Targeting the Difficult-to-Drug CD71 and MYCN with Gambogic Acid and Vorinostat in a Class of Neuroblastomas

Although neuroblastoma is a heterogeneous cancer, a substantial portion overexpresses CD71 (transferrin receptor 1) and MYCN. This study provides a mechanistically driven rationale for a combination therapy targeting neuroblastomas that doubly overexpress or have amplified CD71 and MYCN. For this subset, CD71 was targeted by its natural ligand, gambogic acid (GA), and MYCN was targeted with an HDAC inhibitor, vorinostat. A combination of GA and vorinostat was then tested for efficacy in cancer and non-cancer cells. Microarray analysis of cohorts of neuroblastoma patients indicated a subset of neuroblastomas overexpressing both CD71 and MYCN. The viability with proliferation changes were measured by MTT and colony formation assays in neuroblastoma cells. Transfection with CD71 or MYCN along with quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting were used to detect expression changes. For pathway analysis, gene ontology (GO) and Protein-protein interaction analyses were performed to evaluate the potential mechanisms of GA and vorinostat in treated cells. For both GA and vorinostat, their pathways were explored for specificity and dependence on their targets for efficacy. For GA-treated cells, the viability/proliferation loss due to GA was dependent on the expression of CD71 and involved activation of caspase-3 and degradation of EGFR. It relied on the JNK-IRE1-mTORC1 pathway. The drug vorinostat also reduced cell viability/proliferation in the treated cells and this was dependent on the presence of MYCN as MYCN siRNA transfection led to a blunting of vorinostat efficacy and conversely, MYCN overexpression improved the vorinostat potency in those cells. Vorinostat inhibition of MYCN led to an increase of the pro-apoptotic miR183 levels and this, in turn, reduced the viability/proliferation of these cells. The combination treatment with GA and vorinostat synergistically reduced cell survival in the MYCN and CD71 overexpressing tumor cells. The same treatment had no effect or minimal effect on HEK293 and HEF cells used as models of non-cancer cells. A combination therapy with GA and vorinostat may be suitable for MYCN and CD71 overexpressing neuroblastomas.