Plasma imatinib levels and ABCB1 polymorphism influences early molecular response and failure-free survival in newly diagnosed chronic phase CML patients

Abstract

Achieving early molecular response (EMR) has been shown to be associated with better event free survival in patients with chronic phase chronic myeloid leukemia (CP-CML) on Imatinib therapy. We prospectively evaluated the factors influencing the 2-year failure free survival (FFS) and EMR to imatinib therapy in these patients including day29 plasma Imatinib levels, genetic variants and the gene expression of target genes in imatinib transport and biotransformation. Patients with low and intermediate Sokal score had better 2-year FFS compared to those with high Sokal Score (p = 0.02). Patients carrying ABCB1-C1236T variants had high day29 plasma imatinib levels (P = 0.005), increased EMR at 3 months (P = 0.044) and a better 2 year FFS (P = 0.003) when compared to those with wild type genotype. This translates to patients with lower ABCB1 mRNA expression having a significantly higher intracellular imatinib levels (P = 0.029). Higher day29 plasma imatinib levels was found to be strongly associated with patients achieving EMR at 3 months (P = 0.022), MMR at 12 months (P = 0.041) which essentially resulted in better 2-year FFS (p = 0.05). Also, patients who achieved EMR at 3 months, 6 months and MMR at 12 months had better FFS when compared to those who did not. This study suggests the incorporation of these variables in to the imatinib dosing algorithm as predictive biomarkers of response to Imatinib therapy.

Figure 1

Plasma imatinib levels predict early molecular response at 3 & 6 months and MMR at 12 months post imatinib therapy. (a) Plasma imatinib levels (median, range) on day29 with early molecular response at 3 months and (b) in patients with and without MMR to imatinib at 12 months. Statistical significance was calculated using Mann–Whitney U test.

Figure 2

ABCB1 polymorphism influences plasma imatinib levels and RNA Expression of ABC transporters influence intracellular Imatinib levels (b) Plasma imatinib levels on day29 post imatinib therapy in patients with ABCB1/MDR1 C1236T genotypes (wt (CC) n = 10; Het + Mut (CT + TT) n = 57). (b) Intracellular imatinib levels in patients with above or below median expression of ABCB1 (median expression-21.9), (c) ABCA3 (median expression-505 below median n = 23 vs above median n = 33) and (d) ABCC4 (median expression-28.4; below median n = 30 vs above median n = 26) RNA. The RNA expression of each gene was normalised to GAPDH and relative expression to CML001 using 2^-ddCT method. Statistical significance was calculated using Mann–Whitney U test.

Figure 3

Expression of imatinib influx and efflux transporters in bulk Vs CD34⁺ primary CML cells. (a) Expression of hOCT1, ABCB1/MDR1 and ABCG2 in CML bulk cells compared with expression of transporter expression in CML CD34 + (Leukemic stem cells) LSCs cells. Statistical significance was calculated using paired-T test. (b) Expression of hOCT1, ABCB1/MDR1 and ABCG2 in CD34⁺ cells from normal healthy donors vs. primary CML CD34⁺ cells where higher the dCt lower the expression and vice versa. Statistical significance was calculated using Mann–Whitney U test.

Figure 4

MDR1 polymorphisms, plasma imatinib levels, and RNA expression of efflux transporters influence FFS after imatinib therapy in patients with CP-CML. (a)–(c) Influence of MDR1 genotypes C1236T, G2677T & C3435T on FFS after imatinib therapy. (d) d. Influence of plasma imatinib levels on day29 on FFS. (e)–(f) Influence of ABCA6 and ABCC4 expression on FFS after imatinib therapy. RNA expression was normalised to GAPDH as the housekeeping gene and expressed relative to the expression in CML001 using 2^-ddCT method.