Aurea Echevarria

PLANTAS MEDICINAIS: A NECESSIDADE DE ESTUDOS MULTIDISCIPLINARES

This paper presents a program emphasizing ethnopharmacological approaches that could allow great success in the study of medicinal plants. The minimum ethnopharmacological research team should consist of a botanist, a chemist and a pharmacologist with each carrying the responsibility for answering in sequential fashion critical questions. The chemical composition and pharmacological properties of the very efficient medicinal plant Croton cajucara were investigated according to ethnopharmacological approaches. The study with this Croton proved to be both efficient and successful. This happy situation was only possible because a multidisciplinary team was involved getting the research done correctly. The ethnopharmacological study involving one other especies Copaifera will be cited.

Antimelanoma activity of 1,3,4-thiadiazolium mesoionics: a structure-activity relationship study.

The effect of a series of 4-phenyl-5-(2′-Y, 4′-X or 4′-X-cinnamoyl)-1,3,4-thiadiazolium-2-phenylamine chlorides was evaluated against B16-F10 murine melanoma cells in vitro and against tumors resulting from implanted B16-F10 cells in C57BL/6 mice. These compounds differ from each other only at the cinnamoyl ring substituent (MI-J, X=OH; MI-2,4diF, X=Y=F; MI-4F, X=F and MI-D, X=NO2). The results were compared with those obtained for MI-D, which has already been shown to be a potent and promising drug against melanoma. On exposure of B16-F10 cells to MI-D, MI-2,4diF and MI-4F, all of them at the same micromolar concentration (50 μM) decreased the cell viability to 8, 50 and 22%, respectively, while MI-J did not show any significant effect under the same conditions. However, low doses such as 10 μM MI-D were sufficient to impair cell growth over 72 h, but for MI-2,4diF and MI-4F the effect on B16-F10 proliferation was only observed at a concentration of 25 μM. Furthermore, MI-4F had a slightly better effect than MI-2,4diF in vitro; its effect on tumor growth in vivo was not significant. MI-D inhibited tumor growth by 77%. The greater effectiveness of MI-D compared with MI-2,4diF, MI-4F and MI-J against B16-F10 melanoma cells is probably due to its stronger electron-withdrawing group (NO2), which increases the positive charge on the mesoionic ring and allows extensive conjugation of the side-chain with the exocyclic moiety. This seems to be important for degree of anti-tumor activity of these compounds.

Cytotoxic activities against Ehrlich carcinoma and human K562 leukaemia of alkaloids and flavonoid from two Solanum Species

Diversas especies do genero Solanum apresentam glicoalcaloides e flavonoides com grande variedade de atividades biologicas. O flavonoide tiliroside (1), uma fracao rica em glicoalcaloides denominada GB e o glicoalcaloide solasonina (2) foram obtidos dos tricomas de galhos jovens e frutos de Solanum crinitum Lam e o alcaloide estereoidal solasodina (3), extraido das partes aereas de S. jabrense Agra & M. Nee, tiveram sua atividade citotoxica avaliada frente a celulas do carcinoma de Ehrlich e da leucemia humana K562. O efeito antiproliferativo destas substâncias mostrou comportamento dose-dependente apos avaliacao atraves do metodo do MTT, para ambos os casos. Os resultados indicaram atividade citotoxica para 1, GB e 2, com IC50 = 69,50 mM, 19,5 mg mL-1 e 74,20 mM, respectivamente, quando ensaiadas frente ao carcinoma de Ehrlich, e IC50 = 118,40 mM, 13,65 mg mL-1, 60,35 mM e 76,92 mM para 1, GB, 2 e 2a (derivado peracetilado da solasonina) frente a leucemia K562. A baixa atividade da aglicona solasodina (3) indicou a importância da presenca dos acucares na estrutura do glicoalcaloide e permitiu postular a substância 2, presente na fracao rica em glicoalcaloides (GB), como um dos principios ativos. Alem disso, os resultados mostraram a possibilidade de biomonitoramento atraves do ensaio do MTT na busca de metabolitos com atividade citotoxica.

Cytotoxic effect of a new 1,3,4-thiadiazolium mesoionic compound (MI-D) on cell lines of human melanoma.

The structural characteristics of mesoionic compounds, which contain distinct regions of positive and negative charges associated with a poly-heteroatomic system, enable them to cross cellular membranes and interact strongly with biomolecules. Potential biological applications have been described for mesoionic compounds. 1,3,4-Thiadiazolium mesoionic compound (MI-D), a new mesoionic compound, has been demonstrated to be extremely cytotoxic to B16-F10 murine melanoma cells when compared to fotemustine and dacarbazine, drugs of reference in melanoma treatment protocols, describing inhibition of tumours grown in vitro and in vivo. We now evaluate the effects of mesoionic compound MI-D on different human melanoma cell lines. The drug decreased the viability and proliferation of MEL-85, SK-MEL, A2058 and MEWO cell lines in vitro, showing a considerable cytotoxic activity on these human cells. Adhesion of MEL-85 cells was evaluated in the presence of the drug using different extracellular matrix (ECM) constituents. MI-D decreased MEL-85 adhesion to laminin, fibronectin and matrigel. The morphology and actin cytoskeleton organisation of MEL-85 cells were also modified on MI-D treatment. These results on human melanoma cell lines indicate that MI-D is a very encouraging drug against melanoma, a tumour that is extremely resistant to chemotherapy.

Synthesis and in vivo antitumor activity of new heterocyclic derivatives of the 1,3,4-thiadiazolium-2-aminide class.

Four new mesoionic compounds derivates of 4-phenyl-5-(4- X-cinnamoyl)-1,3,4-thiadiazolium-2-phenylamine chlorides were synthesized and their antitumor activities against Ehrlich carcinoma and Sarcoma 180 (S180) were evaluated. In the schedule assayed, the derivatives where X=OH and X=NO2 injected i.p. in mice at a total dose level of 10 and 30mg/kg respectively caused a significant Inhibition of ascitic S180 growth, and at a dose of 25 mg/kg inhibited the growth of Ehrlich carcinoma. The derivatives where X=H and X=OCH3 did not show activity. There are no significant changes of hematopoietic parameters of the derivatives in this treatment These data suggest that the presence of more polar substltuents, NO2 and OH, strongly Increases the antitumor activity of this class of compounds.

Synthesis of novel naphthoquinone-spermidine conjugates and their effects on DNA-topoisomerases I and II-alpha

Novos derivados do lapachol 2, nor-lapachol 3 e da lausona 4 foram sintetizados atraves do deslocamento nucleofilico das metoxinaftoquinonas 2a, 3a e 4a pela poliamina (PA) N1-Boc-N5-Bn-espermidina 1a. Os produtos, 2b, 3b e 4b, respectivamente, foram obtidos em bons rendimentos e caracterizados por metodos espectroscopicos e analiticos. Os ensaios preliminares de inibicao das enzimas topoisomerases (topo) I e II-a mostraram-se promissores: todos os compostos (1a 2b, 3b e 4b) inibiram a atividade catalitica da enzima topo II-a na dose de 2 µM. Considerando que somente a PA 1a nao inibiu a atividade da enzima na dose de 0,2 µM, as naftoquinonas apresentam-se como fragmentos em potencial para melhorar a atividade de PAs. Nenhum dos compostos inibiu a topo I na dose de 200 µM.

Effect of MI-D, a new mesoionic compound, on energy-linked functions of rat liver mitochondria.

MI‐D (4‐phenyl‐5‐(4‐nitro‐cinnamoyl)‐1,3,4‐thiadiazolium‐2‐phenylamine chloride), a new mesoionic compound, depressed the phosphorylation efficiency of liver mitochondria as deduced from an accentuated decrease of the respiratory control coefficient and ADP/O ratio. Analysis of segments of the respiratory chain suggested that the MI‐D inhibition site is further on than complex I and between complexes II and III. The transmembrane electrical potential (Δψ) was collapsed dependent on MI‐D concentration. ATPase activity was dramatically increased by MI‐D in intact mitochondria, but inhibited in carbonylcyanide p‐trifluoromethoxyphenylhydrazone (FCCP)‐uncoupled mitochondria. These results suggest that MI‐D acts as an uncoupler agent, a property closely related to its structural characteristics.

Unexpected formation of bis-pyrazolyl derivatives by solid support coupled with microwave irradiation

Abstract Starting from 1,3-dimethyl-5-aminopyrazole 1 and p-substituted benzaldehydes 2 (R=H, CH3, NO2), four different compounds have been obtained: the Schiff bases 4, a bis-pyrazolyl Schiff base 6a (R=H), the expected bispyrazolo[3,4-b;4′,3′-e]pyridine 7b (R=CH3) and the carbinol derived from the Schiff base 8c (R=NO2). The products have been characterised by MS, NMR (1H and 13C) and X-ray crystallography (in the case of 6a). A proposal for the relationships between the different compounds and a possible mechanism is presented.

Síntese de 1,3,5-triazinas substituídas e avaliação da toxicidade frente a Artemia Salina leach

The synthesis of ten symmetrically and unsymmetrically substituted 1,3,5-triazines by Phase Transfer Catalysis (PTC) method is described. Their toxicities were determined against Artemia salina Leach. The LD50 values have also been obtained for these compounds.

P-glycoprotein efflux pump plays an important role in Trypanosoma cruzi drug resistance

Drug resistance in protozoan parasites has been associated with the P-glycoprotein (Pgp), an energy-dependent efflux pump that transports substances across the membrane. Interestingly, the genes TcPGP1 and TcPGP2 have been described in Trypanosoma cruzi, although the function of these genes has not been fully elucidated. The main goal of this work was to investigate Pgp efflux pump activity and expression in T. cruzi lines submitted to in vitro induced resistance to the compounds 4-N-(2-methoxy styryl)-thiosemicarbazone (2-Meotio) and benznidazole (Bz) and to verify the stability of the resistant phenotypes during the parasite life cycle. We observed that the EC50 values for the treatment of epimastigotes with 2-Meotio or Bz were increased at least 4.7-fold in resistant lines, and this phenotype was maintained in metacyclic trypomastigotes, cell-derived trypomastigotes, and intracellular amastigotes. However, in epimastigotes, 2-Meotio resistance is reversible, but Bz resistance is irreversible. When compared with the parental line, the resistant lines exhibited higher Pgp efflux activity, reversion of the resistant phenotypes in the presence of Pgp inhibitors, cross-resistance with Pgp modulators, higher basal Pgp ATPase activity, and overexpression of the genes TcPGP1 and TcPGP2. In conclusion, the resistance induced in T. cruzi by the compounds 2-Meotio and Bz is maintained during the entire parasite life cycle. Furthermore, our data suggest the participation of the Pgp efflux pump in T. cruzi drug resistance.