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Macropa-PSMA-ligand conjugates used for targeted alpha-therapy (TAT) with actinium-225 were furnished with an albumin binder to improve their pharmacological behaviour in vivo. [1,2] Additionally, the introduction of an iodine-containing albumin binder provides the basis for the development of a novel theranostic radioconjugate pair using the radiohybrid approach. This involves the complexation of the alpha emitter actinium-225 (half-life: 9.9 d) and the introduction of the easily accessible SPECT-compatible radiohalogen iodine-123 into the same molecule. Advantageously, its ideal physical half-life of 13.2 h and mild radioiodination conditions allows the imaging of longer circulating radioconjugates. The PSMA-binding motif based on the PSMA-617 structure was prepared by a multi-step peptide synthesis followed by subsequent conjugation with the macropa chelator by Cu-catalysed azide-alkyne (CuAAC) click chemistry. The labelling precursor for the introduction of iodine-123 was synthesized by replacing the 4-(p-iodophenyl)butyrate by a trimethylstannyl group to enable labelling by electrophilic aromatic substitution reaction. To determine the binding affinity, LNCaP cells were incubated with the nonradioactive conjugates (with and without nonradioactive lanthanum (La) as congener for actinium-225) in a competition assay and spiked with the radioconjugate [133La]La-PSMA-617. The influence of the complexing agent and the metal ion loading on the binding affinity was evaluated. Two radioconjugates were developed: [123I]I-mcp-M-alb-PSMA with one PSMA-binding motif was prepared from the stannyl precursor (DMSO, Iodogen, 20 min, rt, RCY: 49%) and [123I]I-mcp-D-alb-PSMA with two PSMA-binding motifs was labelled under the same conditions with the exception of adding nonradioactive iodine after completion of radiolabelling to iodinate the second stannyl group (RCY: 20%). Both radioconjugates were purified by HPLC. Beneficially, no influence of chelator loading on cell binding

The Al18F-labeling approach offers a one-step access to radiofluorinated biomolecules by mimicking the labeling process for radiometals. Although these labeling conditions are considered to be mild compared to classic radiofluorinations, improvements of the chelating units have led to the discovery of (±)-H3RESCA, which allows Al18F-labeling already at ambient temperature. While the suitability of (±)-H3RESCA for functionalization and radiofluorination of proteins is well established, its use for small molecules or peptides is less explored. Herein, we advanced this acyclic pentadentate ligand by introducing an alkyne moiety for the late-stage functionalization of biomolecules via click chemistry. We show that in addition to Al18F-labeling, the cyclohexanediamine triazole (CHDT) moiety allows stable complexation of 68Ga and 111In. Three novel CHDT-functionalized PSMA inhibitors were synthesized and their Al18F-, 68Ga-, and 111In-labeled analogs were subjected to a detailed in vitro radiopharmacological characterization. Stability studies in vitro in human serum revealed amongst others a high kinetic inertness of all radiometal complexes. Furthermore, the Al18F-labeled PSMA ligands were characterized for their biodistribution in a LNCaP derived tumor xenograft mouse model by PET imaging. One radioligand, Al[18F]F-CHDT-PSMA-1, bearing a small azidoacetyl linker at the glutamate-urea-lysine motif, provided an in vivo performance comparable to that of [18F]PSMA-1007, but with even higher tumor-to-blood and tumor-to-muscle ratios at 120 min p.i. Overall, our results highlight the suitability of the novel CHDT moiety for functionalization and radiolabeling of small molecules or peptides with Al18F, 68Ga, and 111In and the triazole ring seems to entail favorable pharmacokinetic properties for molecular imaging purposes.

Macropa-PSMA-Konjugate, die zur zielgerichteten Alphatherapie mit Ac-225 dienen, werden mit einem Albuminbinder verknüpft. Neben der Verbesserung des pharmakologischen Verhaltens in vivo bietet die albuminbindende Einheit die Grundlage eines theranostischen Ansatzes. Neben der Komplexierung des Alphaemitters Ac-225 wird zusätzlich die Einführung des SPECT-Nuklids I-123 im gleichen Molekül ermöglicht. Vorteilhaft sind die milden Bedingungen der Radioiodierung sowie eine Halbwertszeit (t1/2 = 13,2 h), welche die Bildgebung länger zirkulierender Substanzen ermöglicht.

Ziel/Aim: Der Einsatz von Actinium-225 mit dem DOTA-Konjugat PSMA-617 befindet sich in der klinischen Entwicklung. DOTA ist jedoch nicht ideal, da hohe Temperaturen für die Markierung benötigt werden und der Komplex in vivo nicht stabil genug ist. Ziel ist es, einen besseren, macropa-basierten Chelator zu finden und mit von PSMA-617 abgeleiteten Bindungsvektoren zu verknüpfen. Methodik/Methods: Es wurden 4 verschiedene Konjugate hergestellt, welche sich hinsichtlich der Anzahl der Bindungsmotive sowie ihrer Fähigkeit, an Albumin zu binden, unterscheiden. Die Stabilität der markierten Komplexe wurde über 10 Tage in Puffer und Serum untersucht. Weiterhin wurden Bindungsaffinitäten und Koloniebildungsassays an PSMA-positiven LNCaP-Zellen durchgeführt. Alle Konjugate wurden hinsichtlich ihrer Organverteilung in LNCaP-Tumor-tragenden SCID-Mäusen untersucht. Ergebnisse/Results: Alle 4 Konjugate wurden unter milden Bedingungen radiomarkiert und zeigen bei Zugabe von Gentisinsäure die höchste Stabilität über 10 Tagen. Die Bindungsaffinitäten der Konjugate wurden als KD-Werte bestimmt und liegen zwischen (10-40) nM. Die Untersuchungen zum Zellüberleben zeigen einen therapeutischen Vorteil der bivalenten gegenüber den monovalenten Konjugaten. Alle vier Konjugate erreichten in unterschiedlichen Zeitspannen (bis 5 d p.i.) Tumoranreicherungen von (12-85) %ID/g. Unerwünschte Anreicherungen traten v. a. bei dem dimeren, albuminbindenden Konjugat in Form von Akkumulationen (Leber, Milz, Nieren) auf. Schlussfolgerungen/Conclusions: Die Verwendung von macropa-basierten Konjugaten für die Therapie mit Actinium‑225 oder die zukünftige Bildgebung mit Lanthan‑133 ist vorteilhaft, da die gebildeten Komplexe stabiler sind und damit eine Anreicherung der Aktivität in off-Target-Regionen verringert werden kann. Weiterhin ergibt sich ein Vorteil im Handling, da die Reaktionen schnell und bei Raumtemperatur durchgeführt werden können, was die spätere Umsetzung in eine GMP-gerechte Herstellung

Objectives and Introduction Parkinson’s disease is caused by degeneration of nigro-striatal dopaminergic neurons and denervation of the target neurons in the neostriatum. The resulting disruption of dopaminergic modulation produces an imbalance between antagonistic pathways in the basal ganglia leading to rigidity, tremor, and bradykinesia [1]. One of several treatment options is the so called deep-brain-stimulation (DBS), whereby an electrode is implanted to re-equilibrate the nervous pathways and rescue the pathological imbalance. Though highly effective, DBS is linked to a very complex surgical procedure and can lead to adverse neurological effects [2,3]. The goal of this project is to enable a selective stimulation of striatal dopaminoceptive neurons from outside the brain through polymeric photovoltaic nanoparticles which are transported to the neostriatum using an engineered M13 bacteriophage as nanocarrier. These phages were chosen as a biovector since their filamentous envelop, formed by the major coat protein P8, offers a large surface area which can be modified easily. To monitor its biodistribution in the organism, the engineered bacteriophage is being with [64Cu]CuCl2 enabling PET imaging. Methods: Methods for analysis of the phages by TLC, HPLC and MALDI-TOF MS have been developed. To allow labeling with 64Cu, the bacteriophages were functionalized with 1,4,7‑triazacyclononane,1‑glutaric acid‑4,7-acetic acid (NODA-GA) and the conjugation reaction was analyzed by MALDI-TOF MS. The M13-NODA-GA conjugates were purified using HPLC-SEC. After labeling of the M13-NODA-GA conjugates with inhouse produced [64Cu]CuCl2 and purification by spin filtration, the radiolabeling efficiency was analyzed by radio-TLC and radio-HPLC-SEC. PET imaging was carried out in mice and scans were taken every 15 min up to 1 h after intravenous injection. The mice were sacrificed 70 min post-injection and the radioactivity accumulated in different organs was measured. Results: Conju

Noninvasive molecular imaging of the PD-1/PD-L1 immune checkpoint is of high clinical relevance for patient stratification and therapy monitoring in cancer patients. Here we report nine small-molecule PD-L1 radiotracers with solubilizing sulfonic acids and a linker–chelator system, designed by molecular docking experiments and synthesized according to a new, convergent synthetic strategy. Binding affinities were determined both in cellular saturation and real-time binding assay (LigandTracer), revealing dissociation constants in the single digit nanomolar range. Incubation in human serum and liver microsomes proved in vitro stability of these compounds. Small animal PET/CT imaging, in mice bearing PD-L1 overexpressing and PD-L1 negative tumors, showed moderate to low uptake. All compounds were cleared primarily through the hepatobiliary excretion route and showed a long circulation time. The latter was attributed to strong blood albumin binding effects, discovered during our binding experiments. Taken together, these compounds are a promising starting point for further development of a new class of PD-L1 targeting radiotracers.

Wissenschaftler*innen aus der Ressourcenökologie und Radiopharmazeutischen Krebsforschung geben dir Einblicke in ihre aktuellen Forschungsarbeiten und berichten, welchen Einfluss Mikroorganismen bei der sicheren Lage¬rung von hoch-radioaktiven Brennelementen haben und wie wir Bakterien zur Herstellung von zielgerichteten radioaktiven Arzneimitteln nutzen können, um damit Krebszellen aufzuspüren und zu zerstören.

Bei diesem Datensatz handelt es sich um analytische Charakterisierungen (ESI-MS, HR-MS, MALDI-TOF-MS) und Radiomarkierungsuntersuchungen zum nonadentaten Bispidin-Chelator bzw. Bispidin-TATE Konjugat mit Lutetium-177, Indium-111 und/oder Actinium-225. 1H, 13 C NMR and crystallographic data stored by collaboration partner (Heidelberg University)

Bei diesem Datensatz handelt es sich um die chemische Charakterisierung der Verbindungen, die in-vitro-, in-vivo- und ex-vivo-Daten.

The prostate-specific membrane antigen (PSMA) is expressed in approx. 80% of prostate cancer at considerably higher levels in tumor cells compared to healthy tissues. Its upregulation occurs in all stages of the disease. Therefore, PSMA has emerged as an attractive target for molecular imaging and especially targeted radionuclide therapy (endoradiotherapy) of metastatic castration-resistant prostate cancer (mCRPC). Due to its favorable nuclear physical properties, actinium-225 belongs to the clinically applied alpha emitters for therapeutic applications. More than ten clinical trials are displayed for actinium-225-DOTA-based conjugates. A trial using [225Ac]Ac-PSMA-617 as the IMP in men with PSMA-positive prostate cancer is projected to start. Actinium-225 can be chelated with the standard DOTA chelator, but requires rather harsh labeling conditions such as high temperatures (80–95°C) or microwave assistance. Alternatively, with the complexing agent macropa mild labeling conditions, low reaction temperature and high in vivo stability can be realized owing to its perfect characteristics for Ac3+ chelation. Moreover, to further improve the tumor uptake for future targeted alpha therapy, albumin binding units based on 4-iodophenylbutyrate were introduced to increase the tumor uptake. Two 225Ac-radioconjugates with albumin binders were prepared, either containing one or two PSMA-binding units (based on PSMA-617), the second one to raise the binding affinity to the PSMA receptor. The synthetic approach consisted of the functionalization of one or two picolinic side arms with a clickable reactive site for the connection of the vector molecules. The azide-functionalized PSMA derivative, which also contains the albumin binder, was prepared using standard peptide coupling conditions. Cell culture-based studies regarding radioligand affinity and clonogenicity were performed using PSMA-positive LNCaP cells and the biodistribution of the radioconjugates wa

Objectives The prostate-specific membrane antigen (PSMA) is expressed in most cases of prostate cancer at considerably higher levels in tumor cells compared to healthy tissues [1-3] and its upregulation occurs in all stage of the disease [4, 5]. Therefore, PSMA has emerged as an attractive target for molecular imaging and especially targeted radionuclide therapy (endoradiotherapy) of metastatic castration-resistant prostate cancer (mCRPC), given the example of [177Lu]Lu-PSMA-617. We recently described the synthesis and in-depth characterization of PSMA radioligands for targeted alpha therapy with actinium-225 [6]. Our present study aimed at the design, synthesis and preclinical evaluation of albumin-binding PSMA ligands in order to optimize their tissue distribution profile and to improve their pharmacokinetic properties. Methods Two novel compounds were prepared by combining a macropa chelator with one or two lysine-ureido-glutamate–based PSMA-binding entities equipped with 4-(p-iodophenyl)butyrate residues. The albumin-binding properties of the 225Ac-labeled conjugates were investigated in vitro using mouse, rat and human serum. The specific interaction of both compounds with human serum albumin was confirmed by microscale thermophoresis. Cell culture-based studies regarding radioligand affinity and clonogenicity were performed on PSMA-positive LNCaP cells. The biodistribution of the radioconjugates was analyzed in LNCaP tumor-bearing mice with ensuing investigation of tissue toxicity by histological examinations. Results Radiolabeling of both PSMA ligands with 225Ac was achieved at up to 5 MBq/nmol with >99% radiochemical purity. In vitro assays confirmed considerable binding of the radioligands to mouse, rat and human serum proteins. Cell binding and survival studies revealed a higher cell binding affinity and an improved cell killing efficiency for the radioconjugate with two PSMA-binding entities compared to the derivative with only one targeting motif. Biodis

Bispidines (3,7-diazabicyclo[3.3.1]nonane) and their derivatives act as bifunctional chelators (BFC), combining the advantages of multidentate macrocyclic and acyclic ligands (e.g., high kinetic inertness, rapid radiolabelling under mild conditions) [1]. This bicyclic chelator system shows a great diversity in terms of its denticity and type of functional groups, yielding a wide range of multidentate ligands that can bind a variety of different metal ions [1-3]. In addition, they allow a facile functionalisation of targeting molecules such as peptides, peptidomimetics, and bispecific antibodies which can also be used as target modules for adapter CAR T-cell cross-linkage [1, 4]. Herein, we present a nonadentate bispidine ligand labelled with [177Lu]Lu3+ and [225Ac]Ac3+ at mild conditions. The radiometal complexes have been obtained with high radiochemical yields (99%) and are stable in human serum [3]. This is unique so far, as many chelators are not able to bind both LuIII and AcIII under mild conditions (physiological pH, T<40°C) with fast complexation kinetics and high molar activities (>100 MBq/nmol for [177Lu]Lu3+ and ~0.2 MBq/nmol for [225Ac]Ac3+). For targeting, the chelator was functionalised with a peptidic somatostatin analogue (Tyr3 -octreotate), which addresses the somatostatin subtype receptor 2 in neuroendocrine tumours. Both 177Lu(III)- and 225Ac(III)-labelled conjugates were investigated towards their binding affinity and internalization in a murine pheochromocytoma (MPC) and human pancreatic carcinoid (BON1) tumour cell line and were compared with [177Lu]Lu(III)- and [ 225Ac]Ac(III)-DOTA-TATE. The presented 177Lu(III)- and 225Ac(III)-labelled bispidine-conjugates show favourable labelling kinetics and high radiostabilities in human serum. The radioconjugates exhibited dissociation constants in the lower nanomolar range (<10 nM) and high internalisation rates (>95 %) in both cell lines. In comparison to the corresponding DOTA-radioconjugates, milder

We report a nonadentate bispidine (3,7-diazabicyclo[3.3.1]nonane) that unveils the potential to bind theranostically relevant radionuclides, including indium-111, lutetium-177 and actinium-225 at mild labeling conditions. This radiopharmaceutical candidate allows the simultaneous application of imaging and treatment (radionuclide theranostics) without changing the type of bioconjugate, i.e. it allows the strong binding to an imaging and a therapeutic radionuclide by the same chelator. Since sophisticated coordination chemistry is required to achieve high thermodynamic and kinetic stability, it is not surprising that only a few chelators have been reported that are able to strongly bind several radionuclides to a satisfactory extent. Bispidine-derived ligands have proven to be ideal for di- and trivalent metal ions with generally fast complexation kinetics and high in vitro and in vivo stabilities. The presented (radio)complexes are formed under mild conditions (pH 6, <40°C) and exhibit thermodynamic stability and inertness in human serum comparable to the corresponding DOTA complexes. The bispidine-based complexing agent was conjugated to a peptide, targeting somatostatin type 2 receptors (SSTR2), overexpressed on neuroendocrine tumors. The 177Lu- and 225Ac-labeled conjugates were investigated, considering their binding to two different SSTR2 positive cell lines, including the human pancreatic carcinoid tumor (BON-SSTR2+) and the murine pheochromocytoma cell line (MPC). The biodistribution and accumulation pattern in MPC tumor-bearing mice was also evaluated. The LuIII and AcIII complexes studied show how ligand structures can be optimized in general by extending the denticity and varying the donor set in order to allow for fast complex formation and medically relevant inertness.

Bispidines (3,7-diazabicyclo[3.3.1]nonane) and their derivatives act as bifunctional chelating agents (BFCAs). Combining the advantages of highly preorganised rigid macrocyclic ligands and the flexibility of open-chain ligands, bispidines are able to form highly stable complexes at mild reaction conditions with a broad range of di- and trivalent metal ions. Of particular interest, they allow the coupling to biological targeting vectors such as peptides, peptidomimetics, T cell receptor derivatives as well as any kind of natural and recombinant antibody derivatives to construct effective radiopharmaceuticals for diagnostic and therapeutic purposes. Here, we present a nonadentate bispidine ligand (Figure 1), which forms stable and inert complexes with [177Lu]LuCl3, [225Ac]AcCl3 and [111In]InCl3 at mild conditions. This is unique so far, as few chelators are able to tightly bind both Lu(III) and Ac(III) under mild conditions (physiological pH, T<40°C) with fast complexation kinetics. We investigated the thermodynamic and kinetic properties of the radio-complexes. For targeting, the chelator was functionalised with a peptidic somatostatin analogue (Tyr3-octreotate, TATE), which addresses the somatostatin subtype receptor 2 in neuroendocrine tumors. The bispidine-TATE conjugate was labelled with 177Lu(III) and 225Ac(III) and investigated in SSTR2-positive mouse pheochromocytoma (MPC) and human pancreatic carcinoid tumour (BON-SSTR2) cell lines. Moreover, quantitative small animal SPECT imaging showed specific uptake of the [177Lu]Lu-conjugate in vivo in naturally SSTR2-positve MPC tumour allografts. Some structural optimisation will be required to further reduce off-target accumulation. However, the bispidine chelator shows a promising potential for a broad application in nuclear medicine, both in imaging and radionuclide therapy.

Currently, targeted alpha therapy is one of the most investigated topics in radiopharmaceutical cancer management. Especially, the alpha emitter 225 Ac provides excellent nuclear properties and is gaining increasing popularity for the treatment of various tumor entities. We herein report on the synthesis of two universal 225Ac-chelators for mild condition radiolabeling and binding sites to conjugate biomolecules via the copper-mediated click chemistry. A convenient radiolabeling procedure was investigated as well as the complex stability proved for both chelators and two PSMA-targeting model radioconjugates. Studies regarding affinity and cell survival were per-formed on LNCaP cells followed by biodistribution studies, which were performed using LNCaP tumor-bearing mice. High efficiency radiolabeling for all conjugates was demonstrated. Cell binding studies revealed a fourfold lower cell affinity for the PSMA conjugate with one targeting vector compared to the conjugate owing two targeting vectors. Additionally, these differences were verified by in vitro cell survival evaluation and biodistribution studies, both showing a higher therapeutic efficiency for the same dose on a cellular leve, a higher tumor up-take (15%ID/g) and a rapid whole body clearance after 24 hours. The synthesized chelators will overcome obstacles of lacking stability and worse labeling needs regarding 225Ac complexation using the DOTA chelator. Moreover, the universal functionalization expands the coverage of these chelators in combination with any sensitive bio(macro)molecule, thus improving treat-ment of any addressable tumor target.

We show the synthesis of an in vivo stable mercury compound with functionality suitable for radiopharmaceuticals. The designed cyclic bisarylmercury was based on the water tolerance of organomercurials, higher bond dissociation energy of Hg-Ph to Hg-S, and the experimental evidence that acyclic structures suffer significant cleavage of one of the Hg-R bonds. The bispidine motif was chosen for its in vivo stability, chemical accessibility, and functionalization properties. Radionuclide production results in 197(m)HgCl2(aq), so the desired mercury compound was formed via a water-tolerant organotin transmetallation. The Hg-bispidine compound showed high chemical stability in tests with an excess of sulphur-containing competitors and high in vivo stability, without any observable protein interaction by human serum assay, and good organ clearance demonstrated by biodistribution and SPECT studies in rats. In particular no retention in the kidneys typical of unstable mercury compounds. The natHg analogue allowed full characterization by NMR and HRMS.

There is currently a surge for the development of novel photosensitizers (PSs) for photodynamic therapy (PDT) since those currently approved are not completely ideal. Among the tested compounds, we have previously investigated the use of Ru(II) polypyridyl complexes with a [Ru(bipy)2(dppz)]2+ and [Ru(phen)2(dppz)]2+ scaffold (bipy = 2,2'-bipyridine; dppz = dipyrido[3,2-a:2′,3′-c]-phenazine, phen = 1,10-phenanthroline). These complexes selectively target DNA. However, since DNA is ubiquitous, it would be of great interest to increase the selectivity of our PDT PSs by linking them to a targeting vector in view of targeted PDT. Herein, we present the synthesis, characterization and in-depth photophysical evaluation of a nanobody containing Ru(II) polypyridyl conjugate selective for the epidermal growth factor receptor (EGFR) in view of targeted PDT. Using ICP-MS and confocal microscopy, we could demonstrate that our conjugate had a high selectivity for the EGFR receptor, which is a crucial oncological target as it is overexpressed and/or deregulated in a variety of solid tumors. However, contrary to expectations, this conjugate was found to not produce reactive oxygen species (ROS) in cancer cells and to be therefore not phototoxic.

Bifunctional chelators as parts of modular metal-based radiopharmaceuticals are responsible for stable complexation of the radiometal ion and for covalent linkage between the complex and the targeting vector. To avoid loss of complex stability, the bioconjugation strategy should not interfere with the radiometal chelation by occupying coordinating groups. The C9 position of the very stable CuII chelator 3,7-diazabicyclo[3.3.1]nonane (bispidine) is virtually predestined to introduce functional groups for facile bioconjugation as this functionalisation does not disturb the metal binding centre. We describe the preparation and characterisation of a set of novel bispidine derivatives equipped with suitable functional groups for diverse bioconjugation reactions, including common amine coupling strategies (bispidine-isothiocyanate) and the Cu-free strain promoted alkyne-azide cycloaddition. We demonstrate their functionality and versatility in an exemplary way by conjugation to an antibody-based biomolecule and validate the obtained conjugate in vitro and in vivo.

Introduction A wealth of preclinical experiments has clearly demonstrated that site-specific protein modification results in a more homogenous product population with defined and tunable properties compared to traditional bioconjugation techniques (1, 2). This is of particular importance for antibodies and their fragments as random conjugation strategies can compromise their functionality and interfere with or abolish their immunoreactivity (3). That specifically applies to small-sized antibody formats such as single chain variable fragments and single-domain antibody-fragments due to their compact structure and limited number of available functional reactive residues outside the antigen-binding site (4-6). Here, we describe a versatile two-step approach for site-specific introduction of bifunctional radiometal-chelating agents into antibody-derived fragments for the generation of highly defined radioimmunotracers. Methods The first step of this approach uses enzyme-mediated bioconjugation for regioselective incorporation of an azide-containing linker into an antibody fragment. The second step of this modular approach involves the modification of the azide-tagged antibody fragment with dibenzocyclooctyne (DBCO)-containing fluorescent dyes or DBCO-modified bispidine via Cu-free strain-promoted alkyne-azide cycloaddition. Results In an exemplary way, we demonstrate the versatility of this two-step approach by the site-specific incorporation of fluorescent dyes or radiometal chelators for fluorescence or positron emission tomographic imaging at physiological conditions. In vitro binding studies on different human cancer cell lines using dye- or 64Cu-labeled antibody fragments showed high specificity, co-localization and a receptor-mediated cellular uptake of the EGFR-specific probes. Noteworthy, we did not observe any detrimental effect to the functionality of the antibody fragments. Discussion and Conclusion The site-specific insertion of a bioorthogonal handle into t

We demonstrate a novel strategy for preparing hydrophilic upconverting nanoparticles (UCNPs) by harnessing the photocrosslinking ability of diacetylenes. Replacement of the hydrophobic oleate coating on the UCNPs with 10,12-pentacosadiynoic acid, followed by overcoating with diacetylene phospholipid and subsequent photocrosslinking under 254 nm irradiation produces water-dispersible polydiacetylene-coated UCNPs. These UCNPs resist the formation of a biomolecular corona and show great colloidal stability. Furthermore, amine groups on the diacetylene phospholipid allow for functionalisation of the UCNPs with, for example, radiolabels or targeting moieties. These results demonstrate that this new surface coating method has great potential for use in the preparation of UCNPs with improved biocompatibility.

The interaction of nanoparticles (NPs) with biomolecules depends on their surface characteristics and has a major influence on their ultimate metabolic fate. Attempts to modulate the NP-biomolecule interaction in complex biological conditions has led to intensive research on the role of NP size, shape, charge, surface structure and the capping molecules in their eventual pharmacokinetic response. Research shows that to avoid accumulation in the organs of the mononuclear phagocyte system (MPS), engineered NPs must resist nonspecific adsorption of proteins (biomolecular corona) onto their surface. To date the most common approach to make NPs corona-resistant includes formation of a hydrophilic, neutral-charged polyethylene glycol coating (PEGylation) on their surface. This route, widely used by many groups, furnishes hydrophilic NPs, but suffers from some serious drawbacks, such as, a substantial increase in the hydrodynamic diameter (Dh) after PEGylation, and the formation of anti-PEG antibodies in vivo. Herein, we present our efforts towards tackling the problem of biomolecular corona formation. To this end, we have explored the use of amphiphilic zwitterionic polymers and low molecular weight entities as capping ligands on the surface of ultrasmall iron oxide nanoparticles (USPIONs) and lanthanide-doped upconverting nanoparticles (UCNPs). Following such surface modification, the hydrophobic NPs were rendered water-dispersible and showed reduced adsorption of serum proteins, but without any significant increase in particle size. Additionally, the availability of reactive functional groups on the surface of the modified NPs makes them ready for further functionalization with, for example, small molecules, peptides, proteins, and antibodies. The presented results highlight the usefulness of our surface functionalization strategy to produce biocompatible materials suitable for multimodal diagnostic/therapeutic applications.

Nanoparticle (NP) size, shape, charge, surface structure and the capping moieties have a significant influence on their eventual pharmacokinetic behaviour. For NPs to avoid accumulation in the organs of the mononuclear phagocyte system (MPS), it is important that they resist nonspecific adsorption of proteins (biomolecular corona) onto their surface. Reported methods to make corona-resistant hydrophilic NPs mostly suffer from serious drawbacks in regards to the in vivo applications of the engineered NMs. The major ones being (1) substantial increase in the hydrodynamic diameter (Dh) of the modified NMs, and (2) the formation of anti-PEG antibodies in vivo. Herein, we will present our efforts towards tackling the problem of biomolecular corona formation in ultrasmall iron oxide nanoparticles (USPIONs) and lanthanide-doped upconverting nanoparticles (UCNPs) by using amphiphilic zwitterionic polymers and low molecular weight entities as capping ligands on the NP surface. Our studies show that such surface functionalization strategy can produce biocompatible NPs that exhibit negligible interaction with biomolecules, and are suitable for developing multimodal imaging/therapeutic agents.