The effects of adriamycin on intracellular calcium concentrations of L1210 murine leukemia cells

Changes in the concentration of intracellular Ca2+ may be an important component of the mechanism of adriamycin toxicity to tumor cells. Adriamycin interacts with the plasma membrane, a phenomenon which may lead to a direct modulation of Ca2+ transport proteins or, since the drug is a quinone, may lead to indirect changes in Ca2+ homeostasis induced by oxidative stress to the cell. The calcium content of L1210 murine leukemia cells treated with adriamycin for up to 6 hr was estimated using the cell-impermeant dye arsenazo-III. Pools of intracellular Ca2+ were released to the extracellular compartment, where they reacted with the dye by sequential treatment of the cells with m-fluorocarbonylcyanidediphenylhydrazone (FCCP) and the Ca2+-ionophore A23187. Pretreatment of L1210 cells with ruthenium red (5 microM) selectively decreased the FCCP-releasable Ca2+ pool, which suggested it was mitochondrial in origin. Continuous exposure of L1210 murine leukemia cells in vitro to 5 or 10 microM adriamycin for 2 hr did not produce any change in the intracellular concentration of releasable Ca2+; at 4 hr, however, the total releasable pool of Ca2+ rose by 29% and 46% for 5 and 10 microM adriamycin respectively. This increase was seen predominantly in the mitochondrial pool. Exposure of L1210 cells to the quinone, menadione, also increased the releasable pools of cellular Ca2+ but like adriamycin, only after an incubation period of 4 hr. These results contrasted with a rapid decrease in mitochondrial Ca2+ concentration produced by a short (5 min) exposure to 500 microM t-butylhydroperoxide, a generator of free radicals. After treatment with 8 mM lidocaine, a membrane fluidizing agent, there was a rapid fall in extramitochondrial Ca2+. These findings suggest that changes in L1210 Ca2+ homeostasis induced by adriamycin and menadione are late, and possibly common, events of quinone toxicity to L1210 cells, adriamycin does not have an immediate effect on Ca2+ ion transport produced by the direct interaction of the antibiotic with the plasma membrane, and oxidative stress induced by redox-active quinones may not be important for the induction of toxicity in neoplastic cells.

Reactivity of thiols towards derivatives of 2- and 6-methyl-1,4-naphthoquinone bioreductive alkylating agents

The stoichiometry and kinetics of the anaerobic reactions between some thiols and derivatives of 2- and 6-methyl-1,4-naphthoquinones in water were measured using stopped flow spectrophotometry. The stoichiometry of the reaction with representative compounds was 1:2 thiol:quinone, a finding consistent with the formation of a hydroquinone as well as a thioether in the reaction. The first-order dependence of rate on thiol concentration, and the pH-dependent rate constants indicated that the thiolate anion was involved in the rate-limiting step, with rate constants at pH 7.6 generally increasing in the order glutathione (GSH) less than cysteamine less than dithiothreitol (DTT) less than cysteine. Despite the lower reactivity of GSH, the half-lives of the uncatalyzed conjugation reaction of these quinones at typical biological concentrations of GSH (e.g. 2 mM) ranged from about 2.0 to 20 s at pH 7.6 and 25 degrees C. The implications of these reactions in the use of naphthoquinones as potential bioreductive alkylating agents and as hypoxic cell radiosensitizers are discussed.

Cytotoxicity and differentiating actions of adriamycin in WEHI-3B D+ leukemia cells

The monomyelocytic leukemia WEHI-3B D+ can be induced to differentiate into mature granulocytes in suspension culture when exposed to 40 nM adriamycin. Treated cells underwent approximately two divisions prior to reaching plateau phase, with approximately 55% of the cell population expressing nitro blue tetrazolium positivity (NBT+) by day 3. Decreased cellular proliferation was paralleled by a progressive increase in morphologically mature granulocytic cells. Maturation was also characterized by a 4.4-fold increase in Fc receptors on the cell surface. An increase in the size of adriamycin-treated cells occurred and correlated with residency in the G2M phase of the cell cycle. Adriamycin-induced NBT+ cells, which contained the highest levels of Fc receptors, were also found to reside in G2M. Adriamycin blocked cells in the G2M phase of the cell cycle by 8 hr (125% above control), and this arrest reached its maximum by 20 hr (194% above control). Concomitant with the block in the cell cycle was the commitment by these cells within 8 hr to the granulocytic pathway of differentiation. Fractionation of cells by centrifugal elutriation into enriched phases of the cell cycle was consistent with the hypothesis that induction of the differentiation program was initiated either in G1 or very late in the cell cycle. Immobilized adriamycin, which does not gain access to the cell interior, did not induce the maturation of WEHI-3B D+ cells, nor did it block their replication in a specific phase of the cell cycle; however, immobilized adriamycin was 30-fold more toxic to WEHI-3B D+ cells than free drug. Incubation of WEHI-3B D+ cells with the semisynthetic adriamycin analog N-trifluoroacetyl adriamycin-14-valerate (AD-32) resulted in approximately 50% of the cell population being NBT+ by day 3. The findings suggest that adriamycin must be able to enter cells to induce maturation, and that at least some portion of its toxicity is associated with an effect at the surface membrane. Furthermore, the results obtained with AD-32 imply that intercalation into DNA is not necessary for induction of the differentiated phenotype.

Induction of the differentiation of HL-60 promyelocytic leukemia cells by palmitoleic and myristoleic acids

Exposure of HL-60 promyelocytic leukemia cells to palmitoleic or myristoleic acids for 6 days produced both functional and morphological granulocytic maturation. Considerably less or no induction of differentiation occurred with a variety of other fatty acids. Combinations of fatty acids with the granulocytic inducer of maturation, DMSO, did not significantly increase the degree of differentiation of HL-60 cells over that produced by the fatty acids alone. A series of HL-60 cell clones were isolated which differed in sensitivity to the differentiation inducing activities of palmitoleic acid, myristoleic acid, and DMSO. These findings imply that myristoleic acid and palmitoleic acid act to initiate the maturation process by events that are distinct from those produced by DMSO. The capacity of myristoleic and palmitoleic acids to induce leukemic cell differentiation is discussed with respect to protein acylation by fatty acids.

The relationship between epidermal growth factor receptors and the terminal differentiation of A431 carcinoma cells

The replication of human epidermoid carcinoma A431 cells is inhibited by epidermal growth factor (EGF), with 5 ng/ml of EGF causing 50% inhibition of cellular proliferation. EGF resistant clones isolated from A431 cells were able to replicate in the presence of 100 ng/ml of EGF. That this insensitivity to EGF was probably due to a decrease in the expression of EGF receptors (EGFR) on the cell surface was shown using an EGFR cDNA probe to detect a 68% to 85% decrease relative to parental cells in the amount of EGFR mRNA in the EGF resistant clones. A corresponding decrease in surface EGFR levels was also detected in EGF resistant clones as measured by 125I-EGF binding. Eighteen percent of A431 cells cultured in serum-free medium for 6 days entered a pathway of terminal differentiation, as expressed by the formation of envelope-competent cells, whereas EGF resistant clones exhibited a considerably greater capacity to mature, even when cultured in serum-containing medium. The findings suggest that the concentration of EGFRs is important for the capacity of epidermal cells to undergo terminal differentiation in vitro.

A sensitive method to quantify the terminal differentiation of cultured epidermal cells

Terminal differentiation of normal and malignant keratinocytes is routinely determined by the ability of these cells to form cornified envelopes after incubation with a calcium ionophore. We have used the human squamous cell carcinoma, SqCC/Y1, to quantify cellular differentiation by the formation of detergent-insoluble protein. The methodology developed employs the metabolic labeling of detergent-insoluble cellular protein with [35S]methionine in the presence of a calcium ionophore. The ratio of filter-retainable radioactivity to that of total cellular protein was shown to be closely correlated to the results obtained by measuring the number of envelope-competent cells when cells were induced to enter a pathway of terminal differentiation in culture by serum deprivation or by treatment with hydrocortisone, and during the inhibition of maturation by either retinoic acid (RA) or epidermal growth factor (EGF). This way of measuring the degree of terminal differentiation of epidermal cells is a relatively simple one that readily allows the simultaneous measurement of multiple samples.

Introduction of deoxyribonucleoside triphosphates into intact cells by electroporation

A simple method, employing high-voltage electric discharge (electroporation), was developed to introduce phosphorylated nucleosides into the cytoplasm of viable cells. HL-60 leukemia cells permeabilized by this technique remained viable and incorporated deoxyribonucleoside triphosphates into nuclear DNA. Furthermore, DNA synthesis was depressed for at least 24 h in HL-60 cells made permeable to 1-beta-D-arabinosylcytosine 5'-triphosphate by this methodology. Electroporation was found to be applicable to the permeabilization of a wide variety of cell lines in culture to nucleotides, suggesting that this methodology may be useful for the introduction into intact cells of a wide variety of molecules that are not normally transported effectively.

Regulation of protein phosphotyrosine content by changes in tyrosine kinase and protein phosphotyrosine phosphatase activities during induced granulocytic and monocytic differentiation of HL-60 leukemia cells

About 1.5% of phosphorylated amino acid residues of HL-60 promyelocytic leukemia cells are phosphotyrosine. Induction of granulocytic differentiation by exposure to dimethylsulfoxide decreased tyrosine phosphorylation to 0.2%. A maximum 3-fold increase in tyrosine kinase activity and a 7-fold increase in protein phosphotyrosine phosphatase activity accompanied this change. Monocytic differentiation induced by 12-O-tetradecanoylphorbol-13-acetate, caused a decrease in phosphotyrosine levels to 0.1%; tyrosine kinase activity maximally increased 2-fold, and protein phosphotyrosine phosphatase activity increased 11-fold in these differentiated cells. Thus, although total tyrosine kinase activity markedly increased during differentiation, this was counteracted by an even greater elevation in protein phosphotyrosine phosphatase activity. The findings support the concept that tyrosine phosphorylation is important in the regulation of growth and differentiation of leukemia cells.

Nitrobenzyl derivatives as bioreductive alkylating agents: evidence for the reductive formation of a reactive intermediate

o- and p-nitrobenzyl chlorides and carbamates were chemically and electrochemically reduced in the presence and absence of the nucleophile morpholine; activation of these compounds by reduction was required to produce an intermediate capable of alkylation. The reduction products formed by the catalytic hydrogenation of each compound were examined by gas chromatography-mass spectrometry. In addition, the products generated by controlled-potential electrolysis were examined by ESR and NMR spectrometry. After a one-electron reduction, o- and p-nitrobenzyl chlorides were activated to the nitrobenzyl radicals, which subsequently dimerized to the dinitrobibenzyl derivatives or reacted with morpholine when present in the reaction medium to form the (nitrobenzyl)morpholine adducts. The nitrobenzyl carbamates were not activated after a one-electron reduction; however, the morpholine and the ether adducts of these agents were observed after catalytic hydrogenation. It was assumed that an intermediate or intermediates formed after the one-electron reduction product, or the full reduction product of the carbamates, were capable of alkylating various nucleophiles. Chemical reduction of the potential bioreductive alkylating agent (o-nitrobenzyl)-6-thioguanine produced (o-aminobenzyl)-6-thioguanine, indicating a lack of formation of a reactive electrophile by reduction. (o-, (m-, and (p-nitrobenzyl)-6-thioguanine analogues were also examined for cytotoxic activity toward EMT6 tumor cells under aerobic and hypoxic conditions. In agreement with the inability of (o-nitrobenzyl)-6-thioguanine to form a reactive species after chemical reduction, no decrease in the survival of neoplastic cells exposed to 10(-4) M drug occurred under either aerobic or hypoxic conditions.

Synthesis and evaluation of 1-(arylsulfonyl)-2-[(methoxycarbonyl)sulfenyl]-1-methylhydrazines++ + as antineoplastic agents

1-(Arylsulfonyl)-2-[(methoxycarbonyl)sulfenyl]-1-methylhydrazines, with the potential to function as biological methylating agents, were synthesized and evaluated as antineoplastic agents against the L1210 leukemia and the B16 melanoma in mice. All of the compounds of this class had significant activity against the B16 melanoma, with the most active compound, 2-[(methoxycarbonyl)sulfenyl]-1-methyl-1-[(4- methylphenyl)sulfonyl]hydrazine, producing percent T/C values for B16 melanoma tumor bearing mice of between 182 and 232 at dosage levels of from 12.5 to 50 mg/kg daily for 6 consecutive days. In contrast to the related class of agents, the N,N'-bis(sulfonyl)hydrazines reported earlier by this laboratory,1 the 1-(arylsulfonyl)-2-[(methoxycarbonyl)sulfenyl]-1-methylhydrazines were found to be inactive against the L1210 leukemia in vivo.

A scanning calorimetric study of the interaction of anthracyclines with neutral and acidic phospholipids alone and in binary mixtures

High sensitivity differential scanning calorimetry was employed to study the thermotropic behavior of multilamellar vesicles of neutral and acidic phospholipids and binary mixtures thereof in the presence of anthracycline antibiotics. Adriamycin and its lipophilic analogue, N-trifluoroacetyladriamycin-14-valerate (AD32) were investigated and compared to chlorpromazine and quinidine with respect to their ability to affect the pretransition and the main transition of the phospholipids suspended in physiological buffer. With liposomes of neutral dipalmitoylphosphatidylcholine the observed effects paralleled to some extent the corresponding octanol/buffer partition coefficients, with adriamycin being the least effective. Calorimetric measurements on liposomes prepared from pure dipalmitoylphosphatidylglycerol or from binary mixtures of dipalmitoylphosphatidylglycerol and dipalmitoylphosphatidylcholine showed that modulation of bilayer properties by adriamycin was greatly enhanced in the presence of negatively charged lipid headgroups presumably as a result of electrostatic interactions. AD32 interacted differently from adriamycin with the acidic bilayers at low drug concentrations, in a manner similar to that of its interaction with neutral bilayers. At high drug concentrations both adriamycin and AD32 produced transitions with multiple peaks not exhibited by chlorpromazine and quinidine which may be the result of a specific association of the anthracyclines with dipalmitoylphosphatidylglycerol. All four drugs produced only minor changes in the enthalpy of the main transition of the investigated lipids. The present findings are discussed in terms of their possible physiological relevance.

One-electron reduction of 2- and 6-methyl-1,4-naphthoquinone bioreductive alkylating agents

The semiquinones, Q.-, of derivatives of 2- and 6-methyl-1,4-naphthoquinones, some incorporating leaving groups with substituents such as CH2Br or CH2OCONHCH3, have been produced by radiolytic reduction of Q by (CH3)2COH radicals. The absorption spectra and decay kinetics of Q.- were all closely similar to that produced from 2-methyl-1,4-naphthoquinone, with no evidence for unimolecular elimination of a leaving group in the semiquinone form, but immediate loss of leaving group upon two-electron reduction of Q to the hydroquinone. The redox equilibria between Q/Q.- and O2/O2.- were characterized, and reduction potentials of the couples Q/Q.- in water at pH 7.6 were calculated. The implications of these observations for the use of these compounds as bioreductive alkylating agents or as radiosensitizers with potential selective activity toward hypoxic cells are discussed.

Cytotoxicity and DNA lesions produced by mitomycin C and porfiromycin in hypoxic and aerobic EMT6 and Chinese hamster ovary cells

Solid neoplasms may contain deficient or poorly functional vascular beds, a property that leads to the formation of hypoxic tumor cells, which form a therapeutically resistant cell population within the tumor that is difficult to eradicate by ionizing irradiation and most existing chemotherapeutic agents. As an approach to the therapeutic attack of hypoxic cells, we have measured the cytotoxicity and DNA lesions produced by the bioreductive alkylating agents mitomycin C and porfiromycin, two structurally similar antibiotics, in oxygen-deficient and aerobic cells. Mitomycin C and porfiromycin were preferentially cytotoxic to hypoxic EMT6 cells in culture, with porfiromycin producing a greater differential kill of hypoxic EMT6 cells relative to their oxygenated counterparts than did mitomycin C. Chinese hamster ovary cells were more resistant to these quinone antibiotics; although in this cell line, porfiromycin was significantly more cytotoxic to hypoxic cells than to aerobic cells, and the degree of oxygenation did not affect the toxicity of mitomycin C. Alkaline elution methodology was utilized to study the formation of DNA single-strand breaks and DNA interstrand cross-links produced by mitomycin C and porfiromycin in both EMT6 and Chinese hamster ovary cells. A negligible quantity of DNA single-strand breaks and DNA interstrand cross-links were produced in hypoxic and aerobic Chinese hamster ovary cells by exposure to mitomycin C or porfiromycin, a finding consistent with the considerably lower sensitivity of this cell line to these agents. In EMT6 tumor cells, no single-strand breaks appeared to be produced by these antitumor antibiotics under both hypoxic and aerobic conditions; however, a significant number of DNA interstrand cross-links were formed in this cell line following drug treatment, with substantially more DNA interstrand cross-linking being produced under hypoxic conditions. Mitomycin C and porfiromycin caused the same amount of cross-linking under conditions of oxygen deficiency; however, mitomycin C produced considerably more DNA cross-linking than did porfiromycin in oxygenated cells. DNA interstrand cross-links were observed in hypoxic EMT6 cells throughout a 24-h period following removal of mitomycin C and porfiromycin, with a decrease in DNA interstrand cross-links observed at 24 h. An increase in DNA interstrand cross-links occurred in aerobic EMT6 cells treated with mitomycin C and porfiromycin at 6 h after drug removal, with a decrease in these lesions being observed by 24 h, suggesting that the rate of formation of the cross-links may be slower and the removal of cross-links more rapid under aerobic conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Transcriptional regulation of the transferrin receptor in differentiating HL-60 leukemic cells

HL-60 promyelocytic leukemia cells were induced to differentiate along the granulocytic pathway by treatment with dimethylsulfoxide. A significant decrease in transferrin receptor specific mRNA was seen as early as 4 hr after exposure to inducer. Relative to untreated controls, transcript levels decreased 5-fold within 24 hr of exposure to dimethylsulfoxide and remained depressed throughout a 6-day treatment period. Reductions in receptor transcripts preceded the loss of surface receptor which in turn preceded the expression of the differentiated phenotype. The findings demonstrate that differentiation-associated regulation of the transferrin receptor can occur at the transcriptional level.

Synthesis and evaluation of 2-substituted 1-methyl-1-(4-tolylsulfonyl)hydrazines as antineoplastic agents

Several N-2 substituted 1-methyl-1-(4-tolylsulfonyl)hydrazines were synthesized and evaluated for antineoplastic activity against the L1210 leukemia and the B16 melanoma. The most active compound to emerge from this study, 2-(methylsulfonyl)-1-methyl-1-(4-tolylsulfonyl)hydrazine, produced maximum percent T/C values with L1210 leukemia and B16 melanoma tumor bearing mice of 207 and 209, respectively. While the attachment of an aryl-, aralkyl-, or alkylsulfonyl moiety to N-2 resulted in retention of activity against both tumor systems, the corresponding benzoyl, 4-nitrobenzoyl, and (2-nitrophenyl)sulfenyl analogues only displayed activity against the L1210 leukemia.

1,2-bis(arylsulfonyl)hydrazines. 2. The influence of arylsulfonyl and aralkylsulfonyl substituents on antitumor and alkylating activity

Several 1,2-bis(arylsulfonyl)-1-methylhydrazines were synthesized and evaluated for antineoplastic activity against the L1210 leukemia. The most active compound to emerge from this study, 2-[(4-chlorophenyl)sulfonyl]-1-methyl-1-(4-tolylsulfonyl)hydrazine , increased the survival time of tumor-bearing mice by 88%. The alkylating activity of the synthesized analogues and several compounds reported earlier was determined by measuring the absorbance at 540 nm of the alkylated product of 4-(4-nitrobenzyl)pyridine. The results obtained support the concept that the ability to alkylate is a necessary but not a sufficient condition for the expression of antitumor activity by agents of this class.

Generation of reactive oxygen radicals through bioactivation of mitomycin antibiotics

Mitomycin C (MC) is a naturally occurring anticancer agent which has been shown to be more cytotoxic to hypoxic tumor cells than to their aerobic counterparts. The mechanism of action of this agent is thought to involve biological reductive activation, to a species that alkylates DNA. A comparison of the cytotoxicity of MC to EMT6 tumor cells with that of the structural analogues porfiromycin (PM), N-(N',N'-dimethylaminomethylene)amine analogue of mitomycin C (BMY-25282), and N-(N',N'-dimethylaminomethylene)amine analogue of porfiromycin (BL-6783) has demonstrated that PM is considerably less cytotoxic to aerobic EMT6 cells than MC, whereas BMY-25282 and BL-6783 are significantly more toxic. The relative abilities of each of these compounds to generate oxygen free radicals following biological activation were measured. Tumor cell sonicates, reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase, xanthine oxidase, and mitochondria were used as the biological reducing systems. All four mitomycin antibiotics produced oxygen radicals following biological reduction, a process that may account for the aerobic cytotoxicity of agents of this class. The generation of relative amounts of superoxide and hydroxyl radical were also measured in EMT6 cell sonicates. BMY-25282 and BL-6783 produced significantly greater quantities of oxygen free radicals with the EMT6 cell sonicate, reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase, and mitochondria than did MC and PM. In contrast, BMY-25282 and BL-6783 did not generate detectable levels of free radicals in the presence of xanthine oxidase, whereas this enzyme was capable of generating free radicals with MC and PM as substrates. MC consistently produced greater amounts of free radicals than PM with all of the reducing systems. BMY-25282, BL-6783, and MC all generated hydroxyl radicals, while PM did not appear to form these radicals. The findings indicate that a correlation exists between the ability of the mitomycin antibiotics to generate oxygen radicals and their cytotoxicity to aerobic EMT6 tumor cells.

Modulation of cell shedding and glycosaminoglycan synthesis of human malignant keratinocytes by all-trans-retinoic acid and hydrocortisone in vitro

Physiologic concentrations (5 X 10(-8) M) of all-trans-retinoic acid (RA) caused a 2- to 3-fold increase in the rate of cell desquamation of a malignant keratinocyte line (SqCC/Y1) grown in serum-free medium. Measurement of the incorporation of [35S]sulfate and [3H]glucosamine into cetylpyridinium chloride-precipitable glycosaminoglycans (GAGS) demonstrated that RA treatment did not alter total GAG production. In addition, compartmental distribution was not affected by RA, with 50-70% of GAGS being recovered from the medium, 25% from the pericellular matrix, and the remainder from the cells. Relatively small amounts of GAGS were associated with shed cells in RA-treated cultures, presumably reflecting a relatively short association of these cells with the monolayer before desquamation. Chondroitin sulfate (Ch-S), heparin/heparan sulfate (Hep-S), and hyaluronic acid (HA) were the GAG species identified in SqCC/Y1 cultures by gel-exclusion chromatography. RA reduced the relative amount of HA in the trypsin-sensitive pericellular compartment by 50%. Since the proportions of Ch-S and Hep-S were not affected by RA, the findings suggest that the altered ratio of HA to sulfated GAGS in this fraction may contribute to the increased cell desquamation. Hydrocortisone (10(-6) M) reversed the effect of RA on cell shedding, and increased the proportion of pericellular HA relative to that found in cultures exposed to RA alone. These findings support the concept that the relative proportion of HA to sulfated GAGS may be important in the intercellular cohesion of keratinocytes. In addition, the relative decrease in HA and the predominance of Ch-S over Hep-S in SqCC/Y1 cultures differed from results reported with normal keratinocytes, indicating that this property may be associated with the malignant phenotype.

Alterations in glycoprotein synthesis and guanosine triphosphate levels associated with the differentiation of HL-60 leukemia cells produced by inhibitors of inosine 5'-phosphate dehydrogenase

The synthetic "C" nucleoside, tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide), its selenium analogue selenazofurin, and the related inhibitor of inosine 5'-phosphate (IMP) dehydrogenase, mycophenolic acid, are effective inducers of the terminal differentiation of HL-60 promyelocytic leukemia cells. The inhibition of cellular replication and the induced maturation produced by these agents appears to be a consequence of the inhibition of IMP dehydrogenase, since growth inhibition is partially reversed and differentiation is completely prevented by the simultaneous exposure of cells treated with inhibitors of IMP dehydrogenase to exogenous guanosine, which serves to circumvent the effects of the blockage of IMP dehydrogenase. The exposure of HL-60 leukemia cells to inhibitors of IMP dehydrogenase caused a marked reduction in the incorporation of [3H]mannose into both cellular glycoproteins and their lipid-linked oligosaccharide precursors; these effects are presumably due to the pronounced decrease in intracellular levels of guanosine triphosphate produced by blockage of IMP dehydrogenase. Maximum effects on glycoprotein biosynthesis occurred within 8 h of exposure to the inhibitors of IMP dehydrogenase. The simultaneous incubation of cells with guanosine and these inducers of differentiation partially prevented the reduction in [3H]mannose incorporation into glycoproteins, supporting a relationship between glycoprotein biosynthesis and guanosine triphosphate formation in the induction of differentiation by inhibitors of IMP dehydrogenase.

Interference with tumor cell-induced degradation of endothelial matrix on the antimetastatic action of nafazatrom

The antithrombotic compound nafazatrom was evaluated in several in vivo and in vitro assays to elucidate the mechanism of its antimetastatic activity. C57BL/6 mice bearing B16 amelanotic subcutaneous tumors treated with 100 mg nafazatrom/kg/day exhibited a sixfold reduction in metastatic pulmonary lesions compared to lesion numbers in controls. The reduction in metastatic lesions was not accompanied by changes in primary tumor growth, and up to 1 microgram nafazatrom/ml did not inhibit tumor cell proliferation in vitro. Treatment of C57BL/6 mice with nafazatrom prior to iv inoculation of tumor cells failed to inhibit lung colony formation. In vitro exposure of exponentially growing B16 amelanotic cells to nafazatrom (1 microgram/ml for 72 hr) in culture did not change their ability to adhere to endothelial cell monolayers. B16 amelanotic cells degraded the matrix material of bovine endothelial cell monolayers; a heparin sulfate proteoglycan appeared to be the predominant matrix component released by these tumor cells, as judged by resistance to chondroitin ABC lyase and sensitivity to heparitinase and pronase degradation. Nafazatrom (1 microgram/ml for 72 hr) inhibited the solubilization of matrix components by approximately 60%. Tumor cell degradation of matrix components is an important event in the pathogenesis of metastasis. Thus the interference with this process appears to provide an explanation for the inhibition of malignant cell dissemination in vivo by nafazatrom.

Differentiation of HL-60 promyelocytic leukemia cells: simultaneous determination of phagocytic activity and cell cycle distribution by flow cytometry

Phagocytosis of fluorescent microspheres by HL-60 promyelocytic leukemia cells following induction of differentiation with dimethyl sulfoxide (DMSO) was monitored using flow cytometry. Initiation of phagocytic capability following initiation of differentiation with 1.5% DMSO coincided with the attainment of respiratory burst activity as measured by NBT (nitro blue tetrazolium) reduction; the degree of phagocytic activity was dependent upon parameters such as microsphere size, microsphere number, and exposure time. Ingestion of fluorescent microspheres did not interfere with the measurement of DNA content using propidium iodide; thus, simultaneous determination of phagocytic activity and the cell cycle phase was possible. Accumulation of cells in the G1/G0 phase of the cell cycle following DMSO treatment was correlated with the acquisition of the capacity to phagocytize. Analysis of two-parameter correlated data also indicated that phagocytosis is coupled with residence in the G1/G0 phase of the cell cycle, further suggesting that the ability to phagocytize fluorescent microspheres is associated with end-stage differentiation.

Differentiation of WEHI-3B D+ monomyelocytic leukemia cells by retinoic acid and aclacinomycin A

WEHI-3B D+ monomyelocytic leukemia cells were induced to differentiate to mature granulocytes when treated with either 30 nM aclacinomycin A or 7 microM retinoic acid. Differentiation was assessed by the appearance of mature granulocytic phenotypes, as measured by the ability to reduce nitro blue tetrazolium, morphological changes, an increase in cell surface Fc receptors, as well as the loss of proliferative capacity. Maximum differentiation occurred 3 days after drug exposure. Analysis of DNA histograms of treated cells indicated that cells accumulated in the G1 phase of the cell cycle after 8 h of exposure to either inducer, with maximum accumulation occurring by 20 h; this arrest was observed prior to the phenotypic appearance of mature cells. The minimum interval of time necessary to commit cells to a differentiation pathway, which was less than one doubling time (9.2 h), closely paralleled the initial accumulation of cells in the G1 phase of the cell cycle. Since drug exposure for more than one cell division was required for maximum differentiation, the observed kinetics of maturation is consistent with a stochastic model. These studies support the idea that this cell line would be a particularly good model for extrapolation of findings with differentiating agents in culture to therapeutic monitoring in animals, since WEHI-3B D+ leukemia cells can be readily propagated in vivo in BALB/c mice.

Biochemistry of misonidazole reduction by NADPH-cytochrome c (P-450) reductase

The biochemical mechanism for the reduction of misonidazole [1-(2-nitro-1-imidazolyl)-3-methoxy-2-propanol] by purified rabbit liver NADPH-cytochrome c (P-450) reductase, the primary nitroreductase of liver, has been studied. Neither the anaerobic nor the futile aerobic reduction velocities exhibited signs of Michaelis-Menten saturation at concentrations less than 5 and 10 mM, respectively. The anaerobic reduction of misonidazole resulted in the formation of glyoxal from fragmentation of the imidazole ring in 25% yield. The rate of glyoxal formation was linear with time and paralleled the reduction of misonidazole, suggesting that it was derived from the partitioning of a reactive intermediate between at least two alternative pathways. Negligible amounts of the 2-amino derivative of misonidazole were formed, however, indicating the existence of alternative reduction/fragmentation pathways.

Mechanisms involved in the induction of malignant cell differentiation

Cancer appears to be a disease of altered maturation, with changes in genetic expression leading to a situation in which the physiological regulation of cellular proliferation and maturation are altered. Environmental factors as well as defined chemical agents have been demonstrated to have the capacity to convert neoplastic cells to end-stage forms with a finite life span through a process characteristic of cellular maturation. The correction of genetic defects by these inducers of differentiation does not appear to be required; the critical feature is that the differentiated cells assume a state in which they no longer possess the capability for continued cellular replication. The extrapolation of these advances, accomplished in experimental systems, to clinical practice should yield significant decreases in the neoplastic cell burden without the degree of morbidity produced by aggressive therapy with cytodestructive agents, especially when employed in multidrug combinations. The ultimate introduction of differentiation as a therapeutic approach to cancer treatment if attained, however, will require a variety of principles to be established, so that optimum efficacy may be obtained from each agent, the fabrication of new agents with major changes in the ratio of the concentrations required to produce cytotoxicity relative to those necessary to initiate maturation is attained, and the elucidation of non-antagonistic combinations of differentiation inducing agents with or without cytotoxic drugs is achieved to combat the problem of tumor cell heterogeneity.