An improved synthesis of NHS-MAG3 for conjugation and radiolabeling of biomolecules with (99m)Tc at room temperature

Noninvasive evaluation of PD-L1 expression in non-small cell lung cancer by immunoPET imaging using an acylating agent-modified antibody fragment

PURPOSE

The aim of this study was to explore an effective ¹²⁴I labeling strategy and improve the signal-to-noise ratio when evaluating the expression of PD-L1 using an ¹²⁴I-iodinated durvalumab (durva) F(ab')₂ fragment.

METHODS

The prepared durva F(ab')₂ fragments were incubated with N-succinimidyl-3-(4-hydroxyphenyl) propionate (SHPP); after purification, the HPP-durva F(ab')₂ was iodinated using Iodo-Gen method. After the radiochemical purity, stability, and specific activities were determined, the binding affinities of probes prepared using different labeling strategies were compared in vitro. The clinical application value of [¹²⁴I]I-HPP-durva-F(ab')₂ was confirmed by PET imaging. To more objectively evaluate the in vivo distribution and clearance of tracers, the pharmacokinetics and biodistribution assays were also performed.

RESULTS

After being modified with SHPP, the average conjugation number of SHPP per durva-F(ab')₂ identified by LC-MS was about 8.92 ± 2.84. The prepared [¹²⁴I]I-HPP-durva F(ab')₂ was obtained with a satisfactory radiochemical purity of more than 98% and stability of more than 93% when incubated for 72 h. Compared with unmodified [¹²⁴I]I-durva F(ab')₂, the specific activity of [¹²⁴I]I-HPP-durva-F(ab')₂ was improved (52.91 ± 5.55 MBq/mg and 15.91 ± 0.74 MBq/mg), while the affinity did not significantly change. The biodistribution experiments and PET imaging showed that the prepared [¹²⁴I]I-HPP-durva-F(ab')₂ exhibited an accelerated clearance and improved tumor-to-background ratio compared with [¹²⁴I]I-durva-F(ab')₂. The specificity of [¹²⁴I]I-HPP-durva-F(ab')₂ to PD-L1 was well demonstrated both in vitro and in vivo.

CONCLUSIONS

A PD-L1 PET imaging probe [¹²⁴I]I-HPP-durva F(ab')₂ was successfully synthesized through the SHPP modification strategy. The prepared probe was able to accurately evaluate the PD-L1 expression level through high-contrast noninvasive imaging.

Methods for Radiolabelling Nanoparticles: SPECT Use (Part 1)

The use of nanoparticles (NPs) is rapidly increasing in nuclear medicine (NM) for diagnostic and therapeutic purposes. Their wide use is due to their chemical–physical characteristics and possibility to deliver several molecules. NPs can be synthetised by organic and/or inorganic materials and they can have different size, shape, chemical composition, and charge. These factors influence their biodistribution, clearance, and targeting ability in vivo. NPs can be designed to encapsulate inside the core or bind to the surface several molecules, including radionuclides, for different clinical applications. Either diagnostic or therapeutic radioactive NPs can be synthetised, making a so-called theragnostic tool. To date, there are several methods for radiolabelling NPs that vary depending on both the physical and chemical properties of the NPs and on the isotope used. In this review, we analysed and compared different methods for radiolabelling NPs for single-photon emission computed tomography (SPECT) use.

Noninvasive Evaluation of EGFR Expression of Digestive Tumors Using 99mTc-MAG3-Cet-F(ab ′ )2-Based SPECT/CT Imaging

Purpose. This study is aimed at investigating the feasibility of cetuximab (Cet) F(ab ${}^{\prime }$ )2 fragment- (Cet-F(ab ${}^{\prime }$ )2-) based single photon emission tomography/computed tomography (SPECT/CT) for assessing the epidermal growth factor receptor (EGFR) expression in digestive tumor mouse models. Methods. Cet-F(ab ${}^{\prime }$ )2 was synthesized using immunoglobulin G-degrading enzyme of Streptococcus pyogenes (IdeS) protease and purified with protein A beads. The product and its in vitro stability in normal saline and 1% bovine serum albumin were analyzed with sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The EGFR expression in the human colon tumor cell line HT29 and the human stomach tumor cell line MGC803 were verified using western blotting and immunocytochemistry. Cet-F(ab ${}^{\prime }$ )2 was conjugated with 5(6)-carboxytetramethylrhodamine succinimidyl ester to demonstrate its binding ability to the MGC803 and HT29 cells. Cet-F(ab ${}^{\prime }$ )2 was conjugated with NHS-MAG3 for 99mTc radiolabeling. The best imaging time was determined using a biodistribution assay at 1, 4, 16, and 24 h after injection of the 99mTc-MAG3-Cet-F(ab ${}^{\prime }$ )2 tracer. Furthermore, 99mTc-MAG3-Cet-F(ab ${}^{\prime }$ )2 SPECT/CT was performed on MGC803 and HT29 tumor-bearing nude mice. Results. HT29 cells had low EGFR expression while MGC803 cell exhibited the high EGFR expression. Cet-F(ab ${}^{\prime }$ )2 and intact cetuximab showed similar high binding ability to MGC803 cells but not to HT29 cells. Cet-F(ab ${}^{\prime }$ )2 and 99mTc-MAG3-Cet-F(ab ${}^{\prime }$ )2 showed excellent in vitro stability. The biodistribution assay showed that the target to nontarget ratio was the highest at 16 h ( $17.29\pm 5.72$ , $n=4$ ) after tracer injection. The 99mTc-MAG3-Cet-F(ab ${}^{\prime }$ )2-based SPECT/CT imaging revealed rapid and sustained tracer uptake in MGC803 tumors rather than in HT29 tumors with high image contrast, which was consistent with the results in vitro. Conclusion. SPECT/CT imaging using 99mTc-MAG3-Cet-F(ab ${}^{\prime }$ )2 enables the evaluation of the EGFR expression in murine EGFR-positive tumors, indicating the potential utility for noninvasive evaluation of the EGFR expression in tumors.

A Comparison of [99mTc]Duramycin and [99mTc]Annexin V in SPECT/CT Imaging Atherosclerotic Plaques

PURPOSE

Apoptosis is a key factor in unstable plaques. The aim of this study is to evaluate the utility of visualizing atherosclerotic plaques with radiolabeled duramycin and Annexin V.

PROCEDURES

ApoE^-/- mice were fed with a high-fat diet to develop atherosclerosis, C57 mice as a control. Using a routine conjugation protocol, highly pure [^99mTc]duramycin and [^99mTc]Annexin V were obtained, which were applied for in vitro cell assays of apoptosis and in vivo imaging of atherosclerotic plaques in the animal model. Oil Red O staining, TUNEL, hematoxylin-eosin (HE), and CD68 immunostaining were used to evaluate the deposition of lipids and presence of apoptotic macrophages in the lesions where focal intensity positively correlated with the uptake of both tracers.

RESULTS

[^99mTc]duramycin and [^99mTc]Annexin V with a high radiochemical purity (97.13 ± 1.52 and 94.94 ± 0.65 %, respectively) and a well stability at room temperature were used. Apoptotic cells binding activity to [^99mTc]duramycin (Kd, 6.92 nM and Bmax, 56.04 mol/10¹⁹ cells) was significantly greater than [^99mTc]Annexin V (Kd, 12.63 nM and Bmax, 31.55 mol/10¹⁹ cells). Compared with [^99mTc]Annexin V, [^99mTc]duramycin bound avidly to atherosclerotic lesions with a higher plaque-to-background ratio (P/B was 8.23 ± 0.91 and 5.45 ± 0.48 at 20 weeks, 15.02 ± 0.23 and 12.14 ± 0.22 at 30 weeks). No plaques were found in C57 control mice. Furthermore, Oil Red O staining showed lipid deposition areas were significantly increased in ApoE^-/- mice at 20 and 30 weeks, and TUNEL and CD68 staining confirmed that the focal uptake of both tracers contained abundant apoptotic macrophages.

CONCLUSIONS

This stable, fast clearing, and highly specific [^99mTc]duramycin, therefore, can be useful for the quantification of vulnerable atherosclerotic plaques.

Mitochondria-Targeted Triphenylphosphonium-Based Compounds: Syntheses, Mechanisms of Action, and Therapeutic and Diagnostic Applications

Mitochondria are recognized as one of the most important targets for new drug design in cancer, cardiovascular, and neurological diseases. Currently, the most effective way to deliver drugs specifically to mitochondria is by covalent linking a lipophilic cation such as an alkyltriphenylphosphonium moiety to a pharmacophore of interest. Other delocalized lipophilic cations, such as rhodamine, natural and synthetic mitochondria-targeting peptides, and nanoparticle vehicles, have also been used for mitochondrial delivery of small molecules. Depending on the approach used, and the cell and mitochondrial membrane potentials, more than 1000-fold higher mitochondrial concentration can be achieved. Mitochondrial targeting has been developed to study mitochondrial physiology and dysfunction and the interaction between mitochondria and other subcellular organelles and for treatment of a variety of diseases such as neurodegeneration and cancer. In this Review, we discuss efforts to target small-molecule compounds to mitochondria for probing mitochondria function, as diagnostic tools and potential therapeutics. We describe the physicochemical basis for mitochondrial accumulation of lipophilic cations, synthetic chemistry strategies to target compounds to mitochondria, mitochondrial probes, and sensors, and examples of mitochondrial targeting of bioactive compounds. Finally, we review published attempts to apply mitochondria-targeted agents for the treatment of cancer and neurodegenerative diseases.

New Insights in the Design of Bioactive Peptides and Chelating Agents for Imaging and Therapy in Oncology

Many synthetic peptides have been developed for diagnosis and therapy of human cancers based on their ability to target specific receptors on cancer cell surface or to penetrate the cell membrane. Chemical modifications of amino acid chains have significantly improved the biological activity, the stability and efficacy of peptide analogues currently employed as anticancer drugs or as molecular imaging tracers. The stability of somatostatin, integrins and bombesin analogues in the human body have been significantly increased by cyclization and/or insertion of non-natural amino acids in the peptide sequences. Moreover, the overall pharmacokinetic properties of such analogues and others (including cholecystokinin, vasoactive intestinal peptide and neurotensin analogues) have been improved by PEGylation and glycosylation. Furthermore, conjugation of those peptide analogues to new linkers and bifunctional chelators (such as AAZTA, TETA, TRAP, NOPO etc.), produced radiolabeled moieties with increased half life and higher binding affinity to the cognate receptors. This review describes the most important and recent chemical modifications introduced in the amino acid sequences as well as linkers and new bifunctional chelators which have significantly improved the specificity and sensitivity of peptides used in oncologic diagnosis and therapy.

99mTc-labeled bevacizumab for detecting atherosclerotic plaque linked to plaque neovascularization and monitoring antiangiogenic effects of atorvastatin treatment in ApoE-/- mice

Atherosclerotic neovascularization plays a significant role in plaque instability as it provides additional lipids and inflammatory mediators to lesions, and resulting in intraplaque hemorrhage. Vascular endothelial growth factor-A (VEGF-A) is considered the predominant proangiogenic factor in angiogenesis. Bevacizumab, a humanized monoclonal antibody, specifically binds to all VEGF-A isoforms with high affinity. Therefore, in this study, we designed ^99mTc-MAG₃-bevacizumab as a probe, and then investigated its usefulness as a new imaging agent for the detection of plaque neovessels, while also assessing the therapeutic effect of atorvastatin treatment. The ApoE^−/− mice treated with atorvastatin were used as the treatment group, and C57BL/6 J mice were selected as the control group. ^99mTc-MAG₃-bevacizumab uptake was visualized on atherosclerotic lesions by non-invasive in-vivo micro-SPECT/CT and ex-vivo BSGI planar imaging. The value of P/B in each part of the aorta of ApoE^−/− mice was higher than in the treatment group and the C57BL/6 J mice, which was confirmed by Oil Red O staining, CD31 staining and VEGF immunohistochemistry staining. ^99mTc-MAG₃-bevacizumab imaging allowed for the non-invasive diagnosis and assessment of plaque neovascularization. Furthermore, this probe may be used as a new molecular imaging agent to assess the antiangiogenic effect of atorvastatin.

Re-188 Enhances the Inhibitory Effect of Bevacizumab in Non-Small-Cell Lung Cancer

The malignant behaviors of solid tumors such as growth, infiltration and metastasis are mainly nourished by tumor neovascularization. Thus, anti-angiogenic therapy is key to controlling tumor progression. Bevacizumab, a humanized anti-vascular endothelial growth factor (VEGF) antibody, plus chemotherapy or biological therapy can prolong survival for cancer patients, but treatment-related mortality is a concern. To improve inhibitory effect and decrease side-effects on non-small-cell lung cancer (NSCLC), we used Re-188, which is a β emitting radionuclide, directly labeled with bevacizumab for radioimmunotherapy in a human A549 tumor model. Cytotoxic assay data showed that, after ¹⁸⁸ReO₄^- or ¹⁸⁸Re-bevacizumab at different concentration for 4 and 24 h, a time- and radioactivity does-dependent reduction in cell viability occurred. Also, an apoptosis assay conformed great apoptosis in the ¹⁸⁸Re-bevacizumab group compared with controls and other treatment groups. In vivo, tumor volumes in the ¹⁸⁸Re-bevacizumab (11.1 MBq/mice) group were not reduced but growth was delayed compared with other groups. Thus, ¹⁸⁸Re-bevacizumab enhanced the therapeutic effect of bevacizumab, suggesting a potential therapeutic strategy for NSCLC treatment.

Gold nanoparticles-based SPECT/CT imaging probe targeting for vulnerable atherosclerosis plaques

In order to realize accurate localization and precise evaluation of vulnerability of atherosclerotic plaques via dual-modal imaging, gold nanoparticles (GNPs) were firstly caped with a thin amino-PEGs cover and then conjugated with the targeting molecular Annexin V and radionuclide Tc-99m simultaneously to form SPECT/CT imaging probe targeting apoptotic macrophages. The as-synthesized (99m)Tc-GNPs-Annexin V was with uniform size (30.2 ± 2.9 nm) and high labeling rate (98.9 ± 0.5%) and stability. Targeting ability of Annexin V for apoptotic macrophages was kept and enhanced. For macrophages with 30% apoptosis, cellular uptakes of 3.52 ± 0.35% for (99m)Tc-GNPs-Annexin V, 2.41 ± 0.53% for (99m)Tc-GNPs and 1.68 ± 0.36% for (99m)Tc-Annexin V were achieved after 2 h incubation. ApoE knock out mice with high fat diet-induced atherosclerosis were scanned via (99m)Tc-GNPs-Annexin V SPECT/CT. With the introduction of targeting molecules, imaging probe was more efficient in accumulating in apoptotic macrophages. In practical evaluation, CT helps to restrict the lesions depiction more accurately, meanwhile, SPECT imaging intensity correlated with pathological changes tightly. In conclusion, Annexin V-modified hybrid gold nanoparticles were successfully synthesized, and this imaging system helped to better localize and diagnose those vulnerable AS plaques via specific targeting the apoptotic macrophages.

99mTc-labelled anti-CD11b SPECT/CT imaging allows detection of plaque destabilization tightly linked to inflammation

It remains challenging to predict the risk of rupture for a specific atherosclerotic plaque timely, a thrombotic trigger tightly linked to inflammation. CD11b, is a biomarker abundant on inflammatory cells, not restricted to monocytes/macrophages. In this study, we fabricated a probe named as ^99mTc-MAG₃-anti-CD11b for detecting inflamed atherosclerotic plaques with single photon emission computed tomography/computed tomography (SPECT/CT). The ApoE-knockout (ApoE^−/−) mice were selected to establish animal models, with C57BL/6J mice used for control. A higher CD11b⁺-cell recruitment with higher CD11b expression and more serious whole-body inflammatory status were identified in ApoE^−/− mice. The probe showed high in vitro affinity and specificity to the Raw-264.7 macrophages, as well as inflammatory cells infiltrated in atherosclerotic plaques, either in ex vivo fluorescent imaging or in in vivo micro-SPECT/CT imaging, which were confirmed by ex vivo planar gamma imaging, Oil-Red-O staining and CD11b-immunohistochemistry staining. A significant positive relationship was identified between the radioactivity intensity on SPECT/CT images and the CD11b expression in plaques. In summary, this study demonstrates the feasibility of anti-CD11b antibody mediated noninvasive SPECT/CT imaging of inflammatory leukocytes in murine atherosclerotic plaques. This imaging strategy can identify inflammation-rich plaques at risk for rupture and evaluate the effectiveness of inflammation-targeted therapies in atheroma.

Tumor Angiogenesis Targeted Radiosensitization Therapy Using Gold Nanoprobes Guided by MRI/SPECT Imaging

Gold nanoparticles (AuNPs) have recently garnered great interest as potential radiosensitizers in tumor therapy. However, major challenges facing their application in this regard are further enhancement of tumor accumulation of the particles in addition to enhanced permeability retention (EPR) effect and an understanding of the optimal particle size and time for applying radiotherapy after the particle administration. In this study, we fabricated novel cyclic c(RGDyC)-peptide-conjugated, Gd- and 99 mTc-labeled AuNPs (RGD@AuNPs-Gd99 mTc) probes with different sizes (29, 51, and 80 nm) and evaluated their potential as radiosensitization therapy both in vitro and in vivo. We found that these probes have a high specificity for αvβ3 integrin positive cells, which resulted in their high cellular uptake and thereby enhanced radiosensitization. Imaging in vivo with MRI and SPECT/CT directly showed that the RGD@AuNPs-Gd99 mTc probes specifically target tumors and exhibit greater accumulation within tumors than the RAD@AuNPs-Gd99 mTc probes. Interestingly, we found that the 80 nm RGD@AuNPs-Gd99 mTc probes exhibit the greatest effects in vitro; however, the 29 nm RGD@AuNPs-Gd99 mTc probes were clearly most efficient in vivo. As a result, radiotherapy of tumors with the 29 nm probe was the most potent. Our study demonstrates that RGD@AuNPs-Gd99 mTc probes are highly useful radiosensitizers capable of guiding and enhancing radiation therapy of tumors.

SPECT imaging of cytochrome c in pressure overload mice hearts

Clinically, pressure overload (PO) occurs in many clinical settings such as hypertension and valvular stenosis especially in the current aging society.

Novel DNA Polymer for Amplification Pretargeting

In this Letter, different from conventional pretargeting, an additional novel DNA polymer with multiple copies of a target was first designed to be administrated between the antitumor antibody, and the labeled effector served as an amplification pretargeting strategy. Two phosphorothioate DNA strands, a bridging and a target strand, were hybridized to form a polymer. Polymer size, as a function of molar ratios, was then monitored by size exclusion HPLC and electrophoretic mobility shift assay. Moreover, binding efficiency of polymers with the radiolabeled effector and polymer size after hybridization were measured by HPLC as well. As the polymer was expected to produce more binding sites that would be targeted by effectors, amplification pretargeting can greatly improve accumulation of effectors in tumor. This novel proof-of-concept was then well demonstrated by the in vitro test of signal amplification in antibody-binding protein L coated plate and LS174T cells. Compared to conventional pretargeting, significantly increasing radioactive signal was observed in this designed amplification pretargeting, which would serve as a useful paradigm of the potential of oligomer polymers to improve pretargeting and other related approaches.

A nuclear chocolate box: the periodic table of nuclear medicine

Radioisotopes of elements from all parts of the periodic table find both clinical and research applications in radionuclide molecular imaging and therapy (nuclear medicine). This article provides an overview of these applications in relation to both the radiological properties of the radionuclides and the chemical properties of the elements, indicating past successes, current applications and future opportunities and challenges for inorganic chemistry.

Gold nanoparticles stabilized with MPEG-grafted poly(l-lysine): in vitro and in vivo evaluation of a potential theranostic agent

As the number of diagnostic and therapeutic applications utilizing gold nanoparticles (AuNPs) increases, so does the need for AuNPs that are stable in vivo, biocompatible, and suitable for bioconjugation. We investigated a strategy for AuNP stabilization that uses methoxypolyethylene glycol-graft-poly(l-lysine) copolymer (MPEG-gPLL) bearing free amino groups as a stabilizing molecule. MPEG-gPLL injected into water solutions of HAuCl4 with or without trisodium citrate resulted in spherical (Zav = 36 nm), monodisperse (PDI = 0.27), weakly positively charged nanoparticles (AuNP3) with electron-dense cores (diameter: 10.4 ± 2.5 nm) and surface amino groups that were amenable to covalent modification. The AuNP3 were stable against aggregation in the presence of phosphate and serum proteins and remained dispersed after their uptake into endosomes. MPEG-gPLL-stabilized AuNP3 exhibited high uptake and very low toxicity in human endothelial cells, but showed a high dose-dependent toxicity in epithelioid cancer cells. Highly stable radioactive labeling of AuNP3 with (99m)Tc allowed imaging of AuNP3 biodistribution and revealed dose-dependent long circulation in the blood. The minor fraction of AuGNP3 was found in major organs and at sites of experimentally induced inflammation. Gold analysis showed evidence of a partial degradation of the MPEG-gPLL layer in AuNP3 particles accumulated in major organs. Radiofrequency-mediated heating of AuNP3 solutions showed that AuNP3 exhibited heating behavior consistent with 10 nm core nanoparticles. We conclude that PEG-pPLL coating of AuNPs confers "stealth" properties that enable these particles to exist in vivo in a nonaggregating, biocompatible state making them suitable for potential use in biomedical applications such as noninvasive radiofrequency cancer therapy.

Preparation and Evaluation of 99mTc-labeled anti-CD11b Antibody Targeting Inflammatory Microenvironment for Colon Cancer Imaging

CD11b, an active constituent of innate immune response highly expressed in myeloid-derived suppressor cells (MDSCs), can be used as a marker of inflammatory microenvironment, particularly in tumor tissues. In this research, we aimed to fabricate a (99m)Tc-labeled anti-CD11b antibody as a probe for CD11b(+) myeloid cells in colon cancer imaging with single-photon emission computed tomography (SPECT). In situ murine colon tumor model was established in histidine decarboxylase knockout (Hdc(-/-)) mice by chemicals induction. (99m)Tc-labeled anti-CD11b was obtained with labeling yields of over 30% and radiochemical purity of over 95%. Micro-SPECT/CT scans were performed at 6 h post injection to investigate biodistributions and targeting of the probe. In situ colonic neoplasma as small as 3 mm diameters was clearly identified by imaging; after dissection of the animal, anti-CD11b immunofluorescence staining was performed to identify infiltration of CD11b+ MDSCs in microenvironment of colonic neoplasms. In addition, the images displayed intense signal from bone marrow and spleen, which indicated the origin and migration of CD11b(+) MDSCs in vivo, and these results were further proved by flow cytometry analysis. Therefore, (99m)Tc-labeled anti-CD11b SPECT displayed the potential to facilitate the diagnosis of colon tumor in very early stage via detection of inflammatory microenvironment.

Biodistribution of (99m)tc tricarbonyl glycine oligomers

^99mTc tricarbonyl glycine monomers, trimers, and pentamers were synthesized and evaluated for their radiolabeling and in vivo distribution characteristics. We synthesized a ^99mTc-tricarbonyl precursor with a low oxidation state (I). ^99mTc(CO)₃(H₂O)₃⁺ was then made to react with monomeric and oligomeric glycine for the development of bifunctional chelating sequences for biomolecules. Labeling yields of ^99mTc-tricarbonyl glycine monomers and oligomers were checked by high-performance liquid chromatography. The labeling yields of ^99mTc-tricarbonyl glycine and glycine oligomers were more than 95%. We evaluated the characteristics of ^99mTc-tricarbonyl glycine oligomers by carrying out a lipophilicity test and an imaging study. The octanol-water partition coefficient of ^99mTc tricarbonyl glycine oligomers indicated hydrophilic properties. Single-photon emission computed tomography imaging of ^99mTc-tricarbonyl glycine oligomers showed rapid renal excretion through the kidneys with a low uptake in the liver, especially of ^99mTc tricarbonyl triglycine. Furthermore, we verified that the addition of triglycine to prototype biomolecules (AGRGDS and RRPYIL) results in the improvement of radiolabeling yield. From these results, we conclude that triglycine has good characteristics for use as a bifunctional chelating sequence for a ^99mTc-tricarbonyl- based biomolecular imaging probe.

Detection of Aspergillus fumigatus pulmonary fungal infections in mice with (99m)Tc-labeled MORF oligomers targeting ribosomal RNA

PURPOSE

Invasive aspergillosis is a major cause of infectious morbidity and mortality in immunocompromised patients. The fungus Aspergillus fumigatus (A. fumigatus) is the primary causative agent of invasive aspergillosis. However, A. fumigatus infections remain difficult to diagnose particularly in the early stages due to the lack of a rapid, sensitive and specific diagnostic approach. In this study, we investigated (99m)Tc labeled MORF oligomers targeting fungal ribosomal RNA (rRNA) for the imaging detection of fungal infections.

PROCEDURES

Three phosphorodiamidate morpholino (MORF) oligomer (a DNA analogue) probes were designed: AGEN, complementary to a sequence of the fungal 28S ribosomal RNA (rRNA) of Aspergillus, as a genus-specific probe; AFUM, complementary to the 28S rRNA sequence of A. fumigatus, as a fungus species-specific probe; and cMORF, irrelevant to all fungal species, as a control probe. The probes were conjugated with Alexa Fluor 633 carboxylic acid succinimidyl ester (AF633) for fluorescence imaging or with NHS-mercaptoacetyl triglycine (NHS-MAG3) for nuclear imaging with (99m)Tc and then evaluated in vitro and in vivo.

RESULTS

The specific binding of AGEN and AFUM to fungal total RNA was confirmed by dot blot hybridization while specific binding of AGEN and AFUM in fixed and live A. fumigatus was demonstrated by both fluorescent in situ hybridization (FISH) analysis and accumulation in live cells. SPECT imaging of BALB/c mice with pulmonary A. fumigatus infections and administered (99m)Tc labeled AGEN and AFUM showed immediate and obvious accumulation in the infected lungs, while no significant accumulation of the control (99m)Tc-cMORF in the infected lung was observed. Compared to non-infected mice, with sacrifice at 1h, the accumulation of (99m)Tc-AGEN and (99m)Tc-AFUM in the lungs of mice infected with A. fumigatus was 2 and 2.7 fold higher respectively.

CONCLUSIONS

In vivo targeting fungal ribosomal RNA with (99m)Tc labeled MORF probes AGEN and AFUM may be useful for A. fumigatus infection imaging and may provide a new strategy for the noninvasive diagnosis of invasive aspergillosis and other fungal infections.

Synthesis of Gemcitabine-(C4-amide)-[anti-HER2/neu] Utilizing a UV-Photoactivated Gemcitabine Intermediate: Cytotoxic Anti-Neoplastic Activity against Chemotherapeutic-Resistant Mammary Adenocarcinoma SKBr-3

Gemcitabine is a pyrimidine nucleoside analog that becomes triphosphorylated intracellularly where it competitively inhibits cytidine incorporation into DNA strands. Another mechanism-of-action of gemcitabine (diphosphorylated form) involves irreversible inhibition of the enzyme ribonucleotide reductase thereby preventing deoxyribonucleotide synthesis. Functioning as a potent chemotherapeutic gemcitabine promote decreases in neoplastic cell proliferation and apoptosis which is frequently found to be effective for the treatment of several leukemias and a wide spectrum of carcinomas. A brief plasma half-life in part due to rapid deamination and chemotherapeutic-resistance restricts the utility of gemcit-abine in clinical oncology. Selective "targeted" delivery of gemcitabine represents a potential molecular strategy for simultaneously prolonging its plasma half-life and minimizing innocient tissues and organ systems exposure to chemotherapy. The molecular design and an organic chemistry based synthesis reaction is described that initially generates a UV-photoactivated gemcitabine intermediate. In a subsequent phase of the synthesis method the UV-photoactivated gemcitabine intermediate is covalently bonded to a monoclonal immunoglobulin yielding an end-product in the form of gemcitabine-(C₄-amide)-[anti-HER2/neu]. Analysis by SDS-PAGE/chemiluminescent auto-radiography did not detect evidence of gemcitabine-(C₄-amide)-[anti-HER2/neu] polymerization or degradative fragmentation while cell-ELISA demonstrated retained binding-avidity for HER2/neu trophic membrane receptor complexes highly over-expressed by chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3). Compared to chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3), the covalent immunochemotherapeutic, gemcitabine-(C₄-amide)-[anti-HER2/neu] is anticipated to exert greater levels of cytotoxic anti-neoplastic potency against other neoplastic cell types like pancreatic carcinoma, small-cell lung carcinoma, neuroblastoma, glioblastoma, oral squamous cell carcinoma, cervical epitheliod carcinoma, or leukemia/lymphoid neoplastic cell types based on their reported sensitivity to gemcitabine and gemcitabine covalent conjugates.

Synthesis of a covalent epirubicin-(C(3)-amide)-anti-HER2/neu immunochemotherapeutic utilizing a UV-photoactivated anthracycline intermediate

The C(3)-monoamine on the carbohydrate moiety (daunosamine -NH(2)-3') of epirubicin was reacted under anhydrous conditions with succinimidyl 4,4-azipentanoate to create a covalent UV-photoactivated epirubicin-(C(3)-amide) intermediate with primary amine-reactive properties. A synthetic covalent bond between the UV-photoactivated epirubicin-(C(3)-amide) intermediate and the ɛ-amine of lysine residues within the amino acid sequence of anti-HER2/neu monoclonal immunoglobulin was subsequently created by exposure to UV light (354 nm) for 15 minutes. Size-separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis combined with immunodetection analysis and chemiluminescent autoradiographic imaging revealed a lack of IgG-IgG polymerization or degradative protein fragmentation of the covalent epirubicin-(C(3)-amide)-[anti-HER2/neu] immunochemotherapeutic. Retained binding-avidity of epirubicin-(C(3)-amide)-[anti-HER2/neu] was validated by cell-ELISA utilizing monolayer populations of chemotherapeutic-resistant mammary adenocarcinoma SKBr-3 which highly overexpress membrane-associated HER2/neu complexes. Between epirubicin-equivalent concentrations of 10(-10) to 10(-6) M the covalent epirubicin-(C(3)-amide)-[anti-HER2/neu] immunochemotherapeutic consistently evoked levels of cytotoxic anti-neoplastic potency that were highly analogous to chemotherapeutic-equivalent concentrations of epirubicin. Cytotoxic anti-neoplastic potency of epirubicin-(C(3)-amide)-[anti-HER2/neu] against chemotherapeutic-resistant mammary adenocarcinoma SKBr-3 challenged with epirubicin-(C(3)-amide)-[anti-HER2/neu] at an epirubicin-equivalent concentration of 10(-6) M was 88.5% (e.g., 11.5% residual survival). Between final epirubicin-equivalent concentrations of 10(-8) and 10(-7) M there was a marked threshold increase in the mean cytotoxic anti-neoplastic activity for epirubicin-(C(3)-amide)-[anti-HER2/neu] from 9.9% to 66.9% (90.2% to 33.1% residual survival).

Engineering of affibody molecules for therapy and diagnostics

Affibody molecules are small and robust non-immunoglobulin affinity ligands capable of binding to a wide range of protein targets. They are selected from combinatorial libraries based on a 58 amino acid, three-alpha-helical Z-domain scaffold. They share no sequence or structural homologies to antibodies and in contrast to antibodies they can be functionally produced both by peptide synthesis and by recombinant expression in Escherichia coli. Protein engineering is used to adapt Affibody molecules binding to a target of interest to the specific demands imposed by the intended application. Obviously, the optimal molecule for molecular imaging will be different from the optimal molecule for therapy. Here, we describe general strategies to optimize Affibody molecules for diagnostic imaging and therapy applications.

Tumor delivery of antisense oligomer using trastuzumab within a streptavidin nanoparticle

PURPOSE

Trastuzumab (Herceptin™) is often internalized following binding to Her2+ tumor cells. The objective of this study was to investigate whether trastuzumab can be used as a specific carrier to deliver antisense oligomers into Her2+ tumor cells both in vitro and in vivo.

METHODS

A biotinylated MORF oligomer antisense to RhoC mRNA and its biotinylated sense control were labeled with either lissamine for fluorescence detection or 99mTc for radioactivity detection and were linked to biotinylated trastuzumab via streptavidin. The nanoparticles were studied in SUM190 (RhoC+, Her2+) study and SUM149 (RhoC+, Her2−) control cells in culture and as xenografts in mice.

RESULTS

As evidence of unimpaired Her2+ binding of trastuzumab within the nanoparticle, accumulations were clearly higher in SUM190 compared to SUM149 cells and, by whole-body imaging, targeting of SUM190 tumor was similar to that expected for a radiolabeled trastuzumab. As evidence of internalization, fluorescence microscopy images of cells grown in culture and obtained from xenografts showed uniform cytoplasm distribution of the lissamine-MORF. An invasion assay showed decreased RhoC expression in SUM190 cells when incubated with the antisense MORF nanoparticles at only 100 nM.

CONCLUSION

Both in cell culture and in animals, the nanoparticle with trastuzumab as specific carrier greatly improved tumor delivery of the antisense oligomer against RhoC mRNA into tumor cells overexpressing Her2 and may be of general utility.

Comparison of 18F PET and 99mTc SPECT imaging in phantoms and in tumored mice

Our objective was to compare the performance of a micro-single photon emission computed tomography (micro-SPECT) with that of a micro-positron emission tomography (microPET) in a Her2+ tumored mice using an anti-Her2 nanoparticle radiolabeled with (99m)Tc and (18)F. Camera performance was first compared using phantoms; then a tumored mouse administered the (99m)Tc-nanoparticle was imaged on a Bioscan NanoSPECT/CT, while another tumored mouse received the identical nanoparticle, labeled now with (18)F, and was imaged on a Philips Mosaic HP PET camera. The nanoparticle was radiolabeled with (99m)Tc via MAG(3) chelation and with (18)F via SFB as an intermediate. Phantom imaging showed that the resolution of the SPECT camera was clearly superior, but even with 4 heads and multipinhole collimators, detection sensitivity was 15-fold lower. Radiolabeling of the nanoparticle by chelation with (99m)Tc was considerably easier and safer than manual covalent attachment of (18)F. Both cameras provided accurate quantitation of radioactivity over a broad range. In conclusion, when deciding between (99m)Tc vs (18)F, an advantage rests with the chelation of (99m)Tc over covalent attachment of (18)F, achieved manually or otherwise, but with these small animal cameras, this choice also results in trading lower sensitivity for higher resolution.

Identification of a high affinity TAG-72 binding peptide by phage display selection

PURPOSE

Phage display was used to select novel peptides that specifically bind the TAG-72 antigen and with properties suitable for imaging TAG-72 positive cancers.

RESULTS

After three rounds of selection against TAG-72 and using two different elution conditions including a long elution, the consensus sequences FRERCDKHPQKCTKFL and DPRHCQKRVLPCPAWL were expressed on phages G3-15 and T3-15 respectively. ELISA, fluorescence-activated cell sorting analysis and fluorescence microscopy provided evidence that both phages specifically bound TAG-72 in vitro. Both peptides are stable in 37oC serum. By a cell binding competition assay, the IC50 for T3-15 was measured as 0.29 nM and therefore 36-fold higher affinity than G3-15 at 10.32 nM. The biodistribution in mice carrying LS-174T tumors in one thigh were similar for both 99mTc-peptides at 30 min, but at 90 min the 99mTc-T3-15 peptide accumulated almost three times higher in the tumor. The SPECT/CT images were consistent with the biodistribution results.

PROCEDURES

The f88-4/Cys6 phage library and two different elution conditions were used to identify two new higher affinity binding peptides for the TAG-72 antigen. One, was a single brief elution with pH 2.2 glycine buffer, and the second began with the glycine elution but was followed with a longer elution with Tris buffered saline (TBS) at pH 7.4. The phages that bound TAG-72 were evaluated by fluorescence-activated cell sorting analysis using TAG-72 positive LS-174T cells and confirmed by immunofluorescence imaging. The consensus peptides displayed on the selected phages were synthesized and conjugated with NHS-MAG3 for radiolabeling with 99mTc. The IC50 for TAG-72 binding was evaluated by cell binding competition in vitro while binding affinity was evaluated in vivo by necropsy and SPECT/CT imaging in a tumor mouse model.

CONCLUSION

We have identified a peptide with a sub nanomolar inhibition constant for the TAG-72 antigen that may have application in cancer imaging.

Radiolabeled nano-peptides show specificity for an animal model of human PC3 prostate cancer cells

OBJECTIVES

Cancer has been investigated using various pre-targeting techniques or models focusing on radiobombesin analogues; however, both are not offered together. In this study, nano-bombesin labeling by a pre-targeting system was undertaken to develop an alternative approach for prostate tumor treatment.

METHODS

A two-step pre-targeting system utilizing a combination of streptavidin (SA), biotinylated morpholino (B-MORF), biotinylated BBN (B-BBN) with two different spacers (b-Ala and PEG), and a radiolabeled cMORF was evaluated in vitro and in vivo.

RESULTS

Final conjugation conditions consisted of a 1:1:2 ratio of SA:B-MORF:B-BBN, followed by addition of 99mTc-cMORF to compensate for free MORF. In vitro binding experiments with prostate cancer cells (PC-3) revealed that total binding was time-dependent for the Ala spacer but not for the PEG spacer. The highest accumulation (5.06 ± 1.98 %) was achieved with 1 hour of incubation, decreasing as time progressed. Specific binding fell to 1.05 ± 0.35 %. The pre-targeting biodistribution in healthy Swiss mice was measured at different time points, with the best responses observed for 7-h and 15-h incubations. The effector, 99mTc-MAG3-cMORF, was administered 2 h later. Strong kidney excretion was always documented. The greatest tumor uptake was 2.58 ± 0.59 %ID/g at 7 h for B-bAla-BBN, with a region of interest (ROI) value of 3.9 % during imaging. The tumor/blood ratio was low due to the slow blood clearance; however, the tumor/muscle ratio was 5.95.

CONCLUSIONS

The pre-targeting approach with a peptide was a viable concept. Further evaluation with modified sequences of MORF, including less cytosine, and additional test intervals could be worthwhile.

A (99m)Tc-labeled triphenylphosphonium derivative for the early detection of breast tumors

INTRODUCTION

A greater mitochondrial membrane potential in tumor cells has been shown to enhance the accumulation of triphenyl phosphonium derivatives. The aim of this study was to synthesize and characterize (99m)Tc-labeled alkyl triphenyl phosphonium ((99m)Tc-Mito(10)-MAG3) for the early detection of breast tumors.

METHODS

Mito(10)-MAG3 was synthesized by coupling (10-aminodecyl)triphenyl phosphonium bromide with NHS-MAG3 and radiolabeled with (99m)Tc. Biodistribution and pharmacokinetics of (99m)Tc-Mito(10)-MAG3 was investigated in female Sprague-Dawley rats. Initially, (99m)Tc-Mito(10)-MAG3 was tested in animals with established breast tumors. In a subsequent longitudinal study, the imaging efficacy of (99m)Tc(10)-Mito-MAG3 for detecting small, nonpalpable breast tumors was assessed after chemically inducting breast carcinoma. Tumors detected by imaging were allowed to grow to palpable size and confirmed by histology. The results were compared with (99m)Tc-MIBI.

RESULTS

The synthesis of Mito(10)-MAG3 was confirmed by mass spectrometry. The compound was radiolabeled with (99m)Tc to > 92% in a single step. The radiopharmaceutical exhibited fast blood clearance and low cardiac uptake. In the initial study, using animals with established breast tumors, (99m)Tc-Mito(10)-MAG3 imaging detected small lesions that were missed by palpation. In the longitudinal study, (99m)Tc-Mito(10)-MAG3 exhibited focal uptake in small breast tumors, which were confirmed by histology.

CONCLUSIONS

Imaging, using (99m)Tc-Mito(10)-MAG3, allowed the early detection of small neoplastic lesions in the mammary glands. The agent significantly reduced cardiac uptake, compared with (99m)Tc-MBIB. The phosphonium-based derivatives warrant further characterization and development as imaging agents for scintimammography.

In vivo delivery of antisense MORF oligomer by MORF/carrier streptavidin nanoparticles

Tumor targeting by oligomers is largely limited by the pharmacokinetics and cell-membrane transport obstacles. In this article, we describe the use of a delivery nanoparticle, in which streptavidin served as a convenient bridge between a biotinylated oligomer and a biotinylated cell-membrane-penetrating peptide, to improve the delivery of an antisense phosphorodiamidate morpholino (MORF) oligomer in vivo. A biotinylated (99m)Tc-radiolabeled MORF oligomer with a base sequence antisense to the RIalpha mRNA and its sense control were incorporated separately into nanoparticles, along with biotinylated tat or polyarginine carrier. The streptavidin nanoparticles were administrated intravenously to both normal and nude mice bearing SUM149 breast tumor xenografts. The biodistributions showed much higher normal tissue levels for the radiolabeled MORFs, independent of antisense or sense or tat or polyarginine, when administered as the nanoparticles, compared to naked. A statistically significant higher accumulation of both antisense nanoparticles, compared to the respective sense control nanoparticles, was observed, along with much higher tumor accumulations, compared to historical naked controls. This study has provided evidence that the in vivo function of an antisense oligomer within the streptavidin nanoparticle is not impeded, and, as such, the MORF/streptavidin/carrier nanoparticles may be suitable for in vivo tumor delivery of antisense MORF and other oligomers.

Auger radiation-induced, antisense-mediated cytotoxicity of tumor cells using a 3-component streptavidin-delivery nanoparticle with 111In

When antisense oligomers are intracellular, they migrate to and are retained in the nucleus of tumor cells and therefore may be used to carry Auger electron-emitting radionuclides such as (111)In for effective tumor radiotherapy.

METHODS

Our nanoparticle consists of streptavidin that links 3 biotinylated components: the antiHer2 antibody trastuzumab (to improve pharmacokinetics), the tat peptide (to improve cell membrane transport), and the (111)In-labeled antiRIalpha messenger RNA antisense morpholino (MORF) oligomer.

RESULTS

As evidence of unimpaired function, tumor cell and nuclear accumulations were orders of magnitude higher after incubation with (99m)Tc-MORF/tat/trastuzumab than after incubation with free (99m)Tc-MORF and significantly higher with the antisense than with the sense MORF. In mice, tumor and normal-tissue accumulations of the (99m)Tc-MORF/tat/trastuzumab nanoparticle were comparable to those of free (99m)Tc-trastuzumab, confirming the improved pharmacokinetics due to the trastuzumab component. Although kidneys, liver, and other normal tissues also accumulated the nanoparticle, immunohistochemical evaluation of tissue sections in mice receiving the Cy3-MORF/tat/trastuzumab nanoparticle showed evidence of nuclear accumulation only in tumor tissue. In a dose escalation study, as measured by the surviving fraction, the nanoparticle significantly increased the kill of SK-BR-3 breast cancer Her2+/RIalpha+ cells, compared with all controls.

CONCLUSION

Significant radiation-induced antisense-mediated cytotoxicity of tumor cells in vitro was achieved using an Auger electron-emitting antisense MORF oligomer administered as a member of a 3-component streptavidin-delivery nanoparticle.

Cell studies of a three-component antisense MORF/tat/Herceptin nanoparticle designed for improved tumor delivery

The three-component nanoparticle of this investigation consisted of an anti-type I regulatory subunit alpha of the cyclic AMP-dependent protein kinase A (RIalpha) antisense phosphorodiamidate morpholino (MORF) oligomer, a tat peptide and the anti-HER2 Herceptin antibody each biotinylated and each linked via streptavidin and tested in SUM190 (HER2+), SUM149 (HER2-) and SK-BR-3 (HER2+) cells in culture, using both radioactivity and fluorescent labels on the antisense and control sense MORF. Within the nanoparticle, the antibody provides specific binding to the target cells, the tat improves cellular delivery and the MORF provides the specific retention of the radioactivity in the target cell nucleus. The results show that within the nanoparticle, the Herceptin was still able to bind to its determinant; that the MORF escaped entrapment with its mRNA-binding ability preserved and that the tat maintained its carrier function. Fluorescence microscopy showed evidence of antisense MORF internalization, separation from Herceptin and migration to the nucleus. In conclusion, streptavidin appears to provide an easy means of mixing and matching components to improve the tumor-specific targeting, cell membrane transport, pharmacokinetics and other properties of antisense and other oligomers. Combining the three components of this investigation with streptavidin apparently did not interfere with the properties of each component in cell culture and significantly improved delivery.