RESUMO
Glutathione transferase P1-1 is over expressed in some cancer cells and contributes to detoxification of anticancer drugs, leading to drug-resistant tumors. The inhibition of human recombinant GSTP1-1 by natural plant products was investigated using 10 compounds isolated from plants indigenous to Southern and Central Africa. Monochlorobimane and 1-chloro-2,4-dinitrobenzene were used to determine GST activity. Each test compound was screened at 33 and 100 µM. Isofuranonapthoquinone (1) (from Bulbine frutescens) showed 68% inhibition at 33 µM, and sesquiterpene lactone (2) (from Dicoma anomala) showed 75% inhibition at 33 µM. The IC(50) value of 1 was 6.8 µM. The mode of inhibition was mixed, partial (G site) and noncompetitive (H site) with K(i) values of 8.8 and 0.21 µM, respectively. Sesquiterpene 2 did not inhibit the CDNB reaction. Therefore, isofuranonapthoquinone 1 needs further investigations in vivo because of its potent inhibition of GSTP1-1 in vitro.
Assuntos
Produtos Biológicos/farmacologia , Inibidores Enzimáticos/farmacologia , Glutationa S-Transferase pi/antagonistas & inibidores , Isoenzimas/antagonistas & inibidores , Produtos Biológicos/química , Produtos Biológicos/isolamento & purificação , Proliferação de Células/efeitos dos fármacos , Relação Dose-Resposta a Droga , Ativação Enzimática/efeitos dos fármacos , Inibidores Enzimáticos/química , Inibidores Enzimáticos/isolamento & purificação , Glutationa S-Transferase pi/isolamento & purificação , Glutationa S-Transferase pi/metabolismo , Humanos , Isoenzimas/isolamento & purificação , Isoenzimas/metabolismo , Cinética , Conformação Molecular , Extratos Vegetais/química , Extratos Vegetais/isolamento & purificação , Extratos Vegetais/farmacologia , Proteínas Recombinantes/antagonistas & inibidores , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Estereoisomerismo , Relação Estrutura-AtividadeRESUMO
Elevated glutathione transferase (GST) E2 activity is associated with DDT resistance in the mosquito Anopheles gambiae. The search for chemomodulators that inhibit the function of AgGSTE2 would enhance the insecticidal activity of DDT. Therefore, we examined the interaction of novel natural plant products with heterologously expressed An. gambiae GSTE 2 in vitro. Five of the ten compounds, epiphyllocoumarin (Tral-1), knipholone anthrone, isofuranonaphthoquinones (Mr 13/2, Mr13/4) and the polyprenylated benzophenone (GG1) were shown to be potent inhibitors of AgGSTE2 with IC(50) values of 1.5 microM, 3.5 microM, 4 microM, 4.3 microM and 4.8 microM respectively. Non-competitive inhibition was obtained for Tral 1 and GG1 with regards to GSH (K(i) of 0.24 microM and 0.14 microM respectively). Competitive inhibition for Tral1 was obtained with CDNB (K(i) = 0.4 microM) whilst GG1 produced mixed type of inhibition. The K(i) and K(i)' for GSH for Tral-1 and GG1 were 0.2 microM and 0.1 microM respectively. These results suggest that the novel natural plant products, particularly Tral-1, represent potent AgGSTE2 in vitro inhibitors.