We recently discovered that inhibition of the lipid peroxidase GPX4 can selectively kill cancer cells in a therapy-resistant state through induction of ferroptosis. Although GPX4 lacks a conventional druggable pocket, covalent small-molecule inhibitors are able to overcome this challenge by reacting with the GPX4 catalytic selenocysteine residue to eliminate enzymatic activity. Unfortunately, all currently-reported GPX4 inhibitors achieve their activity through reactive chloroacetamide groups. We demonstrate that such chloroacetamide-containing compounds are poor starting points for further advancement given their promiscuity, instability, and low bioavailability. Development of improved GPX4 inhibitors, including those with therapeutic potential, requires the identification of new electrophilic chemotypes and mechanisms of action that do not suffer these shortcomings. Here, we report our discovery that nitrile oxide electrophiles, and a set of remarkable chemical transformations that generates them in cells from masked precursors, provide an effective strategy for selective targeting of GPX4. Our results, which include structural insights, target engagement assays, and diverse GPX4-inhibitor tool compounds, provide critical insights that may galvanize development of improved compounds that illuminate the basic biology of GPX4 and therapeutic potential of ferroptosis induction. In addition, our discovery that nitrile oxide electrophiles engage in highly selective cellular interactions and are bioavailable in their masked forms may be relevant for targeting other currently undruggable proteins, such as those revealed by recent proteome-wide ligandability studies.

The photoredox-mediated direct intermolecular C-H functionalization of substituted indoles, pyrroles, and furans with diethyl bromomalonate is described, utilizing the visible light-induced reductive quenching pathway of Ru(bpy)(3)Cl(2). An analysis of reductive quenchers and mechanistic considerations has led to an optimized protocol for the heteroaromatic alkylations, providing products in good yields and regioselectivities, as well as successfully eliminating previously observed competitive side reactions. This methodology is highlighted by its neutral conditions, activity at ambient temperatures, low catalyst loading, functional group tolerance, and chemoselectivity.

Our previous studies into visible light-mediated aza-Henry reactions demonstrated that molecular oxygen played a vital role in catalyst turnover as well as the production of base to facilitate the nucleophilic addition of nitroalkanes. Herein, improved conditions for the generation of iminium ions from tetrahydroisoquinolines that allow for versatile nucleophilic trapping are reported. The new conditions provide access to a diverse range of functionality under mild, anaerobic reaction conditions as well as mechanistic insights into the photoredox cycle.

Lighting the way: In a 10‐step total synthesis of the title compound, visible‐light photoredox catalysis enabled the construction of the key bond by facilitating the direct coupling of a pyrroloindoline‐derived radical with a substituted indole (see scheme; Boc=tert‐butyloxycarbonyl, Cbz=benzyloxycarbonyl, DMF=N,N′‐dimethylformamide). This represents the first implementation of visible‐light photoredox catalysis in a total synthesis.

The PPARG gene encoding the nuclear receptor PPAR-gamma is activated in bladder cancer, either directly by gene amplification or mutation, or indirectly by mutation of the RXRA gene which encodes the heterodimeric partner of PPAR-gamma. Here we show that activating alterations of PPARG or RXRA lead to a specific gene expression signature in bladder cancers. Reducing PPARG activity, whether by pharmacologic inhibition or genetic ablation, inhibited proliferation of PPARG-activated bladder cancer cells. Our results offer a preclinical proof of concept for PPARG as a candidate therapeutic target in bladder cancer.