CHEK1 and pulmonary arterial hypertension: There are many genes involved in DDR, including checkpoint kinase 1 (CHK1), poly(ADP-ribose) polymerase 1 (PARP1), Pim-1, mitochondrial heat shock protein 90 (HSP90) etc. Several studies have shown specific pharmacological inhibitors like MK-8776 (CHK1 inhibitor), ABT-888 (PARP1 inhibitor), SGI-1776 (PIM1 inhibitor) and gamitrinib (mitochondrial HSP90 inhibitor) down-regulated their target genes, leading to reduced proliferation and increased apoptosis, suggesting their therapeutic potential in PAH [14–18].