tumor cell biology program - Sylvester Comprehensive Cancer Center

(VSV), an essentially nonpathogenic
negative-stranded RNA virus, can selectively
induce the cytolysis of numerous
transformed human cell lines in
vitro. The ability of these viruses to selectively
kill tumor cells and not normal
cells was dependent on the PKR/
interferon pathway being defective in
susceptible cells. The research now has
demonstrated in vivo that tumors defective
in p53 function or transformed
with myc or activated ras are also susceptible
to viral cytolysis, and that the
mechanism of viral oncolytic activity
involves the induction of multiple
caspase-dependent apoptotic pathways.
Furthermore, VSV caused significant
inhibition of tumor growth when administered
intravenously in immunocompetent
hosts. Findings suggest that
VSV could be used as a potential oncolytic
agent against a wide variety of
malignant diseases associated with a
diversity of genetic defects. Extensions
of this work now include engineering
VSV to express proteins from viruses
associated with cancer such as hepatitis
C (HCV) and human papilloma
virus (HPV) for vaccine and therapeutic
purposes. For example, chimeric
VSV containing HCV structural proteins
is being examined as a therapeutic
or preventative vaccine.
• Dr. Harrington focuses on the use of
antiviral agents in viral-induced malignancies.
He has found that antiviral
thymidine analogues such as azidothymidine
(AZT) induce marked apoptosis
in Epstein Barr Virus (EBV)
associated lymphomas. This therapy
was very effective in eradicating AIDSrelated
brain lymphoma and now is
being tested in a nationwide clinical
trial. More recently, Dr. Harrington
found that AZT and Interferon alpha
(IFNα) induce apoptosis in human
herpes virus-8 (HHV-8) lymphoma
lines. Interestingly, these agents have no
effect on viral-negative lymphomas.
The data demonstrates that IFNα potentially
induces the death receptor
ligand TRAIL. AZT acts by blocking
NF-κB (p50, p65) translocation into
the nucleus allowing for an unopposed
death signal. A similar mechanism has
been shown to occur in other viral-induced
tumors such as adult T-cell leukemia
(HTLV-I) and post-transplant
lymphoma (EBV). Dr. Harrington’s
team has initiated a new clinical trial
for HHV-8 associated lymphomas that
utilizes parenteral AZT and IFNα
(these tumors are virtually always fatal).
The only patient enrolled is in
complete remission. Current studies are
focused on understanding the specificity
of this therapy for herpes virus associated
lymphomas, the development
of more potent antiviral antilymphoma
thymidine analogues, and the extension
of this approach to other gamma herpes
and lymphomas that occur in the
imuno-compromised patients (post
transplant, hereditary immunodeficiencies).
This work is done in collaboration
with Dr. Mian and Dr. Agarwal.
Dr. Harrington also recently received
a NCI-funded career award (K24)
which will enable him to focus on the
above described laboratory and clinical
studies.
• Dr. Downey and Dr. So have recently
identified a novel protein, polymerase
delta interacting protein (PDIP1). This
protein interacts with the small subunit
(p50) of DNA polymerase delta (the
primary polymerase responsible for cell
growth and differentiation) and the
proliferating cell nuclear antigen
(PCNA). PDIP1 colocalizes with pol
delta and PCNA at replication foci in
the nuclei of S-phase cells and stimulates
its activity (in the presence of
PCNA). The expression of PDIP1 can
be induced by the cytokines tumor
necrosis factor alpha (TNF-α) and IL-
6. PDIP1 is a distal target of IL-6. Increasing
evidence suggests that the
cytokine IL-6 plays an important role
in the pathogenesis of certain types of
AIDS-related lymphomas. Recent
studies have strongly implicated a critical
role for IL-6 in EBV-dependent
lymphoproliferative disease. It also has
been reported that the development of
AIDS-associated Burkitt’s/small noncleaved
cell lymphoma is preceded by
elevated serum levels of IL-6. In addition,
cell lines derived from HHV-8 associated
AIDS Primary Effusion
Lymphomas (PEL) constitutively secret
high levels of both IL-6 and the HHV-
8 IL-6 homologue (vIL-6). Consistent
with these findings is the observation
that the inhibition of NF-κB (by AZT
or other inhibitors) down-regulates
cytokine IL-6 and induces apoptosis in
KSHV-infected primary effusion lymphoma
cells.
• Dr. Boise’s laboratory investigates factors
that regulate the pathways associated
with death receptor-induced
apoptosis. Previous studies have indicated
that cells can utilize one of two
pathways to propagate death signals
resulting from the ligation of the TNF
receptor as well as from CD95 (Fas/
Apo-1). Cells referred to as type I cells
can activate a caspase cascade that does
not require release of factors from the
mitochondria. Expression of antiapoptotic
proteins Bcl-2 or Bcl-x L
are
incapable of inhibiting death receptor
signaling in type I cells. In contrast,
death receptor signaling in type II cells
requires release of mitochondrial factors
and is inhibited by Bcl-2/x L
expression.
Dr. Boise has demonstrated that
cells can utilize both type I and type II
signals and that Bcl-2/x L
can effect type
I death receptor signaling when used
in concert with inhibitors of signaling
caspases. Interestingly, γ-herpes viruses
associated with Kaposi’s sarcoma and
primary effusion lymphomas (PEL) encode
both a Bcl-2 homologue as well
as an inhibitor of CD95 signaling
(vFlip). While it has been previously
suggested that viruses express these
molecules to block distinct death pathways,
based on our results we hypothesize
that vBcl-2 and vFlip may work
in concert to block complex death receptor
signaling. This hypothesis is
currently being tested through the introduction
of these genes into TNFα-
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UM/Sylvester Comprehensive Cancer Center Scientific Report 2002