Multinucleation and cytotoxicity induced by multikinase inhibition in highly proliferative cells

Phenotypic screening using motor neurons derived from the induced pluripotent stem (iPS) cell of a patient with amyotrophic lateral sclerosis led to the identification of Compound X, a novel agent with potent neuroprotective activity that is hypothesized to act by inhibiting hematopoietic progenitor kinase/germinal center kinase-like kinase (HGK). Unlike known HGK inhibitors, including Prostetin and GNE-495, Compound X and related Compounds Y and Z exhibited broader multi-kinase-inhibition profiles, including the strong inhibition of Aurora B kinase and strong-to-moderate inhibition of Src-family kinases in kinase panel screening. Owing to their roles in cytokinesis, we performed in vitro micronucleus tests to assess their genotoxicity. Compounds X, Y, and Z induced the multinucleation of cells at rates of 88.8, 71.5, and 91.8%, respectively, whereas Prostetin and GNE-495 resulted in rates of 0.5 and 1.3%, respectively, which were comparable to the control. A 5-day repeated-dose oral toxicity study of Compound X using mice, at doses of 125, 250, and 500 mg/kg/day, revealed decreased locomotor activity, hypothermia, and mortality at 500 mg/kg/day. Histopathology showed necrosis/hemorrhage in bone marrow cells; single-cell necrosis in the thymus, spleen, and mesenteric lymph nodes; nuclear pleomorphism and single-cell necrosis/necrosis in the gastrointestinal mucosa; and karyomegaly and a reduction in testicular germ cells. These toxicopathological findings suggest that Compound X induces nuclear pleomorphism and necrosis in highly proliferative cells. Although Compound X strongly suppressed HGK, its toxicity may be associated with broader multikinase inhibition, which is consistent with the finding that Prostetin and GNE-495 do not induce multinucleation in vitro.