Src-Family B Kinase Inhibition Promotes Lung Endothelial Dysfunction and Guides Drug Discovery

Protein tyrosine kinase (PTK) inhibition is efficacious in treating conditions ranging from cancer to fibrosis but can be limited by endothelial cell dysfunction. In trials of protein tyrosine kinase inhibitors (TKIs) a broad range of vascular effects is observed, inducing clinically detrimental endothelial cell apoptosis, impaired barrier function, or improved pulmonary vascular resistance in pulmonary arterial hypertension (PAH). We hypothesize this range of effects is due to subsets of PTKs either impairing or promoting endothelial homeostasis by modulating Bone Morphogenetic Protein receptor 2 (BMPR2) signaling, a pathway essential for vascular development and dysfunctional in PAH. In a high-throughput siRNA screen we find SRC-Family B PTKs activate whereas SRC-Family A PTKs suppress BMPR2 signaling, measured by the transcription factor inhibitor of differentiation 1 (Id1). Induced loss of function of the strongest ID1 activating PTK LCK (a Src-B kinase) in human pulmonary artery endothelial cells suppresses BMPR2 signaling and induces multiple measures of endothelial dysfunction. However, loss of function of the strongest ID1 inhibitor PTK FYN (a Src- A kinase) does the opposite. Whole-genome transcriptional analysis identifies two multi-gene signatures inversely regulated by LCK and FYN we term “endothelial” and “inflammatory”. To find TKIs mimicking selective Src-A and Src-B inhibition, we use Connectivity map to identify drugs connecting to the endothelial and inflammatory signatures. We find several TKIs: a pro-inflammatory (Regorafanib), a BMPR2 potentiating (Brivanib), and a BMPR2 suppressing (Quizartinib). Here we show a dichotomy in pathway regulation by Src- A and -B kinases that may have utility in transcriptionally based drug discovery.