Graduate School of Pharmaceutical Sciences, Chiba University, Chuo-ku, Chiba, Japan.
Phytochemistry. 2013 Jul;91:128-39. doi: 10.1016/j.phytochem.2012.04.019. Epub 2012 May 30.
Camptothecin is a monoterpenoid indole alkaloid that exhibits anti-tumor activity. In Ophiorrhiza pumila, production of camptothecin and its related alkaloids was high in the hairy roots, but not in the cell suspension culture derived from hairy roots. To identify the intermediates in camptothecin biosynthesis, expression of genes encoding tryptophan decarboxylase (TDC) and secologanin synthase (SLS), the two enzymes catalyzing the early steps in camptothecin biosynthesis, were suppressed in the hairy roots of O. pumila by RNA interference (RNAi), and metabolite changes were investigated. In most TDC- and SLS-suppressed lines, accumulation of camptothecin and related alkaloids, strictosidine, strictosamide, pumiloside, and deoxypumiloside was reduced. The accumulation levels of secologanin exhibited a strong negative correlation with the expression level of TDC, and that of loganin exhibited a negative correlation with the expression level of SLS. Some hairy root-specific chromatographic peaks detected by liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR-MS) exhibited positive or negative correlation with TDC expression, suggesting their possible involvement in camptothecin biosynthesis.
喜树碱是一种具有抗肿瘤活性的单萜吲哚生物碱。在钩吻中，喜树碱及其相关生物碱在发根中产量较高，但在发根衍生的细胞悬浮培养物中则不然。为了鉴定喜树碱生物合成中的中间产物，采用 RNA 干扰（RNAi）技术抑制钩吻发根中催化喜树碱生物合成早期步骤的色氨酸脱羧酶（TDC）和一叶萩碱合酶（SLS）基因的表达，并研究了代谢产物的变化。在大多数 TDC 和 SLS 抑制的品系中，喜树碱和相关生物碱、斯替罗苷、斯替罗苷酸、钩吻碱和去氧钩吻碱的积累减少。_secologanin 的积累水平与 TDC 的表达水平呈强烈负相关，loganin 的积累水平与 SLS 的表达水平呈负相关。通过液相色谱傅里叶变换离子回旋共振质谱（LC-FTICR-MS）检测到的一些发根特异性色谱峰与 TDC 的表达呈正相关或负相关，提示它们可能参与喜树碱的生物合成。
