Correlation of in vitro clonogenic assay data with in vivo growth delays and cell cycle changes of a human melanoma xenograft

We have reported previously that, in a human melanoma xenograft line, plating efficiency and drug sensitivity in vitro were enhanced under hypoxic conditions. In the present study, we show that the in vitro chemosensitivity data using clonogenic assays at 5% oxygen also correlate better with the drug-induced in vivo growth delay. Tumors implanted in bilaterally symmetrical locations grew at different rates, and response to chemotherapy was also variable. Cell cycle changes in the xenograft, as monitored by flow cytometry, suggest that major changes in cell cycle traverse occur when a drug is active in vitro and also causes in vivo growth delay. These studies indicate the usefulness of the nude mouse human xenografts to study correlations between soft agar clonogenic assays, in vivo growth delay, and cell cycle traverse in response to chemotherapeutic manipulation.