Electrophile Determines Cellular Phenotypes among XPO1-Targeting Small Molecules.

Covalent drug discovery has experienced a renaissance, with numerous electrophilic small molecules recently gaining FDA approval. Many structurally diverse electrophilic small molecules target exportin-1 (XPO1/CRM1) at cysteine 528, including the selective inhibitor of nuclear export (SINE) selinexor, which was FDA-approved as an anticancer agent in 2019. Emerging evidence supports additional pharmacological classes of XPO1 modulators targeting Cys528, including the selective inhibitors of transcriptional activation (SITAs) and probes that induce rapid degradation of XPO1. Here, we analyzed structure-activity relationships across multiple structural series of XPO1 Cys528-targeting probes. We observe that the electrophilic moiety of Cys528-targeting small molecules plays a decisive role in the cellular behavior observed, with subtle changes in electrophile structure being sufficient to convert XPO1-targeting probes to different pharmacological classes. This investigation represents a unique case study in which the electrophile functionality used to target a specific cysteine determines the pharmacological effect among diverse XPO1-targeting small molecules.

Targeting the chromatin binding of exportin-1 disrupts NFAT and T cell activation.

Exportin-1 (XPO1/CRM1) plays a central role in the nuclear-to-cytoplasmic transport of hundreds of proteins and contributes to other cellular processes, such as centrosome duplication. Small molecules targeting XPO1 induce cytotoxicity, and selinexor was approved by the Food and Drug Administration in 2019 as a cancer chemotherapy for relapsed multiple myeloma. Here, we describe a cell-type-dependent chromatin-binding function for XPO1 that is essential for the chromatin occupancy of NFAT transcription factors and thus the appropriate activation of T cells. Additionally, we establish a class of XPO1-targeting small molecules capable of disrupting the chromatin binding of XPO1 without perturbing nuclear export or inducing cytotoxicity. This work defines a broad transcription regulatory role for XPO1 that is essential for T cell activation as well as a new class of XPO1 modulators to enable therapeutic targeting of XPO1 beyond oncology including in T cell-driven autoimmune disorders.

NIR-II emissive donor-acceptor-donor fluorophores for dual fluorescence bioimaging and photothermal therapy applications.

Fluorescence bioimaging with near-infrared II (NIR-II) emissive organic fluorophores has proven to be a viable noninvasive diagnostic technique. However, there is still the need for the development of fluorophores that possess increased stability as well as functionalities that impart stimuli responsiveness. Through strategic design, we can synthesize fluorophores that possess not only NIR-II optical profiles but also pH-sensitivity and the ability to generate heat upon irradiation. In this work, we employ a donor-acceptor-donor (D-A-D) design to synthesize a series of NIR-II fluorophores. Here we use thienothiadiazole (TTD) as the acceptor, 3-hexylthiophene (HexT) as the π-spacer and vary the alkyl amine donor units: N,N-dimethylaniline (DMA), phenylpiperidine (Pip), and phenylmorpholine (Morp). Spectroscopic analysis shows that all three derivatives exhibit emission in the NIR-II region with λemimax ranging from 1030 to 1075 nm. Upon irradiation, the fluorophores exhibited noticeable heat generation through non-radiative processes. The ability to generate heat indicates that these fluorophores will act as theranostic (combination therapeutic and diagnostic) agents in which simultaneous visualization and treatment can be performed. Additionally, biosensing capabilities were supported by changes in the absorbance properties while under acidic conditions as a result of protonation of the alkyl amine donor units. The fluorophores also show minimal toxicity in a human mammary cell line and with murine red blood cells. Overall, initial results indicate viable NIR-II materials for multiple biomedical applications.