DNA is considered an important target for drug design and development. Until recently, the focus was on double-stranded (duplex) DNA structures. However, it has now been shown that single stranded DNA can fold into hairpin, triplex, i-motif and G-quadruplex structures. The more interesting G-quadruplex DNA structures comprise four strands of stacked guanine (G)-tetrads formed by the coplanar arrangement of four guanines, held together by Hoogsteen bonds. The DNA sequences with potential to form G-quadruplex structures are found at the chromosomal extremities (i.e. the telomeres) and also at the intra-chromosomal region (i.e. oncogenic promoters) in several important oncogenes. The formation of G-quadruplex structures is considered to have important consequences at the cellular level and such structures have been evoked in the control of expression of certain genes involved in carcinogenesis (c-myc, c-kit, K-ras etc.) as well as in the perturbation of telomeric organization. It has been shown that the formation of quadruplexes inhibits the telomere extension by the telomerase enzyme, which is up-regulated in cancer cells. Therefore, G-quadruplex structures are an important target for drug design and development and there is a huge interest in design and development of small molecules (ligands) to target these structures. A large number of so-called G-quadruplex ligands, displaying varying degrees of affinity and more importantly selectivity (i.e. the ability to interact only with quadruplex-DNA and not duplex-DNA), have been reported. Access to efficient and robust in vitro assays is needed to effectively monitor and quantify the G-quadruplex DNA/ligand interactions. This tutorial review provides an overview of G-quadruplex ligands and biophysical techniques available to monitor such interactions.

Synthetic oligonucleotides (ONs) are being investigated for various therapeutic and diagnostic applications. The interest in ONs arises because of their capability to cause selective inhibition of gene expression by binding to the target DNA/RNA sequences through mechanisms such as antigene, antisense, and RNA interference. ONs with catalytic activity (ribozymes and DNAzymes) against the target sequences, and ability to bind to the target molecules (aptamers), ranging from small molecules to proteins, are also known. Therefore ONs are considered potentially useful for the treatment of viral diseases and cancer. ONs also find use in the design of DNA microchips (a powerful bio-analytical tool) and novel materials in nanotechnology. However, the clinical success achieved so far with ONs has not been satisfactory, and the major impediments have been recognised as their instability against nucleases, lack of target specificity, and poor uptake and targeted delivery. Tremendous efforts have been made to improve the ON properties by either incorporating chemical modifications in the ON structure or covalently linking (conjugation) reporter groups, with biologically relevant properties, to ONs. Conjugation is of great interest because it can be used not only to improve the existing ON properties but also to impart entirely new properties. This tutorial review focuses on the recent developments in ON conjugation, and describes the key challenges in efficient ON conjugation and major synthetic approaches available for successful ON conjugate syntheses. In addition, an overview on major classes of ON conjugates along with their use in therapeutics, diagnostics and nanotechnology is provided.

Anticancer drugs are often nonselective antiproliferative agents (cytotoxins) that preferentially kill dividing cells by attacking their DNA at some level. The lack of selectivity results in significant toxicity to noncancerous proliferating cells. These toxicities along with drug resistance exhibited by the solid tumors are major therapy limiting factors that result into poor prognosis for patients. Prodrug and conjugate design involves the synthesis of inactive drug derivatives that are converted to an active form inside the body and preferably at the site of action. Classical prodrug and conjugate design have focused on the development of prodrugs that can overcome physicochemical (e.g., solubility, chemical instability) or biopharmaceutical problems (e.g., bioavailability, toxicity) associated with common anticancer drugs. The recent targeted prodrug and conjugate design, on the other hand, hinge on the selective delivery of anticancer agents to tumor tissues thereby avoiding their cytotoxic effects on noncancerous cells. Targeting strategies have attempted to take advantage of low extracellular pH, elevated enzymes in tumor tissues, the hypoxic environment inside the tumor core, and tumor-specific antigens expressed on tumor cell surfaces. The present review highlights recent trends in prodrug and conjugate rationale and design for cancer treatment. The various approaches that are currently being explored are critically analyzed and a comparative account of the advantages and disadvantages associated with each approach is presented.

The relationship between microparticle (MP) size and lung targeting efficiency, intra-lung distribution and retention time was systematically studied after intravenous administration of rigid fluorescent polystyrene MPs of various sizes (2, 3, 6 and 10μm) to Sprague-Dawley rats. Total fluorescence was assessed and it was found that 2μm and 3μm MPs readily passed through the lung to the liver and spleen while 10μm MPs were completely entrapped in the lung for the one-week duration of the study. Approximately 84% of 6μm MPs that were initially entrapped in the lung were cleared over the next 2 days and 15% were cleared over the remaining 5 days. A Caliper IVIS® 100 small animal imaging system confirmed that 3μm MPs were not retained in the lung but that 6μm and 10μm MPs were widely distributed throughout the lung. Moreover, histologic examination showed MP entrapment in capillaries but not arterioles. These studies suggest that for rigid MPs the optimal size range required to achieve transient but highly efficiently targeting to pulmonary capillaries after IV injection is >6μm but <10μm in rats and that systemic administration of optimally sized MPs may be an efficient alternative to currently used inhalation-based delivery to the lung. KeywordsPassive pulmonary targeting; Rigid non-biodegradable microparticle; In vivo imaging

Polymeric hydrogels have been extensively explored for controlled drug-delivery applications, but there is an increasing demand for smart drug delivery combined with tunable physicochemical attributes and tissue engineering potential. In this work, novel xanthan-poly(ethylene glycol) (PEG) hydrogels were developed by cross-linking polysaccharide, oxidized xanthan, and 8-arm PEG hydrazine through dynamic, pH-responsive, and biodegradable hydrazone linkages. Aqueous solutions (pH 6.5) of oxidized xanthan and PEG hydrazine were mixed together at 37 °C to obtain hydrogels within minutes, and the formation of hydrazone linkages was ascertained using Fourier transform infrared spectroscopy. Fabrication of xanthan-PEG hydrogels using hydrazone linkages has not been reported previously. The 3% hydrogels exhibited the storage modulus of 194 Pa, which increased to 770 Pa for 5% hydrogels. When subjected to alternating cycles of varying strains of 1 and 800% (5 cycles), hydrogels demonstrated instant recovery each time the extreme strain was relieved, thus suggesting excellent self-healing capabilities. Doxorubicin (DOX), chemotherapeutic agent, was loaded onto hydrogels, and release studies were carried out at pH 5.5 (tumoral) and 7.4 (physiological). The cumulative release from 3, 4, and 5% hydrogels at pH 5.5 was 81.06, 61.98, and 41.67%, whereas the release at pH 7.4 was 47.43, 37.01, and 35.34% at 30 days. MTT assay showed that oxidized xanthan and PEG hydrazine are not toxic to mammalian cells (NIH-3T3), as the cell viabilities were found to be 84.66 and 102% for concentrations up to 1 mg/mL. The live/dead assay with encapsulated NIH-3T3 cells showed no significant dead cell population, suggesting excellent compatibility of hydrogels in 2D and 3D culture. DOX-loaded hydrogels exhibited cytotoxicity against A549 cells when exposed to media released from hydrogels. Overall, hydrogels developed in this work may have potential applications in drug delivery and 3D cell culture for cell delivery.

Upon the addition of a short EO chain nonionic surfactant, poly(oxyethylene) dodecyl ether (C12EOn), to dilute micellar solution of sodium dodecyl sulfate (SDS) above a particular concentration, a sharp increase in viscosity occurs and a highly viscoelastic micellar solution is formed. The oscillatory-shear rheological behavior of the viscoselastic solutions can be described by the Maxwell model at low shear frequency and combined Maxwell-Rouse model at high shear frequency. This property is typical of wormlike micelles entangled to form a transient network. It is found that when C12EO4 in the mixed system is replaced by C12EO3 the micellar growth occurs more effectively. However, with the further decrease in EO chain length, phase separation occurs before a viscoelastic solution is formed. As a result, the maximum zero-shear viscosity is observed at an appropriate mixing fraction of surfactant in the SDS-C12EO3 system. We also investigated the micellar growth in the mixed surfactant systems by means of small-angle X-ray scattering (SAXS). It was found from the SAXS data that the one-dimensional growth of micelles was obtained in all the SDS-C12EOn (n=0-4) aqueous solutions. In a short EO chain C12EOn system, the micelles grow faster at a low mixing fraction of nonionic surfactant.

[structure: see text] A novel strategy to prepare glycopeptide-oligonucleotide conjugates bearing a glycocluster is reported. The strategy utilizes a cyclodecapeptide scaffold as a key intermediate to anchor the carbohydrate cluster and the oligonucleotide through sequential oxime bond formation. The oligonucleotide glycocluster retains the binding affinity and recognition specificity for the target sequence. Furthermore, the conjugate shows enhanced binding to the specific lectins due to the cooperative effect produced by the carbohydrate cluster.

Fast forming hydrogels prepared by crosslinking a poly(ethylene glycol) (PEG)-based copolymer containing multiple thiol (SH) groups were evaluated for the controlled ocular delivery of pilocarpine and subsequent pupillary constriction. Physical properties of the hydrogels were characterized using UV-Vis spectrophotometry, transmission electron microscopy (TEM), rheometry, and swelling kinetics. Pilocarpine loading efficiency and release properties were measured in simulated tear fluid. The hydrogel formulations exhibited high drug loading efficiency (~74%). Pilocarpine release was found to be biphasic with release half times of ~2 and 94 h, respectively, and 85-100% of the drug was released over 8-days. Pilocarpine-loaded (2% w/v) hydrogels were evaluated in a rabbit model and compared to a similar dose of drug in aqueous solution. The hydrogels were retained in the eye for the entire period of the study with no observed irritation. Pilocarpine-loaded hydrogels sustained pupillary constriction for 24 h after administration as compared to 3 h for the solution, an 8-fold increase in duration of action. A strong correlation between pilocarpine release and pupillary response was observed. In conclusion, the current studies demonstrate that in situ forming PEG hydrogels possess the viscoelastic, retention, and sustained delivery properties required for an efficient ocular drug delivery system.