Abstract 10202: DNA-PKcs: A Novel Therapeutic Target in Pulmonary Arterial Hypertension

Introduction: Pulmonary arterial hypertension (PAH) is a progressive disease characterized by vascular obliteration of small pulmonary arteries (PAs), notably due to excessive proliferation and resistance to apoptosis of pulmonary artery smooth muscle cells (PASMCs). Accumulating evidence indicates that PAH-PASMCs have acquired an over-efficient DNA damage response (DDR) ensuring sensing, signaling, and repair of DNA damages, accounting for their enhanced capacity to survive and proliferate under stressful conditions. DNA-dependent protein kinase (DNA-PK) is a pivotal component of the DNA repair machinery which plays an instrumental role in the overall survival and proliferation of cancer cells. Based on similarities between PAH and cancer cells, we thus hypothesized that increased expression of DNA-PK contributes to vascular remodeling in PAH. Methods and Results: Using Western blot (WB) and immunohistochemistry, we found that expression and activity of DNA-PK were increased in PAH-PASMCs (n=6) compared to controls (n=6, p<0.01). Similarly, DNA-PK was significantly up-regulated in distal PAs from PAH animal models (i.e. MCT rats and Su/Hx rats and mice, n=5/group, p<0.01). In vitro, the pharmacological inhibition of DNA-PK using AZD-7648 or Nedisertib attenuates PAH-PASMC proliferation (Ki67 and EdU labeling, MCM2, PLK1, and PNCA by WB; p<0.05) and resistance to apoptosis (AnnexinV labeling, Survivin by WB)(n=5 cell lines; p<0.05). These effects were associated with reduced expression of gH2AX. As assessed by echocardiography and right heart catheterization, treatment with AZD7648 improved pulmonary hemodynamics (RVSP, mPAP, and TPR) and right ventricular function (CO, PAT/PET, TAPSE) in Su/Hx mice with established PAH (n=10/group; all p<0.01). Accordingly, pulmonary vascular remodeling (EVG) and the proportion of PCNA-positive PASMCs were reduced in AZD7648-treated Su/Hx mice when compared to vehicle-treated Su/Hx mice (p<0.001). Conclusions: We showed for the first time that DNA-PK is overexpressed in human and experimental PAH and contributes to the pro-proliferative and anti-apoptotic phenotype of PAH-PASMCs.