Medicine & Health

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  • (2022) Yu, Tsz Tin
    The rapid emergence and development of antibacterial resistance is a major global threat to public health. There is an urgent need for the development of antibacterial agents with novel therapeutic strategy to tackle the increasing incidence of antibacterial resistance. In recent years, antimicrobial peptides (AMPs) and their synthetic mimics have been under the spotlight of the development of a novel class of antibiotics to combat antibiotic resistance. This research project focused on the utilisation of phenylglyoxamide and benzothiazole scaffolds in the development of antimicrobial peptidomimetics. The synthesis of phenylglyoxamide-based peptidomimetics was achieved via the ring-opening reactions of N-sulfonylisatins with primary amines followed by salt formation. Minimum inhibitory concentrations (MIC) of the peptidomimetics against different bacterial strains were determined to assess their antibacterial activity. Structure-activity relationship (SAR) studies revealed the inverse relationship between the alkylsulfonyl chain length and the bulkiness of the phenyl ring system for high antibacterial activity. The most active peptidomimetics exhibited high antibacterial activity with the lowest MIC to be 4, 16 and 63 μM against S. aureus, E. coli and P. aeruginosa, respectively. These peptidomimetics also showed significant biofilm disruption (up to 50%) and inhibition (up to 70%) against S. aureus at 2–4× MIC. In addition, terphenylglyoxamide-based peptidomimetics synthesised by the ring-opening reaction of N-acylisatins with amines and amino acid esters were evaluated for their quorum sensing inhibition (QSI) activity against P. aeruginosa MH602. The most potent peptidomimetic possessed high QSI activity of 82%, 65% and 53% at 250, 125 and 62.5 μM, respectively, with no bacterial growth inhibition. On the other hand, benzothiazole-based peptidomimetics were synthesised via the Jacobson method of cyclisation of phenylthioamides, followed by the installation of cationic groups. 2-Naphthyl and guanidinium hydrochloride as the hydrophobic and cationic groups, respectively, were important for high antibacterial activity of the peptidomimetics against both Gram-positive and Gram-negative bacteria. The most potent peptidomimetics against S. aureus, E. coli and P. aeruginosa possessed MIC values of 2, 16 and 32 μM, respectively. These active peptidomimetics inhibited 39% of S. aureus biofilm formation and disrupted 42% of preformed S. aureus biofilms at sub-MIC.

  • (2022) Gadde, Satyanarayana
    High-risk neuroblastoma is one of the most aggressive and treatment-refractory childhood malignancies. MYCN (v-myc avian myelocytomatosis viral related oncogene, neuroblastoma derived) is a major oncogenic driver for neuroblastoma (NB) tumorigenesis. Developing direct inhibitors of MYCN has been challenging due to several limitations. Hence, targeting MYCN-binding proteins which regulate the stability of MYCN protein is a promising alternative approach. This study is aimed at developing novel inhibitors of ubiquitin specific protease 5 (USP5), a deubiquitinating enzyme, which is known to prevent MYCN protein degradation by deubiquitination. The first results chapter describes the synthesis of novel pyrido[1,2-a]benzimidazole compounds and their cytotoxicity against MYCN amplified NB cells with high expression of USP5 protein (SK-N-BE(2)-C and Kelly cells). However, none of the tested compounds displayed better cytotoxicity than the parental compound, SE486-11. The second results chapter describes a one-pot synthesis of novel γ-carbolinone, γ-carboline and spiro[pyrrolidinone-3,3′]indoles. One of the γ-carboline compounds (42d) displayed promising cytotoxicity against NB cells (SK-N-BE(2)-C (IC50 = 1.21 μM) and Kelly (IC50 = 3.09 μM)) but showed little therapeutic selectivity when compared to normal human fibroblasts, MRC-5 cells (IC50 = 3.75μM). The synthesis and cytotoxicity of novel pyrimido[1,2-a]benzimidazoles is described in the third results chapter. The active compound, 65a displayed promising cytotoxicity against SK-N-BE(2)-C (IC50 = 0.78 μM) and Kelly (IC50 = 2.00 μM) cells with a reasonable therapeutic window compared to MRC-5 cells (IC50 = 15.0 μM). 65a bound to USP5 protein by microscale thermophoresis assay (Kd = 0.47 µM). USP5 and MYCN protein levels were decreased in NB cells by treatment with 65a. Moreover, the cytotoxicity of 65a was dependant on the expression of USP5 and MYCN proteins. 65a showed synergy in combination with HDAC inhibitors, SAHA and panobinostat. In the fourth results chapter, the synthesis of more potent pyrimido[1,2-a]benzimidazoles with di- and tri- substitutions on the pendant phenyl ring (86b (SK-N-BE(2)-C IC50 = 0.31 μM; Kelly IC50 = 0.65 μM) and 91 (SK-N-BE(2)-C IC50 = 0.03 μM; Kelly IC50 = 0.07 μM)) are described. Importantly, 86b displayed significant in vivo efficacy in TH-MYCN homozygous NB mice when treated with 60 mg/kg for three weeks. The last results chapter describes the synthesis and cytotoxicity of novel benzo[4,5]imidazo[2,1-b]thiazole and pyrido[2,3-b]indole compounds. Collectively, this thesis identifies promising novel scaffolds with great potential for further development.

  • (2023) Chakraborty, Sudip
    Orthopaedic devices and biomaterials have significantly improved the livelihood of patients suffering from debilitating health conditions and have offered healthcare institutions and governments the tools to intervene for better health outcomes. However, like with many other life-saving technologies, there are challenges hindering the optimal effectiveness of orthopaedic biomaterials, key amongst which is bacterial infections. These infections often result in multiple surgeries and implant failure. Traditional therapeutic strategies that have relied on antibiotics are being challenged by the rapid evolution and prevalence of antibiotic resistant bacteria. Therefore, exploring alternative strategies to kill bacteria and reduce medical devices associated infections is the need of the hour. Traditional antibiotics are susceptible to bacterial resistance primarily because of their mechanisms of action which involve identifying and binding to specific targets within bacteria. Alternatives to traditional antibiotics such as antimicrobial peptides and their mimics, quaternary ammonium compounds, antibacterial hydrogels, metal ions, etc., have emerged as potent antibacterial agents, some of which are less susceptible to bacterial resistance due to their non-specific modes of action. In the context of biomedical devices and implants, the attachment strategies employed for tethering antimicrobial compounds to their surfaces play crucial roles in determining the magnitude of antibacterial activity observed on the device surfaces and in the surrounding region. Plasma Immersion Ion Implantation and Deposition (PIIID) has emerged as an exciting single-step process for attaching molecules to material surfaces. It is relatively easy to perform and successfully generates stable coatings for materials. In this, study, we have explored two small-molecule antimicrobial peptidomimetics, an antimicrobial polymer, two antimicrobial peptides, a quaternary ammonium polymer, and an vi antimicrobial hydrogel as coatings and fillings for hydroxyapatite (HA) and polyether ether ketone (PEEK) surfaces. We have explored two strategies for attachment of these compounds to the materials, physical attachment via weak interactions and covalent attachment via PIIID treatment. Chapters 2 and 3 describe the attachment and properties of the peptidomimetics-based coatings for HA surfaces while chapter 4 details the properties of the polymer-based coatings for the same. Chapter 5 deals with the two antimicrobial peptides and chapter 6 talks about the quaternary ammonium polymer-based coating and the antimicrobial hydrogel-based filling for HA discs. Finally, chapter 7 describes the properties of peptidomimetics and polymer-coated PEEK sheets. Overall, several non-traditional strategies for generating antibacterial coatings for materials of relevance in orthopaedics were investigated. All the compounds demonstrated excellent antibacterial activity and were successful in inhibiting the attachment of bacteria (S. aureus (peptidomimetics, peptides, quaternary ammonium polymer and hydrogel), E. coli (polymer, peptides, and hydrogels) and P. aeruginosa (peptides)) to the material surfaces and in the surrounding solution. The covalently coated surfaces could retain their activity over a prolonged period of time while the physically coated surfaces exhibited significant activity immediately after the coating. These compounds and attachment strategies represent exciting alternatives to traditional therapeutic strategies.