Current aspects in resistance against tyrosine kinase inhibitors in chronic myelogenous leukemia

Targeting Aberrant Epigenetic Networks Mediated by PRMT1 and KDM4C in Acute Myeloid Leukemia

Transcriptional deregulation plays a major role in acute myeloid leukemia, and therefore identification of epigenetic modifying enzymes essential for the maintenance of oncogenic transcription programs holds the key to better understanding of the biology and designing effective therapeutic strategies for the disease. Here we provide experimental evidence for the functional involvement and therapeutic potential of targeting PRMT1, an H4R3 methyltransferase, in various MLL and non-MLL leukemias. PRMT1 is necessary but not sufficient for leukemic transformation, which requires co-recruitment of KDM4C, an H3K9 demethylase, by chimeric transcription factors to mediate epigenetic reprogramming. Pharmacological inhibition of KDM4C/PRMT1 suppresses transcription and transformation ability of MLL fusions and MOZ-TIF2, revealing a tractable aberrant epigenetic circuitry mediated by KDM4C and PRMT1 in acute leukemia.

Developing therapies for rare tumors: opportunities, challenges and progress

Introduction

Rare tumors account for one fourth of adult tumors; in children, rare tumors represent approximately 15-20% of childhood malignancies, thus accounting for a significant burden of disease. The rarity of these individual diseases creates many challenges, from developing a thorough understanding of the disease pathophysiology, clinical characterization, to the conduct of meaningful clinical trials and eventually the development of effective therapies.

Areas covered

Despite these challenges, substantial advances have been made in recent years including the development of novel clinical trial designs and endpoints including molecularly driven treatment trials that have resulted in approval of novel therapies for rare diseases. Collaboration amongst basic and clinical researchers, patient advocacy groups, industry and regulatory agencies has proven successful in select cases and holds promise for future progress in the treatment of rare tumors. In this review, we will highlight several examples of trials for rare tumors, with a focus on examples from pediatric oncology, where strong, nationwide collaborative groups have existed for many years.

Expert opinion

Future progress in developing therapies for rare tumors will depend not only on continued scientific advances, but also on collaboration between investigators from various disciplines, institutions, regulatory agencies and patient advocacy groups.

Blockade of the interaction between Bcr-Abl and PTB1B by small molecule SBF-1 to overcome imatinib-resistance of chronic myeloid leukemia cells

In this study, a synthetic steroidal glycoside SBF-1 had strong and preferential antitumor effects on the human chronic myeloid leukemia (CML) cell line K562 and its imatinib-resistant form K562/G. SBF-1 induced apoptosis in both cell lines without any effect on cell cycle arrest. It also inhibited the activation of PI3K/Akt pathway members, such as PI3K and Akt, as well as downstream targets mTOR and Bcl-2. Moreover, the degradation of the Bcr-Abl protein was induced by SBF-1 in a concentration- and time-dependent manner. Using a pull-down assay, SBF-1 was found to bind to both Bcr-Abl and PTP1B and disrupted the interaction between them. SBF-1 triggered the degradation of Bcr-Abl through ubiquitination via the lysosome pathway. Taking together these findings, this study, for the first time, suggests that the blockade of the interaction between Bcr-Abl and PTP1B may be a feasible strategy for the treatment of CML, especially CML with resistance to Bcr-Abl kinase inhibitor imatinib. Our study also indicates that SBF-1 may serve as a leading compound for novel anti-CML therapeutic agents.

UV Differentially Induces Oxidative Stress, DNA Damage and Apoptosis in BCR-ABL1-Positive Cells Sensitive and Resistant to Imatinib

Chronic myeloid leukemia (CML) cells express the active BCR-ABL1 protein, which has been targeted by imatinib in CML therapy, but resistance to this drug is an emerging problem. BCR-ABL1 induces endogenous oxidative stress promoting genomic instability and imatinib resistance. In the present work, we investigated the extent of oxidative stress, DNA damage, apoptosis and expression of apoptosis-related genes in BCR-ABL1 cells sensitive and resistant to imatinib. The resistance resulted either from the Y253H mutation in the BCR-ABL1 gene or incubation in increasing concentrations of imatinib (AR). UV irradiation at a dose rate of 0.12 J/(m²·s) induced more DNA damage detected by the T4 pyrimidine dimers glycosylase and hOGG1, recognizing oxidative modifications to DNA bases in imatinib-resistant than -sensitive cells. The resistant cells displayed also higher susceptibility to UV-induced apoptosis. These cells had lower native mitochondrial membrane potential than imatinib-sensitive cells, but UV-irradiation reversed that relationship. We observed a significant lowering of the expression of the succinate dehydrogenase (SDHB) gene, encoding a component of the complex II of the mitochondrial respiratory chain, which is involved in apoptosis sensing. Although detailed mechanism of imatinib resistance in AR cells in unknown, we detected the presence of the Y253H mutation in a fraction of these cells. In conclusion, imatinib-resistant cells may display a different extent of genome instability than their imatinib-sensitive counterparts, which may follow their different reactions to both endogenous and exogenous DNA-damaging factors, including DNA repair and apoptosis.