The Similarity of the Effect of Podophyllin and Colchicine and Their Use in the Treatment of Condylomata Acuminata

Identification of Novel β-Tubulin Inhibitors Using a Combined In Silico/In Vitro Approach

Due to their potential as leads for various therapeutic applications, including as antimitotic and antiparasitic agents, the development of tubulin inhibitors offers promise for drug discovery. In this study, an in silico pharmacophore-based virtual screening approach targeting the colchicine binding site of β-tubulin was employed. Several structure- and ligand-based models for known tubulin inhibitors were generated. Compound databases were virtually screened against the models, and prioritized hits from the SPECS compound library were tested in an in vitro tubulin polymerization inhibition assay for their experimental validation. Out of the 41 SPECS compounds tested, 11 were active tubulin polymerization inhibitors, leading to a prospective true positive hit rate of 26.8%. Two novel inhibitors displayed IC50 values in the range of colchicine. The most potent of which was a novel acetamide-bridged benzodiazepine/benzimidazole derivative with an IC50 = 2.9 μM. The screening workflow led to the identification of diverse inhibitors active at the tubulin colchicine binding site. Thus, the pharmacophore models show promise as valuable tools for the discovery of compounds and as potential leads for the development of cancer therapeutic agents.

Cancers make their own luck: theories of cancer origins

Cancer has been a leading cause of death for decades. This dismal statistic has increased efforts to prevent the disease or to detect it early, when treatment is less invasive, relatively inexpensive and more likely to cure. But precisely how tissues are transformed continues to provoke controversy and debate, hindering cancer prevention and early intervention strategies. Various theories of cancer origins have emerged, including the suggestion that it is 'bad luck': the inevitable consequence of random mutations in proliferating stem cells. In this Review, we discuss the principal theories of cancer origins and the relative importance of the factors that underpin them. The body of available evidence suggests that developing and ageing tissues 'walk a tightrope', retaining adequate levels of cell plasticity to generate and maintain tissues while avoiding overstepping into transformation. Rather than viewing cancer as 'bad luck', understanding the complex choreography of cell intrinsic and extrinsic factors that characterize transformation holds promise to discover effective new ways to prevent, detect and stop cancer before it becomes incurable.

Mechanisms of Secondary Leukemia Development Caused by Treatment with DNA Topoisomerase Inhibitors

Leukemia is a blood cancer originating in the blood and bone marrow. Therapy-related leukemia is associated with prior chemotherapy. Although cancer therapy with DNA topoisomerase II inhibitors is one of the most effective cancer treatments, its side effects include development of secondary leukemia characterized by the chromosomal rearrangements affecting AML1 or MLL genes. Recurrent chromosomal translocations in the therapy-related leukemia differ from chromosomal rearrangements associated with other neoplasias. Here, we reviewed the factors that drive chromosomal translocations induced by cancer treatment with DNA topoisomerase II inhibitors, such as mobility of ends of double-strand DNA breaks formed before the translocation and gain of function of fusion proteins generated as a result of translocation.

DNA topoisomerases as molecular targets for anticancer drugs

The significant role of topoisomerases in the control of DNA chain topology has been confirmed in numerous research conducted worldwide. The prevalence of these enzymes, as well as the key importance of topoisomerase in the proper functioning of cells, have made them the target of many scientific studies conducted all over the world. This article is a comprehensive review of knowledge about topoisomerases and their inhibitors collected over the years. Studies on the structure-activity relationship and molecular docking are one of the key elements driving drug development. In addition to information on molecular targets, this article contains details on the structure-activity relationship of described classes of compounds. Moreover, the work also includes details about the structure of the compounds that drive the mode of action of topoisomerase inhibitors. Finally, selected topoisomerases inhibitors at the stage of clinical trials and their potential application in the chemotherapy of various cancers are described.

Podophyllotoxin Exposure Causes Spindle Defects and DNA Damage-Induced Apoptosis in Mouse Fertilized Oocytes and Early Embryos

Podophyllotoxin (PPT) is a kind of lignans extracted from the roots and stems of the genus Podophyllum from the tiller family, and it has been widely used in the treatment of condyloma acuminatum, multiple superficial epithelioma in the clinics. However, PPT has been reported to be toxic and can cause liver defects and other organ poisoning. In addition, emerging evidences also indicate that PPT has reproductive toxicity and causes female reproduction disorders. In this study, we used fertilized oocytes and tried to explore the effects of PPT on the early embryonic development with the mouse model. The results showed that exposure to PPT had negative effects on the cleavage of zygotes. Further analysis indicated that PPT could disrupt the organization of spindle and chromosome arrangement at the metaphase of first cleavage. We also found that PPT exposure to the zygotes induced excessive reactive oxygen species (ROS), suggesting the occurrence of oxidative stress. Moreover, in the PPT-exposed embryos, there was positive γH2A.X and Annexin-V signals, indicating that PPT induced embryonic DNA damage and early apoptosis. In conclusion, our results suggested that PPT could affect spindle formation and chromosome alignment during the first cleavage of mouse embryos, and its exposure induced DNA damage-mediated oxidative stress which eventually led to embryonic apoptosis, indicating the toxic effects of PPT on the early embryo development.

Colchicine-Binding Site Inhibitors from Chemistry to Clinic: A Review

It is over 50 years since the discovery of microtubules, and they have become one of the most important drug targets for anti-cancer therapies. Microtubules are predominantly composed of the protein tubulin, which contains a number of different binding sites for small-molecule drugs. There is continued interest in drug development for compounds targeting the colchicine-binding site of tubulin, termed colchicine-binding site inhibitors (CBSIs). This review highlights CBSIs discovered through diverse sources: from natural compounds, rational design, serendipitously and via high-throughput screening. We provide an update on CBSIs reported in the past three years and discuss the clinical status of CBSIs. It is likely that efforts will continue to develop CBSIs for a diverse set of cancers, and this review provides a timely update on recent developments.

Synthesis and evaluation of biological properties of ferrocenyl–podophyllotoxin conjugates

Ferrocenyl–podophyllotoxin conjugates have been synthesised and their antiproliferative activity, influence on cell cycle, and interactions with tubulin were evaluated.

Biotechnological interventions for harnessing podophyllotoxin from plant and fungal species: current status, challenges, and opportunities for its commercialization

Podophyllotoxin is an aryltetralin lignan synthesized in several plant species, which is used in chemotherapies for cancers and tumor treatment. More potent semisynthetic derivatives of podophyllotoxin such as etoposide and teniposide are being developed and evaluated for their efficacy. To meet the ever increasing pharmaceutical needs, species having podophyllotoxin are uprooted extensively leading to the endangered status of selective species mainly Sinopodophyllum hexandrum. This has necessitated bioprospection of podophyllotoxin from different plant species to escalate the strain on this endangered species. The conventional and non-conventional mode of propagation and bioprospection with the integration of biotechnological interventions could contribute to sustainable supply of podophyllotoxin from the available plant resources. This review article is focused on the understanding of different means of propagation, development of genomic information, and its implications for elucidating podophyllotoxin biosynthesis and metabolic engineering of pathways. In addition, various strategies for sustainable production of this valuable metabolite are also discussed, besides a critical evaluation of future challenges and opportunities for the commercialization of podophyllotoxin.

Serendipity in Cancer Drug Discovery: Rational or Coincidence?

Novel drug development leading to final approval by the US FDA can cost as much as two billion dollars. Why the cost of novel drug discovery is so expensive is unclear, but high failure rates at the preclinical and clinical stages are major reasons. Although therapies targeting a given cell signaling pathway or a protein have become prominent in drug discovery, such treatments have done little in preventing or treating any disease alone because most chronic diseases have been found to be multigenic. A review of the discovery of numerous drugs currently being used for various diseases including cancer, diabetes, cardiovascular, pulmonary, and autoimmune diseases indicates that serendipity has played a major role in the discovery. In this review we provide evidence that rational drug discovery and targeted therapies have minimal roles in drug discovery, and that serendipity and coincidence have played and continue to play major roles. The primary focus in this review is on cancer-related drug discovery.

Podophyllotoxin derivatives: a patent review (2012 - 2014)

INTRODUCTION

Podophyllotoxin (PPT) is a naturally occurring antimitotic agent and an interesting lead in the development of anticancer agents. Its optimization led to the development of etoposide and teniposide used in combination chemotherapy with other anticancer drugs; unlike PPT these drugs act by inhibiting topoisomerases. Clinical success and toxicity issues at later stages of etoposide usage inclined researchers to develop structurally modified PPT derivatives. Some of the compounds obtained are under clinical investigations and are anticipated to reach the market.

AREAS COVERED

The present review summarizes the attempts made by researchers across the globe to find out newer anticancer agents based on the PPT structure. It brings out the outline of the inventions filed in the form of patents during the years 2012 - 2014.

EXPERT OPINION

After the successful development of etoposide and teniposide there has been considerable interest in the PPT skeleton to develop newer chemotherapeutic agents. In this regard, several PPT derivatives such as TOP53, GL331, NK611, F11782, and so on, have been developed and are undergoing clinical trials. However, its low natural abundance is a major problem in carrying out research on PPT skeleton. This issue is expected to be addressed with the development of newer synthetic strategies to access structurally modified PPTs.

The effect of molecular structure on the anticancer drug release rate from prodrug nanoparticles

The controlled release of an anticancer agent from drug nanoparticles could be successfully achieved by optimizing the chemical structure of dimeric compounds as prodrug.

Recent progress on C-4-modified podophyllotoxin analogs as potent antitumor agents

Podophyllotoxin (PPT), as well as its congeners and derivatives, exhibits pronounced biological activities, especially antineoplastic effects. Its strong inhibitory effect on tumor cell growth led to the development of three of the most highly prescribed anticancer drugs in the world, etoposide, teniposide, and the water-soluble prodrug etoposide phosphate. Their clinical success as well as intriguing mechanism of action stimulated great interest in further modification of PPT for better antitumor activity. The C-4 position has been a major target for structural derivatization aimed at either producing more potent compounds or overcoming drug resistance. Accordingly, numerous PPT derivatives have been prepared via hemisynthesis and important structure-activity relationship (SAR) correlations have been identified. Several resulting compounds, including GL-331, TOP-53, and NK611, reached clinical trials. Some excellent reviews on the distribution, sources, applications, synthesis, and SAR of PPT have been published. This review focuses on a second generation of new etoposide-related drugs and provides detailed coverage of the current status and recent development of C-4-modified PPT analogs as anticancer clinical trial candidates.

The role of biotechnology in the production of the anticancer compound podophyllotoxin

Podophyllotoxin is a plant-derived compound found in Podophyllum sp. that is used to produce semi-synthetic anticancer pharmaceuticals such as etoposide, teniposide, and etoposide phosphate. This chapter describes the role of biotechnology to produce podophyllotoxin and our attempts to domesticate Podophyllum peltatum L., also known as the American mayapple. The domestication research on mayapple included surveys of the natural population, identification of high yielding genotypes, propagation, cultivation, sustainable harvest procedures and the development of protocols for in vitro germplasm bank.

The effect of podophyllotoxin on tissue metabolism and enzyme systems

Podophyllotoxin, 10^–3_M, inhibits the respiration in vitro of rat lymph nodes, thymus, kidney, tumor, spleen, liver, brain, testis, and chicken embryo. Lymph node and spleen respiration are most sensitive, and the degree of inhibition increases with time. The injection of podophyllotoxin into tumor-bearing mice (20 mg. per kg.) causes a dramatic reduction in the respiration of tumor slices. Within 6 hours, the respiration approaches zero. Inhibition is evident 2 hours after injection of the drug. Spleen respiration is reduced 50 per cent within 6 hours. Kidney and liver respirations remain within normal limits. Marked reductions in the respiration of spleen, lymph nodes, and thymus glands of normal rats are produced by the injection of 15 mg. per kg. Thymus gland is the most sensitive of these three tissues, and its respiration is reduced 66 per cent 24 hours after injection of the drug. The injection of 0.8 microgram podophyllotoxin into the yolk sac of chicken eggs bearing 5 day embryos has no effect on the respiration of the embryo within 8 hours, although this is a sufficiently toxic dose to kill 80 per cent of the embryos (within 24 hours). Kidney respiration in the presence of acetate, glucose, alanine, and glutamate is inhibited to approximately the same degree as in the absence of added substrate. Succinate and pyruvate oxidation by rat kidney slices appear to be less sensitive. Oxidation of acetate and butyrate by rabbit kidney homogenate is more sensitive to podophyllotoxin than oxidation by rabbit kidney homogenate without added substrate. Glucose oxidation by this preparation is not inhibited by 10^–3M podophyllotoxin. The anaerobic glycolysis of chicken embryo, rat brain, and rat testis is stimulated by 10^–5 and 10^–6M podophyllotoxin, and is inhibited by 10^–3M. The following enzymes are not inhibited by 10^–3M podophyllotoxin: succinoxidase from pigeon breast muscle, choline, xanthine and tyrosine oxidase from rat liver homogenate, and leucine oxidase from Proteus vulgaris; alkaline and acid phosphatase from dog serum; adenosine triphosphatase from rat liver; choline esterase from rat brain homogenate; ribonucleodepolymerase from spleen mince and thymonucleodepolymerase from dog serum. High concentrations of podophyllotoxin do not influence the viscosity and degree of polymerization of thymonucleic acid.

Toxic epidermal necrolysis-like reaction secondary to colchicine overdose

Colchicine is a microtubule-inhibiting drug used to treat gout, familial Mediterranean fever and many other skin diseases. Intoxication with colchicine affects multiple organs, often fatally. Cutaneous sequelae of colchicine toxicity are rare. We describe the clinical and histological features of a toxic epidermal necrolysis-like exanthem in a patient who lethally overdosed on colchicine.

Joint action of a chemical carcinogen and a neoplastic virus to induce cancer in rabbits; results of exposing epidermal cells to a carcinogenic hydrocarbon at time of infection with the Shope papilloma virus

Areas of rabbit skin previously rendered hyperplastic with turpentine were scarified, inoculated with the Shope papilloma virus, and covered with a dressing that contained 20-methylcholanthrene (MC) or 9:10-dimethyl-1:2-benzanthracene (9:10). The dressing was left on until healing had been well completed, a matter of 5 to 7 days. The papillomas which subsequently arose often appeared later, were fewer, and remained less vigorous than those due to the action of virus alone, but throughout several months they appeared to differ from these in no other ways. Then, more or less abruptly, the large majority became carcinomatous, frequently at several situations, whereas with few exceptions the control growths underwent no such alteration. The cancers were of the sorts ordinarily deriving, by secondary change, from epidermal cells infected with the virus. Collateral data have made plain that the hydrocarbons acted in their carcinogenic capacity to bring on the cancers. Indeed in control tests 9: 10 sometimes conferred latent neoplastic potentialities on uninoculated epidermis exposed to it while healing after scarification, a fact disclosed months later by painting these expanses with chloroform until hyperplasia occurred. Under the promoting influence of this agent papillomas formed which had the distinctive morphology of those induced by the chemical carcinogens. So strong and enduring were the effects of MC and 9:10 as to cause cancers to arise from many virus papillomas which were retrogressing after months of proliferation, that is to say under circumstances ordinarily unfavorable to malignant change. The facts justify the conclusion that the virus and the hydrocarbons acted jointly and in their carcinogenic capacities.

Prodrugs of 4'-demethyl-4-deoxypodophyllotoxin: synthesis and evaluation of the antitumor activity

A series of prodrugs of 4'-demethyl-4-deoxypodophyllotoxin (DDPT) including carbamates (3-8), a carbonate (9) and water-soluble amino acid derivatives (10-17) were prepared and tested for their antitumor activity. The carbamate 6 (2-hydroxyethylcarbamoyl-DDPT), carbonate 9 (2-chloroethyloxycarbonyl-DDPT), and most of amino acid prodrugs (12-17) showed enhanced antitumor activity.

First synthesis and pharmacological evaluation of benzoindolizidine and benzoquinolizidine analogues of alpha- and beta-peltatin

The benzoindolizidine and quinolizidine analogues of alpha- and beta-peltatin were designed and synthesized by two different synthetic routes involving as the key step the Bischler-Napieralski cyclization of suitably substituted N-acyl-2-arylmethylpyrrolidine and -piperidine derivatives. The in vitro biological activity of these analogues as well as some of their derivatives was subsequently evaluated.

Etoposide: four decades of development of a topoisomerase II inhibitor

Podophyllin-containing materials have been used as folk medicines for centuries. In the 1950s, scientists began a search to identify a more effective podophyllotoxin derivative. These efforts eventually resulted in the development of a new class of antineoplastic agents which target the DNA unwinding enzyme, topoisomerase II. The history of the development of one of the first identified topoisomerase II inhibitors, etoposide, is reviewed in this paper. Critical developments in etoposide's mechanism of action, pharmacology and administration schedule are summarised. The clinical benefits of the recently marketed etoposide prodrug, etoposide phosphate (Etopophos) are also detailed. The current status of other clinically approved anticancer agents which target topoisomerase II is briefly reviewed.

Discovery of podophyllotoxins

This review deals with the historical discovery of particularly important lignan derivatives used in cancer chemotherapy. From isolation of the naturally occurring podophyllotoxin, an inhibitor of microtubule assembly, to hemisynthesis of the clinically important anticancer drugs etoposide and teniposide, it will be demonstrated how the activities and the ability of this class of compounds to inhibit topoisomerase II were discovered by different research teams. By virtue of these discoveries, new hemisynthetic derivatives, with different mechanisms of action, are bringing improvements in the ability to treat cancer.

Podophyllotoxin, steganacin and combretastatin: natural products that bind at the colchicine site of tubulin

A large number of antimicrotubule agents are known that bind to tubulin in vitro and disrupt microtubule assembly in vitro and in vivo. Many of these agents bind to the same site on the tubulin molecule, as does colchicine. Of these, the natural products podophyllotoxin, steganacin and combretastatin are the subjects of this review. For each of these, the chemistry and biochemistry are described. Particular attention is given to stereochemical considerations. Biosynthetic pathways for podophyllotoxin and congeners are surveyed. The binding to tubulin and the effects on microtubule assembly and disassembly are described and compared. In addition, structural features important to binding are examined using available analogs. Several features significant for tubulin interaction are common to these compounds and to colchicine. These are described and the implications for tubulin structure are discussed. The manifold results of applying these agents to biological systems are reviewed. These actions include effects that are clearly microtubule mediated and others in which the microtubule role is less obvious. Activity of some of these compounds due to inhibition of DNA topoisomerase is discussed. The range of species in which these compounds occur is examined and in the case of podophyllotoxin is found to be quite broad. In addition, the range of species that are sensitive to the effects of these compounds is discussed.

Chromosomal changes in Chinese hamster AA8 cells caused by podophyllin, a common treatment for genital warts

Podophyllin, a plant derivative of variable composition, is used widely within New Zealand as a treatment for genital warts. One local source of podophyllin has been tested for ability to cause mutagenic effects in Salmonella typhimurium as well as for effects on chromosomes of Chinese hamster AA8 cells. Although only weakly mutagenic in one strain of Salmonella, podophyllin caused structural aberrations as well as changes in chromosome number in the Chinese hamster cells. The range of aberrations was similar to those caused by teniposide, a close structural relative of the major component, which was used as a positive control in the Chinese hamster cell experiments. A literature review revealed that podophyllin was shown to cause changes of chromosome number in the mouse cervix in vivo, although aberrations were not studied. Patients treated with podophyllin will usually possess one form of the papilloma virus, and this itself may have some oncogenic potential. We suggest that podophyllin could potentiate these effects and question its continued widespread use.

The clinical pharmacology of etoposide

Etoposide, a semisynthetic derivative of podophyllotoxin, is increasingly used to treat cancer. Etoposide is a phase-specific, cytotoxic drug acting in the late S and early G2 phases of the cell cycle. It appears to cause breaks in DNA by either an interaction with DNA-topoisomerase II or the formation of free radicals. Most studies show a biexponential decay after the intravenous (IV) administration of etoposide. The peak plasma concentrations of drug and the area under the concentration versus time curve (AUC) are linearly related to the IV dose. Considerable interpatient variability of pharmacokinetic variables exists after IV etoposide. Various metabolites of etoposide have been identified, but their detection and quantitation are disputed. Approximately 30% to 70% of an etoposide dose is excreted. The bioavailability of oral etoposide is approximately 50%, but its absorption is not linear with increasing doses within the range in clinical use. Considerable interpatient and intrapatient variability exists in the pharmacokinetics of oral etoposide. There is no evidence of etoposide accumulation after multiple consecutive doses by either the IV or oral route. The exact roles of the liver and kidney in metabolism and excretion of etoposide are uncertain. Etoposide has been shown to be a highly schedule-dependent drug in clinical studies. This, together with the phase-specific action of etoposide and its increasingly widespread use in treating cancer, makes the clinical pharmacology of this drug of great clinical importance.

The clinical pharmacology of etoposide and teniposide

Etoposide and teniposide are semisynthetic derivatives of podophyllotoxin and are increasingly used in cancer medicine. Teniposide is more highly protein-bound than etoposide, and its uptake and binding to cells is also greater. Etoposide and teniposide are phase-specific cytotoxic drugs acting in the late S and early G2 phases of the cell cycle. They appear to act by causing breaks in DNA via an interaction with DNA topoisomerase II or by the formation of free radicals. Teniposide is more potent as regards the production of DNA damage and cytotoxicity. Most studies show a biexponential decay following intravenous administration of etoposide and teniposide. The terminal elimination half-life of etoposide is less than that of teniposide, and the plasma and renal clearances of etoposide are greater. The peak plasma concentrations of drug and the area under the concentration versus time curve are linearly related to the intravenous dose of both drugs. Considerable interpatient variability of pharmacokinetic parameters exists following intravenous etoposide and teniposide. Various metabolites of etoposide and teniposide have been identified but their detection and quantitation are disputed. Approximately 30 to 70% of a dose of etoposide is accounted for by excretion, whereas the figure appears to be only 5 to 20% for teniposide. The bioavailability of oral etoposide is about 50% but its absorption is not linear with increasing dose within the range in clinical use. There is considerable inter- and intrapatient variability in the pharmacokinetics of oral etoposide. There is no evidence of accumulation of etoposide and teniposide after multiple consecutive doses by the intravenous or oral routes. The exact roles of the liver and kidney in metabolism and excretion of etoposide and teniposide are uncertain. Etoposide has been shown to be a highly schedule-dependent drug in clinical studies. This together with the phase-specific action of etoposide and teniposide and their increasingly widespread use in cancer medicine make the clinical pharmacology of these drugs of great clinical importance.

Activity of the epipodophyllotoxin VP-16 in the treatment of combination chemotherapy-resistant non-Hodgkin lymphoma

Twenty patients with several histologic subtypes of non-Hodgkin lymphoma who had become resistant to combination chemotherapy were treated with a five-day course of the epipodophyllotixin VP-16. Of 19 evaluable patients, 8 (42%) responded to treatment with 1 complete response and 7 partial responses. The median duration of response was 5.5 months. Seven of the responders had a diffuse lymphoma and 1 had a nodular lymphoma. Of the responders who had diffuse histiocytic lymphoma (DHL), diffuse mixed lymphoma (DML), and diffuse undifferentiated lymphoma (DUL)--the more aggressive histologies in the Rappaport classification--6 of 13 (46%) evaluable patients responded to therapy. Responses were seen in node-dominant, skin-dominant, and marrow-dominant disease. Toxicity was mainly hematopoietic, 53% of patients experiencing leukopenia ( less than 2,000 cells per cu mm) and 68% of patients experiencing thrombocytopenian 2,000 cells per cu mm) and 68% of patients experiencing thrombocytopenia ( less than 100,000 platelets per cu mm). There were two deaths attributable to profound leukopenia with sepsis. The activity of VP-16 in patients who have previously been extensively treated with multiple drugs including vincristine supports its activity in the lymphomas and suggests its lack of cross-resistance with vincristine. The inclusion of VP-16 in primary treatment protocols in the diffuse lymphomas should be considered.