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Abstract As the field of theranostics expands, an imminent need arises for multifaceted polymer‐based nanotechnologies for clinical application. In this work, reversible addition‐fragmentation chain transfer (RAFT) aqueous emulsion polymerization is used to form¹⁹F‐containing amphiphilic hybrid block copolymers (HBCs). Employing a cationic dendritic macromolecular chain transfer agent (mCTA), polymer frameworks comprised of chemically distinctive blocks of differing architectures (i.e., dendritic and grafted/linear) are strategically designed and synthesized. In aqueous media, self‐assembled polymer nanoparticles (PNPs) are formed. Their physicochemical properties and their potential as biomaterials for MRI applications are assessed. By showcasing a newly established mCTA and using these resulting PNPs as imaging probes, the work expands the design space of RAFT polymerization in biomedical research, paving the way for the development of more effective and versatile MRI imaging tools. 

We report a first-in-class responsive, pentafluorosulfanyl (–SF 5 )-tagged 19 F MRI agent capable of reversibly detecting reducing environments via an Fe II/III redox couple. In the Fe III form, the agent displays no 19 F MR signal due to paramagnetic relaxation enhancement-induced signal broadening; however, upon rapid reduction to Fe II with one equivalent of cysteine, the agent displays a robust 19 F signal. Successive oxidation and reduction studies validate the reversibility of the agent. The –SF 5 tag in this agent enables ‘multicolor imaging’ in conjunction with sensors containing alternative fluorinated tags and this was demonstrated via simultaneous monitoring of the 19 F MR signal of this –SF 5 agent and a hypoxia-responsive agent containing a –CF 3 group. 

We report two highly fluorinated Cu-based imaging agents, CuL1 and CuL2 , for detecting cellular hypoxia as nanoemulsion formulations. Both complexes retained their initial quenched 19 F MR signals due to paramagnetic Cu 2+ ; however, both complexes displayed a large signal increase when the complex was reduced. DLS studies showed that the CuL1 nanoemulsion ( NE CuL1 ) had a hydrodiameter of approximately 100 nm and that it was stable for four weeks post-preparation. Hypoxic cells incubated with NE CuL1 showed that 40% of the Cu 2+ taken up was reduced in low oxygen environments. 

Targeting the low-oxygen (hypoxic) environments found in many tumours by using redox-active metal complexes is a strategy that can enhance efficacy and reduce the side effects of chemotherapies. We have developed a series of CuII complexes with tridentate pyridine aminophenolate-based ligands for preferential activation in the reduction window provided by hypoxic tissues. Furthermore, ligand functionalization with a pendant CF3 group provides a 19F spectroscopic handle for magnetic-resonance studies of redox processes at the metal centre and behaviour in cellular environments. The phenol group in the ligand backbone was substituted at the para position with H, Cl, and NO2 to modulate the reduction potential of the CuII centre, giving a range of values below the window expected for hypoxic tissues. The NO2-substituted complex, which has the highest reduction potential, showed enhanced cytotoxic selectivity towards HeLa cells grown under hypoxic conditions. Cell death occurs by apoptosis, as determined by analysis of the cell morphology. A combination of 19F NMR and ICP-OES indicates localization of the NO2 complex in HeLa cell nuclei and increased cellular accumulation under hypoxia. This correlates with DNA nuclease activity being the likely origin of cytotoxic activity, as demonstrated by cleavage of DNA plasmids in the presence of the CuII nitro complex and a reducing agent. Selective detection of the paramagnetic CuII complexes and their diamagnetic ligands by 19F MRI suggests hypoxia-targeting theranostic applications by redox activation. 

New Delhi metallo-β-lactamase (NDM) grants resistance to a broad spectrum of β-lactam antibiotics, including last-resort carbapenems, and is emerging as a global antibiotic resistance threat. Limited zinc availability adversely impacts the ability of NDM-1 to provide resistance, but a number of clinical variants have emerged that are more resistant to zinc scarcity (e.g., NDM-15). To provide a novel tool to better study metal ion sequestration in host–pathogen interactions, we describe the development of a fluorescent probe that reports on the dynamic metalation state of NDM within Escherichia coli. The thiol-containing probe selectively coordinates the dizinc metal cluster of NDM and results in a 17-fold increase in fluorescence intensity. Reversible binding enables competition and time-dependent studies that reveal fluorescence changes used to detect enzyme localization, substrate and inhibitor engagement, and changes to metalation state through the imaging of live E. coli using confocal microscopy. NDM-1 is shown to be susceptible to demetalation by intracellular and extracellular metal chelators in a live-cell model of zinc dyshomeostasis, whereas the NDM-15 metalation state is shown to be more resistant to zinc flux. The development of this reversible turn-on fluorescent probe for the metalation state of NDM provides a new tool for monitoring the impact of metal ion sequestration by host defense mechanisms and for detecting inhibitor–target engagement during the development of therapeutics to counter this resistance determinant. 

Abstract ¹⁹F magnetic resonance (MR) based detection coupled with well‐designed inorganic systems shows promise in biological investigations. Two proof‐of‐concept inorganic probes that exploit a novel mechanism for¹⁹F MR sensing based on converting from low‐spin (S=0) to high‐spin (S=1) Ni²⁺are reported. Activation of diamagneticNiL₁andNiL₂by light or β‐galactosidase, respectively, converts them into paramagneticNiL₀, which displays a single¹⁹F NMR peak shifted by >35 ppm with accelerated relaxation rates. This spin‐state switch is effective for sensing light or enzyme expression in live cells using¹⁹F MR spectroscopy and imaging that differentiate signals based on chemical shift and relaxation times. This general inorganic scaffold has potential for developing agents that can sense analytes ranging from ions to enzymes, opening up diverse possibilities for¹⁹F MR based biosensing.