Global miRNA profiling reveals key molecules that contribute to different chronic lymphocytic leukemia incidences in Asian and Western populations

It has been known for decades that the incidence of chronic lymphocytic leukemia (CLL) is significantly lower in Asia than in Western countries, but the reason responsible for this difference still remains a major knowledge gap. Using GeneChip® miRNA array to analyze the global microRNA expression in B lymphocytes from Asian and Western CLL patients and healthy individuals, we have identified microRNA with CLL-promoting or suppressive functions that are differentially expressed in Asian and Western individuals. In particular, miR-4485 is upregulated in CLL patients of both ethnic groups, and its expression is significantly lower in Asian healthy individuals. Genetic silencing of miR-4485 in CLL cells suppresses leukemia cell growth, whereas ectopic expression of miR-4485 promotes cell proliferation. Mechanistically, miR-4485 exerts its CLL-promoting activity by inhibiting the expression of TGR5 and activating the ERK1/2 pathway. In contrast, miR-138, miR-181a, miR- 181c, miR-181d, and miR-363 with tumor-suppressive function are highly expressed in Asian healthy individuals. Our study suggests that differential expression of several important microRNA with pro- or anti-CLL functions in Asian and Western B lymphocytes likely contributes to the difference in CLL incidence between the two ethnic groups, and that miR-4485 and its downstream molecule TGR5 could be potential therapeutic targets.

Abstract 2697: A novel therapeutic strategy to effectively kill CLL cells in stromal microenvironment by targeting lipid metabolism

The tissue microenvironment promotes cancer cell survival and drug resistance, and thus presents a major challenge in cancer treatment. Recent study suggests that the microenvironmental protection of chronic lymphocytic leukemia (CLL) cells is particular important due to the unique metabolic properties of CLL cells. Emerging evidence suggests that altered fatty acid metabolism may be associated with the pathogenesis of CLL and could potentially provide a biochemical basis for targeting CLL. In the current study, we tested three classes of compounds that respectively inhibit the de novo fatty acids synthesis (FASN), block the transport of fatty acids from cytosol into mitochondria, or suppress fatty acid oxidation, for their ability to kill CLL cells in the presence and absence of bone marrow stromal cells. While all three inhibitors exhibited cytotoxic effect again CLL cells when the leukemia cells were culture alone, only the compound that inhibited the transport of fatty acids into mitochondria was highly effective in killing CLL in the presence of bone marrow stromal cells. Mechanistic study revealed that the cytotoxicity was not due to inhibition of ATP generation through mitochondrial β-oxidation of fatty acids, since there was no significant decrease in mitochondrial respiratory activity. We further showed that inhibition of FA transport into mitochondria suppressed biosynthesis of mitochondrial phospholipid, leading to a significant depletion of cardiolipin (CL), which is essential for maintaining mitochondrial membrane integrity. Depletion of CL by the FA transport inhibitor in CLL cells resulted in mitochondrial depolarization, release of cytochrome c, and massive apoptosis. Since this cell death process was through the intrinsic pathway and could not be rescued by the stromal environment, this might explain why inhibition of FA transport into the mitochondrial was highly effective in killing CLL cells in the presence of stromal cells. Importantly, we found that inhibition of FA transport had low toxicity in normal lymphocytes and stromal cells, suggesting that the normal cells might be less dependent on FA transport for cardiolipin biosynthesis. In summary, our study suggests that inhibition of FA transport into the mitochondria is a novel therapeutic strategy to effectively and selectively kill CLL cells in stromal microenvironment, and may potentially improve the clinical outcome of CLL treatment.

Citation Format: Panpan Liu, Jinyun Liu, Marcia A. Ogasawara, Helene Pelicano, Ruihua Xu, Michael J. Keating, Peng Huang. A novel therapeutic strategy to effectively kill CLL cells in stromal microenvironment by targeting lipid metabolism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2697. doi:10.1158/1538-7445.AM2014-2697

Loss of p53 and altered miR15-a/16-1MCL-1 pathway in CLL: insights from TCL1-Tg:p53(-/-) mouse model and primary human leukemia cells

Chronic lymphocytic leukemia (CLL) patients with deletion of chromosome 17p, where the p53 gene is located, often develop more aggressive disease with poor clinical outcomes. To investigate the underlying mechanisms for the highly malignant phenotype of 17p- CLL and to facilitate in vivo evaluation of potential drugs against CLL with p53 deletion, we have generated a mouse model with TCL1-Tg:p53(-/-) genotype. These mice develop B-cell leukemia at an early age with an early appearance of CD5+ / IgM+ B cells in the peritoneal cavity and spleen, and exhibit an aggressive path of disease development and drug resistance phenotype similar to human CLL with 17p deletion. The TCL1-Tg:p53(-/-) leukemia cells exhibit higher survival capacity and are more drug resistant than the leukemia cells from TCL1-Tg:p53wt mice. Analysis of microRNA expression reveals that p53 deletion resulted in a decrease of miR-15a and miR-16-1, leading to an elevated expression of Mcl-1. Primary leukemia cells from CLL patients with 17p deletion also show a decrease in miR-15a/miR-16-1 and an increase in Mcl-1. Our study suggests that the p53/miR15a/16-1/Mcl-1 axis may be an important pathway that regulates Mcl-1 expression and contributes to drug resistance and aggressive phenotype in CLL cells with loss of p53.

Abstract 3072: Characterization of TCL1-Tg:p53-/- mice that resemble human chronic lymphocytic leukemia with 17p-deletion: alterations in p53→Mir30→EZH2 axis

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the United States and Europe. CLL patients with deletion of chromosome 17p, where the tumor suppressor p53 gene is located, often develop a more aggressive disease with poor clinical outcomes. However, the underlying mechanism remains unclear. We have recently generated mice with Eμ-Tcl1-Tg:p53-/- genotype and showed that these mice develop aggressive leukemia that resembles human CLL with 17p deletion. In the present study, we further demonstrated that the p53 deficiency in the Tcl1 transgenic mice resulted in significant down-regulation of microRNAs miR-15a and miR16-1, associated with a substantial up-regulation of Mcl-1, suggesting that the p53-miR15a/16-Mcl-1 axis may play an important role in CLL pathogenesis. Interestingly, we also found that loss of p53 resulted in a significant decrease in expression of the miR-30 family in leukemia lymphocytes from the Eμ-Tcl1-Tg:p53-/- mice. Consistently, primary leukemia cells from CLL patients with 17p deletion also showed a decrease in the miR-30d expression. To further exam the biological significance of decrease in the miR-30 family in CLL, we investigated the potential involvement of EZH2 (enhancer of zeste homolog 2), a component of the Polycomb repressive complex known to be a downstream target of miR-30d and plays a role in disease progression in several solid cancers. RT-PCR and western blot analyses showed that both EZH2 mRNA transcript and protein levels were significantly increased in the lymphocytes of Eμ-Tcl1-Tg:p53-/- mice relative to Eμ-Tcl1-Tg:p53+/+ mice. Exposure of leukemia cells isolated from Eμ-Tcl1-Tg:p53-/- mice to the EZH2 inhibitor 3-deazaneplanocin (DZNep) led to induction of apoptosis, suggesting EZH2 may play a role in promoting CLL cell survival and this may contribute to the aggressive phenotype of CLL with loss of p53. Our study reveals that the p53-miR30-EZH2 axis may play an important role in CLL pathogenesis, and EZH2 may potentially be a target for CLL treatment.

Citation Format: Jinyun Liu, Marcia A. Ogasawara, Gang Chen, Helene Pelicano, Peng Huang. Characterization of TCL1-Tg:p53-/- mice that resemble human chronic lymphocytic leukemia with 17p-deletion: alterations in p53→Mir30→EZH2 axis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3072. doi:10.1158/1538-7445.AM2013-3072

Imaging and analysis of 3D tumor spheroids enriched for a cancer stem cell phenotype

Tumors that display a highly metastatic phenotype contain subpopulations of cells that display characteristics similar to embryonic stem cells. These cells exhibit the ability to undergo self-renewal; slowly replicate to retain a nucleoside analog label, leading to their definition as "label-retaining cells"; express specific surface markers such as CD44(+)/CD24(-/low) and CD133; and can give rise to cells of different lineages (i.e., they exhibit multipotency). Based on these characteristics, as well as their demonstrated ability to give rise to tumors in vivo, these cells have been defined as tumor-initiating cells (TICs), tumor-propagating cells, or cancer stem cells (CSCs). These cells are highly resistant to chemotherapeutic agents and radiation and are believed to be responsible for the development of both primary tumors and metastatic lesions at sites distant from the primary tumor. Established cancer cell lines contain CSCs, which can be propagated in vitro using defined conditions, to form 3D tumor spheroids. Because the vast majority of studies to identify cancer-associated genes and therapeutic targets use adherent cells grown in 2 dimensions on a plastic substrate, the multicellular composition of these 3D tumor spheroids presents both challenges and opportunities for their imaging and characterization. The authors describe approaches to image and analyze the properties of CSCs within 3D tumor spheroids, which can serve as the basis for defining the gene and protein signatures of CSCs and to develop therapeutic strategies that will effectively target this critically important population of cells that may be responsible for tumor progression.

Small mitochondria-targeting molecules as anti-cancer agents

Alterations in mitochondrial structure and functions have long been observed in cancer cells. Targeting mitochondria as a cancer therapeutic strategy has gained momentum in the recent years. The signaling pathways that govern mitochondrial function, apoptosis and molecules that affect mitochondrial integrity and cell viability have been important topics of the recent review in the literature. In this article, we first briefly summarize the rationale and biological basis for developing mitochondrial-targeted compounds as potential anti-cancer agents, and then provide key examples of small molecules that either directly impact mitochondria or functionally affect the metabolic alterations in cancer cells with mitochondrial dysfunction. The main focus is on the small molecular weight compounds with potential applications in cancer treatment. We also summarize information on the drug developmental stages of the key mitochondria-targeted compounds and their clinical trial status. The advantages and potential shortcomings of targeting the mitochondria for cancer treatment are also discussed.

Redox regulation and its emerging roles in stem cells and stem-like cancer cells

The existence of cancer stem cells has impelled the pursuit to understanding and characterizing this subset of cells, which are thought to be responsible for tumor recurrence and to contribute to therapy resistance. Recent studies suggest that cancer stem cells seem to possess properties similar to those of normal stem cells, revealing a possible therapeutic strategy/target. For this to be feasible, it is imperative to understand the relation between cancer cells, cancer stem cells, and normal stem cells. Cancer cells have been found to be in a state of redox imbalance, an alteration in the homeostasis between oxidants and antioxidants, resulting in increased oxidants within the cell. Studies have shown redox balance plays an important role in the maintenance of stem cell self-renewal and in differentiation. Very little is known about the redox status in cancer stem cells. In this review, we focus on the sites of oxidant generation and the regulation of redox status in cancer cells and stem cells. In addition, evidence that supports the involvement of redox homeostasis for stem cell self-renewal, differentiation, and survival are reviewed. Given the significance of redox in stem cells, we also discuss the possibility of exploiting the redox status in cancer stem cells as a novel therapeutic strategy.

Redox regulation of cell survival

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in regulation of cell survival. In general, moderate levels of ROS/RNS may function as signals to promote cell proliferation and survival, whereas severe increase of ROS/RNS can induce cell death. Under physiologic conditions, the balance between generation and elimination of ROS/RNS maintains the proper function of redox-sensitive signaling proteins. Normally, the redox homeostasis ensures that the cells respond properly to endogenous and exogenous stimuli. However, when the redox homeostasis is disturbed, oxidative stress may lead to aberrant cell death and contribute to disease development. This review focuses on the roles of key transcription factors, signal-transduction pathways, and cell-death regulators in affecting cell survival, and how the redox systems regulate the functions of these molecules. The current understanding of how disturbance in redox homeostasis may affect cell death and contribute to the development of diseases such as cancer and degenerative disorders is reviewed. We also discuss how the basic knowledge on redox regulation of cell survival can be used to develop strategies for the treatment or prevention of those diseases.

Structural simplification of bioactive natural products with multicomponent synthesis. 2. antiproliferative and antitubulin activities of pyrano[3,2-c]pyridones and pyrano[3,2-c]quinolones

Pyrano[3,2- c]pyridone and pyrano[3,2- c]quinolone structural motifs are commonly found in alkaloids manifesting diverse biological activities. As part of a program aimed at structural simplification of bioactive natural products utilizing multicomponent synthetic processes, we developed compound libraries based on these privileged heterocyclic scaffolds. The selected library members display low nanomolar antiproliferative activity and induce apoptosis in human cancer cell lines. Mechanistic studies reveal that these compounds induce cell cycle arrest in the G2/M phase and block in vitro tubulin polymerization. Because of the successful clinical use of microtubule-targeting agents, these heterocyclic libraries are expected to provide promising new leads in anticancer drug design.

Effects of crude aqueous medicinal plant extracts on growth and invasion of breast cancer cells

Plants used in folklore medicine continue to be an important source of discovery and development of novel therapeutic agents. In the present study, we determined the effects of crude aqueous extracts of a panel of medicinal plants on the growth and invasion of cancer cells. Our results showed that extracts of L. tridentata (Creosote Bush) and J. communis L. (Juniper Berry) significantly decreased the growth of MCF-7/AZ breast cancer cells. The latter as well as A. californica (Yerba Mansa) inhibited invasion into the collagen type I gel layer. Furthermore, the phosphorylation levels of extracellular signal-regulated kinase 1 and 2 (ERK1/2) decreased when the cells were exposed to aqueous extracts of L. tridentata, J. communis L. and A. californica. This study provides original scientific data on the anticancer activity of selected aqueous medicinal plant extracts used in traditional medicine.

Antiproliferative and apoptosis inducing properties of pyrano[3,2-c]pyridones accessible by a one-step multicomponent synthesis

4-Arylpyrano-[3,2-c]-pyridones have been prepared by a one-step cyclocondensation of 4-hydroxy-1,6-dimethylpyridin-2(1H)-one with various substituted benzaldehydes and malononitrile. These heterocycles exhibit micromolar and submicromolar antiproliferative activity in HeLa and induce apoptosis in Jurkat cell lines. Structure-activity studies performed on a small library of these compounds show a pronounced cytotoxicity enhancing effect of the bromo substituent at the meta position of the C4 aromatic moiety.

Synthesis and Biological Evaluation of Aromatic Analogues of Conduritol F, l-chiro-Inositol, and Dihydroconduritol F Structurally Related to the Amaryllidaceae Anticancer Constituents

Pancratistatin is a potent anticancer natural product, whose clinical evaluation is hampered by the limited natural abundance and the stereochemically complex structure undermining practical chemical preparation. Fifteen aromatic analogues of conduritol F, l-chiro-inositol, and dihydroconduritol F that possess four of the six pancratistatin stereocenters have been synthesized and evaluated for anticancer activity. These compounds serve as truncated pancratistatin analogues lacking the lactam ring B, but retaining the crucial C10a-C10b bond with the correct stereochemistry. The lack of activity of these compounds provides further insight into pancratistatin's minimum structural requirements for cytotoxicity, particularly the criticality of the intact phenanthridone skeleton. Significantly, these series provide rare examples of simple aromatic conduritol and inositol analogues and, therefore, this study expands the chemistry and biology of these important classes of compounds.