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Paroxysmal Nocturnal Hemoglobinuria

Background

PNH is a rare, chronic, debilitating blood disorder that is most frequently acquired in early adulthood and usually continues throughout the life of the patient. Some of the prominent symptoms of PNH include severe anemia, a condition that results from having too few healthy red blood cells, severe abdominal pain, severe headaches, back pain, excessive weakness, fatigue and recurrent infections. If not treated, PNH results in the death of approximately 35% of affected individuals within five years of diagnosis and 50% of affected individuals within ten years of diagnosis, primarily due to the formation of life-threatening blood clots inside the blood vessels, or thrombosis. Based on prevalence data published in an abstract in a peer-reviewed journal, we estimate that there are approximately 4,700 patients with PNH in the United States.

PNH is caused by the presence of mutant stem cells in the bone marrow that lack important proteins on their surface that protect against activation of the complement system. In patients with PNH, an autoimmune response targets and eliminates normal stem cells, enabling mutant cells to become dominant in the bone marrow. These mutant stem cells lead to mutant platelets and red blood cells that, unlike normal cells, are overly susceptible to activation or destruction by the complement system. Mutant platelets, activated by the membrane attack complex, increase the risk of thrombosis, which is the leading cause of mortality in patients with PNH. Mutant red blood cells are susceptible to destruction by intravascular and extravascular hemolysis. Intravascular hemolysis, which involves the destruction of blood cells within the blood vessels, is caused by the formation of the membrane attack complex on the surface of red blood cells causing them to rupture. Intravascular hemolysis causes severe anemia and contributes to the risk of thrombosis. Extravascular hemolysis, which involves the destruction of blood cells outside the blood vessels, is caused by C3-related opsonization on red blood cells leading to removal of the cells from the blood stream by the liver and the spleen. Extravascular hemolysis further contributes to severe anemia and transfusion dependency in patients with PNH.

Current Therapies and Their Limitations

The only approved drug for the treatment of PNH is eculizumab, marketed as Soliris by Alexion Pharmaceuticals, Inc. Eculizumab had reported worldwide sales of more than $2.8 billion in 2016 for its two approved indications, PNH and atypical hemolytic-uremic syndrome, or aHUS. We believe the price per year for treatment with eculizumab is approximately $500,000 in adults. Eculizumab, which is administered every two weeks intravenously, or directly into the veins, is designed to treat PNH by targeting C5 and preventing the formation of the membrane attack complex and intravascular hemolysis. Many patients with PNH on treatment with eculizumab continue to be anemic. In addition, in a third-party study, 35% to 40% of patients on eculizumab continued to be transfusion dependent for 30 months following the beginning of treatment. We believe that inability of eculizumab to control extravascular hemolysis is responsible in part for these continuing complications.

Benefits of Our Approach

We believe that, because APL-2 inhibits complement activation at the level of C3, APL-2 may provide the following benefits in controlling PNH:
  • Prevention of intravascular hemolysis and its consequences. APL-2 prevents the formation of the membrane attack complex and may thereby prevent the activation of mutant platelets and intravascular hemolysis, thus reducing the risk of thrombosis, the leading cause of mortality in PNH, as well as reducing anemia.
  • Prevention of extravascular hemolysis and its consequences. APL-2 prevents C3b opsonization, and may thereby prevent extravascular hemolysis, further reducing anemia and transfusion dependency in patients with PNH.
  • Ease and convenience of use.We have formulated APL-2 so that it may be self-administered by patients with PNH by subcutaneous injection. Because APL-2 is stable for weeks in liquid, patients will be able to self-administer APL-2 without a visit to the physician. We are initially developing APL-2 for daily administration but plan to explore less frequent dosing regimens. We believe that the ability to self-administer APL-2 on a daily basis could improve the quality of life for patients with PNH. We are developing a drug delivery system to enable patients to self-administer APL-2 and facilitate APL-2’s ease of use and convenience for patients.