Efficient cellular uptake of click nucleic acid modified proteins.

Efficient intracellular delivery of biomacromolecules such as proteins continues to remain a challenge despite its potential for medicine. In this work, we show that mScarlet, a non cytotoxic red fluorescent protein (RFP) conjugated to Click Nucleic Acid (CNA), a synthetic analog of DNA, undergo cell uptake significantly more than either native proteins or proteins conjugated with similar amounts of DNA in MDA-MB-468 cells. We further demonstrate that the process of cell uptake is metabolically driven and that scavenger receptors and caveolae mediated endocytosis play a significant role. Co-localization studies using anti-scavenger receptor antibodies suggest that scavenger receptors are implicated in the mechanism of uptake of CNA modified proteins.

Investigating Protein-Nanocrystal Interactions for Photodriven Activity.

We illustrate how intermolecular interactions facilitate ATP-free electron transfer between either native or engineered MoFe protein (MoFeP) from nitrogenase and a CdS nanorod (NR) by following the reduction of H+ to H2. First, by varying the charge on the surface of the NR, we show the role of electrostatic interactions on MoFeP binding to the particle surface and subsequent H+ reduction. Next, the role of strong, semicovalent thiol-CdS interactions was tested using free cysteines on the MoFeP. By blocking free cysteines, we show that the presence of free thiols on the protein has little to no influence on CdS binding and resultant photocatalytic activity. We next studied methods to covalently bind the protein to CdS by modifying the free cysteines with dibenzocyclooctyne (DBCO) and reacting the CdS NRs capped with a mixture of negatively charged thioglycolic acid and thiol-PEG3-azide ligands. As compared to that of the unmodified proteins, a 32.2 ± 1.5% and 61.7 ± 2.1% increase in H2 production was observed from MoFeP and C-MoFeP, respectively. At last, to test the effect of both charge and covalent tethering, positively charged cysteamine/azide CdS NRs were reacted with DBCO-modified C-MoFeP, which showed little improvement over native C-MoFeP alone under irradiation. These results show the importance of both electrostatic associations between the NR and protein and covalently tethering the protein to the semiconductor surface for enhanced electron transfer and photodriven activity.

Enzymes Photo-Cross-Linked to Live Cell Receptors Retain Activity and EGFR Inhibition after Both Internalization and Recycling.

In this work, we show that a prodrug enzyme covalently photoconjugated to live cell receptors survives endosomal proteolysis and retains its catalytic activity over multiple days. Here, a fusion protein was designed with both an antiepidermal growth factor receptor (EGFR) affibody and the prodrug enzyme cytosine deaminase, which can convert prodrug 5-fluorocytosine to the anticancer drug 5-fluorouracil. A benzophenone group was added at a site-specific mutation within the affibody, and the fusion protein was selectively photoconjugated to EGFR receptors expressed on membranes of MDA-MB-468 breast cancer cells. The fusion protein was next labeled with two dyes for tracking uptake: AlexaFluor 488 and pH-sensitive pHAb. Flow cytometry showed that fusion proteins photo-cross-linked to EGFR first underwent receptor-mediated endocytosis within 12 h, followed by recycling back to the cell membrane within 24 h. These findings were also confirmed by confocal microscopy. The unique cross-linking of the affibody-enzyme fusion proteins was utilized for two anticancer treatments. First, the covalent linking of the protein to the EGFR led to inhibition of ERK signaling over a two-day period, whereas conventional antibody therapy only led to 6 h of inhibition. Second, when the affibody-CodA fusion proteins were photo-cross-linked to EGFR overexpressed on MDA-MB-468 breast cancer cells, prodrug conversion was found even 48 h postincubation without any apparent decrease in cell killing, while without photo-cross-linking no cell killing was observed 8 h postincubation. These studies show that affinity-mediated covalent conjugation of the affibody-enzymes to cell receptors allows for prolonged expression on membranes and retained enzymatic activity without genetic engineering.

Click Nucleic Acid Mediated Loading of Prodrug Activating Enzymes in PEG-PLGA Nanoparticles for Combination Chemotherapy.

The simultaneous delivery of multiple therapeutics to a single site has shown promise for cancer targeting and treatment. However, because of the inherent differences in charge and size between drugs and biomolecules, new approaches are required for colocalization of unlike components in one delivery vehicle. In this work, we demonstrate that triblock copolymers containing click nucleic acids (CNAs) can be used to simultaneously load a prodrug enzyme (cytosine deaminase, CodA) and a chemotherapy drug (doxorubicin, DOX) in a single polymer nanoparticle. CNAs are synthetic analogs of DNA comprised of a thiolene backbone and nucleotide bases that can hybridize to complementary strands of DNA. In this study, CodA was appended with complementary DNA sequences and fluorescent dyes to allow its encapsulation in PEG-CNA-PLGA nanoparticles. The DNA-modified CodA was found to retain its enzyme activity for converting prodrug 5-fluorocytosine (5-FC) to active 5-fluorouracil (5-FU) using a modified fluorescent assay. The DNA-conjugated CodA was then loaded into the PEG-CNA-PLGA nanoparticles and tested for cell cytotoxicity in the presence of the 5-FC prodrug. To study the effect of coloading DOX and CodA within a single nanoparticle, cell toxicity assays were run to compare dually loaded nanoparticles with nanoparticles loaded only with either DOX or CodA. We show that the highest level of cell death occurred when both DOX and CodA were simultaneously entrapped and delivered to cells in the presence of 5-FC.

TiO2-Capped Gold Nanorods for Plasmon-Enhanced Production of Reactive Oxygen Species and Photothermal Delivery of Chemotherapeutic Agents.

Near infrared (NIR)-absorbing noble metal nanostructures are being extensively studied as theranostic agents, in particular for photoacoustic imaging and photothermal therapy. Because of the electric field enhancement at the tips of anisotropic metal nanostructures, positioning photoactive species at these sites can lead to increased energy absorption. Herein, we show the site-specific placement of NIR-active photosensitizers at the ends of gold nanorods (AuNRs) by growing porous TiO2 caps. The surface plasmon resonance of the AuNRs was carefully tuned to overlap with the exciton absorption of indocyanine green (ICG), a NIR photosensitizer with low quantum yields and poor photostability. In conjugating high amounts of ICG to the TiO2 caps, increased amounts of singlet oxygen (1O2) were generated as compared to when ICG was attached to sidewalls of the AuNRs. Because the AuNRs also cause local increases in temperature upon NIR excitation, DNA strands were next attached to the AuNRs sidewalls and loaded with doxorubicin (DOX). We found that the synergistic effect of increased 1O2 and photothermal-induced drug delivery led to significant improvements in tumor cell killing. This work demonstrates that with careful design over hybrid nanostructure synthesis, higher levels of tumor therapy may be achieved.

Synthesis and Assembly of Click-Nucleic-Acid-Containing PEG-PLGA Nanoparticles for DNA Delivery.

Co-delivery of both chemotherapy drugs and siRNA from a single delivery vehicle can have a significant impact on cancer therapy due to the potential for overcoming issues such as drug resistance. However, the inherent chemical differences between charged nucleic acids and hydrophobic drugs have hindered entrapment of both components within a single carrier. While poly(ethylene glycol)-block-poly(lactic-co-glycolic acid) (PEG-PLGA) copolymers have been used successfully for targeted delivery of chemotherapy drugs, loading of DNA or RNA has been poor. It is demonstrated that significant amounts of DNA can be encapsulated within PLGA-containing nanoparticles through the use of a new synthetic DNA analog, click nucleic acids (CNAs). First, triblock copolymers of PEG-CNA-PLGA are synthesized and then formulated into polymer nanoparticles from oil-in-water emulsions. The CNA-containing particles show high encapsulation of DNA complementary to the CNA sequence, whereas PEG-PLGA alone shows minimal DNA loading, and non-complementary DNA strands do not get encapsulated within the PEG-CNA-PLGA nanoparticles. Furthermore, the dye pyrene can be successfully co-loaded with DNA and lastly, a complex, larger DNA sequence that contains an overhang complementary to the CNA can also be encapsulated, demonstrating the potential utility of the CNA-containing particles as carriers for chemotherapy agents and gene silencers.