Target-specific delivery of doxorubicin to retinoblastoma using epithelial cell adhesion molecule aptamer

PURPOSE: To study target-specific delivery of doxorubicin (Dox) using an RNA aptamer against epithelial cell adhesion molecule (EpCAM) in retinoblastoma (RB) cells. METHODS: The binding affinity of the EpCAM aptamer to RB primary tumor cells, Y79 and WERI-Rb1 cells, and Müller glial cell lines were evaluated with flow cytometry. Formation of physical conjugates of aptamer and Dox was monitored with spectrofluorimetry. Cellular uptake of aptamer-Dox conjugates was monitored through fluorescent microscopy. Drug efficacy was monitored with cell proliferation assay. RESULTS: The EpCAM aptamer (EpDT3) but not the scrambled aptamer (Scr-EpDT3) bound to RB tumor cells, the Y79 and WERI-Rb1 cells. However, the EpCAM aptamer and the scrambled aptamer did not bind to the noncancerous Müller glial cells. The chimeric EpCAM aptamer Dox conjugate (EpDT3-Dox) and the scrambled aptamer Dox conjugate (Scr-EpDT3-Dox) were synthesized and tested on the Y79, WERI-Rb1, and Müller glial cells. The targeted uptake of the EpDT3-Dox aptamer caused cytotoxicity in the Y79 and WERI-Rb1 cells but not in the Müller glial cells. There was no significant binding or consequent cytotoxicity by the Scr-EpDT3-Dox in either cell line. The EpCAM aptamer alone did not cause cytotoxicity in either cell line. CONCLUSIONS: The results show that the EpCAM aptamer-Dox conjugate can selectively deliver the drug to the RB cells there by inhibiting cellular proliferation and not to the noncancerous Müller glial cells. As EpCAM is a cancer stem cell marker, this aptamer-based targeted drug delivery will prevent the undesired effects of non-specific drug activity and will kill cancer stem cells precisely in RB.

Aptamer therapeutics: the 21st century's magic bullet of nanomedicine

Aptamers, also known as chemical antibodies, are short single-stranded DNA, RNA or peptide molecules. These molecules can fold into complex three-dimensional structures and bind to target molecules with high affinity and specificity. The nucleic acid aptamers are selected from combinatorial libraries by an iterative in vitro selection procedure known as systematic evolution of ligands by exponential enrichment (SELEX). As a new class of therapeutics and drug targeting entities, bivalent and multivalent aptamer-based molecules are emerging as highly attractive alternatives to monoclonal antibodies as targeted therapeutics.

Aptamers have several advantages, offering the possibility of overcoming limitations of antibodies: 1) they can be selected against toxic or non-immunogenic targets; 2) aptamers can be chemically modified by using modified nucleotides to enhance their stability in biological fluids or via incorporating reporter molecules, radioisotopes and functional groups for their detection and immobilization; 3) they have very low immunogenicity; 4) they display high stability at room temperature, in extreme pH, or solvent; 5) once selected, they can be chemically synthesized free from cell- culturederived contaminants, and they can be manufactured at any time, in large amounts, at relatively low cost and reproducibly; 6) they are smaller and thus can diffuse more rapidly into tissues and organs, leading to faster targeting in drug delivery; 7) they have lower molecular weight that can lead to faster body clearance, resulting in a low background noise for imaging and minimizing the radiation dose to the patient in diagnostic imaging. Thus, the high selectivity and sensitivity, ease of screening and production, chemical versatility as well as stability make aptamers a class of highly attractive agents for the development of novel therapeutics, targeted drug delivery vehicles and molecular imaging.

In the review, we will discuss the latest technological advances in developing aptamers, its application as a novel class of drug on its own, as well as in surface functionalization of both polymer nanoparticles or nanoliposomes in the treatment of cancer, viral and autoimmune diseases.

Aptamer-based therapeutics of the past, present and future: from the perspective of eye-related diseases

 Aptamers have emerged as a novel and powerful class of biomolecules with an immense untapped potential. The ability to synthesise highly specific aptamers against any molecular target make them a vital cog in the design of effective therapeutics for the future. However, only a minutia of the enormous potential of this dynamic class of molecule has been exploited. Several aptamers have been studied for the treatment of eye-related disorders, and one such strategy has been successful in therapy. This review gives an account of several eye diseases and their regulatory biomolecules where other nucleic acid therapeutics have been attempted with limited success and how aptamers, with their exceptional flexibility to chemical modifications, can overcome those inherent shortcomings.

Targeting cancer cell death using aptamer tagged nano-formulated survivin antagonists

 My findings established survivin antagonist SR9 as an efficient anti-cancer therapeutic and highly promising cancer cell and cancer stem cell targeted locked nucleic acid conjugated nanocarriers as a ray of hope for therapy against colon cancer.

Multifunctional nanoparticle-EpCAM aptamer bioconjugates: a paradigm for targeted drug delivery and imaging in cancer therapy

The promising proposition of multifunctional nanoparticles for cancer diagnostics and therapeutics has inspired the development of theranostic approach for improved cancer therapy. Moreover, active targeting of drug carrier to specific target site is crucial for providing efficient delivery of therapeutics and imaging agents. In this regard, the present study investigates the theranostic capabilities of nutlin-3a loaded poly (lactide-co-glycolide) nanoparticles, functionalized with a targeting ligand (EpCAM aptamer) and an imaging agent (quantum dots) for cancer therapy and bioimaging. A wide spectrum of in vitro analysis (cellular uptake study, cytotoxicity assay, cell cycle and apoptosis analysis, apoptosis associated proteins study) revealed superior therapeutic potentiality of targeted drug loaded NPs over other formulations in EpCAM expressing cells. Moreover, our nanotheranostic system served as a superlative bio-imaging modality both in 2D monolayer culture and tumor spheroid model. Our result suggests that, these aptamer-guided multifunctional NPs may act as indispensable nanotheranostic approach toward cancer therapy.

A strain-promoted alkyne-azide cycloaddition (SPAAC) reaction of a novel EpCAM aptamer-fluorescent conjugate for imaging of cancer cells

For the first time, a novel EpCAM aptamer (SYL3C)-DIBO-AF594 fluorescent conjugate was synthesised by bioorthogonal chemistry utilizing a strain promoted alkyne-azide cycloaddition (copper free click) reaction (SPAAC). The ligation efficiency of SPAAC was improved by freeze-thaw cycles. The obtained conjugate showed target specific binding and aided in the imaging of various EpCAM positive cancer cell lines like MCF7, MDAMB453, Weri-RB1 and PC3.

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.

Aptamer-mediated cancer gene therapy

Cancer as a genetic disorder is one of the leading causes of death worldwide. Conventional anticancer options such as chemo- and/or radio-therapy have their own drawbacks and could not provide a cure in most cases at present. More effective therapeutic strategies with less side effects are urgently needed. Aptamers, also known as chemical antibodies, are single strand DNA or RNA molecules that can bind to their target molecules with high affinity and specificity. Such site-specific binding ability of aptamers facilitates the delivery and interaction of exogenous nucleic acids with diseased genes. Thus, aptamer-guided gene therapy has emerged as a promising anticancer strategy in addition to the classic treatment regimen. Aptamers can directly deliver anti-cancer nucleic acids, e.g. small interfering RNA, micro RNA, antimicroRNA and small hairpin RNA, to cancer cells or function as a targeting ligand to guide nanoparticles containing therapeutic nucleic acids. This review focuses on recent progress in aptamer-mediated gene therapy for the treatment of hepatocellular carcinoma and other types of cancers, shedding light on the potential of this novel approach of targeted cancer gene therapy.

An aptamer-mediated siRNA delivery system targeting breast tumourigenic cells

In this study, through developing a RNA interference based gene-knockdown system, the expression of Survivin - a critical gene involved in breast cancer initiation and relapse was silenced. This approach reversed chemo-resistance, transforming Doxorubicin - a classical chemotherapy drug to one able to act on drug-resistant breast cancer stem cells.

Locked nucleic acid aptamer based microfluidic devices for capturing tumor cells

Design and fabrication of novel microfluidic devices for sensitive and specific capture of circulating tumor cells using locked nucleic acid modified aptamers and antibodies targeting EpCAM/Nucleolin expression. These devices also allow re-usability, on-chip characterization of multiple markers and release of viable captured cells for further culture and in vitro characterization for cancer diagnosis, prognosis and therapeutic planning.

Aptamer-targeted oligonucleotide theranostics: a smarter approach for brain delivery and the treatment of neurological diseases

Aptamers represent the novel class of oligonucleotides holding multiple applications in the area of biomedicine. The advancements introduced with the Systematic Evolution of Ligands by EXponential enrichment (SELEX) approach further eased the scope of producing modified aptamers within a short span yet retaining the properties of stability and applicability. In the recent times, aptamers were identified to have the potential for penetrating into the deep human crevices and thus can be utilized in addressing the issues of complex neurological disorders. Considering the specificity and stability enhancement by chemical modifications, aptamer-based nanotechnologies may have great potential for future therapeutics and diagnostics (theranostics). The research community has already witnessed success with the approval of macugen (an anti-vascular endothelial growth factor aptamer) for treating degenerating eye disease, and hopefully those that are in the clinical trials will soon be translated for human application. Herein, we have summarized the aptamer chemistry, aptamer-nanoconjugates and their applications against neurological diseases.

EpCAM aptamer mediated cancer cell specific delivery of EpCAM siRNA using polymeric nanocomplex

BACKGROUND: Epithelial cell adhesion molecule (EpCAM) is overexpressed in solid tumors and regarded as a putative cancer stem cell marker. Here, we report that employing EpCAM aptamer (EpApt) and EpCAM siRNA (SiEp) dual approach, for the targeted delivery of siRNA to EpCAM positive cancer cells, efficiently inhibits cancer cell proliferation. RESULTS: Targeted delivery of siRNA using polyethyleneimine is one of the efficient methods for gene delivery, and thus, we developed a novel aptamer-PEI-siRNA nanocomplex for EpCAM targeting. PEI nanocomplex synthesized with EpCAM aptamer (EpApt) and EpCAM siRNA (SiEp) showed 198 nm diameter sized particles by dynamic light scattering, spherical shaped particles, of 151 ± 11 nm size by TEM. The surface charge of the nanoparticles was -30.0 mV using zeta potential measurements. Gel retardation assay confirmed the PEI-EpApt-SiEp nanoparticles formation. The difference in size observed by DLS and TEM could be due to coating of aptamer and siRNA on PEI nanocore. Flow cytometry analysis revealed that PEI-EpApt-SiEp has superior binding to cancer cells compared to EpApt or scramble aptamer (ScrApt) or PEI-ScrApt-SiEp. PEI-EpApt-SiEp downregulated EpCAM and inhibited selectively the cell proliferation of MCF-7 and WERI-Rb1 cells. CONCLUSIONS: The PEI nanocomplex fabricated with EpApt and siEp was able to target EpCAM tumor cells, deliver the siRNA and silence the target gene. This nanocomplex exhibited decreased cell proliferation than the scrambled aptamer loaded nanocomplex in the EpCAM expressing cancer cells and may have potential for EpCAM targeting in vivo.

Superior performance of aptamer in tumor penetration over antibody : implication of aptamer-based theranostics in solid tumors

Insufficient penetration of therapeutic agents into tumor tissues results in inadequate drug distribution and lower intracellular concentration of drugs, leading to the increase of drug resistance and resultant failure of cancer treatment. Targeted drug delivery to solid tumors followed by complete drug penetration and durable retention will significantly improve clinical outcomes of cancer therapy. Monoclonal antibodies have been commonly used in clinic for cancer treatment, but their limitation of penetrating into tumor tissues still remains because of their large size. Aptamers, as "chemical antibodies", are 15-20 times smaller than antibodies. To explore whether aptamers are superior to antibodies in terms of tumor penetration, we carried out the first comprehensive study to compare the performance of an EpCAM aptamer with an EpCAM antibody in theranostic applications. Penetration and retention were studied in in vitro three-dimensional tumorspheres, in vivo live animal imaging and mouse colorectal cancer xenograft model. We found that the EpCAM aptamer can not only effectively penetrate into the tumorsphere cores but can also be retained by tumor sphere cells for at least 24 h, while limited tumor penetration by EpCAM antibody was observed after 4 h incubation. As observed from in vivo live animal imaging, EpCAM aptamers displayed a maximum tumor uptake at around 10 min followed by a rapid clearance after 80 min, while the signal of peak uptake and disappearance of antibody appeared at 3 h and 6 h after intravenous injection, respectively. The signal of PEGylated EpCAM aptamers in xenograft tumors was sustained for 26 h, which was 4.3-fold longer than that of the EpCAM antibody. Consistently, there were 1.67-fold and 6.6-fold higher accumulation of PEGylated aptamer in xenograft tumors than that of antibody, at 3 h and 24 h after intravenous administration, respectively. In addition, the aptamer achieved at least a 4-time better tumor penetration in xenograft tumors than that of the antibody at a 200 μm distances from the blood vessels 3 h after intravenous injection. Taken together, these data indicate that aptmers are superior to antibodies in cancer theranostics due to their better tumor penetration, more homogeneous distribution and longer retention in tumor sites. Thus, aptamers are promising agents for targeted tumor therapeutics and molecular imaging.