Lysosomal nitric oxide determines transition from autophagy to ferroptosis after exposure to plasma-activated Ringer's lactate.

Non-thermal plasma (NTP), an engineered technology to generate reactive species, induces ferroptosis and/or apoptosis specifically in various-type cancer cells. NTP-activated Ringer's lactate (PAL) is another modality for cancer therapy at preclinical stage. Here we found that PAL induces selective ferroptosis of malignant mesothelioma (MM) cells, where non-targeted metabolome screening identified upregulated citrulline-nitric oxide (NO) cycle as a PAL target. NO probe detected biphasic peaks transiently at PAL exposure with time-dependent increase, which was responsible for inducible NO synthase (iNOS) overexpression through NF-κB activation. NO and lipid peroxidation occupied lysosomes as a major compartment with increased TFEB expression. Not only ferrostatin-1 but inhibitors for NO and/or iNOS could suppress this ferroptosis. PAL-induced ferroptosis accompanied autophagic process in the early phase, as demonstrated by an increase in essential amino acids, LC3B-II, p62 and LAMP1, transforming into the later phase with boosted lipid peroxidation. Therefore, NO-mediated lysosomal impairment is central in PAL-induced ferroptosis.