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

111In-Labeled Ac-Phe-Lys(DTPA)-Tyr-Lys(DTPA)-NH2 (IMP-156)

, PhD
National Center for Biotechnology Information, NLM, Bethesda, MD 20894

Created: ; Last Update: July 27, 2011.

Chemical name:111In-Labeled Ac-Phe-Lys(DTPA)-Tyr-Lys(DTPA)-NH2 (IMP-156)
Abbreviated name:[111In]-IMP-156
Agent Category:Compound
Target:Bispecific PAM4 antibody
Target Category:Antibody
Method of detection:Single photon emission computed tomography (SPECT); gamma planar imaging
Source of signal / contrast:111In
  • Checkbox In vitro
  • Checkbox Rodents
Structure not available in PubChem.



The majority of individuals suffering from pancreatic adenocarcinoma (PAC) do not survive for more than 1 year after diagnosis and fewer than 1% of these patients live beyond 5 years (1). Although surgical resection of the cancer is a possible intervention for this disease only 10 – 25% of the patients are considered suitable for this treatment because usually by the time that neoplasm is detected the malignancy has metastasized to other organs and the tumor load in the patient is too high to warrant surgery (1). Patients with nonresectable PAC are treated either with gemcitabine or radiotherapy or a combination of the two, however, these treatments are not curative because they only prolong survival and improve the quality of life of the patient during that time (1). The detection of this cancer at an early stage can facilitate proper staging of the disease so that a suitable treatment regimen can be initiated to possibly improve patient prognosis (2). In this regard the monoclonal antibody (mAb), PAM4, which specifically targets mucin 1 (MUC1), a glycoprotein, overexpressed only in PAC tumors was developed, radiolabeled with 131I or 111In and shown to detect neoplastic tumors with scintigraphy in patients having pancreatic malignancies (3). However, intact radiolabeled antibodies are of limited utility to visualize cancerous lesions due to their large size (~150 kDa) and long circulating half-life (4). To amplify the signal obtained from an radiolabeled agent that can be used to detect or treat malignant tumors noninvasively, investigators have developed and evaluated a variety of strategies in preclinical studies in animals such as pretargeting the cancer lesion with a suitable mAb (or its derivative) followed by exposing the animals to an appropriate radiolabeled small molecular weight ligand that targets the mAb or its derivative. This technique has been shown to generate a higher signal-to-noise ratios during imaging compared to ratios obtained with a directly labeled mAb alone (5-7). Use of the pretargeting technique for the imaging and therapy of cancer has been discussed in detail elsewhere (8, 9).

Cardillo et al. developed a bispecific F(ab’)2 mAb (bsPAM4; bsmAb) by cross-linking a PAM4 Fab’ fragment (binds the MUC-1 antigen) to a murine anti-indium-diethylenetriaminepentaacetic acid (DTPA) mAb Fab’ fragment (binds the peptide hapten antigen) and used the unlabeled bsmAb to pretarget human CaPan-1 cell xenograft PAC tumors in nude mice (3). After the bsmAb was cleared from blood circulation the animals were injected with a radiolabeled peptide hapten to visualize the PAC lesions by whole body scintigraphy. To confirm the tumor targeting specificity bsPAM4 (the pretargeting bsmAb) the biodistribution of this bsmAb was investigated with 125I-labeled bsPAM4 ([125I]-bsPAM4) in mice bearing human PAC tumors (3). Subsequently two groups of animals pretargeted with bsPAM4 were separately injected with radiolabeled peptide haptens, 111In-labeled Ac-Phe-Lys(DTPA)-Tyr-Lys(DTPA)-NH2 ([111In]-IMP-156) and 99Tc-labeled Ac-Lys(DTPA)-Tyr-Lys(DTPA)-Lys(thiosemicarbazonyl-glyoxyl-cysteinyl-)-NH2 ([99mTc]-IMP-192), and the biodistribution of these radiolabeled peptides was investigated in the tumor bearing rodents. This chapter describes the biodistribution and imaging studies performed with [111In]-IMP-156. The biodistribution of radioiodinated bsPAM4 in non-pretargeted mice (10) and the biodistribution of [99mTc]-IMP-192 in mice pretargeted with bsPAM4 (11) are discussed in separate chapters of MICAD (

Other Sources of Information

Peptide haptens [PubMed]

Clinical trials with bispecific antibodies

Application of multivalent antibodies [PubMed]



The synthesis of bsPAM4 and bispecific retuximab (bsRIT; for use as a control) has been described by Cardillo et al. (3). The cross-linked bsmAbs were purified by size-exclusion chromatography (SEC) and the ratio of each Fab’ fragment in the complex was determined to be 1:1 with high performance liquid chromatography. The two bsmAbs were labeled with 125I using the chloramine-T method to obtain [125I]-bsPAM4 and [125I]-bsRIT as described elsewhere (3). [125I]-bsPAM4 and [125I]-bsRIT were reported to have specific activities (SA) of 492.2 MBq/mg (11.6 mCi/mg) and 403.3 MBq/mg (10.9 mCi/mg), respectively. The radiochemical purity and yield of the radioiodinated bsmAbs was not reported.

In an imaging study [111In]-labeled chimeric PAM4 (cPAM4) with a SA of 32.6 MBq/mg (0.88 mCi/mg was used as a control (3). The radiochemical yield and purity of this labeled antibody was not reported.

IMP-156 was obtained from a commercial source and labeled with 111In after chelation with diethylenetriamine pentaacetic acid (DTPA) and the residual DTPA sites on the peptide were quenched by the addition of nonradioactive indium (3). The number of indium atoms bound to each IMP-156 molecule (that has two DTPA sites within the structure as described above) was not reported. The SA of [111In]-IMP-156 was reported to be 183.2 MBq/nmol (4.95 mCi/nmol) and the radiolabeled peptide was reported to contain no aggregates and <2% unbound radioactivity as determined by instant thin layer chromatography.

The peptide hapten IMP-192 was obtained from the same commercial source as that of IMP-156 and labeled with 99mTc as described by Cardillo et al. (3). The SA of [99mTc]-IMP-192 was 77.7 MBq/nmol (2.1 mCi/nmol) and the amount of aggregates and the unbound radioactivity content was the same as the [111In]-IMP-156 preparation mentioned above. In an earlier study the radiochemical yield of the 99mTc-labeled peptide hapten was reported to be 94-99% with a SA of up to 67.7 GBq/mmol (1.83 Ci/mmol).

In Vitro Studies: Testing in Cells and Tissues


Karacay et al. reported that both IMP-156 and IMP-192 can be stored in a freeze dried form at -20o C for prolonged periods (12).

In a study to investigate the bsmAb binding characteristics of [111In]-IMP-156, 0.15 pmol of the labeled peptide was mixed with 10 pmol bsPAM4 in presence of excess MUC1 (200 μg) and the mixture was incubated at 37o C for 1 h (3). Subsequently, size-exclusion chromatography (SEC) of the mixture revealed that 88% of the tracer bound to bsPAM4. Of the total bsmAb bound fraction 92% of the label was in the MUC1 fraction, 6% in the non-MUC1-reactive bsPAM4 fraction and 2% of the radiocompound bound nonspecifically to the MUC1 antigen.

The in vitro stability of [99mTc]-IMP-192 in normal saline (0.9% sodium chloride), 1% human serum albumin and 10 mM cysteine was reported to be 96%, 96% and 89%, respectively, as determined by reversed-phase high performance liquid chromatography (12).

The bsmAb binding characteristics of [99mTc]-IMP-192 were also studied as described above (3). An analysis of the mixture with SEC showed that 81% of this tracer was bound to bsPAM4 and of the total fraction bound to bsmAb 85% of the label eluted in the MUC1 fraction, 11% in the non-MUC1-reactive bsPAM4 fraction and 4% of the radiocompound bound nonspecifically to the MUC1 antigen.

Animal Studies



The biodistribution of [111In]-IMP-156 was investigated in athymic nu/nu mice bearing human PAC CaPan-1 cell tumors (n = 14 mice/group) pretargeted with either [125I]-bsPAM4 or [125I]-bsRIT (control bsmAb) (3). A group of animals was injected with 10 μCi (150 pmol) [125I]-bsPAM4 and two other groups received 10 μCi (150 pmol) [125I]-bsRIT. Two other groups of animals received the labeled peptides alone. After 40 h a group mice were injected with 35 μCi (15 pmol) [111In]-IMP-156 and the animals were euthanized at 3 and 24 h post injection (p.i.; i. e. 43 and 64 h after administration of the bsmAbs). All organs of interest, including the tumors, were removed from the mice and the amount of radioactivity in the various tissues was determined. Data obtained from this study was presented as percent of injected dose per gram tissue (%ID/g). The biodistribution of [99mTc]-IMP-192 was also investigated in the animals as described above (3). No blocking studies were reported with either labeled peptide hapten.

At 3 h after injecting 111In-labeled IMP-156 the amount of radioactivity in the tumor from animals pretreated with bsPAM4 was determined to be 20.2 ± 5.5%ID/g (P < 0.0001) compared to 0.9 ± 0.1%ID/g in tumors of the bsRIT pretreated animals (3). With [99mTc]-IMP-192 the amount of radioactivity in the tumors of bsPAM4 and bsRIT pretargeted animals were reported to be 16.8 ± 4.8%ID/g (P < 0.0005) and 1.1 ± 0.2%ID/g, respectively. Both the radiolabeled peptides were shown to clear rapidly from the body of the non-pretargeted animals.

At 24 h after the treatment with [111In]-IMP-156 tumors from mice pretreated with bsPAM4 had a radioactivity uptake of 11.1 ± 3.5%ID/g (P < 0.0008) compared to 0.5 ± 0.02%ID/g in animals pretreated with bsRIT (3). In comparison, with [99mTc]-IMP-192 the tumors from animals pretargeted with bsPAM4 and bsRIT showed an accumulation of 12.9 ± 4.2%ID/g (P < 0.0008) and 0.4 ± 0.03%ID/g, respectively, at the same time point.

At 24 h after treatment with either [111In]-IMP-156 or [99mTc]-IMP-192 the tumor-to-nontumor ratios for all tissues obtained from animals pretargeted with bsPAM4 were higher than those obtained from non-pretargeted animals treated with [125I]-bsPAM4 alone (the P value range was <0.0001 to 0.008) (3).

In the animals pretreated with bsPAM4 the tumor-to-blood ratio with [111In]-IMP-156 and [99mTc]-IMP-192 were 274:1 and 80:1, respectively, compared to a ratio of 4:1 obtained with the non-pretargeted mice injected with [125I]-bsPAM4 alone (P<0.0002).

For imaging studies athymic mice bearing CaPan-1 xenograft tumors (n = 2 animals/group) were pretargeted with bsPAM4 and 40 h later injected with [111In]-IMP-156 (3). The control group was administered bsRIT followed an injection of the 111In-labeled peptide. Another group of animals received an injection of only [111In]-IMP-156 and the last group was injected with only [111In]-cPAM4 IgG. The whole body clearance of radioactivity from [111In]-IMP-156 was reported to be >85% at 4 h post injection (p.i.) compared to only 18% with the labeled cPAM4 IgG. The tumors were visible in the pretargeted animals at 0.5 h p.i. and remained visible with little background activity even at 24 to 168 h p.i. indicating that the radiolabeled peptide bound specifically to the tumors and was retained in the lesions during this period. Although tumors were also visible in animals injected with the directly labeled cPAM4 a high background activity was observed in the abdominal regions of the animals. No tumors were visualized by scintigraphy of animals pretargeted with bsRIT or mice treated with the labeled peptides alone (3).

From these studies the investigators concluded that both [111In]-IMP-156 and [99mTc]-IMP-192 were suitable to detect PAC xenograft tumors pretargeted with bsPAM4 in rodents (3).

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 information is currently available.

NIH Support

Studies described in this chapter were supported by National Institutes of Health grants CA-54425 and CA92723.


Gold D.V., Cardillo T., Goldenberg D.M., Sharkey R.M. Localization of pancreatic cancer with radiolabeled monoclonal antibody PAM4. Crit Rev Oncol Hematol. 2001;39(1-2):147–54. [PubMed: 11418312]
Gold D.V., Goggins M., Modrak D.E., Newsome G., Liu M., Shi C., Hruban R.H., Goldenberg D.M. Detection of early-stage pancreatic adenocarcinoma. Cancer Epidemiol Biomarkers Prev. 2010;19(11):2786–94. [PMC free article: PMC2976815] [PubMed: 20810605]
Cardillo T.M., Karacay H., Goldenberg D.M., Yeldell D., Chang C.H., Modrak D.E., Sharkey R.M., Gold D.V. Improved targeting of pancreatic cancer: experimental studies of a new bispecific antibody, pretargeting enhancement system for immunoscintigraphy. Clin Cancer Res. 2004;10(10):3552–61. [PubMed: 15161715]
Ahlgren S., Orlova A., Wallberg H., Hansson M., Sandstrom M., Lewsley R., Wennborg A., Abrahmsen L., Tolmachev V., Feldwisch J. Targeting of HER2-expressing tumors using 111In-ABY-025, a second-generation affibody molecule with a fundamentally reengineered scaffold. J Nucl Med. 2010;51(7):1131–8. [PubMed: 20554729]
Forster G.J., Santos E.B., Smith-Jones P.M., Zanzonico P., Larson S.M. Pretargeted radioimmunotherapy with a single-chain antibody/streptavidin construct and radiolabeled DOTA-biotin: strategies for reduction of the renal dose. J Nucl Med. 2006;47(1):140–9. [PubMed: 16391198]
Liu G., Dou S., Pretorius P.H., Liu X., Chen L., Rusckowski M., Hnatowich D.J. Tumor pretargeting in mice using MORF conjugated CC49 antibody and radiolabeled complimentary cMORF effector. Q J Nucl Med Mol Imaging. 2010;54(3):333–40. [PMC free article: PMC2939249] [PubMed: 20639818]
Uppal J.K., Varshney R., Hazari P.P., Chuttani K., Kaushik N.K., Mishra A.K. Biological evaluation of avidin-based tumor pretargeting with DOTA-Triazole-Biotin constructed via versatile Cu(I) catalyzed click chemistry. J Drug Target. 2011;19(6):418–26. [PubMed: 20678008]
Goldenberg D.M., Sharkey R.M. Radioactive antibodies: a historical review of selective targeting and treatment of cancer. Hosp Pract (Minneap) 2010;38(5):82–93. [PubMed: 20890056]
Sharkey R.M., Goldenberg D.M. Cancer radioimmunotherapy. Immunotherapy. 2011;3(3):349–70. [PMC free article: PMC3123828] [PubMed: 21395378]
Chopra, A., 125I-Labeled anti-mucin 1 bispecific antibody bsPAM4. Molecular Imaging and Contrast agent Database (MICAD) [database online]. National Library of Medicine, NCBI, Bethesda, MD, USA. Available from www​, 2004 -to current. [PubMed: 21834182]
Chopra, A., 99Tc-labeled Ac-Lys(DTPA)-Tyr-Lys(DTPA)-Lys(thiosemicarbazonyl-glyoxyl-cysteinyl-)-NH2 (IMP-192). Molecular Imaging and Contrast agent Database (MICAD) [database online]. National Library of Medicine, NCBI, Bethesda, MD, USA. Available from www​, 2004 -to current. [PubMed: 21834181]
Karacay H., McBride W.J., Griffiths G.L., Sharkey R.M., Barbet J., Hansen H.J., Goldenberg D.M. Experimental pretargeting studies of cancer with a humanized anti-CEA x murine anti-[In-DTPA] bispecific antibody construct and a (99m)Tc-/(188)Re-labeled peptide. Bioconjug Chem. 2000;11(6):842–54. [PubMed: 11087333]
PubReader format: click here to try


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...