Three months after the FDA approved the first inhibitor of sickle hemoglobin polymerisation, Global Blood Therapeutics’ Oxbryta (voxelotor) and seven other hemoglobin-targeting products are in clinical development for the treatment of sickle cell disease.
Oxbryta, which was previously being developed for hypoxia and idiopathic pulmonary fibrosis, was given accelerated approval, breakthrough therapy, orphan drug, fast track, and priority review designations by the FDA. The drug works by altering the shape of deoxygenated hemoglobin. In sickle cell disease, which is inherited in an autosomal recessive pattern, a single-nucleotide polymorphism in the β-globin gene causes glutamic acid to be replaced by valine, which is a hydrophobic amino acid. This has no effect unless in hypoxic conditions where the protein forms fibrous precipitates that can obstruct blood vessels, causing pain and ischemia. The conformational change in deoxygenated hemoglobin induced by Oxbryta increases the oxygen-binding affinity of the protein, preventing the polymerisation of sickle hemoglobin. This in turn stops the sickling of red blood cells, allowing them to pass through blood vessels with ease.
Although anti-anemic therapies such as taking iron supplements are commonly used to manage sickle cell disease, patients with frequent vaso-occlusive crises can require blood transfusions to avoid cardiovascular complications.
Successful results in clinical studies, including the use of animal models, have demonstrated the potential for gene therapy to revolutionise the treatment of sickle cell. As of February 2020, there are 18 gene therapy drug candidates in active development for this indication. There are also three first-in-class products in the pipeline for sickle cell. First-in-class products are defined as products with a molecular target or mechanism of action not found in any approved products globally. The first-in-class products in the pipeline for sickle cell are Novo Nordisk’s decitabine, CSL’s (an Australian biotech company) CSL-200, and ReNeuroGen’s KYC, an inhibitor of myeloperoxidase, an enzyme that derives reactive oxygen species that cause damage to vascular tissues.
As one of the most common inherited blood disorders in countries such as the US and the UK, innovative products entering the market are likely to be rewarded with high sales. Oxbryta is expected to generate sales of $1.8B by 2025, eclipsing the total sales of late-stage pipeline products entering the market between 2020 and 2025, as shown in Figure 1.
Products in the late-stage pipeline for sickle cell disease that will launch in the US market are expected to generate sales of $1.3B. Drugs in this category include Sangamo Therapeutics’ BIVV-003, CRISPR Therapeutics’ CTX-001, and Bluebird bio’s LentiGlobin (betibeglogene autotemcel), which are all stem cell therapies delivered to patients intravenously. Oxbryta will benefit from a competitive advantage over products in the late-stage pipeline for sickle cell because the drug has already launched in the US market while the next-to-market stem cell therapy for sickle cell, LentiGlobin, is expected to launch in the US in 2022.
With four products in Phase III and one drug candidate at the pre-registration stage, the sickle cell market is set to benefit from significant growth in the years ahead, though opportunities remain in the market for treating people with sickle cell disease caused by homozygosity for other types of abnormal hemoglobin, such as hemoglobin C and hemoglobin D.