Phenoxybenzamine-d5 is intended for use as an internal standard for the quantification of phenoxybenzamine by GC- or LC-MS. Phenoxybenzamine is an antagonist of α-adrenergic receptors (α-ARs).1,2 It inhibits norepinephrine-induced inositol phosphate formation in HEK293 cells expressing α1-ARs (EC50s = 125.9-316.2 nM), as well as radioligand binding to α2A-, α2B-, and α2C-ARs in CHO cell membranes (Kis = 60, 10, and 60 nM, respectively). Phenoxybenzamine (0.5-5 μM) decreases norepinephrine-, histamine-, and calcium-induced contractions in isolated rabbit aortic strips.3 It also inhibits proliferation of nine cancer cell lines, including lymphoma, breast, and lung cancer cells, with IC50 values ranging from 29.5 to 99.8 μM.4 Phenoxybenzamine (3-1,000 μg/kg) reduces increases in diastolic blood pressure induced by the α-AR agonists cirazoline , St-587, Sgd 101/75, and B-HT 920 in pithed rats.5 It also decreases the time to find the platform in the Morris water maze, indicating restored spatial memory, in a rat model of fluid percussion-induced traumatic brain injury (TBI).6 Formulations containing phenoxybenzamine have been used in the treatment of hypertension and hyperhidrosis associated with pheochromocytomas, an adrenal medullary neuroendocrine tumor.

|1. Minneman, K.P., Theroux, T.L., Hollinger, S., et al. Selectivity of agonists for cloned α1-adrenergic receptor subtypes. Mol. Pharmacol. 46(5), 929-936 (1994).|2. Frang, H., Cockcroft, V., Karskela, T., et al. Phenoxybenzamine binding reveals the helical orientation of the third transmembrane domain of adrenergic receptors. J. Biol. Chem. 276(33), 31279-31284 (2001).|3. McPherson, G.A., Krstew, E., and Malta, E. Effects of phenoxybenzamine on responses to some receptor agonists and calcium in vitro. Clin. Exp. Pharmacol. Physiol. 12(5), 455-464 (1985).|4. Inchiosa, M.A., Jr. Anti-tumor activity of phenoxybenzamine and its inhibition of histone deacetylases. PLoS One 13(6):e0198514, (2018).|5. Timmermans, P.B., Thoolen, M.J., Mathy, M.J., et al. Effects of the irreversible α-adrenoceptor antagonists phenoxybenzamine and benextramine on the effectiveness of nifedipine in inhibiting α1- and α2-adrenoceptor mediated vasoconstriction in pithed rats. Naunyn Schmiedebergs Arch. Pharmacol. 329(4), 404-413 (1985).|6. Rau, T.F., Kothiwal, A., Rova, A., et al. Phenoxybenzamine is neuroprotective in a rat model of severe traumatic brain injury. Int. J. Mol. Sci. 15(1), 1402-1417 (2014).