Circadian cell kinetics in humans. Aspects related to cancer chemotherapy.

A prerequisite for the investigation of cell kinetics, and especially circadian cell kinetics, has been the development from the 1950s and onwards of several methods for studying kinetic parameters in different mammalian tissues. A large number of such studies have subsequently taken place in the rodent, mostly as non-circadian experiments, but also a large number of studies have now documented on circadian proliferative rhythms in many different murine tissues. Results from cytokinetic studies in the human have also accumulated through the years. Of special interest has been the demonstration of temporal variations in rapidly proliferating tissues studies as the bone marrow and gut mucosa relative to cytotoxic anticancer therapy. Analyses of proliferation in human tumours have also indicated rhythms in malignant solid tumours. Thus, these studies have demonstrated that there exist rhythms in bone marrow and gut cytokinetics which increases the likelihood that certain times of day will be less toxic for the administration of cytotoxic drugs. Furthermore, optimizing anticancer therapy according to a circadian schedule may also increase the tumour cell death rat, due both to an indirect dose-escalating effect and a direct increased tumour effect.