Genetic or pharmacologic inhibition of ceramide-mediated cell death within the vascular endothelium of the gastrointestinal tract (GI) protects mice from death from the Radiation GI Syndrome (RGS). Prophylactic administration of anti-ceramide antibody attenuates endothelial apoptosis, resulting in significant protection of intestinal stem cells and animal survival following lethal radiation exposure. Administration 24 h post radiation exposure similarly protects crypt stem cells and dramatically improves survival, indicating that anti-ceramide antibody represents the first effective antibody of small molecule mitigator of lethal RGS. To improve upon the efficacy of anti-ceramide antibody, we propose to select a recombinant single-chain antibody fusion protein containing the known ceramide-binding regions of anti-ceramide antibody as a novel Medical Radiation Countermeasure. Single-chain antibody fusion proteins are smaller derivatives of full length antibodies, and thus offer the advantage of rapid entering into the bloodstream and increased penetration into tissue compared to full-length antibodies. Additionally, single-chain antibody fusion proteins can be modified by general cloning techniques to display preferred target binding, and from a product development standpoint these fusion proteins can be produced easily and at minimal cost. While in some cases single-chain antibody fusion proteins may not retain full activity of the parent antibody, our preliminary data indicates that similar antibody fragments derived by enzymatic digestion of humanized anti-ceramide antibody results in significant protection and mitigation of radiation-induced crypt stem cell lethality, even 24 h after high single-dose exposure. These data indicate that a single-chain antibody fusion protein can be sufficient to induce therapeutic neutralization of ceramide. As such, a neutralizing anti-ceramide single-chain antibody fusion protein represents a promising candidate to fulfill the Project BioShield mandate for development of countermeasures to mitigate acute radiation syndromes within the first 24 h after a nuclear disaster.
Ceramide Therapeutics is a biotechnology company developing antibody inhibitors of the ceramide signaling pathway as Medical Radiation Countermeasures for the Radiation Gastrointestinal (GI) Syndrome (RGS). Humanized anti-ceramide antibody and antibody fragments mitigate radiation toxicity in mice when administered 24 hrs. post lethal radiation exposure, identifying these reagents as the first effective mitigator of lethal RGS. Here, we propose to select a recombinant single-chain antibody fusion protein containing the antigen-binding domains of humanized anti-ceramide antibody for development as a novel radiation countermeasure.
