Petra Imhof’s research while affiliated with Friedrich-Alexander-University Erlangen-Nürnberg and other places

Mitochondria mediate electron transport chain (ETC) to power ATP synthase. In cancer cells, the ETC is disturbed leading to leakage of electrons that ultimately results in generation of H2O2. This difference between cancer and healthy cells can be used for the design of cancer‐specific prodrugs as confirmed in several proof‐of‐concept studies. Unfortunately, the known prodrugs are either insufficiently cancer cell specific or their activation efficacy is low. In this work, we solved this problem by optimizing the conjugate of a drug camptothecin and a H2O2‐responsive aminoferrocene to obtain the prodrug C. The multistep reaction of the prodrug C with H2O2 is >20‐fold more efficient than that of the parent system. The prodrug is accumulated and activated in mitochondria of cancer cells in a H2O2‐dependent fashion. The anticancer efficacy towards human ovarian cancer A2780 and monocytic leukemia THP1 cells is improved from 573 and >3000 nM (for prodrug B) to 142 and 479 nM (for prodrug C) correspondingly. Additionally to the excellent activity, the new prodrug is not toxic in vivo to a range of blood (red and white blood cells, neutrophils, monocytes, platelets) and bone marrow cells (monocytes, B and T cells and others) in contrast to camptothecin.

Carboxypeptidase is a Zn-dependent protease that specifically recognises and hydrolyses peptides with a hydrophobic side chain at the C-terminal residue. According to hydrolysis mechanisms proposed in the literature, catalysis requires a water molecule to be close to the Zn ion so as to be activated as a nucleophile. Among small molecules that resemble the slowly hydrolysed Gly-Tyr peptide, which have been previously designed as inhibitors and characterised structurally, a variant with the terminal amino acid in a D-configuration has been the most effective. Our molecular dynamics simulations of carboxypeptidase complexed with different variants of those inhibitor ligands as well as variants of the Gly-Tyr peptide show that the strength of the inhibitory effect is not related to the binding strength of the ligand. Our data rather support an earlier notion that the inhibition is, at least partially, due to blocking a coordination site at the Zn ion by the ligand coordinating the metal ion in a bidentate fashion.

Lipids are major constituents of food but are also highly relevant substructures of drugs and are increasingly applied for the development of lipid-based drug delivery systems. Lipids are prone to oxidative degradation, thus affecting the quality of food or medicines. Therefore, analytical methods or tools that enable the degree of lipid oxidation to be assessed are of utmost importance to guarantee food and drug safety. Herein, we report the design, synthesis and application of the first-in-class fluorogenic triacylglycerols that enable dynamic monitoring of lipid oxidation via straightforward fluorescence readout. Our fluorogenic triacylglycerols can be used in both aqueous and lipid-based environments. Furthermore, we showed that the sensitivity of our fluorescent tracers towards oxidation could be tuned by incorporating either saturated or unsaturated acyl chains in their triacylglycerol core structure. With this, we provide a first proof of principle for the applicability of fluorescently labelled triacylglycerols as tracers to monitor the dynamics of lipid oxidation, thus paving the way for novel discoveries in the area of lipid analytics. Graphical Abstract

Lipids are major constituents of food but are also highly relevant substructures of drugs and are increasingly applied for the development of lipid-based drug delivery systems. Lipids are prone to oxidative degradation, thus affecting the quality of food or medicines. Therefore, analytical methods or tools that enable to assess the degree of lipid oxidation are of utmost importance to guarantee food and drug safety. Herein, we report the design, synthesis, and application of the first-in-class fluorogenic triacylglycerols that enable a dynamic monitoring of lipid oxidation via straightforward fluorescence readout. Our fluorogenic triacylglycerols can be used both in an aqueous and lipid-based environment. Further, we showed that the sensitivity of our fluorescent tracers towards oxidation can be tuned by incorporating either saturated or unsaturated acyl chains in their triacylglycerol core structure. With this, we provide a first proof-of-principle for the applicability of fluorescently labelled triacylglycerols as tracers to monitor the dynamics of lipid oxidation, thus paving the way for novel discoveries in the area of lipid analytics.

Supramolecular recognition of nucleobases and short sequences is an emerging research field focusing on possible applications to treat many diseases. Controlling the affinity and selectivity of synthetic receptors to target desired nucleotides or short sequences is a highly challenging task. Herein, we elucidate the effect of substituents in the phenyl ring of the anthracene‐benzene azacyclophane on the recognition of nucleoside triphosphates (NTPs) and double‐stranded DNA. We show that introducing phenyl rings increases the affinity for NTPs 10‐fold and implements groove and intercalation binding modes with double‐stranded DNA. NMR studies and molecular modeling calculations support the ability of cyclophanes to encapsulate nucleobases as part of nucleotides.

Lipids are major constituents of food but are also highly relevant substructures of drugs and are increasingly applied for the development of lipid-based drug delivery systems. Lipids are prone to oxidative degradation, thus affecting the quality of food or medicines. Therefore, analytical methods or tools that enable to assess the degree of lipid oxidation are of utmost importance to guarantee food and drug safety. Herein, we report the design, synthesis, and application of the first-in-class fluorogenic triacylglycerols that enable a dynamic monitoring of lipid oxidation via straightforward fluorescence readout. Our fluorogenic triacylglycerols can be used both in an aqueous and lipid-based environment. Further, we showed that the sensitivity of our fluorescent tracers towards oxidation can be tuned by incorporating either saturated or unsaturated acyl chains in their triacylglycerol core structure. With this, we provide a first proof-of-principle for the applicability of fluorescently labelled triacylglycerols as tracers to monitor the dynamics of lipid oxidation, thus paving the way for novel discoveries in the area of lipid analytics.

Lipids are major constituents of food but are also highly relevant substructures of drugs and are increasingly applied for the development of lipid-based drug delivery systems. Lipids are prone to oxidative degradation, thus affecting the quality of food or medicines. Therefore, analytical methods or tools that enable to assess the degree of lipid oxidation are of utmost importance to guarantee food and drug safety. Herein, we report the design, synthesis, and application of the first-in-class fluorogenic triacylglycerols that enable a dynamic monitoring of lipid oxidation via straightforward fluorescence readout. Our fluorogenic triacylglycerols can be used both in an aqueous and lipid-based environment. Further, we showed that the sensitivity of our fluorescent tracers towards oxidation can be tuned by incorporating either saturated or unsaturated acyl chains in their triacylglycerol core structure. With this, we provide a first proof-of-principle for the applicability of fluorescently labelled triacylglycerols as tracers to monitor the dynamics of lipid oxidation, thus paving the way for novel discoveries in the area of lipid analytics.

Many known chemotherapeutic anticancer agents exhibit neutropenia as a dose-limiting side effect. In this paper we suggest a prodrug concept solving this problem for camptothecin (HO-cpt). The prodrug is programmed according to Boolean “AND” logic. In the absence of H2O2 (trigger T1), e.g. in the majority of normal cells, it exists as an inactive oligomer. In cancer cells and in primed neutrophils (high H2O2), the oligomer is disrupted forming intermediate (inactive) lipophilic cationic species. These are accumulated in mitochondria (Mit) of cancer cells, where they are activated by hydrolysis at mitochondrial pH 8 (trigger T2) with formation of camptothecin. In contrast, the intermediates remain stable in neutrophils lacking Mit and therefore a source of T2. In this paper we demonstrated a proof-of-concept. Our prodrug exhibits antitumor activity both in vitro and in vivo, but is not toxic to normal cell and neutrophils in contrast to known single trigger prodrugs and the parent drug HO-cpt.

Pro-drugs, which ideally release their active compound only at the site of action, i.e., in a cancer cell, are a promising approach towards an increased specificity and hence reduced side effects in chemotherapy. A popular form of pro-drugs is esters, which are activated upon their hydrolysis. Since carboxylesterases that catalyse such a hydrolysis reaction are also abundant in normal tissue, it is of great interest whether a putative pro-drug is a probable substrate of such an enzyme and hence bears the danger of being activated not just in the target environment, i.e., in cancer cells. In this work, we study the binding mode of carboxylesters of the drug molecule camptothecin, which is an inhibitor of topoisomerase I, of varying size to human carboxylesterase 2 (HCE2) by molecular docking and molecular dynamics simulations. A comparison to irinotecan, known to be a substrate of HCE2, shows that all three pro-drugs analysed in this work can bind to the HCE2 protein, but not in a pose that is well suited for subsequent hydrolysis. Our data suggest, moreover, that for the irinotecan substrate, a reactant-competent pose is stabilised once the initial proton transfer from the putative nucleophile Ser202 to the His431 of the catalytic triad has already occurred. Our simulation work also shows that it is important to go beyond the static models obtained from molecular docking and include the flexibility of enzyme–ligand complexes in solvents and at a finite temperature. Under such conditions, the pro-drugs studied in this work are unlikely to be hydrolysed by the HCE2 enzyme, indicating a low risk of undesired drug release in normal tissue.

Many known chemotherapeutic anticancer agents exhibit neutropenia as a dose-limiting side effect. In this paper we suggest a prodrug concept solving this problem for camptothecin (HO-cpt). The prodrug is programmed according to Boolean “AND” logic. It requires for its activation the simultaneous presence of triggers T1 (H2O2) and T2 (pH 8 in mitochondria: Mit). The level of H2O2 in cancer cells is higher than that in normal cells. Thus, T1 discriminates cancer cells from the majority of normal cells excluding neutrophils, known to produce elevated levels of H2O2. T2 discriminates cancer cells from neutrophils, since the former cells have a higher number of Mit. We demonstrated that our prodrug exhibits antitumor activity both in vitro and in vivo, but is not toxic to normal cell and neutrophils in contrast to known single trigger prodrugs and the parent drug HO-cpt.