detection of β-gal activity in living cells. The probe exhibited a weak fluorescence at
pH 7.4 without β-gal, while an obvious high fluorescence increase (1,400-fold) was
observed upon the reaction with β-gal. They further applied probe 3 for imaging
several cultured ovarian cancer cells. The results showed that the enhanced fluorescence could be decreased by a competitive β-gal inhibitor, indicating the high
specificity of 3 to detect intracellular β-gal activity. Further, SHIN3 cells were
used to test the practicability of cancer imaging in a mouse model. The metastases
as small as 1 mm were visualized clearly and specifically after injection of 3 in 5 min.
This results clearly indicated potential value of the probe for fluorescence-guided
diagnosis of peritoneal metastases from ovarian cancers.
In recent years, Zhang et al. [14] reported a small molecule fluorescent probe
named 4-hydroxyl-N-butyl-1,8-naphthalimide–β-gal (NI–β-gal, 4) for the detection
of β-gal. Upon incubation with β-gal, probe 4 would turn into 4-hydroxyl-Nbutyl-1,8-naphthalimide with a large Stokes shift and sharp fluorescent
enhancement according to the restoring of ICT character. The synthetic strategy
was well prepared so as all the reactions conditions were mild. After a three-step
procedure, 4-bromo-1,8-naphthalic anhydride was adopted to afford 4-hydroxyl-Nbutyl-1,8-naphthalimide. Upon addition of β-gal into probe 4 in PBS buffer (pH 7.4),
a large fluorescence increase was observed at 545 nm and a decrease at 440 nm.
Correspondingly, the F 545 /F 440 ratio acted as an enhancement behavior of 680-fold.
Subsequently, probe 4 turned out to be qualified to image stable β-gal expression
within tumors in living mice, and bright fluorescence could be observed in the
transfected tumor at 75 min after administration of 4, whereas the control group
exhibits a negative signal. In comparison with non-transfected tumors, transfected
tumors showed an approximately tenfold higher fluorescence intensity at 2 h after
administration of 4. Therefore, probe 4 maybe a useful tool in biomedical research
such as gene therapy for cancer in the future.
2.2 NIR Fluorescent Probe
Conventional fluorophores with wavelengths less than 600 nm exhibited several
shortcomings in vivo, such as poor tissue penetration and strong background
fluorescence from bio-specimens. In order to overcome preceding drawbacks as
well as elevate the signal-to-noise ratio, near-infrared fluorescent probes targeting
β-gal have been prepared by incorporating β-galactose residues into near-infrared
fluorophores like cyanine and squarylium dye scaffolds.
Redykeisar et al. [15] reported QCy7-based probe 5 targeting β-gal, which
possessed long-wavelength fluorescence and a turn-on option. The fluorophore
named quinone-cyanine-7 (QCy7), which was prepared by a simple two-step procedure, had strong emission in the NIR region but no emission after linking with
β-galactose residues. To assay the turn-on imaging option in vivo, probe 5 were then
injected subcutaneously into mice and the signal was monitored over time. The
results showed that probe 5 possessed excellent in vivo compatibility and exhibited
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A. Bi et al.
pH 7.4 without β-gal, while an obvious high fluorescence increase (1,400-fold) was
observed upon the reaction with β-gal. They further applied probe 3 for imaging
several cultured ovarian cancer cells. The results showed that the enhanced fluorescence could be decreased by a competitive β-gal inhibitor, indicating the high
specificity of 3 to detect intracellular β-gal activity. Further, SHIN3 cells were
used to test the practicability of cancer imaging in a mouse model. The metastases
as small as 1 mm were visualized clearly and specifically after injection of 3 in 5 min.
This results clearly indicated potential value of the probe for fluorescence-guided
diagnosis of peritoneal metastases from ovarian cancers.
In recent years, Zhang et al. [14] reported a small molecule fluorescent probe
named 4-hydroxyl-N-butyl-1,8-naphthalimide–β-gal (NI–β-gal, 4) for the detection
of β-gal. Upon incubation with β-gal, probe 4 would turn into 4-hydroxyl-Nbutyl-1,8-naphthalimide with a large Stokes shift and sharp fluorescent
enhancement according to the restoring of ICT character. The synthetic strategy
was well prepared so as all the reactions conditions were mild. After a three-step
procedure, 4-bromo-1,8-naphthalic anhydride was adopted to afford 4-hydroxyl-Nbutyl-1,8-naphthalimide. Upon addition of β-gal into probe 4 in PBS buffer (pH 7.4),
a large fluorescence increase was observed at 545 nm and a decrease at 440 nm.
Correspondingly, the F 545 /F 440 ratio acted as an enhancement behavior of 680-fold.
Subsequently, probe 4 turned out to be qualified to image stable β-gal expression
within tumors in living mice, and bright fluorescence could be observed in the
transfected tumor at 75 min after administration of 4, whereas the control group
exhibits a negative signal. In comparison with non-transfected tumors, transfected
tumors showed an approximately tenfold higher fluorescence intensity at 2 h after
administration of 4. Therefore, probe 4 maybe a useful tool in biomedical research
such as gene therapy for cancer in the future.
2.2 NIR Fluorescent Probe
Conventional fluorophores with wavelengths less than 600 nm exhibited several
shortcomings in vivo, such as poor tissue penetration and strong background
fluorescence from bio-specimens. In order to overcome preceding drawbacks as
well as elevate the signal-to-noise ratio, near-infrared fluorescent probes targeting
β-gal have been prepared by incorporating β-galactose residues into near-infrared
fluorophores like cyanine and squarylium dye scaffolds.
Redykeisar et al. [15] reported QCy7-based probe 5 targeting β-gal, which
possessed long-wavelength fluorescence and a turn-on option. The fluorophore
named quinone-cyanine-7 (QCy7), which was prepared by a simple two-step procedure, had strong emission in the NIR region but no emission after linking with
β-galactose residues. To assay the turn-on imaging option in vivo, probe 5 were then
injected subcutaneously into mice and the signal was monitored over time. The
results showed that probe 5 possessed excellent in vivo compatibility and exhibited
188
A. Bi et al.