A clinical observation of Chinese chronic myelogenous leukemia patients after discontinuation of tyrosine kinase inhibitors

Combination Therapies in Chronic Myeloid Leukemia for Potential Treatment-Free Remission: Focus on Leukemia Stem Cells and Immune Modulation

Although tyrosine Kinase Inhibitors (TKI) has revolutionized the treatment of chronic myeloid leukemia (CML), patients are not cured with the current therapy modalities. Also, the more recent goal of CML treatment is to induce successful treatment-free remission (TFR) among patients achieving durable deep molecular response (DMR). Together, it is necessary to develop novel, curative treatment strategies. With advancements in understanding the biology of CML, such as dormant Leukemic Stem Cells (LSCs) and impaired immune modulation, a number of agents are now under investigation. This review updates such agents that target LSCs, and together with TKIs, have the potential to eradicate CML. Moreover, we describe the developing immunotherapy for controlling CML.

Tiny Actors in the Big Cellular World: Extracellular Vesicles Playing Critical Roles in Cancer

Communications among cells can be achieved either via direct interactions or via secretion of soluble factors. The emergence of extracellular vesicles (EVs) as entities that play key roles in cell-to-cell communication offer opportunities in exploring their features for use in therapeutics; i.e., management and treatment of various pathologies, such as those used for cancer. The potential use of EVs as therapeutic agents is attributed not only for their cell membrane-bound components, but also for their cargos, mostly bioactive molecules, wherein the former regulate interactions with a recipient cell while the latter trigger cellular functions/molecular mechanisms of a recipient cell. In this article, we highlight the involvement of EVs in hallmarks of a cancer cell, particularly focusing on those molecular processes that are influenced by EV cargos. Moreover, we explored the roles of RNA species and proteins carried by EVs in eliciting drug resistance phenotypes. Interestingly, engineered EVs have been investigated and proposed as therapeutic agents in various in vivo and in vitro studies, as well as in several clinical trials.

Basic knowledge on BCR-ABL1-positive extracellular vesicles

Chronic myelogenous leukemia (CML) is a hematological malignancy characterized by the excessive proliferation of myeloid progenitors. In the case of CML, these extracellular vesicles (EVs) were shown to communicate with hematopoietic stem cells, mesenchymal stem cells, myeloid derived suppressor cells and endothelial cells determining a beneficial microenvironment for the CML clone. Moreover, as these EVs are marked through BCR-ABL1, they were shown to be useful in clinical research in determining the grade of molecular remission with further studies being needed to determine if they are better or worse at predicting CML relapse. More than this, we consider BCR-ABL1-positive EVs to represent only a stepping-stone for other malignancies that also present fusion genes that are loaded in EVs.

The Impact of Tyrosine Kinase Inhibitors on Chronic Myeloid Leukemia Stem Cells and the Implication in Discontinuation

BCR-ABL1 tyrosine kinase inhibitors (TKIs) are selective therapies for patients with chronic myeloid leukemia (CML) and induce deep molecular response (DMR). However, ∼60% of patients relapse after the discontinuation of TKIs. Relapse after discontinuation is likely due the inability of TKIs to eradicate CML stem cells (CML-LSCs). In our previous study, 12 out of 22 patients maintained a stable DMR after TKI withdrawal, and we found that fewer patients who were treated with second-generation TKI relapsed compared with those receiving imatinib. Therefore, we hypothesized that second-generation TKIs and imatinib may have different effects on CML-LSCs, which may affect the clinical outcome after TKI discontinuation. To investigate this, we established a TKI discontinuation model in vitro by treating CML CD34⁺ cells with imatinib and dasatinib continuously for 72 h and then removing the TKI for 24 h. Colony-forming cell (CFC) assays, apoptosis assessment, and proteomic analysis were then performed. We found that TKI discontinuation resulted in less proliferation and CFC output in dasatinib-treated cells compared with imatinib. However, the dasatinib-treated group exhibited increased apoptosis. In the proteomics analysis, we identified 160 upregulated and 151 downregulated proteins when the two TKI discontinuation groups were compared. Importantly, proteins involved in NAD⁺ nucleosidase activity, mitochondrial ATP synthesis coupled proton transport, and oxidative phosphorylation were significantly expressed, which were mainly involved in metabolic processes. In conclusion, we demonstrate that imatinib and dasatinib have clear differential effects on CML-LSCs through the regulation of mitochondria oxidative phosphorylation, which may provide a new target for eliminating CML-LSCs in the context of TKI discontinuation.

Monitoring and Analysis of Chinese Chronic Myeloid Leukemia Patients Who Have Stopped Tyrosine Kinase Inhibitor Therapy

Discontinuation of tyrosine kinase inhibitor (TKI) therapy after achieving a persistent deep molecular response (DMR) is an urgently needed treatment goal for chronic myeloid leukemia (CML) patients and has been included in the National Comprehensive Cancer Network (NCCN) guidelines (version 2.2017) for CML. Indeed, various studies have confirmed the feasibility of discontinuing TKI therapy. In this study, we analyzed data from 45 CML patients who had discontinued TKI therapy. Univariate analysis was performed to predict factors that were potentially related to treatment-free remission (TFR) and identify the differences between early relapse and late relapse. Out of the 45 patients, 20 exhibited molecular relapse after a median follow-up of 18 months (range, 1-54 months), and the estimated TFR at 24 months was 40%. The univariate analysis revealed that a high Sokal score and interruptions or dose reductions during TKI treatment were the only baseline factors associated with poor outcomes. Our results indicate that TKI discontinuation could be successfully put into practice in China.

MiR-657/ATF2 Signaling Pathway Has a Critical Role in Spatholobus suberectus Dunn Extract-Induced Apoptosis in U266 and U937 Cells

Though Spatholobus suberectus Dunn (SSD) has been reported to have anti-virus, anti-osteoclastogenesis, and anti-inflammation activities, its underlying anti-cancer mechanism has never been elucidated in association with the role of miR-657 in endoplasmic reticulum (ER) stress-related apoptosis to date. SSD treatment exerted cytotoxicity in U266 and U937 cells in a dose-dependent manner. Also, apoptosis-related proteins such as PARP, procaspase-3, and Bax were regulated by SSD treatment. Furthermore, Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay revealed that a number of apoptotic bodies were increased by SSD. Interestingly, the ER stress-related proteins such as p-ATF2 and CHOP were elevated by SSD. Interestingly, reactive oxygen species (ROS) generation and cytotoxicity by SSD treatment were significantly reduced by N-Acetyl-L-cysteine (NAC). Among the microRNAs (miRNAs) regulated by SSD treatment, miR-657 was most significantly reduced by SSD treatment. However, an miR-657 mimic reversed SSD-induced apoptosis by the attenuation of the expression of p-ATF2, CHOP, and PARP cleavage. Overall, these findings provide scientific evidence that miR657 is an onco-miRNA targeting the ER stress signal pathway and SSD induces apoptosis via the inhibition of miR-657, ROS, and the activation of p-ATF2 and CHOP as a potent anti-cancer agent for myeloid-originated hematological cancer.