Synthetic intrinsically disordered protein fusion tags that enhance protein solubility.

We report the de novo design of small (<20 kDa) and highly soluble synthetic intrinsically disordered proteins (SynIDPs) that confer solubility to a fusion partner with minimal effect on the activity of the fused protein. To identify highly soluble SynIDPs, we create a pooled gene-library utilizing a one-pot gene synthesis technology to create a large library of repetitive genes that encode SynIDPs. We identify three small (<20 kDa) and highly soluble SynIDPs from this gene library that lack secondary structure and have high solvation. Recombinant fusion of these SynIDPs to three known inclusion body forming proteins rescue their soluble expression and do not impede the activity of the fusion partner, thereby eliminating the need for removal of the SynIDP tag. These findings highlight the utility of SynIDPs as solubility tags, as they promote the soluble expression of proteins in E. coli and are small, unstructured proteins that minimally interfere with the biological activity of the fused protein.

Enzymatic Synthesis of Aptamer-Polynucleotide Nanoparticles with High Anticancer Drug Loading for Targeted Delivery.

We report a targeted prodrug delivery platform that can deliver a cytostatic nucleobase analog with high drug loading. We chose fluorouracil (5FU), a drug used to treat various cancers, whose active metabolite 5-fluorodeoxyuridine monophosphate (5-FdUMP) is the antineoplastic agent. We use terminal deoxynucleotidyl transferase (TdT) to polymerize 5-fluorodeoxyuridine triphosphate (5-FdUTP) onto the 3'-end of an aptamer. We find that (i) addition of hydrophobic, unnatural nucleotides at the 3'-end of the 5-FdU polynucleotide by TdT leads to their spontaneous self-assembly into nuclease resistant micelles, (ii) aptamers presented on the micelle corona retain specificity for their cognate receptor on tumor cells, and (iii) the micelles deliver 5FU to tumor cells and exhibit greater cytotoxicity than the free drug. The modular design of our platform, consisting of a targeting moiety, a polynucleotide drug, and a self-assembly domain, can be adapted to encompass a range of polymerizable therapeutic nucleotides and targeting units.

Genetically Engineered Nanoparticles of Asymmetric Triblock Polypeptide with a Platinum(IV) Cargo Outperforms a Platinum(II) Analog and Free Drug in a Murine Cancer Model.

The development of platinum(Pt)-drugs for cancer therapy has stalled, as no new Pt-drugs have been approved in over a decade. Packaging small molecule drugs into nanoparticles is a way to enhance their therapeutic efficacy. To date, there has been no direct comparison of relative merits of the choice of Pt oxidation state in the same nanoparticle system that would allow its optimal design. To address this lacuna, we designed a recombinant asymmetric triblock polypeptide (ATBP) that self-assembles into rod-shaped micelles and chelates Pt(II) or enables covalent conjugation of Pt(IV) with similar morphology and stability. Both ATBP-Pt(II) and ATBP-Pt(IV) nanoparticles enhanced the half-life of Pt by ∼45-fold, but ATBP-Pt(IV) had superior tumor regression efficacy compared to ATBP-Pt(II) and cisplatin. These results suggest loading Pt(IV) into genetically engineered nanoparticles may yield a new generation of more effective platinum-drug nanoformulations.

Programmable Site-Specific Functionalization of DNA Origami with Polynucleotide Brushes.

Combining surface-initiated, TdT (terminal deoxynucleotidyl transferase) catalyzed enzymatic polymerization (SI-TcEP) with precisely engineered DNA origami nanostructures (DONs) presents an innovative pathway for the generation of stable, polynucleotide brush-functionalized DNA nanostructures. We demonstrate that SI-TcEP can site-specifically pattern DONs with brushes containing both natural and non-natural nucleotides. The brush functionalization can be precisely controlled in terms of the location of initiation sites on the origami core and the brush height and composition. Coarse-grained simulations predict the conformation of the brush-functionalized DONs that agree well with the experimentally observed morphologies. We find that polynucleotide brush-functionalization increases the nuclease resistance of DONs significantly, and that this stability can be spatially programmed through the site-specific growth of polynucleotide brushes. The ability to site-specifically decorate DONs with brushes of natural and non-natural nucleotides provides access to a large range of functionalized DON architectures that would allow for further supramolecular assembly, and for potential applications in smart nanoscale delivery systems.

Enzymatic synthesis and modification of high molecular weight DNA using terminal deoxynucleotidyl transferase.

The recognition that nucleic acids can be used as polymeric materials led to the blossoming of the field of DNA nanotechnology, with a broad range of applications in biotechnology, biosensors, diagnostics, and drug delivery. These applications require efficient methods to synthesize and chemically modify high molecular weight DNA. Here, we discuss terminal deoxynucleotidyl transferase (TdT)-catalyzed enzymatic polymerization (TcEP) as an alternative to conventional enzymatic and solid-phase DNA synthesis. We describe biochemical requirements for TcEP and provide step-by-step protocols to carry out TcEP in solution and from surfaces.

Enhancing Gene-Knockdown Efficiency of Poly(N-isopropylacrylamide) Nanogels.

Polo-like-kinase 1 (PLK1), which is a serine-threonine protein kinase overexpressed in cancer cells, is known to regulate tumor growth and have recently gathered attention as a target gene for RNA interference because of the poor bioavailability and nonspecificity of the available inhibitors. However, the lower transfection efficiency of siRNA and its poor stability in biological mileu necessitate the need of efficient siRNA delivery systems. Here, we report efficacious polymeric nanoparticles for the delivery of PLK1 siRNA in mammalian cancer cells. N-Isopropylacrylamide (NIPAm) and N-isopropylmethacrylamide-co-NIPAm nanogels were synthesized and modified using poly-ε-lysine. Furthermore, their ability to induce gene silencing was investigated by flow cytometry and real-time polymerase chain reaction, and the silencing efficiency observed was related to the polymer composition and its effect on the gene loading and protection ability and the endosomal escape capability. This study attempts to leverage the understanding of the cell-material interaction, thus, addressing the bottlenecks of siRNA delivery for enhancing the efficacy of the poly(N-isopropylacrylamide)-based delivery vehicle.

Probing the nanoparticle-AGO2 interaction for enhanced gene knockdown.

RNAi is emerging as a promising technology for treatment of various diseases due to its ability to silence specific target genes. To date, a number of nanoparticle based formulations have been reported for the delivery of small interfering RNA (siRNA), with continuous modifications in the nanoparticle design for enhancing their efficiency. While majority of the design aspects are focused on avoiding or overcoming endosomal entrapment, limited studies are available that address the role of interaction of nanoparticles with the RNA induced silencing complex (RISC) machinery, which is a crucial aspect deciding the outcome. Here, we systematically probed the effect of steric hindrance of nanoparticles on RISC interaction, by modulating two parameters, nanoparticle size and hardness. An assay was developed for quantifying the extent of RISC interaction of different nanoparticles in vitro, which was then correlated with their gene knockdown efficiency. The results suggest that the soft and small nanoparticles were most efficacious in knocking down polo-like-kinase 1 (PLK1) siRNA, a gene overexpressed in a variety of cancer types.

Influence of Cubosome Surface Architecture on Its Cellular Uptake Mechanism.

Interaction of nanoparticles with biological systems is a key factor influencing their efficacy as a drug delivery vehicle. The inconsistency in defining the optimal design parameters across different nanoparticle types suggests that information gained from one model system need not apply to other systems. Therefore, selection of a versatile model system is critical for such studies. Cubosomes are one of the potential drug delivery vehicles due to their biocompatibility, stability, ability to carry hydrophobic, hydrophilic, and amphiphilic drugs, and ease of surface modification. Here we report the importance of surface architecture of cubosomes by comparing their cellular uptake mechanism with poly-ε-lysine (PεL)-coated cubosomes. Uncoated cubosomes entered cells by an energy-independent, cholesterol-dependent mechanism, whereas PεL-coated cubosomes relied on energy-dependent mechanisms to enter the endosomes. As endosomal entrapment was evaded by uncoated cubosomes, they can be preferably used for cytosolic delivery of therapeutic agents.

Core-Shell Nanoparticles as an Efficient, Sustained, and Triggered Drug-Delivery System.

One of the challenges in designing a successful drug-delivery vehicle is the control over drug release. Toward this, a number of multifunctional nanoparticles with multiple triggers and complex chemistries have been developed. To achieve an efficient and maximum therapeutic effect, a trigger dependent drug-delivery system with sustained release is desirable. In this paper, we report the use of a combination of thermoresponsive gold core and polymeric shell nanoparticles that can provide a sustained, triggered release of doxorubicin, making the system more efficient compared to individual nanoparticles. The selection of the system was dependent on the best trigger applicable in biological systems and a component responsive to that trigger. Because of the best tissue penetration depth observed for radiofrequency (rf), we chose rf as a trigger. Whereas the gold nanoparticles (AuNPs) provided hyperthermia trigger on exposure to rf fields, the thermoresponsiveness was endowed by poly(N-isopropylacrylamide) (pNIPAm)-based polymer shells. AuNPs with three different compositions of shells, only pNIPAm and p(NIPAm-co-NIPMAm) with the ratio of NIPAm/N-(isopropylmethacrylamide) (NIPMAm) 1:1 (pNIPMAm50) and 1:3 (pNIPMAm75), were synthesized. We observed that the polymer coating on the AuNPs did not affect the heating efficiency of AuNPs by rf and exhibited a temperature-dependent release of the chemotherapeutic drug, doxorubicin. The nanoparticles were biocompatible, stable in biologically relevant media, and were able to show a burst as well as a sustained release, which was rf-dependent. Interestingly, we observed that when HeLa cells were treated with doxorubicin-loaded gold core-polymeric shell NPs and exposed to rf for varying times, the mixture of the two polymeric shell nanoparticles induced more cell death as compared to the cells treated with single nanoparticles, suggesting that such multi-nanoparticle systems can be more efficacious delivery systems instead of a single multicomponent system.

Enhancing cubosome functionality by coating with a single layer of poly-ε-lysine.

We report the preparation and characterization of monoolein cubosomes that can be easily surface modified through adsorption of a single layer of cationic poly-ε-lysine. Poly-ε-lysine coated cubosomes show remarkable stability in serum solution, are nontoxic and, are readily internalized by HeLa cells. The poly-ε-lysine coating provides chemical handles for further bioconjugation of the cubosome surface. We also demonstrate that the initial release rate of a hydrophilic drug, Naproxen sodium, from the cubosomes is retarded with just a single layer of polymer. Interestingly, cubosomes loaded with Naproxen sodium, recently shown to have anticancer properties, cause more apoptosis in HeLa cells when compared to free unencapsulated drug.

Mitigating the Cytotoxicity of Graphene Quantum Dots and Enhancing Their Applications in Bioimaging and Drug Delivery.

Despite the promising photophysical properties of fluorescent graphene quantum dots (GQDs), their cellular toxicity needs to be addressed before their full potential could be completely realized in biomedicine. A simple method for mitigating the toxicity of GQDs by embedding them in PEG matrix is reported here. The enhanced biocompatibility of polymer modified, P-GQDs, is attributed to reduced reactive oxygen species generation, as measured by an intracellular ROS assay. We also demonstrate the enhanced loading and efficient intracellular delivery of therapeutics by P-GQDs.