Evaluation of a HER2-targeting affibody molecule combining an N-terminal HEHEHE-tag with a GGGC chelator for 99mTc-labelling at the C terminus

Comparative Preclinical Evaluation of Peptide-Based Chelators for the Labeling of DARPin G3 with 99mTc for Radionuclide Imaging of HER2 Expression in Cancer

Non-invasive radionuclide imaging of human epidermal growth factor receptor type 2 (HER2) expression in breast, gastroesophageal, and ovarian cancers may stratify patients for treatment using HER2-targeted therapeutics. Designed ankyrin repeat proteins (DARPins) are a promising type of targeting probe for radionuclide imaging. In clinical studies, the DARPin [99mTc]Tc-(HE)3-G3 labeled using a peptide-based chelator His-Glu-His-Glu-His-Glu ((HE)3), provided clear imaging of HER2 expressing breast cancer 2-4 h after injection. The goal of this study was to evaluate if the use of cysteine-containing peptide-based chelators Glu-Glu-Glu-Cys (E3C), Gly-Gly-Gly-Cys (G3C), and Gly-Gly-Gly-Ser-Cys connected via a (Gly-Gly-Gly-Ser)3-linker (designated as G3-(G3S)3C) would further improve the contrast of imaging using 99mTc-labeled derivatives of G3. The labeling of the new variants of G3 provided a radiochemical yield of over 95%. Labeled G3 variants bound specifically to human HER2-expressing cancer cell lines with affinities in the range of 1.9-5 nM. Biodistribution of [99mTc]Tc-G3-G3C, [99mTc]Tc-G3-(G3S)3C, and [99mTc]Tc-G3-E3C in mice was compared with the biodistribution of [99mTc]Tc-(HE)3-G3. It was found that the novel variants provide specific accumulation in HER2-expressing human xenografts and enable discrimination between tumors with high and low HER2 expression. However, [99mTc]Tc-(HE)3-G3 provided better contrast between tumors and the most frequent metastatic sites of HER2-expressing cancers and is therefore more suitable for clinical applications.

Novel small 99mTc-labeled affibody molecular probe for PD-L1 receptor imaging

OBJECTIVE

The in vivo imaging of programmed death ligand 1 (PD-L1) can monitor changes in PD-L1 expression and guide programmed death 1 (PD-1) or PD-L1-targeted immune checkpoint therapy. A 99mTc-labeled affibody molecular probe targeting the PD-L1 receptor was prepared and evaluated its tracing effect in PD-L1-overexpressing colon cancer.

METHODS

The PD-L1 affibody was prepared by genetic recombineering. The 99mTc labeling of the affibody was achieved by sodium glucoheptonate and an SnCl2 labeling system. The labeling rate, radiochemical purity, and stability in vitro were determined by instant thin-layer chromatography; MC38-B7H1 (PD-L1-positive) and MC38 (PD-L1-negative) colon cancer cells were used to evaluate its affinity to PD-L1 by cell-binding experiments. The biodistribution of the 99mTc-labeled affibody molecular probe was then determined in C57BL/6J mice bearing MC38-B7H1 tumors, and tumor targeting was assessed in C57BL/6J mice with MC38-B7H1, MC38 double xenografts.

RESULT

The nondecayed corrected yield of the 99mTc-PD-L1 affibody molecular probe was 95.95% ± 1.26%, and showed good stability both in phosphate-buffered saline (PBS) and fetal bovine serum within 6 h. The affinity of the 99mTc-PD-L1 affibody molecular probe for cell-binding assays was 10.02 nmol/L. Single photon emission-computed tomography imaging showed a rapid uptake of the tracer in PD-L1-positive tumors and very little tracer retention in PD-L1-negative control tumors. The tracer was significantly retained in the kidneys and bladder, suggesting that it is mainly excreted through the urinary system. Heart, liver, lung, and muscle tissue showed no significant radioactive retention. The biodistribution in vitro also showed significant renal retention, a small amount of uptake in the thyroid and gastrointestinal tract, and rapid blood clearance, and the tumor-to-blood radioactivity uptake ratio peaked 120 min after drug injection.

CONCLUSION

The 99mTc-PD-L1 affibody molecular probe that we prepared can effectively target to PD-L1-positive tumors imaging in vivo, and clear in blood quickly, with no obvious toxic side effects, which is expected to become a new type of tracer for detecting PD-L1 expression in tumors.

IgG-Binding Nanobody Capable of Prolonging Nanobody-Based Radiotracer Plasma Half-Life and Enhancing the Efficacy of Tumor-Targeted Radionuclide Therapy

Nanobodies have been developed rapidly as targeted probes for molecular imaging owing to their high affinity, outstanding tissue penetration, and rapid blood clearance. However, the short retention time at the tumor site limits their application in targeted radionuclide therapy. In this study, we designed a dual-targeting nanobody referred to as MIRC213-709, which can specifically bind to the HER2 receptor in tumor cell lines with high affinity (by nanobody MIRC213) and endogenous IgG in plasma to prolong the half-life by the MIRC213 C-terminal fusion nanobody, MIRC709. The nanobodies were site-specifically radiolabeled with ^99mTc and ¹⁷⁷Lu, and radiochemical purity was >95% after purification. The long blood circulation time and tumor retention property of ^99mTc/¹⁷⁷Lu-MIRC213-709 were confirmed by a blood clearance assay, single-photon emission computed tomography (SPECT), and a biodistribution study. The blood clearance assay showed that the distribution phase half-life (T_1/2α) and elimination phase half-life (T_1/2β) of ^99mTc-MIRC213-709 were 6.74- and 19.04-fold longer than those of ^99mTc-MIRC213, respectively. The SPECT/CT and biodistribution results showed that the highest uptake of ¹⁷⁷Lu-MIRC213 in the NCI-N87 model was 5.24 ± 0.95% ID/g at 6 h p.i., while the highest uptake of ¹⁷⁷Lu-MIRC213-709 in the NCI-N87 model was 30.82 ± 7.29% ID/g at 48 h p.i. Compared with ¹⁷⁷Lu-MIRC213, ¹⁷⁷Lu-MIRC213-709 had a 16.9-fold increased tumor cumulative uptake (2606 ± 195.1 vs 153.9 ± 22.37% ID/g·h). The targeted radionuclide therapy assay was performed in the NCI-N87 tumor model, and treatment monitoring ended on day 32. The post-treatment/pretreatment tumor volumes were 12.99 ± 1.66, 3.58 ± 0.96, 1.26 ± 0.17, and 1.54 ± 0.50 in the 0, 9, and 18 MBq single-dose groups and the two 9 MBq divided dose group (14 days apart), respectively. All treatment groups showed significant therapeutic effects (P < 0.0001). Thus, fusion with the IgG-binding nanobody MIRC709 provides MIRC213 derivatives with improved metabolic properties for targeted radionuclide therapy.

Advances in the Application of Radionuclide-Labeled HER2 Affibody for the Diagnosis and Treatment of Ovarian Cancer

Human epidermal growth factor receptor 2 (HER2) is a highly expressed tumor marker in epithelial ovarian cancer, and its overexpression is considered to be a potential factor of poor prognosis. Therefore, monitoring the expression of HER2 receptor in tumor tissue provides favorable conditions for accurate localization, diagnosis, targeted therapy, and prognosis evaluation of cancer foci. Affibody has the advantages of high affinity, small molecular weight, and stable biochemical properties. The molecular probes of radionuclide-labeled HER2 affibody have recently shown broad application prospects in the diagnosis and treatment of ovarian cancer; the aim is to introduce radionuclides into the cancer foci, display systemic lesions, and kill tumor cells through the radioactivity of the radionuclides. This process seamlessly integrates the diagnosis and treatment of ovarian cancer. Current research and development of new molecular probes of radionuclide-labeled HER2 affibody should focus on overcoming the deficiencies of non-specific uptake in the kidney, bone marrow, liver, and gastrointestinal tract, and on reducing the background of the image to improve image quality. By modifying the amino acid sequence; changing the hydrophilicity, surface charge, and lipid solubility of the affibody molecule; and using different radionuclides, chelating agents, and labeling conditions to optimize the labeling method of molecular probes, the specific uptake of molecular probes at tumor sites will be improved, while reducing radioactive retention in non-target organs and obtaining the best target/non-target value. These measures will enable the clinical use of radionuclide-labeled HER2 affibody molecular probes as soon as possible, providing a new clinical path for tumor-specific diagnosis, targeted therapy, and efficacy evaluation. The purpose of this review is to describe the application of radionuclide-labeled HER2 affibody in the imaging and treatment of ovarian cancer, including its potential clinical value and dilemmas.

Preclinical Evaluation of 99mTc-ZHER2:41071, a Second-Generation Affibody-Based HER2-Visualizing Imaging Probe with a Low Renal Uptake

Radionuclide imaging of HER2 expression in tumours may enable stratification of patients with breast, ovarian, and gastroesophageal cancers for HER2-targeting therapies. A first-generation HER2-binding affibody molecule [^99mTc]Tc-ZHER2:V2 demonstrated favorable imaging properties in preclinical studies. Thereafter, the affibody scaffold has been extensively modified, which increased its melting point, improved storage stability, and increased hydrophilicity of the surface. In this study, a second-generation affibody molecule (designated ZHER2:41071) with a new improved scaffold has been prepared and characterized. HER2-binding, biodistribution, and tumour-targeting properties of [^99mTc]Tc-labelled ZHER2:41071 were investigated. These properties were compared with properties of the first-generation affibody molecules, [^99mTc]Tc-ZHER2:V2 and [^99mTc]Tc-ZHER2:2395. [^99mTc]Tc-ZHER2:41071 bound specifically to HER2 expressing cells with an affinity of 58 ± 2 pM. The renal uptake for [^99mTc]Tc-ZHER2:41071 and [^99mTc]Tc-ZHER2:V2 was 25–30 fold lower when compared with [^99mTc]Tc-ZHER2:2395. The uptake in tumour and kidney for [^99mTc]Tc-ZHER2:41071 and [^99mTc]Tc-ZHER2:V2 in SKOV-3 xenografts was similar. In conclusion, an extensive re-engineering of the scaffold did not compromise imaging properties of the affibody molecule labelled with ^99mTc using a GGGC chelator. The new probe, [^99mTc]Tc-ZHER2:41071 provided the best tumour-to-blood ratio compared to HER2-imaging probes for single photon emission computed tomography (SPECT) described in the literature so far. [^99mTc]Tc-ZHER2:41071 is a promising candidate for further clinical translation studies.

Optimal His-Tag Design for Efficient [99mTc(CO)3]+ and [188Re(CO)3]+ Labeling of Proteins for Molecular Imaging and Radionuclide Therapy by Analysis of Peptide Arrays

Hexahistidine tags (His-tags), incorporated into recombinant proteins to facilitate purification using metal-affinity chromatography, are useful binding sites for radiolabeling with [^99mTc(CO)₃]⁺ and [¹⁸⁸Re(CO)₃]⁺ for molecular imaging and radionuclide therapy. Labeling efficiencies vary unpredictably, and the method is therefore not universally useful. To overcome this, we have made quantitative comparisons of radiolabeling of a bespoke Celluspots array library of 382 His-tag-containing peptide sequences with [^99mTc(CO)₃]⁺ and [¹⁸⁸Re(CO)₃]⁺ to identify key features that enhance labeling. A selected sequence with 10-fold enhanced labeling efficiency compared to the most effective literature-reported sequences was incorporated into an exemplar protein and compared biologically with non-optimized analogues, in vitro and in vivo. Optimal labeling with either [^99mTc(CO)₃]⁺ or [¹⁸⁸Re(CO)₃]⁺ required six consecutive His residues in the protein sequence, surrounded by several positively charged residues (Arg or Lys), and the presence of phosphate in the buffer. Cys or Met residues in the sequence were beneficial, to a lesser extent. Negatively charged residues were deleterious to labeling. His-tags with adjacent positively charged residues could be labeled as much as 40 times more efficiently than those with adjacent negatively charged residues. ³¹P NMR of [Re(CO)₃(H₂O)₃]⁺ and electrophoresis of solutions of [^99mTc(CO)₃(H₂O)₃]⁺ suggest that phosphate bridges form between cationic residues and the cationic metal synthon during labeling. The trial optimized protein, a scFv targeted to the PSMA antigen expressed in prostate cancer, was readily labeled in >95% radiochemical yield, without the need for subsequent purification. Labeling occurred more quickly and to higher specific activity than comparable non-optimized proteins, while retaining specific binding to PSMA and prostate cancer in vivo. Thus, optimized His-tags greatly simplify radiolabeling of recombinant proteins making them potentially more widely and economically available for imaging and treating patients.

The "Carbonyl Story" and Beyond; Experiences, Lessons and Implications

The complex [^99m Tc(OH₂ )₃ (CO)₃ ]⁺ has become a versatile building block in radiopharmaceutical chemistry, applied by many groups worldwide. However, despite widespread efforts, only one compound has made it right the way through clinical trials. Along the way from its discovery to its development into an eventual product, the author experienced issues that he would handle differently in retrospect. In this article, these experiences are turned into "lessons" that might be helpful for young researchers finding themselves in similar situations. Beside issues with patenting and company strategies, the carbonyl story has provided scientific implications beyond its own story, and insights from which any future ^99m Tc-based chemistry for radiopharmacy or molecular imaging might benefit.

Optimized Molecular Design of ADAPT-Based HER2-Imaging Probes Labeled with 111In and 68Ga

Radionuclide molecular imaging is a promising tool for visualization of cancer associated molecular abnormalities in vivo and stratification of patients for specific therapies. ADAPT is a new type of small engineered proteins based on the scaffold of an albumin binding domain of protein G. ADAPTs have been utilized to select and develop high affinity binders to different proteinaceous targets. ADAPT6 binds to human epidermal growth factor 2 (HER2) with low nanomolar affinity and can be used for its in vivo visualization. Molecular design of ¹¹¹In-labeled anti-HER2 ADAPT has been optimized in several earlier studies. In this study, we made a direct comparison of two of the most promising variants, having either a DEAVDANS or a (HE)₃DANS sequence at the N-terminus, conjugated with a maleimido derivative of DOTA to a GSSC amino acids sequence at the C-terminus. The variants (designated DOTA-C⁵⁹-DEAVDANS-ADAPT6-GSSC and DOTA-C⁶¹-(HE)₃DANS-ADAPT6-GSSC) were stably labeled with ¹¹¹In for SPECT and ⁶⁸Ga for PET. Biodistribution of labeled ADAPT variants was evaluated in nude mice bearing human tumor xenografts with different levels of HER2 expression. Both variants enabled clear discrimination between tumors with high and low levels of HER2 expression. ¹¹¹In-labeled ADAPT6 derivatives provided higher tumor-to-organ ratios compared to ⁶⁸Ga-labeled counterparts. The best performing variant was DOTA-C⁶¹-(HE)₃DANS-ADAPT6-GSSC, which provided tumor-to-blood ratios of 208 ± 36 and 109 ± 17 at 3 h for ¹¹¹In and ⁶⁸Ga labels, respectively.

Influence of composition of cysteine-containing peptide-based chelators on biodistribution of 99mTc-labeled anti-EGFR affibody molecules

Epidermal growth factor receptor (EGFR) is overexpressed in a number of cancers and is the molecular target for several anti-cancer therapeutics. Radionuclide molecular imaging of EGFR expression should enable personalization of anti-cancer treatment. Affibody molecule is a promising type of high-affinity imaging probes based on a non-immunoglobulin scaffold. A series of derivatives of the anti-EGFR affibody molecule ZEGFR:2377, having peptide-based cysteine-containing chelators for conjugation of ^99mTc, was designed and evaluated. It was found that glutamate-containing chelators Gly-Gly-Glu-Cys (GGEC), Gly-Glu-Glu-Cys (GEEC) and Glu-Glu-Glu-Cys (EEEC) provide the best labeling stability. The glutamate containing conjugates bound to EGFR-expressing cells specifically and with high affinity. Specific targeting of EGFR-expressing xenografts in mice was demonstrated. The number of glutamate residues in the chelator had strong influence on biodistribution of radiolabeled affibody molecules. Increase of glutamate content was associated with lower uptake in normal tissues. The ^99mTc-labeled variant containing the EEEC chelator provided the highest tumor-to-organ ratios. In conclusion, optimizing the composition of peptide-based chelators enhances contrast of imaging of EGFR-expression using affibody molecules.

Cyclic versus Noncyclic Chelating Scaffold for 89Zr-Labeled ZEGFR:2377 Affibody Bioconjugates Targeting Epidermal Growth Factor Receptor Overexpression

Zirconium-89 is an emerging radionuclide for positron emission tomography (PET) especially for biomolecules with slow pharmacokinetics as due to its longer half-life, in comparison to fluorine-18 and gallium-68, imaging at late time points is feasible. Desferrioxamine B (DFO), a linear bifunctional chelator (BFC) is mostly used for this radionuclide so far but shows limitations regarding stability. Our group recently reported on fusarinine C (FSC) with similar zirconium-89 complexing properties but potentially higher stability related to its cyclic structure. This study was designed to compare FSC and DFO head-to-head as bifunctional chelators for ⁸⁹Zr-radiolabeled EGFR-targeting ZEGFR:2377 affibody bioconjugates. FSC-ZEGFR:2377 and DFO-ZEGFR:2377 were evaluated regarding radiolabeling, in vitro stability, specificity, cell uptake, receptor affinity, biodistribution, and microPET-CT imaging. Both conjugates were efficiently labeled with zirconium-89 at room temperature but radiochemical yields increased substantially at elevated temperature, 85 °C. Both ⁸⁹Zr-FSC-ZEGFR:2377 and ⁸⁹Zr-DFO-ZEGFR:2377 revealed remarkable specificity, affinity and slow cell-line dependent internalization. Radiolabeling at 85 °C showed comparable results in A431 tumor xenografted mice with minor differences regarding blood clearance, tumor and liver uptake. In comparison ⁸⁹Zr-DFO-ZEGFR:2377, radiolabeled at room temperature, showed a significant difference regarding tumor-to-organ ratios. MicroPET-CT imaging studies of ⁸⁹Zr-FSC-ZEGFR:2377 as well as ⁸⁹Zr-DFO-ZEGFR:2377 confirmed these findings. In summary we were able to show that FSC is a suitable alternative to DFO for radiolabeling of biomolecules with zirconium-89. Furthermore, our findings indicate that ⁸⁹Zr-radiolabeling of DFO conjugates at higher temperature reduces off-chelate binding leading to significantly improved tumor-to-organ ratios and therefore enhancing image contrast.

Comparative evaluation of tumor targeting using the anti-HER2 ADAPT scaffold protein labeled at the C-terminus with indium-111 or technetium-99m

ABD-Derived Affinity Proteins (ADAPTs) is a novel class of engineered scaffold proteins derived from an albumin-binding domain of protein G. The use of ADAPT6 derivatives as targeting moiety have provided excellent preclinical radionuclide imaging of human epidermal growth factor 2 (HER2) tumor xenografts. Previous studies have demonstrated that selection of nuclide and chelator for its conjugation has an appreciable effect on imaging properties of scaffold proteins. In this study we performed a comparative evaluation of the anti-HER2 ADAPT having an aspartate-glutamate-alanine-valine-aspartate-alanine-asparagine-serine (DEAVDANS) N-terminal sequence and labeled at C-terminus with ^99mTc using a cysteine-containing peptide based chelator, glycine-serine-serine-cysteine (GSSC), and a similar variant labeled with ¹¹¹In using a maleimido derivative of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator. Both ^99mTc-DEAVDANS-ADAPT6-GSSC and ¹¹¹In-DEAVDANS-ADAPT6-GSSC-DOTA accumulated specifically in HER2-expressing SKOV3 xenografts. The tumor uptake of both variants did not differ significantly and average values were in the range of 19–21%ID/g. However, there was an appreciable variation in uptake of conjugates in normal tissues that resulted in a notable difference in the tumor-to-organ ratios. The ¹¹¹In-DOTA label provided 2–6 fold higher tumor-to-organ ratios than ^99mTc-GSSC and is therefore the preferable label for ADAPTs.

PET of HER2 Expression with a Novel 18FAl Labeled Affibody

Background: Human epidermal growth factor receptor type 2 (HER2) is abundant in a wide variety of tumors and associated with the poor prognosis. Radiolabeled affibodies are potential candidates for detecting HER2-positive lesions. However, laborious multiple-step synthetic procedure and high abdomen background may hinder the widespread use. Herein, cysteinylated ZHER_2:342 modified with a new hydrophilic linker (denoted as MZHER_2:342) was designed and labeled using ¹⁸FAl-NOTA strategies. The biologic efficacy of the novel tracer and its feasibilities for in vivo monitoring HER2 levels were also investigated in xenograft models with different HER2 expressions.

Method: MZHER_2:342 was conjugated with MAL-NOTA under standard reaction conditions. The affibody molecule was then radiolabeled with ¹⁸FAl complex. The binding specificity of the tracer, ¹⁸FAl-NOTA-MAL-MZHER_2:342, with HER2 was primarily characterized via in vitro studies. MicroPET imaging were performed in nude mice bearing tumors (SKOV-3, JIMT-1 and MCF-7) after injection. The HER2 levels of xenografts were determined using Western blotting analysis.

Results:¹⁸FAl-NOTA-MAL-MZHER_2:342 can be efficiently produced within 30 min with a non-decaycorrected yield of about 10% and a radiochemical purity of more than 95%. In vitro experiments revealed that the modified affibody retained the specific affinity to HER2. PET imaging showed that SKOV-3 and JIMT-1 xenografts were clearly visualized with excellent contrast and low abdomen backgrounds. On the contrary, the signals of MCF-7 tumor were difficult to visualize. The ROI values ranged from16.54±2.69% ID/g for SKOV-3 to 8.42±1.20 %ID/g for JIMT-1 tumors at 1h postinjection respectively. Poor uptake was observed from MCF-7 tumors with 1.71±0.34% ID/g at the same time point. Besides, a significant linear correlation between % ID/g values and relative HER2 expression levels was also found.

Conclusions:¹⁸FAl-NOTA-MAL-MZHER_2:342 is a promising tracer for in vivo detecting HER2 status with the advantages of facile synthesis and favorable pharmacokinetics. It may be useful in differential diagnosis, molecularly targeted therapy and prognosis of the cancers.

Feasibility of imaging of epidermal growth factor receptor expression with ZEGFR:2377 affibody molecule labeled with 99mTc using a peptide-based cysteine-containing chelator

The epidermal growth factor receptor (EGFR) is overexpressed in a number of malignant tumors and is a molecular target for several specific anticancer antibodies and tyrosine kinase inhibitors. The overexpression of EGFR is a predictive biomarker for response to several therapy regimens. Radionuclide molecular imaging might enable detection of EGFR overexpression by a non-invasive procedure and could be used repeatedly. Affibody molecules are engineered scaffold proteins, which could be selected to have a high affinity and selectivity to predetermined targets. The anti-EGFR ZEGFR:2377 affibody molecule is a potential imaging probe for EGFR detection. The use of the generator-produced radionuclide ^99mTc should facilitate clinical translation of an imaging probe due to its low price, availability and favorable dosimetry of the radionuclide. In the present study, we evaluated feasibility of ZEGFR:2377 labeling with ^99mTc using a peptide-based cysteine-containing chelator expressed at the C-terminus of ZEGFR:2377. The label was stable in vitro under cysteine challenge. In addition, ^99mTc-ZEGFR:2377 was capable of specific binding to EGFR-expressing cells with high affinity (274 pM). Studies in BALB/C nu/nu mice bearing A431 xenografts demonstrated that ^99mTc-ZEGFR:2377 accumulates in tumors in an EGFR-specific manner. The tumor uptake values were 3.6±1 and 2.5±0.4% ID/g at 3 and 24 h after injection, respectively. The corresponding tumor-to-blood ratios were 1.8±0.4 and 8±3. The xenografts were clearly visualized at both time-points. This study demonstrated the potential of ^99mTc-labeled ZEGFR:2377 for imaging of EGFR in vivo.

Imaging of human pancreatic cancer xenografts by single-photon emission computed tomography with 99mTc-Hynic-PEG-AE105

The elevated expression of urokinase-type plasminogen activator receptor (uPAR) is associated with the poor prognosis of pancreatic cancer patients. Thus, uPAR is a promising candidate as a molecular target for the non-invasive imaging of pancreatic cancer. The present study aimed to develop a technetium-99m (^99mTc)-labeled uPAR-binding peptide for non-invasive single-photon emission computed tomography (SPECT) assessment of uPAR expression in pancreatic cancer xenograft models. A linear high-affinity uPAR peptide antagonist, Hynic-PEG-AE105, was labeled with ^99mTc. Human uPAR-positive pancreatic cancer BxPC-3 cells were inoculated into nude mice. SPECT was performed in the pancreatic cancer xenograft mice models. The results showed that the rate of the ^99mTc labeling of Hynic-PEG-AE105 was 97.72±1.73%. The tumor uptake of ^99mTc-Hynic-PEG-AE105 was higher than the control inactive peptide ^99mTc-Hynic-PEG-AE105mut at 4 h (3.37±0.11 vs. 1.36±0.18; P<0.001) and 6 h (3.64±0.25 vs. 1.28±0.20; P<0.001) (n=10). Moreover, a significant correlation was observed between the tumor uptake of ^99mTc-Hynic-PEG-AE105 and uPAR expression (r=0.791, P=0.006). In conclusion, in the present study, a peptide-based SPECT tracer, ^99mTc-Hynic-PEG-AE105, with a high purity and specific radioactivity was synthesized. ^99mTc-Hynic-PEG-AE105 is a promising agent for the non-invasive determination of uPAR expression in pancreatic cancer.

Inhibitory effects of H-Ras/Raf-1-binding affibody molecules on synovial cell function

Affibody molecules specific for H-Ras and Raf-1 were evaluated for their ability to inhibit synovial cell function. Affibody molecules targeting H-Ras (Zras122, Zras220, and Zras521) or Raf-1 (Zraf322) were introduced into the MH7A synovial cell line using two delivery methods: transfection with plasmids encoding the affibody molecules or direct introduction of affibody protein using a cell-penetrating peptide reagent. Interleukin-6 (IL-6) and prostaglandin E2 (PGE2) production by MH7A cells were analyzed by enzyme-linked immunosorbent assay after stimulation with tumor necrosis factor-alpha (TNF-α). Cell proliferation was also analyzed. Phosphorylation of extracellular signal-regulated kinase (ERK) was analyzed by western blot. All affibody molecules could inhibit IL-6 and PGE2 production in TNF-α-stimulated MH7A cells. The inhibitory effect was stronger when affibody molecules were delivered as proteins via a cell-penetrating peptide reagent than when plasmid-DNA encoding the affibody moelcules was transfected into the cells. Plasmid-expressed Zras220 inhibited phosphorylation of ERK in TNF-α-stimulated MH7A cells. Protein-introduced Zraf322 inhibited the production of IL-6 and PGE2 and inhibited cell proliferation in MH7A cells. These findings suggest that affibody molecules specific for H-Ras and Raf-1 can affect intracellular signal transduction through the MAP kinase pathway to inhibit cell proliferation and production of inflammatory mediators by synovial cells.

Evaluation of 99mTc-Z IGF1R:4551-GGGC affibody molecule, a new probe for imaging of insulin-like growth factor type 1 receptor expression

Overexpression of insulin-like growth factor-1 receptor (IGF-1R) in several cancers is associated with resistance to therapy. Radionuclide molecular imaging of IGF-1R expression in tumors may help in selecting the patients that will potentially respond to IGF-1R-targeted therapy. Affibody molecules are small (7 kDa) non-immunoglobulin-based scaffold proteins that are well-suited probes for radionuclide imaging. The aim of this study was the evaluation of an anti-IGF-1R affibody molecule labeled with technetium-99m using cysteine-containing peptide-based chelator GGGC at C-terminus. Z_IGF1R:4551-GGGC was efficiently and stably labeled with technetium-99m (radiochemical yield 97 ± 3 %). ^99mTc-Z_IGF1R:4551-GGGC demonstrated specific binding to IGF-1R-expressing DU-145 (prostate cancer) and MCF-7 (breast cancer) cell lines and slow internalization in vitro. The tumor-targeting properties were studied in BALB/c nu/nu mice bearing DU-145 and MCF-7 xenografts. [^99mTc(CO)₃]⁺-(HE)₃-Z_IGF1R:4551 was used for comparison. The biodistribution study demonstrated high tumor-to-blood ratios (6.2 ± 0.9 and 6.9 ± 1.0, for DU-145 and MCF-7, respectively, at 4 h after injection). Renal radioactivity concentration was 16-fold lower for ^99mTc-Z_IGF1R:4551-GGGC than for [^99mTc(CO)₃]⁺-(HE)₃-Z_IGF1R:4551 at 4 h after injection. However, the liver uptake of ^99mTc-Z_IGF1R:4551-GGGC was 1.2- to 2-fold higher in comparison with [^99mTc(CO)₃]⁺-(HE)₃-Z_IGF1R:4551. A possible reason for the elevated hepatic uptake of ^99mTc-Z_IGF1R:4551-GGGC is a high lipophilicity of amino acids in the binding site of Z_IGF1R:4551, which is not compensated in ^99mTc-Z_IGF1R:4551-GGGC. In conclusion, ^99mTc-Z_IGF1R:4551-GGGC can visualize the IGF-1R expression in human tumor xenografts and provides low retention of radioactivity in kidneys. Further development of this imaging agent should include molecular design aimed at reducing the hepatic uptake.

CARMA3 overexpression accelerates cell proliferation and inhibits paclitaxel-induced apoptosis through NF-κB regulation in breast cancer cells

CARMA3 was recently reported to be overexpressed in several cancers and associated with malignant behavior of cancer cells. However, the expression pattern and biological roles of CARMA3 in breast cancer have not been reported. In the present study, we found that CARMA3 was overexpressed in 41.9 % of breast cancer specimens. Significant association was observed between CARMA3 overexpression and TNM stage (p = 0.0223), tumor size (p = 0.0227), and ErbB-2 status (p = 0.0049). Furthermore, knockdown of CARMA3 expression in MDA-MB-435 cells with high endogenous expression decreased cell proliferation and sensitized cell to paclitaxel-induced apoptosis, while overexpression of CARMA3 in MDA-MB-231 cell line promoted cell proliferation and inhibited apoptosis. Further analysis showed that CARMA3 depletion downregulated, and its overexpression upregulated cyclin D1, Bcl-2, and p-IκB levels. In conclusion, our study demonstrated that CARMA3 is overexpressed in breast cancers. CARMA3 facilitates proliferation and inhibits apoptosis through nuclear factor-kappaB signaling.

[99mTc(CO)3]+-(HE)3-ZIGF1R:4551, a new Affibody conjugate for visualization of insulin-like growth factor-1 receptor expression in malignant tumours

PURPOSE

Radionuclide imaging of insulin-like growth factor type 1 receptor (IGF-1R) expression in tumours might be used for selection of patients who would benefit from IGF-1R-targeted therapy. We have previously shown the feasibility of IGF-1R imaging using the Affibody molecule (111)In-DOTA-His(6)-Z(IGF1R:4551). The use of (99m)Tc instead of (111)In should improve sensitivity and resolution of imaging, and reduce the dose burden to patients. We hypothesized that inclusion of a HEHEHE tag instead of a His(6) tag in Z(IGF1R:4551) would permit its convenient purification using IMAC, enable labelling with [(99m)Tc(CO)(3)](+), and improve its biodistribution.

METHODS

Z(IGF1R:4551) was expressed with a HEHEHE tag in the N terminus. The resulting (HE)(3)-Z(IGF1R:4551) construct was labelled with [(99m)Tc(CO)(3)](+). Targeting of IGF-1R-expressing cells using [(99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) was evaluated in vitro and in vivo.

RESULTS

(HE)(3)-Z(IGF1R:4551) was stably labelled with (99m)Tc with preserved specific binding to IGF-1R-expressing DU-145 prostate cancer cells in vitro. In mice, [(99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) accumulated in IGF-1R-expressing organs (pancreas, stomach, lung and salivary gland). [(99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) demonstrated 3.6-fold lower accumulation in the liver and spleen than (111)In-DOTA-Z(IGF1R:4551). In NMRI nu/nu mice with DU-145 prostate cancer xenografts, the tumour uptake was 1.32 ± 0.11 %ID/g and the tumour-to-blood ratio was 4.4 ± 0.3 at 8 h after injection. The xenografts were visualized using a gamma camera 6 h after injection.

CONCLUSION

(99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) is a promising candidate for visualization of IGF-1R expression in malignant tumours.