novobiocin and Breast-Neoplasms

The primary source of failure of cancer therapies is multidrug resistance (MDR), which can be caused by different mechanisms, including the overexpression of ABC transporters in cancer cells. Among the 48 human ABC proteins, the breast cancer resistance protein (BCRP/ABCG2) has been described as a pivotal player in cancer resistance. The use of functional inhibitors and expression modulators is a promising strategy to overcome the MDR caused by ABCG2. Despite the lack of clinical trials using ABCG2 inhibitors, many compounds have already been discovered. This review presents an overview about various ABCG2 inhibitors that have been identified, discussing some chemical aspects and the main experimental methods used to identify and characterize the mechanisms of new inhibitors. In addition, some biological requirements to pursue preclinical tests are described. Finally, we discuss the potential use of ABCG2 inhibitors in cancer stem cells (CSC) for improving the objective response rate and the mechanism of ABCG2 modulators at transcriptional and protein expression levels.

Topics: Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; Breast Neoplasms; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Female; Humans; Neoplasm Proteins; Neoplastic Stem Cells

Resistance to alkylators may potentially be overcome by drugs that inhibits DNA repair, thus improving the efficacy of high-dose chemotherapy. This trial was performed to determine if novobiocin, an agent that inhibits DNA repair, could be given with high-dose alkylators. Study aims were to define the toxicities and maximal-tolerated dose (MTD) of novobiocin and the pharmacokinetics of novobiocin and high-dose cyclophosphamide and thiotepa.. Thirty-eight women with responsive metastatic breast cancer received high-dose cyclophosphamide (3 to 6 g/m2 over 4 days), thiotepa (400 to 800 mg/m2), and novobiocin (0.5 to 5.0 g/d x 7, orally) with autologous marrow support. Toxicity was monitored. The pharmacology of novobiocin, cyclophosphamide, and thiotepa was evaluated.. There were no toxic deaths. The MTD of novobiocin was 4 g/d. All seven patients treated at 5 g/d developed grade III/IV mucositis and vomiting. The severity of mucositis correlated with the plasma levels of novobiocin. Other severe toxicities were not observed. Plasma novobiocin levels > or = 100 micrograms/mL, which are associated with reversal of drug resistance in animal models, were consistently seen at dose levels greater than 2 g. The dispositions of cyclophosphamide and thiotepa were not altered by novobiocin.. Novobiocin may be given with high-dose alkylators in doses that produce plasma levels that augment the activity of these cytotoxics in experimental models. The pharmacology of high-dose cyclophosphamide and thiotepa is unaffected. Novobiocin 4 g/d orally for 7 days is recommended for future study.

Topics: Adult; Anemia, Aplastic; Antineoplastic Combined Chemotherapy Protocols; Breast Neoplasms; Cyclophosphamide; Disease-Free Survival; Drug Administration Schedule; Drug Resistance; Female; Gastrointestinal Diseases; Humans; Length of Stay; Lymphatic Metastasis; Middle Aged; Mouth Mucosa; Neutropenia; Novobiocin; Prospective Studies; Stomatitis; Thiotepa

A series of O-substituted analogs of the C-ring-truncated scaffold of deguelin designed as heat shock protein 90 (HSP90) C-terminal inhibitors were investigated as novel antitumor agents against human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Among the synthesized compounds, compound 37 displayed significant inhibition in both trastuzumab-sensitive and trastuzumab-resistant breast cancer cells with little cytotoxicity to normal cells. Mechanistic studies of compound 37 carried out by HSP90α C-terminal inhibitor screening, the induction of the heat shock response and downregulation of HSP90 client proteins indicated that the antitumor activity of 37 in breast cancer cells could be attributed to the destabilization and inactivation of HSP90 client proteins by the binding of 37 to the C-terminal domain of HSP90. A molecular docking study of compound 37 with a HSP90 homology model indicated that its S-isomer fit well in the ATP binding site of the C-terminal domain, forming key interactions.

Topics: Antineoplastic Agents; Breast Neoplasms; Cell Line; Cell Proliferation; Cell Survival; Dose-Response Relationship, Drug; Drug Discovery; Drug Screening Assays, Antitumor; Female; HSP90 Heat-Shock Proteins; Humans; Molecular Docking Simulation; Molecular Structure; Rotenone; Structure-Activity Relationship

Hsp90 is a promising therapeutic target for the treatment of cancer. Novobiocin is the first Hsp90 C-terminal inhibitor ever identified and recent structure-activity relationship studies on the noviose sugar identified several commercially available amines as suitable surrogates. In an effort to further understand this region of the molecule, analogues containing various N'-amino substituents were prepared and evaluated against two breast cancer cell lines for determination of their efficacy. Compound 37j manifested the most potent anti-proliferative activity from these studies and induced Hsp90-dependent client protein degradation at mid nano-molar concentrations.

Topics: Breast Neoplasms; Cell Line, Tumor; Cell Proliferation; Female; Humans; Molecular Structure; Monosaccharides; Novobiocin; Structure-Activity Relationship

The natural products novobiocin and derrubone have both demonstrated Hsp90 inhibition and structure-activity relationships have been established for each scaffold. Given these compounds share several key structural features, we hypothesized that incorporation of elements from each could provide insight to structural features important for Hsp90 inhibition. Thus, chimeric analogues of novobiocin and derrubone were constructed and evaluated. These studies confirmed that the functionality present at the 3-position of the isoflavone plays a critical role in determining Hsp90 inhibition and suggests that the bicyclic ring system present in both novobiocin and derrubone do not share similar modes of binding.

Topics: Antineoplastic Agents; Breast Neoplasms; Cell Line, Tumor; Cell Proliferation; Female; Flavones; HSP90 Heat-Shock Proteins; Humans; Isoflavones; Molecular Structure; Novobiocin

SET and MYND domain-containing protein 3 (SMYD3) is a histone methyltransferase that plays an important role in transcriptional regulation in human carcinogenesis, and heat-shock protein HSP90A has been shown to increase the activity of SMYD3. We previously reported that overexpression of SMYD3 stimulated the migration of cells. In this study, we further found that novobiocin, a HSP90 inhibitor, could decrease the expression of SMYD3 and dose dependently inhibit the proliferation and migration of MDA-MB-231 human breast cancer cells. As a control, the short hairpin RNA (shRNA) targeting SMYD3 gene also showed similar effects with novobicin. This study is the first to show that novobiocin can inhibit the migration of breast cancer cells and such event may involve the downregulation of SMYD3. These findings might throw light on the development of novel therapeutic approaches to human cancers, and lend further understanding to the potential role of SMYD3 in human carcinogenesis.

Topics: Breast Neoplasms; Cell Line, Tumor; Cell Movement; Cell Proliferation; Female; Gene Expression; Histone-Lysine N-Methyltransferase; HSP90 Heat-Shock Proteins; Humans; Novobiocin; RNA, Small Interfering

Breast cancer resistance protein is a member of the ATP-binding cassette transporter G family that extrudes xenotoxins from cells, mediating drug resistance, and has been recognized as a major cause of failure of various carcinoma chemotherapies. In this study, the modulatory effects of dexamethasone and indomethacin on the cell cytotoxicity of mitoxantrone and on the BCRP protein activity in breast cancer cell lines were examined. MCF cells were seeded at 1 x 10(4) cells per well in 96-well flat-bottomed microplates for 48 hours and treated with increasing doses of dexamethasone, indomethacin, and novobiocin alone or preincubated with increasing doses of the drugs and then coexposed to mitoxantrone. Cell viability was measured after 1-4 days, using the MTT assay. BCRP activity was determined flow cytometrically by measuring mitoxantrone accumulation in the absence and presence of the inhibitor, novobiocin. Cotreatment of mitoxantrone with different concentrations of dexamethasone and indomethacin sensitized parental and resistant MCF-7 cells to mitoxantrone cytotoxicity. Dexamethasone increased the accumulation of mitoxantrone in the MCF-7/MX cell line, indicating an inhibition of BCRP. In spite of increased levels of mitoxantrone cytotoxicity in the presence of indomethacin, the accumulation of mitoxantrone was not increased in indomethacin-treated MCF cells.

Topics: Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Breast Neoplasms; Cell Line, Tumor; Cell Proliferation; Cell Survival; Dexamethasone; Dose-Response Relationship, Drug; Drug Interactions; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; Drug Therapy, Combination; Female; Humans; Indomethacin; Mitoxantrone; Neoplasm Proteins; Novobiocin

A new class of specific breast cancer resistance protein (BCRP) inhibitors was identified, showing no inhibition of the ATP binding cassette (ABC) transporters P-gp and MRP1. Some of these modulators inhibit BCRP with high potency; they are only slightly less potent than Ko143 and could serve as promising lead structures for the design of novel effective BCRP inhibitors. These inhibitors are structurally related to tariquidar (XR9576) and belong to a library of multidrug-resistance modulators synthesized by our research group. The absence of the tetrahydroisoquinoline substructure appears to play a crucial role for specificity; we found that the presence of this substructure is not essential for interaction with BCRP. To determine the type of interaction between pheophorbide A and compounds with and without the tetrahydroisoquinoline substructure, various substrate pheophorbide A concentrations were used in enzyme kinetics assays. The resulting data show that these compounds share a noncompetitive-type interaction with pheophorbide A. Experiments with imatinib and pheophorbide A revealed a mixed-type interaction. The combination of imatinib and compounds with and without the tetrahydroisoquinoline substructure resulted in a positive cooperative effect, indicating that imatinib engages a binding site distinct from that of the new compounds on one side and distinct from that of pheophorbide A on the other side as well. The results of this study suggest that the category of BCRP-specific inhibitors, which includes only fumitremorgin C, Ko143 and analogues, and novobiocin needs to be extended by this new class of inhibitors, which possess three key characteristics: specificity, potency, and low toxicity.

Topics: Adenosine; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Benzamides; Binding Sites; Breast Neoplasms; Cell Line, Tumor; Chlorophyll; Diketopiperazines; Drug Resistance, Multiple; Female; Heterocyclic Compounds, 4 or More Rings; Humans; Imatinib Mesylate; Indoles; Neoplasm Proteins; Novobiocin; Piperazines; Pyrimidines; Quinolines; Structure-Activity Relationship

At the end of the last century tariquidar (XR9576) was synthesized, pharmacologically investigated, and classified as a promising 3rd generation P-glycoprotein (P-gp) modulator. Following the discovery of BCRP in 1998 an increasing number of substances were studied in relation to their potency to interact with this transporter. Recently it has been shown that XR9576 inhibits both P-gp and BCRP transport function similarly to GF120918 (elacridar). This observation prompted us to investigate 5 XR compounds and 25 structurally related derivatives synthesized in our laboratory for their BCRP inhibitory effect. The biological activity data were determined by our new Hoechst 33342 assay that has been transferred from P-gp to BCRP overexpressing cells. 3D-QSAR models (CoMFA and CoMSIA) were generated and validated by the leave-many-out method and the scrambling stability test. The best models yielded an internal predictive squared correlation coefficient higher than 0.8 and contained steric, electrostatic, hydrophobic, and hydrogen bond donor fields. To our knowledge, this is the first 3D-QSAR analysis of BCRP inhibitors. Additionally the biological activity data determined in P-gp overexpressing cells on one side and BCRP overexpressing cells on the other side were compared to identify selective and non-selective inhibitors of P-gp and BCRP. The results may help to get a better insight which structural elements are necessary to direct the interaction of these compounds with P-gp and/or BCRP.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Breast Neoplasms; Crystallography, X-Ray; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Female; Humans; Models, Molecular; Molecular Structure; Neoplasm Proteins; Phthalic Acids; Quantitative Structure-Activity Relationship; Quinolines; Reproducibility of Results; Stereoisomerism; Time Factors; Tumor Cells, Cultured

A new series of coumarin inhibitors of hsp90 lacking the noviose moiety as well as substituents on C-7 and C-8 positions of the aromatic ring was synthesised and their hsp90 inhibitory activity has been delineated: for example, their capacity to induce the degradation of client proteins and to inhibit estradiol-induced transcription in human breast cancer cells. In cell proliferation assay, the most active compound 5g was approximately 8 times more potent than the parent novobiocin natural compound.

Topics: Antibiotics, Antineoplastic; Binding Sites; Breast Neoplasms; Cell Line, Tumor; Cell Proliferation; Coumarins; Drug Screening Assays, Antitumor; Enzyme Inhibitors; Estradiol; HSP90 Heat-Shock Proteins; Humans; Novobiocin; Structure-Activity Relationship; Transcription, Genetic

Selective hsp90 inhibitors simultaneously destabilize and deplete key signaling proteins involved in cell proliferation and survival, angiogenesis, and metastasis. Investigation of novobiocin analogues lacking the noviose moiety as novel inhibitors of hsp90 was carried out. A novel series of 3-aminocoumarin analogues has been produced and screened in cell proliferation, and the molecular signature of hsp90 inhibition was assessed by depletion of estrogen receptor, HER2, Raf-1, and cdk4 in human breast cancer cells. This structure-activity relationship study highlights the crucial role of the C-4 and/or C-7 positions of coumarin which appeared to be essential for degradation of hsp90 client proteins. Removal of the noviose moiety in novobiocin together with introduction of a tosyl substituent at C-4 or C-7 coumarins provides 6e and 6f as lead structures which compared favorably with novobiocin as demonstrated by enhanced rates of cell death. The processing and activation of caspases 7 and 8 and the subsequent cleavage of PARP by 6e suggest stimulation of the extrinsic apoptosis pathway.

Topics: Antineoplastic Agents; Apoptosis; Breast Neoplasms; Caspases; Cell Line, Tumor; Cell Proliferation; Cyclin-Dependent Kinase 4; Drug Screening Assays, Antitumor; Estradiol; Estrogen Receptor alpha; Female; Flow Cytometry; HSP90 Heat-Shock Proteins; Humans; Novobiocin; Proteasome Endopeptidase Complex; Proto-Oncogene Proteins c-raf; Receptor, ErbB-2; Signal Transduction; Structure-Activity Relationship; Transcription, Genetic

Breast cancer resistance protein (BCRP/ABCG2) of an ATP-binding cassette half-transporter confers resistance against mitoxantrone and camptothecin derivatives of topotecan and irinotecan. Novobiocin, a coumermycin antibiotic, is known to enhance anticancer drug sensitivity of cancer cells in vitro and in vivo, the mechanism of which remains undetermined. Here we focused on drug efflux pump and examined whether novobiocin reversed drug resistance in multidrug-resistant cells highly expressing BCRP. To explore the reversal mechanisms, intracellular drug accumulation was measured by flow cytometry, and a topotecan transport study using plasma membrane vesicles was performed. We used PC-6/SN2-5H2 small cell lung cancer and MCF-7/MX breast cancer cells selected with SN-38 of the active irinotecan metabolite and mitoxantrone, respectively, and the BCRP cDNA transfectant MCF-7/clone 8 cells. These cells expressed high levels of BCRP mRNA but not other known transporters. Compared to the parental PC-6 cells, PC-6/SN2-5H2 cells were 141-, 173- and 57.2-fold resistant to topotecan, SN-38 and mitoxantrone, respectively. Novobiocin at 60 microM decreased the degree of the above resistance by approximately 26-fold in PC-6/SN2-5H2 cells, and similarly reversed resistance in MCF-7/MX, MCF-7/clone 8 and un-selected NCI-H460 cells highly expressing BCRP. Furthermore, novobiocin increased the intracellular topotecan accumulation in these cells and inhibited the topotecan transport into the membrane vesicles of PC-6/SN2-5H2 cells. No effects of novobiocin in these assay were observed in the parental PC-6 and MCF-7 cells. The kinetic parameters in the transport study indicated that novobiocin was a inhibitor for BCRP, resulting in competitive inhibition of BCRP-mediated topotecan transport. These findings suggest that novobiocin effectively overcomes BCRP-mediated drug resistance at acceptable concentrations.

Topics: Aminocoumarins; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Breast Neoplasms; Camptothecin; Coumarins; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Humans; Irinotecan; Lung Neoplasms; Mitoxantrone; Neoplasm Proteins; Novobiocin; Topoisomerase I Inhibitors; Topotecan; Tumor Cells, Cultured

Heat shock protein 90 (Hsp90) interacts with and stabilizes several oncogenic protein kinases (e.g., p185(erbB2), p60(v-src), and Raf-1) and is required for the stability and dominant-negative function of mutated p53 protein. Two unrelated antibiotics, geldanamycin and radicicol, bind specifically to an atypical nucleotide-binding pocket of Hsp90, a site that shares homology with the adenosine triphosphate (ATP)-binding domain of bacterial DNA gyrase B. This interaction leads to destabilization of proteins that interact with Hsp90. Since the nucleotide-binding site of gyrase B is targeted by coumarin antibiotics (e.g., novobiocin), we investigated whether these drugs can also interact with Hsp90 and affect its activity.. We used immobilized novobiocin, geldanamycin, or radicicol to isolate either endogenous Hsp90 from cell lysates or Hsp90 deletion fragments translated in vitro. Effects of the coumarin antibiotics novobiocin, chlorobiocin, and coumermycin A1 on several proteins interacting with Hsp90 were assessed in vitro and in vivo.. Hsp90 binding to immobilized novobiocin was competed by soluble coumarins and ATP but not by geldanamycin or radicicol. A carboxy-terminal Hsp90 fragment bound immobilized novobiocin but not immobilized geldanamycin, while a geldanamycin-binding amino-terminal fragment did not bind novobiocin. All three coumarins markedly reduced cellular levels of p185(erbB2), p60(v-src), Raf-1, and mutated p53. Furthermore, novobiocin reduced Raf-1 levels in the spleens of mice treated with the drug.. These coumarin antibiotics, particularly novobiocin, represent a first-generation alternative to other Hsp90-targeting drugs that are not as well tolerated. Novobiocin's unique interaction with Hsp90 identifies an additional site on this protein amenable to pharmacologic interference with small molecules.

Topics: Aminocoumarins; Animals; Antibiotics, Antineoplastic; Blotting, Western; Breast Neoplasms; Carcinoma; Carrier Proteins; Coumarins; DNA Topoisomerases, Type II; Enzyme Inhibitors; Female; Fibroblasts; HSP90 Heat-Shock Proteins; Humans; Intracellular Signaling Peptides and Proteins; Mice; Novobiocin; Oncogene Protein pp60(v-src); Protein Binding; Proto-Oncogene Proteins c-raf; Signal Transduction; Spleen; Topoisomerase II Inhibitors; Tumor Cells, Cultured; Tumor Suppressor Protein p53; Tumor Suppressor Proteins

We conducted the first phase 2 and pharmacologic study to evaluate the combination of novobiocin (a coumeromycin antibiotic that has been shown to augment alkylating agent cytotoxicity in experimental models) and high-dose cyclophosphamide and thiotepa followed by autologous marrow support in women with chemosensitive advanced breast cancer. Its aims were (1) to determine progression-free survival (PFS) and overall survival (OS), (2) to evaluate the pharmacokinetics of cyclophosphamide and thiotepa, and (3) to measure the ability of novobiocin to reverse alkylator drug resistance in vitro. Forty-one women with chemotherapy-responsive advanced breast cancer received cyclophosphamide (4 g/m2) for peripheral blood stem cell mobilization (treatment 1) followed by high-dose cyclophosphamide (1.5 g/m2 per day for 4 days), thiotepa (200 mg/m2 per day for 4 days), and novobiocin (4 g/day orally for 7 days) (treatment 2) and autologous marrow support. The median PFS was 10 months (range, 0.2-70.6 months) and OS, 21.5 months (range, 0.2-70.6 months). There was no statistically significant relationship between PFS or OS and area-under-the-curve values of cyclophosphamide, thiotepa, or 4-hydroxycyclophosphamide. Patient plasma samples (n = 12) obtained during novobiocin therapy were able to reverse alkylator drug resistance in an in vitro colony-forming assay. Correlative laboratory studies in an in vitro model system demonstrated that patient plasma after novobiocin treatment resulted in the magnitude of resistance reversal that had been predicted by prior preclinical experiments. Clinically, however, this activity of novobiocin did not translate into a substantial increase in PFS or OS compared with historical controls treated with high-dose alkylator therapy alone.

Topics: Adult; Aged; Antineoplastic Agents, Alkylating; Antineoplastic Combined Chemotherapy Protocols; Area Under Curve; Breast Neoplasms; Cyclophosphamide; Disease-Free Survival; Drug Resistance, Neoplasm; Drug Synergism; Female; Humans; Middle Aged; Novobiocin; Survival Analysis; Thiotepa; Treatment Failure; Tumor Cells, Cultured; Tumor Stem Cell Assay

Stem cell contamination by tumor is common in many diseases for which autologous bone marrow transplantation is used. In in vitro models chemotherapeutic purging reduces contamination and may have an impact on clinical outcome. Purging, however, delays engraftment. Little is known about the ability of granulocyte colony-stimulating factor (G-CSF) to accelerate myelopoiesis after purged autologous bone marrow transplantation. We treated 22 women with metastatic breast cancer with high-dose cyclophosphamide and thiotepa and, following the infusion of 4-hydroperoxycyclophosphamide-purged marrow, administered G-CSF, 16 micrograms/kg daily, from day 0 to engraftment. Results were compared with a control population of 24 women with breast cancer who received identical chemotherapy and purged marrow but not growth factor. Neutrophil recovery was accelerated in the G-CSF-treated population. An absolute neutrophil count of 500 was reached in 19 days compared with 29 for the historic controls. The median number of days febrile was reduced (8 versus 5.5) as were the number of days of hospitalization from marrow infusion (33 versus 25). There was no difference in the number of days on antibiotics or time to last platelet transfusion. G-CSF was administered without any notable toxicity. G-CSF accelerates myelopoiesis following the infusion of 4-hydroperoxycyclophosphamide-purged autologous marrow and shortens hospitalization.

Topics: Adult; Bone Marrow Purging; Bone Marrow Transplantation; Breast Neoplasms; Combined Modality Therapy; Cyclophosphamide; Female; Filgrastim; Granulocyte Colony-Stimulating Factor; Granulocytes; Humans; Length of Stay; Leukocyte Count; Middle Aged; Neutrophils; Novobiocin; Recombinant Proteins; Thiotepa

Topoisomerase I and topoisomerase II allow a metabolically active cell to mobilize its supercoiled chromosomal DNA and undergo replication, transcription, recombination, and repair. Several topoisomerase inhibitors have recently been shown to be active in preclinical systems. Topotecan (SK&F 104,864), a water-soluble camptothecin analog, is an inhibitor of topoisomerase I. Novobiocin is an inhibitor of topoisomerase II. Lonidamine depletes cellular adenosine 5'-triphosphate (ATP) and may impede energy-dependent DNA repair, MCF-7 human breast-cancer cells were treated in vitro with topotecan, novobiocin, and lonidamine alone, in paired combinations, and in combination with CDDP and melphalan. The three enzyme inhibitors alone and in combination did not increase tumor cell sensitivity to CDDP. However, the combinations of topotecan/novobiocin and lonidamine/novobiocin did enhance the cytotoxicity of melphalan. Mice bearing the FSaII fibrosarcoma were treated in vivo with topotecan, novobiocin, and lonidamine alone, in paired combinations, and in combination with CDDP, melphalan, BCNU, and cyclophosphamide. The combination of topotecan/novobiocin had the greatest impact on tumor cell sensitivity to each cytotoxic agent tested in both tumor cell-survival and tumor growth-delay assays. This sensitization was greatest at the highest concentrations of the cytotoxic agent tested. Combinations of topoisomerase I and topoisomerase II inhibitors may be useful as modulators of antitumor alkylating agents.

Topics: Adenocarcinoma; Alkylating Agents; Animals; Antineoplastic Combined Chemotherapy Protocols; Breast Neoplasms; Camptothecin; Drug Synergism; Female; Fibrosarcoma; Humans; Indazoles; Male; Mice; Mice, Inbred C3H; Novobiocin; Topotecan; Tumor Cells, Cultured

Comparisons have been made of the DNA polymerases of normal human lung and cecum, primary carcinomas of human lung, breast, and cecum, and resting and regeneration rat liver. The picture for the normal human tissues is similar to the one for unstimulated rat liver, that for the human carcinomas resembles regenerating rat liver. The human tissues contain two polymerases with sedimentation coefficients of about 3 and 7 S, the enzymes are restricted to the nucleus, and the specific activities of the 7 S polymerase, but not of the 3 S enzyme, are elevated in the cancers. Just as with the regenerating rat liver polymerases, the 3 S activity of a bronchogenic carcinoma is unaffected by cytosine arabinoside 5'-triphosphate and only little reduced by novobiocin, whereas DNA synthesis by the 7 S enzyme is abolished by both compounds. A variety of other inhibitory agents have similar effects on the 7 S polymerases of the human carcinomas and regenerating rat liver.

Topics: Animals; Breast Neoplasms; Cecal Neoplasms; Cecum; Cell Nucleus; Cytarabine; DNA-Directed DNA Polymerase; DNA, Neoplasm; Humans; Isoenzymes; Liver; Liver Regeneration; Lung; Lung Neoplasms; Neoplasms; Novobiocin; Nucleic Acid Synthesis Inhibitors; Rats