SONIC HEDGEHOG (SHH) PROMOTES BLOOD-BRAIN BARRIER (BBB) INTEGRITY IN DIFFUSE MIDLINE GLIOMA OF THE PONS

Abstract

Abstract Diffuse Midline Glioma of the Pons (DMG-P) is the most common brainstem tumor in children and is universally lethal in this age group. The intact Blood-Brain Barrier (BBB) in these tumors are believed to play a major role in preventing systemically administered therapeutic agents from reaching therapeutic concentrations in the tumor. The factors that contribute to the integrity of BBB in DMG-P is not well understood. Sonic Hedgehog (SHH) signaling promotes BBB integrity in the developing and adult brain and plays an important role in the formation and maintenance of DMG-P tumors. In the present study, we show that DMG-P tumor cells secrete SHH ligand. Secreted SHH present in the tumor conditioned media (TCM) tightens the BBB by increasing electrical impedance and decreased paracellular and transcellular permeability in BBB Endothelial cells (ECs). Mechanistically, SHH in TCM causes tightening of the BBB by increasing the expression of junctional proteins in BBB-ECs, likely by signaling through non- canonical pathways. SHH in the TCM also increased the expression of ATP-binding cassette (ABC) transporter proteins ABCB1(P- glycoprotein) and ABCG2 (BCRP- Breast cancer resistance protein) in the Endothelial cells. These pro-barrier functions of SHH in TCM can be reversed by pharmacological inhibition of the S-acylation of the SHH ligand using Hedgehog acyltransferase (HHAT) inhibitor RUSKI-201. Our study demonstrates a potential therapeutic strategy of altering the BBB permeability to increase the efficacy of systemic therapies in DMG-P tumors. Ongoing studies will validate these findings in orthotopic murine models of DMG-P.