Analysis of Genetic Variants Related to the Hepatic Veno-Occlusive Disease in Pediatric Patients Receiving HSCT with Targeted Dose Busulfan Based Conditioning

Background: Busulfan has a narrow therapeutic range and highly variable pharmacokinetics, so high exposure increases the risk of treatment toxicities such as veno-occlusive disease (VOD). Intensive monitoring and dose adjustment following therapeutic drug monitoring (TDM) of busulfan has improved outcomes after hematopoietic stem cell transplantation (HSCT). However, hepatic VOD still developed after TDM in some patients. In this study, we identified additional genetic variants related to hepatic VOD in pediatric patients receiving targeted dose busulfan based conditioning.

Methods: Targeted once-daily for four days intravenous busulfan with pharmacokinetic modeling was performed to the patients who underwent HSCT at Seoul National University Children's Hospital since January 2009. The first dose of busulfan was 120 mg/m² for patients aged ≥1 year and 80 mg/m² for patients aged < 1 year. The target area under the curve (AUC) was 18,750 mg·h/L/day for the first three days, and the AUC on the fourth day was decided as (75,000 - cumulative AUC during 3 days) mg·h/L/day. Busulfan was used in combination with fludarabine, cyclophosphamide, and etoposide in hematologic malignancies, and melphalan in solid tumors. Targeted sequencing was conducted with DNA from patients' remission samples by a designed panel of 147 genes and 84 single nucleotide polymorphisms known to be involved in the pharmacokinetics or pharmacodynamics of multiple drugs. The relationship between sequenced genotypes and the occurrences of VOD was analyzed. Among detected variants, only nonsynonymous and statistically significant variants were selected.

Results:A total of 123 patients with malignant diseases underwent allogeneic or autologous HSCT with targeted dose busulfan conditioning. The diagnoses were leukemia or lymphoma in 110, solid tumors in 12 patients and myelodysplastic syndrome in 1 patient. VOD developed in 19 patients (15.4 %). The total AUC in patients with or without VOD was 70,456 to 87,448 mg·h/L/day (median, 75,157 mg·h/L/day) and 69,295 to 83,160 mg·h/L/day (median, 74,436 mg·h/L/day), respectively (P=0.20). The genotypes of rs17224367 (MSH2 [MutS Homolog 2], odds ratio [OR] = 4.4, P= 0.047) , rs190420353 (ABCC1 [ATP Binding Cassette Subfamily C Member 1], OR = 59.2; P=0.0037), rs79242783 (UGT2B17 [UDP Glucuronosyltransferase Family 2 Member B17], OR = 15.6 ; P= 0.0030), and rs45547640 (XDH [xanthine dehydrogenase], OR = 5.83 , P= 0.013) were significantly associated with higher risk of hepatic VOD. MSH2, a member of the mismatch repair genes, has been implicated in sensitivities or resistances to alkylating agents such as busulfan. ABCC1, UGT2B17 and XDH are associated with multi-drug resistances and drug-related hepatic and renal toxicities.

Conclusion: Several genotypes were identified to be highly associated with hepatic VOD in pediatric patients. These findings may provide a supplemental information to identify high risk patients for the development of VOD undergoing HSCT despite of targeted dose busulfan based conditioning. For these patients, more attention and prophylactic medications, such as defibrotide, are required. Further validation and replication studies in a larger group of patients are needed.