Synthesis and biological evaluation of analogues of the kinase inhibitor nilotinib as Abl and Kit inhibitors.

The importance of the trifluoromethyl group in the polypharmacological profile of nilotinib was investigated. Molecular editing of nilotinib led to the design, synthesis and biological evaluation of analogues where the trifluoromethyl group was replaced by a proton, fluorine and a methyl group. While these analogues were less active than nilotinib toward Abl, their activity toward Kit was comparable, with the monofluorinated analogue being the most active. Docking of nilotinib and of analogues 2a-c to the binding pocket of Abl and of Kit showed that the lack of shape complementarity in Kit is compensated by the stabilizing effect from its juxtamembrane region.

Pyruvate kinase M2 activators promote tetramer formation and suppress tumorigenesis.

Cancer cells engage in a metabolic program to enhance biosynthesis and support cell proliferation. The regulatory properties of pyruvate kinase M2 (PKM2) influence altered glucose metabolism in cancer. The interaction of PKM2 with phosphotyrosine-containing proteins inhibits enzyme activity and increases the availability of glycolytic metabolites to support cell proliferation. This suggests that high pyruvate kinase activity may suppress tumor growth. We show that expression of PKM1, the pyruvate kinase isoform with high constitutive activity, or exposure to published small-molecule PKM2 activators inhibits the growth of xenograft tumors. Structural studies reveal that small-molecule activators bind PKM2 at the subunit interaction interface, a site that is distinct from that of the endogenous activator fructose-1,6-bisphosphate (FBP). However, unlike FBP, binding of activators to PKM2 promotes a constitutively active enzyme state that is resistant to inhibition by tyrosine-phosphorylated proteins. These data support the notion that small-molecule activation of PKM2 can interfere with anabolic metabolism.

Palau'amine and related oroidin alkaloids dibromophakellin and dibromophakellstatin inhibit the human 20S proteasome.

We report herein that the oroidin-derived alkaloids palau'amine (1), dibromophakellin (2), and dibromophakellstatin (3) inhibit the proteolytic activity of the human 20S proteasome as well as the (i)20S immunoproteasome catalytic core. Palau'amine is found to prevent the degradation of ubiquitinylated proteins, including IκBα, in cell culture, which may be indicative of the potential mechanism by which these agents exhibit their exciting cytotoxic and immunosuppressive properties.

Synthesis and characterization of a BODIPY conjugate of the BCR-ABL kinase inhibitor Tasigna (nilotinib): evidence for transport of Tasigna and its fluorescent derivative by ABC drug transporters.

Tasigna (Nilotinib) is a BCR-ABL kinase inhibitor recently approved by the Food and Drug Administration, which is indicated for the treatment of drug-resistant chronic myelogenous leukemia (CML). The efflux of tyrosine kinase inhibitors by ATP-binding cassette (ABC) drug transporters, which actively pump these drugs out of cells utilizing ATP as an energy source, has been linked to the development of drug resistance in CML patients. We report here the synthesis and characterization of a fluorescent derivative of Tasigna to study its interaction with two major ABC transporters, P-glycoprotein (Pgp) and ABCG2, in in vitro and ex vivo assays. A fluorescent derivative of Tasigna, BODIPY FL Tasigna, inhibited the BCR-ABL kinase activity in K562 cells and was also effluxed by Pgp- and ABCG2-expressing cells in both cultured cells and rat brain capillaries expressing Pgp and ABCG2. In addition, [(3)H]-Tasigna was found to be transported by Pgp-expressing polarized LLC-PK1 cells in a transepithelial transport assay. Consistent with these results, both Tasigna and BODIPY FL Tasigna were less effective at inhibiting the phosphorylation of Crkl (a substrate of BCR-ABL kinase) in Pgp- and ABCG2-expressing K562 cells due to their reduced intracellular concentration. Taken together, these data provide evidence that BODIPY FL Tasigna is transported by Pgp and ABCG2, and Tasigna is transported by Pgp. Further, we propose that BODIPY FL Tasigna can potentially be used as a probe for functional analysis of Pgp and ABCG2 in cancer cells and in other preclinical studies.

Phosphodiesterase 4 inhibitors enhance sexual pleasure-seeking activity in rodents.

Pleasure-seeking deficits, including lack of libido, are a core feature of depression. Animal and preliminary clinical studies both suggest that phosphodiesterase 4 (PDE4) is a target for developing novel antidepressants. This study examined the potential involvement of PDE4 in the pathology of depression in both animal models and human postmortem brains. In humans, PDE4B and PDE4D levels were elevated in cingulate cortical tissue from individuals with major depressive disorder (MDD) compared to controls. Using the female urine smelling test (FUST), a recently refined method for monitoring sexual pleasure-seeking activity in mice, we found that icv infusion of selective potent PDE4 inhibitors enhanced sexual pleasure-seeking activity in male mice that underwent the learned helplessness or serotonin depletion paradigms. The infusion also increased sexual pleasure-seeking activity in naïve male mice. The results suggest that PDE4 may be a plausible contributor to the sexual pleasure-seeking deficits seen in depressed patients; inhibiting PDE4 may restore these deficits.

Evaluation of thieno[3,2-b]pyrrole[3,2-d]pyridazinones as activators of the tumor cell specific M2 isoform of pyruvate kinase.

Cancer cells have distinct metabolic needs that are different from normal cells and can be exploited for development of anti-cancer therapeutics. Activation of the tumor specific M2 form of pyruvate kinase (PKM2) is a potential strategy for returning cancer cells to a metabolic state characteristic of normal cells. Here, we describe activators of PKM2 based upon a substituted thieno[3,2-b]pyrrole[3,2-d]pyridazinone scaffold. The synthesis of these agents, structure-activity relationships, analysis of activity at related targets (PKM1, PKR and PKL) and examination of aqueous solubility are investigated. These agents represent the second reported chemotype for activation of PKM2.

Evaluation of substituted N,N'-diarylsulfonamides as activators of the tumor cell specific M2 isoform of pyruvate kinase.

The metabolism of cancer cells is altered to support rapid proliferation. Pharmacological activators of a tumor cell specific pyruvate kinase isozyme (PKM2) may be an approach for altering the classic Warburg effect characteristic of aberrant metabolism in cancer cells yielding a novel antiproliferation strategy. In this manuscript, we detail the discovery of a series of substituted N,N'-diarylsulfonamides as activators of PKM2. The synthesis of numerous analogues and the evaluation of structure-activity relationships are presented as well as assessments of mechanism and selectivity. Several agents are found that have good potencies and appropriate solubility for use as chemical probes of PKM2 including 55 (AC(50) = 43 nM, maximum response = 84%; solubility = 7.3 microg/mL), 56 (AC(50) = 99 nM, maximum response = 84%; solubility = 5.7 microg/mL), and 58 (AC(50) = 38 nM, maximum response = 82%; solubility = 51.2 microg/mL). The small molecules described here represent first-in-class activators of PKM2.

Exploration and optimization of substituted triazolothiadiazines and triazolopyridazines as PDE4 inhibitors.

An expansion of structure-activity studies on a series of substituted 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine PDE4 inhibitors and the introduction of a related [1,2,4]triazolo[4,3-b]pyridazine based inhibitor of PDE4 is presented. The development of SAR included strategic incorporation of known substituents on the critical catachol diether moiety of the 6-phenyl appendage on each heterocyclic core. From these studies, (R)-3-(2,5-dimethoxyphenyl)-6-(4-methoxy-3-(tetrahydrofuran-3-yloxy)phenyl)-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine (10) and (R)-3-(2,5-dimethoxyphenyl)-6-(4-methoxy-3-(tetrahydrofuran-3-yloxy)phenyl)-[1,2,4]triazolo[4,3-b]pyridazine (18) were identified as highly potent PDE4A inhibitors. Each of these analogues was submitted across a panel of 21 PDE family members and was shown to be highly selective for PDE4 isoforms (PDE4A, PDE4B, PDE4C, PDE4D). Both 10 and 18 were then evaluated in divergent cell-based assays to assess their relevant use as probes of PDE4 activity. Finally, docking studies with selective ligands (including 10 and 18) were undertaken to better understand this chemotypes ability to bind and inhibit PDE4 selectively.

A virtual screen for diverse ligands: discovery of selective G protein-coupled receptor antagonists.

Virtual screening has become a major focus of bioactive small molecule lead identification, and reports of agonists and antagonists discovered via virtual methods are becoming more frequent. G protein-coupled receptors (GPCRs) are the one class of protein targets for which success with this approach has been limited. This is likely due to the paucity of detailed experimental information describing GPCR structure and the intrinsic function-associated structural flexibility of GPCRs which present major challenges in the application of receptor-based virtual screening. Here we describe an in silico methodology that diminishes the effects of structural uncertainty, allowing for more inclusive representation of a potential docking interaction with exogenous ligands. Using this approach, we screened one million compounds from a virtual database, and a diverse subgroup of 100 compounds was selected, leading to experimental identification of five structurally diverse antagonists of the thyrotropin-releasing hormone receptors (TRH-R1 and TRH-R2). The chirality of the most potent chemotype was demonstrated to be important in its binding affinity to TRH receptors; the most potent stereoisomer was noted to have a 13-fold selectivity for TRH-R1 over TRH-R2. A comprehensive mutational analysis of key amino acid residues that form the putative binding pocket of TRH receptors further verified the binding modality of these small molecule antagonists. The described virtual screening approach may prove applicable in the search for novel small molecule agonists and antagonists of other GPCRs.

Identification of a potent new chemotype for the selective inhibition of PDE4.

A series of substituted 3,6-diphenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines were prepared and analyzed as inhibitors of phosphodiesterase 4 (PDE4). Synthesis, structure-activity relationships, and the selectivity of a highly potent analogue against related phosphodiesterase isoforms are presented.

Extending Pummerer reaction chemistry. Synthesis studies in the phakellin alkaloid area.

The syntheses of (+/-)-dibromophakellstatin and, from this species, (+/-)-dibromophakellin are described. Oxidative cyclization of a phenylthiolated dihydrooroidin derivative triggered by a Pummerer reaction constitutes the key step in this biomimetic approach to this family of marine alkaloids.

Synthesis of Substituted 2-phenylhistamines via a Microwave Promoted Suzuki Coupling.

Substitutions on the 2-position of the imidizole ring of histamine have proven useful in a number of biochemical settings. Current art for the synthesis of these constructs relies upon a cumbersome and low-yielding condensation reaction. Here-in we report a new procedure for the synthesis of a series of substituted 2-phenylhistamines utilizing a microwave-promoted Suzuki coupling.

The inhibition and treatment of breast cancer with poly (ADP-ribose) polymerase (PARP-1) inhibitors.

BRCA1 and BRCA2 mutations are responsible for most familial breast carcinomas. Recent reports carried out in non-cancerous mouse BRCA1- or BRCA2-deficient embryonic stem (ES) cells, and hamster BRCA2-deficient cells have demonstrated that the targeted inhibition of poly(ADP-ribose) polymerase (PARP-1) kills BRCA mutant cells with high specificity. Although these studies bring hope for BRCA mutation carriers, the effectiveness of PARP-1 inhibitors for breast cancer remains elusive. Here we present the first in vivo demonstration of PARP-1 activity in BRCA1-deficient mammary tumors and describe the effects of PARP-1 inhibitors (AG14361, NU1025, and 3-aminobenzamide) on BRCA1-deficient ES cells, mouse and human breast cancer cells. AG14361 was highly selective for BRCA1-/- ES cells; however, NU1025 and 3-aminobenzamide were relatively non-selective. In allografts of naïve ES BRCA1-/- cells there was either partial or complete remission of tumors. However, in allografts of mouse, BRCA1-/- mammary tumors, there was no tumor regression or remission although a partial inhibition of tumor growth was observed in both the BRCA1-/- and BRCA1+/+ allografts. In human tumor cells, PARP-1 inhibitors showed no difference in vitro in limiting the growth of mammary tumors irrespective of their BRCA1 status. These results suggest that PARP-1 inhibitors may non-specifically inhibit the growth of mammary tumors.

Extending Pummerer reaction chemistry. Synthesis of (+/-)-dibromophakellstatin by oxidative cyclization of an imidazole derivative.

The diastereoselective oxidative cyclization of a dihydrooroidin derivative is reported. The thioimidate product formed by application of a new variant of the Pummerer reaction serves as a precursor to dibromophakellstatin. [reaction: see text]