Synthesis, characterization, electrochemistry and spectroelectrochemistry of novel soluble porphyrazines bearing unsaturated functional groups

Metalloporphyrazines with a 2-methyl-2-pentenyl group fused to each pyrrole unit were synthesized starting with the corresponding unsaturated dicarbonitrile derivative. The new compounds were characterized by elemental analysis together with FTIR, ¹H-NMR, and UV-Vis spectroscopy and via voltammetric and spectrochemical methods. Electrochemical and spectroelectrochemical measurements demonstrate that while metal-free and magnesium porphyrazines gave common porphyrazine (Pz) ring-based electron-transfer reactions, incorporating redox active metal center, Co^II, into the porphyrazine core extended the redox activity of the ring system with reversible metal-based reduction and oxidation couples of the metal center in addition to the common Pz ring-based electron transfer processes. The unsaturated functional groups of the porphyrazines did not alter the common electrochemical behavior of the complexes. An in situ electrocolorimetric method, based on the 1931 CIE (Commission Internationale de l’Eclairage) system of colorimetry, was applied to investigate the color of the electro-generated anionic and cationic forms of the complexes for possible electrochromatic applications.     

Molecular‐Target‐Based Anticancer Photosensitizer: Synthesis and in vitro Photodynamic Activity of Erlotinib–Zinc(II) Phthalocyanine Conjugates

Targeted photodynamic therapy is a new promising therapeutic strategy to overcome growing problems in contemporary medicine, such as drug toxicity and drug resistance. A series of erlotinib–zinc(II) phthalocyanine conjugates were designed and synthesized. Compared with unsubstituted zinc(II) phthalocyanine, these conjugates can successfully target EGFR‐overexpressing cancer cells owing to the presence of the small molecular‐target‐based anticancer agent erlotinib. All conjugates were found to be essentially non‐cytotoxic in the absence of light (up to 50 μM ), but upon illumination, they show significantly high photo‐cytotoxicity toward HepG2 cells, with IC₅₀ values as low as 9.61–91.77 nM under a rather low light dose (λ=670 nm, 1.5 J cm^?2). Structure–activity relationships for these conjugates were assessed by determining their photophysical/photochemical properties, cellular uptake, and in vitro photodynamic activities. The results show that these conjugates are highly promising antitumor agents for molecular‐target‐based photodynamic therapy.     

Development of Novel Selective Peptidomimetics Containing a Boronic Acid Moiety,Targeting the 20S Proteasome as Anticancer Agents

This paper describes the design, synthesis, and biological evaluation of peptidomimetic boronates as inhibitors of the 20S proteasome, a validated target in the treatment of multiple myeloma. The synthesized compounds showed a good inhibitory profile against the ChT‐L activity of 20S proteasome. Compounds bearing a β‐alanine residue at the P2 position were the most active, that is, 3‐ethylphenylamino and 4‐methoxyphenylamino (R)‐1‐{3‐[4‐(substituted)‐2‐oxopyridin‐1(2H)‐yl]propanamido}‐3‐methylbutylboronic acids ( 3 c and 3 d , respectively), and these derivatives showed inhibition constants (K_i) of 17 and 20 nM , respectively. In addition, they co‐inhibited post glutamyl peptide hydrolase activity ( 3 c , K_i=2.57 μM ; 3 d , K_i=3.81 μM ). No inhibition was recorded against the bovine pancreatic α‐chymotrypsin, which thus confirms the selectivity towards the target enzyme. Docking studies of 3 c and related inhibitors into the yeast proteasome revealed the structural basis for specificity. The evaluation of growth inhibitory effects against 60 human tumor cell lines was performed at the US National Cancer Institute. Among the selected compounds, 3 c showed 50 % growth inhibition (GI₅₀) values at the sub‐micromolar level on all cell lines.     

Semisynthetic Ursolic Acid Fluorolactone Derivatives Inhibit Growth with Induction of p21(waf1) and Induce Apoptosis with Upregulation of NOXA and Downregulation of c-FLIP in Cancer Cells

A series of ursolic acid ((1S,2R,4aS,6aR,6aS,6bR,8aR,10S,12aR,14bS)‐10‐hydroxy‐1,2,6a,6b,9,9,12a‐heptamethyl‐2,3,4,5,6,6a,7,8,8a,10,11,12,13,14b‐tetradecahydro‐1H‐picene‐4a‐carboxylic acid) derivatives with a 12‐fluoro‐13,28β‐lactone moiety were synthesized using the electrophilic fluorination reagent Selectfluor. The antiproliferative effects of these novel compounds were evaluated in AsPC‐1 pancreatic cancer cells, and the structure–activity relationships (SARs) were evaluated. Of the compounds synthesized, ursolic acid derivatives carrying a heterocyclic ring, such as imidazole or methylimidazole, and cyanoenones were among the more potent inhibitors of AsPC‐1 pancreatic cancer cell growth. 2‐Cyano‐3‐oxo‐12α‐fluoro‐urs‐1‐en‐13,28β‐olide, compound 20 , was the most effective inhibitor with IC₅₀ values of 0.7, 0.9 and 1.8 μM in pancreatic cancer cell lines AsPC‐1, MIA PaCa‐2 and PANC‐1, respectively. This compound also exhibited better antiproliferative activities against breast (MCF7), prostate (PC‐3), hepatocellular (Hep G2) and lung (A549) cancer cell lines, with IC₅₀ values lower than 1 μM . The mechanism of action by which these compounds exert their biological effect was evaluated in AsPC‐1 cells using the most potent inhibitor synthesized, compound 20 . At 1 μM , the cell cycle arrested at the G1 phase with upregulation of p21^waf1. Apoptosis was induced at an inhibitor concentration of 8 μM with upregulation of NOXA and downregulation of c‐FLIP. These data indicate that fluorolactone derivatives of ursolic acid have improved antiproliferative activity, acting through arrest of the cell cycle and induction of apoptosis.     

Design and Synthesis of Imidazo[2,1‐b]thiazole–Chalcone Conjugates: Microtubule‐Destabilizing Agents

A series of chalcone conjugates featuring the imidazo[2,1‐b]thiazole scaffold was designed, synthesized, and evaluated for their cytotoxic activity against five human cancer cell lines (MCF‐7, A549, HeLa, DU‐145 and HT‐29). These new hybrid molecules have shown promising cytotoxic activity with IC₅₀ values ranging from 0.64 to 30.9 μM . Among them, (E)‐3‐(6‐(4‐fluorophenyl)‐2,3‐bis(4‐methoxyphenyl)imidazo[2,1‐b]thiazol‐5‐yl)‐1‐(pyridin‐2‐yl)prop‐2‐en‐1‐one ( 11 x ) showed potent antiproliferative activity with IC₅₀ values ranging from 0.64 to 1.44 μM in all tested cell lines. To investigate the mechanism of action, the detailed biological aspects of this promising conjugate ( 11 x ) were carried out on the A549 lung cancer cell line. The tubulin polymerization assay and immunofluoresence analysis results suggest that this conjugate effectively inhibits microtubule assembly in A549 cells. Flow cytometric analysis revealed that this conjugate induces cell‐cycle arrest in the G2/M phase and leads to apoptotic cell death. This was further confirmed by Hoechst staining, activation of caspase‐3, DNA fragmentation analysis, and Annexin V–FITC assay. Moreover, molecular docking studies indicated that this conjugate ( 11 x) interacts and binds efficiently with the tubulin protein.     

Synthesis and Biological Evaluation of Benzo[b]furans as Inhibitors of Tubulin Polymerization and Inducers of Apoptosis

A series of benzo[b]furans was synthesized with modification at the 5‐position of the benzene ring by introducing C‐linked substituents (aryl, alkenyl, alkynyl, etc.). These compounds were evaluated for their antiproliferative activities, inhibition of tubulin polymerization, and cell‐cycle effects. Some compounds in this series displayed excellent activity in the nanomolar range against lung cancer (A549) and renal cell carcinoma (ACHN) cancer cell lines. (6‐Methoxy‐5‐((4‐methoxyphenyl)ethynyl)‐3‐methylbenzofuran‐2‐yl)(3,4,5‐trimethoxyphenyl)methanone ( 26 ) and (E)‐3‐(6‐methoxy‐3‐methyl‐2‐(1‐(3,4,5‐trimethoxyphenyl)vinyl)benzofuran‐5‐yl)prop‐2‐en‐1‐ol ( 36 ) showed significant activity in the A549 cell line, with IC₅₀ values of 0.08 and 0.06 μM , respectively. G₂/M cell‐cycle arrest and subsequent apoptosis was observed in the A549 cell line after treatment with these compounds. The most active compound in this series, 36 , also inhibited tubulin polymerization with a value similar to that of combretastatin A‐4 (1.95 and 1.86 μM , respectively). Furthermore, detailed biological studies such as Hoechst 33258 staining, DNA fragmentation and caspase‐3 assays, and western blot analyses with the pro‐apoptotic protein Bax and the anti‐apoptotic protein Bcl‐2 also suggested that these compounds induce cell death by apoptosis. Molecular docking studies indicated that compound 36 interacts and binds efficiently with the tubulin protein.     

Increased Lipophilicity of Halogenated Ruthenium(II) Polypyridyl Complexes Leads to Decreased Phototoxicity in vitro when Used as Photosensitizers for Photodynamic Therapy

In the fight against cancer, photodynamic therapy is generating great interest thanks to its ability to selectively kill cancer cells without harming healthy tissues. In this field, ruthenium(II) polypyridyl complexes, and more specifically, complexes with dipyrido[3,2-a:2’,3’-c]phenazine (dppz) as a ligand are of particular interest due to their DNA-binding and photocleaving properties. However, ruthenium(II) polypyridyl complexes can sometimes suffer from low lipophilicity, which hampers cellular internalisation through passive diffusion. In this study, four new [Ru(dppz-X₂)₃]²⁺ complexes (X=H, F, Cl, Br, I) were synthesized and their lipophilicity (logP), cytotoxicity and phototoxicity on cancerous and noncancerous cell lines were assessed. This study shows that, counterintuitively, the phototoxicity of these complexes decreases as their lipophilicity increases; this could be due solely to the atomic radius of the halogen substituents.     

New Halogenated Water‐Soluble Chlorin and Bacteriochlorin as Photostable PDT Sensitizers: Synthesis,Spectroscopy, Photophysics,and in vitro Photosensitizing Efficacy

Chlorin and bacteriochlorin derivatives of 5,10,15,20‐tetrakis(2‐chloro‐5‐sulfophenyl)porphyrin have intense absorptions in the phototherapeutic window, high water solubility, high photostability, low fluorescence quantum yield, long triplet lifetimes, and high singlet oxygen quantum yields. Biological studies revealed their negligible dark cytotoxicity, yet significant photodynamic effect against A549 (human lung adenocarcinoma), MCF7 (human breast carcinoma) and SK‐MEL‐188 (human melanoma) cell lines upon red light irradiation (cutoff λ<600 nm) at low light doses. Time‐dependent cellular accumulation of the chlorinated sulfonated chlorin reached a plateau at 2 h, as previously observed for the related porphyrin. However, the optimal incubation time for the bacteriochlorin derivative was significantly longer (12 h). The spectroscopic, photophysical, and biological properties of the compounds are discussed in relevance to their PDT activity, leading to the conclusion that the bacteriochlorin derivative is a promising candidate for future in vivo experiments.     

3-substituted 2-phenylimidazo[2,1-b]benzothiazoles: synthesis, anticancer activity, and inhibition of tubulin polymerization

A new series of 3‐substituted 2‐phenylimidazo[2,1‐b]benzothiazoles ( 3 a – h ) were synthesized by C‐arylation of 2‐arylimidazo[2,1‐b]benzothiazoles using palladium acetate as catalyst, and the resulting compounds were evaluated for their anticancer activity. Compounds 3 a , 3 e , and 3 h exhibited good antiproliferative activity, with GI₅₀ values in the range of 0.19–83.1 μM . Compound 3 h showed potent anticancer efficacy against 60 human cancer cell lines, with a mean GI₅₀ value of 0.88 μM . This compound also induced cell‐cycle arrest in the G₂/M phase and inhibited tubulin polymerization followed by activation of caspase‐3 and apoptosis. A high‐throughput tubulin polymerization assay showed that the level of inhibition for compound 3 h is similar to that of combretastatin A‐4. Molecular modeling studies provided a molecular basis for the favorable binding of compounds 3 a , 3 e , and 3 h to the colchicine binding pocket of tubulin.     

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.     

Structure–Activity Relationships of Glucosamine‐Derived Glycerolipids: the Role of the Anomeric Linkage,the Cationic Charge and the Glycero Moiety on the Antitumor Activity

The potent antitumor activity of 1‐O‐hexadecyl‐2‐O‐methyl‐3‐O‐(2′‐amino‐2′‐deoxy‐β‐D ‐glucopyranosyl)‐sn‐glycerol ( 1 ) was previously shown to arise through an apoptosis‐independent pathway. Here, a systematic structure–activity study in which the effects of the anomeric linkage, the cationic charge and the glycero moiety on the antitumor activity is described. Eight analogues of 1 were synthesized, and their antitumor activity against breast (JIMT1 and BT549), pancreas (MiaPaCa2) and prostate (DU145, PC3) cancer was determined. 1‐O‐Hexadecyl‐2‐O‐methyl‐3‐O‐(2′‐amino‐2′‐deoxy‐α‐D ‐glucopyranosyl)‐sn‐glycerol ( 2 ) consistently displayed the most potent activity against all five cell lines with CC₅₀ values in the range of 6–10 μM . However, replacement of the O‐glycosidic linkage by a thioglycosidic linkage or replacement of the amino group by an azide or guanidino group leads to a threefold or greater decrease in potency. The glycero moiety also contributes to the overall activity of 1 and 2 but its effects are of lesser importance. Investigation into the mode of action of this class of compounds revealed that, in agreement with previous findings, the cytotoxic effects arise through induction of large acid vacuoles.     

C6‐Unsubstituted Pyrazolo[3,4‐d]pyrimidines Are Dual Src/Abl Inhibitors Effective against Imatinib Mesylate Resistant Chronic Myeloid Leukemia Cell Lines

Docking simulations were used to predict the most favorable interaction between the T315I mutated form of Abl (invariably associated with resistance to the tyrosine kinase inhibitor imatinib mesylate, IM) and C6‐unsubstituted and substituted pyrazolo[3,4‐d]pyrimidines previously found to be dual Src/Abl inhibitors. Two C6‐unsubstituted ( 1 and 2 ) and eight C6‐substituted compounds ( 3 – 10 ) were selected and assayed for their effects on the Ba/F3 cell line transducing the wild‐type p210Bcr–Abl construct, which is IM‐sensitive, or three of the most common mutations associated with IM resistance in vivo (T315I, Y253F, and E255K), and driven to drug resistance by saturating doses of IL‐3 or by the expression of the Bcr–Abl construct coding for the p185 protein of acute lymphoblastic leukemia. Compounds 1 and 2 were active against all cell lines assayed (LD₅₀ range: 0.7–4.3 μM ), whereas C6‐substituted compounds exhibited lower activity (LD₅₀～8 μM for compound 3 toward the T315I mutant). Notably, 1 and 2 were also effective toward the T315I mutation, which is insensitive to dual Src/Abl inhibitors. The cytotoxic effects of 1 and 2 on IM‐sensitive and IM‐resistant Ba/F3 cells were attributable, at least in part, to their pro‐apoptotic activity. Taken together, such findings suggest that C6‐unsubstituted pyrazolo[3,4‐d]pyrimidines may represent useful inhibitors to target IM‐resistant chronic myeloid leukemia.     

Synthesis,Antitubulin, and Antiproliferative SAR of C3/C1‐Substituted Tetrahydroisoquinolines

The syntheses and antiproliferative activities of novel substituted tetrahydroisoquinoline derivatives and their sulfamates are discussed. Biasing of conformational populations through substitution on the tetrahydroisoquinoline core at C1 and C3 has a profound effect on the antiproliferative activity against various cancer cell lines. The C3 methyl‐substituted sulfamate (±)‐7‐methoxy‐2‐(3‐methoxybenzyl)‐3‐methyl‐6‐sulfamoyloxy‐1,2,3,4‐tetrahydroisoquinoline ( 6 b ), for example, was found to be ～10‐fold more potent than the corresponding non‐methylated compound 7‐methoxy‐2‐(3‐methoxybenzyl)‐6‐sulfamoyloxy‐1,2,3,4‐tetrahydroisoquinoline ( 4 b ) against DU‐145 prostate cancer cells (GI₅₀ values: 220 nM and 2.1 μM , respectively). Such compounds were also found to be active against a drug‐resistant MCF breast cancer cell line. The position and nature of substitution of the N‐benzyl group in the C3‐substituted series was found to have a significant effect on activity. Whereas C1 methylation has little effect on activity, introduction of C1 phenyl and C3‐gem‐dimethyl substituents greatly decreases antiproliferative activity. The ability of these compounds to inhibit microtubule polymerisation and to bind tubulin in a competitive manner versus colchicine confirms the mechanism of action. The therapeutic potential of a representative compound was confirmed in an in vivo multiple myeloma xenograft study.     

2‐Anilino‐3‐Aroylquinolines as Potent Tubulin Polymerization Inhibitors

Several 2‐anilino‐3‐aroylquinolines were designed, synthesized, and screened for their cytotoxic activity against five human cancer cell lines: HeLa, DU‐145, A549, MDA‐MB‐231, and MCF‐7. Their IC₅₀ values ranged from 0.77 to 23.6 μm . Among the series, compounds 7 f [(4‐fluorophenyl)(2‐((4‐fluorophenyl)amino)quinolin‐3‐yl)methanone] and 7 g [(4‐chlorophenyl)(2‐((4‐fluorophenyl)amino)quinolin‐3‐yl)methanone] showed remarkable antiproliferative activity against human lung cancer and prostate cancer cell lines. The IC₅₀ values for inhibiting tubulin polymerization were 2.24 and 2.10 μm for compounds 7 f and 7 g , respectively, and were much lower than that of the reference compound E7010 [N‐(2‐(4‐hydroxyphenylamino)pyridin‐3‐yl)‐4‐methoxybenzenesulfonamide]. Furthermore, flow cytometric analysis revealed that these compounds arrest the cell cycle at the G₂/M phase, leading to apoptosis. Apoptosis was also confirmed by mitochondrial membrane potential, Annexin V–FITC assay, and intracellular ROS generation. Immunohistochemistry, western blot, and tubulin polymerization assays showed that these compounds disrupt tubulin polymerization. Molecular docking studies revealed that these compounds bind efficiently to β‐tubulin at the colchicine binding site.     

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.     

Design,Synthesis, and in vitro Biological Evaluation of 3,5‐Dimethylisoxazole Derivatives as BRD4 Inhibitors

BRD4 has been identified as a potential target for blocking proliferation in a variety of cancer cell lines. In this study, 3,5‐dimethylisoxazole derivatives were designed and synthesized with excellent stability in liver microsomes as potent BRD4 inhibitors, and were evaluated for their BRD4 inhibitory activities in vitro. Gratifyingly, compound 11 h [3‐((1‐(2,4‐difluorophenyl)‐1H‐1,2,3‐triazol‐4‐yl)methyl)‐6‐(3,5‐dimethylisoxazol‐4‐yl)‐4‐phenyl‐3,4‐dihydroquinazolin‐2(1H)‐one] exhibited robust potency for BRD4(1) and BRD4(2) inhibition with IC₅₀ values of 27.0 and 180 nm , respectively. Docking studies were performed to illustrate the strategy of modification and analyze the conformation in detail. Furthermore, compound 11 h was found to potently inhibit cell proliferation in the BRD4‐sensitive cell lines HL‐60 and MV4‐11, with IC₅₀ values of 0.120 and 0.09 μm , respectively. Compound 11 h was further demonstrated to downregulate c‐Myc levels in HL‐60 cells. In summary, these results suggest that compound 11 h is most likely a potential BRD4 inhibitor and is a lead compound for further investigations.     

In Vitro Photodynamic Activity of N‐Methylated and N‐Oxidised Tripyridyl Porphyrins with Long Alkyl Chains and Their Inhibitory Activity in Sphingolipid Metabolism

A series of N‐methylated and N‐oxidised tripyridyl porphyrins were synthesised, characterised, and their PDT activity was studied with six cell lines. All the tested porphyrins with a long alkyl chain, except one, were more efficient for PDT than an N‐methylated hydrophilic porphyrin and N‐oxidised porphyrin without the long alkyl chain. Generally, N‐methylated tripyridyl porphyrins were more active than those N‐oxidised, but IC₅₀ values for phototoxicity of two N‐oxides, named TOPyP3‐C₁₇H₃₃O and TOPyP3‐C₁₇H₃₅ , were still in the nanomolar concentration range for most of the tested cell lines. However, TOPyP3‐C₁₇H₃₅ did not show phototoxicity on human foreskin fibroblast cells. Two methylated amphiphilic porphyrins, named TMPyP3‐C₁₇H₃₃ and TMPyP4‐C₁₇H_{35 ,} showed significant dark toxicity, whereas none of the oxidopyridyl porphyrins were toxic without light activation. The selected photosensitisers were shown to be apoptosis inducers, and had inhibitory effects on the clonogenic growth of HCT116 and HeLa cells. All three N‐methylated amphiphilic porphyrins significantly reduced the migratory potential of HCT116 cells. Porphyrins TMPyP3‐C₁₇H₃₅ and TOPyP3‐C₁₇H₃₅ reduced the activity of acid ceramidase, whereas TOPyP3‐C₁₇H₃₃O had a significant inhibitory effect on sphingosine kinase 1 activity in HeLa cells. Compounds with this dual activity were shown to be the most promising photosensitisers, with potential to treat invasive cancers.     

Developing an Irreversible Inhibitor of Human DDAH‐1, an Enzyme Upregulated in Melanoma

Inhibitors of the human enzyme dimethylarginine dimethylaminohydrolase‐1 (DDAH‐1) can raise endogenous levels of asymmetric dimethylarginine (ADMA) and lead to a subsequent inhibition of nitric oxide synthesis. In this study, N⁵‐(1‐imino‐2‐chloroethyl)‐L ‐ornithine (Cl‐NIO) is shown to be a potent time‐ and concentration‐dependent inhibitor of purified human DDAH‐1 (K_I=1.3±0.6 μM ; k_inact=0.34±0.07 min^?1), with >500‐fold selectivity against two arginine‐handling enzymes in the same pathway. An activity probe is used to measure the “in cell” IC₅₀ value (6.6±0.2 μM ) for Cl‐NIO inhibition of DDAH‐1 artificially expressed within cultured HEK293T cells. A screen of diverse melanoma cell lines reveals that a striking 50/64 (78 %) of melanoma lines tested showed increased levels of DDAH‐1 relative to normal melanocyte control lines. Treatment of the melanoma A375 cell line with Cl‐NIO shows a subsequent decrease in cellular nitric oxide production. Cl‐NIO is a promising tool for the study of methylarginine‐mediated nitric oxide control and a potential therapeutic lead compound for other indications with elevated nitric oxide production, such as septic shock and idiopathic pulmonary fibrosis.     

Discovery of a Nanomolar Multikinase Inhibitor (KST016366): A New Benzothiazole Derivative with Remarkable Broad‐Spectrum Antiproliferative Activity

Herein we report the discovery of compound 6 [KST016366; 4‐((2‐(3‐(4‐((4‐ethylpiperazin‐1‐yl)methyl)‐3‐(trifluoromethyl)phenyl)ureido)benzo[d]thiazol‐6‐yl)oxy)picolinamide] as a new potent multikinase inhibitor through minor structural modification of our previously reported RAF kinase inhibitor A . In vitro anticancer evaluation of 6 showed substantial broad‐spectrum antiproliferative activity against 60 human cancer cell lines. In particular, it showed GI₅₀ values of 51.4 and 19 nm against leukemia K‐562 and colon carcinoma KM12 cell lines, respectively. Kinase screening of compound 6 revealed its nanomolar‐level inhibitory activity of certain oncogenic kinases implicated in both tumorigenesis and angiogenesis. Interestingly, 6 displays IC₅₀ values of 0.82, 3.81, and 53 nm toward Tie2, TrkA, and ABL‐1 (wild‐type and T315I mutant) kinases, respectively. Moreover, 6 is orally bioavailable with a favorable in vivo pharmacokinetic profile. Compound 6 may serve as a promising candidate for further development of potent anticancer chemotherapeutics.