Downregulation of Receptor Activator of Nuclear Factor kB Ligand (RANKL) in Chronic Myeloid Leukemia Patients Receiving Imatinib Mesylate Is Dose-Dependent.

The receptor activator of the nuclear factor kB ligand (RANKL) is a key molecule in the pathogenesis of malignant osteolytic lesions in multiple myeloma or bone metastases in prostate and breast cancer. Inhibition of RANKL is therefore a promising new therapy for controlling bone loss and pain in bone tumors and associated osteolysis. Changes in bone and mineral metabolism developing in a proportion of patients taking imatinib for either chronic myeloid leukemia (CML) or gastrointestinal stromal tumors have previously been described. The aim of our study was to verify in CML patients the effect of imatinib on RANKL bone marrow molecular expression.

The study included 13 CML patients (7 males, 6 females, median age 37 yrs). Six were treated with imatinib at standard dosage (400 mg) and the remaining 7 at higher doses (> 400 mg). The median duration of imatinib therapy was 28 months (range 13 – 44 months).

The RANKL gene expression level was determined by Real-Time PCR using 1X Platinum SYBR Green qPCR SuperMix-UDG. Variations in RANKL gene expression level were estimated by comparing the values of 2^{−Δ Δ Ct} obtained in CML patients at diagnosis and during imatinib treatment. For each of the tested cases the sample at diagnosis was utilized as calibrator and 28S rRNA was used as reference gene.

Eight (62%) patients showed a downregulation of RANKL gene expression, the fold decrease ranging from 0.01 to 0.47 as compared to the value at diagnosis; among these 8 patients, 6 (75%) were treated with imatinib at standard dosage. Instead, 5 (38%) patients showed an upregulation of RANKL, the gene expression fold increase ranging from 1.43 to 4.94 as compared to the gene level observed at CML onset; all these 5 patients were treated with high doses of imatinib. There was no association between RANKL expression and the duration of imatinib treatment.

These findings suggest that imatinib mesylate could control RANKL expression. At standard dosage, imatinib can downregulate RANKL production. The RANKL upregulation observed in CML patients treated with high doses of imatinib could be explained by the possible activation of the immune system cells, such as T and B cells, induced by the tyrosine kinases inhibitor. Further studies are needed to verify the minimal effective dose of imatinib on RANKL expression, with the aim of administering it as an antiosteolytic agent in such diseases as osteoporosis, metastatic bone disease, and multiple myeloma.