PARENT SESSION

Genomic Maintenance & Repair

(PP344) Genetic analysis of a human ovarian cell line resistant to cis platinum and ionizing radiation.

Lehnert, Shirley ¹, Sadekova, Svetlana¹, Park, Morag¹, Hudson, Thomas², Novak, Jaroslav², ¹ Oncology, Montreal, Quebec, Canada² Montreal Genome Centre, Montreal, Quebec, Canada

ABSTRACT- Cross-resistance between radiation and cis-platinum is well documented, both experimentally and clinically but the the molecular basis of this phenomena remains unknown. We have completed the microarray analysis of the human ovarian tumor cell line A2780, which was derived from an untreated patient biopsy and of A2780^CP a sub-line which was selected for resistance to cis-platinum and is cross-resistant to ionizing radiation. The A2780 sub-lines present an unique opportunity to analyse the genetic profile of radio/drug resistant cells. We utilized the high density Affymetrix microarrays which contain 8,000 known genes and ESTs covering the majority of the mRNAs expressed in the mammalian cell. Cells were treated with the equitoxic doses of radiation or cis-platinum and all the experiments were done in duplicate. The radiation iso-effect doses at S.F. = 0.1 are 3.23 and 7.50 Gy for A2780 and A2780^CP respectively. The IC₅₀cis-platinum is 3.0 M for A2780 and 13.0M for A2780^CP. Micro-array profiling of the cell lines showed 71 genes to be constitutively over-expressed and 47 to be under-expressed in A2780^CP cells compared with wild type A2780. All classes of genes were up-regulated including one group involved in detoxification and protection against oxidative stress which could be protective against both cis-platinum and radiation. The number of genes regulated by radiation in A2780 greatly exceeded those regulated in A2780^CP cells suggesting that the normal mechanisms of radiation response which protect the genome but can result in loss of proliferative capacity are lost in A2780^CP. In contrast, cis-platinum causes regulation of many more genes in A2780^CP than in A2780 indicating mobilization of protective mechanisms. The results suggest that the mechanisms of radiation resistance and drug resistance in A2780^CP cells are largely independent.

Key words: cis-platinum, ionizing radiation, cross-resistance, micro-array