Resistance to imatinib in chronic myelogenous leukemia: mechanisms and clinical implications

Aberrant alternative splicing in breast cancer

Alternative splicing is critical for human gene expression regulation, which plays a determined role in expanding the diversity of functional proteins. Importantly, alternative splicing is a hallmark of cancer and a potential target for cancer therapeutics. Based on the statistical data, breast cancer is one of the top leading causes of cancer-related deaths in women worldwide. Strikingly, alternative splicing is closely associated with breast cancer development. Here, we seek to provide a general review of the relationship between alternative splicing and breast cancer. We introduce the process of alternative splicing and its regulatory role in cancers. In addition, we highlight the functions of aberrant alternative splicing and mutations of splicing factors in breast cancer progression. Moreover, we discuss the role of alternative splicing in cancer drug resistance and the potential of being targets for cancer therapeutics.

Decreased expression of microRNA-214 contributes to imatinib mesylate resistance of chronic myeloid leukemia patients by upregulating ABCB1 gene expression

The aim of the present study was to determine the expression of adenosine triphosphate binding cassette subfamily B member 1 (ABCB1) gene and its protein P-glycoprotein (PGP) in bone marrow mononuclear cells from chronic myeloid leukemia (CML) patients with imatinib mesylate (IM) resistance, or IM-resistant CML K562 cells. In addition, the molecular mechanism of action of microRNA (miR)-214 on ABCB1 in IM resistance was investigated. A total of 26 CML patients with IM resistance were included in the present study. In addition, 31 CML patients who did not have IM resistance were included as the control group. Bone marrow was collected from all subjects. The K562R cell line, which is a K562 cell line with IM resistance, was used for cellular studies. Reverse transcription-quantitative polymerase chain reaction was used to determine the expression of ABCB1 mRNA and miR-214 in cells. Western blotting was employed to determine the expression of PGP. Dual luciferase reporter assay was carried out to identify interactions between ABCB1 mRNA and miR-214. MTT assay was used to determine the survival rate of cells. ABCB1 mRNA and PGP expression was upregulated in bone marrow mononuclear cells from CML patients with IM resistance. K562R cells had higher ABCB1 and PGP expression than K562 cells, potentially due to their different sensitivity to IM. Expression miR-214 was decreased in bone marrow mononuclear cells from patients with IM resistance and K562R cells. Notably, miR-214 was able to bind with the 3′-untranslated region, seed region of ABCB1 mRNA to regulate its expression. In addition, elevated expression of miR-214 restored IM sensitivity to K562R cells potentially by affecting ABCB1 expression. The present study demonstrated that upregulated expression of ABCB1 mRNA and PGP in bone marrow mononuclear cells from CML patients with IM resistance may be associated with the downregulation of miR-214. In addition, miR-214 may participate in the IM resistance of CML patients by regulating ABCB1 expression.

Characterization and targeting of neoplastic stem cells in Ph+ chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of an oncogenic fusion gene, BCR–ABL1. This fusion gene produces a cytoplasmic protein with tyrosine kinase activity that acts as a main driver of oncogenesis and abnormal proliferation of myeloid cells in CML. Targeted therapy with BCR–ABL1 tyrosine kinase inhibitors (TKIs) such as imatinib is followed by long-term responses in most patients. However, despite continuous treatment, relapses occur, suggesting the presence of TKI-resistant neoplastic stem cells in these patients. Here, we discuss potential mechanisms and signaling molecules involved in the prosurvival and self-renewal capacity of CML neoplastic stem cells as well as antigens expressed by these cells. Several of these signaling molecules and cell surface antigens may serve as potential targets of therapy and their use may overcome TKI resistance in CML in the future.

A common BIM deletion polymorphism mediates intrinsic resistance and inferior responses to tyrosine kinase inhibitors in cancer

Tyrosine kinase inhibitors (TKIs) elicit high response rates among individuals with kinase-driven malignancies, including chronic myeloid leukemia (CML) and epidermal growth factor receptor-mutated non-small-cell lung cancer (EGFR NSCLC). However, the extent and duration of these responses are heterogeneous, suggesting the existence of genetic modifiers affecting an individual's response to TKIs. Using paired-end DNA sequencing, we discovered a common intronic deletion polymorphism in the gene encoding BCL2-like 11 (BIM). BIM is a pro-apoptotic member of the B-cell CLL/lymphoma 2 (BCL2) family of proteins, and its upregulation is required for TKIs to induce apoptosis in kinase-driven cancers. The polymorphism switched BIM splicing from exon 4 to exon 3, which resulted in expression of BIM isoforms lacking the pro-apoptotic BCL2-homology domain 3 (BH3). The polymorphism was sufficient to confer intrinsic TKI resistance in CML and EGFR NSCLC cell lines, but this resistance could be overcome with BH3-mimetic drugs. Notably, individuals with CML and EGFR NSCLC harboring the polymorphism experienced significantly inferior responses to TKIs than did individuals without the polymorphism (P = 0.02 for CML and P = 0.027 for EGFR NSCLC). Our results offer an explanation for the heterogeneity of TKI responses across individuals and suggest the possibility of personalizing therapy with BH3 mimetics to overcome BIM-polymorphism-associated TKI resistance.