Search

Abstract Apicidins are a class of naturally occurring cyclic tetrapeptides produced by few strains within the Fusarium genus. These secondary metabolites have gained significant attention due to their antiprotozoal activity through HDAC inhibition, thereby highlighting their potential for the treatment of malaria. Predominantly, apicidins have been isolated from Fusarium semitectum, offering a deep insight into the biosynthetic pathway responsible for their formation. A similar biosynthetic gene cluster has also been identified in the rice pathogenic fungus F. fujikuroi, leading the discovery of three additional apicidins through genetic manipulation. Routine mass spectrometric screening of these compound-producing strains revealed another metabolite structurally related to previously studied apicidins. By optimizing culture conditions and developing an effective isolation method, we obtained a highly pure substance, whose chemical structure was fully elucidated using NMR and HRMS fragmentation. Further studies were conducted to determine cytotoxicity, antimalarial activity, and HDAC inhibitory activity of this new secondary metabolite alongside the previously known apicidins. This work not only expands the apicidin class with a new member but also provides extensive insights and comparative analysis of apicidin-like substances produced by F. fujikuroi. Graphical Abstract

Histone deacetylases (HDACs) play a key role in the control of transcription, cell proliferation, and migration. FDA-approved histone deacetylase inhibitors (HDACi) demonstrate clinical efficacy in the treatment of different T-cell lymphomas and multiple myeloma. However, due to unselective inhibition, they display a wide range of adverse effects. One approach to avoiding off-target effects is the use of prodrugs enabling a controlled release of the inhibitor in the target tissue. Herein, we describe the synthesis and biological evaluation of HDACi prodrugs with photo-cleavable protecting groups masking the zinc-binding group of the established HDACi DDK137 (I) and VK1 (II). Initial decaging experiments confirmed that the photocaged HDACi pc-I could be deprotected to its parent inhibitor I. In HDAC inhibition assays, pc-I displayed only low inhibitory activity against HDAC1 and HDAC6. After irradiation with light, the inhibitory activity of pc-I strongly increased. Subsequent MTT viability assays, whole-cell HDAC inhibition assays, and immunoblot analysis confirmed the inactivity of pc-I at the cellular level. Upon irradiation, pc-I demonstrated pronounced HDAC inhibitory and antiproliferative activities which were comparable to the parent inhibitor I. Additionally, only phototreated pc-I was able to induce apoptosis in Annexin V/PI and caspase-Glo 3/7 assays, making pc-I a valuable tool for the development of light-activatable HDACi.

The degree of acetylation of lysine residues on histones influences the accessibility of DNA and, furthermore, the gene expression. Histone deacetylases (HDACs) are overexpressed in various tumour diseases, resulting in the interest in HDAC inhibitors for cancer therapy. The aim of this work is the development of a novel 18F-labelled HDAC1/2-specific inhibitor with a benzamide-based zinc-binding group to visualize these enzymes in brain tumours by positron emission tomography (PET). BA3, exhibiting high inhibitory potency for HDAC1 (IC50 = 4.8 nM) and HDAC2 (IC50 = 39.9 nM), and specificity towards HDAC3 and HDAC6 (specificity ratios >230 and >2080, respectively), was selected for radiofluorination. The two-step one-pot radiosynthesis of [18F]BA3 was performed in a TRACERlab FX2 N radiosynthesizer by a nucleophilic aliphatic substitution reaction. The automated radiosynthesis of [18F]BA3 resulted in a radiochemical yield of 1%, a radiochemical purity of >96% and a molar activity between 21 and 51 GBq/µmol (n = 5, EOS). For the characterization of BA3, in vitro and in vivo experiments were carried out. The results of these pharmacological and pharmacokinetic studies indicate a suitable inhibitory potency of BA3, whereas the applicability for non-invasive imaging of HDAC1/2 by PET requires further optimization of the properties of this compound.