Cancer stem cells in malignant peripheral nerve sheath tumor: Biology and therapeutic ramifications [abstract]

Neuroscience - Vision and Functional Brain Imaging Poster SessionAlthough monoclonal in origin, most tumors appear to contain heterogeneous populations of cancer cells. One possible explanation of this tumor heterogeneity is that human tumors are not merely monoclonal expansions of a single transformed cell, but rather caricatures of normal tissues, and their growth is sustained by cancer stem cells (CSCs). This conceptual shift has important implications, not only for understanding tumor biology but also for developing and evaluating effective anticancer therapies. These CSCs are thought to be more resistant to apoptosis, to survive therapy and to eventually give rise to second-line tumors, which are harder to eliminate by the first-line therapy. In this proposal, we are introducing our data in detection of CSCs in malignant peripheral nerve sheath tumors (MPNSTs) for the first time, and explain our plans for studying the biology of these cells in order to develop a therapeutic strategy for targeting them. We have identified a sub-population of cells in primary human MPNST cells which are positive for CD133 (a well-known marker for CSCs) and other stem cell markers. We have also studied the characteristics of Ras signaling pathway in these cells showing enhanced activation of Ras, Ral, PI3K and ERK. Now, we plan to not only study the biological characteristics of these cells further but also intend to “custom design” a new protocol for targeting them on the basis of specific characteristics of Ras pathway in these cells. If MPNST CSCs could be targeted, it can result in an efficient regression of tumors and enhancement of therapeutic success in MPNST patients

A Second Generation 2-Methoxyestradiol Prodrug Is Effective Against Barrett's Adenocarcinoma in a Mouse Xenograft Model

This is the author's accepted manuscript. The original is available at http://mct.aacrjournals.org/content/12/3/2552-Methoxyestradiol (2-ME2) is an endogenous metabolite of estradiol. In preclinical models, 2-ME2 is effective against different types of tumors. Unfortunately, only low systemic concentrations of 2-ME2 can be achieved following oral administration, even after very high doses are administered to patients. In an effort to solve this problem we have now synthesized and tested a new prodrug of 2-ME2 that is water soluble due to a bio-reversible hydrophilic group added at the 3-position and more effectively resists metabolic inactivation due to an ester moiety added to mask the 17-position alcohol. We are reporting here for the first time that this double prodrug of 2-ME2 is effective as an antiproliferative and anti-cancer agent for both in vitro and in vivo studies against Barrett's esophageal adenocarcinoma (BEAC), and provided greater potency than 2-ME2 in inhibiting the growth of BEAC xenografts. Finally, studies indicate that, like 2-ME2, the 2-ME2-PD1 exhibits anticancer effect through possible disruption of microtubule-network

SC-01RalA IN BIOLOGY AND THERAPY OF MPNST IN CORRELATION TO CANCER STEM CELLS

For the last 20 years, cellular biologists have been focusing on the role of Ras signaling pathway in neurofibromatosis 1(NF1) and its lethal derivation, malignant peripheral nerve sheath tumors (MPNST). While our team has worked on the influence of Ras pathway on responsiveness of MPNST cells to therapy, we introduced a novel cell signaling pathway down-stream of Ras, i.e. Ral pathway, as an important regulator of the biological features of MPNST with potentials for being targeted for treatment of this malignancy. We have also showed that RalA is overactivated in the cancer stem cell (CSC) fraction of MPNST tumors establishing this pathway to harbor potentials for targeting MPNST CSCs. In summary our preliminary data shed light on following facts: 1- RalA signaling pathway is overactivated in differentiated MPNST cells and human tissues. 2- RalA overactivation is a characteristic of MPNST cancer stem cells. 3- RalA inhibition hinders the malignant phenotype of MPNST cells. 4- Disruption of RalA signaling results in loss of viability and invasion of MPNST cells. In this presentation, we further evaluate the mechanism of RalA overactivation and in-vivo potentials of its inhibition as a therapeutic strategy for MPNST

Inhibition of Mesothelin as a Novel Strategy for Targeting Cancer Cells

Mesothelin, a differentiation antigen present in a series of malignancies such as mesothelioma, ovarian, lung and pancreatic cancer, has been studied as a marker for diagnosis and a target for immunotherapy. We, however, were interested in evaluating the effects of direct targeting of Mesothelin on the viability of cancer cells as the first step towards developing a novel therapeutic strategy. We report here that gene specific silencing for Mesothelin by distinct methods (siRNA and microRNA) decreased viability of cancer cells from different origins such as mesothelioma (H2373), ovarian cancer (Skov3 and Ovcar-5) and pancreatic cancer (Miapaca2 and Panc-1). Additionally, the invasiveness of cancer cells was also significantly decreased upon such treatment. We then investigated pro-oncogenic signaling characteristics of cells upon mesothelin-silencing which revealed a significant decrease in phospho-ERK1 and PI3K/AKT activity. The molecular mechanism of reduced invasiveness was connected to the reduced expression of β-Catenin, an important marker of EMT (epithelial-mesenchymal transition). Ero1, a protein involved in clearing unfolded proteins and a member of the ER-Stress (endoplasmic reticulum-stress) pathway was also markedly reduced. Furthermore, Mesothelin silencing caused a significant increase in fraction of cancer cells in S-phase. In next step, treatment of ovarian cancer cells (OVca429) with a lentivirus expressing anti-mesothelin microRNA resulted in significant loss of viability, invasiveness, and morphological alterations. Therefore, we propose the inhibition of Mesothelin as a potential novel strategy for targeting human malignancies

Crystal structure of the actin-binding domain of alpha-actinin 1: evaluating two competing actin-binding models.

Alpha-actinin belongs to the spectrin family of actin crosslinking and bundling proteins that function as key regulators of cell motility, morphology and adhesion. The actin-binding domain (ABD) of these proteins consists of two consecutive calponin homology (CH) domains. Electron microscopy studies on ABDs appear to support two competing actin-binding models, extended and compact, whereas the crystal structures typically display a compact conformation. We have determined the 1.7A resolution structure of the ABD of alpha-actinin 1, a ubiquitously expressed isoform. The structure displays the classical compact conformation. We evaluated the two binding models by surface conservation analysis. The results show a conserved surface that spans both domains and corresponds to two previously identified actin-binding sites (ABS2 and ABS3). A third, and probably less important site, ABS1, is mostly buried in the compact conformation. However, a thorough examination of existing structures suggests a weak and semi-polar binding interface between the two CHs, leaving open the possibility of domain reorientation or opening. Our results are consistent with a two-step binding mechanism in which the ABD interacts first in the compact form observed in the structures, and then transitions toward a higher affinity state, possibly through minor rearrangement of the domains