BIK (Bcl2-Interacting Killer) CpG Methylation Status in Multiple Myeloma Patients: a Potential Predictor of Relapsed/Refractory Disease.

BIK (bcl2-interacting killer) is the founding member of the BH3-only family proapoptotic proteins and is implicated in the selection of B cells in humans. The expression of BIK in cancer is prevented by chromosomal deletions or by epigenetic silencing. On the other hand, BIK upregulation is induced by proteasome inhibitors such as bortezomib and MG132. Although it has been shown that BIK is a target of epigenetic silencing in the IL-6 dependent multiple myeloma cell line KAS-6/1, no studies exist regarding the CpG methylation status of BIK in primary tumors. We wished to examine the CpG methylation status of BIK in patients with multiple myeloma (MM).

Bone marrow aspirate samples from individuals with MM were obtained at diagnosis. Methylation-specific PCR (MSP) was employed to study methylation in the BIK CpG island. Genomic DNA was isolated and bisulphite modification performed using commercially available kits (QIAmp DNA mini kit, Qiagen and EZ DNA methylation kit, ZymoResearch respectively). Control methylated (CpG GenomeTM Universal Methylated, Chemicon International) and unmethylated genomic DNAs were included in each experiment. Ten bone marrow samples from individuals with borderline thrombocytopenia, that proved to have no haematological malignancy, served as negative controls. Logistic regression analyses were used to measure the association between gene methylation and age, ISS stage, ECOG performance status, extramedullary disease, bone disease, anemia (Hb 10 mg/dl), serum albumin and beta 2 microglobulin levels and relapsed/refractory disease.

Methylation in the BIK CpG island was studied in 40 MM patients (21 male, 19 female, mean age 66). ISS staging were as follows: stage I 14 patients (36%), II 12 patients (31%), III 12 patients (31%). Methylation of the BIK CpG island was founded in 16 patients (40%) and men were more likely to be methylated (OR=3.08, p=0.098). No correlation was found between BIK CpG methylation and age, ECOG performance status, ISS staging, anemia, beta 2 microglobulin levels, albumin levels, and overall survival. Patients methylated for BIK had a 2-fold tendency to have bone disease (p=0.35) and a 3-fold tendency to have extramedullary disease (p=0.14). Notable, patients with methylated BIK had a higher risk of relapsed/refractory disease (OR=5.4, p=0.033).

To the best of our knowledge, this is the first demonstration of aberrant methylation in the BIK CpG island in MM patients. Interesting associations between BIK CpG methylation and some relevant clinical parameters in patients with MM were suggested by the data. Most importantly, BIK CpG methylation in this series of patients was found to be strongly associated with relapsed/refractory disease. These findings warrant further evaluation in a larger sample of patients in order to better define the prognostic and clinical utility of BIK methylation in MM. Patients with refractory/relapsed disease could possibly benefit from agents enhancing BIK expression.

No relevant conflicts of interest to declare.