Study on the Efficacy of a JAK Inhibitor Pharmacological Agent As Inducer of Fetal Hemoglobin Production in Cultured Erythroid Precursors from Sickle Cell and Beta-Thalassemia Patients

Phenotypic improvement of hemoglobinopathies such as sickle cell disease and beta-thalassemia (beta-thal) has been shown in patients with high levels of fetal hemoglobin (HbF). In sickle cell disease (SCD) the beneficial effects of HbF are due to the inhibition of HbS polymerization and to the dilution of HbS determining the reduction of sickling and vascular occlusion. Moreover, in beta-thal, high levels of gamma-chains combined with the redundant alpha-chains, lead to a reduction of dyserythropoiesis and of the requirement for blood transfusions. The only drug approved for the treatment of adult patients with SCD and that has been entered in clinical practice of patients affected by beta-thal is hydroxyurea (HU); however there is a great variability in the responses of patients to HU, in fact some patients are good responder, while others exhibit little or no change in HbF levels after HU treatment; moreover a decrease in the efficacy during long term treatment was observed. Other pharmacological compounds, including  5-azacytidine and thalidomide have been shown to increase HbF production. Due to concerns about the safety of this agents, their use was limited to severe cases for whom conventional therapy was unfeasible. For this reason the search of new inducers of HbF production is important. Ruxolitinib is a JAK inhibitor and decreases the phosphorilation of STAT (Signal transducers and activators of transcription) family proteins, in particular STAT5 and STAT3. Phosphorylation of STAT5 is essential for basal erythropoiesis and for its acceleration during stress erythropoiesis. STAT3 plays an essential role in regulating gene expression of several genes involved in cell growth and apoptosis, in particular it was demonstrated to inhibit gamma-globin gene expression. The decrease of STAT3 phoshorilation could decrease the inhibition of gamma-globin gene expression; for this reason we considered ruxolitinib  a candidate as inducer of HbF production.

 

In our laboratory an ex vivo system was developed predictive of the in vivo response to hydroxyurea treatment by using liquid erythroid cultures, an in vitro culture system that recapitulates the process of human erythropoiesis.

To evaluate the efficacy of ruxolitinib in increasing gamma-globin gene expression we carried out a study in vitro using liquid erythroid cultures. In this study we developed and exposed to ruxolitinib liquid erythroid precursors from 4 SCD and 17 beta-thal intermedia (beta-TI) patients. The use of quantitative Real-Time-polymerase chain reaction allowed us to determine the increase in gamma-globin mRNA expression in human erythroid cells treated with ruxolitinib compared to untreated cells. The results are summarized in Table 1 and showed that ruxolitinib at 200nM is able to determine a significant increase of gamma-globin gene expression (3.4±0.1)compared to HU (2.0± 0.2).

In conclusion our study suggests that ruxolitinib could be considered an inducer of HbF and could be used in vivo for the treatment of hemoglobinopathies, particularly in patients who do not respond to HU therapy or who show a decreased response after long-term treatment.

Table 1. Fold increase of Gamma-globin gene expression in presence of Ruxolitinib in erythroid cultured cells.

Patient	Sex	Genotype	gamma-globin mRNA fold increase in the presence of ruxolitinib
#1	M	b039/aaa	+1
#2	F	b039/aaa	+1.65
#3	F	b039/b039	+1.9
#4	F	b039/IVS1,110	+1.5
#5	M	IVS1,1/aaa	+2.5
#6	M	IVS1,110/IVS1,1	+9.2
#7	M	b039/bs	+6
#8	F	bs/b039	+1.6
#9	F	b039/IVS1,6	+1.7
#10	M	IVS1,6/frcd6	+3
#11	M	IVS1,6/bs	+2.5
#12	M	IVS1,6/frcd6	+8
#13	F	IVS1,6/b039	+9
#14	M	IVS1,1/b039	+2.2
#15	M	db/IVS1,110	+8
#16	F	db/IVS1,110	+1.8
#17	F	IVS2,1/aaa	+3.9
#18	M	b039/-101	+1.4
#19	M	IVS1,6/b039	+1
#20	M	bs/IVS1,110	+1.4
#21	M	IVS1,6/IVS1,6	+1.9

Disclosures: No relevant conflicts of interest to declare.

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