[Chlamydia trachomatis infection and its associated factors among asymptomatic outpatients attending sexually transmitted disease-related clinics]

Objective: To understand the prevalence of Chlamydia trachomatis (CT) infection and its associated factors among asymptomatic outpatients attending sexually transmitted disease (STD)-related clinics in Shenzhen and provide evidence for development of future interventions. Methods: From April 15 to May 16, 2018, a cross-sectional study was conducted and patients attending STD-related Clinics were recruited from 22 medical institutions in Nanshan, Luohu, Bao'an, Longgang, Yantian, and Longhua districts of Shenzhen. After the informed consent from each participant was obtained, social-demographic information was collected through a structured questionnaire and urine samples were collected for CT nucleic acid detection. In addition, logistic regression was used to explore associated factors of CT infection. Results: In asymptomatic outpatients, the prevalence of CT infection was 7.16% (250/3 492). Being single (aOR=2.29, 95%CI:1.65-3.16), without registered Shenzhen residency (aOR=1.49, 95%CI:1.04-2.13), and without previous CT testing in the past year (aOR=2.04, 95%CI:1.03-4.05) were the risk factors of CT infection in asymptomatic outpatients. Among participants without registered Shenzhen residency, 89.25% (2 176/2 438) were college-degree or below, and 51.29% (1 255/2 447) were aged ≤30 years, and the risk of CT infection among those ≤30 years old was 1.73 times higher than those >30 years old (95%CI:1.28-2.34). Conclusions: The prevalence of CT infection was high among asymptomatic outpatients attending STD-related clinics in Shenzhen. Routine CT screening should be carried out for this population, especially for those with sexually active age, being single, with low educational level, and without previous CT testing in the past year. Also, raising their awareness of knowledge and adverse outcomes of CT infection should be considered to promote routine CT screening and timely treatment.

[Effect of duodenal stump reinforcement on postoperative complications in patients undergoing laparoscopic radical gastrectomy]

Objective: To evaluate the influence of duodenal stump reinforcing on the short-term complications after laparoscopic radical gastrectomy. Methods: A retrospective cohort study with propensity score matching (PSM) was conducted. Clinical data of 1204 patients with gastric cancer who underwent laparoscopic radical gastrectomy at the First Affiliated Hospital of Army Medical University from April 2009 to December 2018 were collected. The digestive tract reconstruction methods included Billroth II anastomosis, Roux-en-Y anastomosis and un-cut-Roux- en-Y anastomosis. A linear stapler was used to transected the stomach and the duodenum. Among 1204 patients, 838 were males and 366 were females with mean age of (57.0±16.0) years. Duodenal stump was reinforced in 792 cases (reinforcement group) and unreinforced in 412 cases (non-reinforcement group). There were significant differences in resection range and anastomotic methods between the two groups (both P<0.001). The two groups were matched by propensity score according to the ratio of 1∶1, and the reinforcement group was further divided into purse string group and non-purse string group. The primary outcome was short-term postoperative complications (within one month after operation). Complications with Clavien-Dindo grade ≥ III a were defined as severe complications, and the morbidity of complication between the reinforcement group and the non-reinforcement group, as well as between the purse string group and the non-purse string group was compared. Results: After PSM, 411 pairs were included in the reinforcement group and the non-reinforcement group, and there were no significant differences in baseline data between the two groups (all P>0.05). No perioperative death occurred in any patient.The short-term morbidity of postoperative complication was 7.4% (61/822), including 14 cases of anastomotic leakage (23.0%), 11 cases of abdominal hemorrhage (18.0%), 8 cases of duodenal stump leakage (13.1%), 2 cases of incision dehiscence (3.3%), 6 cases of incision infection (9.8%) and 20 cases of abdominal infection (32.8%). Short-term postoperative complications were found in 25 patients (6.1%) and 36 patients (8.8%) in the reinforcement group and the non-reinforcement group, respectively, without significant difference (χ²=2.142, P=0.143). Nineteen patients (2.3%) developed short-term severe complications (Clavien-Dindo grade ≥IIIa), while no significant difference in severe complications was found between the two groups (1.7% vs. 2.9%, χ²=1.347, P=0.246). Sub-group analysis showed that the morbidity of short-term postoperative complication of the purse string group was 2.6% (9/345), which was lower than 24.2% (16/66) of the non-purse string group (χ²=45.388, P<0.001). Conclusion: Conventional reinforcement of duodenal stump does not significantly reduce the incidence of duodenal stump leakage, so it is necessary to choose whether to reinforce the duodenal stump individually, and purse string suture should be the first choice when decided to reinforce.

[Comparison of clinical efficacy and quality of life between uncut Roux-en-Y and Billroth II with Braun anastomosis in laparoscopic distal gastrectomy for gastric cancer]

Objective: To compare the clinical efficacy and quality of life between uncut Roux-en-Y and Billroth II with Braun anastomosis in laparoscopic distal gastrectomy for gastric cancer patients. Methods: A retrospective cohort study was performed. Inclusion criteria: (1) 18 to 75 years old; (2) gastric cancer proved by preoperative gastroscopy, CT and pathological results and tumor was suitable for D2 radical distal gastrectomy; (3) postoperative pathological diagnosis stage was T1-4aN0-3M0 (according to the AJCC-7th TNM tumor stage), and the margin was negative; (4) Eastern Cooperative Oncology Group (ECOG) physical status score <2 points, and American Association of Anesthesiologists (ASA) grade 1 to 3; (5) no mental illness; (6) able to answer questionnaires independently; (7) patients agreed to undergo laparoscopic distal gastrectomy and signed an informed consent. Exclusion criteria: (1) patients with severe chronic diseases and American Association of Anesthesiologists (ASA) grade >3; (2) patients with other malignant tumors; (3) patients suffered from serious mental diseases; (4) patients received neoadjuvant chemotherapy or immunotherapy. According to the above criteria, clinical data of 200 patients who underwent laparoscopic distal gastrectomy at the Department of General Surgery of the First Affiliated Hospital of Army Medical University from January 2016 to December 2019 were collected. Of the 200 patients, 108 underwent uncut Roux-en-Y anastomosis and 92 underwent Billroth II with Braun anastomosis. The general data, intraoperative and postoperative conditions, complications, and endoscopic evaluation 1 year after the surgery were compared. Besides, the quality of life of two groups was also compared using the Chinese version of the European Organization For Research and Treatment of Cancer (EORTC) quality of life questionnaire-Core 30 (QLQ-C30) and quality of life questionnaire-stomach 22 (QLQ-STO22). Results: There were no significant differences in baseline data between the two groups (all P>0.05). All the 200 patients successfully underwent laparoscopic distal gastrectomy without intraoperative complications, conversion to open surgery or perioperative death. There were no significant differences between two groups in operative time, intraoperative blood loss, postoperative complications, time to flatus, time to removal of gastric tube, time to liquid diet, time to removal of drainage tube or length of postoperative hospital stay (all P>0.05). Endoscopic evaluation was conducted 1 year after surgery. Compared to Billroth II with Braun group, the uncut Roux-en-Y group had a significantly lower incidences of gastric stasis [19.8% (17/86) vs. 37.0% (27/73), χ(2)=11.199, P=0.024], gastritis [11.6% (10/86) vs. 34.2% (25/73), χ(2)=20.892, P<0.001] and bile reflux [1.2% (1/86) vs. 28.8% (21/73), χ(2)=25.237, P<0.001], and the differences were statistically significant. The EORTC questionnaire was performed 1 year after surgery, there were no significant differences in the scores of QLQ-C30 scale between the two groups (all P>0.05), while the scores of QLQ-STO22 showed that, compared to the Billroth II with Braun group, the uncut Roux-en-Y group had a lower pain score (median: 8.3 vs. 16.7, Z=-2.342, P=0.019) and reflux score (median: 0 vs 5.6, Z=-2.284, P=0.022), and the differences were statistically significant (all P<0.05), indicating milder symptoms. Conclusion: The uncut Roux-en-Y anastomosis is safe and reliable in laparoscopic distal gastrectomy, which can reduce the incidences of gastric stasis, gastritis and bile reflux, and improve the quality of life of patients after surgery.

The Genomic Landscape of Intrinsic and Acquired Resistance to Cyclin-Dependent Kinase 4/6 Inhibitors in Patients with Hormone Receptor-Positive Metastatic Breast Cancer

Mechanisms driving resistance to cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in hormone receptor-positive (HR⁺) breast cancer have not been clearly defined. Whole-exome sequencing of 59 tumors with CDK4/6i exposure revealed multiple candidate resistance mechanisms including RB1 loss, activating alterations in AKT1, RAS, AURKA, CCNE2, ERBB2, and FGFR2, and loss of estrogen receptor expression. In vitro experiments confirmed that these alterations conferred CDK4/6i resistance. Cancer cells cultured to resistance with CDK4/6i also acquired RB1, KRAS, AURKA, or CCNE2 alterations, which conferred sensitivity to AURKA, ERK, or CHEK1 inhibition. Three of these activating alterations-in AKT1, RAS, and AURKA-have not, to our knowledge, been previously demonstrated as mechanisms of resistance to CDK4/6i in breast cancer preclinically or in patient samples. Together, these eight mechanisms were present in 66% of resistant tumors profiled and may define therapeutic opportunities in patients. SIGNIFICANCE: We identified eight distinct mechanisms of resistance to CDK4/6i present in 66% of resistant tumors profiled. Most of these have a therapeutic strategy to overcome or prevent resistance in these tumors. Taken together, these findings have critical implications related to the potential utility of precision-based approaches to overcome resistance in many patients with HR⁺ metastatic breast cancer.This article is highlighted in the In This Issue feature, p. 1079.

Aurora A-Selective Inhibitor LY3295668 Leads to Dominant Mitotic Arrest, Apoptosis in Cancer Cells, and Shows Potent Preclinical Antitumor Efficacy

Although Aurora A, B, and C kinases share high sequence similarity, especially within the kinase domain, they function distinctly in cell-cycle progression. Aurora A depletion primarily leads to mitotic spindle formation defects and consequently prometaphase arrest, whereas Aurora B/C inactivation primarily induces polyploidy from cytokinesis failure. Aurora B/C inactivation phenotypes are also epistatic to those of Aurora A, such that the concomitant inactivation of Aurora A and B, or all Aurora isoforms by nonisoform-selective Aurora inhibitors, demonstrates the Aurora B/C-dominant cytokinesis failure and polyploidy phenotypes. Several Aurora inhibitors are in clinical trials for T/B-cell lymphoma, multiple myeloma, leukemia, lung, and breast cancers. Here, we describe an Aurora A-selective inhibitor, LY3295668, which potently inhibits Aurora autophosphorylation and its kinase activity in vitro and in vivo, persistently arrests cancer cells in mitosis, and induces more profound apoptosis than Aurora B or Aurora A/B dual inhibitors without Aurora B inhibition-associated cytokinesis failure and aneuploidy. LY3295668 inhibits the growth of a broad panel of cancer cell lines, including small-cell lung and breast cancer cells. It demonstrates significant efficacy in small-cell lung cancer xenograft and patient-derived tumor preclinical models as a single agent and in combination with standard-of-care agents. LY3295668, as a highly Aurora A-selective inhibitor, may represent a preferred approach to the current pan-Aurora inhibitors as a cancer therapeutic agent.

Aurora A Kinase Inhibition Is Synthetic Lethal with Loss of the RB1 Tumor Suppressor Gene

Loss-of-function mutations in the retinoblastoma gene RB1 are common in several treatment-refractory cancers such as small-cell lung cancer and triple-negative breast cancer. To identify drugs synthetic lethal with RB1 mutation (RB1 ^mut), we tested 36 cell-cycle inhibitors using a cancer cell panel profiling approach optimized to discern cytotoxic from cytostatic effects. Inhibitors of the Aurora kinases AURKA and AURKB showed the strongest RB1 association in this assay. LY3295668, an AURKA inhibitor with over 1,000-fold selectivity versus AURKB, is distinguished by minimal toxicity to bone marrow cells at concentrations active against RB1 ^mut cancer cells and leads to durable regression of RB1 ^mut tumor xenografts at exposures that are well tolerated in rodents. Genetic suppression screens identified enforcers of the spindle-assembly checkpoint (SAC) as essential for LY3295668 cytotoxicity in RB1-deficient cancers and suggest a model in which a primed SAC creates a unique dependency on AURKA for mitotic exit and survival. SIGNIFICANCE: The identification of a synthetic lethal interaction between RB1 and AURKA inhibition, and the discovery of a drug that can be dosed continuously to achieve uninterrupted inhibition of AURKA kinase activity without myelosuppression, suggest a new approach for the treatment of RB1-deficient malignancies, including patients progressing on CDK4/6 inhibitors.See related commentary by Dick and Li, p. 169.This article is highlighted in the In This Issue feature, p. 151.

Genomic Aberrations that Activate D-type Cyclins Are Associated with Enhanced Sensitivity to the CDK4 and CDK6 Inhibitor Abemaciclib

Most cancers preserve functional retinoblastoma (Rb) and may, therefore, respond to inhibition of D-cyclin-dependent Rb kinases, CDK4 and CDK6. To date, CDK4/6 inhibitors have shown promising clinical activity in breast cancer and lymphomas, but it is not clear which additional Rb-positive cancers might benefit from these agents. No systematic survey to compare relative sensitivities across tumor types and define molecular determinants of response has been described. We report a subset of cancers highly sensitive to CDK4/6 inhibition and characterized by various genomic aberrations known to elevate D-cyclin levels and describe a recurrent CCND1 3'UTR mutation associated with increased expression in endometrial cancer. The results suggest multiple additional classes of cancer that may benefit from CDK4/6-inhibiting drugs such as abemaciclib.

Effect of miR-29c and miR-129-5p on epithelial-mesenchymal transition in experimental biliary atresia mouse models

Biliary atresia (BA) is a destructive bile duct disease occurring in newborn children within a few weeks after birth. In this study, the effect of miR-29c and miR-129-5p on epithelial-mesenchymal transition (EMT) in experimental BA was explored by constructing BA mouse models via Rhesus rotavirus vaccine infection. miR-29c and miR-129-5p expression was analyzed by real-time quantitative polymerase chain reaction. EMT was established by induction with transforming growth factor (TGF)-β1. miR-29c and miR-129-5p were overexpressed and inhibited, respectively, by Lipofectamine transfection. EMT-related protein (formin-like 2, FMNL2; E-cadherin; vimentin; and cytokeratin-19, CK-19) expression was analyzed by western blot and immunofluorescent assay. The results indicated that miR-29c and miR-129-5p were downregulated and upregulated in BA mice. TGF-β1 induction caused a time-dependent decrease and increase in miR-29c and miR-129-5p, respectively. Additionally, TGF-β1 induced an increase in FMNL2 and vimentin expression and a decrease in E-cadherin and CK-19 expression (P < 0.05). Overexpression or suppression of miRNA-29c or miR-129-5p, respectively, induced the inhibition of FMNL2 and vimentin, and promotion of E-cadherin and CK-19 expression, in the test groups compared to the non-intervention group (P < 0.05). However, the FMNL2, vimentin, E-cadherin, and CK- 19 expression did not differ between the control and non-intervention groups (P > 0.05). Thus, miR-29c upregulation or miR-129-5p downregulation effectively prevented EMT in BA by regulating the expression of EMT pathway-related proteins. Therefore, miR-29c and miR-129-5p could be utilized as therapeutic targets for BA in the future.

Genomic alterations and molecular subtypes of gastric cancers in Asians

Gastric cancer (GC) is a highly heterogenic disease, and it is the second leading cause of cancer death in the world. Common chemotherapies are not very effective for GC, which often presents as an advanced or metastatic disease at diagnosis. Treatment options are limited, and the prognosis for advanced GCs is poor. The landscape of genomic alterations in GCs has recently been characterized by several international cancer genome programs, including studies that focused exclusively on GCs in Asians. These studies identified major recurrent driver mutations and provided new insights into the mutational heterogeneity and genetic profiles of GCs. An analysis of gene expression data by the Asian Cancer Research Group (ACRG) further uncovered four distinct molecular subtypes with well-defined clinical features and their intersections with actionable genetic alterations to which targeted therapeutic agents are either already available or under clinical development. In this article, we review the ACRG GC project. We also discuss the implications of the genetic and molecular findings from various GC genomic studies with respect to developing more precise diagnoses and treatment approaches for GCs.

Molecular analysis of gastric cancer identifies subtypes associated with distinct clinical outcomes

Gastric cancer, a leading cause of cancer-related deaths, is a heterogeneous disease. We aim to establish clinically relevant molecular subtypes that would encompass this heterogeneity and provide useful clinical information. We use gene expression data to describe four molecular subtypes linked to distinct patterns of molecular alterations, disease progression and prognosis. The mesenchymal-like type includes diffuse-subtype tumors with the worst prognosis, the tendency to occur at an earlier age and the highest recurrence frequency (63%) of the four subtypes. Microsatellite-unstable tumors are hyper-mutated intestinal-subtype tumors occurring in the antrum; these have the best overall prognosis and the lowest frequency of recurrence (22%) of the four subtypes. The tumor protein 53 (TP53)-active and TP53-inactive types include patients with intermediate prognosis and recurrence rates (with respect to the other two subtypes), with the TP53-active group showing better prognosis. We describe key molecular alterations in each of the four subtypes using targeted sequencing and genome-wide copy number microarrays. We validate these subtypes in independent cohorts in order to provide a consistent and unified framework for further clinical and preclinical translational research.

Genomic landscape and genetic heterogeneity in gastric adenocarcinoma revealed by whole-genome sequencing

Gastric cancer (GC) is the second most common cause of cancer-related deaths. It is known to be a heterogeneous disease with several molecular and histological subtypes. Here we perform whole-genome sequencing of 49 GCs with diffuse (N=31) and intestinal (N=18) histological subtypes and identify three mutational signatures, impacting TpT, CpG and TpCp[A/T] nucleotides. The diffuse-type GCs show significantly lower clonality and smaller numbers of somatic and structural variants compared with intestinal subtype. We further divide the diffuse subtype into one with infrequent genetic changes/low clonality and another with relatively higher clonality and mutations impacting TpT dinucleotide. Notably, we discover frequent and exclusive mutations in Ephrins and SLIT/ROBO signalling pathway genes. Overall, this study delivers new insights into the mutational heterogeneity underlying distinct histologic subtypes of GC that could have important implications for future research in the diagnosis and treatment of GC.

A novel CDK9 inhibitor shows potent antitumor efficacy in preclinical hematologic tumor models

DNA-dependent RNA polymerase II (RNAP II) largest subunit RPB1 C-terminal domain (CTD) kinases, including CDK9, are serine/threonine kinases known to regulate transcriptional initiation and elongation by phosphorylating Ser 2, 5, and 7 residues on CTD. Given the reported dysregulation of these kinases in some cancers, we asked whether inhibiting CDK9 may induce stress response and preferentially kill tumor cells. Herein, we describe a potent CDK9 inhibitor, LY2857785, that significantly reduces RNAP II CTD phosphorylation and dramatically decreases MCL1 protein levels to result in apoptosis in a variety of leukemia and solid tumor cell lines. This molecule inhibits the growth of a broad panel of cancer cell lines, and is particularly efficacious in leukemia cells, including orthotopic leukemia preclinical models as well as in ex vivo acute myeloid leukemia and chronic lymphocytic leukemia patient tumor samples. Thus, inhibition of CDK9 may represent an interesting approach as a cancer therapeutic target, especially in hematologic malignancies.

Characterization of LY2228820 dimesylate, a potent and selective inhibitor of p38 MAPK with antitumor activity

p38α mitogen-activated protein kinase (MAPK) is activated in cancer cells in response to environmental factors, oncogenic stress, radiation, and chemotherapy. p38α MAPK phosphorylates a number of substrates, including MAPKAP-K2 (MK2), and regulates the production of cytokines in the tumor microenvironment, such as TNF-α, interleukin-1β (IL-1β), IL-6, and CXCL8 (IL-8). p38α MAPK is highly expressed in human cancers and may play a role in tumor growth, invasion, metastasis, and drug resistance. LY2228820 dimesylate (hereafter LY2228820), a trisubstituted imidazole derivative, is a potent and selective, ATP-competitive inhibitor of the α- and β-isoforms of p38 MAPK in vitro (IC(50) = 5.3 and 3.2 nmol/L, respectively). In cell-based assays, LY2228820 potently and selectively inhibited phosphorylation of MK2 (Thr334) in anisomycin-stimulated HeLa cells (at 9.8 nmol/L by Western blot analysis) and anisomycin-induced mouse RAW264.7 macrophages (IC(50) = 35.3 nmol/L) with no changes in phosphorylation of p38α MAPK, JNK, ERK1/2, c-Jun, ATF2, or c-Myc ≤ 10 μmol/L. LY2228820 also reduced TNF-α secretion by lipopolysaccharide/IFN-γ-stimulated macrophages (IC(50) = 6.3 nmol/L). In mice transplanted with B16-F10 melanoma, tumor phospho-MK2 (p-MK2) was inhibited by LY2228820 in a dose-dependent manner [threshold effective dose (TED)(70) = 11.2 mg/kg]. Significant target inhibition (>40% reduction in p-MK2) was maintained for 4 to 8 hours following a single 10 mg/kg oral dose. LY2228820 produced significant tumor growth delay in multiple in vivo cancer models (melanoma, non-small cell lung cancer, ovarian, glioma, myeloma, breast). In summary, LY2228820 is a p38 MAPK inhibitor, which has been optimized for potency, selectivity, drug-like properties (such as oral bioavailability), and efficacy in animal models of human cancer.

Abstract B229: TBKI kinase inhibition blocks RANTES secretion and exhibits minimal tumor growth inhibition in oncogenic Ras-driven tumor models

TANK-binding kinase 1 (TBK1) is a non-canonical IKK family member and plays a critical role in innate immunity by modulating cytokine production, interferon, and NF-kB signaling. It is recently reported that TBK1 directly engages Akt survival signaling to support oncogenic Ras-driven transformation. TBK1 is also identified as a synthetic lethal partner in KRas mutant NSCLC through systematic RNA interference. In this study, we have characterized LSN3090729, a 4-aryl-2-aminopyrimidine derivative as a selective TBK1 kinase inhibitor. Biochemical and cellular analyses demonstrate that LSN3090729 is a potent TBK1 kinase inhibitor, and selectively inhibits TBK1 based on in vitro activities in biochemical assays developed with a panel of protein kinases. In Panc-1, a pancreatic tumor cell line with KRas mutation, LSN3090729 inhibits EGF-induced phosphorylation of AKT at both Thr308 and Ser473 sites. Pharmacokinetic analysis shows that LSN3090729 has an over 70% of oral bioavailability with an acceptable half life in rodents. In a mouse pharmacology model, LSN3090729 blocks LPS-induced RANTES secretion in a dose-dependent manner with 67%, 79%, and 90% inhibition at 10, 30, and 100 mg/kg, respectively. LSN3090729 is assessed for its anti-proliferation activities in vitro in a panel of tumor cells with KRas mutation or other genetic background. The sensitivity of these tumor cells to LSN3090729 in two dimensional proliferation or three dimensional soft agar growth assays appears not correlated with status of KRas mutation. In xenograft models of HCT116 and Panc-1, both with a KRas mutation, treatment of LSN3090729 exhibits minimal anti-tumor growth activities, suggesting that a combination approach might be required for TBK1 kinase inhibition to be effective in cancer settings.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B229.

Citation Format: Robert Van Horn, Tinggui Yin, Xiaoyi Zhang, Chunping Yu, Youyan Zhang, Xue-Qian Gong, Sean Buchanan, Xiang S. Ye, William McMillen, David Barda, Sheng-Bin Peng. TBKI kinase inhibition blocks RANTES secretion and exhibits minimal tumor growth inhibition in oncogenic Ras-driven tumor models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B229.

Abstract A104: A screening method for the identification of potentially effective drug-drug combinations reveals a synergistic interaction between Aurora-A inhibitor MK-5108 and Bcl-xL inhibitor navitoclax

Recent developments in understanding the molecular mechanisms of cancer, coupled with large genomic datasets that detail the heterogeneity of the disease, have together led to a wealth of new cancer targets and therapeutic options. However, the restricted efficacy of these new agents and the emergence of resistance suggest that broader and more durable responses may be achieved through combination of these new drugs. To identify drug-drug combinations that may be effective in particular tumor types, we have developed an unbiased "synthetic lethal" screening approach to survey combination space across a diverse panel of tumor cell lines. We used this approach to test a panel of targeted drugs in all-versus-all fashion across 63 cell lines. Synergistic interactions were observed with the combination of an Aurora-A inhibitor, MK-5108, with navitoclax, an inhibitor of Bcl-2 family survival proteins. This combination, which was synergistic in a subset of the tumor cells, was further examined to identify the molecular determinants of synergy. Several features emerged from this analysis including the observation that Bcl-xL expression levels predict resistance to the single agent Aurora-A inhibitor and to synergy of combined MK-5108 and navitoclax.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A104.

Citation Format: Xueqian Gong, Shaoling Jin, Farhana Merzoug, Xiang S. Ye, MaryJo Lallena, Jian Du, Yue Webster, Xiwen Ma, Christoph Reinhard, Phillip Iversen, Sean G. Buchanan. A screening method for the identification of potentially effective drug-drug combinations reveals a synergistic interaction between Aurora-A inhibitor MK-5108 and Bcl-xL inhibitor navitoclax. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A104.

Targets of checkpoints controlling mitosis: lessons from lower eukaryotes

Prevention of mitosis if DNA is damaged, or not fully replicated, is a widespread mechanism used by eukaryotic cells to maintain their ploidy and prevent accumulation of mutations. Such 'checkpoints' must inhibit mitotic regulators to prevent mitotic progression when DNA is not ready for segregation. The mitotic regulators targeted for negative regulation by these checkpoints differ among cell types, but two conserved targets have emerged, the anaphase-promoting complex (APC) and tyrosine phosphorylation of p34(cdc2). One potential downstream target of both these regulators has also been identified, the mitosis-promoting NIMA kinase.

Abstract A47: Circulating tumor cell (CTC) assay development for detection of phosphohistone H3 (pHH3) as a clinical pharmacodynamic (PD) marker for LY2523355, an Eg5 kinesin inhibitor

Circulating tumor cells have been shown to be prognostic of survival in metastatic breast, colon, and prostate cancers. Additionally, CTCs are of interest because they may be representative of the phenotype/genotype of the primary and metastatic tumors, and may be a useful tool (i.e. patient stratification) for drug development. CTCs, as “liquid biopsies” are potentially useful as a PD marker as it allows easy repeat sampling before and after drug treatment. We describe the development of a CTC assay that measures the induction of pHH3 by LY2523355, a selective small molecule inhibitor of the human Eg5 kinesin. pHH3 is a biomarker of mitosis. In tumor xenograft mouse models, LY2523355 treatment was shown to reduce tumor volume with elevation of pHH3 in tumors. The CTC assay was developed using the FDA cleared Veridex/CellSearch™ instrument and reagents for enumeration of CTCs from blood. CellSearch defines CTCs as EpCam+/DAPI+/CK 8, 18, 19+/CD45−. For assay development, cells from tumor cell lines representing major solid tumor types were chosen, cultured, treated with LY2523355, or with various standard-of-care chemotherapeutics, and spiked into whole blood drawn into CellSave™ (preservative+EDTA). For initial assay development, mouse whole blood was used and results reproduced subsequently with human whole blood from healthy subjects. The spiked tumor cells in blood samples were recovered using the CellSearch Mouse/Rat CTC kit (for mouse blood) or human CXC kit (for human blood), supplemented with the R-PE conjugated anti-pHH3 antibody. pHH3 in the recovered tumor cells was detected in the open/fourth channel on the CellSearch instrument. About 1–4% of all cultured tumor cells were positive for pHH3 without drug treatment. Significant induction of pHH3 (30–50% cells) in sensitive tumor cell lines was observed with 24 hour treatment with only drugs interfering with mitosis (paclitaxel, taxotere, and LY2523355). The magnitude of the induction of pHH3 in the cells after treatment was dose and cell-line dependent. A dose response of pHH3 induction was observed with 0.5nM-25nM of LY2523355 with several cultured tumor cell lines (Colo205, HCT116, H441, SKBR3, MDA-MB-468), spiked into blood, and assayed using CellSearch. The concentrations of the dose response are similar to the drug exposure levels of that of preclinical tumor xenograft studies. LY2523355 is currently in early phase clinical development, and monitoring CTCs with pHH3 expression post-treatment may be a useful PD marker.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A47.

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 G(2)/M transition. We find that activation of Aurora A first occurs at centrosomes at late G(2) 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.

Discovery of cercosporamide, a known antifungal natural product, as a selective Pkc1 kinase inhibitor through high-throughput screening

The Pkc1-mediated cell wall integrity-signaling pathway is highly conserved in fungi and is essential for fungal growth. We thus explored the potential of targeting the Pkc1 protein kinase for developing broad-spectrum fungicidal antifungal drugs through a Candida albicans Pkc1-based high-throughput screening. We discovered that cercosporamide, a broad-spectrum natural antifungal compound, but previously with an unknown mode of action, is actually a selective and highly potent fungal Pkc1 kinase inhibitor. This finding provides a molecular explanation for previous observations in which Saccharomyces cerevisiae cell wall mutants were found to be highly sensitive to cercosporamide. Indeed, S. cerevisiae mutant cells with reduced Pkc1 kinase activity become hypersensitive to cercosporamide, and this sensitivity can be suppressed under high-osmotic growth conditions. Together, the results demonstrate that cercosporamide acts selectively on Pkc1 kinase and, thus, they provide a molecular mechanism for its antifungal activity. Furthermore, cercosporamide and a beta-1,3-glucan synthase inhibitor echinocandin analog, by targeting two different key components of the cell wall biosynthesis pathway, are highly synergistic in their antifungal activities. The synergistic antifungal activity between Pkc1 kinase and beta-1,3-glucan synthase inhibitors points to a potential highly effective combination therapy to treat fungal infections.

Induction of apoptosis by sphingoid long-chain bases in Aspergillus nidulans

Sphingolipid metabolism is implicated to play an important role in apoptosis. Here we show that dihydrosphingosine (DHS) and phytosphingosine (PHS), two major sphingoid bases of fungi, have potent fungicidal activity with remarkably high structural and stereochemical specificity against Aspergillus nidulans. In fact, only naturally occurring DHS and PHS are active. Further analysis revealed that DHS and PHS induce rapid DNA condensation independent of mitosis, large-scale DNA fragmentation, and exposure of phosphatidylserine, all common morphological features characteristic of apoptosis, suggesting that DHS and PHS induce apoptosis in A. nidulans. The finding that DNA fragmentation requires protein synthesis, which implies that an active process is involved, further supports this proposition. The induction of apoptosis by DHS and PHS is associated with the rapid accumulation of reactive oxygen species (ROS). However, ROS are not required for apoptosis induced by DHS and PHS, as scavenging of ROS by a free radical spin trap has no effect. We further demonstrate that apoptosis induced by DHS and PHS is independent of metacaspase function but requires mitochondrial function. Together, the results suggest that DHS and PHS induce a type of apoptosis in A. nidulans most similar to the caspase-independent apoptosis observed in mammalian systems. As A. nidulans is genetically tractable, this organism should be an ideal model system for dissecting sphingolipid signaling in apoptosis and, importantly, for further elucidating the molecular basis of caspase-independent apoptosis.

Cell cycle progression and cell polarity require sphingolipid biosynthesis in Aspergillus nidulans

Sphingolipids are major components of the plasma membrane of eukaryotic cells and were once thought of merely as structural components of the membrane. We have investigated effects of inhibiting sphingolipid biosynthesis, both in germinating spores and growing hyphae of Aspergillus nidulans. In germinating spores, genetic or pharmacological inactivation of inositol phosphorylceramide (IPC) synthase arrests the cell cycle in G(1) and also prevents polarized growth during spore germination. However, inactivation of IPC synthase not only eliminates sphingolipid biosynthesis but also leads to a marked accumulation of ceramide, its upstream intermediate. We therefore inactivated serine palmitoyltransferase, the first enzyme in the sphingolipid biosynthesis pathway, to determine effects of inhibiting sphingolipid biosynthesis without an accumulation of ceramide. This inactivation also prevented polarized growth but did not affect nuclear division of germinating spores. To see if sphingolipid biosynthesis is required to maintain polarized growth, and not just to establish polarity, we inhibited sphingolipid biosynthesis in cells in which polarity was already established. This inhibition rapidly abolished normal cell polarity and promoted cell tip branching, which normally never occurs. Cell tip branching was closely associated with dramatic changes in the normally highly polarized actin cytoskeleton and found to be dependent on actin function. The results indicate that sphingolipids are essential for the establishment and maintenance of cell polarity via control of the actin cytoskeleton and that accumulation of ceramide is likely responsible for arresting the cell cycle in G(1).

Anomeric reactivity-based one-pot oligosaccharide synthesis: a rapid route to oligosaccharide libraries

The assembly of an oligosaccharide library has been achieved in a practical and efficient manner employing a' one-pot sequential approach. With the help of the anomeric reactivity values of thioglycosides, using a thioglycoside (mono- or disaccharide) with one free hydroxyl group as acceptor and donor coupled with another fully protected thioglycoside, a di- or trisaccharide is selectively formed without self-condensation and subsequently reacted in situ with an anomerically inactive glycoside (mono- or disaccharide) to form a tri- or tetrasaccharide in high overall yield. The approach enables the rapid assembly of 33 linear or branched fully protected oligosaccharides using designed building blocks. These fully protected oligosaccharides have been partially or completely deprotected to create 29 more structures to further increase the diversity of the library.

Interaction between developmental and cell cycle regulators is required for morphogenesis in Aspergillus nidulans

In Aspergillus nidulans, mutation of the transcriptional regulator brlA arrests formation of asexual spore-forming structures called conidiophores but does not hinder vegetative hyphal growth. During conidiophore development a 6-fold, brlA-dependent increase in the kinase activities of NIMX(cdc2) and NIMA occurs. A similar level of kinase induction was promoted by ectopic expression of brlA. Northern and Western analysis revealed marked induction of nimX(cdc2) mRNA after ectopic expression of brlA and increased amounts of NIMX(cdc2). Therefore, nimX(cdc2) is developmentally regulated by brlA indicating a direct role for brlA in the regulation of cell cycle genes. That correct regulation of nimX(cdc2) is important for normal development was further supported by analysis of conidiophore development and septation in cell cycle specific mutants. Most noticeably, the nimX(cdc2AF) mutation promoted inappropriate septation and hindered the switch from filamentous growth to budding growth seen during conidiophore development. Therefore, in contrast to the situation previously reported for other multicellular eukaryotes, interaction between developmental regulators and cell cycle regulators is essential for normal morphogenesis in A.nidulans.

Checkpoint defects leading to premature mitosis also cause endoreplication of DNA in Aspergillus nidulans

The G2 DNA damage and slowing of S-phase checkpoints over mitosis function through tyrosine phosphorylation of NIMX(cdc2) in Aspergillus nidulans. We demonstrate that breaking these checkpoints leads to a defective premature mitosis followed by dramatic rereplication of genomic DNA. Two additional checkpoint functions, uvsB and uvsD, also cause the rereplication phenotype after their mutation allows premature mitosis in the presence of low concentrations of hydroxyurea. uvsB is shown to encode a rad3/ATR homologue, whereas uvsD displays homology to rad26, which has only previously been identified in Schizosaccharomyces pombe. uvsB(rad3) and uvsD(rad26) have G2 checkpoint functions over mitosis and another function essential for surviving DNA damage. The rereplication phenotype is accompanied by lack of NIME(cyclinB), but ectopic expression of active nondegradable NIME(cyclinB) does not arrest DNA rereplication. DNA rereplication can also be induced in cells that enter mitosis prematurely because of lack of tyrosine phosphorylation of NIMX(cdc2) and impaired anaphase-promoting complex function. The data demonstrate that lack of checkpoint control over mitosis can secondarily cause defects in the checkpoint system that prevents DNA rereplication in the absence of mitosis. This defines a new mechanism by which endoreplication of DNA can be triggered and maintained in eukaryotic cells.

Regulation of the anaphase-promoting complex/cyclosome by bimAAPC3 and proteolysis of NIMA

Surprisingly, although highly temperature-sensitive, the bimA1(APC3) anaphase-promoting complex/cyclosome (APC/C) mutation does not cause arrest of mitotic exit. Instead, rapid inactivation of bimA1(APC3) is shown to promote repeating oscillations of chromosome condensation and decondensation, activation and inactivation of NIMA and p34(cdc2) kinases, and accumulation and degradation of NIMA, which all coordinately cycle multiple times without causing nuclear division. These bimA1(APC3)-induced cell cycle oscillations require active NIMA, because a nimA5 + bimA1(APC3) double mutant arrests in a mitotic state with very high p34(cdc2) H1 kinase activity. NIMA protein instability during S phase and G2 was also found to be controlled by the APC/C. The bimA1(APC3) mutation therefore first inactivates the APC/C but then allows its activation in a cyclic manner; these cycles depend on NIMA. We hypothesize that bimAAPC3 could be part of a cell cycle clock mechanism that is reset after inactivation of bimA1(APC3). The bimA1(APC3) mutation may also make the APC/C resistant to activation by mitotic substrates of the APC/C, such as cyclin B, Polo, and NIMA, causing mitotic delay. Once these regulators accumulate, they activate the APC/C, and cells exit from mitosis, which then allows this cycle to repeat. The data indicate that bimAAPC3 regulates the APC/C in a NIMA-dependent manner.

Regulation of p34cdc2/cyclinB H1 and NIMA kinases during the G2/M transition and checkpoint responses in Aspergillus nidulans

In A. nidulans, activation of both p34cdc2/cyclinB H1 and NIMA kinases is required to initiate mitosis. These two kinases are regulated at several levels during interphase and are activated independently as protein kinases during G2. They are also targeted for negative regulation, to prevent mitosis by mitotic entry checkpoint controls, when DNA is not replicated or is damaged. Then, to initiate mitosis, they promote each other's mitotic functions to coordinately promote mitosis upon completion of interphase events. In addition, inactivation of both kinases by mitotic specific proteolysis is also required for progression through mitosis into G1.

Proteolysis and tyrosine phosphorylation of p34cdc2/cyclin B. The role of MCM2 and initiation of DNA replication to allow tyrosine phosphorylation of p34cdc2

Previously, it has been shown that Aspergillus cells lacking the function of nimQ and the anaphase-promoting complex (APC) component bimEAPC1 enter mitosis without replicating DNA. Here nimQ is shown to encode an MCM2 homologue. Although mutation of nimQMCM2 inhibits initiation of DNA replication, a few cells do enter mitosis. Cells arrested at G1/S by lack of nimQMCM2 contain p34(cdc2)/cyclin B, but p34(cdc2) remains tyrosine dephosphorylated, even after DNA damage. However, arrest of DNA replication using hydroxyurea followed by inactivation of nimQMCM2 and bimEAPC1 does not abrogate the S phase arrest checkpoint over mitosis. nimQMCM2, likely via initiation of DNA replication, is therefore required to trigger tyrosine phosphorylation of p34(cdc2) during the G1 to S transition, which may occur by inactivation of nimTcdc25. Cells lacking both nimQMCM2 and bimEAPC1 are deficient in the S phase arrest checkpoint over mitosis because they lack both tyrosine phosphorylation of p34(cdc2) and the function of bimEAPC1. Initiation of DNA replication, which requires nimQMCM2, is apparently critical to switch mitotic regulation from the APC to include tyrosine phosphorylation of p34(cdc2) at G1/S. We also show that cells arrested at G1/S due to lack of nimQMCM2 continue to replicate spindle pole bodies in the absence of DNA replication and can undergo anaphase in the absence of APC function.

The G2/M DNA damage checkpoint inhibits mitosis through Tyr15 phosphorylation of p34cdc2 in Aspergillus nidulans

It is possible to cause G2 arrest in Aspergillus nidulans by inactivating either p34cdc2 or NIMA. We therefore investigated the negative control of these two mitosis-promoting kinases after DNA damage. DNA damage caused rapid Tyr15 phosphorylation of p34cdc2 and transient cell cycle arrest but had little effect on the activity of NIMA. Dividing cells deficient in Tyr15 phosphorylation of p34cdc2 were sensitive to both MMS and UV irradiation and entered lethal premature mitosis with damaged DNA. However, non-dividing quiescent conidiospores of the Tyr15 mutant strain were not sensitive to DNA damage. The UV and MMS sensitivity of cells unable to tyrosine phosphorylate p34cdc2 is therefore caused by defects in DNA damage checkpoint regulation over mitosis. Both the nimA5 and nimT23 temperature-sensitive mutations cause an arrest in G2 at 42 degrees C. Addition of MMS to nimT23 G2-arrested cells caused a marked delay in their entry into mitosis upon downshift to 32 degrees C and this delay was correlated with a long delay in the dephosphorylation and activation of p34cdc2. Addition of MMS to nimA5 G2-arrested cells caused inactivation of the H1 kinase activity of p34cdc2 due to an increase in its Tyr15 phosphorylation level and delayed entry into mitosis upon return to 32 degrees C. However, if Tyr15 phosphorylation of p34cdc2 was prevented then its H1 kinase activity was not inactivated upon MMS addition to nimA5 G2-arrested cells and they rapidly progressed into a lethal mitosis upon release to 32 degrees C. Thus, Tyr15 phosphorylation of p34cdc2 in G2 arrests initiation of mitosis after DNA damage in A. nidulans.

Cell cycle regulation in Aspergillus by two protein kinases

Great progress has recently been made in our understanding of the regulation of the eukaryotic cell cycle, and the central role of cyclin-dependent kinases is now clear. In Aspergillus nidulans it has been established that a second class of cell-cycle-regulated protein kinases, typified by NIMA (encoded by the nimA gene), is also required for cell cycle progression into mitosis. Indeed, both p34cdc2/cyclin B and NIMA have to be correctly activated before mitosis can be initiated in this species, and p34cdc2/cyclin B plays a role in the mitosis-specific activation of NIMA. In addition, both kinases have to be proteolytically destroyed before mitosis can be completed. NIMA-related kinases may also regulate the cell cycle in other eukaryotes, as expression of NIMA can promote mitotic events in yeast, frog or human cells. Moreover, dominant-negative versions of NIMA can adversely affect the progression of human cells into mitosis, as they do in A. nidulans. The ability of NIMA to influence mitotic regulation in human and frog cells strongly suggests the existence of a NIMA pathway of mitotic regulation in higher eukaryotes. A growing number of NIMA-related kinases have been isolated from organisms ranging from fungi to humans, and some of these kinases are also cell-cycle-regulated. How NIMA-related kinases and cyclin-dependent kinases act in concert to promote cell cycle transitions is just beginning to be understood. This understanding is the key to a full knowledge of cell cycle regulation.

Two S-phase checkpoint systems, one involving the function of both BIME and Tyr15 phosphorylation of p34cdc2, inhibit NIMA and prevent premature mitosis

We demonstrate that there are at least two S-phase checkpoint mechanisms controlling mitosis in Aspergillus. The first responds to the rate of DNA replication and inhibits mitosis via tyrosine phosphorylation of p34cdc2. Cells unable to tyrosine phosphorylate p34cdc2 are therefore viable but are unable to tolerate low levels of hydroxyurea and prematurely enter lethal mitosis when S-phase is slowed. However, if the NIMA mitosis-promoting kinase is inactivated then non-tyrosine-phosphorylated p34cdc2 cannot promote cells prematurely into mitosis. Lack of tyrosine-phosphorylated p34cdc2 also cannot promote mitosis, or lethality, if DNA replication is arrested, demonstrating the presence of a second S-phase checkpoint mechanism over mitotic initiation which we show involves the function of BIME. In order to overcome the S-phase arrest checkpoint over mitosis it is necessary both to prevent tyrosine phosphorylation of p34cdc2 and also to inactivate BIME. Lack of tyrosine phosphorylation of p34cdc2 allows precocious expression of NIMA during S-phase arrest, and lack of BIME then allows activation of this prematurely expressed NIMA by phosphorylation. The mitosis-promoting NIMA kinase is thus a target for S-phase checkpoint controls.

Analysis of cell cycle regulation usingAspergillus nidulans

Aspergillus nidulans has proved to be an excellent model system to help unravel the genetic and biochemical control systems that regulate the cell cycle. Many genes that specifically affect progression through G2 into mitosis have been isolated. Study of these genes has helped to formulate concepts about how the cell cycle is regulated. The existence of regulatory networks involving protein phosphorylation and dephosphorylation has been realized, and how the kinases and phosphatases of these networks ensure correct order and timing through the cell cycle is beginning to be understood. Our studies indicate that activation of two protein kinases is essential for progression into mitosis. One, the universal p34cdc2H1 kinase, has been well studied in many systems and is considered the key activator of mitotic initiation. However, in the absence of the NIMA protein kinase p34cdc2cannot promote mitosis. How these two mitotic kinases interact is therefore of great importance to our understanding of cell cycle regulation. The contribution of studies using A. nidulans to the formulation of concepts about how the cell cycle is regulated is the topic of this paper. Key words: Aspergillus nidulans, cell cycle regulation, protein kinase, NIMA, p34cdc2, cyclinB, Cdc25.

Isolation of a functional homolog of the cell cycle-specific NIMA protein kinase of Aspergillus nidulans and functional analysis of conserved residues

To investigate the degree of conservation of the cell cycle-specific NIMA protein kinase of Aspergillus nidulans, and to help direct its functional analysis, we cloned a homolog (designated nim-1) from Neurospora crassa. Over the catalytic domain NIM-1 is 75% identical to NIMA, but overall the identity drops to 52%. nim-1 was able to functionally complement nimA5 in A. nidulans. Mutational analysis of potential activating phosphorylation sites found in NIMA, NIM-1, and related protein kinases was performed on NIMA. Mutation of threonine 199 (conserved in all NIMA-related kinases) inhibited NIMA beta-casein kinase activity and abolished its in vivo function. This site conforms to a minimal consensus phosphorylation site for NIMA (FXXT) and is analogous to the autophosphorylation site of cyclic-AMP-dependent protein kinases. However, mutation of a unique cysteine residue found only in the catalytic site of NIMA and NIM-1 had no effect on NIMA kinase activity or function. Three temperature-sensitive alleles of nimA that cause arrest in G2 were sequenced and shown to generate three different amino acid substitutions. None of the mutations prevented accumulation of NIMA protein during G2 arrest, but all prevented the p34cdc2/cyclin B-dependent phosphorylation of NIMA normally seen during mitotic initiation even though p34cdc2/cyclin B H1 kinase activity was fully activated.

The NIMA protein kinase is hyperphosphorylated and activated downstream of p34cdc2/cyclin B: coordination of two mitosis promoting kinases

Initiation of mitosis in Aspergillus nidulans requires activation of two protein kinases, p34cdc2/cyclin B and NIMA. Forced expression of NIMA, even when p34cdc2 was inactivated, promoted chromatin condensation. NIMA may therefore directly cause mitotic chromosome condensation. However, the mitosis-promoting function of NIMA is normally under control of p34cdc2/cyclin B as the active G2 form of NIMA is hyperphosphorylated and further activated by p34cdc2/cyclin B when cells initiate mitosis. To see the p34cdc2/cyclin B dependent activation of NIMA, okadaic acid had to be added to isolation buffers to prevent dephosphorylation of NIMA during isolation. Hyperphosphorylated NIMA contained the MPM-2 epitope and, in vitro, phosphorylation of NIMA by p34cdc2/cyclin B generated the MPM-2 epitope, suggesting that NIMA is phosphorylated directly by p34cdc2/cyclin B during mitotic initiation. These two kinases, which are both essential for mitotic initiation, are therefore independently activated as protein kinases during G2. Then, to initiate mitosis, we suggest that each activates the other's mitosis-promoting functions. This ensures that cells coordinately activate p34cdc2/cyclin B and NIMA to initiate mitosis only upon completion of all interphase events. Finally, we show that NIMA is regulated through the cell cycle like cyclin B, as it accumulates during G2 and is degraded only when cells traverse mitosis.

Direct detection of beta-1,3-glucanase isozymes on polyacrylamide electrophoresis and isoelectrofocusing gels

A procedure to assay isozymes of beta-1,3-glucanase directly on polyacrylamide gel electrophoresis (PAGE) and isoelectrofocusing (IEF) gels by using 2,3,5-triphenyltetrazolium chloride is described. The reagent reacts with reducing sugars released by beta-1,3-glucanases from the substrate laminarin. Acidic and neutral isozymes of beta-1,3-glucanase were detected and quantified on 17.5% native PAGE gels run with an anodic buffer system. A significant linear relationship (alpha = less than 0.01, R = 0.991) was observed between amounts of beta-1,3-glucanase loaded and intensity of bands stained with the reagent on native PAGE gels. A full isozyme pattern was obtained on 7.5% IEF gels with a pH range of 3.5-9.5. The IEF gels were heated in a microwave oven during the staining process to minimize diffusion.