Beneficial Effects of Soluble Guanylyl Cyclase Stimulation and Activation in Sickle Cell Disease are Amplified by Hydroxyurea: In Vitro and In Vivo Studies.

The complex pathophysiology of sickle cell anemia (SCA) involves intravascular hemolytic processes and recurrent vaso-occlusion, driven by chronic vascular inflammation, which result in the disease's severe clinical complications, including recurrent painful vaso-occlusive episodes. Hydroxyurea, the only drug frequently used for SCA therapy, is a cytostatic agent, although it appears to exert nitric oxide/ soluble guanylyl cyclase (sGC) modulating activity. As new drugs that can complement, or replace, the use of hydroxyurea are sought to further reduce vaso-occlusive episode frequency in SCA, we investigated the effects of the sGC agonists, BAY 60-2770 (sGC activator) and BAY 41-2272 (sGC stimulator), in the presence or absence of hydroxyurea, on SCA vaso-occlusive mechanisms and cell recruitment, ex vivo and in vivo. These agents significantly reduced stimulated human SCA neutrophil adhesive properties, ex vivo, in association with the inhibition of surface β2-integrin activation. A single administration of BAY 60-2770, or BAY 41-2272, decreased TNF-cytokine induced leukocyte recruitment in a mouse model of SCA vaso-occlusion. Importantly, the in vivo actions of both agonists were significantly potentiated by the co-administration of hydroxyurea. Erythroid cell fetal hemoglobin (HbF) elevation is also a major goal for SCA therapy. BAY 41-2272, but not BAY 60-2770, at the concentrations employed, significantly induced gamma-globin gene transcription, in association with HbF production in cultured erythroleukemic cells. In conclusion, sGC agonist drugs could represent a promising approach as therapy for SCA, either for use as stand-alone treatments, or in combination with hydroxyurea. SIGNIFICANCE STATEMENT: This preclinical study demonstrates that stimulators and activators of sGC are potent inhibitors of the adhesion and recruitment of leukocytes from humans and in mice with sickle cell anemia (SCA), and may represent a promising approach for diminishing vaso-occlusive episode frequency in SCA. Hydroxyurea, a drug already frequently used for treating SCA was found to potentiate the beneficial effects of sGC agonists in in vivo studies, implying that these classes of compounds could be used alone or in combination therapy.