Current Cancer Drug Targets, Volume 1, Number 2, 2001
Contents
Selectively Replicating
Adenoviruses for Oncolytic Therapy Pp. 85-107
Tack-Kee Laurent Yoon, Toshiaki Shichinohe, Sylvie
Laquerre and Norii Kasahara
Selective Destruction of
Tumor Cells through Specific Inhibition of Products Resulting from Chromosomal
Translocations
Pp. 109-119
A. Rodriguez-García, M. Sánchez-Martín, J.
Pérez-Losada, P.A. Pérez-Mancera, A. Sagrera-Aparisi, N. Gutiérrez-Cianca, C.
Cobaleda and I. Sánchez-García
Mutant Cell Surface
Receptors as Targets for Individualized Cancer Diagnosis and Therapy Pp. 121-128
Karl-Friedrich Becker and Heinz Höfler
Rational Design of Potent
and Selective EGFR Tyrosine Kinase Inhibitors as Anticancer Agents Pp. 129-140
Sutapa Ghosh, Xing-Ping Liu, Yaguo Zheng and Fatih M.
Uckun
Thymidine Phosphorylase: A
Two-Face Janus in Anticancer Chemotherapy Pp. 141-153
F. Focher and S. Spadari
Microarrays: Spotlight on
Gene Function and Pharmacogenomics Pp. 155-175
M. Nees, and C. D. Woodworth
[Back to top] Selectively Replicating Adenoviruses for Oncolytic Therapy
The most prevalent
problem in cancer therapy is the regrowth and metastasis of malignant cells after standard treatment with
surgery, radiation, and/or
chemotherapy. Gene therapy approaches have suffered from the inadequate
transduction efficiencies of replication-defective vectors that have been used
thus far. Replication-competent vectors, particularly adenoviruses that cause
cytolysis as part of their natural life cycle, represent an emerging technology
that shows considerable promise as a novel treatment option, particularly for
locally advanced or recurrent cancer. A number of oncolytic adenoviruses that
are designed to replicate selectively in tumor cells by targeting molecular
lesions inherent in cancer, or by incorporation of tissue-specific promoters
driving the early genes that initiate viral replication, are currently being
tested in clinical trials. The results of these clinical trials indicate that,
in its current form, oncolytic adenovirus therapy shows the best results and
achieves an enhanced tumoricidal effect when used in combination with
chemotherapeutic agents such as cisplatin, leucovorin and 5-fluorouracil.
Nevertheless, each of the oncolytic adenoviruses in current use exhibits
characteristic shortcomings, and there is still considerable room for
improvement. Current strategies for improving the selectivity and efficacy of
oncolytic adenoviruses include molecular engineering of tumor cell-specific
binding tropism, selective modifications of viral early genes and incorporation
of cellular promoters to achieve tumor-specific replication, augmentation of
anti-tumor activity by incorporation of suicide genes, and manipulation of the
immune response.
[Back to top] Selective Destruction of
Tumor Cells through Specific Inhibition of Products Resulting from Chromosomal
Translocations
A key problem in
the effective treatment of patients with cancer (both leukemia and solid
tumors) is to distinguish between tumor and normal cells. This problem is the
main reason why current treatments for cancer are often ineffective. There have
been remarkable advances in our understanding of the molecular biology of
cancer that provides new selective tumor destruction mechanisms. The molecular
characterization of the tumor-specific chromosomal abnormalities has revealed
that fusion proteins are the consequence in the majority of cancers. These
fusion proteins result from chimeric genes created by the translocations, which
form chimeric mRNA species that contain exons from the genes involved in the
translocation. Obviously, these chimeric molecules are attractive therapeutic
targets since they are unique to the disease (they only exist in the tumor
cells but not in the normal cells of the patient), allowing the design of
specific anti-tumor drugs. Inhibition of chimeric gene expression by anti-tumor
agents specifically kills leukemic cells without affecting normal cells. As
therapeutic agents targeting chimeric genes, zinc-finger proteins,
antisense RNAs or hammerhead-based ribozymes have been used. All of
these agents have some limitations, indicating that new therapeutic tools are
required as gene inactivating agents that should be able to inhibit any
chimeric fusion gene product. Recently, we have used the catalytic RNA subunit
of RNase P from Escherichia coli, which can be specifically directed to
cut any mRNA sequence, to specifically destroy tumor-specific fusion genes
created as a result of chromosomal translocations. In this chapter, we will
review the advances made to selectively destroy tumor cells through specific
inhibition of products resulting from chromosomal translocations.
[Back to top] Mutant Cell Surface
Receptors as Targets for Individualized Cancer Diagnosis and Therapy
The catalogue of
gene alterations in human cancer is growing rapidly. Alterations in specific
genes that play important roles in diverse cellular functions such as cell
adhesion, signal transduction, differentiation, development or DNA-repair have
been identified. Cancer-associated
mutant cell surface molecules are very attractive candidates to target tumor
cells because they offer the possibility of minimizing toxic effects to
non-tumor cells. The cell adhesion molecule E-cadherin has been shown to play a
major role in determining which of the two subtypes of gastric cancer, diffuse
or intestinal type, develops. E-cadherin gene mutations typically affect the
extracellular portion of the homophilic receptor and are frequently found in
patients with diffuse-type tumors. Cancer-specific monoclonal antibodies
against the E-cadherin mutational hot spot region are now available. In cell
culture and in animal studies we have shown that mutation-specific antibodies
exclusively target cells expressing abnormal E-cadherin. Those cells expressing
the normal protein were not affected, demonstrating the specificity of our
approach. After linking to toxins, drugs or radiolabeled mutation-specific
antibodies could serve as very specific agents to treat small tumor deposits.
Patients for this novel individualized cancer therapy can be identified within
a day using routine immunohistochemistry of biopsies.
[Back to top] Rational Design of Potent and Selective EGFR Tyrosine Kinase
Inhibitors as Anticancer Agents
Increasing
knowledge of the structure and function of the Epidermal Growth Factor Receptor
(EGFR) subfamily of tyrosine kinases, and of their role in the initiation and
progression of various cancers has led to the search for inhibitors of
signaling molecules that may prove to be important in cancer therapy. The
complex nature of EGFR biology allows for potential opportunities for EGFR
inhibitors in a number of areas of cancer therapy, including proliferative,
angiogenic, invasive, and metastatic aspects. Different approaches have been
used to target either the extracellular ligand-binding domain of the EGFR or
the intracellular tyrosine kinase region that results in interference with its
signaling pathways that modulate cancer-promoting responses. Examples of these
include a number of monoclonal antibodies, immunotoxins and ligand-binding
cytotoxic agents that target the extracellular ligand binding region of EGFR,
and small molecule inhibitors that target the intracellular kinase domain and
act by interfering with ATP binding to the receptor. During the past 3 years,
significant progress has been made towards the identification of new structural
classes of small molecule inhibitors that show high potency and specificity
towards EGFR. The search for new small molecules that inhibit kinases has
included traditional approaches like the testing of natural products, random
screening of chemical libraries, the use of classical structure-activity-relationship
studies, and the incorporation of structure-based drug design and combinatorial
chemistry techniques. There has been a significant improvement in the
development of selective EGFR inhibitors with the use of a structure-based design
approach employing a homology model of the EGFR kinase domain. Molecular
modeling procedures have been used to generate novel molecules that are
complementary in shape and electrostatics to the EGFR kinase domain topography.
This review focuses on some examples of the successful use of this method.
[Back to top] Thymidine Phosphorylase: A Two-Face Janus in Anticancer
Chemotherapy
Several cytokines and
growth factors modulate angiogenesis through a fine tuned paracrine or
autocrine mode of action. Among them is plateled-derived endothelial cell
growth factor (PD-ECGF), which is highly is expressed in tumors, and is
angiogenic by stimulation of endothelial cell migration. Studies have shown
that PD-ECGF is identical to the well known enzyme thymidine phosphorylase
(TP), which is involved in thymidine
metabolism and homeostasis. Interestingly, PD-ECGF plays an angiogenic
role as a result
of its TP enzyme activity. In light of these findings, PD-ECGF/TP should not be
considered a true growth factor, and its PD-ECGF name is now actually a
misnomer. Recently, TP activity was thought of as an interesting potential
two-face target for controling tumor-dependent angiogenesis. In fact, on one
hand, its high levels of expression in tumors compared to non-neoplastic
regions, and its broad substrate specificity suggested that TP could be used as
an enzymatic tool to locally activate anticancer nucleoside bases or base
analogs. On the other hand, its enzyme-dependent angiogenic activity engendered
the search for specific inhibitors to reduce TP-dependent angiogenesis. This
review will describe TP, its activity, its possible mechanisms of action and
its role in angiogenesis. Particular attention will be focused on the design
and biological characterization of novel TP inhibitors which recently showed
promising anticancer activity.
[Back to top] Microarrays: Spotlight on Gene Function and Pharmacogenomics
The introduction
of microarray technology has dramatically changed the way that researchers
address many biomedical questions. DNA microarrays can measure expression of
thousands of genes simultaneously, providing extensive information on gene interaction and function. Microarray technology is a powerful tool for
identifying novel molecular drug targets and for elucidating mechanisms of drug
action. Furthermore, microarrays can monitor the global profile of gene
expression in response to specific pharmacologic agents, providing information
on drug efficacy and toxicity. Over the last several years, dramatic
advancements have occurred in array technology. In this review we describe
basic aspects of microarray instrumentation and experimentation. Each of the
major array formats including oligonucleotides arrays, spotted arrays, and
macroarrays are examined, and advantages and options for using each format are
presented. Important factors in the design and analysis of microarray
experiments are also discussed. Most importantly, we explore recent
developments in microarray technology that are relevant to pharmacogenomics and
the discovery of gene function.