Investigating drugs that enhance imatinib uptake and factors which contribute to the functional activity of OCT-1 CML Cells.

Abstract

In CML cells, the functional OCT-1 activity (OA) in mononuclear cells (MNC) from de novo chronic myeloid leukaemia patients in chronic phrase (CP-CML) is significantly associated with imatinib-mediated in vitro tyrosine kinase inhibition and is a strong indicator of imatinib response. Here we identified candidate drugs as potential OA enhancers using Connectivity Map analysis (CMAP). Their effects on OA were extensively validated in CML cell lines and patient samples, together with 12 NSAIDs and 11 commonly prescribed drugs. A significant enhancement of OA was observed after the treatment with diclofenac. Importantly this increase in OA translated to a significant increase in BCR-ABL kinase inhibition. Additionally, the long-term co-administration of diclofenac sensitized CML cells to imatinib on cell proliferation. In CML patients’ mononuclear (MNC) samples, diclofenac significantly increased OA especially in patients with low OA. In contrast, ibuprofen significantly decreased the OA in CML cell lines and primary samples. This effect on OA also translated into a reduction in BCR-ABL kinase inhibition and an increase in cell growth in the presence of imatinib. Unlike diclofenac, the inhibitory effect of ibuprofen is also observed in normal cells most likely in an independent manner from OCT-1 protein. The enhancement of OA by diclofenac could be eliminated in the presence of Actinomycin D (a transcription inhibitor), indicating that diclofenac regulated OA at a transcriptional level. However, the expression of SLC22A1 (OCT-1) remained unchanged after treatment with diclofenac. Since diclofenac is an inhibitor for cyclooxygenase-2 (COX-2), the potential involvement of COX-2 in OA regulation was investigated. The plasma concentration of 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2), a prostaglandin product by COX-2, was significantly associated with OA in CP-CML. Given 15d-PGJ2 is a potent agonist for peroxisome proliferator-activated receptor γ (PPARγ) and diclofenac is also a known PPARγ ligand, whether PPARγ had a role in OA regulation was then investigated. Significant increase in OA in KU812 cells was observed after treatment with PPARγ antagonist GW9962, while treatment with PPARγ agonists (GW1929, troglitazone, or rosiglitazone) significantly decreased OA. In addition, there was a significant negative association between OA and the PPARγ transcriptional activity in CP-CML MNC collected at diagnosis. Further identification of the key factor contributing to high PPARγ activation in patients with low OA may provide better understanding of intrinsic OA interpatient variability, as well as the clinical and biological relevance of PPARγ in CML.