Tumour-Specific Uptake of Anti-Cancer Drugs: The Future is Here (original) (raw)
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Because of the particular characteristics of the tumor microenvironment and tumor angiogenesis, it is possible to design drug delivery systems that specifically target anti-cancer drugs to tumors. Most of the conventional chemotherapeutic agents have poor pharmacokinetics profiles and are distributed non-specifically in the body leading to systemic toxicity associated with serious side effects. Therefore, the development of drug delivery systems able to target the tumor site is becoming a real challenge that is currently addressed. Nanomedicine can reach tumor passively through the leaky vasculature surrounding the tumors by the Enhanced Permeability and Retention effect whereas ligands grafted at the surface of nanocarriers allow active targeting by binding to the receptors overexpressed by cancer cells or angiogenic endothelial cells. This review is divided into two parts: the first one describes the tumor microenvironment and the second one focuses on the exploitation and the understanding of these characteristics to design new drug delivery systems targeting the tumor. Delivery of conventional chemotherapeutic anti-cancer drugs is mainly discussed.
Drug delivery to tumours: recent strategies
Journal of Pharmacy and Pharmacology, 2005
Despite several advancements in chemotherapy, the real therapy of cancer still remains a challenge. The development of new anti-cancer drugs for the treatment of cancer has not kept pace with the progress in cancer therapy, because of the nonspecific drug distribution resulting in low tumour concentrations and systemic toxicity. The main hindrance for the distribution of anti-cancer agents to the tumour site is the highly disorganized tumour vasculature, high blood viscosity in the tumour, and high interstitial pressure within the tumour tissue. Recently, several approaches such as drug modifications and development of new carrier systems for anti-cancer agents have been attempted to enhance their tumour reach. Approaches such as drug delivery through enhanced permeability and retention (EPR) effect have resulted in a significant improvement in concentration in tumours, while approaches such as drug-carrier implants and microparticles have resulted in improvement in local chemotherapy of cancer. This review discusses different strategies employed for the delivery of anti-cancer agents to tumours, such as through EPR effect, local chemotherapeutic approaches using drug delivery systems, and special strategies such as receptor-mediated delivery, pH-based carriers, application of ultrasound and delivery to resistant tumour cells and brain using nanoparticles.
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 therapy (U.S. Food and Drug Administration, 2006).
Temporal targeting of tumour cells and neovasculature with a nanoscale delivery system
Nature, 2005
In the continuing search for effective treatments for cancer, the emerging model is the combination of traditional chemotherapy with anti-angiogenesis agents 1 that inhibit blood vessel growth. However, the implementation of this strategy has faced two major obstacles. First, the long-term shutdown of tumour blood vessels by the anti-angiogenesis agent can prevent the tumour from receiving a therapeutic concentration of the chemotherapy agent. Second, inhibiting blood supply drives the intra-tumoural accumulation of hypoxia-inducible factor-1a (HIF1-a); overexpression of HIF1-a is correlated with increased tumour invasiveness and resistance to chemotherapy 2-5 . Here we report the disease-driven engineering of a drug delivery system, a 'nanocell', which overcomes these barriers unique to solid tumours. The nanocell comprises a nuclear nanoparticle within an extranuclear pegylated-lipid envelope, and is preferentially taken up by the tumour. The nanocell enables a temporal release of two drugs: the outer envelope first releases an anti-angiogenesis agent, causing a vascular shutdown; the inner nanoparticle, which is trapped inside the tumour, then releases a chemotherapy agent. This focal release within a tumour results in improved therapeutic index with reduced toxicity. The technology can be extended to additional agents, so as to target multiple signalling pathways or distinct tumour compartments, enabling the model of an 'integrative' approach in cancer therapy.
Polymers
Passive targeting is the foremost mechanism by which nanocarriers and drug-bearing macromolecules deliver their payload selectively to solid tumors. An important driver of passive targeting is the enhanced permeability and retention (EPR) effect, which is the cornerstone of most carrier-based tumor-targeted drug delivery efforts. Despite the huge number of publications showcasing successes in preclinical animal models, translation to the clinic has been poor, with only a few nano-based drugs currently being used for the treatment of cancers. Several barriers and factors have been adduced for the low delivery efficiency to solid tumors and poor clinical translation, including the characteristics of the nanocarriers and macromolecules, vascular and physiological barriers, the heterogeneity of tumor blood supply which affects the homogenous distribution of nanocarriers within tumors, and the transport and penetration depth of macromolecules and nanoparticles in the tumor matrix. To add...
Advances in Enzyme Regulation, 2001
Effective cancer therapy remains one of the most challenging tasks to the scientific community, with little advancement on overall cancer survival landscape during the last two decades. A major limitation inherent to most conventional anticancer chemotherapeutic agents is their lack of tumor selectivity. One way to achieve selective drug targeting to solid tumors is to exploit abnormalities of tumor vasculature, namely hypervascularization, aberrant vascular architecture, extensive production of vascular permeability factors stimulating extravasation within tumor tissues, and lack of lymphatic drainage. Due to their large size, nano-sized macromolecular anticancer drugs administered intravenously (i.v.) escape renal clearance. Being unable to penetrate through tight endothelial junctions of normal blood vessels, their concentration builds up in the plasma rendering them long plasma half-life. More importantly, they can selectively extravasate in tumor tissues due to its abnormal vascular nature. Overtime the tumor concentration will build up reaching several folds higher than that of the plasma due to lack of efficient lymphatic drainage in solid tumor, an ideal application for EPR-based selective anticancer nanotherapy. Indeed, this selective high local concentration of nano-sized anticancer drugs in tumor tissues has proven superior in therapeutic effect with minimal side effects in both preclinical and clinical settings.
Therapeutic Nanoparticles for Drug Delivery in Cancer
Cancer nanotherapeutics are rapidly progressing and are being implemented to solve several limitations of conventional drug delivery systems such as nonspecific biodistribution and targeting, lack of water solubility, poor oral bioavailability, and low therapeutic indices. To improve the bio-distribution of cancer drugs, nanoparticles have been designed for optimal size and surface characteristics to increase their circulation time in the bloodstream. They are also able to carry their loaded active drugs to cancer cells by selectively using the unique pathophysiology of tumors, such as their enhanced permeability and retention effect and the tumor microenvironment. In addition to this passive targeting mechanism, active targeting strategies using ligands or antibodies directed against selected tumor targets amplify the specificity of these therapeutic nanoparticles. Drug resistance, another obstacle that impedes the efficacy of both molecularly targeted and conventional chemotherapeutic agents, might also be overcome, or at least reduced, using nanopar-ticles. Nanoparticles have the ability to accumulate in cells without being recognized by P-glycoprotein, one of the main mediators of multidrug resistance, resulting in the increased intra-cellular concentration of drugs. Multifunctional and multiplex nanoparticles are now being actively investigated and are on the horizon as the next generation of nanoparticles, facilitating personal-ized and tailored cancer treatment.
Applied Biochemistry and Biotechnology, 2011
Successful cancer management depends on accurate diagnostics along with specific treatment protocols. Current diagnostic techniques need to be improved to provide earlier detection capabilities, and traditional chemotherapy approaches to cancer treatment are limited by lack of specificity and systemic toxicity. This review highlights advances in nanotechnology that have allowed the development of multifunctional platforms for cancer detection, therapy, and monitoring. Nanomaterials can be used as MRI, optical imaging, and photoacoustic imaging contrast agents. When used as drug carriers, nanoformulations can increase tumor exposure to therapeutic agents and result in improved treatment effects by prolonging circulation times, protecting entrapped drugs from degradation, and enhancing tumor uptake through the EPR effect as well as receptor-mediated endocytosis. Multiple therapeutic agents such as chemotherapy, antiangiogenic, or gene therapy agents can be simultaneously delivered by nanocarriers to tumor sites to enhance the effectiveness of therapy. Additionally, imaging and therapy agents can be codelivered to provide seamless integration of diagnostics, therapy and follow-up, and different therapeutic modalities such as chemotherapy and hyperthermia can be coadministered to take advantage of synergistic effects. Liposomes, metallic nanoparticles, polymeric nanoparticles, dendrimers, carbon nanotubes, and quantum dots are examples of nanoformulations that can be used as multifunctional platforms for cancer theranostics. Nanomedicine approaches in cancer have great potential for clinically translatable advances that can positively impact the overall diagnostic and therapeutic process, and result in enhanced quality of life for cancer patients. However, a concerted scientific effort is still necessary to fully explore long-term risks, effects, and precautions for safe human use. hyperthermia, immunotherapy, hormone therapy, stem cell therapy, and combinations thereof. In many cases, early detection is the crucial factor that directs the treatment regime and the choice of therapeutic intervention. The stage at which a tumor is detected determines whether it can be surgically resected without need for adjuvant treatment, or whether it will require a combination of approaches, which typically include surgery, radiation, and chemotherapy.