ABSTRACT
Novel epigenetic therapies targeting bromodomain and extra-terminal (BET) family proteins have shown therapeutic efficacy in diverse hematologic malignancies and solid cancers. However, the mechanism of resistance remains poorly understood. In the present study, we evaluated the mechanism of resistance to the BET inhibitor I-BET151 and its signaling pathway to overcome resistance in U937 cells. Treatment with 10 µM I-BET151 significantly induced growth inhibition, apoptosis, and cell cycle modulation, including increases in sub-G1 and G1 phases and decreases in S and G2/M phases, in U937 cells. However, no significant changes in these factors were detected in I-BET151-resistant U937 (U937R) cells. Combined treatment with I-BET151 and IKK inhibitor VII synergistically induced apoptosis in U937 and U937R cells. Increased expression of bromodomain-containing protein (BRD) 2, BRD4, and nuclear NF-κBp65 proteins was detected in U937R cells. IKK inhibitor VII inhibited the activation of NF-κBp65 protein in the nuclear fraction of U937R cells. These findings suggest that resistance to I-BET151 in U937R cells is related to constitutive activation of the NF-κB signaling pathway via increased expression of both BRD2 and BRD4. Targeting the NF-κB signaling pathway may be an effective therapeutic strategy to enhance or restore the sensitivity to I-BET151 in U937 cells.
Subject(s)
Cell Cycle/drug effects , Drug Resistance, Neoplasm/drug effects , Hematologic Neoplasms/metabolism , Heterocyclic Compounds, 4 or More Rings/pharmacology , Neoplasm Proteins/metabolism , Nuclear Proteins/metabolism , Protein Serine-Threonine Kinases/metabolism , Signal Transduction/drug effects , Transcription Factor RelA/metabolism , Transcription Factors/metabolism , Cell Cycle/genetics , Cell Cycle Proteins , Drug Resistance, Neoplasm/genetics , Hematologic Neoplasms/drug therapy , Hematologic Neoplasms/genetics , Hematologic Neoplasms/pathology , Humans , Neoplasm Proteins/antagonists & inhibitors , Neoplasm Proteins/genetics , Nuclear Proteins/antagonists & inhibitors , Nuclear Proteins/genetics , Protein Serine-Threonine Kinases/antagonists & inhibitors , Protein Serine-Threonine Kinases/genetics , Signal Transduction/genetics , Transcription Factor RelA/genetics , Transcription Factors/antagonists & inhibitors , Transcription Factors/genetics , U937 CellsABSTRACT
The pseudohyperkalemia in thrombocytosis is assumed to be due to potassium released from blood cells during blood clotting as reported previously, but its mechanisms remain to be cleared. Although plasma potassium measurements with blood collection tubes containing heparin are performed in many hospitals to avoid pseudohyperkalemia, the burden on patients may come out with further blood sampling by another heparinized tube. Taken together, we investigated laboratory data possibly involved in pseudohyperkalemia in 184 samples from patients with myeloproliferative neoplasma (MPN), and studied estimation capability for true values of serum potassium, driving a correction formula by means of several laboratory data to explain the difference of measured potassium values (K-difference: serum value minus plasma value). Platelet count and mean corpuscular volume (MCV) were adopted as significant variables correlated to K-difference as a result of multiple regression analysis. A correction formula was driven by multiple regression equation with these two variables as follows: y = 0.0006 x 1+0.0004 x 2-0.177 (r= 0.885; x 1, platelet count; x 2, MPV). The correction formula was considered to be useful for estimating the true value of serum potassium in samples from patients with MPN because the corrected serum potassium value correlated highly with plasma potassium value (r = 0.885). These results propose that true values of serum potassium can be estimated by the correction of measured serum potassium values with platelet count and MCV, suggesting that not only quantitative factors but also qualitative factors may be involved in pseudohyperkalemia.
