Genotypes of the Gene Encoding the Membrane Transporter SLC22A4 Are Associated with Molecular Relapse-Free Survival after Discontinuation of Imatinib Therapy in Patients with Chronic Myeloid Leukemia

Introduction: The single nucleotide polymorphism (SNP) rs460089 (G/C) located in the promotor of SLC22A4 (transporter hOCTN1) was identified as a prognostic factor for the outcome of chronic myeloid leukaemia patients treated with imatinib first line (Jaruskova et al. JECCR 2017). Patients with GC genotype had significantly higher probability of achievement of sustained major molecular response (MMR, BCR-ABL≤0.1% IS) as compared with patients with GG. We investigated differences in the outcome after imatinib cessation in EURO-SKI patients according to the genotypes of the SNP rs460089.

Methods: DNA analysis was performed by TaqMan SNP genotyping assay using StepOnePlus RQ-PCR System (Thermofisher Scientific). In addition to the inclusion criteria defined for prognostic analysis in Saussele et al. (Lancet Oncology 2018), all patients with interferon pre-treatment were excluded. Data on sex, duration of IM treatment, of deep molecular response and age at time of imatinib discontinuation as well as molecular status at 6 months thereafter were available for 178 patients. Logistic regression was used to investigate factors affecting MMR maintenance at 6 months. Level of significance was 0.05.

Results: Of 178 patients, 106 (60%) maintained MMR 6 months after imatinib stop. GC genotype was identified in 64 patients, GG in 96 and CC in 18. Most beneficial for MMR maintenance was genotype GC (72%, 95% confidence interval (CI): 60-82%), followed by CC (61%, CI: 38-80%) and GG (51%, CI: 41-61%). Overall, the SNP rs460089 was associated with MMR maintenance (p=0.0335) with a significantly higher odds ratio (OR) for maintenance for GC genotype vs. GG (2.451, CI: 1.247-4.819, p=0.0093) but not for CC vs. GG (1.507, CI: 0.539-4.216, p=0.4343). Only duration of TKI treatment was significant (OR: 1.157, CI: 1.014-1.319, p=0.0303) when added to genotypes in multiple regression. The OR of GC vs. GG was slightly modified to 2.311 (1.164-4.588, p=0.0166).

Conclusions: Based on observed data we suppose that the GC genotype of the SNP rs460089 is associated with sufficient intracellular concentration of imatinib allowing more efficient targeting of CML cells during the treatment. This resulted in a higher proportion of patients who sustained MMR after imatinib stop as compared with patients with GG. Longer duration of imatinib treatment increased the probability of MMR maintenance after imatinib cessation also in patients with GG. The frequency of CC was low and outcome in between GC and GG. The SNP rs460089 may provide an independent prognostic factor for molecular response maintenance after imatinib cessation.

Supported by MZCR 00023736.