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Bispecific antibodies (bsAbs) target two different epitopes. These are an up-and-coming class of biologics, with two such therapeutics (emicizumab and blinatumomab) FDA approved and on the market, and many more in clinical trials. While the first reported bsAbs were constructed by chemical methods, this approach has fallen out of favour with the advent of modern genetic engineering techniques and, nowadays, the vast majority of bsAbs are produced by protein engineering. However, in recent years, relying on innovations in the fields of bioconjugation and bioorthogonal click chemistry, new chemical methods have appeared that have the potential to be competitive with protein engineering techniques and, indeed, hold some advantages. These approaches offer modularity, reproducibility and batch-to-batch consistency, as well as the integration of handles, whereby additional cargo molecules can be attached easily, e.g. to generate bispecific antibody–drug conjugates. The linker between the antibodies/antibody fragments can also be easily varied, and new formats (types, defined by structural properties or by construction methodology) can be generated rapidly. These attributes offer the potential to revolutionize the field. Here, we review chemical methods for the generation of bsAbs, showing that the newest examples of these techniques are worthy competitors to the industry-standard expression-based strategies. Bispecific antibodies are an up-and-coming type of construct among biologics. They are currently being produced by genetic engineering and expression. This Review highlights recently developed chemical methods for their construction.

Background Antibody-drug conjugate (ADC) construction poses numerous challenges that limit clinical progress. In particular, common bioconjugation methods afford minimal control over the site of drug coupling to antibodies. Here, such difficulties are overcome through re-bridging of the inter-chain disulfides of cetuximab (CTX) with auristatin-bearing pyridazinediones, to yield a highly refined anti-epidermal growth factor receptor (EGFR) ADC. Methods In vitro and in vivo assessment of ADC activity was performed in KRAS mutant pancreatic cancer (PaCa) models with known resistance to CTX therapy. Computational modelling was employed for quantitative prediction of tumour response to various ADC dosing regimens. Results Site-selective coupling of an auristatin to CTX yielded an ADC with an average drug:antibody ratio (DAR) of 3.9, which elicited concentration- and EGFR-dependent cytotoxicity at sub-nanomolar potency in vitro. In human xenografts, the ADC inhibited tumour growth and prolonged survival, with no overt signs of toxicity. Key insights into factors governing ADC efficacy were obtained through a robust mathematical framework, including target-mediated dispositional effects relating to antigen density on tumour cells. Conclusions Together, our findings offer renewed hope for CTX in PaCa therapy, demonstrating that it may be reformatted as a next-generation ADC and combined with a predictive modelling tool to guide successful translation.

Antibody-drug conjugates (ADCs) comprise antibodies covalently attached to highly potent drugs using a variety of conjugation technologies. As therapeutics, they combine the exquisite specificity of antibodies, enabling discrimination between healthy and diseased tissue, with the cell-killing ability of cytotoxic drugs. This powerful and exciting class of targeted therapy has shown considerable promise in the treatment of various cancers with two US Food and Drug Administration approved ADCs currently on the market (Adcetris and Kadcyla) and approximately 40 currently undergoing clinical evaluation. However, most of these ADCs exist as heterogeneous mixtures, which can result in a narrow therapeutic window and have major pharmacokinetic implications. In order for ADCs to deliver their full potential, sophisticated site-specific conjugation technologies to connect the drug to the antibody are vital. This Perspective discusses the strategies currently used for the site-specific construction of ADCs and appraises their merits and disadvantages.

The development of methods for carbon-carbon bond formation under benign conditions is an ongoing challenge for the synthetic chemist. In recent years there has been considerable interest in using selective C-H activation as a direct route for generating reactive intermediates. In this article, we describe the use of aldehyde auto-oxidation as a simple, clean and effective method for C-H activation, resulting in the generation of an acyl radical. This acyl radical can be used for carbon-carbon bond formation and herein we describe the application of this method for the hydroacylation of alpha,beta-unsaturated esters without the requirement of additional catalysts or reagents. This methodology generates unsymmetrical ketones, which have been shown to have broad use in organic synthesis.