Cytotoxic Colchicine Alkaloids: From Plants to Drugs

Plants produce and store many organic compounds like amino acids, proteins, carbohydrates, fats, and alkaloids, which are usually treated as secondary metabolites. Many alkaloids are biologically active for humans. For thousand years, extracts from plants containing alkaloids had medicinal use as drugs and they owe their powerful effects thanks to presence of alkaloids. Alkaloids have anti-inflammatory, antibacterial, analgesic, local anesthetic, hypnotic, psychotropic, antimitotic, and antitumor activity. Nowadays, alkaloids from plants are still of great interest to organic chemists, pharmacologists, biologists, biochemists, and pharmacists. Plants of Liliaceae family contain colchicine as the main alkaloid, which has cytotoxic activity. Colchicine has limited pharmacological application because of its toxicity, but many derivatives have been synthesized and their cytotoxic activity and tubulin-binding properties have been tested. Many of the synthetic derivatives showed good cytotoxic activity

Computational Analysis for Regulation of Podophyllotoxin Biosynthesis Pathway in Podophyllum with Potential Substitute Species

 Podophyllum species, the source of important secondary metabolite, podophyllotoxin, is over-exploited for production of anti-cancer drugs endangering this genus globally. Lack of complete knowledge on podophyllotoxin biosynthesis is a major drawback in its cultivation and identification for alternative plants. The current study on secoisolariciresinol dehydrogenase, dirigent protein oxidase and pluviatolide synthase identifies their role in regulating podophyllotoxin biosynthesis. The present computational analysis of podophyllotoxin proposes a correlating interconnected network of pathways for podophyllotoxin biosynthesis besides identifying potential substitute species for the biosynthesis of podophyllotoxin and accounting for possible reason for variation in podophyllotoxin yield from different species of this genu

The Development of N-functionalized 4-azapodophyllotoxins as novel anticancer agents

Chemistry and Polymer Scienc

Design and synthesis of podophyllotoxin, phenanthrene and pyrazole based hybrids as potential anticancer agents

The search for novel and effective drugs is a priority goal for treatment of cancer, due to the rapid development of resistance to chemotherapeutic drugs. Moreover, high toxicity usually associated with some cancer chemotherapy drugs and their undesirable side-effects increase the demand for novel anti-tumor drugs active against untreatable tumors, with fewer side-effects and/or greater therapeutic efficiency. Natural products play an important role in the development of anti-cancer drugs. 30 % of anti-tumor compounds used in medicine are natural products or close relatives of them. However, the number of natural products is limited; millions of hybrids can be prepared as combinations of or parts of different natural products. This new approach seems to be very promising in the development of lead compounds for medicinal use, as the biological activity of many new hybrids is superior to their parent compounds. This concept offers an advantage of high diversity and the inherent biological properties of the hybrids over a combinatorial chemistry. By taking the advantage of hybrid concept, in this thesis different series of new podophyllotoxin, phenanthrene and pyrazole based hybrids were synthesized with a view to produce promising anticancer agents. All the synthesized hybrid molecules were investigated for their anticancer activity on different cancer cells. Some of the synthesized hybrid molecules displayed either improved cytotoxicity or higher binding affinity to the target in comparison to their individual parent compounds. Based on the results from the biological studies; it is evident that some of the synthesized compounds have the potential to be developed as leads and their further structural modifications may produce promising anticancer agents

Marine-derived fungi : a source for structurally new and bioactive secondary metabolites

The marine habitat has been proven to be a rich source for both macro- and microorganisms that produce novel and often highly bioactive natural products. Hence, the investigation of the secondary metabolite spectrum of marine fungi represents a valuable approach in the search for new and bioactive natural products. The present study thus focused on the investigation of marine-derived fungi with the aim to isolate bioactive secondary metabolites via a bioassay-guided isolation strategy. Special emphasis was placed on new structural types and their ability to act as antitumor or, in second priority, antibiotic agents. From the cytotoxicity screening program undertaken within the Institute for Pharmaceutical Biology, five fungal strains with cytotoxic activity towards cancer cells and interesting chemical features, i. e. 1H-NMR and LC-MS data, were chosen for detailed investigation. From these fungal cultures altogether 19 compounds and two peptidic mixtures have been isolated and their structures characterized. The sorbicillin derivatives trichodermanones A-D (1-4) were obtained from the sponge-derived fungus Trichoderma saturnisporium. The trichodermanones are remarkable because of their unprecedented carbon skeletons, most likely originating from two different polyketide units that have been connected via a Diels-Alder reaction during biosynthesis. One of these units can be described as sorbicillin-like, characterized by a cyclohexanone ring with an attached six-membered side chain (sorbyl moiety). The second structural part which is a pyrane ring in 1-3 and a lactone ring in 4 is possibly triketide-derived (ring C). The structures of the compounds, including the absolute stereochemistry, were determined by interpretation of their spectroscopic data (1D and 2D NMR, CD, MS, UV and IR) and molecular modelling calculations. Bioassay-guided isolation of the cytotoxic crude extract of Beauveria bassiana led to the isolation of the new cytotoxic tetramic acid derivative beauversetin. A compound of the same structural type, the tetramic acid sch210972 was found to be produced by the sea weed-derived fungus Microdiplodia sp. and showed strong human leucocyte elastase (HLE) inhibitory activity with an IC50 value of 1.04 µg mL-1. HLE plays a role in several inflammatory diseases such as pulmonary emphysema or chronic bronchitis and thus represents an important target for drug research. Our results show that tetramic acids represent a new lead structure for the development of potent HLE inhibitors. The compounds isolated during this study impressively demonstrate the structural diversity of fungal secondary metabolites. The trichodermanones are a formidable example for unique structures from marine-derived fungi. Furthermore, the discovery of tetramic acids as inhibitors of HLE showed that the marine habitat is a rich source for structurally novel compounds which can serve as lead structures for the development of novel and innovative drugs

Multiple Topoisomerase I (TopoI), Topoisomerase II (TopoII) and Tyrosyl-DNA Phosphodiesterase (TDP) inhibitors in the development of anticancer drugs

DNA Topoisomerases (Topos) are ubiquitous nuclear enzymes involved in regulating the topological state of DNA and, in eukaryotic organisms, Topos can be classified into two structurally and functionally different main classes: TopoI and TopoII. Both these enzymes proved to be excellent targets of clinically significant classes of anticancer drugs. Actually, TopoI or II inhibitors show considerable wide spectrum antitumor activities, an important feature to be included in many chemotherapeutic protocols. Despite their clinical efficacy, the use of inhibitors targeting only one of the two enzymes can increase the levels of the other one, favouring the onset of unwanted phenomena such as drug resistance. Therefore, targeting both TopoI and TopoII can reduce the probability of developing resistance, as well as side effects thanks to the use of lower doses, given the synergistic effect of the dual activity. Moreover, since drug resistance is also due to DNA repair systems such as tyrosyl-DNA phosphodiesterases I and II, inhibiting Topoisomerases concomitantly to Tyrosyl-DNA phosphodiesterase enzymes could allow more efficient and safe drugs. This review represents an update of previous works reporting about dual TopoI and TopoII inhibitors, but also an overview of the new strategy regarding the development of derivatives able to simultaneously inhibit Topo and TDP enzymes, with particular attention to structure-affinity relationship studies. The newly collected de-rivatives are described focusing attention on their chemical structures and their biological profiles. The final aim is to highlight the structural requirements necessary for the development of potent multiple modulators of these targets, thus providing new potential antitumor agents for the clinical usage

Novel cis-selective and non-epimerisable C3 hydroxy azapodophyllotoxins targeting microtubules in cancer cells

Podophyllotoxin (PT) and its clinically used analogues are known to be powerful antitumour agents. These compounds contain a trans fused strained γ-lactone system, a feature that correlates to the process of epimerisation, whereby the trans γ-lactone system of ring D opens and converts to the more thermodynamically stable cis epimer. Since these cis epimers are known to be either less active or lacking antitumour activity, epimerisation is an undesirable feature from a chemotherapeutic point of view. To circumvent this problem, considerable efforts have been reported, amongst which is the synthesis of azapodophyllotoxins where the stereocentres at C2 and C3 are removed in order to preclude epimerisation. Herein we report the identification of a novel C3 hydroxy, cis-selective γ-lactone configuration of ring C in the azapodophyllotoxin scaffold, through an efficient stereoselective multicomponent reaction (MCR) involving fluorinated and non-fluorinated aldehydes. This configuration releases the highly strained trans γ-lactone system in podophyllotoxin analogues into the more thermodynamically stable cis γ-lactone motif and yet retains significantly potent activity. These compounds were evaluated against the human cancer lines MCF-7 and 22Rv1 in vitro. Fourteen out of the seventeen tested compounds exhibited sub-micromolar activity with IC50 values in the range of 0.11–0.91 μM, which is comparable and in some cases better than the activity profile of etoposide in this assay. Interestingly, we obtained strong evidence from spectroscopic and X-ray data analyses that the previously reported structure of similar analogues is not accurate. Molecular modelling performed using the podophyllotoxin binding site on β tubulin revealed a novel binding mode of these analogues. Furthermore, sub-cellular study of our compounds using immunolabelling and confocal microscopy analyses showed strong microtubule disruptive activity, particularly in dividing cells

Improvement of conventional anti-cancer drugs as new tools against multidrug resistant tumors

Multidrug resistance (MDR) is the dominant cause of the failure of cancer chemotherapy. The design of antitumor drugs that are able to evade MDR is rapidly evolving, showing that this area of biomedical research attracts great interest in the scientific community. The current review explores promising recent approaches that have been developed with the aim of circumventing or overcoming MDR. Encouraging results have been obtained in the investigation of the MDR-modulating properties of various classes of natural compounds and their analogues. Inhibition of P-gp or downregulation of its expression have proven to be the main mechanisms by which MDR can be surmounted. The use of hybrid molecules that are able to simultaneously interact with two or more cancer cell targets is currently being explored as a means to circumvent drug resistance. This strategy is based on the design of hybrid compounds that are obtained either by merging the structural features of separate drugs, or by conjugating two drugs or pharmacophores via cleavable/non-cleavable linkers. The approach is highly promising due to the pharmacokinetic and pharmacodynamic advantages that can be achieved over the independent administration of the two individual components. However, it should be stressed that the task of obtaining successful multivalent drugs is a very challenging one. The conjugation of anticancer agents with nitric oxide (NO) donors has recently been developed, creating a particular class of hybrid that can combat tumor drug resistance. Appropriate NO donors have been shown to reverse drug resistance via nitration of ABC transporters and by interfering with a number of metabolic enzymes and signaling pathways. In fact, hybrid compounds that are produced by covalently attaching NO-donors and antitumor drugs have been shown to elicit a synergistic cytotoxic effect in a variety of drug resistant cancer cell lines. Another strategy to circumvent MDR is based on nanocarrier-mediated transport and the controlled release of chemotherapeutic drugs and P-gp inhibitors. Their pharmacokinetics are governed by the nanoparticle or polymer carrier and make use of the enhanced permeation and retention (EPR) effect, which can increase selective delivery to cancer cells. These systems are usually internalized by cancer cells via endocytosis and accumulate in endosomes and lysosomes, thus preventing rapid efflux. Other modalities to combat MDR are described in this review, including the pharmaco-modulation of acridine, which is a well-known scaffold in the development of bioactive compounds, the use of natural compounds as means to reverse MDR, and the conjugation of anticancer drugs with carriers that target specific tumor-cell components. Finally, the outstanding potential of in silico structure-based methods as a means to evaluate the ability of antitumor drugs to interact with drug transporters is also highlighted in this review. Structure-based design methods, which utilize 3D structural data of proteins and their complexes with ligands, are the most effective of the in silico methods available, as they provide a prediction regarding the interaction between transport proteins and their substrates and inhibitors. The recently resolved X-ray structure of human P-gp can help predict the interaction sites of designed compounds, providing insight into their binding mode and directing possible rational modifications to prevent them from becoming P-gp drug substrates. In summary, although major efforts were invested in the search for new tools to combat drug resistant tumors, they all require further implementation and methodological development. Further investigation and progress in the abovementioned strategies will provide significant advances in the rational combat against cancer MDR

CHEMICAL APPROACHES FOR IMPROVING DRUG DELIVERY OF KNOWN ANTICANCER COMPOUNDS

Different classes of squalene conjugates have been prepared: the first one containing a disulfide bond that, in the presence of glutathione, is able to trigger the release of a drug unit, the second one containing a tripepidyl sequence selectively cleaved by plasmin and also able to release a drug unit, the last one containinf a fluorescein 5(6)isothiocyanate unit. These compounds are able to self-assemble in water and can improve the delivery of active drugs to tumor tissues and can be helpful in the understanding of nanoparticle cellular uptake