Synthesis and Biological Evaluation of Imidazo[2,1‐b][1,3,4]thiadiazole‐Linked Oxindoles as Potent Tubulin Polymerization Inhibitors

A series of imidazo[2,1‐b][1,3,4]thiadiazole‐linked oxindoles composed of an A, B, C and D ring system were synthesized and investigated for anti‐proliferative activity in various human cancer cell lines; test compounds were variously substituted at rings C and D. Among them, compounds 7 ((E)‐5‐fluoro‐3‐((6‐p‐tolyl‐2‐(3,4,5‐trimethoxyphenyl)‐imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one), 11 ((E)‐3‐((6‐p‐tolyl‐2‐(3,4,5‐trimethoxyphenyl)imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one), and 15 ((E)‐6‐chloro‐3‐((6‐phenyl‐2‐(3,4,5‐trimethoxyphenyl)imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one) exhibited potent anti‐proliferative activity. Treatment with these three compounds resulted in accumulation of cells in G₂/M phase, inhibition of tubulin assembly, and increased cyclin‐B1 protein levels. Compound 7 displayed potent cytotoxicity, with an IC₅₀ range of 1.1–1.6 μM , and inhibited tubulin polymerization with an IC₅₀ value (0.15 μM ) lower than that of combretastatin A‐4 (1.16 μM ). Docking studies reveal that compounds 7 and 11 bind with αAsn101, βThr179, and βCys241 in the colchicine binding site of tubulin.     

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 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.     

Synthesis and Biological Evaluation of 1‐Methyl‐1H‐indole–Pyrazoline Hybrids as Potential Tubulin Polymerization Inhibitors

A series of 1‐methyl‐1H‐indole–pyrazoline hybrids were designed, synthesized, and biologically evaluated as potential tubulin polymerization inhibitors. Among them, compound e19 [5‐(5‐bromo‐1‐methyl‐1H‐indol‐3‐yl)‐3‐(3,4,5‐trimethoxyphenyl)‐4,5‐dihydro‐1H‐pyrazole‐1‐carboxamide] showed the most potent inhibitory effect on tubulin assembly (IC₅₀=2.12 μm ) and in vitro growth inhibitory activity against a panel of four human cancer cell lines (IC₅₀ values of 0.21–0.31 μm ). Further studies confirmed that compound e19 can induce HeLa cell apoptosis, cause cell‐cycle arrest in G₂/M phase, and disrupt the cellular microtubule network. These studies, along with molecular docking and 3D‐QSAR modeling, provide an important basis for further optimization of compound e19 as a potential anticancer agent.     

A New Class of 1‐Aryl‐5,6‐dihydropyrrolo[2,1‐a]isoquinoline Derivatives as Reversers of P‐Glycoprotein‐Mediated Multidrug Resistance in Tumor Cells

A number of aza‐heterocyclic compounds, which share the 5,6‐dihydropyrrolo[2,1‐a]isoquinoline (DHPIQ) scaffold with members of the lamellarin alkaloid family, were synthesized and evaluated for their ability to reverse in vitro multidrug resistance in cancer cells through inhibition of P‐glycoprotein (P‐gp) and/or multidrug‐resistance‐associated protein 1. Most of the investigated DHPIQ compounds proved to be selective P‐gp modulators, and the most potent modulator, 8,9‐diethoxy‐1‐(3,4‐diethoxyphenyl)‐3‐(furan‐2‐yl)‐5,6‐dihydropyrrolo[2,1‐a]isoquinoline‐2‐carbaldehyde, attained sub‐micromolar inhibitory potency (IC₅₀: 0.19 μm ). Schiff bases prepared by the condensation of some 1‐aryl‐DHPIQ aldehydes with p‐aminophenol also proved to be of some interest, and one of them, 4‐((1‐(4‐fluorophenyl)‐5,6‐dihydro‐8,9‐dimethoxypyrrolo[2,1‐a]isoquinolin‐2‐yl)methyleneamino)phenol, had an IC₅₀ value of 1.01 μm . In drug combination assays in multidrug‐resistant cells, some DHPIQ compounds, at nontoxic concentrations, significantly increased the cytotoxicity of doxorubicin in a concentration‐dependent manner. Studies of structure–activity relationships and investigation of the chemical stability of Schiff bases provided physicochemical information useful for molecular optimization of lamellarin‐like cytotoxic drugs active toward chemoresistant tumors as well as nontoxic reversers of P‐gp‐mediated multidrug resistance in tumor cells.     

Identification of a Small‐Molecule Inhibitor of HIV‐1 Assembly that Targets the Phosphatidylinositol (4,5)‐bisphosphate Binding Site of the HIV‐1 Matrix Protein

The development of drug resistance remains a critical problem for current HIV‐1 antiviral therapies, creating a need for new inhibitors of HIV‐1 replication. We previously reported on a novel anti‐HIV‐1 compound, N²‐(phenoxyacetyl)‐N‐[4‐(1‐piperidinylcarbonyl)benzyl]glycinamide ( 14 ), that binds to the highly conserved phosphatidylinositol (4,5)‐bisphosphate (PI(4,5)P₂) binding pocket of the HIV‐1 matrix (MA) protein. In this study, we re‐evaluate the hits from the virtual screen used to identify compound 14 and test them directly in an HIV‐1 replication assay using primary human peripheral blood mononuclear cells. This study resulted in the identification of three new compounds with antiviral activity; 2‐(4‐{[3‐(4‐fluorophenyl)‐1,2,4‐oxadiazol‐5‐yl]methyl})‐1‐piperazinyl)‐N‐(4‐methylphenyl)acetamide ( 7 ), 3‐(2‐ethoxyphenyl)‐5‐[[4‐(4‐nitrophenyl)piperazin‐1‐yl]methyl]‐1,2,4‐oxadiazole ( 17 ), and N‐[4‐ethoxy‐3‐(1‐piperidinylsulfonyl)phenyl]‐2‐(imidazo[2,1‐b][1,3]thiazol‐6‐yl)acetamide ( 18 ), with compound 7 being the most potent of these hits. Mechanistic studies on 7 demonstrated that it directly interacts with and functions through HIV‐1 MA. In accordance with our drug target, compound 7 competes with PI(4,5)P₂ for MA binding and, as a result, diminishes the production of new virus. Mutation of residues within the PI(4,5)P₂ binding site of MA decreased the antiviral effect of compound 7 . Additionally, compound 7 displays a broadly neutralizing anti‐HIV activity, with IC₅₀ values of 7.5–15.6 μM for the group M isolates tested. Taken together, these results point towards a novel chemical probe that can be used to more closely study the biological role of MA and could, through further optimization, lead to a new class of anti‐HIV‐1 therapeutics.     

Fluorophore‐Labeled Cyclooxygenase‐2 Inhibitors for the Imaging of Cyclooxygenase‐2 Overexpression in Cancer: Synthesis and Biological Studies

A group of cyclooxygenase‐2 (COX‐2)‐specific fluorescent cancer biomarkers were synthesized by linking the anti‐inflammatory drugs ibuprofen, (S)‐naproxen, and celecoxib to the 7‐nitrobenzofurazan (NBD) fluorophore. In vitro COX‐1/COX‐2 inhibition studies indicated that all of these fluorescent conjugates are COX‐2 inhibitors (IC₅₀ range: 0.19–23.0 μM ) with an appreciable COX‐2 selectivity index (SI≥4.3–444). In this study the celecoxib–NBD conjugate N‐(2‐((7‐nitrobenzo[c][1,2,5]oxadiazol‐4‐yl)amino)ethyl)‐4‐(5‐(p‐tolyl)‐3‐(trifluoromethyl)‐1H‐pyrazol‐1‐yl)benzenesulfonamide ( 14 ), which displayed the highest COX‐2 inhibitory potency and selectivity (COX‐2 IC₅₀=0.19 μM ; SI=443.6), was identified as an impending COX‐2‐specific biomarker for the fluorescence imaging of cancer using a COX‐2‐expressing human colon cancer cell line (HCA‐7).     

Design and Synthesis of DNA‐Interactive β‐Carboline–Oxindole Hybrids as Cytotoxic and Apoptosis‐Inducing Agents

A new series of (E)‐3‐[(1‐aryl‐9H‐pyrido[3,4‐b]indol‐3‐yl)methylene]indolin‐2‐one hybrids were synthesized and evaluated for their in vitro cytotoxic activity against a panel of selected human cancer cell lines, namely, HCT‐15, HCT‐116, A549, NCI‐H460, and MCF‐7, including HFL. Among the tested compounds, (E)‐1‐benzyl‐5‐bromo‐3‐{[1‐(2,5‐dimethoxyphenyl)‐9H‐pyrido[3,4‐b]indol‐3‐yl]methylene}indolin‐2‐one ( 10 s ) showed potent cytotoxicity against HCT‐15 cancer cells with an IC₅₀ value of 1.43±0.26 μm and a GI₅₀ value of 0.89±0.06 μm . Notably, induction of apoptosis by 10 s on the HCT‐15 cell line was characterized by using different staining techniques, such as acridine orange/ethidium bromide (AO/EB) and DAPI. Further, to understand the mechanism of anticancer effects, various assays such as annexin V‐FITC/PI, DCFDA, and JC‐1were performed. The flow cytometric analysis revealed that compound 10 s arrests the HCT‐15 cancer cells at the G0/G1 phase of the cell cycle. Additionally, western blot analysis indicated that treatment of 10 s on HCT‐15 cancer cells led to decreased expression of anti‐apoptotic Bcl‐2 and increased protein expression of both pro‐apoptotic Bax and caspase‐3, ‐8, and ‐9, and cleaved PARP with reference to actin. Next, a clonogenic assay revealed the inhibition of colony formation in HCT‐15 cancer cells by 10 s in a dose‐dependent manner. Moreover, upon testing on normal human lung cells (HFL), the compounds were observed to be safer with a low toxicity profile. In addition, viscosity and molecular‐docking studies showed that compound 10 s has typical intercalation with DNA.     

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.     

Design and Synthesis of Aminostilbene–Arylpropenones as Tubulin Polymerization Inhibitors

A series of aminostilbene—arylpropenones were designed and synthesized by Michael addition and were investigated for their cytotoxic activity against various human cancer cell lines. Some of the investigated compounds exhibited significant antiproliferative activity against a panel of 60 human cancer cell lines of the US National Cancer Institute, with 50 % growth inhibition (GI₅₀) values in the range from <0.01 to 19.9 μM . One of the compounds showed a broad spectrum of antiproliferative efficacy on most of the cell lines, with a GI₅₀ value of <0.01 μM . All of the synthesized compounds displayed cytotoxicity against A549 (non‐small‐cell lung cancer), HeLa (cervical carcinoma), MCF‐7 (breast cancer), and HCT116 (colon carcinoma) with 50 % inhibitory concentration (IC₅₀) values ranging from 0.011 to 8.56 μM . A cell cycle assay revealed that these compounds arrested the G2/M phase of the cell cycle. Two compounds exhibited strong inhibitory effects on tubulin assembly with IC₅₀ values of 0.71 and 0.79 μM . Moreover, dot‐blot analysis of cyclin B1 demonstrated that some of the congeners strongly induced cyclin B1 protein levels. Molecular docking studies indicated that these compounds occupy the colchicine binding site of tubulin.     

Synthesis,Biological Evaluation of 1,1‐Diarylethylenes as a Novel Class of Antimitotic Agents

The cytotoxic activities of 23 new isocombretastatin A derivatives with modifications on the B‐ring were investigated. Several compounds exhibited excellent antiproliferative activity at nanomolar concentrations against a panel of human cancer cell lines. Compounds isoFCA‐4 ( 2 e ), isoCA‐4 ( 2 k ) and isoNH₂CA‐4 ( 2 s ) were the most cytotoxic, and strongly inhibited tubulin polymerization with IC₅₀ values of 4, 2 and 1.5 μM , respectively. These derivatives were found to be 10‐fold more active than phenstatin and colchicine with respect to growth inhibition but displayed similar activities as tubulin polymerization inhibitors. In addition, cell cycle arrest in the G₂/M phase and subsequent apoptosis was observed in three cancer cell lines when treated with these compounds. The disruptive effect of 2 e , 2 k and 2 s on the vessel‐like structures formed by human umbilical vein endothelial cells (HUVEC) suggest that these compounds may act as vascular disrupting agents. Both compounds 2 k and 2 s have the potential for further prodrug modification and development as vascular disrupting agents for treatment of solid tumors.     

Effects of the Tumor‐Vasculature‐Disrupting Agent Verubulin and Two Heteroaryl Analogues on Cancer Cells,Endothelial Cells,and Blood Vessels

Two analogues of the discontinued tumor vascular‐disrupting agent verubulin (Azixa®, MPC‐6827, 1 ) featuring benzo‐1,4‐dioxan‐6‐yl (compound 5 a ) and N‐methylindol‐5‐yl (compound 10 ) residues instead of the para‐anisyl group on the 4‐(methylamino)‐2‐methylquinazoline pharmacophore, were prepared and found to exceed the antitumor efficacy of the lead compound. They were antiproliferative with single‐digit nanomolar IC₅₀ values against a panel of nine tumor cell lines, while not affecting nonmalignant fibroblasts. Indole 10 surpassed verubulin in seven tumor cell lines including colon, breast, ovarian, and germ cell cancer cell lines. In line with docking studies indicating that compound 10 may bind the colchicine binding site of tubulin more tightly (E_bind=?9.8 kcal mol^?1) than verubulin (E_bind=?8.3 kcal mol^?1), 10 suppressed the formation of vessel‐like tubes in endothelial cells and destroyed the blood vessels in the chorioallantoic membrane of fertilized chicken eggs at nanomolar concentrations. When applied to nude mice bearing a highly vascularized 1411HP germ cell xenograft tumor, compound 10 displayed pronounced vascular‐disrupting effects that led to hemorrhages and extensive central necrosis in the tumor.     

Biphasic Dose-Dependent G0/G1 and G2/M Cell-Cycle Arrest by Synthetic 2,3-Arylpyridylindole Derivatives in A549 Lung Cancer Cells

A collection of 2,3-arylpyridylindole derivatives were synthesized via the Larock heteroannulation and evaluated for their in vitro cytotoxic activity against A549 human lung cancer cells. Two derivatives expressed good cytotoxicity with IC₅₀ values of 1.18±0.25 μM and 0.87±0.10 μM and inhibited tubulin polymerization in vitro, with molecular docking studies suggesting the binding modes of the compounds in the colchicine binding site. Both derivatives have biphasic cell cycle arrest effects depending on their concentrations. At a lower concentration (0.5 μM), the two compounds induced G0/G1 cell cycle arrest by activating the JNK/p53/p21 pathway. At a higher concentration (2.0 μM), the two derivatives arrested the cell cycle at the G2/M phase via Akt signaling and inhibition of tubulin polymerization. Additional cytotoxic mechanisms of the two compounds involved the decreased expression of Bcl-2 and Mcl-1 antiapoptotic proteins through inhibition of the STAT3 and Akt signaling pathways.     

Room Temperature Highly Enantioselective Nickel‐Catalyzed Hydrovinylation

At room temperature, nickel catalysts based on the new phosphoramidite (11bR)‐N‐[(S)‐1‐(naphthalen‐1‐yl)ethyl]‐N‐[(S)‐1‐(naphthalen‐2‐yl)ethyl]dinaphtho[2,1‐d:1′,2′‐f][1,3,2]dioxaphosphepin‐4‐amine provide excellent selectivities for 3‐arylbut‐1‐enes (93–99%) with high enantioselectivities (90–95% ee) and TOFs (up to 8300 h⁻¹) in the hydrovinylation of electron‐rich and electron‐poor vinylarenes. Within a few minutes, useful chiral building blocks and intermediates can be synthesized using this practical catalytic system.     

Design,Synthesis and Biological Evaluation of 1,4-Disubstituted-3,4-dihydroisoquinoline Compounds as New Tubulin Polymerization Inhibitors

A series of 1,4-disubstituted-3,4-dihydroisoquinoline derivatives designed as tubulin polymerization inhibitors were synthesized. Their cytotoxic activities against the CEM leukemia cell line were evaluated. Most of them displayed moderate cytotoxic activities, and compounds 21 and 32 showed good activities with IC₅₀ of 4.10 and 0.64 μM, respectively. The most potent compound 32 was further confirmed to be able to inhibit tubulin polymerization, and its hypothetical binding mode with tubulin was obtained by molecular docking.     

Design,Synthesis, Structure-Activity Relationship and Docking Studies of Novel Functionalized Arylvinyl-1,2,4-Trioxanes as Potent Antiplasmodial as well as Anticancer Agents

A novel series of synthetic functionalized arylvinyl-1,2,4-trioxanes ( 8 a – p ) has been prepared and assessed for their in vitro antiplasmodial activity against the chloroquine-resistant Pf INDO strain of Plasmodium falciparum by using a SYBR green-I fluorescence assay. Compounds 8 g (IC₅₀=0.051 μM; SI=589.41) and 8 m (IC₅₀=0.059 μM; SI=55.93) showed 11-fold and >9-fold more potent antiplasmodial activity, respectively, as compared to chloroquine (IC₅₀=0.546 μM; SI=36.63). Different in silico docking studies performed on many target proteins revealed that the most active arylvinyl-1,2,4-trioxanes ( 8 g and 8 m ) showed dihydrofolate reductase (DHFR) binding affinities on a par with those of chloroquine and artesunate. The in vitro cytotoxic potentials of 8 a – p were also evaluated against human lung (A549) and liver (HepG2) cancer cell lines along with immortalized normal lung (BEAS-2B) and liver (LO2) cell lines. Following screening, five derivatives viz. 8 a , 8 h , 8 l , 8 m and 8 o (IC₅₀=1.65–31.7 μM; SI=1.08–10.96) were found to show potent cytotoxic activity against (A549) lung cancer cell lines, with selectivity superior to that of the reference compounds artemisinin (IC₅₀=100 μM), chloroquine (IC₅₀=100 μM) and artesunic acid (IC₅₀=9.85 μM; SI=0.76). In fact, the most active 4-naphthyl-substituted analogue 8 l (IC₅₀=1.65 μM; SI >10) exhibited >60 times more cytotoxicity than the standard reference, artemisinin, against A549 lung cancer cell lines. In silico docking studies of the most active anticancer compounds, 8 l and 8 m , against EGFR were found to validate the wet lab results. In summary, a new series of functionalized aryl-vinyl-1,2,4-trioxanes ( 8 a – p ) has been shown to display dual potency as promising antiplasmodial and anticancer agents.     

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 Biological Evaluation of Imidazopyridine–Oxindole Conjugates as Microtubule‐Targeting Agents

A library of imidazopyridine–oxindole conjugates was synthesised and investigated for anticancer activity against various human cancer cell lines. Some of the tested compounds, such as 10 a , 10 e , 10 f , and 10 k , exhibited promising antiproliferative activity with GI₅₀ values ranging from 0.17 to 9.31 μM . Flow cytometric analysis showed that MCF‐7 cells treated by these compounds arrested in the G₂/M phase of the cell cycle in a concentration‐dependent manner. More particularly, compound 10 f displayed a remarkable inhibitory effect on tubulin polymerisation. All the compounds depolarised mitochondrial membrane potential and caused apoptosis. These results are further supported by the decreased phosphorylation of Akt at Ser473. Studies on embryonic development revealed that the lead compounds 10 f and 10 k caused delay in the development of zebra fish embryos. Docking of compound 10 f with tubulin protein suggested that the imidazo[1,2‐a]pyridine moiety occupies the colchicine binding site of tubulin.     

Design,Synthesis, and Evaluation of an 18F‐Labeled Radiotracer Based on Celecoxib–NBD for Positron Emission Tomography (PET) Imaging of Cyclooxygenase‐2 (COX‐2)

A series of novel fluorine‐containing cyclooxygenase‐2 (COX‐2) inhibitors was designed and synthesized based on the previously reported fluorescent COX‐2 imaging agent celecoxib–NBD ( 3 ; NBD=7‐nitrobenzofurazan). In vitro COX‐1/COX‐2 inhibitory data show that N‐(4‐fluorobenzyl)‐4‐(5‐p‐tolyl‐3‐trifluoromethylpyrazol‐1‐yl)benzenesulfonamide ( 5 ; IC₅₀=0.36 μM , SI>277) and N‐fluoromethyl‐4‐(5‐p‐tolyl‐3‐trifluoromethylpyrazol‐1‐yl)benzenesulfonamide ( 6 ; IC₅₀=0.24 μM , SI>416) are potent and selective COX‐2 inhibitors. Compound 5 was selected for radiolabeling with the short‐lived positron emitter fluorine‐18 (¹⁸F) and evaluated as a positron emission tomography (PET) imaging agent. Radiotracer [¹⁸F] 5 was analyzed in vitro and in vivo using human colorectal cancer model HCA‐7. Although radiotracer uptake into COX‐2‐expressing HCA‐7 cells was high, no evidence for COX‐2‐specific binding was found. Radiotracer uptake into HCA‐7 tumors in vivo was low and similar to that of muscle, used as reference tissue.     

Unambiguous Identification of β‐Tubulin as the Direct Cellular Target Responsible for the Cytotoxicity of Chalcone by Photoaffinity Labeling

Chalcone is a simple and potentially privileged structure in medicinal chemistry with a diverse repertoire of biological activities, among which cytotoxicity is of particular interest. The sharp structure–activity relationship (SAR) for chalcone's cytotoxicity suggests structure‐specific target interactions. Despite the numerous putative targets proposed, evidence for direct target interactions in cells is unavailable. In this study, guided by the sharp cytotoxic SAR, we developed a cytotoxic chalcone‐based photoaffinity labeling (PAL) probe, (E)‐3‐(3‐azidophenyl)‐1‐[3,5‐dimethoxy‐4‐(prop‐2‐yn‐1‐yloxy)phenyl]‐2‐methylprop‐2‐en‐1‐one (C95; IC₅₀: 0.38±0.01 μm ), along with two structurally similar non‐cytotoxic probes. These probes were used to search for the direct cellular target responsible for chalcone's cytotoxicity through intact cell‐based PAL experiments, in which β‐tubulin was identified to specifically interact with the cytotoxic probe (i.e., C95) but not the non‐cytotoxic probes. A set of phenotypical and biochemical assays further reinforced β‐tubulin as the cytotoxic target of chalcones. Peptide mass quantitation by mass spectrometric analysis revealed one peptide potentially labeled by C95, providing information on chalcone's binding site on β‐tubulin.