Chris J. Rosen

Biomimetic Actinide Chelators: An Update on the Preclinical Development of the Orally Active Hydroxypyridonate Decorporation Agents 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO)

The threat of a dirty bomb or other major radiological contamination presents a danger of large-scale radiation exposure of the population. Because major components of such contamination are likely to be actinides, actinide decorporation treatments that will reduce radiation exposure must be a priority. Current therapies for the treatment of radionuclide contamination are limited and extensive efforts must be dedicated to the development of therapeutic, orally bioavailable, actinide chelators for emergency medical use. Using a biomimetic approach based on the similar biochemical properties of plutonium(IV) and iron(III), siderophore-inspired multidentate hydroxypyridonate ligands have been designed and are unrivaled in terms of actinide-affinity, selectivity, and efficiency. A perspective on the preclinical development of two hydroxypyridonate actinide decorporation agents, 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO), is presented. The chemical syntheses of both candidate compounds have been optimized for scale-up. Baseline preparation and analytical methods suitable for manufacturing large amounts have been established. Both ligands show much higher actinide-removal efficacy than the currently approved agent, diethylenetriaminepentaacetic acid (DTPA), with different selectivity for the tested isotopes of plutonium, americium, uranium and neptunium. No toxicity is observed in cells derived from three different human tissue sources treated in vitro up to ligand concentrations of 1 mM, and both ligands were well tolerated in rats when orally administered daily at high doses (>100 micromol kg d) over 28 d under good laboratory practice guidelines. Both compounds are on an accelerated development pathway towards clinical use.

Effects of Iron Ions, Protons and X Rays on Human Lens Cell Differentiation

Abstract Chang, P. Y., Bjornstad, K. A., Rosen, C. J., McNamara, M. P., Mancini, R., Goldstein, L. E., Chylack, L. T. and Blakely, E. A. Effects of Iron Ions, Protons and X Rays on Human Lens Cell Differentiation. Radiat. Res. 164, 531–539 (2005). We have investigated molecular changes in cultured differentiating human lens epithelial cells exposed to high-energy accelerated iron-ion beams as well as to protons and X rays. In this paper, we present results on the effects of radiation on gene families that include or are related to DNA damage, cell cycle regulators, cell adhesion molecules, and cell cytoskeletal function. A limited microarray survey with a panel of cell cycle-regulated genes illustrates that irradiation with protons altered the gene expression pattern of human lens epithelial cells. A focus of our work is CDKN1A (p21CIP1/WAF1), a protein that we demonstrate here has a role in several pathways functionally related to LET-responsive radiation damage. We quantitatively assessed RNA and protein expression in a time course before and after single 4-Gy radiation doses and demonstrated that transcription and translation of CDKN1A are both temporally regulated after exposure. Furthermore, we show qualitative differences in the distribution of CDKN1A immunofluorescence signals after exposure to X rays, protons or iron ions, suggesting that LET effects likely play a role in the misregulation of gene function in these cells. A model of molecular and cellular events is proposed to account for precataractous changes in the human lens after exposure to low- or high-LET radiations.

Harderian Gland Tumorigenesis: Low-Dose and LET Response

Increased cancer risk remains a primary concern for travel into deep space and may preclude manned missions to Mars due to large uncertainties that currently exist in estimating cancer risk from the spectrum of radiations found in space with the very limited available human epidemiological radiation-induced cancer data. Existing data on human risk of cancer from X-ray and gamma-ray exposure must be scaled to the many types and fluences of radiations found in space using radiation quality factors and dose-rate modification factors, and assuming linearity of response since the shapes of the dose responses at low doses below 100 mSv are unknown. The goal of this work was to reduce uncertainties in the relative biological effect (RBE) and linear energy transfer (LET) relationship for space-relevant doses of charged-particle radiation-induced carcinogenesis. The historical data from the studies of Fry et al. and Alpen et al. for Harderian gland (HG) tumors in the female CB6F1 strain of mouse represent the most complete set of experimental observations, including dose dependence, available on a specific radiation-induced tumor in an experimental animal using heavy ion beams that are found in the cosmic radiation spectrum. However, these data lack complete information on low-dose responses below 0.1 Gy, and for chronic low-dose-rate exposures, and there are gaps in the LET region between 25 and 190 keV/μm. In this study, we used the historical HG tumorigenesis data as reference, and obtained HG tumor data for 260 MeV/u silicon (LET ∼70 keV/μm) and 1,000 MeV/u titanium (LET ∼100 keV/μm) to fill existing gaps of data in this LET range to improve our understanding of the dose-response curve at low doses, to test for deviations from linearity and to provide RBE estimates. Animals were also exposed to five daily fractions of 0.026 or 0.052 Gy of 1,000 MeV/u titanium ions to simulate chronic exposure, and HG tumorigenesis from this fractionated study were compared to the results from single 0.13 or 0.26 Gy acute titanium exposures. Theoretical modeling of the data show that a nontargeted effect model provides a better fit than the targeted effect model, providing important information at space-relevant doses of heavy ions.

238Pu elimination profiles after delayed treatment with 3,4,3LI(1,2HOPO) in female and male Swiss-Webster mice

Abstract Purpose: To characterize the dose-dependent and sex-related efficacy of the hydroxypyridinonate decorporation agent 3,4,3-LI(1,2-HOPO) at enhancing plutonium elimination when post-exposure treatment is delayed. Materials and methods: Six parenteral dose levels of 3,4,3-LI(1,2-HOPO) from 1–300 μmol/kg were evaluated for decorporating plutonium in female and male Swiss-Webster mice administered a soluble citrate complex of 238Pu and treated 24 hours later. Necropsies were scheduled at four time-points (2, 4, 8, and 15 days post-contamination) for the female groups and at three time-points (2, 4, and 8 days post-contamination) for the male groups. Results: Elimination enhancement was dose-dependent in the 1–100 μmol/kg dose range at all necropsy time-points, with some significant reductions in full body and tissue content for both female and male animals. The highest dose level resulted in slight toxicity, with a short recovery period, which delayed excretion of the radionuclide. Conclusions: While differences were noted between the female and male cohorts in efficacy range and recovery times, all groups displayed sustained dose-dependent 238Pu elimination enhancement after delayed parenteral treatment with 3,4,3-LI(1,2-HOPO), the actinide decorporation agent under development.

Involvement of metals in Aβ aggregation in Alzheimer's disease brain and lens using X-ray Fluorescent Microscopy (XRFM) and Quasi-Elastic Light Scattering (QLS)

enriched tau proteins from the control and transgenic mice were immunoprecipitated with a monoclonal antibody against tau. The immuno-precipitants were then digested with trypsin. The phosphorylated peptides in the control and transgenic mouse samples were enriched once again by the CHT-based method. The phosphopeptides were then analyzed by MALDI-TOF mass spectrometry and the peptide mass profiles of tau protein were compared between the age-matched wild type and transgenic animals to examine the changes in tau protein phosphorylation. Conclusions: Our study demonstrated that CHT-based fractionation is an easy-to-use, fast and convenient method for phosphoprotein/peptide enrichment with high binding capacity. It could potentially be used to enrich highly-phophorylated proteins and facilitate the biochemical study of hyperphosphorylated tau in Alzheimer’s disease.