Background

[PubMed]

The tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) receptor is a member of the tumor necrosis factor superfamily of cytokines that selectively activate a complex apoptotic pathway (caspase cascade) in tumor cells, thereby inducing apoptosis (cell death) (1, 2). There are two cell-surface TRAIL receptors (death receptor 4 [DR4] and 5 [DR5]) that are capable of inducing apoptosis and three decoy TRAIL receptors that are not capable of inducing apoptotic signals (3, 4). Conatumumab is a fully human monoclonal antibody (mAb) that acts as a human DR5 agonist antibody to tumor cells, which causes apoptosis in in vitro and in vivo studies (5, 6). Conatumumab is being evaluated in clinical trials (7, 8). Rossin et al. (9) reported the development of ⁶⁴Cu-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-conatumumab (⁶⁴Cu-DOTA-conatumumab) for positron emission tomography (PET) imaging of DR5 in nude mice bearing tumor xenografts.

Synthesis

[PubMed]

2,2',2''-(10-(2-(2,5-dioxopyrrolidin-1-yloxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (DOTA-N-hydroxysuccinimide) was added to conatumumab (100 nmol) in phosphate-buffered saline (9). The reaction mixture was adjusted to pH 8.5 and incubated for ~2 h at room temperature. DOTA-conatumumab was purified with column chromatography. DOTA-conatumumab (0.6–1.2 nmol) was incubated with 33–222 MBq (1–6 mCi) ⁶⁴CuCl₂ in ammonium acetate buffer (pH 5.5) for 1 h at 37°C. ⁶⁴Cu-DOTA-conatumumab was purified with column chromatography, with a radiochemical purity of >95%. The specific activities were 6 MBq/nmol (0.16 mCi/nmol) and 123 MBq/nmol (3.3 mCi/nmol) for ex vivo biodistribution studies and PET studies, respectively. There were approximately five DOTA molecules per antibody. ⁶⁴Cu-DOTA-conatumumab was stable in mouse serum for 24 h at 37°C.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

Rossin et al. (9) performed competition binding experiments using a conatumumab immobilized Biacore sensor chip. DOTA-conatumumab and conatumumab inhibited the binding of huTR2-Fc (1 nM) with 50% inhibition concentration (IC₅₀) values of 0.389 nM and 0.320 nM, respectively. The potency of DOTA-conatumumab and conatumumab to induce caspase 3/7 activities was compared in Colo205 human colon tumor cells. The effective doses to induce 50% of the maximum caspase 3/7 activities were 0.135 ± 0.31 nM and 0.128 ± 0.30 nM (n = 5), respectively. These data suggest that DOTA-conatumumab and conatumumab exhibit similar immunoreactivity and agonist activity for DR5.

Animal Studies

Human Studies

[PubMed]

No publication is currently available.

NIH Support

CA86307

References

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Kaplan-Lefko P.J. et al. Conatumumab, a fully human agonist antibody to death receptor 5, induces apoptosis via caspase activation in multiple tumor types. Cancer Biol Ther. 2010;9(8):618–31. [PubMed: 20150762]

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Soria J.C. et al. Phase 1b study of dulanermin (recombinant human Apo2L/TRAIL) in combination with paclitaxel, carboplatin, and bevacizumab in patients with advanced non-squamous non-small-cell lung cancer. J Clin Oncol. 2010;28(9):1527–33. [PubMed: 20159815]

9.

Rossin R. et al. Characterization of 64Cu-DOTA-conatumumab: a PET tracer for in vivo imaging of death receptor 5. J Nucl Med. 2011;52(6):942–9. [PubMed: 21571804]