Increased sensitivity to bleomycin in upper aerodigestive tract mucosa of head and neck squamous cell carcinoma patients

Abstract

Previous studies on lymphocytes have suggested that patients with head and neck squamous cell carcinoma (HNSCC) have an increased susceptibility for chromosomal damage induced by bleomycin, a known radiomimetic mutagen. However, it has so far not been possible to study whether this genetic instability is present also in the epithelial component of the upper aerodigestive tract mucosa, the tissue from which HNSCC originates. In the present study, we have successfully cultured epithelial cells and fibroblasts isolated from non-neoplastic mucosa samples of 30 HNSCC patients and 56 controls. All cell cultures were exposed to bleomycin and chromosome instability was assessed by analysis of chromosome breakage in cells harvested after 2 h of exposure and subsequent removal of bleomycin. Furthermore, the status of the fragile histidine triad gene (FHIT) in chromosome band 3p14.2 was studied by fluorescence in situ hybridization (FISH) in epithelial cells that had been cultured after removal of bleomycin. Chromosomal damage, in the form of chromosomal breaks and gaps, was seen in all cell cultures harvested 2 h after exposure to bleomycin. In epithelial cells, the frequency of chromosome breakage was significantly higher among HNSCC patients than among controls [mean breaks per cell (b/c) 1.02 vs. 0.77, p = 0.02]. When subdivided according to smoking status, age, and sex, a significantly higher frequency of chromosome breakage was still found in HNSCC patients (smokers, p = 0.01, age ≤ 70 group, p = 0.03, male, p = 0.02). However, no significant difference was found between fibroblasts from HNSCC patients and controls (b/c 1.21 vs. 1.23). In the cell cultures growing after termination of bleomycin exposure, the frequency of chromosome breakage was generally very low and no significant difference could be found between the HNSCC patients and controls when epithelial cells were examined. In subcultured fibroblasts, a higher frequency was found in HNSCC patients than in controls (b/c 0.59 vs. 0.19, p = 0.03). Interphase FISH on cultured epithelial cells from HNSCC patients ( n = 10) and controls ( n = 12) showed that the frequency of FHIT deletion was significantly higher in HNSCC patients than in controls. Our results support the notion that HNSCC patients accumulate genetic damage more rapidly, possibly due to an inherent susceptibility, which could explain the high risk for multi-focal neoplastic cell transformation.