John E. Toth

Mitotic requirement for aurora A kinase is bypassed in the absence of aurora B kinase

We investigated why treatment of cells with dual aurora A and B kinase inhibitors produces phenotypes identical to inactivation of aurora B. We found that dual aurora kinase inhibitors in fact potently inhibit cellular activities of both kinases, indicating that inactivation of aurora B bypasses aurora A in mitosis. RNAi experiments further established that inactivation of aurora B indeed bypasses the requirement for aurora A and leads to polyploidy. Inactivation of aurora A activates checkpoint kinase BubR1 in an aurora B‐dependent manner. Our results thus show that aurora B is responsible for mitotic arrest in the absence of aurora A.

Complete Inhibition of Anisomycin and UV Radiation but Not Cytokine Induced JNK and p38 Activation by an Aryl-substituted Dihydropyrrolopyrazole Quinoline and Mixed Lineage Kinase 7 Small Interfering RNA

Mixed lineage kinase 7 (MLK7) is a mitogen-activated protein kinase kinase kinase (MAPKKK) that activates the pro-apoptotic signaling pathways p38 and JNK. A library of potential kinase inhibitors was screened, and a series of dihydropyrrolopyrazole quinolines was identified as highly potent inhibitors of MLK7 in vitro catalytic activity. Of this series, an aryl-substituted dihydropyrrolopyrazole quinoline (DHP-2) demonstrated an IC50 of 70 nm for inhibition of pJNK formation in COS-7 cell MLK7/JNK co-transfection assays. In stimulated cells, DHP-2 at 200 nm or MLK7 small interfering RNA completely blocked anisomycin and UV induced but had no effect on interleukin-1β or tumor necrosis factor-α-induced p38 and JNK activation. Additionally, the compound blocked anisomycin and UV-induced apoptosis in COS-7 cells. Heart tissue homogenates from MLK7 transgenic mice treated with DHP-2 at 30 mg/kg had reduced JNK and p38 activation with no apparent effect on ERK activation, demonstrating that this compound can be used to block MLK7-driven MAPK pathway activation in vivo. Taken together, these data demonstrate that MLK7 is the MAPKKK required for modulation of the stress-activated MAPKs downstream of anisomycin and UV stimulation and that DHP-2 can be used to block MLK7 pathway activation in cells as well as in vivo.

Cdk1 Activity Is Required for Mitotic Activation of Aurora A during G2/M Transition of Human Cells

In mammalian cells entry into and progression through mitosis are regulated by multiple mitotic kinases. How mitotic kinases interact with each other and coordinately regulate mitosis remains to be fully understood. Here we employed a chemical biology approach using selective small molecule kinase inhibitors to dissect the relationship between Cdk1 and Aurora A kinases during G2/M transition. We find that activation of Aurora A first occurs at centrosomes at late G2 and is required for centrosome separation independently of Cdk1 activity. Upon entry into mitosis, Aurora A then becomes fully activated downstream of Cdk1 activation. Inactivation of Aurora A or Plk1 individually during a synchronized cell cycle shows no significant effect on Cdk1 activation and entry into mitosis. However, simultaneous inactivation of both Aurora A and Plk1 markedly delays Cdk1 activation and entry into mitosis, suggesting that Aurora A and Plk1 have redundant functions in the feedback activation of Cdk1. Together, our data suggest that Cdk1, Aurora A, and Plk1 mitotic kinases participate in a feedback activation loop and that activation of Cdk1 initiates the feedback loop activity, leading to rapid and timely entry into mitosis in human cells. In addition, live cell imaging reveals that the nuclear cycle of cells becomes uncoupled from cytokinesis upon inactivation of both Aurora A and Aurora B kinases and continues to oscillate in a Cdk1-dependent manner in the absence of cytokinesis, resulting in multinucleated, polyploidy cells.

Effects of diarylsulfonylurea antitumor agents on the function of mitochondria isolated from rat liver and GC3/c1 cells

Diarylsulfonylureas, such as N-(4-chlorophenyl)aminocarbonyl-2,3-dihydro-1-indene-5-sulfonamide (LY186641, Sulofenur) and N-(4-chlorophenyl)aminocarbonyl-4-methylbenzene sulfonamide (LY181984), have been shown to be effective antitumor agents in a variety of in vivo and in vitro animal models. Their mechanism of action is unknown but does not appear to be the result of nonselective destruction of actively dividing cell populations. Mitochondria have been shown to accumulate Sulofenur and therefore may be targets of drug action. The purpose of these investigations was to examine the effects of a variety of diarylsulfonylureas in mitochondria and attempt to determine the relevance of these changes to antitumor activity. Many of the diarylsulfonylureas which were effective antitumor agents in animal models were also uncouplers of mitochondrial oxidative phosphorylation. They increased state 4 respiration and dissipated the mitochondrial membrane potential in a concentration-related fashion. The mechanism of uncoupling appeared to be related to a dissociable hydrogen ion as these molecules had pKa values that ranged from 6.0 to 6.2 and were highly lipophilic. Thus, the uncoupling action appears to be the result of hydrogen ion translocation. The mechanism of antitumor activity does not appear to be the result of uncoupling as no correlation was evident between inhibition of cell growth and uncoupling action of a variety of active and inactive diarylsulfonylureas. In vitro, Sulofenur is cytotoxic at high concentrations and inhibits cell growth at lower concentrations in the absence of any overt cell kill. The inhibition of cell growth also did not appear to be related to the uncoupling action of these drugs. In contrast, uncoupling may have played a partial role in the early, high exposure cell kill that can occur with these compounds.

Synthesis and biological evaluation of cryptophycin analogs with substitution at C-6 (fragment C region).

Analogs of the antitumor agents cryptophycins 1 and 8 with dialkyl substitution at C-6 (fragment C) were synthesized and evaluated for in vitro cytotoxicity against human leukemia cells (CCRF-CEM). The activity of these analogs decreased as the size of the substituents at C-6 increased. The C-6 spirocylopropyl compound (2g) was highly potent in vitro and showed excellent antitumor activity in animal models.

Control of site-specific substitution of aminoglycosides by transition metal cations

Abstract The site of transition metal-directed acylations of apramycin and related aminoglycosides can be altered simply by changing the metal cation employed in the reaction.

The synthesis of o-aminophenyl sulfate metabolites of the oncolytic sulfonylureas

Abstract Application of the Boyland-Sims oxidation to 4-chloro- and 3,4-dichloroaniline is reported.