CDK inhibitors promote neuroblastoma cell differentiation and increase sensitivity to retinoic acid—a promising combination strategy for therapeutic intervention

The rarity of recurrent somatic mutations poses a challenge for the targeted treatment of neuroblastoma (NB). Differentiation therapy is an encouraging prospect, with cyclin-dependent kinase inhibitors (CDKis) representing a promising avenue for promoting NB differentiation. This study investigated three CDKis (abemaciclib, fadraciclib, and dinaciclib) alone or combined with retinoic acid (RA) to assess the effects on morphology, growth, gene expression, and the induction of immunogenic cell death in NB cell lines with (LAN-1 and CHLA-90) and without (CHLA-172) MYCN amplification. All cell lines demonstrated sensitivity to CDK inhibition. Notably, low-dose abemaciclib promoted cellular differentiation, as evidenced by the emergence of stromal-like morphological features and upregulation of the differentiation markers STMN4 and ROBO2. Treatment with abemaciclib or fadraciclib led to the upregulation of calnexin and holocytochrome C, which are part of the global stress response, along with the protein p27, which arrests the cell cycle. Molecularly, CDKis sensitivity correlated with an increased CDK4-specific copy number, along with a partial deletion of CDKN2a in two cases (LAN-1, CHLA-172). The addition of RA augmented the effects of the monotherapy, particularly in LAN-1 cells, in both 2D and 3D culture, and both treatments triggered immunogenic cell death, evidenced by calreticulin translocation. Transcriptomic analysis of LAN-1 and CHLA-90 cells revealed that genes deregulated by monotherapy (fadraciclib or RA) were re-regulated in the presence of the second drug. Combination therapy significantly downregulated CRABP2 and CYP26B1, both of which are involved in RA metabolism and its degradation. Furthermore, CCNE2, MYBL2, and MCM4 were strongly suppressed in the fadraciclib/RA combination, confirming the induction of cell cycle arrest. CDKi treatments promote NB differentiation via ER stress, with cytotoxicity enhanced by RA co-treatment. This may increase NB immunogenicity and support immunotherapy eligibility.