Etgar Levy-Nissenbaum

Targeted nanoparticles for cancer therapy

Over the past decade, there has been an increasing interest in using nanotechnology for cancer therapy. The development of smart targeted nanoparticles (NPs) that can deliver drugs at a sustained rate directly to cancer cells may provide better efficacy and lower toxicity for treating primary and advanced metastatic tumors. We highlight some of the promising classes of targeting molecules that are under development for the delivery of NPs. We also review the emerging technologies for the fabrication of targeted NPs using microfluidic devices.

Nanotechnology and aptamers: applications in drug delivery

Nucleic acid ligands, also known as aptamers, are a class of macromolecules that are being used in several novel nanobiomedical applications. Aptamers are characterized by high affinity and specificity for their target, a versatile selection process, ease of chemical synthesis and a small physical size, which collectively make them attractive molecules for targeting diseases or as therapeutics. These properties will enable aptamers to facilitate innovative new nanotechnologies with applications in medicine. In this review, we will highlight recent developments in using aptamers in nanotechnology solutions for treating and diagnosing disease.

Transepithelial Transport of Fc-Targeted Nanoparticles by the Neonatal Fc Receptor for Oral Delivery

Nanoparticles targeted to the neonatal Fc receptor cross the intestinal epithelium and reach systemic circulation after oral administration. A Spoonful of Nanomedicine Oral delivery of drug-loaded nanoparticles is, to some, the Holy Grail of nanomedicine. Patients can easily pop a pill, which makes them more compliant with a therapeutic regimen. The difficulty with ingesting these tiny particles is that they are not readily absorbed in the intestine, thus eliminating most of the particles from the body and, in turn, limiting efficacy. In response, Pridgen et al. designed polymeric nanoparticles targeting a receptor expressed on the surface of the intestine to actively transport the particle across the cell into the patient’s circulation. The nanoparticles were decorated with Fc fragments that readily bind to the neonatal Fc receptor (FcRn) in the intestinal epithelium. The authors observed that the Fc-targeted nanoparticles crossed the intestinal barrier both in vitro, using human epithelial cells, and in vivo in mice (who also express FcRn), ending up in high concentrations in several organs of the body. By contrast, nontargeted nanoparticles were barely visible. To demonstrate the therapeutic benefits of these Fc-targeted nanoparticles, Pridgen et al. administered insulin-laden targeted and nontargeted particles orally to mice. Free insulin given orally did not generate a glucose response in the animals, similar to the nontargeted, insulin-containing particles. However, Fc-targeted nanoparticles containing insulin produced a significant hypoglycemic response in the mice. To confirm that the targeting and epithelial transport is important for this mode of delivery, the authors showed that animals lacking FcRn did not respond to the insulin-filled Fc-targeted nanoparticles. The ability to deliver nanomedicine orally would open doors to treating many chronic diseases that require daily therapy, such as diabetes and cancer. This study by Pridgen et al. is an exciting proof of concept but will require longer periods of testing in disease models to confirm that FcRn targeting is essential and safe for human use. Nanoparticles are poised to have a tremendous impact on the treatment of many diseases, but their broad application is limited because currently they can only be administered by parenteral methods. Oral administration of nanoparticles is preferred but remains a challenge because transport across the intestinal epithelium is limited. We show that nanoparticles targeted to the neonatal Fc receptor (FcRn), which mediates the transport of immunoglobulin G antibodies across epithelial barriers, are efficiently transported across the intestinal epithelium using both in vitro and in vivo models. In mice, orally administered FcRn-targeted nanoparticles crossed the intestinal epithelium and reached systemic circulation with a mean absorption efficiency of 13.7%*hour compared with only 1.2%*hour for nontargeted nanoparticles. In addition, targeted nanoparticles containing insulin as a model nanoparticle-based therapy for diabetes were orally administered at a clinically relevant insulin dose of 1.1 U/kg and elicited a prolonged hypoglycemic response in wild-type mice. This effect was abolished in FcRn knockout mice, indicating that the enhanced nanoparticle transport was specifically due to FcRn. FcRn-targeted nanoparticles may have a major impact on the treatment of many diseases by enabling drugs currently limited by low bioavailability to be efficiently delivered though oral administration.

HER-2-targeted nanoparticle-affibody bioconjugates for cancer therapy.

Affibodies are a class of polypeptide ligands that are potential candidates for cell- or tissue-specific targeting of drug-encapsulated controlled release polymeric nanoparticles (NPs). Here we report the development of drug delivery vehicles comprised of polymeric NPs that are surface modified with Affibody ligands that bind to the extracellular domain of the trans-membrane human epidermal growth factor receptor 2 (HER-2) for targeted delivery to cells which over express the HER-2 antigen. NPs lacking the anti-HER-2 Affibody did not show significant uptake by these cells. Using paclitaxel encapsulated NP-Affibody (1 wt% drug loading), we demonstrated increased cytotoxicity of these bioconjugates in SK-BR-3 and SKOV-3 cell lines. These targeted, drug encapsulated NPAffibody bioconjugates may be efficacious in treating HER-2 expressing carcinoma.

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.

Abstract 367: Engineering of targeted nanoparticles for cancer therapy using internalizing aptamers isolated by cell-uptake selection

There has been a substantial interest in the development of targeted nanoparticles (NPs) that provide increased efficacy and lower toxicity for cancer therapy. One of the major obstacles has been the paucity of optimal targeting ligands that can discriminate between the expression of antigens on cancer cells and normal cells, and subsequently deliver a therapeutic payload into the cancer cells. Using prostate cancer (PCa) as a model disease, we have addressed the difficulty by developing a “cell-uptake selection” strategy to isolate PCa-specific internalizing 2′-O-methyl RNA aptamers (Apts). Twelve cycles of selection and counter-selection were done to obtain a panel of PCa-specific internalizing Apts, with little or no internalization into non-prostate and normal prostate cells. After Apt characterization, size minimization, improvement of nuclease stabilization, and conjugation of the Apts with fluorescently-labeled polymeric NPs, the NP-Apt bioconjugates exhibit PCa specificity and enhancement in cellular uptake when compared to non-targeted NPs lacking the internalizing Apts. Furthermore, when docetaxel (Dtxl), a chemotherapeutic agent used for the treatment of PCa, was encapsulated within the NP-Apt, a significant improvement in cytotoxicity was achieved in targeted PCa cells. Further application of this Apt by conjugating with gold nanorods demostrated remarkable anti-tumor efficacy in vivo. To our knowledge, this is the first report of designing selection to enrich cancer cell-specific internalizing aptamers rather than highest affinity aptamers in previously reported selection process. A similar cell-uptake selection strategy may be used for developing specific internalizing ligands for a myriad of other diseases and can potentially facilitate delivering various molecules, including drugs and siRNAs, into cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 367. doi:10.1158/1538-7445.AM2011-367