Receptor mediated endocytosis and cytotoxicity of transferrin-mitomycin C conjugate in the HepG2 cell and primary cultured rat hepatocyte

Nanoparticles of folic acid-methyl-β-cyclodextrin (FA-MβCD)/adamantane-albumin exhibit enhanced antitumor activity compared with FA-MβCD alone

Supramolecular drug carriers are a promising approach for delivering anticancer drugs with high blood retention after administration. We previously synthesized folic acid-modified methyl-β-cyclodextrin (FA-MβCD) as an anticancer drug. FA-MβCD has a selective autophagy-mediated antitumor effect on folic acid receptor (FR)-expressing cancer cells. Here, we enhanced the antitumor effect and safety of FA-MβCD by preparing a supramolecular nanoparticle formulation of FA-MβCD via host-guest interactions using an adamantane conjugate with human serum albumin (Ad-HSA). The Ad-HSA/FA-MβCD supramolecular complex prolonged the blood retention of FA-MβCD and improved its antitumor effect and safety after intravenous administration in tumor-bearing mice xenografted with FR-expressing cancer cells. These results suggest that the supramolecular technique using Ad-HSA is a promising approach for the delivery of CD-based anticancer drugs.

Enhanced insulin receptor interaction by a bifunctional insulin-transferrin fusion protein: an approach to overcome insulin resistance

Bifunctional fusion protein design has been widely utilized as a strategy to increase the efficacy of protein therapeutics. Previously, we proposed a novel application of the bifunctional fusion protein design through the introduction of proinsulin-transferrin (ProINS-Tf) fusion protein as a liver-specific protein prodrug to achieve a glucose-lowering effect in type 1 diabetic mice. In this report, we studied the binding characteristics of this activated fusion protein to the insulin receptor to elucidate its mechanism in eliciting insulin receptor-mediated signaling. We found that, with the assistance of the transferrin moiety binding to the transferrin receptor, the activated ProINS-Tf exhibited significantly higher binding affinity to the insulin receptor compared with the native insulin, resulting in a prolonged and stronger Akt phosphorylation. This enhanced induction by activated ProINS-Tf overcame insulin resistance in palmitate-treated HepG2 cells. ProINS-Tf also demonstrated a better glucose-lowering effect than native insulin, even with a much lower dose and less frequent injections, in non-obese diabetic mice with insulin resistance symptoms. The activated ProINS-Tf, serving as a bivalent protein molecule, could be a new insulin analog to overcome insulin resistance, which is associated with several diseases, including type 2 diabetes and non-alcoholic fatty liver disease.

Co-opting biology to deliver drugs

The goal of drug delivery is to improve the safety and therapeutic efficacy of drugs. This review focuses on delivery platforms that are either derived from endogenous pathways, long-circulating biomolecules and cells or that piggyback onto long-circulating biomolecules and cells. The first class of such platforms is protein-based delivery systems--albumin, transferrin, and fusion to the Fc domain of antibodies--that have a long-circulation half-life and are designed to transport different molecules. The second class is lipid-based delivery systems-lipoproteins and exosomes-that are naturally occurring circulating lipid particles. The third class is cell-based delivery systems--erythrocytes, macrophages, and platelets--that have evolved, for reasons central to their function, to exhibit a long life-time in the body. The last class is small molecule-based delivery systems that include folic acid. This article reviews the biology of these systems, their application in drug delivery, and the promises and limitations of these endogenous systems for drug delivery.

Exploiting endocytosis for nanomedicines

In this article, we briefly review the endocytic pathways used by cells, pointing out their defining characteristics and highlighting physical limitations that may direct the internalization of nanoparticles to a subset of these pathways. A more detailed description of these pathways is presented in the literature. We then focus on the endocytosis of nanomedicines and present how various nanomaterial parameters impact these endocytic processes. This topic is an area of active research, motivated by the recognition that an improved understanding of how nanomaterials interact at the molecular, cellular, and whole-organism level will lead to the design of better nanomedicines in the future. Next, we briefly review some of the important nanomedicines already on the market or in clinical development that serve to exemplify how endocytosis can be exploited for medical benefit. Finally, we present some key unanswered questions and remaining challenges to be addressed by the field.

Transferrin as a drug carrier: Cytotoxicity, cellular uptake and transport kinetics of doxorubicin transferrin conjugate in the human leukemia cells

Leukemias are one of most common malignancies worldwide. There is a substantial need for new chemotherapeutic drugs effective against this cancer. Doxorubicin (DOX), used for treatment of leukemias and solid tumors, is poorly efficacious when it is administered systemically at conventional doses. Therefore, several strategies have been developed to reduce the side effects of this anthracycline treatment. In this study we compared the effect of DOX and doxorubicin-transferrin conjugate (DOX-TRF) on human leukemia cell lines: chronic erythromyeloblastoid leukemia (K562), sensitive and resistant (K562/DOX) to doxorubicin, and acute lymphoblastic leukemia (CCRF-CEM). Experiments were also carried out on normal cells, peripheral blood mononuclear cells (PBMC). We analyzed the chemical structure of DOX-TRF conjugate by using mass spectroscopy. The in vitro growth-inhibition assay XTT, indicated that DOX-TRF is more cytotoxic for leukemia cells sensitive and resistant to doxorubicin and significantly less sensitive to normal cells compared to DOX alone. During the assessment of intracellular DOX-TRF accumulation it was confirmed that the tested malignant cells were able to retain the examined conjugate for longer periods of time than normal lymphocytes. Comparison of kinetic parameters showed that the rate of DOX-TRF efflux was also slower in the tested cells than free DOX. The results presented here should contribute to the understanding of the differences in antitumor activities of the DOX-TRF conjugate and free drug.

Nanodelivery strategies in cancer chemotherapy: biological rationale and pharmaceutical perspectives

Nanotechnology is revolutionizing our approach to drug delivery, a key determinant of drug efficacy. Here, we present cancer drug delivery strategies that exploit nanotechnology, providing first an overview of tumor biology aspects that critically affect the design of drug delivery carriers, namely the enhanced permeability and retention effect, the lower tumor extracellular pH and tumor-specific antigens. In general, nanoscience-based approaches have circumvented limitations in the delivery of cancer therapeutics, related to their poor aqueous solubility and toxicity issues with conventional vehicles and resulted in improved pharmacokinetics and biodistribution. Included in the discussion are promising examples and pharmaceutical perspectives on liposomes, nanoemulsions, solid lipid nanoparticles, polymeric nanoparticles, dendrimers, carbon nanotubes and magnetic nanoparticles. As the cardinal features of the ideal multifunctional cancer drug nanocarrier are becoming clear, and drug development challenges are proactively addressed, we anticipate that future advances will enhance therapeutic outcomes by refining the delivery and targeting of complex payloads.

Endocytosis at the nanoscale

Endocytosis is a fundamental process in which eukaryotic cells internalise molecules and macromolecules via deformation of the membrane and generation of membrane-bound carriers. Functional aspects are not only limited to uptake of nutrients, but also play a primary role in evolutionary conserved processes such as the regulation of plasma membrane protein activity (i.e. signal-transducing receptors, small-molecule transporters and ion channels), cell motility and mitosis. The macromolecular nature of the material transported by endocytosis makes this route one of the most important targets for nanomedicine. Indeed, many nanoparticle formulations have been customised to enter cells through endocytosis and deliver the cargo within the cell. In this critical review, we present an overview of the biology of endocytosis and discuss its implications in cell internalisation of nanoparticles. We discuss how nanoparticle size, shape and surface chemistry can control this process effectively. Finally, we discuss different drug delivery strategies on how to evade lysosomal degradation to promote effective release of the cargo (376 references).

Environmentally responsive peptides as anticancer drug carriers

The tumor microenvironment provides multiple cues that may be exploited to improve the efficacy of established chemotherapeutics; furthermore, polypeptides are uniquely situated to capitalize on these signals. Peptides provide: 1) a rich repertoire of biologically specific interactions to draw upon; 2) environmentally responsive phase behaviors, which may be tuned to respond to signatures of disease; 3) opportunities to direct self-assembly; 4) control over routes of biodegradation; 5) the option to seamlessly combine functionalities into a single polymer via a one-step biosynthesis. As development of cancer-targeted nanocarriers expands, peptides provide a unique source of functional units that may target disease. This review explores potential microenvironmental physiology indicative of tumors and peptides that have demonstrated an ability to target and deliver to these signals.

Cellular disposition of arabinogalactan in primary cultured rat hepatocytes

To characterize a targeting property of arabinogalactan (AG) as a carrier to the liver, we examined cellular disposition, such as binding and internalization in primary cultured rat hepatocytes, comparing them to those of asialofetuin (AF). A tyramine derivative of AG was synthesized to allow labeling with 125I. Binding of AG to the cells was concentration-dependent and saturable. The number of binding sites (n) of AG on the cell surface was 4.0 x 10(5) +/- 0.1 x 10(5) sites per cell which was about similar to that of AF. The value of Ka of AG was 2.2 x 10(8) +/- 0.1 x 10(8) M-1 being seven-fold higher than that of AF. The binding of AG was competitively inhibited by AF and was decreased by calcium depletion. These results indicate that AG can bind strongly to hepatocytes probably through the recognition by the asialoglycoprotein receptor (ASGP-R). Both 125I-labeled AG and fluorescein-labeled AG were internalized into the cells. The rate of internalization of AG was faster than that of AF, indicating that AG is effectively endocytosed. Microscopic observations showed that FITC labeled AG accumulated in granules within the primary cultured rat hepatocytes. Subcellular fractionation indicated that the internalized AG was mainly associated with the lysosomal fraction. However, the internalized AG seemed to remain intact in the hepatocytes. In conclusion, we found that AG is effectively internalized in primary cultured rat hepatocytes. Although AG seems a good candidate for targeting to the liver due to its high affinity binding and rapid internalization, it remains to be established whether the apparent lack of biodegradation will result in cytotoxic effects at chronic administration in vivo.

Tumor targeting based on the effect of enhanced permeability and retention (EPR) and the mechanism of receptor-mediated endocytosis (RME)

This review is focused on the macromolecular drug carrier systems by the effect of enhanced permeability and retention (EPR) and the mechanism of receptor-mediated endocytosis (RME). The effect of EPR is thought to be useful for the targeting of the macromolecular drugs to the tumor tissues on a vasculolymphatic level. The RME reveals the selective recognition, high affinity binding, and immediate internalization for the ligand on a cellular level. In the receptor, recognizing transferrin, a level of expression on the tumor cells is higher than that on the normal cells. We have used serum albumin and transferrin as drug carriers to deliver mitomycin C (MMC) to the tumor tissues and into the tumor cells. The properties of the conjugates of MMC to serum albumin and transferrin were examined in vitro and in vivo. We concluded that MMC could be delivered to the tumor tissue and cells by the use of albumin and transferrin as drug carriers.

Transferrin/transferrin receptor-mediated drug delivery

Since transferrin was discovered more than half a century ago, a considerable effort has been made towards understanding tranferrin-mediated iron uptake. However, it was not until recently with the identification and characterization of several new genes related to iron homeostasis, such as the hemochromatosis protein HFE and the iron transporter DMT1, that our knowledge has been advanced dramatically. A major pathway for cellular iron uptake is through internalization of the complex of iron-bound transferrin and the transferrin receptor, which is negatively modulated by HFE, a protein related to hereditary hemochromatosis. Iron is released from transferrin as the result of the acidic pH in endosome and then is transported to the cytosol by DMT1. The iron is then utilized as a cofactor by heme and ribonucleotide reductase or stored in ferritin. Apart from iron, many other metal ions of therapeutic and diagnostic interests can also bind to transferrin at the iron sites and their transferrin complexes can be recognized by many cells. Therefore, transferrin has been thought as a "delivery system" for many beneficial and harmful metal ions into the cells. Transferrin has also be widely applied as a targeting ligand in the active targeting of anticancer agents, proteins, and genes to primary proliferating malignant cells that overexpress transferrin receptors. This is achieved by conjugation of transferrin with drugs, proteins, hybride systems with marcomolecules and as liposomal-coated systems. Conjugates of anticancer drugs with transferrin can significantly improve the selectivity and toxicity and overcome drug resistance, thereby leading to a better treatment. The coupling of DNA to transferrin via a polycation such as polylysine or via cationic liposomes can target and transfer of the extrogenous DNA particularly into proliferating cells through receptor-mediated endocytosis. These kinds of non-viral vectors are potential alternatives to viral vectors for gene therapy, if the transfection efficiency can be improved. Moreover, transferrin receptors have shown potentials in delivery of therapeutic drugs or genes into the brain across blood-brain barrier.