Perceptions and Misconceptions in Molecular Recognition: Key Factors in Self-Assembling Multivalent (SAMul) Ligands/Polyanions Selectivity

Biology is dominated by polyanions (cell membranes, nucleic acids, and polysaccharides just to name a few), and achieving selective recognition between biological polyanions and synthetic systems currently constitutes a major challenge in many biomedical applications, nanovectors-assisted gene delivery being a prime example. This review work summarizes some of our recent efforts in this field; in particular, by using a combined experimental/computation approach, we investigated in detail some critical aspects in self-assembled nanomicelles and two major polyanions—DNA and heparin.

Lost in (Clinical) Translation: Recent Advances in Heparin Neutralization and Monitoring

The heparin family, which includes unfractionated heparin, low-molecular heparin, and fondaparinux, is a class of drugs clinically used as intravenous blood thinners. To date, issues related to both the reversal of anticoagulation and the blood level determination of the anticoagulant at the point-of-care remain: while the only U.S. Food and Drug Administration (FDA) approved antidote for heparin displays serious efficacy and safety drawbacks, the current assays for heparin monitoring are indirect measurements subject to their own limitations and variations. Herein, we provide an update on the numerous recent chemical approaches to tackle these issues, from which it is clear that some new antidotes and sensors for heparin certainly have the potential to exceed current clinical standards. This review aims to review a field that requires close collaborations between physicians, biologists, and chemists in order to foster advances toward clinical translation.

From fundamental supramolecular chemistry to self-assembled nanomaterials and medicines and back again – how Sam inspired SAMul

Personal inspiration led to the development of a programme of research targeting the use of self-assembled systems in nanomedicine, which in the process of approaching a range of applications has uncovered new fundamental concepts in supramolecular science.

Multi-component hybrid hydrogels - understanding the extent of orthogonal assembly and its impact on controlled release

This paper reports self-assembled multi-component hybrid hydrogels including a range of nanoscale systems and characterizes the extent to which each component maintains its own unique functionality, demonstrating that multi-functionality can be achieved by simply mixing carefully-chosen constituents. Specifically, the individual components are: (i) pH-activated low-molecular-weight gelator (LMWG) 1,3;2,4-dibenzylidenesorbitol-4',4''-dicarboxylic acid (DBS-COOH), (ii) thermally-activated polymer gelator (PG) agarose, (iii) anionic biopolymer heparin, and (iv) cationic self-assembled multivalent (SAMul) micelles capable of binding heparin. The LMWG still self-assembles in the presence of PG agarose, is slightly modified on the nanoscale by heparin, but is totally disrupted by the micelles. However, if the SAMul micelles are bound to heparin, DBS-COOH self-assembly is largely unaffected. The LMWG endows hybrid materials with pH-responsive behavior, while the PG provides mechanical robustness. The rate of heparin release can be controlled through network density and composition, with the LMWG and PG behaving differently in this regard, while the presence of the heparin binder completely inhibits heparin release through complexation. This study demonstrates that a multi-component approach can yield exquisite control over self-assembled materials. We reason that controlling orthogonality in such systems will underpin further development of controlled release systems with biomedical applications.

Emergence of highly-ordered hierarchical nanoscale aggregates on electrostatic binding of self-assembled multivalent (SAMul) cationic micelles with polyanionic heparin

Self assembled cationic micelles form well-defined structurally ordered hierarchical nanoscale aggregates on interaction with polyanionic heparin in solution.

Electrostatic binding of polyanions using self-assembled multivalent (SAMul) ligand displays - structure-activity effects on DNA/heparin binding

This paper reports that modifying the ligands in self-assembled multivalent (SAMul) displays has an impact on apparent binding selectivity towards two nanoscale biological polyanions - heparin and DNA. For the nanostructures assayed here, spermidine ligands are optimal for heparin binding but spermine ligands are preferred for DNA. Probing subtle differences in such nanoscale binding interfaces is a significant challenge, and as such, several experimental binding assays - competition assays and isothermal calorimetry - are employed to confirm differences in affinity and provide thermodynamic insights. Given the dynamic nature and hierarchical binding processes involved in SAMul systems, we employed multiscale modelling to propose reasons for the origins of polyanion selectivity differences. The modelling results, when expressed in thermodynamic terms and compared with the experimental data, suggest that DNA is a shape-persistent polyanion, and selectivity originates only from ligand preferences, whereas heparin is more flexible and adaptive, and as such, actively reinforces ligand preferences. As such, this study suggests that inherent differences between polyanions may underpin subtle binding selectivity differences, and that even simple electrostatic interfaces such as these can have a degree of tunability, which has implications for biological control and regulation on the nanoscale.

Chiral recognition at self-assembled multivalent (SAMul) nanoscale interfaces – enantioselectivity in polyanion binding

We investigate structure–activity effect relationships at the nanoscale chiral molecular recognition interface between enantiomeric self-assembled multivalent (SAMul) systems and biological polyanions, heparin and DNA.

Monitoring clinical levels of heparin in human blood samples with an indicator-displacement assay

We report that a "tree-like" polymer of lysine is able to form a multi-ligand complex with a fluorescently labelled peptide, leading to the almost complete extinction of the optical signal that can be restored upon the introduction of heparin. This simple system allows, for the first time, the turn-ON fluorescent sensing of the anticoagulant in human blood at clinically relevant levels.

Structure–activity relationship study of dendritic polyglycerolamines for efficient siRNA transfection

Structure–activity relationship studies were performed through in vitro, in silico, and in vivo analysis in order to evaluate the gene transfection potential of dendritic polyglycerolamines with different amine loadings.

Ultra-sensitive detection of heparin via aPTT using plastic antibodies on QCM-D platform

One of the challenges faced by today's clinics is unavailability of practical, precise and accurate determination of the most commonly used anti-coagulant ‘heparin’ in human blood/plasma in surgery.