Assessment of apoptosis in relation to proliferation and mutational status of p53 gene in head and neck cancers

Abstract

The present studies were undertaken to determine the incidence of apoptosis in plastic embedded head and neck (HN) tumor biopsies (n=31) using in situ end labeling (ISEL) of fragmented DNA. The extent of spontaneous apoptosis in untreated tumors was correlated with histological grade, percent S-phase cells (Labeling Index, LI) and with the mutational status of p53 gene in these tumors. Additionally, the in vivo effects of chemo- and/or radiotherapy on apoptosis were evaluated in seven patients. In the majority of tumors studied (25/31) spontaneous apoptosis was virtually undetectable or was very low (1-15% positively labeled cells). Only 6 tumors showed intermediate to high apoptosis (>15% positively labeled cells). High apoptosis was more frequent in poorly differentiated tumors (similar to 50%), as compared to well and moderately differentiated tumors. The median LI for 31 tumors studied was 20.2%. The mean LI for moderately differentiated tumors (23.7+/-1.7%) was significantly higher than that in well differentiated (15.1+/-2.1%, p=0.005) and was comparable in poorly differentiated tumors (24.5%). Cytotoxic therapy significantly increased the degree of apoptosis in 5/7 specimens studied (p=0.03). Double labeling of 5 of these tumors before and after the therapy, combining ISEL with detection of IUdR/BrdU, showed compartmentalized apoptosis and proliferation with virtually no double labeled cells in any specimen. Interestingly, tumors with a mutated p53 gene (n=6) showed intermediate to high degree of pretherapy, baseline apoptosis in contrast to low or undetectable levels of apoptosis in tumors bearing wild-type p53 (n=13, p=0.034). It appears that low levels of apoptosis and high proliferation may be characteristic of HN tumors. The spontaneous apoptosis in HN tumors seems unrelated to mutations in the p53 gene. Moreover, our data also show that despite overall increase in apoptosis induced by cytotoxic therapy, some proliferating tumor cells escaped the effects of therapy, which may contribute to the tumor relapse.