NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.

Cover of Molecular Imaging and Contrast Agent Database (MICAD)

Molecular Imaging and Contrast Agent Database (MICAD) [Internet].

Show details

99mTc-Labeled tumor-associated glycoprotein 72 binding peptides G3-15 and T3-15

[99mTc]-G3-15 and [99mTc]-T3-15
, PhD
National Center for Biotechnology Information, NLM, Bethesda, MD 20894

Created: ; Last Update: October 27, 2011.

Chemical name:99mTc-Labeled tumor-associated glycoprotein 72 binding peptides G3-15 and T3-15
Abbreviated name:[99mTc]-G3-15 and [99mTc]-T3-15
Agent Category:Peptides
Target:Tumor-associated glycoprotein 72 (TAG-72)
Target Category:Other (glycoprotein)
Method of detection:Single-photon emission computed tomography (SPECT); gamma planar imaging
Source of signal / contrast:99mTc
  • Checkbox In vitro
  • Checkbox Rodents
Structure not available in PubChem.



The tumor-associated glycoprotein 72 (TAG-72) is a high molecular weight mucigenous protein that is found mainly in the extracellular matrix of neoplastic tumors (1). This glycoprotein is usually not expressed in normal tissues but is overexpressed in the tumors of several cancers, such as those of the colon and rectum (colorectal cancer), stomach, pancreas, ovaries, prostate, lung, breast, etc. Therefore, TAG-72 is considered to have much theranostic value (useful for the diagnosis and/or therapy of a disease) because it can be used for antigen-directed surgical resection of cancerous tumors with radiolabeled anti-TAG-72 monoclonal antibodies (mAb) (1). In addition, the detection or absence of TAG-72 expression in colorectal cancer tumors was shown to have prognostic value because individuals who had complete removal of tumors with surgery guided by mouse anti-Tag-72 mAb were shown to have a long-term survival advantage compared to patients who had an incomplete removal of the lesions (2). However, the main limitation of using radiolabeled antibodies (Ab) or their fragments to detect and treat malignant tumors is the long circulation half-life of these molecules and the development of human anti-mouse antibodies in the patients (3). In comparison, synthetic anti-tumor peptides that can be used for the noninvasive imaging and therapy of cancers show rapid clearance from circulation and non-target tissue, have more access and deeper penetration into the lesions, and may not be immunogenic (3-5).

Recently, the peptides GGVSCMQTSPVCENNL (A2-6) and NPGTCKDKWEICLLNGG (A3-10) were identified from a phase-display peptide library (f88-4/cys6) against TAG-72 and labeled with 99mTc to generate [99mTc]-A2-6 and [99mTc]-A3-10 (4). The labeled peptides were then evaluated in mice for the detection of LS-174T cell xenograft tumors that overexpress the TAG-72 antigen. In another study, two new peptides, FRERCDKHPQKCTKFL (G3-15) and DPRHCQKRVLPCPAWL (T3-15), which had a high affinity for the TAG-72 antigen, were identified when a modified procedure (from that used to purify the A2-6 and A3-10 peptides) was used to purify peptides from the f88-4/cys6 phage library (3). These peptides were then labeled with 99mTc to obtain [99mTc]-G3-15 and [99mTc]-T3-15, and the labeled compounds were tested for the detection of LS-174T cell xenograft tumors in mice. This chapter describes the results obtained with [99mTc]-G3-15 and [99mTc]-T3-15. Studies performed with [99mTc]-A2-6 and [99mTc]-A3-10 are described in a separate chapter of MICAD ( (6).



Peptides G3-15 and T3-15 were identified from the f88-4/cys6 phage peptide library by modifying a procedure used earlier to purify peptides from the phage library that bound the TAG-72 glycoprotein (4) as described by Xiao et al. (3). For studies described in this chapter, the new peptides were obtained from a commercial source in their native L-configuration, conjugated with N-hydroxysuccinimidyl-S-acetyl-mercaptoacetyltriglycine, and labeled with 99mTc as described elsewhere (3). The labeled peptides were purified on a Bio-Rad P2 size-exclusion column and had a radiochemical purity of >90% as determined with reversed-phase high-performance liquid chromatography (RP-HPLC) (4). The number of metal chelating molecules conjugated to each peptide, radiochemical yield and specific activity of the labeled peptides were not reported.

The stability of [99mTc]-G3-15 and [99mTc]-T3-15 was determined by incubating the labeled peptides in serum (source not reported) at 37°C for up to 60 min (3). A P2 column size-exclusion HPLC analysis of the peptides at 5 min into the incubation showed that both labeled peptides were intact, but HPLC analysis at 60 min revealed that ~5% of both 99mTc-labeled peptides were bound to serum proteins as indicated by the appearance of two high molecular weight peaks in the HPLC chromatograms (3). The high molecular weight peaks observed with both tracers were not characterized.

In Vitro Studies: Testing in Cells and Tissues


The IC50 values of [99mTc]-G3-15 and [99mTc]-T3-15 were determined with an in vitro competitive binding assay (3). For this, LS-174T cells were incubated with the 99mTc-labeled peptides in the presence of increasing concentrations (10−13 to 10−4 mol/L) of the respective non-labeled peptides, and the IC50 values were calculated as described by Chen et al. (4). The IC50 values of G3-15 and T3-15 were reported to be 10.32 nM and 0.29 nM, respectively.

Animal Studies



The biodistribution of [99mTc]-G3-15 and [99mTc]-T3-15 was investigated in nude mice (n = 4 animals/group) bearing LS-174T cell tumors on the left thigh (3). The animals were injected with either [99mTc]-G3-15 or [99mTc]-T3-15 through the tail vein. The animals were euthanized at 5, 30, and 90 min postinjection (p.i.) to remove all the major organs and determine the amount of radioactivity accumulated in the various tissues. Data were presented as percent of injected dose per gram tissue (% ID/g). Both labeled peptides had a similar pattern of biodistribution in the rodents. The kidneys showed the highest accumulation of label, with both tracers present at all the three time points. At 90 min p.i., most tissues had a radioactivity uptake of <1% ID/g. With [99mTc]-G3-15, the uptake of radioactivity in the tumor decreased from 2.01 ± 0.16% ID/g at 5 min p.i. to 0.17 ± 0.04% ID/g at 90 min p.i. Similarly, with [99mTc]-T3-15, tumor uptake of the tracer decreased from 2.56 ± 0.61% ID/g at 5 min p.i. to 0.45 ± 0.09% ID/g at 90 min p.i. The tumor/muscle (normal thigh) ratios with [99mTc]-G3-15 and [99mTc]-T3-15 increased from 1.10 and 1.02 at 5 min p.i., respectively, to 1.60 and 1.87, respectively at 90 min, p.i.

In another study, single-photon emission computed tomography (SPECT)/computed tomography (CT) whole-body scans were acquired at 20 min and 60 min p.i. from groups of mice (under anesthesia) injected with either [99mTc]-G3-15 or [99mTc]-T3-15 as described by Xiao et al. (3). SPECT/CT images acquired at 20 min p.i. showed that both tracers had cleared from circulation and that the tumor was clearly visible with both the labeled peptides. At this time point, maximum radioactivity was observed in the kidneys, with the radiolabeled compounds and some label present in the intestinal tract, gall bladder, and urinary bladder. At 60 min p.i., the tumor was visible only with [99mTc]-T3-15, indicating that, compared to [99mTc]-G3-15, this tracer had a higher affinity for the TAG-72 glycoprotein as observed during the in vitro studies (see above).

From these studies, the investigators concluded that, by using a modified purification procedure to purify peptides from the f88-4/cys6 phage peptide library, they could identify two new peptides, G3-15 and T3-15, which had a high affinity for the TAG-72 antigen (3). The investigators suggest that further development of these peptides may be useful to produce probes for the imaging and treatment of cancer in humans.

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.

Supplemental Information


No supplemental information is currently available.

NIH Support

A part of the studies reported in this chapter were supported by a National Institutes of Health grant CA111606.


Povoski S.P., Hatzaras I.S., Mojzisik C.M., Martin E.W. Oncologic theranostics: recognition of this concept in antigen-directed cancer therapy for colorectal cancer with anti-TAG-72 monoclonal antibodies. Expert Rev Mol Diagn. 2011;11(7):667–70. [PubMed: 21902525]
Povoski, S.P., I.S. Hatzaras, C.M. Mojzisik, M.W. Arnold, G.H. Hinkle, C.L. Hitchcock, D.C. Young, and E.W. Martin, Jr., Antigen-Directed Cancer Surgery for Primary Colorectal Cancer: 15-Year Survival Analysis. Ann Surg Oncol, 2011.
Xiao N., Cheng D., Wang Y., Chen L., Liu X., Dou S., Liu G., Liang M., Hnatowich D.J., Rusckowski M. Identification of a high affinity TAG-72 binding peptide by phage display selection. Cancer Biol Ther. 2011;11(1):22–31. [PMC free article: PMC3047098] [PubMed: 20980835]
Chen L., Wang Y., Cheng D., Dou S., Liu X., Liu G., Hnatowich D.J., Rusckowski M. Comparing two TAG-72 binding peptides previously identified by phage display as potential imaging agents. Nucl Med Commun. 2011;32(10):920–4. [PMC free article: PMC3164986] [PubMed: 21876403]
Rusckowski M., Gupta S., Liu G., Dou S., Hnatowich D.J. Evidence of specificity of radiolabeled phage display peptides for the TAG-72 antigen. Cancer Biother Radiopharm. 2007;22(4):564–72. [PubMed: 17803452]
Chopra, A., 99mTc-Labeled tumor-associated glycoprotein 72 binding peptides, A2-6 and A3-10. Molecular Imaging and Contrast agent Database (MICAD) [database online]. National Library of Medicine, NCBI, Bethesda, MD, USA. Available from www​, 2004 -to current.
PubReader format: click here to try


  • PubReader
  • Print View
  • Cite this Page
  • PDF version of this page (584K)
  • MICAD Summary (CSV file)

Search MICAD

Limit my Search:

Related information

  • PMC
    PubMed Central citations
  • PubMed
    Links to pubmed

Related citations in PubMed

See reviews...See all...

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...