PI3K/mTOR inhibition promotes the regression of experimental vascular malformations driven by PIK3CA-activating mutations

Abstract

Somatic activating mutations within the PIK3CA gene have been recently detected in sporadic lymphatic and venous malformations, and in vascular malformations (VM) associated to overgrowth syndromes, such as CLOVES and Klippel–Trenaunay syndrome. Although VM are often limited to specific tissue areas and can be well treated, in extended or recurrent lesions novel therapeutic approaches are needed. We generated a mouse model of VM by local expression of PIK3CA-activating mutation in endothelial cells. PIK3CA-driven lesions are characterized by large areas of hemorrhage, hyperplastic vessels, infiltrates of inflammatory cells, and elevated endothelial cell density. Such vascular lesions are ameliorated by administration of dual PI3K/mTOR inhibitor, BEZ235, and mTOR inhibitor, Everolimus. Unexpectedly, the expression of PIK3CA-activating mutations in human endothelial cells results in both increased proliferation rates and senescence. Moreover, active forms of PIK3CA strongly promote the angiogenic sprouting. Treatment with PI3K/mTOR inhibitors restores normal endothelial cell proliferation rate and reduces the amount of senescent cells, whereas treatment with Akt inhibitor is less effective. Our findings reveal that PIK3CA mutations have a key role in the pathogenesis of VM and PIK3CA-driven experimental lesions can be effectively treated by PI3K/mTOR inhibitors.

mTORc1 activity is necessary and sufficient for phosphorylation of eNOSS1177

“…; di Blasio et al. ). Vascular malformations share several functional deficits with other vascular diseases including hypercoagulation, vascular remodeling, endothelial senescence, and inflammation.…”

“…Interestingly, it also serves as a central hub of signal integration of numerous protein kinases including AMPK, CAMKII, as well as AKT. Recently, vascular malformations arising from mutations in PIK3CA have been shown to be sensitive to rapamycin treatment in mice as well as humans (Limaye et al 2015;Castel et al 2016;di Blasio et al 2018). Vascular malformations share several functional deficits with other vascular diseases including hypercoagulation, vascular remodeling, endothelial senescence, and inflammation.…”

Development of Molecular Therapies for Venous Malformations

“…This is supported by the presence of somatic ‘second hits’ in TIE2 in lesions of VMCM patients, as a loss ‐ of ‐ function deletion mutation in trans (deleting a possibly protecting WT allele) or as a second missense mutation in cis , likely potentiating the gain ‐ of ‐ function effect of relatively weaker inherited mutations when compared to mutations found alone in sporadic VMs . On the other hand, TIE2 ‐ L914F, TIE2 double mutations or PIK3CA mutations have never been found as inherited, suggesting that they all are lethal in germline, as already shown for PIK3CA ‐ H1049R using genetic mouse models .…”

“…) . In addition, both VM EC transplantation studies and use of EC ‐ specific Cre drivers together with inducible VM mutations have indicated that TIE2 or PIK3CA mutation in an EC compartment is sufficient for VM lesion formation . Disease mechanisms downstream from a mutated TIE2/PIK3CA are not completely understood.…”

“…In addition, TIE2 ‐ L914F increases the number of human umbilical vein ECs (HUVECs) by extending their lifespan rather than proliferation in vitro , and in the mouse transplantation model, no increase in EC proliferation was observed . On the other hand, VEGF ‐ A‐stimulated PIK3CA ‐ VM‐transduced ECs proliferated more than PIK3CA ‐ WT ECs and Pik3ca H1047R increased EC proliferation but not the rate of apoptosis in genetic mouse models . These discrepancies could be due to the different model systems and time points studied.…”