Discovery of CC-930, an orally active anti-fibrotic JNK inhibitor

In this Letter we describe the discovery of potent, selective, and orally active aminopurine JNK inhibitors. Improving the physico-chemical properties as well as increasing the potency and selectivity of a subseries with rat plasma exposure, led to the identification of four structurally diverse inhibitors. Differentiation based on PK profiles in multiple species as well as activity in a chronic efficacy model led to the identification of 1 (CC-930) as a development candidate, which is currently in Phase II clinical trial for IPF.

Substrate recognition and ubiquitination of SCFSkp2/Cks1 ubiquitin-protein isopeptide ligase

p27, an important cell cycle regulator, blocks the G(1)/S transition in cells by binding and inhibiting Cdk2/cyclin A and Cdk2/cyclin E complexes (Cdk2/E). Ubiquitination and subsequent degradation play a critical role in regulating the levels of p27 during cell cycle progression. Here we provide evidence suggesting that both Cdk2/E and phosphorylation of Thr(187) on p27 are essential for the recognition of p27 by the SCF(Skp2/Cks1) complex, the ubiquitin-protein isopeptide ligase (E3). Cdk2/E provides a high affinity binding site, whereas the phosphorylated Thr(187) provides a low affinity binding site for the Skp2/Cks1 complex. Furthermore, binding of phosphorylated p27/Cdk2/E to the E3 complex showed positive cooperativity. Consistently, p27 is also ubiquitinated in a similarly cooperative manner. In the absence of p27, Cdk2/E and Cks1 increase Skp2 phosphorylation. This phosphorylation enhances Skp2 auto-ubiquitination, whereas p27 inhibits both phosphorylation and auto-ubiquitination of Skp2.

In Vitro SCFβ‐Trcp1–Mediated IκBα Ubiquitination Assay for High‐Throughput Screen

An increasing body of evidence indicates that constitutive activation of NF-kappaB contributes to tumorigenesis and inflammation. Ubiquitination and degradation of IkappaB plays an essential role in NF-kappaB activation. Here we describe an in vitro IkappaBalpha ubiquitination assay system in which purified E1, E2, SCF(beta-Trcp1) E3, IkappaBalpha, IKK2, and Ub were used to generate ubiquitinated IkappaBalpha. The ubiquitination of IkappaBalpha is strictly dependent on its phosphorylation by IKK2, as well as the presence of E1, E2, E3, and Ub. The assay was adapted into 384-well plate format in which an antibody against IkappaBalpha was used to capture IkappaBalpha, and the biotinylated ubiquitin attached to IkappaBalpha was detected with europium (Eu)-labeled streptavidin. This assay can be used to discover inhibitors of IkappaBalpha ubiquitination. Such inhibitors would block NF-kappaB activation by stabilizing IkappaB levels in cells and thus provide a new therapeutic approach to NF-kappaB-related human diseases.

Mechanism-based inactivation of thioredoxin reductase from Plasmodium falciparum by Mannich bases. Implication for cytotoxicity

Thioredoxin reductase (TrxR) is the homodimeric flavoenzyme that catalyzes reduction of thioredoxin disulfide (Trx). For Plasmodium falciparum, a causative agent of tropical malaria, TrxR is an essential protein which has been validated as a drug target. The high-throughput screening of 350000 compounds has identified Mannich bases as a new class of TrxR mechanism-based inhibitors. During catalysis, TrxR conducts reducing equivalents from the NADPH-reduced flavin to Trx via the two redox-active cysteine pairs, Cys88-Cys93 and Cys535'-Cys540', referred to as N-terminal and C-terminal cysteine pairs. The structures of unsaturated Mannich bases suggested that they could act as bisalkylating agents leading to a macrocycle that involves both C-terminal cysteines of TrxR. To confirm this hypothesis, different Mannich bases possessing one or two electrophilic centers were synthesized and first studied in detail using glutathione as a model thiol. Michael addition of glutathione to the double bond of an unsaturated Mannich base (3a) occurs readily at physiological pH. Elimination of the amino group, promoted by base-catalyzed enolization of the ketone, is followed by addition of a second nucleophile. The intermediate formed in this reaction is an alpha,beta-unsaturated ketone that can react rapidly with a second thiol. When studying TrxR as a target of Mannich bases, we took advantage of the fact that the charge-transfer complex formed between the thiolate of Cys88 and the flavin in the reduced enzyme can be observed spectroscopically. The data show that it is the C-terminal Cys 535'-Cys540' pair rather than the N-terminal Cys88-Cys93 pair that is modified by the inhibitor. Although alkylated TrxR is unable to turn over its natural substrate Trx, it can reduce low M(r) electron acceptors such as methyl methanethiolsulfonate by using its unmodified N-terminal thiols. On the basis of results with chemically distinct Mannich bases, a detailed mechanism for the inactivation of TrxR is proposed.

Correlating cell cycle with apoptosis in a cell line expressing a tandem green fluorescent protein substrate specific for group II caspases

BACKGROUND

We describe a rapid flow cytometric assay that correlates cell cycle with apoptotic cell death in a cell line expressing a tandem green fluorescent protein (GFP).

METHODS

A Jurkat cell line was transfected with a gene construct coding for constitutive expression of a tandem GFP molecule carrying a consensus cleavage site (DEVD) for group II caspases (C-2-Y). Cells were treated with CD95 antibody (Ab), then incubated with annexin V-phycoerythrin (PE), propidium iodide (PI), and Hoechst 33342.

RESULTS

After CD95 treatment, the C-2-Y cell line had twice the number of nonapoptotic cells compared with both control cell lines. This proportion of viable, nonapoptotic cells after treatment was unaffected by the level of GFP (DEVD) expression in the cells, as confirmed by sorted populations. The early apoptotic cells in the C-2-Y cell line had an increased G0-G1 phase population compared with the control cell lines.

CONCLUSIONS

Apoptosis is delayed in the C-2-Y cell line and the early apoptotic cells have a higher G0-G1 cell cycle frequency. The artificial substrate competes with the natural substrate(s), thereby slowing the apoptotic process. The expression level of DEVD-GFP does not alter the delayed induction of apoptosis. Caspase activation occurs prior to phosphatidylserine translocation.