Multiple Applications of a Novel Biarsenical Imaging Probe in Fluorescence and PET Imaging of Melanoma.

A new fluorescent biarsenical peptide labeling probe was synthesized and labeled with the radioactive isotopes 11C and 18F. The utility of this probe was demonstrated by installing each of these isotopes into a melanocortin 1 receptor (MC1R) binding peptide, which targets melanoma tumors. Its applicability was further showcased by subsequent in vitro imaging in cells as well as in vivo imaging in melanoma xenograft mice by fluorescence and positron emission tomography.

Discovery of AZD4747, a Potent and Selective Inhibitor of Mutant GTPase KRASG12C with Demonstrable CNS Penetration.

The glycine to cysteine mutation at codon 12 of Kirsten rat sarcoma (KRAS) represents an Achilles heel that has now rendered this important GTPase druggable. Herein, we report our structure-based drug design approach that led to the identification of 14, AZD4747, a clinical development candidate for the treatment of KRASG12C-positive tumors, including the treatment of central nervous system (CNS) metastases. Building on our earlier discovery of C5-tethered quinazoline AZD4625, excision of a usually critical pyrimidine ring yielded a weak but brain-penetrant start point which was optimized for potency and DMPK. Key design principles and measured parameters that give high confidence in CNS exposure are discussed. During optimization, divergence between rodent and non-rodent species was observed in CNS exposure, with primate PET studies ultimately giving high confidence in the expected translation to patients. AZD4747 is a highly potent and selective inhibitor of KRASG12C with an anticipated low clearance and high oral bioavailability profile in humans.

Isotopic Radiolabeling of Crizotinib with Fluorine-18 for In Vivo Pet Imaging.

Crizotinib is a tyrosine kinase inhibitor approved for the treatment of non-small-cell lung cancer, but it is inefficient on brain metastases. Crizotinib is a substrate of the P-glycoprotein, and non-invasive nuclear imaging can be used to assess the brain penetration of crizotinib. Positron emission tomography (PET) imaging using fluorine-18-labeled crizotinib would be a powerful tool for investigating new strategies to enhance the brain distribution of crizotinib. We have synthesized a spirocyclic hypervalent iodine precursor for the isotopic labeling of crizotinib in a 2.4% yield. Because crizotinib is an enantiomerically pure drug, a chiral separation was performed to afford the (R)-precursor. A two-step radiolabeling process was optimized and automated using the racemic precursor to afford [18F](R,S)-crizotinib in 15 ± 2 radiochemical yield and 103 ± 18 GBq/µmol molar activity. The same radiolabeling process was applied to the (R)-precursor to afford [18F](R)-crizotinib with comparable results. As a proof-of-concept, PET was realized in a single non-human primate to demonstrate the feasibility of [18F](R)-crizotinib in in vivo imaging. Whole-body PET highlighted the elimination routes of crizotinib with negligible penetration in the brain (SUVmean = 0.1). This proof-of-concept paves the way for further studies using [18F](R)-crizotinib to enhance its brain penetration depending on the P-glycoprotein function.

Preclinical Comparison of the Blood-brain barrier Permeability of Osimertinib with Other EGFR TKIs.

PURPOSE: Osimertinib is a potent and selective EGFR tyrosine kinase inhibitor (EGFR-TKI) of both sensitizing and T790M resistance mutations. To treat metastatic brain disease, blood-brain barrier (BBB) permeability is considered desirable for increasing clinical efficacy. EXPERIMENTAL DESIGN: We examined the level of brain penetration for 16 irreversible and reversible EGFR-TKIs using multiple in vitro and in vivo BBB preclinical models. RESULTS: In vitro osimertinib was the weakest substrate for human BBB efflux transporters (efflux ratio 3.2). In vivo rat free brain to free plasma ratios (Kpuu) show osimertinib has the most BBB penetrance (0.21), compared with the other TKIs (Kpuu ≤ 0.12). PET imaging in Cynomolgus macaques demonstrated osimertinib was the only TKI among those tested to achieve significant brain penetrance (C max %ID 1.5, brain/blood Kp 2.6). Desorption electrospray ionization mass spectroscopy images of brains from mouse PC9 macrometastases models showed osimertinib readily distributes across both healthy brain and tumor tissue. Comparison of osimertinib with the poorly BBB penetrant afatinib in a mouse PC9 model of subclinical brain metastases showed only osimertinib has a significant effect on rate of brain tumor growth. CONCLUSIONS: These preclinical studies indicate that osimertinib can achieve significant exposure in the brain compared with the other EGFR-TKIs tested and supports the ongoing clinical evaluation of osimertinib for the treatment of EGFR-mutant brain metastasis. This work also demonstrates the link between low in vitro transporter efflux ratios and increased brain penetrance in vivo supporting the use of in vitro transporter assays as an early screen in drug discovery.

Synthesis and Preclinical Evaluation of 6-[18F]Fluorine-α-methyl-l-tryptophan, a Novel PET Tracer for Measuring Tryptophan Uptake.

The positron emission tomography (PET) radioligand α-[11C]methyl-l-tryptophan ([11C]AMT) has been used to assess tryptophan metabolism in cancer, epilepsy, migraine, and autism. Despite its extensive application, the utility of this tracer is currently hampered by the short half-life of the radionuclide used for its labeling (11C, t1/2 = 20.4 min). We herein report the design, synthesis, radiolabeling, and initial in vivo evaluation of a fluorine-18 (18F, t1/2 = 109.7 min) labeled analogue that is fluorinated in the 6-position of the aromatic ring ([18F]6-F-AMTr). In a head-to-head comparison between [18F]6-F-AMTr and [11C]AMT in mice using PET, peak brain radioactivity, regional brain distribution, and kinetic profiles were similar between the two tracers. [18F]6-F-AMTr was however not a substrate for IDO1 or TPH as determined in in vitro enzymatic assays. The brain uptake of the tracer is thus more likely related to LAT1 transport over the blood-brain barrier than metabolism along the serotonin or kynurenine pathways.

Indole-derived arynes and their Diels-Alder reactivity with furans.

Arynes derived from any position of the ubiquitous indole nucleus are unknown. We have now provided the first evidence for the formation and trapping of the 4,5-, 5,6-, and 6,7-indolynes. A series of o-dihalo indoles (Cl, Br, F) were synthesized and reacted under metal-halogen exchange conditions to give Diels-Alder cycloadducts in high yield with furan. The use of an excess of tert-butyllithium resulted in the rearrangement of the initially formed cycloadduct; however, employing only a slight excess of n-butyllithium cleanly gave cycloadducts with furan.

Regioselectivity in C-H activation: reagent control in cyclometallation of 2-(1-naphthyl)-pyridine.

2-(1-Naphthyl)-pyridine () possesses sp(2) C-H bonds in both the γ- and δ-positions and is therefore a suitable substrate for studying the cyclometallation selectivity with different reagents and conditions. Such selectivity studies are reported. Based on deuterium-exchange experiments it is concluded that cycloruthenation with RuCl2(p-cymene) dimer is reversible with kinetic and thermodynamic preference for γ-substitution. Electrophilic cycloborylation, on the other hand, shows unusual δ-substitution. The previously published cyclopalladation and cycloauration of the substrate was studied in detail and was shown to be irreversible; they proceed under kinetic control and give γ- and δ-substitution for palladium and gold, respectively.

Metal controlled regioselectivity in the cyclometallation of 2-(1-naphthyl)-pyridine.

Cyclometallation of 2-(1-naphthyl)-pyridine is described. While cyclopalladation results in a five-membered metallacycle, cycloauration displays a completely orthogonal regioselectivity, resulting in the six-membered ring analogue. Bromination of the gold metallacycle results in the new C-H functionalisation product 2-(8-bromonaphth-1-yl)pyridine.

Crystal structure of (piperidine-1-carbo-di-thio-ato-κ(2) S,S)[2-(pyridin-2-yl)phenyl-κ(2) C (1),N]palladium(II).

The title compound, [Pd(C11H8N)(C6H10NS2)], crystallizes with three similar and discrete mol-ecules in the asymmetric unit. The CNS2 donor set defines a distorted square-planar geometry around the Pd(II) atom, with very small deviations from planarity. The bidentate nature of the ligands gives fairly large deviations from the ideal 90° angles; the C-Pd-N angles are all around 81° and the S-Pd-S angles are around 75°. Mol-ecules pack via dispersion inter-actions.