In vitro and ex vivo evaluation of preclinical models for FAP-targeted theranostics: differences and relevance for radiotracer evaluation.

Background: Fibroblast activation protein (FAP) is an attractive target for cancer theranostics. Although FAP-targeted nuclear imaging demonstrated promising clinical results, only sub-optimal results are reported for targeted radionuclide therapy (TRT). Preclinical research is crucial in selecting promising FAP-targeted radiopharmaceuticals and for obtaining an increased understanding of factors essential for FAP-TRT improvement.

A Trifunctional Theranostic Ligand Targeting Fibroblast Activation Protein-α (FAPα).

Purpose: Fibroblast activation protein-α (FAPα) is uniquely expressed in activated fibroblasts, including cancer-associated fibroblasts that populate tumor stroma and contribute to proliferation and immunosuppression. Radiolabeled FAPα inhibitors enable imaging of multiple human cancers, but time-dependent clearance from tumors currently limits their utility as FAPα-targeted radiotherapeutics. We sought to increase the area under the curve (AUC) by constructing a trifunctional ligand that binds FAPα with high affinity and also binds albumin and theranostic radiometals.

Preclinical Evaluation of a High-Affinity Sarcophagine-Containing PSMA Ligand for Cu/Cu-Based Theranostics in Prostate Cancer.

The application of small molecules targeting prostate-specific membrane antigen (PSMA) has emerged as a highly promising clinical strategy for visualization and treatment of prostate cancer. Ligands that integrate the ability to both quantify the distribution of radioactivity and treat disease through the use of a matched pair of radionuclides have particular value in clinical and regulatory settings. In this study, we describe the development and preclinical evaluation of RPS-085, a ligand that binds PSMA and serum albumin and exploits the Cu radionuclide pair for prostate cancer theranostics.

A general C-labeling approach enabled by fluoride-mediated desilylation of organosilanes.

Carbon-11 (C) is one of the most ideal positron emitters for labeling bioactive molecules for molecular imaging studies. The lack of convenient and fast incorporation methods to introduce C into organic molecules often hampers the use of this radioisotope. Here, a fluoride-mediated desilylation (FMDS) C-labeling approach is reported.

Improved synthesis of the bifunctional chelator p-SCN-Bn-HOPO.

The bifunctional ligand p-SCN-Bn-HOPO, which has four 1,2-hydroxypyridinone groups on a spermine backbone with an isothiocyanate linker, has been shown to be an efficient and stable chelator for Zr(iv) and, more importantly, the radioisotope 89Zr for use in radiolabeling antibodies for positron emission tomography (PET) imaging. Previous studies of 89Zr-HOPO-trastuzumab in mice showed low background, good tumor to organ contrast, and very low bone uptake which show p-SCN-Bn-HOPO to be an important next-generation bifunctional chelator for radioimmunoPET imaging with 89Zr. However, the reported synthesis of p-SCN-Bn-HOPO involves nine steps and multiple HPLC purifications with an overall yield of about 1.

[F]Fluoroethyltriazolyl Monocyclam Derivatives as Imaging Probes for the Chemokine Receptor CXCR4.

Determining chemokine receptor CXCR4 expression is significant in multiple diseases due to its role in promoting inflammation, cell migration and tumorigenesis. [Ga]Pentixafor is a promising ligand for imaging CXCR4 expression in multiple tumor types, but its utility is limited by the physical properties of Ga. We screened a library of >200 fluorine-containing structural derivatives of AMD-3465 to identify promising candidates for in vivo imaging of CXCR4 expression by positron emission tomography (PET).

Albumin-Binding PSMA Ligands: Implications for Expanding the Therapeutic Window.

Despite significant gains in the treatment of metastatic castration-resistant prostate cancer by radioligands targeting prostate-specific membrane antigen (PSMA), 30% of patients never respond to therapy. One possible explanation is insufficient dose delivery to the tumor because of suboptimal pharmacokinetics. We have recently described RPS-063, a trifunctional ligand targeting PSMA with high uptake in LNCaP xenograft tumors but also in kidneys.

A Single Dose of Ac-RPS-074 Induces a Complete Tumor Response in an LNCaP Xenograft Model.

Promising biochemical responses to Ac-prostate-specific membrane antigen (PSMA) 617, even in patients who are refractory to β-particle radiation, illustrate the potential of targeted α-therapy for the treatment of metastatic castration-resistant prostate cancer. However, side effects such as xerostomia are severe and irreversible. To fully harness the potential of targeted α-therapy, it is necessary to increase the therapeutic index of the targeted radioligands.

Ga: A Novelty or a Valuable Preclinical Screening Tool for the Design of Targeted Radiopharmaceuticals?

Emerging interest in extending the plasma half-life of small molecule radioligands warrants a consideration of the appropriate radionuclide for PET imaging at longer time points (>8 h). Among candidate positron-emitting radionuclides, Ga (t = 9.5 h, β+ = 57%) has suitable nuclear and chemical properties for the labeling and PET imaging of radioligands of this profile.

Trifunctional PSMA-targeting constructs for prostate cancer with unprecedented localization to LNCaP tumors.

Purpose: Treatment of late-stage prostate cancer by targeted radiotherapeutics such as I-MIP-1095 and Lu-PSMA-617 has shown encouraging early results. Lu-177 is preferred to I-131 in clinical settings, but targeted radioligand therapy (RLT) with Lu-PSMA-617 has not reached its full potential due to insufficient dose delivery to the tumor. We recently developed a dual-targeting radioiodinated ligand, RPS-027, that targets PSMA and uses albumin binding to enable good tumor uptake and significantly reduced kidney uptake in a preclinical model.

[F]RPS-544: A PET tracer for imaging the chemokine receptor CXCR4.

Introduction: CXCR4 specific [F]-labeled positron emission tomography (PET) imaging agents are needed which would enable general distribution of the radiotracer for clinical investigation. We sought to synthesize, radiolabel and evaluate [F]RPS-544, a novel non-peptide CXCR4 antagonist as a CXCR4 specific probe. We compared [F]RPS-544 with the previously published [F]-3 ([F]RPS-510 in this paper) in a bi-lateral tumor model of differential CXCR4 expression for its ability to selectively target CXCR4 expression.

An Eighteen-Membered Macrocyclic Ligand for Actinium-225 Targeted Alpha Therapy.

The 18-membered macrocycle H macropa was investigated for Ac chelation in targeted alpha therapy (TAT). Radiolabeling studies showed that macropa, at submicromolar concentration, complexed all Ac (26 kBq) in 5 min at RT. [ Ac(macropa)] remained intact over 7 to 8 days when challenged with either excess La ions or human serum, and did not accumulate in any organ after 5 h in healthy mice.

Synthesis and pre-clinical evaluation of a new class of high-affinity F-labeled PSMA ligands for detection of prostate cancer by PET imaging.

Purpose: Current clinical imaging of PSMA-positive prostate cancer by positron emission tomography (PET) mainly features Ga-labeled tracers, notably [Ga]Ga-PSMA-HBED-CC. The longer half-life of fluorine-18 offers significant advantages over Ga-68, clinically and logistically. We aimed to develop high-affinity PSMA inhibitors labeled with fluorine-18 as alternative tracers for prostate cancer.

p-SCN-Bn-HOPO: A Superior Bifunctional Chelator for (89)Zr ImmunoPET.

Zirconium-89 has an ideal half-life for use in antibody-based PET imaging; however, when used with the chelator DFO, there is an accumulation of radioactivity in the bone, suggesting that the (89)Zr(4+) cation is being released in vivo. Therefore, a more robust chelator for (89)Zr could reduce the in vivo release and the dose to nontarget tissues. Evaluation of the ligand 3,4,3-(LI-1,2-HOPO) demonstrated efficient binding of (89)Zr(4+) and high stability; therefore, we developed a bifunctional derivative, p-SCN-Bn-HOPO, for conjugation to an antibody.

Synthesis and evaluation of aporphine analogs containing C1 allyl isosteres at the h5-HT(2A) receptor.

A series of C1 aporphine analogs related to compound 5 and that contain substituted allylic, alkynyl, nitrile, ester and benzyl groups was synthesized and evaluated for affinity at h5HT2A and α1A receptors in functional activity assays that measure calcium release. The presence of branched allylic substituent groups diminished affinity for the h5HT2A receptor. Likewise, the alkynyl, nitrile and ester derivatives evaluated displayed lower 5-HT2A receptor affinity as compared to 5.

A divergent route to 9, 10-oxygenated tetrahydroprotoberberine and 8-oxoprotoberberine alkaloids: synthesis of (±)-isocorypalmine and oxypalmatine.

A new route which is germane to the synthesis of 9,10-oxygenated tetrahydroprotoberberines and 8-oxoprotoberberines is described. The route features the use of a diester () generated from reaction of dimethylmalonate with an aryl halide in the presence of -butyllithium. The amide prepared in subsequent steps is a versatile precursor for the synthesis of tetrahydroprotoberberine and 8-oxoprotoberberine scaffolds using standard high-yielding reactions.

Alternative chelator for ⁸⁹Zr radiopharmaceuticals: radiolabeling and evaluation of 3,4,3-(LI-1,2-HOPO).

Zirconium-89 is an effective radionuclide for antibody-based positron emission tomography (PET) imaging because its physical half-life (78.41 h) matches the biological half-life of IgG antibodies. Desferrioxamine (DFO) is currently the preferred chelator for (89)Zr(4+); however, accumulation of (89)Zr in the bones of mice suggests that (89)Zr(4+) is released from DFO in vivo.

Aporphinoid antagonists of 5-HT2A receptors: further evaluation of ring A substituents and the size of ring C.

A series of ring A-modified analogs of nantenine as well as structural variants in ring C were synthesized and evaluated for antagonist activity at 5-HT2A and α1A receptors. Halogenation improves 5-HT2A antagonist potency in molecules containing a C1 methoxyl/C2 methoxyl or C1 methoxyl/C2 hydroxyl moiety. Bromination or iodination (but not chlorination) with the latter moiety also significantly increased α1A antagonist potency.

Evaluation of structural effects on 5-HT(2A) receptor antagonism by aporphines: identification of a new aporphine with 5-HT(2A) antagonist activity.

A set of aporphine analogs related to nantenine was evaluated for antagonist activity at 5-HT2A and α1A adrenergic receptors. With regards to 5-HT2A receptor antagonism, a C2 allyl group is detrimental to activity. The chiral center of nantenine is not important for 5-HT2A antagonist activity, however the N6 nitrogen atom is a critical feature for 5-HT2A antagonism.

A New Route to Azafluoranthene Natural Products via Direct Arylation.

Microwave-assisted direct arylation was successfully employed in the synthesis of azafluoranthene alkaloids for the first time. Direct arylation reactions on a diverse set of phenyltetrahydroisoquinolines produces the indeno[1,2,3-]isoquinoline nucleus to a high yielding azafluoranthene synthesis. The method was used as a key step in the efficient preparation of the natural products rufescine and triclisine.

New aporphinoid 5-HT2A and α1A antagonists via structural manipulations of nantenine.

A series of C1, C2, C3 and N6 analogs of nantenine (2) was synthesized and evaluated in 5-HT(2A) and α(1A) receptor functional assays. Alkyl substitution of the C1 and N6 methyl groups of nantenine provided selective 5-HT(2A) and α(1A) antagonists, respectively. The C2 alkyloxy analogs studied were generally selective for α(1A) versus 5-HT(2A).

Cytotoxicity of aporphines in human colon cancer cell lines HCT-116 and Caco-2: an SAR study.

A series of synthetic aporphine derivatives structurally related to domesticine and nantenine (ring A, N6 and ring C truncated analogs), was evaluated in MTS cytotoxicity assays against the human colon cancer cell lines, HCT-116 and Caco-2. In general, the C1 position of ring A is tolerant of alkoxy substituents as well as a benzoyl ester functionality. Other modifications evaluated resulted in a decrease in cytotoxic activity.

Synthesis and antihyperglycemic activity profiles of novel thiazolidinedione derivatives.

A number of thiazolidine-2,4-diones derivatives having carboxylic ester appendage at N-3 were synthesized and their antihyperglycemic activity was evaluated. Many of these derivatives as well as their corresponding carboxylic acid showed significant improvement on post-prandial hyperglycemia in normal rats, in contrast to their poor agonist activity at PPARgamma.