Structure-function relationships for a new series of pyridine-2-carboxaldehyde thiosemicarbazones on ribonucleotide reductase activity and tumor cell growth in culture and in vivo

The synthesis of a new series of pyridine-2-carboxaldehyde thiosemicarbazones (HCTs) that have amino groups in the 3- and 5-positions has allowed the comparison of the structure/function relationships with regard to inhibition of ribonucleotide reductase activity, L1210 cell growth in culture and L1210 leukemia in vivo. 3-Aminopyridine-2-carboxaldehyde thiosemicarbazones are more active than the corresponding 3-hydroxy-derivatives. The 3-amino-2-pyridine carboxaldehyde thiosemicarbazones were also more active then the 5-amino-2-carboxaldehyde thiosemicarbazones in inhibiting ribonucleotide reductase activity and L1210 cell growth in culture and in vivo. N-Acetylation of the 3-amino derivative resulted in a compound that was much less active both in vitro and in vivo; N-acetylation of the 5-amino derivative did not alter the in vitro inhibitory properties, but did eliminate the antitumor properties in vivo. When the most active HCTs were studied in more detail, it was found that the incorporation of [3H]thymidine into DNA was inhibited completely without the inhibition of [3H]uridine incorporation into RNA. Further, the conversion of [14C]cytidine to deoxycytidine nucleotides and incorporation into DNA was inhibited by the HCTs without an effect on the incorporation of cytidine into RNA. These data support the conclusion that ribonucleotide reductase is the major site of action of these HCTs. The 3-aminopyridine-2-carboxaldehyde thiosemicarbazones emerge as strong candidates for development for clinical trials in cancer patients.

Evidence for the glycosylation of the granulocyte colony-stimulating factor receptor

The granulocyte colony-stimulating factor receptor (G-CSFR) was overexpressed in WEHI-3B D+ myelomonocytic leukemia cells by the transfection of an expression plasmid containing the murine G-CSFR cDNA. Two different forms of the G-CSFR were observed in these cells by western blotting. Metabolic labeling and cell surface labeling demonstrated that the majority of the G-CSFR exists in a non-mature form and is presumably present in the cytoplasm as a 115-kDa protein. A relatively small portion of the G-CSFR is present as the fully mature form on the cell surface as a 150-kDa protein; this form of the G-CSFR binds to granulocyte colony-stimulating factor (G-CSF). Both the mature and non-mature forms of the G-CSFR appear to be N-glycosylated, as determined by glycanase digestion and inhibition of glycosylation by tunicamycin. Glycosylation of the G-CSFR may be of importance for the transport of the receptor to the cell surface.

Differentiation of HL-60 cells by dimethylsulfoxide activates a Na(+)-dependent nucleoside transport system

Uridine transport in undifferentiated HL-60 cells occurs primarily by facilitated diffusion, but a limited Na(+)-dependent process can be demonstrated (Km = 44 +/- 4.4 microM, Vmax = 0.13 +/- 0.01 microM/s). This latter transport system was inhibited by adenosine and inosine (Ki = 110 and 260 microM, respectively), whereas guanosine and thymidine were less effective (Ki = 1600 and 1200 microM, respectively). Dimethylsulfoxide (DMSO) caused a concentration-dependent decrease in facilitated uridine transport. This change was attributable to a decrease in the number of transporter molecules as determined by the binding of [3H]nitrobenzylthioinosine to cell membranes. Moreover, the Na(+)-dependent transport of uridine was enhanced by DMSO at a concentration of the polar solvent as low as 0.4%. When HL-60 cells were exposed to 1.0% DMSO, a marked increase in Na(+)-dependent uridine transport occurred within 72 hr, a time preceding maximum granulocytic differentiation. This change was attributable to an increase in transport affinity (Km = 1.54 +/- 0.65 microM), with no change in Vmax (Vmax = 0.13 +/- 0.02 microM/s). The consequence of these changes was the generation of a 3- to 4-fold increase in the intracellular concentration of uridine relative to the medium at a physiological concentration of 5 microM uridine. Similar increases in transport affinity were observed for adenosine, inosine, guanosine and thymidine in DMSO-differentiated HL-60 cells (Km values of 2 to 5 microM). These results complement our previous studies with phorbol 12-myristate 13-acetate, in which differentiation to a monocytic phenotype was also associated with enhanced Na(+)-dependent nucleoside transport.

The pH-dependent reduction of Adriamycin catalysed by NADH:cytochrome b5 reductase

Adriamycin is a redox active antineoplastic antibiotic that upon reduction can, in the presence of oxygen, redox cycle to form reactive oxygen species, while in anaerobiosis can generate a reactive quinone methide. NADH:cytochrome b5 reductase catalysed the reduction of adriamycin at pH 6.6 with an apparent Km of 1.8 microM; at pH 7.6, no measurable reduction of adriamycin occurred. Aerobically, in the presence of enzyme and NADH, adriamycin stimulated oxygen consumption and concomitant accumulation of hydrogen peroxide. At pH 7.6, no discernible oxygen consumption nor detectable hydrogen peroxide generation was observed. The findings demonstrate that NADH:cytochrome b5 reductase is capable of reducing adriamycin, in a pH-dependent manner, to species that can redox cycle in the presence of oxygen to form reactive oxygen molecules and thus may contribute to the generation of oxidative stress, a phenomenon suggested to be involved in both the toxicity and the antineoplastic activity of adriamycin.

Studies on the mechanism of decomposition and structural factors affecting the aqueous stability of 1,2-bis(sulfonyl)-1-alkylhydrazines

1,2-Bis(sulfonyl)-1-alkylhydrazines are highly active experimental antineoplastic agents which decompose with first-order kinetics in neutral aqueous solutions. These agents generate approximately 2 mol of the corresponding sulfinate, 1 mol of nitrogen, and 1 mol of the appropriate alcohol, produced as a consequence of the alkylation of water. Increasing the leaving-group ability of the sulfonyl moiety on N-1 shortens the half-life, while the converse happens with N-2 substitutions. Linear Hammett relationships are found for both types of substitutions. The predictable kinetics of decomposition makes these agents potential candidates for use in regional chemotherapy, where compounds with tunable short half-lives may offer some advantage. Prodrugs of extremely short-lived derivatives of this class may also have utility as targeted alkylating agents.

Inhibitors of ribonucleotide reductase. Comparative effects of amino- and hydroxy-substituted pyridine-2-carboxaldehyde thiosemicarbazones

A new series of alpha-(N)-heterocyclic carboxaldehyde thiosemicarbazones (HCTs) was studied for their effects on L1210 cell growth in culture, cell cycle transit, nucleic acid biosynthesis and ribonucleotide reductase activity. 3-Aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP) and 3-amino-4-methylpyridine-2-carboxaldehyde thiosemicarbazone (3-AMP) were the most active compounds tested with respect to inhibition of cell growth and ribonucleotide reductase activity. 5-Aminopyridine-2-carboxaldehyde thiosemicarbazone (5-AP) and 4-methyl-5-aminopyridine-2-carboxaldehyde thiosemicarbazone (5-AMP) were slightly less active. 3-AP, 3-AMP, 5-AP and 5-AMP inhibited the incorporation of [3H]thymidine into DNA without affecting the rate of incorporation of [3H]uridine into RNA. The uptake and incorporation of [14C]cytidine into cellular ribonucleotides and RNA, respectively, were not decreased by 3-AP or 3-AMP; however, the incorporation of cytidine into DNA via ribonucleotide reductase was inhibited markedly. Thus, a pronounced decrease in the formation of [14C]deoxyribonucleotides from radioactive cytidine occurred in the acid-soluble fraction of 3-AP- and 3-AMP-treated L1210 cells. Consistent with an inhibition of DNA replication that occurred at relatively low concentrations of 3-AP and 3-AMP, cells gradually accumulated in the S-phase of the cell cycle; at higher concentrations of 3-AP and 3-AMP, a more rapid accumulation of cells in the G0/G1 phase of the cell cycle occurred, with the loss of the S-phase population, implying that a second less sensitive metabolic lesion was created by the HCTs. N-Acetylation of 3-AMP resulted in a compound that was 10-fold less active as an inhibitor of ribonucleotide reductase activity and 8-fold less active as an inhibitor of L1210 cell growth. N-Acetylation of either 5-AP or 5-AMP did not alter the inhibitory properties of these compounds. The results obtained provide an experimental rationale for the further development of the HCTs, particularly 3-AP and 3-AMP, as potential drugs for clinical use in the treatment of cancer.

Differentiation of WEHI-3B D+ myelomonocytic leukemia cells induced by ectopic expression of the protooncogene c-jun

The product of the protooncogene c-jun is one of the components of the AP-1 transcription factor complex, which is involved in the control of cell proliferation and differentiation. To study the role of c-jun in leukemia cell growth and maturation, a plasmid (pMTJ11) was constructed that contained the rat c-jun complementary DNA under the control of the human metallothionein promoter and the neo gene. Murine myelomonocytic WEHI-3B D+ cells were transfected by electroporation with the linearized pMTJ11 plasmid and subsequently cloned in the presence of G-418. Exposure of these clones to cadmium resulted in a high level of expression of c-jun mRNA and protein, as demonstrated by Northern hybridization and Western blotting. When these clones were examined immediately after their establishment, expression of c-jun was accompanied by the appearance of a mature phenotype in many clones, as measured by the reduction of nitroblue tetrazolium and by the expression of Mac-1 (CD11b), a cell surface marker on differentiated cells. Morphological changes indicative of the differentiated state were also observed by staining. These findings indicate that expression of c-jun is capable of initiating the differentiation of WEHI-3B D+ cells in the absence of an external inducer of maturation. Furthermore, the expression of c-jun led to an enhancement of the induction of the differentiation of WEHI-3B D+ cells by retinoic acid, suggesting an involvement of c-jun in the retinoic acid signal transduction pathway.

Reversal of etoposide resistance in non-P-glycoprotein expressing multidrug resistant tumor cell lines by novobiocin

Previous reports from this laboratory have demonstrated that novobiocin produces supraadditive cytotoxicity and increases the formation of drug-stabilized topoisomerase II-DNA covalent complexes in WEHI-3B myelomonocytic leukemia and A549 lung carcinoma cells when combined with etoposide (VP-16). Inhibition of the efflux of VP-16 by novobiocin is responsible for the increase in VP-16 accumulation, which in turn leads to increased formation of VP-16-stabilized topoisomerase II-DNA covalent complexes and increased cytotoxicity. We now report that novobiocin synergistically enhanced the sensitivity of the multidrug resistant variants, WEHI-3B/NOVO and A549(VP)28, to VP-16, causing almost complete reversal of the resistance to the epipodophyllotoxin. These two tumor cell variants are resistant to several topoisomerase II-targeted drugs, particularly VP-16, but not to Vinca alkaloids; this finding corresponds to the fact that they do not overexpress the P-glycoprotein. The effects of novobiocin in these resistant sublines are mediated through the intracellular accumulation of VP-16, resulting in an increase in the formation of lethal VP-16-induced topoisomerase II-DNA covalent complexes. In the P-glycoprotein expressing multidrug resistant HCT116(VM)34 colon carcinoma and L1210/VMDRC0.06 leukemia cell lines, the latter being transfected with the human mdr-1 gene, novobiocin did not potentiate the cytotoxic activity of VP-16 nor increase the intracellular accumulation of VP-16 and the formation of covalent complexes, whereas their normal counterparts were sensitive to the potentiating activity of novobiocin when used in combination with VP-16. These results indicate that the action of novobiocin on the intracellular transport of VP-16 is not directed at the level of the P-glycoprotein, but that the action of novobiocin is antagonized by the presence of the P-glycoprotein. Since novobiocin is a clinically available antibiotic, has numerous structural analogues available for comparative studies, and has a relatively low toxicity profile, this drug, as well as structurally related agents, would appear to have significant clinical potential in combination with an epipodophyllotoxin for the treatment of non-P-glycoprotein expressing multidrug resistant tumors.

Synthesis and evaluation of 1-acyl-1,2-bis(methylsulfonyl)-2-(2- chloroethyl)hydrazines as antineoplastic agents

A series of 1-acyl-1,2-bis(methylsulfonyl)-2-(2-chloroethyl)hydrazines, conceived as more potent analogs of 1-(2-chloroethyl)-1,2,2-tris(methylsulfonyl)hydrazine, were synthesized and evaluated for antineoplastic activity against the L1210 leukemia in mice. Of these, 1-acetyl-1,2-bis-(methylsulfonyl)-2-(2-chloroethyl)hydrazine produced "cures" of mice bearing the L1210 leukemia at dosage levels that were considerably less than those at which the tris(sulfonyl) analog produced its antineoplastic effects. This compound was also found to have pronounced activity against the P388 leukemia and against several solid tumors, including the B16F10 melanoma, the M5076 reticulum cell sarcoma, and the M109 lung carcinoma. Furthermore, the acyl derivatives were in general considerably more resistant to hydrolysis in aqueous media and more prone to protease- and thiol-mediated activation than the tris(sulfonyl) analog. The former property is important to formulation, while the latter properties may result in some degree of drug targeting and enhancement of the therapeutic indices of these agents.

Adducts of mitomycin C and DNA in EMT6 mouse mammary tumor cells: effects of hypoxia and dicumarol on adduct patterns

6-CH3-3H-Mitomycin C (MC) was used to identify MC-DNA adducts formed in EMT6 mouse mammary tumor cells. DNA was isolated from cells treated with 3H-MC. The DNA was enzymatically digested, and the digest was analyzed for 3H-labeled adducts by high performance liquid chromatography. All four major adducts previously isolated and characterized in cell-free systems were detected: two different monoadducts and two bisadducts forming DNA-interstrand and DNA-intrastrand cross-links, respectively. No MC-DNA adducts other than the DNA interstrand cross-link had been shown previously to be formed in living cells. A MC-deoxyguanosine adduct of unknown structure was also detected in DNA from EMT6 cells; this adduct was also formed with purified EMT6 DNA. High performance liquid chromatography analysis was further applied to study the relationship between DNA adducts and cytotoxicity. The number of adducts increased with the concentration of MC in both aerobic and hypoxic cells. At a constant drug level, more adducts were observed in cells treated under hypoxic conditions than in cells treated aerobically; at 2 microM MC, 4.8 x 10(-7) and 3.1 x 10(-7) adducts/nucleotide were observed under hypoxic and aerobic conditions, respectively. The increased adduct frequency under hypoxia correlates with the known increased cytotoxicity of MC to EMT6 cells under hypoxic conditions. In addition, a higher ratio of cross-linked adducts to monoadducts was observed in hypoxic cells. The high performance liquid chromatography techniques were also used to examine the effects of dicumarol (DIC) on adduct patterns in cells treated simultaneously with 3H-MC. The MC-DNA adduct frequencies in DIC-treated cells were increased 1.5-fold under hypoxia and decreased 1.6-fold under aerobic conditions from those observed without DIC. This finding correlates with the known DIC-induced increase and decrease in the cytotoxicity of MC in hypoxic and aerobic EMT6 cells, respectively. The monoadduct resulting from monofunctionally activated MC was suppressed by DIC under both hypoxic and aerobic conditions. In addition, DIC induced the selective formation of an unknown DNA-associated radiolabeled substance in hypoxic cells; this is hypothesized to be a cytotoxic DNA lesion produced by a DIC-stimulated oxido-reductase. The methodology developed to measure MC adduct patterns may be useful as an indicator of distinct enzymatic activation processes for this drug.

Reductive activation of mitomycin C by NADH:cytochrome b5 reductase

Mitomycin C requires bioreduction in order to exert its cytotoxic action. Activation of mitomycin C to an electrophile was equally supported by NADPH and NADH in EMT6 tumor cell sonicates under hypoxia. No alkylation was observed under aerobic conditions. Purified NADH:cytochrome b5 reductase catalyzed the reduction of mitomycin C with a Km of 23 microM at pH 6.6. At pH 7.6, the rate of enzymatic reduction of mitomycin C was 61% of that at pH 6.6. NADH:cytochrome b5 reductase catalyzed the activation of mitomycin C to alkylating metabolites under both hypoxic and aerobic conditions, with alkylation being 1.5 times greater in hypoxia. Dicumarol at 100 microM inhibited the NADH:cytochrome b5 reductase-catalyzed reduction of mitomycin C by 24% and by 57% at 300 microM. The degree of inhibition of the enzyme by dicumarol was the same at both pH 6.6 and 7.6. NADH:cytochrome b5 reductase exhibited a small but measurable NADH-oxidase activity, which was unaffected by 300 microM dicumarol. These findings demonstrate that (a) NADH:cytochrome b5 reductase can metabolically activate mitomycin C and (b) dicumarol is capable of inhibiting this enzymatic activity.

Enhancement of pertussis-toxin-sensitive Na(+)-dependent uridine transporter activity in HL-60 granulocytes by N-formylmethionyl-leucyl-phenylalanine

N-Formyl-Met-Leu-Phe (FMLP), at concentrations as low as 5 nM, caused an increase in intracellular uridine pools in dimethyl sulphoxide (Me2SO)-differentiated HL-60 cells. Intracellular uridine pools were elevated rapidly and reached a maximum within 10 min of exposure to 10 microM FMLP, followed by a gradual decline. This enhancement by FMLP was a consequence of a 3-fold increase in the Vmax of pertussis-toxin-sensitive Na(+)-dependent uridine transport system, with no change in the apparent Km. Km values of 2.67 +/- 0.45 and 3.85 +/- 0.52 microM and Vmax. values of 0.046 +/- 0.017 and 0.125 +/- 0.020 microM/s were obtained for untreated and FMLP-treated Me2SO-differentiated cells respectively. The effect of FMLP on the Na(+)-dependent transport of uridine in Me2SO-differentiated HL-60 cells was specific, as the facilitated transport of uridine was unaffected. Furthermore, this phenomenon was not observed in undifferentiated, phorbol 12-myristate 13-acetate (PMA)-differentiated or pertussis-toxin-treated Me2SO-differentiated HL-60 cells. Removal of extracellular Ca2+ with EGTA abolished the FMLP enhancement of uridine transport in a reversible manner, suggesting the involvement of Ca2+. However, the Ca2+ ionophore A23187 only partially mimicked the effect of FMLP. Similarly, with PMA the transport was sub-optimally enhanced, but a full activation was observed in cells treated with both A23187 and PMA. These findings suggest that activation of the Na(+)-dependent uridine transporter by FMLP in Me2SO-differentiated HL-60 cells involves a pertussis-toxin-sensitive G-protein with a bifurcating signal-transduction pathway.

Antisense oligonucleotides to the p65 subunit of NF-kappa B block CD11b expression and alter adhesion properties of differentiated HL-60 granulocytes

NF-kappa B is a pleiotropic regulator of a variety of genes implicated in the cellular response to injury. This function has been attributed to the coordinated binding of subunits of NF-kappa B to distinct regions of the promoter elements of numerous genes, including cytokines, growth factor receptors, and adhesion molecules. Antisense phosphorothioate oligonucleotides to the p50 and p65 subunits of the NF-kappa B complex were used to define the physiologic role of this transcription factor in resting and stimulated granulocytes. A reduction in the expression of p65 was produced by treatment with the phosphorothioate antisense oligodeoxynucleotide. This reduction was accompanied by rapid changes in the cellular adhesion of dimethyl sulfoxide-differentiated HL-60 leukemia cells stimulated by 12-O-tetradecanoylphorbol 13-acetate (TPA). These effects were characterized by a marked reduction in CD11b integrin expression on the surface of treated cells. Furthermore, the p65 antisense oligomer effectively abolished an upregulation of CD11b that was produced by formyl-met-leu-phe and TPA. However, the p65 antisense phosphorothioate oligodeoxynucleotide had no significant effect on the production of reactive oxygen intermediates or on phagocytosis by these cells. These findings indicate that antisense oligomers to p65 can be used to define the role of NF-kappa B in the activation pathways of neutrophils.

Cellular pharmacology of quinone bioreductive alkylating agents

The cellular pharmacology of the mitomycin bioreductive alkylating agents is complex. This reflects in part the chemical characteristics of these quinones, which have multiple sites of reactivity and the capacity to produce a large number of different lesions of biological importance. Moreover, at least six different enzymes are capable of activating these compounds; the nature of the active species and the resultant biological lesions can vary with the activating enzyme. The relative activities of these reductases vary in different cell lines and can be modulated by pH and oxygenation. The effects of a quinone bioreductive alkylating agent therefore depend upon both the cell line and the microenvironment. DNA damage appears to be critical to the cytotoxic effects of these compounds. Both monoadducts and bis-adducts (forming interstrand and intrastrand cross-links) have been identified in DNA from drug-treated cells. The pattern of adduct formation varies with the compound and the environment. Alkaline elution studies suggest a correlation between DNA cross-linking and cytotoxicity, both in air and in hypoxia. The rate of production of oxygen radicals and the importance of radical reactions in producing cytotoxic damage vary for different quinones and for different environments. While the potency of the bioreductive quinones varies with their redox potential, the direction and magnitude of the oxic/hypoxic differential cannot yet be predicted from the structures.

Evaluation of rhodamine 123 as a probe for monitoring mitochondrial function in Trypanosoma brucei spp

Rhodamine 123, a membrane potential-specific dye, has been evaluated as a probe to monitor the function of the mitochondrion in long slender bloodstream and procyclic trypomastigotes of several Trypanosoma brucei spp. By epifluorescence microscopy, mitochondrial development has been followed in long slender bloodstream and procyclic organisms stained with rhodamine 123. To photograph stained long slender bloodstream forms, it was necessary to develop a method to completely immobilize viable organisms. In both parasite forms, as the cell cycle progressed, the mitochondrion developed from a thread-like structure to a highly branched organelle. A dramatic reorganization occurred preceding cytokinesis to produce two progeny thread-like structures which were partitioned into newly formed daughter cells. The organelle within the long slender trypomastigote was found to stain optimally at 0.3 microgram/ml of rhodamine 123, while the procyclic form required 3.0 micrograms/ml. The results suggest that the plasma membrane potential is higher in the long slender parasite than in the procyclic form. The effects of inhibitors that disrupt mitochondrial function were examined in long slender and procyclic parasites, and some of these agents were shown to affect rhodamine 123 accumulation and retention. In long slender trypomastigotes the trypanosome alternative oxidase does not appear to be coupled to proton pumping, whereas in procyclic organisms the effects of inhibitors indicate that this oxidase may be coupled to a pathway that is branched preceding an antimycin A1-sensitive site.

Induction of the differentiation of HL-60 and WEHI-3B D+ leukemia cells by lithium chloride

The use of lithium chloride in manic-depressive patients and in patients receiving myelo-suppressive cancer chemotherapeutic agents is accompanied by a sustained leukocytosis due to an increase in granulocyte production. This property suggests that lithium chloride may have effects on hematopoietic differentiation. Treatment of cultured WEHI-3B D+ murine myelomonocytic and HL-60 human promyelocytic leukemia cells with millimolar concentrations of lithium chloride resulted in concentration-dependent increases in the number of differentiated myeloid cells, as determined by the ability of the cells to reduce nitroblue tetrazolium and by the binding of myeloid specific antibodies, and was associated with an inhibition of cellular proliferation. The effects of lithium chloride on growth and differentiation were antagonized by KCl, whereas NaCl had little effect. The induction of leukemic cell maturation by lithium chloride was markedly enhanced by the addition of low levels of retinoic acid. In contrast, other differentiation inducing agents (i.e. dimethyl sulfoxide and selenazofurin) had no effect on the degree of maturation induced by lithium. These findings suggest that the combination of lithium chloride and retinoic acid may have clinical utility in the treatment of leukemia through the induction of terminal differentiation.

Porfiromycin as an adjunct to radiotherapy in young and old mice

Radiobiological data and measurements with O2 microelectrodes show that EMT6 tumors implanted into aged mice have a higher proportion of radioresistant, hypoxic cells than do tumors implanted into young adult animals; radiation is less effective in killing cells in tumors in old mice than in tumors in young adult mice. The studies reported here examine the effects of porfiromycin (POR), a bioreductive alkylating agent shown previously to be preferentially toxic to hypoxic EMT6 cells in vitro and in solid tumors in young adult mice. POR was effective in attacking the hypoxic cells of tumors in aged mice; regimens combining POR with x-rays overcame the radioresistance of tumors in the old animals. Comparisons of the distribution of 3H-labeled POR in young and old mice showed that tumors in aged mice had a slightly larger proportion of areas with necrotic features, which bound higher levels of tritiated POR than did healthy tumor regions without necrotic features. Studies of histology, lissamine green distributions, binding of tritiated POR, and radiation and POR cytotoxicity suggested that tumors in old mice contained a larger proportion of poorly perfused tumor cells, and that cells in these regions were resistant to radiation and sensitive to POR. Studies of the distribution of POR in normal tissues and of the toxicity of POR to bone marrow progenitor cells (CFU-GM) revealed no differences between young and old animals, showing that the differences observed in tumors reflected differences in the microenvironments within the tumors, rather than differences in the processing of drug in young and old animals.

Determination of type I transglutaminase in differentiating normal and neoplastic human keratinocytes by an in situ radioimmunoassay

The presence of type I transglutaminase was determined in the neoplastic human keratinocyte line SqCC/Y1 and in normal human epidermal keratinocytes (NHEK) by an in situ radioimmunoassay which corresponded directly with the measurement of type I transglutaminase enzymatic activity. Dexamethasone induced differentiation of SqCC/Y1 cells caused a marked increase in transglutaminase immunoreactivity and enzymatic activity over non-steroid treated cells in a concentration-related and a time-related fashion. Retinoic acid suppressed the dexamethasone induced increase in type I transglutaminase immunoreactivity in differentiating SqCC/Y1 cells. The type I transglutaminase radioimmunoassay should be useful in studies focusing on the regulation of transglutaminase activity in normal and neoplastic keratinocytes, and for rapidly screening agents for their effects on squamous cell differentiation.

Regulation of the differentiation of WEHI-3B D+ leukemia cells by granulocyte colony-stimulating factor receptor

To investigate the role of the G-CSF receptor (G-CSFR) in mediating the action of G-CSF, WEHI-3B D+ murine myelomonocytic leukemia cells were transfected with a plasmid containing the murine G-CSFR gene. Overexpression of G-CSFR in transfected clones was demonstrated by northern blotting, binding of [125I]rhG-CSF and cross-linking experiments. A high level of expression of the G-CSFR did not promote or suppress cellular proliferation or initiate differentiation; however, exposure of transfected cells to G-CSF in suspension culture caused a large percentage of the population to enter a differentiation pathway, as determined by two markers of the mature state, the ability of cells to reduce nitroblue tetrazolium (NBT) and to express the differentiation antigen Mac-1 (CD11b) on the cell surface. Thus, upon treatment with 10 ng/ml of G-CSF, 60% or more of transfected cells exhibited NBT positivity; whereas, in contrast, nontransfected cells exhibited only 6% NBT positivity in response to G-CSF. An eightfold increase in Mac-1 expression over that of the parental line was also observed in transfected cells exposed to G-CSF. The growth rate of the transfected clones was decreased by exposure to G-CSF, presumably due to terminal differentiation. The findings suggest that the predominant function of G-CSF and its receptor in WEHI-3B D+ cells is to mediate differentiation and that the level of the G-CSFR portion of the signal transduction mechanism in this malignant cell line is important for a response to the maturation inducing function of the cytokine.

Studies on the mechanism of the cytotoxic action of the mitomycin antibiotics in hypoxic and oxygenated EMT6 cells

The mitomycin antibiotics, because of their preferential toxicities for hypoxic cells, have significant potential as adjuncts to ionizing radiation in the treatment of solid tumors. To gain information on the mechanism by which these agents exert their cytotoxicities to hypoxic and aerobic cells, the effects of MC, POR and several of their analogs were studied in EMT6 mammary carcinoma cells. The rate of uptake of POR by these cells was directly correlated with the cytotoxicity produced by this agent under both hypoxia and aeration. At equivalent concentrations, uptake of POR into hypoxic cells was more rapid than into aerobic cells. Hypoxic cells also accumulated the antibiotic in concentrations well in excess of that present in the extracellular medium, presumably as a result of reductive activation and covalent binding of POR to cellular structures. Such activation and binding occur to a much lesser degree in aerated cells, resulting in the rapid efflux of POR from these cells when the antibiotic is removed from the extracellular environment. To gain information on the reaction of POR with DNA, mono- and bis-adducts formed in EMT6 cells exposed to this agent were measured. Three major adducts were formed. Two were mono-adducts consisting of deoxyguanosine linked at its N2-position to the C-1 of POR and of 10-decarbamoyl POR. The third was a bis-adduct in which POR was cross-linked to two deoxyguanosines at their N2-positions. More adducts were formed in hypoxia than in air, and more bis-adducts were present in hypoxic cells. Simultaneous exposure of cells to both POR and DIC reduced the total adduct level and a new unknown adduct was formed, primarily under hypoxia. Several mitomycins were evaluated for their capacity to kill EMT6 cells and to produce DNA cross-links in both hypoxia and aeration. The number of cross-links required to produce a given amount of cell kill was similar, regardless of the mitomycin employed or the degree of oxygenation. The findings support the concept that DNA is a critical target in the action of the mitomycins and that cross-linking of the DNA creates an important lesion for cytodestruction.

Novobiocin-induced accumulation of etoposide (VP-16) in WEHI-3B D+ leukemia cells

A previous report from this laboratory demonstrated that novobiocin produced supra-additive cytotoxicity when combined with etoposide (VP-16) or teniposide (VM-26) in WEHI-3B D+ and A549 cells. The increase in cytotoxicity was accompanied by an increase in the formation of drug-stabilized protein-DNA covalent complexes. We now report that novobiocin increased the amount of VP-16-induced covalent complexes between the 170 kDa form of topoisomerase II and DNA in WEHI-3B D+ cells, as measured by the band-depletion immunoblotting assay, while it did not affect the extractable topoisomerase II activity, measured by the unknotting of P4 phage DNA and by a DNA cleavage assay. Novobiocin progressively increased the steady-state concentration of intracellular VP-16. Removal of novobiocin resulted in a rapid return of VP-16 to levels comparable to those seen with VP-16 alone. The increased accumulation of VP-16 was accounted for by an increase in the exchangeable fraction only. The novobiocin-mediated increase in the steady-state concentration of VP-16 occurred whether novobiocin was added simultaneously with VP-16 or was added after a steady-state level of VP-16 had been achieved. Novobiocin did not affect the initial rate of uptake of VP-16; however, it inhibited the efflux of the epipodophyllotoxin. In fact, when cells were loaded with the same level of VP-16 in the presence or absence of novobiocin, the efflux curves in the presence or absence of novobiocin were significantly different. We conclude that the inhibition of VP-16 efflux by novobiocin is responsible for the increase in VP-16 accumulation, leading to increased formation of VP-16-stabilized topoisomerase-II-DNA covalent complexes and increased cytotoxicity.

Glycosylation of annexin I and annexin II

Human placental annexin I and annexin II were shown to be glycosylated by one-dimensional affinity blotting with the lectin concanavalin A, which recognizes D-mannose and D-glucose residues. Further evidence that annexin I and annexin II are glycosylated was provided by the finding that these proteins incorporated D-[2,6-3H]mannose and D-[6-3H]glucose when they were biosynthesized by the human squamous carcinoma cell line SqCC/Y1. Annexin I and annexin II could be rapidly purified from a human placental membrane extract by concanavalin A-Sepharose, which indicated that these proteins contain two biantennary mannosyl residues.

Synthesis and antitumor activity of amino derivatives of pyridine-2-carboxaldehyde thiosemicarbazone

Various substituted pyridine-2-carboxaldehyde thiosemicarbazones (12 compounds) have been synthesized and evaluated for antineoplastic activity in mice bearing the L1210 leukemia. Oxidation of 3-nitro-2-picoline,5-nitro-2-picoline,3-nitro-2,4-lutidine, and 5-nitro-2,4-lutidine with selenium dioxide was employed to generate the corresponding pyridine-2-carboxaldehydes, which were then converted to cyclic ethylene acetals and subsequently reduced to amino and hydroxyamino derivatives by catalytic hydrogenation. Condensation of nitro aldehydes and acetals with thiosemicarbazide afforded the respective thiosemicarbazones. Acetylation of the amino acetals and alkylsulfonation of the 5-amino acetal, followed by condensation with thiosemicarbazide was employed to yield amide thiosemicarbazones. The most active compounds synthesized were 3-aminopyridine-2-carboxaldehyde thiosemicarbazone and 3-amino-4-methylpyridine-2-carboxaldehyde thiosemicarbazone which produced against the L1210 leukemia, % T/C values of 246 and 255, and 40% 60-day long-term survivors at two daily doses of 40 mg/kg and 10 mg/kg, respectively, for six consecutive days.

Synthesis and antitumor activity of 3- and 5-hydroxy-4-methylpyridine-2-carboxaldehyde thiosemicarbazones

To develop an alpha-(N)-heterocyclic carboxaldehyde thiosemicarbazone with clinical utility as an anticancer agent, two analogues, 3-hydroxy-4-methylpyridine-2-carboxaldehyde thiosemicarbazone (3-HMP) and 5-hydroxy-4-methylpyridine-2-carboxaldehyde thiosemicarbazone (5-HMP), of 5-hydroxypyridine-2-carboxaldehyde thiosemicarbazone (5-HP) have been designed and synthesized by two different methods. 3-HMP and 5-HMP both showed better antitumor activity than their respective parent compounds, 3-hydroxypyridine-2-carboxaldehyde thiosemicarbazone and 5-HP, in mice bearing the L1210 leukemia.

The effects of microtubule disrupting drugs on the differentiation of HL-60 leukemia cells

We and others have previously shown that microtubules (MT) are stained more intensely and are organized differently in differentiating leukemia cells. To study the effects of the MT disrupting drugs, colchicine (Coln) and vincristine (VCR), on the maturation process, HL-60 leukemia cells were pretreated with Coln or VCR for 1 h and then exposed to either retinoic acid (RA) or dimethyl sulfoxide (DMSO). Neither Coln nor VCR induced the differentiation of HL-60 cells, but in combination with RA increased the percentage of nitroblue tetrazolium-positive cells, the expression of the mature myelocyte surface marker Mo 1, and the content of MT over the effects produced by RA alone. In contrast, pretreatment with Coln or VCR delayed the commitment to a differentiation pathway induced by DMSO. The supra-additivity exhibited between Coln and RA required the administration of Coln prior to RA; thus, Coln had no effect when given two days after the cellular exposure to RA. The findings suggest that (a) a combination of non-cytotoxic concentrations of Coln or VCR with RA may have clinical utility as inducers of leukemia cell maturation, and (b) MT may be involved in modulating signal transduction during the initiation of HL-60 cell differentiation.