Celastramycin was found to be a compound that could significantly inhibit PAH-PASMC proliferation, by reducing cytosolic reactive oxygen species (ROS), and reducing RNA levels of multiple TFs, such as HIF1a, NF-KB, and bromodomain-containing protein 4 (BRD4), that are known to regulate smooth muscle cell proliferation and ROS generation. Here, BRD4 is linked to pulmonary arterial hypertension.