Structure and tumor-promoting activity of analogues of anthralin (1,8-dihydroxy-9-anthrone)

DNA barcoding detects contamination and substitution in North American herbal products

BACKGROUND

Herbal products available to consumers in the marketplace may be contaminated or substituted with alternative plant species and fillers that are not listed on the labels. According to the World Health Organization, the adulteration of herbal products is a threat to consumer safety. Our research aimed to investigate herbal product integrity and authenticity with the goal of protecting consumers from health risks associated with product substitution and contamination.

METHODS

We used DNA barcoding to conduct a blind test of the authenticity for (i) 44 herbal products representing 12 companies and 30 different species of herbs, and (ii) 50 leaf samples collected from 42 herbal species. Our laboratory also assembled the first standard reference material (SRM) herbal barcode library from 100 herbal species of known provenance that were used to identify the unknown herbal products and leaf samples.

RESULTS

We recovered DNA barcodes from most herbal products (91%) and all leaf samples (100%), with 95% species resolution using a tiered approach (rbcL + ITS2). Most (59%) of the products tested contained DNA barcodes from plant species not listed on the labels. Although we were able to authenticate almost half (48%) of the products, one-third of these also contained contaminants and or fillers not listed on the label. Product substitution occurred in 30/44 of the products tested and only 2/12 companies had products without any substitution, contamination or fillers. Some of the contaminants we found pose serious health risks to consumers.

CONCLUSIONS

Most of the herbal products tested were of poor quality, including considerable product substitution, contamination and use of fillers. These activities dilute the effectiveness of otherwise useful remedies, lowering the perceived value of all related products because of a lack of consumer confidence in them. We suggest that the herbal industry should embrace DNA barcoding for authenticating herbal products through testing of raw materials used in manufacturing products. The use of an SRM DNA herbal barcode library for testing bulk materials could provide a method for 'best practices? in the manufacturing of herbal products. This would provide consumers with safe, high quality herbal products.

Design, synthesis and in vitro degradation of a novel co-drug for the treatment of psoriasis

Psoriasis is a common, chronic and relapsing inflammatory skin disease. It affects approximately 2% of the western population and has no cure. Combination therapy for psoriasis often proves more efficacious and better tolerated than monotherapy with a single drug. Combination therapy could be administered in the form of a co-drug, where two or more therapeutic compounds active against the same condition are linked by a cleavable covalent bond. Similar to the pro-drug approach, the liberation of parent moieties post-administration, by enzymatic and/or chemical mechanisms, is a pre-requisite for effective treatment. In this study, a series of co-drugs incorporating dithranol in combination with one of several non-steroidal anti-inflammatory drugs, both useful for the treatment of psoriasis, were designed, synthesized and evaluated. An ester co-drug comprising dithranol and naproxen in a 1:1 stoichiometric ratio was determined to possess the optimal physicochemical properties for topical delivery. The co-drug was fully hydrolyzed in vitro by porcine liver esterase within four hours. When incubated with homogenized porcine skin, 9.5% of the parent compounds were liberated after 24 h, suggesting in situ esterase-mediated cleavage of the co-drug would occur within the skin. The kinetics of the reaction revealed first order kinetics, Vmax = 10.3 μM·min-1 and Km = 65.1 μM. The co-drug contains a modified dithranol chromophore that was just 37% of the absorbance of dithranol at 375 nm and suggests reduced skin/clothes staining. Overall, these findings suggest that the dithranol-naproxen co-drug offers an attractive, novel approach for the treatment of psoriasis.

Plumbagin and juglone induce caspase-3-dependent apoptosis involving the mitochondria through ROS generation in human peripheral blood lymphocytes

The phytochemicals plumbagin and juglone have recently been gaining importance because of their various pharmacological activities. In this study, these compounds are shown to induce concentration- and time-dependent toxicity in human peripheral blood lymphocytes via the apoptotic pathway. Flow cytometry data revealed the occurrence of about 28% early apoptotic cells after 6h exposure to 10μM plumbagin and 35% late apoptotic cells and about 43% sub-G1 population after 24h. The cytotoxic effect of plumbagin was at least twofold higher than that of juglone as evidenced by the IC(50) value for cytotoxicity. Characteristic apoptotic features such as chromatin condensation and apoptotic body formation were observed through TEM, and membrane blebbing and cell surface smoothening were seen in SEM studies. Generation of ROS was evidenced through the HPLC analysis of superoxide-specific 2-OH-E+ formation. In addition, a decrease in GSH levels parallel to ROS production was observed. Reversal of apoptosis in both NAC- and Tempol-pretreated cells indicates the involvement of both ROS generation and GSH depletion in plumbagin- and juglone-induced apoptosis. The mechanistic pathway involves a decrease in MMP; alterations in the levels of Bcl-2, Bax, and cytosolic cytochrome c; and PARP-1 cleavage subsequent to caspase-3 activation.

Tumor Growth Inhibitory Effect of Juglone and Its Radiation Sensitizing Potential

The present study aimed at evaluating the anticancer and radiosensitizing potential of juglone against a chemoresistant and radioresistant tumor (B16F1 melanoma) growing on C57BL/6J mice. Volume doubling time, growth delay, and median survival were used to assess the in vivo anticancer and radiosensitizing potential of juglone. In vitro radiosensitizing potential of juglone was studied using clonogenic, comet, and reactive oxygen species induction assays. Treatment of tumor-bearing mice with sublethal doses of juglone caused a dose-dependent inhibition of tumor growth as evident from the growth delay and median survival values. Comet assay using tumor tissue and blood showed differential toxicity of juglone, where higher levels of DNA damage was seen in tumor tissue compared with blood cells. Pretreatment of tumor-bearing mice with optimum dose of juglone before radiation resulted in significant tumor growth inhibition compared with radiation alone. From the clonogenic assay, the authors observed a sensitization enhancement ratio of 1.37 for the combination treatment compared with radiation alone. Furthermore, comet assay studies revealed the potential of juglone to enhance the radiation-induced DNA damage and cause a delay in its repair. Juglone pretreatment before radiation also resulted in a significant elevation in the intracellular reactive oxygen species levels compared with radiation alone. In conclusion, the results of this study show the potential of juglone to inhibit the growth of melanoma in vivo. The study also revealed the potential of juglone to augment the radiation-induced cell death of melanoma cells, which may be attributed to oxidative stress–mediated DNA damage and its delayed repair.

Juglone disrupts root plasma membrane H+-ATPase activity and impairs water uptake, root respiration, and growth in soybean (Glycine max) and corn (Zea mays)

Juglone is phytotoxic, but the mechanisms of growth inhibition have not been fully explained. Previous studies have proposed that disruption of electron transport functions in mitochondria and chloroplasts contribute to observed growth reduction in species exposed to juglone. In studies reported here, corn and soybean seedlings grown in nutrient solution amended with 10, 50, or 100 microM juglone showed significant decreases in root and shoot dry weights and lengths with increasing concentrations. However, no significant differences in leaf chlorophyll fluorescence or CO2-dependent leaf oxygen evolution were observed, even in seedlings that were visibly affected. Disruption of root oxygen uptake was positively correlated with increasing concentrations of juglone, suggesting that juglone may reach mitochondria in root cells. Water uptake and acid efflux also decreased for corn and soybean seedlings treated with juglone, suggesting that juglone may affect metabolism of root cells by disrupting root plasma membrane function. Therefore, the effect of juglone on H+-ATPase activity in corn and soybean root microsomes was tested. Juglone treatments from 10 to 1000 microM significantly reduced H+-ATPase activity compared to controls. This inhibition of H+-ATPase activity and observed reduction of water uptake offers a logical explanation for previously documented phytotoxicity of juglone. Impairment of this enzyme's activity could affect plant growth in a number of ways because proton-pumping in root cells drives essential plant processes such as solute uptake and, hence, water uptake.

Antipsoriatic anthrones with modulated redox properties. 5. Potent inhibition of human keratinocyte growth, induction of keratinocyte differentiation, and reduced membrane damage by novel 10-arylacetyl-1,8-dihydroxy-9(10H)-anthracenones

The synthesis and structure-activity relationships (SARs) of a series of novel 10-arylacetyl-1,8-dihydroxy-9(10H)-anthracenones are described. Acylation of anthralin with either the appropriate arylacetyl chlorides or arylacetic acids in the presence of pyridine or via the coupling agent dicyclohexylcarbodiimide (DCC), respectively, furnished this structural class of antipsoriatic agents. Potential antipsoriatic activity was evaluated in complementary assays specifically addressed to three important aspects of psoriasis. First, several compounds were identified which are equally potent as inhibitors of human keratinocyte growth as the antipsoriatic agent anthralin. Furthermore, improved ratio of antiproliferative activity to cytotoxicity is demonstrated by the reduced potential of the novel analogues to induce membrane damage, which is a benefit of their reduced ability to generate oxygen radicals as documented by deoxyribose degradation. Second, analogue 3o bearing a hydroxamate functional group was also a highly potent inhibitor of LTB(4) biosynthesis in addition to its excellent antiproliferative activity. SARs of these inhibitors of both keratinocyte growth and LTB(4) biosynthesis with respect to the nature of the para-substitution in the 10-phenylacetyl side chain are discussed. Third, the compounds were also evaluated for their ability to induce the formation of cornified envelope protein in keratinocytes. Cross-linking of cellular protein as a marker of terminal differentiation of keratinocytes was observed for many 10-arylacetyl analogues at concentrations required to arrest cell growth. This newly uncovered activity of the novel anthracenones suggests antipsoriatic potential with respect to disturbance of keratinocyte differentiation, in addition to hyperproliferative and inflammatory aspects of psoriasis.

Simple analogues of anthralin: unusual specificity of structure and antiproliferative activity

Fifty-nine simple analogues of the antipsoriatic agent, anthralin, have been prepared by modifying the positions of the 1,8-hydroxyl groups, replacement of the hydroxyl groups, substitution at the oxygen functions, introduction of additional functional groups into various positions of the anthracenone nucleus, or removal of particular structural elements. The compounds were evaluated for their antiproliferative action against human keratinocytes and inhibition of the generation of leukotriene B4 in polymorphonuclear leukocytes, which may be useful to resolve the proliferative and inflammatory aspects of psoriasis, respectively. Even though many anthracenones were more potent inhibitors of leukotriene biosynthesis than anthralin, none of the compounds was substantially more effective as this drug in suppressing keratinocyte cell growth. There is an absolute requirement for two hydroxyl groups peri to a hydrogen bond acceptor such as a keto or an imino group for high potency. In addition to further delineating the nature of the pharmacophore for this class of compounds, also naphthalenedione with a peri hydroxyl group was identified as a pharmacophore with antiproliferative activity against keratinocyte growth.

Cephalosporin 3'-phloroglucide esters and 7-(phloroglucidamido) cephalosporins as novel antibacterial agents

Two series of new phloroglucide derivatives were synthesized that possessed antibacterial activities. The first series includes cephalosporin 3'-phloroglucide esters 19 and 20, which were obtained by condensation of cephalosporin 16 with bioactive phloroglucides 14 and 15, respectively. They exhibited a dual mode of antibacterial action. In comparison with cephalosporins 26 and 27, bearing an acetoxy unit at the C-3' position, the bifunctional cephalosporins 19 and 20 showed a broadened spectrum of activity. Results from the consistent valence force field (CVFF) calculations indicate that the most stable conformational isomer of phenolic acid 14, holding a cis-syn-syn geometry, possessed a cavity. It provides an ideal environment to accommodate metal ions of holoenzymes. Phenolic keto acid 15, however, possessed a trans-anti-syn conformation, which allowed chelation between metal ions and the phenolic hydroxyl groups as well as the carbonyl functionalities. Our biological results show that the cavity formed in phloroglucides plays an important role. The second series includes 7-(phloroglucidamido)cephalosporins 24 and 25, which were synthesized by condensation of cephalosporin 21 with 14 and 15, respectively. Results from the CVFF calculations indicate that cephalosporin 24 also possessed a cavity. Unlike cephalosporin 3'-phloroglucide esters 19 and 20, cephalosporins 24 and 25 were found resistant to beta-lactamases from Staphylococcus aureus 95 and Pseudomonas aeruginosa 18S-H. These new compounds, however, showed notable activities against S. aureus FDA 209P, S. aureus 95, Candida albicans, P. aeruginosa 1101-75, and P. aeruginosa 18S-H.

Syntheses of Anthracenones. 1. Sodium Dithionite Reduction of peri-Substituted Anthracenediones

The reaction of peri-substituted anthracenediones with sodium dithionite in dimethylformamide and water has been investigated. The system selectively reduces the carbonyl group flanked by the peri substituents of the anthracenediones to give the corresponding 4,5-disubstituted 9(10H)-anthracenones and thus provides a route to anthracenones which are otherwise difficult to obtain. Many functional groups can be tolerated, the reaction is compatible with the presence of peri alkoxy groups and unsaturated side chains of the starting anthracenediones, and the reduction does not go beyond the anthracenone stage. However, the formation of anthracenones depends on the nature of the peri substituents. No products were obtained from the 1,8-dimethyl-substituted anthracenedione and the parent compound with no substituents.

Syntheses of Anthracenones. 2. Preparation of 1,8-Dimethoxy- (Dimethylanthralin) and 4,5-Dihydroxy-9(10H)-anthracenone (Isoanthralin): A Revision

The reduction of 1,8-dimethoxyanthracenedione with zinc dust and aqueous ammonia gives a mixture of 1,8-dimethoxyanthracene and 4,5-dimethoxy-9(10H)-anthracenone, rather than the isomeric 1,8-dimethoxy-9(10H)-anthracenone (dimethylanthralin). This isomer was obtained exclusively using SnCl(2) in HCl and acetic acid as reducing agent at room temperature. The structure was confirmed to exist as the tautomeric 1,8-dimethoxy-9-hydroxyanthracene. Furthermore, the reduction of 1,8-diacetoxyanthracenedione with SnCl(2) in HCl and acetic acid leads to 1,8-dihydroxy-9(10H)-anthracenone (anthralin) rather than 4,5-dihydroxy-9(10H)-anthracenone (isoanthralin), which was prepared by ether cleavage of 4,5-dimethoxy-9(10H)-anthracenone. In light of these findings some biological studies on antipsoriatic anthracenones have to be reconsidered.

Anthralin derivatives--inhibition of 5-lipoxygenase--antipsoriatic efficacy

Inhibition of 5-lipoxygenase by anthralin (1) and 41 derivatives is determined: the acids 38 and 39, the lactones 40-42 and 9-anthrone (8) are the most potent inhibitors, the lactone 41 reaching the efficacy of nordihydroguaiaretic acid (NDGA). The results were correlated with the hydrophilic/lipophilic balance of the test compounds and their clinical efficacy as far as known. There is no correlation between the "minimum structure" of Krebs and Schaltegger concerning antipsoriatic activity and the inhibitory effects against 5-lipoxygenase.

Dithranol (anthralin)-induced skin irritation in C57BL/6, NMRI and SENCAR mice

Dithranol-induced skin irritation was compared in C57BL/6, NMRI and SENCAR mice, the strains representing different sensitivity to tumour promotion. Skin irritation was assessed using ear thickness and skin weight measurements, visual estimation of back skin irritation and histopathology. Both single and repeated applications of dithranol caused a delayed skin irritation resulting in the maximal response between 7-11 days after the beginning of the treatment. Contrary to the findings with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), C57BL/6 mice were the most sensitive and SENCAR mice the most resistant to the dithranol-induced skin irritation up to 30 days from the beginning of the treatment. NMRI mice were intermediate. Differences were found in the ear swelling, epidermal hyperplasia, amount of inflammatory cell infiltrate and skin ulceration. During repeated treatment of about 40 days, however, the responsiveness of SENCAR mice increased over that of C57BL/6 and NMRI mice. SENCAR mice had also more epidermal hyperplasia than the other strains at the end of the 74 day period of 3 times weekly applications. The magnitude of epidermal hyperplasia after long term treatment seems to correlate with the sensitivity to tumor promotion in the different mouse strains.

More unusual pigmentations of the gingiva

Three unusual types of oral pigmentation are presented. The first is a brown orange pigmentation caused by the habit of using the bark of Juglans regia for teeth cleaning. The second is a bright yellow pigmentation associated with the habit of chewing the seeds of Cola nitida. The third is a generalized mousy brown pigmentation related to the habit of chewing the leaves of Catha edulis. The purpose of this article is to describe the nature of these pigmentations and to present their clinical and histologic features.

Interpreting the visible absorption bands of 1,4-(dihydroxy)-9,10-anthraquinone and its metal chelates

The visible absorption spectra of 1,4-(dihydroxy)-9,10-anthraquinone and of Co(II), Ni(II), Cu(II) and Zn(II) chelates have been studied in different organic solvents. This system provides a model for the anthracycline antibiotics and their metal chelates. The band structure of the spectrum has been determined using the second and fourth derivatives of the spectrum. The visible absorption band of the parent molecule can be assigned to a single electronic state with a reduced dipole moment in the excited state; structure in this band is ascribed to two overlapping vibrational progressions. In contrast, the dianion (hydroxy protons removed) shows a single electronic state with an increased dipole moment in the excited state; structure in this band can be assigned to a single vibrational progression. All of the metal chelates show spectra which are similar in appearance to that of the dianion although the identity of the metal determines the bathochromic shift of the absorption band. Titration of 1,4-dihydroxyanthraquinone with Cu(ClO4)2.6H2O demonstrates that three chelates with metal-to-ligand ratios of 1:2, 1:1 and 2:1 can form depending on the identity of the metal, ratio of metal to ligand, and donor character of the solvent.

Studies on the contact sensitizing activity of dithranol (anthralin) and 10-butyryl dithranol (butantrone)

The contact sensitizing activity of dithranol and butantrone (10-butyryl dithranol) was studied in 3 animal models: the guinea pig maximization test (GPMT), the closed patch test (CPT), and the mouse ear swelling test (MEST) in 2 different mouse strains. In the GPMT, both dithranol and, to a greater extent, butantrone showed sensitizing potential. Because butantrone was less irritant, the concentrations used were 10x higher than those of dithranol. In the CPT, only butantrone was slightly positive. In the MEST, with both CF-1 and Balb/c mice, dithranol caused less swelling of the test ear after challenge than butantrone. According to the evaluation criteria of the MEST, only butantrone caused sensitization in 50% of the CF-1 mice and in 40% of the Balb/c mice. Thus, the GPMT was the only test which indicated the minor contact sensitizing potential of dithranol. On the other hand, the 10-butyryl analogue of dithranol showed undoubtedly stronger contact sensitizing potential than the parent compound in all tests. Therefore, as compared to dithranol, an increased risk of sensitization should be considered.

Cocarcinogenic and tumor-promoting capabilities of anthralin

Numerous chemicals to which humans are exposed either therapeutically or as a result of living in an industrial environment constitute a potential threat as carcinogens, mutagens, and/or tumor promoters and cocarcinogens. Anthralin, and antipsoriatic agent, acts as a tumor promoter for Balb/c-3T3 mouse embryo cell cultures that were previously exposed to a low dose of either benzo-a-pyrene (BaP), an indirect-acting carcinogen needing metabolic conversion for its carcinogenic action, or beta-propiolactone (BPL), a direct-acting carcinogen which needs no metabolic conversion. As a cocarcinogen, i.e., when exposure of cells to anthralin was simultaneous with exposure to the carcinogen, anthralin enhanced neoplastic transformation only when the carcinogen was BaP. Several explanations are explored. The possibility that cocarcinogens and tumor promotion occur by separate mechanisms is suggested.

Toxicological studies with dithranol and its 10-acyl analogues

The oral LD50 values of an antipsoriatic drug, dithranol, were 1542 mg/kg in NMRI mice and 3216 mg/kg in Wistar rats. Three 10-acyl analogues of dithranol (10-acetyl, 10-propionyl and 10-butyryl dithranol or butantrone) were more toxic both in mice and rats. They were mutagenic only in TA1537 of the five Salmonella typhimurium strains tested. None of them were mutagenic in two Escherichia coli strains. Butantrone was least toxic to test bacteria and had the lowest mutagenic activity on TA1537. In metaphase analysis of in vitro treated human lymphocytes, dithranol, 10-acetyl dithranol and 10-propionyl dithranol produced significant increases in the number of chromosome and chromatid gaps but without a clear dose-response relationship, and without inducing significant breaks. Butantrone did not cause significant increases in gaps or breaks. In the mouse micronucleus test, dithranol and butantrone caused no increases in micronucleated polychromatic or normochromatic erythrocytes, indicating lack of clastogenic activity in vivo at maximum tolerated doses. Hence, dithranol and its 10-acyl analogues have a weak mutagenic activity in vitro. The mutagenic activity of butantrone is lower than that of the other analogues and dithranol.

Effect of application frequency on epidermal ornithine decarboxylase induction by chrysarobin in SENCAR mice

Ornithine decarboxylase (ODC EC 4.1.1.17) induction in mouse epidermis after single or multiple topical applications of chrysarobin differed from that following topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA). Following a single application of 220 nmol chrysarobin, ODC activity began to rise at 24 h reaching a peak at 56 h and returned to normal after 96 h. When 5 separate applications of 220 nmol chrysarobin were applied in multiple application protocols, an alteration in the ODC induction response was observed. With a once per week or twice per week application protocol, ODC was elevated in a multiphasic manner giving multiple peaks of activity after the last application. Interestingly, the magnitude of ODC induction was greater using the once per week, compared to the twice per week, application protocol. Preliminary results indicate that a once per week application protocol is more effective than a twice per week protocol for promoting the development of skin papillomas in SENCAR mice. Thus, the magnitude of the induced ODC response with chrysarobin, although low compared to TPA, correlated with tumor promoting activity.

Skin irritation by dithranol (anthralin) and its 10-acyl analogues in 3 animal models

The skin irritant properties of a single application of dithranol (anthralin), a typical "delayed irritant", and its 10-acyl analogues in acetone or white petrolatum were compared in 3 animals models. Maximal irritation was reached at about 24 h in mouse ear, 48 h in guinea pig back and 1 week in miniature swine back, the last-mentioned serving as a good model of human skin. In all animal species, butantrone was significantly less irritant than dithranol, 10-acetyl dithranol or 10-propionyl dithranol. 10-acetyl dithranol was the most irritant compound. Clinical trials with butantrone on psoriasis are justified.

Anthralin: historical and current perspectives

Anthralin was first synthesized in 1916. Earlier, a natural product, chrysarobin, originally derived from the South American araroba tree, had been used to treat psoriasis. Anthralin was first used in Germany, and later in the Ingram regimen in Britain, but it has never been popular with American dermatologists. This is probably due to the side effects of staining and irritation of the skin. Attempts to reduce these using low concentration, short contact therapy, and concomitant steroid therapy, have been only partially successful. It may be that better instruction of patients and physicians will lead to wider use of this effective topical agent for the treatment of psoriasis. The mode of action of anthralin is thought to be either through its effect on deoxyribonucleic acid (DNA), probably mitochondrial DNA, which reduces cell turnover, or through its effects on various enzyme systems, including those of polyamine synthesis and respiration. The aims of this review are to discuss historical aspects of anthralin and to update its chemistry, pharmacology, and clinical usage.

Anthralin: chemical instability and glucose-6-phosphate dehydrogenase inhibition

The chemical stability of the antipsoriatic drug, anthralin (1,8-dihydroxy-9-anthrone), in solution has been studied using high-performance liquid chromatographic analysis. The time course for decomposition in solution has been correlated with that of the inhibition of glucose-6-phosphate dehydrogenase, one of the most widely documented biochemical properties associated with anthralin. Solutions of anthralin in aqueous buffer (37 degrees, pH 7.5, under light protection) completely within 4 hr giving the 10,10'-dimer (40%), no detectable 1,8-dihydroxy-9,10-anthraquinone, and a greatly increased potency of inhibition of glucose-6-phosphate dehydrogenase. This increased inhibitory potency could not be explained by formation of the dimer which, like anthralin and its quinone, were shown to be only weak inhibitors of the enzyme. In acetone solution exposed to light and air, anthralin decomposed completely within 4 days, in part via the dimer as intermediate. The final solution had the characteristic color of anthralin-brown, contained the quinone (20%), and like decomposed aqueous solutions of anthralin, completely inhibited glucose-6-phosphate dehydrogenase. The results show that neither anthralin, nor either of its two identified decomposition products, is the potent toxic species against glucose-6-phosphate dehydrogenase.

High-pressure liquid chromatographic determination of anthralin in ointments

Anthralin concentration was determined in different ointments by high-pressure liquid chromatography, and results were compared with those of the USP assay technique. Significant differences existed between the claimed and the actual levels of anthralin in some preparations. Varying quantities of anthralin breakdown products were found, and their concentrations appear to be related to the nature of the formulation.

Alterations in polyamine levels induced by phorbol diesters and other agents that promote differentiation in human promyelocytic leukemia cells

Polyamine levels were evaluated in human HL-60 promyelocytic leukemia cells after treatment with inducers of terminal differentiation. Differentiation in these cells was determined by increases in the percentage of morphologically mature cells and in lysozyme activity. Treatment of the HL-60 cells with phorbol 12-myristate-13-acetate (PMA), phorbol 12,13-didecanoate or other inducers of terminal differentiation such as dimethylsulfoxide and retinoic acid resulted in increased levels of putrescine. However, no increase in putrescine could be detected after PMA treatment of a HL-60 cell variant that exhibited a decreased susceptibility to PMA-induced terminal differentiation. Similarly, no increase in putrescine was observed with two non-tumor-promoters (phorbol 12,13-diacetate and 4-O-methyl-PMA) or with anthralin, a non-phorbol tumor promoter. In addition to enhancing putrescine levels, PMA also increased the amount of spermidine and decreased the amount of spermine. The increase in putrescine and spermidine preceded the expression of the various differentiation markers. Unlike the changes observed in the polyamine levels after PMA treatment, the activities of ornithine and S-adenosylmethionine decarboxylases, which are polyamine biosynthetic enzymes, did not significantly change. alpha-Methylornithine and alpha-difluoromethylornithine and methylglyoxal bis(guanylhydrazone), which are inhibitors of the polyamine biosynthetic enzymes, did not affect differentiation in control or PMA-treated cells. Because of these observations, we suggest that the change in polyamine levels involve biochemical pathways other than the known biosynthetic ones. By-products of these pathways may perhaps be the controlling factors involved in the induction of terminal differentiation in the HL-60 and other cell types as well.