Neuroblastoma (NB) is one of the primary causes of death for pediatric malignancies. Given the high heterogeneity in NB’s mutation landscape, optimizing individualized therapies is still challenging. In the context of genomic alterations, MYCN amplification is the most correlated event with poor outcomes. MYCN is involved in the regulation of several cellular mechanisms, including cell cycle. Thus, studying the influence of MYCN overexpression in the G1/S transition checkpoint of the cell cycle may unveil novel druggable targets for the development of personalized therapeutical approaches. Here, we show that high expression of E2F3 and MYCN correlate with poor prognosis in NB despite the RB1 mRNA levels. Moreover, we demonstrate through luciferase reporter assays that MYCN bypasses RB function by incrementing E2F3-responsive promoter activity. We showed that MYCN overexpression leads to RB inactivation by inducing RB hyperphosphorylation during the G1 phase through cell cycle synchronization experiments. Moreover, we generated two MYCN-amplified NB cell lines conditionally knockdown (cKD) for the RB1 gene through a CRISPRi approach. Indeed, RB KD did not affect cell proliferation, whereas cell proliferation was strongly influenced when a non-phosphorylatable RB mutant was expressed. This finding revealed the dispensable role of RB in regulating MYCN-amplified NB’s cell cycle. The described genetic interaction between MYCN and RB1 provides the rationale for using cyclin/CDK complexes inhibitors in NBs carrying MYCN amplification and relatively high levels of RB1 expression.

Subunits of the SWI/SNF chromatin remodeling complex are altered in ~20% of human cancers. Exemplifying the alterations is the ARID1A mutation that occurs in ~50% ovarian clear cell carcinoma (OCCC), a disease with limited therapeutic options. Here, we showed that ARID1A mutations create a dependence on alanine by regulating alanine transporters to increase intracellular alanine levels. ARID1A directly repressed alanine importer SLC38A2 and simultaneously promoted alanine exporter SLC7A8. ARID1A inactivation increased alanine utilization predominantly in protein synthesis and passively through the tricarboxylic acid cycle. Indeed, ARID1A-mutant OCCCs were hyper-sensitive to inhibition of SLC38A2. In addition, SLC38A2 inhibition enhanced chimeric antigen receptor-T cell assault in vitro and synergized with immune checkpoint blockade using an anti-PD-L1 antibody in a genetically engineered mouse model of OCCC driven by conditional Arid1a inactivation in a CD8+ T-cell dependent manner. These findings suggest that targeting alanine transport alone or in combination with immunotherapy may represent an effective therapeutic strategy for ARID1A-mutant cancers.

SLC38A2 inhibition reduces the marker of cell proliferation in ARID1A-inactivated OCCCs.

The effects of SLC38A2 inhibition alone or in combination with anti-PD-L1 on tumor microenvironment.

ARID1A does not create a dependence on GPTs.

ARID1A regulates alanine metabolism in OCCC cells.