Structural insights into the gating of DNA passage by the topoisomerase II DNA-gate.

Type IIA topoisomerases (Top2s) manipulate the handedness of DNA crossovers by introducing a transient and protein-linked double-strand break in one DNA duplex, termed the DNA-gate, whose opening allows another DNA segment to be transported through to change the DNA topology. Despite the central importance of this gate-opening event to Top2 function, the DNA-gate in all reported structures of Top2-DNA complexes is in the closed state. Here we present the crystal structure of a human Top2 DNA-gate in an open conformation, which not only reveals structural characteristics of its DNA-conducting path, but also uncovers unexpected yet functionally significant conformational changes associated with gate-opening. This structure further implicates Top2's preference for a left-handed DNA braid and allows the construction of a model representing the initial entry of another DNA duplex into the DNA-gate. Steered molecular dynamics calculations suggests the Top2-catalyzed DNA passage may be achieved by a rocker-switch-type movement of the DNA-gate

Structural Basis of Type Ii Topoisomerase Inhibition by the Anticancer Drug Etoposide

Type II topoisomerases (TOP2s) resolve the topological problems of DNA by transiently cleaving both strands of a DNA duplex to form a cleavage complex through which another DNA segment can be transported. Several widely prescribed anticancer drugs increase the population of TOP2 cleavage complex, which leads to TOP2-mediated chromosome DNA breakage and death of cancer cells. We present the crystal structure of a large fragment of human TOP2 complexed to DNA and to the anticancer drug etoposide to reveal structural details of drug-induced stabilization of a cleavage complex. The interplay between the protein, the DNA , and the drug explains the structure-activity relations of etoposide derivatives and the molecular basis of drug- resistant mutations. The analysis of protein-drug interactions provides information applicable for developing an isoform-specific TOP2-targeting strategy

On the structural basis and design guidelines for type II topoisomerase-targeting anticancer drugs

ABSTRACT Type II topoisomerases (Top2s) alter DNA topology via the formation of an enzyme-DNA adduct termed cleavage complex, which harbors a transient double-strand break in one DNA to allow the passage of another. Agents targeting human Top2s are clinically active anticancer drugs whose trapping of Top2-mediated DNA breakage effectively induces genome fragmentation and cell death. To understand the structural basis of this drug action, we previously determined the structure of human Top2 b-isoform forming a cleavage complex with the drug etoposide and DNA, and described the insertion of drug into DNA cleavage site and drug-induced decoupling of catalytic groups. By developing a post-crystallization drug replacement procedure that simplifies structural characterization of drug-stabilized cleavage complexes, we have extended the analysis toward other structurally distinct drugs, m-AMSA and mitoxantrone. Besides the expected drug intercalation, a switch in ribose puckering in the 3 0 -nucleotide of the cleavage site was robustly observed in the new structures, representing a new mechanism for trapping the Top2 cleavage complex. Analysis of drug-binding modes and the conformational landscapes of the drug-binding pockets provide rationalization of the drugs' structural-activity relationships and explain why Top2 mutants exhibit differential effects toward each drug. Drug design guidelines were proposed to facilitate the development of isoform-specific Top2-targeting anticancer agents

Primary Small Cell Carcinoma of the Stomach Successfully Treated With Cisplatin and Etoposide

We report a 44-year-old man with primary gastric small cell carcinoma who showed a remarkable response to chemotherapy specific for pulmonary small cell carcinoma. The patient had been admitted to another local hospital because of intermittent epigastralgia. An upper gastrointestinal examination there revealed an ulcerative tumor, 5 cm in diameter, on the lesser curvature side of the cardia, and endoscopic biopsy reported adenocarcinoma. Computed tomography revealed a mass over the lesser curvature of the stomach and some enlarged regional lymph nodes. Radical total gastrectomy, lymph node dissection, Roux-en-Y esophagojejunostomy and splenectomy were performed at our hospital. Pathology revealed gastric mucosa infiltrated by small-sized tumor cells with scanty cytoplasm and hyperchromatic nuclei. Immunohisto- chemically, the tumor cells were positive for synaptophysin, chromogranin A, and CD56. Primary gastric small cell carcinoma was diagnosed. The postoperative course, complicated by shock due to bleeding, wound infection and intra-abdominal abscess, took more than 2 months to resolve. Follow-up computed tomography showed tumor recurrence with multiple enlarged lymph nodes in the aortocaval region and hepatic hilum. The patient received palliative chemotherapy consisting of cisplatin 80 mg/m2 on day 1 and etoposide 80 mg/m2 on days 1–3 every 28 days, and had partial response to the chemotherapy, with a progression-free survival of 10 months. Chemotherapy with cisplatin and etoposide used for small cell carcinoma of the lung is a good treatment for gastric small cell carcinoma

Polymorphisms of the RET Gene in Hirschsprung Disease, Anorectal Malformation and Intestinal Pseudo-obstruction in Taiwan

Mutations in the receptor tyrosine kinase RET gene are associated with Hirschsprung disease (HD), which is also known as congenital intestinal aganglionosis. We found an association with specific alleles in five single nucleotide polymorphism (SNP) sites of the RET gene in our HD patients. Methods: We compared the association of specific RET SNP alleles in patients with severe GI disorders such as anorectal malformation (ARM) or pediatric intestinal pseudo-obstruction (IPO) to that in HD patients. Sixty-four HD, 23 ARM and 35 IPO patients were included. Genomic DNA extracted from blood samples was analyzed by polymerase chain reaction and DNA sequencing analysis. Results: The allele distributions of all five RET SNPs in the HD patients deviated from those in the normal population (p < 0.05), whereas those of the ARM patients did not. The allele distributions of these RET SNPs in the IPO patients were all significantly different from those in the HD patients. Allele distributions of exon 2 and 13 in the IPO patients were also significantly different from those of the normal population. The frequencies of all the HD-predominant alleles were lower in the HD patients than the normal population, and were even lower in the IPO patients. Conclusion: This study strengthens the association of specific RET SNP alleles with typical HD in Taiwan

Structural insights into the gating of DNA passage by the topoisomerase II DNA-gate.

Type IIA topoisomerases (Top2s) manipulate the handedness of DNA crossovers by introducing a transient and protein-linked double-strand break in one DNA duplex, termed the DNA-gate, whose opening allows another DNA segment to be transported through to change the DNA topology. Despite the central importance of this gate-opening event to Top2 function, the DNA-gate in all reported structures of Top2-DNA complexes is in the closed state. Here we present the crystal structure of a human Top2 DNA-gate in an open conformation, which not only reveals structural characteristics of its DNA-conducting path, but also uncovers unexpected yet functionally significant conformational changes associated with gate-opening. This structure further implicates Top2's preference for a left-handed DNA braid and allows the construction of a model representing the initial entry of another DNA duplex into the DNA-gate. Steered molecular dynamics calculations suggests the Top2-catalyzed DNA passage may be achieved by a rocker-switch-type movement of the DNA-gate

Application of simulation-based CYP26 SNP-environment barcodes for evaluating the occurrence of oral malignant disorders by odds ratio-based binary particle swarm optimization: A case-control study in the Taiwanese population.

IntroductionGenetic polymorphisms and social factors (alcohol consumption, betel quid (BQ) usage, and cigarette consumption), both separately or jointly, play a crucial role in the occurrence of oral malignant disorders such as oral and pharyngeal cancers and oral potentially malignant disorders (OPMD).Material and methodsSimultaneous analyses of multiple single nucleotide polymorphisms (SNPs) and environmental effects on oral malignant disorders are essential to examine, albeit challenging. Thus, we conducted a case-control study (N = 576) to analyze the risk of occurrence of oral malignant disorders by using binary particle swarm optimization (BPSO) with an odds ratio (OR)-based method.ResultsWe demonstrated that a combination of SNPs (CYP26B1 rs887844 and CYP26C1 rs12256889) and socio-demographic factors (age, ethnicity, and BQ chewing), referred to as the combined effects of SNP-environment, correlated with maximal risk diversity of occurrence observed between the oral malignant disorder group and the control group. The risks were more prominent in the oral and pharyngeal cancers group (OR = 10.30; 95% confidence interval (CI) = 4.58-23.15) than in the OPMD group (OR = 5.42; 95% CI = 1.94-15.12).ConclusionsSimulation-based "SNP-environment barcodes" may be used to predict the risk of occurrence of oral malignant disorders. Applying simulation-based "SNP-environment barcodes" may provide insight into the importance of screening tests in preventing oral and pharyngeal cancers and OPMD