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MARÍA ÁNGELES GARCÍA Y COLS. AN. R. ACAD. NAC. FARM.

TRAMP-C1. We found that VV-PKR replicates efficiently in prostate tu-
mour TRAMP-C1 cultured cells while it expresses low levels of PKR.
However, inoculation of VV-PKR in mice by either i.n. or i.p. routes
results in reduced virus replication in tissues and animals recovered
from viral infection. Significantly, the establishment of an aggressive
tumour in mice by subcutaneous inoculation of TRAMP-C1 cells was
markedly reduced following systemic inoculation with VV-PKR. This
reduction in tumour burden was similar to that induced by viral vec-
tors lacking TK, similar to VV-LUC or the catalitically inactive mutant
VV-PKR(K296R). Since VV-PKR also lacks TK but has a reduced ca-
pacity to propagate in tissues than either VV-LUC or VV-PKR(K296R),
the fact that the vector inhibits the tumour growth similarly as the two
other vectors, suggest that the contribution of PKR is important to re-
strict tumour growth. This could be mediated by activation of PKR in
infected tumour cells leading to apoptosis and cell death, while nei-
ther VV-LUC or VV-PKR(K296R) are able to induce apoptosis (16, 17).
However, we could not detect virus propagation in most of the animals
inoculated with VV-PKR at the tumour site, while virus was easily
found in tumours from animals inoculated by i.p. with VV-LUC or VV-
K296R. This indicates that factors other than virus replication in tu-
mour cells are responsible for PKR-induced tumour reduction. The re-
duced virus propagation of VV-PKR will have the added advantage that
antibody responses against the vector will be minimized. In fact, we
observed that in mice inoculated i.p. with VV-PKR the levels of anti-
bodies produced against the virus vector are about 5-fold lower than
those triggered by either VV-LUC or VV-PKR (296R). This character-
istic made it possible the administration in vivo of repetitive doses of
VV-PKR at the tumour site or systemically as shown here, while a ful-
ly replicating VACV vector triggering strong antibody response against
itself will be more restricted after additional doses of the vector are in-
oculated.

Why PKR may be an advantage as an inhibitor of tumour growth?
Considering its mode of action, PKR has been shown to act in concert
with major inflammatory kinases and directly interact with a critical
insulin signalling component, suggesting PKR as a core component of
a putative metabolic inflammasome that consist of major elements in
inflammatory signalling and insulin action, which can represent a cen-
tral mechanism for the integration of pathogen response and innate

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