Borinostats: solid-phase synthesis of carborane-capped histone deacetylase inhibitors with a tailor-made selectivity profile

Fusing Bismuth and Mercaptocarboranes: Design and Biological Evaluation of Low-Toxicity Antimicrobial Thiolato Complexes

This study proposes an innovative strategy to enhance the pharmacophore model of antimicrobial bismuth thiolato complex drugs by substituting hydrocarbon ligand structures with boron clusters, particularly icosahedral closo-dicarbadodecaborane (C2B10H12, carboranes). The hetero- and homoleptic mercaptocarborane complexes BiPh2L (1) and BiL3 (2) (L=9-S-1,2-C2B10H11) were prepared from 9-mercaptocarborane (HL) and triphenylbismuth. Comprehensive characterization using NMR, IR, MS, and XRD techniques confirmed their successful synthesis. Evaluation of antimicrobial activity in a liquid broth microdilution assay demonstrated micromolar to submicromolar minimum inhibitory concentrations (MIC) suggesting high effectiveness against S. aureus and limited efficacy against E. coli. This study highlights the potential of boron-containing bismuth complexes as promising antimicrobial agents, especially targeting Gram-positive bacteria, thus contributing to the advancement of novel therapeutic approaches.

Solid-Phase Parallel Synthesis of Dual Histone Deacetylase-Cyclooxygenase Inhibitors

Multi-target drugs (MTDs) are emerging alternatives to combination therapies. Since both histone deacetylases (HDACs) and cyclooxygenase-2 (COX-2) are known to be overexpressed in several cancer types, we herein report the design, synthesis, and biological evaluation of a library of dual HDAC-COX inhibitors. The designed compounds were synthesized via an efficient parallel synthesis approach using preloaded solid-phase resins. Biological in vitro assays demonstrated that several of the synthesized compounds possess pronounced inhibitory activities against HDAC and COX isoforms. The membrane permeability and inhibition of cellular HDAC activity of selected compounds were confirmed by whole-cell HDAC inhibition assays and immunoblot experiments. The most promising dual inhibitors, C3 and C4, evoked antiproliferative effects in the low micromolar concentration range and caused a significant increase in apoptotic cells. In contrast to previous reports, the simultaneous inhibition of HDAC and COX activity by dual HDAC-COX inhibitors or combination treatments with vorinostat and celecoxib did not result in additive or synergistic anticancer activities.

Development of Fluorinated Peptoid-Based Histone Deacetylase (HDAC) Inhibitors for Therapy-Resistant Acute Leukemia

Using a microwave-assisted protocol, we synthesized 16 peptoid-capped HDAC inhibitors (HDACi) with fluorinated linkers and identified two hit compounds. In biochemical and cellular assays, 10h stood out as a potent unselective HDACi with remarkable cytotoxic potential against different therapy-resistant leukemia cell lines. 10h demonstrated prominent antileukemic activity with low cytotoxic activity toward healthy cells. Moreover, 10h exhibited synergistic interactions with the DNA methyltransferase inhibitor decitabine in AML cell lines. The comparison of crystal structures of HDAC6 complexes with 10h and its nonfluorinated counterpart revealed a similar occupation of the L1 loop pocket but slight differences in zinc coordination. The substitution pattern of the acyl residue turned out to be crucial in terms of isoform selectivity. The introduction of an isopropyl group onto the phenyl ring provided the highly HDAC6-selective inhibitor 10p, which demonstrated moderate synergy with decitabine and exceeded the HDAC6 selectivity of tubastatin A.

Carboranes as unique pharmacophores in antitumor medicinal chemistry

Carborane is a carbon-boron molecular cluster that can be viewed as a 3D analog of benzene. It features special physical and chemical properties, and thus has the potential to serve as a new type of pharmacophore for drug design and discovery. Based on the relative positions of two cage carbons, icosahedral closo-carboranes can be classified into three isomers, ortho-carborane (o-carborane, 1,2-C2B10H12), meta-carborane (m-carborane, 1,7-C2B10H12), and para-carborane (p-carborane, 1,12-C2B10H12), and all of them can be deboronated to generate their nido- forms. Cage compound carborane and its derivatives have been demonstrated as useful chemical entities in antitumor medicinal chemistry. The applications of carboranes and their derivatives in the field of antitumor research mainly include boron neutron capture therapy (BNCT), as BNCT/photodynamic therapy dual sensitizers, and as anticancer ligands. This review summarizes the research progress on carboranes achieved up to October 2021, with particular emphasis on signaling transduction pathways, chemical structures, and mechanistic considerations of using carboranes.

Synthesis, Antiplasmodial, and Antileukemia Activity of Dihydroartemisinin–HDAC Inhibitor Hybrids as Multitarget Drugs

Artemisinin-based combination therapies (ACTs) are the gold standard for the treatment of malaria, but the efficacy is threatened by the development of parasite resistance. Histone deacetylase inhibitors (HDACis) are an emerging new class of potential antiplasmodial drugs. In this work, we present the design, synthesis, and biological evaluation of a mini library of dihydroartemisinin–HDACi hybrid molecules. The screening of the hybrid molecules for their activity against selected human HDAC isoforms, asexual blood stage P. falciparum parasites, and a panel of leukemia cell lines delivered important structure–activity relationships. All synthesized compounds demonstrated potent activity against the 3D7 and Dd2 line of P. falciparum with IC₅₀ values in the single-digit nanomolar range. Furthermore, the hybrid (α)-7c displayed improved activity against artemisinin-resistant parasites compared to dihydroartemisinin. The screening of the compounds against five cell lines from different leukemia entities revealed that all hydroxamate-based hybrids (7a–e) and the ortho-aminoanilide 8 exceeded the antiproliferative activity of dihydroartemisinin in four out of five cell lines. Taken together, this series of hybrid molecules represents an excellent starting point toward the development of antimalarial and antileukemia drug leads.