Proteomic analysis of imatinib-resistant CML-T1 cells reveals calcium homeostasis as a potential therapeutic target.

Chronic myeloid leukemia (CML) therapy has markedly improved patient prognosis after introduction of imatinib mesylate for clinical use. However, a subset of patients develops resistance to imatinib and other tyrosine kinase inhibitors (TKIs), mainly due to point mutations in the region encoding the kinase domain of the fused BCR-ABL oncogene. To identify potential therapeutic targets in imatinib­resistant CML cells, we derived imatinib-resistant CML-T1 human cell line clone (CML-T1/IR) by prolonged exposure to imatinib in growth media. Mutational analysis revealed that the Y235H mutation in BCR-ABL is probably the main cause of CML-T1/IR resistance to imatinib. To identify alternative therapeutic targets for selective elimination of imatinib-resistant cells, we compared the proteome profiles of CML-T1 and CML-T1/IR cells using 2-DE-MS. We identified eight differentially expressed proteins, with strongly upregulated Na+/H+ exchanger regulatory factor 1 (NHERF1) in the resistant cells, suggesting that this protein may influence cytosolic pH, Ca2+ concentration or signaling pathways such as Wnt in CML-T1/IR cells. We tested several compounds including drugs in clinical use that interfere with the aforementioned processes and tested their relative toxicity to CML-T1 and CML-T1/IR cells. Calcium channel blockers, calcium signaling antagonists and modulators of calcium homeostasis, namely thapsigargin, ionomycin, verapamil, carboxyamidotriazole and immunosuppressive drugs cyclosporine A and tacrolimus (FK-506) were selectively toxic to CML-T1/IR cells. The putative cellular targets of these compounds in CML-T1/IR cells are postulated in this study. We propose that Ca2+ homeostasis can be a potential therapeutic target in CML cells resistant to TKIs. We demonstrate that a proteomic approach may be used to characterize a TKI-resistant population of CML cells enabling future individualized treatment options for patients.

Interrelations between plasma renin activity, aldosterone, and sympathetic nervous system activity in essential hypertension.

Interrelations were investigated between plasma renin activity (PRA), dopamine-beta-hydroxylase activity (DBH), plasma aldosterone (PA), plasma cortisol (PC) and plasma sodium concentration (PNa) in renal vein blood of essential hypertension patients in recumbent position. The patients were divided in compliance with the WHO classification into two groups of stage I and stage II of essential hypertension. In stage I a negative correlation was found in all samples of blood between PA and PNa. This means that in recumbent position in stage I the mechanism of regulation sodium -- aldosterone is maintained. In stage II there were very significant correlations between DBH and PRA in the samples from both renal veins. The left renal vein blood gives the best information about secretion of the left adrenal gland. In stage II in samples from the left renal vein a negative correlation was proved between PA and PRA, and also two very similar negative correlations PA -- DBH and PC -- DBH were demonstrated. The results indicate that in recumbent position in stage II the renin secretion is mainly under the control of the sympathetic nervous system, even if the activity of the latter is depressed, normal or enhanced. The possible negative relation between sympathetic activity and corticosteroid secretion in stage II of essential hypertension is discussed.