Phenotypic screening of the ReFrame Drug Repurposing Library to discover new drugs for treating sickle cell disease

Abstract

Stem-cell transplantation and genetic therapies offer potential cures for patients with sickle cell disease (SCD) but these options require advanced medical facilities and are expensive. Consequently, these treatments will not be available to the vast majority of patients suffering from this disease for many years. What is urgently needed now is an inexpensive oral drug in addition to hydroxyurea, the only successful drug approved by the FDA that inhibits sickle-hemoglobin polymerization. Here we report results of the first phase of our phenotypic screen of the 12,657 compounds of the Scripps ReFrame drug repurposing library using a recently developed high-throughput assay to measure sickling times following deoxygenation to 0% oxygen of red cells from sickle trait individuals. The ReFrame library is a very important collection because the compounds are either FDA-approved drugs or have been tested in clinical trials. From dose-response measurements, 106 of the 12,657 compounds exhibit statistically significant anti-sickling at concentrations ranging from 31 nM to 10 M. Compounds that inhibit sickling of trait cells are also effective with SCD cells. As many as 21 of the 106 anti-sickling compounds emerge as potential drugs. This estimate is based on a comparison of inhibitory concentrations with free concentrations of oral drugs in human serum. Moreover, the expected therapeutic effect for each level of inhibition can be predicted from measurements of sickling times for cells from individuals with sickle-syndromes of varying severity. Our results should motivate others to develop one or more of these 106 compounds into drugs for treating SCD. Significance StatementThe vast majority of patients suffering from sickle cell disease live in under-resourced countries. Consequently, advanced medical facilities required for curative therapies, such as stem cell transplantation and gene therapy, will be unavailable to them for a long time. Hydroxyurea, approved by the FDA in 1998, is the only effective drug that inhibits polymerization of the mutant hemoglobin S that stiffens and distorts ("sickles") red cells, the root cause of the pathology. What is urgently needed now for these patients are additional, inexpensive oral anti-sickling drugs. Our high throughput phenotypic screen of the ReFrame drug repurposing library reported here discovered 106 compounds that are anti-sickling. On a statistical concentration basis, as many as 21 are predicted to be potential drugs.