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Gene therapy is a therapeutic trend for cancer, genetic disorder
and infectious disease. Introduction of cytokine genes
with immuno- stimulatory or antitumor effects have
demonstrated promise in animal models. Prothymosin a
(ProTa), a member of thymic hormones, can act as an
immunomodulator and has an intracellular function associated
with cell proliferation. It promotes differentiation and
activation of T cells andenhances the antitumor activity in
experimental tumor models. Bladder cancer is responsive
to immunotherapeutic agents and may represent a good
candidate for immunological interventions. We aim to use the
murine MBT-2 bladder tumor model to investigate the feasibility
of ProTa gene therapy of tumors delivered by retroviruses.
A recombinant retroviral vector pRUFNeo / ProTa which contains
ProTa cDNA was constructed and transfected into the ecotropic
helper-free packaging cell line, yCRE. Cell clones stably
transduced with the vector were isolated by G418 selection.
The higher virus titer-producing clones were obtained
through infection of the amphotropic packaging cell line,
yCRIP, with the ecotropic retroviruses. C3H/HeN mice which were
injected with MBT-2 cells mixed with the replication-defective
retroviruses encoding for the ProTa gene showed lower tumor
incidence as well as higher antitumor responses in
vitro. In vitro, the MBT-2 clones infected with the
recombinant retroviruses were selected and the stable
integration of the vector genome checked by detecting the neo
mRNA expression. The higher ProTa mRNA and
biologically active ProTa expressions was detected in
their cultural supernatants compared with its wild-type
counterpart. Moreover, more colony formation on soft-agar as
well as faster growth rate were observed. The MBT-2/
ProTa clone #10 expressing a higher level of
biologically active ProTa exhibited lower tumorigenicity
and induced a stronger antitumor responses in the murine
tumor model. The mice coinjected with g-irradiated MBT-2 /ProTa
clones expressing various levels of ProTa with MBT-2 presented
different degrees of tumor incidence and tumor size in an
inverse correlation to the amount of ProTa expression. In
summary, genetic administration of ProTa might be an
effective approach in bladder cancer therapy.
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