Altered Magnesium Environments Restrict Colorectal HT-29 Spheroid Growth by Disturbing Cellular Mg(2+) Homeostasis.

Dysregulated magnesium (Mg(2+)) homeostasis contributes to colorectal cancer (CRC), yet its context-dependent function within the tumor microenvironment remains unresolved. This study aimed to determine how sustained low and high extracellular Mg(2+) environments affect CRC spheroid (SP) growth and Mg(2+) homeostasis using HT-29 SPs. We analyzed Mg(2+) flux, the expression of Mg(2+) transporters (e.g., Transient Receptor Potential Melastatin (TRPM) 6), viability, apoptotic and autophagic markers, and phospho-/oxidoproteomic alterations. Both Mg(2+) extremes destabilized SP architecture, reduced viability, and induced apoptosis and autophagy, with SPs displaying heightened vulnerability relative to 2D cultures. Mg(2+) stress impaired Mg(2+) influx and eliminated adaptive transporter regulation in SPs. Loss of membrane TRPM6/7 heterodimers, driven by altered phosphorylation (e.g., TRPM6 Serine 141, Serine 1252, Threonine 1851) and elevated oxidation (e.g., Methionine 1755), suppressed channel activity. High Mg(2+) caused profound metabolic failure despite increased total Mg(2+), reflecting functional Mg(2+) deficiency. CRC spheroids are acutely susceptible to Mg(2+) imbalance due to collapsed transporter homeostasis and post-translational inhibition of Mg(2+) channels. These findings reveal a targetable metabolic vulnerability and support the therapeutic potential of localized Mg(2+) modulation in CRC.