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NMR Biomed. 2016 Mar;29(3):309-19. doi: 10.1002/nbm.3466. Epub 2016 Jan 11.

Imaging the intratumoral-peritumoral extracellular pH gradient of gliomas.

Coman D1,2, Huang Y1,2, Rao JU1,2, De Feyter HM1,2, Rothman DL1,2,3, Juchem C1,2,4, Hyder F1,2,3.

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Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA.
Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut, USA.
Biomedical Engineering, Yale University, New Haven, Connecticut, USA.
Neurology, Yale University, New Haven, Connecticut, USA.


Solid tumors have an acidic extracellular pH (pHe ) but near neutral intracellular pH (pHi ). Because acidic pHe milieu is conducive to tumor growth and builds resistance to therapy, simultaneous mapping of pHe inside and outside the tumor (i.e., intratumoral-peritumoral pHe gradient) fulfills an important need in cancer imaging. We used Biosensor Imaging of Redundant Deviation in Shifts (BIRDS), which utilizes shifts of non-exchangeable protons from macrocyclic chelates (e.g., 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate) or DOTP(8-) ) complexed with paramagnetic thulium (Tm(3) (+) ) ion, to generate in vivo pHe maps in rat brains bearing 9L and RG2 tumors. Upon TmDOTP(5-) infusion, MRI identified the tumor boundary by enhanced water transverse relaxation and BIRDS allowed imaging of intratumoral-peritumoral pHe gradients. The pHe measured by BIRDS was compared with pHi measured with (31) P-MRS. In normal tissue, pHe was similar to pHi , but inside the tumor pHe was lower than pHi . While the intratumoral pHe was acidic for both tumor types, peritumoral pHe varied with tumor type. The intratumoral-peritumoral pHe gradient was much larger for 9L than RG2 tumors because in RG2 tumors acidic pHe was found in distal peritumoral regions. The increased presence of Ki-67 positive cells beyond the RG2 tumor border suggested that RG2 was more invasive than the 9L tumor. These results indicate that extensive acidic pHe beyond the tumor boundary correlates with tumor cell invasion. In summary, BIRDS has sensitivity to map the in vivo intratumoral-peritumoral pHe gradient, thereby creating preclinical applications in monitoring cancer therapeutic responses (e.g., with pHe -altering drugs).


CEST; SPIO; extravasation; magnetic susceptibility; metastasis; permeability

[Available on 2017-03-01]
[Indexed for MEDLINE]
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