Abstract 15720: Transmembrane Stem Cell Factor Delivered in Nanocarriers Promotes Angiogenesis in Ischemia Without Mast Cell Activation

Introduction: The current standard cares for peripheral artery disease (PAD) include surgical revascularizations with bypass grafting or percutaneous interventions. However, these interventions cannot be performed in a significant portion of patients, and many do not respond to these surgical procedures. Protein therapy to stimulate the body to create new vasculature is another alternative, which is minimally invasive to patients. Stem cell factor (SCF) is a candidate protein for treating PAD, but clinical use of SCF has been limited due to toxicity related to mast cell activation. SCF also exists in a transmembrane form (tmSCF), possessing differential activities from soluble SCF and has not been explored as a therapeutic agent. Results: To develop tmSCF as a therapeutic we created tmSCF embedded in liposome or lipid nanodisc (Fig. A) . Hindlimb ischemia model on WT and ob/ob mice showed that tmSCF proteliposome (tmSCFPL) and nanodisc (tmSCFND) improved blood flow recovery significantly more than control (Fig. B, C) . Mouse model of anaphylaxis revealed that tmSCF-based therapies did not activate mast cells (Fig. D, E) . Colocalization assay of c-Kit and clathrin/caveolin revealed that mast cells preferentially use clathrin-mediated pathways to internalize SCF and caveolin-mediated pathways for tmSCF-based therapies (Fig. F, G) . Surface c-Kit internalization study on mast cells showed faster uptake of SCF in comparison to tmSCF-based therapies (Fig. H) . Previous study indicates that clathrin-mediated internalization causes increased activation of mast cells. Our studies together with the previous finding suggest that mast cell activation does not occur for tmSCF-based therapies because of the slower uptake, greater utilization of the caveolin internalization pathway and weaker activation of mast cells. Conclusions: TmSCF-based therapies can provide therapeutic benefits without off-target effects on mast cells by tuning activation with nanocarriers.