New pyrazolo[3,4-d]pyrimidines endowed with A431 antiproliferative activity and inhibitory properties of Src phosphorylation

Investigations of Antioxidant and Anti-Cancer Activities of 5-Aminopyrazole Derivatives

To further extend the structure-activity relationships (SARs) of 5-aminopyrazoles (5APs) and identify novel compounds able to interfere with inflammation, oxidative stress, and tumorigenesis, 5APs 1-4 have been designed and prepared. Some chemical modifications have been inserted on cathecol function or in aminopyrazole central core; in detail: (i) smaller, bigger, and more lipophilic substituents were introduced in meta and para positions of catechol portion (5APs 1); (ii) a methyl group was inserted on C3 of the pyrazole scaffold (5APs 2); (iii) a more flexible alkyl chain was inserted on N1 position (5APs 3); (iv) the acylhydrazonic linker was moved from position 4 to position 3 of the pyrazole scaffold (5APs 4). All new derivatives 1-4 have been tested for radical scavenging (DPPH assay), anti-aggregating/antioxidant (in human platelets) and cell growth inhibitory activity (MTT assay) properties. In addition, in silico pharmacokinetics, drug-likeness properties, and toxicity have been calculated. 5APs 1 emerged to be promising anti-proliferative agents, able to suppress the growth of specific cancer cell lines. Furthermore, derivatives 3 remarkably inhibited ROS production in platelets and 5APs 4 showed interesting in vitro radical scavenging properties. Overall, the collected results further confirm the pharmaceutical potentials of this class of compounds and support future studies for the development of novel anti-proliferative and antioxidant agents.

Insights into the medicinal chemistry of heterocycles integrated with a pyrazolo[1,5-a]pyrimidine scaffold

Pyrazolo[1,5-a]pyrimidines are the dominant motif of many drugs; for instance, zaleplon and indiplon are sedative agents and ocinaplon was identified as an anxiolytic agent. The importance of this class of compounds lies in its varied and significant biological activities, and accordingly, considerable methods have been devised to prepare these compounds. Hence, other derivatives of this class of compounds were prepared by substitution reactions with different nucleophiles exploiting the activity of groups linked to the ring carbon and nitrogen atoms. The methods used vary through the condensation reactions of the aminopyrazoles with 1,2-allenic, enaminonitriles, enaminones, 1,3-diketones, unsaturated nitriles, or unsaturated ketones. Alternatively, these compounds are prepared through the reactions of acyclic reagents, as these methods were recently developed efficiently with high yields. The current review highlighted the recent progress of the therapeutic potential of pyrazolo[1,5-a]pyrimidines as antimicrobial, anticancer, antianxiety, anti-proliferative, analgesic, and antioxidant agents, carboxylesterase, translocator protein and PDE10A inhibitors, and selective kinase inhibitors.

Pyrazole Scaffolds: Centrality in Anti-Inflammatory and Antiviral Drug Design

BACKGROUND

Pyrazole is a component of a diversity of bioactive heterocyclic congeners with a broad-spectrum range of biological and pharmacological uses. Designing novel pyrazole and its analogues, revealing new routes for synthesizing this nucleus, exploring various potencies of that heterocycles, and looking for possible applications of pyrazoles are all becoming more important due to their numerous potential applications.

OBJECTIVES

Pyrazole scaffolds have been proven to be successful as anti-viral and anti-inflammatory therapeutic against multiple targets like HSV-1, NNRTI, H1N1, CoX-1, and CoX-2. Due to this miscellany in the biotic area, this moiety has engrossed the consideration of many scientists to study chemistry and pharmacological profile.

RESULTS

The review encompasses pyrazole having various scaffolds with multiple biological activities and attempts have also been made to correlate their structure-activity relationship. Multiple pyrazole correspondents have been synthesized as lead molecules and performed valuation for their actions.

CONCLUSION

The incorporation of pyrazole with other pharmacophores in the molecule might lead to novel potent therapeutic agents that will further help in designing potent lead molecules.

A Molecular Insight into Pyrazole Congeners as Antimicrobial, Anticancer, and Antimalarial Agents

BACKGROUND

Pyrazole is a bioactive heterocyclic congener found in a wide range of biological and pharmacological applications. Due to their multiple prospective uses, developing innovative pyrazoles and analogues, disclosing revolutionary ways for synthesizing this nucleus, investigating diverse potencies of that heterocycle, and seeking for possible applications of pyrazoles are all growing more significant Objectives: Pyrazole scaffolds have been proven to be successful as antimicrobial, anticancer, antimalarial therapeutic against multiple targets like DNA gyrase, topoisomerase IV, Hsp90, and several kinase enzymes. Its moiety has absorbed the attention of many scientists to research chemical and pharmacological profile due to this miscellany in the biotic region.

RESULTS

The review covers pyrazole scaffolds with a variety of biological functions, as well as attempts to connect the structure-activity relationship. Multiple pyrazole analogues have been produced as lead compounds, and their activities have been evaluated.

CONCLUSION

The combination of pyrazole with other pharmacophores in a molecule might lead to novel potent therapeutic medicines, which could aid in the development of potent lead compounds.

Cyclic Peptides as Protein Kinase Inhibitors: Structure-Activity Relationship and Molecular Modeling

Under-expression or overexpression of protein kinases has been shown to be associated with unregulated cell signal transduction in cancer cells. Therefore, there is major interest in designing protein kinase inhibitors as anticancer agents. We have previously reported [WR]₅, a peptide containing alternative arginine (R) and tryptophan (W) residues as a non-competitive c-Src tyrosine kinase inhibitor. A number of larger cyclic peptides containing alternative hydrophobic and positively charged residues [WR]_x (x = 6-9) and hybrid cyclic-linear peptides, [R₆K]W₆ and [R₅K]W₇, containing R and W residues were evaluated for their protein kinase inhibitory potency. Among all the peptides, cyclic peptide [WR]₉ was found to be the most potent tyrosine kinase inhibitor. [WR]₉ showed higher inhibitory activity (IC₅₀ = 0.21 μM) than [WR]₅, [WR]₆, [WR]₇, and [WR]₈ with IC₅₀ values of 0.81, 0.57, 0.35, and 0.33 μM, respectively, against c-Src kinase as determined by a radioactive assay using [γ-³³P]ATP. Consistent with the result above, [WR]₉ inhibited other protein kinases such as Abl kinase activity with an IC₅₀ value of 0.35 μM, showing 2.2-fold higher inhibition than [WR]₅ (IC₅₀ = 0.79 μM). [WR]₉ also inhibited PKCa kinase activity with an IC₅₀ value of 2.86 μM, approximately threefold higher inhibition than [WR]₅ (IC₅₀ = 8.52 μM). A similar pattern was observed against Braf, c-Src, Cdk2/cyclin A1, and Lck. [WR]₉ exhibited IC₅₀ values of <0.25 μM against Akt1, Alk, and Btk. These data suggest that [WR]₉ is consistently more potent than other cyclic peptides with a smaller ring size and hybrid cyclic-linear peptides [R₆K]W₆ and [R₅K]W₇ against selected protein kinases. Thus, the presence of R and W residues in the ring, ring size, and the number of amino acids in the structure of the cyclic peptide were found to be critical in protein kinase inhibitory potency. We identified three putative binding pockets through automated blind docking of cyclic peptides [WR]_(5-9). The most populated pocket is located between the SH2, SH3, and N-lobe domains on the opposite side of the ATP binding site. The second putative pocket is formed by the same domains and located on the ATP binding site side of the protein. Finally, a third pocket was identified between the SH2 and SH3 domains. These results are consistent with the non-competitive nature of the inhibition displayed by these molecules. Molecular dynamics simulations of the protein-peptide complexes indicate that the presence of either [WR]₅ or [WR]₉ affects the plasticity of the protein and in particular the volume of the ATP binding site pocket in different ways. These results suggest that the second pocket is most likely the site where these peptides bind and offer a plausible rationale for the increased affinity of [WR]₉.

Design, Synthesis and Bioactivities of Novel 1,4-Pentadien-3-one Derivatives Containing a Substituted Pyrazolyl Moiety

In this study, in order to find novel biologically active penta-1,4-dien-3-one derivatives, a series of penta-1,4-dien-3-one compounds containing a substituted pyrazole subunit were designed and synthesized. Their structures were characterized by ¹H-NMR, ¹³C-NMR and elemental analysis. The preliminary bioassays displayed that most of the title compounds showed significant antiproliferative activity against HepG2 cell lines. Especially, compounds 7a–m, o, r, s, u, w, y and z were active against HepG2 cells with IC₅₀ values of 0.10–5.05 μM, which were superior to that of the contrast sorafenib (IC₅₀ = 16.20 μM).

Synthesis and biological evaluation of novel pyrazolic chalcone derivatives as novel hepatocellular carcinoma therapeutics

Despite having the second highest mortality associated with cancer, currently Sorafenib is the only FDA-approved chemotherapeutic agent available for liver cancer patients which can only improve survival for few months. In this study, various pyrazolic chalcone analogous compounds were synthesized and evaluated as potential chemotherapeutic agents for the treatment of hepatocellular carcinoma (HCC). Modifying the central pyrazole ring at the C(3)-position with different heteroaryl rings and substituting the C(4)-position of pyrazole with differently substituted chalcone moiety produced fouthy two variant compounds. For all these compounds, cytotoxicity was evaluated using sulforhodamine B assay and real time cell growth tracking, respectively. Based on 50% inhibitory concentration (IC₅₀) values, compounds 39, 42, 49, and 52 were shown to exhibit potent cytotoxic activity against all the cancer cell lines tested, and had better cytotoxic activities than the well-known chemotherapeutic drug 5-FU. Therefore, these compounds were chosen to be further evaluated in a panel of HCC cell lines. Flow cytometric analysis of HCC cells treated with compounds 39, 42, 49, and 52 demonstrated that these compounds caused cell cycle arrest at G2/M phase followed by the apoptotic cell death and impaired cell growth as shown by real-time cell growth surveillance. Consistent with these results, western blotting of HCC cells treated with the compounds resulted in molecular changes for cell cycle proteins, where p21 levels were increased independent of p53 and the levels of the key initiators of mitosis Cyclin B1 and CDK1 were shown to decrease upon treatment. In conclusion, chalcone derivatives 42 and 52 show potent bioactivities by modulating the expression of cell-cycle related proteins and resulting in cell-cycle arrest in the HCC cell lines tested here, indicating that the compounds can be considered as preclinical candidates.

Synthesis, DNA binding and in-vitro cytotoxicity studies on novel bis-pyrazoles

A new series of bis-pyrazoles 6a-t were synthesized from 3,5-dimethyl pyrazole using sequential approach. All these compounds were characterized by IR, ¹H NMR, ¹³C NMR and mass spectral data. The interaction of newly synthesized bis-pyrazoles with DNA was investigated through molecular docking and absorption spectroscopic technique. Among all bis-pyrazoles compounds, the 6h compound showed lower conformational energy through in silico analysis. The interaction of each molecule in this series 6a-t with the various concentrations of DNA was examined through the UV-visible spectroscopic studies. The UV-visible spectroscopy studies on the specific binding of compound 6a, 6b, 6g, 6h, 6d, 6i, 6k, 6n, 6s with DNA have exhibited spectral shifts and the results were discussed. In further the compounds 6a-t were subjected to the in-vitro cytotoxicity studies against human pancreatic adenocarcinoma, human non-small cell lung carcinoma cell lines. Among the screened compounds, N-(3-isopropoxy-1-isopropyl-4-(3,5-dimethyl-1H-pyrazol-1-yl)-1H-pyrazol-5-yl)cyclobutane carboxamide and N-(5'-Isopropoxy-2'-isopropyl-3,5-dimethyl-2'H-[1,4'] bipyrazolyl-3'-yl)-dimethane sulfonamide were found as lead molecules since they have exhibited promising activity against both the cancer cell lines used in this study, whereas the compounds 4-(trifluoromethyl)-N-(3-isopropoxy-1-isopropyl-4-(3,5-dimethyl-2H-pyrrol-2-yl)-1H-pyrazol-5-yl)benzamide and 2,6-difluoro-N-(3-isopropoxy-1-isopropyl-4-(3,5-dimethyl-2H-pyrrol-2-yl)-1H-pyrazol-5-yl) benzamide were found to be active against the pancreatic cell line only. Rest all the other compounds were found to exhibit moderate to good activity towards both the cell lines.

Synthesis of 4,5-dihydropyrazolyl-2H-indenediones by Aldol Condensation of Ninhydrin with 1H-pyrazol-5-ol

A simple and efficient procedure for the synthesis of 2-hydroxy-2-(5-hydroxy-1H-pyrazol-4-yl)-2H-indene-1,3-dione derivatives, proceeding via aldol condensation between ninhydrin and various 3-alkyl-1H-pyrazol-5-ols is described. The syntheses were carried out in ethanol at room temperature and proceeded with short reaction times to give the products with high yields.

SRC Family Kinase Inhibition in Ewing Sarcoma Cells Induces p38 MAP Kinase-Mediated Cytotoxicity and Reduces Cell Migration

Ewing sarcoma (ES) is a highly aggressive bone and soft tissue cancer, representing the second most common primary malignant bone tumor in children and adolescents. Although the development of a multimodal therapy, including both local control (surgery and/or radiation) and systemic multidrug chemotherapy, has determined a significant improvement in survival, patients with metastatic and recurrent disease still face a poor prognosis. Moreover, considering that ES primarily affects young patients, there are concerns about long-term adverse effects of the therapy. Therefore, more rational strategies, targeting specific molecular alterations underlying ES, are required. Recent studies suggest that SRC family kinases (SFKs), which are aberrantly activated in most cancer types, could represent key therapeutic targets also for ES. Here, we challenged ES cell lines with a recently developed selective SFK inhibitor (a pyrazolo[3,4-d]pyrimidine derivative, called SI221), which was previously shown to be a valuable proapoptotic agent in other tumor types while not affecting normal cells. We observed that SI221 significantly reduced ES cell viability and proved to be more effective than the well-known SFK inhibitor PP2. SI221 was able to induce apoptosis in ES cells and also reduced ES cell clonogenic potential. Furthermore, SI221 was also able to reduce ES cell migration. At the molecular level, our data suggest that SFK inhibition through SI221 could reduce ES cell viability at least in part by hindering an SFK-NOTCH1 receptor-p38 mitogen-activated protein kinase (MAPK) axis. Overall, our study suggests a potential application of specific SFK inhibition in ES therapy. J. Cell. Physiol. 232: 129-135, 2017. © 2016 Wiley Periodicals, Inc.

SRC family kinase (SFK) inhibition reduces rhabdomyosarcoma cell growth in vitro and in vivo and triggers p38 MAP kinase-mediated differentiation

Recent data suggest that SRC family kinases (SFKs) could represent potential therapeutic targets for rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma in children. Here, we assessed the effect of a recently developed selective SFK inhibitor (a pyrazolo[3,4-d]pyrimidine derivative, called SI221) on RMS cell lines. SI221, which showed to be mainly effective against the SFK member YES, significantly reduced cell viability and induced apoptosis, without affecting non-tumor cells, such as primary human skin fibroblasts and differentiated C2C12 cells. Moreover, SI221 decreased in vitro cell migration and invasion and reduced tumor growth in a RMS xenograft model. SFK inhibition also induced muscle differentiation in RMS cells by affecting the NOTCH3 receptor-p38 mitogen-activated protein kinase (MAPK) axis, which regulates the balance between proliferation and differentiation. Overall, our findings suggest that SFK inhibition, besides reducing RMS cell growth and invasive potential, could also represent a differentiation therapeutic strategy for RMS.

SRC family kinase inhibition through a new pyrazolo[3,4-d]pyrimidine derivative as a feasible approach for glioblastoma treatment

Glioblastoma (GB) is the most common and aggressive primary tumor of the central nervous system. The current standard of care for GB consists of surgical resection, followed by radiotherapy combined with temozolomide chemotherapy. However, despite this intensive treatment, the prognosis remains extremely poor. Therefore, more effective therapies are urgently required. Recent studies indicate that SRC family kinases (SFKs) could represent promising molecular targets for GB therapy. Here, we challenged four GB cell lines with a new selective pyrazolo[3,4-d]pyrimidine derivative SFK inhibitor, called SI221. This compound exerted a significant cytotoxic effect on GB cells, without significantly affecting non-tumor cells (primary human skin fibroblasts), as evaluated by MTS assay. We also observed that SI221 was more effective than the well-known SFK inhibitor PP2 in GB cells. Notably, despite the high intrinsic resistance to apoptosis of GB cells, SI221 was able to induce this cell death process in all the GB cell lines, as observed through cytofluorimetric analysis and caspase-3 assay. SI221 also exerted a long-term inhibition of GB cell growth and was able to reduce GB cell migration, as shown by clonogenic assay and scratch test, respectively. Moreover, through in vitro pharmacokinetic assays, SI221 proved to have a high metabolic stability and a good potential to cross the blood brain barrier, which is an essential requirement for a drug intended to treat brain tumors. Therefore, despite the need of developing strategies to improve SI221 solubility, our results suggest a potential application of this selective SFK inhibitor in GB therapy.

Cyclic peptides containing tryptophan and arginine as Src kinase inhibitors

A number of cyclic and linear peptides containing various combinations of amino acids were evaluated for their Src kinase inhibitory potency. Among all the peptides, cyclic decapeptide C[RW]5 containing alternative arginine (R) and tryptophan (W) residues was found to be the most potent Src kinase inhibitor. C[RW]5 showed higher inhibitory activity (IC50=2.8 μM) than C[KW]5, L(KW)5, C[RW]4, and C[RW]3 with IC50 values of 46.9, 69.1, 21.5, and 25.0 μM, respectively, as determined in a fluorescence intensity-based assay. Thus, the cyclic nature, the presence of arginine, ring size, and the number of amino acids in the structure of the peptide were found to be critical in Src kinase inhibitory potency. The IC50 value of C[RW]5 was found to be 0.8 μM in a radioactive assay using [γ-(32)P]-ATP and polyE4Y as the substrate. C[RW]5 was a noncompetitive Src kinase inhibitor, showing approximately fourfold more selectivity towards Src than Abl.

Synthesis of pyrazolo[1,5-a]pyrimidine linked aminobenzothiazole conjugates as potential anticancer agents

A series of pyrazolo[1,5-a]pyrimidine linked 2-aminobenzothizole conjugates (6a-t) were synthesized and evaluated for their anticancer activity against five human cancer cell lines. Among them two compounds 6p and 6m showed significant anticancer activity with IC50 values ranging from 2.01 to 7.07 and 1.94-3.46 μM, respectively. Moreover, cell cycle arrest in G2/M and reduction in Cdk1 expression level were observed upon treatment of these compounds and they also induced caspase-3 dependent apoptosis. This was further confirmed by staining as well as DNA fragmentation analysis.

4-Aryl-4H-naphthopyrans derivatives: one-pot synthesis, evaluation of Src kinase inhibitory and anti-proliferative activities

Background

A series of 2-amino-4-aryl-4H-benzo[h or f]chromene-3-carbonitrile derivatives were synthesized and evaluated for inhibition of Src kinase and cell proliferation in breast carcinoma (BT-20) cell lines.

Methods

The one-pot, three-component reaction of α or β-naphthol, malonitrile and an aromatic aldehyde in the presence of diammonium hydrogen phosphate was afforded the corresponding 2-amino-4-aryl-4H-benzo[h or f]chromene-3-carbonitrile derivatives, All target compounds were evaluated for inhibition of Src kinase and cell proliferation in breast carcinoma (BT-20) cell lines.

Results

Among all tested compounds, unsubstituted 4-phenyl analog 4a showed Src kinas inhibitory effect with IC₅₀ value of 28.1 μM and was the most potent compound in this series. In general, the compounds were moderately active against BT-20. 3-Nitro-phenyl 4e and 3-pyridinyl 4h derivatives inhibited the cell proliferation of BT-20 cells by 33% and 31.5%, respectively, and found to be more potent compared to doxorubicin (25% inhibition of cell growth).

Conclusion

The data indicate that 4-aryl-4H-naphthopyrans scaffold has the potential to be optimized further for designing more potent Src kinase inhibitors and/or anticancer lead compounds.

Synthesis and anticancer activity of heteroaromatic linked 4β-amido podophyllotoxins as apoptotic inducing agents

A series of different heteroaromatic linked 4β-amidopodophyllotoxin conjugates (16a-i, 17a-i and 18a-d) were synthesized and evaluated for anticancer activity against five human cancer cell lines. Among the series, one of the compound 17g showed significant antiproliferative activity in A549 (lung cancer) cell line. Flow cytometric analysis showed that 17g arrested the cell cycle in the G2/M phase leading to caspase-3 dependent apoptotic cell death. Further, Hoechst 33258 staining and DNA fragmentation assay also suggests that 17g induces cell death by apoptosis.

Anthranilamide-pyrazolo[1,5-a]pyrimidine conjugates as p53 activators in cervical cancer cells

A library of new anthranilamide-pyrazolo[1,5-a]pyrimidine conjugates were designed, synthesized, and evaluated for their anticancer activity in cervical cancer cells such as HeLa and SiHa that possess low levels of p53. All 24 conjugates showed antiproliferative activity, while some of them exhibit significant cytotoxicity. In assays related to cell-cycle distribution, these conjugates induced G(2) /M arrest in HeLa cells and G(1) cell-cycle arrest in SiHa cells. Immunocytochemistry assays revealed that these compounds cause nuclear translocation of p53, thereby indicating the activation of p53. In cervical cancer cells, the p53 protein is degraded by E6 oncoprotein. Immunoblot and RT-PCR analyses proved the presence of mitochondria-mediated apoptosis with involvement p53 target genes such as BAX, Bcl2, and p21 (CDKI). Moreover, these compounds increased the phosphorylated forms of p53 and provide signals for apoptosis induction. Interestingly, one of the conjugates, (2-phenyl-7-(3,4,5-trimethoxyphenyl)pyrazolo[1,5-a]pyrimidin-5-yl)(4-(2-(thiophen-2-ylmethylamino)benzoyl)piperazin-1-yl)methanone, is the most promising candidate in this series and has the potential to be taken up for further detailed studies.

18F-labeled pyrazolo[1,5-a]pyrimidine derivatives: synthesis from 2,4-dinitrobenzamide and tosylate precursors and comparative biological evaluation for tumor imaging with positron emission tomography

We previously reported ¹⁸F-labeled pyrazolo[1,5-a]pyrimidine derivatives: 7-(2-[¹⁸F]fluoroethylamino)-5-methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile ([¹⁸F]1) and N-(2-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7-ylamino)ethyl)-2-[¹⁸F]fluoro-4-nitro- benzamide ([¹⁸F]2). Preliminary biodistribution experiments of both compounds showed s slow clearance rate from excretory tissues which warranted further investigation for tumor imaging with PET. Here we modified [¹⁸F]1 and [¹⁸F]2 by introducing polar groups such as ester, hydroxyl and carboxyl and developed three additional ¹⁸F-18 labeled pyrazolo[1,5-a] pyrimidine derivatives: (3-Cyano-7-(2-[¹⁸F]fluoroethylamino)pyrazolo[1,5-a]-pyrimidin-5- yl)methyl acetate ([¹⁸F]3), 7-(2-[¹⁸F]fluoroethylamino)-5-(hydroxymethyl)pyrazolo[1,5-a]- pyrimidine-3-carbonitrile ([¹⁸F]4) and (S)-6-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7- ylamino)-2-(2-[¹⁸F]fluoro-4-nitrobenzamido)hexanoic acid ([¹⁸F]5). The radiolabeled probes were synthesized by nucleophilic substitution of the corresponding tosylate and nitro precursors with ¹⁸F-fluoride. In Vitro studies showed higher uptake of [¹⁸F]3 and [¹⁸F]4 than that of [¹⁸F]5 by S180 tumor cells. In Vivo biodistribution studies in mice bearing S180 tumors showed that the uptake of both [¹⁸F]3 and [¹⁸F]4 in tumors displayed an increasing trend while the uptake of [¹⁸F]5 in tumor decreased through the course of the 120 min study. This significant difference in tumor uptake was also found between [¹⁸F]1 and [¹⁸F]2. Thus, we compared the biological behavior of the five tracers and reported the tumor uptake kinetic differences between 2-[¹⁸F]fluoroethylamino- and 2-[¹⁸F]fluoro-4-nitro- benzamidopyrazolo[1,5-a] pyrimidine derivatives.

Discovery of Novel Small Molecule Mer Kinase Inhibitors for the Treatment of Pediatric Acute Lymphoblastic Leukemia

Ectopic Mer expression promotes pro-survival signaling and contributes to leukemogenesis and chemoresistance in childhood acute lymphoblastic leukemia (ALL). Consequently, Mer kinase inhibitors may promote leukemic cell death and further act as chemosensitizers increasing efficacy and reducing toxicities of current ALL regimens. We have applied a structure-based design approach to discover novel small molecule Mer kinase inhibitors. Several pyrazolopyrimidine derivatives effectively inhibit Mer kinase activity at sub-nanomolar concentrations. Furthermore, the lead compound shows a promising selectivity profile against a panel of 72 kinases and has excellent pharmacokinetic properties. We also describe the crystal structure of the complex between the lead compound and Mer, opening new opportunities for further optimization and new template design.

New pyrazolo[3,4-d]pyrimidine SRC inhibitors induce apoptosis in mesothelioma cell lines through p27 nuclear stabilization

Malignant mesothelioma (MM) is a highly aggressive tumor of the serous membranes for which there is currently no effective curative modality. Recent data suggest that hyperactivation of the tyrosine kinase SRC has a key role in MM development and therefore this kinase represents an important molecular target for MM therapy. We tested new pyrazolo[3,4-d]pyrimidine SRC inhibitors on a panel of MM cell lines expressing the active form of SRC. These SRC inhibitors exerted a significant proapoptotic effect on MM cells without affecting the normal mesothelial cell line MET-5A, supporting a possible use of these SRC inhibitors for a safe treatment of MM. We also showed that SRC inhibitor-induced apoptosis occurred concomitantly with an increase in the nuclear stability of the cyclin-dependent kinase inhibitor p27. This finding is remarkable considering that loss of nuclear p27 expression is a well-established adverse prognostic factor in MM, and p27 nuclear localization is crucial for its tumor-suppressive function. Consistently, SRC inhibition seems to promote the increase in p27 nuclear level also by inactivating the AKT kinase and downregulating cyclin D1, which would otherwise delay p27 nuclear import and provoke its cytoplasmic accumulation. To determine whether p27 stabilization has a direct role in apoptosis induced by SRC inhibition, we stably silenced the CDKN1B gene, encoding p27, in MSTO-211H and REN mesothelioma cells by transduction with lentiviral vectors expressing short hairpin RNAs against the CDKN1B transcript. Strikingly, p27 silencing was able to suppress the apoptosis induced by these SRC inhibitors in both MM cell lines, suggesting that p27 has a crucial proapoptotic role in MM cells treated with SRC inhibitors. Our findings reveal a new mechanism, dependent on p27 nuclear stabilization, by which SRC inhibition can induce apoptosis in MM cells and provide a new rationale for the use of SRC inhibitors in MM therapy.