The DNA Synthesis Inhibitor, Hydroxyurea, as a Potential Novel Therapeutic Approach for Fanconi Anemia: Further Studies in Complementation Group D1.

Abstract 4214

Fanconi anemia (FA) is an inherited, cancer-prone bone marrow failure disease. FA is heterogeneous, with 13 complementation groups, but all groups have in common hypersensitivity to agents that produce DNA interstrand cross links (DISCLs), with associated increased clastogenicity, as a diagnostic hallmark. Although progress has been made in treating FA, particularly using bone marrow transplantation (BMT) to prevent bone marrow failure and leukemogenesis, BMT is not a trivial procedure, and treatment remains challenging. Head and neck cancers, which occur in high frequency in FA, are a particular problem that is not well remedied by BMT.

Lymphoblastoid cells from normal subjects and from patients with FA were treated in culture with psoralen plus ultraviolet A radiation (PUVA) in a regimen shown to produce DISCLs. Following this, cells were treated with hydroxyurea, 5-fluorouracil, or high dose thymidine, in doses we have shown to produce a marked decrease in rate of DNA synthesis, for 24 hours. We have previously shown that clastogenicity and cytotoxicity, measured as trypan blue exclusion as well as colony forming ability (CFA), are markedly increased in FA cells, complementation groups A, B, C, and E, associated with deficiencies in their corresponding FA core proteins, but these increases are not observed in these FA cells subsequently treated with any of these other, DNA synthesis retarding agents, which effectively correct the FA phenotype in culture. FA A and C cells genetically corrected for the FANC A and G gene, respectively, display normal clastogenicity and cytotoxicity following PUVA, and do not show this correction following subsequent treatment with hydroxyurea, 5-fluorouracil, or high dose thymidine.

We now report similar results for short term cell viability, and similar, although less marked, results for clastogenicity in FA complementation group D1 cells, associated with a deficiency in BRCA2. When all drugs were removed after these treatments and the cells cultured for 10 days without any drug in CFA assays, the FA group D1 cells resembled normals, however, and did not show this correction.

We propose that the mechanism in FA A, B, C and G cells is related to a decrease in the rate of DNA synthesis, which we have shown occurs in normal but not FA cells following PUVA, and which is also produced by these other agents in the concentrations used here. The partial correction observed in FA group D1 cells may be due to this or a different mechanism. Partial or complete correction appears to apply to multiple FA complementation groups.

Hydroxyurea has been used for many years as a safe and effective treatment for sickle cell anemia and other diseases. It is now proposed as a possible treatment for FA to delay or even prevent development of bone marrow failure and/or other complications, including leukemogenesis and carcinogenesis, with or without prior BMT. In some cases it may serve as a viable alternative where BMT is not fungible. Alternatively it may obviate the need for BMT altogether in responsive patients, or be effectively used in combination with other modalities. Complementation group may be important in determining which patients may be less responsive or require modified regimens.