Strategies for overcoming resistance to Bruton's tyrosine kinase inhibitor zanubrutinib.

Bruton's tyrosine kinase (BTK) inhibitors have revolutionized the treatment of B-cell malignancies. They target BTK, a key effector in the B-cell receptor (BCR) signaling pathway, crucial for B-cell survival and proliferation. The first-in-class irreversible BTK inhibitor, ibrutinib, was approved for various B-cell malignancies but has limitations due to off-target effects. Second-generation inhibitors, such as acalabrutinib and zanubrutinib, offer improved selectivity and reduced side effects. However, resistance to BTK inhibitors, driven by BTK mutations, remains a challenge. Combinatorial therapies with PI3K inhibitors, immune checkpoint inhibitors, BH3 mimetics, and anti-CD20 antibodies show promise in overcoming resistance. Noncovalent BTK inhibitors and proteolysis-targeting chimeras (PROTACs) are emerging strategies with potential to combat resistance. Overall, advancements in BTK-targeted therapies provide hope for improved outcomes in patients with B-cell malignancies and a promising avenue to address drug resistance. Further research is needed to optimize combination therapies and identify optimal treatment regimens.

Synthesis and photodynamic activity of new 5-[(E)-2-(3-alkoxy-1-phenyl-1H-pyrazol-4-yl)ethenyl]-2-phenyl-3H-indoles.

A series of new indole-pyrazole hybrids 8a-m were synthesized through the palladium-catalyzed ligandless Heck coupling reaction from easily accessible unsubstituted, methoxy- or fluoro-substituted 4-ethenyl-1H-pyrazoles and 5-bromo-3H-indoles. These compounds exerted cytotoxicity to melanoma G361 cells when irradiated with blue light (414 nm) and no cytotoxicity in the dark at concentrations up to 10 µM, prompting us to explore their photodynamic effects. The photodynamic properties of the example compound 8d were further investigated in breast cancer MCF-7 cells. Evaluation revealed comparable anticancer activities of 8d in both breast and melanoma cancer cell lines within the submicromolar range. The treatment induced a massive generation of reactive oxygen species, leading to different types of cell death depending on the compound concentration and the irradiation intensity.

Anticancer effect of zanubrutinib in HER2-positive breast cancer cell lines.

Small molecule Bruton's tyrosine kinase (BTK) inhibitors have been developed for the treatment of various haemato-oncological diseases, and ibrutinib was approved as the first BTK inhibitor for anticancer therapy in 2013. Previous reports proved the receptor kinase human epidermal growth factor receptor 2 (HER2) to be a valid off-target kinase of ibrutinib and potentially other irreversible BTK inhibitors, as it possesses a druggable cysteine residue in the active site of the enzyme. These findings suggest ibrutinib as a candidate drug for repositioning in HER2-positive breast cancer (BCa). This subtype of breast cancer belongs to one of the most common classes of breast tumours, and its prognosis is characterized by a high rate of recurrence and tumour invasiveness. Based on their similar kinase selectivity profiles, we investigated the anticancer effect of zanubrutinib, evobrutinib, tirabrutinib and acalabrutinib in different BCa cell lines and sought to determine whether it is linked with targeting the epidermal growth factor receptor family (ERBB) pathway. We found that zanubrutinib is a potential inhibitor of the HER2 signalling pathway, displaying an antiproliferative effect in HER2-positive BCa cell lines. Zanubrutinib effectively inhibits the phosphorylation of proteins in the ERBB signalling cascade, including the downstream kinases Akt and ERK, which mediate key signals ensuring the survival and proliferation of cancer cells. We thus propose zanubrutinib as another suitable candidate for repurposing in HER2-amplified solid tumours.

Synthesis and biological activity evaluation of novel 3,5,7-trisubstituted pyrazolo[1,5-a]pyrimidines.

Mutation of FLT3 protein kinase is often associated with deregulated cell proliferation in acute myeloid leukemia and the inhibition of this kinase is a potential therapeutic strategy. We report a novel series of 3,5,7-trisubstituted pyrazolo[1,5-a]pyrimidines prepared in an effort to study their biological activity particularly toward FLT3-ITD and its downstream regulators as well as toward CDK2 and CDK9. Derivative 10b was capable to strongly inhibit all kinases and its selectivity in FLT3-ITD expressing cell lines MOLM13 and MV4-11 was in line with FLT3-ITD inhibition. Further biochemical analyses and molecular docking confirmed FLT3 as a cellular target of 10b.

Synthesis and biological activity evaluation of novel 2,6,9-trisubstituted purine conjugates as potential protein kinases inhibitors.

Deregulation of protein kinases is often associated with uncontrolled cell proliferation in various tumours and the inhibition of kinase activity remains an important target for anti-tumour drug development. Here, we report a novel series of 2-aminocyclohexylamino-6-(substituted benzylamino/anilino)-9-cyclopentylpurine derivatives conjugated with putrescine, spermidine or spermine moiety in an effort to expand library of highly potent 2,6,9-trisubstituted purine kinase inhibitors. Presented aniline-type conjugates exhibit significant cytotoxic activity in MV4-11 and EOL-1 cell lines which correlates with FLT3-ITD and PDGFRα inhibition. Furthermore, 6-anilinopurines affected MAPK and STAT pathways in the treated MV4-11 cells and induced cell cycle arrest in the G1 phase. 6-Benzylaminopurines showed comparable CDK2 inhibitory activity to 6-anilinopurines, however, the PDGFRα and FLT3-ITD inhibition was strongly suppressed. Our results show that novel compounds containing aniline in the structure can be involved in the development of potent tyrosine kinase inhibitors with strong activity toward acute myeloid leukemia or chronic eosinophilic leukemia.

Development of fluorescent dual-FRET probe for simultaneous detection of caspase-8 and caspase-9 activities and their relative quantification.

A multi-FRET three-fluorophore probe containing coumarin, fluorescein and rhodamine B with two enzymatically cleavable linkers has been synthesized and optimized for the simultaneous activity detection and relative quantification of two proteases - caspase-8 and caspase-9. The probe designed as a ratiometric single-excitation triple-emission system shows specific change in fluorescence intensities upon enzymatic cleavage of individual linkers in model mixtures as well as in a cell lysate. The activation of caspase-8 and caspase-9 is responsible for initiation of extrinsic or intrinsic apoptotic pathway, respectively, and the probe was proposed as a single chemical tool which could help to decipher a mechanism of cell death induced by various stimuli. The main advantage of this probe is the simplicity of its preparation using conventional organic synthesis, easy application for measurement and evaluation of the results.

Synthesis of N-aryl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-amines and their photodynamic properties in the human skin melanoma cell line G361.

A small series of N-aryl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-amines was synthesized from easily accessible 1-phenyl-1H-pyrazol-3-ol via 7-iodo-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine and 7-iodo-4-methyl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine intermediates and their subsequent use in palladium catalyzed Buchwald-Hartwig cross-coupling reaction with various anilines. Majority of the compounds were not significantly cytotoxic to melanoma G361 cells in the dark up to 10 µM concentration, but their activity could be increased by irradiation with visible blue light (414 nm). The most active compound 10 possessed EC50 values of 3.5, 1.6 and 0.9 µM in cells irradiated with 1, 5 and 10 J/cm2, respectively. The treatment caused generation of reactive oxygen species in cells and extensive DNA damage, documented by the comet assay and by detection of phosphorylated histone H2A.X, followed by apoptotic cell death. Our results suggest that N-aryl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-amines could serve as a potential source of photosensitizing compounds with anticancer activities.

Adamantane-Substituted Purine Nucleosides: Synthesis, Host-Guest Complexes with ß-Cyclodextrin and Biological Activity.

Purine nucleosides represent an interesting group of nitrogen heterocycles, showing a wide range of biological effects. In this study, we designed and synthesized a series of 6,9-disubstituted and 2,6,9-trisubstituted purine ribonucleosides via consecutive nucleophilic aromatic substitution, glycosylation, and deprotection of the ribofuranose unit. We prepared eight new purine nucleosides bearing unique adamantylated aromatic amines at position 6. Additionally, the ability of the synthesized purine nucleosides to form stable host-guest complexes with ß-cyclodextrin (ß-CD) was confirmed using nuclear magnetic resonance (NMR) and mass spectrometry (ESI-MS) experiments. The in vitro antiproliferative activity of purine nucleosides and their equimolar mixtures with ß-CD was tested against two types of human tumor cell line. Six adamantane-based purine nucleosides showed an antiproliferative activity in the micromolar range. Moreover, their effect was only slightly suppressed by the presence of ß-CD, which was probably due to the competitive binding of the corresponding purine nucleoside inside the ß-CD cavity.

Synthesis and Structural Optimization of 2,7,9-Trisubstituted purin-8-ones as FLT3-ITD Inhibitors.

Therapy of FLT3-positive acute myeloid leukemia still remains complicated, despite the availability of newly approved kinase inhibitors. Various strategies to avoid the reduced efficacy of therapy have been explored, including the development of dual targeting compounds, which inhibit FLT3 and another kinase necessary for the survival and proliferation of AML cells. We have designed new 2,7,9-trisubstituted 8-oxopurines as FLT3 inhibitors and report here the structure-activity relationship studies. We demonstrated that substituents at positions 7 and 9 modulate activity between CDK4 and FLT3 kinase, and the isopropyl group at position 7 substantially increased the selectivity toward FLT3 kinase, which led to the discovery of compound 15a (9-cyclopentyl-7-isopropyl-2-((4-(piperazin-1-yl)phenyl)amino)-7,9-dihydro-8H-purin-8-one). Cellular analyses in MV4-11 cells revealed inhibition of autophosphorylation of FLT3 kinase in nanomolar doses, including the suppression of downstream STAT5 and ERK1/2 phosphorylation. We also describe mechanistic studies in cell lines and activity in a mouse xenograft model in vivo.

How selective are clinical CDK4/6 inhibitors?

Pharmacological inhibition of cyclin-dependent kinase 4/6 (CDK4/6) has emerged as an efficient approach for treating breast cancer, and its clinical potential is expanding to other cancers. CDK4/6 inhibitors were originally believed to act by arresting proliferation in the G1 phase, but it is gradually becoming clear that the cellular response to these compounds is far more complex than this. Multiple context-dependent mechanisms of action are emerging, involving modulation of quiescence, senescence, autophagy, cellular metabolism, and enhanced tumor cell immunogenicity. These mechanisms may be driven by interactions with unexpected targets. We review cellular responses to the Food and Drug Administration-approved CDK4/6 inhibitors palbociclib, ribociclib, and abemaciclib, and summarize available knowledge of other drugs undergoing clinical trials, including data on their off-target landscapes. We emphasize the importance of comprehensively characterizing drugs' selectivity profiles to maximize their clinical efficacy and safety and to facilitate their repurposing to treat additional diseases based on their target spectrum.

Pseudopeptides with aldehyde or vinylsulfone warheads: Synthesis and antiproteasomal activity.

The comparative study of new proteasome inhibitors based on salicylic acid-modified pseudo-tripeptides terminated with aldehyde or vinylsulfone is presented. We described the synthesis of 11 pairs of pseudopeptides and their properties related to the proteasome inhibition were determined. The effects of integrated amino acids (combinations of leucine, phenylalanine, tryptophan, proline, cyclohexylalanine or norleucine residues) on the activity of the proteasome were investigated. Compounds preferentially inhibited the chymotrypsin ß5-subunit of the proteasome in cell-based assays compared with the ß1- and ß2-subunits, with IC50 values in mid-nanomolar ranges being obtained for the most active members. Our comparative study demonstrated that aldehydes were able to inhibit the proteasome in cells more effectively than vinylsulfones. These results were corroborated by the accumulation of polyubiquitinated proteins in treated cells, GFP accumulation in a reporter cell line and the ability of new compounds to induce apoptotic cell death.

Adamantane-Substituted Purines and Their ß-Cyclodextrin Complexes: Synthesis and Biological Activity.

Cyclin-dependent kinases (CDKs) play an important role in the cell-division cycle. Synthetic inhibitors of CDKs are based on 2,6,9-trisubstituted purines and are developed as potential anticancer drugs; however, they have low solubility in water. In this study, we proved that the pharmaco-chemical properties of purine-based inhibitors can be improved by appropriate substitution with the adamantane moiety. We prepared ten new purine derivatives with adamantane skeletons that were linked at position 6 using phenylene spacers of variable geometry and polarity. We demonstrated that the adamantane skeleton does not compromise the biological activity, and some of the new purines displayed even higher inhibition activity towards CDK2/cyclin E than the parental compounds. These findings were supported by a docking study, which showed an adamantane scaffold inside the binding pocket participating in the complex stabilisation with non-polar interactions. In addition, we demonstrated that ß-cyclodextrin (CD) increases the drug's solubility in water, although this is at the cost of reducing the biochemical and cellular effect. Most likely, the drug concentration, which is necessary for target engagement, was decreased by competitive drug binding within the complex with ß-CD.

Synthesis and Antiproliferative Activity of 2,4,6,7-Tetrasubstituted-2H-pyrazolo[4,3-c]pyridines.

A library of 2,4,6,7-tetrasubstituted-2H-pyrazolo[4,3-c]pyridines was prepared from easily accessible 1-phenyl-3-(2-phenylethynyl)-1H-pyrazole-4-carbaldehyde via an iodine-mediated electrophilic cyclization of intermediate 4-(azidomethyl)-1-phenyl-3-(phenylethynyl)-1H-pyrazoles to 7-iodo-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridines followed by Suzuki cross-couplings with various boronic acids and alkylation reactions. The compounds were evaluated for their antiproliferative activity against K562, MV4-11, and MCF-7 cancer cell lines. The most potent compounds displayed low micromolar GI50 values. 4-(2,6-Diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol proved to be the most active, induced poly(ADP-ribose) polymerase 1 (PARP-1) cleavage, activated the initiator enzyme of apoptotic cascade caspase 9, induced a fragmentation of microtubule-associated protein 1-light chain 3 (LC3), and reduced the expression levels of proliferating cell nuclear antigen (PCNA). The obtained results suggest a complex action of 4-(2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol that combines antiproliferative effects with the induction of cell death. Moreover, investigations of the fluorescence properties of the final compounds revealed 7-(4-methoxyphenyl)-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine as the most potent pH indicator that enables both fluorescence intensity-based and ratiometric pH sensing.

Optimization of norbornyl-based carbocyclic nucleoside analogs as cyclin-dependent kinase 2 inhibitors.

We report on the discovery of norbornyl moiety as a novel structural motif for cyclin-dependent kinase 2 (CDK2) inhibitors which was identified by screening a carbocyclic nucleoside analogue library. Three micromolar hits were expanded by the use of medicinal chemistry methods into a series of 16 novel compounds. They had prevailingly micromolar activities against CDK2 and the best compound of the series attained IC50 of 190 nM. The binding modes were explored in molecular details by modeling and docking. Quantum mechanics-based scoring was used to rationalize the affinities. In conclusion, the discovered 9-hydroxymethylnorbornyl moiety was shown by joint experimental-theoretical efforts to be able to serve as a novel substituent for CDK2 inhibitors. This finding opens door to the exploration of chemical space towards more effective derivatives targeting this important class of protein kinases.

New 2,6,9-trisubstituted purine derivatives as Bcr-Abl and Btk inhibitors and as promising agents against leukemia.

Bcr-Abl and Btk kinases are among the targets that have been considered for the treatment of leukemia. Therefore, several strategies have focused on the use of inhibitors as chemotherapeutic tools to treat these types of leukemia, such as imatinib (for Bcr-Abl) or ibrutinib (for Btk). However, the efficacy of these drugs has been reduced due to resistance mechanisms, which have motivated the development of new and more effective compounds. In this study, we designed, synthesized and evaluated 2,6,9-trisubstituted purine derivatives as novel Bcr-Abl and Btk inhibitors. We identified 5c and 5d as potent inhibitors of both kinases (IC50 values of 40 nM and 0.58/0.66 µM for Abl and Btk, respectively). From docking and QSAR analyses, we concluded that fluorination of the arylpiperazine system is detrimental to the activity against two kinases, and we also validated our hypothesis that the substitution on the 6-phenylamino ring is important for the inhibition of both kinases. In addition, our studies indicated that most compounds could suppress the proliferation of leukemia and lymphoma cells (HL60, MV4-11, CEM, K562 and Ramos cells) at low micromolar concentrations in vitro. Finally, we preliminarily demonstrated that 5c inhibited the downstream signaling of both kinases in the respective cell models. Therefore, 5c or 5d possessed potency to be further optimized as anti-leukemia drugs by simultaneously inhibiting the Bcr-Abl and Btk kinases.

Selective inhibition reveals cyclin-dependent kinase 2 as another kinase that phosphorylates the androgen receptor at serine 81.

Several studies have revealed that cyclin-dependent kinases (CDK) can mediate phosphorylation of steroid receptors at multiple sites, including serine 81 of the androgen receptor (AR). Phosphorylation of S81 is required for AR nuclear translocation, an association with chromatin and also regulates endogenous AR-regulated transcription in response to hormones. Up to date, S81-phosphorylation has been studied using different CDK inhibitors. Nevertheless, most inhibitors are non-selective or have unknown selectivity. We investigated the selectivity of commercially available CDK inhibitors and identified compounds that will be suitable for further studies to identify the CDKs responsible for S81-AR phosphorylation. We confirmed the positive impact of CDK1 and CDK9 on phosphorylation of S81-AR and its transcriptional activity. Although CDK1-mediated phosphorylation was previously shown to occur during mitosis, our experiments did not confirm this finding. By using chemical and genetic inhibition techniques, we identified that CDK2 contributes to S81-AR phosphorylation and transactivation while CDK4 was not shown to be involved in this process.

6-Substituted purines as ROCK inhibitors with anti-metastatic activity.

Rho-associated serine/threonine kinases (ROCKs) are principal regulators of the actin cytoskeleton that regulate the contractility, shape, motility, and invasion of cells. We explored the relationships between structure and anti-ROCK2 activity in a group of purine derivatives substituted at the C6 atom by piperidin-1-yl or azepan-1-yl groups. Structure-activity relationship (SAR) analyses suggested that anti-ROCK activity is retained, and may be further increased, by substitution of the parent compounds at the C2 atom or by expansion of the C6 side chain. These inhibitors of ROCK can reach effective concentrations within cells, as demonstrated by a decrease in phosphorylation of the ROCK target MLC, and by inhibition of the ROCK-dependent invasion of melanoma cells in the collagen matrix. Our study may be useful for further optimization of C6-substituted purine inhibitors of ROCKs and of other sensitive kinases identified by the screening of a broad panel of protein kinases.

Promising 2,6,9-Trisubstituted Purine Derivatives for Anticancer Compounds: Synthesis, 3D-QSAR, and Preliminary Biological Assays.

We designed, synthesized, and evaluated novel 2,6,9-trisubstituted purine derivatives for their prospective role as antitumor compounds. Using simple and efficient methodologies, 31 compounds were obtained. We tested these compounds in vitro to draw conclusions about their cell toxicity on seven cancer cells lines and one non-neoplastic cell line. Structural requirements for antitumor activity on two different cancer cell lines were analyzed with SAR and 3D-QSAR. The 3D-QSAR models showed that steric properties could better explain the cytotoxicity of compounds than electronic properties (70% and 30% of contribution, respectively). From this analysis, we concluded that an arylpiperazinyl system connected at position 6 of the purine ring is beneficial for cytotoxic activity, while the use of bulky systems at position C-2 of the purine is not favorable. Compound 7h was found to be an effective potential agent when compared with a currently marketed drug, cisplatin, in four out of the seven cancer cell lines tested. Compound 7h showed the highest potency, unprecedented selectivity, and complied with all the Lipinski rules. Finally, it was demonstrated that 7h induced apoptosis and caused cell cycle arrest at the S-phase on HL-60 cells. Our study suggests that substitution in the purine core by arylpiperidine moiety is essential to obtain derivatives with potential anticancer activity.

Imidazo[1,2-c]pyrimidin-5(6H)-one as a novel core of cyclin-dependent kinase 2 inhibitors: Synthesis, activity measurement, docking, and quantum mechanical scoring.

We report on the synthesis, activity testing, docking, and quantum mechanical scoring of novel imidazo[1,2-c]pyrimidin-5(6H)-one scaffold for cyclin-dependent kinase 2 (CDK2) inhibition. A series of 26 compounds substituted with aromatic moieties at position 8 has been tested in in vitro enzyme assays and shown to inhibit CDK2. 2D structure-activity relationships have ascertained that small substituents at position 8 (up to the size of naphtyl or methoxyphenyl) generally lead to single-digit micromolar IC50 values, whereas bigger substituents (substituted biphenyls) decreased the compounds' activities. The binding modes of the compounds obtained using Glide docking have exhibited up to 2 hinge-region hydrogen bonds to CDK2 and differed in the orientation of the inhibitor core and the placement of the 8-substituents. Semiempirical quantum mechanics-based scoring identified probable favourable binding modes, which will serve for future structure-based design and synthetic optimization of substituents of the heterocyclic core. In summary, we have identified a novel core for CDK2 inhibition and will explore it further to increase the potencies of the compounds and also monitor selectivities against other protein kinases.

Synthesis, anticancer evaluation, and molecular docking studies of some novel 4,6-disubstituted pyrazolo[3,4-d]pyrimidines as cyclin-dependent kinase 2 (CDK2) inhibitors.

A novel series of 4,6-disubstituted pyrazolo[3,4-d]pyrimidines (7-43) bearing various anilines at C-4 position and thiophenethyl or thiopentane moieties at C-6 position have been designed and synthesized by molecular hybridization approach. All the synthesized compounds were evaluated for in vitro CDK2/cyclin E and Abl kinase inhibitory activity as well as anti-proliferative activity against K-562 (chronic myelogeneous leukemia), and MCF-7 (breast adenocarcinoma) cell lines. The structure-activity relationship (SAR) studies revealed that compounds with thiophenethyl group at C-6 with mono-substituted anilines at C-4 exhibited better CDK2 inhibitory activity compared to alkyl group (thiopentane) at C-6 and di-substituted anilines at C-4 of the scaffold. In particular, compounds having 2-chloro, 3-nitro and 4-methylthio aniline groups at C-4 displayed significant enzymatic inhibitory activity against CDK2 with single digit micromolar IC50 values. The in silico molecular docking studies suggested possible binding orientation and the binding energies were in agreement with the observed SAR as well as experimental results. In addition, some of the synthesized compounds showed anti-proliferative effects against K-562 and MCF-7 cancer cell lines with IC50 values in a micromolar range. Thus, the synthesized compounds could be considered as new anticancer hits for further lead optimization.