Bioluminescence
imaging:
progress
and
applications
Christian
E.
Badr
1,3
and
Bakhos
A.
Tannous
1,2,3
1
Neuroscience
Center,
Department
of
Neurology,
Massachusetts
General
Hospital,
Boston,
MA,
USA
2
Center
for
Molecular
Imaging
Research,
Massachusetts
General
Hospital,
Boston,
MA,
USA
3
Program
in
Neuroscience,
Harvard
Medical
School,
Boston,
MA,
USA
Application
of
bioluminescence
imaging
has
increased
tremendously
in
the
past
decade
and
has
significantly
contributed
to
core
conceptual
advances
in
biomedical
research.
This
technology
provides
valuable
means
for
monitoring
of
different
biological
processes
in
immunol-
ogy,
oncology,
virology
and
neuroscience.
In
this
review,
we
discuss
current
trends
in
bioluminescence
and
its
application
in
different
fields
with
an
emphasis
on
cancer
research.
Bioluminescence
imaging
Some
living
organisms
are
capable
of
converting
chemical
energy
into
light.
This
natural
phenomenon
has
led
to
a
research
field
called
bioluminescence
imaging
(BLI).
The
technique
simply
relies
on
the
detection
of
photons
emitted
from
cells
or
tissues
in
a
living
organism.
Unlike
fluores-
cence,
BLI
does
not
require
light
absorption
for
light
emis-
sion
at
a
longer
wavelength.
Bioluminescence
is
a
biological
process
that
requires
an
enzyme
known
as
luciferase,
a
substrate
(luciferin)
and
oxygen.
Some
luciferases
require
other
cofactors
such
as
ATP
and
Mg
2+
for
full
activity
(Figure
1).
Luciferases
encompass
a
wide
range
of
enzymes
that
catalyze
light-producing
chemical
reactions
in
living
organ-
isms.
Although
many
luminescent
species
exist
in
nature,
generally
in
lower
organisms
(beetles,
bacteria,
algae,
crus-
taceans,
annelids,
mollusks
and
coelenterates),
three
luci-
ferases
have
been
studied
in
detail
and
are
used
in
biomedical
research:
the
Photinus
pyralis
(firefly)
luciferase
(Fluc);
the
sea
pansy
Renilla
reniformis
luciferase
(Rluc);
and
the
marine
copepod
Gaussia
princeps
luciferase
(Gluc).
Gluc
is
naturally
secreted
and,
similar
to
Rluc,
does
not
require
ATP
for
activity,
so
it
can
report
from
the
cell
itself,
as
well
as
its
immediate
environment.
Furthermore,
Gluc
can
be
detected
in
blood
and
urine
of
small
animals,
thereby
allowing
ex
vivo
monitoring
of
biological
processes
[1,2].
However,
cell-associated
luciferases
(Fluc
and
Rluc)
yield
higher
light
output
when
localized
in
vivo.
Fluc
and
Rluc
(or
Gluc)
use
different
substrates
and
therefore
can
be
com-
bined
as
dual
reporters
for
BLI
of
two
different
processes
sequentially
in
cultured
cells,
as
well
as
in
the
same
living
animal,
with
temporally
distinct
kinetics
of
light
production
(glow
vs
flash;
Box
1)
[3,4].
The
blue
bioluminescence
(480
nm
peak)
of
Gluc
and
Rluc,
which
is
more
strongly
absorbed
by
pigmented
molecules
(e.g.
hemoglobin
and
melanin)
and
is
scattered
by
tissues,
makes
them
less
suitable
for
in
vivo
imaging
compared
to
Fluc,
which
emits
green
light
(562
nm).
The
discovery
of
red-emitting
luci-
ferases
from
Pyrophorus
plagiophthalamus
(Jamaican
click
beetle)
[5],
Photinus
pyralis
(American
firefly)
[6],
Luciola
italica
(Italian
firefly)
[7]
and
railroad
worm
(the
only
lucif-
erase
that
naturally
emits
red
light)
[8],
as
well
as
novel
chemical
reactions
leading
to
red-light
output
[6,9–12],
will
greatly
enhance
the
sensitivity
of
BLI
in
deep
tissues.
In
the
past
decade,
BLI
has
become
indispensable
for
noninvasive
monitoring
of
biologic
phenomena
in
vivo,
providing
fast
and
effective
ways
for
validating
findings
in
culture
(Table
1).
Here,
we
describe
recent
advances
in
BLI
and
applications
in
different
biomedical
fields.
Imaging
of
gene
expression
Bioluminescent
reporters
have
been
used
to
study
gene
expression
at
the
transcriptional
level.
Cis-transcriptional
reporter
systems
allow
the
analysis
of
gene
expression
and
gene
regulation.
This
is
performed
by
either
generating
point
mutations
or
deletions
in
a
promoter
region
of
a
gene
of
interest
or
using
different
transcription-factor-binding
sites
linked
to
a
minimal
promoter
to
drive
the
expression
of
a
luciferase.
This
approach
is
useful
for
reporting
different
events
that
affect
transgene
expression
such
as
signal
transduction,
receptor
activation
and
transcription
factor
activity,
and
thus
complements
conventional
in
vitro
meth-
ods
of
molecular
biology
and
biochemistry.
Post-transcrip-
tional
events
at
the
mRNA
level,
such
as
RNA
processing
and
splicing,
have
been
successfully
imaged
using
BLI
reporter
systems.
For
example,
mRNA
stability
is
imaged
by
fusing
a
luciferase
reporter
to
the
full-length
3
0
untrans-
lated
region
(UTR)
of
a
gene
of
interest
[13].
RNA
interfer-
ence
(RNAi)
has
recently
emerged
as
a
therapeutic
strategy
in
many
diseases.
RNAi-mediated
silencing
of
luciferase
expression
is
a
useful
strategy
for
testing
the
delivery
and
targeting
the
efficiency
of
small-interfering
RNAs
(siRNAs)
to
specific
tissues.
The
ability
of
nanoparticles
to
deliver
siRNAs
to
the
liver
was
tested
using
luciferase-targeted
siRNAs.
Knockdown
of
luciferase
gene
expression
was
effi-
ciently
measured
in
the
liver
using
BLI
[14].
MicroRNAs
(miRNAs;
endogenous
small
noncoding
RNAs)
can
also
inhibit
gene
expression
through
translational
repression
or
mRNA
cleavage
by
binding
to
the
3
0
UTRs
of
the
target
mRNA.
By
fusing
luciferase
to
a
miRNA
target
site
at
the
3
0
UTR,
miRNA
function
and
activity
could
be
imaged.
In
one
Review
Corresponding
authors:
Badr,
C.E.
(badr.christian@mgh.harvard.edu);
Tannous,
B.A.
(btannous@hms.harvard.edu).
624
0167-7799/$
–
see
front
matter
ß
2011
Elsevier
Ltd.
All
rights
reserved.
doi:10.1016/j.tibtech.2011.06.010
Trends
in
Biotechnology,
December
2011,
Vol.
29,
No.
12