TARGETED AND UNTARGETED FUSION PROTEINS: CURRENT APPROACHES TO CANCER IMMUNOTHERAPY - Fusion Protein Technologies for Biopharmaceuticals: Applications and Challenges - page 295

12

Control

RGD/tTF (10 g)

chTV-1/tTF (40 µ g)
chTNT 3/tTF (10 µ g)
chTNT 3/tTF (2.5

µ

1.0

g)
chTNT 3/tTF (2.5 µ g)
TV-1/tTF (20

µ

µ g)+RGD/tTF (5 µ g)

0.8

0.6

0.4

0.2

0.0

7 9 11 13 15 17 19 21

Days

FIGURE 19.7 Treatment of COLON 26-bearing BALB/c mice using different tTF fusion proteins.
Mice treated with RGD/tTF and chTV-1/tTF were injected daily 5. Mice treated with chTNT-3/tTF
were injected at three-day intervals 3.

and massive cell necrosis. Of interest, the chTV-1/tTF and
the RGD/tTF fusion proteins induced thrombosis in small-
and medium-sized tumor vessels while the chTNT-3/tTF
induced clotting in relatively larger vessels. Treatment
studies also showed that chTNT-3/tTF and chTV-1/tTF
but not RGD/tTF had a significant inhibition of tumor
growth (Figure 19.7). To attain a significant antitumor effect,
however, these thrombogenic agents had to occlude medium
and large vessels within the tumor. Further studies are
warranted to identify maximal conditions for inducing
therapeutic vascular coagulation as a new and potent method
of cancer therapy.

explore the use of fusion proteins in combination with
immunoregulatory T-cells (T reg ) depletion, are also pre-
sented in this section and promise to afford superior tumor
therapeutic efficacy through normal biological processes
and the induction of a memory response.

19.4.1 Cytokine Fusion Protein Combinations

Owing to the growing number of cytokine fusion proteins
that are being generated, it has been demonstrated that it is
possible to improve antibody-cytokine fusion protein medi-
ated therapy by using them in combination with other cancer
therapies [33]. For example, chTNT-3/cytokine fusion
proteins have been evaluated in multiple solid tumor models
of the BALB/c mouse [91]. Analysis of the cytokine activity
of these fusion proteins using standard in vitro tests shows
that they have between 50% and 85% of the activity of the
comparable free cytokine tested in parallel. Despite these
somewhat lower activity levels, these reagents produced
good tumor suppression in the three tumor models during
and directly after treatment, but 5-7 days after therapy, the
tumors continued to progress in size (Table 19.2). In two of
these models, those mice receiving the combination of
chTNT-3/IL-2, chTNT-3/TNF- a , and chTNT-3/IFN- g had
the best tumor regression estimated to be about 80% of
control groups at day 17. Although individual fusion pro-
teins had varying degrees of effectiveness in these tumor

19.4 COMBINATION FUSION PROTEINS
THERAPY

In recent years, several groups have begun to study the
potential synergistic activity of the combination of fusion
proteins fused to the same antibody molecule [86,87]. For
instance, a large body of data has been generated showing
the advantage in using combinations of cytokine and che-
mokine fusion proteins, compared with their single use, for
enhancing anticancer immune response [88-90]. In particu-
lar, different studies have broadly explored the potential of
combination cancer therapy using cytokine, chemokine, and
co-stimulatory fusion proteins. Other approaches, which