[Analysis of drug sensitivity by successive colony-forming assay]

It is difficult to predict the adequate doses of effective drugs which must be administered in cancer chemotherapy. We have developed a successive colony-forming assay in order to analyze changes of drug sensitivity in human cancer cell lines, and it is used as a model of cancer chemotherapy. Presently, widely used methods include the clonog ceni assay as in vitro sensitivity test established by Salmon and Hamberger et al., for revealing effective drugs. However, formation of a second colony using initial colony-forming cells has not yet been performed. We therefore analyzed the changes occurring in drug sensitivity in 2nd and 3rd colony-forming assays. Using a human lung adenocarcinoma cell line PC-9 (established by Hayata at the Surgical Department in Tokyo Medical School), we measured the changes in sensitivity to CDDP and its derivatives. After picking up the colony-forming cells by micropipette and culturing them in culture medium, we tried to incubate them for 1 hour with the anticancer drug, and then replate them in soft agar. This technique is called "2nd colony-forming assay". We were able to carry this out three times. The results obtained showed that the anti-tumor effect of 254S was the same as that of CDDP, whereas that of CBDCA was less than either of them. Although these tendencies were noticeable even in the 2nd colony-forming assay, the sensitivities to CDDP and its derivatives were diminished in the 3rd colony-forming assay.