Effects of PD-L1 Inhibitors on Mitochondrial Function in Melanoma A375 Cells: Unveiling a Shielded Drug Resistance Mechanism

Background : Resistance to immune checkpoint inhibitors, particularly PD-L1 inhibitors, poses a significant challenge in cancer treatment by limiting patient survival. The intricate mechanisms underlying this resistance remain poorly understood, highlighting a critical gap in oncology research. Objective : This study aimed to delve into the regulatory impacts of PD-L1 inhibitors on mitochondrial function within melanoma cells (A375) and explore the potential correlation between PD-L1 resistance and mitochondrial function. Methods : 1. A375 cells were treated with PD-L1 inhibitors, and the effects on mitochondrial gene expression, respiratory chain complex IV activity, reactive oxygen species (ROS) levels, apoptosis-related genes (BAX and BCL-2) expression, tumor pathogenicity-related indicators (cell viability, migration, and invasion) were observed. 2. Fluorescently labeled mitochondria membrane, cell nucleus, and PD-L1 inhibitors were used in high-resolution confocal microscopy to determine whether PD-L1 inhibitors can enter mitochondria. 3. A375 cells treated with PD-L1 inhibitors were subjected to intervention with mitochondrial respiratory chain inhibitor, succinate carrier inhibitor, to observe the effects on apoptosis-related genes (BAX mRNA and BCL-2 expression), tumor pathogenicity-related indicators (cell viability, migration, and invasion). Results : 1.Through high-resolution confocal microscopy, it was observed that PD-L1 inhibitors penetrated mitochondria, binding to the cristae of the inner mitochondrial membrane without entering the cell nucleus.2.Treatment with PD-L1 inhibitors resulted in increased mitochondrial gene expression and respiratory chain activity, reduced ROS levels, elevated BAX expression, decreased BCL-2 expression, and diminished tumor migration and invasion in A375 cells.3.Inhibition of mitochondrial respiratory chain function by succinate carrier inhibitors impeded the enhancement of mitochondrial function induced by PD-L1 inhibitors in A375 cells. This led to a sustained increase in BAX expression, a significant decrease in BCL-2 expression, and a notable reduction in cell viability, tumor migration, and invasion. Conclusion : PD-L1 inhibitors exhibit the capability to penetrate mitochondria, exerting an inhibitory effect on tumor activity in melanoma cells while significantly enhancing mitochondrial function. Disrupting this enhancement of mitochondrial function by PD-L1 inhibitors reverses their overall anti-tumor efficacy, hinting at a novel mechanism of tumor resistance mediated through the regulation of the mitochondrial pathway by PD-L1 inhibitors.