Our hypothesis is that a tumor can be considered as an entity composed of a variety of cell subpopulations. Each subpopuIation may have its own inherent properties and intrinsic sensitivities to therapies. These different sensitivities can arise from environmental or genetic factors or both. The overall tumor response to anticancer therapies then is a reflection of the responses of the individual cell subpopulations. The central goal of this research proposal continues to be the investigation of the various critical cell subpopulations comprising solid tumors. We will use cell separation techniques including centrifugal elutriation and fluorescence activated cell sorting to isolate and characterize cell subpopulations dispersed from rodent tumors, human tumor xenografts or clinical samples. Emphasis will be placed on determining the biological characteristics of hypoxic cells. There is evidence to suggest that tumors may contain cells which may be chronically or transiently hypoxic. Such cells would result from different mechanisms, have different characteristics, and have different implication for therapies. We plan to probe various rodent and human tumor models for the presence of such cells using tracer dyes combined with histological and flow cytometric techniques as well as radiolabeled sensitizers. Quiescent (Q) cells may represent another cell subpopulation of considerable relevance in clinical anticancer therapy. Experiments are proposed to study the response of such cell to different chemotherapeutic agents. Q cells in rodent tumor models will be characterized by acridin orange (AO) staining and flow cytometry analysis and isolated by centrifugal elutriation. In human tumor cells, FlTC conjugated anti-Ki-67 and anti-p105 antibodies and flow cytometry will be used to determine the percentage of proliferating cells. In parallel with the AO staining and Ki-67 or plO5 analyses, 3H-TdR labelling will be performed. Experiments extending Q cell determinations to human tumor biopsies also are proposed. Since changes in the quiescent cell population, if they occur during the course of therapy, could have a major impact on therapy, it is also our goal to attempt to establish techniques for measuring Q cell fractions in treated tumors. Finally, experiments are designed to gain a better understanding of the biological basis and underlying mechanisms for tumor response to altered fractionation schemes. Ultimately we hope that these approaches can be reliably developed to an extent where the use of human tumor biopsy material may lead to radiotherapy treatments more tailored to the individual patient.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG2-SSS-1 (04))
Program Officer
Stone, Helen B
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Florida
Schools of Medicine
United States
Zip Code
Salmon, Howard W; Siemann, Dietmar W (2004) Utility of 19F MRS detection of the hypoxic cell marker EF5 to assess cellular hypoxia in solid tumors. Radiother Oncol 73:359-66
Mendenhall, W M; Amdur, R J; Siemann, D W et al. (2000) Altered fractionation in definitive irradiation of squamous cell carcinoma of the head and neck. Curr Opin Oncol 12:207-14
Siemann, D W; Hinchman, C A (1998) Potentiation of cisplatin activity by the bioreductive agent tirapazamine. Radiother Oncol 47:215-20
Siemann, D W; Johansen, I M; Horsman, M R (1998) Radiobiological hypoxia in the KHT sarcoma: predictions using the Eppendorf histograph. Int J Radiat Oncol Biol Phys 40:1171-6
Li, L; Rojiani, A; Siemann, D W (1998) Targeting the tumor vasculature with combretastatin A-4 disodium phosphate: effects on radiation therapy. Int J Radiat Oncol Biol Phys 42:899-903
Keng, P C; Siemann, D W (1998) Measurement of proliferation activities in human tumor models: a comparison of flow cytometric methods. Radiat Oncol Investig 6:120-7
Warrington Jr, K H; Teschendorf, C; Cao, L et al. (1998) Developing VDEPT for DT-diaphorase (NQO1) using an AAV vector plasmid. Int J Radiat Oncol Biol Phys 42:909-12
Siemann, D W (1998) The tumor microenvironment: a double-edged sword. Int J Radiat Oncol Biol Phys 42:697-9
Richardson, M E; Siemann, D W (1997) Tumor cell heterogeneity: impact on mechanisms of therapeutic drug resistance. Int J Radiat Oncol Biol Phys 39:789-95
Horsman, M R; Siemann, D W; Chaplin, D J et al. (1997) Nicotinamide as a radiosensitizer in tumours and normal tissues: the importance of drug dose and timing. Radiother Oncol 45:167-74

Showing the most recent 10 out of 34 publications