Editorial
The Future of Precision Medicine in Oncology: Targeting Cancer Stem Cells
Candace M. Howard1, Jagan Valluri2 and Pier Paolo Claudio3,4*
1Department of Radiology, University of Mississippi Medical Center, USA
2Department of Biological Sciences, Marshall University, USA
3Department of BioMolecular Sciences, National Center for Natural Products Research, University of Mississippi, USA
4Department of Radiation Oncology, University of Mississippi Medical Center Cancer Institute, USA
*Corresponding author: Pier Paolo Claudio, Department of BioMolecular Sciences and Radiation Oncology,, National Center for Natural Products Research, University of Mississippi, Jackson, MS 39126, USA
Published: 06 Jan, 2017
Cite this article as: Howard CM, Valluri J, Claudio PP.
The Future of Precision Medicine in
Oncology: Targeting Cancer Stem
Cells. Clin Oncol. 2017; 2: 1187.
Keywords
Precision medicine; Personalized medicine; Drug response assay; Chemo-sensitivity assay; Chemo-resistance assay; Cancer stem cells
Editorial
Precision medicine in oncology has been a popular topic of discussion in the health-care field
since US President Barack Obama announced the Precision Medicine Initiative at his 2015 State of
the Union address. Precision medicine is focused on identifying which therapies are most effective
for individual patients based on the genetic characterization of their cancer [1-3]. Since the late
1990s, the basis of precision medicine has been to develop targeted therapies to inhibit specific
molecular pathways involved in tumor growth and dissemination of cancer cells [2].
Cancer, as we know it, is a heterogeneous and progressive genetic disease caused by genetic
instability. Genetic instability is an inherent and normal process that transforms a normal cell into a
cancer cell. Normal DNA replication, cell division, and repair are not infallible and are influenced by
a variety of inherited and environmental factors. Ultimately, cancer growth and progression is the
end result of a wide variety of genetic changes that accumulate in the cancer cells over time. Mutations
may happen anywhere in genomic DNA of cancer cells; however, only a subset of mutations found
within the genomic landscape of cancer is likely to provide a fitness advantage to the cell. These
mutations that provide a growth advantage to cancer cells are called driver mutations. The detection
of specific gene driver mutations in certain cancers that either stimulate or interrupt important
growthregulatory gene pathways has led to a series of studies aimed at identifyingtreatments against
these genetic changes and the discovery of targeted therapies. However, the fact that targeted
treatment is most successful in a subset of tumors indicates the need for better classification of
clinically related molecular tumor phenotypes based on improved understanding of the mutations
in relevant genes, especially in those oncogenic driver mutations.
There are two fundamental aspects that we need to consider when we think about targeted
anticancer treatments. The first is that targeted therapy, as well as also conventional chemo- and
radiation-therapy, are all known to causeadditional accumulation of genetic changes in cancer
cells due to their genomic instability. The second is that,intrinsically genetic instability and the
accumulation of additional mutations in cancer cells is a way that cancer cells use to adapt to and
survive in a hostile environment such as the one created by these treatment modalities. Collectively,
all these post therapy-induced additional genetic changes, may happen in a gene or in a group of
genes that are located upstream or downstream tothe “driver” mutated gene in a gene pathway, thus
causing the targeted treatment to be unfortunately unsuccessful.
Besides the introduction of targeted therapies for cancer, traditional chemotherapy has been
largely established on cytotoxic drugs that destroy rapidly dividing cells which are chosen empirically
by the treating physicians, and this approach has been used for the past eight decades. Several
studies have been performed to develop diagnostic tools to predict effectiveness of chemotherapy
[4]. Chemo-Sensitivity and Resistance Assays (CSRA), which measure cell death or lack of cell death
by drug-induced apoptosis, are one of such diagnostic tools. Several studies on CSRA focused on
ovarian cancer [5-7], gastric cancer [8], colorectal adenocarcinoma [9], breast cancer [10,11], non-small cell lung cancer [12] and small-cell lung cancer [12,13], have followed similar protocols with minor variations in their assay setup.
All of these assays, which have been developed in the past 20-30
years, used cultures of bulk tumor cells to determine cytotoxicity and
to predict anticancer response.A major breakthrough in the 1990s
in the understanding of cancer initiation and progression has been
the discovery of a cellular subpopulation with stem cell–like features,
commonly referred to as cancer stem cells (CSCs), which is critical
for tumorigenesis, treatment resistance and cancer recurrence [14,15]. CSCsshare many properties with normal adult stem cells,have
been shown to propagate the parental tumor in animal models, and
to be the cause of metastasis[14-17]. Importantly, cancer lethality is
mainly due to the onset of distant metastases and their resistance to
chemotherapy. Several evidence demonstrated that CSCs are widely
protected against commonly used chemotherapeutic agents by
means of different mechanisms, including increased expression of
ATP-binding cassette drug transporters, augmented ability in DNA
damage repair, and activation of PI3K/AKT and Wnt pathways [18].
Because of the presence of therapy resistant CSCs, each time patients
are treated they always have a chance to relapse, and their cancer will
likely become more resistant to therapy [19].
Of note is that selection of effective chemotherapy is extremely
important not only when therapy is first initiated, but for recurrent
disease as well. In fact, administration of ineffective anticancer therapy
is often associated with unnecessary toxicity and the development of
more aggressive cancer cell clones that are resistant to subsequent
therapies[20].
Unfortunately, research on CSCs has failed thus far to discover
universally clear and informative biomarkers, mutations, or geneexpression
patterns [21]. Recently, a new drug response assay has
been developed, which is called ChemoID®that tests separately CSCs
and bulk of tumor cells. This test has been used effectively to predict
the most active chemotherapy agents’ combination to treat individual
cancers [22-27]. Targeting CSCs along with the bulk of other cancer
cells is a new paradigm in cancer treatment, which is fulfilling the
Precision Medicine Initiative that was launched by President Barak
Obama in 2015. The ChemoID® drug response assay in a recent
prospective study of 41 glioblastoma patients, showed a statistically
significant improved response rate (2.2-fold increase) in patients who
were given assay-indicated chemotherapy [28] demonstrating that
the ability to personalize therapy by providing the treating physician
with drug response information on a panel of standard-of-care first
and second choice drugs should aid in the selection of most effective
chemotherapy for individual patients, thus resulting in improved
clinical outcomes.A drug response assay like ChemoID® that targets
CSCs may become a very useful tool for optimizing treatment
selection especially when first-line therapy fails, and when there are
multiple clinically -acceptable and -equivalent treatments available.
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