Pharmacogenetic studies in childhood acute lymphoblastic leukaemia with primary focus on methotrexate

Sammanfattning: Childhood acute lymphoblastic leukaemia is the most common type of cancer in children. Improvement in treatment has increased survival to approximately 85 per cent. Pharmacogenetics can influence the disposition of anticancer agents and can ideally be used as tool to further improve treatment based on the individual child’s pharmacogenetic profile.The hypothesis in this thesis was that polymorphisms in genes responsible for MTX influx (SLC19A1), efflux (ABCB1, studies with MTX monotherapy have demonstrated effect of variations in this gene) or other MTX pathways (ATIC, MTHFR and SHMT) could have impact on efficacy in childhood acute lymphoblastic leukaemia.The uptake of MTX and impact of SLC19A1 80G>A was investigated in vitro and showed that SLC19A1 80GG had decreased uptake in CD+ T cells and B cells caused by reduced capacity on receptor-to-receptor basis.In more than 500 patients the clinical effect of SLC19A1 80G>A genotype was evaluated and showed that patients with the SLC19A1 80AA had better survival, more bone marrow toxicity, but less liver toxicity than patients with SLC19A1 80GG or 80GA variants. Furthermore, it was demonstrated that SLC19A1 80G>A interacts with chromosome 21 copy number in the leukemic clone.The clinical impact of ABCB1 1199G>A, 1236C>T, 2677G<T/A and 3435C>T on the treatment was evaluated. Patients with either the 1199GA or the 3435CC variant had increased risk of relapse compared to patients with the 1199GG or 3435CT/TT variants, respectively. Toxicity was also affected by the ABCB1 polymorphisms.No association between polymorphisms in the ATIC, MTHFR and SHMT genes and outcome was seen. However the 677C>T and 1298 C>A in the MTHFR gene were associated with toxicity.The genotype frequencies between healthy donors and patients were compared, but no association to risk of developing cancer was seen in the investigated polymorphisms.The results in this thesis emphasise the importance of including pharmacogenetic markers in attempts to improve outcome and reduced side effects in childhood ALL.