11C‐ and 18F‐Labeled Radioligands for P‐Glycoprotein Imaging by Positron Emission Tomography

P‐Glycoprotein (P‐gp) is an efflux transporter widely expressed at the human blood–brain barrier. It is involved in xenobiotics efflux and in onset and progression of neurodegenerative disorders. For these reasons, there is great interest in the assessment of P‐gp expression and function by noninvasive techniques such as positron emission tomography (PET). Three radiolabeled aryloxazole derivatives: 2‐[2‐(2‐methyl‐(¹¹C)‐5‐methoxyphenyl)oxazol‐4‐ylmethyl]‐6,7‐dimethoxy‐1,2,3,4‐tetrahydroisoquinoline ([¹¹C]‐ 5 ); 2‐[2‐(2‐fluoromethyl‐(¹⁸F)‐5‐methoxyphenyl)oxazol‐4‐ylmethyl]‐6,7‐dimethoxy‐1,2,3,4‐tetra‐hydroisoquinoline ([¹⁸F]‐ 6 ); and 2‐[2‐(2‐fluoroethyl‐(¹⁸F)‐5‐methoxyphenyl)oxazol‐4‐ylmethyl]‐6,7‐dimethoxy‐1,2,3,4‐tetrahydroisoquinoline ([¹⁸F]‐ 7 ), were tested in several in vitro biological assays to assess the effect of the aryl substituent in terms of potency and mechanism of action toward P‐gp. Methyl derivative [¹¹C]‐ 5 is a potent P‐gp substrate, whereas the corresponding fluoroethyl derivative [¹⁸F]‐ 7 is a P‐gp inhibitor. Fluoromethyl compound [¹⁸F]‐ 6 is classified as a non‐transported P‐gp substrate, because its efflux increases after cyclosporine A modulation. These studies revealed a promising substrate and inhibitor, [¹¹C]‐ 5 and [¹⁸F]‐ 7 , respectively, for in vivo imaging of P‐gp by using PET.     

Why Hydroxamates May Not Be the Best Histone Deacetylase Inhibitors—What Some May Have Forgotten or Would Rather Forget?

Hydroxamate‐based histone deacetylase inhibitors (HDACIs) have been approved as therapeutic agents by the US Food and Drug Administration for use in oncology applications. While the potential utility of such HDACIs in other areas of medicinal chemistry is tremendous, there are significant concerns that “pan‐HDAC inhibitors” may be too broadly acting and/or toxic for clinical use beyond oncology. In addition to the isozyme selectivity challenge, the potential mutagenicity of hydroxamate‐containing HDAC inhibitors represents a major hindrance in their application to other therapeutic areas. Herein we report on the mutagenicity of known hydroxamates, discuss the mechanisms responsible for their genotoxicity, and review some of the current alternatives to hydroxamates. We conclude that the hydroxamate group, while providing high‐potency HDACIs, is not necessarily the best zinc‐binding group for HDACI drug discovery.     

Antivirulence Isoquinolone Mannosides: Optimization of the Biaryl Aglycone for FimH Lectin Binding Affinity and Efficacy in the Treatment of Chronic UTI

Uropathogenic E. coli (UPEC) employ the mannose‐binding adhesin FimH to colonize the bladder epithelium during urinary tract infection (UTI). Previously reported FimH antagonists exhibit good potency and efficacy, but low bioavailability and a short half‐life in vivo. In a rational design strategy, we obtained an X‐ray structure of lead mannosides and then designed mannosides with improved drug‐like properties. We show that cyclizing the carboxamide onto the biphenyl B‐ring aglycone of biphenyl mannosides into a fused heterocyclic ring, generates new biaryl mannosides such as isoquinolone 22 (2‐methyl‐4‐(1‐oxo‐1,2‐dihydroisoquinolin‐7‐yl)phenyl α‐d ‐mannopyranoside) with enhanced potency and in vivo efficacy resulting from increased oral bioavailability. N‐Substitution of the isoquinolone aglycone with various functionalities produced a new potent subseries of FimH antagonists. All analogues of the subseries have higher FimH binding affinity than unsubstituted lead 22 , as determined by thermal shift differential scanning fluorimetry assay. Mannosides with pyridyl substitution on the isoquinolone group inhibit bacteria‐mediated hemagglutination and prevent biofilm formation by UPEC with single‐digit nanomolar potency, which is unprecedented for any FimH antagonists or any other antivirulence compounds reported to date.     

Enantiospecific Synthesis and Cytotoxicity Evaluation of Oximidine II Analogues

Analogues of the anticancer natural product oximidine II were prepared and evaluated for cytotoxicity. One analogue of oximidine II that carries a C15 allylic amide side chain as well as two analogues with C15 vinyl sulfone side chains were found to lack cytotoxicity against the cancer cell line SK‐Mel‐5, thereby confirming the necessity of the C15 enamide side chain of oximidine II for cytotoxicity. Four analogues, designed by comparative molecular similarity index analysis (CoMSIA), that feature a less complex macrolactone scaffold were prepared and tested. The two analogues carrying a C15 vinyl sulfone group and the two analogues with a C15 oximidine II enamide side chain showed weak cytotoxicity against the SK‐Mel‐5 cell line and other cell lines, indicating that the designed simplified macrocycles cannot replace the oximidine II macrocycle.     

Theranostic Polyaminocarboxylate–Cyanine–Transferrin Conjugate for Anticancer Therapy and Near‐Infrared Optical Imaging

Iron chelation therapy has been recognized as a promising antitumor therapeutic strategy. Herein we report a novel theranostic agent for targeted iron chelation therapy and near‐infrared (NIR) optical imaging of cancers. The theranostic agent was prepared by incorporation of a polyaminocarboxylate‐based cytotoxic chelating agent (N‐NE3TA; 7‐[2‐[(carboxymethyl)amino]ethyl]‐1,4,7‐triazacyclononane‐1,4‐diacetic acid) and a NIR fluorescent cyanine dye (Cy5.5) onto a tumor‐targeting transferrin (Tf). The N‐NE3TA–Tf conjugate (without Cy5.5) was characterized and evaluated for antiproliferative activity in HeLa, HT29, and PC3 cancer cells, which have elevated expression levels of the transferrin receptor (TfR). The N‐NE3TA–Tf conjugate displayed significant inhibitory activity against all three cancer cell lines. The NIR dye Cy5.5 was then incorporated into N‐NE3TA–Tf, and the resulting cytotoxic and fluorescent transferrin conjugate N‐NE3TA–Tf–Cy5.5 was shown by microscopy to enter TfR‐overexpressing cancer cells. This theranostic conjugate has potential application for dual use in targeted iron chelation cancer therapy and NIR fluorescence imaging.     

Synthesis and Evaluation of Glycoconjugates Comprising N‐Acyl‐Modified Thomsen–Friedenreich Antigens as Anticancer Vaccines

Thomsen–Friedenreich (TF) antigen is an important tumor‐associated carbohydrate antigen. Its low immunogenicity, however, limits its application in the development of anticancer vaccines. To solve this problem, several N‐acyl‐modified TF derivatives were synthesized and conjugated with carrier protein CRM197 (a mutated diphtheria toxoid cross‐reactive material). The immunological results in BALB/c mice demonstrated that these modified TF antigen conjugates could stimulate the production of higher titers of IgG antibodies that cross‐reacted with native TF antigen. These glycoconjugates showed strong lymphocyte proliferative response, suggesting that they can induce cellular immunity. Furthermore, the elicited antisera reacted strongly with TF‐positive tumor cells (4T1). In particular, the N‐monofluoroacetyl‐modified TF conjugate 4 ‐CRM197 showed the strongest complement‐dependent cytotoxicity effect against 4T1 cells, implying the potential of this glycoconjugate as an anticancer vaccine.     

Exploration of a Library of 3,4‐(Methylenedioxy)aniline‐Derived Semicarbazones as Dual Inhibitors of Monoamine Oxidase and Acetylcholinesterase: Design,Synthesis, and Evaluation

A library of 3,4‐(methylenedioxy)aniline‐derived semicarbazones was designed, synthesized, and evaluated as monoamine oxidase (MAO) and acetylcholinesterase (AChE) inhibitors for the treatment of neurodegenerative diseases. Most of the new compounds selectively inhibited MAO‐B and AChE, with IC₅₀ values in the micro‐ or nanomolar ranges. Compound 16 , 1‐(2,6‐dichlorobenzylidene)‐4‐(benzo[1,3]dioxol‐5‐yl)semicarbazide presented a balanced multifunctional profile of MAO‐A (IC₅₀=4.52±0.032 μm ), MAO‐B (IC₅₀=0.059±0.002 μm ), and AChE (IC₅₀=0.0087±0.0002 μm ) inhibition without neurotoxicity. Kinetic studies revealed that compound 16 exhibits competitive and reversible inhibition against MAO‐A and MAO‐B, and mixed‐type inhibition against AChE. Molecular docking studies further revealed insight into the possible interactions within the enzyme–inhibitor complexes. The most active compounds were found to interact with the enzymes through hydrogen bonding and hydrophobic interactions. Additionally, in silico molecular properties and ADME properties of the synthesized compounds were calculated to explore their drug‐like characteristics.     

Discovery of Highly Potent Dual Orexin Receptor Antagonists via a Scaffold‐Hopping Approach

Starting from suvorexant (trade name Belsomra), we successfully identified interesting templates leading to potent dual orexin receptor antagonists (DORAs) via a scaffold‐hopping approach. Structure–activity relationship optimization allowed us not only to improve the antagonistic potency on both orexin 1 and orexin 2 receptors (Ox1 and Ox2, respectively), but also to increase metabolic stability in human liver microsomes (HLM), decrease time‐dependent inhibition of cytochrome P450 (CYP) 3A4, and decrease P‐glycoprotein (Pgp)‐mediated efflux. Compound 80 c [{(1S,6R)‐3‐(6,7‐difluoroquinoxalin‐2‐yl)‐3,8‐diazabicyclo[4.2.0]octan‐8‐yl}(4‐methyl‐[1,1′‐biphenyl]‐2‐yl)methanone] is a potent and selective DORA that inhibits the stimulating effects of orexin peptides OXA and OXB at both Ox1 and Ox2. In calcium‐release assays, 80 c was found to exhibit an insurmountable antagonistic profile at both Ox1 and Ox2, while displaying a sleep‐promoting effect in rat and dog models, similar to that of the benchmark compound suvorexant.     

Development of Simplified Heterocyclic Acetogenin Analogues as Potent and Selective Trypanosoma brucei Inhibitors

Neglected tropical diseases caused by parasitic infections are an ongoing and increasing concern. They are a burden to human and animal health, having the most devastating effect on the world′s poorest countries. Building upon our previously reported triazole analogues, in this study we describe the synthesis and biological testing of other novel heterocyclic acetogenin‐inspired derivatives, namely 3,5‐isoxazoles, furoxans, and furazans. Several of these compounds maintain low‐micromolar levels of inhibition against Trypanosoma brucei, whilst having no observable inhibitory effect on mammalian cells, leading to the possibility of novel lead compounds for selective treatment.     

4‐Biphenylalanine‐ and 3‐Phenyltyrosine‐Derived Hydroxamic Acids as Inhibitors of the JumonjiC‐Domain‐Containing Histone Demethylase KDM4A

Overexpression of the histone lysine demethylase KDM4A, which regulates H3K9 and H3K36 methylation states, has been related to the pathology of several human cancers. We found that a previously reported hydroxamate‐based histone deacetylase (HDAC) inhibitor (SW55) was also able to weakly inhibit this demethylase with an IC₅₀ value of 25.4 μm . Herein we report the synthesis and biochemical evaluations, with two orthogonal in vitro assays, of a series of derivatives of this lead structure. With extensive chemical modifications on the lead structure, also by exploiting the versatility of the radical arylation with aryldiazonium salts, we were able to increase the potency of the derivatives against KDM4A to the low‐micromolar range and, more importantly, to obtain demethylase selectivity with respect to HDACs. Cell‐permeable derivatives clearly showed a demethylase‐inhibition‐dependent antiproliferative effect against HL‐60 human promyelocytic leukemia cells.