Malignant gliomas are typically treated with surgery, radiation and chemotherapy. In spite of available treatments, recurrence is common and the median survival following diagnosis continues to be less than a year. It is thought that recurrent tumors may arise, in part, from a subpopulation of cells present in the primary tumor that possess genetic and/or epigenetic attributes that confer resistance to radiation and chemotherapy. In addition, the treatments themselves cause DNA damage which can lead to genetic changes in the cells that survive. Many studies have been carried out investigating changes in DNA and RNA that lead to therapy resistance; however, few studies have been done to study the global protein changes that occur between the primary tumor and recurrence following therapy. An understanding of the changes that occur in the cell populations of primary tumors leading to the formation of recurrent tumor may point to additional targets for the design of novel therapies. We have used 2-dimensional polyacrylamide gel electrophoresis (PAGE) to analyze proteins isolated from cells from primary and recurrent tumor pairs with and without in vitro selection for drug resistance. Proteins are separated based on their isoelectric point using an IPG strip (pH 4-7) followed by gradient PAGE to separate the proteins based on molecular weight. The proteins are identified by MALDI-TOF analysis of a tryptic digest. To date we have analyzed total protein samples from 2 primary/recurrent tumor pairs prior to and following selection for resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) - a total of 8 cell lines. Twenty nine protein spots were found to be consistently differentially expressed. These proteins range in pI from 4.65 - 6.22 and they range in size from 28-65 kD. Of these spots, 16 appear to be proteins that are upregulated in cells from recurrent tumor versus primary tumor and 9 appear to be down-regulated. In addition, 4 proteins are differentially regulated in cells from both primary and recurrent tumor following selection for BCNU resistance. Identification of these proteins is in progress, as are the analyses of additional cell and tissue samples from primary and recurrent tumors. Global proteomic analysis of primary and recurrent malignant gliomas will corroborate previously published evidence implicating specific genes in tumor recurrence and therapy resistance, and will lead to the identification of new therapeutic targets for the treatment of recurrent tumor.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]