Biomedical Engineering Reference
In-Depth Information
disease (CD) and atherosclerosis. The chronic inflammation,
that is, a hallmark of these diseases results in increased
expression of MMPs at the sites of disease. Indeed, up-
regulation of the expression of a whole range of MMPs has
been demonstrated for both CD (particularly MMP-1, -3,
and -9; [68,69]) and for atherosclerosis (especially MMPs -8
and -13; [70]). There is long-standing interest in the use of
IL-10 to treat both of these diseases due to the anti-inflam-
matory properties of this cytokine, and there are many
tantalizing hints that IL-10 could indeed be effective in
treating these conditions.
up-regulation of P-selectin [80] and cholesterol esterifica-
tion in macrophages [81] and the net effect of IL-4 may also
vary with the stage of the disease. Use of latent IL-4 could be
used to overcome the pleiotropic effects of this cytokine and
it has recently been demonstrated that latent IL-4 is more
effective in the treatment of fat-diet-induced atherosclerosis
in Apo-E
mice than free IL-4 ([82] submitted). These
effects on atherosclerotic plaque reduction are thought to be
most likely due to the increased serum half-life of the latent
molecule.
The uses of therapeutic cytokines in treating inflamma-
tory conditions as discussed above, is obviously focused on
the potential of cytokines with anti-inflammatory effects, the
most obvious candidates being IFN-
b
, IL-10, and IL-4.
Developing the latent cytokine technology as a treatment
for cancer may involve a quite different pool of therapeutic
cytokines, from agents that enhance NK cell and T cell
function (e.g., IL-2, IL-7, IL-6, and IL-4) to molecules that
enhance tumor antigen presentation (e.g., IFN-
b
, IFN-
g
, and
IL-13). One of the most effective cytokines in the treatment
of cancer to date is IFN-
a
, which has anti-tumor effects in
several hematological malignancies.
Given the evidence that certain cytokines are potentially
extremely effective in the treatment of tumors, but that have
poor pharmacokinetic and/or toxicity profiles, there is a need
to develop novel strategies that will enable these cytokines to
be used effectively in the treatment of these diseases and this
is one area where the LAP technology may prove invaluable.
The up-regulation of MMPs at tumor sites is well docu-
mented [83,84] and their role is to promote tumor growth
and metastatic spread [85]. This MMP activity at the tumor
site will activate any latent cytokine in the vicinity, but
ensures that the potent actions of the cytokines are exerted
only at the sites of disease.
/
16.5.2.2 Interleukine 10
IL-10 knockout mice suffer
from accelerated atherosclerosis, in contrast to IL-10 trans-
genic mice that are relatively protected [71]. Patients with
unstable angina have decreased serum levels of IL-10
compared with patients with chronic stable angina [72].
Similarly, there are encouraging results from treatment of
animal models of colitis with IL-10 [73], and in vitro studies
have shown that IL-10 can down-regulate the pro-inflam-
matory cytokine release from cells isolated from the lamina
propria isolated from patients with CD. However, despite
these results, early clinical studies using recombinant IL-10
to treat CD have been unsuccessful. This is likely due to the
complex biology of IL-10. In addition to the down-regula-
tion of immune responses, IL-10 is also known to exert
immunostimulatory effects via up-regulation of MHC Class
II molecules on B lymphocytes and the induction of cyto-
toxic T cell differentiation. Certainly, the picture that is now
emerging from these in vivo studies on the use of IL-10 in the
treatment of CD is that IL-10 may have both anti- and pro-
inflammatory effects, depending on the local concentrations
achieved, and that high systemic doses of IL-10 can alter the
balance between immunoregulatory and immunostimula-
tory effects [74]. It is also possible that systemic adminis-
tration of IL-10 does not allow delivery of sufficiently high
concentrations of the cytokine to the site of disease, given
that the half-life is in the region of 1.1-2.6 h. Production of
latent IL-10 could solve this problem and prevent the side-
effects of high systemic concentrations of IL-10 found in
some studies [75,76].
16.6 ALTERNATIVES/VARIANTS OF APPROACH
The latent cytokine technology, as it currently stands, con-
sists of a therapeutic cytokine enclosed within the LAP shell,
which can be removed by MMP activity due to the MMP
cleavage site located between the LAP and cytokine. As
described previously, the LAP is situated at the N-terminal
end of the fusion protein to ensure full latency. It has already
been demonstrated that production of the fusion protein with
the LAP at the C-terminus of the fusion protein results in a
cytokine that retains most, although not all, of its biological
activity, and thus, is not fully latent [7]. Therefore, any
variant of the technology should not involve any change in
the positioning of the LAP relative to the cytokine.
There is, however, much scope for producing fusion
proteins that have different cleavage sites and/or different
cytokines/signaling molecules. It is clear that the LAP shell
can accommodate cytokines that are larger in size than the
16.5.2.3 Interleukine 4
The other cytokine of interest in
terms of a potential treatment for atherosclerosis is IL-4.
This is a classic TH2 cytokine, and also has immuno-
suppressive effects on macrophages, including suppressing
the secretion of pro-inflammatory cytokines [77]. IL-4
deficient mice are protected from susceptibility to diet-
induced atherosclerosis [78] and mice deficient in Stat6
(one of the transcription factors activated by IL-4) develop
larger atherosclerotic lesions than their wild-type counter-
parts [79]. However, despite these anti-atherogenic effects,
the highly pleiotropic nature of IL-4 means that this cytokine
also has a number of pro-atherogenic affects such as
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