Growth inhibitory and anti-tumour activities of OSU-03012, a novel PDK-1 inhibitor, on vestibular schwannoma and malignant schwannoma cells

Background: Vestibular schwannomas (VS) frequently express high levels of activated AKT. Small-molecule inhibitors of AKT signalling may have therapeutic potential in suppressing the growth of benign VS and malignant schwannomas. Method: Primary VS and Schwann cells, human malignant schwannoma HMS-97 cells and mouse Nf2^-/- Schwann cells and schwannoma cells were prepared to investigate the growth inhibitory and anti-tumour activities of OSU-03012, a celecoxib-derived small-molecule inhibitor of phosphoinositide-dependent kinase-1. Cell proliferation assays, apoptosis, Western blot, in vivo xenograft analysis using SCID mice and immunohistochemistry were performed. Results: OSU-03012 inhibited cell proliferation more effectively in both VS and HMS-97 cells than in normal human Schwann cells. The IC₅₀ of OSU-03012 at 48 h was approximately 3.1 μM for VS cells and 2.6 μM for HMS-97 cells, compared with the IC₅₀ of greater than 12 μM for human Schwann cells. Similarly, mouse Nf2^-/- schwannoma and Nf2^-/- Schwann cells were more sensitive to growth inhibition by OSU-03012 than wild-type mouse Schwann cells and mouse schwannoma cells established from transgenic mice carrying the NF2 promoter-driven SV40 T-antigen gene. Like VS cells, malignant schwannoma HMS-97 cells expressed high levels of activated AKT. OSU-03012 induced apoptosis in both VS and HMS-97 cells and caused a marked reduction of AKT phosphorylation at both the Ser-308 and Thr-473 sites in a dose-dependent manner. In vivo xenograft analysis showed that OSU-03012 was well tolerated and inhibited the growth of HMS-97 schwannoma xenografts by 55% after 9 weeks of oral treatment. The anti-tumour activity correlated with reduced AKT phosphorylation. Conclusion: OSU-03012 is a potential chemotherapeutic agent for VS and malignant schwannomas.