Use of Nano-Formulated Hydroxyurea Enhances Drug Delivery to Pulmonary Artery Endothelial Cells

The vasculopathy of sickle cell disease (SCD), characterized by a chronic hemolytic anemia, endothelial dysfunction and recurrent vasoocclusive events, underlies most of the clinical complications. Recent work has suggested that hydroxyurea (HU) enhances endothelial nitric oxide (NO) production and reduces adhesion molecule expression which may contribute to its associated observed reduction in vasoocclusive events and improved survival in SCD. However, clinically HU is under-utilized, at least in part related to medication related toxicity, stressing a need for enhanced drug delivery. The use of nano-emulsions, a class of stable emulsions formed by a monolayer of phospholipids and/or biodegradable material such as chitosan, is a mechanism by which to enhance targeted cellular delivery of therapeutics. We hypothesized that a nano-formulation of HU would enhance drug delivery to the endothelium and may be a direct way of targeting endothelial dysfunction in SCD. Nano-formulated HU (nano-HU) was developed using a phospholipid approach and this compound was found to be biologically stable for > 6 months. Human pulmonary arterial endothelial cells (HPAECs) were co-incubated with 25µM, 125µM and 250µM HU, nano-HU, or the empty nano-emulsification preparation for 48 hours. HPAEC were isolated, and stained with propidium iodide (PI) for cell cycle analysis by FACS. HPAEC treated with 25µM nano-HU demonstrated the highest level of cell viability (55%) and similar levels of S phase inhibition as HPAEC treated with 125µM HU (where 10-20% cell viability was observed). RNA isolation of treated HPAECs was performed and qPCR for VCAM1 and SLX4, a regulator of DNA damage which promotes S phase inhibition was performed. 25µM nano-HU significantly decreased VCAM1 and increased SLX4 expression compared with 25µM HU suggesting increased efficacy at lower levels of toxicity. The impact of nano-HU on endothelial gene expression is currently being evaluated by RNA-seq. Nano-formulation of HU produces a molecule which is highly stable, and able to achieve higher intracellular concentrations with lower rates of toxicity in HPAECs .which provides the opportunity to gain greater understanding of the impact of this medication on the vascular endothelium and the potential for a more targeted and better tolerated delivery of this therapeutic to patients with sickle cell disease.