Henryk Kozlowski

The increasing resistance of bacteria and fungi to antimicrobial agents demands therapeutic strategies with higher target selectivity and a lower risk of rapid resistance development. The Biologically Active Metallopeptides (BAM) group develops an approach based on the controlled interaction of metal ions with peptides and pathogen-derived proteins. In our work, metal ions (including Cu(II)/Cu(I), Zn(II), and Ni(II)) are treated as functional modules: they stabilize peptide structure, induce defined conformations and aggregation states, conditionally activate antimicrobial activity, and modulate the pathogen’s access to essential micronutrients. We elucidate the mechanisms of metal uptake and homeostasis in pathogens (including Cu and Zn acquisition systems, zincophores, and metal chaperones), identifying protein fragments that can act either as therapeutic targets or as targeting domains for the selective delivery of antimicrobial agents (a “Trojan horse” strategy). In parallel, we investigate antimicrobial peptides and endogenous peptides in the presence of metal ions, demonstrating that coordination of Cu(II) and Zn(II) can markedly enhance their bactericidal or antifungal activity by enforcing active conformations, inducing aggregation (e.g. fibril formation), and promoting the generation of reactive oxygen species locally at the infection site. Building on these principles, we design selective targeted antimicrobial peptides (STAMPs, ang. specifically targeted antimicrobial peptides) and chemically stabilized peptide and glycopeptide constructs with improved biological stability and tissue selectivity. We show that metal ion coordination chemistry can serve as a platform for engineering a new class of selective antimicrobial therapeutics.

Positron emission tomography (PET) imaging of Aβ plaques, is recognized as a tool for the diagnosis of Alzheimer’s disease. As a contribution to the development of new strategies for early diagnosis of the disease, using PET medical imaging technique, a new copper complex, the [Cu(TE1PA-ONO)]⁺ was synthesized in ten steps. The key step of our strategy is the coupling of a monopicolinate-N-alkylated cyclam-based ligand with a moiety capable of recognizing Aβ plaques via a successful and challenging Buchwald-Hartwig coupling reaction. To our knowledge, it is the first time that such a strategy is used to functionalize polyazamacrocyclic derivatives. The thermodynamic stability constants determined in MeOH/H₂O solvent indicate that the attachment of this moiety does not weaken the chelating properties of TE1PA-ONO ligand in relation to parent HTE1PA. The novel complex described here is able to recognize amyloid plaques in brain sections from Alzheimer's disease patients and shows low toxicity to human neuronal cells. Graphical abstract

Siderophores are unique ferric ion chelators produced and secreted by some organisms like bacteria, fungi and plants under iron deficiency conditions. These molecules possess immense affinity and specificity for Fe³⁺ and other metal ions, which attracts great interest due to the numerous possibilities of application, including antibiotics delivery to resistant bacteria strains. Total synthesis of siderophores is a must since the compounds are present in natural sources at extremely small concentrations. These molecules are extremely diverse in terms of molecular structure and physical and chemical properties. This review is focused on achievements and developments in the total synthesis strategies of naturally occurring siderophores bearing arylthiazoline and aryloxazoline units.

Increasing bacterial and fungal drug resistance makes novel, effective antimicrobial treatments actively sought. Because of the general lack of resistance towards antimicrobial peptides (AMPs), they are being relied on as a novel class of therapeutics aimed to conquer drug-resistant bacteria and fungi. There are numerous ways in which AMPs might interact with pathogens, such as membrane disruption, production of reactive oxygen species, inhibition of cell wall, nucleic acid and protein synthesis or by the withdrawal of essential metal ions. Biologically indispensable metal ions, such as Zn(II) and Cu(II), which are the key players of this project, have a dual effect on the activity of antimicrobial peptides: (i) AMPs bind them, so that microbes cannot get enough metals essential for their life and virulence (withdrawal of metal ions, nutritional immunity) or (ii) AMPs need the given metal ion as a booster of their antimicrobial activity (metal ions affect the AMP charge and/or structure). In this chapter, we discuss the impact of the coordination of Cu(II) and Zn(II) to several antimicrobial peptides, focusing on the thermodynamics, structure and coordination chemistry. The comparison of these data to the outcome of biological growth studies (determination of minimal inhibitory concentration (MIC) of metal- AMP complexes and their derivatives allows to draw conclusions about the relationship between the metal-antimicrobial peptide complex structure, stability mode of action and efficacy. In the nearest future, the most efficient complexes may serve as templates for a rational design of novel, more potent AMP-based therapeutics. Further improvement can be reached through the modification of the most promising AMP complexes using (i) specifically targeted antimicrobial peptides, in which the AMP will be covalently linked to a targeting peptide (Figure 1) or (ii) chimeric compounds comprising AMPs bound to conventional antimicrobials or peptidomimetic modifications (Figure 2).

In the Biological Inorganic Chemistry Group we are inspired to better understand metal ions acquisition and homeostasis in pathogenic bacteria, and in this review we present three different approaches to the role of these processes. The growing importance of a full understanding of the iron transport system in pathogens prompted us to study synthetic analogs of siderophores, used as structural probes in the process of iron uptake by microorganisms. The ferrichrome biomimetic analogs allowed efficient Fe(III) chelation under biological conditions and were recognized better by P. putida. than E. coli, suggesting differences in uptake mechanisms. Addition of a fluorescent probe to the compound allowed to track biological fate of studied complexes [1, 2]. Biomimetics of ferrioxamine E revealed their potential as radioactive 68Ga(III)-based probes [3], and studies of Zr(IV) complexes permitted to explain the in vivo behavior of desferrioxamine B as 89Zr(IV) radionuclide carrier [4], as well as design better chelators for this metal ion [5]. One of the possible mammalian immune system responses to mycobacterial infection is the increase of Zn(II) concentration in phagosomes to a toxic level [6-8]. The mycobacterial SmtB protein is a transcription regulator that in the presence of high concentrations of metals, dissociates from DNA and activates the expression of metal efflux proteins. We focused on α5 Zn(II) binding domains of SmtB/BigR4 proteins [9], looking at the coordination modes and thermodynamics of their Zn(II) and Ni(II) complexes. The study points out the specificity of metal-ligand interactions and the effect of mutations on the coordination properties of studied systems. The project can be considered as an introduction to the new strategies in tuberculosis treatment based on Zn(II)/Ni(II)-sensitive mechanisms. F. nucleatum is an anaerobic bacteria present in the plaque. It leads not only to periodontal diseases but also, angina, purulent inflammation of the lung tissue or reproductive organs [10]. Moreover, F. nucleatum promotes colon cancer growth [11]. This bacteria strain promotes inflammation and tumorigenesis by modulating the tumor immune microenvironment [12, 13]. Microbial pathogens drive tumorigenesis in 15–20% of cancer cases [14]. However, not only microorganisms are considered a major risk factor, but also metal ions play an important role in tumor promotion [15, 16]. Therefore, our primary research goal is to investigate the effect of metal ions coordination on the activity of outer- membrane proteins from F. nucleatum and to answer whether these proteins increase the prooxidative activity of Cu(II) and Fe(II) ions [16-18].

This review focuses on the current knowledge on the involvement of metal ions in signaling processes within the cell, in both physiological and pathological conditions. The first section is devoted to the recent discoveries on magnesium and calcium-dependent signal transduction—the most recognized signaling agents among metals. The following sections then describe signaling pathways where zinc, copper, and iron play a key role. There are many systems in which changes in intra- and extra-cellular zinc and copper concentrations have been linked to important downstream events, especially in nervous signal transduction. Iron signaling is mostly related with its homeostasis. However, it is also involved in a recently discovered type of programmed cell death, ferroptosis. The important differences in metal ion signaling, and its disease-leading alterations, are also discussed.

Zn(II) is an inhibitor of SARS-CoV-2′s RNA-dependent RNA polymerase, and chloroquine and hydroxychloroquine are Zn(II) ionophores–this statement gives a curious mind a lot to think about. We show results of the first clinical trials on chloroquine (CQ) and hydroxychloroquine (HCQ) in the treatment of COVID-19, as well as earlier reports on the anticoronaviral properties of these two compounds and of Zn(II) itself. Other FDA-approved Zn(II) ionophores are given a decent amount of attention and are thought of as possible COVID-19 therapeutics.