Aporphine Alkaloid N-Nornuciferine from Nelumbo nucifera Induces MAPK-Associated Autophagy Under Nutrient Deprivation in Human Pancreatic Cancer Cells.

Background

Pancreatic cancer cells adapt to nutrient stress by activating metabolic pathways that facilitate survival and proliferation within the tumor microenvironment, a phenomenon known as austerity. Targeting this resilience presents a strategy for developing chemotherapeutic agents with anti-austere properties.

Methods

Phytochemical investigation of Nelumbo nucifera petals led to the isolation of six alkaloids: three benzylisoquinolines (1-3), two aporphines (4, 5), and one proaporphine (6). Preferential cytotoxicity under nutrient deprivation was evaluated. The most active compound was further analyzed in MIA PaCa-2 cells using proliferation, migration, colony formation, and three-dimensional spheroid growth assays, with additional selective cytotoxicity assessment in KLM-1 cells. Mechanistic studies examined MAPK family signaling, autophagy-associated alterations, and apoptosis.

Results

(-)-N-nornuciferine (5) exhibited considerable preferential cytotoxicity against MIA PaCa-2 cells (PC50 = 0.53 µM) and KLM-1 cells (PC50 = 1.11 µM). Under nutrient-rich conditions, 5 suppressed the proliferation, migration, colony formation, and spheroid growth of MIA PaCa-2 cells. Under nutrient deprivation, 5 increased MAPK phosphorylation and LC3-II accumulation while reducing p62/SQSTM1 levels. Chloroquine (CQ) further increased LC3-II accumulation, particularly at 10 µM 5, compared with CQ alone. However, autophagy inhibitors did not rescue 5-induced loss of viability, and the pan-caspase inhibitor Z-VAD-FMK also failed to significantly mitigate cytotoxicity. No detectable PARP or caspase-3 cleavage was observed.

Conclusions

(-)-N-nornuciferine (5) exhibits anti-austere and anticancer activities in pancreatic ductal adenocarcinoma (PDAC) models, accompanied by MAPK phosphorylation and autophagy-related changes under nutrient deprivation conditions. Conventional caspase-dependent apoptosis is unlikely to be the main contributor to this process.