Radioprotection in Normal Tissue and Delayed Tumor Growth by Blockade of CD47 Signaling

Radiation-induced damage of normal tissues restricts the therapeutic doses of ionizing radiation that can be delivered to tumors and thereby limits the effectiveness of radiotherapy. Thrombospondin-1 signaling through its cell surface receptor CD47 limits recovery from several types of stress, and mice lacking either gene are profoundly resistant to radiation injury. We describe strategies to protect normal tissues from radiation damage with antibodies to CD47 or thrombospondin-1, a CD47-binding peptide, or antisense suppression of CD47. A morpholino oligonucleotide targeting CD47 confers radioresistance to human endothelial cells in vitro and protects soft tissue, bone marrow, and tumor-associated leukocytes in irradiated mice. In contrast, CD47 suppression in mice bearing melanoma or squamous lung tumors before irradiation results in 89% and 71% smaller tumors, respectively. Thus, inhibition of CD47 signaling maintains the viability of normal tissues after irradiation while increasing the radiosensitivity of tumors.