Larry K. Keefer, Ph.D.
Larry K. Keefer, Ph.D.
Senior Investigator
Head, Drug Design Section

Center for Cancer Research
National Cancer Institute

Building 538, Room 205F
Frederick, MD 21702-1201
301-846-1467

Dr. Keefer is internationally recognized as an authority on the chemistry and pharmacology of nitric oxide (NO), a critical bioeffector molecule with essential roles in the cardiovascular system, sexual function, and immunity, among others. The Keefer lab is noted for having introduced a series of NO-releasing agents that are now used worldwide as tools for studying NO’s biological effects. Several of these compounds were designed for targeted delivery of NO to specific sites in the body for therapeutic benefit, and are under current study for their possible clinical applications.

Link to additional information about Dr. Keefer's  research.

Areas of Expertise
1) nitrosamine chemistry 2) nitric oxide biology 3) chemistry and pharmacology of the diazeniumdiolates 4) organic chemistry

Chemistry and Biology of Nitric Oxide

Nitric oxide (NO) is a potent and multifaceted bioregulatory agent. This project is aimed at finding ways to target NO to specific sites in the body for important research and/or therapeutic applications. Our strategy in pursuing this goal is to begin by characterizing the fundamental chemistry of the NO-releasing diazeniumdiolates (compounds containing the [N(O)NO] functional group). We then attempt to exploit our accumulating knowledge in this area as a platform for solving problems in biomedical research and clinical medicine. We are currently pursuing basic research investigations into the structure, spectra, dissociation to NO and/or HNO, alkylation, arylation, photodegradation, and general reactivity of the diazeniumdiolate functional group with an eye toward designing prodrugs that are stable at physiological pH but that can be activated to generate NO or HNO by enzymatic action. An example is AcOM-PYRRO/NO, an esterase-sensitive diazeniumdiolate that penetrates the cell and generates NO within the cytoplasm on esterase-induced hydrolysis; AcOM-PYRRO/NO has proved to be two orders of magnitude more potent as an inducer of apoptosis in HL-60 leukemia cells in culture than the spontaneously dissociating parent ion, PYRRO/NO.

Link to Diazeniumdiolate Chemistry Database

Other achievements include the design of agents that can be activated for NO release by enzymes of the glutathione S-transferase, glycosidase, and cytochrome P450 families. Other recently introduced diazeniumdiolates have been designed to target nitric oxide delivery to macrophages for antimicrobial activity. Proof-of-concept studies that underscore the substantial clinical promise of these compounds include: inhibition of restenosis after angioplasty; preparation of thromboresistant medical devices; and inhibition of tumor growth in in vivo models. The results of the animal experiments suggest that a variety of problems in clinical medicine might be solved by mining the extensive library of possible diazeniumdiolate structures.

Current collaborators in these efforts include: Sonia Donzelli, Univ. of Hamburg-Eppendorf, Hamburg, Germany; Astrid Weyerbrock, Uni-Klinik Freiburg, Germany; Stefan Chlopicki, Jagellionian Center for Experimental Therapeutics, Krakow, Poland; Jeffrey Deschamps, Naval Research Laboratory; Xinhua Ji, NIH; Melina Kibbe, Northwestern University; Paul Shami, University of Utah; David Wink, NIH; and Regina Ziegler, NIH.

Scientific Focus Areas:
Chemical Biology
  1. Wink DA, Kasprzak KS, Maragos CM, Elespuru RK, Misra M, Dunams TM, Cebula TA, Koch WH, Andrews AW, Allen JS.
    Science. 254: 1001-3, 1991. [ Journal Article ]
  2. Maragos CM, Morley D, Wink DA, Dunams TM, Saavedra JE, Hoffman A, Bove AA, Isaac L, Hrabie JA, Keefer LK.
    J. Med. Chem. 34: 3242-7, 1991. [ Journal Article ]
  3. New nitric oxide-releasing zwitterions derived from polyamines.
    Hrabie JA, Klose JR, Wink DA, Keefer LK.
    J. Organic Chem. 58: 1472-76, 1993. [ Journal Article ]
  4. Saavedra JE, Billiar TR, Williams DL, Kim YM, Watkins SC, Keefer LK.
    J. Med. Chem. 40: 1947-54, 1997. [ Journal Article ]
  5. Keefer LK, Roller PP.
    Science. 181: 1245-7, 1973. [ Journal Article ]

Dr. Keefer received his Ph.D. in organic chemistry from the University of New Hampshire in 1966 and held research positions at the Chicago Medical School and the University of Nebraska College of Medicine before joining the NCI staff in 1971.

Name Position
Zhao Cao Laboratory Technician (Contr)
Kenyatta Cosby M.D. Special Volunteer
Ryan Holland Ph.D. Postdoctoral Fellow (CRTA)
Joseph Hrabie Ph.D. Special Volunteer
Arjun Iyer Special Volunteer
Kazimierz Kasprzak Ph.D. Scientist Emeritus
Youseung Kim Ph.D. Postbaccalaureate Fellow
Anna Maciag Ph.D. Senior Research Assistant (Contr)
Victor Nelson Special Volunteer
Joseph E. Saavedra, Ph.D. Staff Scientist (Contr)

Summary

Dr. Keefer is internationally recognized as an authority on the chemistry and pharmacology of nitric oxide (NO), a critical bioeffector molecule with essential roles in the cardiovascular system, sexual function, and immunity, among others. The Keefer lab is noted for having introduced a series of NO-releasing agents that are now used worldwide as tools for studying NO’s biological effects. Several of these compounds were designed for targeted delivery of NO to specific sites in the body for therapeutic benefit, and are under current study for their possible clinical applications.

Link to additional information about Dr. Keefer's  research.

Areas of Expertise
1) nitrosamine chemistry 2) nitric oxide biology 3) chemistry and pharmacology of the diazeniumdiolates 4) organic chemistry

Research

Chemistry and Biology of Nitric Oxide

Nitric oxide (NO) is a potent and multifaceted bioregulatory agent. This project is aimed at finding ways to target NO to specific sites in the body for important research and/or therapeutic applications. Our strategy in pursuing this goal is to begin by characterizing the fundamental chemistry of the NO-releasing diazeniumdiolates (compounds containing the [N(O)NO] functional group). We then attempt to exploit our accumulating knowledge in this area as a platform for solving problems in biomedical research and clinical medicine. We are currently pursuing basic research investigations into the structure, spectra, dissociation to NO and/or HNO, alkylation, arylation, photodegradation, and general reactivity of the diazeniumdiolate functional group with an eye toward designing prodrugs that are stable at physiological pH but that can be activated to generate NO or HNO by enzymatic action. An example is AcOM-PYRRO/NO, an esterase-sensitive diazeniumdiolate that penetrates the cell and generates NO within the cytoplasm on esterase-induced hydrolysis; AcOM-PYRRO/NO has proved to be two orders of magnitude more potent as an inducer of apoptosis in HL-60 leukemia cells in culture than the spontaneously dissociating parent ion, PYRRO/NO.

Link to Diazeniumdiolate Chemistry Database

Other achievements include the design of agents that can be activated for NO release by enzymes of the glutathione S-transferase, glycosidase, and cytochrome P450 families. Other recently introduced diazeniumdiolates have been designed to target nitric oxide delivery to macrophages for antimicrobial activity. Proof-of-concept studies that underscore the substantial clinical promise of these compounds include: inhibition of restenosis after angioplasty; preparation of thromboresistant medical devices; and inhibition of tumor growth in in vivo models. The results of the animal experiments suggest that a variety of problems in clinical medicine might be solved by mining the extensive library of possible diazeniumdiolate structures.

Current collaborators in these efforts include: Sonia Donzelli, Univ. of Hamburg-Eppendorf, Hamburg, Germany; Astrid Weyerbrock, Uni-Klinik Freiburg, Germany; Stefan Chlopicki, Jagellionian Center for Experimental Therapeutics, Krakow, Poland; Jeffrey Deschamps, Naval Research Laboratory; Xinhua Ji, NIH; Melina Kibbe, Northwestern University; Paul Shami, University of Utah; David Wink, NIH; and Regina Ziegler, NIH.

Scientific Focus Areas:
Chemical Biology

Publications

  1. Wink DA, Kasprzak KS, Maragos CM, Elespuru RK, Misra M, Dunams TM, Cebula TA, Koch WH, Andrews AW, Allen JS.
    Science. 254: 1001-3, 1991. [ Journal Article ]
  2. Maragos CM, Morley D, Wink DA, Dunams TM, Saavedra JE, Hoffman A, Bove AA, Isaac L, Hrabie JA, Keefer LK.
    J. Med. Chem. 34: 3242-7, 1991. [ Journal Article ]
  3. New nitric oxide-releasing zwitterions derived from polyamines.
    Hrabie JA, Klose JR, Wink DA, Keefer LK.
    J. Organic Chem. 58: 1472-76, 1993. [ Journal Article ]
  4. Saavedra JE, Billiar TR, Williams DL, Kim YM, Watkins SC, Keefer LK.
    J. Med. Chem. 40: 1947-54, 1997. [ Journal Article ]
  5. Keefer LK, Roller PP.
    Science. 181: 1245-7, 1973. [ Journal Article ]

Biography

Dr. Keefer received his Ph.D. in organic chemistry from the University of New Hampshire in 1966 and held research positions at the Chicago Medical School and the University of Nebraska College of Medicine before joining the NCI staff in 1971.

Team

Name Position
Zhao Cao Laboratory Technician (Contr)
Kenyatta Cosby M.D. Special Volunteer
Ryan Holland Ph.D. Postdoctoral Fellow (CRTA)
Joseph Hrabie Ph.D. Special Volunteer
Arjun Iyer Special Volunteer
Kazimierz Kasprzak Ph.D. Scientist Emeritus
Youseung Kim Ph.D. Postbaccalaureate Fellow
Anna Maciag Ph.D. Senior Research Assistant (Contr)
Victor Nelson Special Volunteer
Joseph E. Saavedra, Ph.D. Staff Scientist (Contr)