Discovery of compounds inhibiting the ADP-ribosyltransferase activity of pertussis toxin

Abstract The targeted pathogen-selective approach to drug development holds promise to minimize collateral damage to the beneficial microbiome. The AB₅-topology pertussis toxin (PtxS1-S5) is a major virulence factor of Bordetella pertussis, the causative agent of the highly contagious respiratory disease whooping cough. Once internalized into the host cell, PtxS1 ADP-ribosylates α-subunits of the heterotrimeric Gαi-superfamily, thereby disrupting G-protein-coupled receptor signaling. Here, we report the discovery of the first small molecules inhibiting the ADP-ribosyltransferase activity of pertussis toxin. We developed protocols to purify milligram-levels of active recombinant B. pertussis PtxS1 from Escherichia coli and an in vitro high throughput-compatible assay to quantify NAD⁺ consumption during PtxS1-catalyzed ADP-ribosylation of Gαi. Two inhibitory compounds (NSC228155 and NSC29193) with low micromolar IC₅₀-values (3.0 μM and 6.8 μM) were identified in the in vitro NAD⁺ consumption assay that also were potent in an independent in vitro assay monitoring conjugation of ADP-ribose to Gαi. Docking and molecular dynamics simulations identified plausible binding poses of NSC228155 and in particular of NSC29193, most likely owing to the rigidity of the latter ligand, at the NAD⁺-binding pocket of PtxS1. NSC228155 inhibited the pertussis AB₅ holotoxin-catalyzed ADP-ribosylation of Gαi in living human cells with a low micromolar IC₅₀-value (2.4 μM). NSC228155 and NSC29193 might prove to be useful hit compounds in targeted B. pertussis-selective drug development

An unbiased in vitro screen for activating epidermal growth factor receptor mutations

Abstract Cancer tissues harbor thousands of mutations, and a given oncogene may be mutated at hundreds of sites, yet only a few of these mutations have been functionally tested. Here, we describe an unbiased platform for the functional characterization of thousands of variants of a single receptor tyrosine kinase (RTK) gene in a single assay. Our in vitro screen for activating mutations (iSCREAM) platform enabled rapid analysis of mutations conferring gain-of-function RTK activity promoting clonal growth. The screening strategy included a somatic model of cancer evolution and utilized a library of 7,216 randomly mutated epidermal growth factor receptor (EGFR) single-nucleotide variants that were tested in murine lymphoid Ba/F3 cells. These cells depend on exogenous interleukin-3 (IL-3) for growth, but this dependence can be compensated by ectopic EGFR overexpression, enabling selection for gain-of-function EGFR mutants. Analysis of the enriched mutants revealed EGFR A702V, a novel activating variant that structurally stabilized the EGFR kinase dimer interface and conferred sensitivity to kinase inhibition by afatinib. As proof of concept for our approach, we recapitulated clinical observations and identified the EGFR L858R as the major enriched EGFR variant. Altogether, iSCREAM enabled robust enrichment of 21 variants from a total of 7,216 EGFR mutations. These findings indicate the power of this screening platform for unbiased identification of activating RTK variants that are enriched under selection pressure in a model of cancer heterogeneity and evolution