The selective Trk inhibitor AZ623 inhibits brain-derived neurotrophic factor-mediated neuroblastoma cell proliferation and signaling and is synergistic with topotecan

BACKGROUND: TrkB expression is associated with poor prognosis for patients with neuroblastoma. AZ623 is a novel potent and selective inhibitor of the Trk family of tyrosine kinases. The authors hypothesized that AZ623 would inhibit TrkB-mediated signaling in neuroblastoma tumor cells and would be synergistic when combined with chemotherapy. METHODS: Neuroblastoma cell lines were screened for TrkB receptor mRNA expression and for their proliferation rates in response to brain-derived neurotrophic factor (BDNF). The effects of AZ623 on Trk receptor phosphorylation, signaling, and cell growth were evaluated in BDNF-treated neuroblastoma cells. Mice with human neuroblastoma xenograft tumors were treated with AZ623 alone and in combination with topotecan, and tumor growth rates were determined during and after treatment. RESULTS: Neuroblastoma cell lines expressed various levels of the TrkB receptor and demonstrated increased proliferation in response to BDNF. BDNF treatment stimulated TrkB phosphorylation and downstream signaling that could be inhibited by AZ623. Neuroblastoma cells demonstrated in vitro sensitivity to AZ623, with concentration that inhibits 50% (IC50) values between 0.8 to 7 μM. AZ623 treatment was found to inhibit BDNF-mediated neuroblastoma cell proliferation. Mice with human neuroblastoma xenograft tumors demonstrated tumor growth inhibition when treated with AZ623 and with AZ623 combined with topotecan. Limited tumor regrowth was noted in mice with tumors treated with AZ623 combined with topotecan after treatment discontinuation. CONCLUSIONS: AZ623 is a novel selective Trk inhibitor that inhibits BDNF-mediated signaling and neuroblastoma cell proliferation. AZ623 treatment inhibits the growth of human neuroblastoma xenograft tumors, and treatment with AZ623 combined with topotecan results in the prolonged inhibition of tumor regrowth. On the basis of these results, further preclinical development is warranted.