Inter-alu PCR detects high frequency of genetic alterations in glioma cells exposed to sub-lethal cisplatin

Abstract

Increased genomic instability contributes to higher frequency of secondary drug resistance and neoplastic progression in tumors as well as in cells exposed to sub-lethal concentrations of chemotherapeutic agents. We have used PCR based DNA fingerprinting techniques of randomly amplified polymorphic DNA (RAPD) and inter-alu PCR to study this phenomenon in the tumor genome. The choice of the primer, either random (for RAPD) or specific (inter-alu PCR) can determine the nature of alterations being assessed. We have compared the inter-alu PCR and RAPD profiles of U87MG glioblastoma cells exposed to sequentially increasing low doses of cisplatin for 24 passages to that of untreated controls. Inter-alu PCR, with 2 primers, demonstrated a number of alterations in the treated cells, in the form of loss/gain and changes in the intensity of bands. No changes were observed by RAPD analysis with 5 primers, however, indicating a preferential increase in the alu mediated recombination frequency in the treated cells (p=1.866 × 10⁻⁴). The number of changes observed with respect to the corresponding leucocyte DNA in the inter-alu PCR profile of 26 primary tumors (Grade II =13; Grade IV=13), resected before chemotherapy, for the 2 inter-alu primers was very small. We present a novel application of the inter-alu PCR in detecting alterations in long term cultured cells at low dose exposure to a chemotherapeutic agent. Our results suggest that alu mediated recombination may be important in cells exposed to sub-lethal doses of cisplatin but not in the genesis of primary glioma.