Several different in vitro and ex vivo-derived rodent cell lines were developed that recapitulate the specialized asymmetric cell kinetics of adult somatic tissue stem cells in vivo. Previously, these model cells have been used to investigate and define genetic and molecular mechanisms that control adult stem cell kinetics. In the proposed research, the model cells will be used to investigate whether environmental agents, that are known to induce human cancers but with no detectable mutagenic activity, do so by disrupting adult stem cell kinetics. Specifically, the hypothesis that some non-mutagenic carcinogens function by inducing increased rates of stem cell proliferation will be examined. Disruption of asymmetric stem cell kinetics is an essential step in human carcinogenesis. "Kinetotoxic" effects by environmental contaminants, that lead to increased adult stem cell proliferation, may also be important in the etiology of other chronic processes associated with altered cell proliferation (e.g., premature aging). The model cells have already been used to identify 3 organic compounds that switch exposed cells from asymmetric cell kinetics to exponential cell kinetics. The main focus of the proposed research will be to use these cell lines to evaluate well established non-mutagenic environmental carcinogens for kinetotoxicity. Both acute high-dose and chronic low-dose exposures will be investigated. In addition to evaluating non-mutagenic compounds, several well-known mutagenic carcinogens will be examined, as they may exhibit concurrent kinetotoxicity. Chemicals found to induce changes in cell kinetics will be evaluated for molecular effects on cellular genes previously identified as regulators of asymmetric cell kinetics. In preliminary studies, the IARC Group 1 human carcinogen benzene exhibits evidence for kinetotoxicity. Benzene has a well-documented history as a potent non-mutagenic human carcinogen. It will serve as the prototype kinetotoxic agent for developing a systematic approach to revealing kinetotoxic mechanisms. In vitro human cell lines with asymmetric cell kinetics will be derived to provide kinetotoxicity assays that may have greater relevance to human adult stem cell physiology. The proposed research has the goal of providing new insights to the carcinogenic mechanisms of well studied environmental contaminants whose mode of action remains a mystery. Such insights will advance efforts to develop better strategies to limit morbidity associated with exposure to environmental carcinogens.