Abstract 1511: Cancer adaptation to acidic tumor microenvironment

Cancer cells exhibit a characteristic metabolic pattern known as the Warburg effect, which upregulates glycolysis even in aerobic environments. As a result, cancer cells are exposed to an acidic environment due to enhanced excretion of proton and lactate. We have previously reported that this acidic tumor microenvironment induces the activation of the cholesterol biosynthesis pathway and the accumulation of N1-acetylspermidine. Although the acidic tumor microenvironment is known to suppress cancer cell proliferation, the survival strategies employed by cancer cells under such harsh conditions remain unclear. This study aims to elucidate the cell death pathways triggered by acidic pH using an environment even more acidic than physiological conditions and to reveal how cancer cells evade such cell death under physiological conditions. Live imaging was performed by exposing the cervical cancer cell line HeLa to an acidic environment (pH 5.6), which confirmed that cell death with membrane rapture was induced. Furthermore, in the pancreatic cancer cell line PANC1, phosphorylation of RIP1 and MLKL was observed, and cell death was suppressed by treatment with Nec-1, an inhibitor of RIP1. These findings identified Necroptosis induced under pH5.6.In addition, PANC1 cells that transitioned to a floating state under acidic conditions (pH 5.6-6.8) regained their adhesion and proliferation abilities when cultured under normal tissue pH conditions (pH 7.4). These findings indicate that some of the floating cells under acidic conditions avoid cell death and adopt certain survival strategies. Then, RNA-seq was performed on cells fractionated into those in suspension and those remaining adherent under pH6.8. Pathways related to the acquisition of stemness such as HDACs deacetylation pathway and PRC2 methylation pathway were observed to be active in the floating cells. Furthermore, the upregulation of EMT transcription factors was also confirmed. Furthermore, we cultured PANC1 cells under pH6.8, using a genome-wide CRISPR-Cas9 knockout screening system over a 30-day time course and identified key genes essential for the acquisition of tolerance to acidic tumor microenvironment. We elucidated a mechanism in pancreatic cancer cells whereby Necroptosis is avoided in physiologically acidic environments. This cell death-avoidance pathways under acidic conditions could potentially be applied to the development of novel therapeutic strategies that induce cell death in pancreatic cancer cells, which are highly influenced by the tumor microenvironment, particularly in acidic conditions. Citation Format: Manami Hasegawa, Keisuke Maede, Miyuki Nishida, Xu Bo, Sho Aki, Rika Tsuchida, Tsuyoshi Osawa. Cancer adaptation to acidic tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1511.