Bioorthogonal chemistry for (68) Ga radiolabelling of DOTA-containing compounds.

Copper-catalysed 'click' chemistry is a highly utilised technique for radiolabelling small molecules and peptides for imaging applications. The usefulness of these reactions falls short, however, when metal catalysis is not a practically viable route; such as when using metal chelates as radioligands. Here, we describe a method for carrying out 'click-type' radiochemistry in the presence of DOTA chelates, by combining (68) Ga radiolabelling techniques with well-established bioorthogonal reactions, which do not rely upon metal catalysis.

Bioorthogonal chemistry for pre-targeted molecular imaging--progress and prospects.

The aim of this perspective is to critically review the three most prominent bioorthogonal reactions that are used presently, on both a purely chemical level and in the context of biological systems. This includes the uses both for synthesis of therapeutic molecules, modification of large biomolecules or antibodies, and in particular, the exciting use in the field of 'pre-targeting', for both possible treatment and imaging technologies. We will compare the validity of each reaction when compared to others, and their usefulness in biological systems, as each methodology has clear advantages over the others in differing environments.

Synthesis and Evaluation of Camptothecin Antibody-Drug Conjugates.

Antibody-drug conjugates (ADCs) that incorporate the exatecan derivative DXd in their payload are showing promising clinical results in solid tumor indications. The payload has an F-ring that also contains a second chiral center, both of which complicate its synthesis and derivatization. Here we report on new camptothecin-ADCs that do not have an F-ring in their payloads yet behave similarly to DXd-bearing conjugates in vitro and in vivo. This simplification allows easier derivatization of camptothecin A and B rings for structure-activity relationship studies and payload optimization. ADCs having different degrees of bystander killing and the ability to release hydroxyl or thiol-bearing metabolites following peptide linker cleavage were investigated.

Identification and Optimization of Novel Small c-Abl Kinase Activators Using Fragment and HTS Methodologies.

Abelson kinase (c-Abl) is a ubiquitously expressed, nonreceptor tyrosine kinase which plays a key role in cell differentiation and survival. It was hypothesized that transient activation of c-Abl kinase via displacement of the N-terminal autoinhibitory "myristoyl latch", may lead to an increased hematopoietic stem cell differentiation. This would increase the numbers of circulating neutrophils and so be an effective treatment for chemotherapy-induced neutropenia. This paper describes the discovery and optimization of a thiazole series of novel small molecule c-Abl activators, initially identified by a high throughput screening. Subsequently, a scaffold-hop, which exploited the improved physicochemical properties of a dihydropyrazole analogue, identified through fragment screening, delivered potent, soluble, cell-active c-Abl activators, which demonstrated the intracellular activation of c-Abl in vivo.

Stabilization of the Max Homodimer with a Small Molecule Attenuates Myc-Driven Transcription.

The transcription factor Max is a basic-helix-loop-helix leucine zipper (bHLHLZ) protein that forms homodimers or interacts with other bHLHLZ proteins, including Myc and Mxd proteins. Among this dynamic network of interactions, the Myc/Max heterodimer has crucial roles in regulating normal cellular processes, but its transcriptional activity is deregulated in a majority of human cancers. Despite this significance, the arsenal of high-quality chemical probes to interrogate these proteins remains limited. We used small molecule microarrays to identify compounds that bind Max in a mechanistically unbiased manner. We discovered the asymmetric polycyclic lactam, KI-MS2-008, which stabilizes the Max homodimer while reducing Myc protein and Myc-regulated transcript levels. KI-MS2-008 also decreases viable cancer cell growth in a Myc-dependent manner and suppresses tumor growth in vivo. This approach demonstrates the feasibility of modulating Max with small molecules and supports altering Max dimerization as an alternative approach to targeting Myc.

An Array-Based Ligand Discovery Platform for Proteins With Short Half-Lives.

Many promising therapeutic protein targets were previously considered "undruggable" due to a deficit in structural information to guide drug design and/or a lack of an obvious binding pocket. Fortunately, array-based methods for evaluating protein binding against large chemical libraries, such as small-molecule microarray screening, have provided one of several emerging inroads to ligand discovery for these elusive targets. Despite the advance in the area of ligand discovery for poorly structured and intrinsically disordered proteins provided by array-based technologies involving cell lysates, the extension of this technology for screening proteins with short half-lives in physiologically relevant conformations has been technically challenging. In this chapter we present a protocol for leveraging in vitro translation strategies to enable array-based screening of short-lived proteins against large small-molecule libraries for ligand discovery.

Advances in discovering small molecules to probe protein function in a systems context.

High throughput screening (HTS) has historically been used for drug discovery almost exclusively by the pharmaceutical industry. Due to a significant decrease in costs associated with establishing a high throughput facility and an exponential interest in discovering probes of development and disease associated biomolecules, HTS core facilities have become an integral part of most academic and non-profit research institutions over the past decade. This major shift has led to the development of new HTS methodologies extending beyond the capabilities and target classes used in classical drug discovery approaches such as traditional enzymatic activity-based screens. In this brief review we describe some of the most interesting developments in HTS technologies and methods for chemical probe discovery.

A bioorthogonal (68)Ga-labelling strategy for rapid in vivo imaging.

Herein, we describe a fast and robust method for achieving (68)Ga-labelling of the EGFR-selective monoclonal antibody (mAb) Cetuximab using the bioorthogonal Inverse-electron-Demand Diels-Alder (IeDDA) reaction. The in vivo imaging of EGFR is demonstrated, as well as the translation of the method within a two-step pretargeting strategy.

Copper-free click--a promising tool for pre-targeted PET imaging.

The copper-free click (CFC) reaction has been evaluated for its potential application to in vivo pre-targeting for PET imaging. A promising biodistribution profile is demonstrated when employing [(18)F]2-fluoroethylazide ([(18)F]1) and optimisation of the CFC reaction with a series of cyclooctynes shows that reactions proceed efficiently with tantalizing opportunities for application-specific tuning.