PROLIFERATIVE ACTIVITY AND MICRONUCLEUS FREQUENCY AFTER RADIATION OF LUNG-CANCER CELLS AS ASSESSED BY THE CYTOKINESIS-BLOCK METHOD AND THEIR RELATIONSHIP TO CLINICAL OUTCOME

We previously proposed a new assay using the cytokinesis-block micronu cleus (MN) technique to estimate the fraction of cells undergoing mito sis in vitro [dividing fraction (DF)], potential doubling time (T-pot, and radiosensitivity (in terms of MN frequency) of human tumors. In t he present study, we applied this technique to primary lung cancers to evaluate their biological characteristics, and the assay results for the proliferative activity were compared with the treatment outcome. T umor tissues were disaggregated to single cells, which were cultured i n the presence of cytochalasin B after (or without) radiation. At inte rvals, the proportion of multinucleate cells (its maximum value is the DF), the average number of nuclei/cell, and MNs in binucleate cells w ere scored. The T-pot was the extrapolated time for the nuclei:cell ra tio to reach 2.0. Of the 71 tumor samples obtained, the DF and T-pot w ere evaluable in 61 (86%), and the MN frequency was evaluable in 52 (7 3%). The median DF and T-pot values were 23% and 7.7 days, respectivel y, for adenocarcinoma (n = 41), 26% and 8.9 days for squamous cell car cinoma (n = 13), 27% and 6.5 days for large cell carcinoma (n = 3), an d 30% and 7.0 days for small cell carcinoma (n = 4). There was no sign ificant difference in the mean DF or T-pot values according to the his tological type or disease stage. The mean MN frequency after 2 Gy of r adiation (minus the 0 Gy frequency) was 0.15 for adenocarcinoma, 0.17 for squamous cell carcinoma, 0.16 for large cell carcinoma, and 0.20 f or small cell carcinoma. The MN frequency after radiation was positive ly correlated with both the DF and the baseline (at 0 Gy) MN frequency . In non-small cell lung cancer, a DF above the median was associated with an increased recurrence rate after operation, and the T-pot was c orrelated with the time until relapse in patients who developed recurr ence. Although the clinical significance of the MN frequency needs to be clarified in future studies, the DF and T-pot determined by this as say appear to be good parameters of tumor proliferative activity.