Diazoniapolycyclic Ions Inhibit the Activity of Topoisomerase I and the Growth of Certain Tumor Cell Lines

Development of oxoisoaporphine derivatives with topoisomerase I inhibition and reversal of multidrug resistance in breast cancer MCF-7/ADR cells

A series of oxoisoaporphine derivatives with topoisomerase I inhibition and cytotoxic activities. Among them, compound 14 showed the most potent cytotoxic activity against all cancer cell lines tested, and substantially lower cytotoxicity to LO2 cells. Molecular docking studies, dynamics simulation and a follow-up enzyme inhibition assay indicated that 14 could interfere with DNA and significantly inhibit the activity of topoisomerase I. Further mechanistic studies revealed that 14 could arrest cell cycle at the G1 phase, and finally killed MCF-7 cells via apoptosis. In addition, 14 exhibited remarkable chemoreversal ability on multidrug-resistant MCF-7/ADR breast cancer cells. Some of its mechanisms may be related to inhibition of MCF-7/ADR P-gp-mediated Rhodamine (Rh123) efflux function and expression level, as well as inhibition of ROS, increase of ADR accumulation in MCF7/ADR cells, and enhancement of ADR in inducing apoptosis of MCF7/ADR cells. As 14 has little toxic and side effects, it may have the potential for further research.

DNA Related Enzymes as Molecular Targets for Antiviral and Antitumoral Chemotherapy. A Natural Overview of the Current Perspectives

BACKGROUND

The discovery of new chemotherapeutic agents still remains a continuous goal to achieve. DNA polymerases and topoisomerases act in nucleic acids metabolism modulating different processes like replication, mitosis, damage repair, DNA topology and transcription. It has been widely documented that Polymerases serve as molecular targets for antiviral and antitumoral chemotherapy. Furthermore, telomerase is a ribonucleoprotein with exacerbated activity in most of the tumor cell lines, becoming as an emergent target in Cancer treatment.

METHODS

We undertook an exhaustive search of bibliographic databases for peer-reviewed research literature related to the last decade. The characteristics of screened bibliography describe structure activity relationships and show the principal moieties involved. This work tries to summarize the investigation about natural and semi-synthetic products with natural origin with the faculty to inhibit key enzymes that play a crucial role in DNA metabolism.

RESULTS

Eighty-five data references were included in this review, showing natural products widely distributed throughout the plant kingdom and their bioactive properties such as tumor growing inhibitory effects, and anti-AIDS activity.

CONCLUSION

The findings of this review confirm the importance to find new drugs and biologically active natural products, and their potential medicinally useful benefits.

Benzo[b]quinolizinium Derivatives Have a Strong Antimalarial Activity and Inhibit Indoleamine Dioxygenase

The heme-containing enzymes indoleamine 2,3-dioxygenase-1 (IDO-1) and IDO-2 catalyze the conversion of the essential amino acid tryptophan into kynurenine. Metabolites of the kynurenine pathway and IDO itself are involved in immunity and the pathology of several diseases, having either immunoregulatory or antimicrobial effects. IDO-1 plays a central role in the pathogenesis of cerebral malaria, which is the most severe and often fatal neurological complication of infection with Plasmodium falciparum. Mouse models are usually used to study the underlying pathophysiology. In this study, we screened a natural compound library against mouse IDO-1 and identified 8-aminobenzo[b]quinolizinium (compound 2c) to be an inhibitor of IDO-1 with potency at nanomolar concentrations (50% inhibitory concentration, 164 nM). Twenty-one structurally modified derivatives of compound 2c were synthesized for structure-activity relationship analyses. The compounds were found to be selective for IDO-1 over IDO-2. We therefore compared the roles of prominent amino acids in the catalytic mechanisms of the two isoenzymes via homology modeling, site-directed mutagenesis, and kinetic analyses. Notably, methionine 385 of IDO-2 was identified to interfere with the entrance of l-tryptophan to the active site of the enzyme, which explains the selectivity of the inhibitors. Most interestingly, several benzo[b]quinolizinium derivatives (6 compounds with 50% effective concentration values between 2.1 and 6.7 nM) were found to be highly effective against P. falciparum 3D7 blood stages in cell culture with a mechanism independent of IDO-1 inhibition. We believe that the class of compounds presented here has unique characteristics; it combines the inhibition of mammalian IDO-1 with strong antiparasitic activity, two features that offer potential for drug development.

TR-644 a novel potent tubulin binding agent induces impairment of endothelial cells function and inhibits angiogenesis

TR-644 is a novel combretastatin A-4 (CA-4) analogue endowed with potent microtubule depolymerizing activity superior to that of the lead compound and it also has high affinity to colchicines binding site of tubulin. We tested TR-644 anti-angiogenic effects in human umbilical endothelial cells (HUVEC). It showed no significant effects on the growth of HUVEC cells at concentrations below 1,000 nM, but at much lower concentrations (10-100 nM) it induced inhibition of capillary tube formation, inhibition of endothelial cell migration and affected endothelial cell morphology as demonstrated by the disruption of the microtubule network. TR-644 also increased permeability of HUVEC cells in a time dependent manner. The molecular mechanism for the anti-vascular activity of TR-644 was investigated in detail. TR-644 caused G2/M arrest in endothelial cells and this effect correlated with downregulation of the expression of Cdc25C and Cdc2(Tyr15). Moreover TR-644 inhibited VEGF-induced phosphorylation of VE-cadherin but did not prevent the VEGF-induced phosphorylation of FAK. In chick chorioallantoic membrane in vivo assay, TR-644 (0.1-1.0 pmol/egg) efficiently counteracted the strong angiogenic response induced by FGF. Also CA-4, used as reference compound, caused an antagonistic effect, but in contrast, it induced per se, a remarkable angiogenic response probably due to an inflammatory reaction in the site of treatment. In a mice allogenic tumor model, immunohistochemical staining of tumors with anti-CD31 antibody showed that TR-644 significantly reduced the number of vessel, after 24 h from the administration of a single dose (30 mg/Kg).

3,6-bis(3-alkylguanidino)acridines as DNA-intercalating antitumor agents

A series of 3,6-bis(3-alkylguanidino) acridines was prepared and the interaction of these novel compounds with calf thymus DNA was investigated with UV-vis, fluorescence and circular dichroism spectroscopy, in addition to DNA melting techniques. The binding constants K were estimated to range from 1.25 to 5.26 × 10(5) M(-1), and the percentage of hypochromism was found to be 17-42% (from spectral titration). UV-vis, fluorescence and circular dichroism measurements indicated that the compounds act as effective DNA-intercalating agents. Electrophoretic separation proved that ligands 6a-e relaxed topoisomerase I at a concentration of 60 μM, although only those with longer alkyl chains were able to penetrate cell membranes and suppress cell proliferation effectively. The biological activity of novel compounds was assessed using different techniques (cell cycle distribution, phosphatidylserine externalization, caspase-3 activation, changes in mitochondrial membrane potential) and demonstrated mostly transient cytostatic action of the ethyl 6c and pentyl 6d derivatives. The hexyl derivative 6e proved to be the most cytotoxic. Different patterns of cell penetration were also observed for individual derivatives. Principles of molecular dynamics were applied to explore DNA-ligand interactions at the molecular level.