Novel Second Generation Rexinoid Induces Growth Arrest and Reduces Cancer Cell Stemness in Human Neuroblastoma Patient-Derived Xenografts
Background: The poor therapeutic efficacy seen with current treatments for high-risk neuroblastoma may be attributed to stem-like cancer cells (SLCCs), a subpopulation of cancer cells associated with poor prognosis and disease relapse. Retinoic acid (RA) induces growth arrest and differentiation of neuroblastoma cells and is routinely used in maintenance therapy for high-risk neuroblastoma. However, nearly half of children treated with RA develop disease recurrence. 6-Methyl-UAB30 (6-Me) is a second generation rexinoid recently developed to achieve the goals of improved efficacy and reduced toxicity compared to RA. We hypothesized that 6-Me would inhibit cell proliferation and survival, induce cell cycle arrest, and reduce cancer cell stemness in human neuroblastoma patient-derived xenografts (PDXs).
Methods: Two human neuroblastoma PDXs, COA3 and COA6 were utilized. Cells were treated with 6-Me at increasing concentrations for 72 hours. Proliferation, viability, migration, and invasion were assessed using the CellTiter 96®, alamarBlue®, and Transwell assays, respectively. Cell-cycle and CD133 expression were analyzed using flow cytometry. Sphere formation was assessed using in vitro extreme limiting dilution analysis, and mRNA abundance for stemness markers was determined using real-time PCR. Student’s t-test was used with p≤0.05 significant.
Results: Treatment with 6-Me significantly decreased proliferation, viability, migration, and invasion in both neuroblastoma PDXs. In addition, 6-Me treatment induced cell-cycle arrest with an increased cell percentage in G1-phase and decreased cell percentage in S-phase. 6-Me treatment led to decreased cell surface expression of CD133 (Figure 1A), a marker of SLCCs. In addition, 6-Me treatment decreased sphere-forming ability (Figure 1B) and decreased mRNA abundance of three transcription factors associated with stemness, Oct4, Nanog, and Sox2 (Figure 1C), indicating decreased cancer cell stemness.
Conclusion: 6-Methyl-UAB30 induced growth arrest and reduced cancer cell stemness of human neuroblastoma PDXs. These findings warrant further exploration of 6-Me as potential novel therapy for children with high-risk neuroblastoma.