Novel Pharmaceutical Strategy for Selective Abrogation of Thrombospondin 1‐Induced Vascular Dysfunctions via Decoy recombinant CD47
Authors: Yao Mingyi , Sturdivant Jalicia , Elbayoumi Tamer 
Published: November 2023

Substantial elevation in thrombospondin 1 (TSP1)‐plasma levels have been consistently implicated in in pathogenesis of a variety of fatal cardiovascular conditions, such as ischemia‐reperfusion injury, pulmonary hypertension and coronary artery disease.

While domain mapping on monomeric TSP1 reveals a broad interaction network, up to 83 ligands and receptors, TSP1‐initiated signal cascades through its cognate receptor CD47 (a ubiquitous plasma membrane protein) have been directly correlated with cardiovascular dysfunction. There is only one systemic monoclonal antibody ‐ currently in clinical phase I ‐ to interfere with TSP1 and its network, and it is indicated for cancer therapy.

Our work provides “proof‐of‐concept” of a novel anti‐TSP1 pharmacological strategy, relying on extraneous administration of recombinant human CD47‐derived peptide (rh‐CD47p), which serves two distinct, yet equally important goals: First, exogenous rh‐CD47p functions as a circulating decoy receptor protein to specifically bind TSP1 molecules, which are abnormally elevated in plasma. Consequently, rh‐CD47p‐bound TSP1 cannot bind its endogenous receptor CD47 expressed on vascular endothelium, leading to mitigation of all intracellular down‐stream molecules, and improvement of TSP1‐inhibited vasodilation. The second aim can be better achieved via adopting a pharmaceutical liposomal system. Multiple rh‐CD47p coupled onto each nano‐liposome can bind several circulating TSP1 molecles, leading to formation of many complexes between liposomal‐rh‐CD47p and TSP1, which can then be rapidly eliminated via the reticulo‐endothelial system. In principle, the recombinant decoy protein rh‐CD47p is “nano‐modified” into a therapeutic platform to eliminate pathological excess of TSP1 from circulation.

Our pilot studies were carried out in an ex vivo model using isolated mouse thoracic aortic segments. Initially, a pre‐treatment protocol for rh‐CD47p (added 15 min prior to TSP1 incubation) was shown to significantly ameliorate the TSP1‐impairement of endothelium‐dependent vasodilation (p<0.0001, rh‐CD47p+TSP1 vs. TSP1; p>0.05 rh‐CD47p+TSP1 vs. control, n=6). To mimic pre‐existing high circulating levels of TSP1 in patients, a reverse order of incubation was investigated. In this post‐treatment set‐up, where TSP1 incubation was started 15 min prior to rh‐CD47p addition, a marked reversal of TSP1‐impaired vasodilation was observed, back to the same level as controls (p<0.0001 rh‐CD47p+TSP1 vs. TSP1; p>0.05 rh‐CD47p+TSP1 vs. control, n=4). Simultaneously, titration of the binding molar ratios of rh‐CD47p:TSP1 was examined, in order to find the optimal dose of rh‐CD47p for maximum recovery from TSP1‐induced vascular impairment. Stoichiometric binding of rh‐CD47p and TSP1, at different incremental ratios, was further confirmed via western blotting, and immune‐precipitation, both in cell‐free setting.

Our current results indicate the feasibility of exogenous administration of rh‐CD47p as a unique pharmacological strategy to improve TSP1‐impaired endothelium‐dependent vasodilation, thus providing a solid foundation for our novel decoy CD47‐coated nano‐formulation for TSP1‐associated cardiovascular complications.

Support or Funding Information

Midwestern University intramural funding