Ara-C cytokinetic studies in normal tissues in vivo.

The importance of including normal tissues in the design of cytokinetic-based chemotherapeutic schedules is becoming increasingly apparent. However, the lack of rapid analytical techniques to obtain quantitative cytokinetic data on target subpopulations in heterogenous normal tissues, such as the gastrointestinal and hematopoietic system, has limited the inclusion of these tissues in therapy design. Once target subpopulations are identified and/or discriminated, flow cytometry in conjunction with radioactivity measurements by liquid scintillation counting can be used to rapidly obtain quantitative cytokinetic data during drug therapy. The present paper reviews our current cytokinetic techniques and the applications and limitations of these techniques in the analysis of Ara-C-induced perturbations in the small intestine and hematopoietic system. Cell cycle information both prior to and 30 hrs following a single Ara-C treatment was obtained in the intestinal crypts and femoral marrow population using radioactive precursor uptake and flow cytometric techniques. In addition, the relationship between crypt cell survival and animal lethality following Ara-C treatment was determined to better understand the impact of a damage to a regenerative population on the "clinical endpoint" of animal survival. Understanding the principles behind the normal tissue toxicity which occurs during multidose treatment will hopefully allow modulation of this toxicity through the rational design of optimal chemotherapeutic schedules.