Nitric oxide (NO) plays diverse roles in tumor biology, including modulation of blood flow and induction of cell death at high concentrations. In this study, we synthesized a novel NO donor derived from valproic acid (NVA) and investigated its cytotoxic mechanism in human pancreatic cancer cells. NVA released approximately 40% of its total nitrate/nitrite (NOx) immediately after dissolution in phosphate-buffered saline and then remained almost unchanged for 72 h, indicating a rapid initial NO release followed by stabilization. NVA significantly decreased the viability of BxPC-3 cells, whereas valproic acid (VA) alone had little effect. Flow cytometric analysis using Annexin V revealed that NVA-induced cell death was not inhibited by the pan-caspase inhibitor Z-VAD-FMK. Furthermore, Western blotting showed no cleavage of caspase-3 or poly(ADP-ribose) polymerase (PARP) following NVA exposure, suggesting that apoptosis was not the major pathway. These findings indicate that NVA induces NO-dependent, caspase-independent cell death, distinct from classical apoptosis. The present study provides fundamental insights into the potential use of VA-based NO donors as antitumor agents against pancreatic cancer.
Nishi et al. (Wed,) studied this question.