CDK4 and Telangiectasia: In this context, our observation that p-RB1 is potently elevated in ECs of the mouse AVMs and patient telangiectasias prompted us to determine whether pharmacological inhibition of CDK4/6 (the two main kinases targeting Ser807/811 on RB1) using the clinically approved drugs, palbociclib and ribociclib 47, could have beneficial effects in HHT mice.