Development of novel ubiquitin specific protease 5 (USP5) inhibitors to treat neuroblastoma

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Copyright: Gadde, Satyanarayana
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Abstract
High-risk neuroblastoma is one of the most aggressive and treatment-refractory childhood malignancies. MYCN (v-myc avian myelocytomatosis viral related oncogene, neuroblastoma derived) is a major oncogenic driver for neuroblastoma (NB) tumorigenesis. Developing direct inhibitors of MYCN has been challenging due to several limitations. Hence, targeting MYCN-binding proteins which regulate the stability of MYCN protein is a promising alternative approach. This study is aimed at developing novel inhibitors of ubiquitin specific protease 5 (USP5), a deubiquitinating enzyme, which is known to prevent MYCN protein degradation by deubiquitination. The first results chapter describes the synthesis of novel pyrido[1,2-a]benzimidazole compounds and their cytotoxicity against MYCN amplified NB cells with high expression of USP5 protein (SK-N-BE(2)-C and Kelly cells). However, none of the tested compounds displayed better cytotoxicity than the parental compound, SE486-11. The second results chapter describes a one-pot synthesis of novel γ-carbolinone, γ-carboline and spiro[pyrrolidinone-3,3′]indoles. One of the γ-carboline compounds (42d) displayed promising cytotoxicity against NB cells (SK-N-BE(2)-C (IC50 = 1.21 μM) and Kelly (IC50 = 3.09 μM)) but showed little therapeutic selectivity when compared to normal human fibroblasts, MRC-5 cells (IC50 = 3.75μM). The synthesis and cytotoxicity of novel pyrimido[1,2-a]benzimidazoles is described in the third results chapter. The active compound, 65a displayed promising cytotoxicity against SK-N-BE(2)-C (IC50 = 0.78 μM) and Kelly (IC50 = 2.00 μM) cells with a reasonable therapeutic window compared to MRC-5 cells (IC50 = 15.0 μM). 65a bound to USP5 protein by microscale thermophoresis assay (Kd = 0.47 µM). USP5 and MYCN protein levels were decreased in NB cells by treatment with 65a. Moreover, the cytotoxicity of 65a was dependant on the expression of USP5 and MYCN proteins. 65a showed synergy in combination with HDAC inhibitors, SAHA and panobinostat. In the fourth results chapter, the synthesis of more potent pyrimido[1,2-a]benzimidazoles with di- and tri- substitutions on the pendant phenyl ring (86b (SK-N-BE(2)-C IC50 = 0.31 μM; Kelly IC50 = 0.65 μM) and 91 (SK-N-BE(2)-C IC50 = 0.03 μM; Kelly IC50 = 0.07 μM)) are described. Importantly, 86b displayed significant in vivo efficacy in TH-MYCN homozygous NB mice when treated with 60 mg/kg for three weeks. The last results chapter describes the synthesis and cytotoxicity of novel benzo[4,5]imidazo[2,1-b]thiazole and pyrido[2,3-b]indole compounds. Collectively, this thesis identifies promising novel scaffolds with great potential for further development.
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Publication Year
2022
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Thesis
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PhD Doctorate
UNSW Faculty