Tumor-targeted drug delivery with aptamers

Cancer is one of the leading causes of death around the world. Tumor-targeted drug delivery is one of the major areas in cancer research. Aptamers exhibit many desirable properties for tumor-targeted drug delivery, such as ease of selection and synthesis, high binding affinity and specificity, low immunogenicity, and versatile synthetic accessibility. Over the last several years, aptamers have quickly become a new class of targeting ligands for drug delivery applications. In this review, we will discuss in detail about aptamer-based delivery of chemotherapy drugs (e.g. doxorubicin, docetaxel, daunorubicin, and cisplatin), toxins (e.g. gelonin and various photodynamic therapy agents), and a variety of small interfering RNAs. Although the results are promising which warrants enthusiasm for aptamer-based drug delivery, tumor homing of aptamer-based conjugates after systemic injection has only been achieved in one report. Much remains to be done before aptamer-based drug delivery can reach clinical trials and eventually the day-to-day management of cancer patients. Therefore, future directions and challenges in aptamer-based drug delivery are also discussed.     

Nanoparticle-aptamer bioconjugates for targeted antineoplastic drug delivery

Targeted drug delivery technologies can provide physicians with new approaches to treat and manage patients with cancer. Nucleic acid ligands (aptamers) are a novel class of targeting molecules that can be used in a similar manner to antibodies. Beyond use as drugs themselves, aptamers have the potential to serve as targeting ligands to deliver drugs, imaging agents, or other bioactive agents to the intended site of action. Bioconjugates of nanoparticles and aptamers can selectively bind and be taken up by cancer cells. In this article we review progress to date for antineoplastic drug delivery using nanoparticle-aptamer bioconjugates. Aptamers are isolated through a process of in vitro selection, also referred to as systematic evolution of ligands by exponential enrichment (SELEX). There is an increasing numbers of aptamers for cancer targeting being reported in the literature. These aptamers often interact with antigens that are overexpressed exclusively, or preferentially, on cancer cells or in the cancer microenvironment. As novel drug delivery vehicles, nanoparticle-aptamer bioconjugates may be developed to target a myriad of diseases including many cancers by delivering a variety of therapeutic agents specifically to the site of interest. The first in vivo study of antineoplastic drug delivery by a bioconjugate employed nanoparticle encapsulating docetaxel and aptamers that bind certain prostate cancer cells. In this study using a xenograft murine model of prostate cancer, these bioconjugates were shown to significantly improve tumor reduction after intratumoral injection compared with all controls. Furthermore, the docetaxel-loaded nanoparticle-aptamer bioconjugates demonstrated reduced toxicity in terms of acute bodyweight loss compared with the controls. In vitro, the efficacy of the docetaxel-loaded nanoparticle-aptamer bioconjugate was shown to be due to intracellular delivery of the drug to the cancer cells, and the bioconjugate without the drug had no cytotoxicity. Nanoparticle-aptamer bioconjugates may prove to be useful not only for management of cancer but also various other indications. New aptamers, multivalent targeting strategies, and multimodal treatments such as simultaneous radio- and chemotherapy may further increase the efficacy of these bioconjugates and facilitate their clinical translation for therapeutic and diagnostic applications.     

Novel folated and non-folated pullulan bioconjugates for anticancer drug delivery

Two new anticancer polymer therapeutics were designed for tumour cell targeting. The bioconjugates were synthesised by pullulan derivatisation with either doxorubicin or doxorubicin and folic acid. Pullulan was activated by periodate oxidation and functionalised by reductive conjugation with cysteamine and 1.9 kDa PEG(NH₂)₂. The cysteamine thiol groups were conjugated to doxorubicin through a pH-sensitive hydrazone spacer while the pending PEG-NH₂ functions of one derivatised pullulan batch were conjugated to folic acid to obtain one of the two polymer therapeutics. The reaction intermediates and the final products were characterised by mass spectrometry, UV–vis analysis and reverse phase and gel permeation chromatography. The folic acid-free derivative [(NH₂ PEG)-Pull-(Cyst-Dox)] contained 6.3% (w/w) doxorubicin while the folic acid-doxorubicin-coupled derivative [(FA-PEG)-Pull-(Cyst-Dox)] contained 6% (w/w) doxorubicin and 4.3% (w/w) folic acid. Photon correlation spectroscopy showed that (NH₂ PEG)-Pull-(Cyst-Dox) and (FA-PEG)-Pull-(Cyst-Dox) assembled into particles of about 150 and 100 nm diameter, respectively. The two bioconjugates displayed similar drug release profiles either at pH 7.4 buffer or in plasma, where less than 20% of doxorubicin was released within three days. At pH 5.5, both conjugates underwent complete drug release in about 40 h. In vitro studies carried out with KB tumour cells over-expressing folic acid receptor showed that both free doxorubicin and (FA-PEG)-Pull-(Cyst-Dox) were rapidly taken up by the cells, while the internalisation of the non-folated derivative was significantly slower. Cell viability studies did not show relevant difference between the two bioconjugates. After 72 h of incubation with folic acid receptor non-expressing MCF7 cells, the IC₅₀ values of doxorubicin, (NH₂PEG)-Pull-(Cyst-Dox) and (FA-PEG)-Pull-(Cyst-Dox) were 0.3 μM, 1.2 μM and 3.1 μM, respectively. After incubation with KB cells over-expressing folic acid receptor, the IC₅₀ values were 0.4 μM, 1.8 μM and 1.1 μM, respectively. Pharmacokinetic studies showed that 4 h after intravenous administration of the conjugates to Balb/c mice about 40% of the administered drug equivalent dose was present in the bloodstream while in the case of unconjugated doxorubicin, 80% of the drug was cleared within 30 min.These findings suggest that the novel doxorubicin–pullulan bioconjugates possess suitable properties for passive tumour targeting. On the other hand, folic acid conjugation has been found to have limited effect on selective cell up-take.     

表面修饰的LPC纳米粒介导的siRNA肿瘤靶向递送(英文)

本研究构建了能够靶向肿瘤的新型纳米粒(脂质体-鱼精蛋白-硫酸软骨素纳米粒,LPC-NP)。该纳米粒粒径约90 nm,zata电位约+35 mV。采用后插法对LPC纳米粒进行DSPE-PEG_(2000)或DSPE-PEG_(2000)-T7修饰。T7是与转铁蛋白功能类似的七肽,能够靶向转铁蛋白受体过度表达的乳腺癌细胞MCF-7。PEG修饰可显著降低血清对LPC纳米粒的聚集作用,T7修饰的纳米粒显著提高siRNA的细胞摄取和基因沉默效率。体外细胞毒实验表明抗EGFR siRNA显著抑制MCF-7细胞生长。实验结果表明经T7肽修饰的LPC纳米粒有望成为RNA干扰肿瘤治疗的递送载体。     

A biodegradable injectable thermoplastic for localized camptothecin delivery

Camptothecin is an example of a potent drug with a short half-life that would benefit from a localized drug depot system that maintains its stability prior to being released. For this reason, a thermoplastic, biodegradable polymer drug depot was prepared and characterized, and the in vitro release of camptothecin examined. epsilon-Caprolactone oligomers were prepared by ring-opening polymerization initiated by various alcohols. The polymers were characterized via differential scanning calorimeter (DSC) for thermal transitions, and via a parallel plate rheometer for melt viscosity. Camptothecin was loaded into the oligomers and released into PBS buffer. The viscosity of the oligomers was alterable by the initiator used. The oligomers were semi-crystalline with melting points between 37 and 45 degrees C. Camptothecin was released from the oligomers in a diffusion-controlled manner, with the release rate increasing as the melt viscosity of the oligomer decreased. The unreleased camptothecin remained in its active lactone form for a period of up to 16 weeks.     

Tumor-targeted delivery of siRNA by non-viral vector: safe and effective cancer therapy

RNA interference technology has been developed as a potential therapeutic agent for many indications, including cancer. Silencing a specific oncogene in tumor cells brings about cell death both in vitro and in vivo. However, there is a great need for powerful delivery strategies to enhance the therapeutic effect of small interfering RNA (siRNA). This review summarizes different signaling pathways inhibited by siRNA and the advantages of targeted siRNA as a delivery system.     

Comparative evaluation of polymeric and amphiphilic cyclodextrin nanoparticles for effective camptothecin delivery

Camptothecin (CPT) is a potent anticancer agent. The clinical application of CPT is restricted by poor water solubility and instability under physiological conditions. Solubilization and stabilization of CPT were realized through nanoparticulate systems of amphiphilic cyclodextrins, poly(lactide-co-glycolide) (PLGA) or poly-ε-caprolactone (PCL). Nanoparticles were prepared with nanoprecipitation technique, whereas cyclodextrin nanoparticles were prepared from preformed inclusion complexes of CPT with amphiphilic cyclodextrins. Polymeric nanoparticles, on the other hand, were loaded with CPT:HP-β-CD inclusion complex to solubilize and stabilize the drug. Mean particle sizes were under 275 nm, and polydispersity indices were lower than 0.2 for all formulations. Drug-loading values were significantly higher for amphiphilic cyclodextrin nanoparticles when compared with those for PLGA and PCL nanoparticles. Nanoparticle formulations showed a significant controlled release profile extended up to 12 days for amphiphilic cyclodextrin nanoparticles and 48 h for polymeric nanoparticles. Anticancer efficacy of the nanoparticles was evaluated in comparison with CPT solution in dimethyl sulfoxide (DMSO) on MCF-7 breast adenocarcinoma cells. Amphiphilic cyclodextrin nanoparticles showed higher anticancer efficacy than PLGA or PCL nanoparticles loaded with CPT and the CPT solution in DMSO. These results indicated that CPT-loaded amphiphilic cyclodextrin nanoparticles might provide a promising carrier system for the effective delivery of this anticancer drug having bioavailability problems.     

喜树碱衍生物传送技术的研究进展

喜树碱类药物是抗肿瘤药物研究领域的热点,为了解决其存在的溶解度差、不稳定和不良反应大等问题,各种新的药物传送技术都用于此类药物的研究.本文以微粒、大分子前药等新型传送技术为主,对近几年喜树碱及其衍生物传送技术进行综述.相信随着这些技术的不断完善和发展,该类药物将是极具发展前景的一类抗肿瘤药物.     

Nanoparticle-aptamer bioconjugates for cancer targeting

The combination of targeted drug delivery and controlled-release technology may pave the road for more effective yet safer chemotherapeutic options for cancer therapy. Drug-encapsulated polymeric nanoparticle-aptamer bioconjugates represent an emerging technology that can facilitate the delivery of chemotherapeutics to primary and metastatic tumours. Aptamers are short nucleic acid molecules with binding properties and biochemical characteristics that may make them suitable for use as targeting molecules. The goal of this review is to summarise the key components that are required for creating effective cancer targeting nanoparticle-aptamer bioconjugates. The field of controlled release and the structure and properties of aptamers, as well as the criteria for constructing effective conjugates, will be discussed.     

Tumor-targeted induction of oxystress for cancer therapy

Reactive oxygen species (ROS), such as superoxide anion radicals (O.-2) and hydrogen peroxide (H2O2) are potentially harmful by-products of normal cellular metabolism that directly affect cellular functions. ROS is generated by all aerobic organisms and it seems to be indispensable for signal transduction pathways that regulate cell growth and reduction-oxidation (redox) status. However, overproduction of these highly reactive oxygen metabolites can initiate lethal chain reactions, which involve oxidation and damage to structures that are crucial for cellular integrity and survival. In fact, many antitumor agents, such as vinblastine, cisplatin, mitomycin C, doxorubicin, camptothecin, inostamycin, neocarzinostatin and many others exhibit antitumor activity via ROS-dependent activation of apoptotic cell death, suggesting potential use of ROS as an antitumor principle. Thus, a unique anticancer strategy named "oxidation therapy" has been developed by inducing cytotoxic oxystress for cancer treatment. This goal could be achieved mainly by two methods, namely, (i) inducing the generation of ROS directly to solid tumors and (ii) inhibiting the antioxidative enzyme (defense) system of tumor cells. Since 1950s, many strategies have been employed based on the first method, namely, administration of ROS per se (e.g. H2O2) or ROS generating enzyme to tumor bearing animals. However no successful and practical results were obtained probably because of the lack of tumor selective ROS delivery and hence resulting in subsequent induction of severe side effects. To overcome these obstacles, we developed polyethylene glycol (PEG) conjugated O.-2 or H2O2-generating enzymes, xanthine oxidase (XO) and D-amino acid oxidase (DAO) (PEG-DAO) respectively. More recently, a pegylated (PEG) zinc protoporphyrin (PEG-ZnPP) and a highly water soluble micellar formulation of ZnPP based on amphiphilic styrene maleic acid (SMA) copolymer, SMA-ZnPP, are prepared, which are potent inhibitors of heme oxygenase-1 (HO-1). HO-1 is a major antioxidative enzyme of tumors, that is different in mechanism of catalase or superoxide dismutase (SOD). Consequently, both PEG-enzymes and PEG-ZnPP exhibited superior in vivo pharmacokinetics than their parental molecules, particularly in tumor delivery by taking advantage of the EPR effect of macromolecular nature, and thus showed remarkable antitumor effects suggesting the potentials of this anticancer therapeutic for clinical application. Furthermore, it has been well known that many antioxidative enzymes such as catalase, SOD are down-regulated in most solid tumors in vivo. On the contrary, HO-1 is highly upregulated and it plays a very important role of antioxidation, because HO-1 generates biliverdin, which being converted to bilirubin exhibits a very potent antioxidative effect, and hence antiapoptosis in tumors. Thus this oxidation therapy, by inhibiting this HO-1 dependent antioxidant (bilirubin) formation by ZnPP, and by enhancing ROS generation, is expected to offer a powerful therapeutic modality for future anticancer therapy.     

Poly(amido amine) dendrimers as absorption enhancers for oral delivery of camptothecin

Oral delivery of camptothecin has a treatment advantage but is limited by low bioavailability and gastrointestinal toxicity. Poly(amido amine) or PAMAM dendrimers have shown promise as intestinal penetration enhancers, drug solubilizers and drug carriers for oral delivery in vitro and in situ. There have been very limited studies in vivo to evaluate PAMAM dendrimers for oral drug delivery. In this study, camptothecin (5 mg/kg) was formulated and co-delivered with cationic, amine-terminated PAMAM dendrimer generation 4.0 (G4.0) (100 and 300 mg/kg) and anionic, carboxylate-terminated PAMAM generation 3.5 (G3.5) (300 and 1000 mg/kg) in CD-1 mice. Camptothecin associated to a higher extent with G4.0 than G3.5 in the formulation, attributed to an electrostatic interaction on the surface of G4.0. Both PAMAM G4.0 and G3.5 increased camptothecin solubilization in simulated gastric fluid and caused a 2–3 fold increase in oral absorption of camptothecin when delivered at 2 h. PAMAM G4.0 and G3.5 did not increase mannitol transport suggesting that the oral absorption of camptothecin was not due to tight junction modulation. Histologic observations of the epithelial layer of small intestinal segments of the gastrointestinal tract (GIT) at 4 h post dosing supported no evidence of toxicity at the evaluated doses of PAMAM dendrimers. This study demonstrates that both cationic (G.4) and anionic (G3.5) PAMAM dendrimers were effective in enhancing the oral absorption of camptothecin. Results suggest that drug inclusion in PAMAM interior controlled solubilization in simulated gastric and intestinal fluids, and increased oral bioavailability.     

Cross-linked antioxidant nanozymes for improved delivery to CNS

Formulations of antioxidant enzymes, superoxide dismutase 1 (SOD1, also known as Cu/Zn SOD) and catalase were prepared by electrostatic coupling of enzymes with cationic block copolymers, polyethyleneimine-poly(ethylene glycol) or poly(L-lysine)-poly(ethylene glycol), followed by covalent cross-linking to stabilize nanoparticles (NPs). Different cross-linking strategies (using glutaraldehyde, bis-(sulfosuccinimidyl)suberate sodium salt or 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride with N-hydroxysulfosuccinimide) and reaction conditions (pH and polycation/protein charge ratio) were investigated that allowed immobilizing active enzymes in cross-linked NPs, termed "nanozymes." Bienzyme NPs, containing both SOD1 and catalase were also formulated. Formation of complexes was confirmed using denaturing gel electrophoresis and western blotting; physicochemical characterization was conducted using dynamic light scattering and atomic force microscopy. In vivo studies of (125)I-labeled SOD1-containing nanozymes in mice demonstrated their increased stability in both blood and brain and increased accumulation in brain tissues, in comparison with non-cross-linked complexes and native SOD1. Future studies will evaluate the potential of these formulations for delivery of antioxidant enzymes to the central nervous system to attenuate oxidative stress associated with neurological diseases. FROM THE CLINICAL EDITOR: Formulations of antioxidant enzyme complexes were demonstrated along with their increased stability in both blood and brain and increased accumulation in CNS tissue. Future studies will evaluate the potential of these formulations for antioxidant enzyme deliver to the CNS to attenuate oxidative stress in neurodegenerative diseases.     

Nanosized ethosomes bearing ketoprofen for improved transdermal delivery

The potential of ethosomes for delivering ketoprofen via skin was evaluated. The ethosomes were prepared, optimized and characterized. Vesicular shape, size and entrapment efficiency were determined by transmission electron microscopy, dynamic light scattering and minicolumn centrifugation technique, respectively. Vesicle sizes varied from 120.3±6.1 to 410.2±21.8 nm depending on the concentrations of soya phosphatidyl choline (SPC) and ethanol. Entrapment efficiency increased with concentrations of SPC and ethanol. The formulations exhibited entrapment efficiencies of 42–78%. In vitro release through cellophane membrane showed sustained release of drug from ethosomal formulations in contrast to hydroalcoholic drug solution (HA), which released most of the drug within 2–3 h. In vitro drug permeation across human skin revealed improved drug permeation and higher transdermal flux with ethosomal formulations compared to hydroethanolic drug solution. Kinetics of in vitro skin permeation showed zero order drug release from formulations. Based on in vitro transdermal flux, the estimated steady state in vivo plasma concentration from ethosomes attained therapeutic drug levels whereas hydroalcoholic drug solution exhibited sub therapeutic drug concentration with a patch size of 50 cm². Skin permeation of ethosomal formulations assessed by confocal microscopy revealed enhanced permeation of Rhodamine 123 loaded formulation in comparison to the hydroalcoholic solution.     

Drug delivery strategies for improved azole antifungal action

Background: Azole antifungal agents are the most commonly used antifungals in clinical treatment of both superficial and systemic fungal infections. Many azoles are poorly water soluble, which limits their bioavailability and antifungal effects. Objective: To improve the efficacy of azole antifungal drugs by advances in drug delivery. Methods: Manipulation of drug formulations and administration routes to improve the antifungal pharmacokinetics with targeted delivery, rapidly followed by sustained release and prolonged retention of high drug concentration localized at the infection site. Results/conclusion: Formulation and drug delivery strategies can improve the aqueous wetting and dissolution properties by increasing their chemical potential, stabilizing the drug delivery system and targeting high concentration of the azoles to the infection sites, therefore enhancing the bioavailability and therapeutic efficacy of azole antifungals.