Although many in vitro chemosensitivity tests for anticancer agents have been reported, no scientific assessment of the optimum exposure time and dose of anticancer drugs for such tests has been established.
We assessed the cytotoxicity of 4 anticancer agents (CDDP, CBDCA, ADM, MMC) by analyzing the relationships between the IC50 values and the drug exposure time in a study using PC-14 cells. The clinical AUC (Area Under the Curve) of each drug was compared with the dose giving 50% inhibition of the control level for cell growth (IC50) in a conventional MTT assay (C-MTT) . A modified MTT assay, which involved washing out of the drugs and additional incubation (M-MTT) and a HTCA (Human Tumor Clonogenic Assay) was also carried out with PC-9 and PC-14 cells.
The results suggested that all of 4 anticancer drugs were AUC-dependent agents. The HTCA was considered to be the assay giving results closest to the doses effective in clinical practice among the 3 assays tested, while the C-MTT gave a much higher AUC than the clinical AUC. It is suggested the reason is that in the C-MTT all the cells are viable at the end of drug exposure. Thus, not only viable cells with the potential of proliferate but also those without this potential are included in the results.
On the other hand, viable cells with a proliferative potential are better assessed by the M-MTT, which has an additional incubation time.
This study indicated that the C-MTT was unsuitable in vitro chemosensitivity tests for new AUCdependent drugs. In contrast, the HTCA and M-MTT showed the doses of AUC to be effectively closer to those in clinical practice and proved useful for analyzing the cytotoxicity of AUC-dependent drugs.