Human epidermal growth factor receptor type 3 (HER3) is an emerging therapeutic target in several malignancies. To select potential responders to HER3-targeted therapy, radionuclide molecular imaging of HER3 expression using affibody molecules could be performed. Due to physiological expression of HER3 in normal organs, high imaging contrast remains challenging. Due to slow internalization of affibody molecules by cancer cells, we hypothesized that labeling (HE)(3)-Z(HER3:08698)-DOTAGA affibody molecule with non-residualizing [I-125]-N-succinimidyl-4-iodobenzoate (PIB) label would improve the tumor-to-normal organs ratios compared to previously reported residualizing radiometal labels. The [I-125]I-PIB-(HE)(3)-Z(HER3:08698)-DOTAGA was compared side-by-side with [In-111]In-(HE)(3)-Z(HER3:08698)-DOTAGA. Both conjugates demonstrated specific high-affinity binding to HER3-expressing BxPC-3 and DU145 cancer cells. Biodistribution in mice bearing BxPC-3 xenografts at 4 and 24h pi showed faster clearance of the [I-125]I-PIB label compared to the indium-111 label from most tissues, except blood. This resulted in higher tumor-to-organ ratios in HER3-expressing organs for [I-125]I-PIB-(HE)(3)-Z(HER3:08698)-DOTAGA at 4 h, providing the tumor-to-liver ratio of 2.4 +/- 0.3. The tumor uptake of both conjugates was specific, however, it was lower for the [I-125]I-PIB label. In conclusion, the use of non-residualizing [I-125]I-PIB label for HER3-targeting affibody molecule provided higher tumor-to-liver ratio than the indium-111 label, however, further improvement in tumor uptake and retention is needed.

The epidermal growth factor receptor (EGFR) is often overexpressed during prostate cancer (PCa) progression towards androgen-independence after hormone therapy, but the overexpression is lower than in other types of cancers. Despite the low expression, EGFR has emerged as a promising therapeutic target for patients with castration-resistant PCa. Non-invasive methods for determination of EGFR expression in PCa can serve for patient stratification and therapy response monitoring. Radionuclide imaging probes based on affibody molecules (7 kDa) provide high contrast imaging of cancer-associated molecular targets. We hypothesized that the anti-EGFR affibody molecule DOTA-Z(EGFR:2377) labeled with Co-55 (positron-emitter, T1/2=17.5 h) would enable imaging of EGFR expression in PCa xenografts. The human PCa cell line DU-145 was used for in vitro and in vivo experiments and Co-57 was used as a surrogate for Co-55 in the present study. Binding of Co-57-DOTA-Z(EGFR:2377) to EGFR-expressing xenografts was saturable with anti-EGFR monoclonal antibody cetuximab, which would motivate the use of this tracer for monitoring the receptor occupancy during treatment. A significant dose-dependent difference in radioactivity accumulation in tumors and normal organs was observed when the biodistribution was studied 3 h after the injection of 10 and 35 mu g of Co-57-DOTA-Z(EGFR:2377): At lower doses the tumor uptake was 2-fold higher although tumor-to-organ ratios were not altered. For clinically relevant organs for PCa, tumor-to-organ ratios increased with time, and at 24 h pi were 2.2 +/- 0.5 for colon, 7 +/- 2 for muscle, and 4.0 +/- 0.7 for bones. Small animal SPECT/CT images confirmed the capacity of radiocobalt labeled DOTA-Z(EGFR:2377) to visualize EGFR expression in PCa. In conclusion, the present study demonstrated the feasibility of using the radiocobalt labeled anti-EGFR affibody conjugate Z(EGFR:2377) as an imaging agent for in vivo visualization of low EGFR-expressing tumors, like PCa, and for monitoring of receptor occupancy during cetuximab therapy as well as the importance of optimal dosing in order to achieve higher sensitivity molecular imaging.

Different strategies for treatment and prevention of Alzheimer's disease (AD) are currently under investigation, including passive immunization with anti-amyloid beta (anti-A beta) monoclonal antibodies (mAbs). Here, we investigate the therapeutic potential of a novel type of A beta-targeting agent based on an affibody molecule with fundamentally different properties to mAbs. We generated a therapeutic candidate, denoted Z(SYM73)-albumin-binding domain (ABD; 16.8 kDa), by genetic linkage of the dimeric Z(SYM73) affibody for sequestering of monomeric A beta-peptides and an ABD for extension of its in vivo half-life. Amyloid precursor protein (APP)/PS1 transgenic AD mice were administered with Z(SYM73)-ABD, followed by behavioral examination and immunohistochemistry. Results demonstrated rescued cognitive functions and significantly lower amyloid burden in the treated animals compared to controls. No toxicological symptoms or immunology-related side-effects were observed. To our knowledge, this is the first reported in vivo investigation of a systemically delivered scaffold protein against monomeric A beta, demonstrating a therapeutic potential for prevention of AD.

Development of new affinity proteins using combinatorial protein engineering is today established for generation of monoclonal antibodies and also essential for discovery of binders that are based on non-immunoglobulin proteins. Phage display is most frequently used, but yeast display is becoming increasingly popular, partly due to the option of utilizing fluorescence-activated cell sorting (FACS) for isolation of new candidates. Escherichia coli has several valuable properties for library applications and in particular the high transformation efficiency. The use of various autotransporters and intimins for secretion and anchoring on the outer membrane have shown promising results and particularly for directed evolution of different enzymes. Here, the authors report on display of a large naive affibody library on the outer membrane of E. coli using the autotransporter Adhesin Involved in Diffuse Adherence (AIDA-I). The expression cassette is first engineered by removing non-essential sequences, followed by introduction of an affibody library, comprising more than 10(9) variants, into the new display vector. The quality of the library and general performance of the method is assessed by FACS against five different targets, which resulted in a panel of binders with down to nanomolar affinities, suggesting that the method has potential as a complement to phage display for generation of affibody molecules.

Carbonic anhydrase IX (CAIX) is a cancer-associated molecular target for several classes of therapeutics. CAIX is overexpressed in a large fraction of renal cell carcinomas (RCC). Radionuclide molecular imaging of CAIX-expression might offer a non-invasive methodology for stratification of patients with disseminated RCC for CAIX-targeting therapeutics. Radiolabeled monoclonal antibodies and their fragments are actively investigated for imaging of CAIX expression. Promising alternatives are small non-immunoglobulin scaffold proteins, such as affibody molecules. A CAIX-targeting affibody ZCAIX:2 was re-designed with the aim to decrease off-target interactions and increase imaging contrast. The new tracer, DOTA-HE3-ZCAIX:2, was labeled with In-111 and characterized in vitro. Tumor-targeting properties of [In-111]In-DOTA-HE3-ZCAIX:2 were compared head-to-head with properties of the parental variant, [(99)mTc]Tc(CO)(3)-HE3-ZCAIX:2, and the most promising antibody fragment-based tracer, [In-111]In-DTPA-G250(Fab')(2), in the same batch of nude mice bearing CAIX-expressing RCC xenografts. Compared to the (99)mTc-labeled parental variant, [In-111]In-DOTA-HE3-ZCAIX:2 provides significantly higher tumor-to-lung, tumor-to-bone and tumor-to-liver ratios, which is essential for imaging of CAIX expression in the major metastatic sites of RCC. [In-111]In-DOTA-HE3-ZCAIX:2 offers significantly higher tumor-to-organ ratios compared with [In-111]In-G250(Fab']2. In conclusion, [In-111]In-DOTA-HE3-ZCAIX:2 can be considered as a highly promising tracer for imaging of CAIX expression in RCC metastases based on our results and literature data.

Evaluation of human epidermal growth factor receptor 2 (HER2) expression levels in breast and gastroesophageal cancer is used for the stratification of patients for HER2-targeting therapies. The use of radionuclide molecular imaging may facilitate such evaluation in a non-invasive way. Designed ankyrin repeat proteins (DARPins) are engineered scaffold proteins with high potential as probes for radionuclide molecular imaging. DARPin G3 binds with high affinity to HER2 and may be used to visualize this important therapeutic target. Studies on other engineered scaffold proteins have demonstrated that selection of the optimal labeling approach improves the sensitivity and specificity of radionuclide imaging. The present study compared two methods of labeling G3, direct and indirect radioiodination, to select an approach providing the best imaging contrast. G3-H6 was labeled with iodine-124, iodine-125 and iodine-131 using a direct method. A novel construct bearing a C-terminal cysteine, G3-GGGC, was site-specifically labeled using [125I]I-iodo-[(4-hydroxyphenyl)ethyl]maleimide (HPEM). The two radiolabeled G3 variants preserved binding specificity and high affinity to HER2-expressing cells. The specificity of tumor targeting in vivo was demonstrated. Biodistribution comparison of [131I]I-G3-H6 and [125I]I-HPEM-G3-GGGC in mice, bearing HER2-expressing SKOV3 xenografts, demonstrated an appreciable contribution of hepatobiliary excretion to the clearance of [125I]I-HPEM-G3-GGGC and a decreased tumor uptake compared to [131I]I-G3-H6. The direct label provided higher tumor-to-blood and tumor-to-organ ratios compared with the indirect label at 4 h post-injection. The feasibility of high contrast PET/CT imaging of HER2 expression in SKOV3 xenografts in mice using [124I]I-G3-H6 was demonstrated. In conclusion, direct radioiodination is the preferable approach for labeling DARPin G3 with iodine-123 and iodine-124 for clinical single photon emission computed tomography and positron emission tomography imaging.

Proteases are crucial for regulating biological processes in organisms through hydrolysis of peptide bonds. Recombinant proteases have moreover become important tools in biotechnological, and biomedical research and as therapeutics. We have developed a label-free high-throughput method for quantitative assessment of proteolytic activity in Escherichia coli. The screening method is based on co-expression of a protease of interest and a reporter complex. This reporter consists of an aggregation-prone peptide fused to a fluorescent protein via a linker that contains the corresponding substrate sequence. Cleavage of the substrate rescues the fluorescent protein from aggregation, resulting in increased fluorescence that correlates to proteolytic activity, which can be monitored using flow cytometry. In one round of flow-cytometric cell sorting, we isolated an efficiently cleaved tobacco etch virus (TEV) substrate from a 1:100 000 background of non-cleavable sequences, with around 6000-fold enrichment. We then engineered the 3C protease from coxsackievirus B3 (CVB3 3C(pro)) towards improved proteolytic activity on the substrate LEVLFQ down arrow GP. We isolated highly proteolytic active variants from a randomly mutated CVB3 3C(pro) library with up to 4-fold increase in activity. The method enables simultaneous measurement of proteolytic activity and protease expression levels and can therefore be applied for protease substrate profiling, as well as directed evolution of proteases.

Human epidermal growth factor receptor type 3 (HER3) plays a crucial role in the progression of many cancer types. In vivo radionuclide imaging could be a reliable method for repetitive detection of HER3-expression in tumors. The main challenge of HER3-imaging is the low expression in tumors together with endogenous receptor expression in normal tissues, particularly the liver. A HER3-targeting affibody molecule labeled with radiocobalt via a NOTA chelator [Co-57]Co-NOTA-Z(08699) has demonstrated the most favorable biodistribution profile with the lowest unspecific hepatic uptake and high activity uptake in tumors. We hypothesized that specific uptake of labeled affibody monomer might be selectively blocked in the liver but not in tumors by a co-injection of non-labeled corresponding trivalent affibody (Z(08699))(3). Biodistribution of [Co-57]Co-NOTA-Z(08699) and [In-111]ln-DOTA-(Z(08699))(3) was studied in BxPC-3 xenografted mice. [Co-57]Co-NOTA-Z(08699) was co-injected with unlabeled trivalent affibody DOTA-(Z(08699))(3) at different monomer:trimer molar ratios. HER3-expression in xenografts was imaged using [Co-57]Co-NOTA-Z(08699) and [Co-57]Co-NOTA-Z(08699): DOTA-(Z(08699))(3). Hepatic activity uptake of [Co-57] Co-NOTA-Z(08699): DOTA-(Z(08699))(3) decreased with increasing monomer:trimer molar ratio. The tumor activity uptake and tumor-to-liver ratios were the highest for the 1:3 ratio. SPECT/CT images confirmed the biodistribution data. Imaging of HER3 expression can be improved by co-injection of a radiolabeled monomeric affi body-based imaging probe together with a trivalent affibody.