PARENT SESSION

Genomic Maintenance & Repair

(PP311) Differential sensitivity of FancA- and FancD2-deficient cells to complex DNA double strand damage.

Kachnic, Lisa^*,1, Willers, Henning¹, Li, Li¹, Treszezamsky, Alejandro¹, Powell, Simon^{1, 2}, ¹ Department of Radiation Oncology, Boston, MA, USA² Department of Radiation Oncology, St. Louis, MO, USA

ABSTRACT- Fanconi anemia (FA) is a rare hereditary chromosomal fragility disorder characterized by anemia and cancer predisposition. Cells with mutations in any of the FA genes display hypersensitivity to drugs inducing DNA interstrand crosslinks, such as mitomycin-C (MMC). Accumulating evidence suggests that FA cells are hypersensitive to a broader range of chemotherapeutic agents, which has clinical implications, since defects in the FA pathway have been detected in a wide variety of cancers. We sought to determine the sensitivity of FA cells to Tirapazamine (TPZ), which inhibits replication and topoisomerase II selectively in hypoxic tumor cells, as well as to MMC and ionizing radiation (IR). We employed isogenic pairs of human fibroblasts derived from FancA- or FancD2-deficient cells, PD220i or PD20i, respectively. Wild-type FancA or FancD2 status was reconstituted by infection with a retroviral expression vector. Clonogenic cell survival was determined in response to TPZ (under hypoxia), MMC or IR. FancA-deficient cells displayed a marked hypersensitivity to MMC (>10,000-fold reduced survival at 0.50 M concentration) as compared to wild-type cells. By contrast, sensitivity to TPZ was much less pronounced (10-fold, 30 M). The converse outcome was seen with loss of FancD2 function: a 10-fold and >1,000-fold reduced survival for MMC and TPZ treatments, respectively. Neither of the FA lines exhibited radiation hypersensitivity. In conclusion, (1) FancA- and FancD2-deficient cells display a differential sensitivity to MMC and TPZ, suggesting that these proteins have distinct cellular functions in the repair of complex DNA damage. FancD2 appears to be required to repair damage that causes replication stalling. (2) Hypersensitivity of FA cells to TPZ, here shown for the first time, may have important implications for the treatment of squamous cell carcinomas of the cervix and the head & neck, for which studies have shown defects in the FA pathway and the existence of hypoxic cell populations.

Key words: Fanconi anemia genes, DNA double strand damage repair, Tirapazemine, Clonogenic survival