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RESEARCH
INTERESTS
- Translation Initiation and Cancer.
Approximately ten years ago, Hanahan and Weinberg proposed a set of
six traits that cells acquire on their path to becoming malignant.
These essential alterations to cell physiology were: self-sufficiency
in growth signaling, insensitivity to growth-inhibitory signals, evasion
of apoptosis, limitless replicative potential, sustained angiogenesis
and tissue invasion and metastasis. Recent large scale analysis of
gene mutations, deletions, and amplifications in human tumors have
extended this conceptual framework, revealing that cancers exhibit
on average ~60-90 genetic alterations per tumor, the majority of which
reside in genes implicated in a limited set of core regulatory processes
or pathways. One conclusion from these studies is that strategies
targeting oncogenic lesions in human cancers may be too narrow for
drug development. Rather, targeting key signaling nodes residing downstream
of oncogene-activated pathways may offer broader acting therapeutic
opportunities. Translational control resides downstream of many of
these regulatory nodes, making this process an attractive molecular
target for anti-cancer therapies. Indeed, a majority of human cancers
activate pathways that directly stimulate the protein synthesis apparatus
- leading to elevated translation rates. One of our research programs
has been to evaluate the role of deregulated translation in oncogenesis
and the therapeutical potential of targeting this pathway. To achieve
this, we utilize a combination of chemical biology and genetic approaches
to dissect and target various components of this pathway.
- Chemical Biology and Translation.
Small molecule ligands, acting as inhibitors, have provided formidable
insight into the complexity of prokaryotic translation. Similar inhibitors
of eukaryotic translation will be valuable tools to better understand
the intricacies and regulation of this pathway. Moreover, only from
a more complete picture of eukaryotic protein synthesis can one obtain
the necessary means to design therapies that target translation to
treat disease. This arm of our research program is aimed at identifying
inhibitors of mammalian translation, elucidating their mode of action,
and characterizing their molecular targets. Our lab has screened over
250,000 compounds for chemical inhibitors that specifically target
the translation initiation phase under regulation of mTOR signaling.
As a consequence of this effort, we have identified and characterized
several novel translation initiation and elongation inhibitors. Some
of these compounds target an RNA helicase involved in the translation
initiation process, called eIF4A, and we have shown that these show
promising in vivo activity as chemosensitization agents, in a pre-clinical
mechanism-based mouse lymphoma model. Current efforts are aimed at
better understanding the mechanism of action of these compounds.
- Modeling Drug Therapy Response Through Engineered Inducible
and Reversible RNA Interference.
Mouse models are powerful tools for studying gene function in mammalian
systems. In particular, recombination-based systems (e.g.-Cre/loxP
and Flp/FRT) for conditional gene inactivation in mice have been useful
for studying the adult function of genes that are essential for mouse
development. Limitations of this technology however is that these
models are time consuming, recombinase expression can be genotoxic,
and the recombination event irreversibly disrupts the target locus.
In the context of studies to elucidate potential gene function during
development or mimic the effects of targeted therapeutics in models
of human disease, transient and/or tissue-specific inhibition of endogenous
genes is desirable. For this purpose, tet-regulated expression systems
developed for transgenic mice show much promise since they allow spatial
and temporal control of gene over-expresssion – a strategy used
to study mouse embryonic and post-natal development as well as oncogene
addiction. Regulated transcription from the tet-responsive TRE promoter
relies on the activity of the tet transactivator protein, which can
be either activated (rtTA: tet-on) or repressed (tTA: tet-off) by
tetracycline or its analogue doxycycline. Many mouse lines have been
developed that express tTA or rtTA in different tissues.
RNAi holds great promise as an experimental tool for loss-of-function
genetics. Methodology to apply this technology in vivo in mice has
the potential to provide important insight into gene function at the
organismal level, accelerate drug discovery by allowing identification
and in vivo validation of drug targets, and enabling an understanding
into drug efficacy/genotype relationships. We are implementing a platform
developed at Cold Spring Harbor Laboratories (Dr. Scott Lowe’s
Lab), which allows for efficient targeting of tet-responsive shRNAs
to ES cells that, in turn, will be used to rapidly produce germline
transgenic mice. This platform will extend the potential of reverse
genetics in the mouse and has the potential to significantly alter
the drug discovery process. It will allow inducible and reversible
gene silencing at will, under very defined experimental conditions,
not only in the disease tissue, but in normal tissue as well. By focusing
on components of the translation apparatus, we will be able to assess
the consequences of gene knockdown in vivo on translation in normal
and disease tissue.
- shRNA Screens to Identify New Anti-Cancer Targets.
In principle, tumors can be attacked by targeting oncogenes or by
exploiting the rewiring that occurs as a consequence of the oncogenic
state. In theory, the inappropriate rewiring of the translation pathway
that occurs as a consequence of oncogenic transformation presents
a vulnerability that can be exploited for cancer therapy. Such vulnerabilities
are not obvious and are best discovered through genetic exploration.
To this end, shRNA screens based on straight and synthetic lethality
have the potential to identify genes whose inhibition could selectively
impair the growth of tumor cells.
Although much research focus has been on the ribosome recruitment
step of translation, our lab has shown that small molecule inhibitors
of translation elongation also are capable of synergizing with standard
of care therapeutics in the E?-myc model. Hence targeted screens against
the translation pathway can be expected to provide valuable new insights.
We are undertaking RNAi screens using shRNAs directed against all
components of the translation apparatus in an attempt to identify
new targets in this pathway that can synergize with standard of care
therapies.
- RNA Helicases.
RNA Helicases representing unique opportunities for drug targeting.
Our lab has identified the only three natural products known to target
RNA helicases involved in the process of translation, validating the
idea that this class of enzymes can be blocked selectively. We are
interested in this class of proteins – in terms of characterizing
their role in normal and transformed cell proliferation, characterizing
their mode of action, and valdidating them as drug targets in vivo.
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