Avapritinib is in clinical development for the treatment of advanced systemic mastocytosis (SM) in adults. SM is a condition where mast cells grow uncontrollably and accumulate in body organs/tissues such as the skin, internal organs, lymph nodes and bones. Mast cells are immune cells that release inflammatory mediators that are important in the body’s allergic responses. When mast cells are present in large numbers there is a high release of these mediators leading to symptoms such as itching, fever, abdominal pain, nausea and vomiting. In advanced SM, mast cells collect in such high quantities that they lead to organ damage and dysfunction, bone fractures and anaemia.
Avapritinib, formulated for oral administration, works by selectively blocking the active form of the KIT protein kinase. More than 90% of SM cases are due to a KIT D816V mutation that results in KIT being constantly active. In its active state, KIT triggers a series of downstream signals resulting in the accumulation of mast cells and uncontrolled release of inflammatory mediators. By blocking KIT, avapritinib will reduce the accumulation and uncontrolled activation of mast cells. If licenced, avapritinib will offer an additional treatment option for patients with advanced SM.
Mepolizumab is a medicinal product currently in development as an add-on for the treatment of hypereosinophilic syndrome (HES). HES is a rare group of inflammatory disorders characterised by an overproduction of eosinophils (a type of disease-fighting white blood cell). When eosinophils infiltrate certain tissues, they can cause inflammation and organ damage which, over time, can impact patients’ day-to-day ability to function. Although any organ system can be involved in HES, the heart, central nervous system, skin, and respiratory tract are the most commonly affected.