Discovery and Development of Thiazolo[3,2-a]pyrimidinone Derivatives as General Inhibitors of Bcl-2 Family Proteins

Discovery and development of thiazolidine-2,4-dione derivatives as Bcl-2/Mcl-1 dual inhibitors

Increasing the levels of antiapoptotic Bcl-2 proteins is an important way that cancer cells utilize to get out of apoptosis, underscoring their significance as promising targets for anticancer therapies. Lately, a primary compound 1 bearing thiazolidine-2,4-dione was discovered to exhibit comparable Mcl-1 inhibitory activity in comparison to WL-276. Herein, thirty-nine thiazolidine-2,4-dione analogs were yielded through incorporating different biphenyl moieties (R1), amino acid side chains (R2) and sulfonamides (R3) on 1. The findings indicated that certain compounds exhibited favorable inhibitory effects against Bcl-2/Mcl-1, while demonstrating limited or negligible binding affinity towards Bcl-xL. In particular, compounds 16 and 20 exhibited greater Bcl-2/Mcl-1 inhibition compared to AT-101, WL-276 and 1. Moreover, they demonstrated notable antiproliferative effects and significantly induced apoptosis in U937 cells. The western blot and co-immunoprecipitation assays confirmed that 20 could induce alterations in the expression of apoptosis-associated proteins to result in apoptosis through on-target Bcl-2 and Mcl-1 inhibition. In addition, 20 exhibited favorable stability profiles in both rat plasma and rat liver microsomes. In total, 20 could be used as a promising compound to discover Bcl-2/Mcl-1 dual inhibitors with favorable therapeutic properties.

Synthesis, Self-Assembly in Crystalline Phase and Anti-Tumor Activity of 2-(2-/4-Hydroxybenzylidene)thiazolo[3,2-a]pyrimidines

A series of new thiazolo[3,2-a]pyrimidines different by aryl substituents in 2 and 5 positions are synthesized and characterized in solution as well as in the crystalline phase using ¹H and ¹³C NMR-, IR-spectroscopies, mass-spectrometry methods, and single crystal X-ray diffraction (SCXRD). The SCXRD study revealed the role of intermolecular H-bonding in the formation of supramolecular architectures (racemic monomers, centrosymmetric racematic dimers, or homochiral 1D chains) of obtained thiazolo[3,2-a]pyrimidines derivatives depending on solvents (aprotic DMSO or protic EtOH) used upon the crystallization process. Moreover, the in vitro study of cytotoxicity toward different tumor cells showed their high or moderate efficiency with moderate cytotoxicity against normal liver cells which allows to consider the obtained thiazolo[3,2-a]pyrimidine derivatives as promising candidates for application as antitumor agents.

Thiazolopyrimidine Scaffold as a Promising Nucleus for Developing Anticancer Drugs: a Review in Last Decade

The thiazolopyrimidine nucleus is a bioisostericanalog of purine and an important class of N-containing heterocycles. Thiazolopyrimidine scaffolds are considered a promising class of bioactive compounds that encompass diverse biological activities such as antibacterial, antiviral, antifungal, anticancer, corticotrophin-releasing factor antagonists, anti-inflammatory, antituberculosis, and glutamic receptors antagonists. Despite the importance of thiazolopyrimidines from a pharmacological viewpoint, there is hardly a comprehensive review on this important heterocyclic nucleus. Throughout the years, those scaffolds have been studied extensively for its anticancer properties and several compounds were designed, synthesized, and evaluated for their anticancer effects with activity in the µM to nM range. However, there are hardly any reviews covering the anticancer effects of thiazolopyrimidines. In this review, an effort was made to compile literatures covering the anticancer activity of thiazolopyrimidines reported in the last decade (2010-2020). Nearly thirty articles were reviewed and compounds which IC50 < 50 µM against at least 50% of the used cell lines were listed in this review. The best ten compounds (10a, 14b, 17g, 18,25e, 25k, 34e, 41i, 49a, & 49c) show the best anticancer activity against the corresponding cell lines during the last 10 years are highlighted. By highlighting the most active compounds, this review article sheds light on the structural features associated with the strongest anticancer effects to provide guidance to future research aiming to develop anticancer molecules.

Crystalline State Hydrogen Bonding of 2-(2-Hydroxybenzylidene)Thiazolo[3,2-a]Pyrimidines: A Way to Non-Centrosymmetric Crystals

Thiazolopyrimidines are attractive to medical chemists as new antitumor agents due to their high inhibiting activity towards the tumor cells replication process and easy modification of their structure by varying of the number and nature of substituents. The presence of asymmetric C5 carbon atoms requires the development of racemic mixture separation procedures for these heterocycles. One of the more effective ways is the crystallization of a racemic compound as a conglomerate. A prerequisite for such separation is the formation of non-centrosymmetric crystals presenting Sohncke space groups. For the construction of chiral supramolecular ensembles in a crystalline state, hydrogen bonds were chosen as supramolecular synthons. In this context, salicylic derivatives at the C2 atom of thiazolopyrimidines were synthesized. The crystal structures of the obtained compounds were established by SCXRD. The regularities of the solvent’s influence on the crystal packaging were revealed. The conditions for the preparation of crystals with the chiral space group due to intermolecular hydrogen bonds were discovered.

The Evaluation of DHPMs as Biotoxic Agents on Pathogen Bacterial Membranes

Herein, we present biological studies on 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) obtained via Biginelli reaction catalyzed by NH4Cl under solvent-free conditions. Until now, DHPMs have not been tested for biological activity against pathogenic E. coli strains. We tested 16 newly synthesized DHPMs as antimicrobial agents on model E. coli strains (K12 and R2–R4). Preliminary cellular studies using MIC and MBC tests and digestion of Fpg after modification of bacterial DNA suggest that these compounds may have greater potential as antibacterial agents than typically used antibiotics, such as ciprofloxacin (ci), bleomycin (b) and cloxacillin (cl). The described compounds are highly specific for pathogenic E. coli strains based on the model strains used and may be engaged in the future as new substitutes for commonly used antibiotics in clinical and nosocomial infections in the pandemic era.

Design, synthesis and biological evaluation of hydantoin derivatives as Mcl-1 selective inhibitors

As a member of Bcl-2 protein family, myeloid cell leukemia-1 (Mcl-1) plays a critical role in cell apoptosis and has become a promising anti-cancer drug target. Herein, we designed and synthesized a series of hydantoin derivatives as novel Mcl-1 inhibitors based on our previously developed lead compound. Among them, compound M23 and M24 exhibited good binding affinities against Mcl-1 with K_i values of 0.49 μM and 0.33 μM respectively. Especially, compound M23 exhibited good selectivity over Bcl-xL, whereas compound M24 possessed good selectivity over both Bcl-2 and Bcl-xL. Furthermore, we also investigated the effects of these new Mcl-1 inhibitors on cell proliferation, apoptosis and mitochondrial membrane potential, as well as the stability in plasma.

Structure-Based Optimization of 3-Phenyl-N-(2-(3-phenylureido)ethyl)thiophene-2-sulfonamide Derivatives as Selective Mcl-1 Inhibitors

Selective Mcl-1 inhibitors may overcome the drug resistance caused by current anti-apoptotic Bcl-2 protein inhibitors in tumors with Mcl-1 overexpression. Based on previously discovered compounds with a 3-phenylthiophene-2-sulfonamide core moiety, in this work, we have obtained new compounds with improved binding affinity and/or selectivity under the guidance of structure-based design. The most potent compounds achieved sub-micromolar binding affinities to Mcl-1 (K_i ∼ 0.4 μM) and good cytotoxicity (IC₅₀ < 10 μM) on several tumor cells. ¹⁵N-heteronuclear single-quantum coherence NMR spectra suggested that these compounds bound to the BH3-binding groove on Mcl-1. Several cellular assays revealed that FWJ-D4 as well as its precursor FWJ-D5 effectively induced caspase-dependent apoptosis, and their target engagement at Mcl-1 was confirmed by co-immunoprecipitation experiments. Treatment with FWJ-D5 at 50 mg/kg every 2 days on an RS4;11 xenograft mouse model for 22 days led to 75% reduction in tumor volume without body weight loss.

Development of Mcl-1 inhibitors for cancer therapy

The myeloid leukemia cell differentiation protein (Mcl-1) is an anti-apoptotic protein of the B-cell lymphoma 2 (Bcl-2) family, which regulates cellular apoptosis. Mcl-1 expression plays a key role in survival of cancer cells and therefore serves as a promising target in cancer therapy. Besides, its importance as a cancer target, various peptides and small-molecule inhibitors have been successfully designed and synthesized, yet no Mcl-1 inhibitor is approved for clinical use. However, recent development on the understanding of Mcl-1's role in key cellular processes in cancer and an upsurge of reports highlighting its association in various anticancer drug resistance supports the view that Mcl-1 is a key target in various cancers, especially hematological cancers. This review compiles structures of a variety of inhibitors of Mcl-1 reported to date. These include inhibitors based on a diverse range of heterocycles (e.g. indole, imidazole, thiophene, nicotinic acid, piperazine, triazine, thiazole, isoindoline), oligomers (terphenyl, quaterpyridine), polyphenol, phenalene, anthranilic acid, anthraquinone, macrocycles, natural products, and metal-based complexes. In addition, an effort has been made to summarize the structure activity relationships, based on a variety of assays, of some important classes of Mcl-1 inhibitors, giving affinities and selectivities for Mcl-1 compared to other Bcl-2 family members. A focus has been placed on categorizing the inhibitors based on their core frameworks (scaffolds) to appeal to the chemical biologist or medicinal chemist.

Design, synthesis and antiproliferative evaluation of new tricyclic fused thiazolopyrimidines targeting topoisomerase II: Molecular docking and apoptosis inducing activity

A novel series of thiazolopyrimidines and fused thiazolopyrimidines was designed and synthesized as topoisomerase II alpha inhibitors. All synthesized compounds were screened by the National Cancer Institute (NCI), Bethesda, USA for anticancer activity against 60 human cancer cell lines representing the following cancer types: leukemia, non-small cell lung, colon, CNS, melanoma, ovarian, renal, prostate, and breast cancers. Compound 3a was found to be the most potent inhibitor on renal cell line (A-498) causing 83.03% inhibition (IC₅₀ = 1.89 μM). DNA-flow cytometric analysis showed that compound 3a induce cell cycle arrest at G2/M phase leading to cell proliferation inhibition and apoptosis. Moreover, fused thiazolopyrimidines 3a showed potent topoisomerase II inhibitory activity (IC₅₀ = 3.19 μM) when compared with reference compound doxorubicin (IC₅₀ = 2.67 μM). Docking study of all the synthesized compounds showed that compound 3a interacts in a similar pattern to etoposide and stabilizing the topoisomerase cleavage complex (Top2-cc) that accounts for its high potency.

Discovery of novel indazole-acylsulfonamide hybrids as selective Mcl-1 inhibitors

Overexpressing myeloid cell leukemia sequence 1 (Mcl-1) protein is an important way to confer the resistance of cancer cells to conventional anti-cancer treatments. Therefore, developing Mcl-1 inhibitors has become an attractive strategy for cancer therapy. In the studies, a series of new indazole-acylsulfonamide hybrids were designed, synthesized and evaluated as potent Mcl-1 inhibitors. Among them, the most potent compound 17 (K_i = 0.43 μM) showed a little better inhibitory activity against Mcl-1 protein than positive control AT-101 (K_i = 0.45 μM). Pleasingly, it displayed > 40-fold selectivity over Bcl-2 (K_i = 18 μM) and Bcl-xL (no activity). Furthermore, compound 17 had good inhibitory activities against PC-3, MDA-MB-231 and K562 cells (IC₅₀ = 12.3, 10.6 and 6.62 μM, respectively) and could effectively induce apoptosis and the activation of caspase-3 in a dose-dependent manner in K562 cells.

Structure-based virtual screening, biological evaluation and biophysical study of novel Mcl-1 inhibitors

Aim: Targeting the protein-protein interactions (PPIs) associated with Mcl-1 has become a promising therapeutic approach for cancer. Herein, we reported the discovery of novel Mcl-1 inhibitors using an integrated computational approach. Results: Among 30 virtual screening hits, five compounds show inhibitory activities against Mcl-1. The most potent inhibitors M02 (K _i  = 5.4 μM) and M08 (K_i = 0.53 μM) exhibit good selectivity against Bcl-2 and Bcl-xL. Compound M08 exhibits anti-proliferation activity and induces caspase-3 activation in Jurkat cancer cells. Moreover, ¹H⁄¹⁵N HSQC NMR experiments suggested that compound M08 likely binds in the P2 pocket of Mcl-1 and engages R263 in a salt bridge. Conclusion: Our study provides a good starting point for future discovery of more potent Mcl-1 selective inhibitors.

Synthesis, crystal structure and activity evaluation of novel 3,4-dihydro-1-benzoxepin-5(2H)-one derivatives as protein-tyrosine kinase (PTK) inhibitors

Four new 3,4-dihydro-1-benzoxepin-5(2H)-one derivatives, namely (E)-4-(5-bromo-2-hydroxybenzylidene)-6,8-dimethoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, (7), (E)-4-[(E)-3-(5-bromo-2-hydroxyphenyl)allylidene]-6,8-dimethoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, (8), (E)-4-(5-bromo-2-hydroxybenzylidene)-6-hydroxy-8-methoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, C₁₈H₁₅BrO₅, (9), and (E)-4-[(E)-3-(5-bromo-2-hydroxyphenyl)allylidene]-6-hydroxy-8-methoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, (10), have been synthesized and characterized by FT-IR, NMR and MS. The structure of (9) was confirmed by single-crystal X-ray diffraction. Crystal structure analysis shows that molecules of (9) are connected into a one-dimensional chain in the [010] direction through classical hydrogen bonds and these chains are further extended into a three-dimensional network via C-H...O interactions. The inhibitory activities of these compounds against protein-tyrosine kinases (PTKs) show that 6-hydroxy-substituted compounds (9) and (10) are more effective for inhibiting ErbB1 and ErbB2 than are 6-methoxy-substituted compounds (7) and (8). This may be because (9) and (10) could effectively bind to the active pockets of the protein through intermolecular interactions.

Design, synthesis and preliminary biological evaluation of indole-3-carboxylic acid-based skeleton of Bcl-2/Mcl-1 dual inhibitors

The B-cell lymphoma-2 (Bcl-2) family proteins are attractive targets for cancer therapy. In our previous work, the structure-activity relationship of WL-276 was studied. According to the results, rhodanine derivatives show potent binding affinity for Bcl-2 and Mcl-1 protein and show weaker activity against Bcl-X_L protein. Based on the previous results, a new class of indole-3-carboxylic acid-based derivatives were designed and synthesized as Bcl-2/Mcl-1 dual inhibitors. Among them, compound 17 has a K_i value of 0.26μM for Bcl-2 protein and is better than WL-276. Furthermore, it inhibits the myeloid cell leukemia sequence 1 (Mcl-1) protein with a K_i value of 72nM. Especially, compound 31 can selectively acting on Bcl-2 and Mcl-1 protein but not Bcl-X_L protein, which has great significance for developing dual inhibitors targeting Bcl-2 and Mcl-1 protein, as well as specific antitumor abilities in cells.

Identification of Small-Molecule Inhibitors of the Antiapoptotic Protein Myeloid Cell Leukaemia-1 (Mcl-1)

Protein-protein interactions (PPIs) control many cellular processes in cancer and tumour growth. Of significant interest is the role PPIs play in regulating apoptosis. The overexpression of the antiapoptosis regulating Bcl-2 family of proteins is commonly observed in several cancers, leading to resistance towards both radiation and chemotherapies. From this family, myeloid cell leukemia-1 (Mcl-1) has proven the most difficult to target, and one of the leading causes of treatment resistance. Exploiting the selective PPI between the apoptosis-regulating protein Noxa and Mcl-1, utilising a fluorescence polarization assay, we have identified four small molecules with the ability to modulate Mcl-1. The identified compounds were computationally modelled and docked against the Mcl-1 binding interface to obtain structural information about their binding sites allowing for future analogue design. When examined for their activity towards pancreatic cell lines that overexpress Mcl-1 (MiaPaCa-2 and BxPC-3), the identified compounds demonstrated growth inhibition, suggesting effective Mcl-1 modulation.

Small molecules targeting Mcl-1: the search for a silver bullet in cancer therapy

Progress towards the development of potent and selective inhibitors of the pro-survival protein Mcl-1 is reviewed.

Synthesis and Characterisation of Some Novel Fused Thiazolo[3,2-A] Pyrimidinones and Pyrimido[2,1-B][1,3]Thiazinones

Reactions of 7,9-bis(4-methoxyphenyl)-2-thioxo-2,3-dihydropyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(1H)-one with α-haloketones, chloroacetonitrile and DMAD, afforded the corresponding fused thiazolo[3,2-a]pyrimidinone derivatives. The reaction of the thione with chloroacetic acid and an appropriate aromatic aldehyde yielded the respective 2-arylidene-2H-pyrido[3′,2′:4,5]thieno[3,2-d]thiazolo[3,2-a] pyrimidine-3,5-diones. Also, the treatment of thione with arylidenemalononitriles gave the fused pyrimido[2,1-b][1,3]thiazine derivatives, respectively. The structures of the synthesised products were confirmed by IR, 1H NMR and mass spectral techniques. The cytotoxic activity of the new products against breast carcinoma (MCF-7) and hepatocellular carcinoma (HepG2) cell lines were determined and the results revealed promising activity.

Design, synthesis and preliminary bioactivity studies of imidazolidine-2,4-dione derivatives as Bcl-2 inhibitors

Anti-apoptotic B-cell lymphoma-2 (Bcl-2) proteins are promising targets for cancer therapy. In the present study, a series of imidazolidine-2,4-dione derivatives were designed and synthesized to test their inhibitory activities against anti-apoptotic Bcl-2 proteins. Among them, compound 8k had better growth inhibitory effects on K562 and PC-3 cell lines compared to lead compound WL-276.

Design, synthesis and preliminary bioactivity studies of 2-thioxo-4-thiazolidinone derivatives as Bcl-2 inhibitors

The B-cell lymphoma-2 (Bcl-2) protein is a promising target for cancer therapy. In the present study, a series of 2-thioxo-4-thiazolidinone derivatives were designed and synthesized as Bcl-2 inhibitors. Most of them possessed decent inhibitory activity for anti-apoptotic Bcl-2 proteins. Among them, compound 31 has similar growth inhibition towards K562 compared to (R)-Gossypol. In addition, it inhibits the myeloid cell leukemia sequence 1 (Mcl-1) protein with a Ki value of 74 nM.

Biological evaluation of halogenated thiazolo[3,2-a]pyrimidin-3-one carboxylic acid derivatives targeting the YycG histidine kinase

With an intention to potent inhibitors of YycG histidine kinase, a series of halogenated thiazolo[3,2-a]pyrimidin-3-one carboxylic acid derivatives were synthesized and evaluated for their antibacterial, antibiofilm and hemolytic activities. The majority of the compounds showed good activity against Staphylococcus epidermidis and Staphylococcus aureus, with MIC values of 1.56-6.25 μM, simultaneously presented promising antiobifilm activity against S. epidermidis ATCC35984 at 50 μM. The test of inhibitory activity on YycG kinase suggested the antibacterial activities of these derivatives are based on inhibiting the enzyme activity of the YycG HK domain. The hemolytic activity test suggested these compounds exhibited in vitro antibacterial activity at non-hemolytic concentrations.

Development of 3-phenyl-N-(2-(3-phenylureido)ethyl)-thiophene-2-sulfonamide compounds as inhibitors of antiapoptotic Bcl-2 family proteins

Antiapoptotic Bcl-2 family proteins, such as Bcl-xL , Bcl-2, and Mcl-1, are often overexpressed in tumor cells, which contributes to tumor cell resistance to chemotherapies and radiotherapies. Inhibitors of these proteins thus have potential applications in cancer treatment. We discovered, through structure-based virtual screening, a lead compound with micromolar binding affinity to Mcl-1 (inhibition constant (Ki )=3 μM). It contains a phenyltetrazole and a hydrazinecarbothioamide moiety, and it represents a structural scaffold not observed among known Bcl-2 inhibitors. This work presents the structural optimization of this lead compound. By following the scaffold-hopping strategy, we have designed and synthesized a total of 82 compounds in three sets. All of the compounds were evaluated in a fluorescence-polarization binding assay to measure their binding affinities to Bcl-xL , Bcl-2, and Mcl-1. Some of the compounds with a 3-phenylthiophene-2-sulfonamide core moiety showed sub-micromolar binding affinities to Mcl-1 (Ki =0.3-0.4 μM) or Bcl-2 (Ki ≈1 μM). They also showed obvious cytotoxicity on tumor cells (IC50 <10 μM). Two-dimensional heteronuclear single quantum coherence NMR spectra of three selected compounds, that is, YCW-E5, YCW-E10, and YCW-E11, indicated that they bind to the BH3-binding groove on Bcl-xL in a similar mode to ABT-737. Several apoptotic assays conducted on HL-60 cells demonstrated that these compounds are able to induce cell apoptosis through the mitochondrial pathway. We propose that the compounds with the 3-phenylthiophene-2-sulfonamide core moiety are worth further optimization as effective apoptosis inducers with an interesting selectivity towards Mcl-1 and Bcl-2.

Ethyl (Z)-2-(2-fluoro-benzyl-idene)-7-methyl-3-oxo-5-phenyl-3,5-dihydro-2H-thia-zolo[3,2-a]pyrimidine-6-carboxyl-ate

The title compound, C₂₃H₁₉FN₂O₃S, a fused-pyrimidine derivative, displays dihedral angles between the thia­zole ring and the benzene ring and substituted benzene ring of 7.10 (14) and 3.48 (12)°, respectively. The dihydro­pyrimidine ring adopts a flattened boat conformation. The olefinic double bond is in a Z configuration.