Protein scaffold-based molecular probes for cancer molecular imaging

Abstract

Protein scaffold molecules are powerful reagents for targeting various cell signal receptors, enzymes, cytokines and other cancer-related molecules. They belong to the peptide and small protein platform with distinct properties. For the purpose of development of new generation molecular probes, various protein scaffold molecules have been labeled with imaging moieties and evaluated both in vitro and in vivo. Among the evaluated probes Affibody molecules and analogs, cystine knot peptides, and nanobodies have shown especially good characteristics as protein scaffold platforms for development of in vivo molecular probes. Quantitative data obtained from positron emission tomography, single photon emission computed tomography/CT, and optical imaging together with biodistribution studies have shown high tumor uptakes and high tumor-to-blood ratios for these probes. High tumor contrast imaging has been obtained within 1 h after injection. The success of those molecular probes demonstrates the adequacy of protein scaffold strategy as a general approach in molecular probe development.

Fig. 1

Representative imaging probes with various size based on different platform (FDG: abbrev of fluorodeoxyglucose) (objects are not drawn in proportional size)

Fig. 2

Structure cartoons of representative protein scaffolds. Various parts of protein scaffolds like α-helix (red), β-sheets (yellow) or loops (green) can be used for in vitro display selection. Disulfide bridges are shown as orange lines. The PDB IDs used to generate this figure are given in parentheses: a nanobody [1QD0], b EETI II [2IT7], c Affibody [1Q2N], d anticalin [1T0V], e cytochrome b-562 [1M6T], f DARPins [1N0R], g 10 Fn-III [1FNA], h AgRP [1HYK]

Fig. 3

Gamma-camera imaging with Affibody molecules based probes. a Imaging of HER2 expression in SKOV-3 xenograft in BALB/c nu/nu mice with ^99mTc-maEEE-Z_HER2:342. b, c Imaging of HER2 expression in LS174T and SKOV-3 xenografts in BALB/c nu/nu mice with ^99mTc-Z_HER2:2395-C. d Imaging of EGFR expression in A431 xenografts in BALB/c nude mice using ¹¹¹In-Bz-DTPA-Z_EGFR:1907 (left) and ¹¹¹In-Bz-DTPA-(Z_EGFR:1907)₂ (right) (Tran et al. 2007a; Ahlgren et al. 2009; Tolmachev et al. 2009)

Fig. 4

PET and optical imaging with Affibody molecule-based probes. Imaging of HER2 expression in BT474 xenografts in BALB/c nu/nu mice with a ¹⁸F-FBEM-Z_HER2:342. Imaging of HER2 expression in SKOV-3 xenografts in BALB/c nu/nu mice with b ⁶⁴Cu-DOTA-Z_HER2:477 and c ABD-(Z_HER2:342)₂-AlexaFluo750. d Imaging EGFR expression in A431 xenografts in BALB/c nu/nu mice with ⁶⁴Cu-DOTA-Z_EGFR:1907. Arrows are pointed at tumors (Kramer-Marek et al. 2009; Cheng et al. 2009; Lee et al. 2008; Miao et al. 2009b)

Fig. 5

PET and optical imaging with 2-helix small proteins, cystine knot EETI and AgRPs based probes. a Monitoring Her2 expression reduction in SKOV3 xenografts in BALB/c nu/nu mice treated with (bottom) or without (top) 17-DMAG. Imaging of integrins expression in U87MG xenografts in BALB/c nu/nu mice with (b) ⁶⁴Cu-DOTA-2.5F, ⁶⁴Cu-DOTA-2.5D (top), Cy5.5-2.5F, Cy5.5-2.5D (bottom) and c ⁶⁴Cu-DOTA-AgRP-7C. Arrows are pointed at tumors (Ren et al. 2009; Kimura et al. 2009a; Jiang et al. 2010)

Fig. 6

SPECT and SPECT/CT imaging with nanobody based probes. a Imaging of carcinoembryonic (CEA) expression in LS174T xenografts in BALB/c nu/nu mice with ^99mTc-His₆-CEA-nanobody. b Imaging of EGFR expression in A431 xenografts in BALB/c nu/nu mice with ^99mTc-His₆-Nanobody-8B6. c Fused SPECT/CT imaging of EGFR expression in A431 xenografts in BALB/c nu/nu mice with ^99mTc-His₆-nanobody-7C (L liver, T tumor) (Huang et al. 2008; Gainkam et al. 2008)