Camptothecin: An alkaloid isolated from the stem wood of the Chinese tree, Camptotheca acuminata. This compound selectively inhibits the nuclear enzyme DNA TOPOISOMERASES, TYPE I. Several semisynthetic analogs of camptothecin have demonstrated antitumor activity.Topoisomerase I Inhibitors: Compounds that inhibit the activity of DNA TOPOISOMERASE I.DNA Topoisomerases, Type I: DNA TOPOISOMERASES that catalyze ATP-independent breakage of one of the two strands of DNA, passage of the unbroken strand through the break, and rejoining of the broken strand. DNA Topoisomerases, Type I enzymes reduce the topological stress in the DNA structure by relaxing the superhelical turns and knotted rings in the DNA helix.Antineoplastic Agents, Phytogenic: Agents obtained from higher plants that have demonstrable cytostatic or antineoplastic activity.Topotecan: An antineoplastic agent used to treat ovarian cancer. It works by inhibiting DNA TOPOISOMERASES, TYPE I.Topoisomerase Inhibitors: Compounds that inhibit the activity of DNA TOPOISOMERASES.Camptotheca: A plant genus of the family NYSSACEAE (sometimes classified in the CORNACEAE family). It is a source of CAMPTOTHECIN.DNA Damage: Injuries to DNA that introduce deviations from its normal, intact structure and which may, if left unrepaired, result in a MUTATION or a block of DNA REPLICATION. These deviations may be caused by physical or chemical agents and occur by natural or unnatural, introduced circumstances. They include the introduction of illegitimate bases during replication or by deamination or other modification of bases; the loss of a base from the DNA backbone leaving an abasic site; single-strand breaks; double strand breaks; and intrastrand (PYRIMIDINE DIMERS) or interstrand crosslinking. Damage can often be repaired (DNA REPAIR). If the damage is extensive, it can induce APOPTOSIS.Teniposide: A semisynthetic derivative of PODOPHYLLOTOXIN that exhibits antitumor activity. Teniposide inhibits DNA synthesis by forming a complex with topoisomerase II and DNA. This complex induces breaks in double stranded DNA and prevents repair by topoisomerase II binding. Accumulated breaks in DNA prevent cells from entering into the mitotic phase of the cell cycle, and lead to cell death. Teniposide acts primarily in the G2 and S phases of the cycle.Topoisomerase II Inhibitors: Compounds that inhibit the activity of DNA TOPOISOMERASE II. Included in this category are a variety of ANTINEOPLASTIC AGENTS which target the eukaryotic form of topoisomerase II and ANTIBACTERIAL AGENTS which target the prokaryotic form of topoisomerase II.Organosilicon Compounds: Organic compounds that contain silicon as an integral part of the molecule.Antineoplastic Agents: Substances that inhibit or prevent the proliferation of NEOPLASMS.Rubiaceae: The Madder plant family of the order Rubiales, subclass Asteridae, class Magnoliopsida includes important medicinal plants that provide QUININE; IPECAC; and COFFEE. They have opposite leaves and interpetiolar stipules.Enzyme Inhibitors: Compounds or agents that combine with an enzyme in such a manner as to prevent the normal substrate-enzyme combination and the catalytic reaction.Aphidicolin: An antiviral antibiotic produced by Cephalosporium aphidicola and other fungi. It inhibits the growth of eukaryotic cells and certain animal viruses by selectively inhibiting the cellular replication of DNA polymerase II or the viral-induced DNA polymerases. The drug may be useful for controlling excessive cell proliferation in patients with cancer, psoriasis or other dermatitis with little or no adverse effect upon non-multiplying cells.Organic Chemistry Phenomena: The conformation, properties, reaction processes, and the properties of the reactions of carbon compounds.Tumor Cells, Cultured: Cells grown in vitro from neoplastic tissue. If they can be established as a TUMOR CELL LINE, they can be propagated in cell culture indefinitely.Apoptosis: One of the mechanisms by which CELL DEATH occurs (compare with NECROSIS and AUTOPHAGOCYTOSIS). Apoptosis is the mechanism responsible for the physiological deletion of cells and appears to be intrinsically programmed. It is characterized by distinctive morphologic changes in the nucleus and cytoplasm, chromatin cleavage at regularly spaced sites, and the endonucleolytic cleavage of genomic DNA; (DNA FRAGMENTATION); at internucleosomal sites. This mode of cell death serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth.Drug Screening Assays, Antitumor: Methods of investigating the effectiveness of anticancer cytotoxic drugs and biologic inhibitors. These include in vitro cell-kill models and cytostatic dye exclusion tests as well as in vivo measurement of tumor growth parameters in laboratory animals.Etoposide: A semisynthetic derivative of PODOPHYLLOTOXIN that exhibits antitumor activity. Etoposide inhibits DNA synthesis by forming a complex with topoisomerase II and DNA. This complex induces breaks in double stranded DNA and prevents repair by topoisomerase II binding. Accumulated breaks in DNA prevent entry into the mitotic phase of cell division, and lead to cell death. Etoposide acts primarily in the G2 and S phases of the cell cycle.KB Cells: This line KB is now known to be a subline of the ubiquitous KERATIN-forming tumor cell line HeLa. It was originally thought to be derived from an epidermal carcinoma of the mouth, but was subsequently found, based on isoenzyme analysis, HeLa marker chromosomes, and DNA fingerprinting, to have been established via contamination by HELA CELLS. The cells are positive for keratin by immunoperoxidase staining. KB cells have been reported to contain human papillomavirus18 (HPV-18) sequences.DNA Topoisomerases, Type II: DNA TOPOISOMERASES that catalyze ATP-dependent breakage of both strands of DNA, passage of the unbroken strands through the breaks, and rejoining of the broken strands. These enzymes bring about relaxation of the supercoiled DNA and resolution of a knotted circular DNA duplex.Cell Line, Tumor: A cell line derived from cultured tumor cells.DNA, Superhelical: Circular duplex DNA isolated from viruses, bacteria and mitochondria in supercoiled or supertwisted form. This superhelical DNA is endowed with free energy. During transcription, the magnitude of RNA initiation is proportional to the DNA superhelicity.Amsacrine: An aminoacridine derivative that intercalates into DNA and is used as an antineoplastic agent.DNA: A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).Drug Resistance: Diminished or failed response of an organism, disease or tissue to the intended effectiveness of a chemical or drug. It should be differentiated from DRUG TOLERANCE which is the progressive diminution of the susceptibility of a human or animal to the effects of a drug, as a result of continued administration.DNA Cleavage: A reaction that severs one of the covalent sugar-phosphate linkages between NUCLEOTIDES that compose the sugar phosphate backbone of DNA. It is catalyzed enzymatically, chemically or by radiation. Cleavage may be exonucleolytic - removing the end nucleotide, or endonucleolytic - splitting the strand in two.DNA Replication: The process by which a DNA molecule is duplicated.Iridoid Glucosides: A subclass of iridoid compounds that include a glucoside moiety, usually found at the C-1 position.DNA Repair: The reconstruction of a continuous two-stranded DNA molecule without mismatch from a molecule which contained damaged regions. The major repair mechanisms are excision repair, in which defective regions in one strand are excised and resynthesized using the complementary base pairing information in the intact strand; photoreactivation repair, in which the lethal and mutagenic effects of ultraviolet light are eliminated; and post-replication repair, in which the primary lesions are not repaired, but the gaps in one daughter duplex are filled in by incorporation of portions of the other (undamaged) daughter duplex. Excision repair and post-replication repair are sometimes referred to as "dark repair" because they do not require light.Cell Survival: The span of viability of a cell characterized by the capacity to perform certain functions such as metabolism, growth, reproduction, some form of responsiveness, and adaptability.Leukemia L1210Drug Resistance, Neoplasm: Resistance or diminished response of a neoplasm to an antineoplastic agent in humans, animals, or cell or tissue cultures.Intercalating Agents: Agents that are capable of inserting themselves between the successive bases in DNA, thus kinking, uncoiling or otherwise deforming it and therefore preventing its proper functioning. They are used in the study of DNA.Cell Cycle: The complex series of phenomena, occurring between the end of one CELL DIVISION and the end of the next, by which cellular material is duplicated and then divided between two daughter cells. The cell cycle includes INTERPHASE, which includes G0 PHASE; G1 PHASE; S PHASE; and G2 PHASE, and CELL DIVISION PHASE.Ellipticines: Pyrido-CARBAZOLES originally discovered in the bark of OCHROSIA ELLIPTICA. They inhibit DNA and RNA synthesis and have immunosuppressive properties.Secondary Metabolism: A physiochemical process which occurs in a wide range of organisms which unlike BASAL METABOLISM is not required for or essential to short-term survivability but to long-term general well-being of the organism.Lactones: Cyclic esters of hydroxy carboxylic acids, containing a 1-oxacycloalkan-2-one structure. Large cyclic lactones of over a dozen atoms are MACROLIDES.Leukemia P388: An experimental lymphocytic leukemia originally induced in DBA/2 mice by painting with methylcholanthrene.Chemistry, Organic: The study of the structure, preparation, properties, and reactions of carbon compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)DNA, Neoplasm: DNA present in neoplastic tissue.Tumor Suppressor Protein p53: Nuclear phosphoprotein encoded by the p53 gene (GENES, P53) whose normal function is to control CELL PROLIFERATION and APOPTOSIS. A mutant or absent p53 protein has been found in LEUKEMIA; OSTEOSARCOMA; LUNG CANCER; and COLORECTAL CANCER.Poly(ADP-ribose) Polymerases: Enzymes that catalyze the transfer of multiple ADP-RIBOSE groups from nicotinamide-adenine dinucleotide (NAD) onto protein targets, thus building up a linear or branched homopolymer of repeating ADP-ribose units i.e., POLY ADENOSINE DIPHOSPHATE RIBOSE.Neoplasms: New abnormal growth of tissue. Malignant neoplasms show a greater degree of anaplasia and have the properties of invasion and metastasis, compared to benign neoplasms.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Indenes: A family of fused-ring hydrocarbons isolated from coal tar that act as intermediates in various chemical reactions and are used in the production of coumarone-indene resins.Naphthoquinones: Naphthalene rings which contain two ketone moieties in any position. They can be substituted in any position except at the ketone groups.S Phase: Phase of the CELL CYCLE following G1 and preceding G2 when the entire DNA content of the nucleus is replicated. It is achieved by bidirectional replication at multiple sites along each chromosome.Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.Iridoids: A type of MONOTERPENES, derived from geraniol. They have the general form of cyclopentanopyran, but in some cases, one of the rings is broken as in the case of secoiridoid. They are different from the similarly named iridals (TRITERPENES).Prodrugs: A compound that, on administration, must undergo chemical conversion by metabolic processes before becoming the pharmacologically active drug for which it is a prodrug.Alkaloids: Organic nitrogenous bases. Many alkaloids of medical importance occur in the animal and vegetable kingdoms, and some have been synthesized. (Grant & Hackh's Chemical Dictionary, 5th ed)Nucleic Acid Synthesis Inhibitors: Compounds that inhibit cell production of DNA or RNA.HeLa Cells: The first continuously cultured human malignant CELL LINE, derived from the cervical carcinoma of Henrietta Lacks. These cells are used for VIRUS CULTIVATION and antitumor drug screening assays.Leishmania donovani: A parasitic hemoflagellate of the subgenus Leishmania leishmania that infects man and animals and causes visceral leishmaniasis (LEISHMANIASIS, VISCERAL). The sandfly genera Phlebotomus and Lutzomyia are the vectors.Acrylamides: Colorless, odorless crystals that are used extensively in research laboratories for the preparation of polyacrylamide gels for electrophoresis and in organic synthesis, and polymerization. Some of its polymers are used in sewage and wastewater treatment, permanent press fabrics, and as soil conditioning agents.HT29 Cells: Human colonic ADENOCARCINOMA cells that are able to express differentiation features characteristic of mature intestinal cells such as the GOBLET CELLS.Drug Synergism: The action of a drug in promoting or enhancing the effectiveness of another drug.DNA Fragmentation: Splitting the DNA into shorter pieces by endonucleolytic DNA CLEAVAGE at multiple sites. It includes the internucleosomal DNA fragmentation, which along with chromatin condensation, are considered to be the hallmarks of APOPTOSIS.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Catha: A plant genus of the family CELASTRACEAE. The leafy stems of khat are chewed by some individuals for stimulating effect. Members contain ((+)-norpseudoephedrine), cathionine, cathedulin, cathinine & cathidine.Drug Carriers: Forms to which substances are incorporated to improve the delivery and the effectiveness of drugs. Drug carriers are used in drug-delivery systems such as the controlled-release technology to prolong in vivo drug actions, decrease drug metabolism, and reduce drug toxicity. Carriers are also used in designs to increase the effectiveness of drug delivery to the target sites of pharmacological actions. Liposomes, albumin microspheres, soluble synthetic polymers, DNA complexes, protein-drug conjugates, and carrier erythrocytes among others have been employed as biodegradable drug carriers.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Diterpenes: Twenty-carbon compounds derived from MEVALONIC ACID or deoxyxylulose phosphate.HL-60 Cells: A promyelocytic cell line derived from a patient with ACUTE PROMYELOCYTIC LEUKEMIA. HL-60 cells lack specific markers for LYMPHOID CELLS but express surface receptors for FC FRAGMENTS and COMPLEMENT SYSTEM PROTEINS. They also exhibit phagocytic activity and responsiveness to chemotactic stimuli. (From Hay et al., American Type Culture Collection, 7th ed, pp127-8)DNA-Binding Proteins: Proteins which bind to DNA. The family includes proteins which bind to both double- and single-stranded DNA and also includes specific DNA binding proteins in serum which can be used as markers for malignant diseases.Colonic Neoplasms: Tumors or cancer of the COLON.Caspases: A family of intracellular CYSTEINE ENDOPEPTIDASES that play a role in regulating INFLAMMATION and APOPTOSIS. They specifically cleave peptides at a CYSTEINE amino acid that follows an ASPARTIC ACID residue. Caspases are activated by proteolytic cleavage of a precursor form to yield large and small subunits that form the enzyme. Since the cleavage site within precursors matches the specificity of caspases, sequential activation of precursors by activated caspases can occur.Dichlororibofuranosylbenzimidazole: An RNA polymerase II transcriptional inhibitor. This compound terminates transcription prematurely by selective inhibition of RNA synthesis. It is used in research to study underlying mechanisms of cellular regulation.Mitoxantrone: An anthracenedione-derived antineoplastic agent.Flavanones: A group of FLAVONOIDS characterized with a 4-ketone.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Cell Division: The fission of a CELL. It includes CYTOKINESIS, when the CYTOPLASM of a cell is divided, and CELL NUCLEUS DIVISION.Cricetinae: A subfamily in the family MURIDAE, comprising the hamsters. Four of the more common genera are Cricetus, CRICETULUS; MESOCRICETUS; and PHODOPUS.Inhibitory Concentration 50: The concentration of a compound needed to reduce population growth of organisms, including eukaryotic cells, by 50% in vitro. Though often expressed to denote in vitro antibacterial activity, it is also used as a benchmark for cytotoxicity to eukaryotic cells in culture.RecQ Helicases: A family of structurally-related DNA helicases that play an essential role in the maintenance of genome integrity. RecQ helicases were originally discovered in E COLI and are highly conserved across both prokaryotic and eukaryotic organisms. Genetic mutations that result in loss of RecQ helicase activity gives rise to disorders that are associated with CANCER predisposition and premature aging.Granulocyte Precursor Cells: The cells in the granulocytic series that give rise to mature granulocytes (NEUTROPHILS; EOSINOPHILS; and BASOPHILS). These precursor cells include myeloblasts, promyelocytes, myelocytes and metamyelocytes.Staurosporine: An indolocarbazole that is a potent PROTEIN KINASE C inhibitor which enhances cAMP-mediated responses in human neuroblastoma cells. (Biochem Biophys Res Commun 1995;214(3):1114-20)Molecular Structure: The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.Kinetics: The rate dynamics in chemical or physical systems.Doxorubicin: Antineoplastic antibiotic obtained from Streptomyces peucetius. It is a hydroxy derivative of DAUNORUBICIN.Mice, Nude: Mutant mice homozygous for the recessive gene "nude" which fail to develop a thymus. They are useful in tumor studies and studies on immune responses.Caspase 3: A short pro-domain caspase that plays an effector role in APOPTOSIS. It is activated by INITIATOR CASPASES such as CASPASE 9. Isoforms of this protein exist due to multiple alternative splicing of its MESSENGER RNA.