonfunctional moiety glucosylceramide, is overexpressed in many MDR tumor types and has been implicated in cell survival in the presence of chemotherapy. The purpose of this study was to investigate the therapeutic strategy of coadministering ceramide with paclitaxel, a commonly used chemotherapeutic agent, in an attempt to restore apoptotic signaling and overcome MDR in the human ovarian cancer cell line SKOV3. Poly(ethylene oxide)-modified poly(epsilon-caprolactone) (PEO-PCL) nanoparticles were used to encapsulate and deliver the therapeutic agents for enhanced efficacy. Results show that indeed the cotherapy eradicates the complete population of MDR cancer cells when they are treated at their IC(50) dose of paclitaxel. More interestingly, when the cotherapy was combined with the properties of nanoparticle drug delivery, the MDR cells can be resensitized to a dose of paclitaxel near the IC(50) of non-MDR (drug sensitive) cells, indicating a 100-fold increase in chemosensitization via this approach. Molecular analysis of activity verified the hypothesis that the efficacy of this therapeutic approach is indeed due to a restoration in apoptotic signaling, although the beneficial properties of PEO-PCL nanoparticle delivery seemed to enhance the therapeutic success even further, showing the promising potential for the clinical use of this therapeutic strategy to overcome MDR.

Multi-functional nanocarriers for targeted delivery of drugs and genes

In this review article, we describe the different nano-platforms developed in our laboratory at Northeastern University in Boston, MA for the targeted delivery of drugs and genes. Special emphasis is placed on nano-platforms that offer opportunities for multi-functionalization to allow for targeted stimuli-responsive and/or simultaneous strategic delivery of multiple drugs, genes, as well as the combination of therapeutic systems with image contrast enhancers. Polymeric and lipid-based nanocarriers can provide versatile platforms for the delivery of multiple pharmacological agents, specifically to enhance therapeutic effect and overcome drug resistance in cancer. In addition, polymeric nanoparticles and nanoparticles-in-microsphere oral system (NiMOS) are useful for systemic and oral gene therapy, respectively.

Evaluations of combination MDR-1 gene silencing and paclitaxel administration in biodegradable polymeric nanoparticle formulations to overcome multidrug resistance in cancer cells.

In this study, the effect of MDR-1 gene silencing, using small interfering RNA (siRNA), and paclitaxel (PTX) co-therapy in overcoming tumor multidrug resistance was examined. Poly(ethylene oxide)-modified poly(beta-amino ester) (PEO-PbAE) and PEO-modified poly(epsilon-caprolactone) (PEO-PCL) nanoparticles were formulated to efficiently encapsulate MDR-1 silencing siRNA and PTX, respectively. Upon administration in multidrug resistant SKOV3TR human ovarian adenocarcinoma cells, siRNA-mediated MDR-1 gene silencing was evident at 100 nM dose. Combination of MDR-1 gene silencing and nanoparticle-mediated delivery significantly influenced the cytotoxic activity of PTX in SKOV3TR cells similar to what was observed in drug sensitive SKOV3 cells. We speculate that the enhancement in cytotoxicity was due to an increase in intracellular drug accumulation upon MDR-1 gene silencing leading to an apoptotic cell-kill effect. Taken together, these preliminary results are highly encouraging for the development of combination nano-therapeutic strategies that combine gene silencing and drug delivery to provide more potent therapeutic effect, especially in refractory tumors.

Biodistribution and Pharmacokinetic Analysis of Paclitaxel and Ceramide Administered in Multifunctional Polymer-Blend Nanoparticles in Drug Resistant Breast Cancer Model

In this study, we have investigated the biodistribution and pharmacokinetic analysis of paclitaxel (PTX) and the apoptotic signaling molecule, C6-ceramide (CER), when administered in a multifunctional polymer-blend nanoparticle formulation to female nude mice bearing an orthotopic drug sensitive MCF7 and multidrug resistant MCF7TR (MDR-1 positive) human breast adenocarcinoma. A polymer-blend nanoparticle system was engineered to incorporate temporally controlled sequential release of the combination drug payload. Hereby, PTX was encapsulated in the pH-responsive rapid releasing polymer, poly(beta-amino ester) (PbAE), while CER was present in the slow releasing polymer, poly(d,l-lactide-co-glycolide) (PLGA) within these blend nanoparticles. When particle formulations were administered intravenously to MCF7 and MCF7TR tumor bearing mice, higher concentrations of PTX were found in the blood due to longer retention time and an enhanced tumor accumulation relative to administration of free drug. In addition, the PLGA/PbAE blend nanoparticles were effective in enhancing the residence time of both drugs at the tumor site by reducing systemic clearance. Overall, these results are highly encouraging for development of multifunctional polymer-blend nanoparticle formulations that can be used for temporal-controlled administration of two drugs from a single formulation.

Augmentation of Therapeutic Efficacy in Drug-Resistant Tumor Models Using Ceramide Coadministration in Temporal-Controlled Polymer-Blend Nanoparticle Delivery Systems

The development of multidrug resistance (MDR) is a major hindrance to cancer eradication as it renders tumors unresponsive to most chemotherapeutic treatments and is associated with cancer resurgence. This study describes a novel mechanism to overcome MDR through a polymer-blend nanoparticle platform that delivers a combination therapy of C6-ceramide (CER), a synthetic analog of an endogenously occurring apoptotic modulator, together with the chemotherapeutic drug paclitaxel (PTX), in a single formulation. The PTX/CER combination therapy circumvents another cellular mechanism whereby MDR develops, by lowering the threshold for apoptotic signaling. In vivo studies in a resistant subcutaneous SKOV3 human ovarian and in an orthotopic MCF7 human breast adenocarcinoma xenograft showed that the PTX and CER nanoparticle combination therapy reduced the final tumor volume at least twofold over treatment with the standard PTX therapy alone. The study also revealed that the cotherapy accomplished this enhanced efficacy by generating an enhancement in apoptotic signaling in both tumor types. Additionally, acute evaluation of safety with the combination therapy did not show significant changes in body weight, white blood cell counts, or liver enzyme levels. The temporal-controlled nanoparticle delivery system presented in this study allows for a simultaneous delivery of PTX + CER in breast and ovarian tumor model drug, leading to a modulation of the apoptotic threshold. This strategy has tremendous potential for effective treatment of refractory disease in cancer patients.

Multifunctional Polymeric Nanosystems for Tumor-Targeted Delivery

Cancer is the second leading cause of morbidity and mortality in the United States, with occurrences portraying an upward trend for the future. In 2007, approximately 10 million cases of cancer will occur globally, with a total of around 1.5 million new cancer cases and over 560,000 deaths expected in the United States (U.S. National Institute of Health, 2006). Strikingly, remarkable advances in diagnosis and therapy of cancer have been made over the past few decades resulting from significant advances in fundamental cancer biology. What lacks in this case is clinical translation of these advances into effective therapies. A major hurdle in cancer diagnosis and therapy is the targeted and efficacious delivery of agents to the tumor site, while avoiding adverse damage resulting from systemic administration. While systemic drug delivery already hinges largely on physicochemical properties of the drug, such as size, diffusivity, and plasma protein binding affinity, tumors possess a dense, heterogeneous vasculature and an outward net convective flow that act as hurdles to efficient drug deposition at the target site (Jang et al., 2003). Nanocarriermediated delivery has emerged as a successful strategy to enhance delivery of therapeutics and imaging agents to tumors, thereby increasing the potential for diagnosis at an earlier stage or for therapeutic success (or both). Based on the initial observation by Maeda and Matsumura that tumors possess a fenestrated vasculature, with pores on average ranging between 200 and 800 nm, and a lack of lymphatic drainage, together termed the enhanced permeability and retention (EPR) effect, it was found that colloidal carriers in the nanometer size range could target tumors passively, by specific extravasation through these fenestrations, and are retained at the site for prolonged time because of lack of lymphatic drainage (Matsumura and Meada, 1986). This physiological advantage has been used successfully to enhance delivery of diagnostic and therapeutic agents, leading to the U.S. Food and Drug Administration (FDA) approval of nanoparticle formulations such as Feridex ® for diagnostic applications and Doxil ® and Abraxane ® for cancer

Therapeutic nanomedicine: Polymeric nanosystems for drug and gene delivery

In this article, we describe the different polymeric nanoparticle platforms developed in our laboratory for the targeted delivery of drugs and genes. Based on their versatility, biodegradable synthetic and natural polymers, such as poly(epsilon-caprolactone) (PCL), poly(D,L-lactide-co-glycolide) (PLGA), poly(beta-amino ester) (PbAE) and gelatin, are uniquely suited for the fabrication of targeted delivery systems for various types of therapeutic payloads. PCL, PLGA, and PbAE nanoparticle systems were used for systemic combination drug therapy a cytotoxic agent and the apoptotic signal modulator (C6-ceramide) to overcome multidrug resistance in cancer. Gelatin and modified gelatin nanoparticles were used for the delivery of reporter and therapeutic plasmid DNA. Lastly, we have formulated nanoparticles-in-microsphere oral system (NiMOS) for oral gene delivery and transfection in specific regions of the gastrointestinal tract. In each case, special emphasis is placed on the use of safe materials and delivery systems that offer opportunities for multi-functionalization to allow for targeted stimuli-responsive and/or simultaneous strategic delivery of multiple drugs and genes to disease target. Amiji, M Eur J Nanomed 2008; 1:6-14