Grant Renewal to Continue Work to Improve Vascular Function in People with Sickle Cell Disease

Kirkwood A. Pritchard, Jr., PhD

Professor, Division of Congenital Heart Surgery

Sickle Cell Disease Impairs Vascular Function by Inducing a Destructive Cycle.

The destructive cycle starts with myeloperoxidase (MPO) released from activated neutrophils and other myeloid cells (Figure 1). MPO generates toxic oxidants that injure and kill the cells that makeup blood vessels. Dead and dying cells release high mobility group box-1 (HMGB1) from the cell’s nucleus which plays an essential role in maintaining DNA structure and regulating gene expression. However, when cells die, they passively release HMGB1 outside the cell, turning it into a potent inflammatory molecule that increases inflammation and recruitment of neutrophils to the vessel wall. After the neutrophils arrive, they bind to the endothelium lining the vessel wall and crawl into the vessel wall, where they become activated and cause even greater inflammation and tissue injury. Although all cells make HMGB1, even blood vessel cells, when released from dead and dying cells, HMGB1 impairs the blood vessel’s ability to vasodilate, mediate blood flow, or repel activated neutrophils, damaged sickled RBC and activated platelets from the vessel wall. In this way, the MPO-HMGB1 destructive cycle increases vascular adhesion of neutrophils, RBC, and platelets. Our studies suggest the MPO-HMGB1 destructive cycle is a novel inflammatory pathway that sickle cell disease uses to injure the vessel wall and increase the risk of acute crises. Current Therapies for Sickle Cell Disease

Hydroxyurea, L-glutamine, oxbryta, and crizanlizumabtmca are currently the only therapies approved by the FDA for treating SCD. Hydroxyurea and L-glutamine reduce sickle crisis and vasocongestion. Hydroxyurea is a chemotherapeutic agent that reduces leukocyte counts and leukocyte-dependent inflammation. It also increases fetal Hb and decreases Hb polymerization. Finally, hydroxyurea even releases nitric oxide. Oral L-glutamine provides the energy that RBC use to metabolize oxidized lipids and reduce glutathione disulfide, thereby minimizing sickling and vasocongestion. Oxbryta inhibits hemoglobin S polymerization. Crizanlizumab-tmca binds to P-selectin on activated endothelial cells that line the blood vessel inner wall and circulating platelets to prevent adhesion of sickled red cells to the vessel wall. While all of these therapies help reduce vascular inflammation and RBC injury, sickling, and sticking to the vessel wall, none of these treatments target the mechanisms by which sickle cell disease induces vasculopathy as defined above in the destructive cycle (Figure 1). My laboratory designed and developed N-acetyllysyltyrosylcysteine amide (KYC), a first-in-class, multimodal, systems pharmacology agent for treating sickle cell disease. Unlike the FDAapproved drugs listed above, KYC inhibits the mechanisms

Figure 1. Vasculopathy in Sickle Cell Disease is caused by a Destructive Cycle.

in the destructive cycle. KYC inhibits MPO’s ability to generate toxic oxidants that kill cells. Interestingly, MPO oxidizes KYC into a new novel anti-inflammatory agent that inactivates HMGB1 and activates other proteins in the cell that increases antioxidant enzyme expression to protect the vessel wall from oxidative damage and cell death. KYC effectively improves vascular function, reducing RBC vasocongestion in the lungs and brains of sickle cell mice, thereby decreasing the risk of acute crisis and stroke. Bench to Bedside

Besides being awarded a new grant to continue my NIH research program in sickle cell disease at the Medical College of Wisconsin, MCW, myself and several past lab members were awarded a patent for KYC. Because KYC is a system pharmacology agent, it is highly effective for treating sickle cell disease, multiple sclerosis, stroke, traumatic brain injury, and bronchopulmonary dysplasia. With such potential for treating many dysregulated innate immune diseases, I started a company five years ago called ReNeuroGen LLC to develop KYC. Last year, ReNeuroGen LLC completed a phase I SBIR proposal to obtain proofof-concept data showing that KYC reduces vasocongestion in the lungs and brains of sickle mice. Last September, ReNeuroGen LLC submitted a preclinical phase II SBIR application to develop KYC further for treating people with sickle cell disease. This time is exciting for me, members of my lab, and my collaborators because we can continue our NIH-funded academic research program in sickle cell disease and watch the company move KYC from bench to bedside in real-time.

FOR ADDITIONAL INFORMATION on this topic, visit mcw. edu/surgery or contact Dr. Kirkwood A. Pritchard Jr., at kpritch@mcw.edu.

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