RESUMO
Notch signaling plays crucial roles in cell differentiation and proliferation, but aberrant activation of this signaling results in tumorigenesis and cancer progression. Notch signaling is thus a promising drug target for oncotherapy, and the development of Notch signaling inhibitors is eagerly awaited. Notch inhibitory activity-guided fractionation of a Spilanthes acmella extract led to the identification of five sesquiterpene lactones: tagitinin A (1), 1ß,2α-epoxytagitinin C (2), tagitinin C (3), orizabin (4), and 2α-hydroxytirotundin (5). 1ß,2α-Epoxytagitinin C (2) exhibited Notch signaling inhibition, with an IC50 of 25.6 µM, and was further evaluated for its activity against HPB-ALL, a Notch-activated leukemia cell line. Compound 2 showed potent cytotoxicity against HPB-ALL (IC50 1.7 µM) and arrested the cell cycle at the G2/M phase, but did not induce apoptotic cell death. Notch inhibitory mechanism analysis suggested that compound 2 transcriptionally suppresses Notch1 mRNA. In addition, we found that oxidative stress induction is critical for Notch signaling inhibition and the cytotoxicity of compound 2. This is the first mechanism of small molecule Notch inhibition. Our results demonstrate that 1ß,2α-epoxytagitinin C (2) is a potential anti-leukemia agent and further investigation of this compound is warranted.
Assuntos
Leucemia , Apoptose , Linhagem Celular Tumoral , Humanos , Leucemia/tratamento farmacológico , Estresse Oxidativo , Transdução de SinaisRESUMO
Since Notch signaling plays important roles in cell proliferation and differentiation, aberrant activation of this signaling contributes to cancer progression. In neural stem cells, Notch signaling inhibits differentiation by activating HES1 expression. Therefore, Notch signaling inhibitors may be candidates for new anticancer drugs or have applications in neural regenerative medicine. In this study, six naturally occurring Notch inhibitors were isolated from the methanol (MeOH) extract of Lansium domesticum using our novel cell-based assay. Hongherin (2), a cardiac glycoside, demonstrated potent Notch inhibitory activity with an IC50 of 0.62 µM and was found to be cytotoxic in HPB-ALL human T cell acute lymphoblastic leukemia cells. Hongherin (2) also induced the differentiation of C17.2 neural stem cells to neurons, causing a 65% increase in differentiation compared to the control. Mechanistically, hongherin (2) reduced the amount of Notch1 (full length) and mastermind-like protein (MAML). This indicates that hongherin (2) inhibits Notch signaling through a dual mechanism involving the reduction of both Notch1 and MAML protein levels.
Assuntos
Cardenolídeos/química , Plantas/química , Receptores Notch/antagonistas & inibidores , Humanos , Transdução de SinaisRESUMO
Aberrant activation of Notch signaling contributes to the pathogenesis of several different types of cancer, and Notch pathway inhibitors may have significant therapeutic potential. Using a unique cell-based assay system, we isolated twelve compounds, including one new natural product from Garcinia speciosa, that inhibit the Notch signaling pathway. HES1 and HES5 are target genes of the Notch cascade, and compound 2, referred to as cowanin, decreased the protein levels of HES1 and HES5 in assay cells. Furthermore, cowanin (2) showed potent cytotoxicity against human leukemic HPB-ALL cells. The Notch signaling inhibitory activity of cowanin (2) is linked to the increased degradation of nicastrin, which is one of the components of the γ-secretase complex. To the best of our knowledge, this is the first example of a compound with Notch pathway inhibitory activity mediated by nicastrin degradation.
Assuntos
Secretases da Proteína Precursora do Amiloide/metabolismo , Glicoproteínas de Membrana/metabolismo , Receptores Notch/metabolismo , Taninos/farmacologia , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Produtos Biológicos/química , Produtos Biológicos/farmacologia , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Garcinia/química , Garcinia/metabolismo , Células HEK293 , Humanos , Camundongos , Plasmídeos/genética , Plasmídeos/metabolismo , Receptores Notch/antagonistas & inibidores , Receptores Notch/genética , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Transdução de Sinais/efeitos dos fármacos , Taninos/química , Fatores de Transcrição HES-1/genética , Fatores de Transcrição HES-1/metabolismoRESUMO
Neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease occur due to loss of the structure and function of neurons. For the potential treatment of neurodegenerative diseases, accelerators of neuronal differentiation of neural stem cells (NSCs) have been focused on and a cell-based assay system for measuring Notch signaling pathway activity was constructed. Using this assay system, eight compounds isolated from Calotropis gigantea were identified as inhibitors of the Notch signaling pathway. Hes1 and Hes5 are target genes of the Notch signaling pathway, and compound 1, called uscharin, decreased the protein levels of Hes1 and Hes5 in assay cells and MEB5 cells (mouse NSCs). Furthermore, uscharin (1) enhanced the differentiation of MEB5 cells into neurons. The mechanism of uscharin (1) for the Notch signaling inhibitory activity would be acceleration of the degradation of the Notch intracellular domain (NICD) in the MEB5 cells.
