Neuroblastoma (NB) is the most common extra-cranial solid tumor in childhood. The long-term, event-free survival of high-risk NB remains ∼ 50% despite intensive multi-modality treatments. Activated JAK/STAT3 pathway plays an important role in many human cancers. In NB patients, cytokines activating STAT3 have been associated with poor patient outcome and have been implicated in the survival of a rare population of NB tumor initiating cells. Thus targeting STAT3 may be a promising therapeutic strategy for high-risk NB. To evaluate the biologic consequences of genetic targeting of STAT3, we assessed the effects of inhibition of STAT3 in NB cell lines containing a tetracycline (Tet)-inducible STAT3 expression plasmid. Additionally we evaluated pharmacogenomic inhibition of STAT3 using AZD9150, a generation 2.5, 16-nucleotide, antisense oligonucleotide (ASO) that is now in Phase I/II clinical trials. Studies were conducted in 3 representative NB cell line models (AS (MYCN-WT) and NGP and IMR32 (MYCN-Amplified)). Both the Tet-inducible STAT3 shRNA and AZD9150 reduced endogenous STAT3 mRNA and protein levels causing decreased transcription and expression of STAT3 target genes, such as CyclinD1, D3, and MYC/MYCN. In functional in vitro studies Tet-inducible STAT3 shRNA and AZD9150 decreased NB cell migration and clonogenicity in soft agar. In vivo, STAT3 inhibition by Tet-inducible STAT3 shRNA or AZD9150 alone had little effect on the growth of established tumors nor did it alter the survival of tumor-bearing mice, despite decreases in STAT3, P-STAT3 and target gene expression in xenografts from AZD9150-treated mice compared to those from ASO-treated mice. To assess whether inhibition of STAT3 altered the tumor initiating potential of NB cells, NB tumor xenograft cells from ASO or AZD9150 treated mice were re-implanted and secondary tumor growth assessed. At 200,000 and 20,000 ASO-treated NB cells, 100% of mice had tumors while only 40 and 20%, respectively of AZD9150-treated mice had tumors. These results indicate that the inhibition of STAT3 decreased the frequency of tumor initiating cells in the NB xenograft from AZD9150 treated mice. Since tumor initiating or stem-like cells are frequently more resistant to cytotoxic agents, we next evaluated a combination therapy with cisplatin. We found that in vitro either genetic shSTAT3 or AZD9150 mediated pharmacogenomic inhibition of STAT3 significantly increased the sensitivity of NB cells to cisplatin. Furthermore, in established NB tumors xenografts, the combination of STAT3 inhibition with cisplatin caused a 30% decrease in tumor size (P = 0.0092) and increased the survival of AZD9150 treated tumor-bearing mice compared to ASO-treated mice (P = 0.026). Our study supports the development of strategies targeting STAT3 in combination with conventional chemotherapy for patients with high-risk NB.

Citation Format: Seiichi Odate, Shuang Yan, Veronica Veschi, Norris Lam, Zhihui Liu, Carol J. Thiele. Inhibition of STAT3 with the generation 2.5 antisense oligonucleotide, AZD9150 increases the chemosensitivity and decreases tumor-initiating potential of neuroblastoma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2439.