Down-regulation of MYCN protein by CX-5461 leads to neuroblastoma tumor growth suppression

Abstract

Purpose: MYCN oncogene amplification is an independent predictor of poor prognosis in neuroblastoma. CX-5461 is a small molecular inhibitor that prevents initiation of ribosomal RNA (rRNA) synthesis by RNA Pol I, down-regulating MYCN/MYC proteins. We hypothesize that neuroblastoma tumor growth can be suppressed by CX-5461. Methods: MYCN-amplified (KELLY, IMR5) and non-amplified (SY5Y, SKNAS) neuroblastoma cells were treated with CX-5461. MYCN/MYC expression after 24-48 hours was determined by Western blot. Orthotopic neuroblastoma tumors created in mice using KELLY cells were treated with CX-5461-loaded silk films implanted locally. Tumor growth was monitored using ultrasound. Histologic evaluation of tumors was performed. Results: IC 50 for KELLY, IMR5, SY5Y, and SKNAS cells to CX-5461 was 0.75µM, 0.02µM, 0.8µM, and 1.7µM, respectively. CX-5461 down-regulated MYCN and MYC proteins at 0.25-1.0µM on Western blot analysis. CX-5461-loaded silk film released 23.7±3µg of the drug in 24 hours and 48.2±3.9µg at 120 hours. KELLY tumors treated with CX-5461-loaded film reached 800mm 3 after 7.8±1.4 days, while those treated with control film reached the same size on 5.1±0.6 days (p=0.03). CX-5461-treated tumors showed collapse of nucleolar hypertrophy and MYCN protein downregulation. Conclusion: We demonstrated that local delivery of CX-5461 via sustained release platform can suppress orthotopic neuroblastoma tumor growth, especially those with MYCN/MYC overexpression.

Targeting the RNA Polymerase I Transcription for Cancer Therapy Comes of Age

“…Indeed, results from the first-in-human clinical trial for CX-5461 strongly suggests that a functional p53 protein is a potential biomarker for treatment outcome. Although the number of patients in this study was limited, patients with WT p53 appear to respond better to the treatment [93]. In solid tumours, the response to Pol I transcription inhibition does not appear to correlate with p53 status, although increased sensitivity to Pol transcription inhibitors is also observed in some p53 WT tumours [56,88].…”

“…CX-5461 has recently completed a Phase I clinical trial in patients with advanced haematological cancers [93]. In this first-in-human, phase I dose-escalation study, CX-5461 was determined safe and the maximum tolerated dose was identified.…”

The chemotherapeutic agent CX-5461 irreversibly blocks RNA polymerase I initiation and promoter release to cause nucleolar disruption, DNA damage and cell inviability

“…In recent years, several small molecule cytotoxic drugs have been identified as specific inhibitors of ribosome biogenesis ( 8–10 ). CX-5461 is one such drug that has also demonstrated anticancer potential for a wide range of malignancies ( 9 , 11–23 ), and is presently under phase I trials for the treatment of both haematological cancers and solid tumours ( 24 , 25 ). CX-5461 was initially characterized as an inhibitor of the transcription of the ribosomal RNA genes (rDNA) by RNA polymerase I (RPI/PolR1/PolI) ( 9 ).…”

BDP1 Variants I1264M and V1347M Significantly Associated with Clinical Outcomes of Pediatric Neuroblastoma Patients Imply a New Prognostic Biomarker: A 121-Patient Cancer Genome Study

“…Inhibitors that downregulate MYCN/MYC proteins can suppress N.B. tumor growth [ 22 ]. Mutations in the tyrosine kinase domain of Anaplastic lymphoma kinase ( ALK ) have also been identified in N.B.…”