Lignanamides and other constituents from the seeds of Annona squamosa L. and their cytotoxic activity

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Abstract
Objectives: The aim of the project was the isolation, structure elucidation, and cytotoxic evaluation of compounds from Annona squamosa L. seeds. Methods: Chromatographic techniques were used to isolate cytotoxic compounds from the methanol extract of A. squamosa seeds. The structures of compounds were elucidated by analyses of mass spectra and nuclear magnetic resonance data. Compounds were evaluated using cytotoxic assays. Results: One new lignanamide, squamosamide, and seven known compounds, cannabisin M ( 2 ), trans - N -caffeoyltyramine ( 3 ), cyclo(L-Ala-L-Ile-L-Pro-L-Met-L-Tyr-L-Thr-L-Val) ( 4 ), annosquacin B ( 5 ), squamocin M ( 6 ), 34,5-trimethoxyphenyl- β -glucopyranoside ( 7 ), and 34,5-trimethoxyphenyl-1- O -β-apiofuranosyl-(1ʹʹ→6ʹ)- β -glucopyranoside ( 8 ) were isolated from the methanol extract of A. squamosa seeds. Compounds 5 and 6 displayed significant cytotoxic activity on both KB and PC9 cancer cell lines with IC 50 values ranging from 6.8 to 8.7 µM. Compounds 1 – 3 exhibited significant cytotoxicity on PC9 cancer cell line with IC 50 values ranging from 6.9 to 9.4 µM and moderate activity on KB cancer cell line with IC 50 values ranging from 11.2 to 16.7 µM. Mechanistic assays in PC9 cells showed that compounds 1 , 2 , 3 , 5 , and 6 increased caspase-3 activity (2.41-3.40-fold) and PARP1 cleavage (2.01-3.40-fold), indicating involvement of the intrinsic apoptotic pathway. Conclusions: The seeds of A. squamosa yielded one new lignanamide and seven known compounds, several of which demonstrate potent cytotoxicity associated with apoptosis. Compounds 5 and 6 emerge as promising leads for further investigation.

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