In vitro analysis of the response of multicellular tumor spheroids exposed to chemotherapeutic agents in vitro or in vivo.

Multicellular tumor spheroids (MTS) have been exposed to chemotherapeutic agents in vitro (nitrogen mustard) or in vivo (cyclophosphamide) and analyzed in vitro in terms of altered growth patterns. Whether the MTS were exposed in vitro or in vivo, the major effect of the drugs was to induce a dose-dependent lag period before the normal MTS growth rate resumed. Exposure of MTS in the peritoneal cavity to i.v. injection cyclophosphamide results in patterns similar to the in vitro exposure system, except that a host anti-MTS reaction was detected. In combination, these two methods allow the study of the responses of these complex tumor forms to chemotherapy.