Aarthi Jayanthan

Polo‐Like Kinase 1 Inhibition Kills Glioblastoma Multiforme Brain Tumor Cells in Part Through Loss of SOX2 and Delays Tumor Progression in Mice

Glioblastoma multiforme (GBM) ranks among the deadliest types of cancer and given these new therapies are urgently needed. To identify molecular targets, we queried a microarray profiling 467 human GBMs and discovered that polo‐like kinase 1 (PLK1) was highly expressed in these tumors and that it clustered with the proliferative subtype. Patients with PLK1‐high tumors were more likely to die from their disease suggesting that current therapies are inactive against such tumors. This prompted us to examine its expression in brain tumor initiating cells (BTICs) given their association with treatment failure. BTICs isolated from patients expressed 110‐470 times more PLK1 than normal human astrocytes. Moreover, BTICs rely on PLK1 for survival because the PLK1 inhibitor BI2536 inhibited their growth in tumorsphere cultures. PLK1 inhibition suppressed growth, caused G2/M arrest, induced apoptosis, and reduced the expression of SOX2, a marker of neural stem cells, in SF188 cells. Consistent with SOX2 inhibition, the loss of PLK1 activity caused the cells to differentiate based on elevated levels of glial fibrillary acidic protein and changes in cellular morphology. We then knocked glial fibrillary acidic protein (GFAP) down SOX2 with siRNA and showed that it too inhibited cell growth and induced cell death. Likewise, in U251 cells, PLK1 inhibition suppressed cell growth, downregulated SOX2, and induced cell death. Furthermore, BI2536 delayed tumor growth of U251 cells in an orthotopic brain tumor model, demonstrating that the drug is active against GBM. In conclusion, PLK1 level is elevated in GBM and its inhibition restricts the growth of brain cancer cells. STEM CELLS2012;30:1064–1075

Targeting the Bcl-2 family of proteins in Hodgkin lymphoma: in vitro cytotoxicity, target modulation and drug combination studies of the Bcl-2 homology 3 mimetic ABT-737

With currently available treatment, patients with refractory Hodgkin lymphoma (HL) or those who relapse multiple times have an extremely poor prognosis. Therefore, new agents and novel therapeutic approaches are urgently needed. Anti-apoptotic proteins such as Bcl-2 and Bcl-x have been associated with the growth and survival of Hodgkin Reed–Sternberg cells and are potential therapeutic targets. ABT-737 is a small molecule that inhibits the Bcl-2 family of apoptosis regulators. In this study, we show the concentration-dependent and time-dependent cytotoxicity of ABT-737 against cell lines derived from patients with HL. A concurrent reduction in a number of intracellular cell growth and survival related molecules, such as Bcl-2, Bcl-xl, NF-κB and survivin was also seen. Drug combination studies using a panel of conventional and novel therapeutic agents show that ABT-737 potentiates the activity of agents that have inherent anti-lymphoma activity and provide support for the evaluation of ABT-737 in the clinical setting.

Effects of 17-allylamino-17-demethoxygeldanamycin (17-AAG) on pediatric acute lymphoblastic leukemia (ALL) with respect to Bcr-Abl status and imatinib mesylate sensitivity.

As more and more effective targeted therapeutics have been developed to treat adults with cancer, it is of critical importance to devise appropriate in vitro experimental models to study their use in pediatric patients. Acute lymphoblastic leukemia (ALL) with Bcr-Abl translocation is one of the most difficult to treat and deadly diseases in children. The targeted kinase inhibitor imatinib mesylate has been shown to induce an initial response but resistance often develops. Recently, the geldanamycin family of antibiotics has been found to induce apoptosis in many malignant cells, including adult CML and AML. We describe experiments in which 17-allylamino-17-demethoxygeldanamycin (17-AAG) was evaluated in the context of Bcr-Abl and resistance to imatinib mesylate. Pediatric ALL cell lines with varying Bcr-Abl status and imatinib mesylate sensitivity were generated and their growth inhibition by 17-AAG was studied in vitro. Western blots were used to follow the changes in proteins that correlate with cell survival. Results show that apoptosis was induced in all lines with an increased 50% inhibitory concentration (IC50) for Bcr-Abl positive but imatinib mesylate–resistant cells. Addition of 17-AAG greatly increased imatinib sensitivity in vitro. A decrease in p53, survivin, Her2/neu, and WT1 was seen in cells that expressed these proteins. With some notable exceptions, when combined with 17-AAG, the IC50 of most of the common chemotherapeutic agents decreased. We describe an experimental approach to investigate the complex interaction between Bcr-Abl status, imatinib mesylate sensitivity, and 17-AAG in pediatric ALL. Information from such an approach will provide means to devise combined treatment approaches and to follow their effectiveness in vitro.

Cytotoxicity, drug combinability, and biological correlates of ABT‐737 against acute lymphoblastic leukemia cells with MLL rearrangement

ABT‐737 is a BH3 mimetic small‐molecule inhibitor that binds with high affinity to Bcl‐2 to induce apoptosis in malignant cells and has shown promise as an effective anti‐leukemic agent in pediatric preclinical tests. This study focuses on the effects of ABT‐737 on leukemia cells with MLL rearrangement and identifies some of the biological correlates of its activity.

Profiling pathway-specific novel therapeutics in preclinical assessment for central nervous system atypical teratoid rhabdoid tumors (CNS ATRT): Favorable activity of targeting EGFR- ErbB2 signaling with lapatinib

Despite intensifying multimodal treatments, children with central nervous system atypical teratoid/rhabdoid tumor (CNS ATRT) continue to endure unacceptably high mortality rates. At present, concerted efforts are focusing on understanding the characteristic INI1 mutation and its implications for the growth and survival of these tumors. Additionally, pharmaceutical pipeline libraries constitute a significant source of potential agents that can be taken to clinical trials in a timely manner. However, this process requires efficient target validation and relevant preclinical studies. As an initial screening approach, a panel of 129 small molecule inhibitors from multiple pharmaceutical pipeline libraries was tested against three ATRT cell lines by in vitro cytotoxicity assays. Based on these data, agents that have strong activity and corresponding susceptible cellular pathways were identified. Target modulation, antibody array analysis, drug combination and in vivo xenograft studies were performed on one of the pathway inhibitors found in this screening. Approximately 20% of agents in the library showed activity with IC50 values of 1 μM or less and many showed IC50 values less than 0.05 μM. Intra cell line variability was also noted among some of the drugs. However, it was determined that agents capable of affecting pathways constituting ErbB2, mTOR, proteasomes, Hsp90, Polo like kinases and Aurora kinases were universally effective against the three ATRT cell lines. The first target selected for further analysis, the inhibition of ErbB2‐EGFR pathway by the small molecule inhibitor lapatinib, indicated inhibition of cell migration properties and the initiation of apoptosis. Synergy between lapatinib and IGF‐IR inhibition was also demonstrated by combination index (CI) values. Xenograft studies showed effective antitumor activity of lapatinib in vivo. We present an experimental approach to identifying agents and drug combinations for future clinical trials and provide evidence for the potential of lapatinib as an effective agent in the context of the biology and heterogeneity of its targets in ATRT.

Curcumin Blocks Kv11.1 (erg) Potassium Current and Slows Proliferation in the Infant Acute Monocytic Leukemia Cell line THP-1

Acute Myeloid Leukemia (AML) accounts for approximately one fifth of all childhood leukemia yet is responsible for a significant proportion of morbidity and mortality in this population. For this reason, research to identify novel targets for the development of effective AML therapeutics has intensified in the recent past. The THP-1 cell line, which was originally established from an infant diagnosed with AML, provides an experimental model for functional, pre-clinical therapeutics and target identification studies of AML. Here we show the expression of the voltage gated potassium channel Kv11.1 in THP-1 cells as opposed to normal hematopoietic stem cells. In addition, curcumin, a natural polyphenol derived from the plant Curcuma longa, effectively blocked Kv11.1 activity and also inhibited the proliferation of these cells. Curcumin was rapidly internalized by THP-1 cells and possibly exerts potential growth inhibitory activity by interacting with intracellular epitopes of the ion channel. Inhibition of ionic currents carried by Kv11.1 resulted in depolarization of cell membrane potential. We propose that the inhibition of Kv11.1 activity by curcumin may lead to interference with leukemic cell physiology and consequently the suppression of survival and proliferation of AML cells.

Establishment of atypical-teratoid/rhabdoid tumor (AT/RT) cell cultures from disseminated CSF cells: a model to elucidate biology and potential targeted therapeutics

Atypical teratoid/rhabdoid tumor (AT/RT) is a highly malignant central nervous system neoplasm that usually affects infants and young children. In this report, we describe culture conditions that enabled the sustained growth of tumor cells obtained from the cerebrospinal fluid (CSF) of an infant with AT/RT. These cells retained the morphological and biomarker characteristics of the original tumor. A screening of receptor tyrosine kinases identified the presence of phosphorylated ErbB4, Insulin-R, PDGFR and IGF-IR, which appear to depend on Hsp90 to maintain their active form. IGF-IR activity is consistent with data from other established AT/RT cell lines. Inhibition of IGF-IR by the small molecular weight inhibitor AEW541 led to growth suppression of cultured AT/RT cells. In addition, neutralizing antibodies to IGF-II also inhibited the growth of these cells suggesting a potential autocrine function for this cytokine. We also compared cultured AT/RT cells to established cell lines to identify consistent drug sensitivity patterns among these cells. In addition to previously described cell lines and xenograft models, continuous culture of CSF derived cells may also provide an effective way to study the biology of AT/RT and to identify potential targets for future therapeutics for this tumor.

CHILDHOOD ACUTE LYMPHOBLASTIC LEUKEMIA (ALL) PRESENTING WITH SEVERE OSTEOLYSIS: A Model to Study Leukemia-Bone Interactions and Potential Targeted Therapeutics

Interference with the molecular mechanisms that generate tumor supportive niches in the bone microenvironment is a rational approach to inhibit the growth of hematological malignancies. However, the advancement of knowledge in this area has been slowed down by the lack of in vitro models to facilitate the screening of potential candidate agents. The rare cases of acute lymphoblastic leukemia (ALL) in children presenting with extensive bone involvement may represent an exaggerated form of some aspects of the normal tumor-bone interactions. Thus, these cases can provide insight into processes that are otherwise challenging to uncover. The authors describe the case of a 6-year-old child who presented with severe osteopenia that resolved at the time of leukemic remission. Compared to control sera, serum taken at disease presentation contained increased levels of a group of osteolytic cytokines and was effective in activating preosteoclast cells in culture. Based on these findings, the authors describe an experimental model to identify agents that would interfere with leukemia mediated osteolytic process.

Double-deleted vaccinia virus in virotherapy for refractory and metastatic pediatric solid tumors.

Previous studies have shown successful antitumor effects of systemically delivered double‐deleted vaccinia virus (vvDD) against a number of adult tumor models, including glioma, colon and ovarian cancers. The purpose of this study was to investigate the oncolytic potential of vvDD against a panel of cell lines representative of pediatric solid tumors that are currently difficult to cure.

Induction of apoptosis in pediatric acute lymphoblastic leukemia (ALL) cells by the therapeutic opioid methadone and effective synergy with Bcl-2 inhibition.

Although recent decades have seen a significant improvement in the treatment outcome of leukemia in the pediatric population, those who are treated for relapsed disease still face significant morbidity and mortality. However, current salvage regimens are often assembled with agents that have similar mode of activity as the chemotherapeutics used in the initial treatment. Hence, novel therapeutic agents that are capable of distinct and diverse mechanisms of activity in, now resistant, leukemia cells are of great interest. We have investigated the opioid agonist methadone for its anti-leukemic activity, initially reported in studies with cell lines derived from adult patients. Our findings show that, compared to normal cells, methadone has enhanced cytotoxicity against specimens and cell lines established from refractory childhood leukemia. In addition, methadones activity synergized with that of the anti-Bcl-2 agent ABT-737 and was characterized by the induction of distinct changes in tumor cell mitochondria. Data presented also identify biological correlates and a potential mechanism for methadone activity by its effects on Mcl-1 and other members of the apoptosis cascade. We provide mechanistic data for the therapeutic potential of a family of agents that is largely unexplored for anti-leukemic activity.