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MedChemComm
DOI: 10.1039/C5MD00534E
expression of probe 2 in the cancerous cells was almost three
times to that observed in the normal cells (Figure 5B). As control
without using a tumorꢀtargeting tag is demonstrated. The signal is
potentially switchable and nonꢀswitchable depending on the local
experiments, we did not observe difference of fluorescence in 20 conditions, being nonꢀfluorescent at pH 6.5 and fluorescent at pH
cancer and nonꢀcancer cells with compound 4, 6 and 7.
7.5 and hence providing the advantage of signal amplification.
The effect gets reversed at pH >8.5. Both experimental results
and theoretical calculations show that the protonating/
deprotonating features of the molecule contribute to the
5
Although we did not measure cellular pH directly but the
combined results of biological and nonꢀbiological experiments
along with the literature support (difference in pH of cancer and
nonꢀcancer cells) confirm that probe 2 is capable to label the 25 fluorescence changes within a narrow pH range. The nonꢀtoxicity
cancerous cells and hence the notion of pH change of tumor cells
can be translated to the paradigm of a diagnostic technique. The
sensitivity of the technique may certainly be helpful in initial
stage detection of cancer and consequently reduction in the
of the probe to normal cells under the working concentration,
permeability to the cell membrane and reversibility of its action
further add to the biomedical applications of the probe.
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Financial assistance by DST and CSIR, New Delhi is gratefully
cancer mortality rate which otherwise is responsible for 15% of 30 acknowledged. AK, SK and MG thank CSIR, New Delhi for
1
3,14
the total deaths worldwide.
fellowship. University Grants Commission, New Delhi is
acknowledged for grant under University with potential for
Excellence and CPEPA to Guru Nanak Dev University.
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5
In conclusion, inspired by a natural process, the working of a
pH dependent, highly photostable (Figure S32, S36A) fluorescent
probe for differentiating the cancer cells from nonꢀcancer cells
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5
Figure 5: (A) Confocal images of the compound 2 expression in C6 glioma cells. (Scale Bar 50 ꢀm) (a) Undifferentiated C6 glioma cells
exposed to compound 2 for 24 h. (b) RA differentiated C6 glioma cells group: Undifferentiated C6 glioma cells first treated with 10 µM RA a
potent differentiation inducer, after every 48 h for 5 days, then exposed to the compound 2 for 24 h. DAPI (4',6ꢁdiamidinoꢁ2ꢁphenylindole) is
the fluorescent stain that emits blue fluorescence on binding to the AꢁT rich region of the DNA. Both cancer and normal cells showed
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fluorescence intracellularly in the cytosol of the cell. Images were captured using A1R Nikon Confocal Laser Scanning Microscope at λex
=
488 nm and λem range 500–550 nm. To highlight the function of probe 2, a negative control sample treated by DMSO has been performed
both in cancer cells and normal cells in DIC channel as DMSO itself is nonꢁfluorescent and no fluorescence signal was detected (Figure
S36B). (B) Histogram represents the relative change in the optical intensity of compound 2 in different treated groups as compared to
control. *p<0.05 represents the statistically significance difference between the treated groups and control.
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Notes and references
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Studies, Guru Nanak Dev University, Amritsarꢀ143005. India.
Fax: 91 183ꢀ2258819; Tel: 91 183 2258802 x 3495; Eꢀmail:
Biotechnology, Guru Nanak Dev University, Amritsarꢀ143005
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b
Department
of
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†
Electronic Supplementary Information (ESI) available:
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[General procedure, mass spectra, NMR spectra, Fluorescence
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