01. Gene therapy Boulikas.pdf - Gene therapy & Molecular Biology

G. Deoxycytidine kinase/ara-C and
nitroreductase/5-(aziridin-1-yl)-2,4dinitrobenzamide
The human deoxycytidine kinase (dCK) can
phosphorylate the prodrug cytosine arabinoside (ara-C), a
cytidine analog, and catalyze its conversion into a toxic
drug inducing lethal strand breaks in DNA. Although ara-
C is a potent antitumor agent for hematologic
malignancies it is ineffective against solid tumors;
transduction of the dCK cDNA with adenovirus and
retrovirus into the 9L gliosarcoma cell line followed by
establishing intradermal and intracerebral gliomas in
syngeneic rats demonstrated the efficacy of systemic ara-C
treatment of the animals in eradicating these tumors
(Manome et al, 1996).
The prodrug 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB-
1954) is a weak, monofunctional alkylating agent which
can be activated by Escherichia coli nitroreductase to a
potent dysfunctional alkylating agent which crosslinks
DNA. Transduction of colorectal and pancreatic cancer
cell lines with the nitroreductase gene using a retroviral
vector rendered them 50 to 500-fold more sensitive than
parental cells to CB1954; concentrations of CB1954
Boulikas: An overview on gene therapy
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which were minimally toxic to nontransduced cells
achieved 100% cell death in a 50:50 mix of parental cells
with transduced cells expressing nitroreductase due to
"bystander" cell killing (Green et al, 1997).
H. Preferential expression of suicidal genes
in cancer cells using promoters/ enhancers
from tumor-specific genes
The principle of VDEPT (virus-directed enzyme
/prodrug therapy) was used to target hepatocellular
carcinoma using the regulatory region from the tumorspecific
α-fetoprotein gene to drive the Varicella zoster
thymidine kinases gene (Huber et al, 1991).
A similar gene therapy approach has been developed
for the treatment of primary and metastatic hepatic tumors
based on the overexpression of the suicidal gene cytosine
deaminase (CD) from E. coli under control of the
regulatory regions of the tumor marker gene
carcinoembryonic antigen (CEA) (Richards et al, 1995);
this created a chimeric gene that was specifically
expressed in neoplastic cells. Development of this strategy
has necessitated the identification of the regulatory regions
of
Figure 26. A nude mouse xenograft model was developed bearing malignant gliomas by s.c. injection of D54MG human cells or
D54MG human cells transduced and expressing E. coli PNP which are called D54-PNP cells; tumors were successfully eradicated with