APOPTOSIS IN ORAL CANCER

点击翻译按钮获取中文摘要

Oral cancer remains a major cause of cancer mortality. The five year survival rate in patients diagnosed with oral cancer is under 50%; a survival rate that is significantly below many other carcinomas including breast, colon, and renal carcinomas. One major reason for treatment failure is the development of radiation and/or chemotherapeutic resistance in recurrent tumors. This proposal seeks to address whether alterations in the susceptibility of tumor cells to undergo programmed cell death (apoptosis) contributes to either the pathogenesis or recurrence of carcinomas in the oral cavity or pharynx. In particular, the role of members of the bcl-2 family in regulating programmed cell death in carcinomas of the oral cavity/pharynx as well as in normal oral epithelium and premalignant lesions will be examined. Members of the bcl- 2 gene family can both positively and negatively regulate apoptosis in response to a wide variety of physiologic and pharmacologic stimuli. Studies will be undertaken to analyze the expression of bcl-2 family members, bcl-2, bcl-xL, bcl-xS, bax, bad, and bak in normal mucosa as well as biopsy specimens of lesions including leukoplakia and squamous cell carcinoma. The role of bcl-2 genes in regulating the survival and chemotherapeutic/ radio-therapeutic sensitivity of established cell lines from carcinomas of the oral cavity or pharynx will also be studied. Over 30 early passage squamous cell carcinoma cell lines derived from the oral cavity or pharynx of patients with known clinical histories have been established. A significant number of these cell lines display radiation resistance despite the presence of a wild-type p53 gene. The sensitivity of these established cell lines to undergo apoptosis in response to a wide variety of stimuli including chemotherapy and radiation will be investigated and correlated with the expression of bcl-2 family members. If an association can be made between expression of an individual member of the bcl-2 family, efforts will be made to determine whether the gene is important for the in vitro survival and/or chemo/radiotherapy sensitivity by manipulating the expression of the genes using either antisense oligonucleotides or adenoviral-delivered transdominant inhibitors. In addition, determinations will be made as to whether growth factors that act on oral epithelial cells will modulate the expression of these cell survival genes. Finally, in an in vivo attempt to determine if resistance to apoptosis can contribute to the pathogenesis of oral or pharyngeal malignancies, transgenic animals have been produced which overexpress the cell survival gene bcl-xL in their oral mucosa. These animals will be examined for their development of oral cancer either spontaneously, or upon breeding to additional transgenic mice that overexpress epithelial growth factors such as TGF-alpha. In addition, these animals will be examined for their ability to develop tumors in response to classical initiating agents like benzanthracene. Together these studies should help to determine whether inhibition of apoptosis can play either a primary or secondary role in the development of oral carcinoma. These studies should help to determine whether specific manipulation of the expression of cell survival genes-will be a useful adjunct therapy to increase the sensitivity of oral/pharyngeal carcinomas to radiation and/or chemotherapy.