SOD3-Mimetic As a Complement for Genetic Therapy in Sickle Cell Disease

Background and Objectives: Genetic therapy relieves transfusion-dependence in patients 12 years and older with ß-Thalassemia (1) There is an urgent need to develop a complementary approach to genetic therapy for children younger than 12 years of age. The objective of this report is to describe the potential development of an extracellular superoxide dismutase-mimetic (SOD3-mimetic) to relieve sickle cell disease (SCD) children susceptible to stroke from being transfusion-dependent in order to avoid stroke. SanFlow [aka polynitroxylated pegylated hemoglobin (PNPH)], a SOD3-mimetic has been evaluated and approved by the FDA for further development as drug for the treatment of traumatic brain injury (TBI) complicated by hemorrhagic shock (HS), stroke, and SCD. PK&PD studies demonstrated that SanFlow works as a macromolecular SOD3-mimetic by protecting the endogenous vascular nitric oxide (NO) leading to enhanced blood flow. SanFlow has been shown to protect against superoxide induced hypoxia and inflammation in transgenic SCD and rat model of ischemic stroke as well as a mouse model of TBI+HS. In a rat middle cerebral artery occlusion (MCAO) model of stroke the spreading of the hypoxic core of the ischemic brain as measured by Pial arterial diameter is maintained over 2 hours post onset of stroke with associated reduction in inflammatory markers and brain infraction (3). In a mouse TBI+SH model, SanFlow was shown to be superior to fresh shed whole blood. The safety and efficacy of SanFlow was tested over a 50 fold dose range (i.e. from 0.1 to 5 times the shed blood volume). SanFlow was shown to work at extremely low volume in conjunction with volume replacement crystalloid to substitute whole blood resuscitation (3).

Experimental Results: Using Berkeley model of sickle mice (Hba0/0 Hbb0/0Tg (HuminiLCRα1GγAγδβS) we have measures the PK&PD of SanFlow as a complementary or a substitute for genetic therapy. We have non-invasively measured the blood flow and vasoconstriction using transgenic SS mice (N=7) against WT littermates (N=4) as control. A single bolus dose of SanFlow (20ml/kg at hemoglobin of 4g/dl) significantly corrected the aortic stiffness and pulmonary flow of the SS mice to that of WT littermates (P<0.05). This is also correlated with the decrease of superoxide level in the lung as measure by Luminol activity assays (which fluoresces in the presence of superoxide) (P<0.05). Plasma cGMP (downstream effector of NO and natriuretic peptide activity) and NOx (breakdown product of NO and a measure of NOS activity) concentrations were measured in plasma of mice after infusion of SanFlow. SanFlow infusion was shown to significantly increased plasma cGMP concentrations in plasma. SanFlow infusion also resulted in a significant increase in NOx in plasma after infusion (P<0.05). SanFlow resulted in an increase in plasma cGMP and NOx in SS mice. Thus, the pathophysiological defects or difference of SS mice and WT littermates are corrected by SanFlow infusion.

Conclusions:The present results support development of SanFlow, delivered through continuous infusion, for anemic SCD children to prevent the development of blood transfusion dependency in order to avoid stroke and painful vaso-occlusive crisis (VOC). These results also demonstrated that SanFlow can be used safely and effectively in the elimination of serious painful vaso-occlusive crisis and protect silent and major strokes. Clinical trials of SanFlow in SCD children, prior to their transfusion dependence, as well as in transfusion-dependent teenagers and adults with SCD patients are warranted. By extension, ß-Thalassemia patients can also be treated like SCD patients using SanFlow to relieve them from dependence on life-long blood exchange transfusion. However, these patients would be treated with SOD3-mimetic while waiting for genetic therapy.

References:

• Thompson AA., et.al. Eng. J. Med 2018; 398: 1479-1493

• Brockman EC., et. al. 2017 Neurotrauma, 34(7):1337-50

• Cao S., et. al. 2017 J. Am Heart Assoc., 6(9):e006505.