Cloning, expression and in vitro evaluation of recombinant canine Tum5, an angiostatic domain of mammalian type IV collagen

The process of new blood vessel formation within and around neoplastic tissue, termed angiogenesis, is a significant factor in the development, progression and metastasis of malignant tumours in all species. A major cause of death in cancer patients is the development of treatment‐resistant metastatic disease, which may be avoided by therapies that target the genetically stable population of vascular endothelial cells within tumours. Tumstatin is a small protein formed by the cleavage of the alpha‐3 subunit of the non‐collagenous domain of mammalian type IV collagen. Recombinant human Tumstatin has been shown to have potent angiostatic properties in vitro and in vivo. Tumstatin is a potent initiator of apoptosis and inhibits the proliferation and migration of vascular endothelial cells in cell culture. Recently, a fragment of Tumstatin, termed Tum5, has been shown to have biologic activity similar to the parent compound. The systemic administration of angiostatic proteins like Tum5 may result in the remission of established tumours, while preventing or delaying the onset of clinically detectable metastasis. Recombinant canine Tum5 (cTum5) was cloned and its protein expression induced in a prokaryotic vector. The resulting cTum5 protein caused dose‐dependent inhibition of vascular endothelial cells in vitro, which appears to be mediated through apoptosis.