Over-representation of specific regions of chromosome 22 in cells from human glioma correlate with resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea

Abstract

BackgroundGlioblastoma multiforme is the most malignant form of brain tumor. Despite treatment including surgical resection, adjuvant chemotherapy, and radiation, these tumors typically recur. The recurrent tumor is often resistant to further therapy with the same agent, suggesting that the surviving cells that repopulate the tumor mass have an intrinsic genetic advantage. We previously demonstrated that cells selected for resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) are near-diploid, with over-representation of part or all of chromosomes 7 and 22. While cells from untreated gliomas often have over-representation of chromosome 7, chromosome 22 is typically under-represented.MethodsWe have analyzed cells from primary and recurrent tumors from the same patient before and after in vitro selection for resistance to clinically relevant doses of BCNU. Karyotypic analyses were done to demonstrate the genetic makeup of these cells, and fluorescent in situ hybridization analyses have defined the region(s) of chromosome 22 retained in these BCNU-resistant cells.ResultsKaryotypic analyses demonstrated that cells selected for BCNU resistance were near-diploid with over-representation of chromosomes 7 and 22. In cells where whole copies of chromosome 22 were not identified, numerous fragments of this chromosome were retained and inserted into several marker and derivative chromosomes. Fluorescent in situ hybridization analyses using whole chromosome paints confirmed this finding. Additional FISH analysis using bacterial artificial chromosome probes spanning the length of chromosome 22 have allowed us to map the over-represented region to 22q12.3–13.32.ConclusionCells selected for BCNU resistance either in vivo or in vitro retain sequences mapped to chromosome 22. The specific over-representation of sequences mapped to 22q12.3–13.32 suggest the presence of a DNA sequence important to BCNU survival and/or resistance located in this region of chromosome 22.

MicroRNA and Brain Tumors: A Cause and a Cure?

“…In preliminary studies reported for BCNU, the authors identified four miRNAs (let-7b, mir-125b-2, mir133a-1, and mir-183) that were differentially expressed in both primary vs. recurrent GBMs and BCNU sensitive vs. resistant cells. Of these, let-7b is mapped to chromosome 22q12, a region previously correlated by the same group to be correlated with GBM resistance to BCNU (Hank et al, 2006).…”

Pharmacotherapy for adults with tumors of the central nervous system

“…This can be verified in individual cases by methylation-specific PCR on resected tumor tissue which allows identification of patients more likely to respond favourably to the treatment (Paus et al, 2007). Glioma cells that are resistant to BCNU typically have overrepresentation of chromosome 22q12.3-13.32, implying that this chromosome region contains genes important for BCNU resistance (Hank et al, 2006). Resistance of gliomas to alkylators and recurrence of disease after therapy with alkylators are also proportional to the activity in these tumors of apurinic/apyrimidinic endonuclease, a DNA repair enzyme that cleaves DNA at the abasic sites formed by alkylating chemotherapy and radiation (Bobola et al, 2004).…”