Nanotechnology has the potential to revolutionize cancer diagnosis and therapy. Advances in protein engineering and materials science have contributed to novel nanoscale targeting approaches that may bring new hope to cancer patients. Several therapeutic nanocarriers have been approved for clinical use. However, to date, there are only a few clinically approved nanocarriers that incorporate molecules to selectively bind and target cancer cells. This review examines some of the approved formulations and discusses the challenges in translating basic research to the clinic. We detail the arsenal of nanocarriers and molecules available for selective tumour targeting, and emphasize the challenges in cancer treatment.

Nanocarriers as an emerging platform for cancer therapy

After infection and a prolonged incubation period, the scrapie agent causes a degenerative disease of the central nervous system in sheep and goats. Six lines of evidence including sensitivity to proteases demonstrate that this agent contains a protein that is required for infectivity. Although the scrapie agent is irreversibly inactivated by alkali, five procedures with more specificity for modifying nucleic acids failed to cause inactivation. The agent shows heterogeneity with respect to size, apparently a result of its hydrophobicity; the smallest form may have a molecular weight of 50,000 or less. Because the novel properties of the scrapie agent distinguish it from viruses, plasmids, and viroids, a new term "prion" is proposed to denote a small proteinaceous infectious particle which is resistant to inactivation by most procedures that modify nucleic acids. Knowledge of the scrapie agent structure may have significance for understanding the causes of several degenerative diseases.

http://science.sciencemag.org/content/sci/216/4542/136.full.pdf

Novel proteinaceous infectious particles cause scrapie

We have developed novel nucleic acid probes that recognize and report the presence of specific nucleic acids in homogeneous solutions. These probes undergo a spontaneous fluorogenic conformational change when they hybridize to their targets. Only perfectly complementary targets elicit this response, as hybridization does not occur when the target contains a mismatched nucleotide or a deletion. The probes are particularly suited for monitoring the synthesis of specific nucleic acids in real time. When used in nucleic acid amplification assays, gene detection is homogeneous and sensitive, and can be carried out in a sealed tube. When introduced into living cells, these probes should enable the origin, movement, and fate of specific mRNAs to be traced.

Molecular Beacons: Probes that Fluoresce upon Hybridization

Biological barriers to drug transport prevent successful accumulation of nanotherapeutics specifically at diseased sites, limiting efficacious responses in disease processes ranging from cancer to inflammation. Although substantial research efforts have aimed to incorporate multiple functionalities and moieties within the overall nanoparticle design, many of these strategies fail to adequately address these barriers. Obstacles, such as nonspecific distribution and inadequate accumulation of therapeutics, remain formidable challenges to drug developers. A reimagining of conventional nanoparticles is needed to successfully negotiate these impediments to drug delivery. Site-specific delivery of therapeutics will remain a distant reality unless nanocarrier design takes into account the majority, if not all, of the biological barriers that a particle encounters upon intravenous administration. By successively addressing each of these barriers, innovative design features can be rationally incorporated that will create a new generation of nanotherapeutics, realizing a paradigmatic shift in nanoparticle-based drug delivery.

/pdf/principles-of-nanoparticle-design-for-overcoming-biological-4c2c5quqtc.pdf

Principles of nanoparticle design for overcoming biological barriers to drug delivery

Drug delivery systems (DDS) such as lipid- or polymer-based nanoparticles can be designed to improve the pharmacological and therapeutic properties of drugs administered parenterally. Many of the early problems that hindered the clinical applications of particulate DDS have been overcome, with several DDS formulations of anticancer and antifungal drugs now approved for clinical use. Furthermore, there is considerable interest in exploiting the advantages of DDS for in vivo delivery of new drugs derived from proteomics or genomics research and for their use in ligand-targeted therapeutics.

http://science.sciencemag.org/content/sci/303/5665/1818.full.pdf

Drug Delivery Systems: Entering the Mainstream

Large unilamellar and oligolamellar vesicles are formed when an aqueous buffer is introduced into a mixture of phospholipid and organic solvent and the organic solvent is subsequently removed by evaporation under reduced pressure. These vesicles can be made from various lipids or mixtures of lipids and have aqueous volume to lipid ratios that are 30 times higher than sonicated preparations and 4 times higher than multilamellar vesicles. Most importantly, a substantial fraction of the aqueous phase (up to 62% at low salt concentrations) is entrapped within the vesicles, encapsulating even large macromolecular assemblies with high efficiency. Thus, this relatively simple technique has unique advantages for encapsulating valuable water-soluble materials such as drugs, proteins, nucleic acids, and other biochemical reagents. The preparation and properties of the vesicles are described in detail.

https://www.pnas.org/content/pnas/75/9/4194.full.pdf

Procedure for preparation of liposomes with large internal aqueous space and high capture by reverse-phase evaporation

Dendrimers are branched, synthetic polymers with layered architectures that show promise in several biomedical applications. By regulating dendrimer synthesis, it is possible to precisely manipulate both their molecular weight and chemical composition, thereby allowing predictable tuning of their biocompatibility and pharmacokinetics. Advances in our understanding of the role of molecular weight and architecture on the in vivo behavior of dendrimers, together with recent progress in the design of biodegradable chemistries, has enabled the application of these branched polymers as anti-viral drugs, tissue repair scaffolds, targeted carriers of chemotherapeutics and optical oxygen sensors. Before such products can reach the market, however, the field must not only address the cost of manufacture and quality control of pharmaceutical-grade materials, but also assess the long-term human and environmental health consequences of dendrimer exposure in vivo.

Designing dendrimers for biological applications.

IAbbreviations used in this article are as follows: AraC= l -,B-d arabinofuranosyl cytosine, Chol=cholesterol, DNA=deoxyribonucleic acid, DMPA=dimyristoyl phos­ phatidic acid, DMPC = dimyristoyl phosphatidylcholine, DMPE = dimyristoyl phos­ phatidylethanolamine, DOPC = dioleoyl phosphatidylcholine, DOPE = dioleoyl phos­ phatidylethanolamine, DPPA=dipaJmitoyl phosphatidic acid, DPPC=dipaJmitoyl phos­ phatidylcholine, DPPG = dipaJmitoyl phosphatidylglycerol, DPPS;= dipalmitoyl phos­ phatidylserine, DSPC = distearoyl phosphatidylcholine, EPC = egg phosphatidylcholine, EDTA=ethylene diamine tetracetic acid, HDL=high density lipoprotein, HPLC=high performance liquid chromatography, LUV = large unilamellar vesicle, MLV = multilamellar vesicle, NT A = nitrilotriacetic acid, NMR = nuclear magnetic resonance, PA phosphatidic acid, PC = phosphatidylcholine, PE = phosphatidylethanolamine, PO = phosphatidylglycerol, PS = phosphatidylserine, REV = reverse-phase evaporation vesicle, RNA = ribonucleic acid, SUV=small unilameUar vesicle, Tc=transition temperature. 2Present address: Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111.

Comparative Properties and Methods of Preparation of Lipid Vesicles (Liposomes)

The disclosure is of a method for encapsulating biologically active materials in synthetic, oligolamellar lipid vesicles (liposomes). The method comprises providing a mixture of lipid in organic solvent and an aqueous mixture of the material for encapsulation, emulsifying the provided mixture, removing the organic solvent and suspending the resultant gel in water. The method of the invention is advantageous over prior art methods of encapsulating biologically active materials in that it provides a means for a relatively high capture efficiency of the material for encapsulation. The disclosure is also of intermediate compositions in the encapsulation method, the product vesicles, compositions including the product vesicles as an active ingredient and their use.

Francis C. Szoka

Papers

Procedure for preparation of liposomes with large internal aqueous space and high capture by reverse-phase evaporation

Designing dendrimers for biological applications.

Comparative Properties and Methods of Preparation of Lipid Vesicles (Liposomes)

Method of encapsulating biologically active materials in lipid vesicles

Polyamidoamine cascade polymers mediate efficient transfection of cells in culture