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Imaging using radiolabelled targeted proteins: radioimmunodetection and beyond. EJNMMI Radiopharm Chem 2020; 5:16. [PMID: 32577943 PMCID: PMC7311618 DOI: 10.1186/s41181-020-00094-w] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Accepted: 04/14/2020] [Indexed: 12/18/2022] Open
Abstract
The use of radiolabelled antibodies was proposed in 1970s for staging of malignant tumours. Intensive research established chemistry for radiolabelling of proteins and understanding of factors determining biodistribution and targeting properties. The use of radioimmunodetection for staging of cancer was not established as common practice due to approval and widespread use of [18F]-FDG, which provided a more general diagnostic use than antibodies or their fragments. Expanded application of antibody-based therapeutics renewed the interest in radiolabelled antibodies. RadioimmunoPET emerged as a powerful tool for evaluation of pharmacokinetics of and target engagement by biotherapeutics. In addition to monoclonal antibodies, new radiolabelled engineered proteins have recently appeared, offering high-contrast imaging of expression of therapeutic molecular targets in tumours shortly after injection. This creates preconditions for noninvasive determination of a target expression level and stratification of patients for targeted therapies. Radiolabelled proteins hold great promise to play an important role in development and implementation of personalised targeted treatment of malignant tumours. This article provides an overview of biodistribution and tumour-seeking features of major classes of targeting proteins currently utilized for molecular imaging. Such information might be useful for researchers entering the field of the protein-based radionuclide molecular imaging.
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Chittoor B, Krishnarjuna B, Morales RAV, MacRaild CA, Sadek M, Leung EWW, Robinson SD, Pennington MW, Norton RS. The Single Disulfide-Directed β-Hairpin Fold. Dynamics, Stability, and Engineering. Biochemistry 2017; 56:2455-2466. [PMID: 28437072 DOI: 10.1021/acs.biochem.7b00120] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Grafting bioactive peptide sequences onto small cysteine-rich scaffolds is a promising strategy for enhancing their stability and value as novel peptide-based therapeutics. However, correctly folded disulfide-rich peptides can be challenging to produce by either recombinant or synthetic means. The single disulfide-directed β-hairpin (SDH) fold, first observed in contryphan-Vc1, provides a potential alternative to complex disulfide-rich scaffolds. We have undertaken recombinant production of full-length contryphan-Vc1 (rCon-Vc1[Z1Q]) and a truncated analogue (rCon-Vc11-22[Z1Q]), analyzed the backbone dynamics of rCon-Vc1[Z1Q], and probed the conformational and proteolytic stability of these peptides to evaluate the potential of contryphan-Vc1 as a molecular scaffold. Backbone 15N relaxation measurements for rCon-Vc1[Z1Q] indicate that the N-terminal domain of the peptide is ordered up to Thr19, whereas the remainder of the C-terminal region is highly flexible. The solution structure of truncated rCon-Vc11-22[Z1Q] was similar to that of the full-length peptide, indicating that the flexible C-terminus does not have any effect on the structured domain of the peptide. Contryphan-Vc1 exhibited excellent proteolytic stability against trypsin and chymotrypsin but was susceptible to pepsin digestion. We have investigated whether contryphan-Vc1 can accept a bioactive epitope while maintaining the structure of the peptide by introducing peptide sequences based on the DINNN motif of inducible nitric oxide synthase. We show that sCon-Vc11-22[NNN12-14] binds to the iNOS-binding protein SPSB2 with an affinity of 1.3 μM while maintaining the SDH fold. This study serves as a starting point in utilizing the SDH fold as a peptide scaffold.
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Affiliation(s)
- Balasubramanyam Chittoor
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
| | - Bankala Krishnarjuna
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
| | - Rodrigo A V Morales
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
| | - Christopher A MacRaild
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
| | - Maiada Sadek
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
| | - Eleanor W W Leung
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
| | - Samuel D Robinson
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
| | | | - Raymond S Norton
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
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Cho EH, Lim JC, Lee SY, Jung SH. An assessment tumor targeting ability of (177)Lu labeled cyclic CCK analogue peptide by binding with cholecystokinin receptor. J Pharmacol Sci 2016; 131:209-14. [PMID: 27430985 DOI: 10.1016/j.jphs.2016.06.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Revised: 06/21/2016] [Accepted: 06/22/2016] [Indexed: 01/14/2023] Open
Abstract
The cholecystokinin (CCK) receptor is known as a receptor that is overexpressed in many human tumors. The present study was designed to investigate the targeting ability of cyclic CCK analogue in AR42J pancreatic cells. The CCK analogues, DOTA-K(glucose)-Gly-Trp-Nle-Asp-Phe (DOTA-glucose-CCK) and DOTA-Nle-cyclo(Glu-Trp-Nle-Asp-Phe-Lys-NH2) (DOTA-[Nle]-cCCK), were synthesized and radiolabeled with (177)Lu, and competitive binding was evaluated. The binding appearance of synthesized peptide with AR42J cells was evaluated by confocal microscopy. And bio-distribution was performed in AR42J xenografted mice. Synthesized peptides were prepared by a solid phase synthesis method, and their purity was over 98%. DOTA is the chelating agent for (177)Lu-labeling, in which the peptides were radiolabeled with (177)Lu by a high radiolabeling yield. A competitive displacement of (125)I-CCK8 on the AR42J cells revealed that the 50% inhibitory concentration value (IC50) was 12.3 nM of DOTA-glucose-CCK and 1.7 nM of DOTA-[Nle]-cCCK. Radio-labeled peptides were accumulated in AR42J tumor in vivo, and %ID/g of the tumor was 0.4 and 0.9 at 2 h p.i. It was concluded that (177)Lu-DOTA-[Nle]-cCCK has higher binding affinity than (177)Lu-DOTA-glucose-CCK and can be a potential candidate as a targeting modality for a CCK receptor over-expressing tumors.
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Affiliation(s)
- Eun-Ha Cho
- RI Research Division, Research Reactor Utilization Department, Korea Atomic Energy Research Institute (KAERI), Daejeon 305-353, Republic of Korea.
| | - Jae Cheong Lim
- RI Research Division, Research Reactor Utilization Department, Korea Atomic Energy Research Institute (KAERI), Daejeon 305-353, Republic of Korea
| | - So-Young Lee
- RI Research Division, Research Reactor Utilization Department, Korea Atomic Energy Research Institute (KAERI), Daejeon 305-353, Republic of Korea
| | - Sung-Hee Jung
- RI Research Division, Research Reactor Utilization Department, Korea Atomic Energy Research Institute (KAERI), Daejeon 305-353, Republic of Korea
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Jiang L, Tu Y, Kimura RH, Habte F, Chen H, Cheng K, Shi H, Gambhir SS, Cheng Z. 64Cu-Labeled Divalent Cystine Knot Peptide for Imaging Carotid Atherosclerotic Plaques. J Nucl Med 2015; 56:939-44. [PMID: 25908832 DOI: 10.2967/jnumed.115.155176] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/08/2015] [Indexed: 01/24/2023] Open
Abstract
UNLABELLED The rupture of vulnerable atherosclerotic plaques that lead to stroke and myocardial infarction may be induced by macrophage infiltration and augmented by the expression of integrin αvβ3. Indeed, atherosclerotic angiogenesis may be a promising marker of inflammation. In this study, an engineered integrin αvβ3-targeting PET probe, (64)Cu-NOTA-3-4A, derived from a divalent knottin miniprotein was evaluated in a mouse model for carotid atherosclerotic plaques. METHODS Atherosclerotic plaques in BALB/C mice, maintained on a high-fat diet, were induced with streptozotocin injection and carotid artery ligation and verified by MR imaging. Knottin 3-4A was synthesized by solid-phase peptide synthesis chemistry and coupled to 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) before radiolabeling with (64)Cu. PET probe stability in mouse serum was evaluated. Mice with carotid atherosclerotic plaques were injected via the tail vein with (64)Cu-NOTA-3-4A or (18)F-FDG, followed by small-animal PET/CT imaging at different time points. Receptor targeting specificity of the probe was verified by coinjection of c(RGDyK) administered in molar excess. Subsequently, carotid artery dissection and immunofluorescence staining were performed to evaluate target expression. RESULTS (64)Cu-NOTA-3-4A was synthesized in high radiochemical purity and yield and demonstrated molecular stability in both phosphate-buffered saline and mouse serum at 4 h. Small-animal PET/CT showed that (64)Cu-NOTA-3-4A accumulated at significantly higher levels in the neovasculature of carotid atherosclerotic plaques (7.41 ± 1.44 vs. 0.67 ± 0.23 percentage injected dose/gram, P < 0.05) than healthy or normal vessels at 1 h after injection. (18)F-FDG also accumulated in atherosclerotic lesions at 0.5 and 1 h after injection but at lower plaque-to-normal tissue ratios than (64)Cu-NOTA-3-4A. For example, plaque-to-normal carotid artery ratios for (18)F-FDG and (64)Cu-NOTA-3-4A at 1 h after injection were 3.75 and 14.71 (P < 0.05), respectively. Furthermore, uptake of (64)Cu-NOTA-3-4A in atherosclerotic plaques was effectively blocked (∼90% at 1 h after injection) by coinjection of c(RGDyK). Immunostaining confirmed integrin αvβ3 expression in both the infiltrating macrophages and the neovasculature of atherosclerotic plaques. CONCLUSION (64)Cu-NOTA-3-4A demonstrates specific accumulation in carotid atherosclerotic plaques in which macrophage infiltration and angiogenesis are responsible for elevated integrin αvβ3 levels. Therefore, (64)Cu-NOTA-3-4A may demonstrate clinical utility as a PET probe for atherosclerosis imaging or for the evaluation of therapies used to treat atherosclerosis.
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Affiliation(s)
- Lei Jiang
- Department of Nuclear Medicine, Zhongshan Hospital, Fudan University, Shanghai, China; and Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
| | - Yingfeng Tu
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
| | - Richard H Kimura
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
| | - Frezghi Habte
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
| | - Hao Chen
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
| | - Kai Cheng
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
| | - Hongcheng Shi
- Department of Nuclear Medicine, Zhongshan Hospital, Fudan University, Shanghai, China; and
| | - Sanjiv Sam Gambhir
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
| | - Zhen Cheng
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University, Stanford, California
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Jiang L, Kimura RH, Ma X, Tu Y, Miao Z, Shen B, Chin FT, Shi H, Gambhir SS, Cheng Z. A radiofluorinated divalent cystine knot peptide for tumor PET imaging. Mol Pharm 2014; 11:3885-92. [PMID: 24717098 PMCID: PMC4212002 DOI: 10.1021/mp500018s] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
A divalent
knottin containing two separate integrin binding epitopes
(RGD) in the adjacent loops, 3-4A, was recently developed and reported
in our previous publication. In the current study, 3-4A was radiofluorinated
with a 4-nitrophenyl 2-18F-fluoropropinate (18F-NFP) group and the resulting divalent positron emission tomography
(PET) probe, 18F-FP–3-4A, was evaluated as a novel
imaging probe to detect integrin αvβ3 positive tumors
in living animals. Knottin 3-4A was synthesized by solid phase peptide
synthesis, folded, and site-specifically conjugated with 18/19F-NFP to produce the fluorinated peptide 18/19F-fluoropropinate-3-4A
(18/19F-FP–3-4A). The stability of 18F-FP–3-4A was tested in both phosphate buffered saline (PBS)
buffer and mouse serum. Cell uptake assays of the radiolabeled peptides
were performed using U87MG cells. In addition, small animal PET imaging
and biodistribution studies of 18F-FP–3-4A were
performed in U87MG tumor-bearing mice. The receptor targeting specificity
of the radiolabeled peptide was also verified by coinjecting the probe
with a blocking peptide cyclo(RGDyK). Our study showed that 18F-FP–3-4A exhibited excellent stability in PBS buffer (pH
7.4) and mouse serum. Small animal PET imaging and biodistribution
data revealed that 18F-FP–3-4A exhibited rapid and
good tumor uptake (3.76 ± 0.59% ID/g and 2.22 ± 0.62% ID/g
at 0.5 and 1 h, respectively). 18F-FP–3-4A was rapidly
cleared from the normal tissues, resulting in excellent tumor-to-normal
tissue contrasts. For example, liver uptake was only 0.39 ± 0.07%
ID/g and the tumor to liver ratio was 5.69 at 1 h p.i. Furthermore,
coinjection of cyclo(RGDyK) with 18F-FP–3-4A significantly
inhibited tumor uptake (0.41 ± 0.12 vs 1.02 ± 0.19% ID/g
at 2.5 h) in U87MG xenograft models, demonstrating specific accumulation
of the probe in the tumor. In summary, the divalent probe 18F-FP–3-4A is characterized by rapid and high tumor uptake
and excellent tumor-to-normal tissue ratios. 18F-FP–3-4A
is a highly promising knottin based PET probe for translating into
clinical imaging of tumor angiogenesis.
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Affiliation(s)
- Lei Jiang
- Department of Nuclear Medicine, Zhongshan Hospital, Fudan University , 180 Fenglin Road, Shanghai, China 200032
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Zhu X, Li J, Hong Y, Kimura RH, Ma X, Liu H, Qin C, Hu X, Hayes TR, Benny P, Gambhir SS, Cheng Z. 99mTc-labeled cystine knot peptide targeting integrin αvβ6 for tumor SPECT imaging. Mol Pharm 2014; 11:1208-17. [PMID: 24524409 PMCID: PMC3993876 DOI: 10.1021/mp400683q] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Integrin
αvβ6 is overexpressed
in a variety of cancers, and its expression is often associated with
poor prognosis. Therefore, there is a need to develop affinity reagents
for noninvasive imaging of integrin αvβ6 expression since it may provide early cancer diagnosis, more
accurate prognosis, and better treatment planning. We recently engineered
and validated highly stable cystine knot peptides that selectively
bind integrin αvβ6 with no cross-reactivity
to integrins αvβ5, α5β1, or αvβ3, also
known to be overexpressed in many cancers. Here, we developed a single
photon emission computed tomography (SPECT) probe for imaging integrin
αvβ6 positive tumors. Cystine knot
peptide, S02, was first conjugated with a single amino
acid chelate (SAAC) and labeled with [99mTc(H2O)3(CO)3]+. The resulting probe, 99mTc-SAAC-S02, was then evaluated by in
vitro cell uptake studies using two αvβ6 positive cell lines (human lung adenocarcinoma cell line
HCC4006 and pancreatic cancer cell line BxPC-3) and two αvβ6 negative cell lines (human lung adenocarcinoma
cell line H838 and human embryonic kidney cell line 293T). Next, SPECT/CT
and biodistribution studies were performed in nude mice bearing HCC4006
and H838 tumor xenografts to evaluate the in vivo performance of 99mTc-SAAC-S02. Significant
differences in the uptake of 99mTc-SAAC-S02
were observed in αvβ6 positive vs
negative cells (P < 0.05). Biodistribution and
small animal SPECT/CT studies revealed that 99mTc-SAAC-S02 accumulated to moderate levels in antigen positive tumors
(∼2% ID/g at 1 and 6 h postinjection, n =
3 or 4/group). Moreover, the probe demonstrated tumor-to-background
tissue ratios of 6.81 ± 2.32 (tumor-to-muscle) and 1.63 ±
0.18 (tumor-to-blood) at 6 h postinjection in αvβ6 positive tumor xenografts. Co-incubation of the probe with
excess amount of unlabeled S02 as a blocking agent demonstrated
significantly reduced tumor uptake, which is consistent with specific
binding to the target. Renal filtration was the main route of clearance.
In conclusion, knottin peptides are excellent scaffolds for which
to develop highly stable imaging probes for a variety of oncological
targets. 99mTc-SAAC-S02 demonstrates promise
for use as a SPECT agent to image integrin αvβ6 expression in living systems.
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Affiliation(s)
- Xiaohua Zhu
- Molecular Imaging Program at Stanford (MIPS), Department of Radiology, and Bio-X Program, Canary Center at Stanford for Cancer Early Detection, Stanford University , Stanford, California 94305-5344, United States
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Stern LA, Case BA, Hackel BJ. Alternative Non-Antibody Protein Scaffolds for Molecular Imaging of Cancer. Curr Opin Chem Eng 2013; 2. [PMID: 24358455 DOI: 10.1016/j.coche.2013.08.009] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The development of improved methods for early detection and characterization of cancer presents a major clinical challenge. One approach that has shown excellent potential in preclinical and clinical evaluation is molecular imaging with small-scaffold, non-antibody based, engineered proteins. These novel diagnostic agents produce high contrast images due to their fast clearance from the bloodstream and healthy tissues, can be evolved to bind a multitude of cancer biomarkers, and are easily functionalized by site-specific bioconjugation methods. Several small protein scaffolds have been verified for in vivo molecular imaging including affibodies and their two-helix variants, knottins, fibronectins, DARPins, and several natural ligands. Further, the biodistribution of these engineered ligands can be optimized through rational mutation of the conserved regions, careful selection and placement of chelator, and modification of molecular size.
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Affiliation(s)
- Lawrence A Stern
- Department of Chemical Engineering and Materials Science, University of Minnesota - Twin Cities, Minneapolis, MN 55455
| | - Brett A Case
- Department of Chemical Engineering and Materials Science, University of Minnesota - Twin Cities, Minneapolis, MN 55455
| | - Benjamin J Hackel
- Department of Chemical Engineering and Materials Science, University of Minnesota - Twin Cities, Minneapolis, MN 55455
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Microfluidics for synthesis of peptide-based PET tracers. BIOMED RESEARCH INTERNATIONAL 2013; 2013:839683. [PMID: 24288688 PMCID: PMC3833028 DOI: 10.1155/2013/839683] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Revised: 09/14/2013] [Accepted: 09/17/2013] [Indexed: 02/06/2023]
Abstract
Positron emission tomography (PET) is a powerful noninvasive tool for acquisition of the physiological parameters in human and animals with the help of PET tracers. Among all the PET tracers, radiolabeled peptides have been widely explored for cancer-related receptor imaging due to their high affinity and specificity to receptors. But radiochemistry procedures for production of peptide-based PET tracers are usually complex, which makes large-scale clinical studies relatively challenging. New radiolabeling technologies which could simplify synthesis and purification procedures, are extremely needed. Over the last decade, microfluidics and lab-on-a-chip (LOC) technology have boomed as powerful tools in the field of organic chemistry, which potentially provide significant help to the PET chemistry. In this minireview, microfluidic radiolabeling technology is described and its application for synthesis of peptide-based PET tracers is summarized and discussed.
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Moore SJ, Leung CL, Norton HK, Cochran JR. Engineering agatoxin, a cystine-knot peptide from spider venom, as a molecular probe for in vivo tumor imaging. PLoS One 2013; 8:e60498. [PMID: 23573262 PMCID: PMC3616073 DOI: 10.1371/journal.pone.0060498] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Accepted: 02/26/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Cystine-knot miniproteins, also known as knottins, have shown great potential as molecular scaffolds for the development of targeted therapeutics and diagnostic agents. For this purpose, previous protein engineering efforts have focused on knottins based on the Ecballium elaterium trypsin inhibitor (EETI) from squash seeds, the Agouti-related protein (AgRP) neuropeptide from mammals, or the Kalata B1 uterotonic peptide from plants. Here, we demonstrate that Agatoxin (AgTx), an ion channel inhibitor found in spider venom, can be used as a molecular scaffold to engineer knottins that bind with high-affinity to a tumor-associated integrin receptor. METHODOLOGY/PRINCIPAL FINDINGS We used a rational loop-grafting approach to engineer AgTx variants that bound to αvβ3 integrin with affinities in the low nM range. We showed that a disulfide-constrained loop from AgRP, a structurally-related knottin, can be substituted into AgTx to confer its high affinity binding properties. In parallel, we identified amino acid mutations required for efficient in vitro folding of engineered integrin-binding AgTx variants. Molecular imaging was used to evaluate in vivo tumor targeting and biodistribution of an engineered AgTx knottin compared to integrin-binding knottins based on AgRP and EETI. Knottin peptides were chemically synthesized and conjugated to a near-infrared fluorescent dye. Integrin-binding AgTx, AgRP, and EETI knottins all generated high tumor imaging contrast in U87MG glioblastoma xenograft models. Interestingly, EETI-based knottins generated significantly lower non-specific kidney imaging signals compared to AgTx and AgRP-based knottins. CONCLUSIONS/SIGNIFICANCE In this study, we demonstrate that AgTx, a knottin from spider venom, can be engineered to bind with high affinity to a tumor-associated receptor target. This work validates AgTx as a viable molecular scaffold for protein engineering, and further demonstrates the promise of using tumor-targeting knottins as probes for in vivo molecular imaging.
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Affiliation(s)
- Sarah J. Moore
- Department of Bioengineering, Stanford University, Stanford, California, United States of America
| | - Cheuk Lun Leung
- Department of Chemical Engineering, Stanford University, Stanford, California, United States of America
| | - Heidi K. Norton
- Department of Bioengineering, Stanford University, Stanford, California, United States of America
| | - Jennifer R. Cochran
- Department of Bioengineering, Stanford University, Stanford, California, United States of America
- Department of Chemical Engineering, Stanford University, Stanford, California, United States of America
- Stanford Cancer Institute and Bio-X Program, Stanford, California, United States of America
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