Pathogenic mycobacteria pose a sustained threat to global human health. Recently, cytochrome bcc complexes have gained interest as targets for antibiotic drug development. However, there is currently no structural information for the cytochrome bcc complex from these pathogenic mycobacteria. Here, we report the structures of Mycobacterium tuberculosis cytochrome bcc alone (2.68 Å resolution) and in complex with clinical drug candidates Q203 (2.67 Å resolution) and TB47 (2.93 Å resolution) determined by single-particle cryo-electron microscopy. M. tuberculosis cytochrome bcc forms a dimeric assembly with endogenous menaquinone/menaquinol bound at the quinone/quinol-binding pockets. We observe Q203 and TB47 bound at the quinol-binding site and stabilized by hydrogen bonds with the side chains of _QcrBThr³¹³ and _QcrBGlu³¹⁴, residues that are conserved across pathogenic mycobacteria. These high-resolution images provide a basis for the design of new mycobacterial cytochrome bcc inhibitors that could be developed into broad-spectrum drugs to treat mycobacterial infections.

The RNA-dependent RNA polymerase (RdRp), 3C-like protease (3CL^pro), and papain-like protease (PL^pro) are pivotal components in the viral life cycle of SARS-CoV-2, presenting as promising therapeutic targets. Currently, all FDA-approved antiviral drugs against SARS-CoV-2 are RdRp or 3CL^pro inhibitors. However, the mutations causing drug resistance have been observed in RdRp and 3CL^pro from SARS-CoV-2, which makes it necessary to develop antivirals with novel mechanisms. Through the application of a structure-based drug design (SBDD) approach, we discover a series of novel potent non-covalent PL^pro inhibitors with remarkable in vitro potency and in vivo PK properties. The co-crystal structures of PL^pro with lead compounds reveal that the residues D164 and Q269 around the S2 site are critical for improving the inhibitor’s potency. The lead compound GZNL-P36 not only inhibits SARS-CoV-2 and its variants at the cellular level with EC₅₀ ranging from 58.2 nM to 306.2 nM, but also inhibits HCoV-NL63 and HCoV-229E with EC₅₀ of 81.6 nM and 2.66 μM, respectively. Oral administration of the GZNL-P36 results in significantly improved survival and notable reductions in lung viral loads and lesions in SARS-CoV-2 infection mouse model, consistent with RNA-seq data analysis. Our results indicate that PL^pro inhibitors represent a promising SARS-CoV-2 therapy.

Jumonji C-domain-containing protein 6 (JMJD6), an iron (Fe²⁺) and α-ketoglutarate (α-KG)-dependent oxygenase, is expressed at high levels, correlated with poor prognosis, and considered as a therapeutic target in multiple cancer types. However, specific JMJD6 inhibitors that are potent in suppressing tumorigenesis have not been reported so far. We herein report that iJMJD6, a specific small-molecule inhibitor of JMJD6 with favorable physiochemical properties, inhibits the enzymatic activity of JMJD6 protein both in vitro and in cultured cells. iJMJD6 is effective in suppressing cell proliferation, migration, and invasion in multiple types of cancer cells in a JMJD6-dependent manner, while it exhibits minimal toxicity in normal cells. Mechanistically, iJMJD6 represses the expression of oncogenes, including Myc and CCND1, in accordance with JMJD6 function in promoting the transcription of these genes. iJMJD6 exhibits suitable pharmacokinetic properties and suppresses tumor growth in multiple cancer cell line– and patient-derived xenograft models safely. Furthermore, combination therapy with iJMJD6 and BET protein inhibitor (BETi) JQ1 or estrogen receptor antagonist fulvestrant exhibits synergistic effects in suppressing tumor growth. Taken together, we demonstrate that inhibition of JMJD6 enzymatic activity by using iJMJD6 is effective in suppressing oncogene expression and cancer development, providing a therapeutic avenue for treating cancers that are dependent on JMJD6 in the clinic.