Phytochemical profiling of Nothapodytes nimmoniana to understand camptothecin biosynthesis using tandem mass spectrometry

Nothapodytes nimmoniana is a medicinally important plant producing camptothecin (CPT) which is a well-known anti-cancer drug. Its analogues viz. topotecan and irinotecan are currently used to treat variety of cancers like lung, colon, ovarian cancers. The CPT is a monoterpene indole alkaloid class of compound and synthesised by the combination of terpene and indole pathway. Secologanin from terpene pathway and tryptamine from indole pathway condense together to form strictosidine which is a precursor of CPT. In this study, four different tissues viz. root, leaf, bark and fruit of N. nimmoniana were subjected to LC-QTOF-MS analysis. Total sixteen intermediate compounds in the CPT biosynthetic pathway with their relative accumulation were detected and confirmed by tandem mass spectrometry analysis. Two or more than two isomers of post-strictosidine pathway intermediates like deoxypumiloside, pumiloside and strictosamide, strictosamide epoxide were detected in roots and bark. Accumulation pattern of intermediate metabolites in roots suggests active biosynthesis of CPT in roots. Moreover, unlike Camptotheca acuminata (another CPT producing plant), presence of both carboxylic acid derivatives and methyl esters of iridoid pathway intermediates such as loganic acid/ loganin, secologanic acid/ secologanin and strictosidinic acid/ strictosidine suggests existence of two or more interwoven pathways leading to CPT biosynthesis in N. nimmoniana.