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.
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