Preclinical evaluation of the proteasome inhibitor ixazomib (MLN2238) on nasopharyngeal cacinoma (NPC)

Background: Nasopharyngeal carcinoma (NPC) is a common cancer in the South Asia and is closely associated with EBV infection. The standard treatment for newly diagnosed NPC is radiotherapy alone or in combination with adjuvant chemotherapy and there is currently no targeted therapy available for NPC. About 30% of the NPC patient will progress within 5 years after treatment, so study on new therapeutic agents is in need. Proteasome inhibitor is emerged as an effective antitumor therapeutic agent in both haematological and solid tumour. Studies have reported that proteasome inhibitor can inhibit nuclear factor-kB (NF-kB) signalling pathway which was found constitutively activated in NPC. Here, we examined the antiproliferation effect and molecular mechanisms of the second-generation, selective and reversible proteasome inhibitor ixazomib (MLN2238) on NPC in-vitro and in-vivo. Ixazomib is the first oral proteasome inhibitor approved by the FDA for multiple myeloma treatment and has shown less side effect and more selective to proteasome than the first-generation proteasome inhibitor, bortezomib. Method: Three human EBV positive NPC cell lines (C666-1, NPC43 and C17) and two PDXs (Xeno113 and Xeno76) PDXs were used. Results: In our study, we showed that Ixazomib can inhibit cell viability and proliferation in EBV-associated NPC cells C666-1, NPC43 and C17 in a time- and dose-dependent manner. The IC50 of 72h treatment of ixazomib in NPC cells is 11-40nM which is more sensitive than other solid tumour, e.g. hepatocellular carcinoma (260-428nM) and breast cancer (43-1007nM). Induction of apoptosis by ixazomib was confirmed by flow cytometry analysis of Annexin V staining and western blotting of caspase-3/9 activation and PARP cleavage. S and G2/M cell cycle arrest was observed after Ixazomib treatment, which is demonstrated by flow cytometry analysis of PI staining. Evaluation of the expression level of EBV lytic genes by RT-qPCR and western blot showed that Ixazomib associates with EBV lytic cycle activation in NPC. Consistent with the previous studies, inhibition of canonical NF-kB signalling pathway was seen after 12h of ixazomib treatment in NPC cells. In animal study, 4 or 8mg/kg of ixazomib was administered orally 2 times per week for 3 weeks on NPC cells/PDX transplanted BALD/c-nu/nu and NOD/SCID mice and all showed statistical significant inhibition on NPC growth. Combination treatment of ixazomib and cisplatin showed additive effect in both in-vitro and in-vivo studies. Conclusions: Ixazomib is a potential therapeutic agent for NPC treatment and the preclinical data supports further evaluation and clinical trial of ixazomib for NPC. Citation Format: Ka Yee Li, Victor Ho Fun Lee, George Sai Wah Tsao. Preclinical evaluation of the proteasome inhibitor ixazomib (MLN2238) on nasopharyngeal cacinoma (NPC) [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P186.