Self-assembled structures in Nature play essential roles in living systems, such as, in protein folding and the formation of biological membranes. The formation of most biological nanostructures is driven by self-assembly processes. For example, the self-assembly of phospholipids forms cell membranes, DNA forms a double helix through specific hydrogen bonding of individual strands, and proteins form by the folding of polypeptide chains to make defined tertiary and quaternary structures. Nature has inspired us to make biomimetic self-assembled structures. Furthermore, the assembly and transformation of biomacromolecules in response to a signal (or a stimulus) is an important component to most of Nature’s functions and signaling mechanisms. Given the versatile nature of such stimuli-responsive assembly and disassembly processes, it is desirable to understand and develop ways by which artificial, responsive supramolecular assemblies could be achieved. Development of artificial assemblies with nature’s specificity and versatility stands as an enormous intellectual challenge and custom-designed stimuli-sensitive supramolecular assemblies have potential in a variety of applications.
The research theme of the Ryu research group is the development of new disease therapy using supramolecular approach (Supramolecular Therapeutics). The Ryu group have developed the drug-free approach for a new anti-cancer therapy, that intracellular (supramolecular) polymerization inside the mitochondria induced the dysfunction of mitochondria by disrupting the membrane, resulting in the selective apoptosis of cancer cells. In addition, the Ryu group have developed a facile synthetic method for highly stable, polymer/protein-modified hollow nanoparticles using a non-covalent approach to enhance in vivo efficacy and target ability to caner.
Intracellular Bioactive Supramolecular Assembly
The formation of most biological nanostructures is driven by self-assembly processes and the structured biomaterials have biochemical activities such as enzyme activity and protein signaling. The artificial assembly of synthetic building units inside a living cell and the interaction of these units with the cellular components have rarely been studied, but are emerging as an intriguing strategy to control cellular fate. In particular, self-assembly inside cellular organelles is challenging because of the practical difficulty in observing the complex intracellular environment, and thus has not yet been reported. Achievement of artificial self-assembly of small molecules inside such organelles could be an advanced strategy for an efficient external control over organelle function and manipulation of the cellular fate.
Organelle Localization Induced Self assembly of Peptide Amphiphile to Control the Cell fate
Self assembly is a well established phenomenon over decades, however self assembly of building units to form interesting nano structures inside living cells are something amazing and is exciting when they could control the cellular fate like proliferation, apoptosis and metabolism. Self assembly is an equilibrium process between the individual building units and their aggregated state, and the concentration of the molecules should be over the critical value to induce assembly. So it is critical to think about reducing the effective concentration for more practicability. An Organalle Localization Induced Self assembly (OLISA) is more promising and reliable. In here, the building units accumulate inside cellular organelle, thereby increasing the effective concentration (~500-1000) compared with feeding concertation. OLISA is a pioneering approach which open up huge possibility to control the cell fate as well as investigating cellular pathways and functions.
The artificial assembly of synthetic building units inside a living cell and the interaction of these units with the cellular components have rarely been studied, but are emerging as an intriguing strategy to control cellular fate. In particular, self-assembly inside cellular organelles is challenging because of the practical difficulty in observing the complex intracellular environment, and thus has been rarely reported. Achievement of artificial self-assembly of small molecules inside such organelles could be an advanced strategy for an efficient external control over organelle function and manipulation of the cellular fate. Considering the role of vicious mitochondrial fibril proteins such as amyloid beta (Aβ) in Alzheimer’s disease, we hypothesized that artificial induction of fibril formation inside the mitochondria could promote mitochondrial dysfunction and induce cell damage. Amphiphilic peptides with a mitochondrial targeting unit selectively accumulate in the mitochondria and self-assemble into an ordered structure because inside the confined organelle, the concentration of the peptides is significantly increased over their critical aggregation concentration. The fibrous structure inside the mitochondria then disrupts the mitochondrial membrane to cause leakage of the mitochondrial contents into the cytosol, resulting in severe damage to the cells. This was the first example showing spatiotemporal self-assembly of peptide amphiphiles to cause mitochondrial dysfunction.
Nanomedicine for Cancer Therapy
Noncovalent Polymer Gatekeeper in Mesoporous Nanparticles
Non-covalently binding drug molecules and then releasing them in response to an external trigger has been an important goal. Mesoporous silica nanoparticles with gatekeeper strategies could release the drug molecules in response to specific stimuli. However, it requires complex chemical modification of mesoporous silica nanoparticles, hence limiting their capability to encapsulate high amount of drug and versatility for ligand functionalization. We developed a novel polymer gatekeeper that can noncovalently block the pores of mesoporous silica nanoparticles and be simply modified with targeting ligands. Hydrophilic/hydrophobic drug molecules can be encapsulated at high doses, since the mesoporous silica nanoparticles are not chemically modified, thereby providing maximum pore volume. Moreover, noncovalently encapsulated drugs can be released in response to intracellular glutathione concentrations after cellular internalization by receptor-mediated uptake.
Protein Gatekeeper in Mesoporous Nanparticles
As a ‘Magic Bullet’ concept, cancer targeting nanomaterials have been extensively attempted by coating their surfaces with small molecules, peptides, proteins, and antibodies, but the tumor targeting and therapeutic efficacy still exhibits only a modest improvement. There is increasing evidence (Dawson et al. Nat Nanotechnol(2013), Stauber et al. Nat Nanotechnol(2013), and Wurm et al. Nat Nanotechnol(2016)) that the inefficient targeting can be associated with deleterious interactions of nanomaterials with proteins and consequent change (protein corona formation) on the surfaces when exposed to physiological environments. However, molecular mechanism of the interactions occurring on the interfaces between nanomaterials and proteins remains largely unknown and furthermore there is a challenge to regulate the nanoparticle–biological interactions that provides profound impacts on cancer therapy. We showed the development of supramolecularly pre-coated protein corona shield on nanoparticles and the investigation for the mechanism involved in regulating the nanoparticle– biological interactions. We developed mesoporous nanoparticles pre-coated with a recombinant fusion protein featuring HER2-binding affibody molecule and glutathione-S-transferase. Upon stabilized in preferred orientations on nanoparticle, the pre-coated proteins as a corona minimize interactions with serum proteins to prevent the clearance of these particles by macrophages, while ensuring their targeting function in vitro and in vivo. These findings provide a new targeting platform for the biomedical community.
Nanomachine for Cell Penetration
Mitochondria Targeting Drug
Mitochondrial TRAP1 inhibitor
The crystal structures of human TRAP1 complexed with Hsp90 inhibitors conjugated to a mitochondria-targeting moiety was developed, and we investigated the rational development of a mitochondria-targeted Hsp90 inhibitor to specifically inactivate TRAP1. We showed crystal structures of both the open and closed TRAP1 conformations, and can, therefore, suggest molecular mechanisms of conformational change during the TRAP1 ATPase cycle, which will also aid in understanding the general mechanisms of Hsp90 chaperone function. In regard to development of mitochondrial Hsp90 inhibitors as cancer drugs, we clearly demonstrated that TRAP1 predominates over Hsp90 in cancer cell mitochondria and showed limitations of current Hsp90 inhibitors for inactivating the mitochondrial pool of TRAP1, primarily due to inefficient accumulation in mitochondria. Instead of designing specific inhibitors to the TRAP1 ATP pocket, we generated mitochondrial TRAP1-selective inhibitors by modifying current Hsp90 inhibitors to become “mitochondria-specific”. The concept of “organelle-specific” can be broadly applied to increase drug efficacy and minimize side effects for many drugs targeting proteins in mitochondria.
Mitochondrial Targeted Photodynamic Therapy
Photodynamic therapy (PDT) has widely accepted as a non-invasive tool for cancer treatment. However, there are few limiting factors that retard the therapeutic efficacy of the techniques. Targeting mitochondria has proven to be an effective strategy in many treatment modalities. Near IR absorbing dye, particularly IR-780 was widely used in PDT because of their high absorption in the far red/NIR region and mitochondria targeting ability. However, poor photostabilty, water solubility, and low mitochondrial co-localization limit the efficacy. We introduced a new indocyanine derivative (IR-Pyr), which was chemically modified with two pyridinium ions, to make highly water soluble, exhibit higher mitochondrial localization and better photostability than IR-780. In order to make it more specific to cancer-mitochondria we constructed a supramolecular aggregate using electrostatic interactions between the positively charged IR-Pyr and negatively charged hyaluronic acid (HA). The cancermitochondria targeting strategy assures the high PDT efficacy that proved by in vitro and in vivo experiments.
The low selectivity of sensitizers for cancer cells has still been an issue of the unwanted side effect into healthy tissue and overexpression of antiapoptotic agents during PDT is a major hurdle to attaining high therapeutic efficacy. We designed and synthesized a multifunctional conjugate IR-PU that addresses these issues. IR-PU contains mitochondria targeting group (pyridinium), heat shock protein (HSP) inhibitor (PU-H71 moiety), and the photosensitizer (indocyanine derivative). IR-PU binds Hsp90 family proteins such as Hsp90 and TRAP1 with 100-times greater affinity in cancer cells than it does the inactive forms of these proteins in normal cells, leading to selective accumulation in cancer cells and concomitant inhibition of their molecular chaperon activity. Furthermore, mitochondria-targeted PDT can rapidly damage the biological functions of the organelles under photoactivation, leading to the death of tumor cells. The approach will be useful in the production of a new generation of active molecules with improved therapeutic efficacy.
Supramolecular Assembly for Energy Materials
Multifunctional Molecular Design as an Efficient Polymeric Binder for Silicon Anodes in Lithium-Ion Batteries