Propranolol responsiveness in vascular tumors is not determined by qualitative differences in adrenergic receptors

Propranolol, a beta 1 (ADBR1) and beta 2 (ADBR2) adrenergic receptor blocker, accelerates regression of proliferating infantile hemangiomas (IH-P) while not affecting non-involuting congenital hemangiomas (NICH) and nonproliferating IH (IH-NP). To determine the expression of ADBRs in vascular tumors, immunofluorescent staining and confocal microscopy were employed to determine the in situ cellular distribution of ADBRs in formalin-fixed paraffin-embedded tissue sections of IH-P, IH-NP, and NICH. In situ cellular proliferation, indexed by Ki-67 expression, distinguished IH-P (n = 3) from both IH-NP (n = 3) and NICH (n = 2). In IH-P, IH-NP, and NICH tumor sections, both ADBR1 and ADBR2 were co-localized in both endothelial cells (ECs; GLUT1(+) in IH; CD31+ in NICH) and pericytes (smooth muscle actin). We tentatively conclude that either EC and/or pericytes in IH-P could be target(s) of propranolol. Cell proliferation, but not absence of either class of ADBR, distinguished the propranolol responsive IH-P from the nonresponsive IH-NP and NICH.