Friday, November 17, 2006 Klemmer’s Banquet Center 10401 West Oklahoma Avenue Milwaukee, WI (414) 541-0401

DIRECTIONS

Bleomycin (Blm) is an unusually large and complex antibiotic with significant clinical anti-cancer properties. The molecule has several functional domains, including a broadly reactive metal binding region that is tethered by a peptide to a DNA intercalation/binding region and a disaccharide unit with ill-defined function. Its cellular activity depends on site-selective, DNA double-strand cleavage. An inquiry into Blm's cellular properties demonstrates the requirement for Fe, its limited accumulation by the nucleus, and probable activation of Fe(III)Blm by cytochrome P450 reductase. Our chemical model studies have been based on the pioneering work of Peisach that showed Fe(III)Blm was reductively activated to HOO-Fe(III)Blm. We have used Co analogs as robust models for understanding the structure-reactivity relations among FeBlm species.

In particular, NMR analysis of HOO-Co(III)Blm and its DNA adduct reveal that drug interacts with DNA as a folded structure, establishing a precise steric relationship between the hydroperoxide ligand and its site of reaction on DNA. Moreover, the mysterious disaccharide provides key second coordination sphere stabilization of Fe binding and formation of HOO-Fe(III)Blm. Structural studies also suggest that the activation/cleavage process involves a complex interplay between FeBlm bound to non-specific as well as specific base sequences. Properties are also revealed that may be crucial for DNA double strand cleavage, including the capacity of the drug to bind selectively to single strand cleavage sites. Concluding remarks will address FeBlm as a model for oxygen activation, how its anti-tumor activity might be enhanced, what still needs to be learned about its chemistry, and the general enjoyment gained from seeing how nature embodied in Blm "does it her way" not our way.

David H. Petering is University Distinguished Professor of Chemistry and Biochemistry at the University of Wisconsin-Milwaukee, where he began his career in 1971. He graduated from Wabash College with a B.A. and from the Department of Biological Chemistry at the University of Michigan with a Ph.D., working with Graham Palmer on iron-sulfur protein chemistry.

Petering's postdoctoral research was carried out with Fred Basolo and Brian Hoffman at Northwestern University. Broadly working in the field of metal ions in biological systems, Petering created one of the first highly successful bioinorganic models, cobalt-substituted hemoglobin, as a postdoctoral fellow. He was an early proponent of metal-based drugs and has extensively studied the inorganic and cellular properties of metal-thiosemicarbazones complexes, cis-dichlorodiammine Pt(II), and bleomycin to gain cohesive insight into their mechanisms of action. A complementary research area has focused on understanding mechanisms of cadmium toxicity in the kidney and cellular protection strategies against cadmium. In the process, Petering has played a major role in understanding structure-reactivity-function relationships of the key cadmium-binding protein, metallothionein, and recently, of zinc finger proteins that are potential targets for reaction with cadmium and other xenobiotics. Themes running through both of these general areas of research are the interaction of chemicals with cellular thiols and redox reactions resulting in dioxygen activation. Lastly, Petering has maintained a long-standing interest in tumor cell zinc metabolism that is currently focused on understanding exactly what is being imaged microscopically by cellular Zn fluorescent probes and the use of inductively coupled plasma mass spectrometry to study Zn-trafficking with stable isotope markers.

Since 1987 Dr. Petering has served as Director of the National Institute of Environmental Health Sciences Marine and Freshwater Biomedical Sciences Center at UW-Milwaukee. The Center's mission is to develop and utilize aquatic animal models in environmental health research; members have been instrumental in adapting the zebrafish model for vertebrate development for developmental toxicology studies. This past year the Center and scientists in the Children's Research Institute of Children's Hospital of Wisconsin have merged to form the Children's Environmental Health Institute, with Petering as Co-director. Finally, in 2002 Petering became director of the new UWM Institute of Environmental Health and in that capacity has helped to develop young investigators in environmental health at UWM and to link environmental health science to Hmong, Latino, and Native American communities.