Synthesis and evaluation of novel pyrimidine-based dual EGFR/Her-2 inhibitors

A structure-activity relationship study of 4-anilinopyrimidines for dual EGFR/Her-2 inhibitor has resulted in the identification of 4-anilino-5-alkenyl or 5-alkynyl-6-methylpyrimidine derivatives that have exhibited effective inhibitory activity against both enzymes. The presence of 5-alkenyl or 5-alkynyl moiety bearing terminal hydrophilic group played important role for inhibition of these enzymes. Selected compounds in the series demonstrated some activity against Her-2 dependent cell line (BT474).     

Imaging Axl expression in pancreatic and prostate cancer xenografts

The receptor tyrosine kinase Axl is overexpressed in and leads to patient morbidity and mortality in a variety of cancers. Axl–Gas6 interactions are critical for tumor growth, angiogenesis and metastasis. The goal of this study was to investigate the feasibility of imaging graded levels of Axl expression in tumors using a radiolabeled antibody. We radiolabeled anti-human Axl (Axl mAb) and control IgG1 antibodies with ¹²⁵I with high specific radioactivity and radiochemical purity, resulting in an immunoreactive fraction suitable for in vivo studies. Radiolabeled antibodies were investigated in severe combined immunodeficient mice harboring subcutaneous CFPAC (Axl^high) and Panc1 (Axl^low) pancreatic cancer xenografts by ex vivo biodistribution and imaging. Based on these results, the specificity of [¹²⁵I]Axl mAb was also validated in mice harboring orthotopic Panc1 or CFPAC tumors and in mice harboring subcutaneous 22Rv1 (Axl^low) or DU145 (Axl^high) prostate tumors by ex vivo biodistribution and imaging studies at 72 h post-injection of the antibody. Both imaging and biodistribution studies demonstrated specific and persistent accumulation of [¹²⁵I]Axl mAb in Axl^high (CFPAC and DU145) expression tumors compared to the Axl^low (Panc1 and 22Rv1) expression tumors. Axl expression in these tumors was further confirmed by immunohistochemical studies. No difference in the uptake of radioactivity was observed between the control [¹²⁵I]IgG1 antibody in the Axl^high and Axl^low expression tumors. These data demonstrate the feasibility of imaging Axl expression in pancreatic and prostate tumor xenografts.     

Molecular modelling studies on d-annulated benzazepinones as VEGF-R2 kinase inhibitors using docking and 3D-QSAR

Chemotypes comprising the d-annulated 1,3-dihydro-2H-1-benzazepin-2-one scaffold derived from the paullone structure were found to be potent vascular endothelial growth factor receptor 2 (VEGF-R2) kinase inhibitors. Three-dimensional quantitative structure-activity relationship (3D-QSAR) and docking studies were performed on a series of d-annulated benzazepinones with VEGF-R2 kinase inhibition activities. The comparative molecular field analysis and comparative molecular similarity indices analysis models using 32 molecules in the training set gave r²_cv values of 0.811 and 0.769, r² values of 0.962 and 0.953, respectively. 3D contour maps generated from the two models revealed that the electron-withdrawing groups at R₁ and the bulky, electron-withdrawing as well as hydrogen bond donor groups at R₂ position are favourable; the bulky, hydrogen bond acceptor substituent at R₃ and the minor groups at R₄ position may benefit the potency. We have designed a series of novel VEGF-R2 inhibitors by utilizing the SAR results revealed in the present study, which were predicted with excellent potencies in the developed models. The results may aid in designing of potential VEGF-R2 inhibitors with better activities.     

受体酪氨酸激酶Axl对胶质母细胞瘤细胞增殖、凋亡和侵袭的影响

摘要 目的：研究受体酪氨酸激酶Axl在胶质母细胞瘤组织和细胞系U-118MG细胞中的表达情况及其对U-118MG细胞增殖、凋亡、侵袭的影响。方法：收集2015年3月至2018年5月在本院进行手术切除并经病理分型证实的胶质母细胞瘤组织标本（n=30）,另取脑外伤手术中因作内减压而切除的正常脑组织作为对照（n=28）。采用荧光实时定量 (qRT-PCR)检测正常脑组织和胶质母细胞瘤肿瘤组织中Axl mRNA表达水平;采用Western blot检测人小神经胶质HM细胞、U-118MG细胞以及Axl-shRNA转染后U-118MG细胞中Axl蛋白表达水平;采用CCK-8检测Axl-shRNA转染后U-118MG细胞增殖能力;采用流式细胞术检测Axl-shRNA转染后U-118MG细胞凋亡水平;采用Transwell小室实验检测Axl-shRNA转染后U-118MG细胞的侵袭能力。结果：在胶质母细胞瘤组织中Axl mRNA表达水平显著高于正常脑组织（P<0.05）;U-118MG细胞Axl蛋白表达水平显著高于人小神经胶质细胞系HM细胞,差异有统计学意义（P<0.05）;转染Axl-shRNA后,U-118MG细胞中Axl蛋白表达水平显著降低（P<0.05）。与U-118MG细胞和转染control-shRNA细胞相比, 转染Axl-shRNA的U-118MG细胞增殖能力降低（P<0.05）,凋亡水平升高（P<0.05）,侵袭能力降低（P<0.05）。结论：在胶质母细胞瘤组织和U-118MG细胞中,Axl表达水平显著增高,并且Axl表达水平与U-118MG细胞增殖、凋亡及侵袭密切关联。     

Discovery of quinazolin-4-amines bearing benzimidazole fragments as dual inhibitors of c-Met and VEGFR-2

Both c-Met and VEGFR-2 are important targets for the treatment of cancers. In this study, a series of N-(2-phenyl-1H-benzo[d]imidazol-5-yl)quinazolin-4-amine derivatives were designed and identified as dual c-Met and VEGFR-2 inhibitors. Among these compounds bearing quinazoline and benzimidazole fragments, compound 7j exhibited the most potent inhibitory activity against c-Met and VEGFR-2 with IC₅₀ of 0.05 μM and 0.02 μM, respectively. It also showed the highest anticancer activity against the tested cancer cell lines with IC₅₀ of 1.5 μM against MCF-7 and 8.7 μM against Hep-G2. Docking simulation supported the initial pharmacophoric hypothesis and suggested a common mode of interaction at the ATP-binding site of c-Met and VEGFR-2, which demonstrates that compound 7j is a potential agent for cancer therapy deserving further researching.     

Discovery of novel phenoxybenzamide analogues as Raf/HDAC dual inhibitors

Histone deacetylase (HDAC) inhibitors as an important epigenetic therapeutic strategy affect signaling networks and act synergistically with kinase inhibitors for the treatment of cancer. Herein we presented a series of novel phenoxybenzamide analogues with inhibition of Raf and HDAC. Among them, compound 10e showed potent antiproliferative activities against Hepg2 and MDA-MB-468 in cellular assays. This work may lay the foundation for developing novel dual Raf/HDAC inhibitors as potential anticancer therapeutics.     

Discovery of novel cathepsin inhibitors with potent anti-metastatic effects in breast cancer cells

It is still challenging to determine the potential targets of natural products, which is essential for further drug research and development. Due to its novel mechanism of action of inducing autophagy effects in breast cancer cells, asperphenamate has received our considerable attention. However, its unknown target inevitably impedes further study. In our previous work, the target enzyme of asperphenamate was predicted as cathepsin by the natural product consensus pharmacophore strategy. Then, asperphenamate and its three derivatives were chosen to study in detail by molecular docking calculations with AutoDock 4 suite. The docking results showed the three derivatives interacted more tightly with either cathepsin L or cathepsin S than with asperphenamate. The ortho-benzyloxyl phenylacetyl derivative 1 and p-toluenesulfonyl derivative 3 showed similar interactions with cathepsin L and adopted a better geometric shape within the binding pocket than did the N-CBZ-piperidyl analog 2. On the other hand, compound 2 formed more hydrogen bonds than 1 and 3 to make it tightly bind within cathepsin S. The cathepsin inhibitory activity assay verified the molecular simulation results. Compound 2 was remarkably less active than 1 and 3 against cathepsin L. However, compound 2 showed the strongest potency against cathepsin S with IC₅₀ of 13.12 ± 0.29 μM. Considering that cathepsin S plays a vital role in the process of metastasis in breast cancer cells, the inhibitory effect of 2 on migration and invasion was further studied in human breast cancer MDA-MB-231 cells by wound healing and transwell chamber assays. The results illustrated that 2 exhibited an apparent inhibitory ability to the metastasis of MDA-MB-231 cells. Next, 2 will be chosen as a lead compound to develop novel double functional chemotherapeutic agents with both novel mechanisms of action against apoptosis-resistant cancer cells, such as inducing autophagy and inhibiting cancer metastasis.     

Discovery of indazoles as inhibitors of Tpl2 kinase

Synthesis, modeling and structure-activity relationship of indazoles as inhibitors of Tpl2 kinase are described. From a high throughput screening effort, we identified an indazole hit compound 5 that has a single digit micromolar Tpl2 activity. Through SAR modifications at the C3 and C5 positions of the indazole, we discovered compound 31 with good potency in LANCE assay and cell-based p-Erk assay.     

Discovery of potent and efficacious pyrrolopyridazines as dual JAK1/3 inhibitors

A series of potent dual JAK1/3 inhibitors have been developed from a moderately selective JAK3 inhibitor. Substitution at the C6 position of the pyrrolopyridazine core with aryl groups provided exceptional biochemical potency against JAK1 and JAK3 while maintaining good selectivity against JAK2 and Tyk2. Translation to in vivo efficacy was observed in a murine model of chronic inflammation. X-ray co-crystal structure determination confirmed the presumed inhibitor binding orientation in JAK3. Efforts to reduce hERG channel inhibition will be described.     

Discovery of thiapyran-pyrimidine derivatives as potential EGFR inhibitors

A series of novel thiapyran-pyrimidine derivatives (10a–10h, 11a–11g, 12a–12f, 13a–13f, 14a–14f) were synthesized and their antiproliferative activities were tested. Most of the target compounds showed good activity on one or more cancer cell lines but low activity on human normal cell LO2. The most promising compound 13a exhibited the similar IC₅₀ values on A549 and H1975 cell lines to the lead drug Olmutinib, and exhibited excellent activity and selectivity on EGFR^T790M/L858R in the kinase experiment. AO and Hoechst33258 staining indicated that 13a could effectively induce H1975 cells apoptosis. Cell cycle and apoptosis analysis suggested that 13a could block cancer cells in G2/M phase and induce into late apoptosis in a manner of concentration-dependent. The structure–activity relationship of 13a was analyzed to explore its mechanism. All the results showed that 13a was a promising EGFR inhibitor.     

Structure-based optimization of 1H-imidazole-2-carboxamides as Axl kinase inhibitors utilizing a Mer mutant surrogate

Axl has been a target of interest in the oncology field for several years based on its role in various oncogenic processes. To date, no wild-type Axl crystal structure has been reported. Herein, we describe the structure-based optimization of a novel chemotype of Axl inhibitors, 1H-imidazole-2-carboxamide, using a mutated kinase homolog, Mer(I650M), as a crystallographic surrogate. Iterative optimization of the initial lead compound (1) led to compound (21), a selective and potent inhibitor of wild-type Axl. Compound (21) will serve as a useful compound for further in vivo studies.     

Discovery of novel thienoquinoline-2-carboxamide chalcone derivatives as antiproliferative EGFR tyrosine kinase inhibitors

Novel thienoquinoline carboxamide-chalcone derivatives were prepared via the cyclization of acylated chalcones and 2-mercaptoquinoline-3-carbaldehyde in DMF with K₂CO₃. Thienoquinolines 9a–f, h exhibited promising antiproliferative effect against all the tested cell lines and gave a significant activity as EGFR inhibitors, with IC₅₀ values ranging from 0.5 and 3.2?µM, and compounds 9e and 9f being the most active of the series. They also showed better activity than Erlotinib against melanoma cancer cell line A375. Moreover, compound 9f influenced pre G1 apoptosis and cell cycle arrest at G2/M phase. The binding mode of the best EGFR inhibitor 9e in the EGFR active site revealed that the thienoquinoline ring occupied the ATP-binding site while the chalcone moiety is located in the allosteric site and is responsible for the enhanced activity of these compounds.     

Axl is essential for VEGF-A-dependent activation of PI3K/Akt

Herein, we report that vascular endothelial growth factor A (VEGF-A) engages the PI3K/Akt pathway by a previously unknown mechanism that involves three tyrosine kinases. Upon VEGF-A-dependent activation of VEGF receptor-2 (VEGFR-2), and subsequent TSAd-mediated activation of Src family kinases (SFKs), SFKs engage the receptor tyrosine kinase Axl via its juxtamembrane domain to trigger ligand-independent autophosphorylation at a pair of YXXM motifs that promotes association with PI3K and activation of Akt. Other VEGF-A-mediated signalling pathways are independent of Axl. Interfering with Axl expression or function impairs VEGF-A- but not bFGF-dependent migration of endothelial cells. Similarly, Axl null mice respond poorly to VEGF-A-induced vascular permeability or angiogenesis, whereas other agonists induce a normal response. These results elucidate the mechanism by which VEGF-A activates PI3K/Akt, and identify previously unappreciated potential therapeutic targets of VEGF-A-driven processes.     

Discovery of quinolinone derivatives as potent FLT3 inhibitors

Recently some fms-like tyrosine kinase 3 (FLT3) inhibitors have shown good efficacy in acute myeloid leukemia (AML) patients. In an effort to develop anti-leukemic drugs, we investigated quinolinone derivatives as novel FLT3 inhibitors. Two substituted quinolinones, KR65367 and KR65370 were subjected to FLT3 kinase activity assay and showed potent inhibition against FLT3 kinase activity in vitro, with IC₅₀ of 2.7 and 0.57 nM, respectively. As a measure of selectivity, effects on the activity of other kinases were also tested. Both compounds have negligible activity against Met, Ron, epidermal growth factor receptor, Aurora A, Janus kinase 2, and insulin receptor; with IC₅₀ greater than 10 μM. KR compounds showed strong growth inhibition in MV4;11 AML cells and increased the apoptotic cell death in flow cytometric analyses. A decrease in STAT5 phosphorylation by KR compounds was observed in MV4;11 cells. Furthermore, in vitro evaluation of compounds structurally related to KR65367 and KR65370 showed a good structure-activity relationship.     

A systematic analysis of the resistance and sensitivity of HER2YVMA receptor tyrosine kinase mutant to tyrosine kinase inhibitors in HER2-positive lung cancer

Human epidermal growth factor receptor 2 (HER2) has become a well-established target for the treatment of HER2-positive lung cancer. However, a frequently observed in-frame mutation that inserts amino acid quadruplex Tyr776-Val777-Met778-Ala779 at G776 (G776^YVMA) in HER2 kinase domain can cause drug resistance and sensitivity, largely limiting the application of reversible tyrosine kinase inhibitors in lung cancer therapy. A systematic investigation of the intermolecular interactions between the HER2^YVMA mutant and clinical small-molecule inhibitors would help to establish a complete picture of drug response to HER2 G776^YVMA insertion in lung cancer, and to design new tyrosine kinase inhibitors with high potency and selectivity to target the lung cancer-related HER2^YVMA mutant. Here, we combined homology modeling, ligand grafting, structure minimization, molecular simulation and binding affinity analysis to profile a number of tyrosine kinase inhibitors against the G776^YVMA insertion in HER2. It is found that the insertion is far away from HER2 active pocket and thus cannot contact inhibitor ligand directly. However, the insertion is expected to induce marked allosteric effect on some regions around the pocket, including A-loop and hinges connecting between the N- and C-lobes of HER2 kinase domain, which may exert indirect influence to inhibitor binding. Most investigated inhibitors exhibit weak binding strength to both wild-type and mutant HER2, which can be attributed to steric hindrance that impairs ligand compatibility with HER2 active pocket. However, the cognate inhibitor lapatinib and the non-cognate inhibitor bosutinib were predicted to have low affinity for wild-type HER2 but high affinity for HER2^YVMA mutant, which was confirmed by subsequent kinase assay experiments; the inhibitory potencies of bosutinib against wild-type and mutant HER2 were determined to be IC₅₀?>?1000 and =27?nM, respectively, suggesting that the bosutinib might be exploited as a selective inhibitor for mutant over wild-type HER2. Structural examination revealed that formation of additional non-bonded interactions such as hydrogen bonds and hydrophobic contacts with HER2 A-loop region due to G776^YVMA insertion is the primary factor to improve bosutinib affinity upon the mutation.     

Discovery of (7-aryl-1,5-naphthyridin-2-yl)ureas as dual inhibitors of ERK2 and Aurora B kinases with antiproliferative activity against cancer cells

A novel series of (7-aryl-1,5-naphthyridin-2-yl)ureas was discovered as dual ERK2 and Aurora B kinases inhibitors. Several analogues were active at micromolar and submicromolar range against ERK2 and Aurora B, associated with very promising antiproliferative activity toward various cancer cell lines. Synthesis, structure activity relationship and docking study are reported. In vitro ADME properties and safety data are also discussed.     

In brain, Axl recruits Grb2 and the p85 regulatory subunit of PI3 kinase; in vitro mutagenesis defines the requisite binding sites for downstream Akt activation

Axl is a receptor tyrosine kinase implicated in cell survival following growth factor withdrawal and other stressors. The binding of Axl's ligand, growth arrest-specific protein 6 (Gas6), results in Axl autophosphorylation, recruitment of signaling molecules, and activation of downstream survival pathways. Pull-down assays and immunoprecipitations using wildtype and mutant Axl transfected cells determined that Axl directly binds growth factor receptor-bound protein 2 (Grb2) at pYVN and the p85 subunit of phosphatidylinositol-3 kinase (PI3 kinase) at two pYXXM sites (pY779 and pY821). Also, p85 can indirectly bind to Axl via an interaction between p85's second proline-rich region and the N-terminal SH3 domain of Grb2. Further, Grb2 and p85 can compete for binding at the pY821VNM site. Gas6-stimulation of Axl-transfected COS7 cells recruited activated PI3 kinase and phosphorylated Akt. An interaction between Axl, p85 and Grb2 was confirmed in brain homogenates, enriched populations of O4+ oligodendrocytes, and O4− flow-through prepared from day 10 mouse brain, indicating that cells with active Gas6/Axl signal through Grb2 and the PI3 kinase/Akt pathways.     

Discovery of alkoxyl biphenyl derivatives bearing dibenzo[c,e]azepine scaffold as potential dual inhibitors of P-glycoprotein and breast cancer resistance protein

We recently reported alkoxyl biphenyl derivatives bearing dibenzo[c,e]azepine scaffold as novel P-glycoprotein (P-gp, ABCB1) inhibitors. In this study, their ability to reverse breast cancer resistance protein (BCRP, ABCG2)-mediated multidrug resistance was tested in HEK293/BCRP cells which was BCRP-transfected stable HEK293 cells. It was observed that compounds 4d, 4h, 4i increased mitoxantrone accumulation in HEK293/BCRP cells via inhibiting BCRP efflux function. Notably, the inhibitory activity of 4i was comparable to that of the classical BCRP inhibitor Ko143 at an equimolar concentration. Interestingly, 4i had little inhibitory effect on multidrug resistance-associated protein 1 (MRP1, ABCC1), another drug efflux transporter. These results, together with the previous findings, suggest that 4i may be a dual inhibitor of P-gp and BCRP to warrant further investigation.     

Discovery of N-substituted-3-phenyl-1,6-naphthyridinone derivatives bearing quinoline moiety as selective type II c-Met kinase inhibitors against VEGFR-2

New N-substituted-3-phenyl-1,6-naphthyridinone derivatives are designed and synthesized, based on structural modification of our previously reported compound 3. Extensive enzyme-based SAR studies and PK evaluation led to the discovery of compound 4r, with comparable c-Met potency to that of Cabozantinib and high VEGFR-2 selectivity, while Cabozantinib displayed no VEGFR-2 selectivity. More importantly, at oral doses of 45 mg/kg (Q.D.), compound 4r exhibits significant tumor growth inhibition (93%) in a U-87MG human gliobastoma xenograft model. The promising selectivity against VEGFR-2 and excellent tumor growth inhibition of compound 4r suggest that it could be used as a new lead molecule for further discovery of selective type II c-Met inhibitors.