Premature chromosome condensation and cell separation studies in biopsies from head and neck tumors for radiosensitivity prediction.

BACKGROUND AND
PURPOSE: Intrinsic radiosensitivity of tumor cells from biopsies, assayed by colony formation after in vitro irradiation, has shown significant correlations with outcome after radiotherapy. Alternatives to the colony assay have been sought due to its long and cumbersome nature. We have previously shown good correlations between colony formation and radiation-induced chromosome aberrations in human tumor cell lines. In addition, we and others have shown on cell lines that premature chromosome condensation (PCC) induced with phosphatase inhibitors can be used to aid rapid assessment of aberrations in interphase cells, reducing the selection problem with metaphases. The purpose of this study was to translate the in vitro results to human cancer, with the aim of developing a rapid assay for intrinsic radiosensitivity. METHODS AND
RESULTS: The problem of admixtures of normal and malignant cells in biopsies was addressed using magnetic bead separation (MACS) employing antibodies to human fibroblasts. This proved to be a reliable and efficient method, enriching mean tumor cell fractions from 20 to almost 80%. PCC could be induced in human normal and tumor cell lines, and in sorted or unsorted suspensions from biopsies, with the phosphatase inhibitor calyculin A. Maximum PCCs were achieved after 1-week culture of biopsy-derived cells. Mean fractions of aneuploid tumor cell PCCs were, however, less than 1%. PCCs were predominantly from S and G2 phase, of which only G2 were scorable for aberrations. Almost no G1 PCCs were found. More scorable PCCs were found after 1h of calyculin A than metaphases after 5h of colcemid, but these were calculated to be too few to yield reliable estimates of chromosome damage after radiation.CONLCUSIONS: Tumor cells can be satisfactorily separated from fibroblasts in fresh suspensions from cancer biopsies, but poor growth of tumor cells in short term culture and low yields of PCCs combine to prevent the routine use of such cytogenetic assays for pre-treatment prediction of radiotherapy outcome.