Rapid nutrient depletion to below the physiological range by cancer cells cultured in Plasmax

Mammalian cell culture is a fundamental tool used to study living cells. Presently, the standard protocol for performing cell culture involves the use of commercial media that contain an excess of nutrients. Although this reduces the likelihood of cell starvation, it creates nonphysiologic culture conditions that have been shown to "re-wire" cellular metabolism. Recently, researchers have developed new media like Plasmax, formulated to approximate the nutrient composition of human blood plasma. Although this represents an improvement in cell culture practice, physiologic media may be vulnerable to nutrient depletion. In this study, we directly addressed this concern by measuring the rates of glucose and amino acid depletion from Plasmax in several cancer cell lines (PC-3, LNCaP, MCF-7, and SH-SY5Y) over 48 h. In all cell lines, depletion of glucose from Plasmax was rapid such that, by 48 h, cells were hypoglycemic (<2 mM glucose). Most amino acids were similarly rapidly depleted to subphysiological levels by 48 h. In contrast, glucose and most amino acids remained within the physiological range at 24 h. When the experiment was done at physiological oxygen (5%) versus standard (18%) with LNCaP cells, no effect on glucose or amino acid consumption was observed. Using RNA sequencing, we show that this nutrient depletion is associated with enrichment of starvation responses, apoptotic signaling, and endoplasmic reticulum stress. A shift from glycolytic metabolism to mitochondrial respiration at 5% O₂ was also measured using Seahorse analysis. Taken together, these results exemplify the metabolic considerations for Plasmax, highlighting that cell culture in Plasmax requires daily media exchange.