Discovery of novel serine palmitoyltransferase inhibitors as cancer therapeutic agents.

We pursued serine palmitoyltransferase (SPT) inhibitors as novel cancer therapeutic agents based on a correlation between SPT inhibition and growth suppression of cancer cells. High-throughput screening and medicinal chemistry efforts led to the identification of structurally diverse SPT inhibitors 4 and 5. Both compounds potently inhibited SPT enzyme and decreased intracellular ceramide content. In addition, they suppressed cell growth of human lung adenocarcinoma HCC4006 and acute promyelocytic leukemia PL-21, and displayed good pharmacokinetic profiles. Reduction of 3-ketodihydrosphingosine, the direct downstream product of SPT, was confirmed under in vivo settings after oral administration of compounds 4 and 5. Their anti-tumor efficacy was observed in a PL-21 xenograft mouse model. These results suggested that SPT inhibitors might have potential to be effective cancer therapeutics.

A novel PET probe to selectively image heat shock protein 90α/ß isoforms in the brain.

BACKGROUND: Heat shock proteins (HSPs) are present throughout the brain. They function as molecular chaperones, meaning they help with the folding and unfolding of large protein complexes. These chaperones are vital in the development of neuropathological conditions such as Alzheimer's disease and Lewy body disease, with HSP90, a specific subtype of HSP, playing a key role. Many studies have shown that drugs that inhibit HSP90 activity have beneficial effects in the neurodegenerative diseases. Therefore, HSP90 PET imaging ligand can be used effectively to study HSP90 in neurodegenerative diseases. Among four HSP90 isoforms, two cytosolic isoforms (HSP90α and HSP90ß) thought to be involved in the structural homeostasis of the proteins related to the neurodegenerative diseases. Currently, no useful PET imaging ligands selectively targeting the two cytosolic isoforms of HSP90 have been available yet. RESULTS: In this study, we developed a novel positron emission tomography (PET) imaging ligand, [11C]BIIB021, by 11C-radiolabeling (a positron emitter with a half-life of 20.4 min) 6-Chloro-9-[(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]-9H-purin-2-amine (BIIB021), an inhibitor with a high affinity for and selectivity to HSP90α and HSP90ß. [11C]BIIB021 was synthesized with a high yield, molar activity and radiochemical purity. [11C]BIIB021 showed a high binding affinity for rat brain homogenate as well as human recombinant HSP90α and HSP90ß proteins. Radioactivity was well detected in the rat brain (SUV 1.4). It showed clear specific binding in PET imaging of healthy rats and autoradiography of healthy rat and human brain sections. Radiometabolite was detected in the brain, however, total distribution volume was well quantified using dual-input graphical model. Inhibition of p-glycoprotein increased brain radioactivity concentrations. However, total distribution volume values with and without p-glycoprotein inhibition were nearly the same. CONCLUSIONS: We have developed a new PET imaging agent, [11C]BIIB021, specifically targeting HSP90α/ß. We have been successful in synthesizing [11C]BIIB021 and in vitro and in vivo imaging HSP90α/ß. However, the quantification of HSP90α/ß is complicated by the presence of radiometabolites in the brain and the potential to be a substrate for p-glycoprotein. Further efforts are needed to develop radioligand suitable for imaging of HSP90α/ß.

Anti-angiogenic and anti-tumor effects of TAK-593, a potent and selective inhibitor of vascular endothelial growth factor and platelet-derived growth factor receptor tyrosine kinase.

We recently reported that TAK-593, a novel imidazo[1,2-b]pyridazine derivative, is a highly potent and selective inhibitor of the vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) receptor tyrosine kinase families. Moreover, TAK-593 exhibits a uniquely long-acting inhibitory profile towards VEGF receptor 2 (VEGFR2) and PDGF receptor ß (PDGFRß). In this study, we demonstrated that TAK-593 potently inhibits VEGF- and PDGF-stimulated cellular phosphorylation and proliferation of human umbilical vein endothelial cells and human coronary artery smooth muscle cells. TAK-593 also potently inhibits VEGF-induced tube formation of endothelial cells co-cultured with fibroblasts. Oral administration of TAK-593 exhibited strong anti-tumor effects against various human cancer xenografts along with good tolerability despite a low level of plasma exposure. Even after the blood and tissue concentrations of TAK-593 decreased below the detectable limit, a pharmacodynamic marker (phospho VEGFR2) was almost completely suppressed, indicating that its long duration of enzyme inhibition might contribute to the potent activity of TAK-593. Immunohistochemical staining indicated that TAK-593 showed anti-proliferative and pro-apoptotic effects on tumors along with a decrease of vessel density and inhibition of pericyte recruitment to microvessels in vivo. Furthermore, dynamic contrast-enhanced magnetic resonance imaging revealed that TAK-593 reduced tumor vessel permeability prior to the onset of anti-tumor activity. In conclusion, TAK-593 is an extremely potent VEGFR/PDGFR kinase inhibitor whose potent anti-angiogenic activity suggests therapeutic potential for the treatment of solid tumors.

Design, synthesis, and evaluation of novel VEGFR2 kinase inhibitors: discovery of [1,2,4]triazolo[1,5-a]pyridine derivatives with slow dissociation kinetics.

For the purpose of discovering novel type-II inhibitors of vascular endothelial growth factor receptor 2 (VEGFR2) kinase, we designed and synthesized 5,6-fused heterocyclic compounds bearing a anilide group. A co-crystal structure analysis of imidazo[1,2-b]pyridazine derivative 2 with VEGFR2 revealed that the N1-nitrogen of imidazo[1,2-b]pyridazine core interacts with the backbone NH group of Cys919. To retain this essential interaction, we designed a series of imidazo[1,2-a]pyridine, [1,2,4]triazolo[1,5-a]pyridine, thiazolo[5,4-b]pyridine, and 1,3-benzothiazole derivatives maintaining a ring nitrogen as hydrogen bond acceptor (HBA) at the corresponding position. All compounds thus designed displayed strong inhibitory activity against VEGFR2 kinase, and the [1,2,4]triazolo[1,5-a]pyridine 13d displayed favorable physicochemical properties. Furthermore, 13d inhibited VEGFR2 kinase with slow dissociation kinetics and also inhibited platelet-derived growth factor receptor (PDGFR) kinases. Oral administration of 13d showed potent anti-tumor efficacy in DU145 and A549 xenograft models in nude mice.

Structure-based design, synthesis, and evaluation of imidazo[1,2-b]pyridazine and imidazo[1,2-a]pyridine derivatives as novel dual c-Met and VEGFR2 kinase inhibitors.

To identify compounds with potent antitumor efficacy for various human cancers, we aimed to synthesize compounds that could inhibit c-mesenchymal epithelial transition factor (c-Met) and vascular endothelial growth factor receptor 2 (VEGFR2) kinases. We designed para-substituted inhibitors by using co-crystal structural information from c-Met and VEGFR2 in complex with known inhibitors. This led to the identification of compounds 3a and 3b, which were capable of suppressing both c-Met and VEGFR2 kinase activities. Further optimization resulted in pyrazolone and pyridone derivatives, which could form intramolecular hydrogen bonds to enforce a rigid conformation, thereby producing potent inhibition. One compound of particular note was the imidazo[1,2-a]pyridine derivative (26) bearing a 6-methylpyridone ring, which strongly inhibited both c-Met and VEGFR2 enzyme activities (IC50=1.9, 2.2 nM), as well as proliferation of c-Met-addicted MKN45 cells and VEGF-stimulated human umbilical vein endothelial cells (IC50=5.0, 1.8 nM). Compound 26 exhibited dose-dependent antitumor efficacy in vivo in MKN45 (treated/control ratio [T/C]=4%, po, 5mg/kg, once-daily) and COLO205 (T/C=13%, po, 15 mg/kg, once-daily) mouse xenograft models.

Discovery of N-[5-({2-[(cyclopropylcarbonyl)amino]imidazo[1,2-b]pyridazin-6-yl}oxy)-2-methylphenyl]-1,3-dimethyl-1H-pyrazole-5-carboxamide (TAK-593), a highly potent VEGFR2 kinase inhibitor.

Vascular endothelial growth factor (VEGF) plays important roles in tumor angiogenesis, and the inhibition of its signaling pathway is considered an effective therapeutic option for the treatment of cancer. In this study, we describe the design, synthesis, and biological evaluation of 2-acylamino-6-phenoxy-imidazo[1,2-b]pyridazine derivatives. Hybridization of two distinct imidazo[1,2-b]pyridazines 1 and 2, followed by optimization led to the discovery of N-[5-({2-[(cyclopropylcarbonyl)amino]imidazo[1,2-b]pyridazin-6-yl}oxy)-2-methylphenyl]-1,3-dimethyl-1H-pyrazole-5-carboxamide (23a, TAK-593) as a highly potent VEGF receptor 2 kinase inhibitor with an IC50 value of 0.95 nM. The compound 23a strongly suppressed proliferation of VEGF-stimulated human umbilical vein endothelial cells with an IC50 of 0.30 nM. Kinase selectivity profiling revealed that 23a inhibited platelet-derived growth factor receptor kinases as well as VEGF receptor kinases. Oral administration of 23a at 1 mg/kg bid potently inhibited tumor growth in a mouse xenograft model using human lung adenocarcinoma A549 cells (T/C=8%).

A novel pyrrolo[3, 2-d]pyrimidine derivative, as a vascular endothelial growth factor receptor and platelet-derived growth factor receptor tyrosine kinase inhibitor, shows potent antitumor activity by suppression of tumor angiogenesis.

We recently reported that compound 20d (comp.20d), a novel pyrrolo[3, 2-d]pyrimidine derivative, is a potent and selective inhibitor of tumor angiogenesis-related kinases, including vascular endothelial growth factor receptor (VEGFR) and platelet-derived growth factor receptor (PDGFR). In this study, we show that comp.20d potently blocks the VEGF- and PDGF-stimulated cellular phosphorylation (IC(50) = 2.5 and 3.6 nM, respectively) and proliferation of HUVECs and human coronary artery smooth muscle cells with IC(50) values of 2.8 and 9.6 nM, respectively, and potently inhibits the VEGF-induced tube formation of endothelial cells cocultured with fibroblasts (IC(50) = 3.3 nM). Given orally twice daily, comp.20d at the doses of 1.5-6 mg/kg showed antitumor effects in mice bearing various human cancer xenografts. Consistent with the anti-angiogenic mechanism of action, histological examination of tumors from comp. 20d-treated mice indicated a decrease in microvessel density and inhibition of pericyte recruitment to microvessels, and these were concomitant with decreased interstitial fluid pressure that allowed for therapeutic intratumoral uptake of CPT-11 (irinotecan hydrochloride). In conclusion, comp.20d is an extremely potent inhibitor of VEGFR/PDGFR kinases whose activities suggest therapeutic potential for the treatment of solid tumors that rely on angiogenesis for their survival.

Design, synthesis, and evaluation of imidazo[1,2-b]pyridazine derivatives having a benzamide unit as novel VEGFR2 kinase inhibitors.

The vascular endothelial growth factor (VEGF) signaling pathway has been implicated in tumor angiogenesis, and inhibition of the VEGF pathway is considered an efficacious method for treating cancer. Herein, we describe synthetic studies of imidazo[1,2-b]pyridazine derivatives as VEGF receptor 2 (VEGFR2) kinase inhibitors. The imidazo[1,2-b]pyridazine scaffold was designed and synthesized as a hinge binder according to the previously reported crystal structure of pyrrolo[3,2-d]pyrimidine 1 with VEGFR2. Structure-activity relationship studies revealed that meta-substituted 6-phenoxy-imidazo[1,2-b]pyridazine derivatives had potent affinity for VEGFR2. In particular, N-[3-(imidazo[1,2-b]pyridazin-6-yloxy)phenyl]-3-(trifluoromethyl)benzamide (6b) exhibited strong inhibitory activity against VEGFR2 with an IC(50) value of 7.1 nM, and it inhibited platelet-derived growth factor receptor ß kinase with an IC(50) value of 15 nM.

Biochemical characterization of TAK-593, a novel VEGFR/PDGFR inhibitor with a two-step slow binding mechanism.

Inhibition of tumor angiogenesis leads to a lack of oxygen and nutrients in the tumor and therefore has become a standards of care for many solid tumor therapies. Dual inhibition of vascular endothelial growth factor receptor (VEGFR) and platelet-derived growth factor receptor (PDGFR) protein kinase activities is a popular strategy for targeting tumor angiogenesis. We discovered that TAK-593, a novel imidazo[1,2-b]pyridazine derivative, potently inhibits tyrosine kinases from the VEGFR and PDGFR families. TAK-593 was highly selective for these families, with an IC(50) >1 µM when tested against more than 200 protein and lipid kinases. TAK-593 displayed competitive inhibition versus ATP. In addition, TAK-593 inhibited VEGFR2 and PDGFRß in a time-dependent manner, classifying it as a type II kinase inhibitor. Analysis of enzyme-inhibitor preincubation experiments revealed that the binding of TAK-593 to VEGFR2 and PDGFRß occurs via a two-step slow binding mechanism. Dissociation of TAK-593 from VEGFR2 was extremely slow (t(1/2) >17 h), and the affinity of TAK-593 at equilibrium (K(i)*) was less than 25 pM. Ligand displacement analysis with a fluorescent tracer confirmed the slow dissociation of TAK-593. The dissociation rate constants were in good agreement between the activity and ligand displacement data, and both analyses supported slow dissociation of TAK-593. The long residence time of TAK-593 may achieve an extended pharmacodynamic effect on VEGFR2 and PDGFRß kinases in vivo that differs substantially from its observed pharmacokinetic profile.

Biochemical characterization of a novel type-II VEGFR2 kinase inhibitor: comparison of binding to non-phosphorylated and phosphorylated VEGFR2.

A pyrrolo[3,2-d]pyrimidine-based type-II vascular endothelial growth factor receptor 2 (VEGFR2) kinase inhibitor, compound 20d, displayed time-dependent inhibition of the non-phosphorylated catalytic domain of VEGFR2. In contrast, 20d did not show time-dependent inhibition of the phosphorylated enzyme. Dissociation of 20d from non-phosphorylated VEGFR2 was slow and the half-life of the complex was longer than 4h. In contrast, dissociation of 20d from the phosphorylated enzyme was very fast (half-life <5min). A fluorescent tracer based displacement assay and surface plasmon resonance (SPR) analysis confirmed the slow dissociation of 20d from only non-phosphorylated VEGFR2. Thus, activity based and binding kinetic analyses both supported slow dissociation of 20d from only non-phosphorylated VEGFR2. Additionally SPR analysis revealed that association rates were rapid and nearly identical for these two phosphorylation forms of VEGFR2. From these results, the preferential effect of 20d on non-phosphorylated VEGFR2 is dominated by its slow dissociation from the enzyme and this characteristically long residence time may increase its potency in vivo. The present findings may assist in the design of novel type-II kinase inhibitors.

N-phenyl-N'-[4-(5H-pyrrolo[3,2-d]pyrimidin-4-yloxy)phenyl]ureas as novel inhibitors of VEGFR and FGFR kinases.

We have recently reported the discovery of pyrrolo[3,2-d]pyrimidine derivatives 1a and 1b as potent triple inhibitors of vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), and Tie-2 kinases. To identify compounds having strong inhibitory activity against fibroblast growth factor receptor (FGFR) kinase, further modification was conducted using the co-crystal structure analysis of VEGFR2 and 1b. Among the compounds synthesized, urea derivative 11l having a piperazine moiety on the terminal benzene ring showed strong inhibitory activity against FGFR1 kinase as well as VEGFR2 kinase. A binding model of 11l complexed with VEGFR2 suggested that the piperazine moiety forms additional interactions with Ile1025 and His1026.

Design, synthesis, and evaluation of 5-methyl-4-phenoxy-5H-pyrrolo[3,2-d]pyrimidine derivatives: novel VEGFR2 kinase inhibitors binding to inactive kinase conformation.

We synthesized a series of pyrrolo[3,2-d]pyrimidine derivatives and evaluated their application as type-II inhibitors of vascular endothelial growth factor receptor 2 (VEGFR2) kinase. Incorporation of a diphenylurea moiety at the C4-position of the pyrrolo[3,2-d]pyrimidine core via an oxygen linker resulted in compounds that were potent inhibitors of VEGFR2 kinase. Of these derivatives, compound 20d showed the strongest inhibition of VEGF-stimulated proliferation of human umbilical vein endothelial cells (HUVEC). The co-crystal structure of 20d and VEGFR2 revealed that 20d binds to the inactive form of VEGFR2. Further studies indicated that 20d inhibited VEGFR2 kinase with slow dissociation kinetics and also inhibited PDGFR and Tie-2 kinases. Oral administration of the hydrochloride salt of 20d at 3mg/kg/day showed potent inhibition of tumor growth in a DU145 human prostate cancer cell xenograft nude mouse model.

New Series of Potent Allosteric Inhibitors of Deoxyhypusine Synthase.

Deoxyhypusine synthase (DHPS) is the primary enzyme responsible for the hypusine modification and, thereby, activation of the eukaryotic translation initiation factor 5A (eIF5A), which is key in regulating the protein translation processes associated with tumor proliferation. Although DHPS inhibitors could be a promising therapeutic option for treating cancer, only a few studies reported druglike compounds with this inhibition property. Thus, in this work, we designed and synthesized a new chemical series possessing fused ring scaffolds designed from high-throughput screening hit compounds, discovering a 5,6-dihydrothieno[2,3-c]pyridine derivative (26d) with potent inhibitory activity; furthermore, the X-ray crystallographic analysis of the DHPS complex with 26d demonstrated a distinct allosteric binding mode compared to a previously reported inhibitor. These findings could be significantly useful in the functional analysis of conformational changes in DHPS as well as the structure-based design of allosteric inhibitors.

Discovery of Novel Allosteric Inhibitors of Deoxyhypusine Synthase.

Deoxyhypusine synthase (DHPS) utilizes spermidine and NAD as cofactors to incorporate a hypusine modification into the eukaryotic translation initiation factor 5A (eIF5A). Hypusine is essential for eIF5A activation, which, in turn, plays a key role in regulating protein translation of selected mRNA that are associated with the synthesis of oncoproteins, thereby enhancing tumor cell proliferation. Therefore, inhibition of DHPS is a promising therapeutic option for the treatment of cancer. To discover novel lead compounds that target DHPS, we conducted synthetic studies with a hit obtained via high-throughput screening. Optimization of the ring structures of the amide compound (2) led to bromobenzothiophene (11g) with potent inhibitory activity against DHPS. X-ray crystallographic analysis of 11g complexed with DHPS revealed a dramatic conformational change in DHPS, which suggests the presence of a novel allosteric site. These findings provide the basis for the development of novel therapy distinct from spermidine mimetic inhibitors.

Fragment-based discovery of selective inhibitors of the Mycobacterium tuberculosis protein tyrosine phosphatase PtpA.

The development of low muM inhibitors of the Mycobacterium tuberculosis phosphatase PtpA is reported. The most potent of these inhibitors (K(i)=1.4+/-0.3 microM) was found to be selective when tested against a panel of human tyrosine and dual-specificity phosphatases (11-fold vs the highly homologous HCPtpA, and >70-fold vs all others tested). Modeling the inhibitor-PtpA complexes explained the structure-activity relationships observed in vitro and revealed further possibilities for compound development.

A Novel LSD1 Inhibitor T-3775440 Disrupts GFI1B-Containing Complex Leading to Transdifferentiation and Impaired Growth of AML Cells.

Dysregulation of lysine (K)-specific demethylase 1A (LSD1), also known as KDM1A, has been implicated in the development of various cancers, including leukemia. Here, we describe the antileukemic activity and mechanism of action of T-3775440, a novel irreversible LSD1 inhibitor. Cell growth analysis of leukemia cell lines revealed that acute erythroid leukemia (AEL) and acute megakaryoblastic leukemia cells (AMKL) were highly sensitive to this compound. T-3775440 treatment enforced transdifferentiation of erythroid/megakaryocytic lineages into granulomonocytic-like lineage cells. Mechanistically, T-3775440 disrupted the interaction between LSD1 and growth factor-independent 1B (GFI1B), a transcription factor critical for the differentiation processes of erythroid and megakaryocytic lineage cells. Knockdown of LSD1 and GFI1B recapitulated T-3775440-induced transdifferentiation and cell growth suppression, highlighting the significance of LSD1-GFI1B axis inhibition with regard to the anti-AML effects of T-3775440. Moreover, T-3775440 exhibited significant antitumor efficacy in AEL and AMKL xenograft models. Our findings provide a rationale for evaluating LSD1 inhibitors as potential treatments and indicate a novel mechanism of action against AML, particularly AEL and AMKL. Mol Cancer Ther; 16(2); 273-84. ©2016 AACR.

Discovery of a piperidine-4-carboxamide CCR5 antagonist (TAK-220) with highly potent Anti-HIV-1 activity.

We incorporated various polar groups into previously described piperidine-4-carboxamide CCR5 antagonists to improve their metabolic stability in human hepatic microsomes. Introducing a carbamoyl group into the phenyl ring of the 4-benzylpiperidine moiety afforded the less lipophilic compound 5f, which possessed both high metabolic stability and good inhibitory activity of HIV-1 envelope-mediated membrane fusion (IC(50) = 5.8 nM). Further optimization to increase potency led to the discovery of 1-acetyl-N-{3-[4-(4-carbamoylbenzyl)piperidin-1-yl]propyl}-N-(3-chloro-4-methylphenyl)piperidine-4-carboxamide (5m, TAK-220), which showed high CCR5 binding affinity (IC(50) = 3.5 nM) and potent inhibition of membrane fusion (IC(50) = 0.42 nM), as well as good metabolic stability. Compound 5m strongly inhibited the replication of CCR5-using HIV-1 clinical isolates in human peripheral blood mononuclear cells (mean EC(50) = 1.1 nM, EC(90) = 13 nM) and exhibited a good pharmacokinetic profile in monkeys (BA = 29%). This compound has been chosen as a clinical candidate for further development.

[Late onset epilepsy associated with migration disorder: a case report].

We reported a 57-year-old female patient recently suffering from frequent seizures such as motionless staring and oral automatism. Electroencephalograms showed spikes in the right sphenoidal derivation and magnetic resonance images revealed an abnormal region, most likely related with a migration disorder such as a focal cortical dysplasia. She was diagnosed as mesiotemporal lobe epilepsy associated with a migration disorder. Seizure disappeared after medication therapy was done. No previous literature has described such a case, thus this is the first report of an epilepsy associated with migration disorder newly onset in a patient older than 50 years old.

A case of leptomeningeal carcinomatosis from esophageal basaloid carcinoma diagnosed by quantitative reverse transcription-polymerase chain reaction for carcinoembryonic antigen.

We describe herein the case of a 68-year-old man who experienced leptomeningitis after esophagectomy from an esophageal basaloid carcinoma. Although the patient had a good operative course for the first 10 days after surgery, he suddenly had general convulsions with unconsciousness. He was placed on mechanical ventilation in an intensive care unit. Computed tomography and magnetic imaging resonance did not reveal any abnormal findings. No abnormal data in the cerebrospinal fluid were found by biochemical, virological, and cytological examination. The positive expression of carcinoembryonic antigen messenger ribonucleic acid in cerebrospinal fluid was detected by a quantitative reverse transcription-polymerase chain reaction method. Immunohistochemical staining using an anticytokeratin antibody confirmed the presence of tumor cells in the cerebrospinal fluid. Spontaneous breathing was recovered after treatment with systemic chemotherapy. Six months after surgery, computed tomography revealed multiple brain metastases. This case demonstrates that the quantitative reverse transcription-polymerase chain reaction method of analyzing carcinoembryonic antigen messenger ribonucleic acid may be a sensitive and useful method for determining leptomeningeal metastasis before the detection of tumors by cytological and imaging examinations in patients with cancer.

[Complete response in an elderly patient with advanced gastric cancer treated with TS-1].

The patient was an 89-year-old woman whose complaints were anorexia and weight loss. As a result of various examinations, she was diagnosed with advanced gastric cancer, Borrmann 3. TS-1 was administered at 75 mg/day for two weeks followed by one-week discontinvation during hospitalization; This course was then repeated after discharge. Anorexia and weight loss improved after two weeks, and complete response (CR) was obtained after 10 months of treatment. No cancer cells were confirmed by endoscopic biopsy. During this period no severe toxicities occurred. This TS-1 administration schedule appears to be a feasible and effective therapy for elderly patients with advanced gastric cancer.