Affino-Proteomic Analysis of Bumped Kinase Inhibitor BKI-1708 in Toxoplasma gondii and Human Fibroblast Host Cells

Bumped kinase inhibitor 1708 (BKI-1708), previously demonstrated to target apicomplexan kinases and CDPK1 and MAPKL1, exhibits remarkable activity against Toxoplasma gondii infection both in vitro and in vivo. Notably, BKI-1708 does not affect the viability of mammalian cells. Upon exposure to BKI-1708, T. gondii tachyzoites form large multinucleated complexes named baryzoites and remain trapped within host cells. In this study, proteins binding to BKI-1708 were identified in soluble extracts of T. gondii ME49 tachyzoites and human foreskin fibroblasts (HFF) using differential affinity chromatography coupled to mass spectrometry (DAC-MS). Beyond kinases, secondary interactions in T. gondii involved the binding of proteins associated with cell division, cytoskeleton, vesicular trafficking, secretory organelles, and transcriptional and translational regulators. In non-infected HFFs, BKI-1708 interactors included cytoskeletal regulators along with multiple RNA/DNA-binding proteins. Upon infection, this profile shifted, with cytoskeletal components no longer detected, while nucleic acid-binding proteins remained present, consistent with infection-induced chromatin and transcriptional remodeling. These results suggest that multi-target interference could contribute to the impaired cytokinesis and the formation of multinucleated baryzoites, aligning with the concept that antiprotozoal drugs exert efficacy through coordinated perturbation of multiple cellular processes rather than a single dominant target.