Inositol hexakisphosphate (IP6) is an abundant metabolite synthesized from inositol 1,3,4,5,6-pentakisphosphate (IP5) by the single IP5 2-kinase (IP5K). Genetic and biochemical studies have shown that IP6 usually functions as a structural cofactor in protein(s) mediating mRNA export, DNA repair, necroptosis, 3D genome organization, HIV infection, and cullin-RING ligase (CRL) deneddylation. However, it remains unknown whether pharmacological perturbation of cellular IP6 levels affects any of these processes. Here, we performed screening for small molecules that regulate human IP5K activity, revealing that the antiparasitic drug and polysulfonic compound suramin efficiently inhibits IP5K in vitro and in vivo The results from docking experiments and biochemical validations suggested that the suramin targets IP5K in a distinct bidentate manner by concurrently binding to the ATP- and IP5-binding pockets, thereby inhibiting both IP5 phosphorylation and ATP hydrolysis. NF449, a suramin analog with additional sulfonate moieties, more potently inhibited IP5K. Both suramin and NF449 disrupted IP6-dependent sequestration of CRL by the deneddylase COP9 signalosome, thereby affecting CRL activity cycle and component dynamics in an IP5K-dependent manner. Finally, nontoxic doses of suramin, NF449, or NF110 exacerbate the loss of cell viability elicited by the neddylation inhibitor and clinical trial drug MLN4924/pevonedistat, suggesting synergistic ef-fects. Suramin and its analogs provide structural templates for designing potent and specific IP5K inhibitors, which could be used in combination therapy along with MLN4924/pevonedistat. IP5K is a potential mechanistic target of suramin, accounting for suramin's therapeutic effects.
Keywords: COP9 signalosome; E3 ubiquitin ligase; IP5K; cancer chemoprevention; cullin–RING ligase; inhibitor; inositol phosphate; neddylation; protein degradation; suramin.
© 2020 Zhang et al.