The development of addition reactions wherein the product is the simple sum of the reactants plus anything else (only needed catalytically) constitutes an important goal for enhanced synthetic efficiency. The C−H bond of terminal alkynes (the donor alkynes) can be added to either terminal alkynes (self-coupling) or activated internal alkynes (cross-coupling) (the acceptor alkynes) in the presence of a catalytic amount of palladium acetate and an electron rich sterically encumbered ligand, tris(2,6-dimethoxyphenyl)phosphine. The activated internal alkynes for cross-coupling (the acceptor alkyne) include alkynes bearing an ester, sulfone, and ketone. Self-coupling is completely overwhelmed by cross-coupling, even at 1:1 ratios of donor and acceptor alkynes. The reaction exhibits extraordinary chemoselectivity with free carboxaldehydes, alcohols, ketones (saturated and conjugated), esters (saturated and conjugated), sulfones (saturated and conjugated), malonates, and silyl ethers all proving to be compatible. A 1:2 donor/acceptor alkyne adduct can also be optimized. Ethyl propiolate fails as an acceptor but its C-silylated analogue serves with the proper choice of silyl substituent. The products of the latter serve as useful precursors to β-keto esters. An iterative sequence is readily performed and led to a novel conformationally rigid retinoid analogue. The mechanism of this mild method for construction of conjugated enynes, versatile building blocks, is discussed.

SignificanceTumor-associated microglia and macrophages (TAMs) constitute up to one half of the cells in glioblastoma multiforme (GBM) and are known to promote tumor growth. Therefore, modulation and reeducation of the TAM pool is a promising antitumor strategy against GBMs. We recently showed that disruption of the SIRPα-CD47 signaling axis is efficacious against various brain tumors including GBM primarily by inducing tumor phagocytosis. Here, we show that tumor-associated microglia are capable of in vivo tumor cell phagocytosis in response to anti-CD47 blockade. The activation of microglia was associated with distinct morphological and transcriptional changes. In fact, microglia show a dampened inflammatory response upon anti-CD47 therapy compared with macrophages, making them an attractive target for clinical applications especially in the confined regions of the brain.

Identifying protein-protein interactions (PPIs) is essential for understanding various disease mechanisms and developing new therapeutic approaches. Current methods for assaying cellular intermolecular interactions are mainly used for cells in culture and have limited use for the noninvasive assessment of small animal disease models. Here, we describe red light-emitting reporter systems based on bioluminescence resonance energy transfer (BRET) that allow for assaying PPIs both in cell culture and deep tissues of small animals. These BRET systems consist of the recently developed Renilla reniformis luciferase (RLuc) variants RLuc8 and RLuc8.6, used as BRET donors, combined with two red fluorescent proteins, TagRFP and TurboFP635, as BRET acceptors. In addition to the native coelenterazine luciferase substrate, we used the synthetic derivative coelenterazine-v, which further red-shifts the emission maxima of Renilla luciferases by 35 nm. We show the use of these BRET systems for ratiometric imaging of both cells in culture and deep-tissue small animal tumor models and validate their applicability for studying PPIs in mice in the context of rapamycininduced FK506 binding protein 12 (FKBP12)-FKBP12 rapamycin binding domain (FRB) association. These red light-emitting BRET systems have great potential for investigating PPIs in the context of drug screening and target validation applications.optical imaging | reporter gene P rotein-protein interactions (PPIs) are a prerequisite to most cellular processes, and their pharmacologic control offers promising avenues for therapeutic intervention in a variety of diseases (1). Developing techniques to identify and analyze these transient protein-protein associations is, therefore, of high importance. Several methods are available to investigate PPIs in vitro and in cell culture (2, 3). However, ex vivo analysis of interacting proteins neglects the intricate effects of physiologic and pathophysiologic stimuli that occur in the native microenvironment within living organisms. Similarly, in vitro drug validation ignores the pharmacokinetic properties of prospective pharmacophores. To investigate PPIs in their actual biological context, imaging technologies that enable direct translation of cell culture assays to deep tissues of living subjects are required. Current approaches for monitoring PPIs rely on the two-hybrid system (4), FRET (5), split reporter protein complementation and reconstitution (6-8), and bioluminescence resonance energy transfer (BRET) (9-11). Because most of these PPI detection schemes are optical approaches, signal attenuation by tissues constitutes the primary impediment for studying PPIs in animal models, and it results in low sensitivity for these assays, especially in the context of deep-tissue tumor models.Bioluminescence-based methods hold particular promise for imaging of PPIs in small living subjects (12, 13). Although both BRET and FRET detection schemes rely on the Förster resonance energy transfer mechanism (14), BRET systems provide enhanced sens...

A major barrier to successful use of allogeneic hematopoietic cell transplantation is acute graft-versus-host disease (aGVHD), a devastating condition that arises when donor T cells attack host tissues. With current technologies, aGVHD diagnosis is typically made after end-organ injury and often requires invasive tests and tissue biopsies. This impacts patient prognosis as treatments are dramatically less effective at late disease stages. Here we show that a novel positron emission tomography (PET) radiotracer, 2′-deoxy-2′-[18F]fluoro-9-β-D-arabinofuranosylguanine ([18F]F-AraG), targeted towards two salvage kinase pathways preferentially accumulates in activated primary T cells. [18F]F-AraG PET imaging of a murine aGVHD model enabled visualization of secondary lymphoid organs harboring activated donor T cells prior to clinical symptoms. Tracer biodistribution in healthy humans showed favorable kinetics. This new PET strategy has great potential for early aGVHD diagnosis, enabling timely treatments and improved patient outcomes. [18F]F-AraG may be useful for imaging activated T cells in various biomedical applications.

Sigma-1 receptor (S1R) radioligands have the potential to detect and monitor various neurological diseases. Herein we report the synthesis, radiofluorination and evaluation of a new S1R ligand 6-(3-fluoropropyl)-3-(2-(azepan-1-yl)ethyl)benzo[d]thiazol-2(3H)-one ([18F]FTC-146, [18F]13). [18F]13 was synthesized by nucleophilic fluorination, affording a product with >99% radiochemical purity (RCP) and specific activity (SA) of 2.6 ± 1.2 Ci/Amol (n = 13) at end of synthesis (EOS). Positron emission tomography (PET) and ex vivo autoradiography studies of [18F]13 in mice showed high uptake of the radioligand in S1R rich regions of the brain. Pre treatment with 1 mg/kg haloperidol (2), non radioactive 13, or BD1047 (18) reduced the binding of [18F]13 in the brain at 60 min by 80%, 82% and 81% respectively, suggesting that [18F]13 accumulation in mouse brain represents specific binding to S1Rs. These results indicate that [18F]13 is a promising candidate radiotracer for further evaluation as a tool for studying S1Rs in living subjects.