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At least 19 recordsLinked to original sources
PubMed1977

Podophyllotoxin as a probe for the colchicine binding site of tubulin.

The binding of [3H]podophyllotoxin to tubulin, measured by a DEAE-cellulose filter paper method, occurs with an affinity constant of 1.8 X 10(6) M-1 (37 degrees at pH 6.7). Like colchicine, approximately 0.8 mol of podophyllotixin are bound per mol of tubulin dimer, and the reaction is entropy-driven (43 cal deg-1 mol-1). At 37 degrees the association rate constant for podophyllotoxin binding is 3.8 X 10(6) M-1 h-1, approximtaely 10 times higher than for colchicine; this is reflected in the activation energies for binding which are 14.7 kcal/mol for podophyllotoxin and 20.3 kcal/mol for colchicine. The dissociation rate constant for the tubulin-podophyllotoxin complex is 1.9 h-1, and the affinity constant calculated from the ratio of the rates is close to that obtained by equilibrium measurements. Podophyllotxin and colchicine are mutually competitive inhibitors. This can be ascribed to the fact that both compounds have a trimethoxyphenyl ring and analogues of either compound with bulky substituents in their trimethoxyphenyl moiety are unable to inhibit the the binding of either of the two ligands. Tropolone, which inhibits colchicine binding competitively, has no effect on the podophyllotoxin/tubulin reaction. Conversely, podophyllotoxin does not influence tropolone binding. Moreover, the tropolone binding site of tubulin does not show the temperature and pH lability of the colchicine and podophyllotoxin domains, hence this lability can be ascribed to the trimethoxyphenyl binding region of tubulin. Since podophyllotoxin analogues with a modified B ring do not bind, it is concluded that both podophyllotoxin and colchicine each have at least two points of attachment to tubulin and that they share one of them, the binding region of the trimethoxyphenyl moiety.

Animals↗
PubMed1975

Microtubules and axoplasmic transport. Inhibition of transport by podophyllotoxin: an interaction with microtubule protein.

Pharmacological evidence is presented for the involvement of microtubules in the process of fast axoplasmic transport. A quantitative measure of the inhibition of axoplasmic transport in an in vitro preparation of rat sciatic nerve is described. The alkaloids colchicine, podophyllotoxin, and vinblastine, which are known both to disrupt microtubules and to bind to the protein subunit of microtubules, are inhibitors of axoplasmic transport. Lumicolchine and picropodophyllin, unlike their respective isomers colchicine and podophyllotoxin, are poor inhibitors of axoplasmic transport. The dissociation constants for the binding of colchicine, lumicolchicine, podophyllotoxin, and picropodophyllin to purified microtubule protein from rat brain have been measured. Inhibition of axoplasmic transport by these drugs correlates favorably with their affinities of microtubule protein.

Animals↗
PubMed1979

Comparison of a water-soluble and a water-insoluble podophyllotoxin derivative in murine neoplasms.

Comparison of a water-soluble (27-487) with a water-insoluble (VP-16-213) podophyllotoxin derivative in seven murine neoplasms revealed slight therapeutic superiortiy of VP-16-213 but also slightly greater toxicity when compared with 27-487. A strikingly good response of the Taper liver tumor to both compounds was observed, providing further incentive to the use of podophyllotoxin derivatives in human hepatomas.

Animals↗
PubMed1978

Correlation of tubulin-binding and antitumor activities of podophyllotoxin analogs.

The tubulin-binding affinities of podophyllotoxin and 12 related compounds have been compared with the effectiveness of these drugs in three assays of antitumor activity: (1) The mastocytoma assay of inhibited tumor cell growth in vitro; (2) the 37 sarcoma assay of tumor remission in vivo; and (3) the Stentor regeneration inhibition assay which detects a requirement for microtubule polymerization. The results indicate that there is a positive Spearman rank correlation coefficient between the inhibition constant for the binding of colchicine to tubulin in the presence of these compounds and the effectiveness of the compounds in the three assays of tumor growth inhibition. It is suggested that tubulin-binding assays may be a useful step in the screening of podophyllotoxin-like compounds suspected of disrupting mitosis by binding to microtubule protein.

Animals↗
PubMed1978

Topical treatment of penile condylomata acuminata with podophyllin, podophyllotoxin and colchicine. A comparative study.

The effect of alcoholic solutions with 20% podophyllin from Podophyllum peltatum and Podophyllum emodi, 8% podophyllotoxin, and 8% colchicine, when applied to penile condylomata acuminata in 227 men, were statistically alike. Of the patients initially judged to be cured after 1-2 applications, 13% showed recurrence, thus bringing down the permanent cure frequency to only 43%. Local side effects were absent after only half the series of colchicine applications, whereas as much as about 3/4 of the treatment course with podophyllin and pure podophyllotoxin could be completed without provoking discomfort. Warts in the urinary meatus healed significantly less well than warts on the other genital mucous membranes. Eighty-nine per cent of patients who had previously been cured of concylomata became wart-free after 1-2 treatments, as opposed to only 40% of those who had never had this wart type previously. The use of the commercially available colchicine offers an opportunity to establish a standardized therapy; following application of an 8% solution, rinsing off should be performed after 6-8 hours.

Administration, Topical↗
PubMed1979

Podophyllotoxin derivative VP 16-213.

VP 16-213, a derivative of podophyllotoxin, is currently entering phase-III studies. Its mode of action is incompletely understood, but differs markedly from that of its parent compound. The greatest lethal damage is experienced by cells in the late S and G2 phases. In the L 1210 system the drug shows marked schedule dependency: prolonged administration may be more effective than single bolus administration. As a single agent, VP 16-213 is the most active compound yet tested against small-cell bronchial carcinoma. It may also prove to be a useful agent in patients with other types of lung tumour, testicular teratomas, and some types of leukaemia. No long-term or cumulative toxicity has been reported. Most side effects are predictable and reproducible.

Animals↗
PubMed1975

[Therapeutic experiences using the new podophyllotoxin derivative VP 16-213 in malignant human tumors].

The new semisynthetic epipodophyllotoxin VP 16-213 has been tested for antitumor activity and toxicity in a non-randomized phase II trial. The study included 33 patients with solid tumors and acute leukemias. The drug was given in 5-day courses every 3 weeks, parenterally for the first 2 courses and thereafter orally. Subjectively VP 16-213 was well tolerated in both i.v. and oral administration, but almost universally induced leukothrombopenia and hair loss. The best results were achieved in 12 patients with oat cell carcinoma of the lung (4 good and 4 less good responses). Remissions of lesser quality were also observed in anaplastic lung cancer, ovarian carcinoma and acute myelomonocytic leukemia. VP 16-213 possesses proven, clinically valuable cytostatic activity against various human neoplasms. Complementary studies to establish its optimum dosage and administration, and its place in combination chemotherapy, are in progress.

Adenocarcinoma↗
PubMed1978

Evidence for involvement of microtubules in the action of vasopressin in toad urinary bladder. I. Functional studies on the effects of antimitotic agents on the response to vasopressin.

The antimitotic agents colchicine, podophyllotoxin, and vinblastine inhibit the action of vasopressin and cyclic AMP on osmotic water movement in the toad urinary bladder. The alkaloids have no effect on either basal or vasopressin-stimulated sodium transport or urea flux across the tissue. Inhibition of vasopressin-induced water movement is half-maximal at the following alkaloid concentrations: colchicine, 1.8 X 10(-6) M; podophyllotoxin, 5 X 10(-7)M; and vinblastine, 1 X 10(-7)M. The characteristics of the specificity, time-dependence and temperature-dependence of the inhibitory effect of colchicine are similar to the characteristics of the interaction of this drug with tubulin in vitro, and they differ from those of its effect on nucleoside transport. Inhibition of the vasopressin response by colchicine, podophyllotoxin, and vinblastine is not readily reversed. The findings support the view that the inhibition of vasopressin-induced water movement by the antimitotic agents is due to the interaction of these agents with tubulin and consequent interference with microtubule integrity and function. Taken together with the results of biochemical and morphological studies, the findings provide evidence that cytoplasmic microtubules play a critical role in the action of vasopressin on transcellular water movement in the toad bladder.

Animals↗
PubMed1975

A correlation between the effects of anti-mitotic drugs on microtubule assembly in vitro and the inhibition of axonal transport in noradrenergic neurones.

1. Podophyllotoxin, colchicine and griseofulvin inhibit the intra-axonal movement of noradrenaline storage vesicles in cat hypogastric nerve/inferior mesenteric ganglion preparations maintained in vitro, cause the disappearance of axonal microtubules and inhibit the assembly of microtubules from tubulin in vitro. The order of potency of the three effects is podophyllotoxin greater than colchicine greater than griseofulvin. 2. Lumicolchicine is without effect on the three parameters and does not interfere with the binding of tritiated colchicine to tubulin. 3. Podophyllotoxin causes a more rapid loss of microtubules from axons than the same concentration of colchicine. 4. The experiments provide strong evidence that microtubules are components of the system responsible for the intra-axonal migration of noradrenaline storage vesicles.

Animals↗
PubMed1978

Evidence for involvement of microtubules in the action of vasopressin in toad urinary bladder. II. Colchicine binding properties of toad bladder epithelial cell tubulin.

Colchicine, podophyllotoxin and vinblastine have been found to inhibit the action of vasopressin on water movement in the toad urinary bladder. Tubulin is the major colchicine binding component of toad bladder epithelial cells, accounting for approximately 3.3% of the total cell protein. More than 99% of the tubulin is found in the soluble fraction after sonication, the remainder is in the particulate fraction. Similar to the characteristics of the binding of colchicine to tubulins from other sources, the binding of colchicine to toad bladder tubulin is temperature- and time-dependent, is inhibited competitively by podophyllotoxin (Ki= 5.5 x 10(-7)m), and has a binding constant of 1 X 10(6) liters/mole at 37 degrees. Binding activity decays according to first-order kinetics and is stabilized by vinblastine. The characteristics of the interactions of colchicine and podophyllotoxin with epithelial cell tubulin in vitro closely parallel the ability of these drugs to inhibit the response to vasopressin in vivo. These results, coupled with those of functional and morphological studies, support the view that the ability of these drugs to affect vasopressin-induced water movement across toad bladder epithelial cells is related to the depolymerization of cytoplasmic microtubules.

Animals↗
PubMed1975

A clinical trial of the oral form of 4'-demethyl-epipodophyllotoxin-beta-D ethylidene glucoside (NSC 141540) VP 16-213.

A clinical trial of the oral form of VP 16-213 (NSC-141540), a semisynthetic podophyllotoxin, was undertaken. In 20 patients, treatment was started at 200 mg/day p.o. for 5 days; courses were repeated after a rest period of 16 days. Five patients were treated at the same dose, repeated with only 9-day rest periods. Subsequently, 65 patients were given 300-400 mg/day for 5 days, with rest periods of 9 days between courses. The side effects encountered included anorexia, nausea and vomiting, stomatitis, diarrhea, leukopenia, thrombocytopenia, alopecia, and pruritus. Substernal discomfort with or without palpitations was reported by 18 patients; no explanation for this symptom could be found. No complete remissions (CR) were observed. Parital remissions (PR) and improvement (IMP) were seen as follows: small cell carcinoma, lung (10 patients)--2 PR, 3 IMP; adenocarcinoma, lung (4 patients)--1 PR; alveolar cell carcinoma, lung (1 patient)--1 IMP; mesothelioma (4 patients)--1 IMP; ovarian cancer (12 patients)--3 PR, 3 IMP; breast cancer (20 patients)--4 IMP; colon cancer (8 patients)--2 IMP; bladder cancer (4 patients)--2 IMP; histiocytic lymphoma (7 patients)--2 PR, 3 IMP; chronic myeloid leukemia (1 patient)--1 IMP.

Adenocarcinoma↗
PubMed1977

Treatment of small cell anaplastic carcinoma of the lung with the oral solution of VP-16-213 (NSC 141540, 4'-demethylepipodophyllotoxin 9-(4,6-O-ethylidene-beta-D-glucopyranoside).

The semisynthetic podophyllotoxin derivative VP-16-213 (NSC 141540) has been evaluated in a phase II study in patients with small cell anaplastic carcinoma of the lung. The drug was administered as an oral solution, the drinking ampoule, in doses of 100 mg twice a day for 4 days in 30 patients previously treated with intensive combination chemotherapy and for 5 days in 10 untreated patients. The courses were repeated every third week with dose modifications according to individual tolerance. All patients had measurable disease and objective responses were obtained in 20 patients (50%), 15 previously treated (50%) and 5 untreated patients (50%). The median time for response after the start of treatment was 15 days (range 6-42) and the median duration of response was 56 days (range 16-147). Dose-limiting toxicity was principally hematologic, consisting of leukopenia, but gastrointestinal toxicity and alopecia were also observed. The study demonstrated that VP-16-213 administered as an oral solution is highly effective against small cell anaplastic carcinoma of the lung without clinical cross-resistance to CCNU, cyclophosphamide, methotrexate, or vincristine.

Administration, Oral↗
PubMed1979

A quantitative microdensitometric and autoradiographic study of the effect of 4'-demethyl-epipodophyllotoxin-beta-D-thenylidene glucoside (VM-26) on the cell cycle of cultured fibroblasts.

The effect of 4'-demethyl-epipodophyllotoxin-beta-D-thenylidene glucoside (VM-26) , a semi-synthetic derivative of podophyllotoxin, on the cell cycle was studied with chick embryo fibroblasts cultivated in vitro. DNA, RNA and protein content, as well as NADH-diaphorase activity were determined by quantitative microdensitometry and cytofluorometry. The incorporation of [3H]thymidine and [3H]leucine into DNA and proteins were analysed by autoradiography. These metabolic data correlated with morphological observation showed that VM-26 blocks the cell cycle at different moments of its kinetics depending on both the dose and the time exposure. NADH-diaphorase activity is the first to be affected, then biochemical changes (involving the metabolism of RNA and proteins) and morphological alterations (especially of mitochondria) follow. This suggests that VM-26 may act primarily upon the mechanism of respiration of the cell.

Animals↗
PubMed1979

Microtubules inside the plasma membrane of squid giant axons and their possible physiological function.

The effects of application of the microtubule-disassembling reagents to squid giant axons upon resting potential, the height of the propagated action potential, and the threshold to evoke action potential were studied using colchicine, podophyllotoxin, vinblastine, griseofulvin, sulfhydryl reagents including NEM, diamide, DTNB and PCMB, and Ca2+ ions. At the same time, the effects of concentrations of K halides and K glutamate on the above physiological properties were studied in comparison with in vitro characteristics of microtubule assembly from purified axoplasmic tubulin. It was found that there was good correlation between conditions supporting maintenance of membrane excitability and microtubule assembly. The experiments suggest that associated with the internal surface of the plasma membrane there are microtubules which regulate in part both the resting and action potentials.

Action Potentials↗
PubMed1978

Opposite end assembly and disassembly of microtubules at steady state in vitro.

Measurements of tubulin exchange into and from bovine brain microtubules at steady state in vitro were made with 3H-GTP as a marker for tubulin addition to or loss from microtubules. Tubulin has an exchangeable GTP binding site that becomes nonexchangeable in the microtubule. We found that tubulin addition to and loss from microtubules under steady state conditions occurred at equivalent rates, that loss and gain were linear, and that exchange rates (percentage of total tubulin in microtubules lost or gained per hour) were dependent upon microtubule length. Furthermore, we found that podophyllotoxin blocked steady state assembly, but did not alter the rate of steady state tubulin loss. When the assembling microtubule end was pulsed with 3H-GTP at steady state, the label was almost completely retained during a subsequent chase. We conclude that the microtubule assembly-disassembly "equilibrium" is a steady state summation of two different reactions which occur at opposite ends of the microtubule, and that assembly and disassembly occur predominantly and perhaps exclusively at the opposite ends under steady state conditions in vitro.

Brain↗