Synthesis and cytotoxicity of thieno[2,3-b]quinoline-2-carboxamide and cycloalkyl[b]thieno[3,2-e]pyridine-2-carboxamide derivatives

3-Amino-5,6,7,8-tetrahydrothieno[2,3-b]quinoline-2-carbonitrile: A fluorescent molecule that induces differentiation in PC12 cells

Neural differentiation is triggered by the activation of multiple signaling pathways initiated by various neurotrophic factors. An elucidation of these mechanisms is anticipated to facilitate the prevention of diseases and the development of novel therapeutic approaches. Alternative small-molecule inducers for neuroscience studies are required instead of protein-based reagents for more efficient and convenient experiments. We demonstrated that small molecules of thieno[2,3-b]pyridine derivatives that induce neural differentiation, compounds 3a and 9a in particular, exhibited significant neuritogenic activity in rat pheochromocytoma (PC12) cells. Moreover, 3a displayed pronounced fluorescence and a discernible Stokes shift. Furthermore, the outcome of the experiment conducted on the NGF-insensitive clones of rat PC12 cells, and the results of the intercellular uptake analyses suggested that the 3a-mediated activation of neural differentiation occurred independently of the TrkA receptor. Therefore, 3a portrays potential applicability both as a small molecule reagent to replace novel neurotrophic factors and as a potent fluorescent reagent for various techniques, including bioimaging.

Synthesis and Anti-Proliferative Activity of 5-Benzoyl and 5-Benzylhydroxy Derivatives of 3-Amino-2-Arylcarboxamido-Thieno[2-3-b]Pyridines

3-Amino-2-arylcarboxamido-thieno[2-3-b]pyridines have been previously described as having potent anti-proliferative activity against MDA-MB-231 and HCT116 cancer cell lines. The mechanism by which these molecules prevent cancer cell growth is proposed to be through interfering with phospholipid metabolism via inhibition of PI-PLC, along with other cellular processes. Previously, 5-cinnamyl derivatives of these thieno[2-3-b]pyridines have been shown to have enhanced anti-proliferative activity compared to compounds lacking this moiety, indicating a tethered aromatic ring is important for this western region of the pharmacophore. Herein, we report the synthesis and biological evaluation of a library of 40 novel thieno[2-3-b]pyridine analogues containing shorter benzoyl or secondary benzyl alcohol tethers at the 5-position, in addition to various substituents on the two phenyl rings present on the molecule. Compounds bearing alcohol functionality had improved efficacy compared to their benzoyl counterparts, in addition to a 2-methyl-3-halogen substitution on the 2-arylcarboxamide ring being important for maximising anti-proliferative activity. The most potent molecules 7h and 7i demonstrated IC₅₀ concentrations of 25-50 nM against HCT116 and MDA-MB-231 cells, a similar level of activity as previous thienopyridine compounds bearing cinnamyl moieties, suggesting that these novel derivatives with shorter tethers were able to maintain potent anti-proliferative activity, while allowing for a more concise synthesis.

Novel Thieno [2,3-b]pyridine Anticancer Compound Lowers Cancer Stem Cell Fraction Inducing Shift of Lipid to Glucose Metabolism

Due to the role of cancer stem cells (CSCs) in tumor resistance and glycosphingolipid (GSL) involvement in tumor pathogenesis, we investigated the effect of a newly synthesized compound (3-amino-N-(3-chloro-2-methylphenyl)-5-oxo-5,6,7,8-tetrahydrothieno[2,3-b]quinoline-2-carboxamide 1 on the percentage of CSCs and the expression of six GSLs on CSCs and non-CSCs on breast cancer cell lines (MDA-MB-231 and MCF-7). We also investigated the effect of 1 on the metabolic profile of these cell lines. The MTT assay was used for cytotoxicity determination. Apoptosis and expression of GSLs were assessed by flow cytometry. A GC–MS-coupled system was used for the separation and identification of metabolites. Compound 1 was cytotoxic for both cell lines, and the majority of cells died by treatment-induced apoptosis. The percentage of CSCs was significantly lower in the MDA-MB-231 cell line. Treatment with 1 caused a decrease of CSC IV⁶Neu₅Ac-nLc₄Cer+ MDA-MB-231 cells. In the MCF-7 cell line, the percentage of GalNAc-GM1b+ CSCs was increased, while the expression of Gg₃Cer was decreased in both CSC and non-CSC. Twenty-one metabolites were identified by metabolic profiling. The major impact of the treatment was in glycolysis/gluconeogenesis, pyruvate and inositol metabolism. Compound 1 exhibited higher potency in MBA-MB-231 cells, and it deserves further examination.

Disruption of Crystal Packing in Thieno[2,3-b]pyridines Improves Anti-Proliferative Activity

3-Amino-2-arylcarboxamido-thieno[2,3-b]pyridines have been shown to have anti-proliferative activity, but are also known to have poor solubility. This has been previously proposed to be due to their extensive planarity, which allows for intermolecular stacking and crystal packing. We herein report the synthesis of fifteen novel thieno[2,3-b]pyridines that have incorporated bulky, but easily cleavable, ester and carbonate functional groups in an effort to decrease crystal packing. The addition of these ‘prodrug-like’ moieties into the thieno[2,3-b]pyridine resulted in compounds with increased activity against HCT-116 colon cancer cells and the triple-negative breast cancer cell line MDA-MB-231.

Tethered Aryl Groups Increase the Activity of Anti-Proliferative Thieno[2,3-b]Pyridines by Targeting a Lipophilic Region in the Active Site of PI-PLC

The compounds 2-amino-3-carboxamido-thieno[2,3-b]pyridines have demonstrated excellent anti-proliferative activity against human cancer cell lines, including the triple-negative breast cancer cell line MDA-MB-231. In this study, 81 novel thieno[2,3-b]pyridines were synthesised in four series to further improve their anti-proliferative activity, in particular by targeting an adjacent lipophilic pocket in the putative target enzyme phosphoinositide phospholipase C (PI-PLC). Overall, it was found that appending a propyl-aryl group at C-5 on 2-amino-3-carboxamido-thieno[2,3-b]pyridine resulted in compounds with potent biological activity, exhibiting IC50 values in the nanomolar range. The propyl linker could be an α,β-unsaturated ketone or a saturated propyl ketone, but the highest activity was obtained when allylic alcohols were the tether between thieno[2,3-b]pyridine and the appended aryl group, with compound 21r having IC50 values lower than 50 nM. Compounds with one extra carbon in the tether (i.e., a four-atom chain) were found to be considerably less active. Molecular modelling revealed this propyl tether places the newly introduced aryl ring in an untargeted lipophilic pocket within the active site of the phosphoinositide phospholipase C (PI-PLC) enzyme.

New pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-one hybrids linked to arene units: synthesis of potential MRSA, VRE, and COX-2 inhibitors

In the current study, we reported the tandem synthesis of two series of arene-linked pyrimidinone hybrids with related fused thieno[2,3-b]pyridine moiety. The target hybrids were prepared, in moderate to excellent yields, by the reaction of a ternary mixture of the appropriate of 3-aminothieno[2,3-b]pyridine-2-carboxylate, DMF-DMA, and a series of aryl amines in dioxane at 110 °C for 8 h. The antibacterial activity of the new hybrids was estimated against six susceptible ATCC strains. Hybrids 5g and 7g, linked to a sulfonamide unit, showed the best efficacy against S. aureus and E. faecalis strains with minimum inhibitory concentration (MIC) values of 1.7–1.8 μM, which exceed ciprofloxacin. Furthermore, some of new hybrids were examined as potential inhibitors of four different MRSA and VRE strains. Hybrids 5g and 7g demonstrated more potent efficacy than linezolid against MRSA strains with MIC values of 3.6/3.4 and 1.8/1.7 μM against ATCC:33591 and ATCC:43300 strains, respectively. The prior hybrids displayed a comparable efficacy with linezolid against VRE strains with MIC values of 7.3/6.9 and 3.6/3.4 μM against ATCC:51299 and ATCC:51575 strains, respectively. Additionally, some of the new hybrids were examined as potential COX-2 inhibitors using the reference celecoxib (IC50 of 0.117 µM). Hybrid 7g revealed more potent inhibitory efficacy than celecoxib with IC50 of 0.112 µM, whereas hybrid 5g showed almost inhibitory activity equivalent to celecoxib with IC50 of 0.121 µM. Molecular docking was performed to predict the possible binding interactions between hybrids 5g and 7g with the target COX-2 enzyme.

Exploring of tumor-associated carbonic anhydrase isoenzyme IX and XII inhibitory effects and cytotoxicities of the novel N-aryl-1-(4-sulfamoylphenyl)-5-(thiophen-2-yl)-1H-pyrazole-3-carboxamides

A series of novel N-aryl-1-(4-sulfamoylphenyl)-5-(thiophen-2-yl)-1H-pyrazole-3-carboxamides was synthesized and examined as inhibitors of cytosolic (human) hCA I and hCA II, and cancer-related transmembrane hCA IX and hCA XII isoenzymes. AC2 was the most selective inhibitor towards cancer-related hCA IX while AC8 and AC9 selectively inhibited hCA XII over off-target isoenzymes. Anticancer effects of the compounds were evaluated towards human oral squamous cell carcinoma (OSCC) cell lines, human mesenchymal normal oral cells, breast (MCF7), prostate (PC3), non-small cell lung carcinoma cells (A549), and non-tumoral fetal lung fibroblast cells (MRC5). Compounds moderately showed cytotoxicity towards cancer cell lines. Among others, AC6 showed cell-specific cytotoxic activity and induced apoptosis in a dose-dependent manner without a significant change in the cell cycle distribution of MCF7. These results suggest that pyrazole-3-carboxamides need further molecular modification to increase their anticancer drug candidate potency.

Validating TDP1 as an Inhibition Target for the Development of Chemosensitizers for Camptothecin-Based Chemotherapy Drugs

Cancer chemotherapy sensitizers hold the key to maximizing the potential of standard anticancer treatments. We have a long-standing interest in developing and validating inhibitors of the DNA repair enzyme tyrosyl-DNA phosphodiesterase 1 (TDP1) as chemosensitizers for topoisomerase I poisons such as topotecan. Herein, by using thieno[2,3-b]pyridines, a class of TDP1 inhibitors, we showed that the inhibition of TDP1 can restore sensitivity to topotecan, results that are supported by TDP1 knockout cell experiments using CRISPR/Cas9. However, we also found that the restored sensitivity towards topoisomerase I inhibitors is likely regulated by multiple complementary DNA repair pathways. Our results showed that one of these pathways is likely modulated by PARP1, although it is also possible that other redundant and partially overlapping pathways may be involved in the DNA repair process. Our work thus raises the prospect of targeting multiple DNA repair pathways to increase the sensitivity to topoisomerase I inhibitors.

Thieno[2,3-b]Pyridine Derivative Targets Epithelial, Mesenchymal and Hybrid CD15s+ Breast Cancer Cells

The adhesion of cancer cells to vascular endothelium is a critical process in hematogenous metastasis and might be similar to the recruitment of leukocytes at the site of inflammation. It is mediated by E-selectin and its ligands, of which the most stereospecific is a glycoconjugate sialyl Lewis x (CD15s), which may be expressed as an oligosaccharide branch of the CD44 glycoprotein, as well as a self-contained glycosphingolipid. It is also known that increased sialylation of glycoconjugates is a feature of malignant cells. The aim of the study was to analyse the effect of a novel thieno[2,3-b]pyridine, compound 1, in MDA-MB-231 triple-negative breast cancer cells (TNBCs) upon CD15s and CD44 expression in different cell subpopulations using flow cytometry. CD15s expression was compared between mesenchymal-like cancer stem cells (CSC, CD44⁺CD24⁻), epithelial cells without CD44 (CD44⁻CD24⁺ and CD44⁻CD24⁻), and CD44⁺CD24⁺ cells that exhibit mesenchymal and epithelial features. In addition, expression of CD44 in CD15s⁺CSC and CD15s⁻CSC was determined. Compound 1 significantly decreased the percentage of CD15s⁺CSC, CD15s⁺CD44⁺CD24⁺, and CD15s⁺CD44⁻ subpopulations, as well as the expression of CD15s in CD44⁺CD24⁺ and CD44⁻ cells, and therefore shows potential as a treatment for TNBC.

Improving the solubility of anti-proliferative thieno[2,3-b]quinoline-2-carboxamides

Thieno[2,3-b]pyridines are a class of compounds known for their potent anti-proliferative activities against a range of human cancer cell lines. In this research, a number of strategies to generate analogues that have improved aqueous solubility whilst retaining the potent anti-proliferative actions, compared to previously-explored compounds in this class, were made. Herein we report the synthesis of 80 novel compounds, comprising two series, all based on the thieno[2,3-b]pyridine core structure. Overall, it was found that introducing alternative heterocycles did not notably improve the solubility or retain anti-proliferative activity seen in previously-reported analogues. However, pleasingly it was discovered, that the best strategy for improving the solubility was the alteration of the appended alkyl ring to introduce polar groups such as alcohols, ketones and substituted amine groups. In addition to this finding, we have discovered a thieno[2,3-b]pyridine, 15e, with greater aqueous solubility that has ever been seen for this class of compounds that is also a potent inhibitor of cancer cell growth, with IC₅₀'s in the nanomolar range. This new lead structure will form the basis of future explorations into this class of compounds.

Investigation into Improving the Aqueous Solubility of the Thieno[2,3-b]pyridine Anti-Proliferative Agents

It is now established that the thieno[2,3-b]pyridines are a potent class of antiproliferatives. One of the main issues encountered for their clinical application is their low water solubility. In order to improve this, two strategies were pursued. First, a morpholine moiety was tethered to the molecular scaffold by substituting the sulphur atom with nitrogen, resulting in a 1H-pyrrolo[2,3-b]pyridine core structure. The water solubility was increased by three orders of magnitude, from 1.2 µg/mL (1-thieno[2,3-b]pyridine) to 1.3 mg/mL (3-pyrrolo[2,3-b]pyridine), however, it was only marginally active against cancer cells. The second strategy involved loading a very potent thieno[2,3-b]pyridine derivative (2) into a cholesteryl-poly(allylamine) polymer matrix for water solubilisation. Suppression of human pancreatic adenocarcinoma (BxPC-3) viability was observed to an IC₅₀ value of 0.5 μg/mL (1.30 μM) in conjunction with the polymer, which is a five-fold (×5) increase in potency as compared to the free drug alone, demonstrating the utility of this formulation approach.

GPCR Modulation of Thieno[2,3-b]pyridine Anti-Proliferative Agents

A panel of docking scaffolds was developed for the known molecular targets of the anticancer agents, thieno[2,3-b]pyridines, in order to glean insight into their mechanism of action. The reported targets are the copper-trafficking antioxidant 1 protein, tyrosyl DNA phosphodiesterase 1, the colchicine binding site in tubulin, adenosine A2A receptor, and, finally, phospholipase C-δ1. According to the panel, the A2A receptor showed the strongest binding, inferring it to be the most plausible target, closely followed by tubulin. To investigate whether the thieno[2,3-b]pyridines modulate G protein-coupled receptors (GPCRs) other than A2A, a screen against 168 GPCRs was conducted. According to the results, ligand 1 modulates five receptors in the low µM region, four as an antagonist; CRL-RAMP3 (IC₅₀—11.9 µM), NPSR1B (IC₅₀—1.0 µM), PRLHR (IC₅₀—9.3 µM), and CXCR4 (IC₅₀—6.9 µM). Finally, one agonist, GPRR35, was found (EC₅₀ of 7.5 µM). Molecular modelling showed good binding to all of the receptors investigated; however, none of these surpass the A2A receptor. Furthermore, the newly-identified receptors are relatively modestly expressed in the cancer cell lines most affected by the thieno[2,3-b]pyridines, making them less likely to be the main targets of the mechanism of action for this compound class. Nevertheless, new modulators against GPCRs are of an interest as potential hits for further drug development.

Thieno[2,3-b]pyridine derivatives are potent anti-platelet drugs, inhibiting platelet activation, aggregation and showing synergy with aspirin

Drugs which inhibit platelet function are commonly used to prevent blood clot formation in patients with Acute Coronary Syndromes (ACS) or those at risk of stroke. The thieno[3,2-c]pyridine class of therapeutic agents, of which clopidogrel is the most commonly used, target the P2Y₁₂ receptor, and are often used in combination with acetylsalicylic acid (ASA). Six thieno[2,3-b]pyridine were assessed for in vitro anti-platelet activity; all derivatives showed effects on both platelet activation and aggregation, and showed synergy with ASA. Some compounds demonstrated greater activity when compared to clopidogrel. These compounds, therefore, represent potential novel P2Y₁₂ inhibitors for improved treatment for patients.

Synthesis and antiproliferative activity of 2-chlorophenyl carboxamide thienopyridines

3-Amino-2-arylcarboxamide-thieno[2,3-b]pyridines are a known class of antiproliferative compounds with activity against the phospholipase C enzyme. To further investigate the structure activity relationships of these derivatives a series of analogues were prepared modifying key functional groups. It was determined that modification of the 3-amino and 2-aryl carboxamide functionalities resulted in complete elimination of activity, whilst modification at C-5 allowed compounds of greater activity to be prepared.