Bohnacker et al. recently investigated the primary site of action of the anti-cancer therapeutic BKM120 (a.k.a., Buparlisib), a clinically-advanced phosphoinositide 3-kinase (PI3K) inhibitor. Although PI3K inhibition is considered the primary mechanism of action, some studies report that BKM120 exerts potent off-target effects on tubulin, which raises questions about its substrate. Here, the authors aimed to decipher BKM120’s molecular interactions with tubulin and PI3K to identify its anti-tumorigenic site of action. The authors reported that BKM120’s anti-cancer activity is through mitotic arrest via microtubule destabilization, rather than PI3K inhibition. Chemical derivatives of BK120 were synthesized and examined to separate targeting of PI3K versus tubulin in pursuit of a more potent and selective PI3K inhibitor. The BKM120-derived molecule, PQR309, strongly inhibited PI3K with no detectable effect on tubulin polymerization and/or microtubule stability. Cytoskeleton’s 99% pure porcine brain tubulin, tubulin polymerization assay kit, biotinylated porcine brain tubulin, and TRITC rhodamine-labeled tubulin (Cat.# T240, BK006P, T333P, and TL590M, respectively) were essential reagents in this study, providing the tools necessary to examine how BKM120 and BKM120-derived molecules affected tubulin polymerization and microtubule dynamics as assessed by in vitro assembly and microtubule plus-end tracking assays, with the goal of designing novel, specific, and potent PI3K inhibitors.
Alpha/beta tubulin heterodimer in complex with tubulin tyrosine ligase, stathmin-4, and the small molecule compound BKM120 (Buparlisib).