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.

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.

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.

LNA aptamer based multi-modal, Fe3O4-saturated lactoferrin (Fe3O4-bLf) nanocarriers for triple positive (EpCAM, CD133, CD44) colon tumor targeting and NIR, MRI and CT imaging

This is the first ever attempt to combine anti-cancer therapeutic effects of emerging anticancer biodrug bovine lactoferrin (bLf), and multimodal imaging efficacy of Fe3O4 nanoparticles (NPs) together, as a saturated Fe3O4-bLf. For cancer stem cell specific uptake of nanocapsules/nanocarriers (NCs), Fe3O4-bLf was encapsulated in alginate enclosed chitosan coated calcium phosphate (AEC-CP) NCs targeted (Tar) with locked nucleic acid (LNA) modified aptamers against epithelial cell adhesion molecule (EpCAM) and nucleolin markers. The nanoformulation was fed orally to mice injected with triple positive (EpCAM, CD133, CD44) sorted colon cancer stem cells in the xenograft cancer stem cell mice model. The complete regression of tumor was observed in 70% of mice fed on non-targeted (NT) NCs, with 30% mice showing tumor recurrence after 30 days, while only 10% mice fed with Tar NCs showed tumor recurrence indicating a significantly higher survival rate. From tumor tissue analyses of 35 apoptotic markers, 55 angiogenesis markers, 40 cytokines, 15 stem cell markers and gene expression studies of important signaling molecules, it was revealed that the anti-cancer mechanism of Fe3O4-bLf was intervened through TRAIL, Fas, Fas-associated protein with death domain (FADD) mediated phosphorylation of p53, to induce activation of second mitochondria-derived activator of caspases (SMAC)/DIABLO (inhibiting survivin) and mitochondrial depolarization leading to release of cytochrome C. Induction of apoptosis was observed by inhibition of the Akt pathway and activation of cytokines released from monocytes/macrophages and dendritic cells (interleukin (IL) 27, keratinocyte chemoattractant (KC)). On the other hand, the recurrence of tumor in AEC-CP-Fe3O4-bLf NCs fed mice mainly occurred due to activation of alternative pathways such as mitogen-activated protein kinases (MAPK)/extracellular signal-regulated kinases (ERK) and Wnt signaling leading to an increase in expression of survivin, survivin splice variant (survivin 2B) and other anti-apoptotic proteins Bad, Bcl-2 and XIAP. Apart from the promising anti-cancer efficacy and the exceptional tumor targeting ability observed by multimodal imaging using near-infrared (NIR) imaging, magnetic resonance imaging (MRI) and computerized tomographic (CT) techniques, these NCs also maintained the immunomodulatory benefits of bLf as they were able to increase the RBC, hemoglobin, iron calcium and zinc levels in mice.

Aptasensors design considerations

With the advancement of biotechnology, aptamer-based sensors have received intense attention in both research and commercial worlds. This is driven by the advantages of small molecule size, chemical stability, and cost effectiveness of aptamers over the conventional analyte detection using antibodies. This paper explores the aptasensors from a designer perspective and discusses the aptasensor design considerations by giving an overview of surface functionalization techniques and the existing mechanisms used to detect biomolecular interactions. It also expounds the factors that influence the accuracy and sensitivity of aptasensors.

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.

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.

Molecular insights and oligonucleotide based targeted gene therapy against cancer

The thesis helps to unravel the function of T lymphoma invasion and metastasis protein (TIAM1) and nucleolin, a nucleolar protein in retinoblastoma tumorigenesis. Aptamer based targeted imaging; drug and gene delivery to retinoblastoma and epithelial cancer cells was attained. The work work finally opened up avenues for cancer stem cell targeting using aptamers, imaging of cancer cells using novel bio-orthogonal agent and use of aptamer for blocking the miRNA-17-92 cluster maturation.

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.

Nucleic acid-based aptamers: applications, development and clinical trials

Short single-stranded oligonucleotides called aptamers, often termed as chemical antibodies, have been developed as powerful alternatives to traditional antibodies with respect to their obvious advantages like high specificity and affinity, longer shelf-life, easier manufacturing protocol, freedom to introduce chemical modifications for further improvement, etc. Reiterative selection process of aptamers over 10-15 cycles starting from a large initial pool of random nucleotide sequences renders them with high binding affinity, thereby making them extremely specific for their targets. Aptamer-based detection systems are well investigated and likely to displace primitive detection systems. Aptamer chimeras (combination of aptamers with another aptamer or biomacromolecule or chemical moiety) have the potential activity of both the parent molecules, and thus hold the capability to perform diverse functions at the same time. Owing to their extremely high specificity and lack of immunogenicity or pathogenicity, a number of other aptamers have recently entered clinical trials and have garnered favorable attention from pharmaceutical companies. Promising results from the clinical trials provide new hope to change the conventional style of therapy. Aptamers have attained high therapeutic relevance in a short time as compared to synthetic drugs and/or other modes of therapy. This review follows the various trends in aptamer technology including production, selection, modifications and success in clinical fields. It focusses largely on the various applications of aptamers which mainly depend upon their selection procedures. The review also sheds light on various modifications and chimerizations that have been implemented in order to improve the stability and functioning of the aptamers, including introduction of locked nucleic acids (LNAs). The application of various aptamers in detection systems has been discussed elaborately in order to stress on their role as efficient diagnostic agents. The key aspect of this review is focused on success of aptamers on the basis of their performance in clinical trials for various diseases.

Wireless video-based sensor networks for surveillance of residential districts

Compared to traditional wired video sensor networks to supervise a residential district, Wireless Video-based Sensor Networks (WVSN) can provide more detail and precise information while reduce the cost. However, state-of-the-art low cost wireless video-based sensors have very constrained resources such as low bandwidth, small storage, limited processing capability, and limited energy resource. Also, due to the special sensing range of video-based sensors, cluster-based routing is not as effective as it apply to traditional sensor networks. This paper provides a novel real-time change mining algorithm based on an extracted profile model of moving objects learnt from frog's eyes. Example analysis shows the extracted profile would not miss any important semantic images to send to the Base Station for further hazards detection, while efficiently reducing futile video stream data to the degree that nowadays wireless video sensor can realize. Thus it makes WVSN available to surveillance of residential districts.

Targeting cancer cells using LNA-modified aptamer-siRNA chimeras

Aptamers are chimerized with drug or antisense oligos or nanoparticles to generate targeted therapeutics for cancer. Aptamer chimerized siRNA rescues nonspecific delivery and, thereby, enhances the availability of siRNA to target cells. EpCAM RNA aptamer (EpApt or Ep) has potential for siRNA chimerization due to its secondary structure. Stathmin and survivin proteins are reported to aid oncogenicity in retinoblastoma (RB), breast cancer and other cancers. Thus, chimerization of EpCAM Apt with siRNA against survivin and stathmin, respectively, was performed by incorporating Locked Nucleic Acid (LNA) modification. The LNA-modified chimeric aptamers were stable until 96 h and got internalized into RB, WERI-Rb1 and breast cancer, MDAMB453 cell lines. The constructs were studied using the recombinant dicer enzyme for the siRNA generation. Quantitative polymerase chain reaction and immunofluorescence by microscopic analysis of chimeras in vitro exhibited silencing of stathmin and survivin in the RB and breast cancer model. The chimeric constructs showed significant inhibition of cell proliferation of breast cancer cells. Thus, LNA-modified aptamer-based siRNA delivery aids in cell targeting and necessitates further studies in animal models.

Object grasping and safe manipulation using friction-based sensing.

This project provides a solution for slippage prevention in industrial robotic grippers for the purpose of safe object manipulation. Slippage sensing is performed using novel friction-based sensors, with customisable slippage sensitivity and complemented by an effective slippage prediction strategy. The outcome is a reliable and affordable slippage prevention technology.

A low-cost intelligent gas sensing device for military applications

The field of electronic noses and gas sensing has been developing rapidly since the introduction of the silicon based sensors. There are numerous systems that can detect and indicate the level of a specific gas. We introduce here a system that is low power, small and cheap enough to be used in mobile robotic platforms while still being accurate and reliable enough for confident use. The design is based around a small circuit board mounted in a plastic case with holes to allow the sensors to protrude through the top and allow the natural flow of gas evenly across them. The main control board consists of a microcontroller PCB with surface mount components for low cost and power consumption. The firmware of the device is based on an algorithm that uses an Artificial Neural Network (ANN) which receives input from an array of gas sensors. The various sensors feeding the ANN allow the microcontroller to determine the gas type and quantity. The Testing of the device involves the training of the ANN with a number of different target gases to determine the weightings for the ANN. Accuracy and reliability of the ANN is validated through testing in a specific gas filled environment.