Azulenic retinoids: novel nonbenzenoid aromatic retinoids with anticancer activity

Several novel azulene-containing retinoids were prepared and evaluated for their ability to suppress carcinogen-induced neoplastic transformation and to concomitantly up-regulate gap junctional communication in the in vitro mouse fibroblast C3H/10T1/2 cell bioassay. The azulenic retinoids were divided into two groups: compounds 1-6 were modeled after retinoic acid with flexible polyenic side chain whereas retinoids 7-13 featured a benzoic acid moiety analogous to the prototypic retinobenzoate (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2- naphthalenyl)-1-propenyl]benzoic acid (TTNPB). Within this latter group the side chains for compounds 7, 10, and 11 were attached at the 1-, 2-, and 8-positions of the azulenic terminus, respectively. Biological activities were determined for all the new compounds. Two of these novel retinoids, azulenic retinobenzoic acid derivatives 7 and 11, were completely effective inhibitors of transformation at 10(-6) M. The most active azulenic retinoids also enhanced gap junctional communication in untransformed cells; this was associated with up-regulated expression of connexin 43, a structural protein of the gap junction. Two fluorinated analogs were also tested. The azulenic fluoro acid 5 was found to be more potent than the trifluoromethyl analog 6. Azulenic analogs with hydroxyl or carboxaldehyde side chain functional groups were ineffective transformation inhibitors. In general, azulenic retinobenzoic acid analogs structurally akin to TTNPB were more effective than flexible side chain analogs related to retinoic acid.

Selective block of transient Ca channel current in mouse neuroblastoma cells by U-88779E

Antioxidants and T-type Ca channel antagonists are neuroprotective during ischemia or other central nervous system traumas. U-88779E (1-[(4-chlorophenyl-phenyl)-methyl]-4-[(7-methoxy-5-isopropyl- 2,4,6-cycloheptatrien-1-one)-2-methyl]piperazine) has been shown to have both antioxidant activity and the ability to block Ca fluxes in cardiac microsomes. In this study, we examined the effect of U-88779E on Ca, Na and K channels in a neuronal cell line, N1E-115 cells. The drug blocked transient barium current (IBa) through low-threshold Ca channels (T-type) with little effect on other noninactivating IBa including the nifedipine-sensitive one. The drug at 20 microM reduced transient IBa at a constant rate, -7.2% of the control per min, and abolished the current within 15 min. This implies a continuous accumulation of the drug in cell membranes probably because of its high lipophilicity (log P = 7.003). U-88779E also blocked Na and K currents but at a rate about 8 times slower than that observed with transient IBa. Further studies on interactions of the drug with T-channels revealed that the drug had no effect on the shape of current-voltage curve, activation and inactivation kinetics, and steady-state activation curve. The drug, however, induced a hyperpolarizing shift in steady-state inactivation curve and became more potent under conditions where the channels in inactivated states prevail. These observations are consistent with the view that U-88779E has a higher affinity to T-type channels in inactivated states than in resting or open states.(ABSTRACT TRUNCATED AT 250 WORDS)

Design, synthesis, and pharmacology of 3-substituted sodium azulene-1-sulfonates and related compounds: non-prostanoid thromboxane A2 receptor antagonists

A series of novel azulene-1 carboxylic acid derivatives 28-30, azulene-1 sulfonic acid sodium salts 41a-c, and related compounds were synthesized. These compounds were tested for TXA2 receptor antagonistic activity. The inhibitory concentrations (IC50) of these compounds for vascular contraction (TXA2 tau receptor) and platelet aggregation (TXA2 alpha receptor) induced by (15S)-15-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5(Z),13(E)- dienoic acid (U-46619) were obtained. Azulene-1-sulfonic acid sodium salts 41a-c were over 3 times more potent than azulene-1-carboxylic acids 28-30. The most potent compound, 41b was 4 orders of magnitude more potent than a TXA2 antagonist, BM13,177, in inhibiting vascular contraction (tau receptor) and had an IC50 of 9.0 x 10(-10) M. Compound 41b was also found to be a tau receptor selective antagonist (IC50 of contraction/IC50 of aggregation = 378) and to have no TXA2 synthetase inhibitory activity at concentrations up to 10(-4) M and no partial agonistic activity at concentrations up to 10(-5) M in rabbit aorta (tau receptor) and up to 10(-4) M in rabbit platelet-rich plasma (alpha receptor). In a radioligand binding assay using rabbit gel-filtered platelets, compound 41b had a high-affinity binding for the TXA2 receptor. In an in vivo study, compound 41b inhibited U-46619-induced sudden death in mice at a dose of 0.3 mg/kg and its duration of action was over 8 h when administered orally at 3 mg/kg.

Pharmacologic properties of KT2-962 (6-isopropyl-3-[4-(p- chlorobenzenesulfonylamino)-butyl]-azulene-1-sulfonic acid sodium salt); a new TXA2/prostaglandin endoperoxide receptor antagonist

Pharmacologic properties of KT2-962 (6-isopropyl-3-[4-(p-chlorobenzenesulfonylamino)butyl]-azulene+ ++-1-sulfonic acid sodium salt, KT) were studied in isolated rat aorta, rat tail artery, rabbit aorta, rabbit renal artery, and pig coronary artery. KT competitively inhibited the contractions induced by thromboxane A2 (TXA2) mimetic, U46619 (pA2 values 9.95, 8.85, 7.87, 8.49, and 9.12, respectively). KT also inhibited the contraction of rabbit aorta induced by prostaglandin2 alpha (PGF2 alpha, pA2 value 7.85) and the contraction of guinea pig ileum induced by LTD4 (pA2 value 5.48) but did not alter the contractions induced by norepinephrine (NE), Ca2+, serotonin, and histamine. KT did not alter the contractions of guinea pig ileum, which did not contract with U46619, induced by PGE2 and PGF2 alpha. KT inhibited the aggregations of rabbit platelets induced by U46619, arachidonic acid, and collagen (IC50 values 7.9, 140, and 16 microM, respectively) but not those induced by ADP. It also inhibited the specific binding of TXA2/PGH2 receptor antagonist, [3H]SQ29,548, to rabbit gel-filtered platelets with an IC50 value of 1.5 x 10(-8) M. In in vivo experiments with mice, oral administration of KT protected the U46619-induced sudden death with the minimum effective dose of 0.3 mg/kg and provided such protection for > 8 h at 1.0 mg/kg. These results indicate that KT is a new nonprostanoid type TXA2/PGH2 receptor antagonist that is orally effective and long acting.

Effect of U88999E on experimental cerebral vasospasm in rabbits

U88999E, 7-[4,(4, 4'-difluorobenzhydryl)piperazino-1-methyl]-4- isopropyl-2-methoxy-2,4,6-cycloheptatrien-1-one hydrochloride, is a recently developed tropolone derivative that inhibits lipid peroxidation and also acts as a calcium antagonist. The effects of U88999E on basilar artery tone were examined in two model systems: 1) an in vitro preparation of arterial rings that measures isometric tension, and 2) an in vivo model of cerebral vasospasm measuring arterial diameter. U88999E elicited dose-dependent relaxation of preconstricted arterial rings maintained in vitro. Ring preparations were preconstricted using elevated potassium (40 mmol/L), uridine triphosphate (10(-3) mol/L), or endothelin-1 (10(-8) mol/L); U88999E reversed these constrictions across a concentration range of 10(-8) to 10(-5) mol/L. The potency of U88999E for relaxing preconstricted vessels was slightly less than that observed for flunarizine or diltiazem. A dose-dependent, relaxing effect of U88999E on potassium-induced contractions was observed in the presence of calcium concentrations ranging from 0.03 to 20 mmol/L. Vasospasm of basilar arteries after subarachnoid hemorrhage was inhibited in a dose-dependent and significant manner by intravenous injections of U88999E. Animals receiving intraperitoneal injections of U88999E also exhibited a tendency for reduced vasospasm; however, this effect did not achieve statistical significance. These findings suggest that U88999E may be useful in the prevention of cerebral vasospasm after subarachnoid hemorrhage.

Synthesis and biological activities of 1-[2-(dimethylamino)ethyl]- and 1-[3-(dimethylamino)propyl]-substituted 3-methyl-1,8-dihydrocycloheptapyrazol-8-ones and related compounds

3-Methyl-1,8-dihydrocycloheptapyrazol-8-ones (2a-c), prepared from 3-acetyltropolones (1a-c), were treated with diazomethane, methyl iodide, dimethyl sulfate, and diethyl sulfate to give 1- and 2-alkylated compounds. The 1,8-dihydrocycloheptapyrazol-8-one (2a) also reacted with 2-(dimethylamino)ethyl, 2-(diethylamino)ethyl, 3-(dimethylamino)propyl, and 2,3-dihydroxypropyl chloride to afford the corresponding 1-substituted products. A preliminary study was made of the biological activities of some of the obtained compounds.

Age-related acute depletion of cerebral glutathione by peroxidative stress

Cyclohexene-1-one and cycloheptene-1-one cause a severe age-related depletion of reduced glutathione (GSH) in the forebrain of 5- or 15- or 25-month-old rats. Chronic pretreatment with phosphatidylcholine partially inhibits the GSH depletion in old forebrains by the prooxidants tested, suggesting that in aged animals alterations in mitochondrial inner membrane phospholipid composition and/or cytochrome oxidase activity might play a role in oxygen free-radical production.

Influence of aging on the acute depletion of reduced glutathione induced by electrophilic agents

A severe age-dependent depletion of reduced glutathione (GSH) occurs in rat forebrain at 1-3 h from intraperitoneal injection of the electrophilic agents cyclohexene-1-one and cycloheptene-1-one. Chronic pretreatment with central dopamine agonists (i.e., ergot alkaloids; particularly, dihydroergocriptine) partially counteracts the GSH depletion induced in 15-month-old forebrains by the prooxidants tested. In contrast, chronic pretreatment with a vasodilator agent (i.e., papaverine) magnifies the GSH depletion.

Benzo[6,7]cyclohepta[1,2-b]pyran derivatives with platelet antiaggregating and other activities

The synthesis of some N,N-disubstituted 4-amino-6,7-dihydro-3-phenylbenzo[6,7]cyclohepta[1,2-b]pyran-2(5H) -ones by reaction of phenylchloroketene with a series of N,N-disubstituted 6-aminomethylene-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ones, followed by dehydrochlorination of the primary adducts with DBN, is described. Some compounds showed a platelet antiaggregating activity in vitro superior or comparable to that of acetylsalicylic acid, as well as a weak local anesthetic activity in mice and antiinflammatory activity in rats.

Studies on anti-ulcer agents. II. Synthesis and anti-ulcer activities of 6-isopropylazulene-1-sodium sulfonate derivatives

A series of alkylazulene-1-sodium sulfonate derivatives which has an isopropyl group at 6-position were synthesized, and their anti-ulcer activities were examined in Shay pylorus-ligated rats. The values of lipophilicity (log P) as a parameter of these new azulene derivatives were also examined in reference to the structure-activity relationship. The optimum value of log P, which showed maximal anti-ulcer activity, was about -0.46. Among the derivatives of azulene examined, 3-ethyl-6-isopropylazulene-1-sodium sulfonate (compound IXb:XT1-785) exhibited the most potent inhibitory action against Shay ulcer, and its anti-peptic activity was similar to that of 3-ethyl-7-isopropylazulene-1-sodium sulfonate (KT1-32). It also had more activity than guaiazulene sodium sulfonate (GAS). Furthermore, KT1-785 was extremely stable under heating as compared to GAS.

[Functional alterations of human platelets following 111In labeling with different ligands and incubation media]

We studied the effects of various 111In-water soluble chelates and incubation media on labeling efficiency of platelets and in vitro platelet aggregability. High labeling efficiency of platelets in ACD-saline was achieved with 111In-oxine sulfate, 111In-tropolone and 111In-MPO (2-mercaptopyridine-N-oxide). In the condition with 4.8 x 10(6)/mm3 platelets in ACD-plasma, 111In-oxine-sulfate had low labeling efficiency and inconsistent labeling, while 111In-tropolone and 111In-MPO had high labeling efficiency. In vitro platelet aggregability (ADP 2 microM) was reduced when platelets were labeled in the absence of plasma. However, there was no significant difference in platelet aggregability among 111In-platelets labeled by three different chelates. In conclusion, to maintain aggregation activity of the platelets with relatively high labeling efficiency, the best result was obtained by using MPO or tropolone chelate in plasma at 4.8 x 10(6)/microliters platelet concentration.

Convulsant and anticonvulsant cyclopentanones and cyclohexanones

The convulsant and/or anticonvulsant activity of unsubstituted and mono-alkyl-substituted cyclopentanones and cyclohexanones were examined by testing the ability of these compounds to produce seizures or to inhibit seizures induced by pentylenetetrazol and maximal electroshock in CF-1 mice. In addition, these compounds were tested for their ability to bind to the picrotoxin receptor. The unsubstituted compounds, cyclopentanone and cyclohexanone, prevented both pentylnetetrazol- and maximal electroshock-induced seizures. Cyclopentanones and cyclohexanones with small (less than 3 carbon atoms) alkyl substituents in the 2-position were also anticonvulsant; all of these compounds, except 2-ethylcyclohexanone, blocked both pentylenetrazol- and maximal electroshock-induced seizures. 2-Ethylcyclohexanone was very effective against pentylenetetrazol seizures but did not prevent maximal electroshock seizures. Cyclohexanones with larger alkyl substituents in the 2-position, 2-propylcyclohexanone and 2-t-butylcyclohexanone, caused clonic seizures following injection into mice. Of the cyclopentanones and cyclohexanones with alkyl substitutions in the 3-position that were studied, one was an anticonvulsant (3-methylcyclopentanone), one was a mixed convulsant/anticonvulsant (3-ethylcyclohexanone), and the other two (3-ethylcyclopentanone and 3-t-butylcyclohexanone) were convulsants. Finally, two cyclohexanones with alkyl substituents in the 4-position were studied. Both 4-ethylcyclohexanone and 4-t-butylcyclohexanone produced convulsions when injected into mice. All the neuroactive cyclopentanones and cyclohexanones competitively displaced [35S]t-butylbicyclophosphorothionate, a ligand specific for the picrotoxin receptor, from rat brain membranes. The convulsant compounds were generally more potent than the anticonvulsants. The cyclohexanones were more potent than their corresponding cyclopentanones and the binding potency of both increased as the size of the alkyl substituent increased. These results suggest that cyclopentanone, cyclohexanone, and their alkyl-substituted derivatives act at the picrotoxin receptor to increase or decrease neuronal activity. Thus, they appear to have sites and mechanisms of action similar to those of the neuroactive gamma-butyrolactones and gamma-thiobutyrolactones.

Cytoplasmic microtubules in human neutrophil degranulation: reversible inhibition by the colchicine analogue 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1- one

The colchicine analogue 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-on e (MTC) was found to inhibit concanavalin A- and formyl-methionyl-leucyl-phenylalanine-stimulated human neutrophil degranulation and to depolymerize the microtubule network at low concentrations. The inhibitory capacity of MTC for neutrophil degranulation was similar to that of nocodazole and taxol. The mechanistically distinct actions of these three drugs on microtubules support the notion that microtubules are required for neutrophil enzyme release in response to different stimuli. MTC affected both degranulation and microtubule integrity rapidly and reversibly, after only a 5-min preincubation. At these short periods of incubation, colchicine irreversibly affected neutrophil degranulation only at concentrations in the millimolar range and behaved similarly to its microtubule-inactive analogue lumicolchicine. At longer times of incubation (30-60 min), low concentrations of both MTC and colchicine induced a drastic shortening and depolymerization of microtubules, preserving the microtubule-organizing center, but only MTC was able to completely inhibit the secretory response of neutrophils. These results suggest that the colchicine effect on neutrophil degranulation is not specifically mediated by its action on the microtubule network of these cells. In contrast, the specific and reversible effects of the colchicine analogue MTC suggest that it may be a useful agent with which to study the role of microtubules in this cellular function.

Effects of bencyclane on normal and cevadine-modified Na channels in frog skeletal muscle

The effect of 10(-5) mol/l bencyclane on the repetitive electrical activity of muscle membrane was studied with the conventional microelectrode technique. Electrical activity was induced by repetitive stimulation in normal Ringer solution (train) or by a single depolarizing current pulse in the presence of 10(-6) mol/l cevadine (volley). Bencyclane decreased, in a use-dependent manner, the maximum rates of depolarization and repolarization (Vmax+ and Vmax-, resp.) of the action potentials both of the train and the volley. The inhibition of Vmax+ and Vmax- was proportional; however, it was stronger for the volleys than for the trains. The cycle length (mean interspike interval) of the volley was increased by bencyclane; the prolongation was progressive during consecutive cycles. The dissociation of bencyclane from the Na channel was studied by applying trains of different durations with equal pulse numbers. Bencyclane at a higher concentration (5 x 10(-5) mol/l) caused a reversible tonic block: the overshoot potentials, Vmax+ and Vmax- were markedly reduced. The reduction of Vmax- was slightly stronger than that of Vmax+. Slow membrane potential oscillation (SMPO) was evoked by treating the muscle with 10(-4) mol/l of cevadine. The administration of 5 x 10(-6) mol/l bencyclane decreased the frequency of SMPO, while 10(-5) mol/l bencyclane terminated the slow oscillation activity without changing its baseline potential. The present results indicate that bencyclane induces use-dependent inhibition of Na channels in muscle, similarly as do class 1 antiarrhytnmic drugs. Inhibition was observed with both normal and cevadine-modified Na channels.

Synthesis and biological evaluation of substituted benzo[h]cinnolinones and 3H-benzo[6,7]cyclohepta[1,2-c]pyridazinones: higher homologues of the antihypertensive and antithrombotic 5H-indeno[1,2-c]pyridazinones

Several substituted benzo[h]cinnolinones 3 and 3H-benzo[6,7]cyclohepta[1,2-c]pyridazinones 4, which were designed as less rigid congeners of 5H-indeno[1,2-c]pyridazinones 2, were synthesized and tested as antihypertensive, inotropic, antithrombotic, antiinflammatory, and antiulcer agents. While the seven-membered ring derivatives displayed only antithrombotic properties, which were comparable to that of acetylsalicylic acid, most of the benzo[h]cinnolinones exhibited significant antihypertensive, inotropic, and antithrombotic properties. In this respect, the 8-amino (3b) and 8-acetylamino (3c) together with the 4,4a-dehydro analogue of 3c (11) were found to possess the most potent and long-lasting antihypertensive activity. In particular, the dextro isomer of 3c was more active than the racemic form, with lower tachycardiac effects. Unlike the lower homologues 2, none of the compounds showed significant antiinflammatory or antiulcer activity.

Methods for depleting brain glutathione

To search for a technique to deplete reduced glutathione (GSH) in brain, the influence of various types of compounds on brain GSH levels was investigated in mice. Of the compounds tested, cyclohexene-1-one, cycloheptene-1-one and diethyl maleate were shown to be potent GSH depletors in brain as well as in liver. The depletion of cerebral GSH ranged about 40-60% of control levels at 1 and 3 hr after intraperitoneal injection. Cyclohexene, cycloheptene, phorone, acetaminophen, and benzyl chloride caused mild depletion of cerebral GSH, but buthionine sulfoximine did not alter cerebral GSH levels. Further, intracerebroventricular injection of cyclohexene-1-one and cycloheptene-1-one caused depletion of brain GSH to about 60-80% of control levels at 1 hr after injection, and the effects persisted for at least 6 hr. Under these conditions, hepatic GSH was not altered. These results demonstrated that cyclohexene-1-one and cycloheptene-1-one can cause not only a marked depletion of brain GSH by systemic administration, but also depletion of cerebral GSH by intracerebroventricular injection by virtue of being water-soluble compounds. Thus, methods for depleting brain GSH employing both compounds are available for exploring possible functions of cerebral GSH in in vivo systems.

Antibacterial activity of selected tropones and tropolones

The antibacterial activity of 33 substituted and unsubstituted seven-member ring tropones and tropolones was examined on 14 reference strains representing Gram-positive and Gram-negative bacteria. It was shown that the chemical character and position of the substituent plays a distinct role in the biological activity of investigated compounds. Depending on the substituent the antibacterial effect may be either increased or diminished. C-1 thio and C-2 nitro derivatives of tropone are significantly more active than tropone. The dibenzotropone derivatives display no antibacterial activity. Hydroxymethyl derivatives of tropolone are more active than tropolone, while hydroxy-, isopropyl-, methyl- as well as tropolone acetates are equipotent.

New inhibitors for aminoglycoside-adenylyltransferase

Two hydroxymethyltropolones and two tropolone acetate derivatives were found to inhibit an aminoglycoside-adenylyltranferase in a gentamicin-resistant Escherichia coli strain. The inhibitory effect of tropolones depends on the nature of the aminoglycoside antibiotic subject to adenylation. Combinations of hydroxymethyltropolones with tobramycin were more active compared with tropolone acetates against gentamicin-resistant strains displaying adenylyltransferase activity. On the contrary a combination of the investigated acetate with gentamicin was of lower activity. It could be shown that these inhibitors inhibit, to a varying degree, the transfer of radioactive ATP to different aminoglycoside molecules.

Use-dependent blockade of sodium channels induced by bencyclane in frog skeletal muscle and canine cardiac Purkinje fiber

Applying conventional microelectrode technique, the effect of bencyclane was studied on the maximal rate of rise (Vmax) of the transmembrane action potential in frog skeletal muscle and canine cardiac Purkinje fiber. Bencyclane (10 microM) decreased the Vmax from 333.7 +/- 6.9 V/sec to 302.7 +/- 10.2 V/sec (n = 6, p less than 0.05) in skeletal muscle without changing the resting membrane potential. If repetitive stimulation with different constant cycle lengths was applied, a further, frequency-dependent decrease of Vmax developed in both tissues with similar frequency-dependence. In skeletal muscle bencyclane increased the time of 50% repolarization by 33.3 +/- 2.5% (n = 7, p less than 0.01) and decreased the overshoot potential by 11.3 +/- 0.72 mV (n = 7, p less than 0.01) measured at 250 msec cycle length. In cardiac Purkinje fiber bencyclane shortened the action potential duration (APD90) from 258.3 +/- 15.4 msec to 241.7 +/- 12.1 msec (n = 6, p less than 0.05) without changing the resting membrane potential and action potential amplitude measured at 500 msec cycle length. The comparable size of the Vmax-block at the same cycle lengths observed in skeletal muscle (short APD) and Purkinje fiber (long APD) suggests that the inhibition may by mainly attributed to the open sodium channel population. It was concluded that the antiarrhythmic action of bencyclane, based on the use-dependent blockade of sodium channels, might be an important component of the therapeutic effect of bencyclane.

On the role of O-methylation in the metabolism of S-adenosylmethionine in rat brain

The effects of tropolone and pyrogallol in areas of the rat brain with a high and low density of catecholaminergic innervation, i.e. the striatum and cortex, on S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) concentrations were studied and related to the extent of catechol-O-methyltransferase (COMT) inhibition. Moreover, the effects of drugs enhancing dopamine (DA) or noradrenaline (NA) utilization in these areas were also investigated. Pyrogallol reduced the concentrations of SAM in a similar manner in both areas and increased SAH much more in the cortex than in the striatum; these effects corresponded to that on O-methylation in terms of dose-effect relationships, indicating that there is no compartmentation of SAM with respect to the methylation process in which it is used. Tropolone increased SAM and decreased SAH in the striatum only, and these effects occurred at somewhat higher doses than the inhibition of COMT. Together with the data showing that DA antagonists decrease SAM in the striatum, this suggests that a significant proportion of SAM metabolism in this area results from O-methylation of DA (or its deaminated metabolite). A number of antidepressants did not alter the levels of SAM in either area, but some of the drugs increased SAH in the cortex. However, this was not correlated with their effects on the noradrenergic system. Inhibition of the synthesis and decarboxylation of SAM by cycloleucine and methylglyoxal bis(guanylhydrazone) (MGBG), respectively, did not cause the expected pattern of changes, i.e. decreases of both SAM and SAH in the former case and either increase or no change in both parameters in the latter. Instead, both cycloleucine and MGBG increased SAH while decreasing SAM, suggesting an involvement of other properties of these drugs.

Reversible inhibition of microtubules and cell growth by the bicyclic colchicine analogue MTC

2-methoxy-5-(2,3,4-trimethoxyphenyl) 2,4,6-cycloheptatrien-1-one (MTC) is a synthetic colchicine analogue, lacking the B ring of the alkaloid (Fitzgerald: Biochem. Pharmacol. 25:1381-1387, 1976). MTC has been shown to bind reversibly to the colchicine binding site of tubulin and to inhibit microtubule assembly in vitro (Andreu et al: Biochemistry 23:1742-1752, 1984; Bane et al: J. Biol. Chem. 259:7391-7398, 1984). Its action on different cultured cell lines (PtK2, Pk15, and SV-3T3) has now been studied. 0.2 X 10(-6) M MTC stopped Pk15 and SV-3T3 cell growth, inducing an accumulation of mitoses in a few hours. Removal of MTC from the culture medium rapidly restored normal mitotic index and growth rates. Partial depolymerization of the cytoplasmic microtubules of PtK2 cells was observed at concentrations ranging from 2 to 5 X 10(-7) M. Maximal microtubule network depolymerization was obtained after 4 h of treatment with 2 to 5 X 10(-6) M MTC or at a higher MTC concentration (2 X 10(-5) M) for less than 2 h. Removal of 2 X 10(-5) M MTC (the highest MTC concentration used) from the culture medium resulted in almost complete microtubule polymerization after 10 min of drug recovery and a normal microtubule network in 20-30 min. MTC constitutes an antimitotic drug directed to the colchicine site. It is water-soluble, shows a fast and reversible action, and may therefore be employed as a convenient tool to study cellular microtubule-dependent functions.