Postdoctoral Researcher, The University of Chicago, Institute for Molecular Engineering
Using molecular engineering to elucidate the fundamental properties of self-assembling systems
My research goals are based on the applications of chemical techniques to tune the supramolecular interactions of self-assembling molecules. In self-assembly processes, fundamental building blocks organize themselves into functional structures as driven by the physicochemical properties of the system. Sufficient combinations of rationally placed interactions can produce the reversible self-assembly of stable structures, with these structures presenting a highly tunable and modular platform for a variety of applications. I use these powerful methodologies to surmount the key challenges for peptide-based therapeutics, diagnostics, and delivery platforms for biomedical applications. Furthermore, I use these approaches to elucidate the fundamental properties of self-assembling systems, in order to push the boundaries of molecular science for clinical applications. I am using my expertise to engineer programmable self-assembling peptides to expand the field of drug development. With both chemical tools and engineering approaches, I aim to understand and manipulate biological systems using biocompatible therapeutics at the nanoscale. To enable new translational clinical technologies, my research focuses on molecular designs that incorporate these aspects into novel materials.
Abstract: Attacking the supportive vasculature network of a tumor offers an important new avenue for cancer therapy. Herein, a near-infrared (NIR) laser-activated "nanobomb" was developed as a noninvasive and targeted physical therapeutic strategy to effectively disrupt tumor neovasculature in an accurate and expeditious manner. This "nanobomb" was rationally fabricated via the encapsulation of vinyl azide (VA) into c(RGDfE) peptide-functionalized, hollow copper sulfide (HCuS) nanoparticles. The resulting RGD@HCuS(VA) was selectively internalized into integrin αvβ3-expressing tumor vasculature endothelial cells and dramatically increased the photoacoustic signals from the tumor neovasculature, achieving a maximum signal-to-noise ratio at 4 h post-injection. Upon NIR irradiation, the local temperature increase triggered VA to release N2 bubbles rapidly. Subsequently, these N2 bubbles could instantly explode to destroy the neovasculature and further induce necrosis of the surrounding tumor cells. A single-dose injection of RGD@HCuS(VA) led to complete tumor regression after laser irradiation, with no tumor regrowth for 30 days. More importantly, high-resolution photoacoustic angiography, combined with excellent biodegradability, facilitated the precise destruction of tumor neovasculature by RGD@HCuS(VA) without damaging normal tissues. These results demonstrate the great potential of this "nanobomb" for clinical translation to treat cancer patients with NIR laser-accessible orthotopic tumors.
Pub.: 05 Jun '17, Pinned: 04 Jul '17
Abstract: In recent years, spherical nanoparticles has been studied extensively on biomedical applications including bioimaging and biosensing, diagnostics and theranostics, but the effect of the shape of nanoparticles has received little attention. In the present study, we designed three different shaped fluorescent mesoporous silica nanoparticles (MSNs), long rod nanoparticles (NLR), short rod nanoparticles (NSR), and spherical nanoparticles (NS) to systematically examine their behavior in vivo after oral administration. The results of the ex vivo optical imaging study in mice indicated that rod nanoparticles had a longer residence time in the gastrointestinal compared with spherical nanoparticles. The in vivo biodistribution showed that all the orally administered MSNs were mainly taken up by the liver, and kidney. NLR had a great capacity to overcoming rapid clearance by the RES and exhibited a longer circulation in the blood than NSR and NS. During renal excretion, the spherical nanoparticles were cleared faster than rod nanoparticles. In addition, it was also found that MSNs can be degraded in vivo and NSR were degraded faster than NLR and NS probably owing to their higher specific surface area. The pharmacokinetic results demonstrated that nifedipine(NI)-loaded NLR had a higher bioavailability than NI-loaded NSR and NS.
Pub.: 25 Jun '17, Pinned: 04 Jul '17
Abstract: The development of biomaterials with desirable biocompatibility has presented a difficult challenge for tissue engineering researchers. First and foremost, materials themselves tend to be hydrophobic and/or thrombogenic in nature, and face compatibility problems upon implantation. To mediate this problem, researchers have attempted to graft protein fragments onto biomaterial surfaces to promote endothelial cell attachment and minimize thrombosis. We envisioned a novel approach, based on the capability of biomolecules to self-assemble into well-defined and intricate structures, for creating biomimetic biomaterials that promote cell adhesion and proliferation. One of the most intriguing self-assembly processes is the folding of peptide chains into native protein structures. We have developed a method for building protein-like structural motifs that incorporate sequences of biological interest. A lipophilic moiety is attached onto a N alpha-amino group of peptide chain, resulting in a "peptide-amphiphile." The alignment of amphiphilic compounds at the lipid-solvent interface is used to facilitate peptide alignment and structure initiation and propagation, while the lipophilic region absorbs to hydrophobic surfaces. Peptide-amphiphiles containing potentially triple-helical or alpha-helical structural motifs have been synthesized. The resultant head group structures have been characterized by CD spectroscopy and found to be thermally stable over physiological temperature ranges. Triple-helical peptide-amphiphiles have been applied to studies of surface modification and cell receptor binding. Cell adhesion and spreading was promoted by triple-helical peptide-amphiphiles. Cellular interaction with the type IV collagen sequence alpha 1(IV) 1263-1277 increased signal transduction, with both the time and level of induction dependent upon triple-helical conformation. Collectively, these results suggest that peptide-amphiphiles may be used to form stable molecular structure on biomaterial surfaces that promote cellular activities and improve biocompatibility.
Pub.: 15 Aug '98, Pinned: 04 Jul '17
Abstract: Bottom-up fabrication of self-assembled nanomaterials requires control over forces and interactions between building blocks. We report here on the formation and architecture of supramolecular structures constructed from two different peptide amphiphiles. Inclusion of four alanines between a 16-mer peptide and a 16 carbon long aliphatic tail resulted in a secondary structure shift of the peptide headgroups from α helices to β sheets. A concomitant shift in self-assembled morphology from nanoribbons to core-shell worm-like micelles was observed by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). In the presence of divalent magnesium ions, these a priori formed supramolecular structures interacted in distinct manners, highlighting the importance of peptide amphiphile design in self-assembly.
Pub.: 15 Apr '11, Pinned: 04 Jul '17
Abstract: Peptide amphiphile molecules (PA) are remarkably versatile and useful as building blocks for construction of complex supramolecular structures in a bottom-up fashion. Worm-like micelles of PA have been demonstrated to have successful application to creation of synthetic extracellular matrix materials for tissue engineering and regenerative medicine. However, the pathway of the self-assembly process of the PA worm-like micelle has not been fully characterized or understood. This work analyzes the self-assembly process leading to worm-like micelle formation in our designed PA with small-angle neutron scattering and atomic force microscopy. The experimental results demonstrate the existence of transient spherical micelles in the early stage of the process and subsequent micelle chain elongation by attachment of spherical micelles to the end of growing cylindrical micelles to form worm-like micelles in a process mimicking chain-growth polymerization.
Pub.: 06 Dec '11, Pinned: 04 Jul '17
Abstract: We have constructed a novel class of "double-hydrophobic" block polypeptides based on the hydrophobic domains found in native elastin, an extracellular matrix protein responsible for the elasticity and resilience of tissues. The block polypeptides comprise proline-rich poly(VPGXG) and glycine-rich poly(VGGVG), both of which dehydrate at higher temperature but form distinct secondary structures, β-turn and β-sheet respectively. In water at 45 °C, the block polypeptides initially assemble into nanoparticles rich in β-turn structures, which further connect into long (>10 μm), beaded nanofibers along with the increase in the β-sheet content. The nanofibers obtained are well-dispersed in water, and show thermoresponsive properties. Polypeptides comprising each block component assemble into different morphologies, showing that the conjugation of poly(VPGXG) and poly(VGGVG) plays a role for beaded fiber formation. These results may provide innovative ideas for designing peptide-based materials but also opportunities for developing novel materials useful for tissue engineering and drug delivery systems.
Pub.: 19 Mar '13, Pinned: 04 Jul '17
Abstract: Inducing a strong and specific immune response is the hallmark of a successful vaccine. Nanoparticles have emerged as promising vaccine delivery devices to discover and elicit immune responses. Fine-tuning a nanoparticle vaccine to create an immune response with specific antibody and other cellular responses is influenced by many factors such as shape, size, and composition. Peptide amphiphile micelles are a unique biomaterials platform that can function as a modular vaccine delivery system, enabling control over many of these important factors and delivering payloads more efficiently to draining lymph nodes. In this study, the modular properties of peptide amphiphile micelles are utilized to improve an immune response against a Group A Streptococcus B cell antigen (J8). The hydrophobic/hydrophilic interface of peptide amphiphile micelles enabled the precise entrapment of amphiphilic adjuvants which were found to not alter micelle formation or shape. These heterogeneous micelles significantly enhanced murine antibody responses when compared to animals vaccinated with nonadjuvanted micelles or soluble J8 peptide supplemented with a classical adjuvant. The heterogeneous micelle induced antibodies also showed cross-reactivity with wild-type Group A Streptococcus providing evidence that micelle-induced immune responses are capable of identifying their intended pathogenic targets.
Pub.: 28 Sep '16, Pinned: 30 Jun '17
Abstract: We have used tumor-homing peptides to target abraxane, a clinically approved paclitaxel-albumin nanoparticle, to tumors in mice. The targeting was accomplished with two peptides, CREKA and LyP-1 (CGNKRTRGC). Fluorescein (FAM)-labeled CREKA-abraxane, when injected intravenously into mice bearing MDA-MB-435 human cancer xenografts, accumulated in tumor blood vessels, forming aggregates that contained red blood cells and fibrin. FAM-LyP-1-abraxane co-localized with extravascular islands expressing its receptor, p32. Self-assembled mixed micelles carrying the homing peptide and the label on different subunits accumulated in the same areas of tumors as LyP-1-abraxane, showing that Lyp-1 can deliver intact nanoparticles into extravascular sites. Untargeted, FAM-abraxane was detected in the form of a faint meshwork in tumor interstitium. LyP-1-abraxane produced a statistically highly significant inhibition of tumor growth compared with untargeted abraxane. These results show that nanoparticles can be effectively targeted into extravascular tumor tissue and that targeting can enhance the activity of a therapeutic nanoparticle.
Pub.: 03 Oct '08, Pinned: 30 Jun '17
Abstract: Micellar nanoparticles are showing promise as carriers of diagnostic and therapeutic biofunctionality, leading to increased interest in their properties and behavior, particularly their size, shape, and stability. This work investigates the physical chemistry of micelles formed from DSPE-PEG(2000) monomers as it pertains to these properties. A melting transition in the lipid core of spheroidal DSPE-PEG(2000) micelles is observed as an endothermic peak at 12.8 degrees C upon heating in differential scanning calorimetry thermograms. Bulky PEG(2000) head groups prevent regular crystalline packing of lipids in both the low-temperature glassy and high-temperature fluid phases, as evidenced by wide-angle X-ray scattering. Equilibrium micelle geometry is spheroidal above and below the transition temperature, indicating that the entropic penalty to force the PEG brush into flat geometry is greater than the enthalpic benefit to the glassy core to pack in an extended configuration. Increased micelle stability is seen in the glassy phase with monomer desorption rates significantly lower than in the fluid phase. Activation energies for monomer desorption are 156+/-6.7 and 79+/-5.0 kJ/mol for the glassy and fluid phases, respectively. The observation of a glass transition that increases micelle stability but does not perturb micelle geometry is useful for the design of more effective biofunctional micelles.
Pub.: 11 Apr '09, Pinned: 30 Jun '17
Abstract: This work investigated the stability of DSPE-PEG(2000) micelles in the presence of bovine serum albumin (BSA). DSPE-PEG(2000) was found to exist in equilibrium among monomeric, micellar, and BSA-bound states, and this equilibrium shifted toward the BSA-bound state when the temperature increased from 20 to 37 °C. The micellar state is thermodynamically unstable at both temperatures when the concentration of BSA approaches that of DSPE-PEG(2000), and micelle breakup occurs with a first-order time constant of 130 ± 9 min at 20 °C and 7.8 ± 1.6 min at 37 °C. Thus, previous targeting experiments that demonstrate synergistic effects in multiply functionalized DSPE-PEG(2000) micelles are likely due to targeting that occurs on a timescale faster than that of micelle breakup. Micelle breakup was limited by diffusion at 20 °C whereas at 37 °C monomer desorption from the micelle was the rate-limiting step. These findings give clear guidance concerning the lifetimes of micelles that may be used as diagnostic and therapeutic nanoparticles.
Pub.: 11 Sep '10, Pinned: 30 Jun '17
Abstract: Peptides and peptide-conjugates, comprising natural and synthetic building blocks, are an increasingly popular class of biomaterials. Self-assembled nanostructures based on peptides and peptide-conjugates offer advantages such as precise selectivity and multifunctionality that can address challenges and limitations in the clinic. In this review article, we discuss recent developments in the design and self-assembly of various nanomaterials based on peptides and peptide-conjugates for medical applications, and categorize them into two themes based on the driving forces of molecular self-assembly. First, we present the self-assembled nanostructures driven by the supramolecular interactions between the peptides, with or without the presence of conjugates. The studies where nanoassembly is driven by the interactions between the conjugates of peptide-conjugates are then presented. Particular emphasis is given to in vivo studies focusing on therapeutics, diagnostics, immune modulation and regenerative medicine, and challenges and future perspective are presented.
Pub.: 14 Aug '16, Pinned: 30 Jun '17