Bone marrow microenvironment (BMM) is the main sanctuary of leukemic stem cells (LSCs) and protects these cells against conventional therapies. However, it may open up an opportunity to target LSCs by breaking the close connection between LSCs and the BMM. The elimination of LSCs is of high importance, since they follow cancer stem cell theory as a part of this population. Based on cancer stem cell theory, a cell with stem cell-like features stands at the apex of the hierarchy and produces a heterogeneous population and governs the disease. Secretion of cytokines, chemokines, and extracellular vesicles, whether through autocrine or paracrine mechanisms by activation of downstream signaling pathways in LSCs, favors their persistence and makes the BMM less hospitable for normal stem cells. While all details about the interactions of the BMM and LSCs remain to be elucidated, some clinical trials have been designed to limit these reciprocal interactions to cure leukemia more effectively. In this review, we focus on chronic myeloid leukemia and acute myeloid leukemia LSCs and their milieu in the bone marrow, how to segregate them from the normal compartment, and finally the possible ways to eliminate these cells.
Antibody‐drug conjugates (ADCs) are a new class of anti‐cancer drugs that consist of a monoclonal antibody, a highly potent small‐molecule cytotoxic drug, and a chemical linker between the two. ADCs can selectively deliver cytotoxic drugs to cancer cells leading to a reduced systemic exposure and a wider therapeutic window. To date, nine ADCs have received marketing approval, and over 100 are being investigated in nearly 600 clinical trials. The target antigens of at least eight out of the nine approved anti‐cancer ADCs and of 69 investigational ADCs are present on extracellular vesicles (EVs) (tiny particles produced by almost all types of cells) that may carry their contents into local and distant cells. Therefore, the EVs have a potential to mediate both the anti‐cancer effects and the adverse effects of ADCs. In this overview, we discuss the mechanisms of action of ADCs and the resistance mechanisms to them, the EV‐mediated resistance mechanisms to small molecule anti‐cancer drugs and anti‐cancer monoclonal antibodies, and the EVs as modifiers of ADC efficacy and safety.
Emerging evidence shows that long noncoding RNAs (lncRNAs) participate in various cellular processes, and that plasmacytoma variant translocation 1 (PVT1), a newly described oncogene that interacts with various molecules such as p15, p16, NOP2, and c-Myc, is a major contributing factor in tumor development. However, the role of this oncogene remains unknown in the pathogenesis of acute lymphoblastic leukemia (ALL), the most prevalent form of childhood leukemia. In this study, we first measure the expression level of PVT1 in a Jurkat cell line, then small interfering (siRNA) PVT1 is applied to demonstrate the impact of PVT1 knockdown in apoptosis, proliferation, the cell cycle, and its downstream targets. Our findings show that lncRNA was significantly higher in the ALL cell line than normal lymphocytes and that PVT1 knock-down increased the rate of apoptosis, caused G0/G1 arrest in the cell cycle, reduced the proliferation rate, and, above all, reduced the stability of c-Myc protein. All findings were confirmed at the molecular level. Our results may indicate the role of PVT1 knock-down in the suppression of ALL development and might provide an option for targeted therapy for leukemic conditions.
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