Efaproxiral (RSR13)

Efaproxiral is an allosteric hemoglobin (Hb) modifier that reduces the affinity of Hb for oxygen, increasing the diffusion of oxygen from blood to tissue.¹ In isolated human whole blood, efaproxiral (1.75 mM) increases the partial pressure of oxygen at which Hb is 50% saturated (p50) from 26.75 to 38.63 mm Hg and decreases the percent oxyhemoglobin (Hb-O₂) saturation from 48 to 33.8% at a partial oxygen pressure (pO₂) of 26 mm Hg. Efaproxiral (150 mg/kg) increases tumor pO₂ from 5.2 to 13.1 mm Hg 30 minutes after administration in a RIF-1 mouse fibrosarcoma flank tumor model.² Efaproxiral (100 μM) enhances radiation-induced cytotoxicity in EMT6 mouse breast cancer cells grown under hypoxic conditions and increases radiosensitization and inhibits tumor growth in a hypoxic Lewis lung tumor mouse model when administered at a dose of 100 mg/kg.³ It also increases the running capacity of normal mice and mice with left coronary artery (LCA) ligation-induced myocardial infarction (MI) when administered at a dose of 150 mg/kg.⁴

1.Steffen, R.P.Effect of RSR13 on temperature-dependent changes in hemoglobin oxygen affinity of human whole bloodAdv. Exp. Med. Biol.454653-661(1998) 2.Hou, H., Khan, N., O'Hara, J.A., et al.Effect of RSR13, an allosteric hemoglobin modifier, on oxygenation in murine tumors: An in vivo electron paramagnetic resonance oximetry and bold MRI studyInt. J. Radiat. Oncol. Biol. Phys.59(3)834-843(2004) 3.Teicher, B.A., Wong, J.S., Takeuchi, H., et al.Allosteric effectors of hemoglobin as modulators of chemotherapy and radiation therapy in vitro and in vivoCancer Chemother. Pharmacol.42(1)24-30(1998) 4.Watanabe, T., Takeda, T., Omiya, S., et al.Reduction in hemoglobin-oxygen affinity results in the improvement of exercise capacity in mice with chronic heart failureJ. Am. Coll. Cardiol.52(9)779-786(2008)