Targeted treatment of imatinib-resistant chronic myeloid leukemia: Focus on dasatinib

cAMP Signaling Pathway Prevents Dasatinib-Induced Vascular Hyperpermeability

Dasatinib is a first-line pharmacotherapeutic treatment for chronic myeloid leukemia (CML). It is more effective than traditional treatments but causes adverse effects such as pleural effusion that limits its effective treatment cycle. Since pleural effusion is caused by vascular hyperpermeability and causes discontinuation of treatment with dasatinib, it is important to explore the mechanism of pleural effusion caused by dasatinib and how to prevent it. In this study, we investigated how dasatinib increase vascular permeability, and how it can be prevented. Cytotoxicity was observed in vascular endothelial cells or epithelial cells were exposed to high concentrations of dasatinib. Thus, it was observed in vascular endothelial cells such as human umbilical vascular endothelial cell (HUVEC). Vascular endothelial (VE)-cadherin is one of the important factors that control vascular permeability. When VE-cadherin expression decreases, vascular permeability increases, but it did not change with tyrosine kinase inhibitor exposure. Monolayer permeability significantly increased only with high concentration of dasatinib, but this increase was prevented by cAMP activation. Furthermore, dasatinib affects the cell morphology of HUVEC, with increased inter celluar space compared to control and bosutinib, which were also attenuated by cAMP activation. Dasatinib significantly affected permeability control of vascular endothelial cells compared to bosutinib and imatinib. These results indicated that the cAMP signaling pathway may be involved in the pleural effusion caused by dasatinib in CML patients.

Molecular Response to Imatinib and Its Correlation with mRNA Expression Levels of Imatinib Influx Transporter (OCT1) in Indian Chronic Myeloid Leukemia Patients

Background and objectives:

Imatinib mesylate is approved for the treatment of Chronic Myeloid Leukemia (CML). About 20% of patients with CML do not respond to treatment with Imatinib either initially or because of acquired resistance. In addition to mutated BCR-ABL1 kinase, the organic cation transporter1 (OCT1, encoded by SLC22A1) has been considered to contribute to Imatinib resistance in patients with chronic myeloid leukemia (CML). OCT1 has been reported to be the main influx transporter involved in Imatinib uptake into CML cells. To date, only a few studies have been reported on involvement of influx transporters in development of Imatinib resistance. Therefore this study was aimed to determine the expression level of Imatinib uptake transporter (OCT1) in CML patients and to correlate this level with molecular response.

Methods:

One hundred fifty eight patients on Imatinib were considered for gene expression analysis study for OCT1 gene. Total RNA was extracted from peripheral blood mononuclear cells. Complementary DNAs (cDNAs) were synthesized and Real Time Polymerase Chain Reaction (RQ-PCR) was performed.

Results:

High OCT1 expression was present in 81 (51.8%) patients and low OCT1 expression was in 77 (48.7%) patients. Low Sokal risk score group have a significantly high OCT1 expression (p=0.048). The rate of molecular response was higher in those with high OCT1 expression than in those with low OCT1 expression (p=0.05). Both event-free survival and median overall survival were significantly shorter in patients with low OCT1 expressions when compared to the patients with high OCT1 expression (p=0.03 and p=0.05).

Conclusions:

Our findings demonstrated that the mRNA expression level of OCT1 was significantly correlated with molecular response in CML patients. Based on these findings, present study believes that the pre-therapeutic higher expression of OCT1 may help to predict response to imatinib therapy in CML patients.

Molecular response to imatinib & its correlation with mRNA expression levels of imatinib influx & efflux transporters in patients with chronic myeloid leukaemia in chronic phase

Background & objectives:

Imatinib is the standard first-line treatment for chronic myeloid leukaemia (CML) patients. About 20 to 30 per cent patients develop resistance to imatinib and fail imatinib treatment. One of the mechanisms proposed is varying expression levels of the drug transporters. This study was aimed to determine the expression levels of imatinib transporter genes (OCT1, ABCB1, ABCG2) in CML patients and to correlate these levels with molecular response.

Methods:

Sixty three CML chronic phase patients who were on 400 mg/day imatinib for more than two years were considered for gene expression analysis study for OCT1, ABCB1 and ABCG2 genes. These were divided into responders and non-responders. The relative transcript expression levels of the three genes were compared between these two categories. The association between the expression values of these three genes was also determined.

Results:

No significant difference in the expression levels of OCT1, ABCB1 and ABCG2 was found between the two categories. The median transcript expression levels of OCT1, ABCB1 and ABCG2 genes in responders were 26.54, 10.78 and 0.64 versus 33.48, 7.09 and 0.53 in non-responders, respectively. A positive association was observed between the expression of the ABCB1 and ABCG2 transporter genes (r=0.407, P<0.05) while no association was observed between the expression of either of the ABC transporter genes with the OCT1 gene.

Interpretation & conclusions:

Our findings demonstrated that the mRNA expression levels of imatinib transporter genes were not correlated with molecular response in CML patients. Further studies need to be done on a large sample of CML patients to confirm these findings.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

Intracellular protein trafficking kinetics in chronic myeloid leukemia stem cells using a microfluidic platform

The oncogenic fusion protein BCR-ABL is produced by chronic myeloid leukemia (CML) cells and functions as an abnormal, constitutively active tyrosine kinase that interferes with normal migratory and apoptotic behaviour of cells. Small molecule tyrosine kinase inhibitors (TKIs), such as dasatinib, eliminate CML progenitor cells, but fail to target the stem cell fraction resulting in persistent disease. In order to achieve a cure for CML in the majority of patients, we need an improved understanding of intracellular signalling dynamics, including the shuttling of BCR-ABL between cytosolic and nuclear compartments. In the past, the instability of BCR-ABL in assays using conventional immunohistochemical techniques has made this difficult and has not allowed for reliable analysis at the single cell level. Here we show how the utilization of rapid on-chip cell fixation within a microfluidic platform provides a means to immunofluorescently analyze the spatiotemporal localization of both BCR-ABL and c-ABL, as well as the linked apoptosis mediator, BCL-XL, in arrays of single CD34+ CML stem/progenitor cells, without cell loss. We demonstrate this proceeds up to 4 times faster than benchtop methods. Our results indicate that whilst both BCR-ABL and c-ABL shuttle from the cytoplasm to the nucleus following dasatinib treatment, the temporal dynamics are not synchronized. The microfluidic platform has the potential to provide insights into the intracellular signalling events in single cells. The ability to examine signalling events and assess BCR-ABL expression/activity in isolated cells in "real-time" may help elucidate the characteristics of rare CML stem cell events, which lead to the resistance of CML stem cells to TKIs.