The safety profile of Hemospan®: a new oxygen therapeutic designed using maleimide poly(ethylene) glycol conjugation to human hemoglobin

SUMMARY Hemoglobin-based oxygen carriers have been under development for several decades, but so far none has completed clinical trials due to safety issues, including fundamental concerns regarding hemoglobin-induced vasoconstriction and oxidative reactions. The question becomes whether these attributes are inherent to the hemoglobin molecule itself, or if the molecule can be modified in such a way as to avoid untoward side effects. To this end, Sangart designed a new type of oxygen therapeutic, Hemospan®, based on site-specific, maleimide poly(ethylene) glycol conjugation chemistry. The product, also referred to as MP4, is neither vasoconstrictive nor does it promote oxidation in vivo. The design principles were three-fold: (i) increase hemoglobin molecular size to prolong intravascular retention; (ii) increase oxygen affinity to prevent premature unloading of oxygen in the arterioles, thus avoiding arteriolar vasoconstriction; and (iii) optimize colloidal osmotic pressure and viscosity to enhance blood flow. Preclinical studies with Hemospan in animal models of hemodilution and hemorrhage show maintenance of blood pressure and cardiac output, with improved oxygen delivery compared to early-generation products of cross-linked and polymerized hemoglobins. Four Phase I and II clinical trials have been completed, showing that Hemospan is generally well tolerated in humans, with additional evidence of efficacy through Hemospan's capacity to impart hemodynamic stability in surgical patients. Two multi-center Phase III trials of Hemospan in orthopedic surgery are now underway in Europe.