A. P. Williams1, L. L. Stafman1, J. Aye1, V. R. Atigadda4, J. E. Stewart1, C. Grubbs2, D. Muccio3, K. J. Yoon5, K. Whelan6, E. A. Beierle1 1University Of Alabama at Birmingham,Pediatric Surgery,Birmingham, Alabama, USA 2University Of Alabama at Birmingham,Surgery,Birmingham, Alabama, USA 3University Of Alabama at Birmingham,Chemistry,Birmingham, Alabama, USA 4University Of Alabama at Birmingham,Dermatology,Birmingham, Alabama, USA 5University Of Alabama at Birmingham,Pharmacology And Toxicology,Birmingham, Alabama, USA 6University Of Alabama at Birmingham,Pediatrics,Birmingham, Alabama, USA
Introduction: Current treatments for high risk neuroblastoma (NB) include 13-cis-retinoic acid (RA), but nearly half of children treated with RA develop disease recurrence. A subgroup of NB cells expressing the cell surface marker CD133 have been identified that have stem cell-like qualities and are associated with poor prognosis and disease relapse. These stem cell-like cancer cells demonstrate self renewal, avoid apoptosis, and are therefore promising targets for therapy. Recently, two novel rexinoids, UAB116 and 7-Me-UAB30, were developed to meet the goals of improved efficacy and decreased toxicity profiles over those of RA. We hypothesized that these novel rexinoids would affect NB cells in a fashion similar to that seen with RA, and may be used to target NB cancer stem-like cells.
Methods: Using 2 NB patient derived xenografts (PDXs), COA3 and COA6, UAB116 and 7-Me-UAB30 were evaluated along with RA. Following 72-hour treatment, cell viability was measured using alamarBlue, proliferation was assessed with CellTiter96 assays and fluorescence-associated cell sorting (FACS) analysis was used to detect CD133 expression. Extreme limiting dilution assay (ELDA) was performed to determine the compounds’ impact on tumorsphere formation both in bulk and sorted cell populations. Student’s t-test, extreme limiting dilution analysis, and χ 2 statistics were used with mean ± standard error of the mean reported and p<0.05 significant.
Results: AlamarBlue demonstrated decreased viability following treatment with both UAB116 and 7-Me-UAB30 that was comparable to that seen with RA (Figure) and similar results were obtained for proliferation. Using FACS, we found that CD133 expression decreased following treatment with UAB116 (16% to 5%, treated vs. control, p=<0.001) and 7-Me-UAB30 (16% to 6%, treated vs. control, p=<0.001). Tumorsphere formation was diminished significantly in the NB PDX cells treated with UAB116 or 7-Me-UAB30, decreasing tumorsphere formation in the 1000 cell/well group from 75% to 18% and 42% respectively (p<0.001). When sorted based on CD133 expression, the sphere forming capacity of the CD133 enriched population was significantly decreased after treatment with either compound from 100% in the 500 cell/well group to 58% when treated with UAB116 and 75% when treated with 7-Me-UAB30 (p<0.001).
Conclusion: The novel rexinoids, UAB116 and 7-Me-UAB30, affected NB PDX tumor cell survival and stemness. Treatment resulted in decreased cell viability and proliferation, decreased CD133 expression, and decreased tumorsphere formation. These findings indicate that these compounds should be investigated further as potential novel therapeutics for NB.
