International Journal of Radiation Oncology*Biology*Physics
Biology ContributionMitigation Effect of an FGF-2 Peptide on Acute Gastrointestinal Syndrome After High-Dose Ionizing Radiation
Introduction
Acute gastrointestinal syndrome (AGS) is the predominant cause of death within the first week after exposure to high-dose radiation. AGS is caused mainly by rapid and devastating damage to the gastrointestinal (GI) epithelium, leading to loss of GI function, nutrition malabsorption, electrolyte imbalance, and translocation of GI pathogens. Subsequent bone marrow (BM) failure is worsened by AGS, leading to increased and more rapid BM syndrome-related deaths 1, 2.
Currently, there is no satisfactory mitigation agent for rescuing patients from AGS-related death. Antioxidant radioprotectors such as Amifostine are preventive rather than mitigative; their benefit is minimal unless present in the bloodstream at the time of irradiation (3).
A peptide derived from the receptor binding domain of fibroblast growth factor 2 (FGF-2), FGF-P is a potent mitogen, that promotes stem cell renewal, progenitor cell differentiation, and epithelial proliferation 1, 2, 3. Its receptor is widely distributed and functions in almost all types of cells 4, 5, 6. Because radiation damages a broad range of cells, the stimulation of multiple cell types can help cells and organs support each other and enhance tissue regeneration in response to multiorgan damage 5, 6, 7, 8, 9, 10, 11, 12. The protective and mitigative potential of FGF-2 for radiation toxicity has been demonstrated by a number of studies (13), including ours 14, 15. We have previously shown that FGF-2 protects the small bowel and reduces death from AGS in mice 16, 17, 18, and that circulating levels of FGF inversely correlate with toxicity in human acute radiation injury, indicating the potential for supplemental FGF-2 to reverse some deleterious situations (15).
Notably, the use of intact FGF-2 protein has several disadvantages: it is naturally unstable because of its required molecular confirmation (susceptible to temperature, pH, etc.), is expensive to produce, and has a limited shelf-life. Recently we synthesized a proprietary FGF-2 analog, designated FGF-P, which features the FGF receptor binding domain. The advantages of FGF-P over native FGF-2 are as follows: (1) it is stable under severe conditions, for example boiling; (2) it is enzyme-resistant as dry powder and has a stable shelf-life; (3) it can be administered by victims via intramuscular injection; and (4) this small peptide can be synthesized in large quantities with high purity. In this study, we examined the mitigation effect of FGF-P on AGS.
Section snippets
FGF-P synthesis and preparation
FGF-P is a synthetic peptide based on a 15–amino acid region of FGF-2 known to interact with FGF receptors. FGF-P was synthesized by standard, solid-phase methods (Genemed Synthesis, San Antonio, TX) at a level of 97% purity, as determined by reverse-phase high-performance liquid chromatography (HPLC). The binding of peptide to FGF receptors was monitored by surface plasmon resonance using human FGFR1-IIIb (R&D Systems, Minneapolis, MN) immobilized to a Biacore CM5 sensor chip (GE Healthcare,
Sub-TBI model reduces impact of BM on AGS
Different strains of mice have different BM sensitivities and GI irradiation tolerances. In our hands, the BM LD50/30 for BALB/c, NIH Swiss, C3H/NeN, and C57BL/6 mice were approximately 6.0 ± 0.2, 7.3 ± 0.2, 7.4 ± 0.2, and 9.0 ± 0.3 Gy, respectively, after TBI. When mice were irradiated with a dose of LD50/30× 1.15, 100% died within 20 days (LD100/20). At this dose, however, at 3.5 days post-TBI, there was only minor GI pathologic damage (only a small decrease in villous length and crypt
Discussion
Radiation-induced AGS causes death much faster than BM death 1, 20. In addition, as most radiation events are expected to deliver inhomogeneous exposure, many victims will have some marrow shielding and therefore reduced risk of lethal BM syndrome. Although the impact of AGS is likely to dominate many situations, to date no satisfactorily effective mitigation agents have been demonstrated that can rescue or prolong life after near-TBI–induced AGS.
An appropriate model system is critical for
Conclusion
In conclusion, FGF-P appears to produce the same mitigative GI benefits as human recombinant basic FGF. In addition to previously shown effects of FGF-2, including reductions in apoptosis, increased proliferation, improved survival, and improved crypt survival, FGF-P also reduced hematochezia, hypoglycemia, and toxemia. Doses 400 times higher than those used for therapy produced little or no lethal toxicity within 7 days. FGF-P therefore has many advantages over native FGFs. Further work is
Acknowledgment
The authors thank Amy K. Huser for thoughtful research, writing, and editing assistance.
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This research was supported by 1RC1AI078519-01 and the Centers for Medical Countermeasures against Radiation program, U19-AI067733, National Institute of Allergy and Infectious Diseases (NIAID).
Conflict of interest: Drs. Lurong Zhang and Paul Okunieff developed FGF-P, and a U.S. Patent application has been filed by the University of Rochester.