Nucleinsäure- und Peptidaptamere: Grundlagen und bioanalytische Aspekte

Electrostatics Explains the Position-Dependent Effect of G⋅U Wobble Base Pairs on the Affinity of RNA Kissing Complexes

In the RNA realm, non-Watson-Crick base pairs are abundant and can affect both the RNA 3D structure and its function. Here, we investigated the formation of RNA kissing complexes in which the loop-loop interaction is modulated by non-Watson-Crick pairs. Mass spectrometry, surface plasmon resonance, and UV-melting experiments show that the G⋅U wobble base pair favors kissing complex formation only when placed at specific positions. We tried to rationalize this effect by molecular modeling, including molecular mechanics Poisson-Boltzmann surface area (MMPBSA) thermodynamics calculations and PBSA calculations of the electrostatic potential surfaces. Modeling reveals that the G⋅U stabilization is due to a specific electrostatic environment defined by the base pairs of the entire loop-loop region. The loop is not symmetric, and therefore the identity and position of each base pair matters. Predicting and visualizing the electrostatic environment created by a given sequence can help to design specific kissing complexes with high affinity, for potential therapeutic, nanotechnology or analytical applications.

Syntheses of Platinum-Sulindac Complexes and Their Nanoparticles as Targeted Anticancer Drugs

Platinum(II)-sulindac complexes [{η² -C₅ H₄ SN(O)}Pt(DMSO){O(C=O)Sulindac}], [{η² -C₅ H₄ SN(O)}PtCl{(S=O)Sulindac}], [{η² -C₅ H₄ SN(O)}PtCl{(S=O)Sulindac-succinimide}], and [{η² -C₅ H₄ SN(O)}PtCl{(S=O)Sulindac-thymidine}] were synthesized that exhibited IC₅₀ values of 2.9-4.8 μm against human oral cancer cells OECM1. The poly(lactic-co-glycolic acid) (PLGA) encapsulated [{η² -C₅ H₄ SN(O)}PtCl{(S=O)Sulindac}] also showed cytotoxic activity although less potent than the pristine species.

Nucleic acid aptamer-mediated drug delivery for targeted cancer therapy

Aptamers are emerging as promising therapeutic agents and recognition elements. In particular, cell-SELEX (systematic evolution of ligands by exponential enrichment) allows in vitro selection of aptamers selective to whole cells without prior knowledge of the molecular signatures on the cell surface. The advantage of aptamers is their high affinitiy and binding specificity towards the target. This Minireview focuses on single-stranded (ss) oligonucleotide (DNA or RNA)-based aptamers as cancer therapeutics/theranostics. Specifically, aptamer-nanomaterial conjugates, aptamer-drug conjugates, targeted phototherapy and targeted biotherapy are covered in detail. In reviewing the literature, the potential of aptamers as delivery systems for therapeutic and imaging applications in cancer is clear, however, major challenges remain to be resolved, such as the poorly understood pharmacokinetics, toxicity and off-target effects, before they can be fully exploited in a clinical setting.

Riboswitches based on kissing complexes for the detection of small ligands

Biosensors derived from aptamers were designed for which folding into a hairpin shape is triggered by binding of the cognate ligand. These aptamers (termed aptaswitches) thus switch between folded and unfolded states in the presence and absence of the ligand, respectively. The apical loop of the folded aptaswitch is recognized by a second hairpin called the aptakiss through loop-loop or kissing interactions, whereas the aptakiss does not bind the unfolded aptaswitch. Therefore, the formation of a kissing complex signals the presence of the ligand. Aptaswitches were designed that enable the detection of GTP and adenosine in a specific and quantitative manner by surface plasmon resonance when using a grafted aptakiss or in solution by anisotropy measurement with a fluorescently labeled aptakiss. This approach is generic and can potentially be extended to the detection of any molecule for which hairpin aptamers have been identified, as long as the apical loop is not involved in ligand binding.