CPT1A, LKB1, and AMPKα-1 siRNAs decrease CPT1 enzyme activity in MCF-7 and MDA-MB-231 breast cancer cells. CPT1 enzyme activity assays were performed on cells transiently transfected with siRNAs targeting CPT1A, LKB1, or AMPKα-1. A) In 184B5 cells, treatment with CPT1A siRNA decreased enzyme activity by 30% relative to vehicle (p < 0.05). B) CPT1 enzyme activity was decreased by 17, 22, and 30% relative to vehicle in MCF-7 cells treated with CPT1A, LKB1, and AMPKα-1 siRNAs, respectively (p < 0.05). C) In MDA-MB-231 cells, knock-down of CPT1A resulted in a 24% reduction in enzyme activity relative to vehicle (p < 0.05), and LKB1 and AMPKα-1 siRNAs led to 29 and 23% reductions relative to vehicle, respectively (p < 0.05). Different letters represent statistical differences between groups. Results represent the mean ± SEM of three independent experiments.