A Single Nucleotide Polymorphism in the Cytochrome p450 Gene Positively Impacts Survival Post Cyclophosphamide Conditioning in Autologous Transplants for Lymphoma

Background: Cyclophosphamide (Cy) is a prodrug metabolized by hepatic cytochrome p450 enzymes into active cytotoxin. High dose Cy-containing chemotherapy followed by autologous hematopoietic cell transplant (autoHCT) is often curative for patients with lymphoma; however, relapse occurs in about 50% of patients. We investigated the association between genetic polymorphisms in Cy metabolism and outcomes after autoHCT for lymphoma.

Material and Method:   We studied lymphoma patients who received myeloablative Cy-containing conditioning between 2004-2012 with available DNA samples. Somatic DNA was obtained from pre-transplant bone marrow aspirates, and Sequenom and Taqman genotyping assays were used to analyze 22 genes and 38 single nucleotide polymorphisms (SNP) involved in Cy metabolism. All patients were followed for at least one year. The association of each SNP with overall survival (OS) and disease-free survival (DFS) following autoHCT was analyzed using multivariable Cox regression, with categorical factors for genotype, age (≥ 55 vs. < 55 years), and gender.  A separate model was used for each SNP.  P-values were corrected for multiple testing using the Holm method.

Results: We studied 93 patients (median age 45 years) with lymphoma (52  Hodgkin, 21 diffuse large B cell, 12 mantle cell , 8 others); 55% were male. Two-thirds received Cy (120 mg/kg) combined with BCNU/etoposide conditioning and a third received  Cy (6000 mg/ m²) with total body irradiation (1250 cGy). The majority (96%) had chemosensitive disease with 61% in complete remission pre transplant.  . Two year DFS and OS for the entire cohort was 60% (95%CI 49-69%) and 86% (95%CI 76-91%), respectively.  A single SNP rs3211371 in the CYP2B6 gene significantly impacted survival. This SNP results in Arg487Cys and influences CYP2B6 activity. Adjusted for age and gender, patients heterozygous (CT; n=69) for SNP rs3211371 had significantly better DFS (HR 0.27; 95%CI 0.13- 0.56 ; p=0.024) and OS ( HR 0.09; 95%CI: 0.02-0.35; p=0.03) as compared to homozygous patients (TT; n=21). This association was not confounded by age, gender, disease type, conditioning, or remission status.

Conclusion:  Our results show a strong association between CYP2B6 rs3211371 SNP and survival in lymphoma patients treated with high-dose Cy and autoHCT.  We plan to evaluate serum levels of Cy active metabolites and confirm the potency of this association in a larger study.