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Neuroblastoma, a cancer of the nervous system, is one of the most
common cancers in young children, accounting for nearly 10 percent of
all childhood cancers and for most tumours in babies under one year of
age. Despite aggressive therapy, the cure rate for children with
metastatic or widespread neuroblastoma remains very low.
Ten research projects represent the multiple strands of research and
the collaborations taking place at SickKids and in other Toronto
research hospitals – all part of the drive to find a cure for
neuroblastoma.
Included in these teams are leading cancer researchers Drs. David
Kaplan, Sylvain Baruchel, Paul Thorner, Maria Zielenska, Herman Yeger,
and Meredith Irwin of SickKids, as well as collaborators Dr. Raymond
Reilly from Toronto General Research Institute, and Dr. Jeremy Squire
from the Ontario Cancer Institute at Princess Margaret Hospital.
Significant efforts from key supporters have catalyzed neuroblastoma
research in Canada; and we are grateful to all of our donors who
contribute to this urgent cause, especially Lilah's Fund. Your
vision and commitment have allowed us to take risks with our research
that otherwise would not be funded; to test ideas and out-of-the-box
thinking not funded by traditional agencies; to prove (in some
instances) the viability of our ideas to major granting agencies; and
hence to leverage your donor dollars into funding for large research
projects.
Among the milestones we have marked are
- the discovery of the rare cell in neuroblastoma that may be
responsible for why this tumour keeps reoccurring after
chemotherapy,
- one of the reasons why neuroblastoma cells metastasize to other
organs,
- a way in which neuroblastoma becomes resistant to chemotherapy
and
- new drug treatments for patients.
Research currently underway in our labs includes:
Dr. Sylvain Baruchel, MD, Director of
SickKids' New Agent and Innovative Therapy Program, is lead investigator
in two projects, the second of which follows on from his discovery in
2005 how neuroblastoma tumours resist chemotherapy.
Agents to Reduce the Toxicity of Chemotherapy
High dose chemotherapy is a double-edged sword. On the one hand
it attacks the tumour and achieves for the patient better chances for
disease free survival. On the other hand, such high doses are
associated with significant toxicity. This can compel us to reduce
dosages, or delay treatment, which can limit the positive effects of the
chemotherapeutic drug. New cytoprotective drugs (i.e. drugs which
protect cells from noxious chemicals or other stimuli) offer a possible
solution. These drugs can protect normal tissue from
chemotherapeutic drug damage without interfering with the antitumour
effects of therapy. Critically, this could reduce damage to normal
tissues and organs during therapy. We are interested therefore in
identifying novel cytoprotective agents and in uncovering the molecular
mechanism of cytoprotection. This information will help development of
targeted cytoprotective agents in the future. We have focused our
initial studies on a natural compound called squalene which is found in
olive oil and other sources, and which we have found protects normal
bone marrow stem cells from cisplatin-induced toxicity without
protecting tumour cells from drug-induced death.
Role of VEGF and HIF1-a in Hypoxia-Mediated Drug Resistance
We are interested in the mechanism underlying drug resistance in
aggressive and high-risk neuroblastoma tumours. One way
chemotherapeutic agents act on tumours is to reduce nutrients and oxygen
to the tumour, a process called hypoxia. Tumours however can resist
hypoxia, and our research aims to counter this resistance, and
ultimately maximize the beneficial of the chemotherapeutic agents.
Using both in vitro and in vivo models of hypoxia-mediated drug
resistance, we found that two proteins, VEGF (vascular endothelial
growth factor) and HIF1a (hypoxia inducible factor1a) are involved
together in neuroblastoma drug resistance. This work has been extended
to paediatric sarcomas including osteosarcoma, rhabdomyosarcoma and
Ewing's sarcoma.
Dr. Meredith Irwin, MD, a clinician scientist at SickKids and holder
of the Canada Research Chair in Cancer Biology, is discovering and
evaluating new and potentially important drugs for the treatment of
neuroblastoma.
COX Inhibitor Drugs as a Treatment for Neuroblastoma – Efficacy and
Mechanism of Action
We are interested in how certain genes, in particular the p53 family
of genes, can be activated to cause cell death in response to drug
treatments in neuroblastoma. In an effort to discover new
therapies for this cancer, we investigated novel drugs as potential
treatments. Previously we found that drugs called COX inhibitors,
normally used for pain relief, caused cell death of neuroblastoma cells
from patients whose tumours were resistant to chemotherapy.
Importantly, normal cells were not affected. Over the past several
years we have discovered how these drugs kill neuroblastoma cells by
affecting genes called p53, p73 and MDM2. p53 is a gene used by the
cells to kill damaged or abnormal cells, and in particular, malignant
cells. However, p53 is often inactivated in neuroblastoma tumour cells,
especially at the time of relapse, and thus, a related gene called p73
plays a very important role in cell death pathways in response to many
drug treatments.
In addition to our studies using COX inhibitors, we have also begun
to study the efficacy of another novel drug, nutlin, in neuroblastoma.
Nutlin also affects p53 and MDM2 and we recently discovered that it can
be used to activate p73 killing in neuroblastomas with non-functional
p53.
We are currently performing studies that will determine how to
combine COX inhibitors and nutlins with chemotherapy in patients, how to
determine which patient tumours will be most sensitive, and study the
potential therapeutic role of nutlin alone and together with
chemotherapy in neuroblastoma.
Dr. David Kaplan, Ph.D., Senior Scientist, Cell Biology, at SickKids
Research Institute, and Canada Research Chair in Cancer & Neuroscience,
is leading three projects:
Identification of Cancer Stem Cells in Neuroblastoma
We have isolated a putative “stem cell†from human neuroblastomas
that may represent the cell that produces the tumour cells, and that
therefore may be an ideal target for new anti-cancer drugs. While the
cells produced by cancer stem cells can be killed by cancer drugs, the
rare cancer stem cells themselves are thought to be resistant to those
drugs, and to be responsible for relapse and reoccurrence of the tumour.
We isolate the cells from all patients at SickKids with neuroblastoma
and use them for studies to identify new drugs that can kill those stem
cells. We also screen for genes that “mark†these cells so that we can
determine if drugs can eliminate them specifically from the body, and
identify why they persist and are resistant to presently used drugs.
Drug Discovery Project
The goal of the project is to find drugs that are already in use to
treat other ailments but that also have the potential to treat
neuroblastoma. The advantage of this approach is that drugs that have
been approved for use in other conditions can be brought to the clinic
relatively quickly. In these experiments, we use rare cancer “stem
cells†that we think are the cells that cause patients to relapse
following chemotherapy. We also use non-cancerous stem cells obtained
from the skin of children that we propose are the normal version of
neuroblastoma cells. We (with collaborators from Mt. Sinai) then asked
whether we could find commonly used drugs that will rapidly kill the
neuroblastoma stem cells, but not harm the non-cancerous stem cells.
After treating the cells with thousands of drugs, we did indeed find
several that specifically kill the tumour cells and not the normal
cells. Several drugs kill not only neuroblastoma cells, but also cancer
stem cells from breast tumours, brain tumours, and leukemia. The drugs
that have been successful in killing the cancer stem cells are now being
tested in mice with neuroblastoma in partnering labs. These experiments
are the major step required to proceed to clinical trials. If the drugs
do kill the tumours in mice, our hope is that within the next several
years, we will be able to use these drugs in a few patients, and if
successful, to expand the study to a clinical trial.
The Role of Proneurotrophins in Migration and Metastasis of
Neuroblastoma Cells
In an innovative partnership with Dr. Barbara Hempstead, Co-Chair of
Haematology/Oncology at Weill Medical College in New York City, Dr. Risa
Torkin is studying the potential role of proteins called
proneurotrophins in migration and metastasis of neuroblastoma cells.
Proneurotrophins are the precursor forms of NGF (nerve growth factor)
and BDNF (brain derived neurotrophic factor), which have known
significance in the clinical behaviour of neuroblastoma tumour cells.
Dr. Hempstead's lab previously showed that proNGF induced movement of
melanoma cells, suggesting a role in metastasis. Since melanoma cells
originate from neural crest cells, we extended this study to
neuroblastoma, which shares this common developmental origin.
Preliminary results suggest that proNGF does induce neuroblastoma cells
to migrate, and studies are currently underway to uncover the molecular
mechanism of this action. This project will further the understanding
of the biology underlying the metastatic process which is of great
clinical significance for neuroblastoma patients.
Dr. Raymond M. Reilly, Ph.D. from the Toronto General Research
Institute is investigating, with Dr. Baruchel, the potential of treating
neuroblastoma with radiopharmaceuticals.
Novel Targeted Auger Electron Radiotherapy of Neuroblastoma Using
123I-MIBG.
Iodine-123 MIBG is a radiopharmaceutical (radioactive drug) currently
used for imaging neuroblastoma in children. This study evaluated the
ability of this agent to kill neuroblastoma cells growing in culture
through its known emission of short-range electrons. Our study showed
that indeed, 123I-MIBG was able to kill neuroblastoma cells and was able
to spare normal cells obtained from the bone marrow of adult human
donors. These findings are important because bone marrow toxicity is
dose limiting for iodine-131 MIBG, a related radiopharmaceutical that is
used for treatment of the disease. These results suggest that simply
changing the radioactive element in the radiopharmaceutical from
iodine-131 to iodine-123 could overcome this restriction on treatment of
the disease with MIBG, potentially improving the effectiveness of
treatment.
Drs. Paul Thorner, M.D., Ph.D., Senior Associate Scientist in Cell
Biology, and Maria Zielenska, Ph.D., Director of SickKids
Molecular Pathology Laboratory, and Senior Associate Scientist in
Genetics & Genome Biology, have devised a better way to find variations
of copy numbers (clones) in tumour cells and how to apply this to a
better understanding of neuroblastoma biology.
Identification of Malignant Clones in Neuroblastoma
Amplification of the MYCN gene in neuroblastoma is a powerful
predictor of a poor prognosis. ‘Amplification' means that there are
increased copies (more than two) of a gene in a cell. It was
generally believed that the degree of MYCN amplification is the same
throughout all cells in a tumour and does not change when the tumour
spreads to other sites. This view was based on methods that
averaged the estimate of the number of MYCN genes of pooled cells,
without studying the number of copies at the cell level. We have
developed a method known as Chromogenic In Situ Hybridization (or CISH)
for determination of MYCN copy number that evaluates individual tumour
cells, and that can evaluate the variation in MYCN copy number from cell
to cell. We have found almost 30% of cases show more than 50%
variation in the number of MYCN genes between cells, suggesting that
there are different clones of tumour cells within a single tumour.
This degree of variability has been underestimated in the past and its
role in neuroblastoma biology needs to be investigated. We plan to
continue this study by correlating the MYCN copy number with the biopsy
appearance and patient outcome, and determine whether treatment selects
for the amplified clones within a tumour. At the same time, we
will determine the MYCN copy number in metastases at diagnosis and in
post treatment specimens. This type of study is only feasible
using a method such as CISH and from it we will learn more about
neuroblastoma biology and how MYCN copy number correlates with tumour
differentiation before and after treatment, and how it relates to
metastatic behaviour.
Dr. Herman Yeger, Ph.D., Senior Scientist in Developmental & Stem
Cell Biology, is investigating a novel conceptual approach for the
investigation of tumour biology of neuroblastoma and the means to
identify and validate new therapeutic approaches and agents.
Reversing the Malignant Phenotype: The Neuroblastoma Model
There is growing evidence that tumour cells, including neuroblastoma
tumour cells, are susceptible to cell death, cessation of growth and
conversion into a mature, or differentiated cell with normal features.
We have shown that a variety of natural dietary components including
retinoids (i.e. vitamin A) can induce neuroblastoma tumour cell death
and differentiation. We have made the exciting observation that
retinoids can work together with low concentrations of histone
deacetylase (HDAC) inhibitors and inhibitors of DNA methylation to
promote a higher degree of differentiation by activation of gene
programs that drive this process. We will use cell lines and animal
models to look for combinations of HDAC inhibitors, methylation
inhibitors and retinoids that can promote differentiation. Our studies
will hopefully lead to novel strategies for development of more
effective therapies to improve the outlook for children with
neuroblastoma.
Dr. Maria Zielenska, Ph.D. is leading an investigation with Drs.
Jeremy Squire, Ph.D. of the Ontario Cancer Institute at Princess
Margaret Hospital, and Paul Thorner.
Molecular Profiling of High-Risk Neuroblastoma by cDNA array.
We have examined gene amplification in neuroblastoma tumours using a
technique called Microarray CGH (comparative genomic hybridization).
This molecular method was used to analyze rearrangements in genes that
are associated with resistance of neuroblastoma tumours to chemotherapy.
We plan to extend our use of Microarray CGH and other related
cytogenetic approaches to study a wider spectrum of neuroblastoma tumour
samples drawn from Ontario and other Provinces. The outcome of the
program as it develops will provide the capacity to enhance our
understanding of the contributions of genomic aberrations to
neuroblastoma. When fully implemented, we will significantly enhance the
translational neuroblastoma genomics research at both Princess Margaret
Hospital and The Hospital for Sick Children.
Thank You!
Our sincere thanks to Lilah's Fund for your generous and ongoing
support. With your help we are forging ahead with new initiatives,
and making significant progress in the fight against this aggressive
cancer.
Thank you for your support of this important work.
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