Genetic markers in CYP2C19 and CYP2B6 for prediction of cyclophosphamide's 4-hydroxylation, efficacy and side effects in Chinese patients with systemic lupus erythematosus

Abstract

Aims: The aim of the study was to investigate the combined impact of genetic polymorphisms in key pharmacokinetic genes on plasma concentrations and clinical outcomes of cyclophosphamide (CPA) in Chinese patients with systemic lupus erythematosus (SLE).

Methods: One hundred and eighty nine Chinese SLE patients treated with CPA induction therapy (200 mg, every other day) were recruited and adverse reactions were recorded. After 4 weeks induction therapy, 128 lupus nephritis (LN) patients continued to CPA maintenance therapy (200-600 mg week(-1)) for 6 months, and their clinical outcomes were recorded. Blood samples were collected for CYP2C19, CYP2B6, GST and PXR polymorphism analysis, as well as CPA and its active metabolite (4-hydroxycyclophosphamide (4-OH-CPA)) plasma concentration determination.

Results: Multiple linear regression analysis revealed that CYP2B6 -750 T > C (P < 0.001), -2320 T > C (P < 0.001), 15582C > T (P = 0.017), CYP2C19*2 (P < 0.001) and PXR 66034 T > C (P = 0.028) accounted for 47% of the variation in 4-OH-CPA plasma concentration. Among these variants, CYP2B6 -750 T > C and CYP2C19*2 were selected as the combination genetic marker because these two SNPs contributed the most to the inter-individual variability in 4-OH-CPA concentration, accounting for 23.6% and 21.5% of the variation, respectively. Extensive metabolizers (EMs) (CYP2B6 -750TT, CYP2C19*1*1) had significantly higher median 4-OH-CPA plasma concentrations (34.8, 11.0 and 6.6 ng ml(-1) for EMs, intermediate metabolizers (IMs) and poor metabolizers (PMs), P < 0.0001), higher risks of leukocytopenia (OR = 7.538, 95% CI 2.951, 19.256, P < 0.0001) and gastrointestinal toxicity (OR = 7.579, 95% CI 2.934, 19.578, P < 0.0001), as well as shorter median time to achieve complete remission (13.2, 18.3 and 23.3 weeks for EMs, IMs and PMs, respectively, P = 0.026) in LN patients than PMs (CYP2B6 -750CC, CYP2C19*2*2) and IMs.

Conclusions: Our findings have indicated that genetic markers of drug metabolizing enzymes could predict the 4-hydroxylation, adverse reactions and clinical efficacy of CPA. This is a necessary first step towards building clinical tools that will help assess clinical benefit and risk before undergoing CPA treatment in Chinese SLE patients.

Keywords: CYP2B6; CYP2C19; cyclophosphamide; lupus; pharmacogenetics.

© 2015 The British Pharmacological Society.

Figures

Figure 1

Study algorithm, including patient enrolment, study assignments, exclusion and outcomes

Figure 2

Scatterplots depicting the plasma concentration of cyclophosphamide (CPA) and 4‐hydroxycyclophosphamide (4‐OH‐CPA) classified by the combination genetic marker of CYP2C19*2 and CYP2B6 ‐750 T > C. (A) Scatter plot of CPA concentration grouped by genetic markers. (B) Scatter plot of 4‐OH‐CPA concentration grouped by genetic markers. Each dot represents the concentration data of one patient and the median value in each genotype is shown with a bar. The P values of Kruskal–Wallis H test are listed at the right of each plot. Extensive metabolizer (EM) was defined as CYP2C19*1*1 and CYP2B6 ‐750TT genotype while poor metabolizer (PM) was defined as CYP2C19*2*2 and CYP2B6 ‐750CC genotype. Patients with mixed genotypes at these two loci were defined as intermediate metabolizers (IM)* P < 0.05 (Dunn's multiple comparison tests between two groups).

Figure 3

Kaplan–Meier estimates of response rate in different patients. (A) Primary end point patients. (B) Secondary end point of patients. The primary end point was complete remission after 6 months of treatment. Secondary end points included response (defined as partial remission), changes in clinical parameters (including proteinuria, serum albumin, serum creatinine, and serum C3 values), and adverse effects (including leukopenia, infections, gastrointestinal symptoms, amenorrhea, hair loss, liver function disorder, transient increase in serum creatinine level, etc)