Aromatase and dual aromatase-steroid sulfatase inhibitors from the letrozole and vorozole templates

Concurrent inhibition of aromatase and steroid sulfatase (STS) may provide a more effective treatment for hormone‐dependent breast cancer than monotherapy against individual enzymes, and several dual aromatase–sulfatase inhibitors (DASIs) have been reported. Three aromatase inhibitors with sub‐nanomolar potency, better than the benchmark agent letrozole, were designed. To further explore the DASI concept, a new series of letrozole‐derived sulfamates and a vorozole‐based sulfamate were designed and biologically evaluated in JEG‐3 cells to reveal structure–activity relationships. Amongst achiral and racemic compounds, 2‐bromo‐4‐(2‐(4‐cyanophenyl)‐2‐(1H‐1,2,4‐triazol‐1‐yl)ethyl)phenyl sulfamate is the most potent DASI (aromatase: IC₅₀=0.87 nM ; STS: IC₅₀=593 nM ). The enantiomers of the phenolic precursor to this compound were separated by chiral HPLC and their absolute configuration determined by X‐ray crystallography. Following conversion to their corresponding sulfamates, the S‐(+)‐enantiomer was found to inhibit aromatase and sulfatase most potently (aromatase: IC₅₀=0.52 nM ; STS: IC₅₀=280 nM ). The docking of each enantiomer and other ligands into the aromatase and sulfatase active sites was also investigated.     

Synthesis and Structure–Activity Relationship Studies of Derivatives of the Dual Aromatase–Sulfatase Inhibitor 4‐{[(4‐Cyanophenyl)(4H‐1,2,4‐triazol‐4‐yl)amino]methyl}phenyl sulfamate

4‐{[(4‐Cyanophenyl)(4H‐1,2,4‐triazol‐4‐yl)amino]methyl}phenyl sulfamate and its ortho‐halogenated (F, Cl, Br) derivatives are first‐generation dual aromatase and sulfatase inhibitors (DASIs). Structure–activity relationship studies were performed on these compounds, and various modifications were made to their structures involving relocation of the halogen atom, introduction of more halogen atoms, replacement of the halogen with another group, replacement of the methylene linker with a difluoromethylene linker, replacement of the para‐cyanophenyl ring with other ring structures, and replacement of the triazolyl group with an imidazolyl group. The most potent in vitro DASI discovered is an imidazole derivative with IC₅₀ values against aromatase and steroid sulfatase in a JEG‐3 cell preparation of 0.2 and 2.5 nM , respectively. The parent phenol of this compound inhibits aromatase with an IC₅₀ value of 0.028 nM in the same assay.     

Synthesis of aromatase inhibitors and dual aromatase steroid sulfatase inhibitors by linking an arylsulfamate motif to 4-(4H-1,2,4-triazol-4-ylamino)benzonitrile: SAR, crystal structures, in vitro and in vivo activities

4-(((4-Cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)phenyl sulfamate (6 a) was the first dual aromatase-sulfatase inhibitor (DASI) reported. Several series of its derivatives with various linker systems between the steroid sulfatase (STS) and the aromatase inhibitory pharmacophores were synthesised and evaluated in JEG-3 cells. The X-ray crystal structures of the aromatase inhibitors, DASI precursors 42 d and 60, and DASI 43 h were determined. Nearly all derivatives show improved in vitro aromatase inhibition over 6 a but decreased STS inhibition. The best aromatase inhibitor is 42 e (IC(50)=0.26 nM) and the best DASI is 43 e (IC(50 aromatase)=0.45 nM, IC(50 STS)=1200 nM). SAR for aromatase inhibition shows that compounds containing an alkylene- and thioether-based linker system are more potent than those that are ether-, sulfone-, or sulfonamide-based, and that the length of the linker has a limited effect on aromatase inhibition beyond two methylene units. Compounds 43 d-f were studied in vivo (10 mg kg(-1), single, p.o.). The most potent DASI is 43 e, which inhibited PMSG-induced plasma estradiol levels by 92 % and liver STS activity by 98 % 3 h after dosing. These results further strengthen the concept of designing and developing DASIs for potential treatment of hormone-related cancers.     

MAO Inhibitory Activity of 2‐Arylbenzofurans versus 3‐Arylcoumarins: Synthesis,in vitro Study,and Docking Calculations

Monoamine oxidase (MAO) is an important drug target for the treatment of neurological disorders. Several 3‐arylcoumarin derivatives were previously described as interesting selective MAO‐B inhibitors. Preserving the trans‐stilbene structure, a series of 2‐arylbenzofuran and corresponding 3‐arylcoumarin derivatives were synthesized and evaluated as inhibitors of both MAO isoforms, MAO‐A and MAO‐B. In general, both types of derivatives were found to be selective MAO‐B inhibitors, with IC₅₀ values in the nano‐ to micromolar range. 5‐Nitro‐2‐(4‐methoxyphenyl)benzofuran ( 8 ) is the most active compound of the benzofuran series, presenting MAO‐B selectivity and reversible inhibition (IC₅₀=140 nM ). 3‐(4′‐Methoxyphenyl)‐6‐nitrocoumarin ( 15 ), with the same substitution pattern as that of compound 8 , was found to be the most active MAO‐B inhibitor of the coumarin series (IC₅₀=3 nM ). However, 3‐phenylcoumarin 14 showed activity in the same range (IC₅₀=6 nM ), is reversible, and also severalfold more selective than compound 15 . Docking experiments for the most active compounds into the MAO‐B and MAO‐A binding pockets highlighted different interactions between the derivative classes (2‐arylbenzofurans and 3‐arylcoumarins), and provided new information about the enzyme–inhibitor interaction and the potential therapeutic application of these scaffolds.     

Structure-activity relationship for the first-in-class clinical steroid sulfatase inhibitor Irosustat (STX64, BN83495)

Structure–activity relationship studies were conducted on Irosustat (STX64, BN83495), the first steroid sulfatase (STS) inhibitor to enter diverse clinical trials for patients with advanced hormone‐dependent cancer. The size of its aliphatic ring was expanded; its sulfamate group was N,N‐dimethylated, relocated to another position and flanked by an adjacent methoxy group; and series of quinolin‐2(1H)‐one and quinoline derivatives of Irosustat were explored. The STS inhibitory activities of the synthesised compounds were assessed in a preparation of JEG‐3 cells. Stepwise enlargement of the aliphatic ring from 7 to 11 members increases potency, although a further increase in ring size is detrimental. The best STS inhibitors in vitro had IC₅₀ values between 0.015 and 0.025 nM . Other modifications made to Irosustat were found to either abolish or significantly weaken its activity. An azomethine adduct of Irosustat with N,N‐dimethylformamide (DMF) was isolated, and crystal structures of Irosustat and this adduct were determined. Docking studies were conducted to explore the potential interactions between compounds and the active site of STS, and suggest a sulfamoyl group transfer to formylglycine 75 during the inactivation mechanism.     

Design,Synthesis, and Biological Evaluation of 3‐Benzazepin‐1‐ols as NR2B‐Selective NMDA Receptor Antagonists

Cleavage and reconstitution of a bond in the piperidine ring of ifenprodil ( 1 ) leads to 7‐methoxy‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepin‐1‐ols, a novel class of NR2B‐selective NMDA receptor antagonists. The secondary amine 7‐methoxy‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepin‐1‐ol ( 12 ), which was synthesized in six steps starting from 2‐phenylethylamine 3 , represents the central building block for the introduction of several N‐linked residues. A distance of four methylene units between the basic nitrogen atom and the phenyl residue in the side chain results in high NR2B affinity. The 4‐phenylbutyl derivative 13 (WMS‐1405, K_i=5.4 nM ) and the conformationally restricted 4‐phenylcyclohexyl derivative 31 (K_i=10 nM ) represent the most potent NR2B ligands of this series. Whereas 13 shows excellent selectivity, the 4‐phenylcyclohexyl derivative 31 also interacts with σ₁ (K_i=33 nM ) and σ₂ receptors (K_i=82 nM ). In the excitotoxicity assay the phenylbutyl derivative 13 inhibits the glutamate‐induced cytotoxicity with an IC₅₀ value of 360 nM , indicating that 13 is an NMDA antagonist.     

8‐Benzyltetrahydropyrazino[2,1‐f]purinediones: Water‐Soluble Tricyclic Xanthine Derivatives as Multitarget Drugs for Neurodegenerative Diseases

8‐Benzyl‐substituted tetrahydropyrazino[2,1‐f]purinediones were designed as tricyclic xanthine derivatives containing a basic nitrogen atom in the tetrahydropyrazine ring to improve water solubility. A library of 69 derivatives was prepared and evaluated in radioligand binding studies at adenosine receptor (AR) subtypes and for their ability to inhibit monoamine oxidases (MAO). Potent dual‐target‐directed A₁/A_2A adenosine receptor antagonists were identified. Several compounds showed triple‐target inhibition; one of the best compounds was 8‐(2,4‐dichloro‐5‐fluorobenzyl)‐1,3‐dimethyl‐6,7,8,9‐tetrahydropyrazino[2,1‐f]purine‐2,4(1H,3H)‐dione ( 72 ) (human AR: K_i A₁ 217 nM , A_2A 233 nM ; IC₅₀ MAO‐B: 508 nM ). Dichlorinated compound 36 [8‐(3,4‐dichlorobenzyl)‐1,3‐dimethyl‐6,7,8,9‐tetrahydropyrazino[2,1‐f]purine‐2,4(1H,3H)‐dione] was found to be the best triple‐target drug in rat (K_i A₁ 351 nM , A_2A 322 nm; IC₅₀ MAO‐B: 260 nM ), and may serve as a useful tool for preclinical proof‐of‐principle studies. Compounds that act at multiple targets relevant for symptomatic as well as disease‐modifying treatment of neurodegenerative diseases are expected to show advantages over single‐target therapeutics.     

3D‐QSAR‐Assisted Drug Design: Identification of a Potent Quinazoline‐Based Aurora Kinase Inhibitor

We describe the 3D‐QSAR‐assisted design of an Aurora kinase A inhibitor with improved physicochemical properties, in vitro activity, and in vivo pharmacokinetic profiles over those of the initial lead. Three different 3D‐QSAR models were built and validated by using a set of 66 pyrazole (Model I) and furanopyrimidine (Model II) compounds with IC₅₀ values toward Aurora kinase A ranging from 33 nM to 10.5 μM . The best 3D‐QSAR model, Model III, constructed with 24 training set compounds from both series, showed robustness (r²_CV=0.54 and 0.52 for CoMFA and CoMSIA, respectively) and superior predictive capacity for 42 test set compounds (R²_pred=0.52 and 0.67, CoMFA and CoMSIA). Superimposition of CoMFA and CoMSIA Model III over the crystal structure of Aurora kinase A suggests the potential to improve the activity of the ligands by decreasing the steric clash with Val147 and Leu139 and by increasing hydrophobic contact with Leu139 and Gly216 residues in the solvent‐exposed region of the enzyme. Based on these suggestions, the rational redesign of furanopyrimidine 24 (clog P=7.41; Aurora A IC₅₀=43 nM ; HCT‐116 IC₅₀=400 nM ) led to the identification of quinazoline 67 (clog P=5.28; Aurora A IC₅₀=25 nM ; HCT‐116 IC₅₀=23 nM ). Rat in vivo pharmacokinetic studies showed that 67 has better systemic exposure after i.v. administration than 24 , and holds potential for further development.     

N‐Benzyl Substitution of Polyhydroxypyrrolidines: The Way to Selective Inhibitors of Golgi α‐Mannosidase II

Inhibition of the biosynthesis of complex N‐glycans in the Golgi apparatus influences progress of tumor growth and metastasis. Golgi α‐mannosidase II (GMII) has become a therapeutic target for drugs with anticancer activities. One critical task for successful application of GMII drugs in medical treatments is to decrease their unwanted co‐inhibition of lysosomal α‐mannosidase (LMan), a weakness of all known potent GMII inhibitors. A series of novel N‐substituted polyhydroxypyrrolidines was synthesized and tested with modeled GH38 α‐mannosidases from Drosophila melanogaster (GMIIb and LManII). The most potent structures inhibited GMIIb (K_i=50–76 μm , as determined by enzyme assays) with a significant selectivity index of IC₅₀(LManII)/IC₅₀(GMIIb) >100. These compounds also showed inhibitory activities in in vitro assays with cancer cell lines (leukemia, IC₅₀=92–200 μm ) and low cytotoxic activities in normal fibroblast cell lines (IC₅₀>200 μm ). In addition, they did not show any significant inhibitory activity toward GH47 Aspergillus saitoiα1,2‐mannosidase. An appropriate stereo configuration of hydroxymethyl and benzyl functional groups on the pyrrolidine ring of the inhibitor may lead to an inhibitor with the required selectivity for the active site of a target α‐mannosidase.     

Monoamine Oxidase (MAO) Inhibitory Activity: 3‐Phenylcoumarins versus 4‐Hydroxy‐3‐phenylcoumarins

Monoamine oxidase (MAO) is a useful target in the treatment of neurodegenerative diseases and depressive disorders. Both isoforms, MAO‐A and MAO‐B, are known to play critical roles in disease progression, and as such, the identification of novel, potent and selective inhibitors is an important research goal. Here, two series of 3‐phenylcoumarin derivatives were synthesized and evaluated against MAO‐A and MAO‐B. Most of the compounds tested acted preferentially on MAO‐B, with IC₅₀ values in the micromolar to nanomolar range. Only 6‐chloro‐4‐hydroxy‐3‐(2’‐hydroxyphenyl)coumarin exhibited activity against the MAO‐A isoform, while still retaining good selectivity for MAO‐B. 6‐Chloro‐3‐phenylcoumarins unsubstituted at the 4 position were found to be more active as MAO‐B inhibitors than the corresponding 4‐hydroxylated coumarins. For 4‐unsubstituted coumarins, meta and para positions on the 3‐phenyl ring seem to be the most favorable for substitution. Molecular docking simulations were used to explain the observed hMAO‐B structure–activity relationships for this type of compound. 6‐Chloro‐3‐(3’‐methoxyphenyl)coumarin was the most active compound identified (IC₅₀=0.001 μM ) and is several times more potent and selective than the reference compound, R‐(?)‐deprenyl hydrochloride. This compound represents a novel tool for the further investigation of the therapeutic potential of MAO‐B inhibitors.     

Ex vivo and in vivo Evaluation of [18F]PR04.MZ in Rodents: A Selective Dopamine Transporter Imaging Agent

N‐4‐Fluorobut‐2‐yn‐1‐yl‐2β‐carbomethoxy‐3β‐phenyltropane (PR04.MZ) has been developed as dopamine transporter (DAT) ligand for molecular imaging. It contains a terminally fluorinated, conformationally constrained nitrogen substituent that is well suited for the introduction of fluorine‐18. The present report describes the pharmacological characterisation of [¹⁸F]PR04.MZ. The ligand shows an IC₅₀ value of 2 nM against human DAT, whereas the IC₅₀ value against human serotonin transporter and human noradrenalin transporter are lower (110 nM and 22 nM , respectively). Furthermore, its ex vivo organ distribution, its binding profile in the rat brain and reversibility of binding were examined. A μPET study illuminates a fast kinetic profile and specific binding to rat DAT.     

Fluorine‐Containing 6,7‐Dialkoxybiaryl‐Based Inhibitors for Phosphodiesterase 10 A: Synthesis and in vitro Evaluation of Inhibitory Potency,Selectivity, and Metabolism

Based on the potent phosphodiesterase 10 A (PDE10A) inhibitor PQ‐10, we synthesized 32 derivatives to determine relationships between their molecular structure and binding properties. Their roles as potential positron emission tomography (PET) ligands were evaluated, as well as their inhibitory potency toward PDE10A and other PDEs, and their metabolic stability was determined in vitro. According to our findings, halo‐alkyl substituents at position 2 of the quinazoline moiety and/or halo‐alkyloxy substituents at positions 6 or 7 affect not only the compounds′ affinity, but also their selectivity toward PDE10A. As a result of substituting the methoxy group for a monofluoroethoxy or difluoroethoxy group at position 6 of the quinazoline ring, the selectivity for PDE10A over PDE3A increased. The same result was obtained by 6,7‐difluoride substitution on the quinoxaline moiety. Finally, fluorinated compounds (R)‐7‐(fluoromethoxy)‐6‐methoxy‐4‐(3‐(quinoxaline‐2‐yloxy)pyrrolidine‐1‐yl)quinazoline ( 16 a ), 19 a – d , (R)‐tert‐butyl‐3‐(6‐fluoroquinoxalin‐2‐yloxy)pyrrolidine‐1‐carboxylate ( 29 ), and 35 (IC₅₀ PDE10A 11–65 nM ) showed the highest inhibitory potential. Further, fluoroethoxy substitution at position 7 of the quinazoline ring improved metabolic stability over that of the lead structure PQ‐10.     

3,5‐Bis(benzylidene)‐4‐oxo‐1‐phosphonopiperidines and Related Diethyl Esters: Potent Cytotoxins with Multi‐Drug‐Resistance Reverting Properties

A series of 3,5‐bis(benzylidene)‐4‐piperidones 3 were converted into the corresponding 3,5‐bis(benzylidene)‐1‐phosphono‐4‐piperidones 5 via diethyl esters 4 . The analogues in series 4 and 5 displayed marked growth inhibitory properties toward human Molt 4/C8 and CEM T‐lymphocytes as well as murine leukemia L1210 cells. In general, the N‐phosphono compounds 5 , which are more hydrophilic than the analogues in series 3 and 4 , were the most potent cluster of cytotoxins, and, in particular, 3,5‐bis‐(2‐nitrobenzylidene)‐1‐phosphono‐4‐piperidone 5 g had an average IC₅₀ value of 34 nM toward the two T‐lymphocyte cell lines. Four of the compounds displayed potent cytotoxicity toward a panel of nearly 60 human tumor cell lines, and nanomolar IC₅₀ values were observed in a number of cases. The mode of action of 5 g includes the induction of apoptosis and inhibition of cellular respiration. Most of the members of series 4 as well as several analogues in series 5 are potent multi‐drug resistance (MDR) reverting compounds. Various correlations were noted between certain molecular features of series 4 and 5 and cytotoxic properties, affording some guidelines in expanding this study.     

Design,Synthesis, in vitro MAO‐B Inhibitory Evaluation,and Computational Studies of Some 6‐Nitrobenzothiazole‐Derived Semicarbazones

Monoamine oxidase B (MAO‐B) is an important drug target for the treatment of neurological disorders. A series of 6‐nitrobenzothiazole‐derived semicarbazones were designed, synthesized, and evaluated as inhibitors of the rat brain MAO‐B isoenzyme. Most of the compounds were found to be potent inhibitors of MAO‐B, with IC₅₀ values in the nanomolar to micromolar range. Molecular docking studies were performed with AutoDock 4.2 to deduce the affinity and binding mode of these inhibitors toward the MAO‐B active site. The free energies of binding (ΔG) and inhibition constants (K_i) of the docked compounds were calculated by the Lamarckian genetic algorithm (LGA) of AutoDock 4.2. Good correlations between the calculated and experimental results were obtained. 1‐[(4‐Chlorophenyl)(phenyl)methylene]‐4‐(6‐nitrobenzothiazol‐2‐yl)semicarbazide emerged as the lead MAO‐B inhibitor, with top ranking in both the experimental MAO‐B assay (IC₅₀: 0.004±0.001 μM ) and in computational docking studies (K_i: 1.08 μM ). Binding mode analysis of potent inhibitors suggests that these compounds are well accommodated by the MAO‐B active site through stable hydrophobic and hydrogen bonding interactions. Interestingly, the 6‐nitrobenzothiazole moiety is stabilized in the substrate cavity with the aryl or diaryl residues extending up into the entrance cavity of the active site. According to our results, docking experiments could be an interesting approach for predicting the activity and binding interactions of this class of semicarbazones against MAO‐B. Thus, a binding site model consisting of three essential pharmacophoric features is proposed, and this can be used for the design of future MAO‐B inhibitors.     

Discovery,Synthesis and Characterization of a Highly Muscarinic Acetylcholine Receptor (mAChR)‐Selective M5‐Orthosteric Antagonist,VU0488130 (ML381): A Novel Molecular Probe

Of the five G‐protein‐coupled muscarinic acetylcholine receptors (mAChRs; M₁–M₅), M₅ is the least explored and understood due to a lack of mAChR subtype‐selective ligands. We recently performed a high‐throughput functional screen and identified a number of weak antagonist hits that are selective for the M₅ receptor. Here, we report an iterative parallel synthesis and detailed molecular pharmacologic profiling effort that led to the discovery of the first highly selective, central nervous system (CNS)‐penetrant M₅‐orthosteric antagonist, with sub‐micromolar potency (hM₅ IC₅₀=450 nM , hM₅ K_i=340 nM , M₁–M₄ IC₅₀ >30 μM ), enantiospecific inhibition, and an acceptable drug metabolism and pharmacokinetics (DMPK) profile for in vitro and electrophysiology studies. This compound will be a powerful tool and molecular probe for the further investigation into the role of M₅ in addiction and other diseases.     

The Tertiary Amine Nitrogen Atom of Piperazine Sulfonamides as a Novel Determinant of Potent and Selective β3‐Adrenoceptor Agonists

Novel compounds were prepared in fair to good yields as human β₃‐adrenoceptor (β₃‐AR) agonists. In particular, aryloxypropanolamines 7 a – d (EC₅₀=0.57–2.1 nM ) and arylethanolamines 12 a , b , e (EC₅₀=6.38–19.4 nM ) were designed to explore the effects of modifications at the right‐hand side of these molecules on their activity as β₃‐AR agonists. Piperidine sulfonamides 15 a – c , e – g (EC₅₀=6.1–36.2 nM ) and piperazine sulfonamide derivatives 20 – 29 (EC₅₀=1.79–49.3 nM ) were examined as compounds bearing a non‐aromatic linker on the right‐ and left‐hand sides of the molecules. Some piperazine sulfonamides were found to be potent and selective β₃‐AR agonists, even if the amine nitrogen atom is tertiary and not secondary, as is the case for all β₃‐AR agonists reported so far. (S)‐3‐{4‐{N‐{4‐{2‐[2‐Hydroxy‐3‐(4‐hydroxyphenoxy)propylamino]ethyl}phenyl}sulfamoyl}phenoxy}propanoic acid ( 7 d ; EC₅₀=0.57 nM ), (R)‐N‐{4‐[2‐(2‐hydroxy‐2‐phenylethylamino)ethyl]phenyl}‐4‐(3‐octylureido)benzenesulfonamide ( 12 e ; EC₅₀=6.38 nM ), (R)‐2‐[1‐(4‐methoxyphenylsulfonyl)piperidin‐4‐ylamino]‐1‐phenylethanol ( 15 f ; EC₅₀=6.1 nM ), and (S)‐4‐{2‐hydroxy‐3‐[4‐(4‐methoxyphenylsulfonyl)piperazin‐1‐yl]propoxy}phenol ( 25 ; EC₅₀=1.79 nM ) were found to be the most potent β₃‐AR agonists of the aryloxypropanolamine, arylethanolamine, piperidine sulfonamide, and piperazine sulfonamide classes, respectively. The two most potent compounds were identified as possible candidates for further development of β₃‐AR agonists useful in the treatment of β₃‐AR‐mediated pathological conditions.     

N‐Cinnamoylation of Antimalarial Classics: Quinacrine Analogues with Decreased Toxicity and Dual‐Stage Activity

Plasmodium falciparum, the causative agent of the most lethal form of malaria, is becoming increasingly resistant to most available drugs. A convenient approach to combat parasite resistance is the development of analogues of classical antimalarial agents, appropriately modified in order to restore their relevance in antimalarial chemotherapy. Following this line of thought, the design, synthesis and in vitro evaluation of N‐cinnamoylated quinacrine surrogates, 9‐(N‐cinnamoylaminobutyl)‐amino‐6‐chloro‐2‐methoxyacridines, is reported. The compounds were found to be highly potent against both blood‐stage P. falciparum, chloroquine‐sensitive 3D7 (IC₅₀=17.0–39.0 nM ) and chloroquine‐resistant W2 and Dd2 strains (IC₅₀=3.2–41.2 and 27.1–131.0 nM , respectively), and liver‐stage P. berghei (IC₅₀=1.6–4.9 μM ) parasites. These findings bring new hope for the possible future “rise of a fallen angel” in antimalarial chemotherapy, with a potential resurgence of quinacrine‐related compounds as dual‐stage antimalarial leads.     

Optimisation of Tetrahydroisoquinoline‐Based Chimeric Microtubule Disruptors

Tetrahydroisoquinoline (THIQ)‐based “chimeric” microtubule disruptors were optimised through modification of the N‐benzyl motif, in concert with changes at C3 and C7, resulting in the identification of compounds with improved in vitro antiproliferative activities (e.g. 15 : GI₅₀ 20 nM in DU‐145). The broad anticancer activity of these novel structures was confirmed in the NCI 60‐cell line assay, with 12 e , f displaying MGM values in the 40 nM region. In addition, their profiles as inhibitors of tubulin polymerisation and colchicine binding to tubulin were confirmed. Compound 15 , for example, inhibited tubulin polymerisation with an IC₅₀ of 1.8 μM , close to that of the clinical drug combretastatin A‐4, and also proved effective at blocking colchicine binding. Additionally, compound 20 b was identified as the only phenol in the series to date showing both better in vitro antiproliferative properties than its corresponding sulfamate and excellent antitubulin data (IC₅₀=1.6 μM ). Compound 12 f was selected for in vivo evaluation at the NCI in the hollow fibre assay and showed very good activity and wide tissue distribution, illustrating the value of this template for further development.     

Synthesis and in vitro Anticancer Activity of Octahedral Platinum(IV) Complexes with Cyclohexyl‐Functionalized Ethylenediamine‐N,N′‐Diacetate‐Type Ligands

The present study describes the synthesis and anticancer activity of novel octahedral Pt^IV complexes with cyclohexyl functionalized ethylenediamine‐N,N′‐diacetate‐type ligands. Molecular mechanics calculations and density functional theory analysis revealed that s‐cis is the preferred geometry of these Pt^IV complexes with tetradentate‐coordinated (S,S)‐ethylenediamine‐N,N′‐di‐2‐(3‐cyclohexyl)propanoate. The viability of cancer cell lines (U251 human glioma, C6 rat glioma, L929 mouse fibrosarcoma, and B16 human melanoma) was assessed by measuring mitochondrial dehydrogenase activity and lactate dehydrogenase release. Cell‐cycle distribution, oxidative stress, caspase activation, and induction of autophagy were analyzed by flow cytometry using appropriate fluorescent reporter dyes. The cytotoxic activity of novel Pt^IV complexes against various cancer cell lines (IC₅₀ range: 1.9–8.7 μM ) was higher than that of cisplatin (IC₅₀ range: 10.9–67.0 μM ) and proceeded through completely different mechanisms. Cisplatin induced caspase‐dependent apoptosis associated with the cytoprotective autophagic response. In contrast, the new Pt^IV complexes caused rapid, caspase‐independent, oxidative stress‐mediated non‐apoptotic cell death characterized by massive cytoplasmic vacuolization, cell membrane damage, and the absence of protective autophagy.