Bacterial infections are becoming harder-to-treat with current antibiotics, due to antimicrobial resistance and biofilm-formation. Therefore, there is an urgent need for novel antibacterial agents... Show moreBacterial infections are becoming harder-to-treat with current antibiotics, due to antimicrobial resistance and biofilm-formation. Therefore, there is an urgent need for novel antibacterial agents and antimicrobial peptides (AMPs) may fulfill this role. Herein, three strategies were explored for optimization of our lead AMP SAAP-148 to combat bacterial infections: i) chemical lead-optimization, ii) combination therapy with other antimicrobial agents and iii) innovative AMP delivery systems. The latter strategy was also applied to another promising AMP, the snake cathelicidin Ab-Cath. First, we demonstrated that conjugation of short polyethylene glycol chains to SAAP-148 reduced the peptide’s cytotoxicity and remarkably improved its ability to modulate the immune system to a more pro-inflammatory subset. Second, it was shown that combinations of SAAP-148 and novel antibiotic halicin were more effective than single agent treatment against planktonic bacteria of specific resistant bacterial strains, also in clinically relevant cell models. Third, we demonstrated that hyaluronic acid-based nanogels allow for efficient encapsulation of SAAP-148 and Ab-Cath, thereby improving the selectivity index of both peptides by maintaining antimicrobial activities against resistant bacteria and reducing cytotoxic activities against mammalian cells. Thus, the findings described in this thesis contribute to the development of SAAP-148 and Ab-Cath as therapeutics to combat bacterial infections. Show less
Extending our current arsenal of antibiotics is key to staying ahead in the arms race between humans and resistant bacteria. Classes of antibiotics otherwise limited to the treatment of Gram... Show moreExtending our current arsenal of antibiotics is key to staying ahead in the arms race between humans and resistant bacteria. Classes of antibiotics otherwise limited to the treatment of Gram-positive pathogens may be potentiated against Gram-negative bacteria by disruption of their outer membrane. The work described in this thesis focuses on the development of novel synergists designed to selectively disrupt the outer membrane and in doing potentiate the activity of antibiotics that are otherwise inactive against Gram-negative bacteria. Show less
Metallo-β-lactamases (MBLs) are zinc-dependent bacterial enzymes that inactivate essentially all classes of β-lactam antibiotics including last-resort carbapenems. At present there are no... Show moreMetallo-β-lactamases (MBLs) are zinc-dependent bacterial enzymes that inactivate essentially all classes of β-lactam antibiotics including last-resort carbapenems. At present there are no clinically approved MBL inhibitors, and in order to develop such agents it is essential to understand their inhibitory mechanisms. Herein, we describe a comprehensive mechanistic study of a panel of structurally distinct MBL inhibitors reported in both the scientific and patent literature. Specifically, we determined the half-maximal inhibitory concentration (IC50) for each inhibitor against MBLs belonging to the NDM and IMP families. In addition, the binding affinities of the inhibitors for Zn2+, Ca2+ and Mg2+ were assessed by using isothermal titration calorimetry (ITC). We also compared the ability of the different inhibitors to resensitize a highly resistant MBLexpressing Escherichia coli strain to meropenem. These investigations reveal clear differences between the MBL inhibitors studied in terms of their IC50 value, metal binding ability, and capacity to synergize with meropenem. Notably, our studies demonstrate that potent MBL inhibition and synergy with meropenem are not explicitly dependent on the capacity of an inhibitor to strongly chelate zinc. Show less
The main focus of the thesis is the discovery and development of novel inhibitors of bacterial metallo-β-lactamases (MBLs). Chapter 1 provides an overview of FDA-approved β-lactamase inhibitors as... Show moreThe main focus of the thesis is the discovery and development of novel inhibitors of bacterial metallo-β-lactamases (MBLs). Chapter 1 provides an overview of FDA-approved β-lactamase inhibitors as well as those currently being evaluated in clinical trials. Chapters 2 and 3 describe our evaluation of small-molecule aminocarboxylic acids either commercially available or prepared via chemoenzymatic approaches for their activity against clinically important MBLs. We found that nitrilotriacetic acid and its phosphonic acid isostere, as well as ethylenediamine-N,N′-disuccinic acid (EDDS), are potent inhibitors of New-Delhi metallo-beta-lactamase (NDM-1). Focusing on another class of MBL inhibitors, chapter 4 describes our study of selected thiol-containing compounds. Among them, thiomandelic acid showed the most potent and broad-spectrum synergistic activity when combined with meropenem against MBL-producing gram-negative bacteria. Stability studies, however, showed that thiomandelic acid is oxidized to its corresponding disulfide with the half-life of ca. 5 h. To address the stability and selectivity issue associated with thiols, in chapter 5 we describe a prodrug approach where we synthesized and evaluated a series of thiol conjugates of cephalosporins. Some of these cephalosporin conjugates exhibit potent inhibition of IMP class of MBLs. Finally, chapter 6 describes our biochemical evaluation of a newly identified class A carbapenemase. Show less
Parsa, V.A.; Salehi, E.; Yavari, A.R.; Bodegom, P.M. van 2019
Promoting urban greenery through tree planting strategies has been considered as a measure to mitigate climate change. While it is essential to understand the temporal dynamics of urban forest... Show morePromoting urban greenery through tree planting strategies has been considered as a measure to mitigate climate change. While it is essential to understand the temporal dynamics of urban forest structure as well as its services and contribution to human wellbeing in cities, it has hardly ever been examined whether the future contributions of these services after different possible planting strategies can comply with climate change policy goals; these are topics rarely discussed in urban planning and management. In this paper, the ecosystem services currently provided by urban trees (through carbon sequestration and storage), as well as those potentially provided in the future, were quantified using the i-Tree Eco model, and their contribution to climate change mitigation was evaluated. As a case study in Tabriz, Iran, we developed four possible scenarios. Synergy (urban temperature regulation by UF) and trade-off (tree water requirements) were also analyzed. Future carbon sequestration and storage potential of urban trees was compared with the estimated future carbon emissions. The current contribution in Tabriz is relatively modest (about 0.2%), but it can be tripled through long-term tree planting strategies. Additionally, the temporal cooling effects and tree water requirements increase as climate change mitigation improves through tree planting. We conclude that urban tree planting has a small impact on carbon mitigation in the study area, most likely because of the young age of trees in Tabriz as well as the fact that the planted trees cannot deliver all their benefits over a 20-years period and need more time. Thus, the use of urban trees serves only as a complementary solution rather than an alternative climate mitigation strategy. Our quantitative approach helps urban environmental policymakers to evaluate how much they can rely on urban forest strategies to achieve climate change mitigation targets. Show less
Koppen, B.C.; Mulder, P.P.G.; Boer, L. de; Riool, M.; Drijfhout, J.W.; Zaat, S.A.J. 2019
The p53 tumor suppressor protein plays a key role in cancer and its direct or indirect inactivation is an almost universal feature of human tumors. P53 has a central position in the prevention of... Show moreThe p53 tumor suppressor protein plays a key role in cancer and its direct or indirect inactivation is an almost universal feature of human tumors. P53 has a central position in the prevention of genomic instability and protection of tumorigenesis. This thesis presents novel studies regarding the role of Hdmx in p53 inactivation during tumorigenesis, as well as the use of specific drugs for p53 reactivation as cancer treatment. Chapter 2 shows that constitutive Hdmx overexpression contributes to the neoplastic transformation of human fibroblasts and embryonic retinoblasts, thereby functionally resembling loss of p53. Chapter 3 establishes the importance of Hdmx as an oncogene in a subset of uveal melanomas. Importantly, the results described in this chapter extend the function of Hdmx beyond p53 inhibition. Chapter 4 evaluates the use of the specific p53 activating drugs Nutlin-3 and RITA in synergy studies as potential therapy for uveal melanoma. Chapter 5 is a more detailed analysis of the cellular responses to RITA. In particular, Chk2 is shown to be an essential mediator of the RITA-induced effects. Chapter 6 is a general discussion of the results presented in this thesis, and their implications for clinical exploitation and future research. Show less
