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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2016)
Over the past few years, there have been calls for novel antimicrobials to combat the rise of drug-resistant bacteria. While some promising new discoveries have met this call, it is not nearly enough. The major problem is that although these new promising antimicrobials serve as a short-term solution, they lack the potential to provide a long-term solution. The conventional method of creating new antibiotics relies heavily on the discovery of an antimicrobial compound from another microbe. This paradigm of development is flawed due to the fact that microbes can easily transfer a resistant mechanism if faced with an environmental pressure. Furthermore, there has been some evidence to indicate that the environment of the microbe can provide a hint as to their virulence. Because of this, the use of materials with antimicrobial properties has been garnering interest. Nanoantibiotics, (nAbts), provide a new way to circumvent the current paradigm of antimicrobial discovery and presents a novel mechanism of attack not found in microbes yet; which may lead to a longer-term solution against drug-resistance formation. This allows for environment-specific activation and efficacy of the nAbts but may also open up and create new design methods for various applications. These nAbts provide promise, but there is still ample work to be done in their development. This review looks at possible ways of improving and optimizing nAbts by making them stimuli-responsive, then consider the challenges ahead, and industrial applications.Graphical abstractA graphic detailing how the current paradigm of antibiotic discovery can be circumvented by the use of nanoantibiotics.
    Cover page: Design, challenge, and promise of stimuli-responsive nanoantibioticsCreative Commons 'BY' version 4.0 license
    • Thesis
    • Peer Reviewed
    UC Irvine Electronic Theses and Dissertations (2017)

    Drug-resistant infectious bacteria are a pressing societal challenge with conventional antibiotics are becoming less effective at treating bacterial infections. More specifically, gram-negative intracellular infection provides an additional challenge. An innovative therapy for combating these emerging superbugs requires a paradigm-shift in therapy development. Therefore, a combinatory therapy of nanoantibiotics and gene therapy was developed. Chitosan, has been heralded as a material with applications in gene therapy, antimicrobials, wound healing, and various biomedical fields due to its availability, nontoxicity, and biodegradability, therefore, it was a highly suitable nanoantibiotic. However, the efficacy of chitosan is restricted due to the lack of aqueous solubility and limited response to biological triggers.

    The focus of my work has been to engineer chitosan as an improved gene delivery vector while maintaining the antimicrobial properties. This was achieved by conjugating an amino branch to the primary hydroxyl group via a temporary, acid-cleavable ketal linkage to created acid-transforming chitosan (ATC). The antimicrobial capabilities of ATC were explored, and the possible mechanism of action was determined using transposon insertion sequencing. The efficacy of the free polymer was observed against S. typhimurium, an intracellular pathogen, alone at varying pH conditions which lead to a positive correlation between pH and effects the polymer had on the microbe. Additionally, ATC polyplexes were applied to RAW 264.7 cells infected with S. typhimurium expressing GFP and resulted in a decrease in the levels of bacteria found within the cells as confirmed by flow cytometry. This highlighted the key advantage of using an antimicrobial vector against difficult intracellular infections.

    The temporary conjugated aminoethoxy branch onto chitosan increased the hydrophilicity, promoted cytosolic release in the mildly acidic endosome. The change in hydrophilicity and solubility of ATC was confirmed by dissolving ATC in deionized water and observing a complete dissipation. Acid-triggered reduction of ATC to native chitosan was achieved by incubation at an endosomal pH 5.0, and analyzed by NMR, MALDI-TOF, and FTIR. Improved cytosolic release, which led to improvement in gene delivery, was confirmed by the complexation of ATC with pDNA, and siRNA to form acid-responsive DNA/ATC (D/ATC) and siRNA/ATC (R/ATC) nanoparticles (NPs), The results indicated transfection of 30% and silencing of 85%, for both D/ATC and R/ATC, respectively.

    In summary, this dissertation provides a comprehensive study from synthesis to application of acid-transforming chitosan as a potential synergistic treatment of drug-resistant microbes.

      Cover page: Engineering Physically Active and Genetically Specific Nanoantibiotics
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2021)
      Antibiotics are highly successful against microbial infections. However, current challenges include rising antibiotic resistance rates and limited efficacy against intracellular pathogens. A novel form of a nanomaterial-based antimicrobial agent is investigated for efficient treatment of an intracellular Salmonella enterica sv Typhimurium infection. A known antimicrobial polysaccharide, chitosan, is engineered to be readily soluble under neutral aqueous conditions for systemic administration. The modified biologic, named acid-transforming chitosan (ATC), transforms into an insoluble, antimicrobial compound in the mildly acidic intracellular compartment. In cell culture experiments, ATC is confirmed to have antimicrobial activity against intracellular S. Typhimurium in a concentration- and pH-dependent manner, without affecting the host cells, RAW264.7 macrophages. For improved cellular uptake and pharmacokinetic/pharmacodynamic properties, ATC is further complexed with fragment DNA (fDNA), to form nano-sized spherical polyplexes. The resulting ATC/fDNA polyplexes efficiently eradicated S. Typhimurium from RAW264.7 macrophages. ATC/fDNA polyplexes may bind with microbial wall and membrane components. Consistent with this expectation, transposon insertion sequencing of a complex random mutant S. Typhimurium library incubated with ATC does not reveal specific genomic target regions of the antimicrobial. This study demonstrates the utility of a molecularly engineered nanomaterial as an efficient and safe antimicrobial agent, particularly against an intracellular pathogen.
        Cover page: Eradication of Intracellular Salmonella Typhimurium by Polyplexes of Acid‐Transforming Chitosan and Fragment DNA
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2016)
        Single modal cancer therapy that targets one pathological pathway often turns out to be inefficient. For example, relapse of chronic myelogenous leukemia (CML) after inhibiting BCR-ABL fusion protein using tyrosine kinase inhibitors (TKI) (e.g., Imatinib) is of significant clinical concern. This study developed a dual modal gene therapy that simultaneously tackles two key BCR-ABL-linked pathways using viral/nonviral chimeric nanoparticles (ChNPs). Consisting of an adeno-associated virus (AAV) core and an acid-degradable polymeric shell, the ChNPs were designed to simultaneously induce pro-apoptotic BIM expression by the AAV core and silence pro-survival MCL-1 by the small interfering RNA (siRNA) encapsulated in the shell. The resulting BIM/MCL-1 ChNPs were able to efficiently suppress the proliferation of BCR-ABL+ K562 and FL5.12/p190 cells in vitro and in vivo via simultaneously expressing BIM and silencing MCL-1. Interestingly, the synergistic antileukemic effects generated by BIM/MCL-1 ChNPs were specific to BCR-ABL+ cells and independent of a proliferative cytokine, IL-3. The AAV core of ChNPs was efficiently shielded from inactivation by anti-AAV serum and avoided the generation of anti-AAV serum, without acute toxicity. This study demonstrates the development of a synergistically efficient, specific, and safe therapy for leukemia using gene carriers that simultaneously manipulate multiple and interlinked pathological pathways.
          Cover page: Viral/Nonviral Chimeric Nanoparticles To Synergistically Suppress Leukemia Proliferation via Simultaneous Gene Transduction and Silencing
          • Article
          • Peer Reviewed
          UC Irvine Previously Published Works (2020)
          Targeting the inability of cancerous cells to adapt to metabolic stress is a promising alternative to conventional cancer chemotherapy. FTY720 (Gilenya), an FDA-approved drug for the treatment of multiple sclerosis, has recently been shown to inhibit cancer progression through the down-regulation of essential nutrient transport proteins, selectively starving cancer cells to death. However, the clinical use of FTY720 for cancer therapy is prohibited because of its capability of inducing immunosuppression (lymphopenia) and bradycardia when phosphorylated upon administration. A prodrug to specifically prevent phosphorylation during circulation, hence avoiding bradycardia and lymphopenia, was synthesized by capping its hydroxyl groups with polyethylene glycol (PEG) via an acid-cleavable ketal linkage. Improved aqueous solubility was also accomplished by PEGylation. The prodrug reduces to fully potent FTY720 upon cellular uptake and induces metabolic stress in cancer cells. Enhanced release of FTY720 at a mildly acidic endosomal pH and the ability to substantially down-regulate cell-surface nutrient transporter proteins in leukemia cells only by an acid-cleaved drug were confirmed. Importantly, the prodrug demonstrated nearly identical efficacy to FTY720 in an animal model of BCR-Abl-driven leukemia without inducing bradycardia or lymphopenia in vivo, highlighting its potential clinical value. The prodrug formulation of FTY720 demonstrates the utility of precisely engineering a drug to avoid undesirable effects by tackling specific molecular mechanisms as well as a financially favorable alternative to new drug development. A multitude of existing cancer therapeutics may be explored for prodrug formulation to avoid specific side effects and preserve or enhance therapeutic efficacy.
            Cover page: Biocompatible Chemotherapy for Leukemia by Acid-Cleavable, PEGylated FTY720.Creative Commons 'BY' version 4.0 license
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