Coupling Aptamers to Short Interfering RNAs as Therapeutics

Functional Blockade of E-Selectin in Tumor-Associated Vessels Enhances Anti-Tumor Effect of Doxorubicin in Breast Cancer

Chemotherapy is a mainstay of treatment for solid tumors. However, little is known about how therapy-induced immune cell infiltration may affect therapy response. We found substantial CD45⁺ immune cell density adjacent to E-selectin expressing inflamed vessels in doxorubicin (DOX)-treated residual human breast tumors. While CD45 level was significantly elevated in DOX-treated wildtype mice, it remained unchanged in DOX-treated tumors from E-selectin null mice. Similarly, intravenous administration of anti-E-selectin aptamer (ESTA) resulted in a significant reduction in CD45⁺ immune cell density in DOX-treated residual tumors, which coincided with a delay in tumor growth and lung metastasis in MMTV-pyMT mice. Additionally, both tumor infiltrating T-lymphocytes and tumor associated-macrophages were skewed towards T_H2 in DOX-treated residual breast tumors; however, ESTA suppressed these changes. This study suggests that DOX treatment instigates de novo intratumoral infiltration of immune cells through E-selectin, and functional blockade of E-selectin may reduce residual tumor burden as well as metastasis through suppression of T_H2 shift.

Aptamer Therapeutics in Cancer: Current and Future

Aptamer-related technologies represent a revolutionary advancement in the capacity to rapidly develop new classes of targeting ligands. Structurally distinct RNA and DNA oligonucleotides, aptamers mimic small, protein-binding molecules and exhibit high binding affinity and selectivity. Although their molecular weight is relatively small—approximately one-tenth that of monoclonal antibodies—their complex tertiary folded structures create sufficient recognition surface area for tight interaction with target molecules. Additionally, unlike antibodies, aptamers can be readily chemically synthesized and modified. In addition, aptamers’ long storage period and low immunogenicity are favorable properties for clinical utility. Due to their flexibility of chemical modification, aptamers are conjugated to other chemical entities including chemotherapeutic agents, siRNA, nanoparticles, and solid phase surfaces for therapeutic and diagnostic applications. However, as relatively small sized oligonucleotides, aptamers present several challenges for successful clinical translation. Their short plasma half-lives due to nuclease degradation and rapid renal excretion necessitate further structural modification of aptamers for clinical application. Since the US Food and Drug Administration (FDA) approval of the first aptamer drug, Macugen^® (pegaptanib), which treats wet-age-related macular degeneration, several aptamer therapeutics for oncology have followed and shown promise in pre-clinical models as well as clinical trials. This review discusses the advantages and challenges of aptamers and introduces therapeutic aptamers under investigation and in clinical trials for cancer treatments.

Nucleic acid aptamer-guided cancer therapeutics and diagnostics: the next generation of cancer medicine

Conventional anticancer therapies, such as chemo- and/or radio-therapy are often unable to completely eradicate cancers due to abnormal tumor microenvironment, as well as increased drug/radiation resistance. More effective therapeutic strategies for overcoming these obstacles are urgently in demand. Aptamers, as chemical antibodies that bind to targets with high affinity and specificity, are a promising new and novel agent for both cancer diagnostic and therapeutic applications. Aptamer-based cancer cell targeting facilitates the development of active targeting in which aptamer-mediated drug delivery could provide promising anticancer outcomes. This review is to update the current progress of aptamer-based cancer diagnosis and aptamer-mediated active targeting for cancer therapy in vivo, exploring the potential of this novel form of targeted cancer therapy.

Aptamers: multifunctional molecules for biomedical research

Aptamers are single-stranded oligonucleotides that fold into well-defined three-dimensional shapes, allowing them to bind their targets with high affinity and specificity. They can be generated through an in vitro process called "Systemic Evolution of Ligands by Exponential Enrichment" and applied for specific detection, inhibition, and characterization of various targets like small organic and inorganic molecules, proteins, and whole cells. Aptamers have also been called chemical antibodies because of their synthetic origin and their similar modes of action to antibodies. They exhibit significant advantages over antibodies in terms of their small size, synthetic accessibility, and ability to be chemically modified and thus endowed with new properties. The first generation of aptamer drug "Macugen" was available for public use within 25 years of the discovery of aptamers. With others in the pipeline for clinical trials, this emerging field of medical biotechnology is raising significant interest. However, aptamers pose different problems for their development than for antibodies that need to be addressed to achieve practical applications. It is likely that current developments in aptamer engineering will be the basis for the evolution of improved future bioanalytical and biomedical applications. The present review discusses the development of aptamers for therapeutics, drug delivery, target validation and imaging, and reviews some of the challenges to fully realizing the promise of aptamers in biomedical applications.

Targeted delivery of Epirubicin to cancer cells by PEGylated A10 aptamer

Clinical administrations of anthracyclines are limited by cardiotoxicity and myelosuppression. Targeted delivery of anticancer agents is especially important in reducing their side effects. In this work, A10 (Apt), an aptamer for prostate-specific membrane anytigen (PSMA), was applied for targeted delivery of Epirubicin (Epi) to LNCaP cells (PSMA(+)). Flow cytometry analysis showed that PEG-Apt-Epi complex was internalized effectively to LNCaP cells (PSMA(+)), but not to PC3 cells (PSMA(-)). This fact was confirmed by less cytotoxicity of PEG-Apt-Epi complex in PC3 cells in comparison with Epi alone. No significant change in viability between Epi- and complex-treated LNCaP cells was observed. In conclusion, PEG-Apt-Epi complex is an efficient and simple system for specific delivery of drug to PSMA-expressing cell lines.